Alumina ceramic forming method

There are many methods for forming alumina ceramic products, such as dry pressing, grouting, extrusion, cold isostatic pressing, injection, casting, hot pressing and hot isostatic pressing. In recent years, molding technology methods such as filter press 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: The aluminum oxide ceramic dry pressing technology is limited to objects with a simple shape and an inner wall thickness of more than 1mm, and the ratio of length to diameter not greater than 4:1. The forming method is uniaxial or bidirectional. There are two types of presses: hydraulic and mechanical, and can be semi-automatic or fully automatic. The maximum pressure of the press is 200Mpa. The output can reach 15-50 pieces per minute. Due to the uniform stroke pressure of the hydraulic press, the height of the pressed part is different when the powder filling is different. However, the pressure applied by the mechanical press varies with the amount of powder filling, which easily leads to differences in size shrinkage after sintering, which affects product quality. Therefore, the uniform distribution of powder particles during dry pressing is very important for mold filling. Whether the filling amount is accurate or not has a great influence on the dimensional accuracy control of the manufactured alumina ceramic parts. The powder particles larger than 60μm and between 60-200 mesh can obtain the maximum free flow effect and achieve the best pressure forming effect.

2. Grouting method: Grouting is the earliest molding method used for alumina ceramics. Due to the use of plaster molds, the cost is low and it is easy to form large-sized and complex-shaped parts. The key to grouting is the preparation of alumina slurry. Usually water is used as the flux medium, and then the debonding agent and the binder are added, and the gas is exhausted after being fully ground, and then poured into the plaster mold. Due to the absorption of water by the capillary of the plaster mold, the slurry solidifies in the mold. When hollow grouting, when the mold wall absorbs the slurry to the required thickness, the excess slurry needs to be poured out. In order to reduce the shrinkage of the green body, a high-concentration slurry should be used as much as possible.

The alumina ceramic slurry also needs to add organic additives to form an electric double layer on the surface of the slurry particles so that the slurry is stably suspended without precipitation. In addition, binders such as vinyl alcohol, methyl cellulose, alginate amine, and dispersants such as polypropylene amine and gum arabic must be added, all for the purpose of making the slurry suitable for grouting operations.