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Kasum, Emil (ed.) / The Wisconsin engineer
Volume 52, Number 1 (October 1947)

Tanghe, J.
Electric braking,   pp. 14-15


Page 14


Electric
ENGINEERS have long strived to develop a simple,
    yet flexible, method for coupling prime movers to
industrial machinery and equipment. In many instances
the clutches and brakes needed to accomplish this task
have been highly intricate and costly. Since the war, how-
ever, a new type of electromagnetic clutch has been per-
fected which promises to greatly simplify the problem of
transmission and control of driving torque.
  Previously most magnetic coupling devices consisted of
a solenoid, plunger and cams connected through levers to
a band-type friction brake. The new unit is much simpler
and has only two principal parts-a flat circular electro-
magnet and a disc-type armature of the same diameter
against which the pull of the magnet is applied.
  The operation and theory of this clutch is relatively
simple. The friction needed to engage any two shafts or
members is supplied directly by the pull of the large-
diameter energized coil against the flat, rotating surface
of the armature, the magnetic attraction greatly amplify-
ing the normal coefficient of friction. If the unit is to be
used as a clutch, both armature and magnet are free to
rotate on their respective shafts-current is then fed to the
Electric Clutch Assembly
                 Electric Clutch Exploded
magnet through slip-rings. If the unit is to be used as a
brake or retarder, the magnet is bolted down and the
armature is mounted on the rotating member. Obviously
combined brake and clutch action may be obtained simul-
taneously by using both types.
  The magnet is shaped like one-half of a large metal
doughnut cut lengthwise. The coil which carries the cur-
rent is secured in the shell of the "half-doughnut" by a
mixture of sand and glyptol solidified by baking. Twenty-
five watts of direct current is the average power required
to operate the magnet on full application.
  The armature is made up of segmented steel sections
which together form a flat circular ring having approxi-
mately the same inner and outer diameters as the magnet
itself. A slight spring tension assures that magnet and
armature surfaces ride in light contact with each other at
all times. Since static torque ratings are several times those
of running torques there is no possibility of the clutch
slipping after the magnet and armature have "locked in."
  What advantages are presented by the new electric unit
over other clutch and brake types? Primarily this unit is
unique in its simplicity and compactness, the results of
which are low initial and operating costs, minimum instal-
THE WISCONSIN ENGINEER
14


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