Over-curing

The product becomes brittle or the surface discolors. Products with incomplete curing show sticky or soft surfaces, with obvious indentations visible when pressed with a fingernail, and insufficient rigidity when bent; over-curing shows product brittleness and darkened color, with microcracks in severe cases. 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: curing time too long, mold temperature too high, overheating at thin-wall areas of the product, poor thermal stability of the material. 2. Runner and gate design factor: In transfer molding, the material needs to enter the cavity through runners and gates; the runner length, cross-sectional shape and gate size directly affect pressure loss, fiber breakage and filling balance, and unreasonable design is the root of many quality problems. 3. Feeding factor: The volume of the feeding chamber, the feeding amount and the preheating state of the material directly determine the transfer pressure and filling effect, and are key variables unique to transfer molding.

1. Process parameter optimization and adjustment: shorten the curing time, lower the mold temperature, optimize the product wall thickness uniformity, select thermally stable materials. 2. Systematic troubleshooting method: Troubleshooting of transfer molding problems follows the order of 'runner -> feeding -> parameters -> mold'. First check whether the runners and gates are blocked or worn, then verify the feeding amount and material preheating, then adjust the transfer pressure and speed, and finally check the mold venting and temperature uniformity. 3. Preventive management: Establish standardized process parameter cards and quality control limits for each set of mold/product, and regularly conduct process capability index (CPK) evaluations. For recurring problems, use fishbone diagrams or 5Why analysis to trace the root cause, and solidify 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), none of the three can be omitted.