Crossed Roller Bearings - Details

Crossed Roller Bearings - Overview

The performance of crossed roller bearings is outstanding compared to other slewing rings. Due to the crossed-roller arrangement of the cylindrical rollers they offer advantages such as:

  • Assembly / Mounting
  • Tilting moment
  • Load capacity
  • Rigidity
  • Race Way Accuracy

These properties can be implemented in a single bearing location as a stand-alone solution, instead of the installation of a roller bearing combination to achieve a similar mechanical application. Therefore, it is a highly economical approach, based on the fact, that the effort and costs for the design of the connecting structure and the installation of multiple bearings are reduced.

The crossed-roller design enables:

  • Carrying of radial loads
  • Carrying of axial loads of both directions and
  • Including of tilting moments and multiple load combinations
Carrying of external loads with crossed roller bearings
Carrying of external loads with crossed roller bearings

IBO crossed roller bearings are used as a bearing solution for a variety of applications:

  • Machine tools
  • Centrifuges
  • Manipulators
  • Hoists
  • Luggage scanner
  • Medical technology
  • Antennas such as radar systems and telescopes
  • ‘Out of the standard’ technology
  • Automation, such as robot and handling systems

Product Characteristics of Crossed Roller Bearings

Running Characteristics

The enhanced running accuracy is achieved by designing high precision spacers for the cylindrical rollers. This exceptional designed guidance mechanism prevents skewing of the cylindrical rollers, which increases the running accuracy. Even with reduced or zero clearance (pre-tensioned preloaded inner and outer ring) the cylindrical rollers have no friction.

Rigidity

Due to the crossed-roller arrangement of the cylindrical rollers, the crossed roller bearing design can carry external loads from all directions. Compared to the combination of two angular contact ball bearings, the crossed roller bearings achieve a 3-4 times higher rigidity – with the same dimensions.

Comparison of the axial rigidity characteristics of crossed roller bearings and angular contact ball bearings
Comparison of the axial rigidity characteristics of crossed roller bearings and angular contact ball bearings

The width space requirement for crossed roller bearings is half as large as for angular contact ball bearings. Angular contact ball bearings can transmit tilting moments in an ‘O’- arrangement only.

Comparison of the width of the bearing solution when transferring tilting moments
Comparison of the width of the bearing solution when transferring tilting moments

Load Capacity

Compared to conventional crossed roller bearings with sheet metal cages, the IBO crossed roller bearings have a significant higher load rating. This is possible by using spacers, which increase the contact lines (L1> L2). In addition, the spacers protect the track / raceway system by preventing the rollers from tilting. When using sheet metal cages, the rollers stay at the same place at the raceway and do not ‘circulate’.

IBO crossed roller bearing with spacers and contact length L1
IBO crossed roller bearing with spacers and contact length L1
Crossed roller bearing with sheet metal cage and contact length L2
Crossed roller bearing with sheet metal cage and contact length L2

The spacers improve the load distribution and counteract the roller tilting. Roller tilting can significantly reduce the lifetime of a crossed roller bearing. When using sheet metal cages, the load zones in the inner and outer ring are asymmetrical (see the following illustration). The tilting moment acting on the track / raceway system increases with higher load. This can lead to an inclined position of the cylindrical rollers, which leads to an unevenly higher friction in the bearing and reduces the lifetime.

Symmetrical load distribution with IBO crossed roller bearings with the IBO spacer arrangement
Symmetrical load distribution with IBO crossed roller bearings with the IBO spacer arrangement
Asymmetrical load distribution for crossed roller bearings with sheet metal cages
Asymmetrical load distribution for crossed roller bearings with sheet metal cages

Product Selection

Operating temperature and the anticipated lifetime are key:

Procedure for the product selection with IBO crossed roller bearings
Procedure for the product selection with IBO crossed roller bearings

If the application requires certain materials for the bearing rings, such as corrosion-resistant stainless steels or aluminium materials (as a race system), we can manufacture this for you. Simply send us an inquiry using the contact form.

