Extrusion & Post
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Uneven Thickness of Polypropylene Blown Film
Problem Phenomenon
The thickness of the film fluctuates greatly in the circumferential or longitudinal direction, and the thickness deviation exceeds ±10%.
Uneven thickness affects the mechanical properties and use performance of the film, and may cause deviation or film breakage on automatic packaging machines.
Cause Analysis
(1) The die gap is uneven
(2) The temperature in the circumferential direction of the die is uneven
(3) The air ring cooling is uneven
(4) The extrusion output fluctuates
(5) The haul-off speed is unstable
Solution
(1) Adjust the die gap, with a circumferential error not exceeding ±0.01mm
(2) Check the die heating bands to ensure the circumferential temperature difference does not exceed ±3°C (range 200-280°C)
(3) Check the air ring to ensure uniform air output, and clean the air ring regularly
(4) Stabilize the screw speed and temperature of the extruder
(5) Stabilize the haul-off speed, using a high-precision haul-off control system
Key Takeaway
Uneven film thickness is caused by uneven die gap, temperature, or cooling, and needs to be solved from mold precision and process stability.
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