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 MIL-HDBK-1038
groove offsets and end ramps/steps to establish orderly spooling. The wire rope
spools in parallel wraps for nearly half a circumference, shifts laterally half a
pitch, again spools parallel for nearly half a circumference, and again shifts
laterally half a pitch next to the start of its wrap. The wire rope builds up
higher and wears more rapidly at the offsets (cross-overs) than on the parallel
spooled sections. It is also normal to see some sparking or smoking at the
offsets because of the wire to wire rubbing as the spooling wrap is forced to
shift and cross over an offset of a previous layer.
On custom designed drums, tapped holes for installation of wire rope
clamps are normally provided at the ends of the drum barrel. Alternatively,
reinforced pockets are provided in the drum barrel or the end plates for anchoring
wire rope fittings. Design details of end plates with integral stub shafts must
be analyzed to ensure that the heavy loads do not cause buckling of the end
plates. On standard commercial hoists it is not practical to change anchoring
features on drum.
4.3.6.16 Wire Ropes. Federal Specification RR-W-410 and Wire Rope Users Manual
are accepted by the wire rope manufacturing industry as its standards. These two
standards prescribe acceptance criteria for all types of wire rope used on cranes,
including stationary applications.
Wire ropes are available with either right-hand or left-hand helix,
regular lay or lang lay, and spin-resistant construction. Right-hand regular lay
is the most prevalent and most readily available construction. It is used on all
double reeved systems, except when the hook block must have absolutely no tendency
to rotate under load. When hook block rotation is unacceptable, the double reeved
systems should have opposite-hand wire ropes installed and equalized at an
equalizer bar. (A one-piece double reeved system, even with spin-resistant wire
rope, cannot ensure against some block rotation under a heavy load.)
Wire ropes are assembled from strands, which in turn are assembled from
individual wires. The strands are twisted around a central core of either an
independent fiber, wire strand, or wire rope. Both the strands and the wires are
pre-formed to eliminate their tendency to untwist if the ends are not clamped.
Right regular lay wire rope has the strands twisted in a right-hand helix, and the
wires within the strands in a left-hand helix. Left regular lay wire rope has the
helixes twisted in the opposite directions. When assembled in this fashion, the
wires exposed on the wire rope exterior are aligned parallel with the wire rope
axis. Lang lay wire ropes, whether right or left, have the strand and wire
helixes in the same direction. Lang lay wire ropes are more flexible but subject
to more rotation under load than their regular lay counterparts.
Spin-resistant wire ropes (also called rotation resistant and non-
rotating) are characterized by an outer ring of strands twisted in one direction,
and an inner ring of stands twisted in the opposite direction. There are also
proprietary constructions with additional refinements to better equalize the
opposite torques developed by the outer and inner groups of strands. This class
of ropes is used on whip hoists (with single line hook block and long lifts) to
minimize the tendency of the hook block to rotate under load. As a further
precaution against rotation, higher design factors (usually 8:1) are prescribed
for these wire ropes. (Some mobile crane manufacturers use spin-resistant wire
ropes with multiple-reeved hoists. In such cases, a design factor of 5:1 is
used.)
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