Metal ARC Welding
Arc welding is the process of joining two pieces by melting their edges by an arc.
An electric arc is produced when there is a small air gap (2 to 4 mm) between two conductors.
The work piece acts as one conductor and the electrode acts as another conductor.
When the current is passed,an electric arc having temperature 4000°C to 7000°C is produced between the work piece and electrode.
The edges of work piece and the electrode are melted by this high temperature.
The melted metal piece are joined together and cooled to give permanent joint it is simply know as weld.
The electrode supplies additional filler material into the joint.
The current is supplies by a transformer or a generator.
Metal Inert Gas (MIG) Welding
In this arc Welding,an electric arc is produced between the consumable electrode and the work piece.
During welding,the inert gas produces a gas shield around the electric arc.
This prevents the molten metal to react with atmosphere air.
Argon or helium is used,as the inert gas.
The consumable electrode wire is continuously fed from a wire reel.
The electrode is used as a filler material and to produce arc.
When power supply is given,the edges of the work pieces are melted by the electric arc and joined together.
Application:
Aluminum,cast iron,steel and magnesium can be welded.
Advantages:
No flux is needed.
Welding speed is high.
Quality welding joint can be obtained.
Both ferrous and non-ferrous metals can be welded.
Tungsten Inert Gas (TIG) Welding
In this welding an electric arc is produced between a non-consumable electrode and the work piece.
There is an electrode holder in which the non-consumable tungsten electrode is fixed.
When the arc is produced between the electrode and work,the inert gas from the cylinder passes through the welding head around the electrode.
The inert gas surrounds the arc and protects the weld from atmospheric effects.
So welds are made without defects.
Application
Cast iron, aluminium, stainless steel,nickel alloys can be welded.
Advantages
No flux is needed.
Welding speed is high.
Quality welding joint can be obtained.
Non-ferrous metals can also be welded.
Submerged Arc Welding:
It is also called hidden arc or sub arc welding.
A bare electrode is continuously supplied and an electric arc is produced between the electrode and the work piece.
Flux powder is continuously supplied in the welding area.
The arc,molten metal and the end of electrodes are completely submerged by the flux powder.So the arc is not visible.
This prevents the molten metal to react with atmospheric air and froms defect free weld.
The fused flux froms slag with the impurities and deposits on the weld.
The feeding of electrode and flux are carried out by an automatic mechanism.
Application
It is used for welding low carbon steel and alloy steel.
It is also used for welding in fabrication of pressure vessel and boiler.
Advantages
Welding speed is high.
Good quality welding joint is obtained.
Worm pieces with more thickness and length can be easily welded.
It is a safe process.
Disadvantages
It is difficult to guide the electrode as the weld cannot be seen.
It cannot be used for welding in vertical and inclined position.
Electro Slag Welding
This process bis commonly used for welding metal plate with thickness from 25mm to 35mm, although with special arrangement higher thickness can also be successfully welded.
Construction
The equipment consists of
A power supply (A.C).
A mechanism for feeding the electrode wire.
A bopper to carry flux with a tube of feed this flux into the joint.
A vertical rail along which the entire welding unit can travel in a vertical direction inside proper guides.
The workpiece to be welded are held on the bottom plate with uniform gap.
Two sliding plates are fitted both sides of the workpiece.
The flux is filled in the gap between the workpiece and sliding plates.
Working
When the supply is switched on,an electric arc is produced between the flux and the electrode.
The flux melts and a slag od 2 or 3 mm thick is formed,Now the arc stops.
The current passes from the electrode to the workpiece directly through the Slag.
The Slag gives high resistance to the current.
This produces high heat (1900°C).
The heat melts the edges of workpiece to from welding joint.
This slag always remains at the top of the molten metal and prevents the atmospheric reaction.
A drivinge mechanism moves the electrode upwards at the specific speed.
