Chapter 5
Rolling Bearings According to DIN ISO 281

    5.1   Start the Calculation Module
    5.2   General Inputs
    5.3   Selection of Manufacturer and Bearing Type
    5.4   Specification of Bearing Load
    5.5   Nominal Rating Life
    5.6   Modified Rating Life Theory
    5.7   Bearing Selection
    5.8   Message Window
    5.9   Quick Info: Tooltip
    5.10   Calculation Results
    5.11   Diagrams
    5.12   Documentation: Calculation Report
    5.13   How to Save the Calculation
    5.14   The Button ‘Redo’ and ‘Undo’
    5.15   The Button ‘Options’
    5.16   Calculation Examples: Rolling Bearing According to DIN ISO 281

5.1 Start the Calculation Module

Please login with your username and your password. To start the calculation module for rolling bearings, please click the menu item ‘Shaft/Bearings’ on the left side and then select ‘Rolling bearings calculation’.

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Figure 5.1: General overview

Please Note: All results will be calculated during every input and will be displayed in the result panel. A recalculation occurs after every data input. Any changes that are made to the user interface take effect immediately. Press the Enter key or move to the next input field to complete the input. Alternatively, use the Tab key to jump from field to field or click the ‘Calculate’ button after every input.

5.2 General Inputs

5.2.1 Number of Bearings

The calculation module allows to define any number of bearings.

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Figure 5.2: General inputs

The following listbox ‘Current view’ allows you to select between the several bearings.

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Figure 5.3: Number of bearings

You can add a description or a short comment to the bearing.

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Figure 5.4: Description of the respective bearing

5.2.2 How to Delete a Bearing

If you want to delete a bearing, please enter the new number of bearings and confirm the input with the Enter key.

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Figure 5.5: Reduce the number of bearings

Now select the bearing you want to delete and click the button ‘Delete the selected bearings!’.

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Figure 5.6: Delete a bearing

Please note: If you want to delete multiple bearings at once, select the bearings you want to delete. Click the button ‘Delete the selected bearings!’.

5.3 Selection of Manufacturer and Bearing Type

5.3.1 Bearing Manufacturer

The extensive bearing database provides over 20,000 bearings from different manufacturers. Select the bearing manufacturer (NSK, SNR, SKF, KOYO) from the listbox.

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Figure 5.7: Manufacturer

5.3.2 Fatigue Limit Load

The stress of the raceway fatigue depends primarily on the internal load distribution in the bearing. In order to simplify the calculation, the fatigue limit load \(C_{u}\) was introduced. Usually, the bearing manufacturer specifies the values for \(C_{u}\). In case these values are missing, the equations defined in DIN ISO 281 will be used. These equations apply for bearings \(D_{pw} <\) 150 mm.

Roller bearings:

\[C_{ur} \approx \frac {1}{8.2} \times C_{0r} \quad \mbox {and}\quad C_{ua} \approx \frac {1}{8.2} \times C_{0a}\]

Ball bearings:

\[C_{ur} \approx \frac {1}{27} \times C_{0r} \quad \mbox {and}\quad C_{ua} \approx \frac {1}{27} \times C_{0a}\]

The bearing selection allows to define your own fatigue limit load. Open the bearing selection and activate ‘User defined’, select the option ‘Specify \(C_{u}\)’. Enter the value for the fatigue limit load. If you do not specify the fatigue limit load or if the bearing selection does not include the fatigue limit load, then fatigue limit load is calculated in accordance with DIN ISO 281.

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Figure 5.8: Own input of \(C_{u}\) in bearing selection

5.3.3 Bearing Types

Rolling bearings are ready-to-fit machine elements. Rolling bearings are an assembly of several parts - rings with raceway, rolling elements (a set of balls or rollers) and a cage which separates the rolling elements and holds them in place. The rings of radial rolling bearings are called inner and outer rings. Generally, the outer ring fits on the housing, the inner ring on the shaft. For axial bearings, the inner ring is called shaft washer and the outer ring is called housing washer. Because of the very small contact surface, balls cause high Hertzian stresses. Rollers have lower Hertzian stresses and are suitable for high loads.

