Tribology Introduction

LUBRICATION AND ROTOR DYNAMICS (ME – 60072)

INTRODUCTION: Study of Lubrication and rotary machinery

Mihir Sarangi

Assistant Professor

Department of Mechanical Engineering

Introduction to Lubrication& Rotor Dynamics

January, 2011Department of Mechanical Engineering Indian Institute of Technology, Kharagpur

Rotor Bearing System Lubrication

Introduction to Lubrication and Rotor Dynamics

DiscBearing

Shaft

Support

Wr

ω

Wa

Rolling Element Bearings

Many machine elements that are fluid film-lubricated have surfaces that do not conform to each other well. The full burden of the load must then be carried by the small lubricant area. Some example of nonconformal surfaces are mating gear teeth, cams and followers, and rolling-element bearings.

Hydrodynamic Bearings (Journal Bearings)

Conformal surfaces fit snugly into each other with a high degree of geometrical conformity, so that the load is carried over a relatively large area. Fluid film journal bearings and slider bearings have conformal surfaces.

02Department of Mechanical Engineering Indian Institute of Technology, Kharagpur


Bearings

Magnetic bearing

Rolling Element Bearings Journal bearing

Thrust pad bearing



Selection of Bearings



Fluid Film Bearings

Types of Fluid film bearings: Hydrodynamic bearings

Full (3600) journal bearings are widely used bearings in industrial machinery. These bearings can take up rotating radial load. As high speed is essential to generate fluid film self-action, hydrodynamic bearings have found applications mostly in high speed machinery such as turbines, turbogenerators, turbopumps etc.



Types of Fluid film bearings: Hydrostatic bearings

Hydrostatic bearing is used to provide full film lubrication when the speed of the mating surfaces is not large enough to create hydrodynamic lubrication. The load supporting film is maintained by an external source. Hence these bearings are also called externally pressurized bearings, can meet some extreme requirements, such as

But the major disadvantages associated with# auxiliary equipment (pump, filter, oil supply line etc.) are required, hence more complicated, expensive and liable to failure, and# overall power loss (pumping and fiction) is not necessarily low.

very low frictional characteristics # heavy loads at low speeds # high positional accuracy.



The squeeze-film technology is mainly seen in the following machine components:

• The time of approach of faces of disc clutch under lubricated conditions.

• The mechanism of walking with rubber soles on wet or icy pavements.

• The absorption of vibrations in jet engines using annular squeeze films between the engine bearings and their support, and

• The rolling characteristics of an automobile tire on a wet road.

Types of Fluid film bearings: Squeeze film bearings

Parallel surface bearing

Step bearing (A)

A circular cylinder near a plane (B)

A parallel circular plate (C)

A sphere near a plane

A sphere in a spherical seat

A rectangular plate on a plane surface

A journal bearing

(A) (B) (C)



Types of Fluid film bearings: Hybrid fluid film bearings

Externally pressurized multi-recess journal bearings system

Hydrodynamic thrust and journal bearing



Types of Fluid film bearings: Special purpose fluid film bearings

Pivoted tilting pads

Tilting pad journal bearing

Cooling coils

Oil containerPivoted tilting thrust pads

Tilting pad thrust bearing



Types of Fluid film bearings: Special purpose fluid film bearings

Herringbone grooved journal bearing (hard disk drive)

Textured thrust pad bearing (for low leakage and reverse pumping)



Oil lubrication

Gas / Air lubrication

Types of Fluid film lubrication:

For gas / air lubrication:

• The surfaces should be finished with high accuracy

• The alignment between the journal and bearing must be very good

• The dimensions and clearances must be accurate

• The speed must be high

• The load should be relatively low

Fluid film bearings

Self instability in journal bearings: half whirl instability

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Stable Marginally Stable Unstable



Instability in fluid film journal bearings

300 MW steam turbine generator

Pressurized fluid bearings1 2 3 4 5 6 7



I affirm, that if a weight of a flat surface moves on a similar plane their movement will be facilitated by inter-posing between them balls or rollers; and I do not see any difference between balls and rollers save the fact that balls have universal motion while rollers can move in one direction alone. But if balls or rollers touch each other in their motion, they will make the movement more difficult than if there were no contact between them, because their touching is by contrary motions and this friction cause contrariwise movements.

But if the balls or rollers are kept at a distance from each other, they will touch at one point only between the load and its resistance… and consequently it will be easy to generate this movement.

The potential of true rolling motion for low-friction supports was fully recognized by Leonardo da Vinci, for he wrote in the Codex Madrid I:





Classification of rolling element bearings :

Based on loading:

Radial Thrust Combined radial and thrust

Based on geometry (type of rolling element):

Ball bearing

Roller bearing Needle bearing



General Classification of rolling element bearings :

Rolling Element Bearing Manufacturers

Check their websites for more information !!!

