The technique method of reducing the shrinkage way in plastic mold processing

Shrinkage in the thicker parts of the plastic mold, such as ribs or protrusions, is more severe than in the adjacent areas, because the cooling rate in the thicker area is much slower than that in the surrounding area.Different cooling rates lead to the formation of depressions at the joint surfaces, known as shrinkage marks.This defect seriously restricts the design and molding of precision plastic mold products for home appliances, especially for large thick-walled products such as beveled case and monitor shell of TV sets.

Shrinkage marks may be caused by one or more factors, including machining methods, part geometry, material selection, and die design.The geometry and material selection are usually determined by the raw material supplier and are not easily changed.But there are many other factors on the die manufacturer's part about the design of the die that may affect shrinkage.Cooling runner design, gate type, gate size may have a variety of effects.

For example, a small gate such as a tubular gate cools much more quickly than a tapered gate.Premature cooling at the gate increases the chance of shrinkage marks by reducing the filling time in the mold cavity.For molding workers, adjusting processing conditions is one way to solve the shrinkage problem.Filling pressure and time significantly affect shrinkage.After the component is filled, excess material continues to be filled into the cavity to compensate for material shrinkage.Too short a filling phase will lead to increased shrinkage, resulting in more or larger contraction marks.This method by itself may not reduce the shrinkage mark to a satisfactory level, but the shaper can modify the filling conditions to improve the shrinkage mark.