Welding

Practice
Welding Practice

Brian D. Smith
Tech Eng, Tech Weldl, MITO, CGIA
Registered Welding Education Technician
Acknowledgements
The author expresses his thanks to the following organizations for their support and their
supply of information and illustrations:

Air Products PLC

Arc Speed Services, Derbyshire
Arco Ltd: safety signs (colour plates)
The British Oxygen Company (BOC), Guildford and Derby: gas cylinder identification
chart (colour plates and Figure 1.1)
The British Standards Institute, Milton Keynes
CENTRA, Manchester
Chubb Fire Ltd: fire extinguishers (colour plates)
East Midlands Further Education Council, Nottingham
ESAB Group (UK) Ltd, Waltham Cross
Gas Control Equipment, Skelmerdale
The Health and Safety Executive
Migatronic Welding Equipment Ltd, Loughborough
C. S. Milne Ltd, Leicester
Trueweld, Derby
The Welding Institute, Abington, Cambridge

Special thanks to Mr Len Gourd, BSe FWeldI, for his continuing support.
Every possible effort has been made to trace copyright holders. Any rights not acknowledged
here will be acknowledged in subsequent printings if notice is given to the publisher

Butterworth-Heinemann
An imprint of Elsevier Science
Linacre House, Jordan Hill, Oxford 0X2 8DP
225 Wildwood Avenue, Woburn MA 01801-2041

First published 1996

Transferred to digital printing 2002

Copyright © 1996, Brian D. Smith. All rights reserved.

The right of Brian D. Smith to be identified as the author of this work has been asserted
in accordance with the Copyright, Designs and Patents Act 1988

Nopartofthispublicationmaybereproducedinanymaterialfonn (includingphotocopyingorstoringinanymedium
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EnglandWIT4LP.Applicationsforthecopyrightholder'swrittenpermissionto reproduceanypart ofthispublication
shouldbeaddressedtothepublisher

British Library Cataloguing in Publication Data

A catalogue record for this book is available from the British Library

ISBN 0 340 61406 4

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visit our website at www.bh.com

Printed and bound in Great Britain by Antony Rowe Ltd, Eastbourne

 Contents
1. Underpinning information 1
Arc welding safety
Welding terminology
Weld symbols (BS499 part 2 1980)
Types of joints
Features of a welded joint
Distortion control
Weld defects
Inspection
Welding procedure and welder qualifications

2. Manual metal arc welding 29

Manual metal arc welding equipment
Striking the arc
Stop/starts
Electrode angles
Weaving
Electrode classification
Electrode size and current capacity
Electrode coatings
Welding positions for plates
Positional welding
Plate positions
Summary

3. Metal arc gas-shielded welding 47

MAGS welding process
Choice of shielding gas
Electrode wires
Wire feed system
Metal transfer modes
The self-adjusting arc
Contact tip, nozzle settings
Electrode extension
Burn back
Current and voltage settings
British Standards for wires and fillers
Features of the process
Weaving
Flux-cored arc welding
Self-shielded flux-cored arc welding
vi CONTENTS

Gas-shielded flux-cored arc welding

MAGS positional welding

4. Tungsten arc gas-shielded welding 61

TAGS welding equipment
Equipment selection
Surge injector
DC suppressor
Contactor
Arc striking
Electrode types and diameters
Gas nozzles
Gas lens
Torches
Shielding gas
AC/DC non-consumable electrode arcs

5. Oxyacetylene welding and cutting 77

Standard welding/cutting equipment
Safety precautions to be observed when using
oxygen and acetylene cylinders
Regulators
Safety
Flashback arrestors
Hoses (BSS120)
Purging
Hose connectors
Hose check valves
'0' clips
Welding torches
Nozzles
Equipment assembly (welding and cutting)
Lighting-up procedure
Flame settings
Extinguishing the flame
Welding techniques
High- and low-pressure systems
Filter glasses
Plate edge preparation
Oxyacetylene positional welding
Bronze welding
Fluxes
Oxyfuel gas cutting
Torches
Fuel gases
 CONTENTS vii

Nozzles
Hand cutting
Quality of cut
Supporting materials
Cutting techniques

6. Questions 99
Health and safety
MMA welding
MAGS welding
TAGS welding
Gas welding and cutting
Answers to questions

Appendix 1: Welding processes 107

Welding processes and their numerical representation

Appendix 2: Useful information 109

Index 113
 Underpinning
information
Table 1.1 Recommended filter glasses for welding
Arc welding safety
Filter glasses for manual metal arc welding
Under the Health and Safety at Work Act 1974 EWF up to 100 amps
8-9
welders have a responsibility to take reason- 10-11 EWF 100-300 amps
able care for their safety and that of others 12-13-14 EWF over 300 amps
by cooperating with safety requirements. Filter glasses for oxyfuel gas welding:
Welding and the welding environment can 3 GWF Aluminium and alloys
create many hazards, but can be carried out 4 GWF Brazing and bronzing welding
quite safely if you play your part and observe 5 GWF Copper and alloys
6 GWF Thick plate and pipe
some basic safety rules. There are a number of
factors to be considered; a few of these are list- Filter glasses are usually protected on the outside
by a separate, clear plastic cover lens. This will give
ed below.
protection from spatter particles and prolong the
life of the filter lens.

Personal protection
toes from damage by falling objects, while also
Personal protection for the welder is most giving the best protection against sparks enter-
important, apart from the most obvious dan- ing the footwear. Some boots have a flap up
gers of burns, stray sparks and falling objects, the front, others may be one piece with high
the arc gives off ultraviolet and infrared rays. legs giving good protection to the foot and leg.
These will affect the skin and eyes much in the Low shoes or trainers are not the ideal foot-
same way as long periods of exposure to the wear for the welder.
sun. Suitable protection must be worn at all Many types of eye protection are available
times to guard against these and other danger- in the form of spectacles, goggles, face visors,
ous occurrences. clear glasses for use with welding helmets/
Protective clothing comes in the form of shields, etc. The most important aspect when
gauntlets, leather coats, aprons, sleeves, spats choosing any form of eye protection is that it
and capes. must conform to British Standard (BS)2092.
The eyes should always be protected by a Eye protection must be worn for all cutting,
shade of filter glass suitable for the welding grinding, chipping and welding operations.
operation and amperage being used, or a clear
glass for the chipping of slag. Table 1.1 details
the recommended filter glasses. Working at heights
Protection for the feet in the form of safety
boots with a toecap is an essential part of the In your profession as a welder it is possible
welder's protective clothing. Boots protect the that you may have to work off scaffolding,
2 UNDERPINNING INFORMATION

trestles, elevated platforms and so on. In most d) placing the source of extraction as close to
instances these elevated platforms will be the point of welding as possible without
erected or operated by qualified people elimi- disturbing the gas shield
nating the possible risk of collapse. e) siting the source of extraction to pull the
As a welder working from such platforms, fumes away from the welder
extra care must be taken to avoid even the f) avoid welding on contaminated surfaces,
slightest risk of electric shock. Although the such as oil, grease, paint, galvanised metal,
effects of the shock may be dismissed, it could etc.
lead to loss of balance and falling with serious R b f h' h' I d .
or fatal results. emem ~r, urnes:, IC mc u e POlS?~oUS
gases whIch asphyxIate are not always vIsIble.
Remem
.
b er a 1ways
.
t a k e ex t ra care w h en Where It ... IS not possIble to use the above meth-
wor k mg a t h eig ht s.. ods, then breathmg apparatus may be
required, supplied either from an airline or a
Responsibilities of the welder personal body pack.
If in doubt ask!
Under the Health and Safety at Work Act 1974,
individuals are held responsible for their own
safety as well as that of colleagues and those Storage and handling of gas cylinders
working in close proximity.
Always ensure you have taken all reason- The most com~on .method of ~upplying gases
able, practical precautions to avoid the risk of use.d for weldmg IS from c~hnders. All gas
accidents and fires, for example: cyhnders should be treated wIth respect, han-
dled carefully and stored in well-ventilated
a) good housekeeping; keep a tidy work area conditions. Never allow cylinders to come into
b) wear protective clothing on feet, body and contact with heat, contaminants containing
eyes oil and grease, and observe the following han-
c) screening of workstation to protect dling and storage conditions:
passers-by ...
d) use and position extraction equipment a) always keep cyhnders, flttmgs and connec-
correctly tions fre~ from oil ~nd grease
e) carry out safety checks on equipment b) store cyhnde~s upnght ..
f) do not tamper with safety posters or signs. c) transport cyhnders upnght.
d) store flammable and non-flammable gases
These are just a few points to consider before separately
work commences. How many more can you e) store full and empty cylinders separately
think of? f) avoid cylinders coming into contact with
heat
Welding fumes g) secure cylinders by 'chaining up' during
storage, transport and use
Welding fumes are virtually impossible to h) open cylinder valves slowly
eliminate from the welding process. However, i) only use recommended leak-detection
fumes can be rendered harmless by observing sprays
the following simple rules: j) report damaged cylinders to the supplier
.... k) always check for leaks
a) the welder positlOnmg hIm/herself out of I) SWltC. h 0 ff gas supp Iyater
f use.
th e fume pa th
b) using adequate ventilation either natural Gas cylinders find their way into many differ-
or mechanical - fans and extraction equip- ent environments from schools and colleges to
ment, for instance heavy fabrication. Wherever gases are used the
c) correct positioning of source of ventilation - operator, supervisor and management should
some gases are heavier than air and will sink be aware of the dangers and familiar with the
to the bottom of a confined area; in these operating conditions, safety requirements,
cases extraction should be at a low level handling and storage conditions. Gas suppli-
 WELDING TERMINOLOGY 5

These are just a few points for you to think Remember that where there is a suspected
about. Always consider the working environ- risk of electric shock, due to working condi-
ment and ask yourself: what could cause a fire? tions or environment, adequate precautions
- remove it and prevent it from happening. must be taken.
However minor the incident may appear,
always ensure that the injured person is seen
Electrical hazards by a doctor.
The risk of electric shock is something which It is also advisable that those involved with
the welder should always be aware of, both to electric arc welding be trained in the basic
themselves and colleagues. Injury resulting practice of mouth-to-mouth resuscitation.
from electric shock can be burns, loss of con-
sciousness or death. Welding terminology
If you come across someone who you sus-
pect has received an electric shock, switch off Welding, gas and arc, is a widely used process
the supply immediately and only remove the to join metals by fusion welding, brazing or
injured person from contact by means of suit- bronze welding.
ably insulated protection. For normal arc The terminology tends to vary somewhat
welding voltages, sufficient protection will be from county to county, and only contact, con-
given by their clothing - provided it is dry. versation and experience can create an aware-
When freeing the injured person from the ness of the wide range of names used.
electrical source, it must be done with the use This book has put together a list of terms
of a non-conducting material. based on the most widely used to describe the
Where staff trained in first aid are available, in- various features of the process. Table 1.2 gives
form them immediately so they are able to admin- terms relating to the gas and arc welding
ister the correct treatment. If no-one is available, processes. Table 1.3 specifically relates to terms
and the situation is serious, attempt mouth-to- used in the thermal cutting of metals, and
mouth resuscitation while you send for help. Table 1.4 deals with testing and examination.

Table 1.2 Terms relating to gas and arc welding

Term Definition
Actual throat thickness The perpendicular distance between two parallel lines joining
the weld toes
Arc blow A disturbance of a DC welding arc caused by magnetic fields
set up in the work
Arc voltage The voltage between electrodes or between an electrode and
the work during welding
Backfire Retrogression of the flame into the blowpipe neck or body
with rapid self-extinction
Back-step sequence A welding sequence in which short lengths of weld are
deposited in a direction opposite to the direction of progress
along the joint to produce a continuous or intermittent weld
Backing strip (backing ring pipe) A piece of metal placed at a root and penetrated by weld metal. It may
remain as part of the joint or removedby machining or other means
Backing bar (backing ring pipe) A piece of metal or other material placed at a root and used
to control the root penetration bead
Burn back Fusing of the electrode wire to the current contact tube in any
form of automatic or semi-automatic metal-arc welding process
Burn off rate The linear rate of consumption of a consumable electrode in
any consumable electrode process
Burn through (melt through) A localised collapse of the molten pool due to excess localised heat-
ing, resulting in a hole in the underlying weld run or parent metal
Cutting/welding torch A device for mixing and burning gasesto produce a flame for weld-
ing, brazing, bronze welding, cutting, heating and similar operations
6 UNDERPINNING INFORMATION

Table 1.2 Continued

CO2 flux cored welding Metal arc welding in which a flux cored electrode is deposit-
(cord wire welding) ed under a shield of carbon dioxide
CO2 welding Metal arc welding using a continuous bare wire electrode.
The arc and molten pool being shielded by carbon dioxide
shielding gas
Concave fillet weld A fillet weld in which the weld face is concave (curved inwards)
Cone The inner part of a flame adjacent to the nozzle orifice -
known as the inner cone (oxyfuel gas welding)
Continuous weld A weld along the entire length of a joint
Convex fillet weld A fillet weld in which the weld face is convex (curved outwards)
Covered filler metal A filler metal having an outer covering of flux can be in the
form of a continuous covering or contained in indentations
along its length
Crack Discontinuity in the welded joints. Cracks may be longitudi-
nal, transverse, edge, crater, centre line, fusion zone under-
bead, weld metal or parent metal
Crater pipe A depression due to shrinkage at the end of a run (crater)
where the source of heat was removed
Deposited metal Metal after it becomes part of a weld or joint
Dip transfer A method of metal-arc welding in which fused particles of
the electrode wire in contact with the molten pool are
detached from the electrode in rapid succession by the short
circuit current, which develops every time the wire touches
the molten pool
Dual shield welding Semi-automatic welding using a flux covered wire and a
shielding gas
Excess penetration bead Metal prottuding through the root of a weld made from one
side only in excess of the stated limits
Feather The carbon-rich zone, visible in a flame, extending around
and beyond the cone when there is an excess of fuel gas
Fillet weld A fusion weld, other than a butt or edge weld, which is
approximately triangular in cross-section
Filler metal (filler wire or filler rod) Metal added during welding
Flame snap-out Retrogression of the flame beyond the blowpipe body into
the hose, with possible subsequent explosion
Flashback arrester A safety device fitted in the oxygen and fuel gas system to
prevent any flashback reaching the gas supply
Flux Material used during welding to prevent atmospheric oxida-
tion and to reduce impurities or float them to the surface.
Can also have a cleansing action on the surfaces to be joined
Fusion penetration The depth to which the parent metal has been melted into
the fusion faces
Fusion welding Joining together to form a union between metals in a molten
state without the application of pressure
Fusion zone An area of the parent metal at the fusion face which is melt-
ed to form part of the weld
Gas economiser A device designed for temporarily cutting off the supply of
gas to the welding equipment. A pilot jet may be fitted for
relighting
Gas envelope The gas surrounding the inner cone of an oxyfuel gas flame
Gas pore (gas cavity) A cavity formed by entrapped gas during the solidification of
molten metal
Gas regulator A device for attachment to a gas cylinder or pipeline for
reducing and regulating the cylinder or line pressure to the
working pressure required
Globular transfer Metal transfer which takes place as large globules transferred
from the electrode to the weld area
-'
8 UNDERPINNING INFORMATION

Table 1.2 Continued

Slag-trap A feature in a joint or joint preparation which may lead to

the entrapment of slag
Slot weld A weld made between two overlapping components by
depositing a fillet weld round the periphery of a hole in one
component so as to join it to the other component
Spray transfer Metal transfer which takes place as a steam of small droplets
transfers from the electrode to the weld area
Stack cutting The thermal cutting of a stack of plates usually clamped
together
Staggered intermittent weld An intermittent weld on each side of a joint arranged so that
the welds lie opposite to one another
Striking voltage The minimum voltage required to strike an arc
Submerged arc welding Metal arc welding in which a bare wire or electrodes are
used, the arc or arcs are covered by a flux, some of which
fuses to form a removable slag on the weld. Some flux is
recovered
Sustained backfire Retrogression of the flame into the blowpipe, the flame
remaining slight. 'Popping' or 'squealing' with a small point-
ed flame coming from the nozzle or as a rapid series of
minor explosions
TIG welding (inert gas tungsten arc welding) Inert gas welding using a non-consumable electrode of pure
or activated tungsten
Touch welding Metal arc welding using a covered electrode. The covering is
kept in contact with the parent metal during welding
Toe The boundary between a weld face or root and the parent
metal, or between a weld face and any underlying welds
Tungsten inclusion An inclusion of tungsten in the weld from the electrode in
TIG welding process
Two-stage regulator A gas regulator in which the cylinder or line pressure is
reduced to the working pressure in two stages
Undercut An irregular groove at a toe of a run in the parent metal at
root, face or in previously deposited weld metal
Weld A joint between pieces of metal made liquid by heat, or by
pressure, or by both. A filler metal mayor may not be added
Weld junction The boundary at the extent of melting and the heat-affected
zone
Weld metal The metal melted during the making of a weld and retained
in the weld joint
Weld zone The area of parent metal affected by the weld deposit
Welding procedure A detailed list of actions to be followed during the produc-
tion of a weld. The list will include materials, consumable,
amps, volts, gases, joint details, etc.
Welding sequence The order and direction in which welds are deposited in the
joint
Welding technique The manner in which the operator controls the electrode or
blowpipe during welding
Worm-hole An elongated or tubular cavity formed by entrapped gas dur-
ing solidification of molten metal
WELDING TERMINOLOGY 9
WELD SYMBOLS (BS499 PART 2 1980) 11
12 UNDERPINNING INFORMATION
TYPE OF JOINTS 13
FEATURES OF A WELDED JOINT 15
16 UNDERPINNING INFORMATION

Fillet weld profiles

As can be seen from the three examples shown
in Fig. 1.22, the finished weld profile and the
angle between the joint faces can affect the
throat thickness of the weld. The dimension a
design throat thickness is used by the design
engineer to calculate the strength of the weld-
ed joint and hence that of the total structure
to ensure it will stand up to service conditions.
This dimension is not easy to determine or
to control by the welder during the welding
operation.

Figure 1.22 Throat thickness and leg length of a

fillet weld.

To enable the design engineer to achieve the

calculated throat thickness required details are
conveyed to the welder by using the leg length
dimension that will result in achieving the
desired throat thickness.
By using this method the welder has some
visual dimension to work to and thus achieves
the previously calculated design throat thick-
ness.

Features of the weld

See Fig. 1.23.

