What Is Ceramic Forming
Ceramic forming refers to the process of making a ceramic blank into a blank with a certain shape and specification. Ceramic forming methods include plastic forming, grouting and dry pressing. A method of making a blank in a plastic state by plastic deformation under the action of an external force. The moisture content of this kind of billet is generally 18-26%, and it should have a high yield value to make the billet shape stable enough during molding; it should also have a large amount of extension deformation to ensure that the billet does not crack during molding.
The ingredients are made into green bodies of specified size and shape and with certain mechanical strength. There are dry pressing, semi-dry pressing, plastic forming, grouting, etc., and isostatic pressing. Among them, the isostatic pressing method is an emerging ceramic production process. The ceramic workpiece produced by the method has high strength, uniform density and good machinability after being sintered and formed. Ancient pottery has moulding, mud stick coil construction, kneading method and so on.
The ceramic forming process is roughly: the raw materials are formed by plaster or resin master mold by means of low pressure quick discharge or high pressure grouting, etc. – drying – glazing – firing – assembly – packaging, each process needs to go through full inspection or experiment.
- Slurry molding: any method in which the barren material is made into a slurry with certain fluidity and suspension by the action of temperature and plasticizer, and then injected into the model to solidify and form.
- Press molding: a molding method of pressing dry powder billets into a dense billet in a steel mold Plastic molding method: using the external force generated by the movement of the mold or tool to process the plastic billet, so that the billet is under the action of external force. A method of forming plastic deformation
- Isostatic pressing: refers to a technical scale in which the powder is uniformly pressed in all directions at the same time: according to the size and tolerance requirements of the product drawing specifications, the shrinkage rate of the blank and process factors are used in the ceramic precision machining and molding and preparation of the working mold. The influence of shrinkage can increase the corresponding size. Spinning uses a rotating plaster mold and a template knife to form the mud; in the rolling forming, a rotating gypsum mold and a rotary type rolling head are used to form the mud.
The Operation Method Of Ceramic Forming
Drawing Blank Section
The blank section is placed on the rotating reel car, and the blank body is drawn by hand (Figure 1). Drawing billet is an ancient billet making method. China appeared in the late Dawenkou culture, and it became more and more popular in the Longshan culture. This process is purely manual operation, no model is required, labor-intensive, and requires skilled operators. It is suitable for producing ceramics with small batches and simple shapes. Although drawing forming is not used as the main method, it is still used in special cases.
Forming And Spinning
A method in which a plastic blank placed in a rotating plaster model is subjected to extrusion, scraping and shearing with a knife to form a blank. Spinning is divided into two types: female mold forming and male mold forming. The gypsum mold formed by the female mold is concave, and the blank is placed in the mold. The inner wall of the model determines the shape of the blank, and the knife determines the internal shape of the blank. It is mostly used for the molding of products such as cups and bowls with large shapes, deep inner holes and small diameters. The cream mold formed by the male mold is convex, and the blank is placed on the mold. The convex surface of the model determines the inner surface of the blank, and the rotation of the knife determines its outer surface. It is mostly used for the molding of products with shallow shapes and larger diameters such as plates and dishes. The molding equipment of spinning molding is simple, but the blank is extruded, the arrangement is disordered, the density of the blank is low, the moisture content is high, and the product is easily deformed.
A method of rolling a plastic blank in a model that rotates in the same direction with a rotating roller to spread the blank evenly to form a blank. Rolling can also be divided into female molding and male molding, and can also be divided into hot rolling (when the rolling head is working, it is generally heated to 120-130 ° C) and cold rolling (the rolling head works at room temperature). The moisture content of the mud material used for rolling forming is 20-22%, and both rolling and sliding during forming are mainly affected by the calendering force. When this method is used, the pressure of the mud is large and uniform, so the deformation of the product is small. In the production of daily-use ceramics, the hot rolling method of the male mold is ideal.
There are many types of roll forming machines, which can be divided into fixed type, rotary type, reciprocating type, elliptical chain type roll forming machine and universal roll forming machine according to the structure; according to the transmission mechanism, it can be divided into mechanical type and hydraulic type. Figure 2 shows the rotary table type roll forming machine, which is mainly used for the production of plates, dishes, bowls and other products.
Forming the blank is a method of placing the blank in the model and extruding it by hand to make it stretch and shape according to the contour of the inner surface of the model.
Engraving And Carving
A method of carving, inlaying, and bonding blanks by hand to make blanks.
A method of making a slurry from a blank, injecting it into a porous model (usually a plaster mold), and using the water absorption of the model to absorb part of the water that the slurry contacts the inner surface of the model to form a green body. The fluidity and suspension of the grouting mud is required to be good, so the water content is generally above 30%, but the water content should be reduced as much as possible under the premise of meeting the requirements to reduce the dehydration time, reduce drying shrinkage, and increase the green body strength. . Grouting is divided into hollow grouting and solid grouting.
The mud is injected into the porous model, and when the mud attached to the mold wall loses water to form a mud layer to the required thickness, the excess mud is poured out to form a grouting method of hollow casting. Generally, vases, teapots, sugar jars, etc. in daily-use ceramics can be formed by hollow grouting. In the past, manual pouring was required for hollow grouting, and centrifugal grouting is now widely used.
The slurry is injected into the gap between the inner and outer two-layer molds, and the water in the slurry is absorbed by the mold from both sides, forming an injection part between the two molds, and there is no excess slurry discharged. The improved solid grouting adopts the high-head groove pressure grouting method to accelerate the absorption of water by the model. Using this method, the water content of the green body can be less, the suction time can be shortened, the drying shrinkage can be reduced, and the density of the green body can be improved. Another improved method is vacuum grouting. Solid grouting is generally used for the production of special-shaped discs (such as fish discs).
The method of placing the blank with little water content into the bottom die of the press, and pressurizing it by the pressing rod equipped with the upper die to form a compact body, due to the low water content and high pressure, the drying shrinkage of the blank after molding is small. , accurate shape, less deformation, short drying time.
The blanks used in dry pressing must first be made into a granular mass, so it is difficult to obtain a uniform density in pressing large products. The firing temperature of dry pressing is relatively low, and it is generally used in the production of industrial or architectural ceramics.
Isostatic pressing is a modified form of dry pressing. It is different from the pressure rod when the blank is only limited to two sides to be pressed. In operation, the granular blanks are put into an elastic mold (usually made of rubber or plastic) and sealed, and then put into a high-pressure container with liquid or gas, and the liquid or gas is pressurized by a pump, so that the mold is subjected to liquid or gas. The uniform pressure transmitted by the gas medium is transmitted to the blank, so that the blank is compacted into a blank similar to the mold. The moisture content of the blanks used for isostatic pressing can be 1-4%, which can greatly increase the forming pressure.