1 Bearing Manufacturer Technical and Engineering Sites
Boca Bearings : ABEC and ISO standards
ABEC and ISO bearing standards in table form. The best presentation we've seen of this often-confusing
pair of standards and how they compare side-by-side. More importantly, it points out that ABEC and ISO
standards do not cover: "radial play, raceway curvature, surface finish, material, ball
complement, number, size or precision level, retainer type, lubrication, torque, cleanliness
at assembly, packaging and other factors that may be essential to the desired bearing performance."
GGB (formerly Glacier Garlock Bearings) product and technical literature
Online specifications offered in seven languages from the world's largest manufacturer of
metal-polymer plain bearings (all in PDF format).
Comprehensive technical information, for over 30 materials: metal-polymer, solid polymer,
fibre-reinforced plastic composites, monometallics, and over a dozen other, nonstandard
materials and subassemblies.
INA / FAG Medias Product Selection and Information System
Alongside SKF's offerings, possibly the most comprehensive bearing product selection
and information suite on the Internet.
Beyond comprehensive product descriptions, the site includes operating principles,
bearing life calculation, lubrication considerations, engineering contacts, application
examples, and links to deeper value-added products and services.
Minebea / NMB Engineering Information Product Catalogs
A "secret" site with all of Minebea company product catalogs and engineering information.
Look for the bearing search-by-size feature, which interactively helps whittle down parameters
for a database search in real time, so you can watch the effects of narrowing your search criteria.
Most catalogs are available in both plain text and PDF format.
NSK TeC Technical e-source Center
A wide array of tools from vibration calculators to an online catalog.
Sections include Library, Troubleshooting, Calculations, e-Catalog, CAD data, Handbook, and Interchange.
NTN Technical and Engineering Support
While it used to be better, there is a wealth of good information. Much of
it is still here, and you can find it buried under the "Applications" and "Technical Support" menus.
NTN once had a wonderful array of technical documents here: Basic introductions to all types
of bearings, 16 documents covering ball and roller bearing technical data,
9 more for mounted units, and segments for cleaning, care, maintenance, and product specification sheets,
along with complete online catalogs of NTN-Bower, NTN-BCA, NTN-A1000 VI, and specialty applications.
Bring it back! We can handle it.
SKF Interactive Engineering Catalog
Alongside INA/FAG's Medias, the most comprehensive set of bearing-related resources on the web.
Detailed sections are divided among Roller Bearings, Plain Bearings,
Bearing Housings, Bearing Units, and Seals. The site also contains a wealth
of information from Product Tables, online Calculators, and CAD drawings.
Some sections (i.e. access to CAD drawings) require free registration.
Brochures and technical documents (all in PDF format) covering various
SKF products and product applications.
SKF Maintenance Products
Bearing maintenance tools, oriented toward maintenance engineers; information, catalogs,
resource guides, Material Safety Data Sheets, product information leaflets and
brochures (all in PDF format), in ten languages. How to use instrumentation,
bearing heaters, tools, indicators, and automated lubricators.
SKF : OEM hub units vs. aftermarket
A brochure comparing SKF OEM wheel bearing hub unit construction to
some of the low quality units in the aftermarket. Perhaps unintentionally, this brochure is
also a good overview of hub
unit engineering and construction techniques.
Timken Online Services
Timken's bearing catalogs, searchable by size or part number. Also bearing tolerance
data, assembly component information, and bearing periodic frequency analysis.
Bearing Specialists Association (BSA)
An organization of authorized bearing distributors with roots dating to 1941. It is involved in
education, training, and promoting manufacturer relationships with authorized distributors.
Its Educational Services Committee (ESC) publishes occasional educational white papers:
Virtual Tribology Institute
An deep, broad online resource into all aspects of the science of tribology.
VTI's mission: "To bring together competencies in the field of tribology, enhance the use
of technology, and the transfer of research results to industry."
"In all its activities, the VTI supports European industry, particularly SME's, in developing
sustainable economic growth."
Clickable Index Map of Mathematics
A visual index to the subfields of mathematics, from number theory to topology to numerical analysis,
differential equations, physics, science and engineering, and others.
For the bearing industry, the science and engineering section is a mine of information
about thermodynamics, fluid mechanics, deformable solids mechanics, and more.
Donald Knuth's homepage
Listed in honor of Don Knuth. Decades ago, many of us had our first introduction to rigor in The
Art of Computer Programming (TAOCP) through Knuth's Fundamental Algorithms and went on from there.
In 2000, his first three books were named among the best twelve physical-science monographs of
the century by American Scientist, along with: Dirac on quantum mechanics, Einstein on relativity,
Mandelbrot on fractals, Pauling on the chemical bond, Russell and Whitehead on foundations of
mathematics, von Neumann and Morgenstern on game theory, Wiener on cybernetics, Woodward and
Hoffmann on orbital symmetry, Feynman on quantum electrodynamics, Smith on the search for
structure, and Einstein's collected papers.
If you already own the first three volumes, the fourth, Combinatorial Algorithms, is now
due sometime between 2007 and 2010.
Bearings and harmonic analysis go hand in hand. This wiki site is now the
comprehensive guide to databases, surveys, notes, books, courses and conferences.
OnlineConverters.com : measurement converters and calculators
A collection of measurement calculators and converters for all occasions. Most of them are
There are dozens of converters on this site, everything from trigonometric functions
to radioactive decay. No bearing-specific converters or calculators here, however.
3 Museums, Educational Displays and Videos
How Things Are Made : ball bearings
Discovery Channel show video shot at NTN Canada, via YouTube
[ 4 minutes 29 seconds; requires Flash ]
Engine bearings and plain bearings explained [ 4 minutes 25 seconds ]
An extremely thorough video presentation covering all types of internal combustion
engine bearings, but which also applies to almost any plain bearing or hydrodynamic bearing.
In addition, the video gives coverage to engine bearing materials and construction, including
all commonly-used alloys and white metal.
Leonardo da Vinci : ball bearing animated model
Via a traveling exhibition of working models built
from Leonardo da Vinci's drawings. Leonardo's ball bearing design executed in wood as specified.
"Working model after Leonardo da Vinci. Leonardo exerted
himself to find ingenious techniques of reducing friction. Here, eight concave-sided spindles
rotating on their own axes prevent lateral movements by the balls, which, however, can rotate
freely. The sphere-and-spindle system reduces friction, allowing the top platform to turn easily
even when carrying a heavy load."
Bearing frequency analysis
A laboratory experiment illustrating the effect of shaft speed on
signature vibrations of bearings mounted in pillow blocks.
High-quality and low-quality bearings are compared.