Rolling bearings can be also classified according to the direction in which the load is applied. Radial bearings carry radial loads and axial bearings carry axial loads. Rolling bearings divide into two main classifications: ball bearings and roller bearings. A further feature is how the bearings guide a shaft. There are bearings that allow axial displacements and bearings that guide a shaft in one or both axial directions. Types of rolling bearings are given in the following figure below.

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Figure 5.9: Classification of rolling bearings

The following bearing types can be selected from the listbox:

Please Note: There is a graphical representation for every bearing type.

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Figure 5.10: Representation of a deep groove ball bearing

5.4 Specification of Bearing Load

Here you can define the radial force, the axial force and speed.

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Figure 5.11: Radial force, axial force, speed
How to Change the Unit System

eAssistant provides two unit systems: the metric system and the U.S. customary unit system. You can quickly switch between the units. To select the unit system, click the button ‘Options’ and decide for a unit.

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Figure 5.12: Change the unit

It is also possible to change the unit by clicking the label field. When you click the label field, a context menu will open providing all available units within the unit system. The change should take effect immediately. All settings will be saved to the calculation file. As soon as you select a unit, the current field value will be converted automatically into the chosen unit.

5.4.1 Calculation with Load Collectives

If you activate the option ‘Use load collective’, you can consider load collectives for your calculation.

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Figure 5.13: Use load collectives

You can define any number of load cases. For every loading case a specification for time slice, speed, radial force, axial force, temperature and cleanness is possible. A listbox shows you the degree of impurities.

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Figure 5.14: Load collectives

The respective lubrication method or the contamination coefficient is available by using the listbox. If you select ‘User defined’ from the listbox, you can enter your own contamination factor \(e_{c}\).

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Figure 5.15: Degree of impurities

The load collectives can be opened and saved independently from the underlying bearing calculation. For that purpose use the button ‘Open’ and ‘Save’.

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Figure 5.16: Open and save the load collectives

Please note: With the definition of the load cases, the entries for the modified rating life will be set.

5.4.2 Lubricant Contamination Factor

According to DIN ISO 281, contaminations in the lubricant cause dents in the raceways and can damage the smooth surfaces of the bearing components. Rough surfaces tent to cause stress concentrations resulting in shorter bearing life. The lubricant contamination factor \(e_{c}\) considers the influence of the contaminants on the rating life.

Lubricant Contamination Factor \(e_{c}\) According to DIN ISO 2811

Grade of Contaminations

Lubricant Contamination Factor \(e_{c}\)


\(D_{pw} < 100\ mm\) \(D_{pw} \geq 100\ mm\)

Extreme Cleanliness:

1 1

Particle size within the height of the lubricant film under laboratory conditions

High Cleanliness:

0.8 to 0.6 0.9 to 0.8

Oil is filtered by extremely fine filters, sealed, greased bearings

Standard Cleanliness:

0.6 to 0.5 0.8 to 0.6

Oil is filtered by fine filters, greased bearings with shields

Slight Contaminations:

0.5 to 0.3 0.6 to 0.4

Slight contamination of oil

Typical Contaminations:

0.3 to 0.1 0.4 to 0.2

Bearing contaminated with abraded material from other machine elements

Strong Contaminations:

0.1 to 0 0.1 to 0

Bearing environment is strongly contaminated, inadequate sealing of bearing arrangement

Very strong contaminations

0 0
1 from: DIN ISO 281 Rolling Bearings - Dynamic Load Ratings and Rating Life (ISO 281: 2007), 2010, p. 33, table 13

The values given in the table above apply for solid particles. Other contaminations such as water or liquids are not taken into account.

5.5 Nominal Rating Life

The following factors have a significant influence on the rating life of bearings:

The calculation method for the nominal rating life \(L_{10}\) is defined in DIN ISO 281. The rating life \(L_{10}\) of a large group of identical ball bearings is the life in millions of revolutions that 90 percent of the group will complete or exceed before material fatigue occurs.

