Extrusion & Post
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Flash/Burrs Appearing on Low-Density Polyethylene Injection Molded Products
Problembeschreibung
Thin sheet-like overflow appears at the product parting line, ejector pin holes, slider joints, etc., i.e., flash or burrs.
Flash affects the appearance and dimensional accuracy, increases the post-processing workload, and in severe cases causes the product to stick in the mold and makes demolding difficult.
Ursachenanalyse
（1）The clamping force is insufficient, and the mold is stretched open by the melt pressure during injection, producing a gap
（2）The injection pressure is too high or the holding pressure is too large, exceeding the mold clamping force
（3）The mold parting line is worn or does not fit well, and there is a gap
（4）The barrel temperature is too high, the melt viscosity is low and the flowability is too good, and it is easy to overflow
（5）The mold vent grooves are too deep, and the melt overflows into the vent grooves to form flash
Lösung
（1）Check and increase the clamping force to ensure the clamping force is 1.2-1.5 times greater than the melt pressure in the cavity
（2）Appropriately reduce the injection pressure and holding pressure, and use the lowest pressure on the premise of ensuring quality
（3）Reduce the barrel temperature to a lower value within the 160-220°C range to increase the melt viscosity
（4）Check the mold parting line, re-grind the clamping surfaces, and ensure the gap is less than 0.02mm
（5）Check the vent groove depth; the vent groove depth of polyolefin materials does not exceed 0.03mm
Wichtigste Erkenntnis
Flash is a manifestation of the mismatch between the mold clamping force and the injection pressure, and needs to be controlled from three aspects: clamping force, injection pressure, and mold precision.
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