Method for Forming Alumina Ceramics

The forming methods of alumina ceramic products include dry pressing, grouting, extrusion, cold isostatic pressing, injection, tape casting, hot pressing and Hot isostatic pressing, etc. 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 product shapes, sizes, complex shapes, and precision require different forming methods. Introduction to common molding methods:

1. Dry pressing forming: The dry pressing forming technology of alumina ceramics is only limited to objects with simple shapes and inner wall thickness exceeding 1mm, and the ratio of length to diameter not exceeding 4:1. The forming methods can be uniaxial or bidirectional. There are two types of presses: hydraulic and mechanical, which can be semi automatic or fully automatic forming. 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 parts varies when there are differences in powder filling. The pressure applied by the mechanical press varies depending on the amount of powder filling, which can easily lead to differences in size shrinkage after sintering and affect product quality. Therefore, the uniform distribution of powder particles during the dry pressing process is very important for mold filling. The accuracy of filling quantity has a significant impact on the dimensional accuracy control of manufactured alumina ceramic parts. Powder particles larger than 60 μ m. The maximum free flow effect and the best pressure forming effect can be obtained between 60 and 200 meshes.

2. Injection molding method: Injection molding is the earliest molding method used for alumina ceramics. Due to the use of gypsum molds, the cost is low and it is easy to shape large-sized and complex components. The key to injection molding is the preparation of alumina slurry. Usually, water is used as the flux medium, followed by the addition of glue remover and binder. After thorough grinding, exhaust is discharged, and then poured into the gypsum mold. Due to the adsorption of moisture by the capillary of the gypsum mold, the slurry solidifies inside the mold. When hollow grouting is carried out, when the slurry adsorbed on the mold wall reaches the required thickness, the excess slurry needs to be poured out. To reduce the shrinkage of the billet, high concentration slurry should be used as much as possible.

Organic additives need to be added to the alumina ceramic slurry to form a double layer on the surface of the slurry particles, ensuring stable suspension and no precipitation of the slurry. In addition, adhesives such as vinyl alcohol, methyl cellulose, Alginic acid amine, and dispersants such as polypropylene amine and arabic gum should be added to make the slurry suitable for grouting and molding operations.

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