Lifetime Calculation

The lifetime for crossed roller bearings is calculated as follows:

Calculation of lifetime of crossed roller bearings
Calculation of lifetime of crossed roller bearings

An operating temperature above 80°C reduces the lifetime and is considered via the factor fB.

The influence of the operating temperature and the lifetime with the operating temperature factor
The influence of the operating temperature and the lifetime with the operating temperature factor

For the lifetime calculation, application-specific criteria are considered by using the application factor fA. The values listed in the following table are assumptions for each application and the specific application criteria.

Application Requirement Criteria Application Factor fA
General Application Smooth operation, without impact loads 1,00
Allgemeine Anwendung Operation with high shock loads 3,00
Automation Rigidity 1,25
Radar System Accuracy 1,50
Medical Technology Smooth Running 1,50
Machine Tooling Accuracy 1,50
Measuring Technology Smooth Running 2,00

 

The additional safety factor is defined with fS = 1 when there is no customer input. The standard situation does not need an additional safety factor to be included in the equation. There are exceptional cases, e.g. specifications approvals, internal factory re regulations, requirement of audit firms. This must be communicated to IBO in advance and taken into consideration before the lifetime calculation.

The radial dynamic equivalent load is calculated as follows:

Berechnung der dynamischen, äquivalenten Belastung
Berechnung der dynamischen, äquivalenten Belastung

The values ​​for the load factors X and Y can be found in the table below:

Classification X Y
1,00 0,45
0,67 0,67

Static safety factor

If concussions (hefty vibrations) and or shock loads occur for a limited period, this must be considered as follows:

Consideration of shock loads
Consideration of shock loads

The values ​​for the static safety factor fstat are listed in the following table:

Type of the load Sicherheitsfaktor f stat
Normale Belastung 1,00
Stoßbelastung 0,67

Statically equivalent radial load

The static equivalent radial load is calculated as follows:

Calculation of the static equivalent radial load
Calculation of the static equivalent radial load

Permissible static tilting moment

The permissible static tilting moment is calculated as follows:

Calculation of the permissible static tilting moment
Calculation of the permissible static tilting moment

Statically equivalent radial load

The permissible static axial load is calculated using the following formula:

Calculation of the permissible static axial load
Calculation of the permissible static axial load

Influences for the lifetime of crossed roller bearings

The lifetime of a crossed roller bearing is the actual time in utilisation. The lifetime can deviate significantly from the calculated nominal lifetime due to wear and / or fatigue. Possible causes are:

  • Oscillating bearing movements with very small swivel angles (risk of false brinelling)
  • Vibrations during downtime (stand still of the non-operating machine)
  • Incorrect design or deformation of the connecting construction
  • Too high operating temperature
  • Incorrect maintenance or lubrication
  • Pollution
  • Wrong mounting of the bearing
  • Insufficient pre-tensioning / -loading of the fastening screws

Due to the variety of designs and the resulting installation and operating condition scenarios, the lifetime calculation is not a given real-world fact. With its’ mathematical formulas and algorithms built on real installation and operating conditions an approximate value, which is considered as a pretty accurate prediction of a roller bearing lifetime.

Product lines

IBO manufactures crossed roller bearings of the PXU series according to the dimension series 10, 18 and 19 of DIN616. These correspond to the outer dimensions of the series of angular contact ball bearings 710, 718, 719, deep groove ball bearings 610, 618, 619 and cylindrical roller bearings N10, N18 and N19.

We also produce the PXB series. This is a very compact series and gives the user the opportunity to obtain a bearing solution, which is optimized for installation space in terms of concentricity (running accuracy) and rigidity.

The rings of the crossed roller bearings in the PXU and PXB series are standardised heat-stabilized for operating temperatures up to + 200 ° C (S1).

PXU series

Cross roller bearings of the PXU series are:

  • available in different versions regarding the dimensional- and running accuracy and the bearing (axial/radial) clearance as well
  • not sealed
  • greased when dispatched

Due to the outer ring split in the circumferential direction, this design is suitable for applications with a rotating inner ring.

