Slip Rolls (Possibly)

Time to delurk for a while.
For an upcoming project, it looks as though I'm going to need to acurately bend some 4 to 6 mm thick sheet (or should it be plate?) metal into partial
cylinders (max cylinder will be about 270 degrees). The max width I'll need to form is 350mm, with diameters in the 5" to 8" range.
I've been searching for slip roll plans, but have so far failed in finding anything suitable. So, it looks as though I'm going to have to design my own slip roll.
The design I'm looking to build is one with two upper rollers that are geared together, with a lower adjustable roller for setting the formed diameter. But the question is, what kind of forces are involved, what material would be best of rollers, and most important, is this a suitable method for such thick metal?
thanks moray
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M Cuthill wrote:

On 4-6 mm probably a lot more force than you could apply by hand ...me thinks
your going to have to think up someway to motorise it .
and heat the stuff at the same time.
all the best..mark
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Motorisation wouldn't be too much of a problem. I'd prefer manual operated, and I'm not worried if it's got to have quite low gearing to do it, as this project will only be a one off for now. If becomes more than a one off, then I'd quite quickly be motorising it with a hydraulic motor.

I've also got access to OA, but it means having to move everything 5miles to use it, so it would be a needs must solution.
moray
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Uh! That is a bit unhandy. The bent sheet will touch the table / stand. All (I have seen) designs have two lower rollers and one upper roller.

How wide do you want the rolls to be? How thick is the sheet metal?
Nick
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wrote:

Good point! Only reason I had the rollers around that way was I seen a picture of one built that way during my searches, and it was built up on it's own stand, so underneath was clear except for the connecting bar for holding it all together.

Wide enough to form 350mm wide sheet.plate, and material will mostly be either 4 or 5mm thick, but there may be the odd thicker, but narrrower bit.
moray
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I know its not much help but I very occasionally roll 1 mm on my rolls manually and I know I'm doing it.
Martin P
"Moray Cuthill cuthill_at_v21.me.uk>" <moray<dot> wrote in message wrote:

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"Moray Cuthill" <moray<dot> wrote:

You won't roll that by hand. Or you have a gear 1:zillion For the bending forces, I'll come back.
Nick
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Thought that I have something at hand, but I was wrong.
Nick
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wrote:

Thanks for looking. I done some googling last night, and found a link to what looks like a good source of information for calculating the required bending forces, but I was getting a bit tired by that point and nothing was making any sense. It did contain a chart showing the required tonnage for air bending mild steel, which is what I was looking for, so I'll have another read of it when I get some time. That should give me the information about the forces involved, so I can design the slip rolls accordingly. Only other thing I'll need figures for, is how much force the steel rollers will take before bending. I'd like to use as small rollers as possible, but would prefer to find out what I can get away with by doing some calculations, rather than trial and error.
And once I've done that, I just need to sit down and translate the figures into how much force will be required to turn the rollers, so I can select suitable gears.
thanks moray
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wrote:

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Moray,
A simple approach is to look at commercial machines able to do the rolling you need, and get figures for roller diamater, end plate size etc from them, thus getting you into the right zone at least.
AWEM
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I would do if I could find some suitable machines. Only machines I've found so far that are capable of doing 6mm plate, are all quite wide (in the region of 3ft upwards), and these are using 6+ inch rollers.
Now since I don't need that width, I should get away with rollers that are quite a bit smaller.
And taking some figures from two seperate industrial machines. One can handle 50" width using 6.3" rollers. Other can handle 80" using 8" rollers.
Now doing some calculations, cross sectional area of each roller is 31.16, and 50.24 sq.in. Now divide that by the length, gives 0.6232, and 0.628 cross sectional area for each inch of roller width, so take 0.63 as a rough average. Multiply by 14 inches, gives 8.82 sq.in, and convert back to diameter gives roughly 3.35 inch.
Off course that figure is for hardened rollers, so 4" (100mm) unhardened rollers should give quite a large safety margin. And just looking at a diagram from one of the sites, the two powered rollers can be a smaller diameter than the unpowered press roller, as they share the load. So two bottom rollers could be 75mm, with the top one being 100mm.
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Hardened or unhardened doesn't make a difference in stiffness. What you want to know is how much the rollers bend under load. Hard to say how much is allowable. The more it bends, the less accurate your work. Maybe something in the ballpark of 0.1mm for you setup?
The bending is calculated (in this case. supported in bearings on both ends, load evenly distributed):
f = 5 * q * l^4 / (348 * E * I)
With: q: load in [N] l: lenght in [mm] E: elasticity modulus in [N / mm^2] for steel it is about 2.1E5 [N / mm^2] I: I think you call that sectional momentum in [mm^4]
For a round bar, I is calculated: I = pi * d^4 / 64
with: pi: 3.14 :-) d: diameter in [mm]
HTH, Nick
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"Moray Cuthill" <moray<dot> wrote:

And if you want to roll a tube, how do you get this one out? Cut off a leg?
Nick
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wrote:

The Model Engineers Workshop Manual by G.H.Thomas has a design for a set of slip rolls that you could use as a guide. The sizes you are talking about are probably a factor of 5-10 more than those rolls are capable of though. George's design will work for you but you will have to upgrade the design from 1 1/8" rollers to 2 1/2" to stand a chance with that size of plate. At that point, you will probably either have to have some long handles or a gearbox if you want to be able to operate it.
Nothing impossible, just quite ambitious. If you could survive less accuracy then a hearth, tongs, length of bar, striker and a hammer would do the job handily :-)
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I'm really going to have to buy GHT's Workshop Manual. Bought his Workshop Techniques book a few years ago, but never quite got round to buying the manual.
At the moment, I've got a rough idea of a plan in my head. Since the longest bend I need will only be about 180 degrees (probably be less), I don't need to have above or below the rollers clear. This means I can build a sturdy frame (thinking 20/25mm plate for end plates), ball or needle bearings for mounting the rollers (figure these will offer less friction than a plain bearing under load), and then have supports above/below the rollers with additional track roller bearings to help prevent the rollers from bending. Power will either be elbow grease via quite a bit gearing (1st choice),or I'll mount a hydraulic motor to do the donkey work (2nd option due to the pain of having to borrow the motor and plumb it up)

Most of my projects are extremely ambitious! This project will be physically one of the smallest machines I'll of built, but it's going to be one of the hardest in terms of the parts required, and problems to be solved (bending the metal is going to be the easy bit, it's what's to be done with it afterwards that's going to be hard) Unfortunately, accuracy is required for this particular. If radiuses aren't accurate to within a millimetre, then the machine will most likely not work.
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Moray Cuthill

Have you considered sourcing tubing of appropriate diameter and wall thickness for your needs? That would be the first thing I'd look for. And if I could not find tubing the right size, I'd have a long look at my design to suit tube or pipe that was available, I think.
You might also look to a silversmiths rolls for a little design inspiration. Most of the ones I have seen had only two rollers, but were geared down considerably, and were very sturdilly built. They use them for rolling sheet to thickness as well as drawing wires from bar. Pretty high load stuff.
Cheers Trevor Jones
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"Moray Cuthill cuthill_at_v21.me.uk>" <moray<dot> wrote in message

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I really wouldn't want to use roller or ball bearings for that sort of crushing slow speed application. Plain bearings may give a small extra amount of friction but at least they will take the huge sideways force. The contact area of (particularly) ball races and rollers (to a lesser extent) is very small.
AWEM
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I have a set of rolls which have 41/2" diam rollers six foot long, its maximun bending thickness is .250 its electric motor is 5 hp and weighs about 11/2 ton. How the hell your going to roll that plate by hand I dont know. Regards Ben

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The George Thomas book "The Model Engineer's Workshop Manual" has a detailed description of the design and construction of a set of 3-roller bending rolls, with a geared version optional. As usual with GHT, the description is first rate, and there is a very useful discussion of the principles involved. Thus, even if you find the design is not suitable, the chapter is worth reading anyway. The ungeared version he built would handle 10", and bent 1/2"x5/32" strip down to 14" radius, the geared ones would have gone further.
Would be too small for you, but you should be able to scale up the design, though your requirements are a little extreme for a piece of "hobby workshop" equipment. Maybe some of the more large-scale contributors will have some suggestions....
Best of luck.
David
--
David Littlewood

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Thanks for the replies so far guys.
Sourcing tubing may be suitable for some parts, but given that things may have to be tweaked quite a bit, and even possibly remade using slightly altered dimensions, I'd rather build the equipment so I can shape what I want.
Having now thought about the design of a suitable slip roll, I'll design it around plain bearings, as it means less material has to be removed from the end plates (a suitable ball bearing would be quite a bit larger in diameter than a plain bearing), with end plates being 20mm thick with welded in wider bosses to give the bearings a larger surface area. Also, designing it around a hydraulic motor will most likely be the best way forward, but with the option of sticking a handle on it. As for the rollers, I'm thinking about 2 1/2" diameter, and made from a hardenable steel. Thinking something like EN24, which has quite a bit of strength, even when it's not hardened.
Does anybody have alink to suitable formulas/figures for working out the bending forces involved, or at least suitable google sugestions?
And for the poster who mentioned my ideas are not quite 'home hobbyist' size, they're quite right. I like to think of it more as professional hobbyist, due to the fact quite a large chunk of the stuff I build just now is built to work, even though I don't make any money out what the work done. I just get the joys/headaches of designing and building stuff, and going further into the negative availability of workshop space!
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