Gas welding is also called oxy fuel gas welding.it derives heat from the combustion of a fuel gas such as acetylene in combination with oxygen.it is a fusion welding process because the joint is completely melted to obtain the fusion.
TYPES OF FLAME
- Neutral flame
- Oxydizing flame
- Carburizing(reducing) flame
- The neutral flame is the flame in which the amount of oxygen is enough for burning, and neither oxidation nor reduction occurs. A flame with a good balance of oxygen is clear blue.
- There is no excess oxygen(ratio 1:1)
- The oxidizing flame is a flame with produce excessive amount of oxygen. when amount of oxygen increases flame is shorten and its color became dark.
- This flame is harmful especially for steels, because it oxidizes the steel.only in the welding of copper and copper alloys an oxidizing flame is desirable.
- If the ratio of oxygen is deficient the flame become reducing.the temperature of reducing flame is lower so it is suitable for brazing,soldering and flame hardening.
OXY-ACETYLENE GAS WELDING:
- It uses acetylene as general fuel gas because it generates high temperature. fuel gases contains carbon and hydrogen in different amount which burn in combination with oxygen and release the required heat the melting the metal.
- Oxy-acetylene welding reaction:
- The temperature range of oxy-acetylene gas welding is very high(3300 derg Celsius)
- Other fuel gases such as hydrogen, methyl acetylene propadiene can use.natural gas,propane and butane are not suitable because their heat output is low or because the flame is oxidizing.
OTHER TYPES OF WELDING
- Percussion welding
- Explosion welding
- Diffusion welding
- Ultra sonic welding
- Thermit welding
- Atomic hydrogen welding
- Electro gas welding
- Electro slag welding
- Electron beam welding
- Laser beam welding
In this method the electric energy for welding may be stored in a capacitor.and power is discharged within 1 to 10 millisecond to develop localized high heat of the joint.
the process is useful where heating of the component adjacent to the joint is avoide as electronic assemblies.
In explosion welding process is applies detonating a layer of explosive flat has been placed over one of the component has been joined.
it is particularly suitable for cladding a plate or slab with dissimilar metal.
Diffusion welding is process in which the strength of the weld results primarily from diffusion and secondarily from plastic deformation of the flying surfaces.this process requires temperature temperature of about 0.5T.its strength depend on pressure,temperature,time of contact and cleanness of surface .
Ultra sonic welding:
Ultrasonic plastic welding is the joining or reforming of thermoplastics through the use of heat generated from high-frequency mechanical motion. That mechanical motion, along with applied force, creates frictional heat at the plastic components’ mating surfaces (joint area) so the plastic material will melt and form a molecular bond between the parts.
thermit welding, is a welding process that employs molten metal to permanently join the conductors.it is use for thick plates and large sections.
exothermic reaction of thermit mixture is use to generate heat.