Hardening Of The Tuba Arteries?

[Gongadin]

Yeah, I realize that there will probably be a lot of double entendres posted, but I'm going to ask anyways.

I took an older tuba in for an overhaul, and now it's finished. The repairman was commenting on its free-blowing qualities, and the fact that it has an excellent low register. He did say that some of the middle range is taking some work to play because the bell is starting to harden. He recommends matching a mouthpiece to the horn to ensure that the middle register won't take so much work to play.
Does anyone else play on older instruments that are starting to harden?
How do you get around some of the annomalies?

[UDELBR]

Does anyone else play on older instruments that are starting to harden?

Nope, nobody does. Not even you, because brass doesn't age-harden!

Maybe time to look for a different repairman.

[Gongadin]

Is there another process that causes brass to harden, if not age?
I'm going to pick up the tuba in a few hours; I'll get a full explanation at that point and either add to or delete this post!

[tjs]

I recall talking with my local brass repair guy about something similar and he mentioned something about how the metal has a tendency to get "stiffer" as dents are taken out of the metal over and over again. I don't know if this is the same "hardening" characteristic that your guy is referring to. I guess one question would be whether or not the horn has undergone significant repair work in the past?

Tim

[UDELBR]

Is there another process that causes brass to harden, if not age?

There's "work-hardening", that comes from hammering, bending, or planishing. These all harden brass after annealing.

Some metals do age-harden (e.g. aluminum), but brass doesn't.

[Rick Denney]

Does anyone else play on older instruments that are starting to harden?

Point 1, the hardness of the metal affects only its strength, not its stiffness. For example, steel tensile strength ranges from perhaps 36,000 for cold-rolled steel (which is already work-hardened to some extent) to 200,000 psi for fancy heat-treated alloys. But they all have the same stiffness of 29,000 KSI. The same is true for all the common structural metals, including brass. It is the stiffness that controls the resistance to vibrational excitation, unless that excitation causes the metal to exceed its yield strength and become plastic. Any tuba that did that would fall apart forthwith. Thus, the "hardness" (really strength) of the brass has no effect on its resonance. If the resonance is not affected by hardness, then it won't affect the impedance of the instrument and cannot therefore be influenced by the mouthpiece.

Point 2. As has been pointed out, brass does not age-harden to any significant extent. It can be hardened by working it. When it is hammered and when dents are rolled out, it gets stronger and more brittle. This is why overworked brass is prone to cracking and must be annealed back to a dead soft state before new repairs can be made. If there is a grain of truth in what the repairman was saying, it would be that this bell had been repaired as much as it can be without risking cracks and other failures from excessive work hardening.

Point 3. Even if the hardness of the brass affected its stiffness (which is doesn't), changes in the stiffness of the metal have an extremely subtle effect on the tone it produces, unhearable by mortals. There are players who profess to hear these subtle differences, and I'm not good enough myself to disprove what they say based on observation. But I can't hear it.

Point 4. One thing that can affect the way an instrument plays and feels is internal stresses. If the parts of an instrument have to be flexed into shape during assembly, the instrument will have considerable internal stresses, meaning that parts of the instrument are fighting other parts of the instrument. This preloads the brass so that it takes a higher excitation for to established resonance in the brass. One of the things that master techs do to make an instrument feel better is to properly fit parts so that they go together without those stresses. I suspect this would be unhearable by mortals, though it might be feelable. I doubt any change in mouthpiece could affect it much.

Point 5. It is possible to work brass such that parts of the metal are fighting other parts of the metal just because of the deformation process required to shape the parts. These can sometimes settle out over time, if the stresses are high enough to cause microscopic areas of yield. As these areas where the stresses are highest yield, the overall stress evens out a bit. This can happen over time with, for example, aluminum, and it might well be true with brass. I suspect this isn't much of an effect--if it was, you'd see fatigue failures in the parts of the isntrument with the highest stress as a result of added stress from the vibration of playing the instrument. If that vibration isn't enough to fatigue a piece of brass already at the point of yielding, then it likely isn't enough to be affected by the yielding.

Bottom line: The guy is trying to sell you a mouthpiece.

Rick "who doesn't mind matching a mouthpiece to an instrument, but not at all for the reasons stated" Denney

[Dan Schultz]

Rick... I can't argue with your lengthy post and wouldn't want to anyway. The issue is not that important. However... please explain to me why I've seen cracks appear in brass for no apparent reason. Could it be due to the vibrations of the brass causing it to harden? Brass does harden when it is flexed or 'worked'. This vibrating or 'working' over a prolonged period of time HAS to have an affect on the hardness..... probably not to the point of affecting the timbre noticibly but certainly to the point of metal fatigue. Heck, I can see where just the rubbing of the brass during polishing could produce enough flexing to produce hardening.

