Discoloration / Color Difference

The color of the part does not match the standard part or local discoloration occurs. Discoloration forms include overall color difference, local yellowing, color deepening near the gate, or color streaks appearing along the flow direction. For light-colored and transparent parts, discoloration is particularly obvious. The root cause of discoloration is usually that a component in the material has undergone a chemical change — thermal degradation breaks molecular chains to form chromophoric groups, oxidation reactions generate quinone-type yellow substances, or pigments decompose and lose color at high temperatures. Discoloration is not only an appearance problem but also an external sign of material performance deterioration.

1. Equipment factors: excessive barrel temperature causing pigment decomposition, excessive residence time, incomplete color change, uneven dispersion of color masterbatch. 2. 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, reduce residence time, thoroughly clean the barrel, increase screw back pressure to improve dispersion. 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.

This problem is a typical manifestation of discoloration/color difference in '2079851475616104452; the core of the solution lies in eliminating the root cause of the defect through systematic optimization of process parameters (temperature, pressure, speed) and rationality checks of mold design. It is recommended to start with process parameter adjustment and gradually go deeper into the equipment and mold levels.