Half a croissant, on a plate, with a sign in front of it saying '50c'
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Nitinol Spiral Bifilar Binding

Loose-leaf spiral binding
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I like the way spiral binding works to allow notebooks and calendars to lie flat. But occasionally I'd like the ability to add a sheet in the middle of an already-filled section.

Enter: Nitinol Spiral Binding!

Simply remove the bifilar-wound spring by snapping on a 9V battery, and watch as the binding detaches itself from the pages. Now add a sheet from the end of the sheaf, disconnect the battery, and allow the nitinol wire to cool and regain its shape, carefully rebinding the newly added sheet in place.

(A similar electrically-alterable structure may be used to form your croissants.)

csea, Feb 23 2009

Nitinol http://en.wikipedia.org/wiki/Nitinol
Shape-memory wire [csea, Feb 23 2009]

Spiral Binding http://www.lse.ac.u...lSpiralBinding2.gif
The type of binding to which I refer [csea, Feb 23 2009]

Bifilar Winding http://www.answers....pic/bifilar-winding
definition [csea, Feb 23 2009]

[link]






       Cold, Nitinol stays in any form given to it; warm, it returns to the original form. So if the original form was the open binder, you'd have to manually close it again, or vice versa. So where does the automatic open+close come from?
loonquawl, Feb 23 2009
  

       [loonquawl], Good point. Perhaps there are two sets of wires mechanically bonded, but thermally and electrically insulated from eachother, and a switch to select "open" or "close".   

       Might depend if the force when heated exceeds the bending requirement when cold. Hence the halfbakedness.
csea, Feb 23 2009
  

       It's the last sentence of P2 that throws me. There is no way a straight wire, if placed next to a sheaf of paper, is going to be able to spiral itself through the holes. I think that would require a more complicated system then simply memoryform wire. Since you can screw and unscrew spiral bindings why do we need to straighten out the wire at all?
WcW, Feb 23 2009
  

       [csea] posted a picture of the "spiral binding" - it is not a spiral, but looks superficially similar
loonquawl, Feb 23 2009
  
      
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