Stress Relief Annealing cartridge brass

[Alantoo]

Very interesting and informative post Alan. Can you please qualify whether you heated the aluminium from the back (ie placed into a holder and heated the back face to ensure temperature indication relates to the aluminium temperature throughout) or whether you the flame was direct to each sample onto the face with the soap)?

A genuine question here, but unless you're applying the soap via a thin brush to the inside of the necks, how do you know that you are consistently achieving the stress relieving consistently through the thickness of the case neck?

Must admit that I use 750F tempilaq on the inside of the case necks and watch for the flame colour as the brass is heated until the tempilaq indicates 750F has been reached. Rather than paint every case to be annealed I then set the annealer timer to this setting but appreciate that varying case neck thickness then becomes an issue. There's greater chance though of inconsistent results playing with the machine timer for every case so unless I just anneal by hand again as I used to like you do, it seems there's little else to be done with machine annealers. Proof of the pudding though is that ES figures from the chrono plus very tight group sizes would seem to indicate consistent neck tension and perhaps this is the only reliable method of measuring whether our stress relieving has been achieved with sufficient consistency?

Yes, I heated the full width of the aluminium from the underside with a large torch in order that it was the aluminium temperature rather than the flame contact that affected the soap and tempilaq. All three of the squiggly samples arrived at the same heat at the same time.

Not 100% contact free from the flame obviously, but more useful for our purposes and more in context than using a flame-free hot plate. I used the thicker material and just heated a couple of inches of the end of the bar to better demonstrate the variation of colours the soap achieves on the way to the 400˚C.

I did video the heating process but it is a bit like watching paint dry...but I could post it or email it if you are interested.

Given that a case mouth is only a few thou thick I think it unlikely that you would be able to achieve a variation in temperature through its thickness in any consistent fashion with a flame heat source...you are much more likely to get a variation along the length between the case mouth and the shoulder areas, because the case mouth will have a swirl of flame on both inside and out, whereas the areas away from the opening will have less heat playing inside and the shoulder is larger in diameter/perimeter and therefore mass.

I think you are also more likely to get a variation across the case just because the case wobbles slightly or rotates slightly eccentrically and one side may be passing through a slightly hotter area of the flame than the other.

It would be an interesting test for the precision of a timed annealing machine to see if you could consistently cause tempilaq or soap to change colour on the outside of the neck without it being affected on the inside...I would think that almost impossible due to the thinness of the case material and its capacity for heat conductivity. Do you fancy trying with yours?

There is arguably an advantage to rotating the case holding the drill freehand as per my video, in that if you see the soap turning brown at the mouth but not at the shoulder you can adjust the position in the flame to favour the shoulder.

I am sure, as we all recognise, that the important thing is doing the same thing to each case. ...even if you under-heat within the 250/350˚C range with its hugely variable hardness outcomes as long as you were consistent the out come will not be a disaster...but there is a lot more tolerance in the process and less variation in hardness relative to temperature once you get it to 400˚C.

For these reasons I do feel it more logical and prefer the basis of using the soap temperature indicator to determine the temperature rather than using time.

It just reduces some of the variables.

The timed annealing machines produces perfectly good results as you say. However for those without such machines, the soap tell-tale trick is a handy and economic solution...and certainly much more accurate than counting to 7!

Alan

 

[ChesterP]

Thanks Alan, a well considered and logical post which makes perfect sense, so thank you for taking the time and trouble. I may give the soap trick an outing on a small batch and compare results in the field with the chrono against the machine annealed brass just to compare MV and group consistencies. That would seem like the next logical step to me

 

[Alantoo]

I will be interested to see the results of your comparison.

By the way if anybody wants a pot of 750˚F / 399˚C Tempilaq I have one here they can have it at a good price...only used once for the above experiment!

Alan

 

[trajan]

Alan. Thank you for this write up. I have an induction annealer and i used to anneal till the 750 F Tempilaq changed colour. However, while seating the bullets i noticed quite a bit of variation in force required. so i just kept bumping up the temperature on each lot of subsequent batch of 3 cases till i found that the most consistent seating force required was when the case neck just started to glow red in light. No issues noted with decreased in accuracy on the range as yet. Since, as you said that Annealing is a function of temperature + time, i suspect that the induction method could push the temperatures on the neck higher without destroying the brass in the necks?

