Sphericalplain

SKF spherical plain bearings
and rod ends

Contents

The SKF brand now stands for more than ever before, 1 Product information ................................................ 4
and means more to you as a valued customer.
Where self-alignment is called for ................................ 4
When flexibility pays ...................................................... 6
While SKF maintains its leadership as the hallmark of
An incomparable range ................................................. 9
quality bearings throughout the world, new dimensions
Multi-purpose performance .......................................... 12
in technical advances, product support and services
have evolved SKF into a truly solutions-oriented supplier,
creating greater value for customers.
2 Recommendations .................................................. 16
Selection of bearing size ............................................... 16
These solutions encompass ways to bring greater Load ratings ................................................................. 16
productivity to customers, not only with breakthrough Basic rating life ............................................................ 17
application-specific products, but also through leading- Load ............................................................................. 18
edge design simulation tools and consultancy services, Equivalent dynamic bearing load ............................ 18
plant asset efficiency maintenance programs, and the Equivalent static bearing load ................................. 20
industry’s most advanced supply management Permissible loads for rod ends................................ 20
techniques. Requisite bearing size.................................................. 21
Specific bearing load............................................... 21
The SKF brand still stands for the very best in rolling Mean sliding velocity ............................................... 21
bearings, but it now stands for much more. Basic rating life ............................................................ 24
Sliding contact surface combinations
SKF – The knowledge engineering company requiring maintenance: steel-on-steel and
steel-on-bronze ....................................................... 24
Maintenance-free sliding contact surface
combination steel/sinter bronze composite ............ 26
combination steel/PTFE fabric ................................ 27
combination steel/PTFE composite ........................ 29
Variable load and sliding velocity ............................ 30
Calculation examples................................................... 30
Friction ............................................................................ 35
Application of bearings.................................................. 36
Radial location of bearings .......................................... 36
Axial location of bearings............................................. 40
Sealing ......................................................................... 43
Designing the bearing arrangement for easy
mounting and dismounting .......................................... 46
Lubrication ...................................................................... 48
Spherical plain bearings requiring maintenance.......... 48
Maintenance-free spherical plain bearings.................. 48
Rod ends requiring maintenance................................. 50
Maintenance-free rod ends.......................................... 50
Maintenance ................................................................... 51
Mounting ......................................................................... 52
Spherical plain bearings ............................................. 52
Rod ends ..................................................................... 54
Dismounting.................................................................... 55
Spherical plain bearings ............................................. 55
Rod ends ..................................................................... 55

2

3 Product data ............................................................ 57
Radial spherical plain bearings
Product information . . . . . . . . . . . . . . . . . . . . . . . 4 1
requiring maintenance .................................................. 58
General ....................................................................... 58
Steel-on-steel spherical plain bearings
with metric dimensions............................................ 62
with inch dimensions............................................... 66
Recommendations . . . . . . . . . . . . . . . . . . . . . . . . 16 2
with extended inner ring .......................................... 70
Maintenance-free radial spherical plain bearings ...... 72
General ....................................................................... 72
Bearings with sliding contact surface combination
steel/sinter bronze composite ................................ 76
Product data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 3
steel/PTFE fabric ..................................................... 78
steel/PTFE composite ............................................ 82
Angular contact spherical plain bearings .................... 86
Radial spherical plain bearings
General ........................................................................ 86
Maintenance-free bearings with sliding contact
requiring maintenance . . . . . . . . . . . . . . . . . . . . . 58 3.1
surface combination steel/PTFE composite ............... 90
Spherical plain thrust bearings ..................................... 92
General ........................................................................ 92
Maintenance-free radial spherical
Maintenance-free bearings with sliding contact
surface combination steel/PTFE composite ................ 94
plain bearings . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 3.2
Rod ends requiring maintenance ................................. 96
General ....................................................................... 96
Steel-on-steel rod ends
with female thread ...................................................100
with female thread for hydraulic cylinders ..............102
Angular contact spherical plain bearings . . . . . 86 3.3
with male thread .....................................................104
with cylindrical section welding shank ....................106
with rectangular section welding shank .................108
Steel-on-bronze rod ends
with female thread ...................................................110
Spherical plain thrust bearings . . . . . . . . . . . . . . 92 3.4
with male thread .....................................................112
Maintenance-free rod ends ...........................................114
General ........................................................................114
Maintenance-free rod ends
with female thread, steel/sinter bronze composite 118
Rod ends requiring maintenance . . . . . . . . . . . . 96 3.5
with male thread, steel/sinter bronze composite ....120
with female thread, steel/PTFE fabric .....................122
with male thread, steel/PTFE fabric ........................124
with female thread, steel/PTFE composite..............126
with male thread, steel/PTFE composite ................128
Maintenance-free rod ends . . . . . . . . . . . . . . . . . 114 3.6
Special solutions and related products........................130
Plain bearings for road vehicles ..................................130
Plain bearings for rail vehicles ....................................130
Spherical plain bearings and rod ends for
airframe applications ..................................................131
Special solutions and related products . . . . . . . 130 3.7
Dry sliding bushings and flanged bushings .................132
Dry sliding thrust washers and strip ...........................133

