Causes of swelling and bubbling of injection moulded products


Rigid plastic parts such as PS form dense ripples on th […]

Rigid plastic parts such as PS form dense ripples on the surface near the gate, centered on the gate, sometimes called a shock pattern. The reason is that when the melt viscosity is too large and the mould is filled in a stagnant form, the front end material will quickly condense and shrink when it contacts the surface of the cavity, and the later melt expands the contracted cold material to continue the process. Constant alternating causes the stream to form a surface grain in the forward direction.


1. Increase the barrel temperature, especially the nozzle temperature, and increase the mould temperature.

2. Increase the injection pressure and speed to quickly fill the model cavity.

3. Improve the size of the runners and gates to prevent excessive resistance.

4. The mould exhaust should be good, and a large enough cold well should be set.

5. Do not design the parts too thin.

Some plastic parts quickly swell or swell on the back of the metal insert or in a particularly thick part after the mould is demoulded. This is because the plastic that is not completely cooled and hardened is caused by the release of gas under the action of the pulsation.


1. Effective cooling. Reduce the mould temperature, extend the mould opening time, and reduce the drying and processing temperature of the material.

2. Reduce the filling speed, reduce the forming cycle and reduce the flow resistance.

3. Increase pressure and time.

4. Improve the condition that the wall of the workpiece is too thick or the thickness changes greatly.

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