Injection Molding
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Nozzle drooling in general-purpose polyethylene '2079851475616104452
Problem Phenomenon
After the screw pre-plasticizing or holding is completed, the melt flows out of the nozzle opening to form a drooling phenomenon.
Drooling causes cold material to be injected into the cavity in 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 easy to flow out
（2）The back pressure is too high, and the melt flows out of the nozzle under pressure
（3）The nozzle hole diameter is too large or the nozzle structure is improper
（4）The anti-drooling function is not enabled or is improperly set
（5）The screw back distance is insufficient (the suck-back amount is not enough), and the residual pressure in the nozzle is high
Solution
（1）Appropriately lower the nozzle temperature to 5-15°C lower than the front barrel temperature (within the range of 160-260°C)
（2）Appropriately reduce the back pressure to 3-6MPa
（3）Select a nozzle with a suitable hole diameter, and use a spring needle valve nozzle if necessary
（4）Enable the anti-drooling 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
Drooling 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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