[Rick Denney]

Rick... I can't argue with your lengthy post and wouldn't want to anyway. The issue is not that important. However... please explain to me why I've seen cracks appear in brass for no apparent reason. Could it be due to the vibrations of the brass causing it to harden? Brass does harden when it is flexed or 'worked'. This vibrating or 'working' over a prolonged period of time HAS to have an affect on the hardness..... probably not to the point of affecting the timbre noticibly but certainly to the point of metal fatigue. Heck, I can see where just the rubbing of the brass during polishing could produce enough flexing to produce hardening.

If the material was formed in such a way that left a lot of internal stresses (hydroforming could do this easily, it seems to me, as could stamping, but dent removal has to be the king-daddy of internal stress causes), then those internal stresses might be really close to the yield strength of the material. Vibration could cause fatigue cracking at those points if they didn't yield first. Fatigue is not much of a problem in brass (compared, say, to aluminum), but if you apply enough stress cycles at high enough stresses, it will fatigue and crack. I can't imagine how vibration could create stresses high enough to do this unless they were piled on top of high internal stresses. Fatigue doesn't get easier with age, by which I mean the material doesn't change. But there is a relationship between the stress and the number of stress cycles. The higher the stress, the fewer the stress cycles to fatigue failure. At some low-enough value of stress, the material will never fatigue. How long does it take to create a million stress cycles? It could be a while, depending on the history of the instrument.

But it isn't age-hardening, which is a molecular change in the grain of material over time.

As to real work-hardening, I think you'll need to exceed the yield point to produce significant work hardening. Burnishing does that (on the surface, at least), but not polishing. Dent removal does to a much greater extent, as you know. Vibration doesn't by itself create that much stress.

Rick "who has spent years debunking the myth that bicycle frames go soft" Denney

[Gongadin]

Just returned from the repair shop.
Anyhow, I clarified what he was talking about during our pre-pickup telephone conversation.
He was indeed referring to work hardening. He was pointing out places on the bell that have been repeatedly de-dented over the years. He was just saying that he didn't want to take a hammer to those areas, that he just rolled out what he could.
His mouthpiece comment referred to the fact that the horn has a glorious, effortless bottom end, and he doesn't feel that the middle range is as effortless. So, what he was saying was that I should try out some mouthpieces that emphasize some of the middel register, as the "money notes" already bloom on their own. He wasn't trying to sell me a mouthpiece, although I can see how my post might have suggested otherwise.
Thanks for everyone's input, and for teaching me a thing or two.

[Gongadin]

Hi, Harold;
Okay, let's get Rick more riled up....
*ahem*; apparently brass can become brittle and cracked just by removing it from a dark, comfy place...such as a padded case.
Many vintage instruments that have spent their lives in vintage velvet-lined cases are losing various frequencies as we debate this brass-hardening issue. My horn has lost all frequencies below the G# 26 spaces down the staff, and all of the frequencies above The Yukon Territories. Quite a few department store clerks that I have surveyed have attributed this phenomenon to the instrument residing in a case.
(Harold....psst! How did I do??)
Back to your mouthpiece question; the repairguy play-tested the horn with an Arnold Jacobs mouthpiece. He was recommending a Denis Wick 3L, or a smaller, real expensive Panantone mouthpiece...y'know the kind that Italians give each other every Christmas?
Neither of them were items that he carried at his shop.

[Ryan_Beucke]

Correct me if I'm wrong, but I think that the vibrations from playing a brass instrument or even just polishing the horn will only "flex" the brass, whereas a dent would push the metal past the point of distortion. Just like how springs *technically* will not lose their springiness over years of use unless they are pushed or pulled past their point of distortion. In other words, the metal will always return to it's original position as long as it's not pushed too hard. Forgive me if I'm just repeating something that's been said already but in different words.

[Rick Denney]

Correct me if I'm wrong, but I think that the vibrations from playing a brass instrument or even just polishing the horn will only "flex" the brass, whereas a dent would push the metal past the point of distortion. Just like how springs *technically* will not lose their springiness over years of use unless they are pushed or pulled past their point of distortion. In other words, the metal will always return to it's original position as long as it's not pushed too hard. Forgive me if I'm just repeating something that's been said already but in different words.

Your "point of distortion" is my "yield". Same thing.

If you take a hunk of material and stretch it in an Instron machine, it will plot the stress on the material (which is the force applied divided by the cross-sectional area of the sample) against the strain (which is how much the material moves in response to that force, measured in inches of stretch per inch of original length).

With most metals, the resulting plot shows a pretty straight line, meaning that for each incremental increase of stress you get the same incremental increase in stretch. Also, if you release the machine, the plot will travel back down that same straight line, meaning that the material is elastic. Another way to describe elasticity is that the material returns to its original shape, giving up all the energy stored in it when it was stretched. Springs are highly elastic, for example.

