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using heat while removing dents?

1923 Views 6 Replies 5 Participants Last post by  abadcliche
Brass tends to get more brittle as it is worked. There is a risk of cracks if an area is overworked. For example, a bow that gets repeatedly dented and repaired. Could a small amount of heat from a torch be used on the area to be worked to reduce the chance of cracking? This is a method used in Auto body repair when straightening metal panels, albeit, for different reasons.
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Yes, within reason in certain applications. Annealing is the process of heating the brass cherry-red to soften it. This is where a large torch is better. This works well on large brass instruments such as tubas and baritones, which get bashed hard and often. However on saxophones, this would require the removal of the bow, and separation from the bell and main body tube. If there are posts, guards, caps etc. in the area to be annealed, they are going to fall off due to the high heat. Hope this helps.
Another downside is that in order to anneal the brass the heat required would crystallize the lead in the surrounding solder joints. Crystallized lead requires extreme heat to re-melt (above the melting point of the brass) and is extremely hard. Almost impossible to remove. :( Most saxophone dents work out fine without heat.
tb, you've been scarece lately!

OK, you've caught my attention. Do you have any sourced of this information you can lead me to?

(I know heat damages lead soldering, compromimsing its strength, but I have never had to exceed the melting point of brass to melt solder in the vicinity of a once-heated object. The only problem I have ever had is that the soldered parts fall off.)

Willing and eager to learn more...
Gordon, I read that in a warning from a solder manufacturer many years ago. It explained that once lead crystallized it actually changed molecular form. Similar to that of aluminum vs. aluminum oxide.

I actually screwed up and overheated lead on brass once many moons ago and went through hell trying to remove it. Actually wore a file out trying to get that stuff off. :x
Aluminium is a metal. Aluminium is a very hard abrasive, used for (white) abrasive wheels and "sand" paper. (Aluminium very quickly oxidises on its surface, which is what makes aluminium foil a useful abrasive agent.)

Lead is normally a very soft metal. So are we actually talking about another state of lead here, or a lead oxide?

Or are we talking about where lead solder is used on a base metal, and when over-heated, it alloys with the base metal, greatly raising its melting point? I believe (by instruction and experience) that this is an issue with any soldering of sterling silver, which is why it should be done quickly, so as to reduce the alloying.

So many things to discover!
I have seen what tbone is talking about- once, and that was enough! Although I don't know exactly what is happening chemically, I do know that if you are for instance silver soldering a post back to its foot (off the body), and the lead solder was not TOTALLY cleaned off of the foot, the solder will get extremely hard, and will not melt at normal soft solder temperatures, and filing it off is really the only thing you can do.
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