K. T. Nguyen

Temperature measurement of polymer extrusion by ultrasonic techniques

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 a die-casting process using buffer rods

On-line ultrasonic monitoring of die casting of an aluminum plate with steps of different thicknesses is studied using pulse-echo techniques. Clad buffer rods are inserted into the die wall for the monitoring. The flow front of molten aluminum inside the die has been probed by a two-channel acquisition system with a time resolution up to 1 ms. This information may be used to control the plunger movements. The gap development, due to the shrinkage of the part in the die, and the part solidification are also monitored for the understanding of the cooling process. As expected, it is observed that thicker sections take longer to solidify. The die wall temperature variation derived from the changes in ultrasonic travel time in the buffer rod is also observed.

Recent progress in online ultrasonic process monitoring

On-line ultrasonic monitoring of polymer co-extrusion and gas-assisted injection molding are presented. During the co- extrusion of high density polyethylene 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 thermocouple. 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.

Optimization of cooling channel design and spray patterns in aluminum die casting using infrared thermography

A protocol for infrared thermal analysis of die surfaces is proposed. The most suitable infrared camera has a spectral response in the 8 - 10 micrometer of the infrared spectrum as the emissivity is higher and more uniform across the surface of the die than in the 3 - 5 micrometer region of the spectrum. Through the prudent use of shielding, die surface temperatures can be measured, thermal gradients are detected, the effectiveness of cooling lines can be evaluated and spray patterns are optimized. The technique is not suitable for examining aluminum parts as the emissivity of aluminum is low and the optical properties of the surface oxide layer change as the part cools.

Ultrasonic temperature determination during industrial materials processing

Two technologies for measuring temperature with ultrasound during the processing of materials are presented. Both methods use clad buffer rods. These approaches present the great interest of being able of providing, in addition to the temperature measurement, the simultaneous monitoring of other parameters of the material being processed such as its elastic properties. The first method uses clad buffer rods with two steps machined at the probing end contacting the material being processed. The ultrasonic time delays in the two regions which are between the rod end and the first step, and between the first and the second step can be calibrated versus temperature variation. The measurement of these time delays during material processing, associated with a conduction heat transfer model provide an accurate temperature at the probing end. For molten zinc processing at temperature ranging between 350 and 700 °C, good agreement was obtained between the temperatures measured ultrasonically and those measured by ...