Characterization of heat insulating and lubricating ability of powder lubricants for clean and high quality die casting

It is known that the insulating ability of powder lubricant is higher than that of conventional oil-soluble or water-soluble lubricants. This will be effective to prevent the formation of scattered chill structure. Influence of the components and composition of powder lubricants on insulating ability and lubricating ability were investigated. Furthermore, the interaction between powder lubricants and molten alloy was observed with high-speed video system. In the binary components powder lubricants, which include inorganic (talc or Al(OH)3) and polyethylene wax, the wax content was changed from 10 to 60 mass%. Maximum heat insulation was found in the composition of talc (or Al(OH)3)—15–25 mass% of wax. The result of in-situ observation revealed that superior insulating ability at 25 mass% of wax was due to formation of thin gaseous film between molten alloy and die by vaporized wax. Regarding the lubricating ability, when castings were released from mold, the ejection force of ejector pin decreased with increasing the wax content. Thus, it was found that the lubricant contains 40 mass% or more of wax that will be appropriate for die lubricant. On the other hand, the high insulating lubricant contains 25 mass% of wax that will be suitable for sleeve lubricant.