Feature Drives & Controls
pened in 2004, the recycling plant converts discarded plastic into high density polyethylene (HDPE) pellets, which are used for manufacturing a range of heavy duty products such as civil engineering pipes, marine buoys, equipment for the agricultural and construction sectors and artificial grass.
Going greener with AC drives O
A plastic recycling plant has reduced its maintenance costs after it replaced the DC drive on the critically important compounder with a variable speed AC system. Mitsubishi Electric pick up the story
The motor driving the main com- pounder, like all DC motors, required regular maintenance for brush wear and refurbishment of the armature. This proved to be a major task that was also disruptive to production, so the site engineers decided to explore possibili- ties for switching to a brushless AC motor and asked Newton Tesla (Electric Drives) for some specialist support. This Warrington-based company specialises in supplying large drive packages, usu- ally up to 1,000kW and based on an AC motor and inverter to give variable speed capability. Newton Tesla engineers developed a proposal that would provide the neces- sary low speed torque operating charac- teristic, while the reliability reduced the regular maintenance requirement.
Savings across the board “We included a Mitsubishi inverter in the design, as this would contribute to a substantial reduction in power con- sumption and would further enhance the environmental credentials of the recy-
The recycling plant (right) opened in 2004 and converts discarded plastic into high density polyethylene (HDPE) pellets (below), which are used for manufacturing a range of heavy duty products
cling plant,” recalled George Newton, managing director of the drives engineer- ing company. “And of course there were significantly reduced energy bills as well as the maintenance savings.”
Newton also recalled that tradition-
ally, DC solutions were used for low speed applications, such as com- pounders and extruders, but as inverter technology has developed AC has moved more and more into favour. He said, “The AC drive package we proposed would require no ongoing maintenance work other than routine bearing lubrication.” Newton paired a 400kW 6-pole motor with an 866A inverter as the core of the drive system - the latter being a 740 series Mitsubishi Electric variable frequency unit.
The 740 inverters are often referred to as ‘pump and fan drives’, as this is a major application area for them. However, they are equally appropriate for other duties, where their ability to enhance the energy balance of the driven machine can generate energy savings of 60% or more.
“If there is a volumetric flow involved - of air, gas, liquid or molten plastic - energy savings are proportional to the cube of the difference between operating speed and maximum speed,” Newton explained. “A compounder or extruder runs way below its maximum speed the vast majority of the time, so the energy savings are considerable.”
Compact worm gear drives
an improved oil seal design for reduced maintenance requirements. The reducers are available in a range of sizes and offer a compact design. The design follows Tsubaki’s €co & Eco philosophy which embraces economy and ecology to deliver products which offer high performance with reduced total life costs. Tsubaki has developed a range of modular prod- ucts which allows users to customise the products to meet the application requirements precisely - ensuring a compact and efficient solution. Starting with the compact base unit, a choice of input and output shaft types can be selected followed by the shaft and mounting style required by each situation. The Troi Drive and Worm Power Drive products employ a worm gear to wheel configuration which enables them to provide a high reduction ratio - gener- ally 1:10 to 1:60, with a self locking ability. Reduction ratios of 1:100 to 1:3,600 are also available by select- ing a double reduction drive. Because the power is
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subaki Europe has launched a new range of Troi Drive and Worm Power Drive reducers which feature
transmitted through a regular sliding contact, the use of a worm gear results in low vibration and noise, even when dealing with high torque loads. The enhanced design means that the entire range is able to provide increased power when compared to competitor prod- ucts of the same size. This means that smaller units can be specified for a compact and efficient solution. The smaller, compact design of the Worm Power Drive range is capable of producing an output torque from 12Nm up to 5,700Nm. It is available with either solid or hollow output shafts with a range of mounting options, making it suitable for a variety of applications. Improvements to the oil seal design on both the input and output shafts has dou- bled the life of the oil seals. Additionally, the envi- ronmental credentials have been improved by changing the paint process to electrostatic baking and by removing the use of paint thinners. The larger, Troi Drive TD series reducer uses a drum shaped troidal worm gear, which provides premium performance and efficiency. Solutions are
Additional savings are made possi- ble by Mitsubishi Electric’s OEC (Optimum Excitation Control) technol- ogy. This system ensures that the opti- mum magnetic flux is always applied to the motor, thus reducing losses. The result is maximum utilisation of motor capacity at maximum efficiency. “Energy prices have gone up and up in recent years and are expected to con- tinue to do so. Any plant operator still using DC drives is well advised to think about swapping to an inverter fed AC solution,” advised Newton. “This will produce immediate savings in power bills, reduce maintenance and can be integrated with plant wide energy man- agement controls systems.”
Mitsubishi Electric
automation.mitsubishielectric.co.uk T: 01707 276 100
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available in medium to large sizes (125-315), with both solid or hollow output shafts, and output torques from 1,100Nm up to 47,000Nm. The Troi Drive reducers can deliver the same output, but from a unit two frame sizes smaller - a significant benefit with the trend for more compact equipment. Tsubakimoto Europe
tsubaki.eu T: +31 078 620 4000
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