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Last Updated on Friday, 10 June 2011 12:48

Written by Super User

Internal Gas - 'Full Shot' Method

1. After mould closing the plastic is injected to fill or nearly fill the mould cavity, but the plastic is not packed by the moulding machine.

2. After a selected time delay, first phase gas is injected.

3. Second phase gas penetration to compensate for volumetric shrinkage of the plastic as it cools.

4. A uniform gas pressure is applied throughout the plastic.

5. Gas is exhausted to atmosphere or for recovery before mould opens.

6. Plastic refill commences after the nozzle valve is closed or after the plastic feed gate has solidified.

Diagram

Typical Applications
The 'Full Shot' method is normally applicable for components in which there are thick and thin sections. The gas flows into the path of least resistance in the thicker sections where the plastic interior is still in a molten state.

Advantages

1. The use of the gas as a means of transmitting pressure uniformly throughout the moulding.
2. Elimination of sink marks.
3. Avoidance of plastic packing from the moulding machine.
4. Reduced in-mould pressures by up to 70%, and therefore reduced press lock forces enabling larger mouldings on smaller machines.
5. Reduced power consumption.
6. Reduced moulded in stress, and therefore improved dimensional stability with no distortion.