Ultrasonic monitoring of materials during extrusion manufacture

In this paper we present a new method to monitor polymeric materials as they are being extruded. The ultrasonic technique makes use of both thru-transmission and backscattered signals from sensors that do not contact the extrusion. A novel aspect of the approach is the use of the liquid inherent within the heated polymer to provide coupling of the ultrasonic waves. Initial experiments have been conducted on extrusions of energetic polymers used in solid rocket motors. A number of extrusions were "seeded" with flaws to test the sensitivity of the ultrasonic system. These extrusions were later characterized by off-line radiographic tests. Comparisons of these two tests indicate that the on-line ultrasonic technique agreed with the baseline radiographic measurements for 83% of the extrusions. The technique provides good sensitivity to all flaw types. Our goal is to provide quality information on the motor extrusions at an early stage in the manufacturing process