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8077Re: [new_distillers] Re: bending copper tubing

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  • Mike Nixon
    Jun 10, 2003
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      w G wrote:
      Subject: RE: [new_distillers] Re: bending copper tubing

      Just out of curiosity,  instead of filling the tube with salt or sand,  was wondering if anyone had considered sealing the ends up and heating it,  the increase in internal air pressure should keep it balooned out and round,  just my 2c worth...
      Nice idea!  Unfortunately, the pressure would not be enough to prevent buckling of the tube, even though that pressure would increase as the tube collapses, and in any event would be applied evenly over the entire inside surface.  Even filling the tube with water, which is non-compressible, wouldn't work.  You want the most resistance on those surfaces that are tending to squeeze together, but do not want pressure on the sides that are tending to bulge out.  To achieve those criteria, you need something solid inside, and fine sand or salt behaves like a solid when confined, even though it pours like water when not.  Some have tried freezing water so the tube is packed with ice, but this again doesn't work as ice liquifies under pressure.
      There are very low melting point bismuth alloys available (eg. Cerrobend) ... they melt below the boiling point of water ... and these offer the best way possible as they solidify inside the tube to a totally incompressible yet flexible filler which melts easily and pours out after use.  Unfortunately, they are expensive and can also pose a health risk.  Not recommended for amateur use!  Very fine dry sand or salt are still the best methods in the home workshop if annealing and bending carefully without a filler still results in buckling.
      Mike N
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