Injection Molding
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Large weight fluctuation of homopolymer polypropylene injection products
Problem Phenomenon
Product weight is unstable in continuous production from the same mold, fluctuating more than ±2%.
Weight fluctuation reflects process instability, directly affecting dimensional accuracy and mechanical property consistency, especially critical in precision injection.
Cause Analysis
(1) Screw non-return ring worn or damaged, inconsistent injection amount each time
(2) Unstable plasticizing back pressure, melt density fluctuation
(3) Large barrel temperature fluctuation, melt density changes with temperature
(4) Unstable injection speed, hydraulic system pressure fluctuation
(5) Discontinuous raw material supply, bridging at the feed opening or unstable material level
Solution
(1) Check the screw non-return ring; replace if wear exceeds 0.1mm, ensure consistent injection amount each time
(2) Stabilize back pressure at 5-8MPa, back pressure fluctuation not exceeding ±0.5MPa
(3) Stabilize barrel temperature, control fluctuation of each zone within ±3°C (200-280°C range)
(4) Check hydraulic system pressure stability, repair hydraulic pump and valves when necessary
(5) Ensure smooth feeding, install magnetic grate on the hopper to prevent metal impurities, avoid bridging
Key Takeaway
Weight fluctuation is caused by unstable plasticizing and metering; it needs to be solved from screw non-return ring, temperature control, and hydraulic system stability.
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