Alumina ceramic manufacturers: Alumina ceramic molding methods
Alumina ceramic products can be formed by dry pressing, grouting, extrusion, cold isostatic pressing, injection, pouring, hot pressing and hot isostatic pressing. In recent years, several molding technologies and methods have been developed at home and abroad, such as filter press molding, direct solidification injection molding, gel injection molding, centrifugal grouting molding, and solid phase-free molding. Products with different shapes, sizes, complex shapes, and different precision require different molding methods.
Alumina ceramic manufacturers: Introduction to common molding of alumina ceramics:
1. Dry pressing molding: The dry pressing molding technology of alumina ceramics is limited to objects with simple shapes, inner wall thickness exceeding 1mm, and aspect ratio not greater than 4:1. The forming method is uniaxial or bidirectional. There are two types of presses, hydraulic and mechanical, which can be semi-automatic or fully automatic. The maximum pressure of the press is 200 MPa. The output can reach 15~50 pieces per minute. Since the stroke pressure of the hydraulic press is uniform, the height of the pressed parts is also different when the powder filling is different. However, the pressure exerted by the mechanical press varies with the powder filling amount, which easily leads to differences in dimensional shrinkage after sintering and 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. When the particle size of the powder is greater than 60 μm, and the particle size is between 60 and 200 mesh, the effect of free flow is the greatest, and the effect of pressure forming is the best.
2. Grouting molding method: Grouting molding is an earlier molding method of alumina ceramics . Due to the use of plaster molds, the cost is low, and it is easy to form parts with large sizes and complex shapes. The key to slip casting is the preparation of alumina slurry. Usually water is used as the flux medium, then peptizer and binder are added, exhausted after full grinding, and then poured into the plaster mold. The slurry sets in the mold as the capillaries of the plaster mold absorb water. During hollow grouting, when the grout absorbed on the mold wall reaches the required thickness, the excess grout should be poured out. In order to reduce the shrinkage of the green body, high-concentration slurry should be used as much as possible.
Organic additives should also be added to the alumina ceramic slurry to form an electric double layer on the surface of the slurry particles, so that the slurry can be suspended stably without precipitation. In addition, binders such as vinyl alcohol, methylcellulose and amine alginate, and dispersants such as polyacrylamide and gum arabic should be added to make the grout suitable for grouting.