POLYMER SHRINKAGE
Mould shrinkage is defined as the difference between the dimensions of the mould and the moulded part. It is expressed either in millimetres per millimetre or, more commonly, as a percentage.
Usually a general shrinkage value is quoted. Alternatively, two figures may be given – parallel (in line of flow) and perpendicular to the flow (cross-flow). This is particularly important in the case of glass-filled materials, for example, as there can be a significant difference between the two figures.
Other factors affecting shrinkage include part design, mould design, mould temperature, injection pressure and cycle time.