Fuel tanks

Ludwig II

Ludwig II

Well-Known Member
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.
 
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
 
2door said:
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
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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

05ca010c.jpg

http://www.cdc.gov/niosh/face/stateface/ca/05ca010.html
 
2door said:
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
Click to expand...

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.
 
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Ludwig II said:
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.
Click to expand...


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 -


20pd5xf.jpg



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


ej649j.jpg



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


20pd5xf.jpg



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


ej649j.jpg



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


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
 
CroMagnum said:
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.
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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.
 
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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.

tumblr_m81lfjeXVj1r3dyaj.gif
 
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Ludwig II said:
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
Click to expand...


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.
 
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?
 
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.
 
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.
 
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.
 
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.

VRod01-frame-lg.jpeg.jpg
 
dracothered said:
I think the hardest part would be knowing what shape to cut the peaces of metal before shaping them.
Click to expand...

ok heres a technique I use a sheet of paper reacts much like steel if you try an bend it , it will show you were it wants to stretch an also where it needs shrunk , cut your proposed shape in paper first seal with tape an use air pressure to gently inflate it it will show you almost exactly what will happen when you try to use steel or aluminum , doing things this way will keep costs down so you dont have to scrap all the failed attempts an keep buying metal as well as you will learn what shape the metal will have to have to get your desiered shape. that being said , if I were to form a tank , I prefer to use slightly lighter gauge steel than say 16 gauge do a test run with air pressure as you can hook up an control the pressure from a distance that would be how ever long your air hose is , once you get a decent one that way move up to the hydroform . the key to this is slow an methodical but worth it in the end . I have tried it didnt like it much .
personally I prefer to hand form on a english wheel then use different hot an cold techniques , as well as hammer an dolly to get the final result . ya just have more control over the metal my way .if anyone would like to see some pics I built the tanks on threads mock up kinda rough , build no.2 wifes beach trike , an , felt guilty been holding out on one build . all done with hand forming techniques.
Gary
 
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