In the standard version, the bearings are manufactured according to the tolerance class P0 which is given in WN001 and WN002. All bearing sizes mentioned in the dimension tables can  be delivered up to a tolerance class P5. On request we are glad to offer dimensions, which are not listed in the dimension tables. Please contact us.

IBO crossed roller bearings in the CRBSU08 series
IBO crossed roller bearings in the CRBSU08 series

CRBSU08 series

Crossed roller bearings in the CRBSU08 series:

  • have a concentricity (running accuracy) of 0.01mm
  • are pre-loaded (zero or minus (axial/radial) bearing clearance)
  • are sealed on both sides
  • are lubricated at the factory with grease according to DIN 51825 KP2N 25

On request we offer dimensions, which are not listed in the dimension tables. Please contact us.

The CRBSU08 crossed roller bearings have two axial or radial grease nipples for relubrication according to the application. According to IT6, the inner- and outer diameter have attached centre markings for a precise adjustment (centring). The bearing rings can be installed directly to the connecting construction via the drilled-through holes in the inner and outer rings.

IBO Kreuzrollenlager der Baureihe CRBSU08
IBO Kreuzrollenlager der Baureihe CRBSU08

CRBSU14 series

Crossed roller bearings in the CRBSU08 series:

  • have a concentricity (running accuracy) according to the information in the dimension tables
  • are sealed on both sides and
  • are lubricated at the factory with grease according to DIN 51825 KP2N 25.

On request we offer dimensions, which are not listed in the dimension tables. Please contact us.

There are 4 conical grease nipples on the outer diameter of the outer ring for relubrication during operation. According to IT7, the inner- and outer diameter have attached centre markings for a precise adjustment (centring). The bearing rings can be installed directly to the connecting construction via the drilled through-holes in the inner and outer rings.

IBO crossed roller bearings of the CRBSU14 series
IBO crossed roller bearings of the CRBSU14 series

Bearing design

PXU and PXB series

To utilize the advantages of crossed roller bearings, the connecting construction must be designed rigid accordingly. Crossed roller bearings are basically thin-walled. If the connecting construction, the housing, the mounting flange, or the mounting screws are not sufficiently designed, the bearing rings cannot carry load evenly. If there is no equally distributed contact between the cylindrical roller and the raceway system (here line contact), this can lead to deformations. This results in the reduction of the lifetime. Therefore, it is mandatory, to ensure an equal support in the circumferential direction and the height of the bearing ring as well (see the following figure).

Equal support of the bearing rings through the connecting construction
Equal support of the bearing rings through the connecting construction

The design of the connecting construction is explained in the following sub-items.

Installation with a mounting flange

So-called mounting flanges are useful for attaching the crossed roller bearings PXU and PXB (see following illustration).

IBO crossed roller bearings PXU and PXB fixed with mounting flange
IBO crossed roller bearings PXU and PXB fixed with mounting flange

The minimum thickness S for the mounting flange as well as for the connection flange is determined as follows:

Calculation of the minimum thickness
Calculation of the minimum thickness

The through-holes and the counterbores are designed according to DIN 74, form J. Fixing screws according to DIN 6912. For deeper counterbores, the thickness of the clamping ring S must be increased by the amount of the additional countersink depth.

For screws of strength class 10.9, the minimum strength under the screw heads or nuts must be 500 N / mm2. No washers are required for these screws.

For fastening screws of strength class 12.9, the minimum strength must not be less than 850 N / mm2, or tempered washers must be used under the screw heads or nuts.

Depth of the bearing seat

For the mounting flange to hold the bearing securely, the depth of the bearing seat t must be as shown in the following illustration.

The depth of the bearing seat influences the bearing clearance and the rotational resistance.

Lagersitztiefe
Lagersitztiefe

The bearing seat depth t is calculated as follows:

Calculation of the bearing seat depth
Calculation of the bearing seat depth

Bearings with a preload (suffix VSP), have a higher rotational resistance in general!

If there are special requirements regarding the rotational resistance, the depth t should be defined in correspondence with the respective height of the bearing ring. It has been proven and tested to use for the depth t the same or further narrowed tolerances as the dimension h in the dimension tables . However, for safety reasons your own tests should be carried out.

