Stress cracking of the product after contact with chemical reagents

In the rotational molding production process, the product exhibits the quality defect of "Stress cracking of the product after contact with chemical reagents".The specific manifestation is The product cracks after contact with specific chemical reagents.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 Stress cracking of the product after contact with chemical reagents 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. Poor chemical resistance of the resin.Material selection and handling are the foundation of forming quality.The 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 moisture content of raw materials, mixed impurities and improper regrind ratios will all cause various defects during processing. 2. Large residual stress.This factor causing the problem reflects that certain process conditions or material properties in rotational molding do not meet the optimal forming requirements.Such problems are often cumulative and concealed, and should be investigated and verified as key focus items during process debugging and finalization to ensure hidden dangers are eliminated at the source. 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 Stress cracking of the product after contact with chemical reagents 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 Stress cracking of the product after contact with chemical reagents problem.

1. Select chemical-resistant resin.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. 2. Reduce residual stress.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. Improve wall thickness uniformity.Optimization work must be based on accurate diagnosis of the root cause of the problem; blind attempts must be avoided.It is recommended to first determine the key influencing factors and their interactions through process DOE test methods or historical production data analysis, and then carry out targeted parameter optimization and structural improvement to achieve twice the result with half the effort. 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 "Stress cracking of the product after contact with chemical reagents" problem can be attributed to the combined action of multiple factors such as Poor chemical resistance of the resin, Large residual stress.To solve this problem, it is necessary to start from aspects such as Select chemical-resistant resin, Reduce residual stress 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.