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Forum Index : Other Stuff : bending stainless steel tubing
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imsmooth Senior Member  Joined: 07/02/2008 Location: United StatesPosts: 214 |
I am working on a liquid nitrogen project that I plan to document and make a tutorial. I have acquired an oil-free compressor that can do 3300 psi, although I plan to just go to 2500. I need to make a condensor coil and I am going to use 316 cold rolled steel 1/4" OD, 0.05" wall. My question is will I be able to bend this into a helical coil that is 1 foot (1/3M) in diameter over a form by hand? I know there are tube benders, but I don't want to buy something I am only going to use once. I would fill the tube with sand. I have done this with copper, but I know steel is harder. However, since it is just 1/4" I wanted to know if anyone here thinks it is doable or has any tips. |
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mac46 Guru  Joined: 07/02/2008 Location: United StatesPosts: 412 |
316 SS is about like spring steel...12 inch diameter may be doable by hand. It'll try to flatten out even with sand inside...take it slow. Mac46 I'm just a farmer |
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| imsmooth Senior Member Joined: 07/02/2008 Location: United StatesPosts: 214 |
Most of the tools for bending are meant for 90deg bends. What should I do if I want a helix? If I bend it on a large pulley with a groove will this help prevent it from flattening? |
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Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
It is best to rotate the mandrel and wind the tube onto it (not the other way around), i would not use a pulley and just use a wooden mandrel, it would be best to wind the tube tight side by side and then stretch the coils out like a spring after. Once you start winding dont stop until you have finished, as if you release the tention the coil will expand and then not pull down correctly when you start winding again. Forget the sand it wont help as you can not pack it tight enough, also you will not be able to remove all the sand / grit after and might cause problems with the compressor or other processes. I think you will bent the tube like butter in a 12" dia around a mandrel, done much of it in the Gas/oil fields. Sometimes it just works |
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yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
The best way to coil tube is to build a 3 wheel roller. I have one for making wheat silo base rings. I put pressure on the centre roller with a hydraulic ram and also drive the centre roller with a geared hydromotor. The trick for getting a good coil is to find/make/bodge a pulley profile that will support the sides of the tube as it is stretched to avoid kinks. .o5" wall thickness should resist kinking better than the thinner stuff. The idea is to run it back and forth a number of times and work up to the curve you need. You may need to install smaller diameter centre die to finish the coil as things get pretty tight towards the finish. Have a look at this topic on HomeBrewTalk.com I would experiment on some smaller bits to get the hang of it first. I'm confused, no wait... maybe I'm not... |
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| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
A rope sheave like this in 1/4" should only be a couple of $ 
I'm confused, no wait... maybe I'm not... |
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| imsmooth Senior Member Joined: 07/02/2008 Location: United StatesPosts: 214 |
Thanks for the info. Just to keep this all in one thread, my compressor that does over 3000psi had some brass and stainless fittings. I have these 1/4 NPT to 37deg flare couplers that go to the compression hose. Is there any benefit of stainless over brass fittings, or the other way around? I know steel has a higher psi rating, and brass has less corrosion. Anything else? |
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fillm Guru Joined: 10/02/2007 Location: AustraliaPosts: 730 |
Hey Yahoo, do you have a link to the makers or suppliers of this sheave . PhillM ...Oz Wind Engineering..Wind Turbine Kits 500W - 5000W ~ F&P Dual Kits ~ GOE222Blades- Voltage Control Parts ------- Tower kits |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
[quote]Anything else?[/quote] liquid nitrogen has a habit to freeze stuff which changes the properties of metals, brass will shrink much more then SS, and when using different metals on connections this can cause problems and leaks. Working with energized liquids should not be taken lightly, its not like working with liquids or gas, its far worst, and in the case of a failure the energized liquid just keeps unloading with great force. I was trained in pumping energized liquids (nitrogen) for oil and gas well applications, and have seen how distructive a failure can be, we actually distroyed treating lines in controlled bunkers to demostrate the dangers of working with energized fluids, its amazing to watch and would not want to be around a failure. In our case everything was pressure tested with water first to 2 times our working pressure, before any nitrogen was pumped. Our treating lines were rated to 15,000 psi or greater. Be careful. Pete. Sometimes it just works |
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| imsmooth Senior Member Joined: 07/02/2008 Location: United StatesPosts: 214 |
Thanks, but the fittings in question go on just the compressor part. The temperatures are on the warm side (100-400F) like any scuba compressor application. The compressed air will then go through a condensation coil in ice water to remove the heat. The cooled air will then go through a regenerative coil to bring the temperature lower before it goes throug a needle valve for expansion. The expanded gas should liquify and get collected in a dewar. All the fittings for the condensation coil are SS. The lowest rated one is a female-female connector at 6600PSI. The straight fitting can do over 8000 psi. The needle valve is rated for 5000 psi and this will see cryogenic temperatures. |
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| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
Sorry no, I can tell you it is made by National Mfg Co probably called a wall mount or ceiling mount pulley and usually it is a 3/8" width nickel sheave. It SHOULD cost about $8 and the replacement sheave $1.50 other brands I have seen are battalion and campbell. They are not generally sold by brand, every large chain store will have their own stock codes and they are lumped in with swivels, eye hooks and snap hooks (and usually out of stock  ).I'm confused, no wait... maybe I'm not... |
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