Design of the bearing - connecting dimensions
Design of the bearing - connecting dimensions
Gestaltung der Lagerung - Anschlussmaße
Gestaltung der Lagerung - Anschlussmaße

Note: number 2 in the figure above represents pull-off threads for a non-destructive dismounting possibility. At least 3 pull-off threads each must be provided for the inner and outer ring. No excessive force must be exerted on the bearing.

The nominal dimensions for the connecting construction are calculated as follows:

Note: The values ​​for D Ri and d Ra in the sealed version of the PXB series differ from the above values. For details send your inquiry to tec@ibo-tec.de.

The following table shows the quantity and the size of the fastening screws:

Outer diameter D quantity size
about bis
100 200 min. 12 M4 - M8
200 500 min. 16 M5 - M12
500 1.250 min. 24 M12 - M16

The associated tightening torques are defined based on the VDI2230 and can be found in the table below:

Mounting screw Tightening torque
M5 9
M6 14
M8 30
M10 70
M12 120
M16 200

 

Installation tolerances

For crossed roller bearings of the PXU series, the tolerance for the shafts are h7 and the housing bore is K7. If there are increased demands on running accuracy, then the shaft must be tolerated according to h6 and the housing bore according to K6.

In the PXB series with GX clearance, the tolerance for the shaft must be h5 and the housing bore is H7. In the case of G0-clearance, the shaft must be tolerated according to j5, the housing bore must also be defined according to H7. With normal clearance G0 and shock load or high tilting moments, the shaft tolerance must be k5 and the housing bore is J7.

For crossed roller bearings with preload: the preload can increase due to press fits, for this reason, press fits should be avoided with crossed roller bearings with preload. A transition fit with clearance "0" should be aimed for. For the mounting activity, as a service, we mark the deviation of the nominal dimensions for the inner Ø and outer Ø on the bearing ring. If this is required, it must be stated in the article description with SQ181.

Series CRBSU08 and CRBSU14

The bearing rings of the CRBSU series can be screwed directly into the connecting construction. No press or transition fit is required. To ensure a proper functioning of the crossed roller bearings, a rigid connecting construction is required. For a proper screw connection, a non-positively connection between the bearing rings and the connecting structure must be implemented.

As shown in the figure below, the respective wall thickness s must be equal to h of the connecting construction. The individual ring heights can be found in the respective dimension table or the associated delivery drawing. Furthermore, the connecting construction must be dimensioned in a way, that the bearing rings are supported over the entire contact surfaces.

Connection construction CRBSU series
Connection construction CRBSU series

The mounting /assembly centring marks ease the assembly. The customer can implement this for a bearing ring or omit it entirely.

The specifications for the shape and the position tolerances of the connecting construction can be found in the table below:

Connecting construction of the CRBSU series
Connecting construction of the CRBSU series

Shape and position tolerances of the CRBSU connecting construction:

Abbreviation

δE [mm]

δG [mm]

δRa [mm]

δRi [mm]

CRBSU080168

0,060

0,030

0,015

0,013

CRBSU080188

0,060

0,030

0,015

0,013

CRBSU080218

0,060

0,030

0,016

0,013

CRBSU080258

0,060

0,030

0,016

0,015

CRBSU080318

0,070

0,035

0,018

0,016

CRBSU080398

0,070

0,035

0,020

0,018

CRBSU140414

0,070

0,035

0,030

0,030

CRBSU140544

0,080

0,040

0,035

0,030

CRBSU140644

0,080

0,040

0,040

0,035

CRBSU140744

0,090

0,045

0,045

0,040

CRBSU140844

0,090

0,045

0,045

0,040

CRBSU140944

0,100

0,050

0,055

0,045

CRBSU141094

0,100

0,050

0,055

0,055

Installation Instructions

PXU and PXB series

The split outer ring of the PXU series is held together by 3 tooth lock washers and must under no circumstances be subjected to tensile stress.