Reference Values for Required Rating Life2

Vehicles (full load)

Passenger cars

900 to 1,600 hours

Trucks and busses

1,700 to 9,000 hours

Railway vehicles

Axle bearing mine cars

10,000 to 34,000 hours

Streetcars

30,000 to 50,000 hours

Passenger carriages

20,000 to 34,000 hours

Locomotives

30,000 to 100,000 hours

Gears for railway vehicles

15,000 to 70,000 hours

Agricultural machinery

2,000 to 5,000 hours

Construction machinery

1,000 to 5,000 hours

Electric motors for household appliances

1,500 to 4,000 hours

Series engines

20,000 to 40,000 hours

Large engines

50,000 to 100,000 hours

Machine tools

15,000 to 80,000 hours

Gears for general mechanical engineering

4,000 to 20,000 hours

Large gearboxes

20,000 to 80,000 hours

Ventilators, fans

12,000 to 80,000 hours

Gear pumps

500 to 8,000 hours

Crushers, mills, sieves

12,000 to 50,000 hours

Paper and printing machines

50,000 to 200,000 hours

Textile machinery

10,000 to 50,000 hours
2 from: Taschenbuch fuer den Maschinenbau/Dubbel, 1997, p. G173, appx. G4 table 2

5.6 Modified Rating Life Theory

In some cases it can be sufficient to determine the nominal rating life. The nominal rating life is associated with 90 percent reliability. But for some applications it can be very insightful to determine the rating life for a higher reliability and to consider the influence of the bearing quality and operating conditions. By using the modified rating life, these criteria can be further investigated.

The modified rating life theory is activated by default. If the load collectives are not activated, then enter you individual specifications for the requisite reliability, operating temperature or cleanness. You can enter your own cleanness factor for the grade of contaminations. Select ‘User-defined’ from the listbox.

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Figure 5.17: Modified rating life theory

5.6.1 Lubricant Selection

The purpose of lubricating the bearing is to cover the rolling and sliding contact surfaces with a thin oil film to avoid direct metal to metal contact. The most important function of a lubricant is to protect the sliding and rolling surfaces from wear and friction. The extensive lubricant database provides different kind of oils and greases for the calculation of the modified rating life. In case you are missing the right lubricant for your calculation, please define your own lubricant. The lubrication has a considerable influence on the operating life of the bearing. Oil and greases are the most common lubricants for rolling bearings. In special cases, rolling bearings are lubricated with solid or dry lubricants. The choice of lubrication and lubricant depends on speed and operating temperature of the bearing. The selection of the lubrication method depends on operating conditions and environmental influences.

Most rolling bearings are lubricated using grease. Grease lubrication consists of a base oil and a thickener. There are two main types of base oil: mineral and synthetic oil. The thickener and the additives in the grease enhance the lubricating effect so that no life reduction has to be expected. Calcium, aluminum, sodium and lithium soap greases can be used for heavy-loaded rolling bearings. Most of greases contain additives in order to improve the properties of the grease. It is necessary to renew the lubricating grease at regular intervals. The lubrication interval depends on many factors, such as the grease type, bearing and working conditions. Grease lubrication is easy to handle and provides excellent protection against contamination.

Grease lubrication is widely used. Approximately 90 percent of all bearings are lubricated with grease. The main advantages of grease lubrication are (according to Braendlein ‘Die Waelzlagerpraxis’):

Oil lubrication is generally used for rolling bearings when adjacent system components are lubricated with oil or when cooling is required. Oil lubrication is also used when very high speeds or very high loads preclude the use of grease as a lubricant. The selection of the oil type depends on the requirements of the components. For the lubrication of rolling bearings, mineral oils and synthetic oils are suitable. Oils with a mineral oil base are most common. The better the contact surfaces are separated by the lubricating film, the better the bearing life and safety against wear. The lubricating film thickness increases with the oil viscosity, so an oil with a high operating viscosity should be selected.

The viscosity, as well the dependence of the density and viscosity on the pressure and the temperature play an important role for the technical application of lubricants. Viscosity is one very important property of a lubricant and determines the oils lubricating efficiency. Thin oils have low viscosities while thicker oils have high viscosities. In addition to the base oil viscosity, thickener and additives have a decisive influence on greases. The density of lubricating oils is between 0.86 and 0.93 \(kg/dm^{3}\). The viscosity of the oil decreases with increasing temperature. As the temperature falls, the viscosity of the oil increases. It is therefore necessary to indicate the temperature dependence of an oil’s kinematic viscosity. The viscosity at \(40^\circ \)C and at \(100^\circ \)C (for thicker oils) are typical values.

