Extrusion & Post
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Dimensional fluctuation of general-purpose polyethylene extruded products
Problem Phenomenon
The outer diameter, wall thickness, or width of the extruded product fluctuates periodically or randomly in the longitudinal direction.
Dimensional fluctuation affects the fitting accuracy and use performance of the product, and is common in pipe and profile extrusion.
Cause Analysis
（1）The screw speed is unstable, and the output fluctuates
（2）The haul-off speed is unstable and does not match the extrusion speed
（3）The barrel temperature fluctuates greatly, and the melt viscosity changes
（4）The raw material feeding is uneven, and the feeding fluctuates
（5）The cooling water temperature or flow rate fluctuates
Solution
（1）Check the extruder drive system and stabilize the screw speed
（2）Check the haul-off machine speed control system to ensure stable haul-off speed
（3）Stabilize the barrel temperature, and control the fluctuation within ±3°C (within the range of 160-260°C)
（4）Check the hopper feeding to ensure continuous and uniform feeding
（5）Stabilize the cooling water temperature and flow rate, and add a constant temperature device if necessary
Key Takeaway
Dimensional fluctuation is caused by unstable extrusion or haul-off, and each process parameter needs to be systematically stabilized.
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