WELDING 7.1. Introduction, 7.2. Weldability, 7.3. Cla cation of Welding Process, 14 Pipes of Weng, 5. Advan , 1.6. Dis-advantages of Welding, 7.7. Practical Applications of Welding, Sune 78 bectsioar Walle, 710. Are Welding Process, 7.11. Carbon-are Welding (C&W 7-12. Shielded-metal-arc Welding (SMAW), 7.13. Tungsten-inert Gas Welding, 7.14. Metal-inert Gas Wel (MIG), 7.15, Sub: aerged-are Welding(SAW), 7.16. Electric Resistance Welding, 7.17. Spot Welding, 7.18. Seam Weldir 3, 7.19. Projection Welding, 7.20. Butt Welding, 7.21. Flash Welding, 7.22. Pressure ‘Welding, 7.23. Col pressure Welding, 7.24. Explosive Welding, 7.25. Ultrasonic Welding, 7.26. Friction ‘Welding, 7.27. Induction Welding, 7.28. Thermit Welding, 7.29. Brazing, 7.30. Gas Cutting, 7.31. Defectsin ‘Welded Joints, 7.32. Welding Symbol and Indentification, 7.33. Review Questions, 7.1.INTRODUCTION ‘The welding is a process of joining two or more, similar or dissimilar metals by heating them toa suitable temperature, with or without the application of pressure, filler material and flux. The eat may be supplied by electric are (In case of are welding), combustion of gas (in case of gas welding), electrical resistance (in case of resistance welding) or by black Simith’s fire (in case of forge welding). The filler material has a similar composition and melting paint less than that of the base metal. The filler rod is used to supply the extra material, to fill the gap between joint and to produce a round, oval or fillet. Also, its function is to make-up the losses during welding process. A flux is sometimes used to remove the oxides formed during process, in the form of fusible slag which floats on the r.:ten metal. This also prevents the re-formation of Oxides by environmental conditions. Welding of similar metals without filler material is known as aufogeneous welding while with filler material is called homogeneous welding. On the other hand, welding of dissimilar metals with filler rod is called hetrogeneous welding. Welding phenomenon is comes into existence since 1930. Its growth is very fast in fabrication industries. It is analternative method for casting or forging. Today, the scope of welding technology is wide and extensive It is successfully employed in daily use items like automobile vehicles, aircrafts, ships, houseliold appliances, electronic equipments, bridge construction, building construction, pressure vessels, tanks, Rail and road equipments, Pipings and pipelines, trucks, trailers, trusses etc. 7.2, WELDABILITY Weldability defined as “the property of a metal which indicates the ease with which it can be welded to form an inseparable and strong joint, having a homogeneous structure of proper strength”. A metal is said to have good weldability ift can be welded easily in a fabricated structure. Weldability ofa metal depends upon the following various factors 1, Composition of metal. 2. Melting point of metal. 3. Thermal expansion of metal. 4, Thermal conductivity of metal, 5. Brittleness of metal. 6. Strength of metal 7. Micro-Structure of metal. Welding technique i.c., with or without flux and filler material.the welding which is done at solid state of metal workpiece is called solid state welding. This again classified into wo groups / welding. Explosive wel some diffe pressure welding and electrical resistance 157 wane song tes to rai the required properties, heat weatment of metal before uae is necessary Hon sai wchaiiy, Ofer materials in decreasing order of weldabilty ar carbon scel,Can iron, lowealloy ren jess sec igh speed sel ete “ A SIFICATION OF WELDING PROCESS Mehl mrcess cam be classified on the basi of certain riteria mensined below : a te basis of type of interaction, onthe basis of sou of heat * on the basis of metallurgical aspect, {Qn the basis of Type of lnternetion : Ths ean be divided in following thtce groups {a Fusion welding (Non-pressure welding) as (iy Forge welding (Pressure or plastic welding). {c) Soli state Welding (a) Fusion welding; fasion or non peste welding, he edges ofthe metal pieces tobe joined and ‘he filler wnaterial are heated together to-a melting temperature, and then allowed to solidify. Ths i nnast widely used welding provess, (i) Forge welding: tn forge or pressure or plastic welding, the metal pieces tobe joined are heated to ition welding, Ultrasonic welding and Cold-pressure welding are cot types of soild-state welding, aplastic state and then forced together by applying mechanical pressure, with the help of hammer. No filler material is required in this type of welding, (0) Salil -state weld 2. On the basis of Source of Heat : This can be divided in following different groups : (u) Blectrie Are Welding, (0) Gas Welding (c) Resistance Welding (v) Thermo-Chemical Reaction Welding (Thermit welding). i Energy Welding, basis of Met («) Autogeneous Welding, (0) Homo lurgical Aspect : This can be divided in followi neous Welding, (c) Heterogeneous Welding, w) Autogencous Welding : The process of joining similar metals without the addition of filler material, is known as Autogenous welding, (h) Homogeneous Welding : The process of joining similar metals with the