Features of the joint

See Fig. 1.24.
18 UNDERPINNING INFORMATION

length and strength to prevent movement. In

the absence of other information tack weld
lengths can be two to three times the thickness
of the plates being welded.
Jigs are designed mainly for the ease of
assembly, but they can also incorporate
clamps to prevent the movement of the parts
during welding. A good jig will allow good
access to the weld area and enable 50% of the
welds to be completed before removing the
component.
Pre-setting the plates in the opposite direc-
tion to the contraction will allow the plates to
be pulled back into line as the_contraction
takes place. It is not easy to estimate the
amount of pre-set, but a good guide is the
thickness of the plate in the opposite direction
to the contraction (see Fig. 1.29).
22 UNDERPINNING INFORMATION

Table 1.5 Continued

Excess reinforcement Incorrect balance of volts and amps - incorrect technique

Incorrect profile Wrong torch angle - incorrect speed of travel - incorrect
weld sequence
Incomplete fill See MMA
Spatter Incorrect volts/amps setting, common on spray transfer
Cracking See MMA
Slag inclusions Small amounts of silica slag but no real problem
Irregular stop/start Poor technique - inadequate instruction and training

Tungsten gas shielded (TIG)

Undercut Torch angle - high amperage - manipulation of torch and
filler rod - too small a filler rod speed - too fast - incompati-
ble filler rod and metal
Gas holes No shielding gas - dirty plate incompatible filler rod and
metal - technique - manipulation of torch - speed too fast -
shielding gas low - gas shield being blown away - no gas
shield on root ('V' joints)
Excess penetration Gap too large - speed slow - too large a tungsten electrode -
too small a root face ('V' joints) - amperage too high - torch
and filler rod manipulation
Lack of interrun fusion Torch and filler rod manipulation - incorrect torch angle - torch
and filler rod position - low amperage - too large a filler rod
Poor or no penetration Gap too small ('V' joints) - too large a root face ('V' joints) -
misalignment of plates - low amperage - low voltage - torch
and filler rod manipulation - incorrect joint preparation, i.e.
too narrow a 'V' preparation ('V' joints)
Lack of side-wall fusion Technique - torch and filler rod manipulation - torch angle -
torch position - low amperage
Excess reinforcement Low amperage - excess filler
Incorrect profile Wrong torch angle - excess filler - incorrect speed of travel -
incorrect weld sequence
Incomplete fill Speed of travel too fast - incorrect weld sequence - not
enough filler (single passes) - not enough passes
Cracking See MMA
Slag inclusions Not possible (may be solid inclusions)

Oxyacetylene (OA)
Undercut Overheated plate - excessive flame temperature - oversize
nozzle - torch angle - speed too fast - incorrect flame - gap
under vertical plate (fillets) - technique
Gas holes/piping Incorrect flame - rusty plate - oil on plate - incompatible filler
rod/plate - water on plate - speed of movement too slow/fast
Lack of penetration Plate misalignment - too small a gap/root face ('V' joints) -
too small a nozzle - too large a filler rod - incorrect flame -
low heat in flame - torch angle - technique
Lack of side-wall fusion Torch angle - position of torch - low flame heat - incorrect
flame - incompatible filler rod/plate - oil/dirt on plate -
plate preparation - technique
Excess penetration Too much filler - incorrect torch angle - work too cold
Incorrect profile Incorrect: angle of filler wire, welding speed, welding
sequence, torch angle
Incomplete fill See TIG
Cracking See MMA
26 UNDERPINNING INFORMATION

ply with the welding procedure is the welder,

as this will set out the previously tried and
tested methods required to achieve the desired
quality.
Some of the requirements listed on the pro-
cedure that will directly affect the welder are:
a) Welding processes: ensure that the correct
process is being used.
b) Joint type: does this comply with that
specified on the procedure?
c) Weld run: sequence/position of weld runs
in the preparation.
d) Metal thickness: as stated on the procedure.
e) Filler metal type: ensure compliance with
procedure.
f) Filler metal classification: as procedure.
g) Gas!f1ux type (if used): as specified.
h) Welding current AC-DC: as specified.
i) Welding parameters: amps and volts.
Welding procedure and j) Welding polarity.
- k) Welding position.
fi ions
we Ider qua II Icat 1) Pre-heat/post-heat and interpass tempera-
When designing a fabricated structure, one of tures.
the principal factors to consider is the service The above list is by no means exhaustive, all of
conditions, i.e. what are the conditions in these may well be considered as the welder's
which the fabrication has to function. Such responsibility and are considered essential
conditions may range from extreme high to criteria in the production of quality
extreme low temperatures, or both. Whatever welds.
the circumstances, designers, engineers, fabri- The tinted areas shown in Table 1.6 are
cators, welders and, not least of all, the cus- details of which the welder should be aware,
tomer, must be confident that the finished although they may not all be effective at the
welded structure has the desired properties to same time. For example, when MMA welding
withstand the service conditions. This is gas shielding will not be relevant.
achieved by choosing the correct raw materi- Pre-heating may be the responsibility of
als, in this case steel, selecting the most suit- other departments or even companies special-
able fabricating processes/techniques and ising in these methods. On the other hand,
working procedures, all of which contribute to observing the stated pre-heat, interpass and
achieving a product of the required properties post-heat temperatures may well affect the
and quality. successful achievement of acceptable welding
Achieving the properties of the fabrication conditions, resulting weld quality and service
depends to a large extent on the way the welds conditions of the component.
are made. Production of welds at this level is The prime function of a weld procedure is to
controlled by the use of tried and tested weld- achieve a level of quality applied to the pro-
ing procedures and qualified welders. duction of a welded component or structure.
Everyone involved in the production The prime function of a welder qualification
process will be affected by working proce- is to approve a welder to carry out the welds
dures. Welding procedures are particularly on a welded structure to a set quality standard.
important to ensure weld quality and will A weld procedure in its simplest form is a
specify everything from material specification list of requirements laid down that produce a
through to inspection standards. welded joint achieving the desired mechanical
The person most obviously required to com- properties required to maintain a 'safe in oper-
28 UNDERPINNING INFORMATION

Welders may experience many qualification to produce welds to a specific quality or proce-
tests during their career. It is not like an acad- dure, thus providing a level of welding quality
emic examination that once you have passed control applied to a component or structure.
it lasts for ever. If you change jobs, process Weld quality is of utmost importance and at
metals, consumables, joint type, thickness of the forefront of all design engineers' criteria. It
metal, etc., you may find yourself doing anoth- is also important to the welder. One of the 'in'
er welder approval test to a different procedure. phrases when I was on the welding circuit was
The purpose of the welder qualification test is that 'you are only as good as your last butt'.
to measure the welder's ability and competence
 Manual metal
arc welding
Manual metal arc welding A DC supply gives the operator a choice of
• polarity: electrode positive (+ve) or electrode
equipment (see Fig.2.1) negative (-ve). This means that the electrode
can be connected to the +ve or -ve output ter-
Manual metal arc (MMA) welding uses both minal of the power source.
alternating current (AC) and direct current Connecting the electrode to the +ve termi-
(DC). Generally AC is associated with shop work nal will result in two-thirds of the arc heat
and DC with site work, as the DC supply in the being concentrated at the electrode and one-
form of a generator is much more portable. Also third at the work. Connecting the electrode to
with the lower open circuit voltage (OCV) of DC the -ve terminal will result in one-third of the
it is safer in damp, confined or dangerous con- arc heat being concentrated at the electrode
ditiollS, where there is a higher risk of electric and two-thirds at the work. A typical use for
shock or accidents resulting from electric shock. the latter is for the first or root runs in open
AC current will tend to pull the user into the butts with low-hydrogen (hydrogen-controlled)
electrical supply, DC will push the user away. electrodes on plates and/or pipes.
30 MANUAL METAL ARC WELDING

One of the disadvantages of using a DC Transformer

supply is the occurrence of arc blow. This is
when metal is expelled from the arc or molten The purpose of a transformer is to provide a
pool caused by magnetic fields set up in the single function of changing the high volt-
work. The effect of this can be reduced by: age/low amperage mains supply to one of low
. · · ' voltage/high amperage welding supply. The
a ) c h angmg
. · · t IOn 0f we Id mg
th e d Hec OCV wIll .. vary dependmg on the size and type
1
b) . movmg th e pOSIt IOn 0 f th e re t urn camp .
of eqUlpment, but usually ranges from 40 to
c ) usmg sma. II er e I ec t ro d es 100 volts. ThIS ... IS the voltage avallable for the
d) wrappmg th e re t urn ca bl e aroun d th e wor k ...
imtial stnkmg of the arc. Once the arc is estab-
I
or return camp. 1ISh e d t h e vo Itage WI·11d rop to b etween 2 5 an d
·
Mains electricity as supplied is not suitable 40 volts. This remains constant while the
for welding purposes, as it is supplied at high amperage will have adjustments of between 45
voltage and low amperage. For welding the and 110 amps on smaller sets, to 50-350 amps
reverse is required. Therefore, the purpose of and over on larger sets.
the welding plant is to reduce the voltage and Most modern welding sets have a total vari-
increase the amperage. able amperage control; some of the older
There are three main types of welding plant: types, however, may have stepped-type adjust-
• transformer = AC input to suitable AC output ments or plug-type settings.
• rectifier = AC input to suitable AC and DC
output Rectifier
• generator = generated DC only.
O · . · The rectifier can be a separate piece of equip-
O ver th IS range 0f eqUlpmen t th e open CHCUlt ment connected to a transformer, although m .
vo. It age (OCV) ranges from 40 t 0 100 ·vo It· s, modern weldmg . plant the transformer and the
h h
. 0 f 25 t 0. 40· vo It s - W lC IS rectIfIer
WIth an arc vo It age .... are usually contamed m one package
th e vo It age reqUlre d t 0 maIn t am th e arc. referred to as a transformer/rectIfIer... The pur-
pose of the rectifier is to change the previously
transformed AC mains supply into DC for
welding.

Generators
Generators are usually driven by a primary
source such as an electric motor from the
mains supply, or engine driven, the latter
being the most popular, as this gives much
more flexibility to the welding set for site
operations where a mains supply is not always
available. The OCV generated is between 40
and 60 volts, and is normally adjustable bet-
ween these limits.
Current capacity will vary with the size of
the generator, 150-400 amp range generators
are common.
A piece of equipment which combines the
transformer and the rectifier and is known as
Figure 2.2 AC transformer: (1) current selector the .tra.nsfo~mer/re~tifier is quite popular ~or
control handle; (2) remote switch socket; (3) on/off statIc sItuatIOns. ThIS offers the welder a chOlce
switch; (4) return cable socket; (5) electrode cable of suitable welding current in both AC and DC
socket; (6) current indicator. supply. This equipment also allows the flexi-
,
 STRIKING THE ARC 31

bility of AC and DC with less moving parts

than the generator, thus reducing maintenance
costs. With correct maintenance the trans-
former/rectifier will give many years of service.
Wi thout placing themselves in dangerous
situations, welders should always check their
plant is in satisfactory working order. Any
damages to cables, switches, insulation, any
power loss, overheating, noise or excessive
vibration should be reported to the supervisor.

Open circuit voltage (OCV) Figure 2.3 Principle of manual metal arc welding.
The maximum OCV allowed for MMA welding
is 100 volts, nor~ally associated with the AC pletely cover the end of the electrode and the
p~wer supply. SlIghtly lower OCVs are used weld area to form a protective environment in
wIth the DC power output: which the weld is deposited. Other functions
• AC SO-800CV of the electrode coa.:ing are to act as a fluxing
80-1000CV agent to dean the weld area, and for carrying
• DC 60-800CV additional elements to the weld. These addi-
" tional elements can exist as iron powder parti-
The MMA process, or stick weldmg process des which will increase the amount of metal
as it i~ commonly known,. is well. establi.shed deposited for a given size of electrode (in-
a~d wIdely ~sed. The eqUipment IS rel.atlVely crease its metal recovery), to improve mechan-
SImp:e, ma.kmg the process very. versatile and ical properties or corrosive resistance. The end
mobIle, sUitable for shop and sIte work. The result of the melted coating is slag forming on
process uses a covered electrode to create an the surface of the deposited weld which then
arc between ~h~ end of an el~ctrode and the solidifies on cooling. The slag will protect the
plates t~ be lomed. The arc IS the source of metal during cooling and, if not removed, will
heat whIch. melts the edg~s of the plates. The give some degree of protection to the finished
whole of thIS molten area IS ~nown as the w~ld weld until a surface protection is applied. The
po.ol. The covered ~lectrode IS used up dun?g coatings on electrodes used for positional
thIS process, meltmg the electrode matenal welding have what is known as a 'quick freez-
and ~late edges :0 form the weld.
WIth all weldlI~g processes, the base metal,
ing slag' so that, when welding in the vertical
position, for example, the slag will give some
the weld metal bemg transferred across the arc help in forming the shape of the weld deposit.
to the weld pool and the en~ of. the electrode However, it must be recognised that this does
are all exposed. to c~ntammatI.on fr~r.n the not reduce the level of operator skill required
atmosphere WhICh wIll allow ImpuntIes to when positional welding.
combine with the molten metal. This results in
reducing the mechanical properties (strength)
and corrosion resistance of the weld, and pos- Striking the arc
sibly of the base metal. This means that the
molten weld area, the end of the filler or elec- For the beginner, initial striking of the arc can
trode and the transferring metal must be pro- be a strange experience from the point of view
tected from atmospheric contamination. In that with the common type of welding screen
the four welding processes being considered, it is not possible to see the position of the end
this protection is achieved in different ways. of the electrode in relation to the joint until
In MMA welding the arc is shielded by the arc is struck. The following simple rules
lasses produced by the burning of the elec- will help overcome this initial problem (see
trode coating (see Fig. 2.3). These gasses com- Fig. 2.4).
32 MANUAL METAL ARC WELDING

Stop/starts
Stop/starts should be as smooth as possible,
although a slight bump will be seen. To keep
this to a minimum it is important that move-
ment into the crater of the previous weld is
done as quickly as possible once the arc is sta-
biIised (see Fig. 2.6).

Locate the end of the electrode over the

point where the weld is to start (position 1).
Now bring the welding screen in front of your
face to protect your face and eyes. Lower the
electrode onto the plate with a gentle stroking
motion (position 2). The arc will then be
established.
Lift the electrode until the visible arc length
Electrode angles
is 3-4 mm (position 3). The arc should then be When making a weld, either on a flat plate or
stabiIised (kept burning) at this level before between two pieces of metal, one of the basic,
moving forward in the direction of travel (pos- but most essential, skills of which to gain mas-
ition 4). It is important to maintain this dis- tery is electrode angles.
tance between the end of the electrode and the There are two angles which affect the suc-
work. This is known as the arc length. cessful deposition of the weld metal. These are
When the electrode has been consumed the angles to either side of the electrode,
(used up), a new electrode is placed in the elec- known as the tilt angle and the angle between
trode holder and the same procedure is fol- the electrode and the plate surface in the
lowed as in (1) to (4) above. The start position direction of travel, known as the slope angle
of the new weld (position 1) is slightly in (see Fig. 2.7).
advance of the previous weld run. Once the arc
is established, move quickly into the weld
pool of the previous weld and move along the
joint. This point on the weld is called the
stop/start point. By adopting this method at
stops and starts it will enable continuity of the
weld size and help reduce the effect of weld
defects at this point (see Fig. 2.5).

Although these angles will be affected by

many other things in the welding process,
they will play an important role in the suc-
cessful deposition of the weld bead, regardless
of the type of process being used. It is there-
fore important to learn the skill of electrode
angle control at an early stage in the develop-
ment of welding competence.
 ELECTRODE ANGLES 33

There is a base point from which this skill The effect is common to any of the welding
can be developed, and Fig. 2.8 shows the elec- processes where there is some form of flux
trade angles suitable for depositing the first or medium for protecting the weld metal during
root deposit in a fillet welded 'T' joint. deposition, in MIG/MAG when using flux-
cored wires, oxyacetylene welding where flux-
es are used or MMA welding with covered
electrodes.
When depositing a weld bead onto a plate
surface, or along the joint line between two
plates, it is important that the molten weld
metal is deposited equally to either side of the
joint. In order to get the required penetration
into each plate, imagine the electrode as a
pipe, and the molten metal as water flowing
from it. The water will flow whichever way
you direct the pipe; the same effect happens
When welding with covered electrodes, the with the electrode and the molten metal. The
electrode coating melts off in the arc to re- means of controlling this is by the control of
form and solidify on the weld surface in the the 'tilt' angle.
form of a slag, helping to protect the weld If the electrode is moved to either side of
metal from contamination by the atmosphere the centre line of the joint, the molten metal
during cooling and, to some degree, the slag will tend to do the same. This will have the
will protect the weld metal after solidification effect of the weld metal being deposited to one
has taken place. It is only a temporary protec- side of the joint line. This results in missing
tion; permanent surface protection coverage the plate edges and causing weakness in the
should be considered in the long term. joint area (see Fig. 2.10).
Controlling the flow of this molten slag is
achieved by the 'slope' angle of the electrode.
If the slope becomes too steep there is a ten-
dency for the molten slag to run around and in
front of the electrode and into the weld pool
(see Fig. 2.9). This will tend to form a barrier
between the end of the electrode and the
plates being welded, preventing penetration
into the plate surface or root of the joint. It is
also likely to result in weld defects, such as
slag inclusions, lack of penetration and lack of
fusion.
34 MANUAL METAL ARC WELDING

Some of the defects associated with this are Weaving

missed plate edges, lack of side wall fusion and
unequal leg length. All these will have a seri- Weaving of the electrode refers to the side-to-
ous effect on the strength of the joint and its side movements of the electrode. This is some-
performance in service. times required to spread the molten metal
This section has considered the electrode across the joint width or, in the case of pos-
angles of 'slope' and 'tilt' and the problems ition welding, to control the heat input.
associated with poor control of these angles. It Textbooks show many different weave pat-
is also important to remember that controlling terns which may be suitable in various situa-
the 'tilt' angle can be used to our advantage, tions, and some of these are shown in Fig. 2.12.
especially in the case of multi-run welds. By The maximum weave width for a given size
varying the 'tilt' angle slightly, it is possible to of electrode is two to three times its diameter.
direct the molten metal to the desired area of Any greater than this and the edges of the
the weld joint. joint tend to become cold. This gives a coarse
In Fig. 2.11 A shows the tilt angle for depo- weave pattern or, even worse, lack of fusion,
sition of the first or root run in a 'T' joint. B fusion penetration or inter-run fusion.
shows the 'tilt' angle for depositing the second
run in a multi-run fillet welded 'T' joint.
Slope and tilt angles can work for, and
against, the welder. Gaining control and being
aware of the effects in changing 'slope' and
'tilt' angles will be most rewarding and benefi-
cial to the skilled welder in controlling the
weld pool and achieving sound quality welds
)f correct shape and size.

