Unit 6 gas oxyacetylene welding ppt.pptx

oxyacetylene gas welding

1. Unit 6: Gas Welding Er Saurav Kumar Thakur 1

2. 6.1 Introduction to oxyacetylene (Gas) welding 6.1.1 Oxy-acetylene welding principle The principle of oxy-acetylene welding  relies on the intensely hot flame produced by mixing and burning oxygen and acetylene gases in a welding torch, which melts the base metal and filler material together to create a weld . Er Saurav Kumar Thakur 2

3. 6.1 Introduction to oxyacetylene (Gas) welding 6.1.1 Oxy-acetylene welding principle It has a two stage reaction The first stage primary reaction involves the acetylene disassociating in the presence of oxygen to produce heat, carbon monoxide, and hydrogen gas. 2C2H2 + 2O2 = 4CO + 2H2 + Heat ---------- (1 ) A secondary reaction follows where the carbon monoxide and hydrogen combine with more oxygen to produce carbon dioxide and water vapor. 4CO + 2H2 + 3O2 = 4CO2 + 2H2O + Heat--------- (2) Er Saurav Kumar Thakur 3

4. 6.1 Introduction to oxyacetylene (Gas) welding 6.1.2 Advantages and application of oxy-acetylene welding Advantages To do welding in areas where electricity is not available. To join thin metal sheets No need for high skill operator Initial equipment cost is generally lower compared to other welding methods.  Easy to maintenance and repair Dissimilar metals can easily be joined Er Saurav Kumar Thakur 4

5. 6.1 Introduction to oxyacetylene (Gas) welding Disadvantages of gas welding Gas welding involves manual operation. Gas welding process is slow. Welding speed is low due to the rate of metal joining. By the end of the welding process, there will be large heat-affected areas. Welding Titanium,  Zirconium , or High-Speed steel (HSS) is not recommended for gas welding. It is suitable for thinner sheet metals but not thicker sheet metals. Er Saurav Kumar Thakur 5

6. 6.1 Introduction to oxyacetylene (Gas) welding Applications This welding process is used for joining non-ferrous metals, cast iron, carbon steel, nickel, alloys of aluminum, etc .(dissimilar metal can also be joined) It is used to join thin metals which have as low as 1.6 mm thickness. It is commonly used in sheet metal industries, joining thin tubes, pipes. rebuilding broken gear tooth(later milled to give shape) They are used in automobile industries, shipbuilding, heavy vehicle manufacturing, and agricultural machinery manufacturing to weld thinner sections . Cutting and case(Flame) hardening operation too. Er Saurav Kumar Thakur 6

7. Case hardening Oxy-fuel cutting Pipe joints welding Er Saurav Kumar Thakur 7

8. 6.1 Introduction to oxyacetylene (Gas) welding 6.1.3 Safety precaution in oxy-acetylene welding Personal protective equipment   Wear a welding helmet, goggles, gloves, apron, and safety shoes Protect your eyes from sparks, slag, and bright light Protect your skin from hot metal and chemical burns b) Check for leaks   Check for leaks in the equipment, including O-rings and other seating surfaces Install reverse flow check valves or flashback arrestors Using soapy water to check leaks   Er Saurav Kumar Thakur 8

9. Er Saurav Kumar Thakur 9

10. 6.1 Introduction to oxyacetylene (Gas) welding C) For Fire Prevention :Treat the flame with respect Keep the flame away from people, hoses, and cylinders Don't lay down a lighted torch Don't walk around with a lighted torch Control flashbacks and backfires Never use oil on welding equipment. Oil and grease may ignite spontaneously, when in contact with oxygen. Have a fire extinguisher of proper type and size on hand in the work area, know where they are located in the shop; Do not smoke or allow anyone else to smoke near the oxy-fuel gas welder. If fuel gas were to leak from the unit, smoking could provide ignition and cause a fire or an explosion Er Saurav Kumar Thakur 10