addition of filler material, {s known as Homogenous welding. (0) Heterogeneous Welding : The process of joining dis-similar metals with the addition of filler material, is known as Hetrogenous welding. }4.1YPES OF WELDING Today, there ae about 30 different welding process in use by different industries. In general, various nny and related processes are classified as under : (0) Gay Welding (#) Oxy-acetylene welding Gi) Air-acetylene welding, (iu) Oxy-hydroven welding (iv) Oxy-fuel welding. (h) Blersie-Are Wel (0 otal are weld (ii) Carbon are welding (0) Tungsten inert gas welding (TIG) (iv) Metal inert gas welding (MIG) 1%A 138 Production Process (0) Submerged are welding (vi) Plasma are welding (i) Stud arc welding (vii) Flux cored are welding (ix) Electro slag welding (x) Electro gas welding (o) Resistance Welding a‘ (@) Spot welding (Gi) Seam welding (iti) Projection welding (iv) Butt welding (0) Flash welding (vi) Pereussion welding. (a) Solid-State Welding (i) Cold welding (ii) Friction welding (iii) Ultrasonic welding (iv) Diffusion welding (») Explosive welding (01) Roll welding. (c) Thero-chemical Welding (i) Thermit welding. (ii) Atomic hydrogen welding. () Radiant energy Welding (Newer welding) (i) Laser beam welding (ii) Electron beam welding. (g) Low Temperature Welding Processes (i) Soldering (ii) Brazing (iti) Bronze welding (iv) Hard facing. (i) Welding Related Processes (i) Gas Cutting (ii) Are cutting 7.8. ADVANTAGES OF WELDING 1. Light, strong and permanent joint : The welding joints are normally lighter than bolted or riveted Joints. A good welded joint is stronger as the base metal. It produces a permanent joint. 2. Cheap, portable and easily available equipment : The welding equipments are cheaper, portable and everywhere available. 5. Provides maximum efficiency : The welding joint provides maximum efficiency (upto 90-95%) among other related joints #04 Smooth and pleasing appearance: The welding structure looks smooth and pleasing is appearance 5. Wide range of welded material: A variety of metals bot similar and dissimilar can be joined by this process. 6. Wide range of welded products : Welding offers variety of easy to complex shape proruts which ray not be possible in riveting o otherwise. 7. Flexibility in future work : In welded structures, addition and alteration can be easily made. This process provides flexibility of further expansion or correction work. 8. Freedom in design : Welded joints permit considerable freedom in designing of structure. 9. Economical and faster process : Welding process is much faster and economical as compared 0 riveting and other similar processes. 10. Leads to automation : The continuous welding process may be mechanized. This leads to automation technology. 76. DISADVANTAGES OF WELDING 1. Possibility of distortion, eracks and residual stresses: Due to uneven heating and cooling dursg fabrication, the possibility of distortion, cracks and residual stresses are powerful. 2. High degree of skill and supervision : The welding process requires a high degree of skill and supervision to produce a good welding job 3. Edge preparation and cleaning : The welding process requires edge preparation and cleaning of workpiece before being weld. ‘4 Jigs and fixtures : The welding process requires jigs and foxtures to hold and position the pats © welded.- “an 159 5, Produces metallurgical changes : The welding process produces metallurgical changes in the work structure is distorted during process, wt gi Needs heat treatment : A welded joint, needs stress-elief heat treatment. 7, Harmful to human health : The welding process produces the harmful radiations, fumes, gases, rwhich adversely affects the human health, U. PRACTICAL APPLICATIONS OF WELDING ‘Welding plays an important role in engineering industries. Itis a major tool for fabrication and repairing ofmetal products. Welding has proved its ability in manufacturing, construction, fabrication and maintenance. ‘few important applications of welding are listed below 1, Automobile Applications (i) Automobile frames (iit) Arc welded car wheels (v) Automobile body 2, Aireraft Applications (0) Aircraft engine assembly (Gi) Turbine frames for jet engine. (iii) Rocket fuel tanks (iv) Oxidizer tanks (+) Ducts, fittings, cowling components, ee 3. Bridge Applications (# Paler construct (in) Frames 4. Building Applications (i) Erection of column (i) Automobile brackets (iv) Stee! rear axle housing (v7) Truck and trailers, ete n (ii) Section lengths (iv) Truss assembly, ete, (ii) Column base plates ii) Trusses: (iv) Doors and window, ete. 5, Pressure Vessels and Tank Applications (i) Dom and shell construction (1 Joining of steel plates (iii) Nozzle and shell assembly. ete. 6. Pipelines and Piping Applications i) Open and closed pipe joints (ii) Rolled plate pipings (iii) Gasoline pipelines (i) Oil pipelines, ete 7. Rail Road equipment Applications (i) Locomotives (ii) Engines {ii) Aiv receiver 8, Repair and Maintenance Applications (av) Front and rear hoods, ete (i) Toots and dies (ii) Punches (iti) Gears, (iv) Press and machine tool frames, etc 9. Ship Applications (i) Shell frames, (W Girders (fit) Column