The alumina powder entering the factory is prepared into powder materials according to different product requirements and different molding processes. The particle size of the powder is below 1μm. If high-purity alumina ceramic products are manufactured, in addition to the alumina purity of 99.99%, ultra-fine pulverization and uniform particle size distribution are required. When extrusion molding or injection molding is used, binder and plasticizer should be introduced into the powder, generally thermoplastic plastic or resin with a weight ratio of 10-30%. The organic binder should be at a temperature of 150-200 with alumina powder. Mix uniformly under the bottom to facilitate the molding operation. The powder raw material formed by the hot pressing process does not need to add a binder. If semi-automatic or fully automatic dry pressing is used, there are special technological requirements for the powder, and the powder needs to be processed by spray granulation to make it spherical, so as to improve the fluidity of the powder and facilitate the automatic filling of the mold during the molding. wall. In addition, in order to reduce the friction between the powder and the mold wall, it is necessary to add 1 to 2% of lubricants, such as stearic acid, and binder PVA.
When dry pressing is desired, the powder must be sprayed and granulated, and polyvinyl alcohol is introduced as a binder. A research institute in Shanghai developed a water-soluble paraffin to be used as a binder for Al203 spray granulation, which has good fluidity under heating. The powder after spray granulation must have good fluidity, loose density, and flow angle friction temperature less than 30℃. Ideal particle gradation ratio and other conditions to obtain a larger green density.