11. 6.1 Introduction to oxyacetylene (Gas) welding d) Ventilate the welding area Don't weld or cut in a confined space  Store welding gases in a cool, dry, and well-ventilated area  Keep them away from open flames, heat sources, and electrical equipment e) Hoses care Use RMA-CGA Grade T hose for fuel gas (including acetylene) to prevent hose failures. Grades R and RM are for use with acetylene only; Examine hose regularly for leaks, wear, and loose connections. Immerse pressured hose in water, bubbles indicate leaks; Standard color coding denote using black hose for oxygen and red hose for acetylene or fuel. Er Saurav Kumar Thakur 11

12. 6.1 Introduction to oxyacetylene (Gas) welding f) Cylinders care Remove regulators and replace protective caps before transporting cylinders, Do NOT lift cylinders off the ground by their valves or caps, or by chains, slings, or magnets; Never stand in front of a regulator while opening a tank valve. Do NOT expose cylinders to excessive heat, sparks, slag, and flame, etc. that may cause rupture; Never use a cylinder or its contents for other than its intended use. Open acetylene cylinder valves 1.5 turns only . Er Saurav Kumar Thakur 12

13. 6.1 Introduction to oxyacetylene (Gas) welding g) Lighting Torch(Blow Pipe) Purge daily: Open each torch valve separately to clear air and contaminants. Close one before opening the other. Never purge in confined spaces or near flames/people. Point away: Always direct the torch tip away from yourself and others. Use proper ignition: Light with a spark lighter or pilot light—never use matches or lighters to avoid burns. Lighting process: Open the fuel valve, ignite the gas, adjust fuel for steady flow, then adjust oxygen for the desired flame Er Saurav Kumar Thakur 13

14. 6.2 Properties, uses, storages and handling of oxygen and acetylene gases Er Saurav Kumar Thakur 14

15. Properties: Oxygen: Colorless, odorless gas  Highly reactive, supporting combustion readily  Can become liquid under high pressure  Acetylene(C2H2): Colorless gas with a faint garlic-like odor  (nauseating odor) Highly flammable   Can decompose explosively under certain conditions  Usually stored dissolved in acetone within a porous filler in the cylinder Heat content is 1299 kJ/ mol at standard conditions (25°C).    Er Saurav Kumar Thakur 15

16. Uses: Oxygen: Medical applications (respiration), industrial processes (oxidation), welding and cutting  Acetylene: Primarily used in welding and cutting applications due to its high flame temperature when combined with oxygen  Also used in brazing ,case hardening, straightening, heating, cleaning. Er Saurav Kumar Thakur 16

17. Storage and Handling Precautions Never store oxygen and acetylene cylinders together; keep them physically separated in dedicated storage areas.  Always check cylinders for damage before use, ensure valves are properly closed and secured with protective caps when not in use.  Store cylinders upright and securely fastened to prevent tipping or rolling  Store cylinders in a well-ventilated area  Oil and fatty substance must not come In contact with oxygen( can cause explosion) Cylinders must not be subjected to knocks or high temperature and must not be dropped .  Always use valve protection caps when cylinders are not in use.  Never lift cylinders by the valve or valve cap; use a suitable cradle or lifting device.  Er Saurav Kumar Thakur 17

18. 6.3 Oxyacetylene welding equipment and accessories 6.3.1 Oxygen cylinder 6.3.2 Acetylene cylinder/generator 6.3.3 Acetylene cylinder/generator 6.3.4 Oxygen and acetylene regulator 6.3.5 Wrenches 6.3.6 Hoses, hose clips and hose coupler 6.3.7 Welding torch-low pressure, equal pressure 6.3.8 Welding nozzle-solid piece, multiple piece 6.3.9 Filler rod holder 6.3.10 Gas lighter 6.3.11 Operator’s safety accessories Er Saurav Kumar Thakur 18

19. The basic equipment used to carry out gas welding are: Oxygen gas cylinder (green) Acetylene gas cylinder (maroon/red) Oxygen pressure regulator Acetylene pressure regulator Oxygen gas hose(Blue) Acetylene gas hose(Red) Welding torch or blow pipe with a set of nozzles and gas lighter Trolleys for the transportation of oxygen and acetylene cylinders Set of keys and spanners Filler rods and fluxes Protective clothing for the welder (e.g., asbestos apron, gloves, goggles, etc.) Er Saurav Kumar Thakur 19

