Track Shoe Design

[Tsiolkovsky]

I'm currently investigating a dozer/rock-clearer used in the mines to clear blast ore. The problem is that the slope condition in the working area is not only downhill but tilting downwards to the side as-well. Even if the dozer can resist sliding forward it may still have a dangerous tendency to "yaw" or "slip" to the side. After sliding, the machine sustains heavy knocks and with no damping systems whatsoever, this results in part failures. Even worse, the sliding machine can take out a mine ceiling supporting column or "stick". It may also harm nearby miners.

Anyhow, this problem must be solved by increasing traction. One thing that I noticed particularly were the current track shoes. They have triple grouser bars. Now the theory behind grousers is that they deform the ground into the grouser profile and the tracks compressive strength on the flanks of the grousers is transferred into internal shear stress within the soil itself (see Attachment 1). So now the traction derives from the soils ability to withstand its own shearing. This principle only works if the ground is deformed around the grouser bar. The problem arises in the surface condition in the mines. Its basically hard substrate rock with a thin covering of fine, dry and low shear strength mine "silt". So the hard underlying rock does not deform. And even if its thin covering of silt does deform (in other words the grousers manages to "bite in" the silt), its such a thin layer with poor shear resistance and with a poor shear resisting shear silt/hard rock interface (see Attachment 2).

An actual picture of the tracks and the hard substrate with the fine silt covering is seen in Attachment 3 and Attachment 4 (Notice the grousers inability to bite in the surface)..

Ultimately my conclusion is that the grouser principle counts for nothing on this surface condition and a new track shoe design must be utilized.

I ultimately need your opinions on:

1) Is my ultimate conclusion correct? (That the grousers are ineffective on this surface condition)
2) If my conclusion is correct, to what degree can a new track shoe design offer better traction?
3) Is this problem worth investigating further with a solution needed? (My boss wasn't too concerned about this problem mainly because solution finding was not heavily stressed in my job description, but I'm increasingly obsessed with a solution even willing to experiment and test from my own pocket to a viable new track shoe design)

Also note that the environment contains residual Chrome particles which abrade everything and anything in their path (in-case you're wondering about using rubber shoe attachments).

Any further comments or ingenious solutions are welcome!

 

[Tsiolkovsky]

Unfortunately the initial post only displayed attachment 4 (as only 1 attachment is allowed I presume). Here is another attachment with pictures showing separately each intended attachment 1, 2 and 3:

 

[Ron]

It would seem to me that if the substrate won't bend to conform to the plate, then have the plate "bend" to conform to the substrate to increase contact.

The plate could be divided into multiple pieces, each attached as part of a single plate section, but each articulating independently to provide contact.

 

[EngineerTex]

I think that you are correct in that you've got a difficult situation wherein you have two very hard surfaces (tread and substrate) with a powdered substance between them, making the grousers pretty ineffective. Like most problems, this can be helped by a trip to the bar. This is quite similar to a shuffleboard table. You slide the pucks from one end to the other on an almost perfectly flat table with a light dusting of sand. Check it out:

http://www.youtube.com/watch?v=kpfuiaTR19I

So yeah, your problem is going to be difficult.

Just a few ideas:

1) If you have found success in preventing forward or backward sliding, then it seems that the orientation of the treads may be key, which means that you should add grousers perpendicular to the existing grousers, which would mean that your tread pattern would leave squares behind as opposed to parallel track marks.

2) If you're having difficulty in all directions, you might try applying a hardfacing/Stellite weld to each tread. This process might end up being the easiest solution, but you could very well have to spend a while perfecting the exact weld pattern you would use. You might try to weld a bunch of teats on the face of each grouser. You might try making lines on each grouser parallel to the treads or you might also try them perpendicular to the treads. Maybe a bunch of parallel lines where half of them are on a 45 degree bias to the left and the other half on a 45 degree bias to the right. There are probably an infinite number of different combinations you could consider, but most any of them would likely be just fine, because you would significantly increasing the surface pressure between the tread and the substrate and I think that is key.

3) Can you install a sweeper brush fore and aft of the tread to sweep all of the dust out of the way between the tread and the substrate?

It's an interesting problem.

Engineering is not the science behind building. It is the science behind not building.

 

[IRstuff]

I think if the teeth are actually digging in, then the earth itself would resist lateral movement, as the teeth must continue to groove sideways, which requires work to push earth out of the way.

However, one could possibly improve that lateral resistance with a zigzag tooth pattern, like /\/\/\/\

TTFN

FAQ731-376

 

[kingnero]

This is probably not a valid idea, depending on the hardness off the underground: but what about studs/spikes?