In practice, the following sequence for crossed roller bearings has proven to be useful:

At the start of the assembly all components must be cleaned and checked for burrs. The actual dimensions

  • Housing bore Da
  • Shaft diameter di
  • Bearing seat height H4

must be documented before assembling the components.

For the next step, insert the crossed roller bearing into the housing bore and fix it with the associated mounting flange. Tighten the fastening screws crosswise according to the following illustration:

Installation of outer ring series PXU and PXB
Installation of outer ring series PXU and PXB
Installation of outer ring series PXU and PXB
Installation of outer ring series PXU and PXB

The tightening to the nominal tightening torque takes place in 2 steps.

In the first step ‘Tan x 0.5’. Now turn the inner ring several times so that any tension in the bearing system is released.

In the next step, the shaft is mounted on the inner ring and the mounting flange for the inner ring is attached as shown in the figure below. It is important to ensure that the screws are tightened in the order shown:

Installation of outer ring series PXU and PXB
Installation of outer ring series PXU and PXB

It should be noted that the tightening to the nominal tightening torque of the fastening screws takes place in 3 - 4 steps and the inner ring must be turned several times in each step.

Series CRBSU08 and CRBSU14

At first, the outer ring is installed in the housing.

This can be done with the following steps:

  1. The crossed roller bearings are matched with the centring marks of the outer diameter in the connecting construction (housing) and align the bolt circle diameters of the outer ring and the housing to each other. If there is no centring used, the bolt circle diameter and the eye must be aligned concentrically.
  2. In the next step, the outer ring is fixed using the fastening screws including the washers. Here, the screws are tightened crosswise and the nominal tightening torque of the screws is tightened in 3 steps with even distribution to avoid a preload of the bearing rings.
  3. Turn the inner ring per tightening torque step: at least 50% of all screw pitches, one complete turn if possible.
  4. The nominal tightening torque can be found in the table "Tightening torques for fastening screws" above.
Assembly of outer ring series CRBSU
Assembly of outer ring series CRBSU

The assembly sequence of the inner ring is as follows:

  1. Position the associated connecting construction above the inner ring assembly centring and position the bolt circle diameter for the screw connection concentrically to each other. If no assembly centring is used, the bolt circle diameters must be aligned concentrically with each other using the eye.
  2. In the next step, the inner ring is fixed to the connecting construction using the fastening screws including the washers. Here, the screws are tightened crosswise and the nominal tightening torque of the screws is tightened in 3 steps with even distribution to avoid a preload of the bearing rings.
  3. Turn the inner ring per tightening torque step: at least 50% of all screw pitches, one complete turn if possible.
  4. The nominal tightening torque can be found in the table "Tightening torques for fastening screws" above.
  5. To check the assembly, the following criteria must be checked:
    1. Accuracy with dial gauge; Values ​​according to the delivery drawing
    2. Rotational resistance: the rotational resistance installed is higher as in the delivery condition
    3. Storage temperature: after the distribution of grease, the bearing temperature must remain constant when the load and speed is constant
Montage Innenring Baureihen CRBSU
Montage Innenring Baureihen CRBSU

Tolerances

The running accuracies of the IBO crossed roller bearings are based on DIN620 and ISO492 and are summarized in WN001 .

In principle, crossed roller bearings can be manufactured within the accuracy classes PN, P6 and P5. Project-specific versions can be delivered in coordination with IBO. Please contact us.

Tolerances PXU Series

The tolerances for all dimensions of the PXU series, the inner diameter is K6 and outer diameter is h6. The installation height H and the height of a single ring are tolerated according to the following table:

Bore hole code

bearing height

Ring hight PXU18

Ring hight PXU19

Ring hight PXU10

H 1)

h1)

h1)

h1)

max.

min.

max.

min.

max.

min.

max.

min.

