Shrinkage in thicker parts of a plastic mold, such as ribs or protrusions, is more severe than in adjacent parts because the cooling rate in thicker areas is much slower than in the surrounding areas. The cooling rate is different, resulting in the formation of concave joints, known as shrinkage marks. This defect seriously limits the design and molding of precision plastic mold products for household appliances, especially large thick-walled products such as inclined housing of TV sets and display housing.
There may be one or more causes for shrinkage marks, including machining methods, geometric shapes of parts, selection of materials, and die design. Geometric and material selection is usually determined by the supplier of raw materials and is not easy to change. However, there are many factors that affect the shrinkage of mold design. Cooling channel design, gate type and gate size may produce multiple effects. For example, a small gate, such as a tube gate, is much cooler than a cone-shaped gate. Premature cooling at the gate reduces the filling time in the cavity, thereby increasing the probability of shrinkage. For molding workers, adjusting the processing conditions is a way to solve the shrinkage problem. Filling pressure and time significantly affect shrinkage. After the components are filled, the excess material continues to fill into the cavity to compensate for the shrinkage of the material. Too short filling stage will result in increased shrinkage and eventually produce more or larger shrinkage marks. The method itself may not reduce the shrinkage mark to a satisfactory level, but the molding worker can adjust the filling conditions to improve the shrinkage mark. Precision plastic
In addition to modifying the mold, the simple solution is to modify the conventional core hole, but you want it to apply to all resins is impossible. In addition, the gas assisted method is also worth a try.
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