GB578936A - Improvements in or relating to electrical contacts - Google Patents

Abstract

578,936. Switch contacts. NEWTON, E. P. (Baker & Co., Inc., and American Platinum Works). July 6, 1944, No. 12961. [Class 38 (v)] [Also in Groups II and XXII] An electrical contact member comprises a compressed sintered powder mixture of silver and carbonyl iron. The mixture may comprise 5-50 per cent. carbonyl iron, but preferably from 10-40 per cent. In one example a mixture of 60 per cent. fine silver powder and 40 per cent. carbonyl iron powder was compressed at 12 tons per square inch and sintered for one hour at 940‹C. in a hydrogen atmosphere. The resulting billet was cold rolled to a reduction of 20 per cent. in thickness, annealed for half an hour at 900‹C. in a hydrogen atmosphere. Electrical contacts were stamped out of the sheet thus produced. Alternatively a billet compressed and sintered as above but containing 70 per cent. silver and 30 per cent. carbonyl iron was cold rolled at a pressure of 25 tons per square inch and then annealed as above. A contact comprising pure silver with a facing of the mixture was formed by spreading 90 parts by weight of silver powder in a rectangular die and covering with a layer of 10 parts by weight of a mixture of 60 per cent. silver powder and 40 per cent. carbonyl iron powder and then heating as in the first example. In an electrical make-andbreak system, one contact may comprise a mixture of silver and carbonyl iron and the other a dissimilar conducting material such as pure silver.