Bubbles on the Product Surface (Large Area)

In the rotational molding production process, the product exhibits the quality defect of 「Bubbles on the Product Surface (Large Area)」. The specific manifestation is that large-area bubbles appear on the product outer surface. 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 Bubbles on the Product Surface (Large Area) 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. Moisture or oil stains on the mold surface. 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, and insufficient demolding draft angle, will directly lead to molding defects. The machining accuracy, surface treatment quality, and daily maintenance status of the mold also directly affect product quality. 2. Volatiles in the release agent. 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. Gas produced by resin decomposition. 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 Bubbles on the Product Surface (Large Area) problem.

1. Clean the mold surface. 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 material and operating cycle. Use dedicated cleaning tools and cleaning materials to avoid scratching the cavity surface or electrolytic corrosion caused by improper operation. After cleaning, re-inspect and confirm that the key gaps are accurate. 2. Use a release agent without volatiles. Before introducing new tools, new materials, or new methods, adequate applicability evaluation and small-batch verification should be carried out. It is recommended to first conduct offline tests or simulation analysis outside production conditions, and introduce them into the formal production line only after confirming effectiveness and safety. Make good change management records to facilitate subsequent traceability and experience accumulation. 3. Reduce the heating temperature. 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. 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 「Bubbles on the Product Surface (Large Area)」 problem can be attributed to the combined effects of multiple factors such as moisture or oil stains on the mold surface and volatiles in the release agent. To solve this problem, it is necessary to start from aspects such as cleaning the mold surface and using a release agent without volatiles 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.