Does My Trumpet Have a Temper?
The softness or hardness of brass does make a difference in the resonance of the instrument. Brass is not tempered, it is annealed or 'work-hardened'.
Brass Annealing (Heat)
Bells and braces are formed by hammering and burnishing. They are annealed several times during the process to re-soften the metal, which keeps it from cracking and achieves the required softness and strength. Hammering and burnishing spreads the molecules so they are unevenly spaced in the metal, which makes it brittle and stressed. Heating to a high temperature and then quickly cooling redistributes the molecules more evenly and makes the metal softer. This is most important in the bell, as it greatly affects the tone and resonance. The below quote is taken from 'The Art of the Trumpet-Maker by Robert Barclay, Oxford University Press, page 54'
On the secondary level, the alloy exhibits a grain structure. As it cools and solidifies, it begins to crystallize. Crystals begin forming and meet each other to produce grains which give brass its' characteristic granular texture. Each grain has a precise crystal orientation based upon the lattice structure but the individual grains bear a random relationship to each other in orientation. The interfaces of these grains are known as grain boundaries.
Unlike such iconic crystalline structures like salt, metals have the ability to deform plastically, the atoms of the metal can slip over one another causing deformation of the microstructure, rather than breaking. Slipping takes place in specific planes of atoms which are oriented to the lattice structure. This planar slipping takes the form of dislocation lines. Paradoxically, the energy required to initiate slipping is not sufficient to allow it to continue. The energy required to propagate an existing slip or to start one on a new plane, increases as the metal is already strained. This feature gives brass it's characteristic work-hardening properties. The motion of a dislocation line is further inhibited in brasses by large impurities. Locking of the atom planes due to dissimilar sized atoms prevents slippage.
Microscopic examination of brass before and after cold working shows the effect of stress on the grains. Rapid cooling of a hot, disordered alloy results in a fine crystalline structure, and a consequently soft and easily deformed metal. Rapid cooling was found to be essential when working with older brasses because only under these conditions do the impurities tend to remain in the solution.
Proper assembly of a brass instrument would require the bell and slides to be annealed after working, and the braces to be work-hardened for strength. Badly dented bells can be annealed after the dent removal process to relieve the stress, as the brass will now be work-hardened. There will always be residual stress in the assembly process of low-temperature soldering, as parts draw together very tightly in the cooling. However...
Brass Aging
Age relieves stress by allowing the molecules in the metal to evenly space themselves, although this generally takes at least 35 years. Examples of this are the New York and Mt. Vernon Bach Trumpets, Selmer MK VI Saxophones and the Kruspe and Geyer French Horns. They have better resonance because the metal is less stressed. During the process of making of the bell and slides from sheet metal, annealing would have taken place several times. However, there is inherent stress involved in the assembly process of low-temperature soldering, which means parts are drawn together very tightly whilst cooling. Aging would deal with all of this.
Cryogenic Process: Myth or Magic?
CRR, or cryogenic resonance restoration, is the gradual lowering (1 degree per minute to -325 degrees)and raising of the temperature of the instrument. Theoretically, it relieves stress and tension in the metal and improves the instrument's response and resonance. It also makes the keywork more resistant to wear. This is a controversial method and the jury is still out as to whether it actually makes a difference. It has yet to be proven in blind listening tests. Most people who have had this done to their instrument say it makes a difference to the extent that it will make a good instrument play better, but it won't make a great instrument out of a bad one.
I have done a great deal of reading on Cryogenics. Based on the fact that heat, not cooling, is what redistributes the molecules in the brass to relieve the stress, it really doesn't make sense that an extreme cooling process would do anything to the brass. In addition, brass is hardened through working (hamering and burnishing). There are some parts of the trumpet that need to be stronger and harder than the rest (like the braces!). Still, there are many websites singing the praises of Cryogenics, and many testimonials. Below is a quote from the website of Nitrofreeze Cryogenic Services.
Residual stresses exist in all metals and metal components. But why does cryogenic treatment relieve these stresses? The answer is found in observations made by Einstein and Bose of Germany. Both of these noted physicists observed that matter is at its most relaxed state or condition when it has the least amount of kinetic energy or molecular activity. The process of freezing is not one of putting cold into an object. Rather, it is the removal of heat. When we remove heat, we are removing energy and slowing down the molecular activity (kinetic energy) of the object being frozen. This is evident to every high school science student who studies the effects of heat - and its removal - on water. Absolute zero, which is –459º F or 0º Kelvin is that point where no further energy can be extracted. Many people believe that at absolute zero there is no molecular action at all. This is not the case. But absolute zero provides a theoretical point where matter (or material) is at its most relaxed state.
Based on a paper that examined the effect of cryogenic treatment on semiconductor wafers, (which have copper conductive traces) we believe that the crystal structure becomes more efficiently aligned through the mechanical compression that occurs when the copper is exposed to extended dwells at cryogenic temperatures. This modification (as seen in semiconductors wafers) promoted more efficient electron exchange resulting in faster signal speeds and reduced heat production. It is reasonable to believe that a similar action is at play in conventional copper (and other) wires.
Read on for some opinions from a metallurgist and a scientist on CRR:
I know a lot about metals also (I taught metalworking at a High school) and was somewhat skeptical. I think that freezing was a fad about five or six years ago (maybe longer) and that some musicians were having it done mainly to brass instruments. I saw an ad for it a couple of days ago on the net while looking for a particular horn and that raised the question. I just never heard one way or another if it did anything. I could see that it would cause all your corks and pads to pop but probably wouldn't harm a trumpet much.
I was just wondering if anyone had had it done on any instrument and what the results were. I wonder what effect gold plating the inside of the necks of saxes would do other than prevent pitting and possibly minimize gunk buildup. I don't know if I could even tell if anything wax changed. Again I was wondering if anyone had it done.
Sometimes we as musicians think that something is great but really isn't. Right now Mark VI alto saxes are going for $2375 - $4700 on e-bay which means true believers still exist. hanks for your input
As a metallurgist I regard cryogenic treatment as highly unlikely to relieve any residual stress in any metals or alloys. Sress-relieving ('tempering') is done by increasing the temperature. Room temperature also relieves residual stresses, but usually takes a long time (depending on the metal or alloy). Lead for example tempers rapidly at room temperature, whereas brass takes several decades before the effect is noticeable. It would be impracticable to stress-relieve musical instruments because the temperature involved would damage non-metallic parts including the lacquer.
I am looking for information on the effects of cryogenically freezing non- ferrous metals (brass, copper, silver, and gold) down to temperatures as low as -375 F. Would like to know if it is possible to stress relieve these metals by freezing. Trying to remove residual stress left in these metals in the forming or shaping process. Can it be done? How much stress can be released? Where or who can I talk to in regards to this subject?
Response by David Munoz - Internet ForumI always thought that the annealing temperatures were pretty high (approxi- mately 500 C). Even though I am not a metallurgist, it would seem that the cryogenic temperature would "freeze" the state disallowing stress relax- ation.
Response by Edward Barth - Internet ForumPeriodically I have heard bits and pieces about this idea of stress relief or other effects of taking brass to low temperatures, although never with any supporting data or information. Certainly conventional stress relief is done at high temp and would only slow down below room temperature. It is conceivable that there are phase changes at low temperature, but off the top of my head, I doubt it.
