Page 158 - Module DMV20173

8.0 POWDER PROCESSING

stronger.

iii. Graphite commonly is used as a punch and die material, and protective
atmospheres usually are employed during pressing.

c) Wet Pressing
i. In wet pressing, the part is formed in a mould while under high pressure in a
hydraulic or mechanical press.
ii. This process generally is used to make intricate shapes. Moisture content
usually ranges from 10 to 15%.

iii. Production rates are high; however, (a) part size is limited, (b) dimensional
control is difficult to achieve because of shrinkage during drying, and (c)
tooling costs can be high.

d) Isotatic Pressing
i. Isostatic pressing also is used for ceramics in order to obtain uniform
density distribution throughout the part during compaction.
ii. Used extensively in powder metallurgy.

EXERCISE 8.3

Explain the characteristics of particle powders which produce a high density
product.

V) INJECTION MOULDING

1. Injection moulding is used extensively for the precision forming of ceramics
in high-technology applications, such as for rocket-engine components.
2. The raw material is mixed with a binder, such as a thermoplastic polymer
(polypropylene, polyethylene or ethylene vinyl acetate) or wax.

3. The binder usually is removed by pyrolysis (inducing chemical changes by
heat).
4. The part then is sintered by firing.

BPLK 190 DMV 20173