20. Er Saurav Kumar Thakur 20

21. Er Saurav Kumar Thakur 21

22. 6.3.1 ) OXYGEN GAS CYLINDER Oxygen cylinder is drawn from a piece of high strength steel plate and is available in The oxygen volume in a cylinder is directly proportional to its pressure. In other words, if the original pressure of a full oxygen cylinder drops by 10% during welding, it means 1/10th of the cylinder contents have been consumed. The oxygen cylinder valve is made largely of brass with right hand threads Er Saurav Kumar Thakur 22

23. 6.3.2) ACETYLENE GAS CYLINDER Usually shorter and wider than oxygen cylinder . They have left handed threads . An acetylene cylinder is also a solid drawn steel cylinder Cylinder pressure is 250 PSI when filled. An acetylene cylinder is painted maroon(red) and the valves are screwed left handed (with grooved hex on nut or shank). Acetylene is extremely unstable in its pure form at pressure above 15 PSI A cetylene cylinders should always be stored in the upright position to prevent the acetone form escaping thus causing the acetylene to become unstable To ensure safety in storing acetylene ,cylinder is packed with porous material saturated with acetone( a chemical liquid that dissolves large amount of acetylene , 1litre of acetone dissolves 25 litres acetylene Opened by means of T wrench, 1.5 turns Er Saurav Kumar Thakur 23

24. 6.3.3) Acetone generator In industry acetylene gas generator is more economical to use than acetylene cyinders . Two types 1) Water to carbide generator Water is sprinkled on the calcium carbide stones and acetylene gas produced. 2) Carbide to water generator carbide is dropped in water and acetylene gas is produced Carbide to water Er Saurav Kumar Thakur 24

25. Water to carbide generator Er Saurav Kumar Thakur 25

26. 6.3.4)OXYGEN & ACETYLENE PRESSURE REGULATORS The pressure of the gases obtained from cylinders is considerably higher than the gas pressure used to operate the welding torch. The purpose of using a gas pressure regulator is: • To reduce the high pressure of the gas in the cylinder to a suitable working pressure, and • To produce a steady flow of gas under varying cylinder pressures. Er Saurav Kumar Thakur 26

27. Er Saurav Kumar Thakur 27

28. Gas pressure regulators may be classified as: Single stage Regulator b ) Two stage Regulator Er Saurav Kumar Thakur 28

29. 6.3.6) Wrenches and spindle key: Spindle key Tank wrench Er Saurav Kumar Thakur 29

30. 6.3.6) GAS HOSES & CLAMPS: The hoses used to make the connections between the torch and the regulators must be strong, nonporous, light, and flexible enough to make torch movements easy. The most common type of cutting and welding hose is the twin or double hose that consists of the fuel hose and the oxygen hose joined together side by side. Oxygen hoses are green(black) in color and have right hand thread. Acetylene hoses are red in color with left hand thread Er Saurav Kumar Thakur 30

31. Hose Clamps: A metal clamp is used to attach the welding hose to a nipple. There are basically two types of connections that can be used. The first is using a jubilee clip. The second option is using a crimped connector. The second option is probably safer as it is harder for this type of connection to come loose. The hoses should also be clipped together at intervals approximately 3 feet apart. Er Saurav Kumar Thakur 31

32. 6.3.7) WELDING TORCH & BLOW PIPE A welding torch mixes oxygen and acetylene in the desired proportions, burns the mixture at the end of the tip, and provides a means for moving and directing the flame. Er Saurav Kumar Thakur 32

33. There are two types of welding torches, namely: a) High pressure (or equal pressure) type b) Low pressure (or injector) type In high pressure blow torch, both the oxygen and acetylene are fed at equal pressures and the gases are mixed in a mixing chamber prior to being fed to the nozzle tip. The high pressure torch also called the equal pressure torch is most commonly used . In low pressure type oxygen is at higher pressure than fuel. Er Saurav Kumar Thakur 33