structures {iv) Webs and plating, ete. 10, Storage tank applications (H Oil tanks (i) Gas tanks (iii) Gas cylinders (iv) Water storage tanks, ete. 78. GAS WELDING 7.8.1. Introduction : Gas welding is a fusion welding process in which the heat for welding is obtained by the combustion of oxygen and fuel gas. The fuel gas may be acetylene, hiydrogen, propane or butane. An intense gas flame is thus produced which melts the edges ut the parts to be welded. The molten metal is Allowed to flow to Solidify together and continuous joint is obtained. The gas cling is particularly suitable for joining metal sheets and plates having thickness of 2 to 50 ‘mm. An additional metal called filer material is used for thickness more than 1 Sm. This filler metal is used inthe form of welding rod. The Composition of filler rod is usually same as that of base metal. The filler metal is —_ ——fen Production Process Used to fill up the ea impu ry made during edge preparation, A flux materia! is also used during welding to remy es and oxides present on the metal surfaces to be joined. Ditferent combination of gases are used to produce hot gas flame, e-g.. Oxygen and acetylene, oxygen and hydrogen, oxygen and propane, air and acetylene ete. The combination of oxygen and acetylene ig mo widely used. This combination burns to produce a highest flame temperature of about 3200°C. Such a Name produced is known as Oxy-acenlene flame. The approximate ternperature produced by different combination, are listed below {) Oxy-acetylene, 3200°C (ii) Oxy-hydrogen, 2800°C (iii) Oxy-butane, 2700°C (iv) Oxy-propane, 2200°C (9) Oxy-coal yas, 2100°C (vi) Air-acetylene, 200°C (vid) Aitchydrogen, 1800°C (ti) Air-propane, 1750°C Oxy-acetylene flame is used for welding metals, having high melting temperature such as mild steel, high, carbon steel ete. On the other hand, Oxy-hydrogen flame is used for welding metals having low melting temperature such as aluminium, lead, magnesium, et, 7.8.2. Oay-Acetylene Welding When a combination of oxygen and acetylene is used in correct proportions, to produce an intense gas fame, the process is known as Oxy-acetylene welding, An Oxy-acetylene gas flame has a temperature of abou, 320°C an thas can meltall commercial available metals. A filler rod of the same material is used to fill up the cavity made during edge preparation, ifmetal thickness is more than 15 mm. A flux is used to remove impunies and oxides present on the metal surface. To ignite flame, open the acetylene control valve of the welding torch. The necessary oxygen is draw from the atmosphere to burn acetylene partially. The oxygen control valve is then open to adjust the required volumie of acetylene and oxygen mix and burn. The three different types of gas flames produced by changing the mix volumes. There are two systems available for Oxy-acetylene welding, (a) low pressure Oxy-acetylene welding ;(6) high pressure Oxy-acetylene welding. These are discussed brief in the following articles 7.8.3. Low-pressure Gas Welding The low pressure gas welding uses low pressure acetylene which is produced in a generator (low pressure cylinder) through a controlled reaction of calcium carbide and water, as in equation below 4 Sse cacun Seine cares ——$ SBES” Ereaetns contro. vawe —_ BER / ONDER ACETYLENE Fig, 7.1. Low pressure uectylene generator. Cac, + 2H,0 —> C,H, +Ca (OH), (Calcium carbide) (water) (Acetylene gas) (lime) “The acetylene produced by this method is ala low pressure, slightly above atmospheric pressure T™ {pss in carried 1m pipes to the work site where being used. An injector type blow pipe is used which a™*a 163 Osygencylinder. 2 acelene cinder pens 3, Welding torch. or 4, Welding tip (nozzle). Waiter oo 5, Pressure regulator. 66. Hose and hose fittings. Ktyene 7, Goggles and glasses. cent & Gloves and apron. 9, Spark lighter, key set, spanners, ‘estore eee 10, Filler rod and flux material. on COnygen ier \We will discuss the above equipments one by one Fig. 7.3. Oxy-acetylene welding equipment. 1. Oxygen Cylinder : The function of oxygen cylinders is to storage of oxygen used to produce the gas ume. The important properties of this cylinder are PROTECTOR (Standard colour : Black painted (a) CAP (ii) Construction material : Mild steel and alloyed steel. wave (ii), Construction Process : Solid drawn, Roza sarter (iv) Usual size : 40 liter. am (v) Cylinder Pressure : 154 kgfienm or 154 bar (15400 KN/mm?). (0) Gas filling remperature : 21°C. (vi) Full Cylinder weight : About 66 ke. % (viii) Outlet valve serewed : Right handed. Fig. 7.4. Oxygen cylinder. (ix) Protection cap + A protector cap (removable steel cap) is screwed on the cylinder to protect the ‘opening valve from any damage during storage and transportation of cylinder. (0) Opening valve : The eylinder is provided with a high pressure opening valve atthe top, which can be operated by turning a hand whee! as shown in Fig, 7.4 (si) Cylinder dimensions : Inside diameter 21.6 cm (8.5”), wall thickness 0.650 mm., length 127.5 em 61") (wii) Fusible plug : A fusible plug is usually provided in the cylinder valve for protection. 