Caterpillar Dozer Rimpull Question?

[fensoncont.]

Hello,
Right now I am working with rimpull on Caterpillar dozers on pages 1-10 - 1-14My question is how do I use the chart to get to the point where I can slide my finger over and see how many lbs of pull it will have?? It only has speed at the bottom and rimpull on the left, I don't know what factors to use to get there. In the scraper section is has machine weight and rolling and grade resistance. I want to know if I need a bigger dozer.

[Wulf]

I'm no expert but here's my 2 cents...

I've only ever seen these specs used for comparison of dozers rather than production projection because the charts are identifying maximum useable force under conditions of maximum possible traction based on the standard weight of the dozer at a given gear selection and ground speed.

For an accurate calculation you would need (I believe) the coefficient for a specific ground material.

In actual working conditions, the ground type and condition, length of track on the ground will change, even the type of undercarriage elevated vs oval, bogie type or rigid will make a difference.

Surely a highly productive dozer for pushing or ripping needs a blend of good drawbar pull, travel speed and fuel efficiency and a machine can't be selected on drawbar or rimpull alone?

[digger242j]

In the scraper section is has machine weight and rolling and grade resistance.

This is high theory, which is not something I've ever had occasion to deal with in real life, but that's never stopped me from taking a guess at anything before...

Rolling resistance might be a factor with scrapers because they have wheels that actually roll on the ground, and that will vary with the size of the load and the type of footing.

Dozers are different. If you think about it, they are running on a track, much like a train would. That track is stationary on the ground. The fact that they pick it up from behind them and lay it down in front of them continuously doesn't really make any difference--the "rolling" they do is always done on that track. Therefore, "rolling resistance" is a constant, determined by the friction between the rollers and the tracks, and whatever the ground surface is doesn't really enter into it, and there's no need to list it.

Whatever the rimpull is only tells you how much force is available to move the machine forward on the track. Track length and width determines how well the tracks will stay put on the various ground conditions, but the way the machine interacts with the tracks will remain essentially the same.

Or so it would seem to me...

[fensoncont.]

Thanks guys! That helps a lot. I will go ahead and use what you guys said about the maxmum rimpull avalible.

[Tigerotor77W]

Nolan, note also that the notes on 1-10 state that the drawbar pull depends on the "weight and traction" of the tractor, and that there is assumed to be less than 5% track slip.

Drawbar pull is an interesting mix of physics that I don't fully understand yet -- I can try to get a more-precise version of how the Cat data is compiled, but it might take a while (perhaps even indefinitely).

[Squizzy246B]

Nolan, note also that the notes on 1-10 state that the drawbar pull depends on the "weight and traction" of the tractor, and that there is assumed to be less than 5% track slip.



Wise man Xing makes very good point....he no talketh with forked tongue:rolleyes:

But its a huge factor. As the drawbar load is increased so the conditions will determine the effective traction...the difference between track speed and over the ground speed. We did a large number of trials with Cat/Challenger using different track designs and the difference in effective traction was huge on different ground. As the limit is approached the slippage is almost exponential and 5% slippage is not much in the real world. For a comparison on deep ripping we hooked up an old D8 and were obtaining 3-5% slippage on gravel with moderate loads. Its all relative and a test/trial, keen eye and observations will tell you more than the figures.

[digger242j]

Squizz, I was kinda taking a guess with my comments about rolling resistance and rimpull. Did any of that make sense?

And, is drawbar pull going to be fairly equivalent to what the blade can push, or are there different factors at play there?

[Tigerotor77W]

And, is drawbar pull going to be fairly equivalent to what the blade can push, or are there different factors at play there?

I was wondering the same thing. I also posted the question at another forum; we'll see if anything comes up there.

[Squizzy246B]

Geez you guys...stop it with the techonogical questions I'm trying to have a nana nap ere!.

In a nutshell NO but Xing's point about the specs being practically and totally dependent on the operator and the ground conditions still stands.