Department of Mechanical Engineering Indian Institute of Technology, Kharagpur

Ball Bearings

Deep groove Ball Bearing Angular contact Ball Bearing



Roller Bearings

Unless rollers are contoured, they can support load in only one direction (radial or thrust) Most roller bearings support, both radial and thrust loads If contact angle is less than 450, bearing has larger radial load capacity

Large capacity Long-life requirements

Long endurance for heavy loads Long endurance for shock forces

Cylindrical Roller Bearing Tapered Roller Bearing Spherical Roller Bearing



Thrust Bearings

Thrust ball bearing Thrust Roller bearing




Compensate for certain degree of misalignment

Very limited axial load capacity, only radial load



Special application Bearings

Linear motion bearings

Precise linear motion

Used as liner actuators / sensors

Very low friction compared to conventional screw arrangements

Both radial and axial load capacity

Miniature bearings



Radial Deep Groove Ball Bearing

Radial Deep Groove Ball Bearing Filling Slot

Radial Deep Groove Ball Bearing External Alignment

Angular Contact Ball Bearing

Angular Contact Ball Bearing Filling Slot

Self – Aligning Ball Bearing

Thrust Ball Bearing

Cylindrical Roller Bearing

Tapered Roller BearingNeedle Roller Bearing with Hardened Raceways

Needle Roller Bearing Drawn Cup Self – Aligning Roller Bearing

Thrust Roller Bearing

Thrust Needle Roller Bearing

Thrust Tapered Roller Bearing Thrust Spherical Roller Bearing

Today's Rolling Element Bearings




Type Code Series Bore Suffix

1 - Self-aligning ball bearing

2 - Wide self-aligning ball bearing

22 - Self-aligning roller bearing

23 - Wide self-aligning roller bearing

3 - Double-row angular contact ball bearing

4 - Double-row ball bearing

5 - Thrust ball bearing

6 - Single-row deep groove ball bearing

16 - Thin section single-row deep groove ball bearing

7 - Single-row angular contact bearing

R - Inch (non-metric) bearing

7 - Not sure

8 - Extra thin section

9 - Very thin section

0 - Extra light

1 - Extra light thrust

2 - Light

3 - Medium

4 - Heavy

** x 5 = bore diameter

09 - 45mm

11 - 55mm

except

00 - 10mm

01 - 12mm

02 - 15mm

03 - 17mm

Z - Single shielded

ZZ - Double shielded

RS - Single sealed

2RS - Double sealed

V - Single non-contact seal

VV - Double non-contact seal

DDU - Double contact seals

NR - Snap ring and groove

M - Brass cage

single-row deep groove ball bearing, light weight, with bore diameter 17mm, double shielded,

Bearing Nomenclature: Part number 6203ZZ



Ball Bearings

Yesterday Today Tomorrow

More than 125 Rolling Element Bearings are manufactured per second Worldwide

NTN Bearing Corporation


Roller Bearings

Ball Bearings

ELASTOHYDRODYNAMIC LUBRICATION (EHL)

Elastohydrodynamic lubrication is form of hydrodynamic lubrication, where the elastic deformation of the lubricated surfaces becomes significant. The features important is a hydrodynamically lubricated slider bearing – converging film thickness, sliding motion, and a viscous fluid between the surfaces – are also important here. Elastohydrodynamic lubrication is normally associated with nonconformal surfaces.

EHL Pressure development



Lubricant properties

Types of lubricant:

(i) Mineral oils , (ii) Greases , (iii) Synthetic oils , (iv) Solid lubricants

Mineral oil or liquid petrolatum is a by-product in the distillation of petroleum to produce gasoline. It is a chemically inert, transparent, colorless oil. Types: (a) Paraffins , (b) Napthenes , (c) Aromatics (Unsaturated)

Greases are oils that are thickened with solids to form semi-fluid products.

Solid lubricants are used for high temperature and/or low pressure, normal lubricants are unstable.

Should have (a) thermal stability, (b) low shear strength , (c) surface protection , (d) good bonding properties

Like graphite and molybdenum disulphide

Synthetic oil is oil consisting of chemical compounds which were not originally present in crude oil (petroleum) but were artificially made (synthesized) from other compounds. Synthetic oil could be made to be a substitute for petroleum or specially made to be a substitute for a lubricant oil such as conventional (or mineral) motor oil refined from petroleum. When a synthetic oil is made as a substitute for petroleum, it is generally produced because of a shortage of petroleum or because petroleum is too expensive.



Lubricant properties

Electro-, Magneto- and/or Electro-Magneto-Rheological fluids.

Side-view photographs showing the chain formation of ER fluid under an electric field for corn starch mixed with Si oil at 0.5 Wt% under E= 900 V mm−1, respectively.

Electro-rheological (ER) and/or Electo-magneto-rheplogical (EMR) fluids are vital in the development of miniature bearings for space application and also for medical systems.



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