5 NASA Technical Reports - from NASA Technical Reports Server
(now includes Langley Technical Reports Server)
http://ntrs.nasa.gov Unfortunately, that most NASA technical research study reports
involving bearings are not yet available in electronic format.
What follows is a representative selection of reports with the widest interest.
Misalignment in Gas Foil Journal Bearings: An Experimental Study
2008 : 20 pages : PDF format
As gas foil journal bearings become more prevalent in production machines, such as small gas turbine
propulsion systems and microturbines, system-level performance issues must be identified and quantified
in order to provide for successful design practices. Several examples of system-level design parameters
that are not fully understood in foil bearing systems are thermal management schemes, alignment
requirements, balance requirements, thrust load balancing, and others. In order to address some of
these deficiencies and begin to develop guidelines, this paper presents a preliminary experimental
investigation of the misalignment tolerance of gas foil journal bearing systems. Using a notional gas
foil bearing supported rotor and a laser-based shaft alignment system, increasing levels of misalignment
are imparted to the bearing supports while monitoring temperature at the bearing edges. The amount of
misalignment that induces bearing failure is identified and compared to other conventional bearing types
such as cylindrical roller bearings and angular contact ball bearings. Additionally, the dynamic response
of the rotor indicates that the gas foil bearing force coefficients may be affected by misalignment.
Gas Foil Bearing Technology Advancements for Closed Brayton Cycle Turbines
2007 : 20 pages : PDF format
Closed Brayton Cycle (CBC) turbine systems are under consideration for future space electric
power generation. CBC turbines convert thermal energy from a nuclear reactor, or other heat source,
to electrical power using a closed-loop cycle. The operating fluid in the closed-loop is commonly a
high pressure inert gas mixture that cannot tolerate contamination. One source of potential
contamination in a system such as this is the lubricant used in the turbomachine bearings. Gas
Foil Bearings (GFB) represent a bearing technology that eliminates the possibility of contamination
by using the working fluid as the lubricant. Thus, foil bearings are well suited to application in
space power CBC turbine systems. NASA Glenn Research Center is actively researching GFB technology
for use in these CBC power turbines. A power loss model has been developed, and the effects of a very
high ambient pressure, start-up torque, and misalignment, have been observed and are reported here.
Development and Testing of a Radial Halbach Magnetic Bearing
2006 : 40 pages : PDF format
The NASA John H. Glenn Research Center has developed and tested a revolutionary Radial Halbach
Magnetic Bearing. The objective of this work is to develop a viable non-contact magnetic bearing
utilizing Halbach arrays for all-electric flight, and many other applications. This concept will
help reduce harmful emissions, reduce the Nation s dependence on fossil fuels and mitigate many of
the concerns and limitations encountered in conventional axial bearings such as bearing wear, leaks,
seals and friction loss. The Radial Halbach Magnetic Bearing is inherently stable and requires no
active feedback control system or superconductivity as required in many magnetic bearing designs.
The Radial Halbach Magnetic Bearing is useful for very high speed applications including turbines,
instrumentation, medical applications, manufacturing equipment, and space power systems such as
flywheels. Magnetic fields suspend and support a rotor assembly within a stator. Advanced technologies
developed for particle accelerators, and currently under development for maglev trains and rocket
launchers, served as the basis for this application. Experimental hardware was successfully designed
and developed to validate the basic principles and analyses. The report concludes that the
implementation of Radial Halbach Magnetic Bearings can provide significant improvements in
rotational system performance and reliability.
Bearing and Seal Technology
1969 : 121 pages : PDF format
NASA derived improvements in seals and bearings for utilization by electric power industry.
Authors: Anderson and Ludwig.
Rotordynamic Instability Problems in High-Performance Turbomachinery
1994 : 436 pages : PDF format
Numerical, theoretical, and experimental results and control methods for seals, bearings, and
dampers with some attention given to variable thermospherical properties and turbulence measurements
are reported along with field experiences.
Instability in Rotating Machinery
1985 : Symposium reports : 480 pages : PDF format
The proceedings contain 45 papers on a wide range of subjects including flow generated instabilities
in fluid flow machines, cracked shaft detection, case histories of instability phenomena in compressors,
turbines, and pumps, vibration control in turbomachinery (including antiswirl techniques), and the
simulation and estimation of destabilizing forces in rotating machines. The symposium was held to serve
as an update on the understanding and control of rotating machinery instability problems.
Steady-state and transient analysis of a squeeze film damper bearing for rotor stability
1975 : 110 pages : PDF format
A study of the steady-state and transient response of the squeeze film damper bearing is presented. Both
the steady-state and transient equations for the hydrodynamic bearing forces are derived. The bearing
equivalent stiffness and damping coefficients are determined by steady-state equations. These coefficients
are used to find the bearing configuration which will provide the optimum support characteristics based
on a stability analysis of the rotor-bearing system. The transient analysis of rotor-bearing systems is
performed by coupling the bearing and journal equations and integrating forward in time. The effects of
unbalance, cavitation, and retainer springs are included in the analysis. Methods of determining the
stability of a rotor-bearing system under the influence of aerodynamic forces and internal shaft friction
are discussed with emphasis on solving the system characteristic frequency equation and on producing
stability maps. It is shown that for optimum stability and low force transmissability the squeeze bearing
should operate at an eccentricity ratio epsilon 0.4.
Effect of Silicon Nitride Balls and Rollers on Rolling Bearing Life
2004 : 31 pages : PDF format
Three decades have passed since the introduction of silicon nitride rollers and balls into conventional
rolling-element bearings. For a given applied load, the contact (Hertz) stress in a hybrid bearing will
be higher than an all-steel rolling-element bearing. The silicon nitride rolling-element life as well
as the lives of the steel races were used to determine the resultant bearing life of both hybrid and
all-steel bearings. Life factors were determined and reported for hybrid bearings.
Under nominal operating speeds, the resultant calculated lives of the deep-groove, angular-contact,
and cylindrical roller hybrid bearings with races made of post-1960 bearing steel increased by
factors of 3.7, 3.2, and 5.5, respectively, from those calculated using the Lundberg-Palmgren
equations. An all-steel bearing under the same load will have a longer life than the equivalent
hybrid bearing under the same conditions. Under these conditions, hybrid bearings are predicted
to have a lower fatigue life than all-steel bearings by 58 percent for deep-groove bearings, 41
percent for angular-contact bearings, and 28 percent for cylindrical roller bearings.