When a weave pattern is used to suit joint

requirements, this pattern is usually reflected
in the finished weld. If the movements are
erratic or inconsistent then the finished weld
appearance may suffer from what could be
called a weld defect. One example of this is
shown in Fig. 2.13.
If the progression along the joint is pro-
gressed in a coarse movement, the weld
appearance will be as shown in Fig. 2.13.
Steady progression along the joint will
achieve a smoother weld profile and a com-
plete filling of the joint (see Fig. 2.14).
Slight pauses at the sides of the weave will
also help in this situation, but if this is exces-
sive, overheating may occur and the molten
metal may sag or overlap the edges of the
ELECTRODE SIZE AND CURRENT CAPACITY 35

Although this may be the case, it is not totally

acceptable in all situations, and for this reason
a more standardised method of recognition is
needed.
All MMA electrodes are covered by a classifi-
cation scheme, according to their flux coat-
ings, welding position suitability, current
capacity and mechanical properties. The spec-
ifications for MMA welding electrodes are cov-
ered in BS639 (1986) Electrodes for MMA
welding of Carbon and Carbon Manganese
Steels. An example of a typical electrode spec-
ification is given on page 36.

Electrode size and current

capacity
Something else important to the welder about
the stick welding electrode is the amperage
range for a particular size of electrode. This
information is usually listed on the side of the
electrode carton and, therefore, readily avail-
able. But with experience the welder will get to
know the amperage ranges. The size of the
electrode refers to the diameter of the core
wire (see Fig. 2.16).
36 MANUAL METAL ARC WELDING

85639 Fourth Digit - Impact Value - 4

Digit Temp. C, for 47J ave CVN.
Note: All weld metal mechanical properties. ExxxOx not specified
The mechanical properties of the deposited weld Exxx1x +20
metal refer to ALL-WELD METAL PROPERTIES when Exxx2x 0
deposited in the flat position. These may have little Exxx3x -20
relevance to the properties of a real joint achieved in Exxx4x -30
practice since this will depend on the dilution from Exxx5x -40
the base material, welding position, bead sequence Exxx6x -50
and heat input. Apart from their use for quality con- Exxx7x -60
trot purposes, the mechanical properties of the all Exxx8x -70
weld metal test provide the designer with an initial
Covering - BB
guide to the selection of electrodes.
ExxxxB Basic
This is particularly important in regard to Charpy
ExxxxBB Basic, high recovery
impact grading. Thus electrodes which have the
ExxxxC Cellulosic
highest gradings are more likely to offer better
ExxxxR Rutile
Charpy properties when used in practice. They will
ExxxxRR Rutile, heavy coated
not necessarily give the Charpy results in a joint
Exxxx5 other types
which they give in an all weld metal test piece.
85639:1986
Efficiency - 130
This specification is divided into two parts, the com-
pulsory strength, toughness and covering (STC) code The normal electrode efficiency is the ratio of the
which appears on each electrode and the additional mass of weld metal to the mass of core wire con-
coding showing efficiency, welding positions, power sumed for a given electrode. It is quoted to the near-
est 10% and is included if the figure is equal to or
supply requirements and when appropriate, hydro-
greater than 110.
gen control. Use of this classification system is best
illustrated by an example: Welding position - 3
5TC code Additional 1 all positions
Ferromax E5144BB 2 all positions except vertically down
[130 3 1 H]
3 flat and horizontal-vertical
Consumable Type - E 4 flat

E is for covered electrode for manual metal arc weld- 5 flat, vertically down and horizontal-vertical
ing. No other consumables are covered by this spec- 6 any position or combination not included above
ification.
Power supply requirement - 1
Digit Polarity for DC OCV for AC
Strength - 51 0 as recommended not suitable
Designation T5 min YS min elongation, % 1 + or- 50
N/mm2 N/mm2 when 3rd digit in 2 - 50
classification is 3 + 50
0.1 2 3,4,5 4 + or- 70
E43xxx 430-550 330 20 22 24 5 - 70
E51xxx 510-650 360 18 18 20 6 + 70
7 + or- 80
Third Digit - Impact Value - 4 8 - 80
Digit Temp. C, for 28J ave CVN. 9 + 80
ExxOxx not specified
Exx1xx +20 Hydrogen controlled electrodes - H
Exx2xx 0
The letter H is included for electrodes which deposit
Exx3xx -20
not more than 15 ml diffusible H2/1 00 g deposited
Exx4xx -30 weld metal.
Exx5xx -40
Courtesy of 851, Milton Keynes.
 WELDING POSITIONS FOR PLATES 37

Electrode coatings Iron powder electrodes

Electrode coatings for MMA electrodes are Iron powder electrodes get their name from
grouped into four main types. These are cellu- the addition of iron powders to the coating
losic, rutile, basic and iron powder. which tend to increase efficiency of the elec-
trode. For example, if the electrode efficiency
is 120%, 100% is obtained from the core wire
Cellulosic electrode and 20% from the coating. Deposited welds are
very smooth with an easily removable slag;
Cellulosic electrode coatings are made of welding positions are limited to horizontal,
materials containing cellulose, such as wood vertical fillet welds and flat or gravity position
pulp and flour. The coating on these elec- fillet and butt welds.
trades is very thin and easily removed from
deposited welds. The coating produces high Irrespective of the type of coating, electrodes
levels of hydrogen and is therefore not suit- need to be handled and stored with care. If
able for high-strength steels. This type of elec- they are subject to knocks or mishandling
trade is usually used on DC+ and suited to then the coating will be damaged or chipped,
vertical down welding. possibly making the electrode unusable.
Electrode coatings can sometimes be off
centre, in this case the electrode coating will
Rutile electrodes tend to burn away faster on one side during
use. This will cause the arc to be uncontrol-
Rutile electrodes, or general-purpose as they lable causing possible defects in the deposited
are sometimes known, contain or have coat- weld (see Fig. 2.17).
ings based on titanium dioxide. These elec-
trodes are widely used in the fabrication
industry as they produce acceptable weld
shape and the slag on deposited welds is easily
removed. Strength of deposited welds is
acceptable for most low-carbon steels and the
majority of the electrodes in this group are
suitable for use in all positions.

Basic or hydrogen-controlled
electrodes
Basic or hydrogen-controlled electrode coat-
ings are based on calcium fluoride or calcium
carbonate. This type of electrode is suitable for
welding high-strength steels and the coatings
have to be dried. This drying is achieved by
baking at 450°C holding at 300°C and storing
at 150°C until the time of use. By maintaining
these conditions it is possible to achieve high-
strength weld deposits on carbon, carbon
manganese and low-alloyed steels. Most elec-
trodes in this group deposit welds with easily
removable slags, producing acceptable wel.d Welding positions for plates
shape in all positions. Fumes given off by thIS
electrode are greater than with other types of Several examples of welding positions for
electrodes. plates are given in Fig. 2.18 overleaf.
40 MANUAL METAL ARC WELDING

Corner joints welded in the flat (gravity)

position (10 mm) do not present so much of a
problem, although, for example, the size of
electrode and current values used will vary in
order to control burn-through on the first run.
For the first or root run a 2.5- or 3.2S-mm
electrode may be required to control the
degree of penetration through the joint.
Subsequent runs with a 4 or 5 mm electrode
may be acceptable, providing no rollover
(overlap) is maintained at the top edges (see
Figure 2.24 Electrode angles for outside corner Fig. 2.26).
joint (90°).

joint, although great care has to be taken to

avoid rollover on the horizontal edge of the
vertical plate (Fig. 2.24a) and burning away of
the top corner on the vertical edge of the hor-
izontal plate (Fig. 2.24b). This will result in a
misshapen weld profile and a reduction in the
throat thickness of the weld, causing weakness Figure 2.26 Open outside corner joint welded in
of the joint at the corner. the flat (gravity) position.
When welding corner joints in the horizon-
tal vertical position it becomes more difficult
to maintain the plate thickness on the corner; A single 'V' butt joint (10 mm) welded in
achieving this continuity of thickness is the flat (gravity) position is very similar to the
important to the strength of this joint. The corner joint above, only the joint preparation
root of first run in this joint also requires a is different. Instead of being a naturally
greater degree of control to avoid excessive formed 90° of the square edge plates, the plate
penetration on the inside of the corner. To get edges of the 'V' butt are machined or flame cut
this may require smaller electrodes (2.5 or 3.25 to 30-35° to form an included angle of 60-70°.
mm) and lower current values (see Fig. 2.25). Where the degree of penetration through the
joint (welded from one side) has to be con-
trolled, a small electrode (2.5 or 3.25 mm) can
be used (see Fig. 2.27).
Weaving should not be necessary, although
a slight side-to-side motion may be used to
control the heat input and therefore penetra-
tion. Root face and root gap will also playa

In order to achieve the correct profile and

avoid burning away of the top edge and over-
lap at the bottom edge, the joint may demand
the use of smaller electrodes and lower current
values.
 PLATE POSITIONS 41

large part in controlling the degree of penetra-

tion through the joint. Increasing the root gap
will allow ease of penetration and vice-versa.
Increasing the root face will reduce the degree
of melting at the root and vice-versa.
Subsequent runs can be deposited with larger
electrodes, providing that the 'V' is sufficient-
ly wide to allow access of the electrode to any
underlying runs. Otherwise fusion penetration
will be at risk (see Fig. 2.28).

weave techniques demand high skill levels of

the operator.
Weave patterns possibly unique to this
welding position are to weave back towards
the top edge of the joint, away from the direc-
tion of travel. This means that the weld metal
on the bottom edge of the joint slightly pre-
There is also the added risk that using too cedes that at the top, affording some degree of
large an electrode with high current values support. Pausing slightly at the top edge will
will burn through the first or root run causing ensure complete fill up of the joint. Stops and
excessive penetration or even total collapse of starts should always be made on the bottom
the root deposit. Slope angle for this joint will be edge to avoid slag traps and manipulation
60-80° to the line of the weld and the tilt angle problems (see Fig. 2.30).
equal to each side of the electrode. The appear-
ance of the finished weld should be blended
smoothly with the base metal at the weld toes,
with even ripples and no excess metal.

Horizontal-vertical position
Single 'V' butts joint (10 mm) welded in the
horizontal-vertical position have a different
plate edge preparation, although the included
angle will be the same as in the flat 'V' butt
(see Fig. 2.29).
Depositing the root or first run in the joint
will require the same degree of control as for
the flat 'V' butt, although care must be taken Larger electrodes can be used for subsequent
to prevent the molten metal sagging away deposits, remembering the point made earlier
from the top edge. Some degree of support will about access by the electrode to the first and
be given by the lower joint preparation, but in any underlying deposits. When depositing the
addition to this the electrode should be direct- final layer or capping runs, care must be taken
ed slightly toward the top edge. Other meth- to avoid the molten metal from rolling over
ods of control are the use of smaller diameter onto the bottom face of the plate and burning
electrodes with lower current values. Bead away the top edge, causing undercutting (see
techniques are usually used in this position; Fig. 2.31).
42 MANUAL METAL ARC WELDING

The slope angle will beas for other joints

listed above 60-80°, while the tilt angle will
vary to suit the positioning of the weld
deposits in the 'V'. See Fig. 2.32.

Verticalposition
Joints welded in the vertical position require
the use of the weave technique to a greater
extent than some of the earlier examples. The
various weave patterns are mentioned above,
and there is no hard and fast rule as to which
one is used; this will probably be dictated by
the joint type or nothing more than the per-
sonal choice of the operator. Whatever pattern
is chosen will require time to perfect - espe-
cially for the beginner.
One of the difficulties to overcome is the
control of the molten weld pool, to prevent
sagging and the excessive convex weld profile
of the finished weld. One of the major influ-
ences is the heat input, which is closely linked
to the size of the electrode and the current
used. Using the weave technique will also
influence the amount of heat at anyone point
at anyone time, i.e. moving the electrode the joint and the electrode will prevent pene-
within the confines of the joint will help tration taking place. It is for this reason that
spread the heat. This is common to all vertical when depositing the root run, the electrode
welds such as corners, butts and fillets. angle must not be allowed to be too steep, cer-
tainly no more than 5-10° below 90° to the
joint. If the angle becomes too steep then there
Vertical'T' fillet is a tendency to prevent the molten flux coat-
ing (slag) flowing from the joint, or even push-
Achieving and controlling penetration either ing it up into the corner and trapping it under
into or through the root of the joint is the main the weld, forming slag inclusions and/or lack of
concern in all situations. In the case of the ver- penetration at the root (see Fig. 2.33).
tical 'T' fillet (10 mm) the root of the joint is Commence to deposit the root run starting
known as closed (no gaps) and therefore any from the bottom of the joint; weaving should
obstruction, such as slag, between the root of be kept to a minimum, but a slight inverted 'V'
 electrodes of 2.5 or 3.25 mm diameter; above
this will involve higher current values, causing
difficulties with penetration and weld pool
control.
It is also important not to burn away the
two outer corners of the plate edges and for
this reason it may be necessary to restrict the
size of the electrode used for the capping run.
Although a weaving technique is used to con-
trol the sagging of the metal, large diameter
electrodes, high heat inputs and therefore
large weld pool size will result in sagging of
the molten metal, convex weld shape, mis-
motion will reduce the convexity of the root shapen weld profiles and excessive burning
deposit (flatten it out). For subsequent runs away of the corners giving rise to undercutting
the weave pattern should be chosen to achieve (see Fig. 2.35).
the desired leg length (in this case 10 mm) and
weld profile. The slope angle as mentioned
earlier should be no more than 5-10° below a
line 90° to the joint; the tilt angle equal to
each side of the electrode and the plates (see
Fig. 2.34).

Open outside comer joints

Open outside corner joints welded in the ver-
tical position (10 mm) are much the same as
the vertical 'T' fillet, in that the weld is
deposited between two 90° faces - but this
time controlling penetration through the
joint. This can be achieved by using small
44 MANUAL METAL ARC WELDING

Vertical 'V' butt welds quick freezing of the deposited weld metal to
keep it in position. Initial difficulties may be
For vertical 'V' butt welds (10 mm) the tech- experienced achieving a penetration bead on
nique will be similar to the vertical corner the upper surface of the joint. Depositing the
joint. This time the plate edge preparation will root run will require a 2.5-3.25 mm electrode
form a 60-70° 'V', rather than a 90° 'V', and slope angle of 60-80° to the line of the weld -
the problem of the plate corers has been elim- with the end of the electrode right up into the
inated, although the same care will be 'V' at the front edge of the deposit. This will
required when capping to avoid undercutting assist in the fusion of the plate edge and give a
at the weld toes. slight protrusion through the joint onto the
As mentioned in earlier examples with 'V' upper face. For subsequent runs 3.25 or 4.00
butt preparations, some degree of penetration mm electrodes may be used, maintaining the
control can be achieved by varying the root same slope angle and keeping weaving to a
gap and face, but this has limitations. minimum. Although weaving the cap is possi-
Achieving acceptable penetration will require ble it can be deposited in bead formation
the use of smaller diameter electrodes as in rather than a weave over the full width of the
vertical corner joints. Subsequent runs can be joint. This will help control the sagging of the
deposited by using 3.25 or 4 mm electrodes. molten metal (see Fig. 2.37).
Remember the points made earlier regarding The arc length must be kept short at all
electrode access to the joint and underlying times, caution being taken to avoid the elec-
deposits, and also the effects of large diameter trode freezing in the weld pool, the root or
electrodes, high heat inputs and large weld sides of the joint. Welding in this position is
pool sizes (see Fig. 2.36). most difficult and may require lots of practice.

Overhead 'T' filters

Overhead 'T' filters (10 mm) are to somt
Figure 2.36 Electrode angles for vertical single extent a repeat of the horizontal vertical 'T'
'V' butt joint. fillet, flat position for both root and subse-
quent runs. As with all square edge 'T' fillet
Overhead 'V' butt welds joints the mass of parent metal at the root is
far more than with the 'V' butt joint. This will
Overhead 'V' butts (10 mm) make excessive permit larger electrodes to be used with higher
demands on the skill of the operator to over- current values in order to achieve fusion pene-
come the gravitational forces and produce tration.
acceptable welds. In this position the root face For the root run, keeping a short arc with a
and gap will play an important role along with slope angle of 70-80° and a tilt angle equal to
the size of the electrode and heat input in the either side of the electrode, commence weld-
 SUMMARY 45

ing at one end of the joint. Normal procedure Summary

for subsequent runs is to position the runs
from the bottom upwards (see Fig. 2.38). In all of the exercises above a plate thickness
Therefore the second run will overlap the root of 10 mm was chosen. When welding other
run above its centre line and onto the face of thicknesses, first consider all the points that
the vertical plate with a tilt angle of 30-40° to have been discussed in relation to the joint
the vertical plate keeping weaving to a mini- type, plate thickness, welding position and
mum. The third run is positioned between the weld size. This will then help the welder
peak of the second run and the top (horizon- decide on:
tal) plate with a tilt angle approximately equal · 0 • o

to elt. h er SI·d eat f h e e Iectro d e. a ) e Iectro d e SIze an d h eat Input In re 1a t IOn t a

o

Successful welds 10 the overheat posItIOn

•• 0
I
pate t h ICk nesses
o f 1 h· . th . fIt d b) size of root gap and root face for heat
requIre care u c Olce 10 e SIze 0 ~ ec ro e transfer and enetration
and current values, as well as the SkIll of the . P .
operator ... C ) SlOg1e b ea d or weave tec h nlque to over-
As weavIng... has to be kept to a mimmum, to come gravitatIOna.. 1 f orces
avo Id saggIng, we Id· SIzes are ac h Ieve d b y th e
° 0 o d) slope
. and tIlt. angles of electrode 10 rela-
.
mu 1tI-run .
tec h mque, so In some Ins t ances
0 • twn ...to d eposlt .. ' '
it may be necessary to repeat the sequence of) e posItIOnIng ate f h d eposit In th e V or cor-
ner
runs. f) number of runs required to achieve weld
size
g) any difficulties associated with the joint as
with corner joints
h) access of the electrode into the 'V'
i) finished weld acceptance levels.