About 150 products of the following manufacturer are available:

Select a lubricant from the listbox.

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Figure 5.18: Lubricants from a listbox

Select the lubricant directly from the listbox or click the button ‘Lubricant’.

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Figure 5.19: Button ‘Lubricant’

The lubricant selection is opened. Here you get all information to the selected lubricant.

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Figure 5.20: Lubricant selection

The two cursor keys ‘Up’ and ‘Down’ of your keyboard allows you to navigate through the lubricant database, so you can compare the different lubricant values with each other.

5.6.2 Define Your Own Lubricant

In case you cannot find the lubricant you are looking for in our extensive database, simply define your individual lubricant. You will find the entry ‘User-defined’ in the listbox. If you select this option, the according input fields will be enabled, so that you can specify your own input values or add a comment. In order to confirm your inputs, click the button ‘OK’. Please be advised that changing the lubricant will delete your defined inputs and you have to enter the inputs again.

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Figure 5.21: Define your own inputs

5.7 Bearing Selection

After you choose the manufacturer and the bearing type, please select the bearing from the list or use bearing selection search to find the right bearing. Click the button ‘Bearing selection’.

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Figure 5.22: Bearing selection

5.7.1 Bearing Database

Click the button ‘Bearing selection’ to open the bearing database.

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Figure 5.23: Bearing selection

We have an extensive range of bearings but search filters have been developed to assist in searching the extensive amount of bearings and to quickly find the bearing you are looking for. You might filter bearing types by diameter or rating life so that you can only see bearing types with this particular diameter or rating life. The following parameters can be provided to further refine the search:

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Figure 5.24: Different parameters

Use the Tab key to move from input field to input field. The more values you enter into the input fields the more you will narrow your search. If you have already entered values into the input fields and you now wish to add again an arbitrary inner or outer diameter, then delete your own value and click on any input field. You can also press the Tab key. The option ‘Any’ will then be used again and the number of bearings also increases again. After entering all reqired data, click the ‘Search’ button.

With the display of the found bearings you can re-sort the list by clicking on the column headers. If the bearings are to be sorted in reverse order, then click on the column headers again.

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Figure 5.25: Found bearings

Here you can get additional information on the selected bearing.

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Figure 5.26: Bearing details

Please note: For radial deep groove ball bearings the selection for increased bearing clearance C3 or C4 is additionally integrated in the bearing selection search, which is taken into account in the rating life calculation. When using this option, it should be noted that the bearing clearance should be selected which is present in operation after the bearing has been fitted.

For SKF bearing data, there is a filter function that simplifies finding common bearings (button ‘popular item’) in the bearing selection search. In addition, SKF Explorer bearings are marked accordingly and the corresponding page of the SKF online catalog can be opened for the selected bearing. The appropriate button is located in the bearing database in the lower left corner. After determining the desired bearing type, it may be helpful to select a suitable bearing from the manufacturer’s range of common bearings. Popular items have a high level of availability and generally provide a cost-effective solution. SKF Explorer bearings are designed for heavy-duty applications. They run with less friction and have longer rating lifes than standard rolling bearings.

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Figure 5.27: Popular item

5.7.2 Define Your Own Bearing

You can select a bearing from the bearing database or you can define your individual bearing. Activate the option ‘User defined’, the input fields will be enabled and you can enter your own input values. Please confirm your inputs with the ‘OK’ button.

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Figure 5.28: Activate ‘User defined’

5.8 Message Window

The calculation module provides a message window. This message window displays detailed information, helpful hints or warnings about problems. One of the main benefits of the program is that the software provides suggestions for correcting errors during the data input. If you check the message window carefully for any errors or warnings and follow the hints, you are able to find a solution to quickly resolve calculation problems.

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Figure 5.29: Message window

5.9 Quick Info: Tooltip

The quick info feature gives you additional information about all input fields and buttons. Move the mouse pointer to an input field or a button, then you will get some additional information. This information will be displayed in the quick info line.

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Figure 5.30: The quick info

5.10 Calculation Results

All results will be calculated during every input and will be displayed in the result panel. A recalculation occurs after every data input. Any changes that are made to the user interface take effect immediately. Press the ‘Enter’ key or move to the next input field to complete the input. Alternatively, use the Tab key to jump from field to field or click the ‘Calculate’ button after every input. Your entries will be also confirmed and the calculation results will displayed automatically.