SKF – The knowledge engineering company ......... 134

3

1 Product information 2 Recommendations 3 Product data
User benefits Page .............. 16 Page .............. 57

Where self-alignment is called for

Spherical plain bearings
Spherical plain bearings are standard-
ized, ready-to-mount mechanical com-
ponents that are self-aligning and en-
able multi-directional alignment move-
ments to be made. The inner ring has
a sphered convex outside diameter
and the outer ring a correspondingly
sphered but concave inside surface
Operational reliability is high even when Misalignment is not a problem for
(➔ fig 1 ). The forces acting on the a design is made more compact – edge spherical plain bearings
bearing may be static or may occur stresses and overloading do not occur
when the bearing makes oscillating
or recurrent tilting and slewing move-
ments at relatively low speeds.
The advantages inherent in the de-
sign of spherical plain bearings mean
that in practice

• errors of alignment or angular mis-
alignment do not influence bearing
life
• deformation of surrounding compo-
nents in operation has no effect
• edge stresses and excessive stress-
ing of adjacent components do not
occur
• operational reliability of lightweight
constructions is enhanced
• reasonably wide manufacturing
tolerances allow the use of cost-
favourable welded constructions

Fig 1 Spherical plain
bearing
1 1 Outer ring
2 2 Sliding contact
3 surfaces
4 3 Seal
5 4 Inner ring
6 5 Lubrication hole
6 Lubrication groove

4

User benefits Page .............. 16 Page .............. 57

1

Rod ends
Rod ends are bearing units that con-
sist of a spherical plain bearing in an
eye-shaped head with integral shank:
the rod end housing (➔ fig 2 ). They
are used primarily on the ends of pis-
ton rods or together with hydraulic as
well as pneumatic cylinders to join the
cylinder to associated components.
Deformation in operation does not have Wide manufacturing tolerances are
influence on bearing life accommodated = cost-favourable
welded constructions

Rod end Fig 2
1 Spherical plain
bearing
1
2 Rod end
2a Rod end hous-
ing (eye)
2b Rod end shank 2a
3 Lubrication
3 2
nipple
2b

5

Design features Page .............. 16 Page .............. 57

When flexibility pays

SKF spherical plain bearings and rod • heavy static loads and
ends should be the first choice for total • heavy alternating loads and Radial spherical
plain bearing
design economy. These state-of-the- • high-frequency alignment or oscil-
art products are stocked in a wide lating movements
range of designs, dimension series
and sizes. occur.
Whether a large bearing is required, They are also relatively insensitive to
or a small maintenance-free rod end – contamination and high temperatures.
both are available from SKF and offer: These advantages come at a price – in
this case the need for maintenance. Angular contact
spherical plain
• long service life, Therefore, lubrication holes and bearing
• simple maintenance and grooves are provided in both the inner
• high operational reliability. and outer rings of all bearings – with
the exception of a few small sizes – to
Easy replaceability is also provided facilitate relubrication. To further en-
as all SKF spherical plain bearings and hance lubrication, all bearings having
rod ends are standardized products. an outside diameter of 150 mm and
Spherical plain
Their worldwide availability goes with- above incorporate the “multi-groove
thrust bearing
out saying – thanks to the global SKF system” in the sliding surface of the
sales organisation. outer ring.
It is not just total economy considera- SKF steel-on-bronze rod ends also
tions that point to SKF spherical plain require maintenance, although require-
bearings and rod ends, but also their ments are less stringent than for steel-
unparalleled design characteristics. on-steel rod ends, as the emergency
Some of the advantages are outlined running properties are better.
in the following. Rod end with
female thread
The multi-groove system
Mature, well-proven designs Standard steel-on-steel spherical plain
SKF spherical plain bearings and rod bearings that have to perform minor
ends offer the performance to meet alignment movements under very
application demands. The designs, heavy, constant direction loads have a
materials and manufacturing quality lubricant starvation problem. The SKF
have been selected for long service multi-groove system is the answer to
lives and reliability. “Fit and forget” is this. The multi-groove system Rod end with male
thread
a philosophy embraced by SKF.
• improves lubricant supply to the
Easily maintainable sliding contacts loaded zone,
for heavy loads • enlarges the lubricant reservoir in the
SKF steel-on-steel spherical plain bearing,
bearings have high-strength sliding • enables relubrication under load,
contact surfaces of carbon chromium • permits extended relubrication inter-
(rolling bearing) steel which are phos- vals and Rod end with
welding shank
phated and treated with a special • provides space for wear particles and
running-in lubricant. Their prime areas contaminants to be deposited
of use are where
All in all the system improves lubri-
cant distribution in the heavily loaded
zone and thus extends the service life
and/or maintenance intervals.

