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  1. #1
    KIMFAB's Avatar
    KIMFAB is offline Stainless
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    Default Need some thinwall copper tubing

    I am looking for a source for copper tubing about 1/4 to 5/16 dia with a wall thickness of .010"

    Most of the stuff out there is between .020 and .030 which is way too thick for my application and the suppliers of the thinwall stuff want to sell you at least 500 lbs.

    Any ideas?

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    rcoope's Avatar
    rcoope is offline Aluminum
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    Fascinating. Both McMaster and Small Parts have 1/16 to 5/32 in 0.014" which doesn't help. Could you get something like 3/16 OD x .03" wall and swage it out by forcing a ball through it? Like how they make trumpet tubing etc? That might not work but it would be fun to try. You'd have to use a thicker wall pipe as a forming die perhaps....

    R

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    rcoope's Avatar
    rcoope is offline Aluminum
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    By the way could you elaborate on what these tubes are for? I always wonder in these situations if someone (an engineer perhaps) has asked you to make these where they really could get away with something much simpler but they don't know any better.

    RC (who is an engineer)

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    KIMFAB's Avatar
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    I have thought about swaging but don't want to get too involved yet.

    As for the application all I can say is it has to have a minimum thermal mass.

    I too am an engineer, I even have my own hat.

    But yes I know of what you speak, many times significant savings can be had with a little tweak.

  5. #5
    9100's Avatar
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    If you can use 300 series stainless, New England Small Tube has it and will sell small quantities. Be careful about ordering long lengths. A couple of times other suppliers crated it in wood and the shipping charge exceeded the cost of the tubing. Contact New England Small Tube
    I have been making liquid helium transfer lines which are a small tube inside a larger one with the space between evacuated, essentially a 10 ft thermos bottle with an opening on each end. Thermal mass of the inner tube is important because you boil away helium until it gets down to the liquid temperature. I made the last one with 5/32" OD, .006" wall SS. I am waiting for results on helium, but we tested it with liquid nitrogen. Performance was far superior to previous efforts. These lines have 4 90 degree bends. Getting the inner tube to follow them without kinking is not simple, but it can be done.

    Bill

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    jim rozen is offline Diamond
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    Would brass tubing work? If so, Small Parts Inc. sells foot-long lengths of
    telescoping brass tubing, with 0.015 wall.

    9100, I guess you are in my business then - although it's been a long time
    since I've transferred helium. These days most of our work is using closed
    cycle cryogen-free systems.

    A tip for LHe transfer lines: The inners and outers can be spaced away using
    small triangles of thin phenolic, the tips are big enough to slide inside the
    OD tube, and the hole is sized to just fit the inner through. Another good way
    is to tie small nylon beads in a set of three, around the inner, using cord.
    Again, three point contacts on both the ID and OD.

    You can wrap superinsulation around the parts as well. Alternating layers of
    alumized mylar and nexus cloth. Tie with dental floss or use kapton tape.

    Make the inner tubing with as LARGE a bore as you can. I like to specify 3/16 ID
    because it makes the transfer line 'fast.' The faster you move the liquid around,
    the less loss there is.

    A mass spec helium leak checker is very handy to check the vacuum jacket.
    The vacuum in the jacket does not have to be very good as the tube will
    cryopump once you get liquid in it. But it MUST be leak tight or you will
    get a lot of cold gas in the jacket which has nowhere to go when it warms up.

  7. #7
    9100's Avatar
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    Jim,

    I am using thin teflon washers for spacers. I have found that the spacing along the line and number of them doesn't seem to make much difference. In the straight sections they are as much as 5" apart while curves are as close as .8". There isn't much difference in temperature between the straights and curves. That is just feeling the line, not using instrumentation. I use round washers. The 3 and 4 sided ones are just more trouble to make and don't help much because they are only touching the outside line in one place anyway. The washers are a press fit on the inner line. When I started, I had a series of failures until I realized that when I pumped a line down or let air back in, I was blowing the washers out of place. One of the biggest factors is leaving space for the inner line to shrink. I calculated that the last line I made would shrink .260" from room temperature to LH temp in the longest straight section. I use smaller OD spacers in corners to allow some movement and push the line in to make the spacers in curves go against the outer wall, giving them max room to pull in.