34. Er Saurav Kumar Thakur 34

35. 6.3.8 ) Welding Nozzles or Tips To change the power of the welding torch, it is only necessary to change the nozzle tip (size) and increase or decrease the gas pressures appropriately. The welding nozzle or tip is that portion of the torch which is located at the end of the torch and contains the opening through which the oxygen and acetylene gas mixture passes prior to ignition and combustion. Depending upon the design of the welding torch, the interchangeable nozzles may consist of; Two type Solid piece type Multipiece type Er Saurav Kumar Thakur 35

36. Solid tip Two piece tip Nozzle/tip Er Saurav Kumar Thakur 36

37. The following factors are important in the selection of appropriate welding nozzle: The position of the weld b ) The type of joint c ) Job thickness and the size of welding flame required for the job d ) The metal/alloy to be welded . To provide for different amounts of heat, to weld metals of different thicknesses, welding tips are made in various sizes Er Saurav Kumar Thakur 37

38. 6.3.9) Gas Lighter A gas (spark) lighter provides a convenient, safe and inexpensive means of lighting the torch. Match sticks should never be used for this purpose because the puff of the flame produced by the ignition of the acetylene flowing from the tip is likely to burn the welder's hand. Spark lighters are constructed from flint and steel . Er Saurav Kumar Thakur 38

39. Check Valve A check valve lets gas flow in one direction only and is positioned at the torch inlet, and at the regulator outlet. The purpose of check valve is to prevent flame or oxygen-fuel mixture being pushed back into cylinder and causing backfire, flashback and explosion Backfire: A backfire is caused by the flame going out suddenly on the torch. A backfire may occur when: The tip is touched against the work piece; If the flame setting is too low; If the tip is dirty, damage or loose, or; If the tip is overheated. Er Saurav Kumar Thakur 39

40. 6.4 Filler rod and flux: classification, selection, use and storages A filler rod is a metal rod used to provide additional material during welding. Flux is a substance that helps protect the weld pool from contamination by creating a shielding gas and facilitating the melting process Er Saurav Kumar Thakur 40

41. Classification of Filler Rods: By Base Metal Compatibility:  Mild steel, stainless steel, aluminum, copper, nickel alloys, etc.  By Chemical Composition:  Low carbon, high carbon, alloyed with elements like manganese, silicon, molybdenum, etc.  Classification of Flux: By Chemical Composition:  Acidic, neutral, basic (based on the pH level)  Er Saurav Kumar Thakur 41

42. Selection of Filler Rods : (Well general rule is to use rod diameter equal to thickness of parent metal.) 1)Base Metal Analysis: Always choose a filler rod that matches the chemical composition of the base metal to ensure a strong weld.   2)Welding Position: Different filler rods are designed for flat, horizontal, vertical, or overhead welding positions.  3)Desired Weld Properties: Consider required strength, toughness, corrosion resistance, and other mechanical properties.  Er Saurav Kumar Thakur 42

43. Selection of Flux: Base Metal Compatibility:  Selecting a flux that is compatible with the base metal to prevent harmful reactions  Welding Temperature:  Select a flux with a melting point appropriate for the welding heat.   Desired Weld Properties:  Choosing a flux that promotes the desired weld characteristics like penetration, slag removal, and surface finish Er Saurav Kumar Thakur 43

44. Storage of Filler Rods and Flux: Store in original sealed containers to prevent moisture absorption and contamination.  Maintain a consistent, moderate temperature to avoid condensation or degradation  Keep storage area clean and dry  Always follow the manufacturer's instructions for specific storage requirements.  Er Saurav Kumar Thakur 44

45. 6.5 Oxy-acetylene flame: types, properties and use Three distinct types of flames are possible on adjusting the proportions of acetylene and oxygen: 1. Neutral Flame (Acetylene oxygen in equal proportions) The neutral flame is obtained when approximately one volume of oxygen and one volume of acetylene are mixed. (1:1) It’s termed “neutral” because it will usually have no chemical effect on the metal being welded. It will not oxidize the weld metal; it will not cause an increase in the carbon content of the weld metal. The temperature of the neutral flame is of the order of about 3200ºc of inner core and 1250ºc at outer core . Er Saurav Kumar Thakur 45

