Ressource KRW Product Bearing basics

General Basics

Functions of Rolling Bearings

Rolling bearings are machine elements and serve to support shafts and axles. Depending on their design, they absorb radial and/or axial loads and simultaneously enable rotation of the shaft or the components mounted on an axle. The force is transmitted via spherical or roller-shaped rolling elements. The advantages include the following points:

  • low friction even when starting from standstill

  • low cooling and lubrication requirements, grease lubrication usually sufficient

  • radial, axial and combined loading capacity achievable with little effort

  • almost backlash-free or preloaded operation possible

  • rolling bearings are available worldwide as ready-to-install standard part series

 

Bearing Types

Rolling bearings are divided into different bearing types and designs. Based on the ball bearing which represents the starting point, the starting point for the technical development of rolling bearings, today there are a large number of bearing types used for very specific operating conditions. Any design of a rolling bearing, however, will be a technical compromise determined by a wide variety of criteria. Rolling bearings are selected according to:

  • the available installation conditions,

  • the type and extent of the load,

  • speeds or motion cycles in general,

  • the required guidance accuracy of the machine and plant components,

  • the rigidity of the bearings,

  • the ambient conditions,

  • the installation and removal options

Apart from the technical parameters of a rolling bearing, such as static and dynamic load carrying capacity and permissible speeds, the bearing clearance or preload, the appropriate cage modification and the required lubrication method must be considered when selecting the bearing type.

 

Deep Groove Ball Bearing

Deep Groove Ball Bearings, single row

Due to its simple construction and potential to absorb radial, axial, and combined loads, the deep groove ball bearing is described as the best known and most frequently used rolling bearing in literature. Deep groove ball bearings cannot be dismantled and only allow a small tilting angle. A further advantage is low friction and the associated high speed suitability.

Angular Contact Ball Bearing

Angular Contact Ball Bearings, single row

Angular contact ball bearings are divided into single-row and double row bearings. They are suitable for very high speeds and absorb both axial and radial loads. Due to the contact angle, an axial load is generated even with a pure radial load. Single-row angular contact ball bearings should therefore always be fitted in pairs or in combination with another angular contact bearing. The contact angle differs depending on the dimensional series. In preloaded condition, angular contact ball bearings exhibit high rigidity and good guidance accuracy.

Four Point Contact Ball Bearing

Four Point Contact Ball Bearing

Four-point contact bearings are a special type of single row angular contact ball bearings. They absorb alternating axial forces in both directions. A radial load on the bearings must be avoided. Four-point contact ball bearings are categorized into two types. Bearings with a split inner ring are referred to as QJ, bearings with a split outer ring as Q. The split design of the bearing rings ensures particularly easy assembly, e.g. in gear construction.

Cylindrical Roller Bearing

Cylindrical Roller Bearings

This bearing type has a very wide range of possible variations due to the wide variety of designs, without having to accept limitations of the high radial load capacity. As a rule, cylindrical roller bearings have a higher load capacity than comparable deep groove ball bearings. Individual designs of cylindrical roller bearings are capable of absorbing one-sided axial loads. Cylindrical roller bearings are manufactured as single-row, multiple-row, with and without cage, and can be dismantled. Therefore, they are easy to assemble for the user. Depending on the series, a maximum tilt angle of 3 to 4 angular minutes is permissible. Double row cylindrical roller bearings have a large radial load carrying capacity. Depending on the version, the absorption of low axial forces is possible. Tilting of multi-row bearings must always be avoided. Multi-row cylindrical roller bearings have the highest radial load carrying capacity and are mainly used in heavy industry (e.g. in rolling mills or roll crushers). Speed suitability is greatly reduced compared to single-row bearings. Full complement cylindrical roller bearings do not have a cage. Further cylindrical rollers are inserted in its place. These bearings have a significantly higher radial load carrying capacity than cage bearings, but the speed is lower due to rolling element friction.

Overview Cylindrical Bearings symbols

Types of Cylindrical Roller Bearings

Tapered Roller Bearing

Tapered Roller Bearing

Tapered roller bearings absorb axial and radial forces similar to angular contact ball bearings. Due to its design, tapered roller bearings are capable of absorbing very high axial and radial forces. With a radial load, an axial force always occurs due to the contact angle which must be absorbed. For this reason, tapered roller bearings should always be fitted in pairs. The speed suitability of tapered roller bearings is lower than that of angular contact ball bearings. Tapered roller bearings can be dismantled and are divided into an outer ring and an inner ring with a Cone. Bearings are usually in metric but also in inch dimensions, the latter have a different designation scheme though.

Spherical Roller Bearing

Spherical Roller Bearing

Bearings with barrel rollers are divided into barrel roller bearings (single-row) and spherical roller bearings (double row). Both variants are able to compensate for misalignments. This is possible due to the spherical contour of the outer and inner ring raceways and the barrel-shaped rolling elements. Barrel roller bearings are used for lower loads. Spherical roller bearings are mainly used for high radial forces, shocks and misalignments. Compared to barrel roller bearings, spherical roller bearings are capable of absorbing larger axial forces. Both types cannot be dismantled.

Cylindrical Roller Thrust Bearing

Cylindrical Roller Thrust Bearings, single direction

Cylindrical roller thrust bearings are characterized by shaft and housing washers. These bearings are used for large axial forces. Some designs can be mounted on both sides. The absorption of radial loads is not possible due to the geometry. Due to the kinematics of axial cylindrical roller bearings, which are subject to an increasing relative speed of the rolling elements with increasing raceway diameter, their speed suitability is limited. A minimum axial load is required for optimum performance.

Deep Groove Thrust Ball Bearing

Deep Groove Thrust Ball Bearings, single direction

Deep groove thrust ball bearings are separable axial bearings manufactured in single and double direction. They are suitable for absorbing axial loads, but not radial loads. Due to the kinematic characteristics, medium to high speeds can be achieved with this bearing design. A minimum axial load is required for optimum function.

Special Bearings

Special Bearings

KRW develops, designs and manufactures special designs on the basis of the bearing types mentioned above. Special designs are required above all when special properties of the rolling bearing have to be derived from the operating conditions. KRW offers current-insulated bearings (e.g. for electric motors), bearings with particularly thin-walled cross-sections (e.g. for textile machine construction) or bearings with a sophisticated internal design for realizing maximum load carrying capacities (e.g. for rolling mill construction).

