Training in Accra
Ghana
4th April to 8th April 2016
Brazing competencies
05/10/2021 Page 1
Learning targets
✓ Know the theoretical basics of brazing
✓ Understand the importance of high quality brazed joints
✓ Know the differences between brazing rods and their range of use
✓ Acquire an overview of the right brazing tools for specific purposes
✓ Gain practical experience in brazing operation
✓ Distinguish between “Well” & “Poorly” brazed joints
05/10/2021 Brazing competencies Page 2
Agenda
Introduction & safety
Norms
Theory of brazing
Brazing operation
Piping preparation
Brazing tools
Brazing competency certification
05/10/2021 Brazing competencies Page 3
Brazing definition
➢ Brazing is a process that allows the joining of similar or dissimilar
metals by using a third metal (filler metal) as “glue” and applying heat.
➢ The filler metal has a melting temperature above 450°C (840°F) but
below the melting point of the metals that are joined.
Page 4
Proper working temperatures for brazing
The base metal (i.e. the metal(s) you are attempting to join) is never
actually melted, as in conventional welding, but the base metal must reach
the proper temperature to allow molecular bonding with the filler metal.
➢ Working temperatures up to 450°C → soldering.
➢ Working temperatures above 450°C → brazing.
Page 5
Brazing basics
• Brazing is different from welding, as it does not involve melting components
• Brazing creates joints that can withstand pressure, vibrations, shocks and tension etc.
• Used for copper/copper, copper/aluminum or copper/steel connections
Page 6
Why brazing matters for HC refrigeration systems
Purpose:
➢ Achieving sealed refrigerant circuits
➢ i.e. avoiding detachable (e.g. screwed)
connections
Significance for HC chillers:
➢ Permanent joint connections reduce
the risk of leakage and increase
system reliability.
Page 7
Safety matters: general requirements for brazing
Basic safety requirements during brazing work:
• Accident prevention
• Site safety
• Safety of equipment and tools
• Fire precautions and alarm procedures
• Permission for hot work (if needed)
Page 8
Agenda
Introduction & safety
Norms
Theory of brazing
Brazing operation
Piping preparation
Cost-benefit considerations
Brazing competency certification
05/10/2021 Bracers competences Page 9
Norms: Refrigeration & air-conditioning tubing
European standard EN 378-2 covers the safety and environmental aspects
of the design, construction and installation of refrigeration systems.
• Joints must not be damaged by freezing of water on the outside. Soft
soldered joints are not suitable for refrigeration pipework.
• Copper tubes for brazing should be in accordance with EN 12735–1.
• Brazing may be applied to tubes up to 54 mm diameter, larger tubes
should be welded.
• For durable and reliable copper tube joining, fittings should be used
according to EN 1254–1 (up to 104 mm diameter).
• Using filler metals compliant with EN 1044 is the preferred method for
making non-detachable joints.
Page 10
Challenges of brazing
Attention: poorly brazed joints may look similar to well brazed joints, but
can have VERY low strength.
➢ The metal used to bond the two parts may be different in colour than
the parts being bonded. This can present a problem.
➢ Long-term effects of dissimilar metals in constant contact may need to
be examined for special applications.
Filler metal not entirely penetrated Overheated joint connection, indicated
by small bubbles
Page 11
Agenda
Introduction & safety
Norms
Theory of brazing
Brazing operation
Piping preparation
Brazing tools
Brazing competency certification
05/10/2021 Bracers competences Page 12
Quality of brazed joints: important aspects
• Under-heating is the principal cause for inferior joints.
• Maintain proper temperature range along the whole brazing joint
(the whole gap length needs to be at working temperature).
➢ Note the quality difference:
Gap length
Excessive clearances
between joints can
cause voids inside
Properly brazed
connection
Page 13
Capillary action
• In brazing, a thin film of filler metal is sucked into the joints by capillary
action.
• The bigger the gap, the less capillary action is possible.
Capillary action in effect No capillary action
Page 14
Capillary forces: maximum achievable gaps
0.5 mm gap
= approx.
1.5 cm rise
heights
Capillary brazing is
suitable for gaps
≤ 0.5 mm only!
With a parallel gap of 0.1 mm, the capillary pressure is at approx. 100 mbar
(10 kPa). This corresponds to a filler metal rise height of 10 cm
(filler metal density = 10 g/cm³).
