Chair Mould manufacturers

How to reduce shrinkage in plastic mold processing Shrinkage is the enemy of plastic mold processors, especially for large-scale home appliances precision plastic mold products with high surface quality requirements, shrinkage is a stubborn disease. Therefore, various technologies have been developed to minimize shrinkage and improve product quality. In the thicker position of the plastic mold parts of the Huangjiang, such as the ribs or protrusions, the shrinkage is more serious than the adjacent position, because the cooling rate of the thicker area is much slower than the surrounding area.

The difference in cooling rate causes a depression at the joint surface, which is a familiar shrinkage mark. This kind of defect severely limits the design and molding of precision plastic mold products for home appliances, especially large-scale thick-walled products such as the bevel case and display case of TV sets.

In fact, for the demanding products such as household electrical appliances, the shrinkage marks must be eliminated, and for products such as toys that have low surface quality requirements, shrinkage marks are allowed. There may be one or more reasons for the formation of shrink marks, including processing methods, component geometries, material selection, and mold design. The geometry and material selection are usually determined by the raw material supplier injection moulding manufacturers and are not easily changed. But moldmakers still have a lot of factors about mold design that can affect shrinkage. Cooling runner design, gate type, gate size can have multiple effects. For example, small gates such as tubular gates cool much faster than tapered gates. Premature cooling at the gate reduces the fill time in the cavity, which increases the chance of shrink marks. For molding workers, adjusting the processing conditions is one way to solve the shrinkage problem. Filling pressure and time significantly affect shrinkage.

After the part is filled, the excess material continues to fill the cavity to compensate for the shrinkage of the material. Too short a filling phase will result in increased shrinkage and eventually more or larger shrinkage marks. This method may not reduce the shrinkage marks to a satisfactory level by itself, but the molder 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 suitable for all resins. In addition, the gas-assisted method is also worth a try.