Annealing copper and brass

Clock · Oct 22, 2021

I have turned commercially made brass and aluminum rod as well as aluminum rod that I casted for making small parts on my wood lathe. Yes I know that I shouldn't turn metal on a wood lathe.
I recently cast copper and brass into rods. The copper was from clean electrical wire and the brass was clean plumbing brass. The cast brass and copper rods were so hard that the chisels barely made a scratch. I attempted annealing them but it barely made a difference. Based on my research annealing is heating to a cherry red and quench. I accidentally heated to orange,lowered to red and kept at that temperature for about 20 minutes since the rods were 1 1/2" in diameter.
Is there anything that I can do to soften them so that I can work with them? I would really appreciate any help. This post is long but I tried to include as much information as I could.
Thanks

BoxcarPete · Oct 22, 2021

Brass might be a little different, but for pure copper it doesn't matter the cooling rate. Once you got it up to temp, which is below red by the way, they say red just to make sure you're above it, then it is annealed. It removes the residual strains from cold working, that's all.

So, your cast copper should have been in an annealed state already. Heating it again will do nothing, there is something else that caused a hard skin to form on it if you're asking me. Likely the same for the brass.

Clock · Oct 22, 2021

When you say a 'hard skin' does that mean that if you get past a certain depth the metal will be softer? I have turned about an 1/8" in the copper and it is not any softer.
Thanks for the reply

eKretz · Oct 22, 2021

How are you determining the hardness? Annealing either should just take heating and letting it cool down. Quenching isn't necessary, it's just frequently done so the part that's been annealed is cool enough to be worked immediately afterward. Being able to see a slight red glow in a dark room should be sufficient heat.

If this isn't working, something else is going on. During casting, how long did you hold the liquid metal at temperature, and how did you control the temperature? Did you use any flux? What did you use as a vessel to hold the liquid? What did you pour into? I agree with Pete, something in there caused a problem if it won't soften to a normal level.

Gordon Heaton · Oct 22, 2021

eKretz said:
. . . Did you use any flux? What did you use as a vessel to hold the liquid? What did you pour into?. . .

Somewhere in these questions lies the answer. It doesn't take much contamination to make copper cranky. Even when its relatively pure it isn't fun to turn. On the Hi-Def plasma table at work, we cut great quantities of copper almost exclusively and the slag buildup between cleanings gets to about 3/8" thick in spots. It's not the same thing, of course, and there are occasional infusions of steel where the cut crosses the rails just right, but that stuff is HARD! A hammer and chisel won't dent it, you have to get under an edge and pry it up. Its still high enough copper content that the recycler pays a good price for it.

Ries · Oct 22, 2021

The problem is that there are a million different alloys of copper- depending on what they are alloyed with, it can range from dead soft to hard as tool steel. And home melting is pretty uncontrolled, and who knows what was in your "plumbing brass". 360 brass is soft, and its full of zinc and lead. Silicon Bronze, which is usually around 95% copper, is pretty hard, because 2% of silicon is a big difference. You pays your money, you takes your chances. If you buy a known alloy, you get a known hardness.
Thats why most shops actually pay that high price.
Turning some copper alloys will require more horsepower, and carbide tooling.

Greenwud · Oct 22, 2021

Copper dissolves it's own oxide which makes it hard and somewhat less malleable. Brass too but less so.

You need a cover flux for melting otherwise oxidation is cignificant with wire material

James H Clark · Oct 25, 2021

I was always told that softening brass is the same process as hardening steel. Heat it up to almost red and quench it in water. That is the way we anneal work hardened brass rifle cases

JH

sfriedberg · Oct 25, 2021

James H Clark said:
I was always told that softening brass is the same process as hardening steel. Heat it up to almost red and quench it in water. That is the way we anneal work hardened brass rifle cases

Yeah, both involve heating, but not the same thing going on at all. For steel, the quench is necessary. For aluminum, brass, copper, the quench is just a convenience. Letting it air cool would do just as well. For steel, you need much higher temperatures, depending on the alloy anywhere from 1200F to 1800F, which is dull red to orange-going-on-yellow. (And HSS needs significantly higher than that!) For aluminum, brass, copper, you don't need anything like that high a temperature. 800F would be ample.