6


Maintenance-free,
Maintenance-free, long-life sliding The self-lubricating dry sliding ma- long-life sliding
contact surfaces terials of the maintenance-free sliding contact surfaces 1
All freedom, as also freedom from contacts are not as strong as steel Sinter bronze
maintenance, has a price. In this case and consequently deform more under composite
a one-off cost – the purchase price. load. This makes these bearings more
Once installed, maintenance-free sensitive to alternating or “hammer-
spherical plain bearings and rod ends ing” loads so that steel-on-steel bear-
require no or very little maintenance. ings should be used under such con-
The initial higher price is largely com- ditions. Maintenance-free spherical PTFE fabric
pensated by the cost of the mainten- plain bearings and rod ends are de-
ance that is avoided. As to offer main- signed for types of duty where
tenance-free solutions in a large num-
ber of applications SKF produces • loads are heavy and are of constant
spherical plain bearings and rod ends direction, or PTFE composite
with different sliding contact surface • friction should be low and also con-
combinations (partly size-dependent): stant, or
• relubrication is impossible or
• steel/sinter bronze composite, undesirable.
• steel/PTFE fabric and
• steel/PTFE composite.

In the first two combinations, the steel
is hard chromium plated.

7


Free choice of materials Wide operating temperature range
There is a free choice of materials. In Temperature is not a problem. There is
most applications, SKF spherical plain a choie of SKF spherical palin bear-
bearings of through hardened steel are ings and rod ends for temperatures
the best choice; but in difficult environ- ranging from –50 to +300 °C.
mental conditions, SKF maintenance-
free stainless steel spherical plain bear- Minimal maintenance
ings may be preferred. Please contact Fit and forget applies to most SKF
the SKF application engineering ser- spherical plain bearings and rod ends.
vice for other options. It is not neces- They are maintenance-free. In some
Choice of materials
sary to be limited or make comprom- applications, where heavy loads and Bearings of rolling bearing steel for normal
ises. difficult environments prevail, there conditions and, for difficult environments,
might be a need for some mainten- bearings of stainless steel
With or without seals ance. However, this need is minmal for
SKF also provides a choice of seals. SKF plain bearings, as there is an opti-
The most popular sizes of standard mal choice of five different sliding con-
bearings are available with and without tact surface combinations and also
seals. Sealed bearings provide oppor- seals executions are available.
tunities to solve many sealing prob-
lems simply by using standard bear- Exhaustive range
ings, saving space and above all ex- The SKF range starts with bearings
pense. The double lip seal integral having a 4 mm bore and the rod end
with the face of the outer ring efficient- range covers almost all normal require-
ly protects the sliding contact surfaces ments. More information will be found
from contaminants in normal environ- in the following section.
With or without seals
ments. If environmental conditions are Many sealing problems can be solved eco-
difficult, the SKF high-performance nomically and in a space-saving manner
seals of the LS design should be con- using sealed bearings that dominate the
sidered (➔ page 44). The operational SKF range
reliability of the bearing arrangement
will be much enhanced – a benefit for
original equipment manufacturers as
well as their customers. +300

–50

Wide permissible operating temperature
range
Open steel-on-steel spherical plain bear-
ings can operate at temperatures ranging
from –50 to +300 °C

N N
N SKF

Minimum maintenance
The multi-groove system dramatically
extends maintenance intervals for steel-on-
steel spherical plain bearings

8

Product overview Page .............. 16 Page .............. 57

An incomparable range 1

All the products shown here belong to
the SKF standard range.

• Radial spherical plain bearings
requiring maintenance
• Maintenance-free spherical plain
bearings
• Angular contact spherical plain bear-
ings
• Spherical plain thrust bearings
• Steel-on-steel rod ends requiring
maintenance
• Steel-on-bronze rod ends requiring
maintenance
• Maintenance-free rod ends

If the standard range does not fulfill
the requirements, SKF can produce
special bearings, provided quantities
permit manufacturing economy. The
design will be specially tailored to
meet particular application demands.
Nothing is too much trouble.

9

Product range overview Page .............. 16 Page .............. 57

GE .. E GE .. ES GEM .. ES GEG .. ES GEZ .. ES GEH .. ES

GE .. ES-2RS GEM .. ES-2RS GEG .. ES-2RS GEZ .. ES-2RS GEH .. ES-2RS
GE .. ES-2LS

Radial spherical plain bearings requiring maintenance

GE .. C GE .. TXE-2LS GE .. TXGR GEC .. FSA GEP .. FS GEH .. C
GE .. TXG3E-2LS

GE .. CJ2 GE .. TXA-2LS GE .. TXG3A-2LS GEZ .. TXE-2RS GEC .. TXA-2RS GEH .. TXE-2LS

Maintenance-free radial spherical plain bearings

Angular contact spherical plain bearings Spherical plain thrust bearings

GAC .. F GAC .. TX GAC .. SA GAZ .. SA GX .. F GX .. TX

to order to order to order to order

10

Product range overview Page .............. 16 Page .............. 57

SI(L) .. E SI(L) .. ES/ES-2RS SI(L)A .. ES-2RS SIJ .. ES SIR .. ES SIQG .. ES SI(L)KAC .. M 1
SA(L) .. E SA(L) .. ES/ES-2RS SA(L)A .. ES-2RS SA(L)KAC .. M

Rod ends with threaded shank requiring maintenance

Designation Dry sliding surface
suffix
SC .. ES SCF .. ES
C sinter bronze composite
F PTFE composite
TX PTFE fabric, embedded in
phenolic or epoxy resin

For detailed information on these materials, see page 72

Identification of maintenance-free sliding materials Rod ends with welding shank requiring
maintenance

