Injection Molding
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Flatness out of tolerance of general-purpose polyethylene injection molded products
Fenómeno del problema
The flatness of large flat plate products exceeds the tolerance requirements, and the surface shows undulations or bending.
Flatness out of tolerance affects product assembly and appearance, and is especially prominent in large-area thin-walled products.
Análisis de la causa
（1）General-purpose polyethylene crystalline material shrinks inconsistently in all directions, which is more pronounced on large flat surfaces
（2）The mold cooling is uneven, and the cooling rates of each part of the large flat surface differ
（3）The wall thickness of the product is uneven, and the distribution of reinforcing ribs is asymmetric
（4）The gate position is improper, and the single melt flow direction leads to anisotropy of orientation shrinkage
（5）The cooling time is insufficient, and the product continues to shrink and deform after demolding
Solución
（1）Optimize the mold cooling system, the cooling water channels in the large flat area are evenly distributed, and the temperature difference does not exceed 5°C
（2）Optimize the product design, the reinforcing ribs are symmetrically arranged, and the wall thickness is uniform
（3）Use multi-point gates or fan gates to make the melt flow uniformly and reduce orientation differences
（4）Extend the cooling time to ensure that the product is fully cooled before demolding
（5）Appropriately raise the mold temperature to the higher value within the range of 30-80°C to reduce internal stress
Conclusión clave
Flatness out of tolerance is a manifestation of uneven shrinkage of large-area products, and it is necessary to control the uniformity of shrinkage in all directions by optimizing cooling, gates, and product design.
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