Principles of bearing selection and application 8 Angular contact ball bearings 112 Cylindrical ...

161 Pages·2003·8.34 MB·English

Principles of bearing selection and application 8
Angular contact ball bearings 112
Cylindrical roller bearings 180
Double direction angular contact thrust ball bearings 214
Single direction angular contact thrust ball bearings 234
Locking devices 260
Copyright SKF 2003
Gauges 286
The contents of this publication are the
copyright of the publisher and may not be
reproduced (even extracts) unless
permission is granted.Every care has
beentaken to ensure the accuracy of the
information contained in this publication
butno liability can be accepted for any Other products and services 298
lossor damage, whether direct, indirect
orconsequential arising out of the use
ofthe information contained herein.
www.skf.com
Publication 5002 E
Products index 301
2003 - 02
The SKF Group
– a worldwide corporation
SKF has developed the Channel
The SKF Group is the first major concept in factories all over the
SKF is an international industrial Group The business of the Group consists
bearing manufacturer to have world.This drastically reduces
operating in more than 130 countries and is ofbearings, seals, special steels and a been granted approval according thelead-time from raw material
world leader in bearings. comprehensive range of other high-tech to ISO 14001, the international toend product as well as work
The company was founded in 1907 industrial components.The experience standard for environmental The SKF Engineering & Research inprogress and finished goods
following the invention of the self-aligning gained in these various fields provides SKF management systems. Centre is situated just outside instock.The concept enables
Thecertificate is the most Utrecht in The Netherlands. faster and smoother information
ball bearing by Sven Wingquist and, after with the essential knowledge and expertise comprehensive of its kind Inanarea of 17000 square flow, eliminates bottlenecks and
only a few years, SKF began to expand required in order to provide the customers andcovers more than 60 SKF metres (185000 sq.ft) some bypasses unnecessary steps in
allover the world. with the most advanced engineering production units in 17 countries. 150scientists, engineers and production.The Channel team
Today, SKF has some 40000 employees products and efficient service. support staff are engaged in the members have the knowledge
further improvement of bearing andcommitment needed to share
and around 80 manufacturing facilities
performance.They are developing the responsibility for fulfilling
spread throughout the world.An international technologies aimed at achieving objectives in areas such as quality,
sales network includes a large number better materials, better designs, delivery time, production flow etc.
ofsales companies and some 7000 better lubricants and better seals
– together leading to an even
distributors.Worldwide availability of SKF
better understanding of the
products is supported bya comprehensive
operation of a bearing in its
technical advisory service. application.This is also where
The key to success has been a consistent theSKF Life Theory was evolved,
emphasis on maintaining the highest quality enabling the design of bearings
that are even more compact and
of its products and services.Continuous
offer even longer operational life.
investment in research and development
has also played a vital role, resulting
inmany examples of epoch-making
innovations.
SKF manufactures ball bearings,
roller bearings and plain bearings.
The smallest are just a few
millimetres (a fraction of an inch)
in diameter, the largest several
metres.SKF also manufactures
bearing and oil seals that prevent
dirt from entering and lubricant
from leaking out.SKF’s subsidiaries
CR and RFT S.p.A.are among the
world’s largest producers of seals.
2 3
Foreword
Wherever there is rotation, there is a need Machine tool applications require superior the more important it is to make use of SKF
for some form of bearing.The function of performance from the bearings used to know-how in the manufacture and application
arolling bearing is to reduce or eliminate support spindles and precision ball screws. of high-precision rolling bearings.
the friction between a fixed and a moving They must exhibit this in terms of speed
surface and to carry a load.The life of a capability, system temperature stability, Where to find information
rolling bearing must be compatible with the rigidity, accuracy and noise level;such The bearing tables and technical data on
life of the application in which it is mounted. characteristics are rarely met by bearings the following pages provide information for
for general-purpose applications.Therefore, bearing selection and application design.
