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Spherical ball bearings are bearings with two rows, two divided raceways on the inner ring and one shared concave raceway on the outer ring. They are particularly suitable for compensation of misalignments between shaft and housing. Spherical ball bearings can absorb radial and axial forces and are suitable for smooth and cool operation at increased speeds due to low friction.

Dimensions and Tolerances

KRW supplies spherical ball bearings with normal tolerance (PN) in accordance to DIN 620-2 (Tolerances for roller bearings) and ISO 492 (Radial bearings - Dimensional and geometrical tolerances). All other deviating or special tolerances must be specified with the order.

 

Rolling Bearing Tolerances

Standards

The general dimensions of spherical ball bearings are standardised in ISO 15 (Radial bearings - Boundary dimensions, general plan), DIN 616 (Rolling bearings - Dimensions), and DIN 630 (Rolling bearings - Self aligning ball bearing).

 

Variations of Spherical Ball Bearings

Versions of spherical ball bearings

Bearing Design

Spherical ball bearings are self-latching bearings that cannot be disassembled. They can absorb high radial forces as well as low axial forces from both directions. The minimum load of the bearing is very low. Spherical ball bearings can be delivered with cylindrical or tapered bore.

 

Bearing Clearance

KRW supplies spherical ball bearings in normal clearance (CN) in accordance with DIN 620-4 (Radial internal clearance) and ISO 5753-1 (Rolling bearings - Internal clearance), but they are also available in all clearance classes with restricted clearance or special clearance.

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KRW cages

Cage

By default, spherical ball bearings by KRW come with a two-piece roller-riding solid brass cage (suffix: M). Other cage designs are available on request or chosen for specific applications and labelled accordingly on the bearing.

 

General Cage Information

Compensation of angular misalignment in a spherical ball bearing

Compensation of angular misalignment in a spherical ball bearing

Compensation of Angular Misalignments

Spherical ball bearings are suitable for compensation of misalignments between inner and outer bearing rings due to shaft deflections, angular errors and housing deformation. The admissible angular misalignment with static and circulating inner ring differs between versions. The maximal angular adjustment α is available on request.

 

Speed

KRW distinguishes between kinematic limiting speed nG and thermal reference speed nth. The kinematic limiting speed is a practical mechanical limit value and is based on the mechanical fatigue strength of the rolling bearing as a function of its installation situation and lubrication. The limit speed must not be exceeded even under optimum operating conditions without prior consultation with KRW.

The thermal reference speed represents the equilibrium between the heat generated in the bearing by friction and the heat flow dissipated. It is standardised in DIN ISO 15312 (Rolling bearings - Thermal reference speed).

Admissible Operating Temperatures

The admissible operating temperature of a bearing is limited by cage material, dimensional stability of the bearing components (ball race and rolling elements), as well as lubrication. By default, KRW bearings are stabilised up to 200°C (S1). KRW provides roller bearings for higher operating temperatures on request.

 

General Information to Cage Material

Dimensioning

For dynamically loaded bearings

The service life formula according to ISO 281 L10 = (C/P)p for dynamically loaded bearings requires an equivalent load (P) from constant direction and size. To calculate P, calculation factors and the ratio of axial and radial load are required.

Equivalent dynamic bearing load P

The equivalent bearing service life for spherical ball bearings depends on the ratio Fa/Fr (axial force / radial force). The equivalent dynamic bearing load can then be determined using the following formula:

Pequivalent dynamic load[kN]
Frdynamic radial force[kN]
Fadynamic axial force[kN]
ecalculation factor, see chart[-]
Y1calculation factor, see chart[-]
Y2calculation factor, see chart[-]

 

For statically loaded bearings

Dynamic dimensioning loses its validity for bearings rotating at very low speeds (n x dm ≤ 4000 mm/min). The static load safety factor S0 is calculated as follows:

S0static load safety factor[-]
C0basic static load rating (from bearing chart)[kN]
P0 equivalent static bearing load[kN]
nbearing speed[min-1]
dmmean bearing diameter [dm = (D+d)/2][mm]

 

Static load capacity

F0, rmax. radial static load[kN]
F0, amax. axial static load[kN]
Y0calculation factor, see chart[-]

 

Axial load capacity

The axial load capacity of spherical ball bearings is low due to the broad osculation on the outer ring.

When using spherical ball bearings with clamping sleeves on smooth shafts it must be made sure that, despite enough security, the max. occurring axial loads are lower than the pressed connection between shaft and bearing bore. For a professional installation, the following formula can be used to estimate the admissible axial load capacity:

Fa,zulmax. admissible axial load[kN]
Bbearing width, see product chart[mm]
dbore diameter, see product chart[mm]

 

 

Minimum Radial Load

A minimum load is required for the reliable operation of a rolling bearing. If the minimum load is not reached, slippage may occur. The minimum radial load for spherical ball bearings is roughly assumed to be 1% of the static load rating C0 of the bearing. If the value falls below this value, consult KRW Application Engineering.

 


 

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