Bias-Ply tire failure in non-automotive industrial application 5

[MrReliability]

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 pipe thrust one way or another without issue so I am not sure that bias is the proper tire for this application. Any help would be appreciated.

 

[MrReliability]

crystal1clear,
Yes there is 3 pipe, on smaller sizes, on 4 axles. The outside axles are idlers so they are independant. We do not have any problem with the tires slipping. The tires are replaced as a tandem or an entire axle.
CapriRacer,
This is a brand-new piece of equipment. The old equipment had steel wheels on the bottom and radial tires that came down from the top. The large steel wheels caused millions of dollars worth of damage, due to high-spin fractures that could only be found after installation. This is an engineered piece of equipment and the only one in the world so nobody knows anything about it. A ME designed and built it but he has little to no experience in tires. Just by calculating the load is how he determined the tire.

 

[CapriRacer]

Mr. Reliability,

Thanks for the info. On the previous piece of equipment, what size were the radial tires and how much load was applied to them? In other words, I am wondering if there is enough load carring capacity.

 

[patprimmer]

Could you replace the wheel tyre combination with solid rubber or solid polyurethane tyres on heavy steel wheels. This would still give some, but much reduced compliance under load.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[crysta1c1ear]

Pat mentioned 100 psi on trucks.

If I've got this right, failure is occurring often enough and without damage (other than the tyres), so experimenting to find a better setup seems reasonable to me. My paragliding teacher used to design his own shutes and there failure is critical - so his approach was to make marginal changes in design and to keep them if they made an improvement. If you can't make bold changes as a test, you could make incremental changes and look at the effect statistically to see if there are improvements.

Tyres are convex. Where they meet the road the road forces the shape to be flat: the inner and outer radius of curvature at the contact patch is effectively infinite. It seems to me that what the pipes are trying to do is make the tyres buckle inwards at the contact patch.

I assume that inward buckling is beyond what the tyres are designed for. CapriRacer seems to be the man in the know - the tyre expert.

The inward buckling would be reduced by higher tyre pressures. On the other hand there is the driving force at the contact patch which is trying to shear the tread off tyre. The purpose of dropping the pressure from 70 psi to 45 psi might have been to increase the size of the contact patch and therefore reduce this shearing force on any square inch of the contact patch.

On a safety note, are workers well clear of the machine when it is in operation? If tyre failure was considered unlikely when the machine was designed and is now a common occurence in operation ... ugh.

We haven't mentioned horsepower. Are the pipes brutally brought up to speed to get the job done as fast as possible, or gently spun up to speed? If the spin-up time is short, ie the motor is very powerful, can this be done slower, as a test.

The same for stopping. Is the motor turned off or gently brought back down from running power to zero?

On Pat's point about solid rubber tyres, I believe the reason we have air in tyres is passenger comfort on undulating surfaces. You have neither passengers nor undulating surfaces. I'm no tyre expert; these are just my thoughts.

If increasing tyre pressure causes failure due to more shearing on a smaller contact patch, and lowering pressures causes failure due to the tyres buckling inwards, then I'd be tempted to say the curvature of the pipes (compared to the flatness of a road) is the cause of the problem and I'd wonder if using more wheels would be a solution.

There are no strange chemicals coming into contact with the tyres are there? THey aren't getting covered with cement dust or whatever. [Not that I would expect cement dust to influence tyres. I just ask so that we can eliminate chemical attack as a possible cause.]

Sorry for the disjointed nature of this posting - I am being pestered to go an eat!

 

[CapriRacer]

I am entirely onboard with Chrystal's analysis.

A pnuematic tire has more ability to absorb shock loads than a solid rubber tire - and I think this was the point of going this direction.

I wasn't considering the horsepower - and I think that may be significant particularly in view of the shear forces at the tread face.

I also think a radial tire might be worse. I can imagine that a radial would be more compliant for rotational shock loads - starting and stopping the spinning. But I don't think that is the issue here. But a very real side issue would be when a failure occurs. A bias tire will throw chunks off the tread, but a radial generally throws the entire tread as more or less a unit - and while it is coming off, it will flap around damaging anything within distance.

One last thought:

It is common for there to be tire chunking problems when new cars are tested on dynamometers - mostly during the braking portion at the end of the test. Coasting basically eliminates the problem.

