Comparison between work and rack arrangement and hydraulic cylinder 1

[saindip]

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?
Thanks in advance.

 

[MintJulep]

Really?

 

[desertfox]

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

 

[hydtools]

What is your definition of efficient?

Ted

 

[drawoh]

saindip,

Have you tried analysing them?

--
JHG

 

[Jboggs]

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.

 

[FACS]

The worm and rack will be.

 

[hydtools]

Worm and rack? Worm gear is not very efficient.

Ted

 

[drawoh]

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

 

[dvd]

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.

 

[GregLocock]

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

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

 

[drawoh]

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

 

[mfgenggear]

all I have to say is lead screw

 

[BrianPetersen]

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).

 

[saindip]

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.

@dvd thanks for your reply. I think your input proves our decision to be best.

 

[dvd]

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.

 

[Jboggs]

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?

 

[saindip]

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.

 

[Compositepro]

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

 

[Jboggs]

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.