Injection Molding
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Low tensile strength of random copolymer polypropylene injection molded products
Fenómeno del problema
The tensile strength test value of the product is lower than material standard requirements, and plastic deformation or fracture easily occurs under stress.
Low tensile strength directly affects the service life and safety performance of the product.
Análisis de la causa
(1) Melt temperature is too high; the material thermally degrades in the barrel and molecular weight decreases
(2) Screw speed is too fast; shear overheating causes molecular chain breakage
(3) Too much regrind is used; repeated thermal processing reduces molecular weight
(4) Holding pressure is insufficient, and there are shrinkage cavities or pores inside the product
(5) The product contains impurities or unevenly dispersed color masterbatch forming weak points
Solución
(1) Control barrel temperature at a reasonable value within the 190-260°C range to avoid overheating
(2) Reduce screw speed to 50-100rpm to reduce shear
(3) Control the regrind proportion to no more than 20%, and fully mix new material and regrind
(4) Increase holding pressure to 80-120MPa and extend holding time to ensure full shrinkage compensation
(5) Check raw material purity to ensure uniform dispersion of color masterbatch and additives
Conclusión clave
Low tensile strength is mainly caused by material degradation or internal defects; processing temperature, shear and regrind proportion need to be controlled.
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