DEVELOPMENT OF COPPER-CHROMIUM ELECTRICAL CONTACT MATERIALS BY POWDER FORGING

Abstract

The electrical contacts form an integral part of switchgear or circuit interrupters. The desirable properties for a contact material are high mechanical strength, high electrical and thermal conductivity, high wear and weld resistance etc. Cu-Cr alloys are accepted widely as a suitable material for electrical contacts. The mechanical properties are improved by precipitation hardening and conductivity is also maintained by the negligible solubility of Cr in Cu. Cu-Cr contact materials are widely used in medium voltage switchgear Cu-Cr alloys are manufactured by different techniques like electro-slag crucible melting, vacuum continuous melting, vacuum arc smelting, etc. Liquid phase sintering, solid phase sintering and infiltration are the industrial practices currently followed for the production of Cu-Cr electrical contacts. Electro slag crucible melting gives rough surface finish and vacuum continuous casting causes relatively low electrical conductivity and mechanical strength. Sintering causes porosity in the materials Powder forging is an efficient method for the production of electrical contacts. It involves sintering followed by hot forging of the materials. Being a solid-state process and having such high densification factor which gives a relative density around unity are the advantages of this process. In the present study Cu-Cr30 wt.% alloys are prepared from elemental powders by sinter-forging. Nb is also added in varying quantities to improve the electrical and mechanical properties and the forging temperature is also varied. The variation in the contact material properties due to these changes are tabulated and compared. 'H The thesis includes six chapters in which Chapter 1 gives the introduction of the electrical contact materials, Cu-Cr alloys, powder forging and it the objective of the report. Chapter 2 discusses literature review about Cu alloys used as electrical contacts in switch gear, powder metallurgy and comparison of other processing methods with powder forging. Chapter 3 describes the experimental procedure. Chapter 4 analyses the results obtained. Chapter 5 gives the Conclusions. Scope for future work is also discussed at the end of the thesis.