    In my view, doing this without a mass spec leak detector is pointless. I use an old VEECO MS-9, which is ancient technology, but a leak is a leak and anything that will detect it is doing the job. Mine has a Stirling engine chiller on the vapor trap, so all I need to run it is electricity and compressed air. Since it can run unattended, if there isn't a leak, I leave it on to pump the lines down. SS makes a good heating element, so I clip jumper cables to each end and put enough current through it to heat it to about 100 C, leaving it overnight. In the morning, the ion gauge on the MS-9 is down around -6. Pinching off the copper evacuation tube was a whole R&D project of its own. Simple, once you figure out how, but frustrating until you get there.

    We experimented with self cryopumping and found that it worked, sort of, but was nowhere near as good as a serious vacuum. Doing it with LN is interesting because the residual air only condenses into a liquid, not frost. Apparently it drips on the outer tube and boils, repeating until it all gets somewhere that the drop hangs on the inner line and stops dripping. LH works better because the air condenses as frost and stays in place.

    These are used in slam freezers that freeze tissue samples so fast that they skip the crystalline phase. I tried to promote a project for a replacement like you use, but even with the rising shortage of helium, I couldn't get any interest.

    Bill

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    jim rozen is offline Diamond
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    The MS-9s are actually the same as the later veecos, up to the MS-17s in terms of
    the actual vacuum hardware. The electronics are a bit less advance but not much.

    You don't need to tip off the vacuum in a transfer stick like that, just fit a good
    nupro bellows valve and that's fine. You can pump them out again if need be.

    The triangle-shaped phenolic spacers, they can't blow out of place...!

  9. #9
    Close Work is offline Cast Iron
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    How long does the tubing have to be and how many pieces? Have an electroplater plate an a piece or pieces of aluminum tubing with copper to whatever thickness you need then etch the aluminum tubing out with a caustic like NaOH. If you need to bend the tubing you probably need to anneal it as it maybe fairly had in the as-plated condition depending on the plating process. For very short pieces you can cut the copper plated aluminum tubing and then use liquid nitrogen to shrink the aluminum more than the copper and you might then press the aluminum out of the copper electroplate. You can also electroplate the low temp melting metals called cerabend. Cast a rod of that stuff in hot water using a plastic straw and then have it electroplated with copper and melt the cerabend out. The low melt alloys go for $100-200/lb but you can use it over and over. Plating a rod of regular solder would also work at a higher temperature.

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    9100's Avatar
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    For most aluminum alloys you need an electroless zinc coating between it and the copper. Then you need some sort of additive to make the copper stick to the zinc. I lost a pile of money because no one at the plating supply company or the chemical manufacturer told me about it. I set up a whole line to plate heat sinks using their recommendation and couldn't get the copper to stick. If you use aluminum, you should have thin wall tubing so you can pump caustic through it. Otherwise, it will take a long time for it to eat its way through.

    Bill

  11. #11
    9100's Avatar
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    Quote Originally Posted by jim rozen View Post
    You don't need to tip off the vacuum in a transfer stick like that, just fit a good
    nupro bellows valve and that's fine. You can pump them out again if need be.
    Once they leave here, they are out of my jurisdiction. Most of the time, I don't even know where they go as part of the whole kit. There is one in Japan where the customer claims the vacuum has failed and wants a replacement on warranty. We keep telling him we will send the replacement as soon as we receive the bad one. I need to evaluate the failure and can probably repair it. They have refused for months, possibly trying to get two for the price of one.

    Bill

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    Close Work is offline Cast Iron
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    Note I suggested having an electroplater plate the aluminum tube or whatever with copper. Getting in the electroforming business to do a few tubes doesn't seem like a good idea. I think you want someone in the electroplating business do the electroplating. Thin plating of circuit boards and decorative plating is much easier than thick electroplating.

    You are best off having an "electroformer" do the job as they specialize in thick plating and know how to control the stresses and required cleanliness over the longer plating process. Electroformer people are much more knowledgeable than electroplaters in my experience and a better buy since they usually get it done right the first time. Talking about zincates and other tricks of the plating trade with someone in the plating business will likely run up the price they quote.

  13. #13
    jim rozen is offline Diamond
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    Another approach on this is to call up Uniform Tubes.

    Name: Uniform Tubes Inc
    Street: 200 West 7th Avenue
    Collegeville, pa 19426-2112
    Phone: (610) 489-0300

    Occasionally they have over-runs that are stored, and they
    might just have what you want.

  14. #14
    KIMFAB's Avatar
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    Thanks for the help,
    Unfortunately the tubes will have to be copper and will have a sharp bend in them.

    As for Uniform tube I will give them a try on Monday.
    What is amazing is that doing a google search for them turns up porn sites for about a third of the replies.

    I'm going to try some swaging ideas today.

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