Tribology Introduction
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Transcript of 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
Introduction to Lubrication& Rotor Dynamics
Bearings
Magnetic bearing
Rolling Element Bearings Journal bearing
Thrust pad bearing
03Department of Mechanical Engineering Indian Institute of Technology, Kharagpur
Introduction to Lubrication& Rotor Dynamics
Selection of Bearings
04Department of Mechanical Engineering Indian Institute of Technology, Kharagpur
Introduction to Lubrication& Rotor Dynamics
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.
05Department of Mechanical Engineering Indian Institute of Technology, Kharagpur
Introduction to Lubrication& Rotor Dynamics
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.
06Department of Mechanical Engineering Indian Institute of Technology, Kharagpur
Introduction to Lubrication& Rotor Dynamics
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)
07Department of Mechanical Engineering Indian Institute of Technology, Kharagpur
Introduction to Lubrication& Rotor Dynamics
Types of Fluid film bearings: Hybrid fluid film bearings
Externally pressurized multi-recess journal bearings system
Hydrodynamic thrust and journal bearing
08Department of Mechanical Engineering Indian Institute of Technology, Kharagpur
Introduction to Lubrication& Rotor Dynamics
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
09Department of Mechanical Engineering Indian Institute of Technology, Kharagpur
Introduction to Lubrication& Rotor Dynamics
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)
10Department of Mechanical Engineering Indian Institute of Technology, Kharagpur
Introduction to Lubrication& Rotor Dynamics
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
0.2
0.4
0.6
0.8
1
30
210
60
240
90
270
120
300
150
330
180 0
MW=11
0.2
0.4
0.6
0.8
1
30
210
60
240
90
270
120
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150
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180 01 3
2
4
MW=12 Wr=0.36
0.2
0.4
0.6
0.8
1
30
210
60
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90
270
120
300
150
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180 0
MW=13
Stable Marginally Stable Unstable
11Department of Mechanical Engineering Indian Institute of Technology, Kharagpur
Introduction to Lubrication& Rotor Dynamics
Instability in fluid film journal bearings
300 MW steam turbine generator
Pressurized fluid bearings1 2 3 4 5 6 7
12Department of Mechanical Engineering Indian Institute of Technology, Kharagpur
Introduction to Lubrication& Rotor Dynamics
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:
Rolling Element Bearings
13Department of Mechanical Engineering Indian Institute of Technology, Kharagpur
Introduction to Lubrication& Rotor Dynamics
Rolling Element Bearings
14Department of Mechanical Engineering Indian Institute of Technology, Kharagpur
Introduction to Lubrication& Rotor Dynamics
Rolling Element Bearings
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
15Department of Mechanical Engineering Indian Institute of Technology, Kharagpur
Introduction to Lubrication& Rotor Dynamics
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
17Department of Mechanical Engineering Indian Institute of Technology, Kharagpur
Introduction to Lubrication& Rotor Dynamics
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
18Department of Mechanical Engineering Indian Institute of Technology, Kharagpur
Introduction to Lubrication& Rotor Dynamics
Thrust Bearings
Thrust ball bearing Thrust Roller bearing
19Department of Mechanical Engineering Indian Institute of Technology, Kharagpur
Introduction to Lubrication& Rotor Dynamics
Rolling Element Bearings
Compensate for certain degree of misalignment
Very limited axial load capacity, only radial load
20Department of Mechanical Engineering Indian Institute of Technology, Kharagpur
Introduction to Lubrication& Rotor Dynamics
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
21Department of Mechanical Engineering Indian Institute of Technology, Kharagpur
Introduction to Lubrication& Rotor Dynamics
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
22Department of Mechanical Engineering Indian Institute of Technology, Kharagpur
Introduction to Lubrication& Rotor Dynamics
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
23Department of Mechanical Engineering Indian Institute of Technology, Kharagpur
Introduction to Lubrication& Rotor Dynamics
Ball Bearings
Yesterday Today Tomorrow
More than 125 Rolling Element Bearings are manufactured per second Worldwide
NTN Bearing Corporation
Rolling Element Bearings
25Department of Mechanical Engineering Indian Institute of Technology, Kharagpur
Introduction to Lubrication& Rotor Dynamics
Rolling Element Bearings
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
26Department of Mechanical Engineering Indian Institute of Technology, Kharagpur
Introduction to Lubrication& Rotor Dynamics
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.
27Department of Mechanical Engineering Indian Institute of Technology, Kharagpur
Introduction to Lubrication& Rotor Dynamics
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.
28Department of Mechanical Engineering Indian Institute of Technology, Kharagpur
Introduction to Lubrication& Rotor Dynamics