Quantcast Mechanical Criteria for Brakes -Cont.

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MIL-HDBK-1038
If a caliper disc brake system is provided on the wire rope drum, only one
electro-mechanical brake, rated at 150 percent of rated motor torque (minimum), is
required.  Hoist drive brakes are required to be adjustable down to 50 percent of
their torque ratings by reducing the tension of the spring which serves as the
brake's setting mechanism.  Electro-mechanical shoe brakes are sized and designed
in accordance with the applicable requirements of NEMA Standards Publication No.
ICS 9 and of AISE Standard No. 11; both documents only address shoe brakes having
wheel diameters of 8 inches or larger.  Magnet operated shoe brakes are available
with wheels having diameters from 8 inches to 30 inches.  Solenoid operated shoe
brakes are available with wheels having diameters from 4 to 8 inches.  Electro-
mechanical shoe brakes, except brake wheels, are required to be of all steel
construction; including shoes, shoe levers, armatures, pull rods, torque springs,
bases, etc.  Brake wheels may be steel, ductile cast iron, or gray cast iron.
Electro-mechanical brake shoe or pad linings are required to be of a non-asbestos
material.
The hoist drives on portal, floating, and other cranes with operator's
cabs on the same structure as the hoist, may include a foot operated hydraulic
hoist brake in addition to the other brakes for speed modulation if their electric
drives are load sensitive.  Alternatively, instead of an independent hydraulic
brake, an electro-mechanical brake may be equipped with an integral hydraulic
system for over-riding the electrical release and applying the brake.  Each hoist
brake is required to be rated at 130 percent of rated motor torque (minimum).
Hydraulic brakes, when used, are required to be capable of applying 130 percent of
rated motor torque based on an operator applied foot pedal force of 60 pounds.
One electro-mechanical shoe or disc brake, rated at 100 percent of rated
motor torque (minimum), is required to be provided for each travel drive mechanism
and for each rotate drive mechanism on a portal crane.  Electro-mechanical disc
brakes are sized and designed in accordance with the applicable requirements of
NEMA Standard Publication No. ICS 9; their selection is required to be based upon
these ratings.  Travel drive and rotate drive brakes are required to each be
adjustable down to 50 percent of their torque rating by reducing the tension of
the springs which serve as the brake's setting mechanism.
On portal and floating cranes with load sensitive electric drives or
drives with a drift point, each rotate drive mechanism is also required to be
provided with a spring released, hydraulically applied, shoe type brake.  Each
rotate drive brake is required to be rated at 100 percent of rated motor torque
(minimum).  Hydraulic brakes, when used, are required to be capable of applying
100 percent of rated motor torque based on an operator applied foot pedal force of
60 pounds.
Certain hoist wire rope drums are required to be provided with a fail-
safe caliper disc brake system.  The brake controls are required to employ a
failure detection system to set the disc brake mechanism whenever there is a 5
percent change in the ratio of drum shaft to motor shaft speeds.  The disc brake
mechanism is required to have a torque rating of not less than 150 percent of
rated hoisting torque at the point of application; however, the energy which would
have to be absorbed, with no contribution from the other brake in the drive train,
and dissipated during an emergency stop is also required to be taken into
consideration.  All metal components are required to be steel with the exception
of the brake housing, which may be gray or ductile cast iron.  The brake pads are
required to be a non-asbestos material.
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