Advances in infrared technology 011 for the online monitoring of injection moulding: application to the understanding of the nature of contact at the polymer-mould interface

We describe a novel online infrared method for remote sensing of the surface and the bulk temperatures of polymers 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 optical fibre that is incorporated into the injection mould to transmit the thermal radiation from the target to the sensor. The main characteristic of the hollow optical fibre 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 article, we present the first online 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 probe inserted near the polymer-mould interface, and with infrared imaging after the polymer part was ejected from the injection mould. In the second part of the paper, we show how the new infrared device can be used to give a better insight on the time evolution of the thermal contact between polymer and mould through the different phases of a typical injection moulding cycle. The experimental results show that thermal contact between polymer and mould is not negligible and not constant with time.