Injection Molding
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Nozzle drooling in random copolymer polypropylene '2079851475616104452
Problembeschreibung
After screw preplasticizing or the end of holding pressure, 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 shot, producing cold slug marks, flow marks and other defects, and in severe cases dripping melt damages the mold.
Ursachenanalyse
(1) Nozzle temperature is too high; melt viscosity is low and it flows out easily
(2) Back pressure is too high; 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) Screw retraction distance is insufficient (suck-back is not enough), and residual pressure in the nozzle is high
Lösung
(1) Appropriately reduce nozzle temperature to 5-15°C lower than the front barrel temperature (190-260°C range)
(2) Appropriately reduce back pressure to 3-6MPa
(3) Select a nozzle with a suitable hole diameter, using a spring needle valve nozzle if necessary
(4) Enable the anti-drooling function, setting a screw suck-back distance of 5-10mm
(5) Check the fit between the nozzle and the mold sprue to ensure tight contact
Wichtigste Erkenntnis
Drooling is caused by high nozzle temperature and residual pressure and is solved by lowering temperature, adjusting back pressure and increasing suck-back.
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