Injection Molding
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Short shot/flash alternation caused by metering fluctuation in PP '2079851475616104452
Problem Phenomenon
Under the same process, short shots and flash appear alternately, the part weight fluctuates lighter and heavier, and the cushion fluctuates greatly.
Cause Analysis
Unstable hopper feeding (bridging), a high proportion of regrind, or uneven particle size causes fluctuation in screw conveying efficiency; wear or material sticking of the non-return ring causes melt backflow during injection, resulting in inconsistent actual shot volume per cycle, manifested as alternating short shots and flash.
Solution
①Check whether hopper feeding is smooth and whether hopper throat cooling is normal; ②control the proportion and particle size of regrind; ③continuously monitor cushion fluctuation (e.g., 30 shots); ④disassemble and inspect the wear and sealing of the non-return ring, replacing it if necessary; ⑤stabilize back pressure and screw speed.
Key Takeaway
When short shots and flash appear alternately, first suspect the 'metering system' (feeding and non-return ring), not the process parameters; cushion fluctuation is the most intuitive signal—stabilize it first, and the process becomes meaningful.
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