 

[Tsiolkovsky]

@ Ron. I was also thinking about making the track somehow form around the ground by adding some articulation or even better some soft track shoe. Unfortunately the former may require too much adjustment and the latter solution is rendered too abrasion prone due to chrome environment. However I have sent a request to a certian rubber track manufacturer if they have a rubber shoe track that is ultra abrasion resistant.

@EngineerTex. Your point 1 does make sense in that if sideways slippage is present, while forward slippage is not present, then it surely must have something to do with tread. But once again, theory tells us that treads/grousers are useless in hard ground AND ground that doesn't support shear (like the silt covering). Point 2, yes I can try different patterns maybe and even though theory dictates any grouser pattern is useless maybe there is something more to it we don't see. Maybe, just maybe, even though the grousers don't work, they at least get to go through the silt layer and reach the bedrock in which the traction is derived simply from co-efficient of friction between grouser tip and rock substrate.
Point three, its an interesting proposal to use sweepers to rid the top layer I guess ill have to research to what extent the top layer hampers traction.

@IRStuff, indeed you are correct in saying if they do dig in they should resist lateral slippage but the majority of the time they don't and hence even the VVVV tread wont work or the square tread EngineerTex mentioned. But once again maybe there's more to the mechanics of traction than I see.

@kingnero. Indeed, studs spikes is a very natural solution to think of. After all, if the rock is hard and you cant penetrate using flat grouser, simply minimizing contact area (hence increasing pressure)(hence spikes) could work. However the rock is very hard and I don't think the highest pressure spikes or studs can penetrate let alone penetrate and last an acceptable time. BTW, current shoes are replaced once every 500 hours of working time.

I am thinking that I need some empirical experimentation. What if I scale the weight and dimensions of the machine to a smaller model and take the same rock and silt samples and make a miniature slope environment and test old miniature shoes and another design and get results? Scaling the problem shouldn't effect results can it? And I have attached a solid works model of the track shoe if anyone's interested.

 

[IRstuff]

Well, that's about as good as it's going to get, I think. It is impossible, given a normal vehicle architecture, for the lateral slip performance to be anywhere close to its longitudinal slide performance. The orientation of the tracks and the physical aspect ratio of the vehicle are all impediments to good lateral slip performance. Additionally, one can imagine that the track most likely is unable to be in fully engagement with the ground on a lateral slope, simply because the track is able to pivot on its contact area with the road wheels.

The only way to really improve the performance would be to make the tracks wider, and the road wheels substantially wider, so that they are as wide as the tracks. This would keep the tracks from lifting on their downslope edges.

Additionally, the lateral dimensions of a vehicle generally make the vehicle more prone to tipping sideways, so working laterally on a slope is already ill-advised.

TTFN

FAQ731-376

 

[ornerynorsk]

Military tracked vehicles often have rubber pads as an integral part of their track shoe. Would this help in your situation? Just a thought.

 

[DesignerGuy16]

Regardless of penetration, wouldn't a diamond / titanium carbide coated spike at least act as a grip instead of a wear surface? Ultimate goal is to increase friction, not necessarily surface penetration. You might get more penetration with more weight to bear on the surface from the dozer itself. That with point contact on the suface you might break through, but man that's a nasty combination for sure.

James Spisich
Design Engineer, CSWP

 

[DesignerGuy16]

You might look at snowmobile stud design for inspiration as it's a similar situation of a weak surface (snow) material above earth type condition. Even if the earth isn't hardened carbon deposits.

James Spisich
Design Engineer, CSWP

 

[IRstuff]

I suspect that on sufficiently hard surfaces, snowmobiles will slide downhill on a traverse. Tough enough to traverse with razor-sharp, hardened steel ski edges as it is, sometimes.

TTFN

FAQ731-376

 

[ivymike]

perhaps there's nanotech for this situation - a series of penetrating spikes to get through the dust, w/"gecko hairs" on the tips to interact with the hard surface beneath?

 

[KENAT]

My first thoughts were spikes like king nero & Jspisich, though not having played with snow mobiles I was just thinking of studded snow tires.

If your vehicle skid steers, rather than putting one track in reverse and the other forward then you might have issues steering. Or maybe you can get around it by only studding the track on one side. Also, unless the layer of mine silt is fairly consistent you may have problems optimizing the spike length.

