The Molding Methods of Graphite Crucibles

The Molding Methods of Graphite Crucibles

Isostatic Pressing

The molding process forms graphite crucibles by isostatic pressure using powder metallurgy. Equal pressure is applied to the powder to uniformly compact it to the proper density and microstructure. The process can be performed cold or hot. Graphite crucibles formed by this method have excellent properties that are uniformly distributed throughout the entire mass without a grain direction, or are anisotropic.

The high density and small particle size of this type of crucible creates a very strong machinable graphite tool with resistance to high temperatures in controlled environments, electro-conductivity, and self lubricating properties.

Compression Molding

Compression molding follows the same principles as isostatic molding where a fine powder is placed under great pressure. To form the crucible, hydraulic pressure is applied to graphite powder in a steel mold. The advantages of compression molding are its simple process, short production cycle, high efficiency, low labor costs, less shrinkage, and high product quality.

Graphite crucibles produced by compression molding have a fine grain structure that can be used to replace more expensive isostatically pressed graphite crucibles. The limitation to the process is the restriction on the dimensions of the crucibles.

Vibration Molding

Vibration molding is used to produce large crucibles and includes the use of a pasty mixture of graphite. The pasty mixture is placed in the mold and a metal plate is placed over it. The mixture is compacted by vibrating the mold. After compacting, the molded crucible is baked for two or three months at temperatures close to 1000o C. In order to avoid cracks or defects, the temperature is precision controlled. At the end of the baking process, the crucible will have achieved its desired hardness.

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