Every graphite deposit in the world has a different chemical signature. Some are defined by the flake size, or the carbon content, or the various impurities that occur within the specific ore body. This is important in many graphite product applications, including Powder Metallurgy where only a constant raw material quality and reproducible process parameters guarantee the dimensional accuracy and perfect quality of precision parts made in powder-metallurgy processes.
In the automobile industry parts made in powder metallurgy processes are of ever increasing importance. In sintered parts metal powders are mixed with small quantities of additives such as waxes and graphite. Under high pressure, these powder mixtures are then pressed into so-called green compacts. In this process, graphite both ensure reduced wear of the press die and internal lubrication of the powder mixture, because it allows maximum compression. In the sintering process, where the green compacts are heated to slightly below the melting point, the material is then further compressed. Fine graphite also goes into solution in the metal and increases the mechanical strength of the work piece.
There are special powder mixture applications for self-lubricating sintered parts. These special mixtures contain coarser graphite that goes into solution during the sintering process. The graphite particles are incorporated into the matrix of the work piece mostly in intact condition, and are exposed step by step during the life of the part, which allows graphite to develop its lubricating effect.