When talking (in general) drawbar pull you are talking about an articulated attachment which only applies a more or less load against the forward plane of the machine.....generally horizontal or just below...so a scraper or a plow (which has an articulated hitch) gives a line pull. Of course some of these attachments can dig in..lowering the line of pull and helping improve the tractive effort of the traction machine. But they don't change the footprint pressure a whole deal if they ride up over some hard ground.

A dozer or grader blade on the other hand resists not only the forward push but of course trys to lift the machine up and break the tractive effort. This is why when you get a bunch of old blademen together...give them a couple of beers..and mostly they will talk about how light (or heavy) a machine is in the front end.....they'll go on and on about this machine an that machine pushes this that the front's too light...........:spaz .....all with very good reason. They know from the seat of their pants when the machine is really earning its keep and some serious work is happening...they look to "balance" the machine ...and only a well experienced operator can tell you when and how that is acheived.

The ripper tends to do the opposite to the blade when you are trying to drive it in to hard ground and lift the rear of the machine..again breaking the tractive effort.

Does drawbar pull approximate to push??...I'd think it would be hard to make a relative technical comparison (but I'll bow to a more informed authority)...however 1) you have already answered the question (it depends mostly on the conditions) and 2) it would be maybe better to ask a more real world question like can a machine that pushes like steam also rip really well?...and in that case you'd be talking to Deas...not a loader operator like me.

Better still, to get back to production/estimating and technical aspects that pit bosses and site managers have to deal with; lets say "IF" I was ripping some some gravelly stoney stuff out of the side of a hill for road building, I'd say "Deas old son, how much of this crap are you going to push out of here in a day" and he'd say "oh about a 1000 cubes"...I'd go tell the powers that be that production is expected at 800 cubes a day and grin like cheshire cat when Deas does 1200. May not be the most techonogically approach but I know it works for many. You need experienced operators that know their ground. Good companies keep very detailed records of their production and this information forms the basis of their estimates and bids for contracts...more so than theoretical figures.

[Countryboy]

:eek: :thumbsup All I got to say is WOW!

[Squizzy246B]

I might add that your site Geo report is a mightily important document when it comes to estimated production on big sites.....either that or its a worthless piece of half forged paper that sends you broke in the process...clay?..what clay?:mad:

(bitter twisted sarcasm based on past experience)

[Tigerotor77W]

Note to self: never **** off squizz.

Oh -- and it wasn't my point about weight and ground conditions; it was the Performance Handbook's note. I just copied it here.

I think the points of push vs. pull make sense. I've still gotta figure out if there's research being done/have been done on that traction stuff, because if not, hey, there's my master's thesis! Now all I need is some money... :yup

[fensoncont.]

Thanks for all the help guys!! Much appreciated! I will use this info and see if I have more questions.

[Deas Plant]

Hi, Folks.
To answer the pulling Vs pushing question, Squizzy is right - to a point. If you are trying to get a dozer blade, be it a crawler or a wheel dozer, into hard ground that is lifting the front of the machine, you are going to have LESS traction. However, if you can get some weight on that blade by way of a bladeful of dirt or a scraper push block or similar, that pushing machine will dig its toes and really give you some grunt on ground.

Also, given equal horsepower, a well-balanced crawler dozer will pretty much always outpull a bare crawler of the same weight as the entire dozer, simply because the weight of the blade is out in front holding the front down and helping to keep the entire track on the ground.

And never under-estimate the tractive force generated by a ripper buried in the ground and hooked under something like a tree root or a rock when that ripper is lifted, Sure, it may lift the front of the tracks off the ground but consider how much extra weight it is placing on the track that IS left on the ground. How often do you see a dozer in such a situation spinning its tracks once that ripper has maximum lift force applied to it?

Personally, I had never heard of the term 'rimpull' applied to crawlers. It is more usually applied to things like scrapers and wheel loaders.