Abnormal shrinkage rate of EPP molded products after demolding

EPP products shrink beyond the normal range after demolding. 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) Process factor: insufficient steam heating causing inadequate plasticization of bead surfaces and retraction after cooling; this factor affects the '2079851475616104453 and final quality of the product. (2) Process speed aspect: cooling rate too fast; speed parameters affect the synchronization of material flow state and reaction progress. (3) Material aspect: resin system curing volume shrinkage rate too large, lacking effective constraint. (4) Process aspect: curing rate too fast, shrinkage stress has no time to relax and release. (5) Design aspect: large wall thickness differences causing inconsistent shrinkage in various regions.

(1) Parameter adjustment: increase steam pressure and heating time; needs to be evaluated in combination with equipment capacity, gradually increase pressure and check product compactness and dimensional changes. (2) Formulation adjustment: reduce cooling rate, adjust gradually and verify the effect, ensuring that other performance indicators of the product are not affected. (3) Formulation optimization: appropriately increase internal gas pressure of pre-foamed beads., determine the optimal addition amount through small-batch tests, and verify the impact on the comprehensive performance of the product. (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.