 

[Alantoo]

Alan. Thank you for this write up. I have an induction annealer and i used to anneal till the 750 F Tempilaq changed colour. However, while seating the bullets i noticed quite a bit of variation in force required. so i just kept bumping up the temperature on each lot of subsequent batch of 3 cases till i found that the most consistent seating force required was when the case neck just started to glow red in light. No issues noted with decreased in accuracy on the range as yet. Since, as you said that Annealing is a function of temperature + time, i suspect that the induction method could push the temperatures on the neck higher without destroying the brass in the necks?

Interesting. I am sure that doing the same thing each time is the key, and is much more important than whether you fully anneal or just stress relieve the neck and shoulders.

The point I would argue over and over is that you won't destroy brass by getting it to red heat. It is an alloy. If you could burn out the zinc in the second or two it was at 600deg C then any brass object that was silver soldered would be ruined. Similarly if it were true, it would be impossible to cast brass, by the time it was molten and pourable you would only be left with copper, all the zinc having burned away. The yellow flame you get as the brass approaches 400 degrees is not the zinc burning out...it is most likely contamination and the tarnish/oxide layer burning off the surface. As soon as you clean the brass it shows up yellow, if the zinc had gone it would have changed colour to copper.

You don't need to get it to red heat though in order to extend the life of the cases. That will happen at 400 deg C.

As I understand it the advantage of the stress relieving temperature of 400 deg.C 700 deg F is that it will prevent stress cracks enabling a greater number of reloads. It is the lowest temperature at which all the previous amounts or states of work hardening come together, which means you have a tolerance for consistency. By staying below the recystallisation temperature it retains a similar strength that the case neck came with from the factory.

I found like you, that it will still work if annealed at a higher temperature even if is softer, and of course it will work harden again through being resized and fired. With flat bottomed bullets the Lee flare tool seems to make seating smooth as silk with just the 400 degree C soap black system.

Alan

 

[rodp]

then any brass object that was silver soldered would be ruined

And I believe Brass steam pressure boilers are silver soldered ? Which wouldn't be allowed if the brass was compromised. Just as an aside, I used to use the soap method when gas welding ally, it gave a good indication of just how quickly the metal was coming up to temperature.

 

[Alantoo]

And I believe Brass steam pressure boilers are silver soldered ? Which wouldn't be allowed if the brass was compromised. Just as an aside, I used to use the soap method when gas welding ally, it gave a good indication of just how quickly the metal was coming up to temperature.

Now that really is an old school skill! Much respect! A retired welder friend of my father's (who welded up my first Morris Traveller) could gas weld aluminium...I reckoned it was nearer witchcraft than metalwork! I only manage to tig and mig it. I do use the soap indicator for full annealing of aluminium, and as an indicator for approaching the forging temperature. The "greasy stick" and charring the hammer handle comes in a hundred degrees or so above.

Alan

 

[rodp]

Now that really is an old school skill! Much respect! A retired welder friend of my father's (who welded up my first Morris Traveller) could gas weld aluminium...I reckoned it was nearer witchcraft than metalwork! I only manage to tig and mig it. I do use the soap indicator for full annealing of aluminium, and as an indicator for approaching the forging temperature. The "greasy stick" and charring the hammer handle comes in a hundred degrees or so above.

Alan

Ha ha, no witchcraft, it's just (as you say) an old school thing, and I'm old But thank you for your kind comments, you're obviously a man that knows there's more to metal work than meets the eye sometimes

 

[Alantoo]

This is the last batch of cases I annealed with the soap technique. The top two rows are Hornady and the bottom row Lapua. The consistent regularity of the heating is what I am trying for. The soap shows each case has achieved the 400 deg C and helps to prevent efficiency creep occurring as you go through the batch.

Alan

 

[Odders]

I bit the bullet & bought a case annealing machine last week.
Now I need a decent gas torch to get it up & running.

 

[ChesterP]

I bit the bullet & bought a case annealing machine last week.
Now I need a decent gas torch to get it up & running.
View attachment 91782

Use a fine flame torch like the Go System torch (about £16) and Rothenberger Propane cylinders with that (I use the same one). Propane shortens the time that the case has to be in the flame which is a good thing. 308/6.5 cases only need about 3.5 seconds when the torch's fine inside blue flame tip is on the case neck. 223 are done in a second less for me.

 

[smokey]

you are over thinking this just anneal and shoot as long as you do not anneal the body you will be ok( verified by a PHD in material science)

 

[Alantoo]

snip..

Thank you. I hope a metallurgist will be able to confirm or refute it, but it should be good for discussion...
snip...

you are over thinking this just anneal and shoot as long as you do not anneal the body you will be ok( verified by a PHD in material science)

Ouch!