Maintenance-free rod ends with threaded shank

SI(L) .. C SI(L) .. TXE-2LS SI(L)A .. TXE-2LS SI(L)KB .. F
SA(L) .. C SA(L) .. TXE-2LS SA(L)A .. TXE-2LS SA(L)KB .. F
Caption heading

11

Application areas Page .............. 16 Page .............. 57

Multi-purpose performance

Long life, high reliability, minimum Application areas where maintenance- Suspended roof
maintenance and a representative free spherical plain bearings and rod SKF steel-on-steel spherical plain
product range are strong arguments ends are used include bearings have been in service in an
for SKF spherical plain bearings and unusual, but world-renowned applica-
rod ends. As this benefits the user as • conveyors, tion for more than 30 years – the roof
well as the operator, a wide range of • industrial robots, of the Olympia Stadium in Munich. Al-
applications in almost all sectors of • textile and printing machinery, though this type of bearing requires
industry has evolved. Typical use of • switching levers, maintenance, none has been given to
spherical plain bearings and rod ends • packaging as well as food and bever- these particular bearings.
requiring maintenance are found in age treatment machines, and last The roof is constructed of a number
but not least of prestressed steel ropes in a net-
• the steel construction industry, • the many uses in segment gates, work. At the torque-free nodal points
• cranes, barrages and similar installations. of the network 225 completely normal
• fork lift trucks, SKF steel-on-steel spherical plain
• hydraulic cylinders, SKF spherical plain bearings and bearings having bore diameters rang-
• stabilizers, rod ends are in use around the world. ing from 160 to 300 mm do their duty.
• mineral processing equipment, Some well-proven applications are The nodes are statically loaded but
• rolling mill equipment and shown in the following as examples. must allow occasional oscillations of
• linkages of all kinds in construction the roof construction.
and earth-moving machines and What better proof could there be for
equipment. staying power, robustness and
longevity?

Nodal point of
suspended roof
construction

12


Articulated pendulum joint previously led to lubricant starvation,
of a wheel loader this has been solved. 1
Three SKF steel-on-steel spherical Heavy-duty performance at no extra
plain bearings with the multi-groove cost provides much extended service
lubrication system are used for the lives even with long maintenance inter-
bearing arrangement of the articulated vals.
pendulum joint of this wheel loader.
Two of the bearings provide the articu-
lation. The third bearing together with a
cylindrical sliding bushing in the pen-
dulum joint serves to compensate for
uneven ground so that the driven
wheels adhere well to the surface.
The multi-groove lubrication system
of SKF spherical plain bearings im-
proves the transport of lubricant to the
loaded zone and also enlarges the
lubricant reservoir in the bearing.
Neglection of lubrication intervals

Articulated pendulum joint
of a wheel loader

13


Dam gate
Truck twin-axle supports
The purpose of the bearing arrange-
ment of a truck twin-axle support is to
provide even load distribution between
the two axles on bumpy roads or off-
highway. This means that the arrange-
ment is subjected to heavy loads and,
depending on the road/off-highway
conditions, heavy shock loads and
highly frequent alignment movements.
The bearings are hidden behind the
tyres and are difficult to access. It is
evident that any sudden bearing dam-
age, calling for immediate on site re-
pairs need to be avoided.
A pair of SKF angular contact spher-
ical plain bearings mounted back-to-
back make sure that such emergen-
cies will not occur. They can withstand
all the rigours of truck duty, are simple
to install and also to maintain. Dam gates
Segment gates for dam bar-
rages are the home of large-
size SKF maintenance-free
spherical plain bearings. The
reference list is long – over
3 000 applications being included
to date.
As main bearings, they compensate
for non-alignment of their seatings,
alterations in length as a result of tem-
perature changes, elastic deformation
of the dam gates as well as changes
Truck twin-axle support caused by settling of the foundations.
They cope with the heavy radial loads
caused by the water pressure as well
as axial loads arising from the inclined
position of the support arms.
SKF bearings not only serve as heav-
ily loaded bearings under static condi-
tions; they also serve in the frequently
operated linkage attachments of the
lifting and plunger cylinders as well as
the flaps.

14

Application areas Page .............. 16 Page ............... 57

Hydraulic and For pneumatic cylinders with working Newspaper conveyor
pneumatic pressures up to approximately 1 MPa Speed is all-important when producing 1
cylinders steel-on-bronze rod ends are mainly newspapers, not only in the printing
SKF steel-on-steel used as well as maintenance-free rod but also in their transportation. The
and steel-on-bronze ends at the piston rod end and at the conveyor system from the printing
rod ends are main- other end SKF rod ends with welding press to the distribution point is there-
ly used in these shank are employed. fore important if the newspapers are to
applications. They come out on time.
act as the link be- The endless conveyor chain is one
tween the cylinder such system. It consists of a multitude
and its attachments. They are able to of links which together provide the flex-
transmit high mechanical forces. ibility required. In the example shown
Hydraulic cylinders (e.g. to DIN more than 1 000 SKF maintenance-
24336) are often fitted with steel-on- free spherical plain bearings GEH 10 C
steel rod ends with female thread are used. They have been in daily ser-
(compressible) at one end and steel- vice without any maintenance whatso-
on-steel rod ends with welding shank ever for many years now.
at the other. Such hydraulic cylinders
are found in all types of construction
equipment, agricultural machinery, lift-
ing equipment and shutters, recycling
depot presses as well as other heavily
loaded manoeuvering equipment.

