Extrusion & Post
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PE Blown Film Bubble Instability
Problem Phenomenon
LDPE/LLDPE/HDPE blown film bubbles sway left and right, shake and even break, with thickness and lay-flat width fluctuations, making normal production impossible.
Cause Analysis
Extrusion output fluctuations (unstable feeding, screw wear, screen pack blockage), uneven air ring cooling and environmental airflow disturbances all make the bubble unstable; LLDPE has low melt strength and inherently poor bubble stability, more susceptible to disturbances.
Solution
①Stabilize the feeding and extrusion output, and check the screw wear and screen pack pressure differential; ②supply air uniformly from the air ring and calibrate the air volume distribution; ③shield the workshop airflow; ④LLDPE can be blended with LDPE to increase the melt strength; ⑤stabilize the melt temperature and haul-off.
Key Takeaway
Bubble stability = 'stable extrusion + uniform air ring + still airflow': first suppress the extrusion fluctuations, then even out the air ring, and finally manage the environment; when the LLDPE bubble is unstable, blending to increase the melt strength often works immediately.
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