Series Overview

Rolling Bearing DesignExamples of series (further dimensional series on request)

Deep Groove Ball Bearings, single-row

160, 618, 619
60, 62, 63, 64

Angular Contact Ball Bearings, single-row

708, 709, 718, 719, 70, 72B, 73B

Angular Contact Ball Bearings, double-row

SKZ, (0)32, (0)33

Four Point Contact Ball Bearings

Q10, QJ10, Q2, QJ2, Q3, QJ3, QJ4

Spherical Ball Bearings

12, 13, 22, 23

Angular Contact Thrust Ball Bearings

2344, 2347

Deep Groove Thrust Ball Bearings

511, 512, 513, 514, 532, 533, 534, 
522, 523, 524, 542, 543, 544

Cylindrical Roller Bearings, single-row

NU18, NU19, NU10, NU20, NU2, NU22 (corresponding to all designs, preferably in performance-enhanced version)

NU3, NU23, NU4

Cylindrical Roller Bearings, double-row and multi-row

NN30, NNU49, NNU60

Cylindrical Roller Bearings (full complement), single-row

NCF...V, NJG23...V

Cylindrical Roller Bearings (full complement), double-row

NNC...V, NNCL...V, NNCF...V

Cylindrical Roller Bearings (full complement), multi-row

NNU60...V

Cylindrical Roller Wheelset Bearings

WJ/WJP

Cylindrical Roller Thrust Bearings

811, 812, 893, 894, WS811, GS811, K811

Tapered Roller Bearings

329, 320, 330, 331, 302, 322, 332, 303, 313, 323, 323

Barrel Roller Bearings / Spherical Roller Bearings (single-row)

202, 203, 204

Spherical Roller Bearings (with cylindrical/tapered bore)

222, 223, 230, 231, 232, 239, 240, 241, 248, 249

Spherical Roller Thrust Bearings

292, 293, 294

Thin-section Bearings

 

Current-insulated Bearings

 

Special Bearings

 

Clamping Sleeves

H2, H23, H3, H30, H31, H32, H39
OH23, OH30, OH31, OH32, OH39

Withdrawal Sleeves

AH2, AH3, AH22, AH23, AH 30, AH 31,
AH 39, AOH2, AOH22, AOH23, AOH30,
AOH31, AOH39

Angle Rings

HJ

Cylindrical Rollers

ZRO

Barrel Rollers

TORO

Tapered Rollers

KERO

 

Technical Terms in Rolling Bearing Technology

Rolling Bearing Element Designations

Rolling Bearing Element Designations
1Width of bearing9Cicular groove
2Outer ring10Outer ring front side
3Outer ring on-board diameter11Outer ring raceway
4Cage12Rolling element
5Inner ring on-board diameter13Inner ring front side
6Inner ring14Edge radius
7Bore diameter of the inner ring15Inner ring raceway
8Pitch circle diameter  
Bezeichungen der Waelzlagerelemente Kegelrollenlager
1Total widths of the bearing7Snap ring
2Sheath diameter of the outer ring8Rolling element
3Outer ring front side9Inner ring front side
4Cage10Inner ring
5Retaining lip11Contact angle
6Bore diameter of the inner ring  
Rolling Bearing Element Designations
1Shaft washer4Rolling element
2Cage5Mounting sleeve
3Housing washer  

 

Standardisation and Nomenclature

Rolling bearings are internationally standardized in their dimensions (bore, outside diameter, width). The rolling bearing designations consist of logically structured combinations of letters and numbers reflecting the bearing’s design, size and properties. In addition to the standard bearings, there are special bearings or standard bearings in special designs whose designation system varies depending on the manufacturer. The DIN standard DIN 623 defines the basic principles for the designation and marking of rolling bearings.

Standardization of bearing types

DesignBearing TypeTermStandard NumberISO Number
Ball Bearings and Roller Bearings

1

Spherical ball bearing

DIN 630

 

6

Magneto bearing

DIN 615

 

 

6

Deep groove ball bearing, single-row

DIN 615-1

ISO 15

4

Deep groove ball bearing, double-row

DIN 625-3

 

7

Angular contact ball bearing, single-row

DIN 628-1

DIN 628-6

ISO 15

SKZ, (0)

Angular contact ball bearing, double-row

DIN 628-3

ISO 15

Q, QJ

Four point contact ball bearing

DIN 628-4

ISO 15

2

Spherical roller bearing, single-row (Barrel roller bearing)

DIN 635-1

ISO 15

2

Spherical roller bearing, double-row

DIN 635-2

ISO 15

*) N, NU, NUP, NJ

Cylindrical roller bearing, single-row

DIN 5412-1

ISO 15

*) RNU, RN

Cylindrical roller bearing, Ring with cage assemblies

 

 

*) NNU, NN

Cylindrical roller bearing, double-row

DIN 5412-4

ISO 15

*) NC

Cylindrical roller bearing (full complement), single-row

 

ISO 15

*) NNC, NNCF

Cylindrical roller bearing (full complement), double-row

DIN 5412-9

ISO 15

*) WJ, WJP

Cylindrical roller wheelset bearing

DIN 5412-11

 

Tapered Roller Bearings

3

Tapered roller bearing, single-row

DIN 720

ISO 355

Single Direction Deep Groove Thrust Ball Bearings with flat Housing Washer, Cylindrical Roller Thrust Bearings and Spherical Roller Thrust Bearings

5

Deep groove thrust ball bearings, single direction

DIN 711

ISO 104

8

Cylindrical roller thrust bearing, single direction

DIN 722

ISO 104

2

Spherical roller thrust bearing, single direction

DIN 728

ISO 104

Double Direction Deep Groove Thrust Ball Bearings with flat Housing Washer

5

Deep groove thrust ball bearings, double direction

DIN 715

ISO 104

Clamping Sleeves

H

Rolling bearing clamping sleeve

DIN 5412

ISO 113-1

Withdrawal Sleeves

AH, AHX

Rolling bearing withdrawal sleeve

DIN 5416

ISO 113-1

Angle Rings for Cylindrical Roller Bearings

HJ

for cylindrical roller bearings, single-row

DIN 5412-1

ISO 15

 

 

in standard design

 

ISO 246

 

 

in performance-enhanced design

  

*)  Further designs can be derived from the designs of cylindrical roller bearings listed in DIN 5401-1. Technical properties such as load ratings and speeds remain unchanged.

 

Rolling Bearing Designation System

In accordance with DIN 623-1, each rolling bearing is uniquely identified by a standard designation. The next figure shows an example of a bearing designation.

Rolling Bearing Designation System
Identification
I PrefixesII Base characterIII SuffixesIV Supplementary character

I.1 Bearing Parts

II.1 Bearing series

II.2 Bearing bore

NG 1: Internal construction

NG 2: External shape

NG 3: Cage

NG 4.1: Tolerance classes

NG 4.2: Bearing pairs

NG 4.3 Bearing clearance

NG 5.1: Material

NG 5.2: Heat Treatment

NG 6: Lubrication

 

NG 7.1: Technical specifications

NG 7.2: Supplementary symbol according to manufacturer's specifications

I.2 Material

II.1.1 Bearing type

Dimension series according to DIN 616

 

 

II.1.2 Width or height row

II.1.3 Diameter series

  

 

The order within the prefixes and base characters shall be as set out in Section I and Section II. The sequence of the suffixes and supplementary symbols may vary depending on the bearing design and modality. The order shown in Section III should be used for orders, but manufacturer specific variations are permitted.

Base characters must always be specified in full. The prefixes, suffixes and supplementary characters may then be missing from the abbreviation, if

  • according to Section I.2, only materials for the normal case are used,

  • the characteristics designated by them are not present,

  • no suffixes for special design variants (e.g. PN, CN and SN) are specified for the normal case in accordance with Section III,

  • no specifications have been agreed for these characteristics; the design shall then be determined at the choice of the manufacturer in accordance with the standard numbers.

Prefixes and suffixes can be added beyond the standard character strings. The statement of the standardized character string must be retained, it may only be supplemented.

f.e.:    JP3    window cage made of sheet steel, manufacturer variant 3

The names of rolling bearing types introduced according to DIN ISO 5593 are used to form names in accordance with standards, indicating the type of rolling element and the raceway geometry, e.g. deep groove ball bearings, spherical roller bearings.