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Figure 5.31: The results

5.11 Diagrams

For a further illustration the following diagrams are available:

The listbox contains the different diagrams and you can decide which diagram should be displayed.

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Figure 5.32: Selection of diagrams

Choose the diagram and click on the button ‘Diagram’ next to the listbox.

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Figure 5.33: Button ‘Diagram’

The diagram with the values for the rating life and for the modified rating life will be displayed immediately.

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Figure 5.34: Diagram radial force

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Figure 5.35: Diagram axial force

5.12 Documentation: Calculation Report

After the completion of your calculation, you can create a calculation report. Click on the ‘Report’ button.

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Figure 5.36: Degree of impurities

You can navigate through the report via the table of contents that provides links to the input values, results and figures. This calculation report contains all input data, the calculation method as well as all detailed results. The report is available in HTML and PDF format. The calculation report saved in HTML format, can be opened in a web browser or in Word for Windows.

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Figure 5.37: Calculation report

You may also print or save the calculation report:

5.13 How to Save the Calculation

When the calculation is finished, it is easy to save the calculation. You can save your calculation either to the eAssistant server or to your computer. Click on the button ‘Save’.

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Figure 5.38: Button ‘Save’

Before you can save the calculation to your computer, you need to activate the checkbox ‘Local’ in the calculation module. A standard Windows dialog for saving files will appear. Now you will be able to save the calculation to your computer.

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Figure 5.39: Windows dialog for saving the file

In case you do not activate the option in order to save your files locally, then a new window is opened and you can save the calculation to the eAssistant server. Please enter a name into the input field ‘Filename’ and click on the button ‘Save’.

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Figure 5.40: Save the calculation

5.14 The Button ‘Redo’ and ‘Undo’

The button ‘Undo’ allows you to reset your input to an older state. The button ‘Redo’ reverses the undo.

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Figure 5.41: The button ‘Redo’ and ‘Undo’

5.15 The Button ‘Options’

Click the button ‘Options’ to change the default settings, for example the unit system or the number of decimal places for the calculation report. The unit can also be changed directly for each individual input value. Simply click on the label of the corresponding input field and select the unit from the context menu. You will see the change of the unit of measurement immediately in the label of the input field. The current field value will be converted to the corresponding unit.

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Figure 5.42: Button ‘Options’

A new window opens up that provides a possibility to choose the diagrams that shall be added to the calculation report.

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Figure 5.43: Settings for the calculation report

5.16 Calculation Examples: Rolling Bearing According to DIN ISO 281

5.16.1 Start the Calculation Module

Please login with your username and your password. To start the calculation module for rolling bearings, please click the menu item ‘Shaft/Bearings’ on the left side and then select ‘Rolling bearings’.

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Figure 5.44: Start the calculation module

5.16.2 First Calculation Example

Bearing for a Rope Sheave of a Pulley Block

The wrap angle for rope sheaves of pulley blocks is \(180^{\circ }\). Therefore, the load on the bearing is twice the rope pull. The axial forces and the resulting moments are low. When the diagonal pull is \(5^{\circ }\), then the axial forces have to be considered for the calculation of the rating life. Adequate bearing spread for load accommodation is achieved by mounting either two bearings or one double-row bearing. In the following example the rating life and modified rating life are to be calculated. We have taken this example from: J. Braendlein: Die Waelzlagerpraxis: Handbuch zur Berechnung und Gestaltung von Waelzlagern (1995, p. 466-470).

Please enter the following input values:

Bearing load 65 kN

Type of bearing Tapered roller bearing (single row)

Speed n 30 min\(^{-1}\)

Built-in bearing Tapered roller bearing (100 x 150 x 67)

For-life lubrication Grease with EP-additive

Illustration of a rope sheave of a pulley block including the tapered roller bearing. (The following figure: J. Braendlein: Die Waelzlagerpraxis, p. 467).

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Figure 5.45: Rope sheave of a pulley block

5.16.3 The Calculation

Define Number of Bearings

In this example we would like to calculate one bearing of a tapered roller bearing pair. When you open the calculation module, usually one bearing is shown. So it is not necessary to change the number of the bearings. You can enter a description into the comment field, for example ‘Bearing of the rope sheave’.

