As we all know, most toilets on the market are made of ceramics. The production process of ceramics includes raw materials, molding, glazing and firing. What is the ceramic molding in the production process, and what its process methods are there?
Ceramic molding is one of the ceramic manufacturing processes, which refers to making raw materials with specified size,shape and certain mechanical strength. There are grouting molding, plastic molding, dry pressing, semi dry pressing, isostatic pressing, etc. Among them, the molding methods of sanitary ceramics include grouting molding and pressing molding, mainly grouting molding.
1. Grouting forming:
Grouting molding refers to the method of selecting an appropriate glue remover (anti flocculant) to make powdered raw materials evenly suspended in the solution, mixing them into slurry, pouring them into an absorbent model (generally gypsum model) to absorb water, and molding them into green bodies according to the model. This method is often used to manufacture household ceramics and architectural ceramics with complex shape and low precision requirements.
The general grouting molding is based on the characteristics of porous gypsum mold to absorb water, and the grouting process can be basically divided into three stages:
The first stage is from the time when the slurry is injected into the gypsum mold and the mold wall absorbs water to the time when the thin mud layer is formed. The forming force at this stage is the capillary force of the gypsum mold, that is, under the action of the capillary force of the gypsum mold, the water in the slurry close to the mold wall, the solutes dissolved in water and the blank particles smaller than micrometers are absorbed into the capillary of the gypsum mold. As the water is sucked away, the particles in the mud are close to each other, forming the initial thin wall layer.
After the thin wall layer is formed, the mud layer gradually thickens until the injection part is formed, which is the second stage. In this stage, the capillary force of gypsum mold continues to absorb water, and the thin wall layer continues to dehydrate. At the same time, the water in the mud diffuses to the thin wall layer and is sucked into the pores of the gypsum mold through the mud layer. The diffusion power is the concentration difference and pressure difference of water. At this time, the mud layer is like a filter screen. As the mud layer gradually thickens, the resistance of water diffusion gradually increases. When the mud layer is thickened to the required injection thickness, the residual slurry is poured out to form the green body.
The third stage is the shrinkage demoulding stage from the formation of the green billets to the demoulding. As the gypsum mold continues to absorb water and the moisture on the surface of the green body begins to evaporate, the green body starts to shrink, and forms a green body when it is separated from the model. When the green body has a certain strength, it can be demoulded. Demoulding means the completion of grouting.
2. Press forming:
(1) Dry pressing: put the granulating powder with fluidity and proper particle size ratio into the mold, and press the powder to make a green body of certain shape.
(2) Semi dry press molding: add a small amount of water in the ingredients, stir evenly, and press under high pressure.
(3) Isostatic pressure forming: place the specimen to be pressed in a high-pressure vessel, and uniformly pressurize the specimen from all directions by using the incompressibility of the liquid medium and the property of uniformly transmitting pressure. When the liquid medium is injected into the pressure vessel through the pressure pump, its pressure is unchanged and uniformly transmitted to all directions, so that the barren powder can be formed into a dense green body.