Manufacturing Process of Tungsten Crucible-Sintering

Intermediate frequency sintering is mainly applied in powder metallurgy process, especially in producing the relatively large workpieces or requiring for a higher firing temperature, and then the firing method must be used. Wolfram is often used as firing equipment for intermediate frequency sintering, since the high melting point of wolfram which just below the melting point of the carbon. In addition, in case of high temperature, wolfram still has a high mechanical strength and hardness. Therefore, nowadays, the intermediate frequency firing furnace main adopt tungsten crucible.

The process of firing mainly through five steps: preparation of raw materials, shake raw materials evenly. After mixing, assort the materials in a proper proportion. Mixing those raw materials and pelletizing them. Furthermore, spread the firing materials on the firing pallet for firing. Finally, freeze the finished product. Under the conditions of the high temperatures produced by fuel and a series of chemical reactions of tungsten granules, some soluble materials of mixture would soften and partially melt, producing an amount of liquid, wetting particles which are not melted. In the cooling process, the liquid will paste particles into a massive form, this process is called firing.

Wolfram crucible is commonly formed by welding and powder metallurgy technology with inert gas. The thickness of the wolfram crucible formed by welding is generally less than 3 mm, life time and heating performance of this type of wolfram crucible are not as good as wolfram crucible which is made by powder metallurgy technology. Wolfram crucible for firing can ensure that the uniformity furnace temperature and the fast speed for heating. Therefore, wolfram crucible is one of the necessary equipment for the firing process. Wolfram crucible has a longer life which has a less impact on the environment, and it can be repeatedly used to control environmental pollution produced by firing.

Control of temperature is very important to the firing process, since grain-boundary diffusion and volume diffusion rely heavily upon temperature, the size and distribution of particles of the material, the materials composition, and often the firing environment to be controlled. When using wolfram crucible for firing, users should pay attention to improve the production installed furnace conditions in order to avoid negative phenomena, such as sliding produced by controlling the shrink of lower part of wolfram crucible, which has a great impact on avoiding producing waste and defective products.

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