Not sure you have to explicitly scale the tracks. Make a big enough representative slope and then you could maybe use individual full size tracks.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[Tsiolkovsky]

Ultimately what Im thinking is that pure flat shoes will be better than grousered. Indeed it is far from ideal and yes its on a bad surface, yes it may slip but surely it is better than grousered tracks since their function of digging in is rendered useless. In other words, the traction from grouser bars is SOLELY derived from co-efficient of friction between the grouser teeth and the hard substrate and NOT by digging in and utilizing the grounds sheer strength. This is because even though the tracks at times dig into the silt, the silt itself will have a poor shear strength between itself and the hard ground interface. Now if you rid the grouser bars and install flat shoes, you are STILL relying solely on the co-efficient of friction BUT the only two differences are:
1) You have INCREASED surface area thus better traction between the shoes and silt layer.
2) However in flat shoes, the co-efficient of friction is between the shoe and the silt, not the hard ground underneath (unlike grousered shoes). Also the silt may shear itself unlike the hard ground.

Point 1 benefits flat shoes however point 2 benefits grousered shoes because they "reach out" into the underlying rock and utilize the the shoe-hard rock co-efficient of friction and the rock wont shear on itself unlike silt.

If the former point weighs more heavily then flat shoes are desired and if the latter counts for more then grousered shoes are unfortunately the only way to go.

I have also got a reply from a certain manufacturer of add on grouser polyurethane shoes. Mechanically these will no doubt offer more grip. But my management has told me the chrome containing sand will rip through anything and everything and will eat those tracks in two weeks (which is true because another company did try and results werent good). I argued that the pads they used were

1)Not polyurethane but a weeker substance
2) They were not add-on pads but an actual complete rubber track (hence wears out on sides quicker unlike add ons)
3) A bit of R&D has happened since then.
4) We did not rey on our own dozer and its worth investigating.

Mangement wont budge at this moment in time, so im thinking to draw out my own pocket and order like pads, do a trial and see how many hours they withstand.

 

[ornerynorsk]

Tsiolkovsky, I think you are on the right track, if you'll pardon the unintended pun, with urethane. There are many grades and hardnesses of urethane, and as you pointed out, a previous attempt at using an elastomeric pad was not urethane but some other material. In my very limited experience with heavy equipment, I believe a pad system on a purpose-built track will outlive a uni-track. I've built 2 sets of my own design "tank treads" for skidsteer loaders, so I have some validation and reason for making this statement.

On the military tracked vehicles I mentioned in a previous reply, these carry 50 to 70 ton vehicles over asphalt and cement, dirt, gravel, truly all terains, with a relatively long life. Fine sands and pulverized materials are very abrasive, but only a true test will allow you to see what the lifespan might be.

Good luck in your project!

 

[arunmrao]

Elastomeric pads clad to the track shoes is quite common. Also you could consider as some have suggested carbide inserts either embedded or brazed on the track pads. This is akin to drill heads which have such armour to improve wear life and better drilling.

 

[rstupplebeen]

Since this is operating in a mine I assume that there will be a man-made (cutting machines) or possibly natural pattern (rock grain) to the floor. I would try to match this average pattern with the spacing of the tracks in Attachment 1. Also match a similar tooth pattern in the out of plane direction. Each track does not have to be the same so that you can grip on one floor best with the even tracks. I hope this helps.

Rob Stupplebeen

 

[MikeHalloran]

The first thing that came to mind was crossed grouser bars. I.e., milling grooves in two directions, so the pad winds up with a rectangular array of square projections.

... which does not solve the problem of weakness of the underlying, er, dust.

That problem might yield, pardon the pun, to angled faces on the grouser bars/pins, such that each looks like a truncated pyramid.



Mike Halloran
Pembroke Pines, FL, USA

 

[dhengr]

Tsiolkovsky:
What about flat shoes with diamond patterned hard surfacing beads .125 or .25" high. This way you get some irregular height bite or frictional interaction with the hard rock, as opposed to the slick, slippery, one directional contact of the blunt grousers. This pattern might also contain and compress the silt for whatever friction and confined shear it offers. This repair and maintenance could be done right on the machine, as opposed to replacing shoes.

If you have traction for digging or pushing, then what about a second set of grousers, perpendicular to the current ones and right under the running wheels for max. pressure without bending of the shoes. Maybe hard surfacing tits on the wearing surfaces of the grousers. These might penetrate the hard rock and hold, where the whole grouser surface just slips on the hard rock. This would probably req’r. more frequent maintenance, but again, right on the machine.

Can a mining cutting machine scarify the hard rock surface to give you some bite or traction?

Should you be digging into your own pocket to finance this effort? If the company doesn’t care, why do you? Before you spend your money to solve their problems, go to them with this offer: since you won’t spend the money, quit grousing (pun intended) about the problem; alternatively I will spend some of my own time and money to solve your problem, and if I do, I expect five years worth of maintenance and shoe repalcement $$$ for the solution, and/or to be addressed henceforth as V.P. Tsiolkovsky not just M.E. Tsiolkovsky.