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KISSsoft Tutorial: Roller Bearings

__________________________________________________________________________________________ For release 10/2008

kisssoft-tut-007-E-bearings.doc Last modification 29/10/2008 16:13:00 __________________________________________________________________________________________

1 Problem

1.1 General Remarks

The lifetime of a bearing is normally calculated from within the shaft analysis module in KISSsoft (the analysis of hydrodynamic bearings is not covered here but is also available in KISSsoft). The roller bearing is considered as a part of a system consisting of a shaft, loads and the roller bearings. The great advantage of this approach is that the calculation of the loads acting on the bearings is performed automatically by the shaft analysis module and is hence less susceptible to user errors. This must be emphasized for statically over-determined systems. The direct (without using the shaft analysis module) analysis of a bearing with given loads is also possible, see section 2.4.

1.2 Problem Overview

The roller bearings as shown in Fig. 1.2-1 shall be analysed. The system is statically over-determined, the first bearing is located inside the hollow shaft, and the third bearing is an axial ball bearing supported on its right side. The bearings number one, two and four do not take any axial loads.

Fig. 1.2-1: Example problem.

KIS

Ss

oft

Tu

tori

al

00

7: R

oll

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Be

ari

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s

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Position y [mm] Label Type Type of bearing Dimensions

10 Koyo 6205 Deep groove ball bearing (single row)

Floating bearing d=25mm D=52mm

92 Koyo 16006 Deep groove ball bearing (single row)

Floating bearing d=30mm D=55mm

145 Koyo 51106 Deep grooved thrust ball bearing (one sided)

Thrust bearing adjusted on right side →

d=30mm D=47mm

200 Koyo 6304 Deep groove ball bearing (single row)

Floating bearing d=20mm D=52mm

Tab. 1.2-1: Types of bearings and their positions.

1.3 Modeling the System

Firstly, the shaft geometry is modeled as depicted in Fig. 1.2-1, (see Tutorial 006: Shafts editor. Secondly, two force elements, bevel gear and helical gear, have to be defined according to the data given in Table 1.3-1.

Angle Position

[mm] Type Pressure

[°]

Helix

[°]

Pitch

diameter

[mm]

Facewidth

[mm]

Power

[kW] Direction

110 bevel 20 0 80 20 30 driven 173 helical 20 15 40 20 30 driving

Table 1.3-1: Loads.

The reference cone angle is ä=30°.

Fig. 1.3-1: Definition of loads.

The following system should be displayed in the Shaft editor:

Fig. 1.3-2: Model of the shaft with loads.

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1.4 Introducing Bearings

Right-click the group �Bearing� in the �Elements-tree� und choose the option �Roller Bearing� from the context menu (see Fig. 1.4-1).

Fig. 1.4-1. �Elements-tree� with context menu of group ,Bearing�

As depicted in Fig. 1.4-2 the �Elements-editor� displays the most-important bearing parameters.

Arranged the bearing at position y=10mm within the shaft by activating the radio button next to the �drop-down list� for Outside diameter. Choose the option 52.00mm from the respective �drop-down list� and �Koyo 6205 (d=25mm, D=52mm, B=15mm)� from the �drop-down list� for Label. Have KISSsoft size the respective diameter according to shaft�s geometry at given

position by clicking the size button next to the �drop-down list� for Inside diameter or Outside diameter.

Fig. 1.4-2: �Elements-editor� with roller bearing parameters.

If you are missing the Koyo 6205 in the list of available bearings check if Koyo is activated as bearing manufacturer. Proceed as follows :

1. Click Calculation from the menu bar.

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2. Choose the option �Settings�. The window �Module specific settings� opens. 3. Check if Koyo is included in the set of available Bearing manufacturers. Activate Koyo

by placing a checkmark in the respective checkbox if necessary.

4. Exit the window by clicking OK.

The system comprising shaft, loads and bearings should now look as shown in Fig. 1.2-1.

1.5 Calculation Results

Carrying out the shaft calculation by clicking from the tool bar or pressing F5 the roller bearing calculation is executed as well. A quick overview of the calculation results can be found in the results window (see Fig. 1.5-1). Note that the labels of the bearings were input manually.

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Fig. 1.5-1: window �Results� with a quick overview of the roller bearing calculation results.

