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 MIL-HDBK-1038
1.50 inch diameter.) The fitting manufacturer's provisions for the connecting pin
or pocket seat, as limited by the hole diameter, loop opening, or button diameter
is considered adequate if the intended pin, bolt, or seat design is used; and
stress analysis is not required.
5.3.13.3 Non-Permanent Wire Rope Retention Hardware. Wedge sockets, clips, and
clamps are used as non-permanent fittings on wire ropes. Wedge sockets are
standard commercial items designed for quick fastening of wire ropes in sizes up
to 2.00 inch diameter. The basket is cast steel, and the wedge is cast steel or
ductile cast iron. Properly made connections develop 75 to 80 percent of the wire
rope breaking strength and are used as terminal dead end connections on mobile
cranes. Wire rope clips are assemblies composed of a U-bolt, saddle, and two
nuts; or two threaded interlocking L-shaped fist grips and two nuts. The clips
are intended to grasp two parts of wire rope looped over a thimble. Sets of
clips, installed per manufacturer's directions, develop 80 percent to 90 percent
of the wire rope breaking strength. The U-bolt type is available for wire rope
sizes up to 3.50 inch diameter, and the fist grip type up to 1.50 inch diameter.
(Wire Rope Users Manual provides directions for the proper application of wire
rope clips and sizing of wire rope ends.) The clips should be used only in
accessible locations because they require periodic inspection and re-tightening as
the wire rope stretches and shrinks in diameter.
Clamps are used to secure wire rope dead ends to the drum. The spooling
of the wire rope on the drum is always required to provide at least two dead
(inactive) wraps ahead of the clamp when the hook is at floor or ground level.
Depending on whether the rope is clean/dry or greasy, two dead wraps reduce drum
line pull to 20 percent to 40 percent at the clamp. (The friction coefficients
are 0.120 and 0.070, respectively.) The short loop or another full wrap of wire
rope that is interposed between the two grooves of the clamp is not considered in
the analysis. The required clamping force is normally provided by a pair of bolts
threaded into the drum barrel, flange, or end plate. The bolts should not be
smaller than the wire rope diameter, should be torqued to obtain a solid clamping
grip, and lock wired to each other.
Regardless of the type of retention, the ends of the wire rope must be
seized with 8 to 10 wraps of low carbon steel wire.
5.3.14
Reeving Systems. With the exception of whip hoists, all hoists are
normally double reeved. Double reeved systems have an equalizing feature between
the two mirror image halves of the system to maintain equal loads on the wire rope
or ropes. Either an equalizer sheave or an equalizer bar, mounted in or adjacent
to the upper load block, is used for this purpose. With the equalizer bar the
option of using two wire ropes of opposite hand lay is available to avoid any
block rotation. The equalizer sheave or bar must be mounted in a pivoting bracket
or frame to keep it in line with the wire ropes as the reeving geometry changes
during hoisting and lowering. The orientation of the equalizer sheave or bar
should be at right angle to the running sheaves. (Some older cranes have the
equalizer sheave on the same pin parallel with the running sheaves. This
arrangement requires one loop of the wire rope to be twisted to form a cross-over.
The direction of the twist must be in the direction of countering the inherent
block rotation.)
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