Injection Molding
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Low tensile strength of low density polyethylene injection products
Problem Phenomenon
The tensile strength test value of the product is lower than the material standard requirement, and plastic deformation or fracture easily occurs under stress.
Low tensile strength directly affects the service life and safety performance of the product.
Cause Analysis
(1) Melt temperature too high; the material undergoes thermal degradation in the barrel, molecular weight decreases
(2) Screw rotation speed too fast; shear overheating causes molecular chain breakage
(3) Excessive use of regrind; repeated thermal processing reduces molecular weight
(4) Insufficient holding pressure; shrinkage voids or pores exist inside the product
(5) The product contains impurities or unevenly dispersed color masterbatch particles forming weak points
Solution
(1) Control barrel temperature at a reasonable value within the 160-220°C range, avoid overheating
(2) Reduce screw rotation speed to 50-100rpm to reduce shear
(3) Control regrind ratio not exceeding 20%, fully mix virgin material and regrind
(4) Increase holding pressure to 80-120MPa, extend holding time to ensure sufficient shrinkage compensation
(5) Check raw material purity, ensure uniform dispersion of color masterbatch particles and additives
Key Takeaway
Low tensile strength is mainly caused by material degradation or internal defects; processing temperature, shear, and regrind ratio need to be controlled.
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