Too Fast Curing

The material gels prematurely in the mixing head or in the mold. 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. Mold design factors: excessive catalyst dosage, raw material temperature too high, mold temperature too high, residence time after mixing too long.

1. Process parameter optimization and adjustment: reduce catalyst dosage, lower raw material and mold temperature, shorten the conveying distance and time from the mixing head to the mold. 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.