Injection Molding
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Unstable screw retraction in low density polyethylene '2079851475616104452
Problem Phenomenon
The screw jumps during plasticizing retraction, retracts at uneven speed, or fails to retract in place, with large fluctuations in pre-plasticizing position.
Unstable screw retraction causes inconsistent injection amounts each time, directly affecting product weight and dimensional stability.
Cause Analysis
(1) Back pressure set too high or unstable, large plasticizing resistance
(2) Uneven barrel temperature; low melting zone temperature causes plasticizing difficulty
(3) Severe screw wear, reduced plasticizing efficiency
(4) Uneven raw material particle size or excessive powder content, uneven feeding
(5) Improper matching of screw rotation speed and back pressure
Solution
(1) Appropriately reduce back pressure to 3-8MPa, ensure stable back pressure
(2) Check the temperature of each barrel zone, ensure melting zone temperature at a reasonable value within the 160-220°C range
(3) Check screw wear; if flight clearance exceeds 0.2mm, the screw needs to be replaced
(4) Screen raw material, control powder ratio not exceeding 5%
(5) Adjust the matching relationship between screw rotation speed and back pressure, rotation speed 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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