On‐line measurement of polymer orientation using ultrasonic technology

Abstract

The propagation velocity of an ultrasonic shear wave can be used to detect anisotropic behavior in the mechanical properties of a solid. Thus, an ultrasonic shear transducer imbedded in an injection mold produces a signal that is sensitive to polymer orientation. This results in a non‐invasive, on‐line technique for monitoring the orientation of polymer in an injection mold cavity during part cooling and solidification. The technique is shown to be quite sensitive for semicrystalline polymers, but much less effective for amorphous polymers. Sensor results are compared to mechanical tests.

Ultrasonic measurement of orientation in HDPE/iPP blends obtained by dynamic packing injection molding

“…That is, when HDPE forms the matrix, HDPE chains are oriented along flow direction and when iPP forms the matrix, iPP chains in parent lamella are oriented along flow direction while chains in daughter lamella are perpendicular to flow direction. The remaining question is how we understand that V p is always lower than V v in oriented HDPE matrix, which is contrary to the propagation behavior in oriented LDPE sample [19]. A very low crystallinity and orientation exists in oriented LDPE due to its highly branched structure.…”

“…Edwards et al used tensile property to verify the ultrasound data and some conflicts between the ultrasound data and tensile strength was mentioned in Ref. [19]. In our work, since PP and HDPE are crystalline, 2D-WAXS was preferentially chosen for comparison, and the consistency of the ultrasound data with 2D-WAXS was observed.…”

“…Edwards et al [19] demonstrated a technique using a normal incident shear wave transducer to measure the orientation in injection molded low density polyethylene (LDPE). They observed that the shear wave traveled in different velocities with respect to the particle displacement direction.…”

A review of current developments in process and quality control for injection molding

“…[76][77][78][79][80] It was reported that ultrasonic sensors had been employed to investigate a wide range of process characteristics such as the melting behavior of the resin in the injection barrel, temperature and pressure variation in the nozzle, melt-front flow inside the cavity, cavity pressure, solidification behavior in the cavity, polymer orientation, and some quality responses such as part dimension.…”

An in‐process ultrasonic approach to investigating the relaxation of orientation and disorientation of polymer melts

“…These are off-line methods and cannot provide a continuous observation on the sample during melt deformation. The degree of orientation of injectionmolded parts at the solidification stage has been studied by using ultrasonic shear wave transducers [16,17]. Again, the method only applies to solid samples.…”