In order to keep the designation short, the "radial" prefix contained in customary designations is generally suppressed. Abbreviations are used for the same reason. The standardized designations and their abbreviations are listed in DIN 623-1. This table also contains the standard numbers. When the standard designation is formed, only the main standard number is specified.

Note: Related character blocks can be divided against each other by blanks or the graphic characters hyphen (-), slash (/), horizontal cross (x) or dot (●).

 

I Prefixes

I.1 Bearing Parts

The prefixes are used to identify parts of complete rolling bearings.

K

Cage with rolling elements (rolling element ring, e.g. K81110 for the axial cylindrical roller ring of the axial cylindrical roller bearing 81110)

For some rolling bearing types (e.g. cylindrical roller bearings, tapered roller bearings) the free rings or the roller and cage assemblies with the non-detachable rings can also be ordered separately. These parts are identified by the prefixes before the base character.

L

Free ring (e.g. LNU 419 for the inner ring of the bearing NU 419 or LN 419 for the inner ring of the bearing N 419)

R

Ring (inner or outer ring) with rolling element set (e.g. RNU 419 for the roller and cage assembly with the outer ring of the bearing NU 419 or RN 419 for the inner ring with the roller and cage assembly of the bearing N 419)

WS

Shaft washer of a bearing

GS

Housing washer of a bearing

The parts marked L and R of a particular bearing type form a complete bearing arrangement. However, its full functionality can only be guaranteed if the parts are supplied by the same manufacturer. If the free ring consists of several parts, e.g. inner ring and flanged pulley on the cylindrical roller bearing NUP, the prefix L for the inner ring with associated flanged pulley applies accordingly.

I.2 Material

Inner and outer rings and rolling elements are normally made of rolling bearing steel according to DIN EN ISO 683-17.

Rolling bearings made of stainless steel usually have the prefix S (e.g. S 6205) or W (e.g. W 6205). A comparison of conventional rolling bearing material is shown in chapter "Rolling bearing material in comparison".

 

 

II Base Character

The base character indicates the type and size of the bearing. It usually consists of one character or character group for each (exceptions see below):

  • Bearing series (see section II.1)

  • Bearing bore (see section II.2)

The above system does not apply to needle roller/axial cylindrical roller bearings, needle roller/axial ball bearings, drawn cup needle roller bearings, drawn cup needle bushes, drawn cup needle roller bearings, radial needle roller and cage assemblies, axial needle roller and cage assemblies and axial washers. Here the base character is composed of characters for :

  • Bearing design

  • Characteristic dimension(s)

The corresponding assembly system is shown in DIN 623.

&nbs

II.1 Bearing Series

The bearing series consists of the bearing type and the dimensional series. Each bearing series is identified by a group of numbers or letters or by a combination of numbers and letters.

There are two different designation systems for tapered roller bearings according to DIN 720 and ISO 355. DIN 720 corresponds to the rules of this standard, ISO 355 contains its own systematics.

 

II.2 Lagerbohrung

The symbol for the bearing bore consists of digits and is generally appended directly to the symbol for the bearing series, but in defined cases also with a slash.

Symbols for bearing bore:

Bore diameter (mm)Symbol for bearing boreExamples
overto
-9

The bore dimension in mm is appended unencrypted with a slash to the abbreviation for the bearing series, even for decimal fraction dimensions.

Deep groove ball bearing of bearing series 618 with 3 mm bore diameter of the inner ring.

618/3

  

In the following exceptions, the slash was removed:

 
Deep groove ball bearings: 602, 603, 604, 605, 606, 607, 608, 609, 623, 624, 625, 626, 627, 628, 629, 633 634, 635, 636, 637, 638, 639 


Spherical ball bearings: 108, 126, 127, 129, 135

Angular contact ball bearing: 705, 706, 707, 708, 709 (not included in product standards, previously common types)

Deep groove ball bearing of bearing series 62 with 5 mm bore diameter of the inner ring: 62 5

Spherical ball bearing of bearing series 12 with 6 mm bore diameter of the inner ring: 12 6

Angular contact ball bearings of bearing series 70 with 6 mm bore diameter of the inner ring: 70 6

1017

Bore code in bearing row

00 = 10 mm bore

01 = 12 mm bore

02 = 15 mm bore

03 = 17 mm bore

For all bearing series except E, B0, L, M, UK, UL, UM and radial insert ball bearings YEN 203/12, YEN 203/15, YAL 203/12, YAL 203/15.

Deep groove ball bearing of bearing series 62 with 12 mm bore of the inner ring: 6201

Needle roller bearings of bearing series NA 49 with 15 mm bore of inner ring: NA4902

20480

Bore code = 1/5 of the bore diameter in mm on bearing row.

For diameters up to 45 mm, a zero is set before the hole number.

For all bearing series except series E, B0, L, M, UK, UL, UM and bores 22, 28 and 32 mm as well as radial insert ball bearing YEL 214/65.

Spherical roller bearing of bearing series 232 with 120 mm bore of inner ring: 23224

Angular contact ball bearings of bearing series 73 with 30 mm bore of the inner ring: 7306

Intermediate sizes

Bore diameter in mm for intermediate sizes with 22, 28 and 32 mm bearing bore; bore diameter separated by slash on bearing row.

Deep groove ball bearings of bearing series 62 with 22 mm bore of inner ring: 62/22

500all sizes

Bore diameter in mm separated by slash on bearing row, for new designs follow dimension plan DIN 616.

Spherical roller bearing of bearing series 230 with 500 mm bore of inner ring: 230/500

all sizes

Bore diameter in mm to bearing series E, B0, L, M, UK, UL and UM.

Magneto bearing of the bearing series B0 with 17 mm bore of the inner ring: B017

 

III Suffixes

Suffixes are written after the base character and are used to identify

  • NG 1: internal construction

  • NG 2: external shape

  • NG 3: cage design

  • NG 4.1: tolerances

  • NG 4.2: bearing pairs

  • NG 4.3: bearing clearance

  • NG 5.1: material

  • NG 5.2: heat treatment

  • NG 6: lubrication

 

NG 1  - Internal Construction

AModified internal design
ASpherical roller bearings: Modified internal design, inner ring with two lateral retaining ribs and one central rib
ATapered roller bearings: Modified internal design
ACylindrical roller bearing: Modified internal design
BModified internal design
BAngular contact ball bearings: Modified internal design, contact angle 40°
BTapered roller bearings: Modified internal design, contact angle 20°
CModified internal design
CAngular contact ball bearings: Modified internal design, contact angle 15°
CSpindle bearings: Modified internal design, contact angle 15°
EModified internal design
EAngular contact ball bearings: Modified internal design, contact angle 25°
ESpindle bearings: Modified internal design, contact angle 25°
ECylindrical roller bearings: Modified internal design, Increased capacity design
EXCylindrical roller bearings: Modified internal design, adapted according to norm, Bearing parts not interchangeable with the previous E version
EASpherical roller bearings: Modified internal design, inner ring with two lateral retaining ribs
EASpherical roller thrust bearings: Modified internal design, in connection with mounting dimensions
DModified internal design
DAngular contact ball bearings: Modified internal design, contact angle 20°
DSpindle bearings: Modified internal design, contact angle 20°

