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Extrusion
| Get the right machine As with injection moulding, using large extruders for small profiles wastes energy and costs money. It is often possible to switch extruder motors to match the size of the job. This is sometimes a cost-effective operation if the cost of changing the motor is less than the extra energy used. AC motors and VSDs Extrusion costs can be reduced by replacing DC motors with high efficiency AC motors and VSDs. The energy savings will be in the region of 4% but the main advantages are the increased reliability, decreased maintenance load and ease of motor replacement. Motor sizing Check the loading on extruder motors and modify gear ratios to optimise the energy usage. Extruder motor gear ratios can be managed to optimise the motor load and maximise energy efficiency. Where belt drives are used then replacing the standard V-belt drives with toothed belts can give 2-3% energy savings. Insulation Barrel insulation in extrusion is not generally needed and can lead to a ‘runaway process’ because shear heating should supply most of the heating load. Shear heating is also much more energy efficient than electrically applied heating. In most cases, extruders will need barrel blowers to remove excess shear heat generated. It is important to check the heating and cooling controls to make sure that heating and blowing are not fighting one another. Insulation is cost effective in areas where shear heating is low such as the first zone where the incoming material absorbs a lot of heat and for most areas forward of the screw tips where there is little shear heating. Areas forward of the screw tips suitable for insulation include:
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