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MIL-HDBK-1038
hardnesses up to 615 BHN.  Smaller wheels are machined from round bar stock.
Flange heights are approximately 1 inch and if the wheels are required to cross
rail head gaps at frogs or track switches, the flanges must be designed to carry
the full wheel load.  The flange interior angle (of approximately 12 degrees) is
slightly wider than the rail head angle and the fillet radius between the tread
and the flange is slightly less than the corner radius of the rail head.  Other
details of the wheel tread are adjusted to accommodate the site conditions.  Idler
wheels are pressed onto the rotating axles; the drive wheels are additionally
keyed to the axles.  Paired drive wheels, such as those on A-1 and A-5 bridge
drives, and those driven by an idler gear in portal crane travel trucks, must have
their tread diameters matched to 0.001 inch per inch of diameter but not to exceed
0.010 inch.
Idler wheels of roller path assemblies are relatively small and are
usually machined from steel bar stock.  They rotate on bushings and fixed axles.
Since these wheels are closely spaced and are intended to share the load imposed
on either quadrant of the roller path, their tread diameters must be held to 0.001
inch per inch of diameter.
Wheels that operate on patented track are part of the standard commercial
carrier yokes and drive heads. They are single flanged or, if their carrier yokes
or drive heads are equipped with side guide rollers, flangeless.  The driven
wheels of the drive heads have extended flanges with gear teeth cut into their
circumference.  Cast or forged steel wheels are preferred, but cast iron wheels
and wheels stamped out of steel sheet may be used when approved by NCC.  These
wheels rotate on stationary cantilevered pins and bearings.  The bearings are
either permanently lubricated and sealed, or the pins have provisions for grease
lubrication of the bearings.
4.3.6.15 Wire Rope Drums.  Wire rope drums of built-up hoists are always custom
designed.  Drums on older cranes are usually cast, together with the end plates
and reinforcing gussets.  On newer cranes, the drums are welded either entirely
from steel plate or a combination of steel plate, steel pipe, and steel castings.
The drums are subjected to the highest torque of the hoist assembly, and the
larger the hoist capacity, the more likely that it will have a drum gear as the
last connection to its drive train.  With the exception of whip hoists, all custom
designed drums are grooved with two opposite-hand helixes; and with rare
exceptions, the drums are sized to spool all wire rope in one layer.  Single-
reeved standard commercial packaged hoists may have single-helix grooved or smooth
drums and may spool their wire ropes in multiple layers.  On single-reeved
packaged hoists, with one part of the wire rope winding/unwinding from the drum
and going directly to the hook block, the hook is forced to shift its position
horizontally during vertical travel.  On mobile cranes and whip hoists, the hook
positions do not shift because the wire rope winding/unwinding from the drum is
routed to a fixed (non-shifting) sheave before it goes to the hook block.  In the
case of mobile cranes, the drums are smooth (ungrooved) and, because of space
restrictions, spool the wire rope in many layers.  The spooling, even with various
proprietary guiding devices, is often disordered causing accelerated wear and
somewhat erratic hook travel.
When spooling of wire rope in multiple layers cannot be avoided on custom
designed drums, the spooling can be kept uniform and orderly by installing
parallel grooved half-shells (Lebus lagging) on a smooth drum.  The half-shells
are steel castings, which are welded or bolted to the drum, and include half-pitch
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