Further Development of an Optimal Design Approach Applied to Axial Magnetic Bearings
2005 : 6 pages : PDF format
Classical design methods involved in magnetic bearings and magnetic suspension systems
have always had their limitations. Because of this, the overall effectiveness of a design has always relied
heavily on the skill and experience of the individual designer. This paper combines two approaches that
have been developed to aid the accuracy and efficiency of magnetostatic design. The first approach
integrates classical magnetic circuit theory with modern optimization theory to increase design
efficiency. The second approach uses loss factors to increase the accuracy of classical magnetic circuit
theory. As an example, an axial magnetic thrust bearing is designed for minimum power.
High Speed Operation and Testing of a Fault Tolerant Magnetic Bearing
2004 : 14 pages : PDF format
Research activities undertaken to upgrade the fault-tolerant facility, continue testing high-speed
fault-tolerant operation, and assist in the commission of the high temperature (1000 degrees F) thrust
magnetic bearing as described. The fault-tolerant magnetic bearing test facility was upgraded to
operate to 40,000 RPM. The necessary upgrades included new state-of-the art position sensors with high
frequency modulation and new power edge filtering of amplifier outputs. A comparison study of the new
sensors and the previous system was done as well as a noise assessment of the sensor-to-controller
signals. Also a comparison study of power edge filtering for amplifier-to-actuator signals was done;
this information is valuable for all position sensing and motor actuation applications. After
these facility upgrades were completed, the rig is believed to have capabilities for 40,000 RPM
operation, though this has yet to be demonstrated. Other upgrades included verification and upgrading of
safety shielding, and upgrading control algorithms. The rig will now also be used to demonstrate motoring
capabilities and control algorithms are in the process of being created. Recently an extreme temperature
thrust magnetic bearing was designed from the ground up. The thrust bearing was designed to fit within
the existing high temperature facility. The retrofit began near the end of the summer, 04, and
continues currently. Contract staff authored a NASA-TM entitled 'An Overview of Magnetic Bearing
Technology for Gas Turbine Engines', containing a compilation of bearing data as it pertains to
operation in the regime of the gas turbine engine and a presentation of how magnetic bearings can
become a viable candidate for use in future engine technology.
Transmission Bearing Damage Detection Using Decision Fusion Analysis
2004 : 26 pages : PDF format
A diagnostic tool was developed for detecting fatigue damage to rolling element bearings in an OH-58
main rotor transmission. Two different monitoring technologies, oil debris analysis and vibration, were
integrated using data fusion into a health monitoring system for detecting bearing surface fatigue
pitting damage. This integrated system showed improved detection and decision-making capabilities as
compared to using individual monitoring technologies. This diagnostic tool was evaluated by collecting
vibration and oil debris data from tests performed in the NASA Glenn 500 hp Helicopter Transmission Test
Stand. Data was collected during experiments performed in this test rig when two unanticipated bearing
failures occurred. Results show that combining the vibration and oil debris measurement technologies
improves the detection of pitting damage on spiral bevel gears duplex ball bearings and spiral bevel
pinion triplex ball bearings in a main rotor transmission.
An Oil-Free Thrust Foil Bearing Facility Design, Calibration, and Operation
2005 : 30 pages : PDF format
New testing capabilities are needed in order to foster thrust foil air bearing technology development
and aid its transition into future Oil-Free gas turbines. This paper describes a new test apparatus
capable of testing thrust foil air bearings up to 100 mm in diameter at speeds to 80,000 rpm and
temperatures to 650 C (1200 F). Measured parameters include bearing torque, load capacity, and
bearing temperatures. This data will be used for design performance evaluations and for validation of
foil bearing models. Preliminary test results demonstrate that the rig is capable of testing thrust
foil air bearings under a wide range of conditions which are anticipated in future Oil-Free gas turbines.
Torque as a function of speed and temperature corroborates results expected from rudimentary performance
models. A number of bearings were intentionally failed with no resultant damage whatsoever to the
test rig. Several test conditions (specific speeds and loads) revealed undesirable axial shaft
vibrations which have been attributed to the magnetic bearing control system and are under study.
Based upon these preliminary results, this test rig will be a valuable tool for thrust foil bearing
research, parametric studies and technology development.
Monte Carlo Simulation of Sudden Death Bearing Testing
2003 : 21 pages : PDF format
Monte Carlo simulations combined with sudden death testing were used to compare resultant bearing
lives to the calculated hearing life and the cumulative test time and calendar time relative to
sequential and censored sequential testing. A total of 30 960 virtual 50-mm bore deep-groove ball
bearings were evaluated in 33 different sudden death test configurations comprising 36, 72, and 144
bearings each. Variations in both life and Weibull slope were a function of the number of bearings
failed independent of the test method used and not the total number of bearings tested. Variation in
L10 life as a function of number of bearings failed were similar to variations in lift obtained from
sequentially failed real bearings and from Monte Carlo (virtual) testing of entire populations.
Reductions up to 40 percent in bearing test time and calendar time can be achieved by testing to
failure or the L(sub 50) life and terminating all testing when the last of the predetermined bearing
failures has occurred. Sudden death testing is not a more efficient method to reduce bearing test
time or calendar time when compared to censored sequential testing.
Fault Tolerant Homopolar Magnetic Bearings
2003 : 23 pages : PDF format
Magnetic suspensions (MS) satisfy the long life and low loss conditions demanded by satellite
and ISS based flywheels used for Energy Storage and Attitude Control (ACESE) service. This paper
summarizes the development of a novel MS that improves reliability via fault tolerant operation.
Specifically, flux coupling between poles of a homopolar magnetic bearing is shown to deliver desired
forces even after termination of coil currents to a subset of failed poles . Linear, coordinate decoupled
force-voltage relations are also maintained before and after failure by bias linearization. Current
distribution matrices (CDM) which adjust the currents and fluxes following a pole set failure are
determined for many faulted pole combinations. The CDM s and the system responses are obtained utilizing
1D magnetic circuit models with fringe and leakage factors derived from detailed, 3D, finite element
field models. Reliability results are presented vs. detection/correction delay time and individual
power amplifier reliability for 4, 6, and 7 pole configurations. Reliability is shown for two success
criteria, i.e. (a) no catcher bearing contact following pole failures and (b) re-levitation off of the
catcher bearings following pole failures. An advantage of the method presented over other redundant
operation approaches is a significantly reduced requirement for backup hardware such as additional
actuators or power amplifiers.
