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3. SELECTION OF BEARING TYPES

3.1 Allowable Bearing Space 3.3 Permissible Speed and Bearing Types Permissible bearing misalignment is given at the 3.5 Rigidity and Bearing Types
beginning of the dimensional tables for each bearing
The allowable space for a rolling bearing and its The maximum speed of rolling bearings varies type. When loads are imposed on a rolling bearing, some
adjacent parts is generally limited so the type and size depending, not only the type of bearing, but also its elastic deformation occurs in the contact areas between
of the bearing must be selected within such limits. size, type of cage, loads, lubricating method, heat θ the rolling elements and raceways. The rigidity of the
In most cases, the shaft diameter is fixed first by the dissipation, etc. Assuming the common oil bath bearing is determined by the ratio of bearing load to
machine design; therefore, the bearing is often selected lubrication method, the bearing types are roughly θ the amount of elastic deformation of the inner and
based on its bore size. For rolling bearings, there are ranked from higher speed to lower as shown in Fig. outer rings and rolling elements. For the main spindles
numerous standardized dimension series and types, 3.3. Fig. 3.4 Permissible Misalignment of Spherical Roller of machine tools, it is necessary to have high rigidity
and the selection of the optimum bearing from among Bearings of the bearings together with the rest of the spindle.
them is necessary. Fig. 3.1 shows the dimension series 3.4 Misalignment of Inner/Outer Rings and θ Consequently, since roller bearings are deformed
of radial bearings and corresponding bearing types. Bearing Types less by load, they are more often selected than ball
θ bearings. When extra high rigidity is required, bearings
3.2 Load Capacity and Bearing Types Because of deflection of a shaft caused by applied are given a preload, which means that they have a
loads, dimensional error of the shaft and housing, negative clearance. Angular contact ball bearings and
The axial load carrying capacity of a bearing is closely and mounting errors, the inner and outer rings are tapered roller bearings are often preloaded.
related to the radial load capacity (see Page A24) slightly misaligned. The permissible misalignment
in a manner that depends on the bearing design as varies depending on the bearing type and operating 3.6 Noise and Torque of Various Bearing
shown in Fig. 3.2. This figure makes it clear that when conditions, but usually it is a small angle less than Types
bearings of the same dimension series are compared, 0.0012 radian (4').
roller bearings have a higher load capacity than ball When a large misalignment is expected, bearings Since rolling bearings are manufactured with very
bearings and are superior if shock loads exist. having a self-aligning capability, such as self-aligning high precision, noise and torque are minimal. For
ball bearings, spherical roller bearings, and certain deep groove ball bearings and cylindrical roller
bearing units should be selected (Figs. 3.4 and 3.5). bearings particularly, the noise level is sometimes
specified depending on their purpose. For high
Width Series 01 2 34 5 6 precision miniature ball bearings, the starting torque is
4 specified. Deep groove ball bearings are recommended
3 08 I I for applications in which low noise and torque are
09 required, such as motors and instruments.
Diameter Series 20891 00
01 3.7 Running Accuracy and Bearing Types
Dimension 02
Series 03 For the main spindles of machine tools that require
04 high running accuracy or high speed applications like
Deep Groove Ball Bearings 18 superchargers, high precision bearings of Class 5, 4 or
Angular Contact Ball Bearings 19 2 are usually used.
Self-Aligning Ball Bearings 10 The running accuracy of rolling bearings is specified
Cylindrical Roller Bearings 29 in various ways, and the specified accuracy classes
Spherical Roller Bearings 20 vary depending on the bearing type. A comparison
Needle Roller Bearings 22 of the inner ring radial runout for the highest running
Tapered Roller Bearings 23 accuracy specified for each bearing type is shown in
39 Fig. 3.6.
30 For applications requiring high running accuracy, deep
31 groove ball bearings, angular contact ball bearings, and
32 cylindrical roller bearings are most suitable.
33
48 3.8 Mounting and Dismounting of Various
49 Bearing Types
40
41 Separable types of bearings like cylindrical roller
59 bearings, needle roller bearings and tapered roller
50 bearings are convenient for mounting and dismounting.
69 For machines in which bearings are mounted and
dismounted rather often for periodic inspection, these
II I I II types of bearings are recommended. Also, self-aligning
ball bearings and spherical roller bearings (small ones)
II II II with tapered bores can be mounted and dismounted
relatively easily using sleeves.
II II II II I
II I I II I II I II

I II II I II Fig. 3.5 Permissible Misalignment of Ball Bearing Units

II III I

Fig. 3.1 Dimension Series of Radial Bearings Highest
accuracy
Bearing Type Radial load capacity Axial load capacity Bearing Types Relative permissible speed Bearing Types specified Tolerance comparison of
Class 2 inner ring radial runout
1 4 7 10 Deep Groove Ball
Bearings Class 2 12345

1234 1234 13 Angular Contact Class 2
Ball Bearings
Single-Row Deep Deep Groove Class 4
Groove Ball Bearings Ball Bearings Cylindrical Roller
Bearings Normal
Single-Row Angular Angular Contact
Contact Ball Bearings Ball Bearings Tapered Roller
Bearings
Cylindrical Roller(1) Cylindrical Roller
Bearings Bearings Spherical Roller
Bearings
Needle Roller
Bearings

Tapered Roller Tapered Roller
Bearings Bearings

Spherical Roller Spherical Roller
Bearings Bearings

Thrust Ball Bearings Fig. 3.6 Relative Inner Ring Radial Runout of Highest
Accuracy Class for Various Bearing Types
Remarks Oil bath lubrication
Note(1) The bearings with ribs can take some axial loads. With special measures to increase speed limit

Fig. 3.2 Relative Load Capacities of Various Bearing Types Fig. 3.3 Relative Permissible Speeds of
Various Bearing Types

A 18 A 19