The shrinkage of plastic containers

Update:27 Feb 2018
Summary:

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 with high surface quality, shrinkage is a chronic disease. So people have developed a variety of technologies to minimize the problem of shrinkage and improve the quality of the packaging containers.
Shrinkage of plastic containers:
Shrinkage problems often appear in the injection molding plastic parts with thick, such as ribs or protuberance, to be more serious than the adjacent position, because of this defect seriously limits the design and molding of plastic products, especially large thick wall products, such as TV display shell casing and slope. In China, we must eliminate the shrinkage marks for the demanding products of household appliances, while for the products with low surface quality such as toys, we can allow shrinkage marks.
There may be one or more reasons for the formation of the shrinkage marks, including the processing method, the geometric shape of the components, the selection of the material, and the design of the mold. The selection of geometry and material is usually determined by the raw material supplier and is not easy to control.
For the molding workers, the processing conditions are adjusted, which is a way to solve the shrinkage problem of plastic containers. The filling pressure and time significantly affect the contraction. After the component is filled, the excess material continues to be filled into the cavity to compensate for the shrinkage of the material. This method may not control the shrinkage mark to the standard level, but the molding worker can adjust the filling condition and improve the shrinkage mark.
In addition, there is another way to reduce the shrinkage phenomenon by modifying the die and modifying the conventional core hole, but this method is not suitable for all resins at the present time, and the gas assisted method is also worth a try.

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