Injection Molding
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Large injection pressure fluctuation in general-purpose polyethylene '2079851475616104452
Problem Phenomenon
The pressure gauge reading fluctuates greatly during the injection process, and the pressure difference within the same cycle or between different cycles exceeds ±5%.
Pressure fluctuation leads to unstable product weight, dimensions, and quality, and in severe cases short shots or flash appear alternately.
Cause Analysis
（1）The hydraulic system pressure is unstable, the hydraulic pump is worn or the hydraulic oil is contaminated
（2）The screw non-return ring is worn, and the injection amount is inconsistent each time
（3）The barrel temperature fluctuates greatly, and the melt viscosity change causes pressure fluctuation
（4）The feeding is uneven, and the plasticizing amount is inconsistent each time
（5）The screw speed is unstable, and the plasticizing quality fluctuates
Solution
（1）Check the hydraulic system, repair or replace the worn hydraulic pump, and replace the hydraulic oil
（2）Check the non-return ring, and replace it if the wear exceeds 0.1mm
（3）Stabilize the barrel temperature, and control the fluctuation of each section within ±3°C (within the range of 160-260°C)
（4）Check the feeding system to ensure smooth feeding from the hopper and stable material level
（5）Stabilize the screw speed and back pressure to ensure plasticizing consistency
Key Takeaway
Injection pressure fluctuation is caused by unstable hydraulic system or inconsistent plasticization, and the hydraulic, screw, and temperature control systems need to be systematically investigated.
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