Maybe I should have been more careful what I wished for...

For a Doctor of Material Science to dismiss all the work by his fellow PhD's I quoted (and provided links to)...and, after the 6 pages of discussion about the various nuances different annealing temperatures make to the hardness of the brass...the phrase "just anneal" I find rather a disappointing contribution.

For an academic to describe research into a subject in order to understand it as "over thinking" seems really strange to me. (Verified by a lifetime of trying to be open minded learning about and making things in metal since I finished my college studies)

Maybe you could expand on "just anneal" with a bit more useful/descriptive information for us?

The Copper Development Association list the range of 250˚C to 680˚C for Stress Relieving Annealing through to Full Annealing temperatures.

Temperatures between 250˚C and 350˚C have widely different hardness results...Temperatures above 400˚C will cause recrystallisation and will produce much less neck tension than when originally manufactured.

What temperature in that range does your "just anneal" equate to?

Alan

 

[pinkfoot1]

Take a serious look at salt bath annealing, it is controllable and repeatable. Despite the Prophets of Doom on here -IT WORKS!

 

[Alantoo]

Take a serious look at salt bath annealing, it is controllable and repeatable. Despite the Prophets of Doom on here -IT WORKS!

It does sound interesting.

The questions I have are mainly as a result of my failed attempt to use a molten lead bath as the heat source.

What temperature are you aiming to take the case neck and shoulder to?

How do you monitor and control the temperature of the salt?

How do you gauge when the case has reached that temperature?

How do you monitor the temperature drop in the salt bath each time you introduce a case?

Is the temperature drop insignificant...ie the heat reservoir of the salt and the input heating element is sufficient to get back up to temperature within the annealing cycle time / between subsequent cases?

Do you have to wait between each case for the heat to be regained, or can you just continue through the batch as fast as you can dip them?

Do you find any salt residue inside the cases? If so how is it removed?

Alan

 

[pinkfoot1]

It does sound interesting.

The questions I have are mainly as a result of my failed attempt to use a molten lead bath as the heat source.

What temperature are you aiming to take the case neck and shoulder to?

How do you monitor and control the temperature of the salt?

How do you gauge when the case has reached that temperature?

How do you monitor the temperature drop in the salt bath each time you introduce a case?

Is the temperature drop insignificant...ie the heat reservoir of the salt and the input heating element is sufficient to get back up to temperature within the annealing cycle time / between subsequent cases?

Do you have to wait between each case for the heat to be regained, or can you just continue through the batch as fast as you can dip them?

Do you find any salt residue inside the cases? If so how is it removed?

Alan

Hi Alan,
1. Target temperature is 500 deg C
2. I built a PID controller which keeps the salts within a couple of degrees of target temperature
3. 5 seconds immersion suffices
4. I only use two calibres, 0.308 & 6BR so they are dipped 5 & 4 seconds respectively because of slightly differing case neck volumes (soap to on body to monitor heat transfer until I was happy with my timings.
5. The PID is connected to a thermocouple strategically held in the bath and a readout is always visible
6. There is rarely a need to allow the salts to return to temperature, it only happens if I insert a case when the heating is at the bottom of a cycle, i.e. 2 degees below 500 and it is back up to 500 within about 5 seconds
7. I use a metronome on my tablet and just tick-tock through it case after case
8. I keep a pot of warm water on the floor and just drop each case in as it comes out the bath. This serves to arrest any heat transfer up the body but also washes off any residual salts

Here are my observations which I have shared with others;

OBSERVATIONS ON USE OF LEE MELTER FOR MOLTEN SALT BATH ANNEALING
I began the salt bath journey a couple of months ago and have been perfectly happy with the results.
A paper by AMP, manufacturers/marketers of induction annealing equipment for cartridge brass, in which they claimed salt bath annealing simply did not work set me thinking.
Having already spoken with an independent annealing company here in the UK who confirmed that flash dipping my case necks in molten salts at 500 deg. C for 5 seconds would do the job and with greater certainty than using flame systems I set to work.
The case holder jig is arranged with a bottom plate 1” below the top of the melter pot.
It has holes in it for location of the case such that the shoulder is just in the hole.
The level of salt is set at 1” below the top of the melter pot so that none of the case body is immersed.
I took a number of identical S & B 0.308W cases all of which had been fired five times, neck sized, never heat treated. They were seperated into two random batches.
All necks measured 0.334” at case mouth.
I took a pair of mole grips and measured the pitch of their adjusting screw. It was 14 threads per inch which equates to 0.0714” per revolution. I felt that this would give me a fine enough control to detect neck deflection in which I was interested.
I placed the moles in the vice and carefully closed the jaws on the raw, untreated
cases by winding in the adjusting screw .
At 3/8 of a turn equivalent to crushing 0.0270” there was complete springback to the original diameter of 0.334”
At ½ of a turn equivalent to crushing 0.0358” there was a permanent deflection of 0.002”.
When testing cases where the necks had been flash dipped at 500 deg C for 5 seconds the necks were permanently deformed 0.0010” at 3/8 of a turn and 0.004” at ½ a turn.
This indicated that the salt bath had certainly reduced stress in the necks.
To further test I placed a raw, untreated case neck in in the moles and barely closed the jaws then continued to tighten until I could go no further using fingers only. I just achieved one full turn.
When I repeated this with a flash dipped case the difference was immediately apparent as much less effort was required and I was able to achieve slightly over a turn and a half.
I AM HAPPY TO SAY I AM UNABLE TO ACCEPT AMP'S ASSERTION!

