MOLTEN STATE OF THERMOPLASTIC RESIN IN AN INJECTION MOULDING BARREL

In recent years, polymer products have required superior mechanical properties, a particular strength and dimensional accuracy. One of the most popular moulding methods for polymer materials is injection moulding. Compared to other moulding methods, injection moulding is better at making complicated shapes quicker; however, injection moulding suffers from many kinds of moulding faults. Various solutions to reduce the number of faults on a production line have been developed as a result of many years of studies. However, to further decrease the number of faults, researchers need to focus on the basic state of the plasticized resin. In injection moulding, it is important to determine how uniformly a resin is melted because the uniformity of temperature is related to the characteristics of a product. Therefore, melting completion does not mean that resin is uniform. The uniformity of melting must be accurately determined to achieve high quality. First, this study uncovers some effects of screw behaviours on plasticization. The injection moulding machine performs the metering and injection processes with the screw in the barrel. In the metering process, the screw retreats to the metering stroke while maintaining back pressure. In the injection process, the screw advances to the tip of the nozzle. While the screw repeats these movements, the pellets are provided from the hopper to the moving screw. This method of adding the pellets creates differences in the distance that the resin must travel within the screw channel. The longest distance that the resin must travel during an injection cycle is equal to the metering stroke. The viscosity of the resin depends on the barrel temperature, although the viscosity is also influenced by other moulding conditions. An experiment is performed by changing the metering stroke and the barrel temperature. To understand the condition of the resin just before the injection, an original nozzle with a pressure sensor is produced. Thus, the injection pressure waveform can be recorded during each cycle. As changes in the waveform are reflected in the behaviour of the resin, a non-uniform temperature can be visually confirmed by a disturbance in the waveform.