Material Drying
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Bubbles/gas pores on the surface of heat-resistant polyethylene extruded products (Variant: mass production scenario)
Problem Phenomenon
Bubbles or gas pores appear on the surface or cross-section of the extrudate, and the product density decreases.
Bubbles not only affect the appearance, but also reduce the mechanical strength and pressure resistance of the product, and are common in pipe and profile extrusion.
In particular, in continuous mass production, this problem is more prominent and needs key attention.
Cause Analysis
（1）The moisture content of the raw material exceeds the standard, and the water vaporizes at high temperature to produce bubbles
（2）The screw venting is poor, and the melt entrains air
（3）The barrel temperature is too high, and the material is thermally degraded to produce gas
（4）The screw speed is too fast, and the venting time is insufficient
（5）The content of low molecular volatiles in the raw material is high
（6）In continuous mass production, process parameter fluctuations or equipment status changes have aggravated this problem
Solution
（1）Fully dry the raw material, and control the moisture content of heat-resistant polyethylene below 0.02%
（2）Check the venting section design, and use a vented extruder if necessary
（3）Appropriately lower the barrel temperature to a reasonable value within the range of 190-230°C
（4）Reduce the screw speed and increase the residence time of the material in the venting section
（5）Select raw material grades with low volatile content
（6）And establish standardized work instructions, with special attention to parameter stability in continuous mass production
Key Takeaway
Bubbles are caused by water vaporization or gas entrainment, and need to be solved from raw '2079851475616104451 and venting system.
In different production scenarios, targeted preventive measures need to be taken.
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