Determination of Rolling-Element Fatigue Life From Computer Generated Bearing Tests
2003 : 28 pages : PDF format
Two types of rolling-element bearings representing radial loaded and thrust loaded bearings were
used for this study. Three hundred forty (340) virtual bearing sets totaling 31400 bearings were
randomly assembled and tested by Monte Carlo (random) number generation. The Monte Carlo results
were compared with endurance data from 51 bearing sets comprising 5321 bearings. A simple algebraic
relation was established for the upper and lower L(sub 10) life limits as function of number of
bearings failed for any bearing geometry. There is a fifty percent (50 percent) probability that
the resultant bearing life will be less than that calculated. The maximum and minimum variation
between the bearing resultant life and the calculated life correlate with the 90-percent confidence
limits for a Weibull slope of 1.5. The calculated lives for bearings using a load-life exponent
p of 4 for ball bearings and 5 for roller bearings correlated with the Monte Carlo generated bearing
lives and the bearing data. STLE life factors for bearing steel and processing provide a reasonable
accounting for differences between bearing life data and calculated life. Variations in Weibull slope
from the Monte Carlo testing and bearing data correlated. There was excellent agreement between
percent of individual components failed from Monte Carlo simulation and that predicted.
Unbalance Response Prediction for Rotors on Ball Bearings Using Speed and Load Dependent Nonlinear
2003 : 14 pages : PDF format
Rolling-element bearing forces vary nonlinearly with bearing deflection. Thus an accurate rotordynamic
analysis requires that bearing forces corresponding to the actual bearing deflection be utilized.
For this work bearing forces were calculated by COBRA-AHS, a recently developed rolling-element
bearing analysis code. Bearing stiffness was found to be a strong function of bearing deflection,
with higher deflection producing markedly higher stiffness. Curves fitted to the bearing data for
a range of speeds and loads were supplied to a flexible rotor unbalance response analysis.
The rotordynamic analysis showed that vibration response varied nonlinearly with the amount of rotor
imbalance. Moreover, the increase in stiffness as critical speeds were approached caused a large
increase in rotor and bearing vibration amplitude over part of the speed range compared to the case
of constant bearing stiffness. Regions of bistable operation were possible, in which the amplitude at
a given speed was much larger during rotor acceleration than during deceleration. A moderate amount of
damping will eliminate the bistable region, but this damping is not inherent in ball bearings.
Design and Fabrication of High-Temperature, Radial Magnetic Bearing for Turbomachinery
2003 : 18 pages : PDF format
Motors, magnetic bearings, and other electromagnetic actuators that can operate at 1000 F (540 C) hold
great promise for providing increased efficiency in machinery for many applications ranging from
pebble-bed nuclear reactors and chemical processing to aircraft and unmanned aerial combat vehicle
(UCAV) propulsion systems. This report discusses in detail the design and fabrication of a high-temperature,
heteropolar, radial magnetic bearing that was operated at 1000 F (540 C). The development of
high-temperature wire and a coil fabrication process are two significant technical barriers overcome
by the Army Research Laboratory (ARL), the NASA Glenn Research Center, and the Texas A&M University
(TAMU) team. This is ARL/NASA/TAMU s third-generation high-temperature magnetic bearing. The
motivation for this research came from the pursuit of a more electric gas turbine engine and a
high-temperature, large-diameter, 4-million-DN (diam in millimeters times rotor speed in
revolutions per minute) rotor support system.
Permanent Magnetic Bearing for Spacecraft Applications
2003 : 16 pages : PDF format
A permanent, totally passive magnetic bearing rig was designed, constructed, and tested.
The suspension of the rotor was provided by two sets of radial permanent magnetic bearings operating
in the repulsive mode. The axial support was provided by jewel bearings on both ends of the rotor.
The rig was successfully operated to speeds of 5500 rpm using an air impeller. Radial and axial
stiffnesses of the permanent magnetic bearings were experimentally measured and then compared to
finite element results. The natural damping of the rotor was measured and a damping coefficient
Transient Vibration Prediction for Rotors on Ball Bearings using Load-Dependent Non-Linear Bearing Stiffness
2002 : 14 pages : PDF format
Rolling-element bearing forces vary nonlinearly with bearing deflection. Thus an accurate rotordynamic
transient analysis requires bearing forces to be determined at each step of the transient solution.
Analyses have been carried out to show the effect of accurate bearing transient forces (accounting
for non-linear speed and load dependent bearing stiffness) as compared to conventional use of average
rolling-element bearing stiffness. Bearing forces were calculated by COBRA-AHS (Computer Optimized Ball
and Roller Bearing Analysis - Advanced High Speed) and supplied to the rotordynamics code ARDS
(Analysis of Rotor Dynamic Systems) for accurate simulation of rotor transient behavior. COBRA-AHS
is a fast-running 5 degree-of-freedom computer code able to calculate high speed rolling-element
bearing load-displacement data for radial and angular contact ball bearings and also for cylindrical
and tapered roller beatings. Results show that use of nonlinear bearing characteristics is essential
for accurate prediction of rotordynamic behavior.
The Role of Radial Clearance on the Performance of Foil Air Bearings
2002 : 19 pages : PDF format
Load capacity tests were conducted to determine how radial clearance variations affect the load
capacity coefficient of foil air bearings. Two Generation III foil air bearings with the same
design but possessing different initial radial clearances were tested at room temperature against
an as-ground PS304 coated journal operating at 30,000 rpm. Increases in radial clearance were
accomplished by reducing the journal's outside diameter via an in-place grinding system. From
each load capacity test the bearing load capacity coefficient was calculated from the rule-of-thumb
(ROT) model developed for foil air bearings. The test results indicate that, in terms of the load
capacity coefficient, radial clearance has a direct impact on the performance of the foil air
bearing. Each test bearing exhibited an optimum radial clearance that resulted in a maximum load
capacity coefficient. Relative to this optimum value are two separate operating regimes that are
governed by different modes of failure. Bearings operating with radial clearances less than the
optimum exhibit load capacity coefficients that are a strong function of radial clearance and are
prone to a thermal runaway failure mechanism and bearing seizure. Conversely, a bearing operating
with a radial clearance twice the optimum suffered only a 20 percent decline in its maximum load
capacity coefficient and did not experience any thermal management problems. However, it is
unknown to what degree these changes in radial clearance had on other performance parameters,
such as the stiffness and damping properties of the bearings.
Wave Journal Bearings Under Dynamic Loads
2002 : 16 pages : PDF format
The dynamic behavior of the wave journal bearing was determined by running a three-wave bearing
with an eccentrically mounted shaft. A transient analysis was developed and used to predict
numerical data for the experimental cases. The three-wave journal bearing ran stably under
dynamic loads with orbits well inside the bearing clearance. The orbits were almost circular
and nearly free of the influence of, but dynamically dependent on, bearing wave shape.
