1. Powder Preparation
The incoming aluminum oxide powder is prepared into powder materials according to different product requirements and different molding processes. The particle size of the powder is 1 μ If the purity of high-purity aluminum oxide ceramic products is less than 99.99%, it also needs to be ultra-fine crushed and its particle size distribution is uniform. When extrusion molding or injection molding is adopted, binder and plasticizer shall be introduced into the powder. Generally, thermoplastic plastic or resin organic binder with a weight ratio of 10-30% shall be uniformly mixed with aluminum oxide powder at a temperature of 150-200 to facilitate molding operation. The powder raw materials formed by hot pressing process do not need to add binder. If semi-automatic or full-automatic dry pressing molding is adopted, there are special process requirements for the powder, and the powder needs to be treated with spray granulation method to make it spherical, so as to improve the powder fluidity and facilitate automatic filling of the mold wall during molding. In addition, in order to reduce the friction between the powder and the die wall, 1-2% lubricant, such as stearic acid and adhesive PVA, should be added.
For dry press molding, the powder shall be spray granulated, in which polyvinyl alcohol shall be introduced as the binder. A water-soluble paraffin developed by a research institute in Shanghai is used as the binder of 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 ℃. The particle size ratio is ideal, so as to obtain higher green density.
2. Forming 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, filter pressing, direct solidification injection molding, gel injection molding, centrifugal injection molding and solid free molding have been developed at home and abroad. Different products with different shapes, sizes, complex shapes and precision require different molding methods.
