SPECIAL BEARINGS IN MECHANICAL ENGINEERINGPresented bySidharth Sankar Adhikari1307555016CENTRE FOR ADVANCE POST-GRADUATE STUDIESBPUT,ROUKELA

CONTENTS BEARING SPECIAL BEARING MAGNETIC BEARING DESCRIPTION BASIC OPERATION CLASSIFICATION MAGNETIC BEARING PERFORM WORKING PRINCIPLE BEARING FAILURE ANALYSIS APPLICATIONS ANALYSIS OF ADVANTAGES AND DISADVANTAGES OF SPECIAL BEARINGS (BASED ON APPLICATION) SCOPE FOR RESEARCH CONCLUSION REFERENCES

A Bearing is a machine element which support another moving element.

It permits relative motion between the contact surfaces of the members while carrying a load.

Most bearings support rotating shafts against either radial or axial loads.

BEARING

SPECIAL BEARING

•A special bearing is not of conventional type .• Its unique features No need of lubrication No contamination make them suitable compared to ball bearings in many cases.

A magnet bearing

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MAGNETIC BEARING A Magnetic bearing is a

bearing which supports a load using magnetic levitation.

A Magnetic bearing support moving machinery without physical contact,for example,they can levitate a rotating shaft and permit relative motion without friction or wear.

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Magnetic bearing are design to support rotating and linear moving machinery elements, without contact with rotor, this is accomplished by electro magnet (bearing) which attracts a ferromagnetic material(rotor),using this principle rotor can be suspended in magnetic field which is generated by bearing.

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DESCRIPTIONIt is difficult to build a magnetic bearing using permanent magnets due to diamagnetic materials are relatively undeveloped.As a result, most magnetic bearing require continuous power input and an active control system to hold the load stable. Because of this complexity, the magnetic bearing also typically require some kind of back-up bearing in case of power or control system failure.

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BASIC OPERATIONAn active magnetic bearing (AMB) works on the principle of electromagnetic suspension and consists ofan electromagnet assembly, a set of power amplifiers which supply current to the electromagnets, a controller, and gap sensors with associated electronics to provide the feedback required to control the position of the rotor within the gap.

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•The power amplifier supplies equal bias current to two pairs of electromagnets on opposite sides of a rotor. This constant tug-of-war is mediated by the controller which offsets the bias current by equal and opposite perturbations of current as the rotor deviates from its center position.•The gap sensors are usually inductive in nature and sense in a differential mode. The power amplifiers in a modern commercial application are solid state devices which operate in a pulse width modulation (PWM) configuration. The controller is usually a microprocessor or DSP

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CLASSIFICATION According to

Control action – Active– Passive – HybridAccording to Forcing action – Repulsive – AttractiveAccording to Sensing action – Sensor sensing – Self sensing

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•According to Load support – Axial or Thrust – Radial or Journal – Conical•According to Magnetic effect – Electro magnetic – Electro dynamic

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MAGNETIC BEARING PERFORMLubrication FreeClean & Contamination FreeReliabilityHigh Surface SpeedLow VibrationLow EnergyConsumptionNon-ContactingSubmerged Operation

WORKING PRINCIPLEThe load capacity of the depends on the arrangements and the geometry of the electromagnets, the magnetic properties of the material, of the power electronics and the control laws.The basic law of physics states ∫H.ds=n.iThe relationship between H(magnetic field) and B(flux density) is given by B=μο.μr.H .

Basic set up of AMB

Force of magnet and geometry of radial bearing

•That the inductions are same in iron core and air gap.•The force f exerted can be derived by considering the energy (Wa) stored in the air gap between rotor and the magnet.

Geometry of a radial bearing magnet

In an AMB static stiffness is defined as

The dynamic stiffness is dependent on frequency.Speed-The features characterizing a high speed rotor can be with respect to rotational speed, circumferential speed of rotor at bearing or largest diameter.

Plot of carrying force of a radial bearing vs bearing width and bearing diameter.

•The theoretical achievable speed is

•In industrial applications the speed usually is limited not by the bearings,but by the mechanical design of the motor drive.

•For high speeds permanent magnet synchronous drives are used where the rotor is wound with carbon fibers.

•In AMB technology the controller has to be designed carefully to enable a stable and well damped rotor behavior.

(Rotor ring ,broken under centrifugal load)Achievable circumferential

speeds for a full disc

BEARING FAILURE ANALYSIS

APPLICATIONS

Used in compressors ,turbines, pumps ,motors ,generators.

Used in watt-hour meters.

Flywheels also use AMBs.

Maglev trains. Artificial hearts.

Maglev train

Artificial heart using magnetic bearing. Magnetic

levitation

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ANALYSIS OF ADVANTAGES AND DISADVANTAGES OF SPECIAL BEARINGS(BASED ON APPLICATION)

Maglev train

Advatages Very low and predictable frictionBearing have the ability to run without lubrication and in a vacuum. Low noise and smooth ride by eliminating physical contact surfaces can be achieved.Disadvantages High costHeavy weightRelatively large size

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ANALYSIS OF ADVANTAGES AND DISADVANTAGES OF SPECIAL BEARINGS(BASED ON APPLICATION)

Artificial heart using magnetic bearing

Advatages The cost of operation is very less compare to normal heart plantation and operation.Bearing have the ability to run without lubrication and in a vacuum. Effective Performance can be achieved that of normal operation

Disadvantages Bearing material may cause impact to artery and other body partsRelatively large sizeFunctioning failure may cause serious problem to the body

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ANALYSIS OF ADVANTAGES AND DISADVANTAGES OF SPECIAL BEARINGS(BASED ON APPLICATION)

Advatages A MagLev is way faster than usual bullet train. MagLevs can reach speeds up to 500 kilometres per hour.MagLevs use 30% less energy than normal trains

DisadvantagesThe MagLev's track is much more expensive than railroad tracks.Whole new sets of tracks would have to be built for the MagLev to run.Although MagLevs are pretty quiet, noise caused by air disturbance still occurs.

Magnetic levitation

SCOPE FOR RESEARCH

HT-AMBs are a field of potential research. Electrodynamics bearing. Reliability of special Bearing Bearing Failure Analysis at dead load and

live loads

CONCLUSION Maximum load depends on design .

Specific load depends on the available ferromagnetic material and its saturation properties.

Maximum achieved rotation speed is about 300kHz in laboratories and in industrial uses about 6kHz.

Circumferential speeds are limited by strength of material and about 250-300mis

High temperature bearings have been realized at about 600degree centigrade.

REFERENCES

1) Active magnetic bearings-chances and limitations,Schweitzer G.

2) Introduction To Tribology Of Bearings,B.C.MAJUMDAR

3) “An overview of Tilting pad journal bearing” by Luis San Andres

4)” Sliding contact Bearings” Vedat Temiz 5) “Tribology of Bearings” by B.C. Majumdar 6) www.kingsbury.com 7) www.machinerylubrication.com

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THANK YOU.....