Blow Molding
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Severe parison sag of general-purpose polyethylene '2079851475616104457
Fenómeno do problema
The extruded parison sags and becomes longer due to its own weight before the mold is closed, with the upper part becoming thinner and the lower part becoming thicker.
Parison sag causes uneven wall thickness distribution of the product, and in severe cases the parison breaks or the mold cannot be closed normally.
Análise das causas
（1）The melt temperature is too high, and the melt strength of general-purpose 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 ambient temperature aggravates the sag
Solução
（1）Appropriately lower the extrusion temperature to the lower value within the range of 160-260°C to increase the melt strength
（2）Increase the extrusion speed and 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 to avoid high temperature
Conclusão principal
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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