3 Replies Latest reply on Mar 17, 2015 3:13 AM by Jared Conway

    slewing ring, 45 degree rolles, how to simulate?

    Markku Sutinen

      Dear higly respected and goodwill experts all aroung the SWX-universe,

       

      Could someone please assist me with this case: I have a crane pedestal column, let's say ø 1000 mm diameter and wall thickness of 8mm or so. On top of that pipe there is a flange, 40mm thick. Unfortunately flange is much larger in diameter than pipe because slewing ring is ø1400mm. So in practice bolt pattern has 200mm greater radius than pipe. This produces bending moment and all kind of twistings to flange. Beneath the flange there is a pattern of gussets for support. On flange there is a deformable solid ring with bolt holes representing slewing ring (its outermost part), which is constrained to flange with preloaded bolt elements and no-penetration contact set (friction µ=0). There is no goorve etc, only bolts holding that system in its place.

       

      I've placed force(s) (tipping moment+weight) as remote load, direct transfer. If I just put that load on top face of the slewing ring, everything is somewhat ok and stress levels are tolerable, even plane deviations are in allowed limits. Second method was to split that top face to 4 (90 degree) segments and recalculate remote moments etc to normal forces pushing an pulling two opposite surfaces up and down. No significant difference so far, but next thing is where I run out of my skills:

       

      If I placed that same load on 45 degree surfaces, stress levels escalates to 2000, even 10 000+ MPa and displacements 60 to 100+mm (I suspect that solver crashes at some point and results are not reliable?).

       

      According my understanding 45 degree roller surface produces as non-desired side effect a equal lateral force and this makes my slewing ring deform to ellipse, which in turn further bends my flange, which in adverse makes slewing ring to deform like a Möbius curvature..  My next task would be to define required corrections, but in order to do that, I'd need a working FE study at first.

       

      I don't have a non-linear lisence available, but assuming that linear steady state study is/ shall be enough, could someone pelase give hints, how to proceed:

      Q1: is my assumption of "45 degree side effect" correct?

      Q2: Is there anything too careful in my load case (I assume that no, because 360 degree direct transfer force gives about same results as 2 forces on two 90 degree sections)

      Q3: if inner ring somehow supports or prevents outer ring's deformations, is there any commonly approved methods to apply that effect in my study? I've heard about "equivalent modulus of elasticity?)

       

      Thanks in advance for your prompt replies..

      Markku

        • Re: slewing ring, 45 degree rolles, how to simulate?
          Jared Conway

          This load case needs some pictures and i'd suggest attacking one problem at a time.

            • Re: slewing ring, 45 degree rolles, how to simulate?
              Markku Sutinen

              Hi Jared, thanks for the comment.

              Due NDA restrictions I cannot publish actual model, but I made a principal level drawing representing that situation.

              Diamond and inner ring are not included in FE model.

              2015-03-15 18_09_04-SolidWorks Premium 2013 x64 Edition - [Sketch1 of Principal_drawing _].png

              I have a stong feeling that my assumption (two relatively small sufraces pushed up & down) may be an overkill and actual load distribution is more like a parbola, thus local bending moment, rotational displacements, sliding etc. are significantly smaller. On the other hand, I need something where I can put my signature on and sleep well and it should be achieved using my own tools and licenses.

               

              I found a paper dealing with rollers' contact forces, but presented equations required non-linear springs (rollers' & raceways' Herz stresses) and slightly complex iterative calculations. Nothing too complex for me to be done with a spreadsheet, but unfortunately I'm running out of time with this. One bigger engineering office suggested to build an unlinear FE study in order to find actual stiffness of the bearing assembly.

               

              All issues raise up / disappear depending on what surface I place my loads on. So this is

              a.) question about slewing ring's behavior under certain load (is F,lateral equal to F,vertical) and is that 45° surface correct place to put loads on

              b.) real load distribution on slewing ring (even S/R's manufacturer refused to comment or did not know it)

              c.) how to model it in SWX Simulation using only linear analysis (no unlinear spring elements available )

               

              So any further comments and hints are warmly welcome..

               

              Markku