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Thread: Sheetmetal roller with soft platen

  1. #1
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    Default Sheetmetal roller with soft platen

    This project was inspired by a YouTube link in another HFM thread. If you missed it the first time click here for the link.

    In the video is a sheet metal roller that uses a plastic platern below the driven roller. The idea seems to be that the driven roller presses the metal sheet into the plastic platen forming a "dish".

    The whole idea got me going and I subsequently spent some time looking at other uses for plastic, including plastic springs etc.

    An advantage of the plastic platen appears to be that the usual "flat tip" at ends of the sheet being rolled are much reduced.

    I had a suitable piece of plastic so set about working up a design for it. The driven roller is 50mm, the plastic platen is 110mm and runs on 2 supporting idler rollers of 35mm each. I determined not to try and bore a hole thru the plastic platen and add a shaft. In the model the end plates are 300mm apart; though plan would be to go as wide as possible (say) 400 or even 500mm.



    The worm drive would not be essential but I do have it, having acquired it for about $15 in an auction. The reduction is 60:1 and motor is 1440RPM; hence the resultant 24RPM feels about right. My minds eye was making the leap that a possible advantage in using the gearbox would be that the screws pushing down the driven roller could be tweeked while the unit was running ... not to mention that all that cranking would go away ... plus I would not need to hold the whole thing down while cranking.



    Envisage me at this point on my computer tinkering with the Alibre CAD model. I am at the point of determining what size and how many bolts I would need in order to effectively push the driven roller into the platen without stripping threads.

    Decided I had better do a test; so setup the 12ton press, as in image below, and cranked up the pressure till I could see a distortion in the strip of strapping. The strapping is 1.3mm thick and 30mm wide. The test "driven roller" is 35mm ... the one modeled in CAD is 50mm. The plastic platen is 110mm diameter.



    The press has a large dial attached to the hydraulic hose; it took 2 tons of press to get to the distortion in the image below ... way too much in my book.

    Last edited by Norman Bain; 08-11-2019 at 10:40 PM.

  2. #2
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    I determined I needed to get the pressure down to 1ton or less. In the image below the plastic platen is removed and some conveyor belting is used.

    It is clear that the driven roller can press into to the softer material way easier.



    Next tried a 110mm portion from a 2mm sheet. At 1 ton it also showed that that too was "formable".



    Now here are the questions:
    1) Is the test with the plastic platen correct? That is, was it actually working ok enough to stay with that design?

    2) I figure that I could use a length of the conveyor belting and just run it back and forward; essentially place conveyor belting between the plastic roller and the work in the CAD image. Would probably rework the design to use 1 metal driven roller and 1 metal idler roller under the conveyor belting. Would this work? Would the conveyor belting be "too soft"? Would the conveyor belting delaminate or otherwise not remain flat?

  3. #3
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    The plastic is far too stiff,the conveyor belt a little too soft,but might work .The Arcotech website lists the roller as being covered in 90 Shore A urethane.

    https://www.acrotechinc.com/roller-manufacturing/

    I've given some thought to using urethane caster wheels.

    http://www.durableusa.com/polyurethane-wheels.html
    I just need one more tool,just one!

  4. #4
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    Thanks wierdscience.

    It looks like the Shore A scale of hardness is will assist the material selection process.

    If the roller in the video was "Shore A 90" then perhaps 80 or 85 is the place to start.



    I have quite a collection of plastic having purchased some when a local machine shop that used plastics for prototyping closed down. Some of it is labelled but nothing clear as to the Shore rating.

    So ... cause we all just need one more tool ... I purchased a $23 Shore A Tester ... it should be with me in a day or three.

  5. #5
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    Hockey pucks are around 90 shore A if 3" diameter suits your needs.
    Maybe harder to find in Australia but in here they go for about 1eur/usd per piece.

  6. #6
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    The Shore A Durometer has arrived.

    Essentially they are a "shaped pin" that is below a spring. You push the pin into the material till the flat surface of the meter touches the material. So it is a "how much does the shaped tip press into the material" thing being measured.

    I did note that the Shore D Durometer for harder material had a much sharper point ... makes sense.

    I did note that on soft material, if you pushed harder than required, the flat surface would compress the material and give an increasingly higher reading as the material became more compressed/dense.



    The stiffer of the foams that came in the box gave a reading of Shore A 25. The metal bar holding the gauge (sort of vertical in the image) was putting about the right pressure on the material ... so reading was pretty good. If I left it for a time I did note that the pin would press further into the material (making a dent in the foam) and the reading would drop to 20.



    The "plastic platen" that I used originally in the press came in at Shore A 98.
    The "conveyor rubber" that was used in the press comes in at Shore A 82.
    There is another section of "conveyor rubber" (that is 15mm thick) that measures Shore A 75.

    So it looks like I have some flat rubber sheet that will work. Of course a rubber roller around 120mm diameter and Shore 80 - 85 would be better ... but I do not have such a thing as yet. I note online there does seem to be a conveyor roller called an "impact roller" that has rubber sections in a row ... but thus far all those have gaps in between. Maybe the roller could be taken apart and just the full diameter sections used.

    As currently modelled the CAD tool, the model is now probably overkill. Could probably get an acceptable result using 2 x 50mm rollers, one driven and one an idler; and put the rubber sheet in between.

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