Hydraulic and
pneumatic Newspaper
cylinders conveyor

15

Page ................ 4 Load ratings Page .............. 57

Selection of bearing size

Load ratings sired rating life. The basic dynamic the associated components of the
load ratings quoted in the product bearing arrangement. In order to fully
There is no standardized method for tables are based on the specific load exploit the static load rating of a spher-
determining the load ratings of spher- factor K (➔ Table 4 , page 21) and ical plain bearing it is generally neces-
ical plain bearings and rod ends, nor the effective projected sliding surface. sary to use shafts and housings of
is there any standardized definition. high-strength materials. The basic
As different manufacturers define load Basic static load rating static load rating must also be consi-
ratings differently, it is not possible to The basic static load rating C0 repre- dered when bearings are dynamically
compare the load ratings of bearings sents the maximum permissible load loaded if they are also subjected to
produced by one manufacturer with that may be applied to a bearing when additional heavy shock loads. The
those published by another manufac- there is no relative movement of the total load in such cases must not
turer. sliding contact surfaces (➔ fig 2 ). exceed the basic static load rating.
For spherical plain bearings the For rod ends it is the strength of the
Basic dynamic load rating basic static load rating represents the eye-shaped head of the rod end (hous-
The basic dynamic load rating C is maximum load which the bearing can ing) at room temperature under a con-
used, together with other influencing accommodate at room temperature stant load acting in the direction of the
factors, to determine the basic rating without its performance being impaired shank axis which is the determining
life of spherical plain bearings and rod as a result of inadmissible deform- factor. The basic static load rating rep-
ends. As a rule it represents the max- ations, fracture or damage to the slid- resents a safety factor of at least 1,2
imum load that a spherical plain bearing contact surfaces. The basic static relative to the yield strength of the ma-
ing or rod end can sustain at room tem- load ratings quoted for SKF spherical terial of the rod end head under the
perature when the sliding contact sur- plain bearings are based on a specific above conditions.
faces are in relative motion (➔ fig 1 ). static load factor K0 (➔ Table 4 ,
The maximum permissible load in any page 21) and the effective projected
individual application should always sliding surface. It is assumed that the
be considered in relation to the de- bearing is adequately supported by

Dynamic bearing load Static bearing load Angle of oscillation

Fig 1 Fig 2 Fig 3

β
1
3 0
2
4
ϕ
ϕ = angle of oscillation = 2 β
A complete oscillation is from point 0 to point 4 and
=4β

16

Page ................ 4 Basic rating life Page .............. 57

Basic rating life basic rating life and the service life ac-
tually achieved.
Spherical plain bearings belong to the The basic rating life is a guideline
category “dry sliding bearings”. In con- value which will be attained or ex-
trast to, say, hydrodynamic plain bear- ceeded by the majority of a large num-
ings, no lubricant film can form to fully ber of apparently identical bearings
separate the sliding surfaces. There- under the same test conditions. 2
fore, under dynamic loads wear is nat- The service life achieved by identi-
urally produced which enlarges the cal bearings has been found to differ,
internal clearance. as the service life depends on the ac-
The service life of a spherical plain tual operating conditions. These inclu- Calculation of basic rating life
bearing or rod end represents the op- de not only the magnitude and type of By using the SKF Interactive Engin-
erating period under test conditions load but also other factors such as eering Catalogue it is possible to per-
which is ended when one of the criteria contamination, corrosion, load and form all the necessary calculations for
listed in Table 1 for the end of service movement cycles of high frequency, spherical plain bearing selection at the
life is reached. The life is expressed and shock loads. These factors are click of a mouse using the programs
either in operating hours or in the num- difficult or even impossible to quantify. incorporated in the catalogue. The
ber of oscillating movements (➔ fig 3 ). product data necessary for the calcu-
A distinction is made between the lations is automatically put in by select-
ing a spherical plain bearing or rod end
from the product tables. It is then only
necessary to fill in the fields for the
operating data.
The SKF Interactive Engineering
Catalogue is available on CD-ROM or
online at www.skf.com.

