Injection Molding
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Nozzle Drooling in Polypropylene '2079851475616104452
Problem Phenomenon
After screw pre-plasticization or the end of holding, the melt flows out from the nozzle opening, forming 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, the melt viscosity is low, and it easily flows out
(2) The back pressure is too high, and the melt flows out from 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 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-section barrel temperature (range 200-280°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 when 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 tight contact
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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