 

NG 2  - External Shape

DHThrust bearings, single direction with two housing washers
DSThrust bearings, single direction with two shaft washers
EKThrust ball bearings without housing washer
HBearings with two lubrication holes on the non-thrust side in the outer ring
HSpindle bearing: Bearings with two lubrication holes on the non-thrust side in the outer ring
H1Bearings with two lubrication holes on the thrust side in the outer ring
H1Spindle bearing: Bearings with two lubrication holes on the thrust side in the outer ring
KTapered bore, taper 1:12
K30Tapered bore, taper 1:30
LBearings with annular groove and two lubrication holes on the non-thrust side and two annular groove fitted with O-rings in the outer ring
LSpindle bearing: Bearings with annular groove and two lubrication holes on the non-thrust side and two annular groove fitted with O-rings in the outer ring
L1Bearings with annular groove and two lubrication holes on the thrust side and two annular groove fitted with O-rings in the outer ring
NSnap ring groove in the outer ring
NRSnap ring groove in the outer ring, with snap ring
NBSnap ring groove in the outer ring (with one-sided sealed bearings on the sealed side)
N1One locating slot in one outer ring side face
N2Two locating slot in one outer ring side face, 180° apart
N3One locating slot on one side face and one snap ring groovein on the other side in the outer ring
N4Two locating slot in one outer ring side face and one snap ring groovein on the other side in the outer ring
N5One locating slot and snap ring groove on one side in the outer ring
N6Two locating slot and one snap ring groove on one side in the outer ring
OBCylindrical roller bearing without loose rib (does not apply to NUP and NP execution)
T..Suffix T followed by a number indicates the total width of matched bearings, arranged back-to-back or in tandem
RBearings with a flange on outer ring
SBearings with annular groove and three lubrication holes in the outer ring
S6Bearings with annular groove and six lubrication holes in the outer ring
SIRBearings with annular groove and three lubrication holes in the inner ring
SIR6Bearings with annular groove and six lubrication holes in the inner ring
WBearings without annular groove and lubrication holes in the outer ring
W20Bearings with three lubrication holes in the outer ring
W22Bearings with two lubrication holes in the inner ring
W24Bearings with four lubrication holes in the inner ring
W26Bearings with six lubrication holes in the inner ring
W30Bearings with three lubrication holes in the inner ring
W77Bearing with plug added lubrication holes in the outer ring
XTapered roller bearings: Bearings with, boundary dimensions adapted to ISO standards

 

NG 3 - Cage Design

MSolid brass cage, rolling elements guided
MASolid brass cage, rib-guided on outer ring
MASSolid brass cage, rib-guided on outer ring, with lubricating grooves
MBSolid brass cage, rib-guided on inner ring
MBSSolid brass cage, rib-guided on inner ring, with lubricating grooves
M2Two-piece solid brass cage, riveted (steel rivet), rolling elements guided
M2ATwo-piece solid brass cage, riveted (steel rivet), rib-guided on outer ring / guided on housing washer
M2BTwo-piece solid brass cage, riveted (steel rivet), rib-guided on inner ring / guided on shaft
M2ASTwo-piece solid brass cage, riveted (steel rivet), rib-guided on outer ring/ guided on housing washer, with lubricating grooves
M2BSTwo-piece solid brass cage, riveted (steel rivet), rib-guided on inner ring / guided on shaft, with lubricating grooves
M3Two-piece solid brass cage, crosspiece riveted, rolling elements guided
M3ATwo-piece solid brass cage, crosspiece riveted, rib-guided on outer ring / guided on housing washer
M3BTwo-piece solid brass cage, crosspiece riveted, rib-guided on inner ring / guided on shaft
M3ASTwo-piece solid brass cage, crosspiece riveted, rib-guided on outer ring / guided on housing washer
M3BSTwo-piece solid brass cage, crosspiece riveted, rib-guided on inner ring, with lubricating grooves
M4Two-piece solid brass cage, bolted, rolling elements guided
M4ATwo-piece solid brass cage, bolted, rib-guided on outer ring / guided on housing washer
M4BTwo-piece solid brass cage, bolted, rib-guided on inner ring
M4ASTwo-piece solid brass cage, bolted, rib-guided on outer ring / guided on housing washer, with lubricating grooves
M4BSTwo-piece solid brass cage, bolted, rib-guided on inner ring / guided on shaft, with lubricating grooves
MPSolid brass window cage, rolling elements guided
MPASolid brass window cage, rib-guided on outer ring / guided on housing washer
MPADSolid brass window cage, rib-guided on outer ring, by special cage pocket geometry of the cage with the rolling elements can be removed from the outer ring
MPBSolid brass window cage, rib-guided on inner ring / guided on shaft
MPASSolid brass window cage, rib-guided on outer ring / guided on housing washer, with lubricating grooves
MPBSSolid brass window cage, rib-guided on inner ring / guided on shaft, with lubricating grooves
MPESolid brass window cage, modified, rolling elements guided
MPEASolid brass window cage, modified, rib-guided on outer ring / guided on housing washer
MPEBSolid brass window cage, modified, rib-guided on inner ring / guided on shaft
MPEASSolid brass window cage, modified, rib-guided on outer ring / guided on housing washer, with lubricating grooves
MPEBSSolid brass window cage, modified, rib-guided on inner ring / guided on shaft, with lubricating grooves
ALPSolid aluminum alloy window cage, rolling elements guided
FSolid steel cage, rolling elements guided
F2Two-piece solid steel cage, riveted (steel rivet), rolling elements guided
FPSolid steel window cage, rolling elements guided
FRPin type cage, rolling elements guided
HPASolid bronze window cage, rib-guided on outer ring / guided on housing washer
JSheet steel cage, rolling elements guided
JHSheet steel snap-type cage, rolling elements guided
JNSheet steel cage, riveted (steel rivet), rolling elements guided
JPSheet steel window cage, rolling elements guided
TSolid textile laminated phenolic cage, rolling elements guided
TASolid textile laminated phenolic cage, rib-guided on outer ring / guided on housing washer
TBSolid textile laminated phenolic cage, rib-guided on inner ring / guided on shaft
THSolid snap-type textile laminated phenolic cage, rolling elements guided
THASolid snap-type textile laminated phenolic cage, rib-guided on outer ring / guided on housing washer
THBSolid snap-type textile laminated phenolic cage, rib-guided on inner ring / guided on shaft
TPSolid textile laminated phenolic window cage, rolling elements guided
TPASolid textile laminated phenolic window cage, rib-guided on outer ring / guided on housing washer
TPASpindle bearing: Solid textile laminated phenolic window cage, rib-guided on outer ring
TPBSolid textile laminated phenolic window cage, rib-guided on inner ring / guided on shaft
TESolid PEEK (polyether ether ketone) cage, rolling elements guided
TEASolid PEEK (polyether ether ketone) cage, rib-guided on outer ring / guided on housing washer
TEPASolid PEEK (polyether ether ketone) window cage, rib-guided on outer ring / guided on housing washer
TNSolid polyamide PA66 cage, rolling elements guided
TNHSolid snap-type polyamide PA66 cage, rolling elements guided
TNPSolid polyamide PA66 window cage, rolling elements guided
TVSolid polyamide PA66-GF25 window cage, rolling elements guided
TVHSolid snap-type polyamide PA66-GF25 cage, rolling elements guided
TVPSolid polyamide PA66-GF25 window cage, rolling elements guided
YSheet brass cage, rolling elements guided
VFull complement ball or roller bearing (without cage)
VHFull complement ball or roller bearing (without cage), self-retaining