Experimental observations for both the absolute bearing-housing-center orbits and the relative
bearing-housing-center-to-shaft-center orbits agreed well with the predictions. Moreover, the
subsynchronous whirl motion generated by the fluid film was found experimentally and predicted
theoretically for certain speeds.
Effect of Bearing Dynamic Stiffness on Gear Vibration
2002 : 10 pages : PDF format
Noise is a major consideration in the design of high performance geared transmissions,
such as for helicopters. Transmission error, that is, the accuracy with which the driven gear
follows the driver gear, is a common indicator of noise generation. It is well known that
bearing properties have a strong influence on shaft dynamics. However, up to now the
contribution of bearings to transmission error has received little attention. In this paper,
a torsional-axial-lateral geared rotor analysis is used to determine dynamic transmission error
as a function of bearing stiffness and damping. Bearings have a similar effect as found in shaft
dynamics; transmission error can be reduced more than 10 decibels by appropriate selection of
Comparison Between Oil-Mist and Oil-Jet Lubrication of High-Speed, Small-Bore, Angular-Contact Ball Bearings
2001 : 16 pages : PDF format
Parametric tests were conducted with an optimized 35-mm-bore-angular-contact ball bearing on a
high-speed, high-temperature bearing tester. Results from both air-oil mist lubrication and
oil-jet lubrication systems used to lubricate the bearing were compared to speeds of 2.5 x 10(exp 6)
DN. The maximum obtainable speed with air-oil mist lubrication is 2.5 x 10(exp 6) DN. Lower bearing
temperatures and higher power losses are obtained with oil-jet lubrication than with air-oil mist
lubrication. Bearing power loss is a direct function of oil flow to the bearing and independent of
oil delivery system. For a given oil-flow rate, bearing temperature and power loss increase with
increases in speed. Bearing life is an inverse function of temperature, the difference in temperature
between the individual bearing ring components, and the resultant elastohydrodynamic (EHD) film
thicknesses. Bearing life is independent of the oil delivery system except as it affects temperature.
Cage slip increased with increases in speed. Cage slip as high as 7 percent was measured and was
generally higher with air-oil mist lubrication than with oil-jet lubrication.
Rotordynamic Influence on Rolling ELement Bearing Selection and Operation
2001 : 14 pages : PDF format
Three case studies are presented that illustrate the importance of dynamic considerations in
the design of machinery supported by rolling element bearings. The first case concerns a milling
spindle that experienced internal rubs and high bearing loads, and required retrofit of an
additional . damped bearing. The second case deals with a small high-speed generator that
suffered high vibration due to flexible mounting. The third case is a propulsion fan simulator
rig whose bearings failed catastrophically due to improper bearing installation (which resulted
in inadequate dynamic bearing stiffness) and lack of health monitoring instrumentation.
Rolling Bearing Life Prediction-Past, Present, and Future
2000 : 12 pages : PDF format
Comparisons were made between the life prediction formulas of Lundberg and Palmgren, Ioannides and
Harris, and Zaretsky and full-scale ball and roller bearing life data. The effect of Weibull slope
on bearing life prediction was determined. Life factors are proposed to adjust the respective life
formulas to the normalized statistical life distribution of each bearing type. The Lundberg-Palmgren
method resulted in the most conservative life predictions compared to Ioannides and Harris, and Zaretsky
methods which produced statistically similar results. Roller profile can have significant effects on
bearing life prediction results. Roller edge loading can reduce life by as much as 98 percent. The
resultant predicted life not only depends on the life equation used but on the Weibull slope assumed,
the least variation occurring with the Zaretsky equation. The load-life exponent p of 10/3 used in
the American National Standards Institute (ANSI)/American Bearing Manufacturers Association
(ABMA)/International Organization for Standardization (ISO) standards is inconsistent with the
majority roller bearings designed and used today.
Design and Operating Characteristics of High-Speed, Small-Bore Cylindrical-Roller Bearings
2000 : 20 pages : PDF format
The computer program SHABERTH was used to analyze 35-mm-bore cylindrical roller bearings
designed and manufactured for high-speed turbomachinery applications. Parametric tests of
the bearings were conducted on a high-speed, high-temperature bearing tester and the results
were compared with the computer predictions. Bearings with a channeled inner ring were
lubricated through the inner ring, while bearings with a channeled outer ring were lubricated
with oil jets. Tests were run with and without outer-ring cooling. The predicted bearing life
decreased with increasing speed because of increased contact stresses caused by centrifugal load.
Lower temperatures, less roller skidding, and lower power losses were obtained with channeled
inner rings. Power losses calculated by the SHABERTH computer program correlated reasonably
well with the test results. The Parker formula for XCAV (used in SHABERTH as a measure of oil
volume in the bearing cavity) needed to be adjusted to reflect the prevailing operating
conditions. The XCAV formula will need to be further refined to reflect roller bearing
lubrication, ring design, cage design, and location of the cage-controlling land.
Life of Pennzane and 815Z-Lubricated Instrument Bearings Cleaned with Non-CFC Solvents
1999 : 14 pages : PDF format
Life tests were conducted on instrument scanner ball bearings cleaned with 3 types of
non-ozone depleting solvents and compared with those cleaned with a conventional CFC-113
(Freon) solvent. The test bearings were lubricated with the standard space oil
(Bray 815Z, Fomblin Z25) and a more recent synthetic space oil (Pennzane 2001).
Lives with replacement solvents equaled or exceeded those obtained with CFC-113 baseline,
indicating that alternate cleaning solvents were acceptable. Pennzane lubricated bearings
enjoyed a significant life advantage (>5X) over those lubricated with Bray 815Z oil in
these oscillatory gimbal bearing tests. Many of the Pennzane bearings are still exhibiting
acceptable torque traces after more than 25,000 hr of test.
Design and Operating Characteristics of High-Speed, Small-Bore, Angular-Contact Ball Bearings
1998 : 26 pages : PDF format
The computer program SHABERTH was used to analyze 35-mm-bore, angular-contact ball bearings
designed and manufactured for high-speed turbomachinery applications. Parametric tests of the
bearings were conducted on a high-speed, high-temperature bearing tester and were compared with the
computer predictions. Four bearing and cage designs were studied. The bearings were lubricated either
by jet lubrication or through the split inner ring with and without outer-ring cooling. The predicted
bearing life decreased with increasing speed because of increased operating contact stresses caused by
changes in contact angle and centrifugal load. For thrust loads only, the difference in calculated
life for the 24 deg. and 30 deg. contact-angle bearings was insignificant. However, for combined
loading, the 24 deg. contact-angle bearing gave longer life. For split-inner-ring bearings, optimal
operating conditions were obtained with a 24 deg. contact angle and an inner-ring, land-guided
cage, using outer-ring cooling in conjunction with low lubricant flow rates. Lower temperature
and power losses were obtained with a single-outer-ring, land-guided cage for the 24 deg.
contact-angle bearing having a relieved inner ring and partially relieved outer ring. Inner-ring
temperatures were independent of lubrication mode and cage design. In comparison with measured
values, reasonably good engineering correlation was obtained using the computer program SHABERTH
for predicted bearing power loss and for inner- and outer-ring temperatures. The Parker formula
for XCAV (used in SHABERTH, a measure of oil volume in the bearing cavity) may need to be refined
to reflect bearing lubrication mode, cage design, and location of cage-controlling land.
