Patent ID: 6524525
Filing Date: 2003-02-25
Classification: B22F,C22C,H01H

Abstract:
A method for producing a contact material made of copper and chromium in a proportion of 40 to 75 wt.-% copper and 25 to 60 wt.-% of chromium in a form of a semi-finished product, from which individual contact pieces are produced for use in vacuum switch devices, the method comprising the steps of:pressing a chromium powder in an amount corresponding to a chromium content of the contact material to be produced into a porous chromium powder compact or pressing a mixture of the chromium powder in an amount corresponding to the chromium content of the contact material to be produced and of a copper powder in an amount which is less by 5 to 15 wt.-% with respect to a copper content of the contact material to be produced into a porous copper-chromium powder compact, using pressures between 200 and 1000 MPa, the porous compact having a density corresponding to 75 to 90% of a theoretical density; covering the porous chromium powder compact or the porous copper-chromium powder compact with an amount of the copper which at least corresponds to a copper amount missing from the contact material to be produced; thereafter, heating the chromium powder compact covered with copper or the porous copper-chromium powder compact covered with copper in a high vacuum to a temperature up to or above a melting point of the copper, wherein the compact is sintered, forming a chromium matrix sinter body or a copper-chromium matrix sinter body, and the chromium matrix sinter bodies or copper-chromium matrix sinter bodies being simultaneously infiltrated by the copper covering the compact, the copper being liquefied; obtaining a copper-infiltrated chromium sinter body or a copper-infiltrated copper-chromium sinter body, the sinter body having a copper content increased in comparison with the compact and a density corresponding to 96 to 98% of the theoretical density; subsequently forming the obtained copper-infiltrated chromium sinter body or the copper-infiltrated copper-chromium sinter body into a semi-finished product constituting the contact material by extrusion in a stretching direction, wherein chromium grains in the sinter bodies are pulled out in the stretching direction to form chromium columns and an elongated straightened structure, and wherein a shaping degree of the sinter bodies is at least 30%; and obtaining a semi-finished contact material product which has a straightened structure and a density which corresponds to at least 99%, in particular 99.5 to 99.9% of the theoretical density.