Why do plastic products crack? Do you know the reason? There are mainly the following reasons:
Processing
Excessive processing pressure, too fast speed, more filling, injection, and long holding time will cause excessive internal stress and cracking.
Adjust the mold opening speed and pressure to prevent demolding cracking caused by rapid strong drawing of the parts.
Appropriately increase the mold temperature to make the parts easy to demold, and appropriately lower the material temperature to prevent decomposition.
Prevent cracking due to weld marks and plastic degradation causing low mechanical strength.
Appropriately use mold release agents, and pay attention to frequently eliminate substances such as aerosols attached to the mold surface.
The residual stress of the parts can be eliminated by annealing heat treatment immediately after molding to reduce the generation of cracks.https://doi.org/10.1016/j.matpr.2022.10.039
Mold aspect
Ejection should be balanced, such as the number of ejector pins and cross-sectional area should be sufficient, the demoulding slope should be sufficient, and the cavity surface should be smooth enough to prevent cracking caused by residual stress concentration during ejection due to external force.
The structure of the part should not be too thin, and the transition part should be arc-shaped as much as possible to avoid stress concentration caused by sharp corners and chamfers.
Use metal inserts as little as possible to prevent the internal stress from increasing due to the different shrinkage rates between the inserts and the parts.
For deep-bottomed parts, appropriate demoulding air inlet channels should be set to prevent the formation of vacuum negative pressure.
The main runner is large enough to allow the gate material to be demoulded before solidification, so that it is easy to demould.
The main runner bushing and the nozzle joint should prevent the drag of cold hard material from causing the part to stick to the fixed mold.
Material aspect
The recycled material content is too high, resulting in low strength of the part.
Excessive humidity causes some plastics to react chemically with water vapor, reducing strength and causing ejection cracking.
The material itself is not suitable for the processing environment or the quality is poor, and contamination will cause cracking.
Machine aspect
The plasticizing capacity of the injection molding machine should be appropriate. If it is too small, the plasticizing will not be sufficient and the mixture will not be completely mixed, which will make it brittle. If it is too large, it will degrade.
Why do plastic products crack? Do you know the reason?
Cracking includes filamentous cracks, microcracks, whitening, cracking on the surface of the parts, and traumatic crises caused by parts sticking to the mold or runner sticking to the mold. According to the cracking time, it is divided into demolding cracking and application cracking.https://solidcomould.com/product/armrest-8/
There are mainly the following reasons:
Processing
Excessive processing pressure, too fast speed, more filling, injection, and long holding time will cause excessive internal stress and cracking.
Adjust the mold opening speed and pressure to prevent demolding cracking caused by rapid strong drawing of the parts.
Appropriately increase the mold temperature to make the parts easy to demold, and appropriately lower the material temperature to prevent decomposition.
Prevent cracking due to weld marks and plastic degradation causing low mechanical strength.
Appropriately use mold release agents, and pay attention to frequently eliminate substances such as aerosols attached to the mold surface.
The residual stress of the parts can be eliminated by annealing heat treatment immediately after molding to reduce the generation of cracks.
Mold aspect
Ejection should be balanced, such as the number of ejector pins and cross-sectional area should be sufficient, the demoulding slope should be sufficient, and the cavity surface should be smooth enough to prevent cracking caused by residual stress concentration during ejection due to external force.
The structure of the part should not be too thin, and the transition part should be arc-shaped as much as possible to avoid stress concentration caused by sharp corners and chamfers.
Use metal inserts as little as possible to prevent the internal stress from increasing due to the different shrinkage rates between the inserts and the parts.
For deep-bottomed parts, appropriate demoulding air inlet channels should be set to prevent the formation of vacuum negative pressure.
The main runner is large enough to allow the gate material to be demoulded before solidification, so that it is easy to demould.
The main runner bushing and the nozzle joint should prevent the drag of cold hard material from causing the part to stick to the fixed mold.
Material aspect
The recycled material content is too high, resulting in low strength of the part.
Excessive humidity causes some plastics to react chemically with water vapor, reducing strength and causing ejection cracking.
The material itself is not suitable for the processing environment or the quality is poor, and contamination will cause cracking.
Machine aspect
The plasticizing capacity of the injection molding machine should be appropriate. If it is too small, the plasticizing will not be sufficient and the mixture will not be completely mixed, which will make it brittle. If it is too large, it will degrade.
