Alumina wear-resistant ceramic products are formed by various methods such as dry pressing, grouting, extrusion, cold isostatic pressing, injection, casting, hot pressing and hot isostatic pressing. In recent years, molding techniques such as pressure filtration molding, direct solidification injection molding, gel injection molding, centrifugal grouting molding and solid free forming have been developed at home and abroad. Different product shapes, sizes, complex shapes and precision products require different molding methods.
Picking up its usual molding introduction:
1. Dry pressing
The alumina wear-resistant ceramic dry pressing technology is limited to objects with a simple shape and an inner wall thickness of more than 1 mm and a length to diameter ratio of not more than 4:1. The molding method is uniaxial or bidirectional. The press is available in hydraulic or mechanical form 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. Since the hydraulic press has a uniform stroke pressure, the height of the pressed parts is different when the powder filling is different. However, the pressure applied by the mechanical press varies depending on how much the powder is filled, which may cause a difference in dimensional shrinkage after sintering, which affects product quality. Therefore, the uniform distribution of powder particles during dry pressing is very important for mold filling. The accuracy of the filling has a great influence on the dimensional accuracy control of the manufactured alumina ceramic parts. The powder particles have a maximum free-flowing effect of more than 60 μm and between 60 and 200 mesh, and the best pressure forming effect is obtained.
2. Grouting molding method
Grouting molding is the earliest molding method for alumina wear-resistant ceramics. Due to the use of plaster molds, the cost is low and it is easy to form large-sized, complex-shaped parts. The key to grout molding is the preparation of alumina slurries. Usually, water is used as a flux medium, and then a debonding agent and a binder are added, fully ground, and then vented, and then poured into a plaster mold. The slurry is solidified in the mold due to the adsorption of moisture by the gypsum mold capillary. In the hollow grouting, when the mold wall adsorbs 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.
An organic additive is also added to the alumina wear-resistant ceramic slurry to form an electric double layer on the surface of the slurry particles to stably suspend the slurry without precipitation. In addition, a binder such as vinyl alcohol, methyl cellulose, alginic acid amine, or a dispersing agent such as polyacrylamide or gum arabic is added, and the purpose is to make the slurry suitable for the slurry molding operation.