 

NG 4.1 - Tolerance

PNDimensional and running tolerances according to ISO to class Normal, is not included in bearing designations
P6XDimensional and running tolerances according to ISO to class 6X
P6Dimensional and running tolerances according to ISO to class 6
P5Dimensional and running tolerances according to ISO to class 5
P4Dimensional and running tolerances according to ISO to class 4
P4SKRW standard, better than dimensional and running tolerances according to ISO to class 4
P2Dimensional and running tolerances according to ISO to class 2
SPTolerance class (KRW), Special precision
UPTolerance class (KRW), Ultra precision

 

NG 4.2 - Bearing Pairs

DBTwo bearings matched for mounting back-to-back, suffix DB followed by sign indicates the the internal preload or clearance of bearing set
DFTwo bearings matched for mounting face-to-face, suffix DF followed by sign indicates the the internal preload or clearance of bearing set
DTTwo bearings matched for mounting tandem, suffix DT followed by sign indicates the the internal preload or clearance of bearing set
DGTwo bearings matched for mounting universal set, suffix DG followed by sign indicates the the internal preload or clearance of bearing set
TGThree bearings matched for mounting universal set, suffix TG followed by sign indicates the the internal preload or clearance of bearing set
QGQuad bearings matched for mounting universal set, suffix QG followed by sign indicates the the internal preload or clearance of bearing set
PGFive bearings matched for mounting universal set, suffix PG followed by sign indicates the the internal preload or clearance of bearing set
TBTThree bearings matched for mounting tandem and back-to-back, suffix TBT followed by sign indicates the the internal preload or clearance of bearing set
TFTThree bearings matched for mounting tandem and face-to-face, suffix TFT followed by sign indicates the the internal preload or clearance of bearing set
TTThree bearings matched for mounting tandem, suffix TFT followed by sign indicates the the internal preload or clearance of bearing set
QBCQuad bearings matched for mounting tandem and back-to-back //\\, suffix QBC followed by sign indicates the the internal preload or clearance of bearing set
QBTQuad bearings matched for mounting tandem and back-to-back ///\, suffix QBT followed by sign indicates the the internal preload or clearance of bearing set
QFCQuad bearings matched for mounting tandem and face-to-face \\//, suffix QFC followed by sign indicates the the internal preload or clearance of bearing set
QFTQuad bearings matched for mounting tandem and face-to-face \///, suffix QFT followed by sign indicates the the internal preload or clearance of bearing set
PBCFive bearings matched for mounting tandem and face-to-face ///\\, suffix PBC followed by sign indicates the the internal preload or clearance of bearing set
PBTFive bearings matched for mounting tandem and face-to-face ////\, suffix PBC followed by sign indicates the the internal preload or clearance of bearing set
USpindle Bearing: Universal bearing, suffix U followed by a letter indicates the the internal preload of bearing set. It is distinguished:
L - light preload
M - medium preload
H - heavy preload
DUSpindle Bearing: Two bearings matched for mounting universal set, suffix DU followed by a letter indicates the the internal preload of bearing set. It is distinguished:
L - light preload
M - medium preload
H - heavy preload
TUSpindle Bearing: Three bearings matched for mounting universal set, suffix TU followed by a letter indicates the the internal preload of bearing set. It is distinguished:
L - light preload
M - medium preload
H - heavy preload
QUSpindle Bearing: Quad bearings matched for mounting universal set, suffix QU followed by a letter indicates the the internal preload of bearing set. It is distinguished:
L - light preload
M - medium preload
H - heavy preload
PUSpindle Bearing: Five bearings matched for mounting universal set, suffix PU followed by a letter indicates the the internal preload of bearing set. It is distinguished:
L - light preload
M - medium preload
H - heavy preload

 

NG 4.3 - Bearing Clearance

C1Radial or axial internal clearance smaller than C2
C2Radial or axial internal clearance smaller than CN
CNRadial or axial internal clearance bigger than C2 and smaller than C3, is not included in bearing designations
C3Radial or axial internal clearance bigger than CN
C4Radial or axial internal clearance bigger than C3
C5Radial or axial internal clearance bigger than C4
..LInternal clearance, reduced clearance range corresponding to the lower half of the actual clearance range
..MInternal clearance, reduced to half the clearance range corresponding to the middle of the actual clearance range
..HInternal clearance, reduced clearance range corresponding to the upper half of the actual clearance range
..NAInternal clearance reduced, Bearing parts not interchangeable
..VGBearings prepared for internal clearance, bearing with rough ground ring raceway, for CN (Normal), suffix CN can be omitted
VG..Suffix VG followed by a number indicates the middle raceway roughing dimension on the ring in the bearing
A..Axial internal clearance in  µm
R..Radial internal clearance in  µm
CABearing for universal matching for fitting in pairs in an X or O arrangement intended, axial internal clearance smaller than Normal (CB)
CBBearing for universal matching for fitting in pairs in an X or O arrangement intended, axial internal clearance Normal
CCBearing for universal matching for fitting in pairs in an X or O arrangement intended, axial internal clearance greater than Normal (CB)
CBearing for universal matching for fitting in pairs in an X or O arrangement intended, axial internal clearance in  µm
GABearing for universal matching for fitting in pairs in an X or O arrangement intended, light preload
GBBearing for universal matching for fitting in pairs in an X or O arrangement intended, moderate preload
GCBearing for universal matching for fitting in pairs in an X or O arrangement intended, heavy preload
G..Bearing for universal matching for fitting in pairs in an X or O arrangement intended, axial internal preload in  µm

 

NG 5.1 - Material

HA..Bearings or bearing parts are made of casehardening steel, suffix followed by a number indicates the affected parts group
HC..Hybrid bearing, bearing parts are made of silicon nitride Si3N4, suffix followed by a number indicates the affected parts group

 

NG 5.2 - Heat Treatment

HB..Bearings or bearing parts hardened bainitic, suffix followed by a number indicates the affected parts group
SNBearing rings or washer heat stabilized for operating temperatures up to 120 °C, is not included in bearing designations
S0Bearing rings or washer heat stabilized for operating temperatures up to 150 °C
S1KRW Standard; Bearing rings or washer heat stabilized for operating temperatures up to 200 °C
S2Bearing rings or washer heat stabilized for operating temperatures up to 250 °C
S3Bearing rings or washer heat stabilized for operating temperatures up to 300 °C
S4Bearing rings or washer heat stabilized for operating temperatures up to 350 °C
..AOuter rings or housing washer heat stabilized according to Suffix for dimensionally stability
..BInner rings or shaft washer heat stabilized according to Suffix for dimensionally stability

 

NG 6 - Lubrication

customer-related determination

 

Here you can find KRW Suffix List (PDF).

 

IV Supplementary character

For specifications that go beyond the symbols from I to III, manufacturer-related supplementary symbols can be specified. The commitments of the relevant product standards must be kept. With addition signs, specifications beyond the product standard are made or tolerances are narrowed.

