to bend a Thin pipe

Hello, I need to bend a very thin pipe (a heat pipe), it's about 19mm diameter and 0.7 mm thick. The raduis of bending is 50 mm and a the inside of the pipe has a precise geometry that cannot be deformed : There are theet of 2mm high and 1mm wide all around the inside, with a 1mm gap between two consecutive theet. It's an aluminium alloy. The pipe has to keep continuous teeth for the capillarity and a constant gap between the teeth. We must be able to clean it up really good if you put smthg in it for bending, and we cannot put sand. Excuse my english. Thanks for any answer.

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snipped-for-privacy@gmail.com says...

Cerrobend alloy, or water.

If water, freeze the water with liquid nitrogen before bending.

Do a test on a sample first, the expansion may crack the tubing at that size.

Jim

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On 5 Dec 2005 08:24:42 -0800, with neither quill nor qualm, jim rozen

Jim, you're the first person I've ever heard who has ever suggested freezing metal (freezing the water freezes the metal) before bending it. Can you explain how this would work? Most things tend to get VERY brittle at freezing and sub-zero temps.

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Towards the end of the 'factory tour' here

http://www.zacharymusic.com/Zachary_Music/ZTR900Factory.htm

there is reference to bending brass tubing after filling with either pitch or a frozen water/soap mix, to support the tube while it is being bent. Also some interesting pictures of metal spinning in progress

Don Valentine

quickly quoth:

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As a low-temperature engineer, I have a) access to cryogens and b) the frequent need to fabricate intricate assemblies from small diameter, thin wall tubing. The tubing can be copper, phos bronze, stainless, or sometimes cupernickel alloy.

The easiest way is to use the tube like a soda straw, you dip it in water, and stick your finger over the end to trap the water by preventing air from coming back into the top of the tube. Then dip into LN2 until the water freezes.

Then bend (typically using gloves) to get the shape (bends, spirals, etc) desired. Keep the water solid by periodically re-dipping into the LN2.

Once the tube is warm, the water just blows right out. The only real problem is for real thin-walled stuff, the expansion can burst the wall of the tubing. Hence my caveat to him to try on a setup piece, first.

My worry is, for 2 cm dia tubing he may have trouble bending no matter what he fills with.

Jim

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On 5 Dec 2005 12:52:08 -0800, with neither quill nor qualm, jim rozen

So cupric alloys do well at low temps, remaining elastic. Interesting.

"Just watch your dipping fingers", eh?

Right.

Could be. Thanks for the info, Jim.

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"jim rozen" wrote: (clip) freeze the water with liquid nitrogen (clip) ^^^^^^^^^^^^^^^^ This brings up a few questions: 1.) Where do you get liquid nitrogen? Especially, where do you get enough to submerge a length of tubing like this? 2.) What kind of container would you use? 3.) Why is liquid nitrogen better for this than, say, the freezing compartment of your fridge? 4.) Finally, as Larry wondered, what does low temperature do the ductility of aluminum?

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Lichtman says...

It's a commercial cryogen, so it's available where I work at the end of nearly every building aisle.

For small pieces I use a large styrofoam coffee cup. Important to empty the coffee out first, and keep telling youself "don't drink, don't drink..."

For larger lengths a small nitrogen dewar is used. This is nothing more than a fiberglass or stainless thermos bottle, deep enought to submerge the tubing. Actually I had a tougher time finding a deep container for the *water* and finally had the glassblower at work make a deep glass beaker for me.

Aside from the fact that it allows the ice to be re-frozen during the bending rapidly, not much. It also allows one to freeze the water rapidly so it does not run out of the tube. Also I don't have a freezer of any size at work.

I certainly hope it doesn't embrittle much. The inner vessels of most of our research dewars are made of aluminum sheet, rolled and welded into cylinders. These are used to hold liquid helium for the most part.

Unlike polymers, the ductitility of most metals is not strongly dependent on temperature.