Category Bearing service life provides you with the following values for each bearing: S0 Static Safety/Static load rating (C0) in [h] Lnh Nominal service life in [h] Lnmh Modified nominal service life in [h]1 Lnrh Nominal service life acc. to ISO 281:2007-02 Annex 4 in [h]2 Lnmrh Modified nominal service life acc. to ISO 281:2007-02 Annex 4 in [h]1,2 Category �Bearing reaction force� lists reaction forces and momentums componentwise (see Fig. 1.5-2). The Fy component quantifies axial load while the My component denotes torque.

Fig. 1.5-2: Components of bearing reaction forces and momentums.

1 Available when �Enhanced bearing service life calculation according ISO 281� in tab �Basic data� is activated. 2 Available when the option �Roller bearing life time according to ISO/TS 16281� in tab �Basic data� is chosen.

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1.6 Settings

Some settings alter the roller bearing calculation explicitly. In the following you will find a collection of those.

Fig. 1.6-1. Group �Strength� in tab �Basic data� with parameters which influence roller bearing calculation directly.

Speed The higher the speed, the shorter service life in [h]. Direction of rotation Change of direction possibly changes sign of axial load, like this is the case for helical gears. Lubricant temperature Higher lubricant temperature decreases service life coefficient. Roller bearing The �drop-down list� for Roller bearing allows for the choice out of four possible options:

1. �Roller bearings, classical calculation (pressure angle not considered)� Predominantly roller bearings are constraints of degrees of freedom for translation and rotation and are modelled as such if this option is chosen. Stiffnesses for translation and rotation can be chosen freely and are therefore independent of type or size of the bearing. Correlations between axial and radial forces (i.e. tapered roller bearings) are neglected.

2. �Roller bearings, classical calculation (pressure angle considered)� See above. Only that correlations between axial and radial forces are taken into account.

3. �Roller bearing stiffness calculation calculated from inner geometry� Considers inner roller bearing geometry, e.g. roller diameter, raceway radii, � to

evaluate bearing stiffness. If no such data is available it will be approximated based on size and type of the bearing.

4. �Roller bearing life time according to ISO/TS 16281� Service life calculation considering the inner bearing�s geometry. Results will be denoted

Lnrh, Lnmrh repsectively in the window �Results�. Enhanced bearing service life calculation according ISO 281 Placing a checkmark into the checkbox makes the bearing calculation consider the effect of lubrication on service life. Results are denoted Lnmh, Lnmrh respectively in the window �Results�.

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Fig. 1.6-2: Group �Material and lubrication� in tab �Basic data� with lubrication parameters.

Lubrication The choice of the type of lubricant effects the service life coefficient. Impurity Impurity eC effects the service life coefficient.

Fig. 1.6-3: Window �Module specific settings� with roller bearing parameters.

Failure probability a1 is used in the roller bearing calculation. By default it is set to 10% and may be altered here. Necessary service life Sets the required service life in the roller bearing calculation. This value has no effect on roller bearing calculation as such. If the evaluated service life drops below this limit a warning is returned to the user. Maximum service life coefficient This input field defines the upper limit of the service life coefficient aISO.

max,max,

max,

ISOISOISO

ISOISOISO

ISOaaa

aaaa

By default it is set to aISO=50 according to ISO 281:2007-2.

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2 Further Calculations

2.1 Calculations with Load Spectra

If load spectra which were defined in �Forces elements� (e.g. Cylindrical gear in Fig. 2.1-2) shall be considered for the calculation activate them via the �drop-down list� for Load spectra (see Fig. 2.1-1). You will find it in tab �Basic data�.

Fig. 2.1-1: �Drop-down list� for Load spectra in tab �Basic data�.

Choose the option �Consider load spectra�.

Fig. 2.1-2. Example for a load spectrum of Forces Element Cylindrical Gear.

Add a load spectrum entry to the database by following these steps:

1. Open the database tool via �Extras�-> �Data base tool�. 2. Answer the write-authorization question with Yes. The data base tool window opens. 3. Double-click the table labeled Load spectra and click Edit. The Data base tool now

displays a list of entries in table LASTKOLL. 4. There are two ways to go from here. Either define your very own load spectrum by not

choosing any entry in the list and click or generate a new entry based on another by

first clicking that item and then press . 5. Either way the window Create a new entry appears. Enter an arbitrary name for your load

spectrum into the input field Label. 6. Enter your load spectrum into the table or type the file name of the pre-defined load

spectrum into the input field �File name�. Note that the file name requires the suffix dat (e.g. myLoadSpectrum.dat) and must be placed within the folder <KISSsoft installation directory>/DAT.

