Rack and Pinion

Do you have a drawing?

I can draw up a rough one for you, Ive been waiting untill I got all the dimension on parts I will be using so I can draw up a scaled version. cheers Dan

You say The load will be at the max 20 000kg... and then later you say: it will be pushing a load to a max of 10 000lb

Well, Which is it?

Its for a drill rig, when you are drilling rods into the ground you use a pushing or feed force of 0 to 10 000lb depending on ground. Each drill rod weighs about 350kg, once you have drilled down to the maximun depth of the machine ( in my case 300 meters ) you need to be able to pull the drill rods out of the ground. 300 meters of drill rods, plus the drill bit and drag on the drill rods that equals the 20 000kg I am refering to. Dan

Something like this....

Yes mate, same thing. Mine will have some different spec to that though the basis is still the same.

The environment where this will be used is full of grit and mud. Why are you proposing a rack and pinion for such conditions? Wear will be a major problem, in field conditions with little or no maintenance facilities. The specification attached to the photograph implies a 6" bore 7' stroke hydraulic cylinder (gives 40% over capacity) to do the same task. Much cheaper than a 21' rack, pinion, gearbox, and hydraulic motor, but simpler and easier to maintain. Any calculated value of module size would have to be at least doubled to take into account your operating conditions. Your competitor has a better design.

Your continuous time of 0 to 6 hours is misleading. You have to stop every 20' to attach or detach a rod. This means stop, unclamp, drive unloaded to the other end of the travel while a rod is added/subtracted, stop, reclamp, restart. All the time the drive is stopped oil will be directed back to tank via an open centre valve, creating heat but doing no work. It gets worse if you intend to operate at high ambient temperatures. Hot oil affects the performance of a hydraulic motor to a much greater extent than a hydraulic cylinder. Your competitor has a better design.

Your brought up some interesting points.

1. yes environment is not on my side bud can be eliminated by some sort of guarding ( same as on a mill for example.

2. The machine in your pictures only has a pull force of 20 000lbs, I need 20 000kg. The 6 to 7 inch bore implies to the size of hole the machine can drill not the hydraulic cylinder bore size. To get 20 000kg out of a cylinder I will need ether 2 smaller ones or 1 very large diameter one which will not fit in with my machines design.

3. A typical cylinder over rope design is basic as you say, but as for wear, take into account the following

1 cylinder

1 travel block with 4 sheave wheels with bearings or sprockets with bearings

2 upper sheave wheels/sprockets with bearings

2 lower sheave wheels/sprockets with bearings

4 sets of chains or wire ropes

And the maintenance that goes into these, time to replace and the amount of spares you need to carry all add to $$$$$.

Also it is a good practice to replace all the above item ( except for the cylinder ) every 12 months and cylinder every 24 months.

2 planetary gear boxes, with hydraulic motors, brakes and counter balance valve cost around $25000 a pair and take little time to replace.

Yes cooling in something I will need to look at as well as wear factors on the rack systems ( which is something I am still working on and no little about that is why I am still in the design stage ).

But ether way I would still like to no how I would go about working out the formula and you odviously no a bit about the wear factors so what sort of life do you get out of a rack and pinion set ( or how could one work that out ). cheers Dan

So more like this...

Hydraulic systems have the advantage of being self lubricating. All of the other parts you listed have the ability to be fitted with an automated lube system. (Vogel, or SKF brands).

If you are determined to use a rack and pinion, you may need to construct it yourself. Use Global as a search site for gear manufacturers. You will likely need to join multiple sections of straight gear racks. And then select a pinion gear and drive system to drive it. The gear manufacturers would be more familiar with the process of setting this up. They are the specialists.

The choice of a pair gear + rack is not at all (whatever you bring as arguments) for this application. I say that knowing from a several years design activity in earth drilling machines what are the problems of this activity. You totally neglect the flank wear which will lead to heavy shocks and variations of the force on the tool which in turn will reduce its life expectancy.

Why do you not think about chains (multiplex) ? To change a chain is a simple operation and the same for the sprockets. Wear will not be so intensive since sliding is in the bushings which are more protected against ingressions as an open rack. On the sprockets wear is only generated by the pitch increase due to bushing-pin wear. The sliding occurs only when under load the chain links rotate to each other i.e. only when the pair comes at the sprocket.

I think that your economical approach is correct but you did focalize on only one solution and you should look at more.