Criteria for end of service life

Table 1
Sliding contact surface combination Increase Coefficient
in bearing of friction
clearance µ

– mm –

Steel-on-steel > 0,004 dk 0,20

Steel-on-bronze > 0,004 dk 0,25

Steel/sinter bronze composite
constant direction load 0,2 0,20
alternating direction load 0,4 0,20

Steel/PTFE fabric
constant direction load 0,3 0,20
alternating direction load 0,6 0,20

Steel/PTFE composite design and 0,25
size dependent

17

Page ................ 4 Load Page .............. 57

Radial load
Load Equivalent dynamic bearing Fig 4
load
When considering load, a distinction is If the load acting on
made between:
• radial and angular contact spherical
• load direction plain bearings is purely radial
– radial loads (➔ fig 4 ) • spherical plain thrust bearings is
– axial loads (➔ fig 5 ) purely axial
– combined (axial and radial) loads • rod ends is purely radial and also in
(➔ fig 6 ) the direction of the shank axis
Axial load Fig 5
• the way in which the load acts
– loads of constant direction and is of constant magnitude, then the
(➔ fig 7 ), i.e. the direction in load can be directly inserted in the
which the load is applied does not equation for the specific bearing load p
change and the same part of the (➔ page 21). In all other cases it is
bearing (loaded zone) is always necessary to calculate the equivalent
subjected to the load dynamic bearing load P. If the load is
– alternating loads (➔ fig 8 ), not of constant magnitude, then the
change direction so that loaded procedure given under “Variable load
zones at opposite positions in the and sliding velocity” (➔ page 30)
Combined load Fig 6
bearing are continuously loaded should be followed.
and unloaded
• the type of load
– dynamic load is when sliding move-
ment takes place in the loaded
bearing
– static load is when no movement
takes place in the loaded bearing.

Constant direction Fig 7
load

Alternating Fig 8
direction load

18

Page ................ 4 Load Page .............. 57

Radial spherical plain bearings Angular contact Fig 9 Spherical plain Fig 10
Radial spherical plain bearings can spherical plain thrust bearings
accommodate a certain amount of bearings Spherical plain
axial load Fa in addition to the simultan- When the resultant thrust bearings can
eously acting radial load Fr (➔ fig 6 ). load (➔ fig 9 ) is carry a radial load
When the resultant load is constant in constant in magni- Fr in addition to the
magnitude, the equivalent dynamic tude, then axial load Fa. How- 2
bearing load can be obtained from ever, the radial load
P = y Fr must not exceed
P = y Fr 50 % of the simultan-
Angular contact Spherical plain
where spherical plain eously acting axial thrust bearing
where P = equivalent dy- bearing under load (➔ fig 10 ). under combined
P = equivalent dynamic bearing load, namic bearing combined load When the resultant load
kN load, kN load is constant in
Fr = radial component of the load, kN Fr = radial component of the load, kN magnitude, then
y = a factor that depends on the ratio y = a factor that depends on the ratio
of the axial to the radial load Fa/Fr of the axial to the radial load Fa/Fr P = y Fa
– for bearings requiring mainten- (➔ Diagram 3 )
ance (➔ Diagram 1 ) where
– for maintenance-free bearings P = equivalent dynamic bearing load,
(➔ Diagram 2 ) kN
Fa = axial component of the load, kN
y = a factor depending on the ratio of
the radial to the axial load Fr/Fa
(➔ Diagram 4 )
Diagram 1

3
y
2,5

2

1,5

1
0 0,05 0,1 0,15 0,2 0,25
Fa
Fr

Factor y for radial spherical plain
bearings requiring maintenance

Factor y for maintenance-free radial Factor y for angular contact spherical Factor y for spherical plain thrust
spherical plain bearings plain bearings bearings

Diagram 2 Diagram 3 Diagram 4

2
2,5 2,5
y y y
Other series
2,25 2,25
1,75
2 2

1,75 1,75 1,5
Series
1,5 GEP .. FS 1,5
1,25
1,25 1,25
1 1 1
0 0,1 0,2 0,3 0,4 0 0,5 1 1,5 2 0 0,1 0,2 0,3 0,4 0,5
Fa Fa Fr
Fr If Fa/Fr > 2, a spherical plain thrust Fr If Fr/Fa > 0,5, an angular contact Fa
bearing should be used instead, or spherical plain bearing should be used
SKF should be contacted instead, or SKF should be contacted

19

Page ................ 4 Load Page .............. 57

Equivalent static bearing load Permissible loads for rod ends Fig 11
If spherical plain bearings and rod Rod ends are primarily intended for the
ends are subjected to load when sta- support of radial loads acting in the dir-
tionary or making only slight alignment ection of the shank axis. If loads act at
movements, then the permissible load right angles to the shank axis (➔ fig
is not limited by wear, but by the 11 ), the maximum permissible load
strength of the sliding contact layer or will be reduced as additional bending
the strength of the rod end housing. stresses occur in the shank. When
If the actual load is a combined radial checking, consideration should also
and axial load, then an equivalent be paid to the rod end head (housing)
static bearing load must be calculated. material which differs depending on
This can be done in a similar way to design and size.
the calculation of the equivalent dy- The load directed at an angle or
namic bearing load, for radial and axially to the rod end (to the direction
angular contact spherical plain of the shank axis) should never ex-
Rod end under combined load
bearings using ceed the value of 0,1 C0. If heavier
loads are involved then a larger rod
P0 = y Fr end should be chosen.
The maximum permissible load for
and for spherical plain thrust bearings a rod end in the direction of the shank
using axis can be calculated from

