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What Caused the Cracks of Injection Moulded Parts

There may be cracks of the injection moulded parts during the injection moulding process, so what caused the cracks of the injection moulded parts? Let's look at these aspects:

Injection moulding process
(1) If the processing pressure is too large, the speed is too fast, the feeding amount is too large, the injection and the pressure holding time are too long, and then the internal stress will be too large, which will cause cracks of injection moulded parts.
(2) Adjusting the mould opening speed and pressure to prevent demoulding cracking caused by quickly forcibly pulling out injection moulded part.
(3) Appropriately increase mould temperature to make injection moulded parts easy to demould, and appropriately reduce material temperature to prevent decomposition.
(4) Avoid cracks of injection moulded parts caused by the weld marks and the reduction of mechanical strength due to plastic degradation. 
(5) Appropriate use of the release agent, and attention should be paid to the elimination of substances such as aerosols adhering to the mould surface.
(6) Residual stress of injection moulded part can be eliminated by annealing heat treatment immediately after moulding to reduce the generation of cracks.
Cracks of injection moulded parts
Injection mould
(1) The ejector is required to be balanced. For example, the number of ejector rod and cross-sectional area are sufficient, the draft angle should be sufficient, and the cavity surface should be sufficiently smooth to prevent cracking due to external force causing residual stress concentration.
(2) The structure of injection moulded part can’t be too thin, and the transition parts try to adopt the arc transition to avoid stress concentration caused by sharp corners and chamfers.
(3) Minimize the use of metal inserts to prevent the internal stress from increasing due to the difference in shrinkage between the insert and the injection moulded part.
(4) Appropriate stripping intake passages shall be provided for deep-bottomed parts to prevent vacuum under pressure.
(5) The runner is large enough to demould before the gate material is cured, which is easy to demould.
(6) The runner bushing and the nozzle connect to prevent the chilled material from being dragged to make injection moulded parts stick to the fixed mould.

Injection moulding material
(1) The content of recycled materials is too high, resulting in too low strength of injection moulded parts, and caused the cracks of injection moulded parts.
(2) The humidity is too large, causing some plastics have chemical reaction with water vapor, reducing the strength and causing the cracks of injection moulded parts.
(3) The material itself is not suitable for the environment that is being processed or quality is poor, and material is polluted, the cracks of injection moulded parts will occur.

Injection moulding machine
The plasticizing capacity of injection moulding machine should be appropriate. If the capacity is too small, it will not be completely mixed and become brittle. When it is too large, it will degrade.

Welcome to ACO Mold injection moulding company and contact us. The mould engineers from ACO Mold will give you the best solution, and recommend the suitable materials for you. We are ready and looking forward to cooperate with your next project. You will be happy and satisfied to be our partner in mould making and injection moluding project.

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