Injection Molding
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Short shot (material shortage) in PP '2079851475616104452
Problem Phenomenon
The product fails to fill at thin-wall ends far from the gate, rib tips, snap hooks, and other locations; the shortage edge is rounded and recurs at the same position.
Cause Analysis
Although PP has good flowability, thin-wall parts have long flow paths and high flow resistance, and the melt front stops flowing before reaching the end due to temperature drop, pressure loss, or trapped-air back pressure; insufficient injection speed/pressure, low melt and mold temperatures, poor venting, and wall thickness below the moldable limit all cause short shots.
Solution
①Prioritize increasing the injection speed and injection pressure; ②appropriately increase the melt temperature and mold temperature to delay front cooling; ③enlarge the gate and runner and shorten the flow length; ④improve venting at the shortage area and at the end; ⑤when the structure permits, appropriately thicken overly thin areas; ⑥switch to a high-flow grade when necessary.
Key Takeaway
For PP short shots, first check 'speed and pressure', then check 'temperature and venting', and finally evaluate structure and grade; the short-shot method (stepwise filling) can quickly locate the last fill point, avoiding flash caused by blindly raising temperature and pressure.
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