Ralph,
Hah! A question for a metallurgist! And my thesis was on metal fatigue.
Let me first point out that the phenomena of metal fatigue is - by definition -
strictly due to alternating stresses, as when you break a paper clip by bending
it back and forth. That's low cycle fatigue - LCF - but millions of cycles at
lower stress can initiate and propagate a crack to failure, too - HCF. I do not
believe there are alternating stresses in a horn great enough to cause fatigue.
Psychological stress in the player is, of course, a frequent source of failure
of another kind.
Some materials can undergo slow internal changes over long periods of time. For
example, some aluminum alloys age-harden at room temperature - they contain
additions that precipitate out of solution to form very small particles. Upon
quenching, steels may slowly continue a transformation at room temperature -
steel is a very complicated material. Brass is too simple for these sorts of
things to happen. There's nothing to precipitate, nothing to transform, the
grain size will not change at room temperature.
The most insidious and common failure mechanism for most metals is corrosion.
Corrosion behavior is nearly always very complicated, and affects everything -
there are phenomena known as "stress corrosion" and "corrosion fatigue", and
many others. If something made of brass sheet metal falls apart after 25 years
outside in an industrial environment, it would undoubtedly be from some sort of
corrosion behavior, perhaps only on some microscopic scale influencing the
behavior of cracks or grain boundaries, and due to some interaction with an
impurity. Even if nominal stresses are very low, most things have residual
stresses - a spun bell that has not been annealed (or "stress relieved") will
have residual stresses approaching yield strength. And there are "fit-up"
stresses from assembly and other manufacturing processes. Welding is notorious
for simultaneously disrupting the normal microstructure of a material and
leaving very high residual stresses behind.
But that's the complicated answer, in the typical manner of engineering - a
field based on fear of failure. We're probably worse than lawyers in this
respect! What I really think is that horns do not change over time, not on
their own. Certainly, there will be players that pull a horn out of a closet
after 25 years and swear it is different. Cheese, certainly. Wine, maybe.
Brass, no way.
And the bonus question: The heat capacity of all brasses are similar ("nickel
silver" is a member of the brass family in this context), so the weight of the
horn would be the major factor in the time it takes to warm up, during which
condensation will be heavy. The internal operating temperature of a nickel
silver horn might be higher, due to lower conductivity, but I think that would
be a small effect (and opposite the one you believe occurs).
Of course, the only fair experiment would be the same design made in different
materials. By far the biggest affect would be in the diameter and curvature of
the tubing where the water collects, if you are going by "time to first
gurgle". And the amount of tubing that drains into this location. If you see a
difference between two horns of different designs and materials, blame the
design, not the material.
Curt Austin
On May 29, 2011, at 6:36 AM, Ralph Hall wrote:
>
> Ralph R. Hall
> [email protected]
>
> Hornlisters,
>
> Here is a question for those of a scientific bent and for those who
> work in repairshops etc.
> What happens to the metal of a horn over, say, a period of 25 years?
> Does it deteriorate; does it soften;
> and if it does either of these (and others) what is the significance
> on the playing qualities of the instrument?
> Please discount ordinary wear and tear such as lacquer peeling off,
> dings, repairs and, like a former colleague who was prone to excessive
> acid in his perspiration, the oddball circumstance where an instrument
> wears through in a couple of years or so.
>
> A subsidiary question; my experience has been that I have more water
> (condensation) when I play a nickel silver horn than when I play
> brass. Explain - in less than 10 e-mails!
>
> Ralph R. Hall
>
> _______________________________________________
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