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The main reasons for the shrinkage during the injection moulding process

Update:30 Sep 2018
Summary:

During the injection moulding process, shrinkage of the […]

During the injection moulding process, shrinkage of the product is a common phenomenon. The main reasons for this are:

1. Machine side:

(1) The nozzle hole is too large to cause the melt to recirculate and shrink, and when it is too small, the resistance is insufficient and the shrinkage occurs.

(2) If the clamping force is insufficient, the flash will also shrink. Check whether the clamping system has any problems.

(3) If the amount of plasticization is insufficient, a machine with a large amount of plasticization should be used to check whether the screw and the barrel are worn.

2. mould aspect:

(1) The design of the parts should be such that the wall thickness is uniform and the shrinkage is consistent.

(2) The cooling and heating system of the mould should ensure that the temperature of each part is consistent.

(3) The pouring system should be ensured to be unobstructed, and the resistance should not be too large. For example, the size of the main channel, the runner, and the gate should be appropriate, the finish should be sufficient, and the transition zone should have a circular transition.

(4) For thin parts, the temperature should be raised to ensure smooth flow, and the mould temperature should be reduced for thick-walled parts.

(5) The gate should be opened symmetrically, as far as possible in the thick part of the part, and the volume of the cold well should be increased.