7. If a file with the given name already exists you can start the editor by clicking the �Edit button�. Change the contents of the file if desired.

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Frequency, efficiency or torque factor and speed factor form a row, seperated by tabulator spaces. Fig. 2.1-3 shows the contents of the file �myLoadSpectrum.dat� as an example. It was opened and edited using the Windows editor.

Fig. 2.1-3: Example for file with self-defined load spectrum data.

The values included in the file scale the reference values power/torque and speed. Example: Suppose you defined the following reference values in tab �Basic data�, within the �Elements-editor� for the Forces element Cylindrical gear respectively: P = 115kW, n = 1500 1/min Moreover you decided to scale power, not torque (see Fig. 2.1-4).

Fig. 2.1-4: Window �Create a new entry� with Efficiency factor (power).

The drop-down list Input allows for choosing if power or torque is to be scaled with the values taken from the load spectrum. Fehler! Verweisquelle konnte nicht gefunden werden. shows the absolute values of power and speed according to the load spectrum given in Fig. 2.1-3.

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frequency [%] power [kW] speed [1/min]

10 0 0 20 103.5 1200 21 34.5 2400 34 69 1500 10 57.5 1650 5 149.5 600

Table 2.1-1: Absolute values of the load spectrum.

2.2 Calculating the Thermally Admissible Service Speed

The definition of the thermal limit of operating speed is described in DIN 732-2 (draft). This limit can differ from other operating speed limits as the reference conditions only apply to fully defined cases. In order to define the thermal operating limit, the reference thermal operating speed has to be defined for each case. It is the speed of rotation reached specific to a particular bearing arrangement and a given set of nominal operating conditions such that an equilibrium is achieved between heat development (friction) and heat dissipation (through bearing contact and lubrication). Mechanical or kinematic criteria are not taken into account for this speed. The reference values (temperatures, loads, viscosity of the lubrication, datum face of the bearing, �)

are fixed so that the reference speed using oil or grease lubricated bearings will result in identical values. Open the input window �Thermally admissible service speed� by first switching into the Roller bearings [W050] calculation module: Single-click the Modules window tab, then double-click Roller bearings [W050] (see Fig. 2.2-1).

Fig. 2.2-1: Switching into the calculation module Roller bearings [W050].

Within the Roller bearings main window open the menu �Calculation� and activate the option �Thermally admissible service speed� as shown in Fig. 2.2-2. The respective input window appears.

Fig. 2.2-2: Activating the input window �Thermally admissible service speed�.

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Fig. 2.2-3: Active Tab �Thermally admissible service speed�.

2.3 Extending the Roller Bearings Data Base

In KISSsoft, several thousand bearings are available in the KISSsoft database (IBC, Koyo, KRW, NSK, SKF, Timken). Missing bearings can be added to the database by following these steps:

1. Open the database tool via �Extras�->�Data base tool�. 2. Answer the write-authorization question with Yes. The �Data base tool�window opens. 3. Double-click the appropriate table taken from the data base W000, e.g. �Deep groove ball

bearing (single row)�, table �W05WNORM10�. Click Edit. The data base tool window then shows a list of entries in �W05WNORM10�.

4. There are two ways to go from here. Either define your very own roller bearing by not

choosing any entry in the list and click or generate a new entry based on another by

first clicking that item and then press . 5. Either way the window �Create a new entry� appears. Enter an arbitrary name for your

roller bearing into the input field �Bearing label�. There are two tabs availabe for parameterization of the bearing: �Basic data� and �Inner geometry�. While Basic data is mandatory �Inner geometry� is optional. If no inner geometry data is available it is approximated based on the data given in �Basic data�.

6. When you are finished confirm with OK. Save your new entry in the data base tool by clicking Save. Note that no message will appear when having successfully saved a file. Your newly added roller bearing appears at the end of the list with a successive number ≥ 20000.

2.4 Calculating a Single Bearing with Known Loads

If a single bearing with known loads is to be calculated (modelling of a system is not required), it is not necessary to model a system including shaft, loads and bearings. Click the tab �Basic data� to open the respective input window.

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Fig. 2.4-1: Input window �Basic data� in the module Roller bearings.

Radial loads are defined for each bearing within the group Bearing data while there is only one axial load to be given in group Working data. Distribution of axial load to the bearings depends on the type of axial support chosen for each bearing. Carry out the calculation by clicking

from the tool bar or by pressing �F5�.