Quantcast Figure 3-18.--Diagram of an oil-ring lubricated bearing.
 

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sleeve bearings requires periodic inspections of
bearing wear and lubrication.
Wear of Bearings.-- Propulsion  generators,
motors, and large ship's service generators are
sometimes provided with a gauge for measuring
bearing wear. You can obtain bearing wear on a
sleeve-bearing machine not provided with a bearing
by measuring the air gap at each end of the machine
with a machinist's tapered feeler gauge. Use a blade
long enough to reach into the air gap without removing
the end brackets of the machine. Before making the
measurements, clean the varnish from a spot on a pole
or tooth of the rotor. A spot should also be cleaned at
the same relative position on each field pole of a dc
machine. For ac machines, clean at least three and
preferably four or more spots spaced at equal intervals
around the circumferences on the stator. Take the air
gap measurement between a cleaned spot on the rotor
and a cleaned spot on the stator, turning the rotor to
bring the cleaned spot of the rotor in alignment with
the cleaned spots on the stator. Compare these
r e a d i n g s with the tolerance stated by the
manufacturer's instruction book.
Oil Rings and Bearing Surfaces.-- An opening
is provided in the top of the bearing for you to check
the condition of the oil rings and bearing surfaces (fig.
3-18). Periodic inspections are necessary to make
Figure 3-18.--Diagram of an oil-ring lubricated bearing.
certain that the oil ring is rotating freely when the
machine is running and is not sticking. With the
machine stopped, inspect the bearing surfaces for any
alarm contractors, which are incorporated in the ship's
signs of pitting or scoring.
alarm system. The contactor is preset to provide an
Trouble Analysis.-- The earliest indication of
alarm when the bearing temperature exceeds a value
sleeve bearing malfunction normally is an increase in
detrimental to bearing life. You should secure the
t h e operating temperature of the bearing.
affected machinery as soon as possible if a bearing
Thermometers are usually inserted in the lubricating
malfunction is indicated. A motor with overheated
oil discharge line from the bearing as a means of
sleeve bearings should be unloaded, if possible,
visually indicating the temperature of the oil as it
without stopping the motor. If you stop it immediately,
leaves the bearing. Thermometer readings are taken
the bearing may seize. The best way to limit bearing
hourly on running machinery by operating personnel.
damage is to keep the motor running at a light load and
However, a large number of bearing casualties have
supply plenty of cool, clean oil until the bearing cools
occurred in which no temperature rise was detected in
down.
thermometer readings; in some cases, discharge oil
Because the permissible operating temperature is
temperature has actually decreased. Therefore, after
often too high to be estimated by the sense of touch,
checking the temperature at the thermometer,
temperature measurements should be taken to
personnel should make a follow-up check by feeling
determine whether a bearing is overheated. A
the bearing housing whenever possible. Operating
thermometer securely fastened to the bearing cover or
personnel must thoroughly familiarize themselves
housing will usually give satisfactory bearing
with the normal operating temperature of each bearing
temperature measurements on machines not equipped
so they will be able to recognize any sudden or sharp
with bearing temperature measuring devices. Do not
changes in bearing oil temperature. Many large
insert a thermometer into a bearing housing, as it may
generators are provided with bearing temperature
3-24

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