Blow Molding
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Severe Parison Sag in High-Density Polyethylene '2079851475616104457
문제 현상
The extruded parison sags and becomes longer due to its own weight before the mold closes, becoming thinner at the top and thicker at the bottom.
Parison sag causes uneven wall thickness distribution of the product, and in severe cases the parison breaks or the mold cannot close normally.
원인 분석
（1）The melt temperature is too high, and the melt strength of high-density polyethylene is low
（2）The parison extrusion speed is slow, and the parison hanging time is long
（3）The parison is too long or the wall thickness is too thin
（4）The raw material MFR is high, and the melt viscosity is low
（5）The high environmental temperature aggravates the sagging
해결 방법
（1）Appropriately reduce the extrusion temperature to a lower value within the 180-260°C range to increase the melt strength
（2）Increase the extrusion speed to shorten the parison hanging time
（3）Shorten the parison length or increase the parison wall thickness
（4）Select a grade with a lower MFR to increase the melt strength
（5）Control the workshop environment temperature and avoid high temperatures
핵심 요약
Parison sag is caused by low melt strength or slow extrusion, and needs to be solved by lowering the temperature, increasing the speed, and selecting materials.
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