2. Acetylene cylinder : The function of acetylene cylinder isto storage of acetylene used to produce the «as lame. The important properties of this eylinder are (0) Standard colour : Maroon or red painted SOCKET (ii) Construction material ; Steel. mxruRE OF GLAND. seorwueNe Ave (itt) Construction process : Solid drawn. HESTON NO SPINDLE (iv), Usual size : 30 t0 60 Titers. mara stea. (v) Cylinder pressure : Low pressure generator, 0.07kgi/em’ to 0.98 kgf em? a Medium pressure cylinder, Ikgf/cm? to 2kgffem? MATERIAL High pressure the cylinder, 15kgf/em?. (01) Full eylinder weight : About 86 kg. SAFETY PLU (ii) Cylinder dimensions : Inside diameter, 30cm (12") Fig. 75. An acetylene cylinder. Wall thickness, 0.438mm Length, 101.25em(40.5") (vitt) Pusible plug + A fusible plug at the bottom of the cylinder is provided. The metal of the plug melts at about 105°C and allows acetone and acetylene to escape in case of fire. (10) Out fet valve screwed : Lef-handed HH ggProduction Process 169 5 ‘material such as charcoal, asbe, « Elements in cylinder: Beetyene gas, Aeztone (guid POV sil ibe, balsa wood, et. ove atmospheric and may decomp tae at eae tis dissolved in acetone. (xi) Acetylene gas : The pure acetylene is not ap to store acetylene at 15 sinosp re ee explosively. Hence, “Acetone is capable of absorbing a (xii) Acetone : The acetone is a chemical ee eoie CH COCH, Iisa liquid of poisonous smell. ATSION acetone at 15°C arm aracetvene and on releasing i, the pressure falls. One vn capacity i and at Tnospberie pressure dissolves about 25 volumes of acciene ving apa acres in proportion ote pressure. At 15 atmospheric acetylene Press ‘one volume of acetone absorbs 25 x 15 = 375 volumes of acetylene. : : (ati) “Dry Porous Material: The cylinder i first filed with a dry Porev eater ike chara ashes, tase arood, Sik fibre, ete, which absorb liquid acetone containing dissolved acetylene 3. Welding Torch : The function of welding torch is to mix acetylene and oxygen in oes volume. The nixed gaves are drven out through a tip called nozzle with desired velocity to bum out Welling Wrshes are tnade in diferent designs and sizes o suit the purpose. These are available commercially in nwo Beneral pes ACETYLENE CONTROL NEEDLEVLAVE gooy INTERCHANGEABLE Low PRESSURE eee ACETYLENE MIXING CH a 0H Nozmeme) Oth NOZZLE PRESSURE: OXGENVA >] Invector MxTURE Low pRessuRE ‘OXYGEN oxen ACETYLENE, an (OXYGEN CONTROL eee tiemue ——_-NEELDEVAIVE NoURS (a) Low pressure welding torch, (6) High pressure welding torch (€) Low pressure hose connection. (d) High pressure hosse connection Fig. (i) Low pressure or injector type. (Gi) High pressure or equal pressure type. (0) Low pressure or injector type : The low-pressure blow pipe or welding torch is used to carry the acetylene a low pressure (0.02 bar) fromacetylene generator. It is used in low pressure oxy-acety lene ‘welding. The pressure of acetylene drawn from the generator is quite low, ic. less than 0.07 ba. ‘The different parts of low press-welding torch is shown in Fig. 7.6 (a), ‘The low pressure welding torch works on the principle of injector. The high pressure (0,7 to 2.8 bat) oxygen coming from cylinder is allowed to go to the mixing chamber through a passage located in the vente of the orch ata very high speed. The high velocity ofthe oxygen causes suction and lov pressure acetylene issckedin hgh tip ioe misig camer Tae Eaneeeoes ea on me ixing chamber and ready o go through a nozzle for combustion, are mixed in proper volume in th165 veins an advantage of OW pressure torch is that small fluctuation in the oxygen supply produces a ing change in the amount of acetylene drawn, this makes volume of the two gases constant. fr) High pressure or equal pressure type : The high pressrur or equal pressure welding torch is used to carry the oxygen and acetylene both at high and equal pressure, from the oxygen and acetylene cylinders respectively. It is used in high pressure oxy-acetylene welding. soth oxygen and acetylene drawn from the cylinders and mixed in mixing chamber at equal and high sie 1 07 bar fo 1 bar. There are two valves provided onthe torch to contro the flow rate ofboth the re ilferent parts of high pressure welding torch i shown in Fig. 7.6 (6). he high pressure welding torch is most commonly used in practice. It had following advantages (i) Light and simple operation, (ii) Does not suffer from back fire. (id) Does not need an injector. (iv) Flow rate of both the gases can be individually controlled, (») Flow rate of acetylene does not suffer from rate of oxygen. 