The size of a linear ball bearing is determined by the demands made in terms of load carrying capacity, rating life and operational security.

The load carrying capacity is described in terms of:

• the basic dynamic load rating C
• the basic static load rating C₀.

The calculation of the basic dynamic and static load ratings given in the dimension tables is based on DIN 636-1.

The basic rating life L is reached or exceeded by 90 % of a sufficiently large group of apparently identical bearings before the first evidence of material fatigue occurs.

The operating life is defined as the life actually achieved by a shaft guidance system. It may differ significantly from the calculated life.

The following influences can lead to premature failure through wear or fatigue:

• misalignment between the guideways and guidance elements
• contamination
• inadequate lubrication
• reciprocating motion with very small stroke lengths (false brinelling)
• vibration during stoppage (false brinelling).

Due to the variety of installation and operating conditions, the operating life of a shaft guidance system cannot be precisely determined in advance. The safest way to arrive at an appropriate estimate of the operating life is comparison with similar applications.

The static load safety factor S₀ indicates the security against impermissible permanent deformations in the bearing and is determined in accordance with the formula below.

For linear ball bearings KH and KN..-B, the value must be S₀ ≧ 4.

In relation to guidance accuracy and smooth running, a value of S₀ ≧ 2 is regarded as permissible. If S₀ ＜ 2, please contact us.

The basic load ratings in the dimension tables are only valid if a ground (R_a0,3) and hardened shaft (at least 670 HV) is provided as a raceway.

If shafts with a surface hardness lower than 670 HV are used (for example, shafts made from X46 or X90), a hardness factor must be applied, see formulae and Figure 1.

The effective load rating of a linear ball bearing is dependent on the position of the load direction in relation to the position of the ball rows:

• the lowest load rating C_min and C_0 min occur in the zenith position, Figure 2
• the highest load rating C_max and C_0 max occur in the symmetrical position, Figure 2.

If the bearings are fitted in correct alignment, the maximum load rating can be used. If aligned fitting is not possible or the direction of loading is not defined, the minimum load ratings must be assumed.

For linear ball bearings and linear ball bearing and housing units where the fitting position of the ball rows is defined, the basic load ratings C and C₀ in the main load direction are given, Figure 3. For other load directions, the effective load ratings can be determined using the load direction factors in Figure 4 to Figure 21.

If the fitting position of the ball rows is not defined, the minimum load ratings are given.

The basic load ratings given in the dimension tables are defined as follows:

• For KH, KN-B, KS, KB and KBS, the minimum and maximum load ratings apply in accordance with Figure 2.
• For KNO-B, KSO and KBO, the basic load ratings apply in the main load direction. For other load directions see Figure 4 to Figure 13.

The basic load ratings given in the dimension tables are defined as follows:

For the units KGHK, KTHK, KGHW, KGHWT, the minimum load rating applies.

For the units KGN, KTN, KTFN, KGNS, KTNS and the open units KGNO, KTNO, KGNC, KGNOS, KTNOS, KGNCS, the basic load rating applies in the main load direction.
For other load directions see Figure 10 to Figure 13.

For the heavy duty range, the basic load rating applies in the main load direction.
For other load directions see Figure 14 to Figure 17.

For the units KGB, KGBA, KTB, KGBS, KGBAS, the minimum load rating applies.

For the open units KGBO, KGBAO, the basic load rating applies in the main load direction.
For other load directions see Figure 20 to Figure 21.

The factors in Figure 4 to Figure 13 are applied as follows:

Misalignment of the shaft impairs the running quality and operating life of linear ball bearings. Guidance systems with one shaft should therefore have at least two bearings, while guidance systems with two shafts should have at least three bearings.

Due to shaft flexing, it is not always possible to avoid misalignment, Figure 22. If it is present, load factors for misalignment should be applied, Figure 23 and Figure 24.

Linear ball bearings KN-B, KNO-B, KS and KSO and linear ball bearing and housing units containing these bearings are self‑aligning. They can compensate misalignments of up to ±30 angular minutes (KN-B and KNO-B) or ±40 angular minutes (KS and KSO) without any detrimental effect on the load carrying capacity.