Cracking, including filamentary cracks, microcracks, whitening, cracking on the surface of the workpiece, or trauma crisis caused by the die sticking of the part and the sticking die of the flow channel. According to the cracking time, the mold is cracked and applied.
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Why plastic products crack?
Written By Jasmine HL
Cracking, including filamentary cracks, microcracks, whitening, cracking on the surface of the
workpiece, or trauma crisis caused by the die sticking of the part and the sticking die of the flow
channel. According to the cracking time, the mold is cracked and applied.
The main reasons are as follows:
Processing
Excessive processing pressure, too fast speed, more filling, longer injection and pressure holding
time will cause excessive internal stress and cracking.
Adjust the mold opening speed and pressure to prevent fast and strong drawing parts from
cracking.
Properly increase the mold temperature to make the part easy to demold, and appropriately
lower the material temperature to prevent decomposition.
Prevents cracking due to welding marks and degradation of plastics due to degradation of the
mechanical strength.
Appropriate use of mold release agent, pay attention to often eliminate aerosol and other
substances attached to the mold surface.
Residual stress of the workpiece can be reduced by the annealing heat treatment immediately
after forming to eliminate the internal stress and reduce the generation of cracks.
In terms of mold
The ejection should be balanced. For example, the number of ejectors and the cross-sectional
area must be large enough. The demolding slope must be large enough. The cavity surface must
be smooth enough to prevent cracking due to the concentrated residual stress caused by external
forces.
The structure of the workpiece should not be too thin, and the transition part should use arc
transition as much as possible to avoid stress concentration caused by sharp corners and
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chamfers.
Minimize the use of metal inserts to prevent the internal stress from increasing due to the
shrinkage of the insert and the part.
Appropriate demolding air inlet channels should be set for deep bottom parts to prevent the
formation of vacuum negative pressure.
The main stream is enough for the ambassador's gate material to have no time to release the
mold during curing, so it is easy to release.
The joining of the main flow bush and the nozzle should prevent the drag of the cold hard
material and make the product stick to the fixed mold.
In terms of materials
The content of recycled material is too high, which causes the strength of the part to be too low.
Excessive humidity causes some plastics to react with water vapor to reduce strength and cause
ejection cracking.
The material itself is not suitable for the environment being processed or of poor quality, and
contamination can cause cracking.
Machine side
The plasticizing capacity of the injection molding machine should be appropriate. If it is too small,
it will not be fully mixed and brittle. If it is too large, it will degrade.