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Figure 5.46: Number of bearings
Select Manufacturer and Bearing Type

The extensive bearing database provides over 20,000 bearings from different manufacturers. Select the bearing manufacturer ‘SKF 2007’ from the listbox. Next, choose the bearing type ‘Tapered roller bearing (single row)’.

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Figure 5.47: Select the manufacturer and bearing type

Specification of Bearing Load

Enter the values for the bearing load now. Please keep in mind that the values will be entered in ‘kN’. Right-clicking allows you to change the unit.

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Figure 5.48: Values for the bearing load in kN
Bearing Selection

Click on the button ‘Bearing selection’ to open the bearing database.

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Figure 5.49: Button ‘Bearing selection’

There are ‘578’ bearings in the database right now. Search filters have been developed to assist in searching this extensive amount of bearings and to quickly find the bearing you are looking for. You can filter the bearing types by the inner and outer diameter so that you can only see bearing types with this particular diameter. Enter the inner and outer diameter and click the button ‘Search’.

Inner diameter of bearing = 100 mm

Outer diameter of bearing = 150 mm

Select the bearing ‘32020 X*’ and confirm with the button ‘OK’.

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Figure 5.50: Found bearings

5.16.4 Calculation Results

Rating Life

All results will be calculated during every input and will be displayed in the result panel. A recalculation occurs after every data input. Any changes that are made to the user interface take effect immediately. First, you get the result for the rating life as well as the static identification number.

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Figure 5.51: Result for the rating life

The result of the rating life is \(L_{10}\) = 27.258,6 h

For rope sheaves, a rating life from 5,000 to 20,000 hours is required. The bearing is sufficiently dimensioned. You will find a note in the message window but you can ignore this message. When the pair is fitted together, then the correct axial clearance and the necessary axial force for the tapered roller bearing occur.

Modified Rating Life Theory

After you get the result for the rating life, please have a look at the modified rating life theory \(L_{nm}\) regarding the operating conditions (lubrication, clearance). The option ‘Use modified rating life theory’ is activated by default.

Now you an define the requisite reliability and the cleanness as well as a lubricant. Please select the grease ‘Klueber Kluebersynth BMQ 72-162 (094073)’. Select this lubricant directly from the listbox. If you need detailed information, please click on the button ‘Lubricant’.

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Figure 5.52: Modified rating life theory

Clicking the button ‘Lubricant’ opens the lubricant database. Here you can see that the grease contains active EP additive.

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Figure 5.53: Lubricant database

Next, you have to estimate the influence of possible impurities by using the cleanness factor. Actually, it is assumed that the ‘highest cleanness’ is used for sealed and greased bearings (for-life-lubrication). But during the entire operating time, a certain wear of the seals could occur which can let light impurities into the bearing. In this case you can assume light impurities. Therefore, choose ‘Light impurities’ from the listbox.

Now you get immediately the result for the modified rating life.

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Figure 5.54: Modified rating life

The result of the modified rating life is \(L_{nm}\) = 19.713,6 h. Finally, the modified rating life \(L_{nm}\) is in the range of the rating life \(L_{10}\).

Please note: Press the ‘Up’ and ‘Down’ arrow to move through the listbox of cleanness parameters. Moving through the listbox changes the modified rating life and the results will be displayed immediately in the result panel, making it very easy to compare the modified rating life with different levels of cleanness. You can also navigate through the lubricant listbox.

Diagrams

Click on the button ‘Diagram’ next to the listbox. The diagram includes the values for the rating life and for the modified rating life. The exact values can be selected directly from the graphical representation. Clicking the ‘Close’ button leads you back to the main mask and you can open another diagram. Use the ‘Options’ button to specify which diagrams should be displayed in your calculation report.

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Figure 5.55: Button ‘Diagram’

5.16.5 Documentation: Calculation Report

After the completion of your calculation, you can create a calculation report. Click on the ‘Report’ button.

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Figure 5.56: Button ‘Report’

You can navigate through the report via the table of contents that provides links to the input values, results and figures. This calculation report contains all input data, the calculation method as well as all detailed results. The report is available in HTML and PDF format. The calculation report saved in HTML format, can be opened in a web browser or in Word for Windows.