As mentioned at the beginning of this chapter,

the stick welding process is a very versatile,
well established, mobile and proven process,
which is widely accepted by both operator and
manufacturer. It is a very mobile process used
for welding in all positions, and although
more suitable processes are available, it is able
to be used for joining most metals in the
hands of a skilled operator. Although the
process has been around for a long time, it still
finds a place in a wide range of workshops and
site situations, and although used to a lesser
degree than in the past, should still be around
for many years to come.
 Metal arc gas-
shielded welding
Choosing the name to describe this process speed increase from 1.9 to 7.6 m/min.
was not without consideration. This type of Therefore, over the wide range of wire sizes
welding is often referred to by many different available, e.g. 0.8, 1.00, 1.2 and 1.6 mm, the
names. The reason for choosing metal arc gas- process is suited to a wide range of current
shielded welding (MAGS) was that it encom- values, metal thicknesses and welding
passes the process without regard to other positions.
influencing factors such as inert or active gas, A power source with a DC output and the
solid, cored or self-shielding wires. Other electrode (wire) connected to the positive pole
names the process is referred to are: metal supplies current to the wire via the contact tip
inert gas (MIG) welding, metal active gas in the welding torch. Current, gas, wire and
(MAG) welding, gas metal arc welding water (in the case of water-cooled torches) are
(GMA W), CO2 welding and semi-automatic supplied to a hand-held torch by means of a
welding. To satisfy the training situation the flexible conduit. Voltage and wire feed speed
description MAGS is used in the text below. (amps) are adjusted at the power source to suit
You will find that the process is most com- welding conditions, e.g. wire diameter, weld-
monly referred to as MIG or MAG in the work- ing position, metal thickness, mode of transfer
place. and type of wire. The welder is then left to
In order to comply with international stan- control the distance between the torch and the
dards a listing of the processes and their work surface and the speed of travel.
numerical representations is given in Appendix As mentioned earlier, the end of the molten
1 at the end of the book. wire electrode, the transferring metal, weld
pool and the molten parent metal must be
protected from atmospheric contamination.
MAGS welding process In the MAGS .welding process this is achieved
by the gas shIeld, not from the electrode but
The MAGS welding process (shown in Fig. 3.1) from a separate gas supplied in cylinders or
can be used on a wide range of metals, positions bulk supply piped to the power source. The
and thicknesses. The process works by creating level of shielding provided by the various
an arc between a continuous wire electrode and gases will vary with the density of the gas; in
the parent metal to be joined. The wire feed general terms, the heavier the gas the better
speed unit controls the rate at which the wire is the shielding, especially in the flat position.
fed to the arc. Increasing the wire feed speed Argon, carbon dioxide and oxygen are the
will proportionately increase the current heayier of the common shielding gases.
(amperage) on the wire. For example, a 1.6 mm
diameter wire will operate over a current range
of 150-400 amps with a proportionate wire feed
48 METAL ARC GAS-SHIELDED WELDING

Choice of shielding gas gaseous form. When using CO2 for gas-shield-
ing purposes a heater/vaporiser is fitted
The shielding gas must be carefully chosen to suit between the cylinder outlet and the regulator.
the application. The selection will depend on: The heater should be allowed to warm up
before welding commences. A flowmeter can
a) The compatibility of the gas with the metal also be incorporated on the outlet side of the
being welded. regulator, if required (see Fig. 3.3).
b) Physical properties of the material.
c) The welding process and mode of opera-
tion. Electrode wires
d) Joint type and thickness.
Welding wires are usually supplied on 12-18
If the material has a high thermal conduc- kg reels layer wound in such a way as to ensure
tivity a shielding gas which increases the heat that the wire releases smoothly during the
transferred to the work piece should be used. welding operation. Steel wires are usually coat-
For copper and aluminium, helium or heli- ed with copper to offer some protection
urn/argon mixtures are particularly useful against corrosion, to reduce friction and to
since they reduce preheat requirements and improve the electrical contact between the
improve penetration on thicker sections. A wire and the contact tip. Not all wires are cop-
summary of common gases and their applica- per coated; these are usually used where the
tion is given in Table 3.1. rate of wire consumption is high and corrosion
Carbon dioxide (C02) supplied in liquid resistance is not a problem. Both types of wires
form tends to cause freezing up of the regula- should be stored in their original packaging in
tor during use as a result of the change to a a dry environment until needed.
 WIRE FEED SYSTEM 49

Figure 3.2 MAGS welding equipment (courtesy means of the trigger of the torch handle by acti-
of Migatronic). (1) Main switch. (2) Central vating it for at least 3 s. Afterwards the wire will
adapter _ for welding torch. (3) Quick release con- inch by the speed selected on the wire speed but-
nector _ for the torch cooling system. (4) ton (position 10). (13) Burn back - adjustable
Inductance output _ 00.6-1.0. (5) Inductance out- delay from the wire feed stops until the welding
put _ 01.2-1.6. (6) Inductance output - 01.6-1.8. voltage is out in order to avoid sticking of the
(7) Inductance output _ 01.8-2.0. (8) Connection wire. Adjustable between 0.05 and 1 s. (14) Gas
for push-pull hose and torch assembly. (9) On - post-flow - gas post-flow time. Adjustable between
lights when the machine has been turned on. (10) 0 and 20 s. (15) Soft start - pre-setting of soft start
Wire speed _ this button is used to set the wanted which means the speed by which the wire starts
wire speed. Adjustable from 1.7 to 24 m/min. (11) before the arc is ignited. Adjustable between 1.7
Trigger mode _ this switch is used for setting of and 5 m/min. In position OFF the wire will start
either 2-stroke or 4-stroke trigger function. (12) by the speed selected by the wire speed button
Inching button _ this button is used for fitting of (position 10). (16) Voltmeter - shows the welding
welding Vlire. When the button is activated the voltage. (17) Ammeter - shows the welding cur-
wire is fed by the speed selected by the wire speed rent. (18) Fine adjustment of welding voltage.
button (position 10). Inching can also be done by (19) Coarse adjustment of welding voltage.

Wire feed system the rollers can be adjusted by means of a ten-

sion screw. Excessive pressure on the rollers
The wire feed (push) system is shown in Fig. may distort or damage the wire, causing feed-
3.4. The electrode wire is fed from the reel to ing problems in the lines or at the contact tip.
the tube via the wire feed rollers. Pressure on This system is known as the push system. In
50 METAL ARC GAS-SHIELDED WELDING

some cases the feed rollers are mounted on the • dip or short circuit transfer
welding torch feeding the wire only a short • spray transfer
distance. This system is known as the pull sys- • pulsed transfer.
tern. A combination ....of both these systems can D·lp t rans f er t a k es p 1ace a t 15- 25 va It s an d
be used where feedmg dIffIcultIes may occur. 40 - 200 amps on wlIe . d·lame t ers up t a 1.2 mm.
This mode of metal transfer is suitable for
Metal transfer modes welding thin sheet, positional welding of
thicker sections and depositing root runs in
The MAGS welding process offers three meth- open butt joints. Metal transfer is a result of
ods of transferring metal across the arc, these reducing the arc gap until the wire comes into
are: contact with the work or molten pool, Le. dip-
 METAL TRANSFER MODES 51

Figure 3.5 Dip transfer.

ping or short circuiting. At the point of short welded in position. This is possible due to the
circuiting a rise in current takes place, melting oxide film which forms on the surface of the
off the end of the wire and reigniting the arc, weld pool retaining the molten metal in pos-
the cycle is repeated 100-200 times per sec- ition. Metal transfer is a result of the increased
ond. If the rise in current during short circuit- current values. At higher current values the
ing is too fast it will cause the molten globule globule size decreases and the rate of metal
to explode out of the weld pool causing exces- transfer increases. This results in the molten
sive spatter. If the current rise is to slow the metal being projected across the arc in small
wire will stub and possibly freeze into the weld droplets in the form of a fine spray with low
pool. This can be controlled by the inductance spatter levels. The high welding speed, rate of
setting, Le. the higher the inductance setting, metal deposition, size of deposits in one pass
the lower the short circuiting occurrence and and good penetration capabilities makes it an
vice-versa (see Fig. 3.5). economical method of welding heavy steel
Spray transfer takes place at 30-50 volts and sections (see Fig. 3.6).
200-400 amps on wire diameters over 1.00 Pulsed transfer has gone some way to com-
mm. This mode of metal transfer is suitable for bine the two modes above by controlling the
welding metal thicknesses above 6 mm with a melting off period in which the droplets are
high rate of deposition and good penetration detached from the electrode. This is made pos-
and a high heat input. Welding is limited to sible by introducing a high current pulse into
butts and horizontal vertical fillet welds in the the circuit, at which stage the droplet transfer
flat position. The exception to this is the weld- takes place whilst a low background current
ing of aluminium and its alloys which can be maintains the arc. The result is a spray mode of
52 METAL ARC GAS-SHIELDED WELDING

over a wide current range (constant potential

or flat output power source) provides a means
of controlling the arc. Any small changes in
arc length are rapidly made up for by an
increase in current (wire feed) which keeps the
arc length constant, Le. self-adjusted.

Contact tip, nozzle settings

The position of the contact tip in relation to
the nozzle is slightly different for the modes of
metal transfer. The contact tip can be set to
protrude beyond the nozzle or set back inside
depending on whether using dip or spray
transfer mode. This will affect visibility, acces-
sibility and gas shielding. The following gives
suggested settings for the mode of metal trans-
fer being used.
Mode of transfer Contact tip
Dip 2-8 mm protruding
Spray 4-8 mm inside
Spray (aluminium) 8-10 mm inside

Electrode extension
The extension of the wire or stick out is usual-
ly measured from the contact tip to the weld
pool. Excessive stick out will reduce the arc
current resulting in less penetration.
Suggested electrode stick out for the respective
modes of transfer are shown below.
Mode of transfer Electrode extension
Dip 4-8 mm
Spray 15-25 mm

Burn back
The result of a burnback is fusing of the elec-
The self-adjusting arc trode wire to the end of the contact tip. The
remedy can be quite simple in some cases, not
In the MAGS welding process the voltage set- so in others depending on the severity of the
ting of the power source governs the arc burnback. It may be possible to release the
length. Small diameter wires up to 1.6 mm wire by pulling it free with a pair of side cut-
burn off at very high rates. The burn-off rate ters; lightly filing the end of the tip may also
will vary with small changes in current caused be helpful. If this is successful the wire will
by variation in arc length due to torch move- spring forward on release. If this is unsuccess-
ment, erratic wire feed or fluctuating current ful switch off the power source and remove the
pick up in the contact tip. A power source contact tip to expose and cut the wire. The
which keeps a moderately constant voltage wire can then be gripped in the vice and by
 WEAVING 53

gently turning the contact tip the wire should Table 3.2 Some of the more important features of
release. In severe cases it may be necessary to the process (comtesy of BOC)
c~t off the end of the contact tip to release the
WlTe or even renew the contact tip.
Feature Comment
Low heat input All modes of transfer, par-
ticularly dip and pulse
Current and voltage give low heat inputs CO.1TI-
pared to the MMA process.
settings This is useful for thin
plate and positional work
The following is a guide to voltage settings for but care must be taken to
MAGS welding. Slight adjustments will be avoid fusion defects on
required to suit plate thicknesses, joint type, thicker material
joint design, welding position, root face, type High operating efficiency.
Continuous operation
of material and procedure demands. High duty cycle.
High productivity
Wire
diameter Vol tage Current High deposition rate Higher deposition rate
(mm) (volts) (amps) compared to the MMA
15-22 50-100 process particularly with
0.6
60-190 spray transfer
0.8 18-25
0.9 18-30 70-250 No heavy slag The absence of slag
1.0 18-32 80-300 means that little cleaning
18-36 120-400 of the weld is required
1.2
220-500 after welding
1.6 27-40
Low hydrogen Absence of flux coating
and the use of dry gas
controls the hydrogen
British Standards for wires level. This reduces the
risk of cold cracking
and fillers
BS2901 - Part 1 Filler Rods and Wires for Gas
Shielded Arc Welding of Ferritic Steels covers
the chemical composition, diameter and toler-
ances of rods and wires, condition of rods and tration into fusion faces on heavy sections or
wires, dimensions of reels of wire, packaging wide preparations. Weaving the electrode is a
and marking. means of overcoming this, ensuring the full
force of the arc is directed toward the fusion
Features of the process faces and any underlying weld deposits to
This may
ensure good fusion penetration.
Some of the more important features of the influence the choice of weave pattern chosen.
process are summarised in Table 3.2.
Stops and starts
Weaving The same rule applies as for MMA welding.
Weave patterns are common to all the process- Strike the arc in advance of the previous weld
es under discussion. In MAGS welding, weav- and within the confines of the weld joint,
refers to the side-to-side moving as quickly as possible into the weld
ing usually
movement of the torch and, as a result, the crater. Stops and starts should blend smoothly
electrode. In this section the weave patterns, without any abrupt change in weld shape.
the reasons for weaving and the associated On completion of the weld it is important to
problems are considered. fill the weld pool (crater) to ensure continued
weld profile, throat thickness, strength, etc.
The MAGS welding process is inclined
to suffer from 'lack of side-wall fusion', pene- When crater fullness has been achieved and
54 METAL ARC GAS-SHIELDED WELDING

the arc extinguished, the torch should be held

at that position, at the eI1d of the weld to
provide gas shielding to the cooling weld
metal, avoiding the risk of contamination by
atmosphere.

Slope and tilt angle

Although the angles are the same as MMA
welding the stance of the operator may change
with the MAGS process. This is due to the large
diameter of the gas nozzle restricting visibility
to some degree. To overcome this the operator
will have to adopt a stance which permits
good visibility of the nozzle-to-work distance,
joint line and weld pool behaviour. Reducing Figure 3.~ Electrode and nozzle arrangement for
the slope angle will enable better visibility of MIG weldmg.
the weld area although this may have a
marked effect on the level of spatter, penetra-
tion, and gas shielding. outer sheath and a core of various powdered
materials (see Fig. 3.9). During the welding
process an extensive slag covering is produced
Direction of travel on the face of the weld bead. The feature that
distinguishes the FCAW process from other arc
The technique used may be referred to as left- welding processes is the enclosure of the flux-
ward or rightward, backhand or forehand but ing ingredients within the electrode.
possibly the most common to the MAGS weld- The continuously wire-fed electrode has
ing process is pushing or pulling. Both tech- remarkable arc operating characteristics. FCAW
niques have their relevance in the process and offers two fundamental process variations that
should be practised by the new operator. Not differ in their method of shielding the arc and
forgetting what was said earlier about restrict-
ed visibility, pushing is possibly the most
widely used, especially on thicker sections.
The pulling technique, although not the most
popular, is particularly suited to vertical down
welding of thin sheet and root runs in open
butt joints (see Fig. 3.8).

Flux-cored arc welding

Flux-cored arc welding (FCAW) is a variation
of the MAGS process. It forms an arc between
a continuous wire electrode and the part to be
welded, forming a weld pool and melting of
the joint faces takes place to produce a welded
joint. The process uses a gas shield produced
by the flux contained within a tubular elec-
trode. It can be used with or without a supple-
mentary shielding gas.
The flux-cored electrode is a made up tubu-
lar filler metal electrode consisting of a metal
 SELF-SHIELDED FLUX-CORED ARC WELDING 55

the weld pool from oxygen and nitrogen welding process and the gas-shielded flux-
atmospheric contamination. One type, self- cored arc welding process.
shielded flux-cored arc welding, protects the
molten metal by vaporisation of the flux core •
in the heat of the arc. The other type, gas- Self-shielded flux-cored arc
shielded flux-cored arc welding, uses an addi- welding
tional protective gas flow to the flux core.
With both methods the core material provides Figure 3.10 shows that the shielding is
a substantial slag covering to protect the obtained from the vaporised flux ingredients
deposited weld metal during solidification. which displace the air and protects the molten
The flux cored arc welding process com- metal droplet during transfer. The vaporised
bines three major features of other arc welding flux then solidifies to protect the weld during
processes. These are: solidification and assists in retarding the cool-
... , ing rate of the deposited metal.
a) the productIvIty rates of contmuous WIfe 0 ne c h arac t··ens tIC 0 f th e se If-s h·le Id e d pro-
e 1ectro d e ' ' cess IS. th e use 0 f 1ong e 1ectro d e extensIOns .
b) t h e .meta
. 11urglca 1 b ene f 1t sot f h e fl ux com- (electrodes extend 109 . beyond the contact
pOSItIOn , an d tube). Electrodes of 19-95 mm are not unusual
c) a slag that supports,
. protects and shapes d epen d·109 on th e app 1Ica
· t·Ion. Th'IS pre h eats
t h e we Id d eposlt. the electrode and lowers the voltage drop
This combines the operating characteristics of across the arc at the same time the welding
the manual metal arc (MMA), metal inert/ current decreases, lowering the heat input.
active gas (MIG/MAG) and the submerged arc The result is the weld bead being narrow with
welding (SAW) processes. As well as the fea- shallow penetration making the process suit-
tures listed above the two processes shown able for welding light-gauge materials (see
below are the self-shielded flux-cored arc Fig. 3.11).
56 METAL ARC GAS-SHIELDED WELDING

Gas-shielded flux-cored arc vary from 60° to 80° in the direction of travel
for vertical down welds on thin sheets and
welding root runs in open butt joints to 90-120° in the
direction of travel for vertical up filling runs
Gas-sh~el.ded flux-~ore? arc welding (GSF- in butt joints and root and subsequent runs in
CAW) IS Illustrated In FIg. 3.12. fillet welds. The tilt angle in most cases will be
The gas-assisted method, the shielding gas, equal to either side of the torch and the plate
either carbon dioxide (C02) or a mixture of
sur f ace.
argon plus CO2 protects the molten droplet Although it was mentioned earlier in this
from atmospheric contamination by forming section that the pulsed transfer mode of MAGS
an envelope around the arc and over the weld welding allows positional welding at higher
pool. Some oxygen m.ay ?e generated by the average current values and the added advan-
break ~p. of the shIeldIng gase.s, but the tages, the initial cost of this equipment is very
compOSItIO~ of the e.le~trode flux. IS.formulat- expensive. This, along with other reasons, is
ed to provIde deoxIdIse.rs to ehmI~ate any why the dip or short circuiting mode of metal
small amount of oxygen In the gas shIeld. transfer is commonly used for positional
welding. With the use of wire diameters up to
1.2 mm for vertical (up and down) and over-
head positions, it is possible to make quick
freezing deposits as a result of the small weld
pool size.
Although the vertical down technique is
common practice for depositing runs at vari-
ous stages on butts and fillets of different
thicknesses, care must be taken to avoid
molten metal running in front of the weld
pool preventing access to the root of the joint.
When discussing the welding positions
below it would be impractical to state precise
welding currents and voltages for any particu-
lar position. For this reason the current and
voltage settings given below will be influenced
by plate thickness, welding position and wire
diameter. They offer a starting point to which
final tuning will be required to achieve the
ideal welding conditions. Other factors affect-
ing these conditions are heat sinks from back-
ing bars, jigs or adjoining plates, joint types,
joint preparation and type of material being
MAGSpositional welding welded. All will have to be considered.

