Impact failure of the product in extremely low-temperature environments

During the rotational molding production process, the product exhibits the quality defect of 「Impact failure of the product in extremely low-temperature environments」. The specific manifestation is that the product impacts and ruptures in extremely low temperature environments (such as below -40°C). 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 Impact failure of the product in extremely low-temperature environments 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. The toughness of the resin drops sharply at extremely low temperatures. 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. Insufficient wall thickness. The uniformity of wall thickness distribution directly relates to the mechanical properties of the product and the consistency of cooling shrinkage. Excessive wall thickness differences lead to inconsistent cooling rates, with sink marks and warpage in thick-walled regions and insufficient strength in thin-walled regions. Wall thickness design should follow the uniform wall thickness principle, and wall thickness changes should transition smoothly. 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 Impact failure of the product in extremely low-temperature environments 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 Impact failure of the product in extremely low-temperature environments problem.

1. Select ultra-low temperature resistant resin (such as LLDPE). 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 analysis outside production conditions, and introduce them into the formal production line only after confirming effectiveness and safety. Keep change management records for subsequent traceability and experience accumulation. 2. Increase wall thickness. When implementing adjustments, it is recommended to use the single-factor variable method, adjusting only one parameter at a time and fully evaluating the effect, to avoid the inability to trace the cause of the problem due to simultaneous changes of multiple parameters. The adjustment amplitude should be small rather than large; each adjustment is recommended to be controlled within 5%~10% of the original value, and after adjustment, run stably for at least 3~5 molding cycles to observe the effect. 3. Add low-temperature toughening agents. Adjustments to the formulation and ratio should be determined on the basis of laboratory small-scale tests, and then verified by online pilot tests. Any change to the formulation should be recorded and evaluated for its full impact on product performance. Automatic metering and batching devices can effectively reduce errors and batch-to-batch fluctuations of manual batching. 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 「Impact failure of the product in extremely low-temperature environments」 problem can be attributed to the combined action of multiple factors such as the toughness of the resin dropping sharply at extremely low temperatures and insufficient wall thickness. Solving this problem requires starting from aspects such as selecting ultra-low temperature resistant resin (such as LLDPE) and increasing wall thickness, 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.