46. 6.5 Oxy-acetylene flame: types, properties and use The neutral flame is commonly used for the welding of: Mild steel Stainless steel Cast Iron Copper Aluminum Er Saurav Kumar Thakur 46

47. 6.5 Oxy-acetylene flame: types, properties and use Er Saurav Kumar Thakur 47

48. 6.5 Oxy-acetylene flame: types, properties and use 2. Oxidizing Flame (Excess of oxygen) The oxidizing flame is produced when slightly more than one volume of oxygen is mixed with one volume of acetylene The temperature of this flame is approximately 3500ºC at the inner cone tip. Er Saurav Kumar Thakur 48

49. 6.5 Oxy-acetylene flame: types, properties and use Uses An oxidizing flame is of limited use in welding. It is not used in the welding of steel. A slightly oxidizing flame is helpful when welding most Copper base metals Zinc base metals, and A few types of ferrous metals, such as manganese steel and cast iron A stronger oxidizing flame is used in the welding of brass or bronze. The oxidizing atmosphere, in these cases, creates a base metal oxide that protects the base metal. For example, in welding brass, the zinc has a tendency to separate and fume away. The formation of a covering copper oxide prevents the zinc from dissipating. Er Saurav Kumar Thakur 49

50. 6.5 Oxy-acetylene flame: types, properties and use 3. Carburizing Flame (Excess of acetylene) A carburizing flame is a welding flame that uses more acetylene than oxygen.  It's smoky, has a lower temperature, and is used to weld high carbon steel and nonferrous alloy Appearance : Has a bluish-white inner core, a white intermediate cone, and a light-blue outer flame  Er Saurav Kumar Thakur 50

51. 6.5 Oxy-acetylene flame: types, properties and use Temperature : Can reach temperatures of 3100°C Uses   Used to weld high carbon steel Used to hard face nonferrous alloys like nickel and Monel Used to anneal metal, making it more malleable and flexible Er Saurav Kumar Thakur 51

52. 6.6 Oxy-acetylene welding operations and welding techniques 6.6.1 Equipment set up 6.6.2 Testing for leaks 6.6.3 Lighting the torch and flame adjustment 6.6.4 Shutting off equipment 6.6.5 Running a bead with filler rod 6.6.6 Backfire and flashback 6.6.7 Restarting the weld 6.6.8 Welding techniques-leftward and rightward welding 6.6.9 Weld movements Er Saurav Kumar Thakur 52

53. 6.1 Equipment set up Following steps are followed Chain the cylinders and keep upright position. Remove the valve protecting caps. Blow out any dust in the regulator connection by cracking . Cracking means opening and closing the valves quickly. Er Saurav Kumar Thakur 53

54. 4. Check the cylinder and regulator threads for damage. A ttach oxygen regulator to oxygen cylinder and acetylene regulator to acetylene cylinder. Also remember acetylene connection has left hand thread and oxygen has right hand thread. Er Saurav Kumar Thakur 54

55. 5. Check that the pressure adjusting screw is turned out. Blow out any dust that may be in regulator. This is done by opening the cylinder valve slowly and then turning in the pressure adjusting screw until small amount of gas flows from the opening to which the hose will be attached .close the cylinder valve ,release the pressure adjusting screw . Er Saurav Kumar Thakur 55

56. 6. Attach oxygen hose to oxygen regulator and acetylene hose to acetylene regulator ,also check for damage in hose. 7. Attach hose other ends to the blow torch. 8.Attach tip/nozzle to torch. Er Saurav Kumar Thakur 56

57. 9. Open oxygen and acetylene cylinder valve slowly . (note: open oxygen valve all the way and acetylene valve one and half turns) 10. Before adjusting the pressure make sure the blow torch valves are closed. Er Saurav Kumar Thakur 57

58. 6.6.2 Testing for leaks To check the leaks soap solution applied to the testing points(mainly at connections such as at valves ,at hose connection to cylinder and blowtorch, regulator connections ). During leak testing the valves at blowtorch must be closed while at regulator must be open. Soap water solution Leakage at tip connection Leakage at regulator hose connection Er Saurav Kumar Thakur 58

