There are many kinds of special ceramic forming methods. In the production, the forming method should be selected according to the shape of the product, and different forming methods require different bonding agents. Common ceramic forming methods, types and amounts of bonding agents are as follows:
Shown as follows:
Special ceramic forming methods, types and dosages of bonding agents
Forming method binder example <; binder dosage (% by mass)
Thousand pressure method polyvinyl butyral and other 1~5
Casting method propylene resin 1~3
Extrusion method, methyl cellulose, etc. 5~15
Injection method polypropylene, etc. 10~25
Isostatic pressing method, ammonium carboxylate, etc. 0~3
The binder can be classified into a lubricant, a plasticizer, a dispersant, a surfactant (having a dispersing agent and a lubricating function), etc., and in order to meet the forming requirements, a combination of a plurality of organic materials is usually employed. To choose a binder, consider the following factors:
1) It is a necessary condition that the binder can be wetted by the powder. Good wetting is achieved when the critical surface tension (yoc) or surface free energy (yos) of the powder is greater than the surface tension (yoc) of the binder.
Special ceramic tools 2) Good bonding agents are easily wetted by the powder and have a high cohesive force. When the binder is wetted by the powder, a gravitational effect occurs between the molecules, and a red bond (primary bond) occurs between the binder and the powder, and at the same time, cohesive force is generated due to the orientation, induction, and dispersion effects in the binder molecule. (secondary combination). Although water can also fully wet the yang material, the water is volatile, the molecular weight is small, and the cohesive force is small, which is not a good binder. According to the order of cohesive force of various organic materials, the base representation can be arranged as follows:
a CONH->;-CONH2>; a COOH>; an OH>;-NO2>;-COOC2H5>; a COOCH5>;-CHO>=CO>;-CH3>=CH2>;-CH2
3) The molecular weight of the binder should be moderate. In order to fully wet, it is desirable that the molecular weight is small, but the cohesive force is weak. As the molecular weight increases, the binding ability increases. However, when the molecular weight is too large, the cohesion is too large to be wetted, and the green body is easily deformed. In order to assist the movement of the segments in the molecule, a plasticizer is appropriately added at this time, and the binder is more soft and easy to form while being easily wetted.
4) In order to ensure product quality, it is also necessary to prevent impurities from being mixed from the bonding agent, raw materials and preparation process, so that the product produces harmful defects.
In the preparation of raw materials, it is mixed with a mechanical method such as pulverization or mixing, a binder, and a dispersing agent to achieve dispersion, and contains as little aggregated particles as possible. The binder is adsorbed on the surface of the raw material particles by the type and its molecular weight, the properties of the surface of the particles, and the solubility of the solvent, and functions to prevent the aggregation of the powder raw material by the steric stabilization effect. In the forming process, the binder provides plasticity to the raw material, has a water retaining function, and improves the strength of the molded body and the workability. In general, since the binder interferes with the sintering of the ceramic, it should be decomposed and volatilized by heating in the degreasing step. Therefore, it is necessary to select an organic material that can be easily removed by scattering and free of harmful inorganic salts and metal ions to ensure product quality.
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