Carbonized lines on the inner wall of the product

In the rotational molding production process, the product exhibits the quality defect of "Carbonized lines on the inner wall of the product".The specific manifestation is Black carbonized lines appear on the inner wall of the product.This defect is more common when processing materials such as LLDPE, HDPE, PVC and PA powders, and its occurrence is usually related to unreasonable settings of heating temperature and time, rotation speed ratio, cooling rate and mold wall thickness.When the Carbonized lines on the inner wall of the product situation is severe, it will cause a series of chain quality defects in the product's appearance, dimensional accuracy, mechanical properties and other aspects, which not only reduces the product's functionality and safety 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. Long-term material accumulation and carbonization inside the mold.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 lead to forming defects.The machining accuracy, surface treatment quality and daily maintenance status of the mold also directly affect product quality. 2. Resin decomposition products deposit on the inner wall of the mold.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 lead to forming 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 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 the process parameters, and the deviation of any parameter may aggravate the degree of Carbonized lines on the inner wall of the product 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 Carbonized lines on the inner wall of the product problem.

1. Regularly clean the inner wall of the mold.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 or electrolytic corrosion of the cavity surface caused by improper operation.After cleaning, re-check and confirm that the key clearances are accurate. 2. Lower the heating temperature.Adjustments should follow the principle of gradual progress; each adjustment should not be too large, and a decrement of 5%~15% of the current value is recommended.After each adjustment, stably observe the product quality changes for at least 5~10 mold cycles, and continue adjusting only after confirming the improvement direction is correct; never make excessive one-step adjustments. 3. Use resin with good thermal stability.Before introducing new tools, new materials or new methods, sufficient applicability evaluation and small-batch verification should be carried out.It is recommended to first conduct offline tests or simulation analyses outside production conditions, and introduce them into the formal production line only after confirming effectiveness and safety.Keep proper change management records to facilitate subsequent traceability and experience accumulation. In terms of material management, incoming inspection of raw materials and in-process testing of work-in-progress should be strengthened, and key performance indicators of LLDPE, HDPE, PVC and PA powders should be strictly controlled to ensure the stability of forming quality from the source.

In summary, the causes of the "Carbonized lines on the inner wall of the product" problem can be attributed to the combined action of multiple factors such as Long-term material accumulation and carbonization inside the mold, Resin decomposition products deposit on the inner wall of the mold.To solve this problem, it is necessary to start from aspects such as Regularly clean the inner wall of the mold, Lower the heating temperature and take systematic governance measures.In actual production, it is recommended to establish a prevention and rapid response mechanism for this problem, achieving stable production and continuous improvement through powder melting uniformity and product wall thickness control.