A. Palmgren Revisited: A Basis for Bearing Life Prediction
1997 : 12 pages : PDF format
Bearing technology, as well as the bearing industry, began to develop with the invention of
the bicycle in the 1850's. At the same time, high-quality steel was made possible by the
Bessemer process. In 1881, H. Hertz published his contact stress analysis. By 1902, R.
Stribeck had published his work based on Hertz theory to calculate the maximum load of a
radially loaded ball bearing. By 1920, all of the rolling bearing types used today were being
manufactured. AISI 52100 bearing steel became the material of choice for these bearings.
Beginning in 1918, engineers directed their attention to predicting the lives of these bearings.
In 1924, A. Palmgren published a paper outlining his approach to bearing life prediction.
This paper was the basis for the Lundberg-Palmgren life theory published in 1947. A critical
review of the 1924 Palmgren paper is presented here together with a discussion of its effect
on bearing life prediction.
High Performance Magnetic Bearings for Aero Applications
1997 : 37 pages : PDF format
Several previous annual reports were written and numerous papers published on the
topics for this grant. That work is not repeated here in this final report. Only the
work completed in the final year of the grant is presented in this final report. This
final year effort concentrated on power loss measurements in magnetic bearing rotors.
The effect of rotor power losses in magnetic bearings are very important for many applications.
In some cases, these losses must be minimized to maximize the length of time the rotating
machine can operate on a fixed energy or power supply. Examples include aircraft gas
turbine engines, space devices, or energy storage flywheels. In other applications,
the heating caused by the magnetic bearing must be removed. Excessive heating can be a
significant problem in machines as diverse as large compressors, electric motors,
textile spindles, and artificial heart pumps.
The Effect of ODC-Free Cleaning Techniques on Bearing Lifetimes in the Parched Elastohydrodynamic Regime
1997 : 16 pages : PDF format
A parched elastohydrodynamic rig was used to determine relative bearing lifetimes as a
function of cleaning procedures in a series of accelerated tests. Two ODC-free cleaning
procedures (super critical CO2 and ultraviolet-ozone) were compared to a CFC-113 control.
Bearings (52100 steel) were run in the counter rotating mode (equivalent to 4600 rpm) with
a full complement (i.e. no retainer) and a single charge of lubricant (Krytox 143 AC). Test
conditions included: an air atmosphere, 445 N load, approx. 1.0 GPa mean Hertz stress. There
was approximately a 50% reduction in life with bearings cleaned with UV/ozone and a 70%
reduction in life with SFE CO2 when compared to the Freon control. Possible reasons for
these decreases in lifetimes are presented.
Sliding Contact Bearings for Service to 700 C
1996 : 24 pages : PDF format
Cylindrical, sliding contact bearings made entirely of a self-lubricating powder
metallurgy composite (PM212) or of super alloy shells lined with clad PM212 were
tested in an oscillating mode at temperatures from 25 to 700 C. Tests of 100 hr
duration or longer were conducted at a bearing unit load of 3.45 Mpa (500 psi). Shorter
duration tests at various unit loads up to 24.1 Mpa (3500 psi) were also conducted. In
comparison tests, bearings lubricated with PM212 had superior anti-wear characteristics
compared to the baseline, unlubricated, super alloy bearings: no galling of PM212-lubricated
bearings occurred, while severe surface damage including galling occurred, especially at
high loads, during the baseline tests. A heat treatment procedure, which dimensionally
stabilizes PM212 and thereby minimizes clearance changes during high temperature bearing
operation, is described.
Comparison of life theories for rolling-element bearings
1995 : 30 pages : PDF format
Nearly five decades have passed since G. Lundberg and A. Palmgren published their life
theory in 1947 and 1952 and it was adopted as an ANSI/ABMA and ISO standard in 1950 and
1953. Subsequently, many variations and deviations from their life theory have been proposed,
the most recent being that of E. Ioannides and T.A. Harris in 1985. This paper presents a
critical analysis comparing the results of different life theories and discussing their
implications in the design and analysis of rolling-element bearings. Variations in the stress-life
relation and in the critical stress related to bearing life are discussed using stress
fields obtained from three-dimensional, finite-element analysis of a ball in a nonconforming
race under varying load. The results showed that for a ninth power stress-life exponent the
Lundberg-Palmgren theory best predicts life as exhibited by most air-melted bearing steels. F
or a 12th power relation reflected by modern bearing steels, a Zaretsky-modified Weibull
equation is superior. The assumption of a fatigue-limiting stress distorts the stress-life
exponent and overpredicts life.
Wave journal bearing. Part 1: Analysis
1995 : 12 pages : PDF format
A wave journal bearing concept features a waved inner bearing diameter of the non-rotating
bearing side and it is an alternative to the plain journal bearing. The wave journal bearing
has a significantly increased load capacity in comparison to the plain journal bearing operating
at the same eccentricity. It also offers greater stability than the plain circular bearing under
all operating conditions. The wave bearing's design is relatively simple and allows the shaft to
rotate in either direction. Three wave bearings are sensitive to the direction of an applied
stationary side load. Increasing the number of waves reduces the wave bearing's sensitivity to
the direction of the applied load relative to the wave. However, the range in which the bearing
performance can be varied decreases as the number of waves increases. Therefore, both the number
and the amplitude of the waves must be properly selected to optimize the wave bearing design for
a specific application. It is concluded that the stiffness of an air journal bearing, due to
hydrodynamic effect, could be doubled and made to run stably by using a six or eight wave
geometry with a wave amplitude approximately half of the bearing radial clearance.