The calculated rise heights have been confirmed in practical tests (Info by Umicore)
Page 15
Working temperatures of braze solders
The rod which joins the filler metal to the base metals is called braze solder
(rod).
Silver braze solder (L-Ag45Sn) Copper braze solder (L-Ag5P)
I = very good wetting 730°C I = very good wetting 815°C
II = good wetting 670°C II = good wetting 710°C
III= bad wetting 600°C III= bad wetting 650°C
IV= no wetting 550°C IV= no wetting 600°C
Page 16
Working temperatures of braze solders
Silver braze solder
Page 17
Applying heat to a filler material: temperature levels
Cherry Red = between 700 and 800°C! Good
for L-Ag5P (copper braze solder)
Phosphor starts to melt at lower working temperature
(visible by the greenish flame), working as a flux.
At slightly higher temperature (> 700°C), the copper brazing
solder starts to melt, visible by cherry red
Page 18
Brazing of copper with CuP brazing filler metals
(CuP: copper phosphate)
Copper to copper connections:
• Copper braze solder with low silver content like L-Ag2P or L-Ag5P.
• The fluxing action is achieved by formation of copper metaphosphate.
19 Page 19
Brazing of copper to brass or copper to steel
Copper to brass joint (uncleaned) Silver braze solder flux coated Flux
Copper to brass or copper to steel connections:
• Braze solder with high silver content like L-Ag45Sn.
• Flux needs to be added.
20 Page 20
Behaviour of flux: example BrazeTech-Paste brass
• Freshly applied flux (room temperature)
• Evaporating of water (ca. 100°C)
• Paste dries and expands because of
evaporation of chemically combined
water (ca. 350°C)
• Flux is melted clear, smelter is
transparent (ca. 550°C)
21 Page 21
Select appropriate filler material for the required
refrigerant temperatures
Brazing rod filler material
The higher the silver content,
➢ the more resistant for low medium temperature application
➢ the lower the working temperature (WT)
Examples:
• 2 % silver for chiller applications ≥ -20°C medium temperature, e.g. L-Ag2P (WT 710 °C)
• 5 % silver for chiller applications ≥ -40°C medium temperature, e.g. L-Ag5P (WT 700 °C)
• 45 % silver for chiller applications ≥ -70°C medium temperature, e.g. L-Ag45Sn (WT 670 °C)
Attention: Using braze solders with working temperatures that are too high will cause
brittle crack!
Page 22
Braze solder (rod) examples
➢ Use of copper-phosphorus filler only for copper / copper joints (no flux
required)
➢ For copper / brass or copper / red-cast, flux is always required
Silver braze solder flux coated Flux
Silver braze solder joint
Page 23
Agenda
Introduction & safety
Norms
Theory of brazing
Brazing operation
Piping preparation
Brazing tools
Brazing competency certification
05/10/2021 Bracers competences Page 24
Step 1 – cleaning
Oxide layers and foreign matter such as rust
and scales must be removed from the brazing
joint either mechanically or chemically.
Tools:
• Metal-free cleaning pad
• Pickling
Thick layers of grease or oil can be wiped off or
removed with solvents (e.g. acetone) for
sensitive components.
Polished components do not require any
cleaning.
Any remaining oxide will be dissolved by the
flux.
25 Page 25
Step 2 – applying flux
• The flux paste is applied to the cold
work piece using a brush or other
suitable equipment.
• Most fluxes are slightly corrosive and
skin contact, particularly with wounds,
should be avoided.
26 Page 26
Step 3 – fixing the work pieces
• The parts to be joined must be fixed in
the correct position until the brazing filler
metals sets.
• A narrow brazing gap of between
0.05 mm and 0.2 mm is to be set if
possible.
27 Page 27
Step 4 – heating the brazing joint evenly
• The flame should be slightly reducing –
lower oxygen supply.
• The brazing gap must be heated evenly
all over to brazing temperature so that
the brazing filler metal can fill the gap.
• The brazing temperature on the part
should be reached in max. 3 minutes for
the selected brazing filler metal.
• Inner cone of the flame should not touch
the work piece – only the outer zone.
28 Page 28
Step 5 – placing the brazing filler metal
• The brazing filler metal can be placed on
the brazing gap when the flux is melted
to an even transparent layer and when
the brazing temperature has been
reached.
• The brazing filler metal fills narrow
brazing gaps and rises upwards against
gravitational force.
