Carbon deposit layer appears on the mold inner wall

During the rotational molding production process, the product exhibits the quality defect of 「Carbon deposit layer appears on the mold inner wall」. The specific manifestation is that a carbonized carbon deposit layer appears on the mold inner wall, affecting product quality. This defect is relatively common when processing materials such as powders such as LLDPE, HDPE, PVC, PA, and its occurrence conditions are usually related to unreasonable settings of heating temperature and time, rotation speed ratio, cooling rate, mold wall thickness. When the Carbon deposit layer appears on the mold inner wall situation is severe, it causes a series of cascading quality defects in the product in terms of appearance, dimensional accuracy, mechanical properties, and other aspects, not only reducing the product's functionality and safety in use, but also directly increasing the scrap rate and production costs. Therefore, this problem requires systematic diagnosis and optimization from multiple dimensions, including material selection, rotational molding machine, heating oven, rotating arm, cooling station condition, and heating temperature and time, rotation speed ratio, cooling rate, mold wall thickness.

1. Deposition of resin decomposition products from long-term use. The selection and handling of materials is the foundation of molding quality. The intrinsic characteristics of the resin, such as molecular weight, molecular weight distribution, and melt index, determine its processing window and final performance. Factors such as excessive moisture content of raw materials, mixing of impurities, and improper proportion of recycled material can all cause various defects during processing. 2. Improper mold cleaning. The mold is the core tool that gives the product its shape and surface quality. Unreasonable mold design, such as improper runner/gate dimensions, insufficient venting, inadequate draft angle, etc., directly causes molding defects. The machining accuracy, surface treatment quality, and daily maintenance status of the mold also directly affect product quality. In addition, the insufficient overall coordination between powder melting uniformity and product wall thickness control is also a factor that cannot be ignored. There are complex interactions and coupling relationships among the process parameters, and the deviation of any parameter may aggravate the degree of Carbon deposit layer appears on the mold inner wall through chain effects. In terms of equipment maintenance, the regular overhaul and precision 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 can also become a potential inducement of the Carbon deposit layer appears on the mold inner wall problem.

1. Regularly clean the mold inner wall. Cleaning work should be incorporated into the equipment preventive maintenance plan, and the cleaning frequency should be reasonably determined according to the actual conditions of the processed materials and operating cycles. Use dedicated cleaning tools and cleaning materials to avoid scratches or electrolytic corrosion of the cavity surface caused by improper operation. After cleaning, re-check and confirm that the key clearances are accurate. 2. Use mold cleaning agents. Cleaning work should be incorporated into the equipment preventive maintenance plan, and the cleaning frequency should be reasonably determined according to the actual conditions of the processed materials and operating cycles. Use dedicated cleaning tools and cleaning materials to avoid scratches or electrolytic corrosion of the cavity surface caused by improper operation. After cleaning, re-check and confirm that the key clearances are accurate. 3. Reduce the heating temperature. Adjustments should follow the principle of gradual progress; each adjustment should not be too large, and it is recommended to decrease by 5%~15% of the current value. After each adjustment, observe the product quality changes for at least 5~10 molding cycles, and continue adjusting only after confirming the improvement direction is correct; avoid one-step excessive adjustment. In terms of material management, incoming inspection of raw materials and in-process inspection of work-in-progress should be strengthened, and the key performance indicators of powders such as LLDPE, HDPE, PVC, PA should be strictly controlled to ensure the stability of molding quality from the source.

In summary, the causes of the 「Carbon deposit layer appears on the mold inner wall」 problem can be attributed to the combined action of multiple factors such as deposition of resin decomposition products from long-term use and improper mold cleaning. Solving this problem requires starting from aspects such as regularly cleaning the mold inner wall and using mold cleaning agents, and adopting systematic governance 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.