The molding process plays a connecting role in the entire ceramic material preparation process and is the key to ensuring the performance reliability and production repeatability of ceramic materials and components.
With the development of society, traditional ceramic hand-kneading methods, wheel molding methods, grouting methods, etc. can no longer meet the production and refinement needs of modern society. So a new molding process was born. There are 9 widely used molding processes for ZrO2 fine ceramic materials (2 dry methods and 7 wet methods). The following is a detailed introduction to the 2 dry methods:
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1. Dry pressingFormingThe essence is to use pressure to press ceramic powder into a green body of a certain shape. Under the action of external force, the powder particles are close to each other in the mold and are firmly combined by internal friction to maintain a certain shape. The main defect in dry-pressed green bodies is spallation, which is due to the internal friction between the powders. Friction and friction between the powder and the mold wall cause pressure loss inside the green body.
The advantages of dry pressing molding are that the green body has accurate dimensions, is simple to operate, and facilitates mechanized operations; the moisture and binder content in the dry pressing green body is less, and the shrinkage during drying and firing is small. It is mainly used to form products with simple shapes and a small aspect ratio. Die grindingThe increase in production costs caused by damage is a shortcoming of dry press molding.
2. Isostatic pressing It is a special molding method developed on the basis of traditional dry pressing molding. It uses fluid to transmit pressure and evenly apply pressure to the powder in the elastic mold from all directions. Due to the consistency of the internal pressure of the fluid, the powder bears the same pressure in all directions, thus avoiding density differences within the body. Isostatic pressing can be divided into wet bag isostatic pressing and dry bag isostatic pressing. Wet bag isostatic pressing can form products with relatively complex shapes, but it can only operate intermittently. Dry bag isostatic pressing can realize automatic continuous operation, but it can only form products with simple shapes such as square, round, tubular cross-sections. Isostatic pressing can produce a uniform and dense green body with small firing shrinkage and uniform shrinkage in all directions. However, the equipment is complex and expensive, and the production efficiency is not high. It is only suitable for the production of materials with special requirements.
