Research On Polishing Isotropic Graphite

Isotropic graphite is a kind of new carbon material formed by isostatic pressing forming and has performances of high purity, high strength and high volume density, which is widely used in fields of edm, nuclear industry, electronic industry and moulds, etc, and has broad application prospect. With its good physical and chemical properties, isotropic graphite material gradually become a kind of important material in mold production.At present, domestic studies of isotropic graphite processing are more concentrated in high speed machining technologies. The surface roughness of graphite after high speed milling can not reach the quality requirement of optical mold. Therefore, grinding and polishing of isotropic graphite materials is necessary.Polishing experiment of the isotropic graphite has been carried out in this paper, and the main research work includes the following several aspects:(1) The application scope, present processing situation, material properties and forming method of isotropic graphite materials were reviewed, and powder forming theory and source of compact strength theory were briefly introduced.(2) Manual polishing tests of isotropic graphite have been carried out, including tests using diamond grinding paste and tests using silicon carbide abrasive paper. R8650 graphite was grinded using three kinds of diamond grinding paste, and seven kinds of silicon carbide abrasive paper were used to polishing R8650 graphite. After these tests, the surface roughness of R8650 graphite reached Ra 25~30nm, which is a sharp decline compared with the surface roughness after the high speed milling which is Ra 0.17μm.(3) Magnetic rheological polishing experiments of isotropic graphite were carried out, New magnetorheological fluid were made up. Polishing experiments of the R8510, R8650 and R8710 graphite were carried out using single factor method, and influences of work clearance, excitation gap, rotational speeds of polishing disk and workpiece, and material properties on polishing effects were studied, and the surface quality of graphite was improved by optimizing processing parameters. After tests, the best surface roughness of R8510, R8650 and R8710 graphite reached Ra 10~15nm, basically met the requirement of optical mold surface quality.The result of the study shows that isotropic graphite with different particle size has their own optimum surface roughness; surface micro porosity of isotropic graphite after polishing includes pores and defective holes caused by graphite particles’ dropping out around the pores.