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.
After a selected time delay, first phase gas
is injected.
Second phase gas penetration to compensate
for volumetric shrinkage of the plastic as it cools.
A uniform gas pressure is applied throughout
the plastic.
Gas is exhausted to atmosphere or for
recovery before mould opens.
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
The
use of the gas as a means of transmitting pressure
uniformly throughout the moulding.
Elimination
of sink marks.
Avoidance of plastic packing from the moulding
machine.
Reduced in-mould pressures by up to 70%,
and therefore reduced press lock forces enabling
larger mouldings on smaller machines.
Reduced power
consumption.
Reduced moulded in stress, and therefore
improved dimensional stability with no distortion.
*The 'Full Shot' method is covered by patents
granted to CGI and Mitsubishi Gas Chemicals in Japan.