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Comparison between work and rack arrangement and hydraulic cylinder

Comparison between work and rack arrangement and hydraulic cylinder

(OP)
I need to design a mechanism to move a load horizontally. So, I came up with two choices viz. Telescopic cylinder and worm and rack arrangement. Which one will be more efficient in terms of operation and cost?

Really?

RE: Comparison between work and rack arrangement and hydraulic cylinder

Hi

Do you have any more information on what you are trying to do or are we supposed to guess?

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

RE: Comparison between work and rack arrangement and hydraulic cylinder

What is your definition of efficient?

Ted

RE: Comparison between work and rack arrangement and hydraulic cylinder

saindip,

Have you tried analysing them?

--
JHG

RE: Comparison between work and rack arrangement and hydraulic cylinder

Not NEAR enough information. Since both types of mechanisms are in common use, there must be a reason. One is preferred in some situations and the other is preferred in other situations. LOTS of factors go into those decisions. And "efficiency" is only one of them. We're not here to do your engineering for you.

RE: Comparison between work and rack arrangement and hydraulic cylinder

The worm and rack will be.

RE: Comparison between work and rack arrangement and hydraulic cylinder

Worm and rack? Worm gear is not very efficient.

Ted

RE: Comparison between work and rack arrangement and hydraulic cylinder

hydtools,

Worms, high ratio ones anyway, are self locking, as are a lot of lead screws. It is too bad we don't know what the OP's requirements are.

--
JHG

RE: Comparison between work and rack arrangement and hydraulic cylinder

A pneumatic cylinder will only allow positioning against a stop, either the stroke of the cylinder, or a set of hard stops. If there are intermediate positions, hydraulic cylinder would be required. For the cylinder you would need a hydraulic power unit, piping and some sort of control system. For the gear rack, infinite positioning is possible. This would require some sort of drive arrangement (assumed electric motor and gear reducer) and a control system.

RE: Comparison between work and rack arrangement and hydraulic cylinder

It is possible to design high efficiency worms that can back drive (that bit's easy, it's just pitch angle vs mu), but typically you'd use a ball screw instead.

Cheers

Greg Locock

New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Comparison between work and rack arrangement and hydraulic cylinder

GregLocock,

I designed a 100:1 worm drive that was not self locking. The question is do you, or do you not want self locking.

--
JHG

RE: Comparison between work and rack arrangement and hydraulic cylinder

all I have to say is lead screw

RE: Comparison between work and rack arrangement and hydraulic cylinder

A lot depends on what sources of motive power the original poster has available, and of course, the rest of us have no way of knowing that.

Come to think of it, the power steering mechanism in my van has both a rack-and-pinion and a hydraulic cylinder as part of the same mechanism, because the nature of the round-and-round manual input motion is different from the nature of the way the power-assistance mechanism works (pump + servo valve + cylinder).

RE: Comparison between work and rack arrangement and hydraulic cylinder

(OP)
Thank you for all your feedbacks. I want to move a load of about 10 tons through a distance of 15 feet horizontally. Whatever mechanism I use, due to space constraints, I'll have to push or pull the load three times to get it in the desired position. I believe the hydraulic cylinder will cost more but will have a quicker operation (depending on the power pack), the worm and rack will be slower but much cheaper. So we are for now fixed on worm and rack.

RE: Comparison between work and rack arrangement and hydraulic cylinder

Saindip, happy to help. A little more information about the load would be useful. How accurately does the load need to be positioned? A roller bed, or wheel bed, conveyor seems like it might be another option to move a 10-ton load 15 horizontal feet.

RE: Comparison between work and rack arrangement and hydraulic cylinder

I think the worm and rack will wear out very quickly, especially if any of the components are exposed to the environment. After all, when you think about it, a worm gear works by a "sliding" action. Think of friction, and think of contaminants at the worm gear/rack interface.

I really don't see how a standard hydraulic cylinder and power unit can be more expensive than a specially designed worm gear and rack arrangement.

Have you considered a roller chain loop?

How is the 10 ton load supported?

RE: Comparison between work and rack arrangement and hydraulic cylinder

(OP)
The load will be supported on rollers. There are other major limitations in our project that rules out hydraulic cylinder. And moreover, it should be telescopic. About that worm and rack arrangement, I am thinking about making it a rack and pinion arrangement because it can be very difficult to manufacture the rack.
@Jboggs the roller chain loop is a good idea but I don't think we have enough space to accommodate it. Anyway, I will think about it.

RE: Comparison between work and rack arrangement and hydraulic cylinder

A roller chain can be used almost exactly like a rack.

RE: Comparison between work and rack arrangement and hydraulic cylinder

Compositepro is right. And I've done it. Works well if you're careful. Anchor the chain at each end of a support rail. Put the drive sprocket on the moving carriage. You have to make sure you get a good wrap (180 degrees if possible) on the drive sprocket. You can do that by positioning idlers on each side of the drive sprocket.

Told ya so

RE: Comparison between work and rack arrangement and hydraulic cylinder

Is this a "one time" move, or something that needs to be done repeatedly?

For a one time move the most efficient mechanism is no mechanism. Hire a rigging company.

You've mentioned pulling. Thus I suggest a winch.

A lot of experienced members participating in this thread, but mostly guessing because of the lack of good information.

RE: Comparison between work and rack arrangement and hydraulic cylinder

(OP)
Sorry if my information is lacking. Our project cannot be disclosed entirely.

