Arc welding methods

Arc welding methods

Metal arc welding

It is a process of joining two metal pieces by melting the edges by an electric arc.

The electric arc is produced between two conductors. 

The electrode is one conductor and the work piece is another conductor. The electrode and the work piece are brought nearer with small air gap. (3mm app.)

When current is passed an electric arc is produced between the electrode and the work piece.

The work piece and the electrode are melted by the arc. Both molten piece of metal become one. 

Temperature of arc is about 4000°c Electrodes used in arc welding are coated with a flux. 

This flux produces a gaseous shield around the molten metal. It prevents the reaction of the molten metal with oxygen and nitrogen in the atmosphere. 

The flux removes the impurities from the molten metal and form a slag. 

This slag gets deposited over the weld metal. This protects the weld seam from rapid cooling.

Equipments:

• A welding generator (D.C.) or Transformer (A.C.) 
• Two cables- one for work and one for electrode 
• Electrode holder 
• Electrode 
• Protective shield 
• Gloves 
• Wire brush 
• Chipping hammer 
• Goggles

Electric Arc Welding Equipments

Advantages 

• Most efficient way to join metals
• Lowest-cost joining method
• Affords lighter weight through better utilization of materials
• Joins all commercial metals
• Provides design flexibility

Limitations 

1. Manually applied, therefore high labor cost.
2. Need high energy causing danger
3. Not convenient for disassembly.
4. Defects are hard to detect at joints.

Carbon arc welding 

In carbon arc welding, the intense of heat of an electric arc between a carbon electrode and work piece metal is used for welding. 

DC power supply is used. 

The carbon electrode is connected to negative terminal and work piece is connected to positive terminal, because positive terminal is hotter (4000°c) than the negative terminal (3000°c) when an arc is produced. 

So carbon from the electrode will not fuse and mix up with the metal weld. If carbon mixes with the weld, the weld will become weak and brittle. 

To protect the molten metal from the atmosphere the welding is done with a long arc. 

In this case, a carbon monoxide gas is produced, which surrounds the molten metal and protects it. Carbon arc welding is used to weld both ferrous and non ferrous metals. 

Sheets of steel, copper alloys, brass and aluminium can be welded in this method.

Carbon Arc Welding