FEATURE BEARINGS MAGNETS LIFT BEARING PERFORMANCE
Magnetic bearings, once the domain of demanding, high-cost applications, are finding their way into mainstream use, as technical advances make them a robust, effective alternative to some traditional bearing configurations. Phil Burge, marketing and communications manager at SKF, explains...
Now, recent technical advances, such as M
agnetic bearings sound like an unattainable dream, at least for
general engineering applications. Rather than using lubrication, they have an air gap, created by magnetic levitation, which makes them virtually frictionless, and maintenance- and wear-free. Of course, this requires precision engineering – which does not come cheap. They have most commonly been used in
industries where performance is key, no matter what the cost. A good example is the oil and gas sector. Here, the demanding conditions, and the difficulty of regular maintenance, makes magnetic bearings the most sensible design choice. A prime example is in deep sea and
Arctic conditions, where it is almost impossible to keep traditional oil- lubricated bearings running. In these and other circumstances, the higher cost and complexity of magnetic bearings is overcome by huge improvements in operating efficiency. Some of the attributes of magnetic
bearings, such as their lubricant-free operation, make them attractive to certain mainstream applications. They are by no means a plug-in solution for all bearings across the manufacturing and process sectors. However, when chosen correctly, magnetic bearings could be an effective design choice in particular applications – where the cost can be justified.
COMPLEX ASSEMBLY A magnetic bearing is a complex assembly. Active magnetic bearings rely on electromagnets to generate radial and axial forces to levitate the shaft, so it rotates in a stable position. Using signals from rotor gap measuring sensors, a control system monitors and adjusts the current in the electromagnets to maintain shaft position.
24 MARCH 2018 | FACTORY EQUIPMENT
Some of the attributes of magnetic bearings – such as their lubricant- free operation – make them attractive to certain mainstream applications
specific algorithm developments, miniaturised electronics and embedded sensors, have helped to bring down costs and open up magnetic bearings to wider use. A magnetic bearing is a highly controllable device, thanks to its associated control system, and to the software algorithms that run within this control system. An example is SKF’s Adaptive Vibration
Control (AVC), which controls the bearing system’s response to shaft imbalance. It can be used in two ways, each of which benefits a particular type of application. Firstly, it can allow the shaft to rotate around its geometric centre, and tightly control it – to eliminate the run-out caused by imbalance. This feature is of particular benefit in machine tool applications. Alternatively, the shaft can rotate around its mass centre – which transfers less vibration to the casing. This is highly valued in turbomolecular pumps and front-end semiconductor manufacturing equipment.
Because magnetic bearings are lubricant- free, they are an ideal choice for machines that operate in a vacuum
LUBRICANT-FREE Because magnetic bearings are lubricant- free, they are an ideal choice for machines that operate in a vacuum, at high or low (particularly cryogenic) temperatures, or where corrosive process fluids are involved. Any machine with zero tolerance for contamination by lubricants or wear particles, or where the lubricant is incompatible with the
process, may be a candidate for a magnetic bearing solution. This could apply to industries as far apart as semiconductor capital equipment and food and beverage processing, and other in between. While the ‘lubrication-free’ angle is the
main benefit of magnetic bearings, there are many others, and these include: • Near-frictionless operation, thanks to
a lack of metal-to-metal contact. • High speed, vibration-free operation. • High energy efficiency. • In-built condition monitoring. Magnetic bearings also rely on a carefully controlled air gap, and certain applications benefit directly from this – such as where process liquid or material has to pass, or in biological and pharmaceutical applications that involve life cell processing.
ENERGY BOOST An offshore industry example illustrates how magnetic bearings can increase both reliability and design flexibility. In a typical natural gas compression
system, using hydraulic oil bearings, motor and compressor are separate, so there is some gas leakage at the shaft that connects the two. The leaked gas, which is lost at around 10m3
per hour, is
flared, without recovering its energy. An alternative design, using SKF’s S2M
magnetic bearing, was used for a 10MW compressor system. Here, motor and compressor are integrated, and both run within the compressed natural gas. There is no hydraulic oil bearing system, so there are energy savings from eliminating the pump, cutting oil use and having a more lightweight design. Overall, the savings for one year was
estimated at 220 tonnes of CO2- equivalent emissions. While the main use of magnetic
Magnetic bearings rely on a carefully controlled air gap, and certain
applications benefit directly from this
bearings will undoubtedly continue to be in applications like this, recent advances in areas like control systems and sensors will help to propel them into more mainstream use.
SKF T: 01582 490049
www.skf.co.uk / FACTORYEQUIPMENT
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57
