The choice of injection unit size therefore has a considerable influence not only on moulded part quality, but also on energy consumption. The highest possible utilisation of the injection unit in relation to its maximum material throughput is decisive for a high degree of efficiency and energy conservation.
The maximum material throughput provides information on the melting capability of an injection unit up to which optimum melt preparation is ensured. The screw pitch volume and the material-specific
dwell time in turn are determining factors for the melting capability. Dwell time can be understood as the time that passes from when a grain of granulate enters the plasticising cylinder to when it exits through the nozzle. The dwell time specific to plastic ranges from approx. 30 to 600 seconds for standard plastics and 60 to 600 seconds for technical plastics. This defines the limit values for maximum possible and minimum necessary melting capability of an injection unit. However, it is recommended not to use the full melting capability of an injection unit, but rather to utilise the optimum working range between 20 and 80 per cent of the total capacity.

Based on material throughput, it is also very easy to determine which injection unit sizes come into question (graph, top). The material throughput of a specific application is dependent on the shot weight and cycle time of the injection process. As illustrated by the lower graph indicating specific energy consumption, efficiency can be improved by a factor of four or more by observing these recommendations.

The higher the utilisation of an injection unit, the greater its efficiency and the lower the specific energy consumption. High utilisation of the injection unit is helped by short cycle times (example: packaging item). Applications with long cycle times, for example, necessarily result in a higher specific energy consumption (example: thick-walled optical parts).
In order to ensure the greatest possible flexibility when adapting the machine size to the injection process, ARBURG offers a comprehensive catalogue of modular machine elements and technologies. Of particular interest here are the varied combination options with regard to clamping units (clamping forces and distances between tie bars) together with injection units and drive technologies. In this way, an ideal combination in terms of energy can be put together, even under unfavourable conditions. This flexibility is particularly useful where the required machine size does not allow for a fully-electric and consequently energy-optimised drive.
However, besides the injection moulding machine, moulds and temperature control devices also exert considerable influence on the energy consumption of an injection moulding process. For example, when moulds have temperature control, it is extremely important to provide appropriate insulation for the mould. Otherwise, as with a poorly insulated house, large quantities of heat will simply be discarded, unutilised, around the injection moulding machine or into the environment. Insulation measures on hot runners also help to save energy. Another important point is that temperature control devices must be designed for the moulds’ specific temperature requirements.