4, Welding Tip (Nozzle) : The welding tip is the end part of the welding torch. It consists an opening, sisough which the gases pass just prior to ignition and combustion. There isa large variety of interchangeable veling tip different in size, shape, design and construction. The tip size is determined by the diameter of the pening ftp. The selection of tip diameter depends upon the thickness and the type of the metal to be welded. ‘ore the thickness to be welded, greater is the diameter of the tip. More the diameter of tip, greater is the mount of heat supplied. The selection of tip size is very important for good welding. Tips of 1.0 mm diameter to 4.0 mm diameters se sed fr thin sheet work to heavy duty work respectively. The following table shows are different sizes of tps for different thickness to be weld. The tips are made of high conductive materials, ¢.g. copper and its alls ‘Table : 7.2. Variation of tip diameter with thickness of work. ‘Thickness of work Tip dia ‘Oxygen acetylene (mm) (mm) Pressure (bar) 0.8 mm Imm| 0.14 bar 1.6mm 15mm 0.14 bar 3.2mm 2mm 0.14 bar 64mm 3mm 0.20 bar {128mm 4mm 0.36 bar The cutting Ups, used for gas cutting differ from the welding tis, in aspect that the welding tip has one onfige opening while the cutting tip has multiple orifices of openings, as shown in Fig. 7.7 fc). A tip can be ‘ ‘ol type or multiple-piece type. == § © (4) Solid Novae. (b) Two Piece Nozzle. (c) Welding Tip, Cutting Tip. Fig 7.7. Welding torch tips (Nozzle) Lm,ee ee) eee eres ee eee ee eee 106 Production Process 5. Pressure Regulators : The pressure of the gases coming out of cylinders is considerably higher than the vas pressure used to operate the welding torch. Therefore, the function of using a pressure regulator are (a) To reduces the cylinder pressure to a suitable working pressure. (+) To produce a steady flow of gas. The important points regarding pressure regulators are : (1) Its fitted with two pressure gauges. One shows the gas pressure in the cylinder and other shows the reduced pressure at which gas is coming out. (11) Itis connected between cylinder and hose. | (i) Itas available in two general types i.¢., single-stage regulator and two-stage regulator. | (iv) The pressure of gases coming out of cylinders are given in table 7.3. ; () There is some difference in oxygen and acetylene pressure regulator which is given in table 7.4. ‘Table. 7.3. Working pressure range in gas welding, S.No. | Type of welding O, Pressure C,H, Pressure Thickness of work | fe | | High Pressure gas welding | 0.15100.7 bar | 0.15 (00.7 bar 1 to 25 mm Over 25 mm 1 2. High Pressure gas welding, 0.90 to 0.98 bar | 0.90 to 0.98 bar 3 | Low Pressure gas welding 0.98 to 2 bar 0.15 bar ‘Table, 7.4. Difference between oxygen and acetylene pressure regulators.> welding 167 6. Hose and Hose Fittings : The function of hoses is to provide the passage for gases from pressure sequltor tothe welding torch. The oxygen hose pipe is coloured black and acetylene hose pipe is ein colour. ‘Fpey should be strong, durable, non-porous, light in weight and flexible. They are made of canvas-reinforced diner These are very robust and capable of withstand high pressure. They may be single or twin type moulded ponded together. Fig, 7.9 (a) shows the oxy-acetylene hose. (a) Oxy-acetylene hose. (8) Oxygen hose connection. () Acetylene hose connection. (4) Hose clip. Fig. 7.9. Hose and hose fitngs. ‘To connect the hose to the pressure regulator and the torch, a standard nipple is used. The nipple consists of serrations all arround so that it force into the hose. ‘One end of the nipple is inserted in to the hose and clamped through a metal clamp, while other end of the nipple is connected to pressure regulator/ welding torch and clamped through nut. In case of oxygen @ single nut is used and in ease of acetylene a double nut is used. There are two nipples used with oxygen hose, one st each end, and two nipples are used with acetylene hose. The standard hose fittings are shown in Fig. 79. hed. 7. Goggles and Glasses : The function of goggles and glasses isto protect eyes from light, ultra violet rays and heat ofthe flame, These are fited with appropriate coloured glasses. 8. Gloves and Apron : The function of gloves is to protect the operator hands from flame and any injury. ‘leather apron is also weared by the operator to protect their clothes. 9. Spark-Lighter, Key Set, Spanners : The function of spark-lightr is to ignite the welding torch. It provides convenient, instant, safe and inexpensive means of lighting the torch. Match sticks should never be tse because the puff ofthe flame, producted of ignition of acetylene, flowing from the tip ofthe nozzle, may buun the operator hand, A set of opening keys and spanner also provided with gas welding setup, for opening and closing ofthe valves = wt aflaa ™ 108 Production Process ono filer od (so called welding rd) provide hg mal meal require to welding. tis generally made of same composition and properties asthe base me 1t shoul be fice fhom dust, grease, rust, non metalic particles, and any other contimination, Sone jy, matenals and theur uses are given inthe table 7.5. Table. 7.8. Different types of filler rod materials No. | Material tobe weld Filler rod material L Ferrous metals ‘Steel rods with high carbon, silicon and magnese 2 Alloy steels Stee! rods with chromium and vanadium, 1 3 Stainless steels 18/8 Chromium-nickel rod. 4 Copper Drawn copper rod. 5 Brass Phosphor branz rod 6 | Grey east iron Special east iron rods. 2. Aluminium sheets and Pare aluminium rods, | itsalloys s Aluminium castings Aluminiurn rod with 12 percent silicon, 8 | Magnesiumalloys Same composion as base material ‘The function of fl isto protect the molten metal from atmospheric oxygen and to remove the oxides formed in weld pool. In addition, it helps to clean and protect the surface of the base metal. They are available ® several forms, such as dry powder, a paste or coatings on welding rod. The commonly used flux for Welding erent metals ae given in the table 7.6. Table. 7.6, Different types of flux materials, SNo. | Material to be weld Flux material Ferrous metals Borex, carbonate, bicarbonate and silicates of sodium. _— 2 | Copperand its Boric acid, mixture of sodium and potassium borates, alloys carbonates, sulphates ete 3 Aluminium and itsalloys | Alkaline chlorides, uorides and bisulphates. [+ | Magnesium and its alloys | Sameas used for aluminium and its alloys. 7.8.7. Types of Gas Flames } Correct type of flame is essential for satisfactory MU selding. The flame must be of the proper temperature, size and shape in order 1 take a highest efficiency, Flame temperature is one of the important parameter for welding. The flame temperature is not constant throughout but varies with zone to zone. The three type of gas flames can be produced by different Proportions of oxygen and acetylene. These are (a) Neutral Flame () Onadising Flame () Carburising Flame, (Reducing Flame). (4) Neural Flame A neutral fame i obtained when equal olume of oxygen and acetylene ate mixed inthe welding torch = a> and burnt atthe np The flame has got maximum temperature of imerciee _Oxvdving Flame. 100°C The neuttal flame has two defined zones (Punlr o Fig. 7.10. Types of gas flames) Am anner cone (luminous and blue) ‘outer cone oF envelope (Bluish to orange) ‘ saner cone heats up the metal and the outer cone protects the molten metal from oxidation by swag the atmospheric oxygen. The neutral flame is extensively used for most of the welding work ae ‘The neutral lame is commonly used for the welding of ) Mild steel (4 Stainless steel (ii) Copper (0) Cast iron! (i) Low alloy steels, ete ‘Aw oxidising flame is obtained when the supply of oxygen is more than that of -nicoe. This flame has highest temperature of3300°C. The oxiding lane has two sones ) An inner cone (Short sharp more pointed and purple colour), sn outer cone or envelope (much shorter) © not used 1@ weld steel as this will result in large grain size, increased bnitleness. lower lame is commonly used for the welding of (i) Brass, (ia) Bronze (») Few ferrous metals (vi) Few cast iron ete sg Flame ): A carburising flame is obtained when the supply of acetylene of oxygen. This flame has a highest temperature of 2900°C. The carburising flame has three nnet cone (Sharp and bluish white colour). ) An intermediate cone (Acetylene feather, whitish colour). n outer cone or envelope (Longer than neutral flame, reddish colour) ‘The length of intermediate cone is an indication of the proportion of excess acetylene inthe flame. A ne does not completely consumes the available carbon in acetylene and hence it produces lower than other two types of flames. In case of weld steel, residual carbon is forced info the weld pull stcel hard, by producing 2 hard substance known as iron carbide. ‘canons = A carburising flame is commonly used for the welding of carbon steel (a Castiron (Gif) Hard surfacing materials. ad (0) Cemented Carbides (1) Satelite, et. 88 Welding Positions 0 the axis of work piece and axis of weld, welding positions are classified as Flat or down hand weld position : When the axis of work piece and the axis of weld are in horizontal postion so thatthe hands ofa operator is in down ward position, itis known as Flat or down hand welding posinon In this, the flame is above the face of the weld as shown in Fig. 7.11 (a). 2 Horizontal weld position : When the plates and the position of grooves are m horizontal plane and the «done from the left to right or right to left itis known as horizontal welding position. This is shown 7116) (a rose! (9 veraI a = 179 Production roces,4 ical weld position : When the plates and the position of grooves are in vertical plane ang welding an bdo aparedounwarddeion tskaowns vere Weng poston Ths ee inFiy.7.11(@) as Md of te operand sy 4. Overhead weld position : When the workpiece is over the head of rator and is in horizon plane itis Knownas overhead welding position. Inthis the Names below the fae ofthe weld as shown in Fig, 7.11 (a). This is most difficult welding position and requires a high degree of skil 5. Inclined weld position : When the workpiece and the weld ae inclined at an angle (8) to one or bot, the planes, it is known as inclined welding position. This is shown in Fig. 7.11 (e). 7.8.9. Gas Welding Techniques (Methods) ‘Thete are different variable factors which have an appriciable effect on the speed and quality ofthe weld, Some factors are, direction of flame travel, tilting of torch, type and position of filler rod etc. Depending on them, the gas welding techniques are clasified as 1. Lefiwar¢ or Forward welding. 2, Rightwa: Lor Backward welding. 