Extrusion & Post
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HDPE film strain hardening
Problem Phenomenon
The film bubble width and internal pressure fluctuate, and wrinkles and weak spots appear on the film.
Cause Analysis
The melt is stretched too fast in the longitudinal direction and undergoes strain hardening, causing the film bubble diameter and internal pressure to become unstable; an excessive draw ratio is the main inducement.; when troubleshooting on site, verify item by item according to this mechanism, and avoid blindly adjusting the machine based only on experience
Solution
①Reduce the draw ratio; ②adjust the formulation to reduce the extensional viscosity; ③stabilize the haul-off speed; ④optimize the cooling gradient.; after adjustment, continuously sample to verify the effect, and resume mass production only after confirming stability
Key Takeaway
Strain hardening is an extensional rheology problem; reducing the stretching load and adjusting the material rheological properties are two solution paths.; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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