Impurities in Tungsten Carbide Process

Except external impurities, the impurity in tungsten carbide manufacturing process is also one of the important reasons. According to different forming agent types, the impurities of forming agent can be divided into rubber type and paraffin type. The main reasons of rubber forming agent includes two aspects, one is rubber dissolved in gasoline the gel formed caused by low solubility. Gel molecules are generally smaller, higher ductility, insufficient pressure in pressing process, can not be sufficiently deformed, easy to form pores after sintering shrinkage; the other is inorganic fillers used in the rubber production process remains in forming agent system introduced metallic impurities. Thus it needs to choose lower content of calcium sulfate or appropriate to add a thermoplastic rubber monomer and polymer resin to reduce the amount of rubber. In the sintering process, paraffin forming agent will directly volatile because of the lower melting point, which has been widely used in tungsten carbide manufacturing. But in practical applications, paraffin emulsion easily precipitate formed from ethane. It has bad performance in tungsten carbide powder cladding and form holes after sintering shrinkage. For this problem, the researchers impels the powder surface modification by organic phase cladding carbide powder such as stearic acid, resin acids, etc., in order to promote the compatibility of the entire system.

In the sintering process, with the increasing sintering temperature, Co binder phase will be in a molten state, due to the different degree of shrinkage in the cooling process, Co phase aggregation can occur during shrinking process and holes appear in tungsten skeleton. Therefore, relevant researchers improve the vacuum sintering process and make sintering and pressing in the same device, so that it is not likely to cause the product oxidation and decarbonization. In addition, there are many new processes, such as auxiliary field sintering process, gradient sintering process and laser sintering process, etc, which promote the matrix densification by reducing the amount of cobalt pool and improving the surface quality of powder.

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