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 MIL-HDBK-1038
4.3.6.17 Wire Rope End Fittings. For wire ropes with ends anchored on the drum
and with two or more intervening dead wraps, only a portion of the wire rope pull
is applied to the fittings. With that reduced loading, two-bolt clamps are
adequate to anchor the wire rope dead ends. On terminal connections, where the
full wire rope pull is imposed on the fitting, the fittings should be swaged or
poured type. Swaged fittings should be selected and installed per the fitting
manufacturer's recommendations. The swaging process uses high pressures on the
outer surface of the fitting sleeve to deform it and force the material on its
inner surface to flow in between the external wires of the wire rope. This
connection is considered to develop the full breaking strength of the wire ropes
with a wire rope core. (Wire ropes with a fiber core must have the end section of
the fiber core replaced with a piece of wire rope or a steel rod.) Poured
(speltered) fittings are made with zinc, following precise cleaning and heating
procedures which are normally established by the local crane engineering
organization. The speltering process requires the molten zinc to fuse with the
wires of the broomed (opened) end of the wire rope. The external shape of the
zinc lump takes the form of, and seats in, the conical cavity of the fitting.
Swaged and speltered fittings are available in the forms of a ferrule (a
straight cylinder) for insertion into an anchor pocket, closed sockets (with a bow
for a loose-fitting pin connection), and open sockets (with two cheek plates bored
for a close-fitting pin connection). The closed type sockets, because of their
complex shape, are always cast. The open type sockets may be cast or forged in
the smaller sizes and cast in the larger sizes.
In recent years resin socketing compounds have become available for
poured fittings. The resin socketing process involves the mixing of two
substances at ambient temperature and pouring the mix over the broomed end of the
wire rope in the socket cavity. The process is simpler and more controllable than
zinc speltering and may be used in all crane applications. The producers of resin
socketing compounds provide details of the socketing process for their particular
products. Wire Rope Users Manual contains a comprehensive description of wire
rope end fittings and their installation. Navy activities that do not have
standard internal procedures for installing speltered fittings, should follow the
recommended procedure of the manual.
4.3.6.18 Hook Blocks. The typical arrangement of hook blocks on double reeved
systems has two symmetrical sets of sheaves mounted on a common pin. The hook is
positioned in the center on a separate pin (trunnion) for capacities over 15 tons
or, for lesser capacities, the sheaves may be mounted on the ends of the hook
trunnion. Each sheave rotates on its own bearings, while the trunnion pivots in
the cheek plates. All sheaves are completely covered except for wire rope
openings. If the sheave bearings require lubrication, the sheave pin (or
trunnion) is drilled from both ends for lubrication passages and fitted with
recessed grease fittings. The hook is supported by and rotates on a thrust
bearing mounted on the trunnion. The hook is installed so that it cannot
inadvertently come loose from its nut but can be easily removed for inspection.
The weight of the hook block must be adequate to overhaul the reeving system and
keep the wire ropes tight. All hook block components in the load path are steel.
Single part (whip hoist) hook blocks have an overhaul ball or cylinder connected
directly to the end of the wire rope with provisions for mounting the hook
underneath. Normally an intermediate swivel fitting is installed above the hook
to permit it to be turned without twisting the wire rope. When the overhaul ball
or cylinder is a separate, non-load-bearing component, it may be made of cast
iron.
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