Gas welding

Gas Welding

1. GAS WELDING By A Nirala SOME, Galgotias University [email protected]

2. Gas Welding Gas welding is a welding process that melts and joins metals by heating them with a flame caused by a reaction of fuel gas and oxygen. The most commonly used method is Oxyacetylene welding, due to its high flame temperature. The flux may be used to deoxidize and cleanse the weld metal. The flux melts, solidifies and forms a slag skin on the resultant weld metal.

3. Oxyacetylene Welding Utilizes oxygen and a fuel gas to heat metal until it is in a molten state and fuse multiple pieces of metal together. Can be used with or without a filler rod. Great for brazing dissimilar metals together. Older technology that can be replaced by GTAW

4. Oxyacetylene Welding Also known as “oxyacetylene welding” Uses an oxyfuel gas flame Can be applied with or without pressure Can be applied with or without the use of filler materials

5. Gas Welding Oxy-acetylene Welding: CaC 2 + 2H 2 O = Ca (OH ) 2 + C 2 H 2 C 2 H 2 +2.5O 2 = 2CO 2 +H 2 O (vapour) + 306.800 cal /mol

6. Gas Welding (Oxy-acetylene) A number of welding processes use a flame produced by burning a mixture of fuel gas and oxygen . The gas usually used is Acetylene but other gases are also used. Separate cylinders and a hose pipe from each cylinder transports the gases to a torch. Gas and fuel mix in the torch.

7. Chemical reactions and temperature distribution in a neutral oxyacetylene The secondary combustion is also called the protection envelope since CO and H 2 here consume the O 2 entering from surrounding air, thereby protecting the weld from oxidation.

8. The Oxy-acetylene welding Flame Primary Combustion zone The oxy-acetylene flame has two distinct zones. The inner zone (Primary combustion Zone) is the hottest part of the flame. The welding should be performed so as the point of the inner zone should be just above the joint edges. C 2 H 2 + O 2 2CO + H 2

9. The outer zone the secondary combustion envelope performs two functions Preheats the joint edges Prevents oxidation by using some of the surrounding oxygen from weld pool for combustion and gives off carbon dioxide and water vapour Secondary Combustion zone CO + H 2 + O 2 CO 2 + H 2 O

10. Oxyacetylene Welding Flame formed by burning a mix of acetylene (C 2 H 2 ) and oxygen Fusion of metal is achieved by passing the inner cone of the flame over the metal Oxyacetylene can also be used for cutting metals

11. Oxyacetylene Welding Uses a high-temperature flame from the combustion of acetylene and oxygen

12. Oxyacetylene welding (a) overall process, (b) welding area. Gas Welding

13. GAS WELDING Sound weld is obtained by selecting proper size of flame, filler material and method of moving torch The temperature generated during the process is 3300 c When the metal is fused, oxygen from the atmosphere and the torch combines with molten metal and forms oxides, results defective weld Fluxes are added to the welded metal to remove oxides Common fluxes used are made of sodium, potassium. Lithium and borax. Flux can be applied as paste, powder,liquid.solid coating or gas.

14. The Oxy-acetylene welding Flame Oxidizing Excess oxygen (1.5:1) (Brasses, Bronzes , copper) Neutral Equal acetylene & oxygen (low carbon steel, mild steels). Reducing or Carburizing Excess acetylene (0.9:1) (Alloy steels and aluminium alloys ) Inner Cone Secondary Combustion envelope Acetylene feather Max. Temp. Zone

15. Types of Flame There are three types of flames in oxyacetylene welding: • Neutral flame - Acetylene (C 2 H 2 ) and O 2 are mixed in equal amounts and burn at the tip of the welding torch. The inner cone gives 2/3 of heat whereas the outer envelope provides 1/3 of the energy. • Reducing flame - The excess amount of acetylene is used, giving a reducing flame. The combustion of acetylene is incomplete (greenish) between the inner cone and the outer envelope. Good for welding aluminium alloys, high carbon steels. • Oxidizing flame - The excess amount of O 2 is used, giving an oxidizing flame. Good for welding brass.

16. Three types of flame in oxyacetylene welding

17. TYPES OF FLAMES Oxygen is turned on, flame immediately changes into a long white inner area (Feather) surrounded by a transparent blue envelope is called Carburizing flame (3000 c) Addition of little more oxygen give a bright whitish cone surrounded by the transparent blue envelope is called Neutral flame (It has a balance of fuel gas and oxygen) (3200 c) Used for welding steels, aluminium , copper and cast iron If more oxygen is added, the cone becomes darker and more pointed, while the envelope becomes shorter and more fierce is called Oxidizing flame Has the highest temperature about 3500 c Used for welding brass and brazing operation

18. Types of Gas Welding 1. Leftward Welding 2. Rightward Welding

19. Gas welding two types

20. GAS WELDING EQUIPMENTS 1. Gas Cylinders Pressure Oxygen – 125 kg/cm2 Acetylene – 16 kg/cm2 2. Regulators Working pressure of oxygen 1 kg/cm2 Working pressure of acetylene 0.15 kg/cm2 Working pressure varies depending upon the thickness of the work pieces welded. 3. Pressure Gauges 4. Hoses 5. Welding torch 6. Check valve 7. Non return valve

21. Oxy-Acetylene welding

22. Gas welding Apparatus 1 . Oxygen cylinder 2. Acetylene cylinder 3. Pressure gauges 4. Valves 5. Hose pipes 6. Torch 7. Welding tip 8. Pressure regulators 9. Lighter 10. Goggles

23. Gas welding torch

24. Gas Welding - Advantages • Simple equipment • Portable • Inexpensive • Easy for maintenance and repair

25. Gas Welding - Disadvantages Limited power density • Very low welding speed • High total heat input per unit length • Large heat affected zone • Severe distortion • Not recommended for welding reactive metals such as titanium and zirconium.