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Author: MULAN -Plastic Molding Manufacturer
Plastic processing is also called plastic molding processing. It is a general term for various processes that convert synthetic resin or plastic into plastic products, and is a large-scale production department of the plastics industry. Plastic processing generally includes composition, molding, machining, joining, decoration, and assembly.
The last four processes are carried out after the plastic is formed into a product or semi-product, also known as plastic secondary processing. So what are the precautions in the production process of injection molds? The following editors from Shanghai Plastic Mold Factory Xingye will introduce them. During the production process, when the plastic melt enters the mold cavity under high temperature and high pressure and is molded under pressure, when the temperature drops, the melt cools and solidifies into plastic parts, and the size of the plastic parts is smaller than the size of the mold cavity, which is called shortening .
The main reasons for the shortening are as follows. When plastic is manufactured, the cross-sectional dimensions of different mold gates are different. A large gate helps to increase the cavity pressure, prolongs the closing time of the gate, and facilitates more melt to flow into the cavity, so the density of the plastic part is also greater, thereby reducing the shortening rate, which would otherwise increase the shortening rate.
Changes in chemical structure during injection mold manufacturing. Some plastics change their chemical structure during the molding process. For example, in thermosetting plastics, the resin molecules change from a linear structure to a bulk structure, and the volume mass of the bulk structure is greater than that of the linear structure, so its total volume is shortened.
Thin-walled plastic parts with uniform wall thickness cool quickly in the mold cavity, and the shrinkage rate is the smallest after demoulding. The longer the cooling time of thick plastic parts with the same wall thickness in the cavity, the greater the shortening after demolding. If the thickness of the plastic parts is different, there will be a certain degree of shortening after demoulding.
In the case of a sudden change in wall thickness, the shortening rate will also change suddenly, resulting in greater internal stress. Changes in residual stress. When plastic parts are molded, due to the influence of molding pressure and shear force, anisotropy, uneven mixing of additives and mold temperature, residual stress exists in the plastic parts after molding, and the residual stress will gradually decrease and redistribute, resulting in plastic parts Shorten again, generally called post-shortening.
For more information about injection molds, please visit the official website of Xingye: http://www.dgxingyesj.com/.