Foam post-shrinkage (dimensional shrinkage)

After demolding, foam products continue to shrink during cooling and storage. Such defects mostly occur in thick-wall transition areas of the product and at the far end of the gate, gradually appearing during the cooling and setting stage. This problem causes product dimensions to exceed the tolerance range, affecting assembly accuracy and product function.

(1) Gas removal aspect: gas in the cells cools and shrinks to form negative pressure; gas retention forms internal defects affecting product compactness. (2) Gas removal aspect: gas in the closed-cell structure diffuses outward, causing internal pressure to decrease; gas retention forms internal defects affecting product compactness. (3) Crystallization behavior aspect: material crystallization or post-curing causes volume shrinkage; changes in crystallinity affect the mechanical properties and dimensional stability of the product.

(1) Process optimization: extend in-mold cooling time to allow gas replacement to reach equilibrium; determine a reasonable time based on product wall thickness and material characteristics, balancing production efficiency and quality. (2) Design optimization: optimize the formulation to improve foam skeleton rigidity; combine process simulation analysis or mold trial verification to continuously iterate and improve the design plan. (3) Implementation measures: appropriately increase the closed-cell ratio to slow gas escape., formulate specific operation plans based on actual production conditions and verify implementation effects. (4) Preventive measures: establish a shrinkage rate database, preset shrinkage compensation amounts based on product structure and material type, and regularly calibrate mold dimensions.

The core of shrinkage defects lies in the contradiction between material curing volume change and insufficient process compensation, which requires comprehensive control through formulation optimization and process adjustment.