Selection of bearing arrangement

A bearing arrangement supports and locates a shaft, radially and axially, relative to other components such as housings. Typically, two bearing supports are required to position a shaft. Depending on certain requirements, such as stiffness or load directions, a bearing support may consist of one or more bearings.

When considering the bearing arrangement, the following items must be investigated:

1. Expansion and contraction of the shaft caused by temperature variations.
2. Ease of bearing mounting and dismounting.
3. Misalignment of the inner and outer rings caused by deflection of the shaft or mounting error.
4. Rigidity of the entire system including bearings and preloading method.
5. Capability to sustain the loads at their proper positions and to transmit them.

The bearing which prevents axial movement of the shaft relative to the housing is called the "fixed side bearing" and the bearing which allows axial movement relatively is called the "floating-side bearing". This allows for expansion and contraction of the shaft due to temperature variation and enables error in bearing mounting clearance to be absorbed.

The fixed side bearing is able to support radial and axial loads. A bearing which can fix axial movement in both directions should therefore be selected. A floatingside bearing that allows movement in the axial direction while supporting a radial load is desirable. Movement in the axial direction occurs on the raceway surface for bearings with separable inner and outer rings such as cylindrical roller bearings, and occurs on the fitting surface for those which are not separable, such as deep groove ball bearings.

In applications with short distances between bearings, shaft expansion and contraction due to temperature fluctuations is slight, therefore the same type of bearing may be used for both the fixed-side and floating-side bearing. In such cases it is common to use a set of matching bearings, such as angular contact ball bearings, to guide and support the shaft in one axial direction only.

Table below shows typical bearing arrangements where the bearing type differs on the fixed side and floating side.

Bearing arrangement (distinction between fixed and floating-side)

Arrangement		Comment	Application (Reference)
Fixed	Floating
		General arrangement for small machinery. For radial loads, but will also accept axial loads.	Small pumps, auto-mobile transmissions, etc.
		Suitable when mounting error and shaft deflection are minimal or used for high rotational speed application. Even with expansion and contraction of shaft, floating side moves smoothly.	Medium-sized electric motors, ventilators, etc.
		Radial loading and dual direction of axial loading possible. In place of duplex angular contact ball bearings, double-row angular contact ball bearings are also used.	Worm reduction gear
		Heavy loading capable. Shafting rigidity increased by preloading the two back-to-back fixed bearings. Requires high precision shafts and housings, and minimal fitting errors.	Reduction gears for general industrial machinery
		Allows for shaft deflection and fitting errors. By using an adaptor on long shafts without screws or shoulders, bearing mounting and dismounting can be facilitated. Self-aligning ball bearings are used for positioning in the axial direction, and not suitable for applications requiring support of axial load.	General industrial machinery
		Widely used in general industrial machinery with heavy and shock load demands. Allows for shaft deflection and fitting errors. Accepts radial loads as well as dual direction of axial loads.	Reduction gears for general industrial machinery
		Accepts radial loads as well as dual direction axial loads. Suitable when both inner and outer ring require tight fit.	Reduction gears for general industrial machinery
		Capable of handling large radial and axial loads at high rotational speeds. Maintains clearance between the bearing's outer diameter and housing inner diameter to prevent deep groove ball bearings from receiving radial loads.	Transmissions for diesel locomotives

Table below shows some common bearing arrangements where no distinction is made between the fixed side and floating side.

Bearing arrangement (no distinction between fixed and floating-side)

Arrangement	Comment	Application (Reference)
	General arrangement for use in small machines. Preload is sometimes applied by placing a spring on the outer ring side surface or inserting a shim. (can be floating-side bearings.)	Small electric motors, small reduction gears, etc.
	Back to back arrangement is preferable to face to face arrangement when moment load applied. Able to support axial and radial loads; suitable for high-speed rotation. Rigidity of shaft can be enhanced by providing preload.	Machine tool spindles, etc.
	Capable of supporting extra heavy loads and impact loads. Suitable if inner and outer ring tight fit is required. Care must be taken that axial clearance does not become too small during operation.	Construction equipment, mining equipment sheaves, agitators, etc.
	Withstands heavy and shock loads. Wide range application. Shaft rigidity can be enhanced by providing preload, but make sure preload is not excessive. Back-to-back arrangement for moment loads, and face-to-face arrangement to alleviate fitting errors. With face-to-face arrangement, inner ring tight fit is facilitated.	Reduction gears, front and rear axle of automobiles, etc.

Vertical shaft bearing arrangements are shown in Table below

Bearing arrangement (Vertical shaft)

Arrangement	Comment	Application (Reference)
	When fixing bearing is a duplex angular contact ball bearing, floating bearing should be a cylindrical roller bearing.	Vertically mounted electric motors, etc.
	Most suitable arrangement for very heavy axial loads. Shaft deflection and mounting error can be absorbed by matching the center of the spherical surface with the center of spherical roller thrust bearings.	Crane center shafts, etc.