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How to Corrugate Thin Stainless Steel?.

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  • Norman Bain
    replied
    Something like this may work. I have exagerated the shape; but essentially a couple of bits of wood hinged at one end and shaped to a die at the other. Scribe a guide circle with a sharpie on the material you want to put the circular curves into.

    Insert the material into the die so the sharpie line is under the die and bang the two halves of the die together with with hammer. Rotate and bang, rotate and bang. Two persons for this task would be way faster.

    I expect that the material will need to stretch to become a flat bellows; so some panel work on the flat surfaces will also be in order.



    Norman

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  • ecar
    replied
    Thanks. Great Ideas.

    You guys are really good. Many really great ideas. Many more experiments for me to try than I had expected.

    I stated the question as broadly as I could so as to not limit ideas. Definitely not disappointed. What I want to do is make yet another attempt at a useful Stirling engine. It will be an air Stirling so the pressure will be relatively low and large size is very helpful. This question was for the power piston. The displacer has a different idea.

    I want to make a sealed "piston/cylinder" without a piston moving in a cylinder. I want the corrugation to be made in one direction in a flat surface (a la rectified sine wave) to minimize dead space since dead space is very detrimental to Stirling engine efficiency. Also, I think it should decrease the maximum stress and be simpler.

    1-800miner gave the first and basically only answer I could conceive. It would take a long time to do, but, since the quantity is one and not several thousand, that does not rule it out.

    I want to investigate an adaptation of Kitno455’s idea even though it might require spending a little money. There is a cheap, thin-walled PVC pipe. DWV?? Get various sizes of the cheapest unions of some sort and cut off ½” lengths. Somehow fix the biggest and smallest to a board. Put the sheet on top of the two and pound the third length of pipe between them. With a foot diameter, I should be able to do that at least 4 times assuming I can find four sets of 3 appropriate diameters. Luckily, precision is not at all necessary.

    When I first started thinking about this, Ian’s idea of using copper flashed through my mind for a brief instant, but I thought, “Who is gonna make sheet copper that thin?” It turns out that at least one somebody does. http://basiccopper.com/thicknessguide.html I have various concerns such as fatigue, but this is another good idea that I did not properly consider. Also, a significant heat transfer advantage.

    Thanks to everybody. Many great ideas. I think somewhere in there is something that will work well enough.

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  • flylo
    replied
    How about using just the right kind of plastic? I'm thinking 12" tupperware type lid with a hole & knob to pull out put your thumb over hole & push in remove thumb pull out with knod & repeat. Simple & cheap if plastic will work.

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  • Ian B
    replied
    Ecar,

    Darryl (above) probably has the best method to do this job that I've seen so far. If this is too difficult, have you considered other ways of doing what you want? Would one of these be of help: http://www.ebay.co.uk/itm/1-75-Exhau...oAAOSwpDdVGPK0

    They come in various sizes. There's a cylindrical stainless bellow inside that braiding; would that, with an end cap do what you want?

    Ian

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  • darryl
    replied
    Make a top and bottom die with the shape according to your diagram, but make it only 1/2 inch wide. You need to make them pivot so they will stay in alignment but will open and close. Now arrange to spin the disc through the gap between them. Set up on an anvil or something really solid. Then progressively hammer on the top die and rotate the disc bit by bit. You will probably have to turn the disc a dozen full turns or more until the corrugations are as deep as the die parts you made. I'll estimate that by the time you've got it done you will have brought the hammer down at least 1000 times.

    If you've followed this idea you will see that you have to overlap each indent to blend it in with the next one, etc, and that you could shape the die curves to suit the radii of the corrugations. Maybe have some Advil on hand for the headache you'll probably get
    Last edited by darryl; 04-03-2017, 03:15 AM.

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  • Ian B
    replied
    Sorry to say, that doesn't look like an easy job at all, considering the equipment that you have. You have one of the hardest materials to work with, especially when it comes to forming. Putting straight corrugations in would be relatively straightforward (basically a series of folds, back & forth), but concentric rings will be really difficult. Doing this with annealed copper would be easier, that maybe a good starting place.

    Good luck!

    Ian

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  • kitno455
    replied
    go to a job site and get several short offcuts of thick walled plastic pipe. Cut them all to the same length, and round one end with progressively finer grades of sandpaper. Attach the other end to a piece of plywood such that they are all concentric. Now you have a male die. For the female die, you could cast it using the male die in plaster or perhaps just set it in a tray filled with sand. Then make a stack with female die on the bottom, shim stock, then male die. Then build a ramp, and drive a car up onto back of the male die.

    allan

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  • MattiJ
    replied
    Originally posted by Magicniner View Post
    For a round diaphragm I'd turn male and female forms and use a press, depending upon the depth of forming required several sets of forms of increasing displacement and annealing between stages might be in order.

    - Nick
    Spin forming again turned form might be also one option if lathe is available.

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  • Magicniner
    replied
    For a round diaphragm I'd turn male and female forms and use a press, depending upon the depth of forming required several sets of forms of increasing displacement and annealing between stages might be in order.

    - Nick

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  • ikdor
    replied
    I would try to hydroform it with a pressure washer.

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  • Jaakko Fagerlund
    replied
    Originally posted by oxford View Post
    If using this as a bellow wont SS work harden with the repeated movements and cause problems?
    Only certain alloys do that.

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  • BCRider
    replied
    ......It is to be used as a sort of diaphragm. I would like as few concentric indentations as possible. I am just a poor, simple, peasant. So, high tech stuff like fire is a little too advanced. I'm thinking more like stones and wood - maybe a bone?

    What I am making might be used as a bellows. If one attached this around the edges to a flat plate having a hole in the center, one could lift the corrugated piece in the center to draw air in and, then, release to force the air out.
    Oxford, can that be forced into rolling the flat circles to do what he wants? I've only used one of those rolling machines once and it was to form a safe edge on some flat sheet metal.

    A diaphragm made in this style with MORE rather than less corrugations would be easier to move with a given amount of push and pull and move more air as a result. The fewer and shallower the concentric corrugations the harder it will be to move it easily or the less volume per stroke you'll move. In effect you need to make it more so you're flexing the corrugations and not trying to stretch the metal like a drum skin.

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  • oxford
    replied
    Round would be easier that square to do but not without tools. If I had to make round tubing like that I would make a set of round male and female dies of the profile I wanted for the "corrugation". Then configure them like a sheet metal bead roller with a throat deep enough to do the tube going from each end. It could be made from scrap materials and doesn't have to be fancy.

    Basically make something like this.

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  • BCRider
    replied
    Originally posted by RichR View Post
    I'd like to offer you an alternative idea. Take a can opener and cut the bottom off of a large coffee can. it already has a circular corrugated
    pattern in it.
    Because you want a set of circular corrugations I think this might be the best option. Folding longitudinal corrugations would be challenging enough on .010 stock. But circular means you can't just "fold" it. You'd need to actually stretch the metal into circular grooves. And on the thinner stuff that means it'll kink and fold badly and on the thicker stuff it'll fight you hard and just your rocks and a stick won't do the job. Either that our you start with two really BIG rocks and wear the pattern you want into them with the stick. One male and one female and then crash them together really accurately with the metal in between. Because a stretch forming action from a big press is about the only way I can see to do something like what you want.

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  • oxford
    replied
    If using this as a bellow wont SS work harden with the repeated movements and cause problems?

    Leave a comment:

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