Extrusion & Post
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Flash/burrs appearing in random copolymer polypropylene injection molded products
Fenómeno do problema
Thin sheet-like overflow, namely flash or burrs, appears at the product parting line, ejector pin holes, slider joints, etc.
Flash affects appearance and dimensional accuracy, increases post-processing workload, and in severe cases causes product sticking in the mold and difficult demolding.
Análise das causas
(1) Clamping force is insufficient; the mold is pushed open by melt pressure during injection, creating a gap
(2) Injection pressure or holding pressure is too high, exceeding the mold clamping force
(3) The mold parting line is worn or fits poorly, with gaps present
(4) Barrel temperature is too high; melt viscosity is low and fluidity is too good, making overflow easy
(5) Mold vent grooves are too deep; the melt overflows into the vent grooves forming flash
Solução
(1) Check and increase clamping force to ensure it is 1.2-1.5 times the melt pressure in the cavity
(2) Appropriately reduce injection pressure and holding pressure, using the lowest pressure while ensuring quality
(3) Lower barrel temperature to the lower value within the 190-260°C range to increase melt viscosity
(4) Check the mold parting line, re-grind the clamping surfaces, ensuring the gap is less than 0.02mm
(5) Check vent groove depth; vent groove depth for polyolefin materials does not exceed 0.03mm
Conclusão principal
Flash is a manifestation of mismatch between mold clamping force and injection pressure and needs to be controlled from three aspects: clamping force, injection pressure and mold precision.
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