Product surface reddening/discoloration

The product has local color abnormality. Discoloration forms include overall color difference, local yellowing, color darkening near the gate, or color streaks along the flow direction. For light-colored and transparent products, discoloration is particularly obvious. The root cause of discoloration is usually a chemical change in a component of the material——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. Mold design factors: local overheating of the mold causes thermal oxidation discoloration of the material, iron impurities in the material, mold rust contamination, uneven curing agent distribution. 2. Preheating factor: The preheating temperature and time of the material (especially thermosetting molding compounds) directly affect its flowability and curing behavior; improper preheating will lead to poor filling or uneven curing, and it is a key control point unique to compression molding. 3. Molding pressure factor: In compression molding, pressure is not only used to overcome flow resistance, but also directly affects the compactness of the product and the degree of fiber impregnation; insufficient pressure is an important cause of product looseness and insufficient strength.

1. Process parameter optimization and adjustment: check the mold heating uniformity, sieve the material to remove impurities, apply rust-proof treatment to the mold, fully mix the curing agent. 2. Systematic troubleshooting method: Troubleshooting of compression molding problems follows the order of 'material -> temperature -> pressure -> mold'. First check the preheating and flowability of the material, then verify the mold temperature distribution and curing time, then adjust the molding pressure and mold closing speed, and finally check the mold venting and demolding conditions. 3. Preventive management: Establish standardized process parameter cards and quality control limits for each set of mold/product, and regularly conduct process capability index (CPK) evaluations. For recurring problems, use fishbone diagrams or 5Why analysis to trace the root cause, and solidify the countermeasures as PFMEA control points.

This problem is a typical manifestation of product surface reddening/discoloration in compression molding; the core of the solution lies in proper preheating of the material and assurance of flowability, as well as precise matching of mold temperature and molding pressure. It is recommended to adjust coordinately from both aspects of material state and process parameters.