Question

State working principle of electric welding. 

Answer 1

Working principle of Electric welding: In resistance welding, sufficiently heavy current at low voltage is passed directly through two metals in contact to be welded. Heat is produced due to I²R losses where ‘R’ is the contact resistance. This heat is utilized to obtain welding temperature (to become a plastic state) When welding temperature is reached supply is cut down and external pressure is applied simultaneously across the job to complete weld.

According to joules law,

Heat produced H =I² Rt …………….. Watt-sec

From this equation it is clear that heat produced depends on

* Square of current (I²)

* Contact resistance (R)

* Duration of current (t)

Hence to obtained more heat in less time high current is necessary. 

Principle of operation of Arc welding can be explained by any one of the following method.

a) By applying High Voltage

b) By separation of two current carrying electrodes suddenly

Explanation:-

a) By applying High Voltage:- Figure:

Operation: * When very high voltage is applied across any two electrodes separated by small air gap then air between two electrodes gets ionized and ionized air is conducting, so current starts flowing from one electrode to another electrode in the form of spark (arc). * This arc produces heat energy which is utilized for melting the charge. * High Voltage is required to produce arc and to maintain arc high voltage is not necessary. * Once arc is struck between two electrodes then low voltage is sufficient to maintain the arc. 

b) By Separation of two current carrying electrodes suddenly:-

Figure:

Operation:- * Another way to produce arc is to short circuit two current carrying electrodes as shown in fig (a) and suddenly withdraw them, then there will be spark between two electrodes as shown in figure (b) * This arc then produce heat energy which is utilized for melting the charge. * In this method high voltage is not necessary to produce the arc.

Applications Electric Welding : In following Major Industrial Sectors electric welding systems are used:- 1. In automotive / auto suppliers industry 2. In electrical / electronics industry 3. In aerospace / air plane industry 4. In train carriage / rail industry 5. In ship building industry. 6. In radiator / container industry 7. In domestic hardware industry 8. In medical instruments industry 9. In nuclear equipment industry 10. In food and drink industry 11. In civil construction industry. 12. During construction of bridge, tunnel etc. 13. Manufacturing of heavy tanks. 14. In tool manufacturing industry. 15. For fabrication and repair work. 16. In other metal processing industries.