Abnormal birefringence of the product under polarized light

In the rotational molding production process, the product exhibits the quality defect of "Abnormal birefringence of the product under polarized light".The specific manifestation is The birefringence pattern of the product is abnormal in polarized light inspection.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 Abnormal birefringence of the product under polarized light 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. Uneven residual stress distribution.Uniformity runs through all stages of the forming process.Uneven temperature, uneven pressure distribution, uneven cooling and uneven material mixing all lead to discreteness in product quality.Ensuring the uniform distribution of physical quantities is a prerequisite for obtaining products with good consistency and stable quality. 2. Inconsistent cooling conditions.Cooling conditions determine the setting process and final internal structure of the product.Uneven cooling causes shrinkage differences and residual stress leading to warpage and dimensional deviation; insufficient cooling makes the product not rigid enough at demolding; too rapid cooling produces large internal stress.The cooling system design should ensure uniform and efficient heat dissipation at all parts. 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 Abnormal birefringence of the product under polarized light 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 Abnormal birefringence of the product under polarized light problem.

1. Optimize cooling 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. 2. Annealing treatment to eliminate stress.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. It is recommended to formulate a preventive checklist for the Abnormal birefringence of the product under polarized light problem, incorporate powder melting uniformity and product wall thickness control 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 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 "Abnormal birefringence of the product under polarized light" problem can be attributed to the combined action of multiple factors such as Uneven residual stress distribution, Inconsistent cooling conditions.To solve this problem, it is necessary to start from aspects such as Optimize cooling uniformity, Annealing treatment to eliminate 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.