Skye Malcolm writes:
>It seems to me that you're on the right track with the steel rods. You =
>might see if you can find one tempered. ...
There are several different ways to harden different types if steels. One
is by heat treating. The typical process is to heat it above the
temperature where all the alloying elements go back into a solid solution
("dissolve") in the iron (typically around 1500 degrees F for
garden-variety hardenable steel alloys), then quench (rapidly cool) the
part so that some of the alloying elements get caught in harder types of
microstructures (such as martensite), since they don't have time to revert
back to their fully-annealed types of microstructures (typically ferrite
for plain-carbon alloys). The resulting fully hardened part is extremely
hard but very brittle. Even dropping it on the floor could result in
shattering (that's also why they have a warning on hammers to not hit the
hardened face against another piece of hardened steel, it could shatter and
send splinters of itself into various soft and fragile things, such as your
eyes). Fully hardened alloys also often have very high internal stresses.
In some cases, just letting it sit around for a while in that state could
result in microcracking.
For this reason, it is normal practice to "temper" a part after quenching.
The part is re-heated to something less than the quench-hardening
temperature (typically around 700 to 900 deg. F for common steel alloys,
with the higher temperature resulting in a softer final part), then slowly
cooling back to room temperature. The alloy loses some of its hardenss but
gains back enough ductility to eliminate the brittleness.
Another type of hardening is work hardening. The alloy is mashed,
stretched, or otherwise physically abused, which causes the buildup of
physical stresses and microstructure changes in the material that have
essentially the same effect as heat treating. In the case of music wire,
the alloy is AISI 1060 steel (that means it's an iron-carbon, or "plain
carbon" alloy, with a carbon content of 0.60%). It is drawn through a
series of dies to work it down from the initial ingot diameter to the final
desired wire size. Each time it gets pulled through a die, it gets work
hardened. After a few steps it's been cold-worked so much that it's just
about fully hard and has lost almost all its ductility. It is then annealed
(slowly heated and then SLOWLY cooled) to make it soft again, and then the
drawing process is continued.
They use the minimum number of annealing steps, so that the wire at its
final diameter is nearly fully hard, about the same hardness as the best
you could get from it by heat treating. It's quite brittle at that point,
which is why music wire can crack and snap if you bend it and then try to
straighten it. It's already been subjected to about all the work hardening
it can stand, and if your bending back and forth imposes more on it, it
says ENOUGH!!
At that hardness it's also close to about the same hardness and strength as
most tool steels, which is why it will leave nice semi-circular dents in
the jaws of your diagonal cutters if you try to use them to cut it. This
also means that going to a heat-treated version of some other alloy (with a
few very exotic exceptions) is not likely to get you any significant
improvement in bending strength. You might get some improvements in
toughness, but the hardness and strength (and therefore the bending load at
which it gets bent) is not likely to see much improvement.
The stiffness of all steel alloys is nearly identical, so the tip
deflection due to elastic bending (i.e.: bending from which it can still
spring back to its original shape) will not be changed in any case.
About the only thing you can do that will significantly improve the bending
strength of the rod is a diameter change.
>Also you might try shortening the rod instead of lengthing it. At some =
>shorter length this will theoretically put more stress into the wing rod =
>sleeves...
This will increase the stresses in the connections between the joiner rod
and the wing spars, but it will not change the stresses in the joiner rod
itself in the middle. There are a certain number of inch-pounds bending
moment created by the lift forces and the length of the wing panels, and
the center of the joiner rod has to absorb that amount of bending moment,
irregardless of how long the joiner is. The only thing that matters at that
center point in the rod is the amount of bending moment, the size and shape
of the joiner's cross-section, and the properties of the joiner's material.
If your joiner is tearing up its sockets in the wing roots, a longer joiner
could help. If your joiner is bending in the middle, the best fix is to get
a fatter joiner.
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