[WRE UPDATE | ADVISOR]
Photo courtesy of Barnhart Crane and Rigging
Photo courtesy of Westech Rigging
cutting or friction damage to synthetic slings, often much quicker than with wire rope slings. A disadvantage with synthetic rope slings is their required D/d ratio in the spliced eye—minimum 2, based on component rope diameter—as opposed to a minimum of 1 with wire rope slings. With the natural torque of a wire rope sling, it would be inadvisable to connect a synthetic rope sling to a wire rope sling in-line, cautions Parnell. T e torque of the wire rope would likely overpower the synthetic sling and cause severe imbalance and loss of strength. Depending on the splice type, torsion can cause a splice to roll out and lose the eye. Even high-capacity pulling slings for the oil/gas and mining industries are making headway in certain regions. Tests are now being conducted to determine whether synthetic ropes may be suitable for hoisting work. T ey may eventually be considered a viable running rope choice for tower cranes, which off er a relatively clean spooling and reeving system.
THE MISSING LINK Wire rope slings and nylon or synthetic slings all have diff erent properties, and Tom Wynn, owner of Peerless Chain in Winona, Minnesota, sees the merits in each depending on the application. “For example, a synthetic sling is especially good if you don’t want to run the risk of marring whatever you’re lifting. For a brass cylinder, synthetic would be a good medium with which to lift. On the other hand, synthetics are subject to UV degradation as well as have a tendency to cut and fray much more easily than say a chain, which will resist nicks and cuts much better.” Wire rope slings have their place as well. T ey are cost eff ective, relatively easy to use and for the most part lighter than chain. T ey resist wear somewhat better than synthetics but not as well as chain in addition to being widely available, according to Wynn. Wynn adds, “T ere has been a lot more advanced technology on the synthetic side than with any of the others as they come up with new types of materials and more technical advancements. But I wouldn’t want to use synthetics around a foundry where there would be sparks or fl ames. While Wynn admits that chain is heavier and costlier, he adds one more critical feature. “Chain is fl exible, resistant to wear and it is ductile and elastic; it will give you a visible sign
76 NOVEMBER-DECEMBER 2013 WIRE ROPE EXCHANGE
it is overloaded, stretching anywhere from 15-20%, before it will break. A user can look at a chain and realize it’s been overloaded due to how much it’s stretched.” With a wire rope or synthetic sling, you don’t get a visible sign of such a sling being overloaded.
CALCULATED CHOICE While each type of rope has distinctive advantages for specifi c industries and jobs, neither one can fully replace the other in the lifting world. Indeed, the two materials appear to be coexisting quite well in a variety of settings. While certain industries are reaping the benefi ts of either steel or synthetic rope application, others are seeing success with a combined approach. “T ere are plenty of job sites out there where you need both synthetic rope and wire,” Carlson notes, “especially in a lot of industrial applications.” Marterella concurs, adding “I would think any of the domestic wire rope manufacturers would be hard-pressed to deny that they’re not working on some combination of those types of products such as in deep shaft mining applications, elevators and other settings. Adding chain to the equation, Wynn also notes that “each one has its place and most of the distributors we deal with will sell and manufacture all three - chain, synthetic and wire rope slings. Every type of material has its pluses and minuses.” It goes without saying that the question of steel versus synthetic begs the answer, “it depends,” and consideration of environment, cost, weight, load, and availability all combine to determine the best material for its intended use. As Parnell concludes, “Our entire training/technical staff
made a recent trip to a manufacturer’s site for more education on design, application and inspection criteria associated with synthetic ropes. Nearly all of our staff has toured a wire rope manufacturer’s facility over their working career as well. New designs and materials continue to drive forward the options both product types off er, and staying educated about their assets and liabilities is critical as our industry moves forward.” With the constant research and development of new
products and applications ongoing both within and benefi tting the lifting and rigging industry, one thing is for certain - what one considers the best options today may be drastically diff erent tomorrow. ❙
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