Uneven product wall thickness

In the rotational molding production process, the product exhibits the quality defect of "Uneven product wall thickness". The specific manifestation is that the wall thickness differences among various parts of the product are large. This defect is relatively common when processing materials such as LLDPE, HDPE, PVC, PA and other powders, and its occurrence conditions are usually related to the unreasonable settings of heating temperature and time, rotation speed ratio, cooling rate, and mold wall thickness. When the "Uneven product wall thickness" situation is severe, it will cause a series of chain quality defects in the product in terms of appearance, dimensional accuracy, mechanical properties, etc., which not only reduces the functionality and safety of the product in use, but also directly increases the scrap rate and production cost. Therefore, this problem requires systematic diagnosis and optimization from multiple dimensions such as material selection, the status of the rotational molding machine, heating oven, rotating arm, and cooling station, and heating temperature and time, rotation speed ratio, cooling rate, and mold wall thickness.

1. Improper mold rotation speed ratio. The speed parameter affects the flow state and time allocation of the melt during the forming process. A speed that is too slow causes premature cooling and insufficient filling; a speed that is too fast causes melt fracture, air entrapment, and shear overheating. The optimization of the speed curve should make the melt flow smoothly and orderly in the cavity. 2. Uneven heating oven temperature. Temperature is the core factor affecting melt fluidity and viscosity. A temperature set too high will cause the melt viscosity to decrease, insufficient melt strength, and even thermal degradation; a temperature that is too low results in poor melt fluidity and insufficient plasticization, making it impossible to fill or form 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. 3. Uneven mold wall thickness causing heat transfer differences. 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 inadequate draft angle, will directly cause molding defects. The machining accuracy, surface treatment quality, and daily maintenance status of the mold also directly affect product quality. 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 the process requirements, which will also become a potential inducement of the "Uneven product wall thickness" problem.

1. Optimize the rotation speed and speed ratio. Optimization work must be based on an accurate diagnosis of the root cause of the problem, and blind attempts must be avoided. It is recommended to first determine the key influencing factors and their interactions through the process DOE test method or historical production data analysis, and then carry out parameter optimization and structural improvement in a targeted manner to achieve twice the result with half the effort. 2. Improve heating uniformity. Optimization work must be based on an accurate diagnosis of the root cause of the problem, and blind attempts must be avoided. It is recommended to first determine the key influencing factors and their interactions through the process DOE test method or historical production data analysis, and then carry out parameter optimization and structural improvement in a targeted manner to achieve twice the result with half the effort. 3. Use a mold with uniform wall thickness. Before introducing new tools, new materials, or new methods, a full applicability assessment 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. Keep change management records to facilitate subsequent traceability and experience accumulation. In terms of material management, incoming inspection of raw materials upon arrival and in-process inspection of work-in-progress should be strengthened, and the key performance indicators of LLDPE, HDPE, PVC, PA and other powders should be strictly controlled to ensure the stability of molding quality from the source.

In summary, the causes of the "Uneven product wall thickness" problem can be attributed to the combined action of multiple factors such as Improper mold rotation speed ratio, Uneven heating oven temperature. Solving this problem requires starting from aspects such as Optimize the rotation speed and speed ratio, Improve heating uniformity 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.