preparation of powder system powdered alumina materials were prepared according to different product requirements and different molding processes. the particle size of the powder is less than 1 m. if the purity of alumina ceramics is 99.99%, it needs ultrafine grinding and uniform particle size distribution. when extruding or injection molding, the binder and plasticizer should be introduced in the powder. generally, the weight ratio of the thermoplastic or resin organic binder in 10-30% should be mixed with alumina powder at 150-200 temperature to facilitate the molding operation. the powder material formed by hot pressing process needs no binder. if the semi-automatic or fully automatic dry pressing is adopted and the powder has special technical requirements, the spray granulation method should be used to treat the powder and make it round ball, in order to improve the fluidity of the powder to facilitate the automatic filling of the mold wall. in addition, in order to reduce the friction between powder and mold wall, 1 to 2% lubricants, such as stearic acid and binder pva, should be added. for dry pressing, powder granulation is needed, and polyvinyl alcohol is used as binder. a water soluble paraffin wax developed by a research institute in shanghai is used as a binder for al203 spray granulation. it has good fluidity under heating conditions. after spray granulation, the powder must have good fluidity and density, and the friction temperature of flow angle is less than 30 c. the particle size ratio is ideal and other conditions to obtain larger bulk density. [1] molding method the forming methods of alumina ceramic products include dry pressing, grouting, extrusion, cold isostatic pressing, injection, tape casting, hot pressing and hot isostatic pressing. in recent years, pressure filtration molding, direct solidification injection molding, gel injection molding, centrifugal grouting and solid free molding have been developed at home and abroad. different product shapes, sizes, complex shapes and precision products require different molding methods. commonly used molding introduction: 1. dry pressing molding: alumina ceramic dry pressing technology is applied to objects whose shape is simple and the inner wall thickness is over 1mm, and the ratio of length to diameter is not greater than 4: 1. the molding method has a single axis or two directions. there are two types of press, hydraulic and mechanical, which can be semi-automatic or fully automatic. the pressure of the press is 200mpa. the output is up to 15~50 pieces per minute. because the stroke pressure of hydraulic press is uniform, the height of pressing parts is different when powder filling is different. the pressure exerted by the mechanical press varies with the amount of powder filling. it is easy to cause differences in size shrinkage after sintering and affect the quality of products. therefore, the uniform distribution of powder particles during dry pressing is very important for mold filling. the accuracy of filling quantity has great influence on the dimensional accuracy control of alumina ceramic parts. the powder particles can obtain super large free flow effect between more than 60 m and 60~200 mesh and achieve super pressure molding effect. 2, grouting molding method: grouting molding is alumina ceramics using super early molding method. because of plaster mold, low cost and easy to shape large size, complex shape parts. the key to grouting is the preparation of alumina slurry. usually, water is used as flux medium, then the adhesive and binder are added. after grinding, the air is exhausted and poured into the plaster mold. the slurry is solidified in the mold due to the adsorption of water by the capillary of the plaster mold. when hollow grouting is applied, the excess slurry must be poured out when the slurry wall reaches the required thickness. in order to reduce shrinkage of billet, high concentration slurry should be used as far as possible. in addition, organic additives are added to alumina slurry to form a double electric layer on the surface of slurry particles to stabilize slurry suspension and precipitate. in addition, it is necessary to add vinyl alcohol, methyl cellulose, alginate and other adhesives, polyamines and arabia gum. the purpose is to make the slurry suitable for grouting.
