Annealing Brass - Any experiences?

[Steven Tribe]

I have a problem with the retaining/mounting brass ring for a front achromat. The last owner managed to unscrew it with a great deal of difficulty, doubtful tools and workmanship. There a pliers/pipe wrench marks all around the front rim with a few starting edge cracks. I am not so worried about the appearance but nervous about "structural stability" - it is 230 years old!

I have checked youtube about annealing brass and the suggested method (from people who reuse ammo casings) seems to be warming to the blue colour - followed by quenching in water - which is the complete opposite of what I do to soften ferrous materials?

Any advice or experience? Otherwise I'll have to do experiments with waste brass!

[IanG]

My experience is annealing 9ct gold, but hey that's mostly brass :D

Normally you heat to blue heat then quench as you say. I'd get some brass strip and test first. Thinking about it we annealed brass castings the same way.

Ian

[goamules]

Annealing the neck of a brass cartridge (or annealing anything) is to soften the metal. It doesn't harden it.

For reloading it makes the neck spring back into shape after firing, instead of cracking.

[IanG]

Annealing hardens metal and helps prevent fracturing, the heating softens metal the molecules which are crystalline align and the quenching hardens.

Yes just heating will soften.

Ian

[Bruce Watson]

I have a problem with the retaining/mounting brass ring for a front achromat. The last owner managed to unscrew it with a great deal of difficulty, doubtful tools and workmanship. There a pliers/pipe wrench marks all around the front rim with a few starting edge cracks. I am not so worried about the appearance but nervous about "structural stability" - it is 230 years old!

I have checked youtube about annealing brass and the suggested method (from people who reuse ammo casings) seems to be warming to the blue colour - followed by quenching in water - which is the complete opposite of what I do to soften ferrous materials?

Any advice or experience? Otherwise I'll have to do experiments with waste brass!

I graduated with a mechanical engineering degree way back in 1978. I've forgotten more than I'd like to think. But the basic concepts are hard to loose.

IMHO, using tools to unscrew a brass fitting isn't going to appreciably cold work a piece of brass. There's almost certainly no need to anneal it.

Firing a gun is completely unlike using ill-fitting tools and poor workmanship on a retaining ring. When you fire a gun the cartridge gets a huge smack (the forces are amazingly large) from the controlled ignition of a change of gunpowder. In the process the neck of the cartridge is physically deformed. And the whole body receives a large thermal shock.

This is completely different than what happened to your retaining ring. So as you might imagine, the need for annealing (AKA stress relieving) is much greater for the higher stresses in the case of firing a gun.

That said, the stress your retaining ring will see in service is minimal at best. It's not like tightening it down is going to cause it to fail in the field. It's structural stability is just fine. It's cosmetic appearance my leave something to be desired, but that often has little to do with a part's ability to perform it's function.

Still, if those are actually cracks and not just deep scratches, annealing the ring won't help. A crack is a crack -- a stress riser. Annealing won't "cure" cracks. If that's what you have, and you're loosing sleep at night thinking it will fail in the field, all you can do is have a replacement ring made.

[Steven Tribe]

My original note/explantion got shorter and shorter as my connection blew everytime I tried to attach a photo and I had to start all over again.
I just want to soften for easier working and to make the brass less brittle. Yes, there are cracks or "tool tears".
I will try and post a photo separately,

[Steven Tribe]

Some illustrations (I hope).

[Bruce Watson]

Annealing hardens metal

The term annealing in engineering and materials science is pretty broad. It can mean hardening. But generally it means to relieve internal stresses. This is done by heating the part up to the point that internal grain boundries can move and the crystal structure can re-normalize. Then the part is cooled in such a way as to preserve these structural improvements. With some materials this requires some level of quenching, others can be air cooled. The end result more often than not is that the material is "softened" in that it looses hardness and gains ductility (among other things).

Annealing is typically done after hot or cold working. IOW after bending, stamping, milling, turning, drilling, etc. For example, when you bend a piece of aluminum, you create regions of higher stress around the bend due to the cold working you've accomplished. Annealing relieves those stresses and returns the part the state it had prior to the cold working.

[Steven Tribe]

Ductability is very much want I want from brass. I'll do some tests over the weekend and find out how quickly brass (in our sort of thickness) gets brittle with hand tool work. I'll also try heating with, and without, quenching in an attempt to recover ductability.
As you see, the lens retaining lip, or what remains of it, is in very bad shape too (nothing to do with me, though).

[Bruce Watson]

My original note/explantion got shorter and shorter as my connection blew everytime I tried to attach a photo and I had to start all over again.
I just want to soften for easier working and to make the brass less brittle. Yes, there are cracks or "tool tears".
I will try and post a photo separately,

Tool marks. Yes. Guy was clumsy as you say. But those don't look like cracks to me. But what do I know from a picture?