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Figure 5.57: Calculation report

You may also print or save the calculation report:

5.16.6 Save the Calculation

When the calculation is finished, it is easy to save the calculation. You can save your calculation either to the eAssistant server or to your computer. Click on the button ‘Save’.

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Figure 5.58: Button ‘Save’

Before you can save the calculation to your computer, you need to activate the checkbox ‘Local’ in the calculation module. A standard Windows dialog for saving files will appear. Now you will be able to save the calculation to your computer.

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Figure 5.59: Windows dialog for saving the file

In case you do not activate the option in order to save your files locally, then a new window is opened and you can save the calculation to the eAssistant server. Please enter a name into the input field ‘Filename’ and click on the button ‘Save’.

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Figure 5.60: Save the calculation

5.16.7 Second Calculation Example

Bearing of a Fan

The impeller of fans can be arranged either between two bearings or in an overhung position. The impeller of small and medium-sized fans is generally overhung. Two separated plummer block housings are suitable for supporting the fan drive shaft.

This calculation example we have taken from: J. Braendlein: Die Waelzlagerpraxis: Handbuch zur Berechnung und Gestaltung von Waelzlagern (1995, p. 516-520, figures: p. 517).

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Figure 5.61: Bearing unit for fan

The unit (figure 5.61) contains a cylindrical roller bearing A and a deep groove ball bearing B in one housing (figure 5.62). The bearing diameter is 70 mm.

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Figure 5.62: Bearing of a fan
Input Values

The input values for bearing A (Cylindrical roller bearing NU 314 ECP)

Load Case No. 1 Load Case No. 2

Time slice \(q_{1}\) = 50% Time slice \(q_{2}\) = 50%

Speed \(n_{1}\) = 3,000 min-1 Speed \(n_{2}\) = 4,500 min-1

Radial force \(F_{r1}\) = 8,500 N Radial force \(F_{r2}\) = 11,000 N

Axial force \(F_{a1}\) = 0 N Axial force \(F_{a2}\) = 0 N

Temperature \(T_{1}\) = \(70^{\circ }\)C Temperature \(T_{2}\) = \(70^{\circ }\)C

All input values for bearing B (deep groove ball bearing 6314)

Load Case No. 1 Load Case No. 2

Time slice \(q_{1}\) = 50% Time slice \(q_{2}\) = 50%

Speed \(n_{1}\) = 3,000 min-1 Speed \(n_{2}\) = 4,500 min-1

Radial force \(F_{r1}\) = 2,000 N Radial force \(F_{r2}\) = 5,000 N

Axial force \(F_{a1}\) = 5,000 N Axial force \(F_{a2}\) = 5,000 N

Temperature \(T_{1}\) = \(70^{\circ }\)C Temperature \(T_{2}\) = \(70^{\circ }\)C

5.16.8 The Calculation

Define the Number of Bearings

In this example we want to calculate the rating life of the cylindrical roller bearing and the deep groove ball bearing. We have to different bearings and we need to change the number of bearings. So enter ‘2’ into the input field ‘Number of bearings to calculate’. Please calculate the bearings one after another separately. The listbox ‘Current view’ allows you to switch between the two bearings.

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Figure 5.63: Number of bearings and add a comment

Add a comment for the first bearing.

Select Manufacturer and Bearing Type

Now select the manufacturer ‘SKF’. Choose the cylindrical roller bearing from the listbox.

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Figure 5.64: Selection of the manufacturer and bearing type

Specification of Bearing Load with Load Collectives

Define the load collective for the first bearing. Activate the option ‘Use load collective’. The input options for the radial and axial force as well as for the speed will be deactivated. Define two load cases for the bearing. Enter the time slice, the radial force, axial force, the temperature and cleanness for each load case. After you made all entries, click the button ‘OK’ to confirm your inputs.

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Figure 5.65: Define the load collective
Bearing Selection

Click on the button ‘Bearing selection’. It is increasingly convenient to use the search filter to quickly find the bearing you are looking for. Enter ‘70 mm’ for the inner diameter and click the button ‘Search’. Now you can choose the cylindrical roller bearing ‘NU 314 ECP’ from the list. Clicking the button ‘OK’ confirms the bearing and leads you back to the main mask.

