Processes

 

Ceramic Injection Moulding is a state of the art powder forming technique designed to make relatively small intricate components in large quantities. The process involves tool design and manufacture, feedstock and raw material preparation, moulding, chemical de-binding, thermal de-binding and sintering. Secondary machining can be done if required.

We differentiate between three main types of casting. Normal Slip Casting involves traditional open and hollow casting techniques where the viscosity of wetted ceramic powders is artificially lowered by means of electrolytes. Water removal takes place in plaster of paris moulds. Medium Pressure Casting involves the same material pressurized into plaster moulds at low pressure, increasing the scope of complexity achievable. All cast products undergo final finishing before being dried out in preparation of final sintering. Fairly intricate mouldings in smaller quantities are achievable.

For coarse-grained refractory components, vibratory casting techniques are frequently used.

Powder compaction is done by means of hydraulic and mechanical uni-axial presses. Pre-blended raw material granules are compacted at pressures of up to 100 MPa to achieve high green densities. This process is suitable for large quantities of fairly simple shapes.

 

Wet bag isostatic pressing involves the compaction of powder granules by submersion into a
pressurized water tank. Compacted billets can be green machined to required geometries before sintering. Advantages of isostatic pressing include even density distribution and low setup costs. Small runs of primarily cylindrical components can be manufactured. Green machining of pressed billets can be done. After pressing, the billets have sufficient strength to be placed in a lathe, or milling machine. Further value addition can be done before the product is sintered.

 

Sintering is the final stage of ceramic product manufacturing. During this process, heat energy is used to densify the pre-shaped ceramic powder components. Most oxide ceramics sinter between 1500° C and 1700° C. Sintering takes place in sintering kilns in an oxidizing atmosphere. After sintering the products are hard, and subsequent machining requires diamond tooling. Depending on the forming process, run-of-kiln ceramic components can be manufactured to tolerances of between 1 and 2 % deviation from nominal.  Should specific surface finishes or tight dimensional tolerances be required, subsequent machining using diamond tooling can be done.

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