The interesting thing is that it looks like he didn't grasp the basic idea that, by squeezing ever harder he was deforming the ring and therefore making it more difficult to remove. The way to turn a ring like this is to use the minimum pressure to maintain traction. I would try a strap wrench probably -- spread the contact all the way around the ring if possible. Ain't hindsight grand?

[Bruce Watson]

Ductability is very much want I want from brass. I'll do some tests over the weekend and find out how quickly brass (in our sort of thickness) gets brittle with hand tool work. I'll also try heating with, and without, quenching in an attempt to recover ductability.
As you see, the lens retaining lip, or what remains of it, is in very bad shape too (nothing to do with me, though).

As you will. Just know that the important things are the temperature you heat too, how long you hold it there, and the cooling ramp. What these should be you'll have to do some research to find out. But it's possible to make it worse instead of making it better. But if you do you can always us the original as a pattern for making a replacement.

[John Jarosz]

What Bruce said. x3

John

[goamules]

You may like to read this:
http://www.6mmbr.com/annealing.html

[Steven Tribe]

The worst problem with these front cell telescope objectives (don't worry - they are being used as meniscus lenses for LF!) is that the graspable width is only between 2 and 3.5mm wide and are completely flush with the brass tube! So instead of using the usual strap solution, I have had to use a piece of an old thick rubber drive belt which can be deformed enough to touch about 3/4 of the circumference. The rubber belt is stiff enough to be able to apply the necessary torque with the hand that bends the belt around the rim edge.

[Steven Tribe]

Thanks Garrett - this is very useful. So slow cooling is an option.
I like the idea of using molten lead as a precaution against overheating. There are a lot of spent cartridges around but not many mounting rings with the right thread. And lead is something I have in some quantities - from the days when making angling equipment in lead was not an environmental hazard.

[rjmeyer314]

In reloading ammunition brass cartridge cases are sometimes pushed through special forming dies to turn cases of a common caliber into those of a rare caliber. This often will destroy the case if it is not annealed first. The way it's usually done there is to heat up a pot full of lead used for bullet casting and dunk the case into the lead. When the case starts to get uncomfortable to hold with your fingers pull it out and place it on the bench. Let it air cool. (I will accept no responsibility if you do this and burn yourself. Proceed at your own risk!)

[mrossano]

Air cooling cartridge brass after heating will produce a brittle result. I will say a prayer for your safety if that is how you are annealing cartridge cases. The brass must be water quenched to produce the desired result for resizing, fireforming, etc. The behaviour of brass and heat-treatable steel are opposites.

[goamules]

"The only way brass can be made harder is to "work" it....Unlike steel, which will be made harder when it is cooled rapidly, brass is virtually unaffected when it is rapidly cooled. Annealing brass and suddenly quenching it in water will have no measurable effect on the brass." http://www.6mmbr.com/annealing.html

I'd have to agree with the above. But I've never annealed any of the thousands of cartridges I ever formed, including some exotics like .40-65, .33 WCF, .40-70 Sharps, etc. Soft, fresh brass forms easily, firing it or hammering on it somehow is what makes it brittle.

[E. von Hoegh]

Certain types of brass - and other zinc based alloys - will become brittle with age, no working is neccesary. Brass MUST be quenched to anneal it. Old cracked brass can be annealed and the cracks brazed up, if it is impotant enough to salvage. I've done this on brass lamps and radiator shells, you'll need a brazing alloy that has a similar color, and a lower melting point than the workpiece.

Cartridge brass is typicall 70% copper and 30% zinc; I anneal the necks on all my brass; with mild loads it lasts until the primer pockets get loose.

[Henry Ambrose]

It'd make a lot of sense to make (or have made) a new part while you still have the old one intact to use as a sample. The if the old one is important to you put it in a drawer to save it after you have the new one.

If it is similar to cartridge brass taking it to about 475 F and letting it cool in air will leave it softer and less likely to split or crack.

BUT

You don't know what the material really is so you don't know how to anneal it. Not really. I would not mess with it.

[Scott Walker]

I have a problem with the retaining/mounting brass ring for a front achromat. The last owner managed to unscrew it with a great deal of difficulty, doubtful tools and workmanship. There a pliers/pipe wrench marks all around the front rim with a few starting edge cracks. I am not so worried about the appearance but nervous about "structural stability" - it is 230 years old!

I have checked youtube about annealing brass and the suggested method (from people who reuse ammo casings) seems to be warming to the blue colour - followed by quenching in water - which is the complete opposite of what I do to soften ferrous materials?

Any advice or experience? Otherwise I'll have to do experiments with waste brass!


