Magnetic bearings

Bearings Bearings are machine elements

which constrains the relative motion to only desired motion and reduces friction between the moving parts

The word “bearing” from the word “to bear” is a machine element that allows one element to bear another

Magnetic bearings A magnetic

bearing is a bearing that supports a load using magnetic levitation

These bearings doesn’t have any physical contact with the moving parts

Magnetic bearings They levitate the

rotating shaft and permit relative motion with very low friction

They have minimum mechanical wear and support highest speeds when compared with all other bearings

They work effectively than all other bearings @ vacum and at high temperatures

Parts of a magnetic bearings: An electromagnet assembly Power amplifiers- supplies current

to the electromagnetic system Gap sensors - electronic circuit

which provide required feedback to control the position of position of rotor within the gap

A controller – controls the rotor motion within the gap

Parts of magnetic bearing :

Types of magnetic bearings :Active magnetic bearings

Passive magnetic bearings

Uses electro magnets for magnetic levitation

Carries varying load Requires input

power supply Easy to design More effective

Uses permanent magnet for magnetic levitation

Carries static load Doesn’t require

any input supply Difficult to design Less effective

Applications of magnetic bearings : Has several industrial

applications due to very low friction and ability to run without lubrication

Several applications of magnetic bearings are

watt-hour meters Maglev trains Centrifugal compressors Artificial hearts

Synchrony novaglide High temperature active magnetic

bearings used for aerospace and defence applications

Designed for using in next generation gas turbine engines where high temperature and high rotational speeds are already prevailing

They have optimized magnetic structure which reduces bearing size

Can operate at a temperature range of -70 F to 500 F

Parts of a novaglide system Two radial

bearings each with a stator and a rotor

One thrust bearing

Position sensors Magnetic bearing

controller

Uninterruptible power supply i.e., a battery backup

Auxillary bearings and bushings

Cables from controller to the bearing

Applications of novaglide High speed

compressors in large refrigeration systems

Expansion turbines Gas turbines High speed

generators Motors as a prime

mover

Zippe type centrifuges A centrifuge designed to enrich the rare fissile

uranium isotope uranium-235 from the mixuture of nature uranium containing u-238

This was first designed in Russia after world war 2

For isotopic seperation the centrifuge must rotate at a very high speed at about 90000 rpm

The shaft of the high speed rotor is supported by means of an active magnetic bearing

Design of zippie type centrifuge

Hollow cylindrical rotor filled with gaseous uranium

The magnetic field created at the bottom by means of supportive magnetic bearings enables the rotor to rotate at a high rpm without any frictional loss

The rotor spins in vacum

Artificial heart

A mechanical device that replaces heart

Artificial hearts bridge the time during heart transplantation

Design and parts of artificial heart : A centrifugal pump provided with

magnetic bearings or a similar axial flow pump can be used as a artificial heart

Artificial heart uses magnetic bearings as they have very less mechanical wear

The pump can regulate both pulmonary and systemic circulation

The centrifugal pump can produce continuous output

Material selection for artificial heart

The material must be flexible non toxic and must bear various stresses

The most commonly used material are silicones