P0 = y Fa Pperm = C0 b2 b6

where where
P0 = equivalent static bearing load, kN Pperm = maximum permissible load, kN
Fr = the radial component of the load, C0 = static load rating, kN
kN b2 = temperature factor
Fa = the axial component of the • for rod ends requiring main-
load, kN tenance (➔ Table 5 , page
y = a factor which depends on the 24)
ratio Fa/Fr • for maintenance-free rod
– for radial bearings requiring ends with the sliding contact
maintenance (➔ Diagram 1 , surface combination Factor b6 for rod end load type
page 19) – steel/sinter bronze composite
– for maintenance-free radial (➔ Diagram 16 , page 26) Table 2
bearings (➔ Diagram 2 , – steel/PTFE fabric Type of load Factor
page 19) (➔ Diagram 17 , page 27) (magnitude and direction) b6
– for angular contact spherical – steel PTFE composite
plain bearings (➔ Diagram 3 , (➔ Diagram 19 , page 29) Constant
page 19) b6 = factor for the type of load
+ Fr
and on the ratio Fr/Fa (➔ Table 2 )
– for spherical plain thrust bear- 1
ings (➔ Diagram 4 , page 19)
Pulsating magnitude (single direction)
+ Fr

0,5
(0,35)

Alternating direction,
+ Fr
0,5
– Fr (0,35)

The values in brackets apply to rod ends with
lubrication hole or nipple

20

Page ................ 4 Selection of bearing size Page .............. 57

Requisite bearing size is calculated. If the calculated rating Specific bearing load
life is shorter than the requisite rating The magnitude of the specific bearing
When determining the requisite size of life, a larger bearing or rod end should load can be determined using
bearing (or rod end), it is necessary to be chosen and the calculation
know the basic rating life required for repeated.
P
the particular application. This is de- If, on the other hand, the first check p = K ––
pendent on the type of machine, the shows the pv range is exceeded, a C 2
operating conditions and the demands bearing having higher load carrying
regarding operational reliability. capacity should be chosen. where
As a first approximation the guide- The bearing (or rod end) size is p = specific bearing load, N/mm2
line values of the load ratio C/P given often dictated to a greater or lesser K = a specific load factor depending on
in Table 3 can be used to obtain the degree by the dimensions of the asso- the basic dynamic load rating
requisite basic dynamic load rating C. ciated components. In such cases the (➔ Table 4 ), N/mm2
A suitable bearing or rod end can then pv diagram should be consulted first P = equivalent dynamic bearing load,
be selected from the product tables. to check that the product can be kN
It should then be checked whether used. C = basic dynamic load rating, kN
the chosen size can be used under the
actual load and sliding velocity condi-
tions using the appropriate diagram for Mean sliding velocity
the sliding contact surface combination The mean sliding velocity for constant
from those shown on pages 22 and 23 movement can be obtained from
(Diagrams 5 to 10 inclusive). The
specific bearing load p and the sliding v = 5,82 × 10–7 dm β f
velocity v needed to perform this check
can be calculated as explained in the where
following sections. v = mean sliding velocity, m/s
If, having checked the pv diagram, When operation is intermittent
it is found that the bearing or rod end (not continuous) the mean sliding
can be used, then the basic rating life velocity should be calculated for a
cycle of operation
dm = mean diameter of inner ring or
shaft washer, mm
dm = dk for radial spherical plain
Guideline values for C/P Specific load factors bearings
dm = 0,9 dk for angular contact
Table 3 Table 4 spherical plain bearings
Spherical plain Load ratio Sliding contact Specific load dm = 0,7 dk for spherical plain
bearings/rod ends C/P surface combination factors thrust bearings
with sliding contact dyn. stat.
surface combination K K0 β = half the angle of oscillation
(➔ fig 3 , page 16), degrees
– N/mm2 For rotation β = 90°
Steel-on-steel 2
f = frequency of oscillation, min–1,
Steel-on-bronze 2 Steel-on-steel or rotational speed, r/min
Metric sizes 100 500
Steel/sinter bronze Inch sizes 100 300
composite 1,6 For intermittent movement, the angle
Steel-on-bronze 50 80 of oscillation is usually given per unit
Steel/PTFE fabric 2
Steel/sinter time. In this case the mean sliding
Steel/glass fibre bronze composite 100 250 velocity can be calculated using
reinforced plastic
GAC .. F 1,25 Steel/PTFE fabric 300 500
GX .. F 1,25 2β
GEP .. FS 1,6 Steel/glass fibre v = 8,73 × 10–6 dm –––
GEC .. FSA 1,6 reinforced plastic t
GAC .. F 50 80
Rod ends 1,25 GX .. F 50 80
GEP .. FS 80 120 where
GEC .. FSA 80 120
β = half the angle of oscillation, degrees
Rod ends 50 80 t = time taken to pass through 2 β
(= whole angle of oscillation), s

21

Page .................... Selection of bearing size Page .............. 57

Diagram 5 pv diagram for sliding contact surface
combination steel-on-steel
See Note 1 for explanation of operating
200 ranges
p
N/mm2
100
IV

