Reasons For The Formation Of Shrinkage Marks In Plastic Molds And Improvement Methods

- Dec 06, 2018-

There may be one or more reasons for the formation of shrink marks, including processing methods, component geometries, material selection, and mold design. The choice of geometry and material is usually determined by the raw material supplier and is not easily changed.


However, from the manufacturer's point of view, there are still many factors related to mold design that may affect the shrinkage effect. 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. Adjusting the processing conditions is also a way to solve the shrinkage problem. The filling pressure and time significantly affect the shrinkage. After the part is filled, the excess material is continuously filled into 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 approach may not reduce the shrinkage marks to a satisfactory level by itself, but experienced suppliers can improve the shrinkage marks by adjusting the filling conditions.