Extrusion & Post
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Melt adhesion to the die caused by insufficient lubrication
Problem Phenomenon
During PVC profile extrusion, the melt adheres to the die exit surface, making product hauling difficult; longitudinal scratches and fuzzing appear on the product surface, and the die needs frequent cleaning once every 2 hours.
Cause Analysis
The internal lubricating component proportion in the calcium-zinc stabilizer is relatively low and external lubricant is insufficient; the die temperature is set too high, reducing melt viscosity and enhancing adhesion; the die material or surface finish is poor with roughness Ra>0.4 μm; the processing temperature does not match the lubrication characteristics of the stabilizer.
Solution
Check the inner wall finish of the die and perform polishing treatment to Ra≤0.2 μm; increase the external lubricant by 0.3-0.5 phr in the formulation (oxidized PE wax + ester composite lubricant); apply PTFE coating treatment to the die to reduce adhesion; appropriately reduce the die temperature by 3-8°C; select a calcium-zinc stabilizer grade with stronger lubrication performance.
Key Takeaway
Solving the melt adhesion problem requires both lubrication formulation adjustment and die surface treatment; using a composite lubrication system works better than a single lubricant.
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