50

20
II I III
10

5

2

1
0,0001 0,001 0,002 0,005 0,01 0,02 0,05 0,1 0,2 0,5
v m/s

combination steel-on-bronze
ranges
100
p
N/mm2
50

20

10

5
II I III
2

1
0,0001 0,001 0,002 0,005 0,01 0,02 0,05 0,1 0,2 0,5
v m/s

combination steel/sinter bronze
composite
ranges
200
p
N/mm2 Note 1
100 pv operating ranges
I Range where rating life equation is
50 valid
II Quasi-static range; before using the
rating life equation, please contact
II I III SKF
20
III Possible range of use, e.g. with
very good lubrication; before using
10
the rating life equation, please con-
tact SKF
5 IV Extended range where rating life
0,0001 0,001 0,002 0,005 0,01 0,02 0,05 0,1 0,2 0,5 1,0 equation is valid provided the load
v m/s is exclusively alternating

22

Page .................... Selection of bearing size Page .............. 57

pv diagram for sliding contact surface Diagram 8
combination steel/PTFE fabric
ranges 500
p
N/mm2
200

2
100

50

20

II I III
10

5
0,0001 0,001 0,002 0,005 0,01 0,02 0,05 0,1 0,2 0,5
v m/s

combination steel/PTFE composite,
FS and FSA designs
ranges
p 120
N/mm2
100

III
50

II I
20

10

5
0,0001 0,001 0,002 0,005 0,01 0,02 0,05 0,1 0,2
v m/s

combination steel/PTFE composite,
F design
ranges

100
Note 2 p
pv operating ranges N/mm2
I Range where rating life equation is 50
valid III
II Quasi-static range; rating life
equation has limited validity, see 20
under “Basic rating life” starting II I
on page 24 10
III Possible range of use, e.g. with
very good heat removal; before
using the rating life equation, 5
please contact SKF 0,0001 0,001 0,002 0,005 0,01 0,02 0,05 0,1 0,2
v m/s

23

Page ................. 4 Basic rating life Page .............. 57

Temperature
factor b2
Table 5 Basic rating life
Operating Temperature
temperature factor
over incl. b2 Sliding contact surface combi-
°C –
nations requiring maintenance:
steel-on-steel and steel-on-
– 120 1,0
bronze
120 160 0,9 For the initial lubrication
160 180 0,8
180 – Please contact SKF 330
Gh = b1 b2 b3 b4 b5 –––––
p2,5 v

and when the product is regularly
relubricated thereafter
The following temperature limits must also be respected
80 °C For bearings of series GEZ .. ES-2RS
(polyurethane seals)
130 °C For all other sealed bearings GhN = Gh fβ fH
(polyester elastomer seals)
120 °C Upper temperature limit for standard grease
or
Sliding factor b3 Diagram 11 GN = 60 f GhN

where
Gh = rating life for the initial lubrica-
tion, operating hours
5 GhN = basic rating life with regular
relubrication, operating hours
b3
GN = basic rating life with regular
relubrication, number of oscilla-
2
tions
b1 = load direction factor,
1 b1 = 1 for constant direction
10 20 50 100 200 500 load
d k mm b1 = 2 for alternating direction
load
b2 = temperature factor (➔ Table 5 )
b3 = sliding factor (➔ Diagram 11 )
b4 = velocity factor (➔ Diagram 12 )
b5 = factor for angle of oscillation
(➔ Diagram 13 ), see also
Velocity factor b4 Diagram 12 under “NB.”
f = frequency of oscillation, min–1
fβ = factor depending on the angle of
15
b4 oscillation (➔ Diagram 14 ), see
Steel-on-bronze
10 also under “NB.”
fH = factor depending on frequency
Steel-on-steel of relubrication (➔ Diagram 15 )
5 p = specific bearing load, N/mm2
(for values of p < 10 N/mm2 use
p = 10 N/mm2)
v = mean sliding velocity, m/s
2

If the basic rating life requirement is
1
not met, then the relubrication interval
0,002 0,005 0,01 0,02 0,05 0,1 N (➔ Diagram 15 ) should be short-
v m/s ened, or a larger bearing or rod end
should be chosen.

24

Page ................ 4 Basic rating life Page .............. 57

Diagram 13 Angle of oscilla-
tion factor b5

10
b5

5 2

I
2

1
5 10 20 45
β°

If ß < 5°, the value of b5 for ß = 5° should be used

Diagram 14 Multiplication
factor fβ
6
fβ

5

4

I
3

NB. 2
SKF steel-on-steel spherical plain
bearings having an outside diam- 1
eter of 150 mm and above are
produced as standard with the
multi-groove feature in the outer 5 10 15 20
ring (➔ page 6). The extra large β°

grease reservoir in the bearing If β < 5°, half the value of fβ for β = 5° should be used
made possible by the multi-groove
system is advantageous, particu- Relubrication
Diagram 15
larly where the load is of constant factor fH
direction, and enables the relubri- 6
fH
cation interval to be extended, and
also the service life. 5
These advantages are consider-
ed in the calculation of the basic 4
rating life by the coloured regions
in Diagrams 13 and 14 for the 3
factors for the angle of oscillation
b5 and fβ. Values of these two fac-
2
tors up to the upper limit of the
coloured area may be used for
1
bearings with the multi-groove
system.
0
1 10 20 30 40 50
H
The frequency of relubrication H is defined as the ratio of the basic rating life Gh to
the relubrication interval N (in h), i.e. H = Gh/N; if H < 5, the values indicated by the
broken line can be used

25

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