Plastics Technology Practice - The Hong Kong Polytechnic University

Plastics Technology Practice
• Feed System
The feed system is the flow-way of plasticized material to the cavity; it consists of
a sprue, runner and gate.
i) Sprue: is the entrance of the feed system. It is a divergent taper and
highly polished.
ii) Runners is the channels through which the plasticized material enters
the gate areas of the mould cavities are called runner. Normally,
runner is round or trapezoidal in cross section.When designing a
runner layout, the runner length should be minimized and balanced.
The large parts and small parts should not be combined.
iii) Gate provides the connection between the runner and the mould
cavity. It must permit enough material to flow into the mould to fill
out the cavity. The followings are common types of gates.
• Cooling system
Cooling means to maintain the
temperature of the mould/die
evenly in the moulding process
by cooling channel, poor cooling
design will affect the functioning
of the mould and the quality of
the moulded part.
• Ejection system
Ejection is necessary for part to be removed from the mould. The hot
materials injected into the cavity will shrink and stick tightly onto the mould
core. The ejector plate will be driven by the injection machine to carry the
whole Ejection system travels sufficiently to clear the moulding from the
mould.
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