Wave journal bearing. Part 2: Experimental pressure measurements and fractional frequency whirl threshold for wave and plain journal bearings
1995 : 11 pages : PDF format
A new hydrodynamic bearing concept, the wave journal bearing, is being developed because it
has better stability characteristics than plain journal bearings while maintaining similar
load capacity. An analysis code to predict the steady state and dynamic performance of the
wave journal bearing is also part of the development. To verify numerical predictions and
contrast the wave journal bearing's stability characteristics to a plain journal bearing,
tests were conducted at NASA Lewis Research Center using an air bearing test rig. Bearing
film pressures were measured at 16 ports located around the bearing circumference at the
middle of the bearing length. The pressure measurements for both a plain journal bearing
and a wave journal bearing compared favorably with numerical predictions. Both bearings
were tested with no radial load to determine the speed threshold for self-excited fractional
frequency whirl. The plain journal bearing started to whirl immediately upon shaft start-up.
The wave journal did not incur self-excited whirl until 800 to 900 rpm as predicted by the
analysis. Furthermore, the wave bearing's geometry limited the whirl orbit to less than the
bearing's clearance. In contrast, the plain journal bearing did not limit the whirl orbit,
causing it to rub.
Modeling of rolling element bearing mechanics. Theoretical manual.
1994 : 96 pages : PDF format
This report documents the theoretical basis for the Rolling Element Bearing Analysis
System (REBANS) analysis code which determines the quasistatic response to external
loads or displacement of three types of high-speed rolling element bearings: angular
contact ball bearings; duplex angular contact ball bearings; and cylindrical roller bearings.
The model includes the effects of bearing ring and support structure flexibility. It is
comprised of two main programs: the Preprocessor for Bearing Analysis (PREBAN) which creates the
input files for the main analysis program; and Flexibility Enhanced Rolling Element Bearing
Analysis (FEREBA), the main analysis program. A companion report addresses the input
instructions for and features of the computer codes. REBANS extends the capabilities of the
SHABERTH (Shaft and Bearing Thermal Analysis) code to include race and housing flexibility,
including such effects as dead band and preload springs.
Detailed study of oxidation/wear mechanism in lox turbopump bearings
1993 : 118 pages : PDF format
Wear of 440C angular contact ball bearings of the phase 2 high pressure oxygen
turbopump (HPOTP) of the space shuttle main engine (SSME) has been studied by means
of various advanced nondestructive techniques (NDT) and modeled with reference to all
known material, design, and operation variables. Three modes dominating the wear scenario
were found to be the adhesive/sheer peeling (ASP), oxidation, and abrasion. Bearing wear
was modeled in terms of the three modes. Lacking a comprehensive theory of rolling contact
wear to date, each mode is modeled after well-established theories of sliding wear, while
sliding velocity and distance are related to microsliding in ball-to-ring contacts.
Microsliding, stress, temperature, and other contact variables are evaluated with analytical
software packages of SHABERTH(TM)/SINDA(TM) and ADORE(TM). Empirical constants for the models
are derived from NIST experiments by applying the models to the NIST wear data. The bearing
wear model so established precisely predicts quite well the average ball wear rate for the
HPOTP bearings. The wear rate has been statistically determined for the entire population
of flight and development bearings based on Rocketdyne records to date. Numerous illustrations are given.
Introduction to Magnetic Bearings
1995 : 23 pages : PDF format
Multi-axis suspension has several advantages over single axis system, in that it provides
control of an object with precision in two or three orthogonal axes. In this report, we discuss
the primary use of magnetic-bearing suspension and it's relevance to what was formally known as
NASA's Annular Suspension and Pointing System (ASPS). This system is an experimental pointing
system with applications for the space shuttle and the space station programs. The objectives
behind this magnetic suspension research project are to provide insight to the use of the ASPS
configuration, to control the solar panels of the space station. This is important to maintain
the correct position of the panels in relation to the sun and orbiting space station for the
continuous supply of solar energy. Since the panels are suspended, they can be aligned with
minimum outside interference. The approach of using magnetic suspension technology guarantees
mechanical isolation since there are no contacting surfaces. This isolation reduces vibration
transmission and mechanical wear which in turn extends the life of the payload and of the carrier.
It should be noted that ASPS has a high pointing accuracy along the line of 0.01 arc-second. This
research will be done in a laboratory setting by incorporating five bearing stations and one motion
control station. We will attempt to suspend an object of dead weight similar to that of a solar panel.
The long term applications may include deep-space navigation, fire control in weapon systems, and an
improved mass transit system.
Application of powder metallurgy techniques to produce improved bearing elements for liquid rocket engines
1994 : 118 pages : PDF format
The objective was to apply powder metallurgy techniques for the production of improved
bearing elements, specifically balls and races, for advanced cryogenic turbopump bearings.
The materials and fabrication techniques evaluated were judged on the basis of their ability
to improve fatigue life, wear resistance, and corrosion resistance of Space Shuttle Main Engine
(SSME) propellant bearings over the currently used 440C. An extensive list of candidate bearing
alloys in five different categories was considered: tool/die steels, through hardened stainless
steels, cobalt-base alloys, and gear steels. Testing of alloys for final consideration included
hardness, rolling contact fatigue, cross cylinder wear, elevated temperature wear, room and
cryogenic fracture toughness, stress corrosion cracking, and five-ball (rolling-sliding element)
testing. Results of the program indicated two alloys that showed promise for improved bearing
elements. These alloys were MRC-2001 and X-405. 57mm bearings were fabricated from the MRC-2001
alloy for further actual hardware rig testing by NASA-MSFC.
Modeling of rolling element bearing mechanics
1991 : 15 pages : PDF format
Roller element bearings provide the primary mechanical interface between rotating and
nonrotating components in the high performance turbomachinery of the Space Shuttle Main
Engine (SSME). Knowledge of bearing behavior under various loading and environmental
conditions is essential to predicting and understanding the overall behavior of turbopumps,
including rotordynamic stability, critical speeds and bearing life. The objective is to
develop mathematical models and computer programs to describe the mechanical behavior of ball
and cylinder roller bearings under the loading and environmental conditions encountered in
the SSME and future high performance rocket engines. This includes characteristics such as
nonlinear load/motion relationships, stiffness and damping, rolling element loads for life
prediction, and roller and cage stability.
