Low-temperature embrittlement of the product

The impact strength drops sharply in low-temperature environments. Embrittled products break under normal use loads, with flat and smooth fracture surfaces without traces of plastic deformation, showing typical brittle fracture characteristics. In impact tests, the notched impact strength of embrittled products may drop below 30% of the normal value. The danger of embrittlement problems lies in the fact that the appearance is often normal and is only exposed when stressed; therefore, for safety-related products (such as helmets, safety seats, electrical housings), embrittlement is an unacceptable major quality accident.

1. Material factor: The formulation glass transition temperature is relatively high, the hard segment content is too high, the crosslinking density is too large, and the plasticizer is insufficient. 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: Reduce the hard segment content, reduce the crosslinking density, add plasticizers, and select low-Tg polyols. 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 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 excessively high degradation), drying temperature (avoid excessively low residual moisture and excessively high causing thermal oxidation), and mold temperature (affecting crystallization and residual stress), as well as controlling the heating history and residence time of the material.