Injection Molding
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Roundness out of tolerance of general-purpose polyethylene injection molded products
Fenómeno do problema
The cross-section of the round product is not round, and the ovality is out of tolerance, affecting the sealing performance and fitting accuracy.
Roundness out of tolerance is common in round products such as tubular products, bottle caps, and gears, and is closely related to uneven shrinkage and cooling differences.
Análise das causas
（1）The mold cavity and core are cooled unevenly, and the shrinkage rates in different directions differ greatly
（2）General-purpose polyethylene shrinks anisotropically, and the shrinkage in the flow direction is different from that in the perpendicular direction
（3）The gate position is improper, and single-side feeding causes asymmetric molecular orientation
（4）The holding pressure distribution is uneven, and the feeding of the cavity in all directions is inconsistent
（5）The wall thickness of the product is uneven, and the shrinkage difference between thick and thin parts is large
Solução
（1）Optimize the mold cooling system, and arrange the cooling water channels of the cavity and core symmetrically
（2）Control the uniformity of the mold temperature, and the temperature difference between each part should not exceed 5°C (within the range of 30-80°C)
（3）Use multi-point gates or ring gates to make the melt fill the mold uniformly and reduce orientation differences
（4）Optimize the holding pressure scheme to ensure uniform feeding of the cavity in all directions
（5）Optimize the product design, the wall thickness should be as uniform as possible, and the inner and outer circles should be concentric
Conclusão principal
Roundness out of tolerance is caused by non-uniform shrinkage, and needs to be improved from three aspects: cooling symmetry, gate design, and wall thickness uniformity.
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