Embrittlement / Insufficient Strength

The impact strength or tensile strength of the part is low. Embrittled parts break under normal service loads, with a flat and smooth fracture surface without traces of plastic deformation, showing typical brittle fracture characteristics. In impact tests, the notched impact strength of embrittled parts may drop to below 30% of the normal value. The danger of embrittlement problems lies in that the appearance is often normal and is only exposed when stressed; therefore, for safety-related parts (such as helmets, safety seats, electrical enclosures), embrittlement is an unacceptable major quality accident.

1. Material factors: incomplete curing, component ratio imbalance, raw material moisture content exceeding standard, insufficient post-curing, improper chain extender dosage. 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. 3. Temperature control factors: raw material temperature affects component viscosity and reaction rate, mold temperature affects the curing process and part surface quality, and both need to be precisely controlled within a narrow window.

1. Process parameter optimization and adjustment: ensure complete curing, calibrate the component ratio, strictly control raw material moisture, fully post-cure, adjust the chain extender dosage. 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 essence of embrittlement is that the material toughness reserve drops to a level that cannot meet the use requirements. The key to control is the "three temperatures" — processing temperature (avoid excessive degradation), drying temperature (avoid too low leaving residual moisture and too high causing thermal oxidation), mold temperature (affecting crystallization and residual stress), as well as controlling the heating history and residence time of the material.