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 C_r w and C_0r 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 F_r per and F_0r 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 C_r w is used. C_r w is used to calculate the basic rating life.

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 C_0r w is used. C_0r w is used to calculate the static load safety factor S₀.

Fatigue limit load

The fatigue limit load C_ur 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 C_y, C_0y, C_z, C_0z and the permissible moment ratings M_0x, M_0y and M_0z.

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

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.

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.

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.

Static and dynamic hardness factors for lower hardness of raceways

f_H0, f_H = hardness factor · HV, HRC = surface hardness

 LFS..-RB, W..-X90 ·

 W..-X46