Uneven Mixing

Layered or streaky color unevenness appears in the cross-section of the part. 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: improper mixing head design, large viscosity difference between the two components, insufficient mixing pressure, insufficient mixing energy. 2. 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: optimize the mixing head structure design, adjust component viscosity matching, increase mixing pressure, increase impingement mixing energy. 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).