6 May 2017

Carbon arc welding

Introduction :

In this welding process produces joining of metals by heating them with an arc between a carbon electrode and the work-piece.

This is the earliest of the arc-welding process but is not used nowadays in many applications because it replaced by twin carbon arc welding.

Electrodes Selection :

In this process, the electrode is made of either carbon or graphite. In contrast to graphite electrodes, carbon electrodes are soft so that can't take up very high current densities. The arc with the carbon electrodes is more controllable. Lower current also adds to the higher electrode life. For use in carbon arc welding, the electrode should be of uniform structure and as far as possible and free from impurities. The life of a graphite electrode is higher than that of the carbon electrode.

How does it work?

In the carbon arc welding, the required filler metal is supplied through a separate filler rod. The arc can be obtained between the carbon electrode and the workpiece. The arc heats and melts the edges of the workpiece thus forming a joint.

Carbon arc welding

In this process generally, a DC power supply with electrode negative is used for single electrode carbon arc welding to minimize the heat generation near to the electrode side so that wear of the electrode is maintained at the minimum rate.

Advantages of carbon arc welding :

  • Because of the separation of the heat source from the filler metal, better control of the heat input is possible.
  • Low distortion of the workpiece.
  • This process is easily automated.
Limitations of carbon arc welding :

  • The major problem is the blowholes that are caused because of the turbulence associated with the DC power source.
  • This process is not suitable for the overhead or vertical welding position but very high mechanized welding speeds could be obtained by the process in the flat position.
  • A carbon of electrode contaminates weld material with carbides.
  • Unstable quality of the weld caused porosity.