PC products causes of internal stress in PC plastic products

1. The internal stress of PC products is mainly caused by orientation stress and temperature stress, and sometimes is also affected by improper demoulding;

2. The thickness of the product also has an effect on the internal stress, and the orientation stress decreases with the increase of the thickness of the product;

3. Temperature stress the temperature difference between the melt temperature and the mold temperature is very large when the plastic is injected, which makes the melt near the mold wall cool more rapidly, resulting in uneven distribution of stress in the volume of the product.

4. The shape and size of the product also have a great influence on the internal stress. the higher the ratio of surface area to volume, the faster the surface cooling, the greater the orientation stress and temperature stress.

5. Through the above analysis, it can be seen that due to the structural characteristics of plastics and the limitations of injection molding process conditions, it is impossible to completely avoid internal stress, and can only minimize the internal stress or try to make the internal stress evenly distributed in the product.

Two, PC plastic products internal stress generation solution

1, The injection temperature has a great impact on the internal stress of PC plastic products, so it is necessary to appropriately increase the temperature of the barrel to ensure that the material is plasticized well, so that the components are uniform to reduce the shrinkage rate and reduce the internal stress;

2, To improve the mold temperature, we should try to use a lower injection pressure, and the pressure holding time should not be too long;

3, The effect of injection rate on the internal stress of injection parts is much smaller than temperature, pressure and other factors, can be used variable speed injection, that is, fast filling mold, when the mold cavity is filled with low speed, variable speed injection on the one hand, fast filling process, reduce weld marks, on the other hand, low speed pressure preservation can reduce molecular orientation. reasonable design gate location, flat products are best to use slit, fan gate; ejector device should be designed to ejector large area;

4, The demoulding slope should be large;

5, The internal stress can be eliminated by heat treatment after the mold. The heat treatment temperature is about 120℃, the time is about 2h;

6, Increase the temperature of the barrel and nozzle, increase the temperature of the mold, in order to reduce the influence of cold material;

7, Slow down the injection rate, increase the injection pressure, so as not to break the melt or interference of the gas in the mold;

8, Adjust the injection time and pressure holding time to avoid excessive filling; reasonable mold gate design can reduce or avoid the formation of cold material spots in advance, the traditional and effective method is to open a cold material trap at the end of the flow channel, so that the forward material is trapped in the trap and not into the mold cavity, and some molds in addition to the cold material trap, but also need to consider the form, size and position of the gate rationality; strengthen mold exhaust;

9, Remove the pollutants in the material, strengthen the drying effect of the material, reduce or replace the lubricant, and use the release agent as little as possible.