How to solve the plastic shrinkage problem in Dongguan blow

Plastic processing shrinkage of blow molded products is one of the most common problems in plastic processing. For plastic products with high surface quality requirements, shrinkage is even more difficult. Therefore, with the continuous improvement of plastic processing technology, it is imperative to minimize plastic processing shrinkage problems and improve product quality.

Blow moldings shrink more in thicker parts of plastic-processed injection-molded plastic parts, such as ribs or protrusions, than in neighboring areas, because thicker areas cool much more slowly than surrounding areas. Different cooling rates lead to the formation of depressions at the connection surfaces, which are familiar shrink marks. This defect severely limits the design and molding of plastic products, especially large thick-walled products such as beveled housings for televisions and display housings. In fact, shrinkage marks must be eliminated for products with strict requirements such as household appliances, while some products with low surface quality such as toys are allowed to have shrinkage marks in plastic processing.

There may be one or more reasons for the formation of shrinkage marks in plastic processing, including processing methods, part geometry, choice of materials, and mold design. The geometry and material choice are usually determined by the raw material supplier and are not easy to change. However, there are still many factors about mold design that may affect the shrinkage of plastic processing. Cooling runner design, gate type, and gate size can have multiple effects. For example, small gates such as tube gates cool much faster than tapered gates. Premature cooling at the gate reduces the filling time in the cavity and increases the chance of shrinkage marks. For molding workers, adjusting the processing conditions is one way to solve the problem of plastic processing shrinkage. Filling pressure and time significantly affect shrinkage. After the part is filled, excess material continues to fill the cavity to compensate for material shrinkage. Too short the filling phase will lead to increased shrinkage and eventually more or larger shrink marks. This method of solving shrinkage in plastic processing itself may not reduce the shrinkage marks to a satisfactory level, but the molding workers can adjust the filling conditions to improve the shrinkage marks.

Another method is to modify the mold. A simple solution is to modify the conventional core hole, but this method cannot be expected to be applicable to all injection molding processes. In addition, the gas-assisted method can also solve the problem of plastic processing shrinkage.