 

NG 7.1 - Technical Specification

BR..Bearings or bearing parts coated (burnished), suffix followed by a number indicates the affected parts group
SJ..Insulated bearing or bearing parts, suffix followed by a number indicates the affected parts group. There is a distinction between:
5 -  Insulated bearing up to 500V, coated outer ring
10 - Insulated bearing up to 1.000V, coated outer ring
30 - Insulated bearing up to 3.000V, coated outer ring
..J - Coated inner ring

 

NG 7.2 - Supplementary symbol according to manufacturer's specification

FV1Traction motor bearings for railway applications according to DIN 43283:1982
FV2Bearing for railway axleboxes in accordance with EN 12080, class 1
FV3

Bearing according to VGN 3050

Main Dimensions

Rolling bearings can be used universally as ready-to-install machine elements. This is mainly because the main dimensions of the common bearings are standardized. ISO 15 applies to radial bearings (except tapered roller bearings), ISO 355 to metric tapered roller bearings and ISO 104 to axial bearings. The dimension plans of the ISO standards were adopted in DIN 616 and DIN ISO 355 (metric tapered roller bearings).

In the dimension plans of DIN 616, several outside diameters and widths are assigned to one bearing bore. Common diameter series are 7, 8, 9, 0, 1, 2, 3, 4 (outer diameter increasing in this order). Within each diameter row there are several width rows 8, 0, 1, 2, 3, 4, 5 (with larger number increasing width). The two-digit number for the dimension series contains first the number of the width series (for axial bearings of the height series), and second the number of the diameter series. When using the width and diameter series in practice, figures are omitted for some bearing types, e.g. for cylindrical roller bearings of width series "0" (NU0220 à NU220)

 

Dimensional series for radial bearings

Dimensional series for radial bearings

Dimensional series for axial bearings

Dimensional series for axial bearings

Designation Example

The following applies to the designation of a spherical roller bearing:
 

Rolling Bearing Designation System

Way of Speaking

The base characters are to be separated between the bearing series and the bearing bore. The separation of the character block for the dimension series and the connection of the separated character with the character for the bearing type are not permitted when speaking.

Correct Speech:

618/3

six hundred and eighteen slash three

625

sixty-two five

6205

sixty-two zero five

30205

three hundred two zero five

22310

two hundred and twenty-three ten

NJ210

N J two ten

 

Cage Types and Designs

General Information

The bearing cage is an important component in the rolling bearing with the following functions:

  • keeps the rolling elements at a distance to prevent contact

  • ensures an equal distance between the rolling elements, thus ensuring even load distribution

  • guides the rolling elements

  • transmits circumferential forces

  • prevents the rolling elements from falling out in bearings that can be dismantled and pivoted

A distinction is made between sheet metal cages, one-piece, and multi-piece solid cages made of different materials.

 

Pressed Steel Cage

Pressed steel cages are bearing cages which are almost always punched or pressed from sheet steel. Rarely, brass sheet is also used. A lower weight and a good lubricant supply to the bearing interior are advantages over solid cages.

Solid Cage Tapered Roller Bearing

Solid Cages

Solid cages are usually used for high cage strength requirements and temperatures up to 250°C. Brass, steel, bronze, aluminum, sintered iron, plastics or hard fabric are the materials used. Solid cages made of metal or hard fabric are produced by turning and milling, solid cages made of plastic by injection molding into molds.

For large, highly loaded bearings and for small series, solid cages, primarily made of brass and steel, are an advantage. Relatively low inertial forces have solid cages made of light metal, plastic or hard tissue and are therefore used in high-speed applications in an outboard version.

Cages made of glass fiber reinforced polyamide (PA66 GF25) are installed in many large series bearings, which have a low weight, high elasticity and good sliding and emergency running properties. This has a positive effect on the life of the bearing.

Special operating conditions require a specially selected cage. However, the operating temperature limit is 120 ° C.

Cages - polyamid and brass

Pin Type Cages

Rolling elements with a central axial bore are used for rolling bearings with a welded pin cage, mostly cylindrical roller bearings, tapered roller bearings and more rarely spherical roller bearings. A steel bolt leads through this hole, which connects two side cage washers and thus ensures high strength.

Pressed Steel Cage Tapered Roller Bearing

Cage Guides

A distinguishing feature is that cages can be guided differently depending on the application. The cages are most frequently guided by the rolling elements (without suffixes). Cage guide on the bearing outer ring, or also known as outboard guidance, is indicated with the suffix A. Cage guide on bearing inner ring, also known as inboard guidance, is indicated by the suffix B.

Cage Guides

Bearing Tolerances

Bearing Tolerances ensure the rolling bearing interchangeability. The values ​​of the dimensional and running tolerances are given in DIN 620. Bearings are generally manufactured in tolerance classes PN, other tolerance classes are available on request or are selected depending on the application.

 

Symbols Bore Diameter

d

Nominal diameter of the bore

d1

Diameter of the theoretical taper surface at the wide end of a tapered bore

d2

Nominal diameter of the bore of the shaft located washer of a double direction bearing

Δds

Deviation of a single shoulder diameter

Δdmp

Deviation of a mean shoulder diameter in one plane

Δd1mp

Deviation of a mean shoulder diameter for the theoreticaltaper surface at the wide end of a tapered bore

Δd2mp

Deviation of the mean bore diameter of the shaft locating washer in one plane of a double direction bearing

Vdp

Variation of the single bore diameters in a radial plane

Vdmp

Variation of the mean bore diameter

α

Nominal taper angle

 

Symbols Outer Diameter

D

Nominal outer diameter

D1

Flange outer diameter

ΔDs

Deviation of a single outer diameter

ΔD1s

Deviation of a single flange outer diameter

ΔDmp

Deviation of a mean outer diameter in one plane

ΔDp

Variation of the outer diameter in one plane

VDmp

Variation of the mean outer diameter

 

Symbols Widths and Height

B, C, C1

Nominal width of inner ring, outer ring and flange

ΔBs, ΔCs

Deviation of a single inner ring width and outer ring width

VBs, VCs, VC1s

Variation of the inner ring width, outer ring width and flange width

ΔC1s

Deviation of a single flange width from nominal dimension

T

Nominal width of the bearing

T1

Nominal width of the inner ring with rolling element set on the tapered roller bearing, measured above standard outer ring

T2

Nominal width of the outer ring of the tapered roller bearing, measured over a standard of the inner ring and rolling element set

ΔT1, ΔT2

Algebraic difference between the largest and smallest fixed individual dimension for T1 or T2

ΔT1s

Deviation of the actual effective width of the inner ring with rolling element set from the effective nominal width

ΔT2s

Deviation of the actual effective width of the outer ring from the effective nominal width

T, T2

(Thrust) Nominal height of a single direction bearing

ΔTS

(Thrust) Deviation of the bearing height of a single direction bearing

T1, T3

(Thrust) Nominal height of a single direction, double direction bearing with washers

ΔT1s, ΔT2s, ΔT3s

(Thrust) Deviation of the bearing height of a single direction and double direction bearing with and without washers

T4

(Thrust) Nominal height of a single direction spherical roller bearing

ΔT4s

Deviation in bearing height of a single direction spherical roller thrust bearing

 

Symbols Run-out Tolerance

Kia

Radial run-out of the inner ring of the assembled bearing

Kea

Radial run-out of the outer ring of the assembled bearing

Sd

Axial run-out of the end face in relation to the bore

SD

Variation of the inclination of the shell, relative to the reference lateral surface

SD1

Variation of the inclination of the shell, relative to the internal flange face

Sia

Axial run-out of the end face in relation to the raceway of the inner ring of the assembled bearing

Sea

Axial run-out of the end face in relation to the raceway of the outer ring of the assembled bearing

Si

Variation in the thickness of the shaft locating washer

Si.1

Wall thickness variation in the contact angle measured generally for angular contact thrust ball bearings, spherical roller thrust bearings and tapered roller thrust bearings (profiled washers)

Se

Variation of the thickness of the housing disk

Se.1

Wall thickness variation in the contact angle measured generally for angular contact thrust ball bearings, spherical roller thrust bearings andtapered roller thrust bearings (profiled washers)

 

The tolerances of our bearing types can be found in the overview "Bearing Tolerances" until further notice.

