Load carrying capacity and rating life

Load carrying capacity and rating life

Permissible radial loads

The thick-walled outer rings of the track rollers can support high radial loads. If these track rollers are used against a shaft as a raceway, the outer rings undergo elastic deformation, ➤ Figure.

Compared to rolling bearings supported in a housing bore, track rollers have the following characteristics:

  • modified load distribution in the bearing. This is taken into consideration by means of the basic load ratings Cr w and C0r w used in the calculation of the rating life
  • bending stress in the outer ring. This is taken into consideration by means of the permissible radial loads Fr per and F0r per. The bending stresses must not exceed the permissible strength values of the material (due to the risk of fracture).

Permissible radial load under dynamic loading

For rotating bearings under dynamic load, the effective dynamic load rating Cr w is used. Cr w is used to calculate the basic rating life.

ACHTUNG

The permissible dynamic radial load Fr per must not be exceeded.

If the basic static load rating C0r w is lower than the basic dynamic load rating Cr w, C0r w is used.

Deformation of the outer ring when used against a flat raceway

Permissible radial load under static loading

For bearings under static load, when stationary or with only infrequent motion, the effective static load rating C0r w is used. C0r w is used to calculate the static load safety factor S0.

ACHTUNG

At the same time, the permissible static radial load F0r per must not be exceeded.

In addition to the permissible radial load of the bearing, the permissible radial load of the mating track must also be taken into consideration.

The basic load ratings stated are valid only in conjunction with a shaft as a mating track that is hardened (at least 670 HV) and ground (Ra 0,3).

Fatigue limit load

The fatigue limit load Cur w is defined as the load below which – under laboratory conditions – no fatigue occurs in the material.

Calculation of the rating life

The general methods for calculating the rating life are:

  • the basic rating life in accordance with DIN ISO 281
  • the adjusted rating life in accordance with DIN ISO 281
  • the expanded calculation of the adjusted reference rating life in accordance with DIN ISO 281-4.

These methods are described in Catalogue HR 1, Rolling Bearings, in the chapter Load carrying capacity and rating life.

Rating life of track rollers

In comparison with Catalogue HR 1, Rolling Bearings, the following values must be exchanged:

    Cr

    =

    Crw

    C0r

    =

    C0r w

    Cur

    =

    Cur w.

The carriages LFCL, LFL..-SF, LFLL, LFKL..-SF and bogie carriage LFDL contain four track rollers LFR.

The equivalent principle applies here. The corresponding par­ameters are taken into consideration in the basic load ratings Cy, C0y, Cz, C0z and the permissible moment ratings M0x, M0y and M0z.

Cy N

Basic dynamic load rating in y direction

C0y N

Basic static load rating in y direction

Cz N

Basic dynamic load rating in z direction

C0zN

Basic static load rating in z direction

M0x Nm

Static moment rating about x axis

M0y Nm

Static moment rating about y axis

M0z Nm

Static moment rating about z axis.

In the case of track rollers with a profiled outer ring, calculation is carried out exclusively by means of the basic rating life to DIN ISO 281.

Load carrying capacity and load directions
Other formulae for calculating the basic rating life
Rating life for carriages with four track rollers
Ls 105 m

Basic rating life in metres

Da mm

Rolling contact diameter of track roller

Cr w, Cy, Cz N

Effective dynamic load rating

Pr N

Equivalent dynamic load (radial load)

p

Ball: p = 3;
needle roller (non-locating bearing track roller or carriage): p = 10/3

Lh h

Basic rating life in operating hours

H m

Single stroke length for reciprocating motion

nosc min–1

Number of return strokes per minute

 m/min

Mean travel velocity

P N.

Equivalent dynamic load in the corresponding load direction (for applications with combined loads, please contact us).

Operating life

The operating life is the life actually achieved by a rolling bearing. It may differ significantly from the calculated rating life.

This may be due to wear or fatigue as a result of:

  • deviations in the operating data
  • insufficient or excessive operating clearance (track roller, guideway)
  • contamination
  • inadequate lubrication
  • operating temperature too high or too low
  • reciprocating motion with very small stroke length, which can lead to false brinelling
  • high vibration load, leading to false brinelling
  • very high shock loads (static overloading)
  • prior damage during mounting.

Due to the variety of mounting and operating conditions, the oper­ating life cannot be precisely calculated in advance. The most reliable way of arriving at a close estimate is by comparison with similar applications.

Static load safety factor

The indicator of static loading is the static load safety factor S0.

This indicates the security against impermissible permanent deformations in the bearing and is determined by means of the following equation:
Static load safety factor for carriages with four track rollers
S0

Static load safety factor

C0r w N

Effective static load rating of track roller

F0r N

Static force acting in radial direction

C0 N

Basic static load rating of carriage

F0 N

Static force acting in y and z direction

M0 Nm

Permissible static moment in x, y, z direction

M Nm

Moment acting in load direction (Mx, My, Mz).

Track rollers are regarded as heavily loaded at a static load safety factor of S0 < 4.

For applications with normal operating conditions, a value S0 > 4 is required.

When using individual track rollers, for example in conjunction with guideways, the decisive factor where required is the permissible load of the guideway.

ACHTUNG

Static load safety factors S0 < 1 cause plastic deformation of the rolling elements and the raceway, which can impair smooth running. This is only permissible for bearings with small rotary motions or in secondary applications.

Minimum load

In order to ensure that the outer ring is driven, that no slippage occurs and that the track roller does not lift from the mating track, the track rollers must be subjected to a minimum load in dynamic operation.

ACHTUNG

In general, the minimum load is calculated using the ratio C0r w/Fr < 60.

Differences
in raceway hardness

If shafts with a lower surface hardness are used (such as X46, X90), a hardness factor must be applied, see ➤ equations and ➤ Figure.

CH N

Effective dynamic load rating

fH

Dynamic hardness factor

C N

Basic dynamic load rating

C0H N

Effective static load rating

fH0

Static hardness factor

C0 N

Basic static load rating.

Static and dynamic hardness factors for lower hardness of raceways
fH0, fH = hardness factor · HV, HRC = surface hardness
 LFS..-RB, W..-X90 ·
 W..-X46

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