The SKF standard product range comprises SKF produces special high-precision More details on bearing technology and
more than 22000 variants, covering all the bearings designed to satisfy the most onother related products can be found
principal bearing types. demanding requirements in the machine inspecific publications, the SKF General
tool environment. Catalogue or the SKF Interactive Engineering
Made by SKFstands for excellence. This catalogue presents the current range Catalogue, available as a CD-ROM or online
Itsymbolises our consistent endeavour of SKF high-precision bearings and related under www.skf.com.
toachieve total quality in everything we do. products. This site also contains further information
For those who use our products, “Made The data in this catalogue are based on the SKF Group, its products, services
bySKF”implies three main benefits. oncurrent production.However, design and contacts.
refinement for continuous improvement
Reliability– thanks to modern, efficient ineither manufacturing or performance
products, based on our worldwide mayresult in changes.
application know-how, optimised materials, The basic load ratings have been
forward-looking designs and the most calculated in accordance with the latest
advanced production techniques. specifications.Earlier catalogues, in which
the data varies from that given here, are
Cost effectiveness– resulting from the rendered invalid.SKF reserves the right
favourable ratio between our product quality tomake changes necessitated by
plus service facilities, and the purchase technological developments.
price of the product. In accordance with ISO (International
Standards Organisation) Standard 1000:
Market lead– which you can achieve 1992, SI units (Système International
bytaking advantage of our products and d’Unités) are used in this catalogue.
services.Increased operating time and
reduced downtime, as well as improved Almost 100 years
output and product quality are the key to of worldwide experience
asuccessful partnership. For almost 100 years SKF has held a
leading position in all major industrial fields
where rolling bearings are used.SKF not
only supplies a wide range of bearings but
also has broad experience in application
engineering, and is at the forefront of
systems design.This background comes
from the partnerships developed over the
years with leading firms in the machine tool
industry.The more complex the problems,
4 5
Principles of bearing
11
selection and application
Contents
Selection of bearing types 8
A wide range of high-precision bearings 8
Bearings materials 9
Accuracy 10
Rigidity 12
Speed 12
Available space 13
Loads 14
Load carrying capacity and life 17
General 17
Rating lives 17
Rating life equation for hybrid bearings 18
Load carrying capacity of bearing sets 19
Equivalent bearing loads 19
Rigidity 21
System rigidity 21
Influence of a loose fit 22
Speed 23
Rotational speed 23
Speed ratings 25
Speed capability of bearing systems 26
Bearing data – general 27
Dimension 27
Tolerances 28
Bearing internal clearance or preload 30
Material for high-precision bearings 31
Application of bearings 34
Bearing arrangements 34
Radial location of bearings 35
Application examples 36
Axial location of bearings 51
Bearing preload 52
Seals 57
Lubrication and maintenance 62
General 62
Grease lubrication 62
Oil lubrication 71
Maintenance 78
Dismounting and mounting 79
Dismounting 79
Mounting 89
Inspection 105
7
1Principles of bearing selection and application
Selection of bearing type Bearing materials
Hybrid bearings
Machine tools, especially machining 1
All-steel bearings centres, can have higher machining
The performance and reliability of rolling efficiencies and higher machining
bearings are determined to a large degree accuracies when operated at higher
by the materials from which the bearing speeds.For this reason, there have been
components are made. ever-greater demands for higher speed
Steels used for high-precision bearing performance of their spindle bearings.
