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Causes and solutions for cracking or breakage of plastic parts

Cracking of the plastic parts, including surface filiform cracks, microcracks, whitening, cracking and damage caused by the mucous membrane of the workpiece, the mucosa of the runner, or the trauma, the cracking is released by time and the crack is applied. Crack refers to the breakage of a molded article when the mold is opened or ejected. Cracks may occur when the product is brittle or the mold is poorly released. The speed at which the needle is ejected also causes the generation of cracks, and the faster the speed, the more likely the cracking occurs.

The reasons for product cracking are roughly analyzed as follows:

1, processing

1 If the processing pressure is too large, the speed is too fast, the more the filling, the injection and the holding time are too long, the internal stress will be too large and crack.

2 Fast and strong drawing products are easy to cause demoulding cracking, and the mold opening speed and pressure should be properly adjusted.

3 Appropriately increase the mold temperature to make the product easy to demould, and properly reduce the material temperature to prevent decomposition.

4 Prevention due to weld marks, plastic degradation caused by mechanical degradation and cracking.

5 Proper use of the release agent, pay attention to the frequent removal of substances such as aerosols attached to the mold surface.

6 product residual stress caused cracking. Internal stress can be eliminated by annealing heat treatment immediately after molding, preventing cracking.

2, mold aspects

1 Ejection should be balanced. For example, the number of ejector pins and the cross-sectional area should be 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 the product should not be too thin, and the transition part should adopt the arc transition as much as possible to avoid sharp corners, and the chamfering causes stress concentration.

3 Use metal inserts as little as possible to prevent the internal stress from being too large due to the different shrinkage ratio of the insert and the product.

4 The main channel is large enough to make the gate material demoulding in the future and curing, and it is easy to demould.

5 pairs of deep-bottom products should be properly set to release the air intake hole to prevent the formation of vacuum negative pressure.

6 The main channel bushing and nozzle joint should prevent the chilled material from being dragged to adhere the product to the fixed mold.

3. Material aspects

1 The content of recycled material is too high, the strength of the product is too low, and it is easy to cause cracking.

2 Humidity is too large, causing chemical reaction between plastic and water vapor, reducing the strength and causing cracking. The molding temperature of each material should be observed, the residence time should be shortened to reduce the decomposition and aging of the resin, and the drying conditions should be strengthened to inhibit the hydrolysis. It is also possible to increase the degree of crystallization of the article by increasing the mold temperature and extending the cooling time.

3 The material itself is not suitable for the processing environment or the quality is poor, and the pollution will cause cracking.

4, machine side

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

Slow down the mold opening speed and the ejection speed to reduce the load on the molded product to reduce cracks.

Add rounded corners to the corners of the molded article to prevent cracking.

Causes and solutions for cracking or breakage of plastic parts