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Last Updated on Friday, 10 June 2011 10:24

Written by Super User

Internal Gas - 'Short Shot' Method

Process Sequence

1. Mould closes and a precise controlled volume of plastic is injected into the mould cavity.

2. After a selected time delay, gas is injected into the molten plastic to complete filling of the cavity and to pack the moulding with gas.

3. Gas then continues to pack the moulding uniformly as it expands to compensate for volumetric shrinkage of the plastic as it cools.
4. Plastic refill in the moulding machine can commence as soon as the plastic feed point has solidified, or after the nozzle valve is closed.
5. Gas is vented to atmosphere before mould opening.

Diagram

Typical Applications
The 'Short Shot' method is used for thick section mouldings, typically handles and tubular components. Care must be taken to avoid 'hesitation' marks at extremity of plastic fill before plastic recommences flow, urged forward by the gas injection.

Advantages
Substantial cost reductions resulting from:

1. Reduction in moulded plastic weights, and therefore cost of material.
2. Reduction in moulding time cycles, and therefore cost of production.
3. Reduced in-mould pressures, and therefore less wear on moulds.