DESIGN CONSIDERATIONS
To ensure components are produced by the most economic route it is important that certain design criteria are recognised. These criteria result from the principal methods employed in the production of alumina products.

AS-FIRED PROFILES
Although alumina can, after firing, be produced to very close tolerances and surface finishes it is essential, in order to reduce costs, that the product be designed to accept an as-fired finish wherever possible. The standard as-fired tolerance is +/-1% on length, width or diameter with a minimum tolerance of +/-0.15mm. Sharp external corners should be avoided to reduce the possibility of chipping and rapid changes of section are not recommended especially where thermocycling is envisaged. There are two principle methods of producing as-fired components:-

ISOSTATIC PRESSING
This method is primarily employed where it is necessary to machine the pressed component before firing as it would be uneconomic or impossible to subsequently machine; it is also used when the production quantities involved are not sufficient to warrant the cost of dry pressing tools.

DRY PRESSING
The most economical production method where the quantities required will support the manufacture of high cost tooling.