Fuel tanks

Discussion in 'Motorized Bicycle General Discussion' started by Ludwig II, Jul 31, 2012.

  1. Ludwig II

    Ludwig II Well-Known Member

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    Has anybody made a tank or know of a tank made using the 2 stroke expansion chamber technique of blowing? You weld 2 flat pieces of steel together along the edges and then pump water in until they balloon outwards. You can get some very swoopy shapes that way.
     
  2. 2door

    2door Moderator
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    Be very very careful trying this. Unless you have a good understanding of metal, welding and the pressures you'd be working with, you could be injured. Hydro forming metal is a job best left to those with the knowledge and the proper equipment. Simply pumping water into a closed vessel without careful engineering could produce a very effective 'pipe bomb'.

    Tom
     
  3. Ibedayank

    Ibedayank New Member

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    http://en.wikipedia.org/wiki/Hydrostatic_test
    Water is commonly used because it is nearly incompressible, therefore requiring relatively little work to develop a high pressure, and is therefore also only able to release a small amount of energy in case of a failure - only a small volume will escape under high pressure if the container fails. If high pressure gas were used, then the gas would expand to pV=nRT with its compressed volume resulting in an explosion, with the attendant risk of damage or injury. This is the risk which the testing is intended to mitigate.


    The cylinder failed at 550bars/8,000psi water pressure during an extended proof test to investigate how the cylinder would rupture after failing visual inspection with extensive internal corrosion.
    http://www.youtube.com/watch?v=AB9QvkvQuvM

    now just using airpressure alone at under 200psi and we get

    [​IMG]
    http://www.cdc.gov/niosh/face/stateface/ca/05ca010.html
     
  4. Pilotgeek

    Pilotgeek New Member

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    You don't know until you try. I hate the mentality of "you have to be a professional blah blah". Sure, you can spend half of your life going to school for something, or you could like, have a little fun in life and just take a shot at it. It would be smart to sit down and do some basic research first, and take a few safety precautions, but at some point in history, there had to be some crazy people to be the first to try something. Plus, water isn't compressible. It wouldn't make a very big explosion anyway. Something needs to detonate very quickly and evenly to make a bomb. Water isn't fast enough and doesn't have enough pressure buildup. It would blow open a hole where all the water would escape from, but it would be very, very unlikely to simply "explode". Any water vessel you have seen explode was from steam / heated water.
     
    #4 Pilotgeek, Jul 31, 2012
    Last edited: Jul 31, 2012
  5. Ludwig II

    Ludwig II Well-Known Member

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    I always think 2 stroke exhausts look like a python's swallowed a baby.
     
  6. CroMagnum

    CroMagnum Member

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    I've never heard of expansion chambers being formed in that way. You want the dimensions of a pipe to be very precise, something not possible by pumping water in between a couple of welded plates.

    Most OEM chambers are made two halves of stamped sheet metal that's been welded together like this -


    [​IMG]


    And most aftermarket pipes are constructed from rolled cones and bent header pipes, again welded together -


    [​IMG]


    Whoever told you that water forming fairy tale was just making things up to see if you'd believe them.
     
  7. Pilotgeek

    Pilotgeek New Member

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    I could definitely see welding up an xchamber and then pumping water to get it to round out a bit. I could most easily see this done to make neat looking gas tanks, though.
     
  8. CroMagnum

    CroMagnum Member

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    So what happens when part of the pipe you don't want to change balloons out and you've lost your dimensions? Not to mention the thousands of PSI you'll need to actually bend metal. Sorry, but while this alleged forming technique may work in Internet Fantasy Land, it worthless, expensive, and dangerous in the real world.
     
  9. Ludwig II

    Ludwig II Well-Known Member

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    Trust me, I can't answer for 2 strokes in America but, in my racing, blown pipes are entirely ordinary, and the same applies across European countries. OK, if you need to change direction or angle somewhere you will have to cut and rotate the sections, but you get far smoother shapes far more easily than with welded up rolled sections.

    There is a downside though, in that harmonic cracking can occur, where the fracture actually goes at an angle through the pipe, like glass breaks. It's effectively impossible to repair when it goes like that.
    Here's the way it's done: http://www.3wheelerworld.com/showthread.php/95083-How-to-build-an-expansion-chamber
     
  10. Pilotgeek

    Pilotgeek New Member

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    Whoa whoa whoa hold the phone. Why are we talking about expansion chambers? The original topic was forming gas tanks, which probably can be done.

