Annealing Brass

[CHARLES lipscombeParticipant @charleslipscombe16059]

I think I shot myself in the foot with a previous enquiry on this subject by tacking it onto an existing thread which covered several subjects. The replies I got mainly concerned the other subjects as people referred to the OP's queries.So I am now trying again starting a new thread.

My question is:

What is the correct procedure for annealing brass? There is plenty of info on the webb but just about every piece of advice seems to be contradicted by the next article.

I am making some petrol filler necks for vintage motorcycles from CZ 26130 brass which is an arsenic containing cartridge brass.It is listed as good for cold working but only fair for hot working. I need to bend a small tab at right angles to the main axis and as-supplied tubing when bent cold, cracks on the outside of the bend. Wall thickness of the tube is 1.63 mms.

In particular, does the brass need cooling rapidly or slowly after heating?

Somehow I have a lot more confidence in the forum and its contributors than You-tube

[CHARLES lipscombeParticipant @charleslipscombe16059]

How to anneal Brass

[Michael GilliganParticipant @michaelgilligan61133]

A first very broad comment, Charles … Brass is not particularly suited to annealing.

It is not a true alloy, and there is a serious risk of Zinc being boiled-off in the attempt.

This de-Zincification then leaves gaps in the micro structure, which is exactly what you don’t need.

That’s my understanding: But I would be very happy to be proved wrong.

MichaelG.

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Edit: Not much detail here, but it seems to endorse my concern

http://www.airproducts.com/industries/Metals/ask-the-experts-metals/heat-treating/dezincificatiion-apply-thermal-processing-brass.aspx

Edited By Michael Gilligan on 01/12/2019 08:34:41

[Mick B1Participant @mickb1]

My metalurgical knowledge is very limited, but from what I've seen with most cartridge brasses I don't think it matters.

Rifle cartridge reloaders sometimes anneal their case necks – though the value of that is somewhat under dispute – and those who do usually use variants of 2 methods:-

i) stand the cases in shallow water in batches, heat the necks together with a blowlamp, then knock them all over into the water to quench, or

ii) use a turntable-type machine that passes cases one-by-one past a gas flame (or sometimes an electrical heater) before dropping them into a receptacle. In this method I haven't *usually* seen them quenched.

Of course cartridge case necks are thin, and can be expected to cool pretty quickly in ambient air whether quenched or not, but your material may well not be thick enough to differ significantly. I'd try it both ways with a bit of scrap brass if you've any available.

There's a very clear requirement in caseneck annealing NOT to anneal the main case body, especially the base (or 'head' ) area, in order to retain strength. Method i) has some advantages in that respect, but considering the typical application involves maybe 10 -20 mm of water in the bottom of a shallow tin tray, a seriously slow cooling of the annealled part would require more elaborate arrangements than I've ever heard tell of.

Edited By Mick B1 on 01/12/2019 08:53:28

Edited By Mick B1 on 01/12/2019 08:54:02

[Michael GilliganParticipant @michaelgilligan61133]

With apologies for digressing so soon !

This article about chemical de-Zincification is useful for reference: **LINK**

https://www.canada.ca/en/conservation-institute/services/conservation-preservation-publications/canadian-conservation-institute-notes/dezincification-brass.html

MichaelG.

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Edit: and here’s a useful summary of characteristics, for general reference

https://www.columbiametals.com/files/products/69.pdf

 

Edited By Michael Gilligan on 01/12/2019 08:51:02

[David JuppParticipant @davidjupp51506]

It is the time at elevated temperature that does the annealing – the quench is not involved in the annealing. With Brass, it is possible to quench, because that doesn't cause a phase change – whereas with Steel, quenching can often harden the metal, by the production of martensite (so when annealing steel, slow cooling is the norm).

[Clive Brown 1Participant @clivebrown1]

The main advantage of quenching would be to save time at possible risk of distortion. The effect mentioned by MG is hot shortness, certainly to be avoided, but would require considerable temperature. Dull red is plenty hot enough, at which point annealing is very rapid.

