Injection Molding
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Nozzle Drool in High-Density Polyethylene '2079851475616104452
Problem Phenomenon
After screw pre-plasticization or the end of the holding pressure, the melt flows out of the nozzle orifice, forming a drool phenomenon.
Drool causes cold material to be injected into the cavity during the next injection, producing defects such as cold material spots and flow marks, and in severe cases the melt drips and damages the mold.
Cause Analysis
（1）The nozzle temperature is too high, and the melt viscosity is low and flows out easily
（2）The back pressure is too high, and the melt flows out of the nozzle under pressure
（3）The nozzle aperture is too large or the nozzle structure is improper
（4）The anti-drool function is not enabled or is set improperly
（5）The screw retraction distance is insufficient (the suck-back amount is not enough), and the residual pressure in the nozzle is high
Solution
（1）Appropriately reduce the nozzle temperature to 5-15°C lower than the front barrel temperature (within the 180-260°C range)
（2）Appropriately reduce the back pressure to 3-6MPa
（3）Select a nozzle with a suitable aperture, and use a spring needle valve nozzle when necessary
（4）Enable the anti-drool function and set the screw suck-back distance to 5-10mm
（5）Check the fit between the nozzle and the mold sprue to ensure a tight fit
Key Takeaway
Drool is caused by high nozzle temperature and residual pressure, and is solved by lowering the temperature, adjusting the back pressure, and increasing the suck-back amount.
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