MACHINERY | EXTRUDER DEVELOPMENTS
Potential benefits of direct drive-based extruders Combined motor/gearbox
Cost/energy efficiency
Friction losses caused by wear-based mechanical components. Fan motors
often used for climate control. High cost due to maintenance intervals
Running noise Space requirements
Service, maintenance, assembly
Increased noise due to gearbox. Fan motors often have extra energy demand Combined motor/gearbox needs a lot of installation space
Regular maintenance intervals needed. Limited service life of gearbox. Use of numerous components complicates assembly
an extrusion plant throughout its life cycle and make compact machine design possible. The market standard is a motor/gearbox solution using an efficient AC motor, but the real potential for efficiency is offered by torque motors. Torque drives further boost efficiency because gearbox losses are eliminated. Force is transmitted to exactly where it is
required. The motors are fully integrated into the machine with no mechanical transmission elements such as gears. It provides maximum torque at very low speeds. The omission of gearbox, coupling and belts leads to a more compact engineering design of the machine and reduces maintenance.
Other factors HDPE rheology affects the thermal efficiency of single screw extrusion, as do processing conditions – such as variation in radial melt temperatures across the die flow path, screw geometry, screw rotation speed, set temperature and polymer viscosity. Bulk temperature and the magnitude of temperature fluctuations increases with increasing melt viscosity. Specific Energy consumption depends on polymer melt viscosity, and its effect on the efficiency of the extrusion process and melt quality has been clearly shown. These results highlight the importance of careful selection of processing conditions and extruder screw geometry on melt homogeneity and process efficiency. The influence of material grade and quality can account for up to 15% of specific energy consumption.
Energy monitoring An important factor behind optimising energy consumption is energy monitoring – which means recording energy streams and calculating the specific energy consumption per kg produced. In this way, the manufacturer has a final value that can
34 PIPE & PROFILE EXTRUSION | July/August 2018
Motor operates with almost no noise, and uses no gearbox. Integrated water cooling Assembly kit solution enables high level of integration, and allows compact design Very low maintenance costs. Long service life of motors. Almost oil-free system. Simple assembly and logistics, as few components needed
be used to get a clear overview of the process and energy input. A plastics company that processes 20,000 tonnes of material will have an electricity bill of approximately €2m. Simple no-cost or low-cost energy reduction practices can reduce this by a minimum of 5% (and by up to 10%) – and so increase profits. This is the equivalent of adding sales of €100,000 – and is a worthwhile investment by any standards. For instance, if an extruder with poor screw design (which runs at 0.28 kWh/kg) is switched for one with a good screw design (at 0.24 kWh/kg), energy savings will be nearly €26,000/year – based on an energy cost of €0.09/kWh, and throughput of 1,000 kg/hr (2200 lbs/hr) running 24 hours/day and 300 days/year. Faced with rising energy costs, energy efficiency should be a crucial issue in manufacturing. A few factors are worth considering: n The cost of energy used during a machine’s life often exceeds its initial purchase cost. Energy efficient machines (η > 80% as class 1) and controls may cost more at the start, but will cost less in the long term.
n As with any capital equipment, initial purchase cost should not dominate decision-making.
n The ‘whole life’ cost of the equipment (initial cost + operating costs) is critical for any plastics processor who wants to continue operating in the long term. Pipe extrusion is highly dependent on electricity
– and purchasing energy-efficient capital equipment will permanently change a company’s overall performance.
n Massimiliano Fenili is technical manager at Tecnomatic in Italy �
www.tecnomaticsrl.net
www.pipeandprofile.com
Direct drive solution
Increased overall efficiency through reduced frictional losses
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