posted on Oct, 6 2012 @ 09:45 AM
reply to post by dentco
It is very simple. Build a form (jig) that can withstand repeated heating without corrosion in the shape of the item you wish to train. Be sure to
secure the Nitinol tightly for best results. Nitinol trains better when annealed under strain. As an example, if you wish to train a piece of wire
to be a spring, cut a length of solid metal rod in the diameter of the spring you wish to train. Drill and thread a screw near each end of the rod,
and on the side of it. Then make a wrap of Nitinol around one of the screws, and tighten the screw securely into the side of the rod with the Nitinol
wrapped around it. Now make as many wraps around the rod with your Nitinol to develop the length of your spring. At the end of the wraps secure the
final end of the Nitinol around the second threaded screw, and tighten securely. The Nitinol needs to be trained (annealed) in the oven so that it
cannot move on the training rod you built, and by securing it between these two screws, you will have accomplished this.
Experiment with different Temp/Time combinations in the oven. Whichever combination you choose, you are ultimately looking for a color of between
blue and purple on the Nitinol wire in the oven. It will slowly change color during training (annealing). To be able to visually see the color
change, you must first start off with Nitinol wire that has had the outer green oxide removed so that it starts out in its original silver color. If
you are using Nitinol wire that still has the green oxide layer on it, the best way to do this is with an acid bath, but you may lightly sand off a
small area of the wire to use as a "color window". Use one end of the wire that you intend to cut off, because the very act of sanding the Nitinol
can disturb the crystalline structure, and reduce the capability of the wire. Most of the wire available on the market already has this green oxide
layer removed, so this may process will usually not be necessary.
Preheat your oven well before introducing the Nitinol into the oven. A good Time/Temp combination to start with would be about 550 degrees Celsius at
15 minutes for 25 mil wire. Verify the color at this time to see if it is near purplish-blue in color. After the time period in the oven, remove the
spring form without touching the wire on it, and allow it to cool slowly on its own. Do not quench in water.
After the wire has cooled completely, remove the wire from your rod and straighten the wire out. It will be as soft as lead. Then stab it into a hot
water bath and it will immediately become a strong spring. A spring that is only a spring when you want it to be one. It may also be activated into
a spring using a light electrical current, but be careful to not overheat it with too much current, or the wire will be damaged beyond repair.
This same method may be used to train Nitinol in just about any other shape as well. Just be sure to secure your Nitinol tightly in the shape you
wish to obtain.