First, the cause of internal stress of 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 plastic in the injection molding melt temperature and mold temperature between the large temperature difference, which makes the melt near the mold wall cooling more rapidly, resulting in uneven distribution of stress in the product volume.
4. The shape and size of the product also have a great impact 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.
Second, the solution to the internal stress of PC plastic products
1, the injection temperature has a great impact on the size of 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, 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 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, after the mold can be used heat treatment to eliminate internal stress. The heat treatment temperature is about 120℃, the time is about 2h;
6, adjust the temperature of the barrel and nozzle, improve the mold temperature, in order to reduce the impact of cold material;
7, slow down the injection rate, increase the injection pressure, so as not to break the melt or the 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, as little as possible with release agent.
