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Contact Stress?

  1. Apr 21, 2008 #1
    Contact Stress???

    I have a "High Spin" rolling system that spins pipe to compact cement lining. We are using tandem 7-14.5LT D/8 bias-ply tires on each end of the axles with the pipe riding in the saddle between two sets of tires. The tires are running approx. 70 MPH for just over a min. The maximum weight of the pipe is 3500 lb. and it is held down with two sets of metal rollers that straddle the pipe with approx. 800 lb of downward force on each set.
    My problem is that we keep separating the tread from the tire.

    The combined weight on 8 tires, 4 sets of tandems, is as high as 5100 lbs. The diameter of the pipe range from 6" to 30" with weights of 30" pipe being around 5100 lbs and 6" pipe being around 2000 lbs.

    The side wall is intact it is just the tread chunking off, on inspection of blown tires you can feel that the tread has seperated completly around the crown of the tire.
    here are 4 axles with the two inside axles being drivers and the outside two are idlers. I agree that the load will not be the same for all of the tires. The pipe has a bell on it that is considerably larger, thicker and heavier. There seems to be no pattern to the chunking. I am thinking that the small footprint of the pipe and the contact stresses from the pipe spinning might be a factor. On one side of the tire there is a footprint and on the other side (45-65 degrees apart) there is another footprint, except for the outside tires. I thought that the idlers would either go more or less frequently because of this but that is not the case.

    I am not sure how to calculate the contact stresses, to see if this might be the culprit, or the forces associated with the tangential acceleration.

    Any help would be greatly appreciated.

    I have attached a photo of the system for your viewing pleasure!
     

    Attached Files:

  2. jcsd
  3. Apr 21, 2008 #2

    Danger

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    Welcome to PF, MrReliability.
    I can't help with calculations, but I'm curious as to whether or not you've tried other types of tires, such as glass-belted radials. If so, were the results the same? Also, have you tried it with different inflation pressures?
     
  4. Apr 21, 2008 #3

    Q_Goest

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    Hi MrR'.
    When determining the normal force on the tires, did you consider the fact the verticle load isn't normal to the tire face? From the picture, it looks as if the pipe is about 30 degrees above verticle which means the normal load is twice the verticle load. If the downward (verticle) load is 5100 pounds, you need to double that for the 30 degree angle. (ie: normal load on tire = verticle load / sin(angle) )

    It's this normal load that you have to compare to the tire's rating, not the verticle load. So what load are the tires rated for?

    If the calculated load is still below the tire's rating, then it may be the radius the pipe makes on the tire that is causing an issue. Tires with a higher rating may help as Danger eludes to.
     
  5. Apr 22, 2008 #4

    FredGarvin

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    Indeed. It would appear that you have a pretty substantial shear force on each tire which would seem to be the real culprit.
     
  6. Apr 22, 2008 #5

    Mech_Engineer

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    As mentioned before, it seems quite possible that your are exceeding the maximum load rating of the tires. Also, you might check to see how hot the tires are getting, as a tire that is spinning at 70mph but doesn't have 70mph wind blowing over it may be getting far hotter than intended...
     
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