Discoloration of the Product Inner Wall (Oxidation)

In the rotational molding production process, the product exhibits the quality defect of 「Discoloration of the Product Inner Wall (Oxidation)」. The specific manifestation is that the product inner wall oxidizes and discolors due to contact with air. This defect is relatively common when processing powder materials such as LLDPE, HDPE, PVC, and PA, and its occurrence conditions are usually related to unreasonable settings of heating temperature and time, rotation speed ratio, cooling rate, and mold wall thickness. When the Discoloration of the Product Inner Wall (Oxidation) situation is severe, it will cause a series of chain quality defects in the product in terms of appearance, dimensional accuracy, and mechanical properties, which not only reduces the product's use functionality and safety, but also directly increases the scrap rate and production cost. Therefore, this problem needs to be systematically diagnosed and optimized from multiple dimensions such as material selection, the rotational molding machine, the heating oven, the rotating arm, the cooling station status, and heating temperature and time, rotation speed ratio, cooling rate, and mold wall thickness.

1. The inner wall being in a high-temperature state for a long time in contact with air. This factor leading to the problem reflects that certain process conditions or material properties in rotational '2079851475616104453ing have not met the optimal molding requirements. Such problems are often cumulative and hidden, and should be investigated and verified as key focus items during process debugging and finalization to ensure that hidden dangers are eliminated from the source. 2. Lack of inert gas protection. This factor leading to the problem reflects that certain process conditions or material properties in rotational '2079851475616104453ing have not met the optimal molding requirements. Such problems are often cumulative and hidden, and should be investigated and verified as key focus items during process debugging and finalization to ensure that hidden dangers are eliminated from the source. In addition, insufficient overall coordination of powder melting uniformity and product wall thickness control is also a factor that cannot be ignored. There are complex interactions and coupling relationships among various process parameters, and the deviation of any parameter may aggravate the degree of Discoloration of the Product Inner Wall (Oxidation) through chain effects. In terms of equipment maintenance, the regular overhaul and accuracy confirmation of the rotational molding machine, heating oven, rotating arm, and cooling station are not in place, causing the actual operating parameters of the equipment to deviate from process requirements, which will also become a potential inducement of the Discoloration of the Product Inner Wall (Oxidation) problem.

1. Shorten the high-temperature exposure time. Adjustments should follow the principle of gradual progress, and each adjustment amplitude should not be too large; it is recommended to decrease in steps of 5%~15% of the current value. After each adjustment, stably observe the product quality changes for at least 5~10 cycles, and continue adjusting only after confirming that the improvement direction is correct; avoid one-step excessive adjustment. 2. Introduce nitrogen to protect the inner wall. Protective treatment of equipment and molds can effectively extend service life and maintain accuracy. Exposed precision surfaces should be coated with anti-rust oil, and molds not used for a long time should be stored sealed. Anti-rust and anti-corrosion agents should be added to the cooling water, and filters should be installed on pipelines. Good protective habits can reduce unplanned downtime and lower maintenance costs. It is recommended to formulate a preventive inspection checklist for the Discoloration of the Product Inner Wall (Oxidation) problem, incorporate powder melting uniformity and product wall thickness control into the scope of daily patrol inspections, and conduct online monitoring of key parameters through the SPC statistical process control method to achieve early warning and rapid response to problems. In terms of material management, incoming inspection of raw materials and in-process inspection of work-in-progress products should be strengthened, and the key performance indicators of powder materials such as LLDPE, HDPE, PVC, and PA should be strictly controlled to ensure the stability of molding quality from the source.

In summary, the causes of the 「Discoloration of the Product Inner Wall (Oxidation)」 problem can be attributed to the combined effects of multiple factors such as the inner wall being in a high-temperature state for a long time in contact with air and lack of inert gas protection. To solve this problem, it is necessary to start from aspects such as shortening the high-temperature exposure time and introducing nitrogen to protect the inner wall and take systematic treatment measures. In actual production, it is recommended to establish a prevention and rapid response mechanism for this problem, and achieve stable production and continuous improvement through powder melting uniformity and product wall thickness control.