Positional welding with MAGS follows many

of the same rules as discussed in the section on IT' fillet and square edge butt joints
position welding with MMA. Where possible,
the work should be manipulated or rotated so IT' fillet and square edge butt joints in 3-mm
that welds can be made in the flat position, thick carbon steel, vertical down. Slope angle
the molten metal being pulled into the joint 60-70° in the direction of travel and tilt angle
by gravitational forces. As mentioned earlier equal to either side of the torch, using 0.8 mm
this is not always possible. wire at 19-21 volts and 90-130 amps. Welding
Both vertical up and vertical down welding vertical down keep the electrode directed at
techniques have a wider application with this the leading edge of the weld pool, taking care
process than with MMA. The slope angle will to avoid wire protrusion through the gap (butt
 MAGS POSITIONAL WELDING 57

joint). Speed of travel will be dictated by the amps weld from right to left (left to right for a
rate of metal deposition. Tack welds should left-handed person) using the push technique
be of sufficient size, strength and quantity deposit the root weld with minimum weave
to prevent movement during welding (see directing the full force of the arc at the root of
Fig. 3.13). the joint. Where it is necessary to use multi-
runs, for example, on heavier sections slope
and tilt angles will change with the respective
Honzontal-vertical'T' fillets run. Examples are shown in Fig. 3.14. Tack
welds should be of sufficient size, strength and
Horizontal-vertical 'T' fillets in 3-mm thick length to prevent movement during welding.
carbon steel, flat position. Slope angle Note, if positioning equipment and joint type
100-120° in the direction of travel and tilt allow, larger diameter wires or flux-cored
angle equal to either side of the torch, using metal wires can be used to achieve heavier
1.0-1.2 mm wire at 18-25 volts and 120-200 weld deposits.

Single 'V' butt

Single 'V' butt 10-mm thick carbon steel, ver-
tical position, vertical down root, vertical up
fill and cap, 1.6-3.0 mm root gap and 1.0-2.0
58 METAL ARC GAS-SHIELDED WELDING

mm root face with a 60° included angle. Using Thicknesses of up to 20 mm can be accom-
1.0-1.2 mm wire at 18-24 volts and 90-240 modated by increasing the number of filler
amps. Minimum weaving will be required on runs. For plate thicknesses over 20 mm differ-
the root run, the wire directed at the leading ent joint preparations (double 'V') or joint
edge of the weld pool ensuring penetration design (thicker root face) may allow vertical
and fusion of both edges. Weaving will be up root runs.
required for filling and capping; suggested
techniques are shown in Fig. 3.15, along with
the slope and tilt angles for the direction of Fillet weld
travel.
Fillet weld in 12-20 mm thick carbon steel
plate, vertical position. Using 1.0-1.2 mm wire
at 18-24 volts and 105-220 amps weld vertical
up, slope angle 105-120° in the direction of
travel. Minimum weaving is required for the
first run concentrating the force of the arc in
the root of the joint. Filling and capping is
achieved by weaving subsequent runs (Fig.
3.16a or b) or block weave (Fig. 3.16c), care
being taken to avoid excessive heat build up or
convexed bead shape.
 MAGS POSITIONAL WELDING 59

Horizontal-vertical butt joints

Horizontal-vertical butt joints in 12 mm and
above carbon steel. Using 1.2-1.6 mm wire at
18-22 volts and 140-220 amps. Slope angle
10-120° in the direction of travel. A bead
rather than a weave is used in this position to
avoid excessive heat build up and sagging
(overlapping) of the molten metal resulting in
lack of fusion penetration into the fusion faces
or underlying weld runs. The number of runs
required will be determined by the plate thick-
ness and type of joint preparation (see Fig.
3.17). Weave techniques are possible but
demand a high level of skill from the operator.
In most instances the arrangement of runs will
be as shown, the previous run affording some
degree of support for the one above. The tilt
angle (to either side of the electrode) will vary
with the run being deposited; a good indica-
tion of this is the correct position of the weld
in the joint preparation and avoiding sagging
of the molten metal shown in Fig. 3.18.
Recommended tilt angles are shown in Fig.
3.19 for the respective weld beads.

If weaving is required, the pattern should be

backwards toward the top edge of the joint.
Any weave pattern adopted should be as small
as possible in keeping with good weld profile,
good fusion, positioning of weld bead and
heat build up (see Fig. 3.20).
The welding process is widely used in a vari-
ety of industrial situations. Wire diameters of
0.8 mm can be used in sheet metalwork and
motor vehicle manufacture and repair where
the heat-affected zone is smaller than that of
60 METAL ARC GAS-SHIELDED WELDING

oxyacetylene welding, thus reducing distor- process is suitable for welding mild and low-
tion and increasing welding speeds. Wires of alloy steels, stainless steels, aluminium and its
2.4 mm flux and metal-cored wires can be used alloys, copper and bronzes. Used with flux-
for heavier fabrication, e.g. offshore install a- cored wires it is possible to deposit wear-resist-
tion manufacture. The process offers competi- ing overlays for the prevention of corrosion,
tion for the MMA process. When choosing a impact and abrasive wear. The process can be
process, likely considerations are initial cost, used for welding in all positions with the asso-
mobility of equipment, working environment, ciated advantages. Training of operators is no
cost of consumables, production rates and more difficult or less important than any of
automation. This list is by no means exhaus- the other processes under discussion. The
tive and the decision must be made carefully. main disadvantages are the initial cost and
MAGS can be used both as a semi-automatic mobility of the equipment.
process, manually operated and as a fully auto- Safety precautions to be observed are the
mated system with the use of robots. The same as those associated with the other
process uses a continuous wire electrode processes and discussed in Chapter 1. The sub-
which eliminates electrode changing and ject of ventilation and fume extraction must
hence the number of stops and starts during be carefully considered, with the type of
welding. By only using a gas shield as a form of shielding gas being used. Bearing in mind that
arc protection it eliminates the use of fluxes CO2 and argon gases are heavier than air there
which reduces deslagging and post-cleaning is the added risk of the exclusion of oxygen
operations of welds where flux residues can which will result in suffocation or carbon
cause corrosion problems. monoxide poisoning. Always ensure that good
With the wide range of shielding gases ventilation and any extraction is correctly
available and the use of flux-cored wires, the sited to remove any harmful gases that may
process has a wide range of applications. The accumulate.
The tungsten arc gas-shielded (TAGS) process ability in a wide variety of industrial applica-
is also known as tungsten inert gas (TIG) weld- tions.
ing, argon arc welding and gas tungsten arc
welding. The reason chosen for using the ••
name TAGS is that it is a good description of Equipment selection
the process. The process uses a non-consum- .
. The power source IS usually a transformer/rec-
able tungsten electrode whIch forms an arc as ·· . '
. tl f ler type WIth b ot h AC an d DC ou t pu.t W 1th
a source of heat to melt the work, all bemg .,
· open CHCUItvo 1tage (OCV) 0 f 80- 100 vo It s, AC
protecte d b y a gas s h Ie Id . WI·11b e requHe . d f or we Id'lng 0 f a 1umlnlUm
.. an d
its alloys. DC is required for welding carbon
TAGSwelding equipment alloy and stainless steel~ copper and. nickel
alloys. The current capaCIty of the eqUipment
The TAGS welding equipment is shown in Figs is chosen to be compatible with the type of
4.1 and 4.2. The TAGS process lends itself to work undertaken. Typical examples are given
welding of both ferrous and non-ferrous met- in Table 4.1 showing current ranges related to
als in a wide range of positions and thickness- plate thicknesses for steel and aluminium.
es, although on thicker sections (above 8 mm) Welding in the high amperage range for
other processes can be more suitable or eco- prolonged periods will mean that water-cool-
nomical. The main difference between this ing is needed on the equipment. Most modern
process and the other arc processes is that in power sources have built-in, self-contained
TAGS welding the electrode is not consumed water-cooling systems. Older power sources
in making the weld, If required, additional may be connected to the water-circulating sys-
metal can be added to the joint in the form of tern in the workshop; water from the mains
a filler wire as is the case with oxyacetylene supply is passed through the torch to a drain.
welding. Alternatively, water is supplied from a tank
By making use of both AC and DC electrode circulated by means of a pump to the welding
diameters of 1.0-6.0 mm and current values torch, returning to the tank via a water cooler.
ranging from 15 to 350 amps means that the The flow of water is governed by the water
process is suitable for both repair work and flow valve and operated by the torch or
manufacture of new installations. Although footpedal switch, which also activates the
TAGS welding is relatively slow when com- welding sequence. Water cooling becomes
pared to other arc welding processes, its abili- necessary at current values over 150 amps.
ty to produce high-quality controllable welds The flow of the argon shielding gas is con-
without the need for fluxes for welding alu- trolled in much the same way, permitting the
minium and stainless steel adds to its accept- gas to be shut off when welding is not in oper-
62 TUNGSTEN ARC GAS-SHIELDED WELDING

Figure 4.2 ACIDC rectifier: description of the

equipment. (1) Function switch. (2) Overload indi-
cator. (3) Ammeter. (4) Green control lamp (not
shown). (5) Automatic high frequency (not
shown). (6) Arc balance. (7) Post-weld gas flow. (8)
Slope down. (9) Current setting. (10) Multiplug.
(11) Remote. (12) Hot start. (13) Pulse current time
(pulsed arc welding only). (14) Base current time.
(15) Pre-weld gas flow. (16) Stop/start current. (17)
Reduced current. (18) Slope up. (19) Spot welding
time. (20) ACIDC selector. (21) Cable socket. (22)
Shielding gas connection. (23) Multi-connect TIG
torch control. (24) Voltage safety control.
 ARC STRIKING 63

Table 4.1 Current ranges in TAGS welding DCsuppressor

Metal thickness When welding aluminium an arc is formed
(mm) Current (amps) Electrode (mm)
between two dissimilar metals: aluminium and
Steels: direct current electrode negative (DC-) tungsten. Although when using AC the ten-
Up to 2 15-90 1.6 dency is for the current to be converted to DC,
2-5 90-200 2.4 it is also more noticeable where metals with
over 5 170-240 3.2
heavy surface oxide films are being welded.
Aluminium: alternating current (A C) Connecting a DC suppressor into the AC cur-
Up to 1.6 25-85 1.6-2.5 rent will allow the passage of AC and effec-
1.6-5.0 80-180 3.2-5.0 tively block any DC. The suppressor is only
over 5.0 160-250 5.0-6.0
necessary when welding with AC and should
always be used on high-quality work.
ation. Operating the footpedal switch (or
torch switch) will allow the gas to flow to the
torch giving protection for the electrode,
molten pool and filler rod. A gas delay switch Contactor
is usually incorporated. This allows a predeter- The contact or allows the arc to be extin-
mined time to be set for the gas to flow after
guished without removing the electrode and
the welding current has been switched off. gas shield from the finished weld. This allows
This is to ensure that the weld metal and the
for continued gas shielding of the weld metal
parent metal are protected during cooling. The until it has cooled. It also provides protection
welding torch should therefore be held at the for the operator by switching off the OCV
end of the weld until the gas flow has ceased.
when the torch is not being used. The contrac-
This will be the pre-set time, for example, 0-10 s. tor can be operated by a trigger switch or but-
ton on the torch, or by means of a footpedal.
The footpedal control also allows current
Additional components adjustment during the welding operation.
Additional components making up the TAGS
equipment are:
• high-frequency unit or surge injector Arc striking
• DC suppressor unit When using the TAGS process problems arise
• contactor when arc initiation (striking) is achieved by
• welding torch with conduit (cables and hoses)
touching the electrode onto the work as this
• electrodes will cause contamination of the work and the
• shielding gas. tungsten electrode. Transfer of tungsten to the
weld (tungsten inclusions) will tend to cause
Surge injector hard spots in the weld, similarly, transfer of
parent metals to the tungsten can affect arc
This provides an alternative means to high fre- stability and contaminate the electrode.
quency (HF) of maintaining arc stability To allow the arc to be struck without the
through the zero pauses, without the disad- electrodes contacting the work a high-frequen-
vantage of HF, i.e. electronic equipment inter- cy spark ionises the arc gap allowing the pre-
ference. The function of the surge injector is set welding current to flow, and the welding to
to provide a high voltage surge or pulse at the start. When using DC the high frequency is
critical period when the negative half cycle of automatically switched off once the arc has
the AC arc changes to the positive half cycle. been established. If AC is being used the high-
The positive half cycle assists in surface oxide frequency facility is left in the circuit and is
removal when welding aluminium and magne- used to assist re-ignition of the arc at zero cur-
sium alloys. rent periods during welding. This helps to
64 TUNGSTEN ARC GAS-SHIELDED WELDING

stabilise the AC arc. This boost takes place at

100 times per second (see Fig. 4.3).
Having this high-frequency facility avail-
able means not having the electrode contact
the work. This assists in maintaining the shape
of the electrode and increases the life
expectancy of the electrode. The disadvantage
of high frequency is the interference with
radio, television, computers and electronic
systems nearby. Most modern equipment will
be manufactured using one of the alternative
methods listed below.

the work creating an arc gap at which point the

current flows, quickly rising (slope up) to the
amperage set at the power source. When
the switch is released the current gently reduces
(slope down) until the arc is extinguished.

Slope up
This is a feature built into a more modern
power source; it enables the operator to work
out the time taken to reach the welding cur-
rent chosen on the power source. This reduces
the risk of burning away the plate edge at the
Scratch start start of the weld (especially on thin-sheet met-
als) and also contamination of the electrode
With this method the tungsten is brought into tip. The time is set by means of a graduated
contact with the work and gently scratched on switch (0-10), this being the time taken in sec-
the work surface to start the arc so that weld- onds to reach the pre-selected current setting.
ing can begin. As mentioned above, contact This control is sometimes referred to as the
between the electrode and the work is not the 'soft start' control and can be switched off
ideal situation and contamination may occur when not required.
during the brief encounter. The contamina-
tion will normally be very small and in most
cases will not seriously affect the strength of Slope down
the weld. Having said that, this method
should be restricted to less critical applica- This is similar to slope up, but refers to the
tions (see Fig. 4.4). time taken to reduce from the welding current
to no current. This gradual current reduction
allows time for weld crater filling; the depres-
Lift start sion associated with the end of a weld run. The
time is set using a graduated switch (0-20),
With this method no high frequency is used, this being the time taken in seconds to reduce
the electrode is brought into contact with the from the welding current to the point where
work at the start point of the weld, the torch the arc is extinguished. This control is some-
switch or footpedal is pressed which makes times referred to as a crater filling device
contact, but no current flows in the circuit. because of the function it carries out (see
At this point the electrode is drawn away from Fig. 4.5).
 ELECTRODE TYPES AND DIAMETERS 65

resulted in two types of electrodes being devel-

oped for manual TAGS welding: thorated elec-
trodes for DC welding and zirconated
electrodes for AC welding.
The electrode diameter is determined by the
current and polarity. Recommended diameters
are given in Table 4.2.

Table 4.2 Recommended electrode types for TAGS

welding (courtesy of BOC)

Electrode type Use

1-2% thoriated DC electrode nega
tungsten tive. Ferrous metals,
copper, nickel, tita-
nium
Ceriated tungsten As above. Improved
restriking and shape
retention
Zirconiated AC. Aluminium and
magnesium alloys

Recommended Current Rating BS3019, Part 1

Maximum current amps
DC electrode (-) AC electrode
Diameter (mm) thoriated zirconiated

0.8 45 -
Footpedal 1.2 70 40
1.6 145 55
The footpedal can be used as an alternative to 2.4 240 90
the slope up/slope down facility. It works on 3.2 380 150
the principal that as the pedal is pressed the 4.0 440 210
current increases (to the maximum set at the 4.8 500 275
- 320
power source); alternatively, as the pedal is 5.6
- 370
released the current will reduce to zero. The 6.4
foot pedal has one additional feature in that
the welding current can be regulated during
the welding operation as well as at the start
and finish of the weld.

Electrode grinding
Electrode types and diameters The angle to which an electrode is ground
Tungsten is a metal with a melting-point tem- depends on its application. The included angle
perature of 3000°C which also possesses good or vertex angle (shown in Fig. 4.6) is usually
electrical and thermal conductivity qualities. smaller for low-current DC applications. To
It was originally considered a suitable elec- obtain consistent performance on a particular
trode material for the TAGS process. It was joint it is important that the same vertex angle
later discovered that by alloying the tungsten is used.
with 1-2% thorium or zirconium helped to To achieve consistency in the grinding of
improve arc stability, improve current carry- electrodes, grinding machines are available
ing capacity, increase electrode life, resist con- with a jig to hold the different sizes of tung-
sten electrodes. This jig ensures that regrind-
tamination and improve arc striking. This
66 TUNGSTEN ARC GAS-SHIELDED WELDING

Gas nozzles I
Ceramic nozzles are used mainly because of '
the resistance to heat generated during weld-
ing, although for currents above 200 amps
water-cooled metal nozzles are available.
Nozzles can be obtained in a variety of bore
sizes ranging from 6 to 15 mm. The size of noz-
zle should be chosen to give correct gas pro-
ing the electrode is done correctly and safely. tection to the weld pool, electrode, filler and,
When freehand grinding of electrodes has in some instances, the deposited metal.
to be carried out, care must be taken to main- Various shapes are available to suit the job in
tain the point angle as this helps to concen- hand, extended nozzles for welding in deep
trate the arc at the electrode tip, improve arc 'V', short nozzles for welding in confined
stability and operator control. spaces, transparent nozzles providing good
When using DC the electrode is ground to a visibility where the electrode projection (stick
point length of between one and three times out beyond nozzle) must be kept to a mini-
the diameter of the electrode. The lower the mum and gas coverage to a maximum.
current the longer the point. Electrodes are Gas nozzles are designed to screw onto the
normally supplied in standard lengths of 75 collet holder, held by the torch body. The gas
and 150 mm and diameters 0.8, 1.2, 1.6, 2.4, nozzle is a delicate piece of equipment; consis-
3.2, 4.0 and 6.4 mm. tent heating and cooling can cause cracking
When using AC a 45° chamber can be and, in extreme cases, pieces break away mak-
ground on one end of the electrode; this tends ing the nozzle unusable.
to help with the formation of the spherical The collet holder screws onto the main body
shape required (balling up) usually carried out of the torch providing a means of clamping
on a carbon block or a piece of the scrap metal the collet and supporting the gas nozzle. The
being welded (see Fig. 4.7). collet holder comes supplied with or without a
gas lens.

Collets
Gas lens
The electrode is held in the torch by a split
copper tube known as a collet. The collet grips Turbulence in the gas flow as it comes from
the electrode in the collet holder by tighten- the nozzle can give poor gas shielding of the
ing the electrode end cap. Collets are available weld area. This can be improved by using a gas
in sizes to suit the various electrode diameters. lens, which will concentrate the gas over the
 AC/DC NON-CONSUMABLE ELECTRODE ARCS 67

weld area. Although the current carrying

capacity is reduced with increasing electrode
extension, using gas lenses allows the elec-
trode extension to be increased, improving
visibility and access in difficult situations. The
use of the gas lens allows a wider variation in
torch angle (slope), but, when combined with
increased electrode extension, slope angles
must be maintained near 90° to plate surface.

