The Reason For The Uneven Shrinkage Of The Injection Molded Parts!

If the plastic parts are unevenly contracted, the internal stress distribution is often uneven. If the stress exceeds the rigidity of the plastic part, the warpage and deformation of the plastic part will be caused, which will affect the dimensional stability of the plastic part. Then Film Tapes Plastic Core Tube Exporter will explain the reason for you today.

Four reasons for uneven shrinkage:

1. The melting temperature is different: the melting temperature is high and the shrinkage is large.

2. Different cooling rates (crystalline materials):

Cause: The cooling rate is fast < The cooling rate is slow (Cause: The molecules with slow cooling rate have time alignment, so the amount of shrinkage is large)

3. The flow direction of the melted rubber is different (amorphous material): in short, the tensile internal force is large along the flow direction, so the amount of shrinkage is large. During the filling process, the plastics cause alignment of the molecular chains due to the flow alignment. The polymer chains to be aligned are subjected to different stretching conditions in the flow direction and the vertical flow direction, and the shrinkage behavior is also different. It is called directional contraction.

In general, the flow direction shrinkage rate is higher than the vertical flow shrinkage rate. This is because the flow direction of the plastic polymer chain is stretched more seriously, and the trend of restoring the unstretched state is greater. The differential shrinkage caused by the flow alignment often causes warpage of the plastic part. Therefore, if the molecular alignment can be broken, it will contribute to the uniformity of shrinkage and reduce the warpage caused by the direction shrinkage.

4. Different sizes: simply speaking, the size is large and the amount of shrinkage is large.

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