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EspañolReasons for the shrinkage of injection molds
For all plastic product, shrinkage problem will accur while molding.
When the injection mold product is demoulded, sometimes the phenomenon of scale reduction will occur, which will affect the accuracy of the product. Then, what are the factors that affect the shrinkage rate of the injection mold?
1. Molding pressure: The greater the pressure in the cavity, the smaller the shrinkage after molding. The shrinkage ratio of the amorphous plastics and the crystalline plastics decreases in a straight line and a curved shape as the internal pressure increases.
2. Injection temperature: When the temperature rises, the expansion coefficient of the plastic will increase, and the shrinkage rate of the plastic product will increase. However, as the temperature increases, the density of the melt increases, and the shrinkage rate decreases. The result of both simultaneous action is generally that the shrinkage decreases with increasing temperature.
3. Mold temperature: Generally, the higher the mold temperature, the more obvious the tendency of shrinkage.
4, molding time: the molding pressure is long, the feeding is sufficient, the shrinkage rate is small. At the same time, the frozen orientation of the plastic is increased, the internal stress of the product is also large, and the shrinkage rate is also increased. The cooling time of the molding is long, the curing of the plastic is sufficient, and the shrinkage rate is also small.
5. Wall thickness of the product: The shrinkage rate of the crystalline plastic (except polyoxymethylene) increases with the increase of the wall thickness. In the non-crystalline plastic, the change of shrinkage rate is divided into the following cases: ABS and polycarbonate. The shrinkage rate is not affected by the wall thickness; the shrinkage of plastics such as polyethylene, acrylonitrile-styrene, and acrylics increases with the increase of wall thickness; the shrinkage of rigid polyvinyl chloride decreases with the increase of wall thickness.
6, the size of the feed port: the size of the feed port is large, the plastic products are dense, and the shrinkage is small.
7. Filling amount of glass fiber or the like: The shrinkage rate decreases as the filling amount increases.
Posted By Leila