• Avoid overheating. This may damage
brazing filler metal and the work piece.
• Flux fumes should be exhausted.
29 Page 29
Step 6 – cooling down
• When the brazing filler metal has filled
the brazing gap, the work piece must be
left to cool until the braze metal has
solidified.
• The component can be removed from
the fixture afterwards.
30 Page 30
Step 7 – removing flux residues
• Corrosive flux residues have to be
removed after brazing.
• As far as possible, remove leftover flux
with water or mechanically e.g. with a
brush.
• Properly brazed joints look smooth and
clean and do not require any rework.
• Paint will not stick to areas covered with
flux.
31 Page 31
Brazing operation: the basic steps
1) Light and adjust the flame (do not use a lighter!) Igniter with spark flint
2) Apply the flame to the parts. The goal is to heat the entirety of both
parts being brazed. Place the flame over the surface of the part, and try
to avoid overheating, which may melt the surface.
3) Apply filler material to the joint line. Do not apply flame directly to the
rod - let the temperature of the parts melt the solder. Continue heating
the parts until the filler material (rod) melts and flows into the joint.
4) Add enough filler material to ensure a good bond line.
→ This requires a little practice.
5) Once you are done, turn off the flame. Close the oxygen pin valve first,
then shut down and clean up.
Page 33
Types of flames in oxy-acetylene & LPG brazing
– Neutral flame (3200°C)
Acetylene (C2H2) and O2 are mixed 50/50 and
burn at the top of the welding torch.
Inner cone gives 2/3rd of the heat whereas the
outer envelope provides 1/3rd of the energy.
– Reducing flame (3000°C)
Excess amount of acetylene is used, giving a
reducing flame. Combustion of acetylene is
incomplete (greenish) between the inner cone
and the outer envelope. Good for brazing
aluminium alloys, high carbon steels.
– Oxidizing flame (3400°C)
Excess amount of O2 is used, giving an
oxidizing flame. Good for welding brass.
➢ Brazing on refrigeration systems requires the reducing flame.
Page 34
Brazing DOES and DON'Ts
➢ Always wear safety goggles and gloves.
➢ Always purge with nitrogen when brazing.
➢ Protect the service valves with wet rags or heat-reducing material.
➢ Use only recommended fillers for various joints.
➢ Never reach temperature beyond limits.
➢ Keep heating both tubes evenly.
➢ Maintain minimum gap between the joints.
Page 35
Use of industrial copper fittings recommended
Industrial copper fittings help to achieve the best results in RAC projects
with the required pressure resistance and reliability.
Page 36
Challenges during heating and cooling down phase
Problems:
• Due to local heating, the
connection pieces increase in
diameter but the bores do not.
• When cooling down, the
connection piece becomes
smaller but the bore does not.
Consequence:
➢ High stresses in the brazed joint
seam with a danger of cracking
when cooling down.
Solution:
➢ Remove the container walls
or weld on brazed connection
pieces.
Page 37
Brazing with nitrogen
A refrigeration cycle must be clean, dry and hermetically sealed.
• Humidity and tinder in a refrigeration cycle lead to damage in the
compressor and general system failures.
➢ Solution: use of nitrogen before putting the system into operation!
• A must for any technician!
• The use of nitrogen is prescribed by all
compressor manufacturers and
manufacturers of equipment.
Attention:
• Nitrogen is harmful in interaction with oil
and will block filters and valves.
• Interaction with oil, tinder, moisture and
high temperatures will cause creation of
acid.
Page 38
Agenda
Introduction & safety
Norms
Theory of brazing
Brazing operation
Piping preparation
Brazing tools
Brazing competency certification
05/10/2021 Bracers competences Page 39
Copper piping preparation: joints
For joining similarly sized tubes:
• Cut tubes and remove burrs
• Use industrial copper fittings
• Clearances to be within 0.05 to 0.50 mm and length of lap joint to be at least
equal to tube diameter (+ 3 mm)
• Correct distortion in the soft annealed copper tubes, before making the joint
• Swage only by using a proper swaging tool
For joining tubes of adjacent sizes (1/4” to 3/8” etc.):
• Ensure that length of smaller tube in the larger is at least 1.5 times the
diameter of the female tube! Consider max. clearance!
