The use of multi-part braided slings appears to be returning to the marketplace. In the fabrication of these slings, generally a single wire rope is braided or helically laid back against its own body to form an eye & eye sling. By design it allows the sling to have the relative bendability of the component wire rope plus a high strength value based on the sum of its parts. The number of component wire ropes in a multi-part sling could be as many as nine or as few as three.
One area in which to use multi-part braided slings is the “super heavyweight” category. A lift may require a sling capacity that cannot be achieved by a single part sling, but can be reached by braiding small component wire ropes together into an eye & eye sling configuration.
Example: A 4” single part, swaged E/E sling in a basket has a rated capacity of 226 tons. The same amount can be lifted by using a 7-part, 1-5/8” multi-part sling in a basket hitch.
A second and more common reason for selecting multi-part slings is their bendability. If a sling is bent around too small a diameter while making its lift, there is a reduction in lifting efficiency. A ratio has been developed to help determine minimum allowable bending diameter for slings.
Example: A 10” horizontal steel shaft is the lifting attachment for a pre-fabricated structure. Weight is 18 tons. (It is determined a wire rope sling is the best type of sling for this application.)
Options:
a) 1-1/8” single part, swaged E/E in a basket hitch will meet the 18 ton requirement; however the 10” steel shaft is too small for 1-1/8” wire rope when applied to D/d ratio. (The standard minimum bending diameter for 1-1/8” wire rope sling is 22½”.)
b) 6 parts of ½” component wire rope braided E/E in a basket hitch will also meet the 18 ton requirement: the standard minimum bending diameter for ½” wire rope is 10”. (This would be an ideal choice for this application.)
Learn more about D/d Ratio and other rigging applications with ITI Rigging Training programs.
This article was written by Mike Parnell, President of Industrial Training International, and can be found at The Pro Rigger.
This is the workshop from The Professional Rigger newsletter, circa 1986. To download this issue of The Professional Rigger, click here.