3. Vertical w cing. 4. Linde welding |. Leftward or Forward welding : in this technique, the torch is held in the right hand and the filler rod {is in de let hand ofthe operator. The welding is started from the right hand end of the plate and travels towards left hand, The torch tip makes an angle of 60-70° and the filler rod makes an angle of 30-40° with the work surface. The flame is given a circular, rotational or side-to-side movement to obtain uniform fusion while the tod should be moved backward and forward along the plate. This technique is used for unbevelled steel plates ‘upto 3 mmand bevelled plates upto 6mm. The plates above 6mm thickness are not economical to weld by tis technique. For plates above 3mm thickness the plate edges are bevelled to produce 'V" of 80-90°. The leftward ot forward welding technique is shown in Fig. 7.12 (a). CT3X1 Ziz>__] (e) Leftward Welding (8) Rightward Welding Fig. 712. 2. Rightward or Backward welding : In this technique, the welding torch is held in the right hand and the filler rod is in the left hand. The welding is started from the left hand end of the plate and travels towards right hand. The torch tip makes an angle of 40-50° and the filler rod makes an angle of 30-40 with the work surface. The filler rod is given circular motion and the torch is moved straight along the joint. This technique is beter and economical for welding heavy stel sections and plates over 6mm thickness. For plates above ‘8mm thickness the plat elges are bevelled to produce ‘V* of 60. The rightward or backward welding technique is shown in Fig. 7.12 (6). This type of welding technique provides a better shielding ofthe welded portion against atmospheric ‘oxidation, The weld produced by this method is stronger, denser and tougher. 3. Vertical Welding : In this technique, the welding is started from the bottom of the welded jot and oes towards top of the joint. This may be carried out either by the leftward or rightward technique. The ‘welding is done by giving oscillating movement to the torch and the filler rod. The torch makes an angle of 25m wen p00". deer al so plates pt 16 thickness. The vertical welding techniques shown in Fig, 7.13. -nding upon the thickness of the plates to be welded. The filler rod makes an angle of 30° with the ‘This method is better and economical for plates thickness of 6mm and above. No edge preparation 090 1 sm) 02 60mm) 0-06) Fig 713. Vertical Welding ‘There are two operators are required for welding plates above Smm thickness. These operators have dentical torches, nozzles, pressure settings, torch and rod angle, speed and travel etc. When using two operators, fusion is more easy. The both sides of the weld then have a uniform convex weld metal. “4. Linde Welding : This is a special welding technique used for butt welding of steel pipes. The edges of the pipes are bevelled at 70° and butted together with a gap of approximately 2.5mm. The seam is welded with «acess acetylene flame. While welding, the pipes are rotated constantly soas to weld the seam inthe horizontal positon only. Rightward welding is adopted inthis technique to weld the pipes. 78.10, Advantages of Gas Welding ‘The following are the advantages of gas welding : |. Portable and most versatile process : Gas welding is probably portable and most versatile process. ‘he range of gas welding products are very wide. Itcan be applied to variety of manufacturing, maintenance and repair work 2. Better control over the temperature : Gas welding provides better control over the temperature of the real inthe weld zone by controlling the gas flame. 3. Better control over filler-metal deposition rate : In gas welding, the source of heat and filler metal are separate unlike are welding. This provides better control over fillr-metal deposition rate. “4 Suitable to weld dissimilar metals: The gas welding can be suitable to weld the dissimilar metals with surtable filler and flux material S. Low cost and maintenance : The cost and maintenance of the gas welding equipments is low as compared to some other welding processes. The equipment is versatile, self suficient and portable. 74.11, Disadvantages of Gas Welding, 1. Nor suitable for heavy sections : Since the heat produced is not sufficient and hence heavy sections can not be jomed economically. 2. Less working temperature of gas flame : The flame temperature is less than the temperature of the arc. 3 Slow rate of heating : The rate of heating and cooling is relatively slow. In some cases this is dvantageous. 4 Not suitable for refractory and reactive metals: Refractory metals like tungsten, molybdeaum and ‘cactive metals like titanium and zireonium can not be welded by gas welding process. OMY1? Production Process, 5. Larger heat affected area Gas welding results in a larger heat affected area du to prolonged heating of joint. 6. Flux shielding is not so effective : Flux-shielding in gas welding is not so effective as in ease of Tig, or MIG welding, The oxidation cannot be avoided completely. : 7. Problem in storage and handling of gases : More safety problems are associated with the storage ang, handling of explosive gases e.g, acetylene and oxygen, 7.8.12, Applications of Gas Welding ‘Oxy-acetylene gas welding is widely used in practical field. Some important applications are 1. For joining most ferrous and non-ferrous metals, carbon steels, alloysteels, cast iron, aluminium and its alloys, nickel, magnesium, copper and is alloys, ete 2. For joining thin metals 3. For joining metals in automotive and aircraft industries. 