How to solve the shrinkage problem of plastic processing of blow molding products?

Author: MULAN -Plastic Molding Manufacturer

The shrinkage problem of plastic processing of blow molding 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 the shrinkage of plastic processing and improve product quality. The shrinkage of blow molded products in thicker parts of plastic processing injection molded plastic parts, such as ribs or protrusions, is more serious than adjacent positions, because the cooling rate of thicker areas is much slower than that of surrounding areas. The difference in cooling rate leads to the formation of depressions at the joining surfaces, which are known as shrinkage marks. This defect severely limits the design and molding of plastic products, especially large thick-walled products such as beveled casings for televisions and monitor casings. In fact, shrinkage marks must be eliminated on products with strict requirements such as household appliances, while plastic processing shrinkage marks are allowed for some products such as toys that do not require high surface quality. There may be one or more reasons for the formation of plastic processing 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 change. But on the part of the mold maker, there are many factors about the mold design that may affect the plastic processing shrinkage link. Cooling runner design, gate type, gate size can have various effects. For example, small gates such as tube gates cool much faster than tapered gates. Premature cooling at the gate will reduce the fill time in the cavity, thereby increasing the chance of shrinkage marks. For molding workers, adjusting processing conditions is a way to solve the problem of plastic processing shrinkage. Fill 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 a filling phase will result in increased shrinkage and eventually more or larger shrinkage marks. This method of solving plastic processing shrinkage itself may not reduce shrinkage marks to a satisfactory level, but molding workers can adjust filling conditions to improve shrinkage marks. Another method is to modify the mold. One 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 shrinkage problem of plastic processing.