 

 

Bearing Clearance

The bearing clearance is the measure about how much a bearing ring can be moved radial and axial from one end position to another. It will be distinguished between the clearance of the disassembled bearing (bearing clearance) and the clearance of the mounted, at operating temperature bearing (operation clearance, operation play). The clearance must be as low as possible for an ideal shaft guidance. During assembly, the bearing clearance is reduced by a tight fit of the bearing rings. Therefore, the bearing clearance must be higher than the necessary operation clearance. During operation, the radial clearance is reduced, if the inner ring is - as it is usually the case - warmer than the outer ring. The DIN standard 620 specifies the radial clearance standard values of roller bearings. Thereby, the standard clearance (clearance group CN) is so assessed, that the bearing has an appropriate clearance at common assembly and operation conditions. The DIN standard 620 additionally defines clearance groups with higher bearing clearance. The ISO standard 5753 for spherical roller bearings contains additional values for the clearance group C5. Divergent assembly and operation conditions, e.g. tight fitting for both bearing rings or a temperature difference greater 10 K, require broader radial clearance groups that are available upon request. A suitable clearance group must be chosen through an assessment of the fittings. The clearance values are indicated for the prime bearing designs.

 

Tolerances for bearing clearance:

You can simply use our bearing clearance calculator, to calculate the bearing clearance tolerances of our bearing designs.

 

Radial clearance reduction by temperature differences

The radial clearance reduction ∆e by temperature differences ∆T between the inner ring and outer ring, amounts for not adjusted bearings approximately:

α

linear expansion coefficient of steel (=0.000012)

[K-1]

d

bearing bore

[mm]

D

outer diameter of bearing

[mm]

ΔT

temperature difference between inner and outer ring

[K]

If warmth is applied or deprived from the bearing surface, a stronger change in the radial bearing clearance must be estimated. The radial clearance is reduced, if warmth is applied on the shaft or deprived over the housing. A greater radial clearance results from heat supply over the housing or heat removal over the shaft. While fast start-up on operation speed, greater temperature differences result between the bearing rings as during steady state. The rotational speed must increase slowly that the bearing does not deform, or a greater radial clearance must be chosen for the as it theoretically would be necessary for the warmed-up bearing.

 

Radial clearance reduction by tight fits

The inner ring race widening of 80% fit oversize and an outer ring race necking of 70% fit oversize can be assumed by approximation (requirements: solid steel shaft, steel housing with normal wall thickness).

 

Rolling Bearing Materials in Comparison

The roller bearing capability is largely influenced by materials and heat treatment used. The material for the roller bearing rings and rolling bodies normally is low-alloy chromium steel, in special cases case-hardened steel. It a matter of high-grade steels with a high standard of purity. Steels according DIN EN ISO 683-17 are used for the roller bearing rings and rolling bodies. Based upon customer wishes, rolling bodies (balls and cylinders) made of ceramic materials (e.g. silicon nitride) In so called hybrid bearings the low density, good tribological behaviour, low thermal expansion as well as high insulation capacities of ceramic materials are used. Silicon nitride as well is used for coating the roller bearing rings (current-insulated bearings).

 

Comparison of roller bearing materials (compared to the reference):

 Standard Materials

100Cr6
Martensite S0

(Reference)

100Cr6
Bainite S1

100CrMnSi6-4

carbonitrided

case-hardened steel

case-hardened

case-hardened steel
carbonidrided

vulnerability against fatigue

identical

better

improved

better

improved

temperature resistance

identical

better

identical

identical

identical

lack of lubrication

(fail-safe running functions)

identical

better

better

better

better

corrosion resistance

impact of media

identical

inferior

inferior

inferior

inferior

costs

identical

identical

a bit pricier

more expensive

more expensive

 

 

Comparison of roller bearing materials (compared to the reference):

 Materials for Special Applications

100Cr6
Martensite S0

(Reference)

X30CrMoN15-1

M50
Martensite

M50NiL

case-hardened

M50NiL,

duplex-hardened

32CrMoV13,
nitrided

Si3N4

(rolling elements)

vulnerability against fatigue

identical

excellent

identical

improved

improved

improved

better

temperature-resistant

identical

identica to much better (depending from heat treatment)

improved

improved

improved

improved

excellent

resistance against lack of lubrication (fail-safe running functions)

identical

improved

identical

improved

improved

improved

improved

corrosion resistance (depending of medium and temperature) and impact of medium

identical

improved

inferior

inferior

inferior

identical

improved

costs (qualitative estimation)

identical

more expensive

more expensive

more expensive

much more expensive

a bit pricier

much more expensive

Dimensioning of Rolling Bearings

Through the overall machine structure or device, the roller bearing bore diameter is already determined. The final determination of the bearing size should be proven by a dimensioning calculation, if the requirements on service life, static safety and the necessary for profitability are fulfilled. Based on this calculation, the bearing load with its load capacity are compared amongst the working condition chosen.
The roller bearing technology distinguishes between static and dynamic load. Static load defines as the loaded bearing stands still, spins very slow or performs a slow pivoting movement. In these cases, the safety to avoid plastic deformation of the bearing race and rolling body is examined. The following requirement for the static load applies:

 

nspeed[min-1]
dmmean bearing diameter d= (d+D)/2[mm]

 

The most roller bearings are dynamically loaded. In these cases, the roller bearings are relatively spinning to each other. The rolling body suits the force transmission and performs a roll motion. With the dimensioning calculation, the safety to avoid premature material fatigue of the bearing race and rolling body is examined. Other material loads are thereby not observed.

 

Static Load

The static load rating C0 is the determinant of a roller bearings static load capacity. The static load rating is defined by DIN ISO 76 for a Hertzian load of rolling bodies on the bearing races of

4.200 MPa for ball bearings (punctate load)
4.000 MPa for roller bearings (linear load)

The static load rating C0 is stated in the measurements tables for each roller bearing.
During roller bearing load with C0 on the most loaded contact point, a plastic deformation of the roller body and race of about 1/10.000 of the roller bodies diameter occur. The static figure fs calculated for the verification that an enough sustainable bearing has been chosen.

fsstatic figure[-]
C0static load figure[kN]
P0equivalent static load[kN]

 

The static figure fs is a measure for the safety to avoid plastic deformations at the bearing body contact points with the bearing race. A great fs figure is necessary for extra smooth-running bearings. A smaller fs figure is enough for lower smooth-running demands. The following static fs figures must be reached in general:

 ball bearingroller bearing
high requirements≥ 2≥ 3
normal requirements≥ 1≥ 2
low requirements≥ 0,6≥ 1

 

 

Equivalent static load P0

P0 is a calculated value that defines the radial load for radial bearings and the axial centrically load for axial bearings. P0 causes the same load in the centre of the highest loaded contact point between rolling body and race like the actual active combined load.

