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Temperature measurement using an ultrasonic sensor consisting of a piezoelectric transducer and an ultrasonic waveguide is presented. The waveguide is a clad rod consisting of a steel core and a stainless steel cladding together with two discontinuities created near the probing end. The temperature information is obtained from information about the time delay between the ultrasonic echoes reflected from these discontinuities and the probing end surface as a function of the temperature. The temperature measured ultrasonically is in good agreement with that obtained by using a commercial thermocouple.

On‐line ultrasonic monitoring of injection molding of a simple polymer box is studied using pulse‐echo techniques. The flow front of molten polymers inside the mold has been probed by a multiple‐channel probing system with a time resolution of 2 ms. This information can be used to control the plunger movements. The gap development, because of the shrinkage of the part in the mold, is also monitored. This information, which is important for the understanding of the part's cooling process, has been found to be superior than that measured by a conventional pressure probe. The relation between the gap formation time and the packing pressure has been investigated at various part locations characterized by different thicknesses. The velocity and the amplitude variations of ultrasonic waves, in a reflection as well as in a transmission configuration, have also been measured in the part's material during its solidification. The behavior of these ultrasonic parameters contributes to the interpretation of the solidification process.

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In-line ultrasonic monitoring of polymer co-extrusion and twin-screw extrusion are presented. Co-extrusion of high density polyethylene (HDPE) and a thermoplastic elastomer based on polypropylene-EPDM (ethylene-propylene-diene monomer) has been investigated by ultrasonic sensors consisting of piezoelectric transducers and clad buffer rods. One extremity of the rod (probing end) was installed flush with the die surface so as not to disturb the material flow. The other end was air cooled in order to protect the transducer from excessive heating. This approach has been demonstrated to be quite convenient for monitoring and controlling industrial material processes: first, it can work at temperatures up to 1000°C; second, the clad buffer rod probing end can be machined to the same shape as those of commercial temperature and pressure sensors commonly used in the extrusion process. Therefore, no modifications are required for the installation in the original equipment. The information obtained includes the position of the interface between polymers and the stability of the process. The same ultrasonic probe has also been installed on a barrel of a twin-screw extruder. This study was performed using polyethylene and polystyrene. It has been verified that the ultrasonic sensor can be successfully operated along the extruder screw and that the ultrasound can give access to the material properties while the polymer is being processed. This means that the technique can be exploited to monitor and control in situ the characteristics of the polymer being transformed in operations typically performed on twinscrew extruders, such as compounding, visbreaking or reactive extrusion.