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Shrinkage of plastic containers

Update:27 Jul 2020

Shrinkage is a common defect in the processing of plast […]

Shrinkage is a common defect in the processing of plastic containers, especially for large plastic products that require high surface quality. Shrinkage is a chronic problem. Therefore, various technologies have been developed to reduce the shrinkage problem and improve the product quality of packaging containers.


The shrinkage of plastic containers:
Shrinkage problems often occur in thicker parts of injection molded plastic parts, such as ribs or protrusions, which are more serious than adjacent positions. This defect severely limits the design and molding of plastic products, especially large thick-walled products, such as Inclined cabinets and display housings of TV sets. For products with strict requirements such as household electrical appliances in my country, shrinkage marks can be eliminated, while for toys and other products with low surface quality requirements, shrinkage marks are allowed.

There may be one or more reasons for the formation of shrinkage marks, including processing methods, part geometry, material selection, and mold design. Among them, the geometry and material selection are usually determined by the raw material supplier and are not easy to control.


For molding workers, adjusting processing conditions is a way to solve the shrinkage problem of plastic containers. Filling pressure and time significantly affect shrinkage. After the part is filled, the excess material continues to be filled into the cavity to compensate for the shrinkage of the material. This method may not be able to control the shrinkage mark to a standard level, but the molding worker can adjust the filling conditions to improve the shrinkage mark.


In addition, there is another method to reduce the shrinkage phenomenon by modifying the mold and modifying the conventional core hole. However, this method is not suitable for all resins. In addition, the gas assist method is also worthwhile Give it a try.