GAS WELDING

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.

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

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

Gas Welding

• Oxy-acetylene Welding: CaC2 + 2H2O = Ca (OH) 2 + C2H2

C2H2+2.5O2= 2CO2+H2O(vapour)+ 306.800 cal /mol

Chemical reactions and temperaturedistribution 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.

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

Oxyacetylene WeldingUses a high-temperature flame from the combustion of acetylene and oxygen

Gas Welding

Oxyacetylene welding (a) overallprocess, (b) welding area.

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.

TYPES OF FLAMES

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.

Three types of flame in oxyacetylene welding

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

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.

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.

Types of Gas Welding

• 1. Leftward Welding• 2. Rightward Welding

Gas welding two types

GAS WELDING EQUIPMENTS

GAS WELDING EQUIPMENTS

1. Gas CylindersPressure

Oxygen – 125 kg/cm2Acetylene – 16 kg/cm2

2. RegulatorsWorking pressure of oxygen 1 kg/cm2Working pressure of acetylene 0.15 kg/cm2 Working pressure varies depending upon the thickness of the

work pieces welded.3. Pressure Gauges4. Hoses5. Welding torch 6. Check valve7. Non return valve

Oxy-Acetylene welding

Gas welding Apparatus

1. Oxygen cylinder2. Acetylene cylinder3. Pressure gauges4. Valves5. Hose pipes6. Torch7. Welding tip8. Pressure regulators9. Lighter10. Goggles

Gas welding torch

Gas Welding - Advantages

• Simple equipment• Portable• Inexpensive• Easy for maintenance and repair

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.