Page 40
Copper piping preparation: joints
Cutting,
deburring
Attention: excess pressure while cutting leaves burrs
Page 41
Copper piping operations: swaging
• Involves enlarging the diameter of one end of a soft copper tube to
enable the end of another tube to slip into it.
• Swaging process needs time for proper preparation.
• Flaring block and punch are used for this purpose.
• Tubes are finally brazed to make a strong, leak-proof joint.
Page 42
Piping operations: swaging – basic steps
• Good for constructing a joint from same sized tubes by making one side
larger
• Place the tube in correct size hole of swaging/flaring block
• Position tube up of size equal to outside diameter + 3 mm
e.g. 6 mm tube will need 9 mm projection
• Tighten both the wing-nuts of swaging block
• Select punch of suitable size and apply to it a thin film of oil
• Fit punch to clamp and fit this assembly to swaging block just above tube
• Apply force to clamp/punch carefully
• Dismantle above assemblies and remove duly swaged tube from swaging
block
Page 43
Piping operations: swaging – tools
➢ Accuracy needed (gap ≤ 0.5 mm for capillary brazing)
Page 44
Piping operations: flaring – how it works
Cleaning-polishing
Completed flared joint
Use torque wrench
for tightening and apply
correct torques
Page 45
Piping operations: flaring – purpose and requirements
Before and after flaring
the tube
RAC tube connections need to endure more than 30 bars of pressure
without leaking.
➢ RAC flare fittings - with 45° angle enable the tube to fit closely
against the fitting. Flare nut compresses flare against fitting to
achieve tight, leak-proof, metal-to-metal contact.
➢ Flare connection, being a mechanical, metal-to-metal contact without
gaskets, needs proper attention and care while making flares.
Page 46
Agenda
Introduction & safety
Norms
Theory of brazing
Brazing operation
Piping preparation
Brazing tools
Brazing competency certification
05/10/2021 Bracers competences Page 48
Brazing sets
Oxygen-propane Oxygen-acetylene Oxygen-acetylene
➢ For small pipe joints ≤ 28mm ➢ For small pipe joints ≤ 28mm ➢ For all pipe dimensions
➢ Handy for service use ➢ Handy for service use ➢ best performance
Page 49
Brazing sets: working pressure recommendations
Adjust working pressure:
(atomizer type)
Working pressure:
Oxygen: 2.5 bar
Acetylene: 0.25 – 0.5 bar
Propane: ~ 1.5 bar
Oxygen-acetylene Oxygen-propane
Page 50
Brazing components: torch
Braze solders
Igniter with spark flint
Brazing torch
Page 51
Brazing components: design of the torch
Page 52
Brazing with nitrogen
➢ The use of nitrogen is an approved technical standard in all fields of
refrigeration and air-conditioning installation, service and maintenance
➢ Nitrogen as protective gas with brazing of copper pipes (N2 flow about
0.2 bar) to avoid scaling (tinder) inside
Page 53
Agenda
Introduction & safety
Norms
Theory of brazing
Brazing operation
Piping preparation
Brazing tools
Brazing competency certification
05/10/2021 Brazing competencies Page 54
Brazing competency certification
• The international regulation ISO 13585-2012 (replacing EN 13133-2000)
describes the essential requirements for brazing qualification and lists
terms and conditions, examination criteria, inspection procedures and
the area of application for a brazing competency test certificate.
• Required brazing competencies are varied among different RAC
sectors (e.g. supermarket refrigeration, air-conditioning or stand-alone
appliances). Manufacturer and installation companies therefore may
describe specific application and testing requirements.
• In countries where the apprenticeship and education for the RAC sector
includes brazing technologies as part of the scope of the competence
certification a separate competency certification according ISO 13585 is
not required.
Page 55
Quality test of practical work sample
➢ Braze solder penetration was not sufficient.
➢ This failure could result in a reduced pressure stability as well as a
reduced stability against vibration.
Page 58
Brazing testing method: X-ray test
➢ X-ray test makes a quality test possible without destroying the pieces.
➢ Easy to see inclusions
Page 59
Key take- aways
✓ Brazing is easy if basics are known
✓ Only brazing work experience will lead to good results
✓ Always use the right tool and material for different kind of connections
✓ Incentives for using brazing for HC chiller appliances
✓ Key advantages of brazing over welding and soldering
✓ Using proper brazing materials and temperatures for different applications
05/10/2021 Brazing competencies Page 60
Thank you for your attention!
Page 61
