Ultrasonic device and methodology for in-process detection of filler concentration in the plastic injection molding process

Raw material variations constitute a significant source of processing problems in injection molding operations. Variations caused by contamination, moisture content, regrind levels, lot-to-lot variations, and filler concentration can significantly affect the performance and efficiency of the injection molding process. In addition, the more stringent quality requirements of today's products reduce the levels of tolerable variations in the material properties. Therefore, it is of vital interest to the industry as a whole to develop sensors which directly measure the intrinsic material properties in-line.; An in-line ultrasonic, material variations sensing system, has been developed in this work. A proprietary device, efficiently couples standard ultrasonic transducers to the nozzle of injection molding machines. The device protects the transducers from the high temperature and pressure without disturbing the flow. The transducer is used in pulse echo mode to inject ultrasonic waves into the polymer residing in the nozzle and receive the echoes returning from the back wall. The reflected waves are captured and analyzed by a high speed wave form digitizer and a computer. The speed of sound and attenuation of the waves are used to detect the physical properties of the polymer such as, filler concentration and uniformity. Further analysis of the ultrasonic waves may yield valuable information regarding the viscosity, filler particle size and dispersion along with other pertinent physical properties.