Three massive aluminium extrusion presses at Alcoa in Hannover depend on Unidrive SPM variable speed drives from Control Techniques which have yielded a claimed increase in throughput of 10% and cut energy consumption by 40%, saving thousands of kilowatt hours of energy every year.
The two biggest extrusion lines, both using the indirect extrusion process, accept billets of aluminium alloy at around 265 and 412 mm diameter and lengths between 400 and 1350 mm, pre-heated to between 300 and 550°C. These billets are then extruded through two high-pressure extruding presses at 56 MN and 33 MN respectively. Both extruders are hydraulically-powered, with the oil pressure being generated by pumps controlled by Control Techniques’ AC drives.
The big press line was first to be upgraded, requiring the installation of twelve 132 kW Unidrives (for 12 pumps), to produce the required maximum pressure of 315 bar. Subsequently the 33 MN line was similarly upgraded with variable speed drives. This time the drives chosen were six 160 kW Unidrive SPM modular drives, producing an oil pressure of 250 bar.
The operation runs around the clock, 365 days a year and so the latest installation was carried out with the line in full operation.
"In both cases, the savings are considerable," explains Herr Stefan Heine, who has responsibility for technical operations and purchasing at the Alcoa plant.
"The original hydraulic plant was designed to give the required thrust with excess oil being sent through a by-pass - so effectively the pumps were running at full speed all the time. Now the variable speed drives integrate with the hydraulic controller using Profibus and give exactly the required power at every stage of the operation. Not only does this save some 40% of the power, but also gives better control, giving improved quality of extrusions. But this is just part of the story. Because the plant (the valves, pumps, pipes and seals) is less stressed, equipment is less susceptible to breakdown and I believe that our throughput has increased by around 10% because of reduced downtime. The oil lasts longer too - a not inconsiderable saving when you consider that the machine incorporates some 15000 litres of oil and 6000 litres passes through the system during each extrusion (this is then cleaned and returned)."
The savings run to thousands of euro per year and have given Alcoa a payback of less than 18 months.
The Unidrive SPM range spans 90 kW to 1,9 MW and comprises compact and innovative I/O modules that enable flexible power configurations to be achieved. Multiple systems such as at Alcoa are mounted on an interconnected DC bus that allows circulation of energy between drives that are motoring and regenerating and also allows regenerated energy to be returned to the mains. Drives can share braking duty and the whole installation requires a single AC power supply, simplifying installation.
The 38 MN extrusion press produces some 800-900 tonnes of aluminium extrusions per month, in a wide range of profiles including stars and tube down to less than 10 mm with wall thicknesses down to 2 mm. Single extrusions can be as long as 45 m in length and the fastest extrusion rate is 15 m per minute.
Each billet is ultrasonically tested and carefully heated to a point just below its 'plastic' state. This depends on the exact composition of the alloy. During the high pressure extrusion process, the pressure takes the material up to the required plastic state, but no further, in order to maintain the structural integrity of the material. Every extrusion is stretched, cut-to-size, 'aged' in an ageing furnace, then tested for hardness, tensile strength and conductivity. It then passes through three-coordinate measurement testing before being approved for delivery.
The Alcoa plant uses Control Techniques' drives for conveyors, fans, pumps, pullers, cut-to-length machines, run-out tables and many other applications.
"We particularly like the modular Unidrive SPM drives," comments Heine. "They are extremely compact and easily fitted into our plant room. We routinely use SmartCards to speed up the setting of parameters when we install a new drive. Most of the drives in our plant are connected by Profibus to the factory management system."
For more information contact Bill Tedd, Control Techniques Southern Africa, +27 (0)11 462 1740, [email protected], www.controltechniques.com
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