GB625394A - Improvements in and relating to valve seats for internal combustion engines - Google Patents

Abstract

A valve seat for an internal combustion engine has at least the working face thereof formed of a sintered composition comprising 50 per cent-90 per cent of a refractory carbide consisting wholly or predominantly of tungsten carbide and the remainder cobalt and silver, and in which a solid solution of tungsten carbide and cobalt is present as a result of sintering, along with unalloyed tungsten carbide and unalloyed silver and a small proportion of unalloyed cobalt. The tungsten carbide should have an average particle size of 1/2 to 5 microns, the cobalt of 1/2 to 10 microns and the silver less than 325 mesh. The mixed powders are compressed to a density of from 5 to 10 grams per cc, an organic binder such as paraffin being included if desired, and are sintered at a temperature of from 1250 DEG C to 1550 DEG C. for from five minutes to one hour. The proportions of the materials are within the ranges tungsten carbide 50-90 per cent, cobalt 0.25 per cent-5 per cent and silver 9.75 per cent-45 per cent. In one example, a powder mixture comprising tungsten carbide 65 per cent, silver 35 per cent and cobalt 2 per cent and compressed to a density of 8 grams per cc. was sintered in a hydrogen atmosphere for thiry minutes at a temperature of 1450 DEG C, shrinking to a density of 12 to 14 grams per cc and silver being exuded to the extent of 2 or 3 per cent. The resulting composition has a Brinell hardness of 350 to 400 at normal temperature and 275 to 300 at 600 DEG C.