Over-curing/scorching

The product surface becomes dark or blackened or becomes brittle. 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, local overheating, poor thermal stability of the material. 2. Preheating factor: The preheating temperature and time of the material (especially thermosetting molding compounds) directly affect its flowability and curing behavior; improper preheating will lead to poor filling or uneven curing, and it is a key control point unique to compression molding. 3. Molding pressure factor: In compression molding, pressure is not only used to overcome flow resistance, but also directly affects the compactness of the product and the degree of fiber impregnation; insufficient pressure is an important cause of product looseness and insufficient strength.

1. Process parameter optimization and adjustment: shorten the curing time, lower the mold temperature, check the mold heating uniformity, select materials with good thermal stability. 2. Systematic troubleshooting method: Troubleshooting of compression molding problems follows the order of 'material -> temperature -> pressure -> mold'. First check the preheating and flowability of the material, then verify the mold temperature distribution and curing time, then adjust the molding pressure and mold closing speed, and finally check the mold venting and demolding conditions. 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.