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Figure 5.66: Bearing selection

5.16.9 Calculation Results

Rating Life of the Cylindrical Roller Bearing (Bearing Location A)

All results will be calculated during every input and will be displayed in the result panel. A recalculation occurs after every data input. Any changes that are made to the user interface take effect immediately. First, you get the result for the rating life as well as the static identification number.

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Figure 5.67: Rating life

The result of the rating life is \(L_{10}\) = 188,391.8 h

The cylindrical roller bearing is sufficiently dimensioned.

Rating Life for the Deep Groove Ball Bearing (Single Row) (Bearing Location B)

Calculate now the rating life for the deep groove ball bearing. Please pay attention that you select ‘Bearing No. 2’ from the listbox ‘Current view’. Select the manufacturer ‘SKF’ and the bearing type ‘Deep groove ball bearing (single row)’.

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Figure 5.68: Bearing selection

Activate the option ‘Use load collective’ and define the load cases. After you made all entries, click the button ‘OK’ to confirm your inputs.

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Figure 5.69: Define the load collective’

Click on the button ‘Bearing selection’. Choose the bearing ‘6314*’ from the list. It is increasingly convenient to use the search filter to quickly find the bearing you are looking for. Enter ‘70 mm’ for the inner diameter and click the button ‘Search’. Then you can select the bearing ‘6314’ from the list. Clicking the button ‘OK’ confirms the bearing and leads you back to the main mask.

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Figure 5.70: Deep groove ball bearing

The result for the rating life is \(L_{10}\) = 5.928,1 h

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Figure 5.71: Nominal rating life

The rating life of the deep groove ball bearing B is lower than the rating life of the cylindrical roller bearing A. This means that bearing B is subjected to higher stresses than bearing A. At least 220,000 hours are required for the rating life of deep groove ball bearings. But with this result, the rating life is not sufficiently dimensioned. It is necessary to take a closer look at the modified rating life \(L_{nm}\) of bearing B.

Modified Rating Life of the Deep Groove Ball Bearing

The next step is to determine the modified rating life for the deep groove ball bearing. The option ‘Use modified rating theory’ is activated by default. Select the grease ‘Lubcon Turmogrease Highspeed L 252 (K HC P 2/3 K-50)’ from the listbox or click on the button ‘Lubricant’ to open the lubricant selection. Choose the lubricant and confirm with the button ‘OK’.

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Figure 5.72: Modified rating life

The result of the modified rating life is \(L_{nm}\) = 49.223,4 h.

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Figure 5.73: Result for the modified rating life

At least 22,000 hours are required and the bearing is sufficiently dimensioned. For the calculation with load collectives, you cannot open all diagrams. But you can open the diagram for the lubricant viscosity.

5.16.10 Documentation: Calculation Report

After the completion of your calculation, you can create a calculation report. Click on the ‘Report’ button. Click the button ‘Options’ and activate the diagram for the ‘Lubricant viscosity’. This diagram will then appear in the calculation report.

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Figure 5.74: Calculation report

You can navigate through the report via the table of contents that provides links to the input values, results and figures. This calculation report contains all input data, the calculation method as well as all detailed results. The report is available in HTML and PDF format. The calculation report saved in HTML format, can be opened in a web browser or in Word for Windows. You may also print or save the calculation report:

5.16.11 Save the Calculation

When the calculation is finished, it is easy to save the calculation. You can save your calculation either to the eAssistant server or to your computer. Click on the button ‘Save’. Before you can save the calculation to your computer, you need to activate the checkbox ‘Local’ in the calculation module. A standard Windows dialog for saving files will appear. Now you will be able to save the calculation to your computer.

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Figure 5.75: Windows dialog for saving the file

In case you do not activate the option in order to save your files locally, then a new window is opened and you can save the calculation to the eAssistant server. Please enter a name into the input field ‘Filename’ and click on the button ‘Save’.

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Figure 5.76: Save the calculation

Our manual is improved continually. Of course we are always interested in your opinion, so we would like to know what you think. We appreciate your feedback and we are looking for ideas, suggestions or criticism. If you have anything to say or if you have any questions, please let us know via telephone +49 (0) 531 129 399-0 or email eAssistant@gwj.de.