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 MIL-HDBK-1038
assemblies and all their components are designed in accordance with the mechanical
design criteria and other unique criteria as they apply.
4.2.6.1
Bent Rail Roller Paths. The bent rail segments are spliced at the webs
with two or three bolts per side and have their bottom flanges secured to the
support structure either with standard rail clips or with through bolts. The rail
flanges must be held tightly against the support structure because they have a
tendency to warp out of the horizontal plane. The bull gear is a separate
assembly of cast segments with machined gear teeth or plate steel segments with
flame cut gear teeth. The bull gear segments are accurately arranged in a circle
centered on the center steadiment. The roller cage is completely freely-rotating,
without any provisions for centering on the center steadiment. The rollers have
straight cylindrical treads and are double-flanged. If the upper rail path is a
full circle, a short, easily removable rail section must be included in the lower
rail circle for the extraction of individual rollers.
4.2.6.2
Cast Rail Roller Paths. With cast rail roller paths, the bull gear may
be separate or integral with the rail segments. The gear teeth and the running
surfaces are machined. The running surfaces may be machined flat (for straight
cylindrical, double-flanged rollers) or conical (for tapered, flangeless rollers).
The corners of the flat surfaced segments are chamfered and the sides are machined
to match the profile of the double-flanged rollers. As in the case of bent rail
roller paths, the rollers are mounted in a completely free-floating roller cage.
Segments with conical surfaces need to be machined only on top, but the cone angle
must match exactly the taper of the rollers. The angles of the conical running
surfaces are selected to eliminate any slippage along the roller-roller path line
of contact.
The conical running surfaces impose an outward radical force on the
rollers, which is taken up by a spider assembly of radial spokes inside the roller
cage. The inner ends of the spokes are secured to a hub, which is centered by,
and rotates on, either section of the center steadiment. The spokes and the
roller cage are designed to permit accurate adjustment of axial position (for load
sharing) of individual rollers within their pockets. The hub has a bushing with
provisions for grease lubrication.
4.2.6.3
Rollers. Rollers are sized for the maximum load that may be applied to
any roller within the rated operating range of the crane. The maximum roller load
is calculated by the method described in paragraph 5.2.6.1. The diameters of
rollers with straight cylindrical treads must be uniform within close tolerances
to ensure proper load sharing among the rollers. The tapered rollers must be
machined with tight tolerances on the taper to ensure full contact with the roller
path running surfaces, and other tolerances adequate to provide the required
adjustment range in the roller cage pockets. Tapered rollers must be equipped
with thrust washers designed to carry the outward radial force imposed on them.
All rollers are required to turn on grease lubricated bushings, and tapered roller
thrust washers are required to have independent grease lubrication.
4.2.6.4
Roller Path Mounting. The mounting surfaces for the lower rail circle
and the front and back quadrants of the upper rail circles require uniform, rigid
structural support. The interface with the rail segment webs must accommodate
closely spaced, tack welded shims for accurate alignment of the running surfaces.
Alternatively, rail segment webs may be set in a poured bed of epoxy resin
compound formulated for such applications. All details of the compound
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