| Introduction
to Wire Rope Slings |
•
Care and Use of Wire Rope Slings
• Rated Capacities of Wire Rope Slings
Wire
rope slings are a basic material handling tool and are the most
frequently used type of sling in industry today. They offer a strong,
dependable and economical option for most lifting applications.
Their popularity is enhanced by the numerous sling configurations
available to support a broad range of applications. These configurations
include single and multi-part slings (such as round braids, flat
braids, Tri-Flex and cable laid slings), grommets, single leg slings,
multiple leg bridles, and a wide variety of fittings and attachments.
A mechanical (or flemish)
splice sling is most
frequently used and is fabricated by unlaying the rope body into
two parts, one having three strands, the other having the remaining
three strands and core. The rope is unlayed far enough back to allow
the eye to be formed by looping one part in one direction and the
other part in the opposite direction and laying the rope back together.
The strands are rolled back around the rope body and a metal sleeve
is slipped over the ends and pressed (or swaged) to secure the ends
to the sling body. A hydraulic swaging press with special dies is
used to bond the sleeve in place. Extreme pressure forces the steel
sleeve to flow into the voids between the wires and strands, creating
an assembly that maintains most of the wire rope's nominal breaking
strength.
Single, double, triple and quad leg
slings can be designed and fabricated within close
tolerances to desired specifications. For safety purposes, it is
essential that all fittings and attachments carry a rated capacity
equal to or greater than that of the wire rope sling. In cases where
this is not possible, the rated capacity of the entire assembly
must be downgraded to the weakest component. In addition to the
basic slings described above, cable laid slings, 8-part braids,
Tri-Flex and hand tucked slings may be selected for their distinctive
characteristics.
Cable Laid slings
are fabricated from a rope comprised of 7 small wire ropes. This
construction creates a very pliable sling and is used where flexibility
and resistance to kinking are more important than resistance to
abrasion. Since the rope is made up of many smaller wire ropes,
the sling can bend around smaller diameters without taking a permanent
set or kink. The small wires, however, are susceptible to abrasion.
8-part braided slings
are fabricated from 8 pieces of smaller diameter wire ropes, braided
together to form one large sling. They are commonly used for high
capacity lifts, can be either flat or round, snug tightly to a load
in a choker hitch, resist kinking and offer the ultimate in flexibility
and versatility.
Tri-Flex slings are
developed from three parts of wire rope to provide high strength
combined with greater flexibility. They were created to replace
large diameter, single-part wire rope slings that had awkward, stiff
handling characteristics. Individual Tri-Flex slings can be temporarily
combined to form a Tri-Flex system for high capacity lifts, then
easily taken apart for regular use.
A hand tucked splice is created by forming
an eye and "tucking" and "locking" a strand
of the wire rope under other adjacent strands. Although not as strong
as mechanically spliced slings, the absence of steel sleeves allows
this sling to be easily removed from underneath loads. Caution must
be exercised, however, as hand tucked splices may unravel if the
sling rotates during use.
Relative to other types of slings, wire rope slings are average
in strength/weight ratio, average in abrasion and cut resistance,
poorest in elongation and flexibility, and average for high temperatures
(IWRC only).
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