Post-Curing Deformation

The part deforms during storage or post-curing. Incompletely cured parts show a sticky or soft surface, with obvious indentations visible when pressed with a fingernail, and insufficient rigidity when bent; over-curing shows the part becoming brittle, darker in color, and in severe cases microcracks appear. The degree of curing can be determined by differential scanning calorimetry (DSC) to detect residual reaction heat, or by Soxhlet extraction to detect gel content. For thermosetting materials, a curing degree below 95% is usually considered incomplete.

1. Reaction process factors: residual stress release, uneven post-curing temperature, uneven part wall thickness causing different curing rates, uneven crosslinking density. 2. Mixing quality factors: in the RIM process, the mixing uniformity of the two components is the foundation of all quality; the Reynolds number of the mixing head, the impingement mixing energy, and the residence time distribution are the key engineering parameters determining mixing quality.

1. Process parameter optimization and adjustment: optimize the curing process to make crosslinking uniform, use fixtures to fix parts during post-curing, control the post-curing heating rate. 2. Systematic troubleshooting method: RIM problem troubleshooting follows the order of "formulation -> mixing -> temperature control -> equipment". First check the two-component ratio and catalyst dosage, then check the mixing head and self-cleaning function, then check the raw material and mold temperature control, and finally check the accuracy of the metering pump and hydraulic system. 3. Preventive management: establish standardized process parameter cards and quality control limits for each mold/product, and regularly conduct process capability index (CPK) evaluation. For recurring problems, use fishbone diagram or 5Why analysis to trace the root cause, and fix the countermeasures as PFMEA control points.

The core of curing abnormality is that the rate and degree of the crosslinking reaction deviate from the optimal window. The adjustment idea is the "three-element method": formulation (precise metering of catalyst/curing agent), temperature (precise control of mold and material temperature), time (standardization of curing time and post-curing conditions); all three are indispensable.