Deformation of the product after long-term storage (post-crystallization)

In the rotational molding production process, the product exhibits the quality defect of "Deformation of the product after long-term storage (post-crystallization)".The specific manifestation is The product changes in size after several months of storage.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 Deformation of the product after long-term storage (post-crystallization) 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. The post-crystallization process of crystalline resin proceeds slowly.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. 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 Deformation of the product after long-term storage (post-crystallization) through chain effects.

1. Accelerate cooling to make crystallization sufficient.Before implementing this measure, its feasibility and expected effects should be fully evaluated, plan details communicated and confirmed with relevant technical personnel, key quality indicator changes closely monitored during implementation, adjustment effects recorded and fed back in a timely manner, forming reusable process experience. 2. Add a nucleating agent.Formula and ratio adjustments should be determined on the basis of laboratory small-scale tests, and then verified by on-line pilot tests.Any change to the formula should be recorded and its impact on all aspects of product performance evaluated.Automatic metering and batching devices can effectively reduce manual batching errors and batch-to-batch fluctuations. 3. Annealing treatment.Before implementing this measure, its feasibility and expected effects should be fully evaluated, plan details communicated and confirmed with relevant technical personnel, key quality indicator changes closely monitored during implementation, adjustment effects recorded and fed back in a timely manner, forming reusable process experience. 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 "Deformation of the product after long-term storage (post-crystallization)" problem can be attributed to the combined action of multiple factors such as The post-crystallization process of crystalline resin proceeds slowly.To solve this problem, it is necessary to start from aspects such as Accelerate cooling to make crystallization sufficient, Add a nucleating agent 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.