Clock · Oct 28, 2021

to EKretz and everyone who responded. For melting the copper and brass i heated to orange until it was all melted and continued heating for approximately 5 minutes to assure that it was hot enough to cast. I used steel pipe for a mold for the rods. The brass and copper would not come out of the pipe and I had to cut the pipe and peel the pipe off. It actually had pieces of the steel on the the rods.
I did not use flux. I used a commercial crucible to melt. I did not have a pyrometer for melting. I heated until all of the metal had melted. The metal was orange.
For annealing my goal was to heat to red but when I walked away and came back to check it was orange. I cooled it down and held for about 20 to assure that the 1.5" diameter rods had heated all the way through.
It is evident that I over heated beyond the 800 to 1,200 annealing range and may have negated the annealing.
I judged the hardness by comparing turning commercially bought rods and the cast rods. The brass commercial rods turned with long chips and the cast rods turned with small chips, like coarse sawdust.
My casting was more "shoot from the hip" than professional or scientific. I thought about using the temperature sticks which would be useful to reach the proper temperature but not so much for the holding temperature.
Maybe I could anneal again properly and soften the metal?
Tom

Gordon Heaton · Oct 28, 2021

I think it might be worth your time to melt again and flux the melt. Borax seems to work for many metals and its cheap. Start the melt with flux, then flux again and skim the slag just before pouring. I've never cast copper, but I've seen the results of no-flux melts on other materials.

eKretz · Oct 28, 2021

Have a look here:

Copper and Copper Alloys Casting Problems

Gordon Heaton · Oct 29, 2021

eKretz said:
Have a look here:

Copper and Copper Alloys Casting Problems

Wow, after looking that article over, it seems casting relatively pure copper isn't worth it.

Peter Colman · Oct 30, 2021

Brass is a mixture and not a genuine alloy, this means that the copper and zinc remain as separate crystals in the mix, free cutting brass has free particles of lead.
On heating brass the zinc burns off and you need to make an addition to get back to spec.
To make a free machining alloy I would aim or 57% copper, 40% zinc and 3% lead
I would weigh out the components, melt the copper then lead and add zinc at the end stir in some borax and cast. Yellow smoke is the zinc oxidising so don’t heat for too long at above casting temperature
There should:be no need to anneal cast material.
When you cast ‘plumbing brass’ you may have included gun metal and bronze giving high levels of other elements.
For your purposes you can use forged not cast parts, machined scrap, metal, brass pressings, old ammunition cases etc.
Avoid aluminium and iron.
Make the mould split in two halves and coat with graphite to aid extraction

dian · Nov 6, 2021

sfriedberg said:
Yeah, both involve heating, but not the same thing going on at all. For steel, the quench is necessary. For aluminum, brass, copper, the quench is just a convenience. Letting it air cool would do just as well. For steel, you need much higher temperatures, depending on the alloy anywhere from 1200F to 1800F, which is dull red to orange-going-on-yellow. (And HSS needs significantly higher than that!) For aluminum, brass, copper, you don't need anything like that high a temperature. 800F would be ample.

depending on the alloy quenching might neccessary for aluminum.

sfriedberg · Nov 6, 2021

dian said:
depending on the alloy quenching might neccessary for aluminum.

Always willing to learn. Any particular families (e.g., 70XX, 30XX) that need a quench for anneal?

dian · Nov 7, 2021

im not so good with non-ferrous, but this seems simple: as the material cools through the precipitation hardening range (roughly 300-400°c) it, well, hardens. if this should be of concern of course depends on what you are doing and on the size of the work also.

edit: 2000, 6000, 7000 series.

sfriedberg · Nov 7, 2021

I thought aluminum precipitation hardening is primarily an aging process, accelerated by higher temperatures, which is why freshly-made aluminum rivets were sometimes kept on ice until immediately before use. Oh well, more to read, I guess.

eKretz · Nov 8, 2021

My understanding was always that aluminum did not need to be quenched during annealing. As far as I know, it generally gets solution heat treated with a quench then artificially aged via a heat soak (precipitation hardening).

sfriedberg · Nov 9, 2021

I suppose if you want annealed or dead soft, then the quench moves the material so rapidly through the temperature range where precipitation hardening takes place that you don't get much hardening (until it spends time at a higher temperature). So now I see dian's point. The quench on precipitation hardening aluminum alloys has sort of the opposite effect as quench on carbon steel. In one the rapid cooling causes the hardening state change, in the other the rapid cooling prevents the state change.

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