Recent progress in on-line ultrasonic process monitoring

On-line ultrasonic monitoring of polymer co-extrusion and gas-assisted injection molding are presented. During the coextrusion of high density polyethylene (HDPE) and Santoprene ultrasonic sensors consisting of piezoelectric transducers and clad ultrasonic buffer rods are used to detect the interface between these two polymers and the stability of the extrusion. The same ultrasonic sensor also measures the surface temperature of the extruded polymer. The results indicate that temperature measurements using ultrasound have a faster response time than those obtained by conventional thermocouples. In gas-assisted injection molding the polymer and gas flow front positions are monitored simultaneously. This information may be used to control the plunger movement.