Excessive Heating (Degradation and Discoloration, Bubbling)

In the rotational molding production process, the product exhibits the quality defect of 「Excessive Heating (Degradation and Discoloration, Bubbling)」. The specific manifestation is that the product discolors or bubbles due to excessive heating. 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 Excessive Heating (Degradation and Discoloration, Bubbling) 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. Heating temperature too high. Temperature is the core factor affecting melt fluidity and viscosity. Too high a temperature setting will cause the melt viscosity to decrease, insufficient melt strength, or even thermal degradation; too low a temperature will result in poor melt fluidity and insufficient plasticization, making it unable to fill or mold smoothly. A reasonable temperature window should be optimized and determined within the recommended range according to the melting characteristics and thermal stability of the material. 2. Heating time too long. 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. 3. Poor resin thermal stability. Material selection and handling are the foundation of molding quality. Intrinsic properties of the resin such as molecular weight, molecular weight distribution, and melt index determine its processing window and final performance. Factors such as excessive raw material moisture content, impurity mixing, and improper proportion of recycled material will all cause various defects during processing. 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 Excessive Heating (Degradation and Discoloration, Bubbling) problem.

1. Reduce the heating temperature and 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. Add heat stabilizer. Formula and ratio adjustments should be determined on the basis of laboratory small-scale tests, and then verified in online pilot tests. Any change in the formula should be recorded and evaluated for its comprehensive impact on product performance. Automatic metering and batching devices can effectively reduce manual batching errors and batch-to-batch fluctuations. 3. Optimize the heating process. Optimization work needs to be based on accurate diagnosis of the root cause of the problem, and blind attempts should be avoided. It is recommended to first determine the key influencing factors and their interactions through process DOE test methods or historical production data analysis, and then carry out targeted parameter optimization and structural improvement to achieve twice the result with half the effort. 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 「Excessive Heating (Degradation and Discoloration, Bubbling)」 problem can be attributed to the combined effects of multiple factors such as heating temperature being too high and heating time being too long. To solve this problem, it is necessary to start from aspects such as reducing the heating temperature and time and adding heat stabilizer 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.