Abstract: A sliding layer (21) of a sintered copper alloy is formed on a sliding surface (12A) of a valve plate (12). That is, the valve plate (12) is formed of iron-based materials such as cast iron or steel. Then, the sliding surface (12A) which is the front side of the valve plate (12) is covered with the sliding layer (21) formed of a sintered copper alloy containing Cu (copper) and Sn (tin) as principal components and the remaining components as the remainder. The remainder has 2 to 6 wt % CaF2 (calcium fluoride) as an essential component, and an average particle size of said CaF2 is controlled to fall within the range from 40 ?m to 350 ?m. A sliding surface (8A) of a cylinder block (8) which is a opposing part sliding surface is not covered with the copper-alloy sliding layer (21) but is covered with a sliding layer of iron-and-steel based materials.

Abstract: There are disclosed a mold material for molding of an optical part, composed of at least the molding surface of a mold for molding, which comprises a sintered body or a coated layer composed mainly of at least one chromium compound selected from chromium oxide, chromium oxycarbide, chromium oxynitride and chromium oxycarbonitride and a process for producing the same.When an optical part is molded by use of the mold of the present invention, the optical part after molding can be easily taken out from the mold, and the mold has a long lifetime, and also the optical part obtained has excellent surface precision.