Transactions of the Institute of Measurement and Control

Real-time, non-intrusive and non-destructive process monitoring of micromoulding has been performed using novel ultrasonic sensors integrated onto the barrel and mould insert with an ultrasonic pulse-echo technique. The relative variation of the polymer melt temperature inside the extrusion barrel can be obtained using the ultrasonic velocities of the melt measured at the barrel during extrusion. Melt flow arrival in the mould, and solidification, shrinkage and detachment of the polymer inside the mould cavity are also successfully monitored. The presented ultrasonic sensors and technique enable optimizing the micromoulding process, and improving quality of the moulded parts and process efficiency.

A fluorescent probe molecule, Nile blue perchlorate, was used to monitor the compounding of nylon 11 with clay filler. Prior to compounding, Nile blue was incorporated into the gallery region between silicate layers of the clay by an ion-exchange process. While residing in the gallery, fluorescence from Nile blue was quenched because of fluorescence resorption in a high dye concentration environment. However, when clay is compounded with the nylon, clay exfoliation allowed the dye to escape the gallery region and to become dispersed in the resin matrix. During batch mixing, we observed that fluorescence increased with time indicating that dye molecules were migrating from the gallery. Experiments carried out using a twin-screw extruder to compound resin and clay showed that twin-screw compounding was much more efficient in producing clay exfoliation than was the batch mixer.

In-line monitoring of the reaction extent of polyurethane during a reactive injection moulding (RIM) process is carried out using fibre-optic near infrared (NIR) spectroscopy. Up to 250 transmission spectra are recorded during the reaction. Univariate and multivariate analysis of transmittance spectra were used to calculate the chemical conversion. A good agreement is observed between first principal component of principal component analysis (PCA), and univariate (Beer—Lambert) results. It is observed that, in this case, the PCA method can provide a good practical estimation of the time-concentration profile during the reaction, without the need of the time-consuming calibration methods. The scores of PC1 are merely linearly correlated to the level of conversion and contain enough information for the quantitative analysis. As expected interactions and hydrogen-bonding play an important role. Hence the spectral region of PCA analysis has to be carefully selected to obtain a good agreement with the Beer—Lambert law. The NIR spectroscopy and the PCA are easy-to-use techniques for on line monitoring of polyurethane reactions and these results open up a low cost effective opportunity for monitoring the fast RIM process.

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.

Over the last decade, there has been an increased drive in the polymer industry toward the development of in-line monitoring techniques for analysis of melt processing. Manufacture of high material volumes combined with stringent quality-control restrictions and the requirement for tailored end-user products, have made the implementation of analytical methods essential for measurement of material characteristics. This paper presents the application of a range of spectroscopic techniques for in-line analysis of polymer extrusion processes. Fourier transform near-infrared (FT-NIR), Raman and fluorescence spectroscopy have been successfully implemented as tools to monitor a range of processing characteristics including copolymer melt and additive composition, material residence time distribution and degree of polymerization. In combination with partial least squares (PLS) chemometric analysis, these spectroscopic techniques are demonstrated to be sensitive and robust tools for monitoring a wide range of chemical and physical parameters at high-temperature and pressure in a polymer-processing environment.

Owing to the complexity and inherent instability in polymer extrusion there is a need for process models which can be run on-line to optimize settings and control disturbances. First-principle models demand computationally intensive solution, while `black box' models lack generalization ability and physical process insight. This work examines a novel `grey box' modelling technique which incorporates both prior physical knowledge and empirical data in generating intuitive models of the process. The models can be related to the underlying physical mechanisms in the extruder and have been shown to capture unpredictable effects of the operating conditions on process instability. Furthermore, model parameters can be related to material properties available from laboratory analysis and as such, lend themselves to retuning for different materials without extensive remodelling work.