minimal pipe diameter

Allan Adler wrote in news: snipped-for-privacy@nestle.ai.mit.edu:

Would it not be the same to use a larger, more easily manufacturable pipe (read cost) for most of the conduit with only a metering section near the end? What process would require this small of a conduit for any appreciable length? The mechanical properties of this type of conduit would be terrible, subseptable to any vibration, mechanical distortion and temperature gradients.

When I needed tiny pipe recently, I used a piece of refrigerator cappilary fropm a junk refrigerator. Probably smaller ID than a syringe but can be bent without closing.

As a thought exercise only, I offer the following possibilities:

1a-start off with a flat sheet, of the right width. form it first into a "u" shape, then into an "0" shape. gently heat the resultant shape using electricity to "weld" the seam together. 1b- syringe needles, joined end to end, with flared joints 1c- make a mold, using tungsten wire as the core. 1d-use an extruding mold, and a metal that's soft enough and melts at a low enough temperature to pass through it. You specify "metal". You don't say which type. 2a-compression fittings 2b-make the bends big enough and the tubing won't kink.

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First of all this type of device is common in precision assembly lines for dispensing glues. Pumping fluids long distances through very narrow pipes is extremely inefficient so a high pressure hose feeds a manifold with capillary tube size nozzles. For two part resin/catylist systems two hoses feed a mixing chamber at the manifold.

Capillary tube is available in copper, aluminum, stainless steel and several plastics. There are even some aramid capillaries with ODs smaller than a human hair. Refrigeration thermostats use a very small ID capillary tube to connect sensor bulbs to a pressure switch. It is relatively thick walled compared to the ID so that it can be bent without crimping.

Metal and therm> One can regard the needle of a syringe as a very thin pipe, but it is also

Tubing, 304SS, welded and drawn - which means they fold a sheet into a "U", then close it the rest of the way and weld the seam, then draw it thru a die (and possibly over a mandrel) to smooth the seam and reduce the diameter. They have 3' lengths as small as

0.012 OD and 0.006 ID. (I expect this is done with multiple stages of drawing.)

tubing - they don't say how it is made, but I imagine it is also drawn down from a larger size. The wall is thicker, and it doesn't come as small a hypodermic tube - they have several sizes, all 0.062 OD, with IDs ranging from 0.005 to 0.030. It is available in _much_ longer lengths, up to 100'. They coil it - the wall is thick enough that you can handle it much like wire of the same OD.

The capillary tubing has walls thick enough that you _can_ bend it into a moderately tight raduis without pinching off. The hypodermic tubing would be more difficult. You could fill it with a low melting alloy like Cerrosafe, bend, then melt out the alloy.

John Kasunich

Microbore capillary tubine is commonly manfuactured from a variety of materials, but specialty draw houses like Uniform Tubes. Basically a billet of material is gun drilled, and then drawn down over successive draws to achieve the desired wall and bore dimensions.

Bending small diameter tubing such as this is trivially done by filling the tubing with water, and then freezing the water with liquid nitrogen. As long as the water is kept solid during the bending by repeated re-freezing, the tube will not collapse or kink. The water is blown out after all the bending is complete.

Jim

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I'd just order ss hypodermic tubing and components from smallparts.com. They're not cheap, but a hell of a lot faster and easier than making the tubing, connectors, and fittings yourself. As far as bending goes... I never tried to bend hypo tube and I hope I never have to.

John B.

P.S. I have no connection with Small Parts Inc. (In fact, I think some of their prices are "down right criminal") but when it comes to low volume orders of small components, they're often the only source - that I have found anyway.

The tubing is available as hypodermic tubing in at least 6 foot lengths. I use it at work quite often, in .109 diameter. Other sizes are available.

RJ

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