59. 6.6.3 Lightening the torch and flame adjustment Hold the torch with your thumb and forefinger on the acetylene valve. Position the striker 3–6″ in front at a slight angle. Open the acetylene valve ¼ to ½ turn and ignite immediately. Adjust the acetylene valve to eliminate soot; the flame should stay attached. Slowly open the oxygen valve to achieve a bright white inner flame and a bluish outer flame. Reduce excess acetylene if needed. When finished, turn off oxygen first, then acetylene. Er Saurav Kumar Thakur 59

60. 6.6.4 Shutting Down Steps in shutting Down Close the acetylene valve. Close the oxygen valve Open the acetylene torch valve to drain the gas from the hose and the regulator. Close the acetylene torch valve Release the pressure adjusting screw Open the oxygen torch valve to drain the hose and regulator Close oxygen torch valve Dismantle regulator,hose,torch,tip. Store equipment in proper storage area. Er Saurav Kumar Thakur 60

61. 6.6.5 Running a bead with filler rod Prepare & Tack Select a filler rod and place it near the work area. Light the torch, adjust to a neutral flame, and wear a face shield. Create small fusion tack welds at both ends (and the middle for long joints). Turn off the torch (oxygen first), check alignment, and adjust if needed. Start Welding Hold the torch at a 45° angle and oscillate in a ¼–½″ circle. Form a molten puddle at the right end. Welding Process Bring the filler rod close to the puddle but not inside it. Move left while oscillating and dipping the rod into the puddle. Finish Weld Continue dipping, oscillating, and moving left. Adjust to a shallower angle near the end to avoid burn-through. Turn off oxygen first, then acetylene. The weld should fully penetrate. Er Saurav Kumar Thakur 61

62. 6.6.6 Backfire When the flame goes out with a loud ‘pop’ sound or snapping noise at the tip, it is called backfire. If a backfire occurs shut off the torch valves immediately and check the point listed below: Has the tip been allowed to touch the metal( most common cause among the beginners) Is there a piece of hot metal blocking the tip orifice? It the tip loose? Is the tip overheated? Er Saurav Kumar Thakur 62

63. Flashback It is a condition that results when the flame flashes back into the torch And burns inside with a shrill hissing or squealing noise accompanied by black smoke issuing from the tip. If a flashback occurs shutoff the torch valves(oxygen first) and then the cylinder valves. In a flashback the flame is burning inside the torch.If this continues the flame could work its way back to cylinders and cause violent explosion . Er Saurav Kumar Thakur 63

64. 6.6.7 Restarting the weld To start the weld puddle reheat the base metal approx. ½ inch or 15 mm in front of the weld puddle and in line with it, once the metal turns glossy colour and neutral dot can be seen flame can be moved slowly back to the weld zone and then after reaching it direction should be reversed and speed should be increased a little bit to avoid defect. Er Saurav Kumar Thakur 64

65. 6.6 Oxy-acetylene welding operations and welding techniques leftward welding technique Flame is directed away from finished weld Mostly used in In welding sheet (steel plate) thickness less than 3mm Welding in vertical positions Welding C.I. and non-ferrous metals Er Saurav Kumar Thakur 65

66. Er Saurav Kumar Thakur 66

67. b) Rightward welding technique This method used when thickness > 3mm Faster welding, less distortion, and more economical use of gas and filler rod The flame is directed towards the completed weld, allowing for better heat control and penetration Er Saurav Kumar Thakur 67

68. 6.6.9 weld movements There are different weld movements as in figure Shown and is used according to ease of use by the welder, in any of these movement the tip of blowtorch should not leave the molten puddle. Er Saurav Kumar Thakur 68

69. 6.9 Testing of welding joints: types and process Bend test(Destructive ) Corner joint should be hammered until its flat Butt joint should be bent until its U Tee joint should have top piece hammered until flat Er Saurav Kumar Thakur 69

