Introduction to 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).