Post-curing cracking

The product cracks during post-curing. Incompletely cured products show sticky or soft surfaces, obvious indentations visible when pressed with a fingernail, and insufficient rigidity when bent; over-cured products show brittleness, darker color, and microcracks in severe cases. The determination of the curing degree can be carried out by differential scanning calorimetry (DSC) to detect the residual reaction heat, or by Soxhlet extraction to detect the gel content. For thermosetting materials, a curing degree below 95% is generally considered incomplete.

1. Reaction process factor: Excessively fast heating during post-curing generates thermal stress, large residual stress in the product, excessively high post-curing temperature, and uneven product wall thickness. 2. Mixing quality factor: 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 that determine the mixing quality.

1. Process parameter optimization and adjustment: Heat slowly, place the product after demolding to release residual stress, control the post-curing temperature, and optimize the wall thickness design. 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, next troubleshoot 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) assessments. For recurring problems, use fishbone diagrams or 5Why analysis to trace the root cause, and solidify 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), and time (standardization of curing time and post-curing conditions), all three of which are indispensable.