But at some point, the material's yield strength will be overcome and it will deform permanently. The plot at this point starts to go curvy and wander around. This is called plastic deformation, with plastic being the opposite of elastic. If you keep on, the material will rupture, and this is called ultimate strength. The more impurities in the metal, the more unpredictable the yield strength, and the smoother the curve of the plot between the elastic and plastic regions.

(Stiffness is the slope of the stress/strain curve in the elastic region below yield strength. It is the same for a given metal no matter what the yield strength.)

When you repair brass, you try to apply force between the yield strength and the ultimate strength. Too little, and the brass doesn't move the way you want it to. Too much, and it breaks.

Fatigue is different. Fatigue happens when a microscopic anomaly in the material ruptures, forming the start of a crack. The tip of the crack concentrates stress to an high degree, such that right at the tip, the material exceeds ultimate strength and ruptures. The crack therefore travels across the material (sometimes slowly, sometimes quickly, but always only a little bit at each stress cycle) until what is left is insufficient to carry the load, at which point it yields or ruptures. If two parts mostly fit back together after breaking, it's a fatigue failure. Ruptures don't fit back together because most of the material around the break yielded first and deformed before rupturing.

The more metals are worked, the harder and more brittle they become, because the working aligns the grains of the metal like the grain of wood. This is why forged steel tools are very much stronger than cast steel tools. But brittle metals transfer higher stresses without yielding, and therefore propagate fatique cracks more easily. Thus, fatigue damage is more likely in hard, brittle metals. Heating to red hot melts these grains and allows them to relax, and this is called annealing. Thus, if a bell has been repaired too many times to allow further repair, it will have to be annealed first. But annealing reduces the yield strength of the material, making it more prone to dents and damage in the future.

Different metals behave differently in fatigue performance. Steel is excellent--the stress cycles have to get very close to the yield strength to cause fatique. Aluminum is poor--even at a small fraction of the yield strength, aluminum will crack and fatigue given enough cycles. Brass is in between, but it is pretty good and generally will only fatigue if the material has been overhardened by too much working. Old instruments that have been repaired too many times without annealing are therefore more subject to fatigue cracks in places where the internal stresses from those past repairs are really high.

The repair tech in this case did the right thing in repairing it as much as possible without trying to make it perfect. Annealing at the site of a potential crack might prevent fatigue at that point, but uneven annealing also creates internal stresses and might cause a problem elsewhere. I've repair dents in wrinkles in my project horns only to have them reappear when I tried to anneal them so that I could make further repairs. The masters know how to work with this while idiots like me don't, and that's why I don't try repairs like these on my good horns.

Rick "who thinks engineers are just beginning to understand fatigue" Denney

[Rick Denney]

Hi, Harold;
Okay, let's get Rick more riled up....
*ahem*; apparently brass can become brittle and cracked just by removing it from a dark, comfy place...such as a padded case.

I absolutely agree. But it can happen to new instruments as well. Their playing qualities are entirely the inverse of the time the instrument spends in the case...unplayed.

Rick "use it or lose it" Denney

[Rick Denney]

Anyhow, I clarified what he was talking about during our pre-pickup telephone conversation.
He was indeed referring to work hardening.

Faith restored.

A little knowledge really helps when communicating with professionals, doesn't it?

Rick "thinking technical details sometimes lose a lot in being translated to and from actual English" Denney

[Daniel C. Oberloh]

Loose slides or broken joints that no longer hold compression?

Worn valves that no longer hold compression?

Worn chops that no longer hold compression

Probably not the brass.

Daniel C. Oberloh
Oberloh woodwind and Brass Works
http://www.oberloh.com

[Rick Denney]

Probably not the brass.

Should I explain it?

Nah.

Rick "with apologies to Dan" Denney

[pjv]

Explain it...please!!! No seriously. I've heard quite a few trumpet and trombone players in my time (I'm 41) that have talked about metal fatigue in the sense of "the ol' gray mule just ain't what she used to be". They claim that the horn has been played-out. Is this possable, or are we just talking too many face lifts?

[Lew]

I've heard this too, and it's nonsense. Valves wear and slides lose compression, but just aging the brass, or playing too much will not render a brass instrument less playable.

[Rick Denney]

I've heard this too, and it's nonsense. Valves wear and slides lose compression, but just aging the brass, or playing too much will not render a brass instrument less playable.

Yes.

For example:

Take a brand new tuba, say, a Yamaha with that nice, durable epoxy lacquer. Store it in an environmentally controlled vault for, say, 2000 years, with occasional reoilings.

Would it play like new? Yes. It would probably even look like new.

The only thing that makes brass change as it ages is the life it leads. "It ain't the years, honey, it's the mileage."

Rick "who has seen lots of Bronze-Age metal objects in good condition" Denney