MIL-HDBK-1038
pitch and two bolts between them. The bolts are installed into tapped holes in
the drum barrel, torqued sufficiently to obtain solid clamping of the wire rope
wraps, and lock wired. Alternatively, the wire rope segment between the clamp
grooves may be bent back at the clamp instead of making a full wrap. Pockets for
end fittings are shaped in the form of a key hole and the larger end is closed
with a pipe plug or similar fashion to preclude dislodging of the end fitting.
The anchor points may also be located on the drum flanges end plates and
the wire rope dead ends anchored as described above or with minor variations.
However, anchoring by means of wedge sockets is prohibited on custom designed
drums.
5.3.13
Wire Ropes. Hoist wire ropes may be improved, extra-improved, or extra-
extra-improved plow steel, bright (uncoated, non-galvanized), pre-formed, regular
lay, with an independent wire rope core, of 6x37 classification, and comply with
Federal Specification RR-W-410 or Wire Rope Users Manual. Proprietary wire ropes
may be used only with the approval of NCC.
With grooved drums, the hand of the lay is of no importance, but right-
hand lay is more readily available and is normally provided. Wire ropes in the
6x37 class have an inherent tendency to untwist under load. This condition is
evident in the small amount of rotation of the lower hoist (hook) block and is
acceptable as long as the parts of line (between the upper and lower hoist blocks)
do not twist up. If lower hoist block rotation cannot be tolerated in a specific
application, the double reeved system must use two wire ropes with opposite-hand
lays anchored to an equalizer bar.
5.3.13.1 Size Selection. Wire ropes are selected on the basis of the drum line
pull (which occurs at the drum during hoisting) calculated as described below to
account for the friction and bending losses at the sheaves:
EQUATION
P = W/NE
(9)
Where
P
=
drum line pull (in pounds)
W
=
total weight supported (in pounds)
N
=
number of parts of line supporting the load
E
=
reeving system efficiency
The reeving system efficiency E is calculated as follows:
(KN 1.00)
EQUATION
for single reeved systems
(10)
E=
N (KS) (K-1.00)
and
2(KN/2
EQUATION
- 1.00) for double reeved systems
(11)
E=
N(KS/2) (K-1.00)
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