Extrusion & Post
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Flash/burrs on homopolymer polypropylene injection products
Fenómeno del problema
Thin sheet-like overflow, i.e., flash or burrs, appears at the parting line, ejector pin holes, slider joints, etc. of the product.
Flash affects appearance and dimensional accuracy, increases post-processing workload, and in severe cases causes mold sticking and demolding difficulty.
Análisis de la causa
(1) Insufficient clamping force; the mold is pushed open by melt pressure during injection, creating gaps
(2) Injection pressure too high or holding pressure too large, exceeding mold clamping force
(3) Mold parting line worn or poorly fitted, gaps exist
(4) Barrel temperature too high; low melt viscosity and excessively good flowability, easy to overflow
(5) Mold vent grooves too deep; melt overflows into vent grooves forming flash
Solución
(1) Check and increase clamping force, ensure clamping force is 1.2-1.5 times the melt pressure in the cavity
(2) Appropriately reduce injection pressure and holding pressure, use the lowest pressure while ensuring quality
(3) Reduce barrel temperature to the lower value within the 200-280°C range, increase melt viscosity
(4) Check mold parting line, re-grind the mating surfaces, ensure gap less than 0.02mm
(5) Check vent groove depth; polyolefin material vent groove depth not exceeding 0.03mm
Conclusión clave
Flash is a manifestation of mismatch between mold clamping force and injection pressure; it needs to be controlled from clamping force, injection pressure, and mold accuracy.
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