Analysis of rolling contact spall life in 440 C steel bearing rims
1991 : 274 pages : PDF format
The results of a two year study of the mechanisms of spall failure in the HPOTP
bearings are described. The objective was to build a foundation for detailed analyses
of the contact life in terms of: cyclic plasticity, contact mechanics, spall nucleation,
and spall growth. Since the laboratory rolling contact testing is carried out in the 3
ball/rod contact fatigue testing machine, the analysis of the contacts and contact lives
produced in this machine received attention. The results from the experimentally observed
growth lives are compared with calculated predictions derived from the fracture mechanics
Vibration transmission through rolling element bearings in geared rotor systems
1991 : 236pages : PDF format
A new mathematical model is proposed to examine the vibration transmission through
rolling element bearings in geared rotor systems. Current bearing models, based on
either ideal boundary conditions for the shaft or purely translational stiffness element
description, cannot explain how the vibratory motion may be transmitted from the rotating
shaft to the casing. Experimental results have shown that the casing plate motion is primarily
flexural. Here, this issue is clarified qualitatively and quantitatively by developing a
comprehensive bearing stiffness matrix of dimension 6 to model precision rolling element
bearings using basic principles. The proposed bearing stiffness matrix is partially
verified using available analytical and experimental data, and is completely characterized.
The study extends the proposed bearing formulation to analyze the overall geared rotor system
dynamics including casing and mounts. The bearing stiffness matrix is included in discrete
system models using lumped parameter and/or dynamic finite element techniques.
Bearing and gear steels for aerospace applications
1990 : 32 pages : PDF format
Research in metallurgy and processing for bearing and gear steels has resulted in
improvements in rolling-element bearing and gear life for aerospace application by
a factor of approximately 200 over that obtained in the early 1940's. The selection
and specification of a bearing or gear steel is dependent on the integration of multiple
metallurgical and physical variables. For most aerospace bearings, through-hardened VIM-VAR
AISI M-50 steel is the material of preference. For gears, the preferential material is
case-carburized VAR AISI 9310. However, the VAR processing for this material is being
replaced by VIM-VAR processing. Since case-carburized VIM-VAR M-50NiL incorporates the
desirable qualities of both the AISI M-50 and AISI 9310 materials, optimal life and
reliability can be achieved in both bearings and gears with a single steel. Hence,
this material offers the promise of a common steel for both bearings and gears for
future aerospace applications.
A study of fracture mechanisms in ATD roller bearing
1991 : 57 pages : PDF format
The purpose was to investigate how microstructures, especially anisotropy, affects
internal stresses and the overall mechanical response of bearings. Samples with the stress
axis along the aligned carbide direction possessed high modulus values compared to those
with their axis perpendicular to the carbide stringers. The difference in the modulus was
found to be more than a factor of two. A series of experiments was conducted on rolled samples
to further investigate this effect; the two sets of results were consistent with each other.
The degree of anisotropy of the microstructure in terms of the carbide and matrix orientations
was determined using x-ray diffraction. The stress state determination was conducted using
neutron diffraction. It was found that there was little variation in the distribution of the
internal stresses amongst different samples, indicating that small changes in the processing
and geometrical conditions did not result in significant variations in the internal stress. A
nominal tensile hoop stress of 39 ksi was obtained for the inner raceway. Furthermore, during
the course of the investigation, it was apparent that there was a need to determine the stress
state induced by the shrink fitting process. Therefore, a series of experiments was conducted
using strain gages to identify the stress distribution in a shrink fitting process in three
different types of geometries. Correlations were obtained to estimate the highest stress values
in the outer and inner groove geometry. A finite element program based on the ANSYS system was
developed to compute the stress distribution in the inner raceway geometry. This analysis indicates
that the highest tensile stress in the system occurs at the ID of the ring with a stress value of
over 5 times that of the applied radial stress. Results from all these facets were correlated with
one another. It appears that the material does not fail as a result of any one single factor, but
results from a combination of the various factors investigated.
Improved oil-off survivability of tapered roller bearings
1988 : 87 pages : PDF format
The aim of this program is to improve the oil-off survivability of a tapered roller bearing when
applied to a helicopter transmission, since the tapered bearing has shown a performance advantage
in this application. However, the critical roller end-rib conjunction is vulnerable to damage in
an oil-off condition. Three powdered metal materials were selected to use as the rib material for
oil-off evaluation. These were: M2 steel to a 65% density, CBS 1000M 65% density, and CBS 1000M
75% density. The bearing styles tested were ribbed cone (inner race) and ribbed cup (outer race).
Carburized solid CBS 600 was also used as a ribbed material for comparison of oil-off results. The
tests were conducted at six speeds from 4000 rpm (0.26 million DN) through 37000 rpm (2.4 million
DN).The ribbed cup style bearing achieved longer lives than the ribbed cone style. A standard bearing
lasted only 10 minutes at 4000 rpm; however, the 30-min oil-off goal was achieved through
11000 rpm using the survivable ribbed cup bearing. The oil-off lives at 37000 rpm were less
than 10 seconds. The grinding of the powder metal materials and surface preparation to achieve
an open porosity is extremely critical to the oil-off performance of the powder metal component.
Mechanisms of rolling contact spalling
1988 : 109 pages : PDF format
The results of a study aimed at analyzing the mechanical material interactions
responsible for rolling contact spalling of the 440 C steel, high pressure oxygen
turbopump bearings are presented. A coupled temperature displacement finite element analysis of
the effects of friction heating under the contact is presented. The contact is modelled as a
stationary, heat generating, 2 dimensional indent in an elastic perfectly plastic half-space
with heat fluxes up to 8.6 x 10000 KW/m sq comparable to those generated in the bearing. Local
temperatures in excess of 1000 C are treated. The calculations reveal high levels of residual
tension after the contact is unloaded and cools. Efforts to promote Mode 2/Mode 3 fatigue crack
growth under cyclic torsion in hardened 440 C steel are described. Spalls produced on 440 C steel
by a 3 ball/rod rolling contact testing machine were studied with scanning microscopy. The shapes
of the cyclic, stress strain hysteresis loops displayed by hardened 440 C steel in cyclic torsion
at room temperature are defined for the plastic strain amplitudes encountered in rolling/sliding
contact. Results of these analyses are discussed in detail.
Lubricant effects on bearing life
1987 : 22 pages : PDF format
Lubricant considerations for rolling-element bearings have within the last two decades
taken on added importance in the design and operation of mechanical systems. The phenomenon
which limits the useful life of bearings is rolling-element or surface pitting fatigue. The
elastohydrodynamic (EHD) film thickness which separates the ball or roller surface from those
of the raceways of the bearing directly affects bearing life. Chemical additives added to the
lubricant can also significantly affect bearings life and reliability. The interaction of these
physical and chemical effects is important to the design engineer and user of these systems.
Design methods and lubricant selection for rolling-element bearings are presented and discussed.
A note about older reports:
Essentially all of NASA's bearing-related reports and studies prior to 1987 have
been replicated and superseded by later studies which better reflect products and
technologies in use today.
For documents published prior to 1959, see the Technical Report Server at
the National Advisory Committee for Aeronautics: http://naca.larc.nasa.gov