Edited By Clive Brown 1 on 01/12/2019 09:11:05

[Simon CollierParticipant @simoncollier74340]

I had to anneal the 0.8 mm brass one piece cladding for my Springbok loco several times to be able to roll it with 3' rolls. I used a large propane torch and heated to just dull red. You have to be careful as you can melt thin brass, but it certainly did anneal and the job was completed satisfactorily. I also anneal brass half round beading to be able to coax it around tight curves edge on. Also brass angle to go around the boiler to spectacle plate joint, etc. it is a routine procedure in my workshop.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Clive Brown 1 on 01/12/2019 09:09:51:

[…]

The effect mentioned by MG is hot shortness, certainly to be avoided, but would require considerable temperature. […]

.

Thanks, Clive … I felt sure there was a specific descriptive term, but couldn’t recall it.

MichaelG.

[DiogenesIIParticipant @diogenesii]

+1 for heating to dull red and allowing to cool naturally.

Could part of the problem be the "right angle" requirement – if you are attempting a sharp 90 degree angle, it's asking a lot of the ductility.. It would be much easier if you were able to form the bend over a radius, if there is scope within the design for this to be practical..

[Clive HartlandParticipant @clivehartland94829]

With brass sections that are formed by extrusion like square or flats they distort when machined. I found out this the hard way and had to re-make bits. Soon learned to anneal the btass and and quench from dull red. Makes it softer as well and machines better.

With brass tubing you will have a problem bending at right angles so here fabricate the bend.

[CHARLES lipscombeParticipant @charleslipscombe16059]

Ah! That's a much better response once I re-sited my request

My thanks to everyone that replied and I conclude that cooling rate is not important for brass annealing.

A problem that arises with this job is well-known to old vehicle restorers – it has to look like the original so different methods e.g. fabrication are not always viable. The problem is more apparent on a restored motorcycle because just about all the parts required are visible. Both Clive and Diogenes' comments are the way I would like to go but………

The consolation is that these articles were made well before WW2 and in mass-production so the job must be do-able and moreover easily done, or it would not have been carried out in mass production. "All" we have to do is solve the "how"

Regards, Chas

[old martParticipant @oldmart]

I was taught to heat to dull red and then quench in water. Another point is that removing sharp corners from the outside of the area to be bent and smoothing the surface, reduces the likelihood of future stress fractures.

Look up "seasonal cracking of brass"

Edited By old mart on 01/12/2019 21:20:51

[CHARLES lipscombeParticipant @charleslipscombe16059]

Thanks for that "Old Mart" . Googling seasonal cracking has revealed a need to anneal brass after the bending etc has been completed. I had not come across that before but it is quite likely to be needed in my application

[Danny M2ZParticipant @dannym2z]

Brass cartridge cases work harden in the neck area after firing expands them and neck resizing with a precision die squeezes them back enough to grip a new projectile. A lot depends on the chamber dimensions.

If this problem is not addressed the useful life of the case is reduced and split necks are usually the end result.

Annealing the necks with a propane torch with the case standing in a tray of water reaching almost to the shoulder means that the heat does not affect the lower part of the case (base and pressure ring) which are left hard by the manufacturer for safety reasons. Tipping the cases into the water stops the process.

Commercial manufacturers and some serious competitors often use induction heating btw. such as this Induction cartridge case annealer although since I found that the temperature of molten lead is ideal for neck annealing cartridge brass a tray of sand heated to when lead melts is less messy and ideal for bulk reloading.

At the end of the day – Brass does work harden, annealing works to alleviate the problem and also, radius your bends.

* Danny M *

[Alan Johnson 7Participant @alanjohnson7]

I anneal the necks of cartridge brass (30-06, 303 and others) by holding the neck area of the case over a low temperature spirit lamp (methylated spirits). I hold the case (in my hand – at the base) over the flame until the case becomes too hot to hold, then drop it into a box with a bit of rag in it so that it can cool naturally. It works.

[CHARLES lipscombeParticipant @charleslipscombe16059]

Success at last

Following the tips given, I accomplished the job with no cracking. There was a very marked reduction in the amount of effort required to form the bend, which leads me to conclude that the new brass tube I purchased was well-and-truely age or stress hardened.

I stress relieved the bends by re-annealing afterwards because of the amount of displacement of the brass but I can see that this would be unnecessary for a cartridge case where little displacement of the metal occurs.

Thanks to everyone who contributed, Chas

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