P0equivalent static load[kN]
Frradial load[kN]
Faaxial load[kN]
X0radial factor[-]
Y0axial factor of bearings static load[-]

 

 

Nominal lifetime calculation

The standardised calculation procedure (DIN ISO 281) for dynamically loaded roller bearings relies on the material fatigue (pitting) as failure cause. The following life span formula is used for the calculations:

L10nominal lifetime[106 revolutions]
Cdynamic load rating[kN]
Pequivalent dynamic load[kN]
plifetime exponent[-]

 

L10 is the nominal life span in million revolutions that at least 90% of a bigger amount of bearings achieve or exceed.

The dynamic load rating C is stated in the measurement tables for each bearing. A load in this height results a L10 life span of 106 revolutions. The dynamic load rating Cr for radial bearings refers to the permanently fixed radial acting load in the bearing shaft only. The dynamic load rating Ca for axial bearings refers to the permanently fixed axial acting load in the bearing shaft only. If the operation temperature of the bearing exceeds 120°C, half of the hardness and therefore the dynamic load decrease due to material structure changes.

The dynamic equivalent load P is a calculational value of a, in size and direction, constant radial load of radial bearings or axial load of axial bearings. P results in the same life span as the actual acting combined load.

Pequivalent dynamic load[kN]
Frradial load[kN]
Faaxial load[kN]
Xradial factor[-]
Yaxial factor[-]

 

The life time exponent p differs for ball and roller bearings.

p = 3  for ball bearings

p = 10/3  for roller bearings

If the bearing life time is constant, the life time can be framed in hours.

 

L10hnominal life time[h]
L10nominal life time[106 Umdrehungen]
nspeed[min-1]

 

 

If e.g. traffic engineering requires the declaration in miles, the mean wheel diameter DW must be included in the life span calculation, so that following applies:

Lkmnominal life time[km]
L10nominal life time[106 Umdrehungen]
DRmean wheel diameter[mm]

 

Extended nominal life time calculation

In most cases, the nominal life span L10h is the adequate criteria for bearing capacity. In most cases of application, a more reliable calculation method is necessary. Therefore, the extended life span calculation according DIN ISO 281 is used It extends life span mentioned above about two factors. The formula shows the correlations.

L10mhextended nominal life time[h]
L10hnominal life time[h]
a1life time coefficient for reliability[-]
a2Life time coefficient from the system assessment[-)

 

The life time coefficient for reliability a1 is defined according to DIN ISO 281 for following values:

Reliability in %Lnma1
90L10m1
95L5m0,64
96L4m0,55
97L3m0,47
98L2m0,37
99L1m0,25
99,2L0,8m0,22
99,4L0,6m0,19
99,6L0,4m0,16
99,8L0,2m0,12
99,9L0,1m0,093
99,92L0,08m0,087
99,94L0,06m0,080
99,95L0,05m0,077

 

The life span coefficient from the system assessment aISO is a function from the relation of fatigue load and actual occurring load.

aISOlife time coefficient for the system assessment[-]
σucritical fatigue load[MPa]
σactual load[MPa]

 

To ease the calculation, the defined critical fatigue load Cu of DIN ISO 281 and the equivalent load P are used. Influences of lubrication r the contaminant level as well as the filtration are included furthermore. Thereby the following equation for the function applies:

aISOlife time coefficient for the system assessment[-]
eCcontaminant coefficient of lubrication[-]
Cucritical fatigue load[kN]
Pequivalent dynamic load[kN]
Κviscosity ratio[-]

 

Solid particles within the lubricant cause permanent wear in the bearings race (scoring) This leads to a life span reduction. The contamination factor ec was introduced, to depict this impact in the extended life span calculation. The following table states indications for the ec value according DIN ISO 281:

 

contaminant coefficienteC
dm < 100 mmdm ≥ 100 mm

extreme cleanliness
particle size as big as the lubrication dimension; laboratory conditions

1

1

high cleanliness
fine filtration of the oil supply; typical conditions of a greased sealed-for-life with sealing washers bearing

0.8 to 0.6

0.9 to 0.8

normal cleanliness
oil filtered by fine filter; typical conditions of a greased sealed-for-life with cover plates bearing

0.6 to 0.5

0.8 to 0.6

slight contamination
slight lubricant contamination

0.5 to 0.3

0.6 to 0.4

moderate contamination
typical conditions of bearing without fixed built-in sealings; coarse filtration; wear particles and environmental foreign particles.   

0.3 to 0.1

0.4 to 0.2

strong contamination
bearing environment heavy contaminated and bearing array is not sealed accordingly

0.1 to 0

0.1 to 0

heavy contamination

0

0

Contamination caused by water or other fluids that are not included in the ec value.

 

The viscosity ratio κ is further explained here. The kinematic operation viscosity and the reference kinematic viscosity ν1 are necessary for the calculation.

 

Κviscosity ratio[-]
νoperation viscosity[mm²/s]
ν1reference kinematic viscosity[mm²/s]

 

The lubricant must hold a certain minimum viscosity at operation temperature, to provide an appropriate lubrication film between the bearing elements. Life span limits can be extended by increasing the operation viscosity ν.
The kinematic reference viscosity ν1 can be determined with the aid of the diagram in the following figure as a function of the speed n and the mean roller bearing diameter dm. The operation viscosity ν can be determined in the following diagram.

Diagram for the determination of the operation viscosity

Diagram for the determination of the reference kinematic viscosity ν1

Diagram for the determination of the reference kinematic viscosity

Diagram for the determination of the operation viscosity v

The aISO coefficient can be determined from the diagram in the following figures containing values of the contamination factors eC, the critical fatigue load cU and the equivalent dynamic load P as well as the viscosity ratio K. The aISO value is defined according DIN ISO 281 as ≤ 50. This limit also applies for (eC · Cu)/P > 5. The calculation must be made with the value k = 4, if the viscosity ratio K exceeds 4.

 

Lebensdauer für Radialkugellager

Life time coefficient aISO for radial ball bearings

Lebensdauer für Radialrollenlager

Life time coefficient aISO for radial roller bearings

Lebensdauer für Axialkugellager

Life time coefficient aISO for axial ball bearings

Lebensdauer für Axialrollenlager

Life time coefficient aISO for axial roller bearings

Critical fatigue load

The critical fatigue load Cis the load for the highest loaded contact point within the bearing, where the critical fatigue load is reached. The calculation for the critical fatigue load is defined in DIN ISO 281. The critical fatigue load Cu must not be the exclusive criteria for the determination of bearings. Roller bearings do not necessarily have an infinite life span, if the bearing load is below the fatigue limits. In practical use cases thin film or partial lubrication and lubrication contamination of roller bearings lead to increased load of the bearing race material, so that even for a bearing running below the critical fatigue load the fatigue limit is exceeded locally on the bearing race surface. These effects of lubrications and lubricant contaminations are considered by the life span calculation method.