The problem you are going to run into if you experiment on scrap pieces of brass is the alloy you are using will definitely not be the same as the scraps you practice on.

Brass is a mix of mostly Copper and Zinc and the alloy varies allot, anywhere from about 50/50 to 95% Copper and 5% Zinc. The higher the copper content the softer and less brittle the alloy will be (as a general rule). Then there are a few other things that get added on occasion with tin being the most common, others are iron, lead nickle and aluminum. these are usually in the range of 1-5% of total.

Your alloy is most likely a combination of about 60% copper 38% zinc 2% tin or iron.

Given the fact that you really do not know the alloy I would recommend heating and cooling quickly by air but not quenching until the temperature is below about 400 f. This will not fully anneal the metal but will be more than adequate for your purposes and eliminates some potential issues.

You may notice that there is a color change after annealing, this is copper and is easily removed with a 5 minute acid bath.

[Steven Tribe]

Thanks for the interesting and lively response. I know, from experience, that the chances of getting a replacement made is small - with all sorts of problems, like hand cutting threads. I'll try first with an unimportant surplus brass ring from a petzval projection lens, rather than super pure modern brass. It certainly has some tin in it. I am sure the maker had no idea what was in it either - probably scrap from a candlestickmaker or brass fitment supplier.

[rdenney]

Like most engineering terms, annealing is subject to interpretation depending on the processes being supported.

For example, when making brass musical instruments, considerable stretching and working of the metal is required. Working the metal causes the grains to align, which make the metal stronger and more brittle. Stronger in that it will take more force to deform it, and more brittle in that it is more likely to crack with further working.

With brass instruments, one anneals the metal to until it begins to glow, and then cooling it by whatever means works (brass cannot be heat-treated too make it stronger and the cooling method for this purpose doesn't matter). It's important to note that in this application, the brass is going to be burnished, rolled, hammered, or otherwise worked which will strengthen it after annealing. For brass that is not going to be further worked, annealing it to fully soft might ruin it for its intended application.

Thus, brass is annealed to soften it to allow further working without causing it to crack. Annealing as a process may be performed to relieve internal stresses, but stress relieving isn't the same thing as annealing. Annealing may also be the first step in heat treating metal to make it harder, but heat treatment is not the same thing as annealing. And, as I said before, heat-treating doesn't work for brass anyway--annealing destroys the grain structure that makes the metal stronger and quenching it does not restore that structure as it does, say, with steel.

I would not want to anneal a threaded ring unless it was deformed, and I wanted to work it back into shape without cracking. There's no way to correct excessive annealing, but once it cracks, it can only be repaired by brazing, which will likely ruin the rest of it. Hitting what might be a small target would be the province of someone with very specialized skills indeed.

Rick "whose brass musical instruments do not have to be particularly hard" Denney

[mrladewig]

Like most engineering terms, annealing is subject to interpretation depending on the processes being supported.


It may be subject to misinterpretation by people outside the metallurgical field, but it has a specific definition.

Annealing means one thing. You are heating the metal up to the point that the crystal boundaries can be reformed. Annealing is the heating side of the cycle. It may or may not have anything to do with work stresses. It can be used simply to gain a preferred type or size of grain for the end application as part of a heat treating cycle.

There are considerations for the cooling side of the cycle as well with options to furnace cool, air cool, oil quench, water quench, etc... Each has with it a rate at which the heat is taken from the metal and that affects the crystal structure and size after cooling. And the crystal structure and size affects how the metal functions in hardness, ductility, toughness, etc..

The total of these cycles is heat treatment though other functions fit into heat treatment as well.

As for the case with brass you're going to have to know the specific brass alloy to look up the annealing properties for that metal. Then you'll need to research some additional texts to find out the working properties of the alloy and determine from there how you want the end metal to function. And then since all these books are written within academic circles, you can expect some variation with real world materials. Really soft brass may not be what you want. I wouldn't choose very soft brass for threaded applications myself.

My honest recommendation is to not do anything to it. I think the tool sheared the metal, but I doubt he worked it to the point of complete brittle failure. If you are intent on reshaping the part, then heat treatment may be your only option, but I'd be prepared to find or make a new one because you may end up with an unworkable mess if it isn't done correctly.

[GPS]

...
I am not so worried about the appearance but nervous about "structural stability" - it is 230 years old!
...
Any advice or experience? Otherwise I'll have to do experiments with waste brass!

It's only now that I checked on your pictures of the ring. My opinion is this - as long as the thread itself is not damaged (it appears to be the case) its "structural stability" is what it was those last 230 years...
I also think Bruce is right with his estimate of the mechanical stress to which the ring is exposed.
Because of that I would suggest to use the KISS method using the ring "as is" while whistling your favourite song...:)