Author: MULAN -Plastic Molding Manufacturer
In the manufacturing process of injection molds, plastic melt is injected into the mold cavity through high temperature and high pressure, and is formed under pressure. After the temperature drops, the melt cools and solidifies into plastic products. The size smaller than the size of the cavity is called shrinkage. The main reasons for the decrease are as follows. For plastic products, the cross-sectional dimensions of different mold gates are different.
A large gate is beneficial to increase the gate pressure, prolong the closing time of the gate, allow more melt to enter the cavity, make the density of the plastic part larger, and reduce the shrinkage rate, otherwise it will increase the shrinkage rate. The following editors from Shanghai Injection Molding Factory Xingye will introduce the issues that need attention in the production of injection molds: The chemical structure of injection molds changes during manufacturing. Some plastics change their chemical structure when they are molded.
As far as thermosetting plastics are concerned, the resin molecules change from a linear structure to a bulky structure, and the volumetric mass of the bulky structure is larger than that of the linear structure, so its overall volume is shortened and shortened. Thin-wall plastic parts with uniform wall thickness have a fast cooling rate in the cavity, and the shrinkage rate tends to be the lowest after demolding. For plastic parts with the same wall thickness, the longer the cooling time in the cavity, the greater the shortening after demoulding.
If the thickness of the plastic parts is different, there will be a certain degree of shrinkage after demoulding. If it is such a sudden change in wall thickness, the shortening rate will also cause a sudden change and generate a large internal stress. Residual stress changes When plastic parts are molded, due to the influence of factors such as molding pressure and shear force, anisotropy, uneven mixing of additives, mold temperature, etc., the plastic parts still have residual stress after molding, and the residual stress will gradually decrease and restart Distribution, so that the plastic part is shortened again, usually called post-shortening.
For more information about injection molds, please visit the official website of Xingye: http://www.dgxingyesj.com/.