Bearing in Electric motors

Type of Bearings 1) Deep groove ball bearings 2) Angular contact ball bearings. 3) Self-aligning ball bearings 4) Cylindrical roller bearings 5) Tapper roller bearings 6) Spherical roller bearings 7) CARB toroidal roller bearings 8) Thrust ball bearings 9) Cylindrical roller thrust bearings 10) Spherical roller bearings

Parts of bearings

1) Outer ring. 2) Inner ring. 3) Rolling element ----- Ball, Rollers.

(cylindrical,needle,tapered) 4) Cage. 5) seal- If sealed.

Function of bearings

Reduce friction. Carry loads. Support shaft. Locate shaft viz a viz housing. To keep the air gap small &

consistent. To transfer loads from the shaft to

the motor frame.

Bearing material Through hardening steels Carbon chromium stall Contains approx. 1% - carbon 1.5% - chromium Cage hardening steels Chromium- nickel alloy. Steel & manganese Chromium alloyed steel 0.15% Carbon

Cages Rolling bearings are available with variety of

cages and cage materials Cage material : polymide cage : Nylon – 25% Ultramide : Glass fibres – 25% Window type sheet steel cage :

Sensitive poor lubrication. Window type solid brass cage

FAILURE OF BEARING

1. Corrosion 2. Electrical Failure 3. Fracture 4. Vibration 5. Misalignment 6. Foreign Particles 7. Faulty Mounting 8. Overloading

HOW BEARING FAILS :

Failure can be------ Poor fitting Inadequate lubrication

Contamination

Trouble free operation :

Five elements : Cleanliness Correctly designated high quality bearing Damage free installation Correct lubrication Efficient sealing

Why rolling bearings:

To support & accurately locate a load

Allowing the load to move with the minimum of friction

Ball Bearing:1. Single row deep groove ball

bearings Its ability to carry both axial and radial loads. Very low friction and low noise. Low maintenance required. It is suitable for high speed and light

loads.

Ball bearing : Self-aligning ball bearings Double row of balls. Outer ring raceway is spherical allows the

rings to be dynamically misaligned making it suitable for use in applications where the misalignment of bearings on a common shaft can occur.

Carry radial and axial loads. Not suitable for heavy or arduous

operation. The number of balls and the contact area

each ball makes with the raceways restrict the capacity or load rating of the bearing.

Integral seals The selection of seal is vital importance to

the proper performance of bearing. SKF supplies bearings with integral = Shields

= Low friction seals = Contact seals All bearings with integral seals on both

sides are filled with a grease of appropriate quality

& quantity.

Selection of Bearing type Available space Speed Minimum loads Misalignment Precision Quiet running Stiffness Axial displacement Mounting & dismounting Integral seals

Selection of bearing size:Parameters to be considers for

design

Lubrication:

Function: Reduce Wear & friction Protects highly finished surfaces

of rolling elements & rings from corrosion.

Lubricant Grease:

Grease : Medium of oil, oil comes out.

A grease is 90% oil held in a thickener(10%). Grease =Base oil+Thickener+

Additives (70-95%) ( 5-30%)

Type of Grease :

Calsium Sodium Lithium Synthetic Complex

Grease Lubrication :

Grease advantage := over oil that it is more easily retained in the bearing arrangement & contributes to sealing the arrangement against contaminants,moisture or water.

Excessive amount of grease will cause the operating temperature within the bearing to rise rapidly.

Friction Friction means “Resistance to motion of

things that touch other things.” Friction i) Sliding friction ii) Rolling friction: Rolling bearings normally generates less friction as compared to plain bearings.

Lubricating grease:

Consist of a mineral or synthetic oil combined with a thickner.

The thickners are usually metallic soaps

Polyurea thickner can be used for superior performance in certain areas

ie. High temperature applications.

Selection of grease :

Most important factors Consistency Operating temperature range Viscosity of base oil Rust inhibiting properties Load carrying ability

Grease temperature chart :

Thickner type Base oil Temp.0c- @ Min Max

Lithium base----- Mineral----- 30 ---- 115Lithium base----- Diester----- 30 ---- 115Lithium complex- Mineral----- 50----- 140Lithium complex—PAO ----- 50------150

Bearing life:

The rated life is defined as the number of revolutions (or number of operating hours at a given constants speed) the bearing could endure.

Service life of a bearing

Depends on------- Large extent

Relubrication intervals :

Amount of grease

Gp= 0.005 D B

Where

Gp = Grease Quantity in Grams.

D = Bearing outside diameter in mm

B = Bearing width in mm.

Grease life :

Life of grease depends on several factors-------------

1. Type of bearing.2. Type of grease.3. Orientation & speed of the motor.4. Operating temp. of the bearing.

Rolling bearings in electric machines--

Purpose of using rolling bearing--------------

To support & locate the rotor To keep air gap small & consistent To transfer loads from shaft to the

motor frame

Rolling bearings in electric machines------------

The bearing should enable high & low speed operation, minimize friction & save power.

The designer has to consider many different parameters when selecting the bearing type & arrangement to meet the requirements of any particular motor application.

Rolling bearings in electric machines -------------

Under all circumstances the design should be economical from both a manufacturing & a maintenance

perspective.

Rolling bearings in electric machines -----------

1. Design requirements== Design parameters:- 1) Power output

2) Boundary dimensions3) Shaft & housing material

Deep groove ball bearing

Self aligning ball bearing

Angular contact ball bearing :

‘Y’ bearing unit

Cylindrical roller bearing :

Tapered roller bearing :

Spherical roller bearing :

CARB ® bearing :

Minimum loads :

Cylindrical seating :

Tapered seating :

Adapter sleeve :

Withdrawal sleeve

Bearings :

Small bearings: bore diameter < 80mm  Medium bearings: bore diameter 80 - 200 mm Large bearings: bore diameter > 200 mm

Tools :

Jawpuller

Basic designation :

In metric system= Ist Digit----- Type of Bearing IInd Digit----Small or larger size Last two Digits--- bore dia.* 5 mm

i.e.-In brg. 6312- 12*5= 60 mm 6220- 20*5=100 mm

Basic designation : Inch system = Brg. - LM 501349 5 = Contact angle 013 = Bore diameter 49 = Inner ring/ outer ring

Cup/cone EC = Higher capacity P = Polymide cage

Principal of induction Heater :

Hot mounting :

Inadequate lubrication :

Grease lubrication : Surface distress Or Abrasive wearFinally reduces bearing life

Inadequate lubrication :

Film lubrication : If thin due to inadequate viscocity or contamination

*** causes metal to metal contact