Torches
Welding torches for use with the TAGS process
are either air or water cooled, fully insulated
and are generally available with a flexible con-
duit assembly containing the power cable, gas
and water tubes (if used). Some modern torch-
es incorporate the switching device for start-
ing the arc. The physical size of the torch is
usually determined by the current capacity.
Torches for use up to 200 amps are light-
weight, small in size and available with flexi-
ble heads. The torch body supports the collet
holder and, in turn, the collet and gas nozzle.
The electrode end cap also screws into the
torch body (see Fig. 4.8).

Shielding gas
Regulator and flowmeter
Pure argon is the most popular choice of
shielding gas supplied in a cylinder containing A typical gas flow for TAGS welding is 8-12
11.01 m3 at 200-230 bar pressure and painted litres/min. The regulator and flowmeter are
light blue, or in bulk on-site storage tanks. To shown in Fig. 4.9.
maintain quality the cylinder pressure should A second flowmeter can be connected to the
not be allowed to drop below 2 bar. Argon is regulator and used to supply and regulate gas
reduced to a suitable working pressure by flow to the root side of the joint (gas backing).
means of a single-stage regulator to control For example, a gas backing is required when
the gas supply, and a flowmeter is used to mea- welding stainless steels, especially for the ini-
sure the quantity of gas being used. Argon gas tial runs. The gas is piped to the root side of
is heavier than air and will displace oxygen; the joint excluding air and preventing atmos-
good ventilation should be ensured at all pheric contamination. Available gas mixtures
times. If this gas has to be used in confined and their applications are listed in Table 4.3.
spaces, adequate ventilation and correctly
sited extraction equipment are essential to
avoid any accumulation of gas. The use of oxy- AC/DC non-consumable
gen meters is recommended to warn of low electrode arcs
atmospheric oxygen levels. General safety pre-
cautions apply to the handling, storage and When using DC approximately two-thirds of
transportation of gas cylinders. the total heat is concentrated at the positive
68 TUNGSTEN ARC GAS-SHIELDED WELDING

pole and one-third at the negative pole. Being

able to choose between electrode positive and
electrode negative enables the choice of heat
at the electrode or the workpiece.
Direct current electrode negative (DC-),
when the electrons flow is from the electrode
to the workpiece means that one-third of the
heat is concentrated at the electrode and two-
thirds at the workpiece. The total result is a
narrow weld bead with good penetration.
Direct current electrode positive (DC+),
when the electrons flow from the workpiece to
the electrode means that two-thirds of the
heat is concentrated at the electrode and one-
third at the workpiece. In this situation the
electrode becomes overheated; possibly melt-
ing to become rounded in shape. The total
result is a wide weld bead with little penetra-
tion. However, using DC+ electrode the
removal of surface oxides from metals is
exceptionally good: in welding metals such as
aluminium for example. The oxide removal
only takes place when the electron flow is
away from the weld pool, but as already men-
tioned this is accompanied by overheating of
the electrode and low penetration.
AC creates a situation where it is possible to
change between electrode positive and elec-
trode negative. These changes take place at
100 times per second, which results in the
Table 4.3 Available gas mixtures and their appli- total heat available being divided equally
cations (courtesy of BOC) between electrode and workpiece. When the
electrode is positive the arc action will lift any
Gas Applications Features oxides from the surface of the work; the weld
Argon TAGS all metals Stable arc perfor- pool appearing bright and clean. When the
mance. electrode changes to negative the electrode is
Efficient shield- cooled and the penetration achieved is
ing. Low cost between that when using electrode positive or
Helium TAGS all metals High heat negative (see Figs 4.10 and 4.11).
especially copper input. Increased
and aluminium arc voltage
Argon + TAGS aluminium, Compromise Filler rods
25-80% copper, stainless between pure
helium steel argon and pure The filler rods used in TAGS welding conform
helium. Lower to BS2901 Part 1, Filler Rods and Wires for Gas
helium contents Shielded Arc Welding of Ferritic Steels, which
normally used for covers the chemical composition, diameter
GTAW and tolerance of rods and wires, condition of
Argon + TAGS austenitic Improved heat rods and wires, dimension of reels of wire,
0.5-15% some copper input, edge wet- packaging and marking. Fillers are available in
hydrogen stainless steel, ting and weld 1.6, 2.4 and 3.2 mm diameter x 750 mm long
nickel alloys bead profile and copper-coated for steels designed specially
 ACIDC NON-CONSUMABLE ELECTRODE ARCS 69

Figure 4.11 Effect of current flow on penetration.

Stops and starts
for TAGS welding. Filler rods should be cleaned The requirements for stops and starts are the
with wire wool before welding. Care should same as previously discussed, e.g. consistent in
also be taken to avoid picking up grease or width with no abrupt change in shape. To
moisture by handling. Thin leather or fireproof restart the weld the electrode is positioned at
cotton gloves are recommended when welding, the back edge of the previous weld crater.
as filler wire manipulation and control is When the arc is established the torch is moved
essential in the achievement of quality welds. slightly forward into the original weld pool
and held until the full molten weld pool is
formed. At this point, filler metal can be added
Direction of travel to the weld pool and progression made along
the joint. Care must be taken to avoid the
TAGS welding can be carried out successfully filler coming into contact with the electrode.
in all positions using the 'leftwards' tech-
nique, where the filler precedes the torch in
the direction of travel. In the case of a right- Fusion runs
handed person the torch is held in the right
hand, filler in the left hand, travelling from Welds can be made without the use of a filler
right to left (see Fig. 4.12). (fusion runs), but some joint types require pre-
70 TUNGSTEN ARC GAS-SHIELDED WELDING

forming to accommodate the weld. To perform will produce quality welds on carbon and
acceptable fusion welds the joint edges must stainless steels and is used for welding sheet
be tightly fitted up and tacks will be closer metal and thin wall (up to 8 mm) pipe welds. It
together. This technique is limited to steels up is also used for depositing root runs in thick
to 1.6 mm thick. Some typical joint designs are wall pipes to achieve control and quality of
shown in Fig. 4.13. root penetration. The success of the process in
depositing root runs led to the introduction of
the fusible root insert, a pre-formed metal
insert which is tack welded into the root when
setting up the joint. By using a fusion run tech-
nique (without filler) the root insert is fused
with the root faces of the joint (see Fig. 4.14).

Weaving Figure 4.14 Good joint fit up is essential when

Weave patterns have been discussed extensive- using root inserts.
ly in the two previous chapters on MMA and
MAGS: the same techniques apply with the
TAGS process. The main difference being that
with the TAGS process weave patterns will The process is suited to producing quality
relate to torch manipulation with the applica- welds on aluminium and its alloys, magne-
tion of filler metal applied separately from a sium and its alloys, copper, nickel alloys and
filler rod. This will also apply to oxyacetylene titanium. It can be used for depositing wear-
welding. Weave patterns and filler rod applica- surfacing materials for protection against
tions will be dealt with in TAGS positional abrasion, impact and corrosion. The process
welding. also lends itself readily to automation.

Processapplications TAGS positional welding

The use of this process finds its way into many If you have progressed through the text in a
industries, particularly nuclear, aircraft, chem- logical order, you should have sufficient
ical plant and equipment, automotive, brewing knowledge on the weave patterns used and the
and food processing. This is mainly due to the electrode angles associated with the different
process eliminating fluxes and not leaving cor- positions. As mentioned earlier in this chap-
rosive residues behind after welding. In the ter, TAGS and oxyacetylene welding differ
hands of a skilled operator the TAGS process slightly in that both torch and filler rod angles
 AC/DC NON-CONSUMABLE ELECTRODE ARCS 71

have to be considered. These will be explained plate. Spot tacks should be sufficient to
relatiye to this process and positions in this restrain plates during welding and approxi-
chapter. If on the other hand this is your start mately 50-75 mm spacing minimum weaving
point it is advisable to read the sections on will be required (see Fig. 4.15).
weaving in the MMA and MAGS chapters.
lt is not the intention of this book to cover
all the welding positions but to give a guide to Table ~.4 Horizontal ~ertical 'T' fill~t. on a 1:6
. '. mm thick plate welded III the flat positIOn, uSlllg a
the torch and fIller rod angles, Slzes of elec- 1.6 mm filler rod and a 1.6 mm electrode DC- at
trodes and amperages and techniques used for 70-95 amps
a range of welding positions. Slight variations
may be required depending on condition of
equipment, thickness and type of material,
joint type, preparation and cleanliness of
material.
The action of dipping the filler wire into the
weld pool will have a slight cooling effect;
therefore, care should be taken to avoid chill-
ing the weld pool, which may result in lack of
fusion or penetration and, in extreme cases,
freezing the filler into the weld pool.
Care should also be taken to ensure that
when the dipping action of the filler rod takes
place the end of the filler is not withdrawn
from the protection of the gas shield as this
may introduce impurities into the weld.
Although sizes of filler are recommended
below, the influencing factors governing the
choice of filler will be:
a) plate thickness
b) joint type
c) joint preparation
d) current setting
e) welding position.
Care should also be taken to ensure that when
movement of the filler takes place the end is
not withdrawn from the protection of the gas
shield as this may introduce impurities into Horizontal-vertical corner joint
the weld. Horizontal vertical corner joint on 3 mm thick
plate welded in the flat position using a 2.4 mm
Horizontal-vertical IT' fillet filler rod and a 2.4 mm electrode DC at 90-140
amps. Slope and tilt angles for the torch and
See Table 4.4. Using the leftward technique, filler rod will be as in Table 4.4, using the same
commence the weld at the right-hand side of procedure as for the horizontal vertical fillet,
the joint by forming the weld pool equal on but concentrating the filler rod more toward
both horizontal and vertical plates. When the the top of the vertical edge of the joint.
weld pool is established progress the weld Although it is not always necessary, by main-
along the joint, feeding the filler into the weld taining the same slope angle and feeding the
pool with regular, consistent movements. The filler wire into the weld pool on the top edge at
filler rod should be fed into the leading edge 90° to the joint line will help prevent excessive
of the pool and slightly toward the vertical sagging of the molten weld metal which may
72 TUNGSTEN ARC GAS-SHIELDED WELDING

Square edge butt joint

See Table 4.6. Although the joint is a square
edge, a slight chamber can be filled or ground
on the face side. This will aid visibility of the
joint line without adverse effect on the joint.
As the weld pool is formed a slight sinking will
Outside cornerjoint occur. The filler rod should be applied to the
pool at this point and progression made along
See Table 4.5. After tacking establish the arc at the joint. Tack welds should be of sufficient
the right-hand end of the joint, allowing the strength to restrain the joint during welding at
weld pool to form until it melts the uppermost 75-100 mm spacing. Pre-setting may be neces-
edges of the joint. The filler rod is then applied sary if a jig is not used (see Fig. 4.18).
to the leading edge of the weld pool with a reg-
ular, consistent dipping action. Progress the
weld along the joint at a speed consistent with
the formation of the weld pool. Spot tack at
intervals of 50-75 mm (see Fig. 4.17).
AC/DC NON-CONSUMABLE ELECTRODE ARCS 73

hand end of the joint to form the weld pool.

This will be to a greater extent on the upper
plate. When the pool is established, a filler rod
can be added, dipping it in the top edge of the
weld pool and allowing it to fuse into both
plate edges. For subsequent runs, torch and
filler rod angles should be adjusted within the
tolerances to achieve the correct weld profile
(see Figs 4.19 and 4.20).
74 TUNGSTEN ARC GAS-SHIELDED WELDING

Vertical fzllet weld Verticalcomer joint

See Table 4.8. After tacking up the joint, estab- See Table 4.9. Tack weld the two plates togeth-
!ish the arc at the bottom of the joint and hold er ensuring the two inner edges of the joint are
until the weld pool is formed equally on each aligned. Establish the arc at the bottom of the
plate, either side of the root. At this point the joint and form the weld pool equally on each
filler rod can be introduced from the top into plate edge either side of the root. For the root
the top edge of the weld pool. Small amounts deposit, pay particular attention to the melt-
of filler metal should be added with a regular ing of the two root edges. A small hole (weld
consistent dipping action. Progression along onion) may appear to indicate this. At this
the joint will be consistent with the formation point the filler wire is introduced from the top
of the weld pool. Weaving will be the mini- to the leading edge of the weld pool. Speed of
mum to achieve weld shape, size and fusion at travel will be consistent with the melting of
both sides of the weld (see Fig. 4.21). the root edges. On completion of the root
deposit establish the arc and weld pool at the
bottom of the joint, this time ensuring that
Table 4.8 Vertical fillet weld on a 3 mm thick melting takes place over the root run and the
plate welded vertical up using a 2.4 mm filler rod outer edges of the joint. This may require
and a 2.4 mm electrode DC- at 100-200 amps slight side to side weaving of the torch. Filler
metal can be added to the weld pool at this
Slope angle Tilt angle stage, which will flow across the joint with the
Torch 80-90° Equal to either weaving motion of the torch. A slight pause at
side the edges of the joint will ensure good fusion.
Filler rod 5-20° Equal to either Care must be taken to avoid adding excess
side filler which will cause sagging of the molten
weld metal, resulting in an incorrect weld pro-
file (see Fig. 4.22).

Single 'V' butt joint

See Table 4.10. After tacking start welding the
root run by establishing the arc at the lower
end of the joint, form the weld pool to achieve
melting on both edges of the joint. At this
stage apply the filler rod from the top into the
leading edge of the weld pool, progressing up
the joint adding filler at the desired rate,
avoiding chilling of the weld pool and freezing
the filler into the pool. For the capping run,
establish the arc at the lower end of the joint
and form the weld pool, ensuring melting of

Table 4.9 Vertical corner joint on a 5 mm thick

plate, welded vertical up using a 2.4 mm filler rod
and a 3.2 mm electrode DC- at 100-200 amps

Slope angle Tilt angle

Torch 70-90° Equal to either side
Filler rod 10-20° Equal to either side
 ACIDC NON-CONSUMABLE ELECTRODE ARCS 75

the root run and the outer edges of the joint

by a side to side weave of the torch. The filler
wire can be kept on centre with no movement,
providing sufficient filling of the joint is
achieved. Alternatively the filler metal can be
dipped into the weld pool at the extremities of
the weave; the molten metal will form the
weld bead shape with the manipulation of the
torch (see Fig. 4.23).

Table 4.10 Single 'V' butt joint on a 5 mm thick

plate, welded in the vertical position using a
2.4 mm filler wire and a 2.4 mm electrode DC- at
100-200 amps, with an included angle of 70-90°. A
root face of 1.0-2.0 mm and a root gap of
0-1.6 mm can be used to achieve the required
degree of penetration

Slope angle Tilt angle

Torch 80-90° Equal to either side
Filler rod 15-25° 90 ± 10°
Oxyacetylene welding (sometimes referred to as • fittings: the cylinder valve has a left-hand
gas welding) gets its name from the two gases thread. This is common to all fittings asso-
commonly used in the process: oxygen and ciated with acetylene.
acetylene. This process can be used for welding · .
. . Th e 0 th er gas use d In th e process IS oxygen
a wIde vanety of ferrous and non-ferrous met- · . · ··
. (0)2 supp 1Ie d In cy 1In d ers up t 0 capaCl t Ies 0 f
als, the latter requiring a flux In most cases. 3 ·
...... 9 66 m an d 200 b ar piessure. O xygen IS
ThIS process of JOInIng fInds a place In both
.. co 1our 1ess, 0 d our 1ess an d a Ith oug h non- fl am-
repair work in the motor vehIcle body repau · ·
ma bl e 1t s t rong 1y suppor t s com b us t IOn. C are
trades, to the fabrication of new components, ·
sh ou Id b e t a k en t 0 avOl d c 10 th Ing or 0 th er
O

...
such as ductwork and pipework InstallatIOns for ' · .
. com b us t 1bl e ma t ena 1s b ecomIng sa t ura t e d
heating, ventilating and spnnkler systems. with the gas. The oxygen cylinder has two
identifying features:
Standard welding/cutting • colour: oxygen cylinders are painted black,
equipment and
• fittings: the cylinder valve has a right-hand
The standard welding/cutting equipment is thread. This is common to all fittings asso-
shown in Fig. 5.1. ciated with oxygen.
The high-pressure system uses acetylene gas
supplied in cylinders. It is the most common f • t b
form of acetylene supply and one which is most Sa ety precaut.on~ 0 e
widely used by industry. The nominal content observed when uSing oxygen
3
of an acetylene cylinder is 8.69 m . The acety- and acetylene Cylinders
lene gas is dissolved in a solvent, acetone, and
is supported in a porous mass of Kapoc. a) Always keep cylinders, fittings and connec-
Acetylene is a colour less gas, which is extreme- tions free from oil and grease.
ly flammable, with a garlic-like odour .and. a b) Store cylinders in the upright position.
flammability range of 2.4-88% volume In au. c) Transport cylinders in the upright position.
Metal alloys containing more than 70% copper d) Store flammable and non-flammable gases
or 43% silver must not ?e used in ac~tylene sys- separately.
terns as this can result In the formatIOn of dan- e) Store full and empty cylinders separately.
gerous or explosive components. The acetylene f) Avoid cylinders coming into contact with
cylinder has two identifying features: heat .
• its colour: acetylene cylinders are painted g) Secure cylinders by 'chaining up' during
maroon, and storage, transport and use.
78 OXYACETYLENE WELDING AND CUTTING
82 OXYACETYLENE WELDING AND CUTTING

Welding torches
The welding torch consists of a shank which
incorporates the oxygen and acetylene flow
control valve, a mixer and a range of copper
nozzles. As mentioned previously, two types
are available:
• high pressure and
• low pressure.

Figure 5.8 Injector. As the oxygen issues at rela-

The high-pressure torch tively high velocity from the tip of the injector, it
draws the proper amount of acetylene into the
The high-pressure torch (see Fig. 5.7) is stream. The oxygen and acetylene are thoroughly
designed for use with high-pressure gases, sup- mixed before issuing from the blowpipe tip.
plied from cylinders. It acts as a mixing device
when supplying approximately equal press~res is always higher than the acetylene pressure.
of oxygen and acetylene where they are mixed This means that as the nozzle becomes blocked
prior t? being burnt at the nozzle t~p. Using the oxygen can backfeed into the acetylene
the hlgh-press~re system on: mixer can line causing premature mixing of the gases
accomm~date dlffer~nt nozzle sizes to en~ble and increasing the risk of backfires. The low-
the weldmg of a wide range of metal thlCk- pressure torch is shown in Fig. 5.9.
nesses, from 1 to 25 mm. The mixer system
ensures that there is a least amount of explo-
sive mixed gas in the system, prior to being
burnt. In general, the welding process is better
performed with mixer-type torches. High-
pressure torches must not be used with low-
pressure systems.

