Introduction to commonly used forming of alumina ceramics

In the actual production process of 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. In recent years, the domestic and foreign have developed the forming technology methods such as filter pressing, direct solidification injection molding, gel injection molding, centrifugal grouting molding and solid free molding. Products with different shapes, sizes, complex shapes and precision need different forming methods. Now let's introduce the two main methods of dry pressing forming of alumina ceramics.

1. Dry pressing molding:

The dry pressing forming technology of alumina ceramics is limited to objects with simple shapes and inner wall thickness exceeding 1mm, and a length to diameter ratio of no more than 4:1. The forming methods are single axial or bidirectional. There are hydraulic and mechanical presses, which can be semi-automatic or fully automatic forming methods.

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. However, 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 the filling amount has a significant impact on the dimensional accuracy control of manufactured alumina ceramic parts. Powder particles with a size greater than 60μ m. The maximum free flow effect and the best pressure forming effect can be obtained between 60 and 200 meshes.

2. Injection molding method:

Grouting molding is the earliest molding method used for alumina ceramics. Due to the use of gypsum molds, it is low-cost and 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 adhesive and adhesive, thorough grinding, exhaust gas, and then poured into the gypsum mold.

Due to the adsorption of moisture by the capillary tube of the gypsum mold, the slurry solidifies inside the mold. During hollow grouting, 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 body, high concentration slurry should be used as much as possible.

Organic additives shall also be added to the alumina ceramic slurry to form a double electric layer on the slurry particle surface so that the slurry can be stably suspended without sedimentation. In addition, adhesives such as vinyl alcohol, methyl cellulose, Alginic acid amine and dispersants such as polypropylene amine and arabic gum shall be added to make the slurry suitable for grouting and molding operations.

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