MIL-HDBK-1038
On a bridge crane, the hoist holding, trolley, and bridge brakes are
required to have, as a minimum, the torque ratings required by CMAA #70. The
brakes may be either shoe or disc type.
5.4.1.2
Electrical Criteria for Brakes. On a portal crane, all electro-
mechanical brakes are required to be direct current type. Half of the travel
drive brakes, in each corner of the crane (if constant potential controls are
used), and, if there are two electro-mechanical brakes, one of the electro-
mechanical brakes in each hoist drive is required to release upon movement of the
drive's master switch handle from the OFF position and is required to be time
delayed in setting after the drive's master switch handle is returned to the OFF
position; all other brakes are required to be non-time delayed. The time delayed
setting of a brake is required to not involve motor control circuitry in any way
but is required to be achieved using a separate brake contactor, energized through
master switch contacts, and a resistance-capacitance (RC) network across the brake
coil, with resistance being adjustable so as to permit timed delay to be from 1 to
3 seconds. All non-time delayed brakes are required to be released upon movement
of the drive's master switch handle from the OFF position and, for hoist drives,
verification of motor current; they are required to be set when the motor(s) have
regeneratively slowed to the predetermined speed. In addition, all non-time
delayed brakes in a drive are required to be set upon loss of power to any motor
in that drive. A switch is required to be provided in the operator's cab to
energize the swing drive brakes at all times, except when power is lost.
When a hoist drive is equipped with a caliper disc brake system and an
electro-mechanical brake, the caliper disc brake system, is required to be
released after the electro-mechanical brake and to be time delayed in setting
during normal stopping.
On a bridge crane, when a hoist drive has more than one
electro-mechanical brake, one brake is required to set upon controller being
returned to off, the second brake is required to be time delayed by an adjustable
amount between 1 and 3 seconds. Bridge and trolley drive
electro-mechanical brakes are required to be set upon controller being returned to
off.
The torque rating of an electro-mechanical brake is for a specific period
of time based upon the brake coil's time rating. A brake is required to be
selected on the basis of its time rating corresponding with that of the associated
drive motor.
5.4.1.3
Mechanical Criteria for Clutches. A micro-drive consists of a motor,
gear reducer electro-mechanical brake, and magnetic friction type clutch or a
toothed-face coupling; it is used to achieve hook or wheel speeds of 2.0 feet per
minute or slower. The clutch permits engagement and disengagement of the micro-
drive from the input shaft of the primary (main) drive train.
The electrically operated, DC magnetic, dry running friction clutch is
required to have ample running clearance when disengaged and is required to be
rated at 150 percent or more of the main drive input torque. A clutch's time
rating corresponds to its coil's time rating. The clutch is required to be
totally enclosed and to be of the type specifically designed for heavy industrial
or steel mill
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