Brake motors are motors equipped
with electrically controlled brakes as an integral part of the motor
assembly. The brake motor manufactured by one company consists of one
or more rotating steel disks splined on a pinion on the motor shaft,
with stationary friction linings on each side of each disk.
A helical spring in the center applies
pressure to provide the required braking, and two, three, or four
magnets, depending on the rating of the brake, supply force to
compress the spring and release the brake while the motor is running.
When power is applied to the motor, the
brake is immediately energized, since the brake leads are connected
directly to the motor leads in the conduit box. The current energizes
the magnets, which pull the armature plate toward the end plate.
This action removes the pressure on the
revolving disks and allows them to move freely between the friction
linings, releasing the brake. Since the rotating disks are separated
from the friction surfaces at all times except during actual braking,
the motor delivers full rated horsepower at the output shaft.
When the motor is disconnected from the
power supply, the magnets are immediately deenergized, and the spring
pushes the armature plate away from the adjustable plate toward the
motor. This applies braking pressure on the surfaces between the
revolving disks and the friction linings, bringing the motor to a
quick, smooth stop.
This inherent smooth action, free from
hammer blow, keeps stresses at the minimum in the brake and in belts,
cables, gears, or chains through which the motor drives.
Gear motors are motors equipped
with a built-in reduction gear as an integral part of the motor
assembly. The motor itself is generally a 60-Hz, nominal 1750-rpm
machine. Output-shaft speeds between 4 and 1430 rpm are available.
These motors can be obtained equipped with almost any type of
general-purpose polyphase induction, singlephase, or dc motor.
Loads of the same horsepower and speed
rating will require different gear sizes, depending upon the type of
load. Therefore, time of operation and frequency and severity of
shock must be determined to select the proper gear motor for a
specific application.
To assist engineers in their selection,
the American Gear Manufacturers Association (AGMA) has defined three
classes of service, according to the degree to which all these
variables are present:
Class I. Steady loads not exceeding the
normal rating of the motor on 8-h-per-day service or moderate shock
loads if service is intermittent.
Class II. Steady loads not exceeding
the normal rating of the motor on 24-h-per-day service or moderate
shock loads running 8 h per day.
Class III. Moderate shock loads on
24-h-per-day service or heavy shock loads running 8 h per day.
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