Gravity permanent mold casting of graphite-dispersed copper-base alloy

摘要

As a direct substitute for lead in plumbing fittings, graphite particulate was introduced into three copper-base alloys by the stir-casting process. In the preliminary experiments, three types of graphite were added to silicon brass (C87500) toestablish the casting characteristics. This was followed by prototype plumbing fitting production, using only one type of graphite in silicon brass, silicon bronze (C57600) and yellow brass (C85500).The three types of graphite used were desulfurized coke, synthetic graphite and purified natural graphite. Of these, the purified natural graphite could not be wetted by stir casting, despite the addition of titanium as the wetting agent. Graphiterecovery for the other two was less than 50% in the induction furnace, when 1wt% graphite and 0.5 wt% Ti were introduced to molten silicon brass by stir casting. Transfer of the graphite-containing alloy, from the induction furnace to the holding furnace, caused further decreases in graphite recovery.Preliminary studies indicate that graphite flotation is not likely to be a problem in thin sections, during permanent-mold casting. However, the melt should be continuously stirred during casting. Casting characteristics, such as fluidity and hot tearingresistance, and machinability of silicon brass were not adversely affected when graphite was introduced by stir casting.Following these preliminary investigations, the single-cavity mold was used to produce faucets in graphite-dispersed silicon brass, silicon bronze and yellow brass. Despite the large difference in density between the copper-base alloys (~ρ= 8.4g/cm{sup}3) and the graphite particulates (ρ= 2.2 g/cm{sup}3), metallography showed reasonably good graphite distribution throughout the faucet casting.All the graphite-dispersed alloys exhibited excellent pressure tightness, similar to those of regular leaded alloys.