13
1
2
3
4 5
6
7
8
9
10
1. MICA CONE INSULATION
2. WEDGE RING
3. MICA PLATE lNSULATION
4. BRUSH SURFACE
5. COPPER SEGMENT (BAR)
6. RISER
7. ARMATURE COIL CONDUCTORS
8. MICA CONE INSULATION
9. SHELL
10. MlCA SHELL INSULATION
FIGURE 17. COMMUTATOR CUTAWAY
6938
SATISFACTORY SURFACE
The commutator usually shows signs of distress before
trouble actually occurs. A discussion of a satisfactory
surface will help identify a surface heading for failure.
The successful operation of the motor depends on
maintaining a proper film on the surface of the
commutator. This film of carbon, graphite, copper oxide
and water vapor is deposited on the commutator surface
by electrochemical action. It is formed by the wiping
action of the brush against the commutator and by the
normal current flow between the brush and the
commutator. The fact that a commutator surface is never
absolutely smooth, although it may feel so to the touch
and look so to the eye, enables the film to stick.
Normally, on a new or reconditioned commutator, the
brush begins to establish the film as soon as current
flows. It may take several hours or several days to
establish a good film. It is important to maintain this
film. Temperature, atmosphere and the grade of brush
used all affect this film. If the film is damaged
electrically or mechanically, both brush and
commutator wear are accelerated. Oil vapors have a
negative effect on film conditions. Not only does the oil
introduce an insulating surface, it also prevents bonding
of the film on the commutator and causes a torn or
mottled film surface. It will also promote rapid metal
transfer.
Some types of brushes establish a heavier film than
others depending on the brush grade. Some grades
require greater current densities [amperes per square
inch (cm
2
) average current] to establish and maintain a
satisfactory film.
Hyster Company selects and provides brush grade
suited to the application of the machine. Use the Hyster
approved parts. Do not mix or change the brush grade as
it could seriously affect the commutation, surface film
and brush life.
The importance of maintaining a proper commutator
surface film cannot be overemphasized. With this film
established and properly maintained good brush
performance (reduced brush and commutator wear) and
satisfactory commutation (no destructive sparking) is
ensured. Changes in color from copper to chocolate
brown should give no cause for worry as long as the
surface is smooth and has a polished appearance.