70. Edge joint should be opened and bent until it forms U joint. Lap joint should be hammered until it resembles a tee joint. Edge joint testing Lap joint testing Er Saurav Kumar Thakur 70

71. Er Saurav Kumar Thakur 71

72. 6.9 Testing of welding joints: types and process Liquid Penetrant Testing (PT): A surface inspection method where a dye is applied to the weld, seeping into cracks or flaws, which are then revealed by a developer solution . Magnetic Particle Inspection (MPI): Used to detect surface and near-surface flaws in ferromagnetic materials by applying a magnetic field and observing the pattern of magnetic particles attracted to defects.    Er Saurav Kumar Thakur 72

73. 6.9 Testing of welding joints: types and process Radiographic Testing (RT): Uses X-rays or gamma rays to create an image of the weld's internal structure, revealing subsurface defects like porosity, cracks, and inclusions.  Ultrasonic Testing (UT): Transmits high-frequency sound waves into the weld and analyzes the reflected echoes to detect internal flaws.  Er Saurav Kumar Thakur 73

74. 6.10 Oxygen gas cutting 6.10.1 Gas cutting principle Oxygen gas cutting, also known as oxy-fuel cutting, uses a flame to heat metal to its ignition temperature, then burns it with pure oxygen to create a cut. Steps  Blowpipe is designed such that ring shaped channel delivers oxyfuel mixture to do preheating. The flame heats steel upto combustion temperature( red hot metal ) Then oxygen jet is released through orifice in centre of nozzle causing rapid oxidization and formation of slag and slag is washed out by oxygen. Er Saurav Kumar Thakur 74

75. 6.10 Oxygen gas cutting Er Saurav Kumar Thakur 75

76. 6.10 Oxygen gas cutting Er Saurav Kumar Thakur 76

77. Er Saurav Kumar Thakur 77

78. 6.10 Oxygen gas cutting 6.10.2 Major influencing factors of gas cutting Composition of steel For effective gas cutting presence of elements in steel shall be in following percentage Carbon : 0.5-1.9% Silicon:4% Manganese:13% Chromium:5% Nickel:35% if carbon content is 0.3% Tungsten:10% Presence of other elements in industrially used steel do not cause any problem Er Saurav Kumar Thakur 78

79. 6.10 Oxygen gas cutting b) Temperature of the work piece Preheating permits a reduction in strength of heating flames and size of nozzle required. This reduces in consumption of gases. Preheating temperature shall be less than the melting point of metal c) Thickness of work piece The thickness of work piece determines the following: Strength of flames Diameter of orifice of the nozzle Speed of cutting Er Saurav Kumar Thakur 79

80. 6.10 Oxygen gas cutting d) Surface defects Surface defects(e.g. oxides, rust etc.) enter the flame, necessating a stronger heating flame and may result in an irregular surface cut. The surface should always be cleaned with a brush ot the flame itself. e) Purity of oxygen With decrease in purity of oxygen, cutting speed decreases considerably and consumption of gas increases. Purity of industrial gas is not less than 97.5%. A 1 % change in purity leads to change in speed of cutting by 13 to 15%. Er Saurav Kumar Thakur 80

81. 6.10 Oxygen gas cutting f) Temperature of oxygen The reheating of cutting oxygen permits a considerable increase in the speed of cutting. Unfortunately, this reheating is difficult on this industrial scale. Er Saurav Kumar Thakur 81

82. 6.11 Cutting methods Er Saurav Kumar Thakur 82

83. 6.12 Selecting of tip and working pressure in manual gas cutting Er Saurav Kumar Thakur 83

84. Er Saurav Kumar Thakur 84

85. 6.13 Cleaning of the cutting tips Tip cleaner front end surface first cleaned with abrasive cloth(finest) Outer tip screwed off by open ended spanner Hole of tip cleaned by tip cleaner Er Saurav Kumar Thakur 85

86. Er Saurav Kumar Thakur 86

87. Er Saurav Kumar Thakur 87

88. Er Saurav Kumar Thakur 88

89. Er Saurav Kumar Thakur 89

90. Er Saurav Kumar Thakur 90