An ultrasound-based system for temperature distribution measurements in injection moulding: system design, simulations and off-line test measurements in water

Abstract

The polymer melt temperature in the screw ante-chamber of an injection moulding machine influences a number of parameters during the polymer process and therefore the final product quality. For measurement of this temperature, a sensor must be non-invasive (because of the axial moved screw during the injection of the plasticized polymer into the mould) and withstand the high pressure (>1000 bar) and temperature (>200 °C) during the injection moulding process. It is well known that the temperature of the polymer melt in the screw ante-chamber is inhomogeneous, and for that reason the sensor system must be able to measure the temperature spatially resolved. Due to the fact that sound velocity is temperature dependent, we developed a non-invasive tomography system using the transit times of ultrasonic pulses along different sound paths for calculating the temperature distribution in a polymer melt. Simulation results and example experiments at a test measurement setup are shown. Moreover, different strategies for the ultrasonic probe design (buffer rods, generation of wide beam angle) are discussed. The results of the proposed system are important for the validation of numerical simulations, a better understanding of the plasticizing process and can be used for the input of a novel temperature control system.

Ultrasound Tomography for Spatially Resolved Melt Temperature Measurements in Injection Moulding Processes

“…From the pvT-relationship the bulk modulus can be calculated using the adiabatic compressibility κ (equation (13)) [8]:…”

“…In this context, an increasing importance for non-invasive measurement techniques is caused by these disadvantages. Several different research approaches were carried out in the last years, such as pyrometry [5], fluorescence spectroscopy [6] or ultrasound [7][8][9]. Recent approaches base on the use of tomographic methods to measure the local temperature distribution.…”

“…Recent approaches base on the use of tomographic methods to measure the local temperature distribution. There are two current approaches: the ultrasound tomography [8,9] and the electrical capacitance tomography (ECT) [10]. Both methods have in common that signals can be introduced into the melt from different directions.…”

“…In the case of ultrasound tomography first the distribution of ultrasound velocities is calculated based on the time of flight measurements and then the temperature field is calculated with the help of further material properties such as the bulk modulus and the shear modulus. The ultrasound tomography used in this work is based on the procedure of Praher et al [8] who suggests using ultrasound signals to measure the temperature field in the screw antechamber of an injection-moulding machine and assumed a radial symmetric temperature distribution to realise a fast temperature…”

Evaluation of Reconstruction Strategies of 3D Temperature Fields for Detecting Hotspots in Grain Bulk

“…The reconstruction of temperature fields based on acoustic tomography [1,2] uses the dependence of sound speed in materials on temperature along the sound ray path. For using this technique, several sound transmitters/receivers have to be arranged around the space of investigation such that the resulting sound ray paths cover the space as uniformly as possible.…”