Page 44 - Wire Rope News & Sling Technology - April 2020
P. 44

         Denny’s                                   How Rope Slings and
         crane and
         crane and                                        I Have Changed
         rigging notes
         rigging notes

                                                               by Dennis J. O’Rourke, CSP

            et me take you back a few years to discuss sling changes.   failure. Even with no fitting applied, that would equal a 5 to 1
          LThree underlying causes for this evolution are reliability,   factor of safety. Today, the two-sides are cut off at the “crotch”
          handleability, and cost. OSHA, in 1971, left sling capacity   of the eye. A tapered steel sleeve is slipped over the crotch and
          up to the users. Tables listed; construction of rope, type of   crimped to hold the eye, to as much as 90% of the ropes break-
          Eye end connections, rope diameter, and how used (choker,   ing strength, keeping the ends locked.
          etc.) for the user to ponder capacity!               Back in the day, the two-sides were closed to the crotch;
           The picture below presents a poor rigging practice. The   the excess is pulled over the rope and re-laid together, form-
          “fold-back” Aluma-Grip fabricated splice forming the sling’s   ing a “pigtail.” Fig. 3. Wire rope clips were used to secure
          eye is unreliable (yellow arrow) and not recommended for   the live end to the pigtail dead-end, locking the eye just as
          hoisting, but still in use.                         the swaged fitting today. Thus, a rigger, on the tailgate of
                                                              his truck, in 15 minutes, could fabricate a completed “field
                                                              splice.” A thimble clip-on was available.
                                                               A field splice is a term I first heard around the Post Ko-
                                                              rean Wartime era. It meant precisely that. The sling, being
                                                              very adaptable, were used for many types of work – in the
                                                              “field.” A guy would form an eye in a wire rope, when and
                                                              where it was needed!
                                                               Those eyes were hand tuck, wire rope clips, wedged sock-
                                                              ets,  Flemish  eyes,  and pored zinc  spelter  sockets.  These
                                                              slings were used to pull equipment, haul logs, tie-down
                                                              trucks, and lift loads.

            Fig. 1

           Why? When fabricating a fold-back eye splice, 100% of the
          eye strength is dependent on the wall thickness of the fit-
          ting, and its clamping force. These non-steel fittings are soft-
          er, and when swaged, they are less likely to hold a uniform
          wall thickness,  thus strength. Examinations  show cracks,
          voids, and wall thickness to a sliver! This method is less ex-
          pensive but lacks reliability.
           The Flemish eye, Molly Hogan, or a Farmer’s eye – all syn-                                    Fig. 3
          onyms – are preferred, reliable. To construct, untwist (open)
          the rope with three strands on one side and three strands
          plus the core on the opposite. The loop develops (eye) when   We realized, there was little consistency of technique or any
          the “two-sides” are re-formed back together. A sling with a   quality control procedures in place. The resulting accidents
          thimble is shown in Fig. 2. Reliable is achieved when the   exposed numerous errors. Pulling a tree could tolerate some
          sleeve is swaged up to 300 tons pressure.           mistakes (perhaps), but deaths, lifting construction material,
           Tests show the frictional grip of the strands, under tension,   was unacceptable. Field-splice became a dirty word!
          will hold up to 22% of the breaking strength of the rope before   “The times they are a-changing boys.” And how! The build-
                                                              ing is faster, higher, heavier, and more costly. People in the
                                                              field  are  erecting  towers,  build  skyscrapers,  or  replacing
                                                              heat exchangers. It’s just too expensive to be sitting around,
                                                              whittling away on wood or forming make-shift eye splices
                                                              from used rope, ah, the good ole days.
                                                               So, the “certified sling” with a capacity tag attached to the
                                                              rope,  load  tested  to  150%  of  capacity,  and  the  quality  con-
                                                              trol program of the fabricator was born. (But the kids should
                                                              know, some of us could do it right – out in the field.)  WRNWRN
                                                               DENNIS J. O’ROURKE, CSP, is the Director of National Crane Services, Inc. He has over
                                                              fifty years’ experience in the industrial, maritime, and construction fields working with heavy
            Fig. 2                                            equipment and material handling devices. As a safety engineer, Mr. O’Rourke has developed
                                                              and/or presented over 300 safety-training programs for all representative elements of govern-
                                                              ment and industry. (
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