A wide range of rings and rolling elements are capable of If the performance required is close to
Depending on the application, one or more being adequately hardened and have high all-steel bearing limits, or if higher rigidity
high-precision bearings
of these factors will have a dominant fatigue strength and wear resistance. orlonger life are needed, hybrid high-
influence.It is therefore, not possible to Moreover they have the structural and precision bearings can be used.Hybrid
It is not always possible to find an setdown general rules for the selection dimensional stability to satisfy the spindle high-precision bearings consist of outer
appropriate solution to application design ofbearing type or bearing series.Where operating temperatures. andinner rings made of bearing steel
and problems using standard bearings demands for high-precision and productivity SKF high-precision bearing rings and andceramic (silicon nitride Si N ) rolling
3 4
forgeneral machinery.This is particularly are exceptionally high, SKF provides a rolling elements are generally made of elements, having density as light as 40%
truein machine tool applications where comprehensive range of hybrid (i.e.bearings through-hardened carbon chromium steel ofbearing steel butyet having a high rigidity
requirements are tougher. with steel rings and ceramic rolling elements) containing approximately 1% carbon and (➔ fig 1 ).
SKF has developed a very comprehensive high-precision angular contact ball bearings 1,5% chromium.
range of high-precision bearings for and cylindrical roller bearings for machine
machine tool spindles, and other tool spindles.
applicationswhere high demands are To make bearing selection easier, the
placed on accuracy and speed capability. properties of the different bearing types
Each of these bearing types has specific aredescribed in the following.
features that make it particularly suitable for
specific applications.
Internal design is state-of-the art, and
differs in many ways from that of a standard
bearing.The design has been optimised
foroutstanding speed capability in
combination with the highest possible
stiffness.When designing a bearing
arrangement it is necessary to consider
anumber of factors, i.e.: Comparison of performance and cost
(cid:3) Accuracy for different bearing design (material)
(cid:3) Available space
(cid:3) Load Fig 1
(cid:3) Required system rigidity
(cid:3) Accommodation of axial displacements
(cid:3) Speed
Bearing material Performances Cost Typical applications
(cid:3) Heat generation.
Machine tools.
Precision equipments.
Full steel High speed rolling mills.
High speed electric motors,
etc.
Machine tools.
Precision equipments.
Hybrids Turbochargers.
High speed electric motors,
etc.
8 9
1Principles of bearing selection and application
Accuracy
forthe different tolerance classes angular contact thrust ball bearings made Dimensional accuracy
comparing bearings with bore diameters. totolerance class UP specifications can be The dimensional accuracy of a bearing is 1
Running accuracy The different standards ABMA and ISO supplied (➔ Table 2 ). important with respect to the fit between
The running accuracy of a bearing are also compared in Table 1 . Normally, the maximum values of K bearing ring and shaft or housing.As the
ia
arrangement is governed by the accuracy Most SKF precision bearings are given in the table are much higher than fitinfluences the clearance or preload of
ofall the component parts of the manufactured to tolerance class P4A, P4C, theactual values.This means for example, mounted bearings, the tolerances for the
arrangement.Where bearings are and SP.P4A is the standard tolerance class that if bearings with class SP tolerances bearing and its seating lie within narrow
concerned, this is primarily determined for angular contact ball bearings;SP the areused, depending on the bearing size limits.Where cylindrical roller bearings with
bythe accuracy of form and position of the standard for cylindrical roller bearings and and whether bearings are properly a tapered bore are concerned, slightly larger
raceways on the bearing rings.When double direction angular contact thrust ball mounted, arunning accuracy of less dimensional deviations are permissible
selecting the appropriate tolerance class bearings, and P4C the standard class for than2µm canbe achieved. thanfor example, angular contact ball
fora particular bearing, the maximum radial single direction angular contact thrust ball bearings with similar running accuracy.
runout of the inner ring (K ) is usually the bearings of the BTM series.For bearing Thisis because the clearance orpreload
ia
determining factor for most applications. arrangements where this standard precision ofthe bearing is determined by driving up
To facilitate comparison, Diagram 1 is inadequate, angular contact ball bearings the inner ring on its tapered seating.
