Injection Molding
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Unstable screw retraction in random copolymer polypropylene '2079851475616104452
Problem Phenomenon
During plasticizing retraction, the screw jumps, retracts at uneven speed or fails to retract in place, and the preplasticizing position fluctuates greatly.
Unstable screw retraction makes each shot volume inconsistent, directly affecting product weight and dimensional stability.
Cause Analysis
(1) Back pressure is set too high or is unstable, resulting in large plasticizing resistance
(2) Barrel temperature is uneven; low melting section temperature makes plasticizing difficult
(3) The screw is severely worn, and plasticizing efficiency declines
(4) Raw material particle size is uneven or contains too much powder, making feeding uneven
(5) Screw speed and back pressure are improperly matched
Solution
(1) Appropriately reduce back pressure to 3-8MPa and ensure back pressure stability
(2) Check the temperature of each barrel section to ensure the melting section temperature is at a reasonable value within the 190-260°C range
(3) Check screw wear; replace the screw if the flight clearance exceeds 0.2mm
(4) Screen the raw material, controlling the powder proportion to no more than 5%
(5) Adjust the matching relationship between screw speed and back pressure, with speed of 40-100rpm
Key Takeaway
Unstable screw retraction is caused by large plasticizing resistance or equipment wear; back pressure, temperature and screw condition need to be optimized.
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