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 MIL-HDBK-1038
When heavy axial loads are present, tapered roller bearings are required.
They can be selected with the tapered rollers at any desired angle to obtain the
proper balance between their radial and axial load capacities. They are normally
used in gear reducers where the helix angles of gear sets cause large axial loads.
The bearing races must be accurately shimmed on their faces to obtain the proper
contact between their conical surfaces and the rollers. Since the internal
arrangement of the tapered roller bearings allows them to carry an axial load in
only one direction, they must often be used in pairs with opposite taper angles.
The bearing manufacturers also offer bearing assemblies where the individual
bearing pairs are combined into a single unit. Tapered roller bearings, whether
in single row or in pairs, are not self-aligning; they maintain a fixed
orientation between the bearing races. Because of this characteristic, tapered
roller bearings are recommended for sheaves to stabilize them against tilting on
their pins. Alternatively, for light duty applications, a single row cylindrical
(straight) roller bearing may be used for sheave mounting.
Thrust bearings are designed primarily for axial loads. They may be in
the form of cylindrical roller bearings; tapered roller bearings; or, if
self-aligning is desired, spherical roller bearings. All thrust bearings have the
rollers arranged with their axes on radial lines. The cylindrical and
tapered roller bearings always maintain their races in parallel alignment. The
self-aligning spherical roller bearings, because they allow their races to tilt
with respect to each other, are used on portal crane gudgeons. All three types of
thrust bearings are used on load hooks.
4.3.6.10 Mounted Bearings. Bearings of all types are available in housings
designed for bolting to support structures. The most common type is the pillow
block. The base of the pillow block, depending on size, may have two or four
mounting bolts. The smaller housings are single piece. The larger housings are
split along the shaft centerline, with the upper half (cap) secured with two or
four bolts. Housings are available with provisions for grease or oil lubrication
of the bearing. Pillow blocks subjected to heavy loads have the bearing inner
races pressed directly onto the shaft or locked to it by a tapered sleeve that is
pulled by a locknut and wedged between the bearing race and the shaft. The
tapered sleeve and locknut are provided as integral components of the bearing
assembly. The housings of these pillow blocks are required to be made of steel
either as castings or machined from rolled plate as a custom made component.
Weldments are prohibited for pillow block housings in these applications.
For light duty applications, such as support of squaring shafts, the
inner race may be locked to the shaft by a setscrew in a protruding extension of
the race. The housings of these pillow blocks may be steel or any class of cast
iron.
Piloted flanged cartridge bearings have accurately machined cylindrical
housings which are intended for a close fit in the support structure. The flanges
have four bolt holes for mounting. These units are often used as axle bearings on
the smaller, light duty bridge cranes. Flanged housings that are subjected to
significant loads must be ductile iron or steel castings; those supporting only
the weight of mechanical components may be cast iron of any class.
4.3.6.11 Bushings. Bushings, also called plain bearings, are copper alloy
(bronze) sleeves which are pressed into bores of mechanical components. Their
function is to
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