Jim

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-snip-

funny this came up tonight. earlier i was out in my (unheated) barn/workshop and was thinking about a post i put up a few months ago in reply to a thread about the steel of the titanic becoming brittle in the cold ocean water. at that time i said it always seemed to me to be b.s. that steel (or were they using wrought iron?) could become measurably more brittle with a difference of only 30 ~ 40 degrees Fahrenheit. (i don't know what the water temperature was at southampton (in april) when they left, or exactly what the water temp was when they hit the iceberg, but i was guessing something like 60 degrees and 28 degrees.) was wondering if there were any metallurgists on the list who could confirm it.

p.s. jim, that sounds like some fun stuff to play with. i thought they always said if you put liquid water into liquid nitrogen it would "blow up". (i'm not doubting you, just one more "myth")

(reminds me, recent story in the local paper, the aluminum extruders in the factory next to what used to be the schrade knife works in ellenville ny, Hydro Aluminum, they had an explosion recently, i think it blew down some walls and blew out some windows, said some rain water got into some kind of aluminum melting device, exploded. wow huh? (i remember months ago someone writing about a re-bar plant somewhere and how you could hear for MILES the explosions when/if some water/ice went into the molten metal vat. wow!)

http://www.recordonline.com / November 28, 2005 Chemical reaction caused explosion

Ellenville - A chemical reaction at the Hydro Aluminum of North America plant Saturday night caused an explosion that blew out wall panels and scattered dust over a 30,000 square foot building. "The local building inspector issued an order to close the building until a structural engineer could come in to evaluate the damage," Bob Newmyer, managing director of the remelt facility, said yesterday. Newmyer described the reaction as rain water that came into contact with the liquid aluminum in the melting furnace. The encounter caused the release of steam and a powerful burst of energy that popped out some wall panels. Napanoch and Ellenville fire departments responded to the scene just after 11 p.m. Saturday. There were no injuries and the release is not considered toxic. Workers at that part of the plant have been asked not to come in until the building inspector says it is safe to re-enter the building and clean up efforts are complete. About five people per shift were affected. "We'll be using regular cleaning crews brooms and vacuums to get the dust off the machinery before we start it back up," Newmyer said. Wawarsing building inspector Robin Coleman said the department would have no comment on the incident until she'd reviewed the structural report. Deborah Medenbach

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Yes, steel gets brittle at lower temperatures. IIRC it is below 30 or 40C. Not all alloys react and some more and some less. And yes, just a little temperature difference makes a big difference in ductility.

Copper, brass, bronce, aluminium and austenitic steels don't get brittle at low temps.

Can't (quickly) find any diagrams for more details.

Nick

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    I've noticed you using this word several times in the past. I *think* that you mean "bronze", not "bronce", which I have never encountered.

    Sorry about the spelling pointer, but overall you do so well in a second language that I had to point this one out since you keep using it. I certainly could not do as well in German as you do in English.

    Enjoy,         DoN.

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Oh, sorry. So it is the same spelling like in German. I didn't look it up in the dictionary. OTOH, we sometimes write "bronce" (old spelling). And this looked more english to me. 8->

Nothing to beg my pardon. And thanks for the flowers! :-)

Nick

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says...

Googling "brittle to ductile transition" will turn up plenty. Here's one interesting link...

http://www.matsci.ucdavis.edu/MatSciLT/EMS - 174L/Files/DuctileBrittleTransition.pdf

The transition can be quite dramatic. I've been working on automation and tooling for forming tungsten and molybdenum, both of which have a well defined BDT within a few hundred degrees of room temperature. Moly wire that seems to break if you look at it sideways becomes pliable with the application of some hot air.

Ned Simmons

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I grew up in Southampton, and trust me, if we ever got 60F in April (yes, I know you mean sea temperature), there would be dancing in the streets :-)

William Wixon wrote: [snip]

[snip]

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To be honest, that's exactly how we do it. But it takes too much time and precaution, to bend a pipe this way, especially when there's more than one to do (you have to let the ice liquify completely, or else you could have locally melted ice that would brake the pipe while refreezing), and we that a competitor bends his pipes at ambient temp already filled with ammonium at saturation ( 8 atmospheres!!), and that works(with a certain but acceptable lost of the efficiency)!! We don't know if it's their shape or an outside guidance of the pipe that prevents their heat pipe from breaking or stop working. So I thought of small rods at the same size of the gap, that would slide on the tube and be less deformed than the pipe (pipe 15% deformated, rods : 1.5%) and stay in the elastic zone, so they can be removed easilly after bending.

But then other problems : what would prevent the expension of the gaps? What kind of metal to use for the rods (elastic enough, but higher young module than alumnium)?

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I guess that even with those fins, you can use a mandrel bender. Only making the mandrel would be a bit tricky (but still doable).

Advantage of the mandel bender: You just have left some oil in the tube after bending. Setup-time only once, and then every bend is just something of 1/2 a minute.

Nick

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