Injection Molding
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Nozzle drooling in low density polyethylene '2079851475616104452
Problem Phenomenon
After screw pre-plasticizing or holding ends, melt flows out from the nozzle orifice, forming drooling.
Drooling causes cold material to be injected into the cavity in the next injection, producing defects such as cold material spots and flow marks; in severe cases, dripping melt damages the mold.
Cause Analysis
(1) Nozzle temperature too high; low melt viscosity makes it easy to flow out
(2) Back pressure too high; melt flows out from the nozzle under pressure
(3) Nozzle hole diameter too large or improper nozzle structure
(4) Anti-drooling function not enabled or improperly set
(5) Insufficient screw retraction distance (insufficient suck-back), high residual pressure in the nozzle
Solution
(1) Appropriately reduce nozzle temperature to 5-15°C lower than the front barrel temperature (160-220°C range)
(2) Appropriately reduce back pressure to 3-6MPa
(3) Select a nozzle with appropriate hole diameter; use a spring needle valve nozzle when necessary
(4) Enable the anti-drooling function, set screw suck-back distance to 5-10mm
(5) Check the fit between the nozzle and the mold sprue, ensure tight contact
Key Takeaway
Drooling is caused by high nozzle temperature and residual pressure; it is solved by lowering temperature, adjusting back pressure, and increasing suck-back.
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