Influence of mold temperature on quality of injection parts
Mold temperature refers to the mold cavity surface temperature in contact with the product during injection molding. Because it directly affects the cooling rate of the product in the mold cavity, and thus has a great influence on the intrinsic performance and appearance quality of the product. In this paper, five points of influence of mold temperature on quality control of injection parts are discussed. The content of the package material system for excellent products is adopted for friends' reference:
Any of various molds and tools used in industrial production to obtain desired products by injection molding, blow molding, extrusion, die casting or forging, smelting, stamping, etc. In short, a mold is a tool used to make a molded object. This tool is made of various parts, and different molds are made of different parts. It mainly through the shape of the material physical state change to achieve the appearance of the processing.
1. Influence of mold temperature on product appearance
Higher temperatures improve the fluidity of the resin, which generally results in a smooth, shiny surface, especially for glass fiber enhanced resin products. It also improves the strength and appearance of the fusion wire.
And for the etching surface, if the mold temperature is low, the melting body is difficult to fill to the root of the texture, so that the product surface appears shiny, "transfer" less than the mold surface of the real texture, improve the mold temperature and material temperature can make the product surface to get the ideal etching effect.
2. The influence on the internal stress of products
Forming internal stress formation is basically due to cooling caused by different thermal shrinkage rate, when the product molding, its cooling is gradually extended from the surface to the interior, the surface first shrinkage hardening, and then gradually to the interior, in this process due to the shrinkage of the difference between the internal stress.
When the residual internal stress in the plastic is higher than the elastic limit of the resin, or under the erosion of a certain chemical environment, the plastic surface will crack. The study of PC and PMMA transparent resins shows that the residual internal stress in the surface layer is in the form of compression, and the inner layer is in the form of stretching.
The surface compressive stress depends on its surface cooling condition. The cold mold makes the molten resin cool down rapidly, so that the molding product produces higher residual internal stress. The mold temperature is the basic condition to control the internal stress. If the mold temperature is changed slightly, the residual internal stress will be greatly changed. Generally, the acceptable internal stress of each product and resin has its own lower mold temperature limit. When forming thin wall or longer flow distance, the mold temperature should be higher than the lower limit of the general molding.
3. Product warping
If the cooling system design of the mold is not reasonable or the temperature of the mold is not controlled properly, the plastic parts are not cooled enough, which will cause the warping deformation of the plastic parts.
For mold temperature control, should according to the structure characteristics of products to determine the male die and female die and mold core and mold wall, temperature difference between the die wall and insert, and using the control of molding parts, cooling contraction speed, plastics mold release more tend towards higher temperature side of traction after bending, the characteristics of differential shrinkage to offset orientation, avoid the parts according to the orientation rule of warping deformation.
For the plastic parts with completely symmetric structure, the mold temperature should be consistent accordingly, so that the cooling of each part of the plastic parts is balanced.
4, affect the shrinkage rate of products
Low MOLD temperature accelerates THE "freezing orientation" OF molecules and increases the frozen layer thickness of melt IN mold cavity. At the same time, low mold temperature hinders the growth of crystallization, thus reducing the forming shrinkage rate of products. On the contrary, high die temperature, melt cooling slow, long relaxation time, low orientation level, and is conducive to crystallization, the actual shrinkage of the product is larger.
5, affect the thermal deformation temperature of products
Especially for crystalline plastics, if the product forming under the lower mold temperature, molecular orientation and crystallization were instantly freeze, when the use of a relatively high temperature environment or under the condition of secondary processing, its molecular chain will be partially rearranged and crystallization process, make product in even far below the material deformation under thermal deformation temperature (HDT).
The CORRECT PRACTICE is to USE THE recommended mold temperature close to the crystallization temperature, so that the product is fully crystallized at the injection molding stage, to avoid such post-crystallization and post-shrinkage at high temperatures.
In a word, the mold temperature is one of the basic control parameters in the injection molding process, and it is also considered in the mold design. Its influence on the molding, secondary processing and use of products can not be underestimated.
