Selection of a rolling bearing.

The following comparison of basic properties of types of rolling bearings may help in selecting the suitable type. When selecting the type, it is necessary to take into account, above all, the following facts:

• Amount and type of the load
• Design of seating and way of lubrication of the bearing
• Operational parameters of the bearing (speed, thermal conditions, etc.)
• Requirements for accuracy
• Requirements for installation and dismantling

Rolling bearings are usually composed of two rings, rolling bodies and a cage. The bearings are divided into several basic types according to their inner design, the shape of rolling bodies and directions of the forces that can be retained.

Basic types of rolling bearings are internationally standardised. Within the scope of each type the bearings are produced in various designs whose properties may differ from the basic design. The following text gives brief characteristics of individual types of rolling bearings; a comparison of their utility properties can be found in the table at the end of this document:

A. Deep groove ball bearings

• The cheapest and most commonly used bearing type; produced in many designs and sizes
• The bearings are characterised by simple designs and cannot be disassembled
• The bearings can handle operational conditions and their maintenance is simple
• The bearings show relatively good load rating both in radial and axial directions
• The bearings are suitable for high and very high speeds
• The bearings require good alignment of the journal and bearing body; the permissible tilting angle is approx. 10'
• The bearings are delivered with shields or seals

B. Angular contact ball bearings

• Orbital paths are offset mutually in the direction of the bearing axis
• Designed to retain combined load with relatively large axial forces (axial load of bearings increases with increasing contact angles)
• Single-row bearings enable the retention of axial forces only in one direction; therefore these bearings are installed in pairs in opposite positions and as close to each other as possible
• The bearings can be paired or double-row bearings can be used to retain axial forces (pairs of bearings are delivered in one packing; as the bearings are paired, bearings from different pairs must not be used together)
• Lower load rating than tapered roller bearings, however, may be used at higher speeds
• Double-row bearings can retain tilting moments in the axial plane. However, these types need perfect alignment and rigidity of seating and do not allow any swinging of shafts
• Double-row bearings are also delivered with shields or seals

C. Self-aligning ball bearings

• Provided with two rows of ball bearings with spherical orbital path on the outer ring
• Their design allows mutual tilting of rings (approx. 2-3°, depending on the design)
• Suitable, above all, for seating, where the shaft shows deflections or misalignment may occur
• Load rating of these bearings is lower than with single-row ball bearings of the same size; not suitable for retaining larger axial forces
• Produced usually with cylindrical or tapered holes
• Delivered also with seals

D. Cylindrical roller bearings

• Dismountable bearings, designed for transmissions of large radial loadings (up to 60% higher load rating compared with ball bearings of the same size)
• High rigidity, therefore suitable for fluctuating and surge loads
• Bearings without cages (full complement) show higher loading capacities; however, bearings with cages can be used for higher speeds
• Bearings with guiding collars on the outer and inner rings allow the retention of higher axial forces. Other designs cannot retain any axial forces, however, allow axial misalignment of the rings
• Cylindrical roller bearings require perfect alignment of the journal and bearing body; the permissible maximum tilting angle is 3-4'
• Double-row cylindrical roller bearings are usually produced with both cylindrical and tapered holes

E. Needle roller bearings

• In fact, needle bearings are cylindrical roller bearings with long slim rollers (acc. to ISO, the roller length is min. 2.5 diameter)
• Show small installation height, high accuracy and rigidity
• Despite their low cross section, the bearings have a high load rating and are therefore very suitable for seating where radial dimensions are limited
• Used, above all, for low speeds or swinging movements; also suitable for fluctuating and surge loads
• Cannot retain any axial forces, however, allow axial misalignment of the rings
• One or both rings may be omitted to reduce the installation height; however, seating surfaces on the shaft must then be hardened and machined carefully
• Show high requirements for alignment of the journal and bearing body, the maximum permissible tilting angle is 3-4'
• Delivered also with seals

F. Taper roller bearings

• Designed usually as dismountable, provided with tapered orbital paths on the outer and inner rings with tapered rollers arranged in the paths
• High load rating; suitable especially for retaining simultaneously acting large radial and axial forces
• Allow the retention of axial forces in one direction only; therefore installed in pairs in opposite positions and as close to each other as possible
• In case of too high loading on the bearing or if axial forces must be retained in both directions, the bearings can be paired (pairs of bearings are delivered in one packing; as the bearings are paired, bearings from different pairs must not be used together)
• Higher load rating than angular contact ball bearings, however, these types are designed for lower speeds
• Seating surfaces for tapered roller bearings must be aligned; the permissible tilting angle is 2-4'

G. Spherical roller bearings

• Two rows of spherical rollers with a common spherical path on the outer ring
• Their design allows mutual tilting of rings (approx. 1.5-2.5°, depending on the design)
• High load rating, retention of radial and simultaneously also axial forces in both directions
• Suitable for large loads with misaligned seating and deflections of shafts
• Produced usually with cylindrical and tapered holes; non-dismountable
• Delivered also with seals

H. Toroidal roller bearings

• Single-row bearings with long, slightly spherical rolling elements; orbital paths of the outer and inner rings are concave and symmetrical along the axis running through the bearing centre
• The design combines the tilting ability of a spherical roller bearing (permissible tilting angle approx. 0.5°) with the ability of axial balancing, typical for rolling elements; they also show relatively small installation height
• High radial load rating even if the bearing must compensate a misalignment or axial shifts
• Reduce vibrations in seating; axial vibrations of the shaft are not transferred to the body
• Load rating of full complement  bearings is significantly higher than bearings with cages
• Produced with both cylindrical and tapered holes
• Delivered also with seals

I. Thrust ball bearings

• Designed only for retaining axial forces; radial forces cannot be retained
• Produced as single direction bearings or double direction bearings for retaining axial forces in one or both directions respectively
• Not suitable for higher speeds; limit speeds are limited by adverse effects of centrifugal forces
• These bearings must not work unloaded to prevent slipping of the balls
• Dismountable bearings; simple shapes and designs
• Correct functioning needs perpendicularity of the rings’ face surfaces to the shaft axis
• The bearings designed with spherical seating surfaces can be used to compensate for misalignment between the support surface in the housing and the shaft

J. Cylindrical roller thrust bearings

• Designed to retain large axial forces in one direction; radial forces cannot be retained
• Form rigid seating; low sensitivity to surge loads
• Usable only at lower speeds; must not be operated unloaded to prevent slipping of rolling elements
• Show simple shapes and designs; dismountable, require small spaces in axial directions
• Correct functioning needs perpendicularity of the rings’ face surfaces to the shaft axis
• Used especially where axial ball bearings cannot provide sufficient load rating

K. Needle roller thrust bearings

• Designed to retain large axial loads in one direction; radial forces cannot be retained
• Form rigid seating with minimum space requirements; low sensitivity to surge loads
• Usable only at lower speeds; must not be operated unloaded to prevent slipping of rolling elements
• Cages can be used in seating with needles independently or in combinations with rings of various designs (all parts must be ordered separately due to possibility to create various combinations)
• Correct functioning needs perpendicularity of the rings’ face surfaces to the shaft axis
• Used especially where space is limited in axial directions

L. Spherical roller thrust bearings

• High axial load rating; can retain radial forces
• Suitable for retaining large axial forces even with relatively high speeds
• Their design allows balancing of misalignment of the shaft and body (permissible tilting of approx. 2-3° depends on the bearing design)
• The shaft ring and cage with spherical rollers form a non-dismountable unit
• These types always need oil lubrication due to their inner arrangement

Comparative table of rolling bearings utility properties

where: