Processing Machinery
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HDPE film bubble instability (spiral swing)
Problem Phenomenon
The film bubble swings in a spiral shape, the frost line fluctuates, and the film thickness changes periodically.
Cause Analysis
Low melt strength, spiral disturbance of the air ring airflow, too low frost line or excessive die lip shear heat can all induce spiral film bubble instability.; when troubleshooting on site, verify item by item according to this mechanism, and avoid blindly adjusting the machine based only on experience
Solution
①Switch to a high molecular weight low melt index formulation; ②open the air vent wider or reduce the air volume to weaken the airflow impact; ③raise the frost line height; ④widen the die gap to reduce shear heat.
Key Takeaway
Spiral swing is a comprehensive problem of melt strength and airflow stability; the formulation and air ring are adjusted in both directions, and the effect is judged by a stable frost line.; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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