20

+0.12

-0.12

0,000

-0.01

-

-

-

-

24

+0.12

-0.12

0,000

-0.01

-

-

-

-

28

+0.12

-0.12

0,000

-0.01

-

-

-

-

32

+0.12

-0.12

0,000

-0.025

-

-

-

-

36

+0.13

-0.13

0,000

-0.025

-

-

-

-

40

+0.13

-0.13

0,000

-0.025

0,000

-0.05

0,000

-0.075

44

+0.13

-0.13

0,000

-0.025

0,000

-0.05

0,000

-0.075

48

+0.13

-0.13

0,000

-0.025

0,000

-0.05

0,000

-0.075

52

+0.13

-0.13

0,000

-0.025

0,000

-0.05

0,000

-0.075

56

+0.13

-0.13

0,000

-0.025

0,000

-0.05

0,000

-0.075

60

+0.14

-0.14

0,000

-0.05

0,000

-0.75

0,000

-0.1

64

+0.14

-0.14

0,000

-0.05

0,000

-0.75

0,000

-0.1

68

+0.14

-0.14

0,000

-0.05

0,000

-0.75

0,000

-0.1

72

+0.14

-0.14

0,000

-0.05

0,000

-0.75

0,000

-0.1

76

+0.14

-0.14

0,000

-0.05

0,000

-0.75

0,000

-0.1

80

+0.15

-0.15

0,000

-0.05

0,000

-0.75

0,000

-0.1

84

+0.15

-0.15

0,000

-0.05

0,000

-0.75

0,000

-0.1

88

+0.15

-0.15

0,000

-0.05

0,000

-0.75

0,000

-0.1

92

+0.15

-0.15

0,000

-0.05

0,000

-0.75

0,000

-0.1

96

+0.15

-0.15

0,000

-0.05

0,000

-0.75

0,000

-0.1

500

+0.16

-0.16

0,000

-0.05

0,000

-0.75

0,000

-0.1

530

+0.16

-0.16

0,000

-0.05

0,000

-0.75

0,000

-0.1

560

+0.16

-0.16

0,000

-0.05

0,000

-0.75

0,000

-0.1

600

+0.16

-0.16

0,000

-0.05

0,000

-0.75

0,000

-0.1

630

+0.18

-0.18

0,000

-0.075

0,000

-0.1

0,000

-0.125

670

+0.18

-0.18

0,000

-0.075

0,000

-0.1

0,000

-0.125

710

+0.18

-0.18

0,000

-0.075

0,000

-0.1

0,000

-0.125

750

+0.18

-0.18

0,000

-0.075

0,000

-0.1

0,000

-0.125

Tolerances PXB Series

The dimensional accuracy tolerances for the inner diameter, outer diameter and the bearing height for the PXB series correspond to DIN620 and ISO492 and are summarized in the company standard WN001 . Our customers can order bearings with dimensional accuracy according to PN and running accuracy according to P5. A possible article name (designation) could be PXB40040 PN5.

Suffix

Suffix

Description

PXU-Series

PXB-Series

G0

Normal clearance

X

X

GX

Reduced clearance

X

X

G1

Increased clearance

 

X

VSP

Preload

X

X

VSP.P5

Preloaded and running accuracy P5 WN001 and WN002

 

X

P05

Dimensional accuracy PN and running accuracy P5

 

X

P

Seal on one side only

 

X

PP

Seal on both sides

 

X

SN

Grease nippel

 

X

S

Stainless steel version

X

X

SQ181

Marks of the deviation from the nominal size of the  inner Ø

X

X



Structure of the order designation

Structure of the order designation
Structure of the order designation

Abbreviation

Abbreviation

Description

Dpw

Running circle diameter of the rolling bearing

d

Inner diameter, inner ring

d1

Rim diameter, inner ring

D

Outer diameter, outer ring

D1

Rim diameter, outer ring

H

Height of the bearing

h

Height of the inner or outer ring

rmin.

Minimal edge shortening (reduction)

K

Size of the 3 lubrication holes on the outer ring

Dimension Tables

Maßtabelle - Baureihe PXB

Maßtabelle - Baureihe PXU

Maßtabelle - Baureihe CRBSU08

Maßtabelle - Baureihe CRBSU14

You can access the dimension tables via this link: Dimension tables - crossed roller bearings .

There you can also download the CAD model for the respective crossed roller bearing.