Poor Mixing Head Cleaning

Residual cured material in the mixing head affects the next injection. In the cross-section of a part with uneven mixing, obvious layered or marble-patterned streaks can be seen, with alternating dark and light colors, and the hardness, density, and mechanical properties of local areas are inconsistent with the whole. In extreme cases, insufficiently mixed components form independent enriched areas inside the part, which may become crack initiation points when stressed. The evaluation of mixing quality can be carried out by microscopic observation of the part cross-section or ultrasonic C-scan non-destructive testing.

1. Process parameter factors: insufficient self-cleaning solvent dosage, insufficient cleaning time, insufficient cleaning pressure, improper cleaning program settings. 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: increase the amount of cleaning solvent, extend cleaning time, increase cleaning pressure, optimize the cleaning program. 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.

RIM mixing quality is the first element determining part consistency. The core control points are: the impingement mixing Reynolds number of the mixing head (to ensure turbulent mixing), the viscosity matching of the two components (to reduce viscosity difference), the accuracy of the metering pump (to ensure constant ratio), and the effectiveness of self-cleaning (to prevent residual curing blockage).