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Thermocouple grids have been shown to provide a unique insight into melt temperature fields and their time dependent behaviour in extruders. These systems have been extended from single axis designs to larger arrays for more detailed temperature measurements. Nine junction (3 × 3) arrays have provided a map of the temperature profile across the melt, and the technique has been used to assess the effect of extrusion conditions such as polymer type, screw geometry and melt pressure. The data are proving invaluable for extruder screw design and to inform more accurate computer modelling of polymer melt flows. Single axis grids have also been applied to twin screw compounding extrusion, and the results showed a significant amount of shear heating with the hottest points being along the centre line of the two screws.

An idealised model of core-out in water assisted injection moulding (WAIM) is set up to isolate the effect of cooling by the water on the deposited layer thickness. Based on simulations, this is investigated for a specific case as a function of Pearson number and power law index. It is found that cooling significantly reduces the layer thickness to the extent that a change in the flow regime ahead of the bubble, from bypass to recirculating flow, is possible. For shear thinning melts with high temperature coefficient of viscosity, the simulations show very low layer thickness, which may indicate unfavourable conditions for WAIM. Although in the real moulding situation, other effects will be superimposed on those found here, the results provide new insights into the fundamentals of WAIM. Investigation of other effects characterised by Fourier and Reynolds numbers will be reported subsequently. Some early process measurement results from an experimental WAIM mould are presented. Reductions in residu...

Process imaging of micromoulding cavity flows has been performed using a transparent mould and high speed camera system creating a powerful method of studying the flow behaviour, shrinkage and internal stresses of polymeric materials during the micromoulding process. Results of these measurements will be presented with discussion of how they may be exploited to further understand crucial process parameters and physical models. An inline optical inspection technique currently under development is described in detail, along with initial results. This system offers 100% product inspection in three dimensions for microscale features.

An ultrasound sensor system has been applied to the mould of both the water and gas assisted injection moulding processes. The mould has a cavity wall mounted pressure sensor and instrumentation to monitor the injection moulding machine. Two ultrasound sensors are used to monitor the arrival of the fluid (gas or water) bubble tip through the detection of reflected ultrasound energy from the fluid polymer boundary and the fluid bubble tip velocity through the polymer melt is estimated. The polymer contact with the cavity wall is observed through the reflected ultrasound energy from that boundary. A theoretically based estimation of the residual wall thickness is made using the ultrasound reflection from the fluid (gas or water) polymer boundary while the samples are still inside the mould and a good correlation with a physical measurement is observed.

Injection moulding techniques have been miniaturised and refined to achieve micromoulding which aims to satisfy the need for mass production of low-cost micro- and nanoscale components. However, the microscale mould cavity features and extreme processing conditions which are inherent in the process can result in larger process variations than conventional injection moulding, with a corresponding increase in the probability of producing an unsatisfactory product. Accurate process diagnosis is required to ensure process reliability but integration of sensors onto the small and highly detailed mould units can be problematic and alternatives may need to be sought. Piezoelectric film ultrasonic transducers were integrated onto the extrusion barrel and mould insert of a micromoulding machine for real-time, non-destructive and non-intrusive process diagnosis with an ultrasonic pulse-echo technique. Polymer degradation owing to excessive heating at the extrusion barrel was successfully probed by measuring the ultrasonic velocities in the polymer at the mould insert. Filling incompleteness of the mould cavity was also sensitively detected by monitoring the ultrasonic energy variation transmitted into the part at different points along the melt flow length. The developed ultrasonic sensors and technique enable optimisation and in-process quality assurance of the moulded parts which ensures that maximum process efficiency can be achieved.

Melt temperature fields have been measured in single screw extrusion using novel thermocouple grid, ultrasound and infrared sensor techniques. The effects of screw and die geometry on the melt temperature profile have been investigated using simple slit and rod dies on a single screw extruder. Comparisons have been made between a general purpose polyolefin screw with gradual melting zone, a rapid transition screw, and a barrier flighted screw with a Maddock mixer. Significant differences in melting and temperature profiles were observed between the three extruder screws. Die geometry of the simple dies studied here was found to have a minor effect on the melt temperature field in regions near the die wall. Die head pressure had a more significant effect on melt temperature distribution.

The relative effects of changes in temperature, pressure and weight percentage filler on ultrasonic velocity through static samples of magnesium hydroxide filled low density polyethylene (LDPE) melt have been determined for a range of temperatures and pressures. Ultrasonic velocity was found to be most sensitive to change in temperature and least sensitive to change in pressure. Using these data and data obtained during extrusion of unfilled LDPE, the amount of magnesium hydroxide present (weight percentage) in LDPE was determined. Values of weight percentage calculated from extrusion data were compared with values obtained from the thermogravimetric analysis of extrudate. Variations in weight percentage of filler between the two sets of data followed the same trend with time of extrusion.