gives relative values of the radial runout made to tolerance class PA9A, and
cylindrical roller bearings and double direction
Comparison of accuracy
of different tolerance classes
Diagram 1
Inner ring radial runout factor
100
100
Comparison of different standards SKFtolerance classes for high-precision bearings
80 Table 1 Table 2
ABMA ISO SKF SKF Boundary Running
60 60 Tolerance Tolerance Standard Tolerance dimensions accuracy
class class Class ISO,ABMA ISO,ABMA
40 ABEC 9 2 PA9A SP ISO 5, ABEC 5 ISO 4, ABEC 7
30
ABEC 7 4 P4 UP ISO 4, ABEC 7 ISO 2, ABEC 9
20
20 ABEC 5 5 P5 P4A ISO 4, ABEC 7 ISO 2, ABEC 91)
10 8
P4C ISO 4, ABEC 7 ISO 4, ABEC 7
0
PA9A ISO 2, ABEC 9 ISO 2, ABEC 9
Normal P6 P5 P4, SP, P4C P4A, PA9A UP
Tolerance class
1)Up to 120 mm bore diameter, for larger sizes, ABEC7
or better
10 11
1Principles of bearing selection and application
Rigidity Speed Available space
formachine tool applications belong to
theISO Diameter Series 9 and 0. 1
The rigidity of a spindle/bearing system There is a limit to the speed at which rolling High-precision bearing arrangements By selecting suitable combinations of
isofparticular importance in machine bearings can be operated.Generally, it is generally call for bearings with a low cross- bearings it is thus possible to achieve an
toolapplications as the magnitude of the permitted operating temperature with section because of the space available, optimum bearing arrangement for specific
thedeflection under load determines the respect to the lubricant being used, or to together with the high requirements in requirements within the same radial space.
productivity and machining accuracy the material of the bearing components respect ofstiffness and running accuracy of For bearing arrangements where less radial
ofamachine tool.Bearing stiffness thatsets the limit.The speed at which this the arrangement.These bearings generally space is available, angular contact ball
influencesthe stiffness of a bearing limiting bearing temperature isreached have a large number of rolling elements bearings and cylindrical roller bearings
arrangement and thus the stiffness of depends on the frictional heat generated andconsequently a high stiffness.They belonging to ISO Diameter Series 9 can be
thecomplete spindle/bearing system. inthe bearing (including any externally also enable relatively large diameter used.Angular contact ball bearings to the
However, bearings alone cannot be the applied heat) and the amount ofheat that spindles to be used for a given housing ISO Diameter Series 2, despite being rarely
onlyreason for high orlow rigidity:when can be transported away from the bearing. bore diameter, and therefore exhibit all the chosen for new designs, are still common
checking the behaviour of a complete Bearing type and size, internal design, load, advantages important for the stiffness and inexisting applications.
system, bending ofthe spindle itself, lubrication and cooling conditions, as well running accuracy of a bearing arrangement, To illustrate the space required, fig 2
position and number of support bearings as cage design, accuracy and internal e.g.aspindle bearing arrangement. shows cross-sections of the most common
and tool overhang mayalso havea great clearance/preload, all play apart in Almostall of the angular contact ball machine tool spindle bearings belonging
influence. determining speed capability. bearings, cylindrical roller bearings and tothe different Diameter Series.
The stiffness of a bearing depends angular contact thrust ball bearings used
onitstype and size, the most important
criteriabeing:
(cid:3) type of rolling elements (rollers or balls)
(cid:3) number and size of the rolling elements,
and
(cid:3) contact angle.
Because of the much larger contact area
between rolling elements and raceways in
aroller bearing than in a ball bearing, roller
bearing stiffness is much higher than ball
bearing stiffness.The number of rolling
elements has a greater influence on
bearing stiffness, than the size of the
rollingelements.Because of this, high-
High-precision bearings cross section
precision bearings almost always have fordifferent Diameter Series
thedimensions of the light Diameter
Series0 or 9.Where high radial stiffness Fig 2
isrequired, bearings having the smallest
possible contact angle should be used.
Conversely, where high axial stiffness
iscalled for, the contact angle should be
aslarge as possible.