4 metals in sheet metal fabricating plants 1 5. ‘materials those requires relatively slow rate of heating and cooling, ete i 7.8.13 Filler Rods in Gas Welding ‘The function of filler rod (also called welding rod) is to provide the additional metal require to Welding, tis wenerally made of same composition and properties as the base metal It should be free from dust, grease, ‘ust, non metallic particles, and any other contimination, Some filler materials and their uses are given inthe abl ‘Table 7.7. Different types of filler tod materials, L S.No. | Material to be weld Filler rod material 1 Ferrous metals Stee! rods with high carbon, sili¢on and magnese, eee Alloy steels Steel rods with chromium and vanadium, . 3 Stainless steels 18/8 Chromium-nickel rod, 4. Copper ‘Drawn copper rod. A § Brass Phosphor branz rod. wie eee Grey cast iron Special cast ion rods. he 7. ‘Aluminium sheets and Pure aluminium rods, | its alloys 8. | Aluminium castings Aluminium rod with 12 pereent silicon, 9. Magnesium alloys ‘Same composion as base material. 7.8.14. Fluxes in Gas Welding sol During the welding operation, the temperature of molten metal is high enough. The so hot! tendency to react with oxygen and nitrogen present in the atmospheric air and to form oxides and nit ty. low strength welds or, in some eases, may even make welding: oxides formed has higher melting temperature than that of base metal, They also distorb the welding rod. ene a In order to avoicl this difficulty, a flux is used during welding, A flux is a chemical prevent, dissolve oF remove the oxides formed during welding. Its fusibleand non metallic chemical eome Flux are available in several forms, such as dry powders, a paste; liquids, or coatings on we ‘welding, the borax, sodium chloride are commonly used as lux material, The dry Mus isapplied by end of the welding rod and dipping it into the powdered material, oxides results in poor q7.9.8. Types of Welded Joints There are five basic types of joints commonly used for fusion (arc and gas) welding. These joints are : 1. Lap Joint : The lap joint is obtained by over lapping the two plates and welding the edges of the plates. It is used to joint the plates having thickness 3 mm or less. The lap joint may be single transverse, double transverse and parallel lap, as shown in Fig. 7.18. 2S DS Qa” cojen| oo Cal |=) Pea. Slot Filet single Transverse Double Transverse Parallel Fig. 7.18. Lap Joint Fig. 7.19. Basic types of fusion lap welds.SS 178 Production Process. 2, Butt Joint : The butt joint is obtained by butt together the two plates lying in the same plane and welding the edges or ends of the plates. It is used to joint the plates having thickness of 3 to 12 mm. Plates having thickness less than Smm do not require bevelling of edges whereas plates having thickness between § to 12mm, should be bevelled to forma single -V, single or double-U, of J-groove. The but joint may be square but, single-V, double-V, single-U, double-U, single-J, double-J etc. as shown in Fig. 7.20. a a zz 2 WAZ Fig, 7.20, But Joint 3. Corner Joint The corner joint is obtained by joining the edges of two plates whose surfaces are at 90° to cach other. This joint is used for both light and heavy thickness sheet metals. The corner joint is shown in Fig. 7.21 — oat ut Joint Corner Joint Fig.7.21, Basic types of Welded Joins 4. T-Joint: The T-Joint is obtained by joining two plates whose surfaces are approximately at right angle to cach other. This joint i suitable forthe plates having thickness upto 3mm. For thickness more than this, welding should be done on both sides. It is generally used to from stands, stiffeners in arc craft etc. The T-joint is shown in Fig. 7.21 5. Edge Joint : The edge joints obtained by joining two parallel plates. This joint is used economically for plates having thickness ess than 6 mm, Itis not suitable for severe loading subjected to tension and bending, This 's generally used for unimportant work and sheet metal work. The edge joint is shown in Fig. 7.21. 7.9.9. Are Welding Electrodes ‘Are welding electrodes can be classified into two broad categories : I. Non-Consumable electrodes. 2. Consumable electrodes. 1. Non-Consumable electrodes :These clectrodes do not consumed during the welding operation, hence they named, non-consumable electrodes. They are generally made of carbon, graphite or tungsten. Carbon electrodes are softer while tungsten and graphite electrodes are hard and brittle. Carbon and graphite electrodes can be used only for D.C. welding, while tungston electrodes can be used for both D.C. and A.C. welding. The filler materials added separately when these type of electrodes are used, Since, the electrodes do not consumed. the are obtained is stable 2, Consumable electrodes : These electrodes get melted during welding operation, and supply the filler They are generally made with similar composition as the metal to be welded. The are length ean be ‘maintained by moving the electrod towards or away from the work. The consumable electrodes may be of following two types