1. GAS WELDING

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: CaC2 + 2H2O = Ca (OH) 2 + C2H2
C2H2+2.5O2= 2CO2+H2O(vapour) cal /mol

6. Chemical reactions and temperature distribution in a neutral oxyacetylene
The secondary combustion is also called the protection envelope since CO and H2 here consume the O2 entering from surrounding air, thereby protecting the weld from oxidation.

7. Oxyacetylene Welding
Flame formed by burning a mix of acetylene (C2H2) 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

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

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

10. 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 33000c
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.

11. TYPES OF FLAMES

12. Types of Flame
There are three types of flames in oxyacetylene welding:
• Neutral flame - Acetylene (C2H2) and O2 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 O2 is used, giving an oxidizing flame. Good for welding brass.

13. Three types of flame in oxyacetylene welding

16. 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 (30000c)
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) (32000c)
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 34000c
Used for welding brass and brazing operation

17. Three basic types of oxyacetylene flames used in oxyfuel-gas welding and cutting operations: (a) neutral flame; (b) oxidizing flame; (c) carburizing, or reducing flame.

18. Three basic types of oxyacetylene flames used in oxyfuel-gas welding and cutting operations:
(a) neutral flame; (b) oxidizing flame; (c) carburizing, or reducing flame.

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

20. Gas welding two types

21. GAS WELDING EQUIPMENTS

22. 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

24. Oxy-Acetylene welding

25. 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

26. Gas welding torch

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

29. 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.