    EDIT: Just looked on wikipedia:
    How expansion chambers are made

    Hydroforming

    Two flat representations of the required finished pipe are cut out of sheet metal. The edges of the two identical flat cutouts are welded together forming a sandwich. On one end of the pipe a fitting is welded and high-pressure water is pumped into the cavity between the sheets. The pressure inflates the flat sheet into its final rounded shape. This method can be quicker than hand forming and only slightly more costly in tooling, however it requires a number of trials before a finished design as accurate as hand formed or stamped can be produced. All curves must be made in a single plane so cutting apart and re-welding is often required but the final product can be as good as a stamped pipe if enough care is taken to be precise.
     
    #10 Pilotgeek, Jul 31, 2012
    Last edited: Jul 31, 2012
  11. Pilotgeek

    Pilotgeek New Member

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    Okay, yes it works, and here's a video of it happening:
    Hydroforming

    As far as safety goes, you can pretty much watch it "inflate" from a distance and remotely shut off the water.

    So, CroMagnum, still think it's impossible? I'm reading more about it, and it seems to be a pretty common real professional practice. "Internet Fantasy Land Fairy Tales" indeed.

    [​IMG]
     
    #11 Pilotgeek, Jul 31, 2012
    Last edited: Jul 31, 2012
  12. CroMagnum

    CroMagnum Member

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    I didn't say it can't be done. It obviously can. But you don't have good control over the internal dimensions, you're forced to work with extremely thin sheet metal, and you have to work with dangerously high pressures. This is a technology with too many problems and limitations to be successful. Plus, you're never going to take an existing chamber made from 18ga. steel and hook it up to your pressure washer and have dents pop out.

    Pilotgeek - did you see how badly the pipe in the video kinked up and changed shape as it "inflated?" Not much control of the final product, which is really what you want.

    I saw a guy on youtube make a steam powered bicycle which actually worked and moved around. But the technology isn't suited for that purpose, so no one but a backyard tinkering crank will ever try and do it. I think the blown pipe makers would be much better served by rolling cones and welding them together. They'd probably make more power and last longer.
     
  13. Ludwig II

    Ludwig II Well-Known Member

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    Cro, I'm baffled. This technique has been around in the 2 stroke racing world for years, and is the method of choice for ultimate accuracy. Why are you having such difficulty with it?
     
  14. Ludwig II

    Ludwig II Well-Known Member

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    Thank you Pilot. The point about pipes and tanks is that they are both thin walled vessels, one for containing fuel and the other for governing and using the energy of a dynamic fluid, which is exhaust gas.
     
  15. Pilotgeek

    Pilotgeek New Member

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    Oh quit it, CroMagnum. You're wrong and you're trying to save face. You said it can't be done and you know it. That was a home-made expansion chamber. I'm sure a professional one with pressure meters and better welding could be near perfect. This was hydroformed. (Even more pics and info )

    As far as perfection... how many people slap some random 50cc pocket bike pipe onto their 66cc china girl with decent results? I've seen it more than once. Yes, it's great to be precise, but these engines aren't very precise to begin with.
     
  16. locell

    locell New Member

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    Lots of bicycle frames are hydroformed, they usually use a hydraulic fluid or oil to do the forming and well, its a pretty standard technique for shaping metal. It works good on aluminum.

    http://en.wikipedia.org/wiki/Hydroforming
     
  17. Pilotgeek

    Pilotgeek New Member

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    Back on topic though, I think making a tank using hydroforming is a wonderful idea. You could get some really nice smooth shapes out of it, even if it may take a few tries.
     
  18. MotorBicycleRacing

    MotorBicycleRacing Active Member

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    Felt, Nirve and many other bicycle frames are hydro formed.
    The aluminum felt frames hold about 1/2 gallon when
    sealed into a gas tank.
     
  19. dracothered

    dracothered New Member

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    I think the hardest part would be knowing what shape to cut the peaces of metal before shaping them.
     
  20. Ibedayank

    Ibedayank New Member

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    Harley-Davidson's Chief Styling Officer, Willie G. Davidson, asked for a frame so beautiful it could sit in a museum. And that's exactly what the Harley-Davidson team of engineers created. Using an innovative process called hydroforming, they were able to form unconventional angles and apply fewer welds by bending and shaping metal pipes with high-pressure water. The result: a sturdy chassis with improved rigidity. To date, The Motor Company is the only major motorcycle manufacturer to use hydroforming to construct frames.

    [​IMG]
     

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