Embrittlement

The impact strength of the part decreases and it becomes brittle. 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: material degradation, excessive melt temperature, excessive drying, excessive proportion of recycled material, too many weld lines. 2. Temperature factors: the settings of barrel temperature and mold temperature directly affect melt fluidity, cooling rate, and crystallization behavior; low temperature is a common cause of filling and molding quality problems, and precise control is required according to the material's recommended processing window. 3. Mold comprehensive factors: in addition to venting, mold design parameters such as cooling water channel layout, gate position and size, and demolding draft angle all have a systematic impact on part quality, and optimization is required from the source of mold design.

1. Process parameter optimization and adjustment: lower barrel temperature, control drying conditions, reduce the amount of recycled material, reduce weld lines. 2. Systematic troubleshooting method: troubleshoot item by item in the order of "parameters -> material -> mold -> equipment". First adjust the parameters that are easiest to change, such as injection pressure and temperature, and observe the effect; if there is no improvement, check the drying and fluidity of the raw material; further check mold venting and gate design; finally check the mechanical condition of the equipment (check ring, screw). Change only one variable at a time to determine the root cause. 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.