holders. Brushes should move freely in their
Operating personnel must thoroughly familiarize
holders. They should not be loose enough to
themselves with the normal operating temperature
vibrate in the holder. Before replacing a worn
of each bearing. They have to recognize any
brush with a new one, clean all dirt and other
sudden or sharp changes in bearing temperature.
foreign material from the brush holder.
Any unusual noise in operating machinery
Replace with new brushes, all brushes that
may also indicate bearing malfunction. When a
strange noise is heard in the vicinity of operating
1. are worn or chipped so they will not move
machinery, make a thorough inspection to
properly in their holders;
determine its cause. Excessive vibration will
2. have damaged shunts, shunt connections,
occur in operating machinery with faulty bearings.
or hammer clips;
Make inspections at frequent intervals to detect
3. have riveted connections or hammer clips
faulty bearings as soon as possible.
and are worn to within 1/8 inch of the
metallic part;
BRUSHES
4. have tamped connections, are without
The brushes used in generators are one or
hammer clips, and are worn to one half or
more plates of carbon bearing against a collector
less of the original length of the brush; or
ring (slip ring). They provide a passage for
5. have spring-enclosed shunts and are worn
electrical current to an internal or external circuit.
to 40 percent or less of the original length
The brushes are held by brush holders mounted
of the brush (not including the brush head,
on studs or brackets attached to the brush-
which fits into one end of the spring).
mounting ring, or yoke. The brush holder studs,
or brackets, and brush-mounting ring comprise
Where adjustable brush springs are of the
the brush rigging. The brush rigging is insulated
positive gradient (torsion, tension, or compres-
from, but attached to, the frame or one end bell
sion) type, adjust them as the brushes wear to keep
of the machine. Flexible leads (pigtails) connect
the brush pressure near constant. Springs of the
the brushes to the terminals of the external
coiled-band, constant-pressure type and some
circuit. An adjustable spring is generally provided
springs of the positive gradient type are not
to maintain constant pressure of the brush on the
adjustable. On these you have to change springs.
slip ring. This is required to retain good contact
You should adjust brush pressure following the
between the brushes and slip rings without
MRC, the manufacturer's technical manual, or
excessive wear of the brushes.
NSTM, chapter 300. To measure the pressure of
Brushes are manufactured in different grades
brushes operating in box-type brush holders,
to meet the requirements of the varied types of
insert one end of a strip of paper between the
service. The resistance, ampere-carrying capacity,
brush and slip ring. Use a small brush tension
coefficient of friction, and hardness of the brush
gauge (such as the 0- to 5-pound indicating scale)
are set by the maximum allowable speed and load
to exert a pull on the brush toward the brush
of the machine.
holder axis as shown in figure 10-7. Note the
reading of the gauge when the pull is just sufficient
Correct Brush Type
to release the strip of paper so it can be pulled
out from between the brush and slip ring without
The correct grade of brush and correct
offering resistance. This reading divided by the
brush adjustment are necessary to avoid brush
contact area may be considered to be the spring
performance trouble.
operating pressure.
Use the grade of brush shown on the drawing
or in the technical manual applicable to the
DISASSEMBLY AND REASSEMBLY
machine. An exception to this is when Naval Sea
OF MOTORS AND GENERATORS
Systems Command instructions issued after the
date of the drawing or technical manual state
When you have to disassemble and reassemble
otherwise. In such cases, follow the Naval Sea
a large motor or generator, follow the procedures
Systems Command instructions.
in the manufacturers' technical manuals. Never
be hasty or careless in disassembling a generator
Brush Care
or motor. Handle the delicate components with
care to prevent or create the need for additional
You should ensure that all brush shunts are
adjustment. Use the proper tools, and label the
securely connected to the brushes and the brush
10-8
