Injection Molding
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POM local discoloration trapped air burning
Problembeschreibung
Local scorched blackening appears at the end of the material flow or at the junction of ribs, and the scorch mark position changes accordingly after adjusting the injection speed.
Ursachenanalyse
Poor mold venting causes the air in the cavity to be adiabatically compressed and heated, making the resin there overheat and decompose; when the injection rate is too high, the compression heat is more concentrated and the burning is more severe.
Lösung
①Open vent grooves on the mold to improve venting; ②reduce the injection rate; ③add vents at weld lines and last-fill areas; ④check and clear existing vent grooves.
Wichtigste Erkenntnis
The root cause of local burning is adiabatic compression of trapped air; venting design and injection speed are the two major adjustment means, and vent groove depth must be opened according to POM characteristics specifications.; after confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence
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