Mixing Head Blockage

The material cures inside the mixing head and blocks the channel. 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. Equipment factors: residual material after mixing not cleaned in time, self-cleaning function failure, material curing too fast, mixing head temperature abnormality.

1. Process parameter optimization and adjustment: execute the self-cleaning program immediately after each injection, repair the self-cleaning plunger, reduce the material curing speed, control the mixing head temperature. 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).