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

In the extrusion '2079851475616104457 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 gradually deforms after several months of storage.This defect is more common when processing materials such as HDPE, PP, PVC and PC, and its occurrence is usually related to unreasonable settings of melt temperature, extrusion speed, blowing pressure and mold temperature.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 extruder, head, die, mold clamping mechanism and blowing system, and melt temperature, extrusion speed, blowing pressure and mold temperature.

1. Slow post-crystallization of semi-crystalline resin causes dimensional changes.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 parison wall thickness control and parison temperature uniformity 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. Increase the mold cooling rate to make crystallization more sufficient.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 simultaneous changes of multiple parameters making the cause of the problem untraceable.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 mold cycles to observe the effect. 2. Adjust the process to reduce residual crystallinity.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. It is recommended to formulate a preventive checklist for the Deformation of the product after long-term storage (post-crystallization) problem, incorporate parison wall thickness control and parison temperature uniformity into the daily inspection scope, and conduct online monitoring of key parameters through the SPC statistical process control method to achieve early warning and rapid response to problems. 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 HDPE, PP, PVC and PC 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 Slow post-crystallization of semi-crystalline resin causes dimensional changes.To solve this problem, it is necessary to start from aspects such as Increase the mold cooling rate to make crystallization more sufficient, Adjust the process to reduce residual crystallinity 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 parison wall thickness control and parison temperature uniformity.