Extrusion & Post
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Dimensional Fluctuation of High-Density 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 service performance of the product and is common in pipe and profile extrusion.
Cause Analysis
（1）The screw rotation 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 material discharge fluctuates
（5）The cooling water temperature or flow fluctuates
Solution
（1）Check the extruder drive system to stabilize the screw rotation speed
（2）Check the haul-off machine speed control system to ensure stable haul-off speed
（3）Stabilize the barrel temperature, with the fluctuation controlled within ±3°C (180-260°C range)
（4）Check the hopper discharge to ensure continuous and uniform feeding
（5）Stabilize the cooling water temperature and flow, and add a constant temperature device when necessary
Key Takeaway
Dimensional fluctuation is caused by unstable extrusion or haul-off, and all process parameters need to be systematically stabilized.
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