Nozzles
The heat value to the flame is governed by the
size of the hole in the nozzle being used. The
heat value of the flame will need regulating to
suit the thickness, thermal conductivity, joint
type and melting temperature of metal being
The low-pressure torch welded. This should be achieved by changing
the nozzle size and not necessarily changing
The low-pressure torch uses the injector sys- the pressure. For example, metal up to 3 mm
tern (see Fig. 5.8) where the higher pressure thick can be welded by changing the nozzle
oxygen draws the lower pressure acetylene size without excessive alteration to gas pres-
into the mixing chamber. The injector is usu- sure (see Table 5.1).
ally included as part of the nozzle, so in this A flame with too Iowa heat value will result
respect each nozzle has its own injector. This in lack of penetration and fusion. Backfiring
type of nozzle is far more expensive than those may also occur. If the flame heat is too high,
used with the high-pressure system. The injec- overheating, lack of control of the molten
tor principle requires that the oxygen pressure metal and weld pool and excessive penetration
 EQUIPMENT ASSEMBLY 83

Table 5.1 Nozzle sizes and material thicknesses (courtesy of BOC)

Operating pressure Gas consumption

Mild steel Tk'ness Nozzle Acetylene Oxygen Acetylene Oxygen
mm in swg size bar Ibt/in2 bar Ibt/n2 l/h ft3/h l/h ft3/h

0.9 20 1 0.14 2 0.14 2 28 I 28 1

1.2 18 2 0.14 2 0.14 2 57 1 57 2
2 14 3 0.14 2 0.14 2 86 3 66 3
2.6 12 5 0.14 2 0.14 2 140 5 140 5
3.2 1/8 10 7 0.14 2 0.14 2 200 7 200 7
4 3/32 8 10 0.21 3 0.21 3 280 10 280 10
5 3/16 6 13 0.28 4 0.28 4 370 13 370 13
6.5 1/4 3 18 0.28 4 0.28 4 520 18 520 18
8.2 8/16 0 25 0.42 6 0.42 6 710 25 710 25
10 3/8 4/0 35 0.83 9 0.63 9 1000 35 1000 35
13 1/2 7/0 45 0.35 6 0.35 6 1300 45 1300 45
25 1+ 90 0.83 9 0.83 9 2500 90 2500 90

will be experienced. Effective flame shape and Before connecting the regulator to the cylin-
heat values can only be maintained if the noz- der 'snifting' (briefly opening and closing the
zle hole is clean and square with the end of the cylinder outlet valve) is recommended to
nozzle. This should be carried out by using a remove any dust or contamination from the
recommended nozzle reamer (nozzle cleaner), outlet. Cylinders are opened and closed by
inserting the reamer into the hole and, with a either a valve wheel or by the use of a spindle
gentle twisting motion, removing any obstruc- key designed for this purpose (see Fig. 5.11).
tion (see Fig. 5.10). During use the spindle key should be left in the
acetylene cylinder outlet valve (if only one key
is available). It is good practice to attach the
key to the cylinder trolley or stand. Connect
the respective regulator to the cylinder check-
ing that the seating face is not damaged. Right-
hand threads = oxygen; left-hand threads =
acetylene. The regulator should be sited so that
it does not interfere with the opening and clos-
ing of the cylinder valve, which should be pos-
sible in a single-movement operation.
Fit flashback arrestors to both oxygen and
acetylene cylinders, use the correct size of
spanner and avoid over-tightening. After purg-
ing the hoses fit the nipple and nut fitting to
the flashback arrestor; avoid over-tightening
and damage to connecting nuts. Connect the
other end of the hoses (hose protector) to the
• respective fitting on the welding/cutting
Equipment assembly (weld- torch. Do not over-tighten. Select and fit a
ing and cutting) suitable welding/cutting nozzle for the job in
hand. This completes the assembly of the
Secure cylinders to a suitable trolley or stand equipment.
by chaining or clamping to prevent them from Before opening the oxygen and acetylene
falling or being pulled over. Failure to do so cylinder valves, ensure that the pressure
will allow acetone to be drawn from the acety- adjustment screws on each regulator are
lene cylinder. released (turned fully anti clockwise). These
 84 OXYACETYLENE WELDING AND CUTTING

allowing the gas to flow for 5-10 s and light

the gas with a suitable spark lighter. Keep the
spark lighter and your hands out of line of the
flame.
The acetylene flame should burn without
smoke or sooty deposit. Adjust the flame if
necessary to the condition.
Open the oxygen control valve on the torch
and adjust until the inner core is clearly
defined.

Flame settings
By adjusting the quantities of oxygen or acety-
lene fed to the flame, it is possible to achieve
three types of flame condition: neutral flame,
oxidising flame and carburising flame.

Neutral flame
The neutral flame (see Fig. 5.12) consists of
approximately equal quantities of oxygen and
acetylene being burnt. The flame has a clearly
defined central (inner) cone with a length two
to three times its width. This flame is used for
most welding applications on steel, cast iron,
copper and aluminium. This is the hottest
flame condition reaching 3000-3200°C at a
point approximately 3 mm forward of the
inner cone.

should be 'captivated' so that it cannot be

screwed completely out of the regulator. The Oxidising flame
cylinder valves can then be slowly opened, the ...
working pressure is adjusted to suit the work The oXIdIsmg flame (see Fig. 5.13) consists of
in hand by turning the pressure adjuster clock- an excess quantity of oxygen being burnt in
wise. The oxygen and acetylene valves on the the flame. It is obtained by first setting the
torch can be opened (one at a time) and final neutral flame and then slightly increasing
adjustments made to the working pressure. the quantity of oxygen. The inner cone will
take on a much sharper pointed shape and the
•• flame is much more fierce with a slight hissing
Lighting-up procedure sound. This flame type is used for welding
brasses. It should be avoided when welding
Open the acetylene control valve on the torch, steels.
 HIGH- AND LOW-PRESSURE SYSTEMS 85

Welding techniques
The process takes advantage of two techniques:
'leftward' (filler rod precedes the torch) and
'rightward' (torch precedes filler rod), in the
direction of welding (see Fig. 5.15).

Carburising flame
The carburising flame (see Fig. 5.14) consists
of an excess quantity of acetylene burning in
the flame. Again, the best way of achieving
this condition is to start with the neutral
flame and then slightly increase the amount of
acetylene. The inner cone will become sur-
rounded by a 'feather' as a result of the excess
acetylene. This flame is used for depositing of
hard surfacing materials; it should be avoided
when welding steels.

Figure 5.15 Leftward and rightward techniques.

Extinguishing the flame
When welding has finished or is paused the . The rig~tward te.chnique enables the weld-
flame is extinguished by first closing the mg of t.hIcker sectIOns (over 6 mm) but t?e
acetylene valve at the torch shutting off the economICS o~ the process wou~d probably dIC-
gas supply immediately followed by closing tate the chOIce of a more SUItable means of
the oxygen valve on the'torch. Place the torch joining metals above this thickness, e.g. MMA,
in a safe position where it cannot be damaged. MAGS.
If the equipment is to be left for any length
of time, leave it in a safe condition by:
1 Closing the cylinder valves on the acetylene High- and low-pressure
then oxygen cylinder. systems
2 Opening and closing the acetylene valve on
the torch. The process can operate from a high- or low-
3 Opening and closing the oxygen valve on the pressure system which gets the name from the
torch. Note that this will release the pressure method of acetylene supply. The low-pressure
from the hoses and the working pressure system uses acetylene produced locally to the
gauge on the regulator should register zero. point of use, and requires the use of a special
4 Releasing the pressure adjustment screw on low-pressure torch. The high-pressure system
the regulator (turn anticlockwise). uses acetylene supplied in cylinders.
86 OXYACETYLENE WELDING AND CUTTING

Filter glasses Oxyacetylene positional

Use the following filters when oxyacetylene welding
welding: As mentioned in the chapter on TAGS welding,
3 GWF for aluminium and alloys both the filler rod and torch angles have to be
4 GWF for brazing and bronzing welding considered when using the oxyacetylene weld-
S GWF for copper and alloys ing process. A selection of welding positions will
6 GWF for thick plate and pipe. be covered in this section giving torch and filler
rod angles, size of filler rod and nozzle size(s) .
• The information relating to oxyacetylene
Plate edge preparation positional welding is intended as a guide only .
. . Slight variations may be required depending
FIgure ~.16 shows t~e plate edge prepar~hon on thickness and type of material, joint type,
dependmg on the thIckness of the matenal to preparation and welding techniques (leftward
be welded. or rightward).
 OXYACETYLENE POSITIONAL WELDING 87

The action of dipping the filler rod into the

weld pool will have a slight cooling effect;
therefore care should be taken to avoid chill-
ing the weld pool which may result in lack of
fusion or penetration and, in extreme cases,
freezing of the filler into the weld pool. The
addition of the filler is a result of dipping the
rod into the weld pool and not melting off the
end of the rod with the flame and allowing it
to drop into the weld pool.
Ensure that when the back and forth dip-
ping action of the filler rod takes place it is not
removed from the protective outer envelope of
~h: f;~me, I:: this may introduce impurities Figure 5.17 Torch and rod angles for fillet weld
ill a e we . lap joint in flat position.

Fillet weld lap joint Fillet welded closedcomer joint

The details for a fillet weld lap joint on a 3- The details of a fillet welded closed corner
mm thick steel plate welded in the flat pos- joint on a 3-mm thick steel plate, welded in
ition using a 2.4 mm filler rod and the the flat position using a 2.4 rom filler rod and
leftward technique are given in Table 5.2. the leftward technique are given in Table 5.3.

Table 5.2 Table 5.3

Oxygen and Plate thickness Nozzle size Oxygen and

Plate thickness Nozzle size
acetylene acetylene

0.21 bar 3 mm 5-7 0.21 bar

3 mm 5-7
3 Ib/in2 3 Ib/in2
Tilt angle Slope angle Tilt angle
Slope angle
50-60° Torch 60-70° Equal to either
Torch 60-70°
45-50° side
Filler 30-40°
Filler 30-40 Equal to either
side

Ensuring close fit up between plate surfaces,

tack along the joint line; use tacks 3-4 mm
long at each end of the joint and at 50-60 mm Ensuring close fit up of the joint (corner to
spacing. Start welding at the right-hand end of corner), tack at each end and along the joint
the joint by forming the weld pool. The free- line at 50-60 mm spacing. Start welding at the
standing vertical edge will tend to melt slight- right-hand end of the joint by forming the
ly quicker than the bottom (flat) plate surface. weld pool. The weld pool should be formed
Melting of both surfaces into the corner of the equally, to the top edge of both plates and
joint is important if full penetration into the down into the bottom of the joint. At this
root is required. The filler wire should be fed stage the filler rod can be added to the leading
into the leading edge of the weld pool toward edge of the weld pool and the weld progressed
the top edge. Progress the weld along the joint along the joint at the rate of formation of the
at the rate of formation of the weld pool and weld pool and achievement of the weld profile
filling out of the weld profile (see Fig. 5.17). (see Fig. 5.18).
88 OXYACETYLENE WELDING AND CUTTING
90 OXYACETYLENE WELDING AND CUTTING

ensuring melting of both plate edges. This is pool. Form the weld pool by melting the two
indicated by the square edges taking a circular edges and into the root of the joint. At this
form at the leading edge of the weld pool. At stage the filler rod can be added from the top
this stage the filler rod can be added from the into the leading edge of the weld pool, allow-
top into the leading edge of the weld pool. ing the weld metal to fill up the joint area.
Manipulation of the torch across the width of Progress slowly up the joint by adding small
the joint area will allow even deposits of the amounts of filler wire consistent with the for-
molten weld metal. Progress the weld up the mation of the weld pool and melting of the
joint consistent with the melting of the plate plate edges. Excessive heat build-up will cause
edges and achievement of the desired weld sagging of the weld metal and incorrect weld
profile. profile. Heat build-up can be controlled by
momentarily removing the flame away from
the weld pool (see Fig. 5.23).
 OXYFUEL GAS CUTTING 91

Table 5.9 to be joined, and is used where melting of the

base metal is undesirable. This method of join-
Plate thickness Nozzle size Oxygen and ing is relatively cheap and, because of the
acetylene lower heat input, distortion can be reduced.
6-8 mm 10-25 0.28-0.42 bar An added requirement of this method of join-
4-6 Ib/in2 ing is the requirement of a flux which further
Slope angle Tilt angle assists in the cleaning process of the weld
Torch 40-50' Equal to either
area.
side
Filler 30-40' Equal to either
side
Fluxes
Fluxes are also required when welding metals
the weld pool and weld metal build-up. It may where the oxide film which forms on the sur-
be possible to fill the whole of the preparation face melts at a higher temperature than the
in one operation; the control of the molten base metal. The purpose of the flux is to
metal and penetration will dictate this. A sec- remove the high melting point surface oxides.
ond pass may be required to get the required Aluminium fluxes, for example, are very corro-
weld profile. sive and must be cleaned off immediately after
The advantages of the rightward technique welding. The importance of flux removal may
are less distortion, faster welding speeds, no result in the choice of an alternative method
joint preparation required up to thicknesses of of welding, e.g. TAGS or MAGS.
8 mm saving on filler wire. Where 'V' prepara- Most fluxes contain compounds which will
tion is required, including angles are smaller cause irritation on skin contact, and when
than for the leftward techniques. heated give off irritating fumes. Observe basic
Even with operators skilled in the process of personal hygiene rules and ensure good venti-
oxyacetylene welding, extensive practice is lation when using fluxes.
required to master this technique, especially The oxyacetylene process has a wide variety
when applied to positional welding. of applications and is used in many industrial
Although the technique is still around, the sectors. Where problems arise, such as flux
development of other processes has limited its removal in the case of aluminium, or the pres-
use. Where thicker sections are to be welded, sure of production rates, alternative welding
consideration should be given to other processes may prove more suitable.
processes for reasons of economy, productivi-
ty, operator fatigue, skill availability and qual-
ity of the finished weld.
Oxyfuel gas cutting
The oxyfuel gas cutting process provides a
Bronze welding means of cutting steel by the chemical action
of oxygen on steel. A controlled stream of oxy-
The oxyacetylene process can also be used for
gen is directed onto the surface of the steel
bronze welding of steel, copper, wrought and
which has been pre-heated to 900-9S0°C (igni-
cast iron. The technique used is similar to that
tion temperature). The result of this action is
used for fusion, although it is not a fusion
that the pre-heated area rapidly becomes oxi-
process. Bronze welding uses a filler which
dised and the oxide is blown away by the oxy-
melts at a lower temperature than the base
gen stream severing the plates. The width of
metal. Filler is deposited in the weld area and
the cut being referred to as the kerf width.
forms a bond between the fusion faces. The
The equipment used for oxyfuel gas cutting
joint faces must be free from oil, grease, scale
will concentrate on the supply of gases in
and rust. Suitable preparation can be achieved
high-pressure cylinders as discussed earlier.
by wire brushing or filing; on some occasions
For this reason the safety precautions relating
light grinding can be used. Bronze welding
to the use of gas cylinders, components in the
produces a strong bond between the surfaces
92 OXYACETYLENE WELDING AND CUTTING
96 OXYACETYLENE WELDING AND CUTTING

If the nozzle-to-work distance is too high supports. Upturned channel sections or angle
.
a ) exceSSIve roun d·mg 0 f t op e d ge iron provides a suitable
. support and allows
.
b) exceSSIve me It·mg 0 f t op e d ge cuts
. to be made wIthout hampering the cut-
tmg process (see Fig. 5.31).
c ) square b 0tt am e d ge
d) lower part of cut may be square
e) gouging at top edge.
If the nozzle-to-work distance is too low
a) square cut face
b) square bottom edge
c) slightly rounded top edge
d) possible heavy beading on top edge.
If the nozzle is contaminated
a) excessively wide kerf width
b) pleated appearance of top edge
c) rounding of top edge
d) irregular bottom edge
e) slag adhesion on bottom edge
f) rough, irregular cut face.
If the speed of travel is too slow
a) excessive rounding on top edge of cut
b) heavy scale on cut face
c) distorted drag lines
d) irregular bottom edge of cut
e) excessive slag adhesion on cut face.
Observing a few basic rules when oxyfuel
gas cutting will help in making good-quality
cuts and remove the need for further or exces-
sive welding preparation:
1 Ensure plate surfaces are clean and free from
scale.
2 Select the correct nozzle for the job in hand.
3 Ensure the nozzle is free of obstruction, pre-
heat and oxygen.
4 Select the correct operating pressures.
5 Use cutting attachments to maintain i) the •
nozzle-to-work distance and ii) the nozzle Cutting techniques
90° to the plate surface in both planes .. I • ,

6 Correct and consistent speed of travel. Havmg followed the eqUIpment assembly
procedure covered earlier, select the correct
operating pressure and nozzle size for the job
Supporting materials in hand. A neutral flame is required for oxy-
acetylene cutting, this can be achieved by
Where it is practical to do so, the metal to be opening the acetylene control valve on the
cut should be supported to make sure that cut- torch and lighting with a spark lighter. The
ting can be done safely, without damage to acetylene flame should burn without excessive
underlying components. There are many dif- smoke or sooty depsosits. Slowly open the
ferent types of support and vary from open lat- oxygen valve until the blue cones of the pre-
tice top bunches to individual adjustable heating flame are clearly defined.
 CUTTING TECHNIQUES 97

Starting from a plate edge: position the noz-

zle over the point where the cut is to start so
that the central hole of the nozzle is on line
with the plate edge and the ends of the pre-
heat cones just clear of the plate surface (see
Fig. 5.32).

Hold the cutting torch at this point until stream of oxygen pierces the plate. When the
the plate edge is bright red in colour. At this hole is established, lower the cutting torch to
point fully depress the cutting oxygen lever the original position and start the cut as
allowing oxygen stream to flow from the cen- before. Figure 5.34 shows the correct sequence:
tral hole, at the same time pulling (or pushing) (1) preheat the plate surface, (2) raise the noz-
the cutting torch along the cutting line. The zle slightly and depress cutting oxygen lever
speed of travel will be consistent with the con- piercing the hole, and (3) lower the nozzle to
tinuous heating of the leading point of the the original position and start the cut.
cut. Continue the process maintaining the
nozzle-to-work distances and a consistent
speed of travel over the required length of cut.
If the correct conditions have been achieved
the cut portion should drop away without
adhesion, leaving a light oxide on the cut face.
The top and bottom edge of the cut should be
square with slightly noticeable vertical drag
lines (see Fig. 5.33).
Starting inside the plate (hole piercing):
start by holding the torch stationary over the
point at which the cut is to start. When the
area has reached the bright red colour, slight-
ly raise the torch before fully depressing the
cutting oxygen level. On depressing the cut-
ting oxygen level, a small amount of metal
may bubble up onto the plate surface while the
 98 OXYACETYLENE WELDING AND CUTTING

Starting the cut on a round face (e.g.

round bar)
Starting cuts on the circumference of a round
bar, although possible, can be difficult. To
overcome this use a diamond point or round
nose chisel and raise a burr at the point at
which the cut is to start. Concentrating the
pre-heat flame and the cutting oxygen stream
at the point will enable an easier, quicker start ..
to t h·e cuttmg operatIOn
. · 5 35)
(see F19... FIgure 5.35 Startmg the cut on a round surface.
Applying the above will provide a basis for
successful cutting of steels. Experience will be
gained with practice. service to part-exchange most of the equip-
In the interests of safety it is strongly ment used, and supply exchange components
advised not to tamper with the equipment which have been serviced to rigid codes and
used for oxyacetylene cutting or welding. standards. If in doubt about any aspect of the
Never attempt to repair the equipment your- process or equipment, it is advisable to seek
self. Manufacturers and suppliers provide a the manufacturer's or supplier's advice.
Health and safety B) the speed of travel is increased
C) the welding current is increased
The Health and Safety at Work Act 1974 states D) a weaving technique is used.
that an employee (welder) is responsible for
. AS The maximum open circuit voltage
A) safety of hImself only allowed for manual metal-arc welding is
B) safety of himself and others A) 100 V
C) wearing of ear plugs at all times B) 220 V
D) providing his own protective equip- C) 330 V
ment. D) 440 V.