Bearings with steel rolling elements
9 0 2 9 0 0 0 0
Bearings with ceramic rolling elements
9 0 2 0 0 0
12 13
1Principles of bearing selection and application
Loads Table 3
1
Diametric Series Bearing Contact Shaft diameters Loading Precision Speed rating
In machine tools – the main application for ISO SKF Series Code angle from up to SKF n dm
high-precision bearings – the load carrying designation α and incl. tolerance
capacity of a bearing is usually of much Class
less importance when determining bearing
– – – deg mm mm – – 106mm/min
size, than in engineering applications in
general.Other criteria such as stiffness,
size of the requisite bore in the spindle, 9 719 ACX A 25 10 30 combined P4A 1,5
719 ACD A 25 35 220 combined P4A 1,5
machining speeds and accuracy are the 719 ACE A 25 20 120 combined P4A 2,2
decisive factors. 719 CX A 15 10 30 combined P4A 1,8
When selecting the bearing type for a 719 CD A 15 10 220 combined P4A 1,8
719 CE A 15 20 120 combined P4A 2,4
given bearing arrangement, however, the
719 ACX/HC Hybrid A 25 10 30 combined P4A 1,8
magnitude and direction of action of
theload play an important part. 719 ACD/HC Hybrid A 25 35 140 combined P4A 1,8
As a general rule, roller bearings can 719 ACE/HC Hybrid A 25 20 120 combined P4A 2,5
719 CX/HC Hybrid A 15 10 30 combined P4A 2,1
carry heavier loads than ball bearings 719 CD/HC Hybrid A 15 35 140 combined P4A 2,1
having the same boundary dimensions 719 CE/HC Hybrid A 15 20 120 combined P4A 2,8
(➔ Table 3 ). NNU 49 B/W33 C2 0 100 240 radial only SP 0,8
NNU 49 BK/W33 C2 0 100 240 radial only SP 0,8
0 70 ACX A 25 10 30 combined P4A 1,5
70 ACD A 25 35 240 combined P4A 1,5
70 ACE A 25 20 100 combined P4A 2,2
70 CX A 15 8 30 combined P4A 1,8
70 CD A 15 35 240 combined P4A 1,8
70 CE A 15 20 100 combined P4A 2,4
70 ACX/HC Hybrid A 25 10 30 combined P4A 1,8
70 ACD/HC Hybrid A 25 35 100 combined P4A 1,8
70 ACE/HC Hybrid A 25 20 100 combined P4A 2,5
70 CX/HC Hybrid A 15 8 30 combined P4A 2,1
70 CD/HC Hybrid A 15 35 100 combined P4A 2,1
70 CE/HC Hybrid A 15 20 100 combined P4A 2,8
N 10 KTN(9) C1 0 40 120 radial only SP 1
N 10 KTNHA C1 0 40 120 radial only SP 1,8
N 10 KTN(9)/HC Hybrid C1 0 40 120 radial only SP 1,15
Main features,speed rating and size range N 10 KTNHA/HC Hybrid C1 0 40 120 radial only SP 2
Radial load for different bearing design ➤ NN 30 C2 0 25 130 radial only SP 0,8
NN 30 K C2 0 25 280 radial only SP 0,8
Fig 3 Codes: 2344(00) B AT2 60 35 200 thrust only SP 0,7
BTM–A AT2 30 60 130 thrust only P4C 1,05
BTM–B AT2 40 60 130 thrust only P4C 0,9
A =Angular Contact Ball Bearing,
Singledirection; 2 72 ACX A 25 10 25 combined P4A 1,5
72 ACD A 25 30 120 combined P4A 1,5
AT2 =Angular Contact Thrust Ball 72 CX A 15 10 25 combined P4A 1,8
Bearing, Double direction; 72 CD A 15 30 120 combined P4A 1,8
C1 =Cylindrical Roller Bearing, 72 ACX/HC Hybrid A 25 10 25 combined P4A 1,8
72 ACD/HC Hybrid A 25 30 60 combined P4A 1,8
Singlerow;
72 CX/HC Hybrid A 15 10 25 combined P4A 2,1
C2 =Cylindrical Roller Bearing, 72 CD/HC Hybrid A 15 30 60 combined P4A 2,1
Doublerow; BSA 2 AT1 60 12 35 combined P4 0,5
Hybrid = Bearing with steel rings
3 BSA 3 AT1 60 25 40 combined P4 0,5
andsilicon nitride (ceramic)
rolling elements – BSD AT1 60 20 50 combined Special 0,5
14 15
1Principles of bearing selection and application
Load carrying capacity
Radial loads Combined loads
