Quantcast Hot (Molten) Metal Service -Cont.

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MIL-HDBK-1038
a)
OET cranes are required to be CMAA #70, Class E or F.
b)
Underrunning cranes are required to be CMAA #74, Class D.
c)
Standard commercial hoist/trolley units are required to be ANSI/ASME
HST-4M, Duty Class H-4.
d)
Operator's cab is required to be enclosed, air conditioned, and
shielded underneath the floor.  The shield must be effective in preventing injury
to the operator from spill, splash, or radiant heat of the molten metal.  A 1/4-
inch steel plate, of the same shape as the floor and suspended 6 inches below it
to provide a fully vented space, is considered acceptable for this purpose.
e)
The pendent pushbutton station should be mounted on a messenger
track or an outrigger away from the hook load.
f)
Heavy sheet metal heat shields are required underneath the trolley
or hoist/trolley unit, and below the load block.
g)
The trolley frame of the hoist/trolley unit is required to include
safety lugs that would limit its drop to 1.0 inch in case of failure of any
component.
h)
Structural and mechanical assemblies and components, whose bolts or
other fasteners are subjected to tensile stress due to the hook load, must include
some means to limit their drop (in case of failure) to 1.0 inch.  (If the bolts or
other fasteners are subjected to mainly shear stress, the drop-limiting feature is
not required.)
i)
Hoists are required to have two braking means; either in the form of
two electro-mechanical holding brakes (each rated at 100 percent of the rated load
hoisting torque), or one holding brake (rated at 150 percent of the rated motor
torque) and a mechanical load brake or, in case of a hoist with a wound rotor
motor, an eddy-current brake.  The eddy-current brake is considered an acceptable
braking means only if resistors (not saturable reactors) are utilized in the rotor
circuit of the hoist motor.  Disc brakes are acceptable, but they should be of the
DC magnet, self-adjusting, type.
j)
Wire rope must be selected to provide a minimum design factor of 8.0
and they must have an independent wire rope core.  Dead end connections that are
subjected to the full wire rope pull must be zinc speltered or swaged fittings
that develop the breaking strength of the wire rope.
k)
A hoist load limit switch, which activates audible and visual
alarms, is required.  The Belleville spring type is recommended.
l)
Electric motors are required to have Class H insulation.
m)
Electrical conductors are required to have high-heat insulation,
selected from the types listed in NEC Table 610-14(a) for
125-degrees Centigrade temperature rating and derated for the appropriate ambient
temperature.
n)
Electrical enclosures are required to be NEMA Type 3 or 12.
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