@MintJulep, depending on the client it will be done once in a while. We are assuming once in a year. It needs to be pulled and pushed so winch is not an option.

@Jboggs, the chain loop is a good idea but we lack support underneath. The whole setup will be bolted to a wall of 3" thickness. In the chain loop system motor and gearbox moves along with the sprocket. Too much moving load. In rack and pinion, rack alone moves so, it is preferred.

RE: Comparison between work and rack arrangement and hydraulic cylinder

There are traction double drum winches that can push and pull:

https://cordem.com/double-drum/

I don't think Cordem's is big enough for your load though. In full disclosure, I have worked for Cordem. I'm sure there are other winch manufacturers that have bigger, similar offerings.

RE: Comparison between work and rack arrangement and hydraulic cylinder

It's interesting the precise and uselessly sparse facts. "3 inch thick wall"
How is the 10 ton load carried when there is a "lack of support from underneath"?

RE: Comparison between work and rack arrangement and hydraulic cylinder

(OP)
The load will have support underneath. But it will occupy all the support there is.

RE: Comparison between work and rack arrangement and hydraulic cylinder

(OP)
@3DDave,
Again I'm sorry for inadequate information. If you would please let me know what other information I should provide.

RE: Comparison between work and rack arrangement and hydraulic cylinder

Quote (Saindip)

please let me know what other information I should provide.

Imagine that you are trying to design a mechanism to move a 10-ton load 15 feet with some constraints.

Tell us the things that you, as an engineer are considering.

RE: Comparison between work and rack arrangement and hydraulic cylinder

You know far more that you aren't telling and cannot solve the problem.

So, there's a wall 3 inch thick. And a 10-ton weight.

I'm going to guess the wall is made of foam rubber and the weight is a block of animal fat.

RE: Comparison between work and rack arrangement and hydraulic cylinder

A picture is worth a thousand words. A diagram please? Show us some of your ideas. That would help. You can do that without disclosing proprietary information.

"In rack and pinion, rack alone moves so, it is preferred."
So, you're moving the rack? Why? It will stick out at each end of travel!

If the moving load is already 10 tons, I don't see how adding a motor and gearbox to drive a pinion or sprocket will add noticeably to the moving weight.

Your initial question was "which is more efficient in operation and cost, worm and rack or telescoping cylinder?" In my opinion, neither of them are desirable. A worm and rack is the picture of wear and inefficiency. A telescoping cylinder is the picture of costly. And a horizontal one is a maintenance headache! There are so many other ways to move a load.

And now you tell us its only once a year! That would have been nice to know. If its only once a year, why do you even care about efficiency? Why power it at all? Get a hand crank winch, call it a day, and move on to the next project.

I don't mean to be rude but I have to ask - have you designed linear motion systems before? If so, you know what information we need to help you. If you haven't that's ok too. We all have to start somewhere. Get some personal advice from an experienced mentor where you work.

wasting time

RE: Comparison between work and rack arrangement and hydraulic cylinder

(OP)
I completely understand. It is my first internship. Part time and WFH. Honestly, after each meeting I am getting new information and I need to implement them in the already built design based on previous inputs.
Fine I'll try to give a gist that contains as many facts as I can give.

There is a rectangular block of 10 ton load. It needs to be pushed or pulled around 15 ft. The load will be moving on rollers. Now I need a mechanism which can do the above task as frequently as once in a year maximum. This whole mechanism should be mounted on a concrete wall of 3" thickness parallel to which the load will be moving. There will be two such walls so two mechanisms. Alignment is very crucial here.
This load and walls and the mechanism are actually a part of a portable product. This whole thing can be deployed anywhere from a well established and levelled concrete or metal platform to the fields of Savannah. So there is no guarantee that I will get proper base to fix some equipments in front/behind of the load to pull or push it.Nevertheless, our product will be first deployed on a well established metal platform for the first time. This platform is just as wide as the load and the walls. By the way, the load will be in between the walls. So there will be no support beneath the mechanism for now. There will space at front and back though but that may not be the case all the time.
Whatever the mechanism is, it might be operated multiple times to get the load in right position (for rack, cylinder, chain loop, etc.). Because the chances are that this mechanism will come fitted from the factory itself and there is a 8ft width restriction for any article that is to be transported by road. So the maximum length of the rack can be 8ft only.
Now the most baffling thing is there may not be any crane at the deployment site. There are trucks that has a loading and unloading system so I guess it will be used to unload the whole product. But that's about it. It can't do anything about the mechanism. So the mechanism should have structure that is easy to move up/down with a chain block. And there will be 4 to 5 men to deploy this whole thing. At least that's what I've been told.

RE: Comparison between work and rack arrangement and hydraulic cylinder

"Alignment is very crucial here." I suggest yous eparate your alignment function from your motion function, and give us an idea of what accuracy is required.

To be honest a hydralic ram or leadscrew just sounds like more trouble than its worth, a 10 ton load horizontally on rollers is a handwinch scale job.

Cheers

Greg Locock

New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Comparison between work and rack arrangement and hydraulic cylinder

(OP)
There is a 10mm gap between the wall and the load. It should remain the same. Basically the side of the load must be parallel to the wall.

RE: Comparison between work and rack arrangement and hydraulic cylinder

Sounds like a recreational vehicle slide mechanism.

Ted

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