Purely radial loads can be supported by Combined loads consist of a radial load and 1
cylindrical roller bearings having one ring a simultaneously acting axial load.This type
without flanges (N, NN and NNU types of load can be accommodated by bearings and life
figs 3 page 14 and 4 ).All other radial having raceways in the inner and outer
bearings can carry some axial load in rings, situated at an angle to the bearing
addition to radial loads;see Combined axis.Where high-precision bearings are
load page16. concerned, the angular contact ball
bearings (series 70, 719 and 72) and the
General Rating lives
Axial loads single direction angular contact thrust ball
Double direction angular contact thrust ball bearings (series BSD and BSA) fall into this
bearings series 2344(00) and BTM are category. All general information on life, basic load Basic rating life equation
designed to take loads that are purely axial The ability to carry axial loads is rating, and life equations described in the For calculation of simple bearing systems,
(➔ fig 5 ).For large bearing arrangements, determined by the angle of contact;the larger SKF General Catalogue or the SKF the classic ISO equation for basic rating life
or those subjected to particularly heavy the angle, the greater the axial load, which Interactive Engineering Catalogue also can be used:
axial loads, special single direction thrust can be accommodated (➔ figs 6 and 7 ). applies to high-precision bearings.
ball bearings or cylindrical roller thrust In general-machinery applications, the L =(C/P)p
10
bearings are recommended.Please consult size of bearing to be used is initially selected
the SKF application engineering service for on the basis of its load carrying capacity in where
more details. relation to the loads to be carried, and the L =basic rating life, millions of revolutions
10
requirements regarding life and reliability. C =basic dynamic load rating, N
For machine tool spindles, bearing size P =equivalent dynamic bearing load, N
isnearly always determined by criteria such p =exponent of the life equation (3 for ball
as stiffness of the system, fixed dimensions bearings, 10/3 for roller bearings)
for the tool holder, or the spindle bore.The
bearings selected according to such criteria Adjusted rating life equation
give arrangements that are often required As there are many other factors influencing
tohave a very long life. bearing life besides load, ISO introduced
For high-precision bearings, determining anadjusted life equation
the load to which a bearing will be subjected
is particularly complex as it involves many L =a a a (C/P)p
na 1 2 3
influencing factors.SKF has therefore
developed special computer programs for or simplyL =a a a L
na 1 2 3 10
the calculation of indeterminate spindle
Radial load Thrust load Combined loads Combined loads bearing systems.Contact SKF for assistance where
in determining the bearing loads and in L =adjusted rating life, millions of
na
Fig 4 Fig 5 Fig 6 Fig 7 designing an optimum bearing arrangement. revolutions (the index n represents
thedifference between the requisite
reliability and 100%)
a =life adjustment factor for reliability
1
a =life adjustment factor for material
2
a =life adjustment factor for operating
3
conditions
16 17
1Principles of bearing selection and application
Rating life equation Load carrying capacity Equivalent bearing loads
SKF Life Theory – rating life equation.
