A hollow waveguide infrared thermometer for polymer temperature measurement during injection moulding

We describe a novel on-line infrared method for remote sensing of the surface and the bulk temperatures of a polymer film during injection moulding. The method may also be applied to other polymer forming processes such as extrusion and blow moulding. The key feature of the new method is the use of a hollow waveguide that is incorporated into the injection mould to transmit the thermal radiation from the target to the sensor. The main characteristic of the hollow waveguide is that it exhibits low transmission loss of the thermal energy in the mid- and far-infrared, and no end reflection. This allows measurement of quite low temperatures, as low as near room temperature. Conventional optical fibre thermometers can neither measure such low temperature ranges nor measure the polymer surface temperature. In this paper, we present the first on-line results of critical tests of the new device. A Husky injection moulding press was used for the experiments. Good correlation was found between the radiometric results and those obtained with a thermal sensor inserted near the polymer mould interface, and with infrared imaging after the polymer part was ejected from the injection mould.