Injection Molding
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Flash on PP '2079851475616104452 (burrs)
Problembeschreibung
Thin flake-like excess material appears at the parting line, ejector pin holes, and the mating areas of sliders and inserts, requiring manual trimming and affecting assembly and appearance; in multi-cavity molds it often appears as flash in some cavities.
Ursachenanalyse
PP melt has low viscosity and good flowability, so during high-pressure filling it very easily penetrates into the tiny mating gaps of the parting line and moving components; excessive injection/holding pressure, insufficient clamping force, a worn or contaminated parting line, and excessive mating clearance all induce flash.
Lösung
①Reduce the injection/holding pressure by 5%~10% each time and observe; ②calculate the clamping force based on the projected area; ③appropriately lower the melt temperature to increase viscosity without overheating; ④clean and repair the parting line, and check the mating clearances of ejector pins/sliders; ⑤in multi-cavity molds, investigate individual cavity overfilling caused by filling imbalance.
Wichtigste Erkenntnis
For PP flash, first 'do subtraction' on the process (reduce pressure, reduce temperature), then 'fill the gaps' on the mold (repair fits, increase clamping); adding clamping force right away regardless of pressure easily crushes the vents and accelerates mold wear.
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