Practical experience and modern research for hybrid bearings of bearing sets 1
have shown that, under special conditions, Equivalent dynamic bearing load
SKF bearings attain a much longer life than Angular contact ball bearings are generally
predicted by standardised life calculation When using hybrid bearings, the effect of The basic load ratings listed in the product subjected to combined loads, i.e.radial and
methods, particularly when loads are light. the different rolling element material should tables for angular contact ball bearings and axial loads acting simultaneously.Preload
These special conditions apply when the also be taken into account. single direction angular contact thrust ball forces are included in the axial load.In all
rolling surfaces (raceways and rolling Under the same external load, the stress bearings apply to single bearings.The basic such cases, it is necessary to calculate the
elements) are effectively separated by in the contact area between a hybrid bearing dynamic load rating for sets of bearings equivalent dynamic bearing load that has
alubricant film, and where the risk of ball and each raceway will be higher than arranged back-to-back, face-to-face or in the same influence on bearing life as
thesurfaces becoming damaged by inan all-steel bearing.This is due to the tandem, is obtained by multiplying the C theactual load to which the bearing is
contaminants are largely non-existent. greater hardness and stiffness of the value for a single bearing by subjected.The equivalent dynamic bearing
Infact,under ideal conditions it is possible ceramic material compared with steel. load can be obtained from the general
to speak of infinite life. As ISO does not provide guidelines 1,62 for sets comprising two bearings equation:
The SKF Life Theory introduces the forcalculating basic load ratings for hybrid 2,16 for sets comprising three bearings
concept of a fatigue load limit P analogous bearings, SKF quotes the same load rating 2,64 for sets comprising four bearings. P =XF +YF
u r a
to that used when calculating other values for hybrid bearings as for all-steel
machinery components.This fatigue load bearings. For the basic static load rating, values for where
limit represents the load below which By introducing a factor a into the life bearing sets can be obtained by multiplying P =equivalent dynamic bearing load, N
HC
fatigue will not occur in the bearing under equations, the higher contact stress is taken the single bearing value by the number of F =actual radial bearing load, N
r
ideal conditions.Due to the complexity, into consideration. bearings in the set, viz.by 2, 3, or 4. F =actual axial bearing load, N
a
adetailed description of the theory is For single direction angular contact thrust X =radial load factor for the bearing
beyond the scope of this publication. L =a (C/P)p ball bearings, refer to the product section, Y =axial load factor for the bearing
10 (hybrid) HC
Forfurther details, please consult SKF L =a a a (C/P)p Table 10 page 247.
na (hybrid) 1 23 HC
application engineering services. L =a a a (C/P)p All information necessary for calculating the
naa (hybrid) 1 SKF HC
Values of the P limit for precision equivalent dynamic bearing load for single
u
bearings are given in the bearing tables. Recent results from practical experience bearings and sets of two bearings is given
The adjusted life equation according to and extensive laboratory testing indicate in the relevant product sections.The
theSKF Life Theory is: that the factor a can be considered equal information does not apply to sets of three,
HC
to 1 both for hybrid ball and roller bearings. or more bearings, as it cannot be assumed
L =a a L In general, experience shows that the that the load is evenly distributed over the
naa 1 SKF 10
service life of hybrid bearings is significantly bearings, and reaction forces caused by
where: longer than that of all-steel bearings under spindle deflection cannot be ignored.
L =adjusted rating life to SKF Life the conditions normally encountered in Special SKF computer programsare used to
naa
Theory, millions of revolutions machine tool operations.Hybrid bearings calculate the equivalent dynamicloads of
L =basic rating life, millions of revolutions are much less susceptible to wear, and such bearing arrangements and other
10
a =life adjustment factor for reliability lubrication conditions are generally superior parameters, e.g.spindle deflection.Further
1
a =life adjustment factor based on SKF to those in an all-steel bearing. information will be supplied on request.
SKF
Life Theory
For details on the a life adjustment factor,
SKF
please consult the SKF General Catalogue
or the SKF Interactive Engineering
Catalogue.
18 19