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 MIL-HDBK-1038
impractical. Except for standard commercial gear reducers, there are no industry
standards for bearing selection for cranes. The criteria listed in Table 2 have
been established by NCC and are mandatory for new crane designs. The L-10 life is
calculated for the speed (RPM) of the bearing at its location in the drive train
or system when the drive motor is operating at the rated speed of the drive. For
reeving systems, the speed of the lead sheave is used for all sheaves in the
system.
Table 2
Bearing Life Determination Criteria
Crane Type
Drive
L-10 Life
% Maximum
(Hours)
Load
Portal and
Main Hoist, including sheaves
5,000
75
Floating
and hook block
Portal and
Auxiliary hoist, including
7,000
75
Floating
sheaves and hook block
Portal and
Whip hoist, including sheaves
8,000
75
Floating
and hook assembly
Portal and
Luffing hoist, including
5,000
75
Floating
sheaves
Portal and
Rotate, excluding the rotate
7,000
85
Floating
bearing
Portal
Travel, including axles
10,000
85
Container
Hoist, including sheaves
25,000
75
Container
Boom hoist, including sheaves
15,000
75
Container
Trolley, including axles
25,000
75
Container
Travel, including axles
15,000
100
Container
Re-reeving devices
15,000
75
5.3.6.2
Hook Thrust Bearings. Hook thrust bearings are selected on the basis of
the published static rating, which must be at least 50 percent greater than the
hoist rating.
5.3.6.3
Bearing Installation. Bearings are installed with a press fit at one of
the races, usually the rotating race. The fit tolerances are published by the
bearing manufacturers, and must be followed. When adequate space is available,
bearings may also be mounted over a tapered slotted sleeve interposed between the
bearing inner race and the shaft. The sleeve is threaded on the smaller end for a
tightening nut that bears against the face of the inner race and pulls the sleeve
into the bearing inner race to obtain the desired press fit. The sleeve, its
tightening nut, and the inner race are furnished as a matched assembly by the
bearing manufacturer. The tightening nut must be installed per the bearing
manufacturer's directions and locked with a tab washer against loosening. For
light service, such as bridge drive shaft support, bearing inner races may be
secured to the shaft with a set screw. The inner race and the shaft are selected
for a loose fit.
148
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