Whether it is the production of long-fiber modified injection molded products or ordinary modified material injection molded parts, there may be cracks and cracks in the finished product in the injection molding process. So what is the reason for the above situation?
Cracking includes filamentous cracks, microcracks, whitening, cracking, and trauma crisis caused by the sticking of parts and runners. According to the cracking time, it is divided into demoulding cracking and application cracking. Two of the cases are analyzed as follows:
1. The plasticizing capacity of the injection molding machine of the injection molding machine should be appropriate. If it is too small, the plasticization will not be fully mixed and it will become brittle. If it is too large, it will degrade.
2. In terms of molds:
(1) The ejection should be balanced, such as the number of ejector pins, the cross-sectional area should be sufficient, the demolding slope should be sufficient, and the cavity surface should be smooth enough, so as to prevent the ejection residual stress from being concentrated and cracking due to external force.
(2) The structure of the part 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 chamfers.
(3) Appropriate demoulding air inlets should be provided for deep-bottomed parts to prevent the formation of vacuum negative pressure.
(4) The main runner is sufficient to allow the gate material to be demolded when it is solidified in the future, so that it is easy to demold.
(5) The sprue bushing and the nozzle joint should prevent the dragging of the chilled material to make the parts stick to the fixed mold.
(6) Runners and gates are too small, resulting in excessive shear rate during mold filling. Use full-circle runners and increase the size of runners and gates to provide acceptable shear rates during mold filling.
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