Injection Molding
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Large injection pressure fluctuation in low density polyethylene '2079851475616104452
Problem Phenomenon
During injection, the pressure gauge reading fluctuates greatly, and the pressure difference within the same cycle or between different cycles exceeds ±5%.
Pressure fluctuation causes unstable product weight, dimensions, and quality; in severe cases, short shots or flash appear alternately.
Cause Analysis
(1) Unstable hydraulic system pressure, hydraulic pump wear or hydraulic oil contamination
(2) Screw non-return ring wear, inconsistent injection amount each time
(3) Large barrel temperature fluctuation; melt viscosity changes cause pressure fluctuation
(4) Uneven feeding, inconsistent plasticizing amount each time
(5) Unstable screw rotation speed, fluctuating plasticizing quality
Solution
(1) Check the hydraulic system, repair or replace the worn hydraulic pump, replace hydraulic oil
(2) Check the non-return ring; replace if wear exceeds 0.1mm
(3) Stabilize barrel temperature; control fluctuation of each zone within ±3°C (160-220°C range)
(4) Check the feeding system, ensure smooth hopper feeding and stable material level
(5) Stabilize screw rotation speed and back pressure, ensure plasticizing consistency
Key Takeaway
Injection pressure fluctuation is caused by hydraulic system instability or plasticizing inconsistency; the hydraulic, screw, and temperature control systems need to be systematically investigated.
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