Influence of Joint Design & Welding Variables on ETP Copper

Copper is second only to iron and steel in commercial application and offers a unique combination of properties among which the most important are electrical and thermal conductivity, strength, corrosion resistance, wear resistance, spark resistance and the last but not the least is its non-magnetic behaviour [1,2]. Apart from silver, the copper has highest electrical and thermal conductivity amongst all the metals and is extensively used in making electrical conductors, radiators, heat exchangers; condensers and machine parts [4]. Electrolytic Tough Pitch (ETP) copper is the most important type of copper and is frequently used for high electrical conductivity applications because of its easy commercial availability and more uniform electrical and mechanical properties [5]. A Short Circuit (SC) ring of ETP copper shown in Fig. 1 is an essential part of induction motor used for carrying the rotor current. The size and thickness of SC rings depends upon the capacity of individual machine and is generally manufactured by forging. It is well known that forging is a costly and time-consuming process. It is also noteworthy to mention that one may have apprehension of high percentage of rejection due to forging defects and discontinuities. To mitigate the above problem, the Scientists of RRL (CSIR), Bhopal and the Engineers of BHEL, Bhopal jointly undertook an R&D programme to fabricate SC rings by welding and to study welding technology aspects of ETP copper.