Injection Molding
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Low Tensile Strength of High-Density Polyethylene Injection-Molded Products
Problem Phenomenon
The tensile strength test value of the product is lower than the material standard requirement, and it is prone to plastic deformation or fracture when stressed.
Low tensile strength directly affects the service life and safety performance of the product.
Cause Analysis
(1) The melt temperature is too high, the material thermally degrades in the barrel, and the molecular weight decreases
(2) The screw speed is too fast, and shear overheating causes molecular chain breakage
(3) Too much regrind is used, and repeated thermal processing reduces the molecular weight
(4) The holding pressure is insufficient, and there are shrinkage cavities or pores inside the product
(5) The product contains impurities or the color masterbatch is unevenly dispersed, forming weak points
Solution
(1) Control the barrel temperature at a reasonable value within the range of 180-260°C to avoid overheating
(2) Reduce the screw speed to 50-100rpm to reduce shear
(3) Control the regrind ratio to not exceed 20%, and fully mix the new material and the regrind
(4) Increase the holding pressure to 80-120MPa and extend the holding time to ensure full shrinkage compensation
(5) Check the purity of the raw material to ensure uniform dispersion of the color masterbatch and additives
Key Takeaway
Low tensile strength is mainly caused by material degradation or internal defects, and the processing temperature, shear, and regrind ratio need to be controlled.
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