Post Moulding Shrinkage Conditioning

Material Stabilization

Semi-crystalline resins require this treatment to transition from the metastable state dictated by the quench rate inside the cold mould to a stable crystalline volume. The cooling water temperature inside the mould determines the initial crystallinity of a part but rarely reaches the necessary levels to prevent future geometric movement. Parts processed without this acceleration often shift in size when exposed to later heat in warehouse environments or operational settings.

Virgin resin grades with high crystallinity potential necessitate longer cycles to ensure the polymer reaches a reliable density.

Economic Control

Frequent dimensional rejects during high tolerance assembly trigger the implementation of this practice to standardize part outputs. Regrind percentages increase the variability of crystalline growth, which forces a moulder to adjust these soak times to mitigate the impact of recycled content on the final shrinkage rate. Moulders justify the energy expense of this step by reducing the scrap rate during downstream automated fitment.

Consistent soaking cycles permit the use of lower tolerance tooling since the variation moves from the tool design to the post processing step.

Processing Limits

Oven temperature settings must remain strictly below the heat deflection temperature of the resin to prevent part deformation or surface degradation. Excessive heat causes the polymer chain mobility to exceed the limit required for simple shrinkage, resulting in internal sagging or unwanted flow patterns. Technicians monitor the soak duration because the rate of shrinkage follows a logarithmic decay curve where marginal stability gains diminish as the dwell time extends.

Precise control of this environment eliminates the risk of over-conditioning where the material properties begin to degrade due to long-term oxidative stress.