Page 10 - Wire Rope News & Sling Technology - February 2020
P. 10

continued from page 8              spooling on the rope drums. The direc-
         ASME) is a consensus committee. This   tion of the lay left/right is to oppose the
         committee conducts the decision-mak-  direction of “fleeting” of the first layer
         ing  with  group  members that repre-  on the drum to reduce gaps in wraps.
         sent  the  stakeholders.  The  committee   Because of modern grooved drums, this
         also interviews “source experts,” which   feature has lost its importance.
         are manufacturers, consultants, or ex-  Now what is important is the fact
         perienced specialists. Thus, they feel   that when a load is placed on a rope,
         proper decisions are arrived at for the   it unwinds in the directions counter to
         majority of the affected population. The   the direction of its lay, Fig. 2. Left lay           Fig. 3
         motives of people who volunteer their   ropes unwind to the right inducing a
         time and expense are always suspect in   torque or a force to the right. And, of
         many people’s  eyes.  So,  open  commit-  course, a right lay rope would act the   ability to resist  rotation. All have op-
         tee hearings are our best hope.    opposite in the same circumstance.  posite strand lays between  the outer
                                              This  counter-torquing  is  of struc-  and inner strands (left vs. right), which
         STANDARD WIRE ROPE                 tural importance; then,  two ropes are   accomplishes the anti-spin characteris-
           These are six-strand wire ropes from   attached to the boom point of a crane.   tics, just as they do when left and right
         seven to forty-two wires in each strand.   When loaded, one rope will torque and   lay ropes are attached to a structure.
         They  can be  closed  to  the  left  or  the   pull  to  the  left,  and the  other  to  the   Category (1)  has  the  greatest resis-
         right but, the IWRC core (lang or regu-  right. Thus, pulling force for both ropes   tance  to  rotating  under  a  load due  to
         lar) must be closed in the same direc-  cancel out each other, and the load on   the equality of left vs. right lay direc-
         tion, which would provide no anti-spin   the boom point is equalized, and no   tion of the strands, or rotation neutral.
         resistance. As in the past, the amount   side loading occurs. This factor appears   Category (2), which provides less inter-
         of wear between the top of the core and   to be more important to European de-  nal wire wear, but, less torque stabil-
         inside of the strands, where it is difficult   signers than Americans, as evidenced   ity. Category (3) has the least anti-spin
         to inspect, is emphasized by the area be-  by cranes that are being built today.   tendencies.
         ing seen with the use of a marlinspike.  Another concern is the direction the   Rotating blocks, and therefore loads,
           The former broken wire replacement   wires in the strand take when placed to   have always been a big problem in rig-
         criteria of lay length have changed from   form a rope (regular or Langs lay, Fig.   ging and hoisting. The greater the dis-
         one 360 degrees of rotation of a strand   3). They can appear to run  along the   tance between the hook and the load,
         to six rope diameters (1/2" rope = 3" rope   center line of the rope, named “regular   the greater  the tendency to twist-up
         lay measure.) The same numbers of bro-  lay” or appear to cut across at about a   the rope. One method to prevent this
         ken wires remain, six randomly distrib-  45-degree angle, “Langs Lay.” The ma-  is to lock the hook in the block and
         uted in the rope lay and three located   jor importance here is wire abrasion.   place tag lines on the load to keep it
         within a single strand in a rope lay. A   At an angle,  there  is  just  more wire   from spinning.
         bit of concussion accrues in the terms   material available to resist the scrub-
         rope lay and strand lay (again word   bing forces when the wires move over
         meaning); they represent important   one another on the drums and sheaves.
         rope design operation characteristics.
           The lay of the rope strands can either   ROTATION-RESISTANT ROPE
         be to the left or to the right (I always   CATEGORIES
         say left first, because I’m left-handed)   Three categories of rotation-resistant
         An older reason for left or right was   ropes are designated based on their

                                                                                 Fig. 4

                                                                                 When strands are spiraled or closed
                                                                               (turned) to the right to form the rope,
                                                                               and a load is placed on them, they want
                                                                               to straighten out and rotate to the left.
                                                                               To counteract this natural tendency to
                                                                               rotate to the left, an equal number of
                                                                               interior strands are closed in the rope
                                                                               to the left and want to untwist to the
                                                                               right,  Fig. 4, counteracting the rota-
                                                                               tion, and a non-rotating rope is born –
                                                                               like magic!
                                                                               HISTORICAL PROBLEMS
                                                                                 Here’s the big “historical” problem for
                                                                               the inspecting of anti-spin ropes from
            Fig. 2                                                             the beginning of their introduction
                                                                                                continued on page 12

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