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 MIL-HDBK-1038
Where
K = 1.00 plus percentage increase in the line pull to overcome the sheave
1.02; for sheaves on bronze bushings, K is taken as 1.05. Sheave pitch
diameters and wire rope construction are not considered.
S = number of running sheaves in the reeving system, including deflector
sheaves that bend the wire rope 45 degrees or more.
The wire rope design factor is defined as the ratio of the nominal
breaking strength of the wire rope and the drum line pull, and must be 5.00 or
greater for 6x37 class of wire ropes. For non-rotating and spin-resistant wire
ropes, used on whip hoists, the design factor must be 8.00 or greater.
5.3.13.2 Wire Rope End Fittings. There are two types of end fittings that are
permanently bonded to the wire rope swaged and poured. Swaged fittings are
forged from mild carbon steel and are available for standard wire rope sizes up to
2.50 inch diameter. They are installed with special hydraulic equipment, normally
provided by the swaged fitting manufacturer, that squeezes the fitting and causes
the fitting metal to cold-flow into the exterior crevices of the wire rope. The
bond that is formed is equal to 100 percent of the wire rope breaking strength.
Swaged fittings are recommended for all wire ropes with an independent wire rope
core. Wire ropes with a fiber core, and subjected to the full wire rope pull,
must have the core segment inside the fitting replaced with a matching piece of
wire rope, strand, or mild steel rod to obtain a bond equal to the breaking
strength of the wire rope. Otherwise, if the fiber core inside the fitting is not
replaced, the strength of the connection must be taken as no more than 90 percent
of the wire rope breaking strength.
Poured sockets have a conical cavity into which the end of the wire rope
is inserted, broomed to separate individual wires, cleaned and acid etched, and
filled with molten zinc to fuse with the wires. (The fiber core, if present, must
be cut out in this section of the wire rope.) The established procedure for zinc
speltering must be carefully followed to obtain the proper bond without annealing
the wires. A properly made zinc speltered socket connection is equal to 100
percent of the wire rope breaking strength. (Babbitt metal and lead are
prohibited for speltered socketing. The strength of such connections is only a
fraction - often as low as 1/4 of the wire rope breaking strength.) It should
be noted that the zinc cone does not have to fuse with the socket cavity and may
shift (rotate) slightly before it seats permanently with use. Resin compounds,
developing connections equal to 100 percent of the wire rope breaking strength,
are also available and may be used for poured sockets. Resin compounds have a
limited shelf life, and must not be used after expiration of that date. Cast
steel poured sockets are made for standard wire rope sizes up to 4.00 inch
diameter. Forged steel poured sockets are also available for wire rope sizes up
to 2.375 inch diameter.
The style of the connecting end of the fittings may be open (in the form
of a clevis with drilled holes), closed (in the form of an eye or an as-cast
loop), or button (plain cylinder). The connecting pin of the closed style must be
closely fitted to the loop opening to minimize the bending stress in the loop.
Ferrule (button) fittings are intended to be inserted into pockets in structural
or mechanical components. (Ferrule fittings are available for wire ropes only up
to
153
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