Quantcast Figure 3-10.--Measuring brush tension.
 

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dc generator brush holder and brush-rigging
have spring-enclosed shunts and are worn to 40
assembly.
percent or less of the original length of the
brush (not including the brush head, which fits
Brushes are manufactured in different grades to
into one end of the spring).
meet the requirements of the varied types of service.
The properties of resistance, ampere-carrying
Where adjustable brush springs are of the positive
capacity, coefficient of friction, and hardness of the
gradient (torsion, tension, or compression) type,
brush are determined by the maximum allowable
adjust them as the brushes wear to keep the brush
speed and load of the machine.
pressure approximately constant. Springs of the
coiled-band, constant-pressure type, and certain
CORRECT BRUSH TYPE.-- The correct grade
springs of the positive-gradient type are not adjustable
of brush and correct brush adjustment are necessary to
except by changing springs. Adjust pressure following
avoid commutation trouble. For good commutation,
the manufacturer's technical manual. Pressures as low
use the grade of brush shown on the drawing or in the
as 1 1/2 psi of contact area may be specified for large
technical manual applicable to the machine, except
machines and as high as 8 psi of contact area may be
where NAVSEA instructions issued after the date of
specified for small machines. Where technical
the drawing or technical manual (such as the
manuals are not available, a pressure of 2 to 2 1/2 psi
instruction for brushes to be used in electrical
of contact area is recommended for integral
propulsion and magnetic minesweeping equipment)
horsepower and integral kilowatt machines. About
state otherwise. In such cases, follow the NAVSEA
twice that pressure is recommended for fractional
instructions. In the case of propulsion and magnetic
horsepower and fractional kilowatt machines. To
minesweeping equipment, only one grade of each of
measure the pressure of brushes operating in box-type
two different brush manufacturers is permitted for any
brush holders, insert one end of a strip of paper
machine. This restriction on brush interchangeability
between the brush and commutator; use a small brush
is based on the vital nature of the machines involved
tension gauge (such as the 0- to 5-pound indicating
and on the impracticability of factory testing these
scale) to exert a pull on the brush in the direction of
machines while operating them with several
brush holder axis, as shown in figure 3-10. Note the
manufacturers' grades, which have been qualified
reading of the gauge when the pull is just sufficient to
under any one of the six military grades. Never mix
release the strip of paper so that it can be pulled out
different types or grades of brushes from the same
manufacturer. Rapid brush wear could result from a
mismatch of brushes.
CARE OF BRUSHES.-- All brush shunts should
be securely connected to the brushes and the brush
holders. Brushes should move freely in their holders,
but they should not be loose enough to vibrate in the
holder. Before replacing a worn brush with a new one,
clean all dirt and other foreign material from the brush
holder.
Replace with new brushes, all brushes that
are worn or chipped so they will not move
properly in their holders;
have damaged shunts, shunt connections, or
hammer clips;
have riveted connections or hammer clips and
are worn to within one-eighth inch of the me-
tallic part;
have tamped connections without hammer clips
and are worn to one-half or less of the original
length of the brush; or
Figure 3-10.--Measuring brush tension.
3-18

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