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4. SELECTION OF BEARING ARRANGEMENT
In general, shafts are supported by only two bearings. If measures to relieve a shaft’s thermal elongation and The distinction between free-end and fixed-end 4.2 Example of Bearing Arrangements
When considering the bearing mounting arrangement, contraction are insufficient, abnormal axial loads are bearings and some possible bearing mounting
the following items must be investigated: applied to the bearings, which can cause premature arrangements for various bearing types are shown in Some representative bearing mounting arrangements
(1) Expansion and contraction of the shaft caused by failure. Fig. 4.1. considering preload and rigidity of the entire assembly,
For free-end bearings, cylindrical roller bearings shaft elongation and contraction, mounting error, etc.
temperature variations. or needle roller bearings with separable inner and are shown in Table 4.1.
(2) Ease of bearing mounting and dismounting. outer rings that are free to move axially (NU, N types,
(3) Misalignment of the inner and outer rings caused etc.) are recommended. When these types are used, Table 4. 1 Representative Bearing Mounting Arrangements
mounting and dismounting are also easier. and Application Examples
by deflection of the shaft or mounting error. When non-separable types are used as free-end
(4) Rigidity of the entire system including bearings and bearings, usually the fit between the outer ring and Bearing Arrangements
housing is loose to allow axial movement of the
preloading method. running shaft together with the bearing. Sometimes, Remarks Application Examples
(5) Capability to sustain the loads at their proper such elongation is relieved by a loose fitting between
the inner ring and shaft. Fixed-end Free-end
positions and to transmit them. When the distance between the bearings is short and
the influence of the shaft elongation and contraction is fThis is a common arrangement in which Medium size electric motors,
4.1 Fixed-End and Free-End Bearings negligible, two opposed angular contact ball bearings abnormal loads are not applied to bearings blowers
or tapered roller bearings are used. The axial clearance even if the shaft expands or contracts.
Among the bearings on a shaft, only one can be a (possible axial movement) after the mounting is
"fixed-end" bearing that is used to fix the shaft axially. adjusted using nuts or shims. fIf the mounting error is small, this is suitable
For this fixed-end bearing, a type which can carry both for high speeds.
radial and axial loads must be selected.
Bearings other than the fixed-end one must be "free-
end" bearings that carry only radial loads to relieve the
shaft's thermal elongation and contraction.
fThis can withstand heavy loads and shock loads Traction motors for rolling
and can take some axial load. stock
AB BEARING A BEARING B fEvery type of cylindrical roller bearing is
⋅ Deep Groove Ball Bearing ⋅Cylindrical Roller Bearing separable. This is helpful when interference is
⋅ Matched Angular Contact (NU, N types) necessary for both the inner and outer rings.
Ball Bearing ⋅Needle Roller Bearing (NA
Fixed-end Free-end (separable bearing) ⋅ Double-Row Angular type, etc.) fThis is used when loads are relatively heavy. Table rollers for steel mills,
Contact Ball Bearing main spindles of lathes
A C ⋅ Self-Aligning Ball Bearing BEARING C(1) fFor maximum rigidity of the fixed-end bearing,
⋅ Cylindrical Roller Bearing ⋅Deep Groove Ball Bearing it is a back-to-back type.
Fixed-end Free-end (non-separable bearing) with Ribs (NH, NUP ⋅Matched Angular Contact
types) Ball Bearing (back-to- fBoth the shaft and housing must have high
DD ⋅ Double-Row Tapered back) accuracy and the mounting error must be small.
Roller Bearing ⋅Double-Row Angular
No distinction between fixed-end and free-end ⋅ Spherical Roller Bearing Contact Ball Bearing fThis is also suitable when interference is Calender rolls of paper making
⋅Self-Aligning Ball Bearing
EE BEARING D,E(2) ⋅Double-Row Tapered necessary for both the inner and outer rings. machines, axles of diesel
⋅ Angular Contact Ball Roller Bearing (KBE type)
Bearing ⋅Spherical Roller Bearing Heavy axial loads cannot be applied. locomotives
⋅ Tapered Roller Bearing
⋅ Magneto Bearing BEARING F
⋅ Cylindrical Roller Bearing ⋅Deep Groove Ball Bearing
(NJ, NF types) ⋅Self-Aligning Ball Bearing
⋅Spherical Roller Bearing
No distinction between fixed-end and free-end
fThis is suitable for high speeds and heavy radial Reduction gears in diesel
loads. Moderate axial loads can also be applied. locomotives
FF Notes: (1) In the figure, shaft elongation and contraction are fIt is necessary to provide some clearance
relieved at the outside surface of the outer ring, but between the outer ring of the deep groove ball
No distinction between fixed-end and free-end sometimes it is done at the bore. bearing and the housing bore in order to avoid
subjecting it to radial loads.
(2) For each type, two bearings are used in opposition.
Fig. 4.1 Bearing Mounting Arrangements and Bearing Types Continued on next page
A 20 A 21