My gut tells me Chrystal hit the nail on the head mentioning this. Go there first!

 

[FoMoCoMoFo]

My 2 cents,
Have you ever operated this unit for an extended time with no pipe smaller than say 20"-24" ? looking at the picture i can see where it may have trouble with smaller diameters.
I am on the high side of the air pressure debate.
Unfortunately the issues i see and every factor discussed so far would seem to argue for at least some increased failure rate of the center tires ?
Good luck

 

[patprimmer]

Measuring the peak and typical operating temperature of each tyre might yield useful information.

Is the mould in balance before the spin up, or is the purpose of the spin up to distribute the concrete evenly. I imagine that the concrete is all on the bottom at the start and the spin distributes it. In this case, initial acceleration rate will be critical to reduce dynamic load from imbalance.

If it is only the small dia pipes that cause the problem, maybe the outside of the mould could be made larger with some sort of wheel that slides over the mould, or like one pipe inside another, held concentric with spacers.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[witchdoc]

You probably have two or three issues that are working together to cause the problem.
1. The steel mold tends to act as a wedge between two opposing tires. If you write the statics equations for this situation, you will find that the vertical component of the load is transmitted to the tire as a radial load. This essentially amplifies the load. I estimate the amplification factor is about 1.6 for the 8 inch mold.
2. 70 mph sounds high for this type of application. At these speeds, you probably have a good bit of dynamic load that adds to the situation.
3. You may also be overloading the tire from a torque perspective.

http://www.forsytheandlong.com

 

[CapriRacer]

Shout out for Mr. Reliability!!!

What's going on? What's happened!!

I see this as a learning opportunity and would be really interested in a progress report.

BTW, on the TV show "Modern Marvels", they showed a similar machine that was used to build the support columns for the trestle part of the Chesapeake Bay Bridge /Tunnel. They claimed the pipes were spinning at 60 mph and it sounded like they spun for 45 minutes at that speed.

 

[MrReliability]

Sorry for disapearing. My plant had a major explosion and I have spent the last month and a half helping to rebuild it. We have just made our first pipe today so things, hopefully, will slowly return to normal. Needless to say this suddenly became a low priority for the plant. I have also talked with a PhD.'s at one of the local universities and he thought that contact sresses sound like it might be one of the root causes. I started calculations on the tangential forces applied and thought I was on the right track but he thinks that I might be spinning my wheels, pun intended. It turns out that the Dean of Mechanical Engineering at the University of Utah is an expert in tire failure analysis, go figure there would be someone in my own back yard. Apparently he has worked with a number of the tire manufacturers. I am going to try to contract him as a consultant, but your feedback is still appreciated and I intend to provide him with all of your helpful information. Please don't stop your recommendations if you have any other ideas, I still find them to be extremely helpful.

 

[MrReliability]

Well it turns out that the Expert that I thought I found thinks that it is out of his area of expertise. I am really needing help here so if anyone is interested or knows someone who might want to consult on this I would really like to find someone.
I am going to go back to crunching numbers, unfortunatly this is not my best area I am more of a design/concept idea engineer. Any help would still be greatly appreciated.

If I have forgotton to answer any questions that were posed please remind me as I have been pretty preoccupied with the plant explosion lately.

 

[Compositepro]

I just looked at the picture you posted again and I find it interesting that one can see wear marks on the pipe where it contacts the tires but no marks where they contact the steel rollers. That seems strange. Also the wear marks seem to be much narrower than the tire tread and at center of the tread which is where you say separation starts.

Have you tried any radial belted tires? Bias ply tires have a round pressure carcass with a cap on top to provide a relatively flat tread. The radial belts in radials might provide more uniforn contact pressure and distribute the shear load between the pipe and the belt over a larger contact area.

However, if the failures are due to excessive flexing of the tread then radials might be worse.

Are you sure the tires are aligned properly? I see there are rollers at the ends of the pipe to keep them from walking-off axially. That's okay as long as that is not concealing an misalignment problem. The load on the end rollers should be quite small.

 

[CapriRacer]

Mr. Reliability,

I just read over all the posts, and where I think we left it was the speed and cycle time.

Can you give us a primer on the actual operation cycle?