PHYSICAL AND CHEMICAL PHENOMENA IN PROCESS OF PREPARATION AND COMPACTION OF GRAPHITE RESIN MIXTURES
The technological process of the preparation of graphite resin mixtures and the compaction of the mixtures in the pressing moulds has been investigated theoretically and, then, experimentally at the plant “Graphitoplast”, Chelyabinsk. The preparation technique of the graphite resin mixtures includes the grinding of the artificial graphite, the mixing of the grinded graphite with the particles of the phenolformaldehyde resin of the novolac type, containing the hardener in the form of the particles of the urotropine. The graphite resin mixture is the polyphase polydispersion powder composition of the filler and the bond. The process of the mixture preparation is accompanied by homogenization leading to the creation of the stabilized homogeneous structure in the two-phase system: graphite-resin. As the mixing process is exothermal, it is accompanied by thermodesorption of gases and steam. The process of the compaction of the graphite resin mixture in the heated mould has been done under the specified force and kinematic conditions. It consists of the following steps: filling the matrix of the mould, heating up to 150-170 °C, compacting the mixture by the plunger at the velocity of 15-30 mm/s and at mouding presure equal to 30-40 MPa with holding time equal to 3-5 minutes. While mixture compacting is taking place, the following phenomena are observed: the thermodesorption of gases and steam, the combining of the phenolformaldehyde resin with the urotropine, resin polymerization, graphite grains wetting by the liquid resin and the hardening of the molded articles. The most important for the creation of better mechanical, physical and chemical properties of the articles are polymerisation of the resin (that is the organizing of the high-moleculer polymer from the low-molecular polymer by means of multiple joining of the low-molecular polymer to the active centers) and graphite grains wetting by liquid resin (that is the polar chemical bond of graphite grains with liquid resin).