Extrusion & Post
7 مشاهدة
Undersized Dimension Below the Lower Limit of High-Density Polyethylene Injection-Molded Products
ظاهرة المشكلة
The actual dimensions of the product are smaller than the lower tolerance limit of the drawing, making assembly difficult or impossible.
Undersized dimensions are usually related to excessive shrinkage, and are especially common in thick-walled products or high-crystallinity materials.
تحليل الأسباب
(1) The holding pressure is insufficient or the holding time is too short, and insufficient shrinkage compensation leads to large shrinkage
(2) The mold temperature is too high, and the high crystallinity of high-density polyethylene leads to large post-shrinkage
(3) The barrel temperature is too high, the melt density is small, and the volume shrinkage is large
(4) The cooling time is insufficient, and the product continues to shrink after demolding (post-shrinkage)
(5) The gate solidifies too early, and the holding pressure cannot be transmitted to the cavity
الحل
(1) Increase the holding pressure to 80-120MPa and extend the holding time to 15-25s
(2) Appropriately reduce the mold temperature to the lower value within the range of 30-80°C
(3) Appropriately reduce the barrel temperature to the lower value within the range of 180-260°C
(4) Extend the cooling time to ensure the product is fully cooled and shaped
(5) Increase the gate size and prolong the gate freezing time
الخلاصة الأساسية
Undersized dimensions are caused by excessive shrinkage, and the shrinkage needs to be controlled by strengthening the holding, lowering the temperature, and extending the cooling time.
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