A6 Two pieces of low carbon steel of 8 mm

thickness are to be butt welded together
MMA welding in the flat position using conventional
Al The purpose of a cover glass in a head- electrodes. The correct joint preparation
shield is to protect the filter lens from would be
A) radiation A) closed square butt
B) infra-red rays B) single vee 30° included angle
C) light C) open square butt
D) spatter. D) single vee 60° included angle.

A2 A welding earth is connected between A7 A root bend test is applied to a butt weld-
ground and ed joint in low carbon steel. If the speci-
A) work men did not fracture, this would
B) welding power unit indicate
C) mains A) correct weld face contour
D) return lead. B) absence of undercut
A3 An electrode size is identified by the C) good root ~usion
A) type of flux coating D) lack of fusIOn.
B) diameter of the core wire ..
' A8 A respIfator IS used to protect the welder
C) Iengt h 0 f th e core WIfe f
D) diameter of the flux coating. r om .
A ) e ectnc
l s h oc k
A4 During manual metal-arc welding, the B) harmful fumes
electrode will be consumed faster if C) infra-red rays
A) the welding current is decreased D) hot metal particles.
100 QUESTIONS

A9 A satisfactory permanent method of con- MAGS welding

necting return lead clamps to work-
benches is by A1 The cable connecting the work to the
A) soldering power source unit is called the welding
B) brazing A) earth
C) bolting B) mains
D) clamps. C) return
AI0 It is an advantage to carry out manual D) output.
metal-arc welding in the flat position A2 The glass tube situated adjacent to the
rather than the horizontal-vertical pos- regulator of a MAGS unit is a
ition because the electrodes used may be A) contents gauge
A) bare wire B) heater unit
B) shorter C) filter unit
C) larger diameter D) flowmeter.
D) smaller diameter. A3 When using liquid CO2 for the MAGS
Bl1 State the purpose of a fuse in an electric welding process, it is necessary to incor-
circuit. porate into the system a
B12 Name TWO welding power units which A) filter
supp Iy d·nec t curren t to a we Id·mg arc. B) h eater
C) coo Ier
B13 State TWO reasons why electrodes for D) by-pass valve.
manual metal-arc welding need careful · . . ·
A4 A cy Im d er pamte d bl ac k WIt h aver t lCaI
storage. · · .
w h Ite Ime con tams
B14 State TWO reasons why the correct arc A) oxygen gas
length should be maintained during B) CO2 gas
manual metal-arc welding. C) CO2 liquid
BIS Give ONE reason why it is essential that D) argon gas.
correct joint preparations are used when AS The gas supplied in blue cylinders with a
manual metal-arc welding. green band contains a mixture of argon
B16 Give TWO reasons for using the multi- and
run technique when producing a hori- A) ox~gen
zontal-vertical tee-fillet weld. B) helIum
C) hydrogen
B17 Give TWO reasons why slag should be D) CO2.
removed before depositing the next run
of weld metal. A6 The filler wire used in MAGS welding is
fed to the weld pool from a
B18 Name TWO items of protection to be A) spool
worn by the welder during manual B) heater
metal-arc welding operations. C) pool
B19 State ONE cause of a bolted electrical D) solenoid.
cable connection overheating during A7 The slope angle of a MAGS gun when
use. making a bead in the flat position
B20 State TWO items of information which should be
may be obtained from a macro-exam in a- A) 30:
tion of a welded joint. B) 40
C) 50°
D) 70°
 GAS WELDING AND CUTTING 103

A2 Oxygen is supplied in cylinders which A9 The size of filler wire diameter required
are painted for welding 1.6 mm low carbon steel is
A) blue A) 1.6 mm
B) red B) 2.4 mm
C) maroon C) 3.2 mm
D) black. D) 4.0 mm

A3 The flame setting used for fusion weld- AlOA macro-examination of a butt weld
ing low carbon steel by the oxy-acety- involves polishing and
lene process is A) etching
A) oxidizing B) bending
B) carburizing C) heating
C) neutral D) fracturing.
D) normalizing. Bll Sketch the end face of an oxy-acetylene cut-
' ' · ting nozzle and indicate the orifice through
A4 Ace t y Iene f1tt mgs h ave th rea d s w h ICh ., ..
whiCh the cuttmg stream of oxygen IS emIt-
are
A) left hand ted.
B) right hand B12 State two functions of a flashback
C) square arrester.
D) round. B13 State why copper must never be used on
AS The oxygen hose on a blowpipe for oxy- an acetylene supply.
acetylene welding is co loured B14 State a safe method generally used for
A) red testing for leaks on oxy-fuel gas welding
B) blue or cutting systems.
C) green
D) grey. BIS State why acetylene cylinders must always be
stored and used standing in the vertical pos-
A6 Gas pressures used in oxy-acetylene ition.
welding are measured in B16 Sketch a neutral oxy-acetylene flame.
A) new t ons
B) bars B17 On the sketch of the acetylene cylinder
C) grams shown in Fig. 6.7, indicate the position
D) tonnes. of
A) the safety valve
A7 The angle of filler wire to the work when B) the fusible plug.
oxy-acetylene welding by the leftward
technique in the fIat position is in the BI8 State the main advantage oE a two-stage
range of regulator compared with a single-stage
A) 10/20° regulator.
B » 20/30° B19 Name two weld defects.
C 30/40°
D) 60/70° B20 State two hazards associated with oxy-
acetylene welding.
A8 The angle of the nozzle to the work
when oxy-acetylene welding by the left-
ward technique in the flat position is in
the range of
A) 10/20°
B) 20/30°
C) 30/40°
D) 60/70°
Welding processes and 23 Projection welding
• 24 Flash welding
their numerical 25 Resistance butt welding
representation 29 Other resistance welding processes
29 HF resistance welding
1 Arc welding 943 Furnace soldering
11 Metal arc welding without
111
112
Metal arc welding
Gravity arc welding with covered electrode
with
gas protection
covered electrode
3
31
G
0 as
Id'
reI
10g ld'
xy ue g,as we l.ng
o • 311 Oxyace ty ene we ld mg
113 Bare wue metal arc weldmg o

o 312 0 xypropane we ld mg
114 Flux cored metal arc weldmg o

o 0 313 0 xy h y d rogen we ld mg
115 Coated wue metal arc weldmg · o

o 0 32 Au- fue I gas we ld Ing

118 Fuecracker weldmg o o

o 321 Au-acety Iene we ld mg

12 Submerged arc weldmg 97 Bid'
121 Submerged arc welding with wire electrode r~z~ we In g
F nctlOn so l denng
0

o 0 0 953
122 Submerged metal arc weldmg wIth stnp
electrode 4 Solid phase welding; pressure welding
13 Gas shielded metal arc welding 41 Ultrasonic welding
131 MIC welding 42 Friction welding
135 MAG welding: metal arc welding with 43 Force welding
non-inert gas shield 44 Welding by high mechanical energy
14 Gas-shielded welding with non-con sum- 45 Diffusion welding
able electrode 47 Gas pressure welding
141 TIC welding 48 Cold welding
149 Atomic-hydrogen
o
welding 7 Oth er we ld' Ing processes
15 Plasma arc weldmg °
ld l~ o
o 71 Th ~/~
t
18 Other arc weldmg processes o

o 72 EIec t ros Iag we ld mg

181 Carbon arc welding
EI ec t rogas we ld mg
o

o 0 73
185 Rotatmg arc weldmg
In d uc t IOn we ld Ing
o o

o 74
915 Salt bath brazmg
LIght ra d la t IOn we ld mg
o o o o

75
2 Resistance welding 751 Laser welding
21 Spot welding 752 Arc image welding
22 Seam welding 753 Infrared welding
221 Lap seam welding 76 Electron beam welding
225 Seam welding with strip 78 Stud welding
108 APPENDIX 1

781 Arc stud welding 941 Infrared soldering

78 Resistance stud welding 942 Flame soldering
9 Brazing, soldering and braze welding 944 Dip soldering
91 Brazing 945 Salt bath soldering
911 Infrared brazing 946 Induction soldering
912 Flame brazing 947 Ultrasonic soldering
913 Furnace brazing 948 Resistance soldering
914 Dip brazing 949 Diffusion soldering
916 Induction brazing 951 Flow soldering
917 Ultrasonic brazing 952 Soldering with soldering iron
918 Resistance brazing 954 Vacuum soldering
919 Diffusion brazing 96 Other soldering processes
923 Vacuum brazing 322 Air-propane welding
924 Vacuum brazing 971 Gas braze welding
93 Other brazing processes 72 Arc braze welding
94 Soldering 441 Explosive welding
 Appendix 2
Useful
informa tion
Chemical symbols Electrode diameters - metric, imperial and
approximate lengths
Al Aluminium Nb Niobium
C Carbon Ni Nickel Diameters Lengths
Cb Columbium 0 Oxygen mm SWG in mm in
(Niobium) P Phosphorus 1/16 250 10
1.6 16
Co Cobalt Pb Lead 14 5/64 300 12
2
Cr Chromium S Sulphur 3/32 350 14
2.5 12
Cu Copper Si Silicon 400 16
3.25 10 1/8
H Hydrogen Sn Tin 8 5/32 450 18
4
Fe Iron Ta Tantalum 3/16 600 24
5 6
Mg Magnesium Ti Titanium 700 28
6 4 1/4
Mn Manganese V Vanadium
8 - 5/16
Mo Molybdenum W Tungsten
N Nitrogen Zn Zinc

Length

m em in ft yd
1 metre 1 100 39.3701 3.28084 1.0936
1 centimetre 0.01 1 0.393701 0.0328084 0.0109361
1 inch 0.0254 2.54 1 0.0833333 0.0277778
1 foot 0.3048 30.48 12 1 0.3333333
1 yard 0.9144 91.44 36 3 1

km mi n.mi
1 kiJometre 1 0.621371 0.539957
1 mile 1.60934 1 0.868976
1 nautical mile 1.85200 1.15078 1
Bar Atmosphere Ib/in2
1 0.986923 14.6959
110 APPENDIX 2

Weight Units and metric conversion factors

1 grain 64.8 mg Abbreviations

1 dram 1.772 g
m metre
16 drams 1 ounce 28.35 g
g gramme
160z 1 pound 0.4356 kg
t tonne (or metric ton)
14 pounds 1 stone 6.35 kg
N newton (SI unit of force)
2 stones 1 quarter 12.7 kg
J joule (SI unit of energy)
4 quarters 1 hundredweight 50.8 kg
W watt (SI unit of power)
20 cwt 1 (long) ton 1.016 tonnes
s second
1 milligram 0.015 grain
M mega (x 1 million)
10 mg 1 centigram 0.154 grain
k kilo (x 1 thousand)
10 cg 1 decimgram 1.543 grain
c centi (1 hundredth)
10 dg 1 gram 15.43 grain
m milli (1 thousandth)
0.035 oz
Jl micro (1 millionth)
1000 g 1 kilogram 2.205 Ib
1000 kg 1 tonne 0.984
Force
(metric ton) (long) ton
Ilbf 4.448 N
1 tonf 9.964 kN
1 kgf 9.807 N
Area IN 0.2248 Ibf
Conversions between Ibf, kgf, etc. are as for
1 are 100 m 2 119.6 yd2
mass units.
1 hectare 100 are 2.471 acres
1 km2 100 hectares 0.387 mi2
Pressure or stress
1 acre 0.4047 hectare 4840 yd 2
1 rood 1011.7 m2 1/4 acre 1 Ibf/in2 0.0703 kgf/cm2
1 mi2 2.59 km2 640 acres 6.895 kN/m2
1 tonf/in2 1.575 kgf/mm2
Cubic measure 15.444 MN/m2
1 kgf/cm2 14.223 Ibf/in2
1 cubic inch 16.4 cm3
98.067 kN/m2
1728 cu in 1 cubic foot 0.0283 m3
1 kN/m2 0.145 Ibf/in2
27 cu ft 1 cubic yard 0.765 m3
1 MN/m2 0.06475 ton/in2
1 cu centimetre 0.061 in3
1000 cu em 1 cu decimetre 0.035 ft3
Energy (work, heat)
1000 cu dm 1 cu metre 1.308 yd2
1 ft Ibf 0.1383 kgf m 1.356 J
Capacity measure 1 kgf m 7.233 ft lbf
1 fluid ounce 28.4 ml 9.81 J
5 fl oz 1 gill 0.142 1 1 kW h 3412 Btu 3.6 MJ
4 gill 1 pint 0.568 1 1 Btu 1.055 kJ
2 pt 1 quart 1.136 1 1J 0.102 kgf m/s
4 qt 1 gallon 4.546 1 1 J/sl 1 N m/s
1 millilitre 0.002 pt lkW 1.341 hp
10 m! 1 cen tili tre 0.018 pt
10 cl 1 decilitre 0.176 pt
10 dl 1 Iitre 1. 76 pt
 Basic conversion factors

To convert into Multiply by

in mm 25.40
mm in 0.0393 701
ft m 0.304 8
m ft 3.280 839 8
Ib kg 0.453592370
kg Ib 2.204 62
ton (long) tonne 1.01605
tonne kg 1000.0
gallon (imp.) 1 (litre) 4.545.96
1 ml 1000.0
ml cm-1 1.000 028
cu. ft. 1 28.3161

Compound conversion factors

tonf/in2 N/mm2 15.444 3

Ibf/in2 N/mm2 006 894 777
N/mm2 tonf/in2 0.064 749
N/mm2 Ibf/in2 145.037 76
ft.lbf. J(joules) 1.355 82
kgf.m J 9.806 650
kgf.m ft.lbf. 7.23301
ft.lbf. kgf.m 0.138255
J ft.lbf. 0.737562
in/min m/hr 1.524 0
m/hr in/min 0.656 168
eu.ft/hr l/min 0.471 95
l/min cu.ft/hr 2.118936
Ib/cu.ft. g/em3 0.01602
g/em3 Ib/cu.ft. 62.43
 Index

AC/DC non-consumable electrode arcs 67 classification 35

Arc striking 31, 63 coatings 37
Arc welding safety 1 extension 52
correct earthing 3 grinding 65
electrical hazards 5 iron powder 36
fire prevention 4 rutile 36
fuses 4 size, current capacity 35
personal protection 1 wires 48
responsibilities of the welder 2 Equipment 30
storage and handling of gas cylinders 2 assembly (welding and cutting) 83
welding fumes 2 selection 61
working at heights 1 Examination
dye-penetrant 23
British Standards for wires and filters 53 magnetic particle 23
Bronze welding 91 radiographic 23
Burn back 52 ultrasonic 24
visual 20
Carburising flame 85 Extinguishing the flame 85
Closed corner joint 90
Collets 66 Features of the process 53
Common gases and their application 50 Filler rods 68
Contact tip, nozzle settings 52 Fillet weld 58
Contactor 63 closed corner joint 87
Current and voltage settings 53 lap joint 87
Cutting techniques 96 profiles 16
Filter glasses 1, 86
DC suppressor 63 Flame settings 84
Direction of travel 69 Flashback arrestors 80
Distortion Flat position 39
control 16 Flux-cored arc welding 54
methods of controlling 17 Fluxes 91
Footpedal 65
Earthing see Arc welding safety, correct earthing Fusion runs 69
Electrode
angles 32 Gas cylinders
basic or hydrogen-controlled 37 identification 3
cellulosic 37 storage and handling 2
114 INDEX

Gas Plate edge preparation 86

le~s 66 Positional welding 38
mixtures and their applications 68 Process applications 70
nozzles 66 Purging 81
welding 105
welding and cutting 102 Quality of cut 95
Gases, fuel 92
Generators 30 Rectifier 30
Hand cutting 93 Regulator and flowmeter 67
Health and Safety at Work Act 1, 2 Regulators 79
High- and low-pressure systems 85
Horizontal-vertical Safety 77, 79 see also Arc welding safety
butt joints 59 Scratch start 64
corner joint 71 Self-adjusting arc 52
position 41 Shielding gas 67
single 'V' butt joint 73 choice of 48
'T' fillet joint 57, 71,88 Single 'V' butt joint 57, 74
Hoses (BS5120) 80 Slope and tilt angle 54
check valves 81 Slope
connectors 81 down 64
up 64
Inspection 19 Square edge butt joint 72, 88, 89, 90
Standard welding/cutting equipment 77
Joint features 16 Stops and starts 32, 53, 69
types 13 Supporting materials 96
Surge injector 63
Lift start 64
Lighting-up procedure 84 IT' fillet and square edge butt joints 56
TAGS positional welding 70, 101
Macro-examination 25 equipment 61
Manual metal arc welding 29, 99, 104 Testing
Metal arc gas-shielded welding 47, 100, 104 bend 24
positional welding 56 destructive 24
Metal transfer modes 50 nick-break 25
impact 25
Neutral flame 84 tensile 25
Non-destructive testing 20 Torch
Nozzle sizes and material thicknesses 83 high-pressure 82
Nozzles 82, 92 low-pressure 82
Torches 67, 92
'0' clips 81 Transfomer 30
Open circuit voltage 31 Transformer/rectifier 30
Operating conditions 94 Tungsten arc gas-shielded welding 61
Outside corner joint 72
Overhead Vertical
IT' fillet 44 corner joint 74
IV' butt welds 44 fillet weld 74
Oxidising flame 84 position 42
Oxyacetylene 'T' fillet 42
positional welding 86 IV' butt welds 44
welding and cutting 77
Oxyfuel gas cutting 91 Weaving 34, 53, 70
 INDEX 115

Weld Welding
defects 19 positions for plates 37
features 16 procedure 26
symbols 10 procedure approval 27
Welded joint, features 14 processes and their numerical
Welder qualifications 26 representation 107
techniques 8S
terminology S
torches 82
Wire feed system 49