As an aside to this it is worth mentioning that having achieved 500 deg C (using a PID controller) I checked temperature at varying depths in the salt by raising and lowering the thermocouple. I feel that as long as the thermocouple probe is held off the base of the pot the salt temperature, to all intents and purposes is uniform throughout the bath.
The above deliberations took quite a while and I noticed the bath temperature dropping even though the PID was indicating it was in heating mode.
(I am using a small LEE melter)
It soon transpired that this was as a result of the Lee melter thermostat cutting out on overheat, presumably to being in a non-vented enclosure adjacent the heating element. This despite turning it up to Max. The best it would achieve was 440 deg. C.
I could have simply bypassed the Lee thermostat but being a cautious guy and wanting it to remain as a backstop in case of any failure of the PID I simply adjusted the stat internally by means of minutely reducing the length of the actuating mechanism. All sorted, job done.

I hope this may help and perhaps relieve any doubts.

 

[pinkfoot1]

SALT BATH ANNEALING – LIST OF MATERIALS​
​	​	​	​	​
ITEM REF.​	QTY.​	DESCRIPTION​	POSSIBLE SOURCE OF SUPPLY/comments​	INDICATIVE COST​
1​	1​	Lee Precision Melter​	CGDS (On-line)​	£54.00​
2​	1​	Project case​	Found on-line, China​	£7.39​
3​	1​	REX – C100 AC PID SSR Controller​	Found on-line, China. Often sold as a kit, controller, thermocouple, solid state relay. BE AWARE, THERE ARE TWO TYPES OF PID. GET THE ONE FOR SSR.​	£10.29​
4​	1​	40amp SS relay. 240v.​
5​	1​	Type K thermocouple, 100mm.​	Found on-line, China. If buying a kit it will probably have a thermocouple with max temp 400 deg C. These are unsuitable. You need one up to 1000 deg C with no more than a 100mm probe.​	£1.72​
6​	1​	Plug c/w panel mounting socket for thermocouple​	Found on-line, China​	£2.75​
7​	1​	Double pole latching switch, panel mounting. 240v. 10a.​	​	£0.99​
8​	1​	Panel mounting female socket. 240v. 10a.​	These are Bulgin style available almost anywhere, including China. Reference to the photos shows a connector of this type.​	£1.53​
9​	1​	Panel mounting male socket. 240v. 10a.​	As Item 8​	£2.62​
10​	1​	Cable mounting male socket​	As Item 8​	£1.53​
11​	1​	Connecting cable 13a. Plugtop to 13a female socket to connect to item 10​	​	£4.00​
12​	2​	Panel mounting fuseholder 240v. 10a.​	Various types available. Cylindrical type with square front readily available.​	£2.99​
13​	1​	4 way terminal strip​	Not essential but can make component/connection swap easier if required.​	£1.00​
14​	1​	Heat sink and heat sink compound.​	Whilst not essential due to the low current I chose to use one to avoid long-term degrading of the plastic enclosure due to warmth. The compound goes between the solid state relay and the heat sink to aid heat transfer.​	£0.99​
15​	​	Miscellaneous bits of wire for connections within project box, 10a and 1a glass fuses, pieces of brass or steel together with nuts and bolts of same material for constructing case holder​	​	£5.00​
​	​	​	MIX RATIO BY WEIGHT​	​
16​	​	KNO3 – Potassium Nitrate​	53%​	£12.00​
17​	​	NaNO3 – Sodium Nitrate​	40%​	£14.00​
18​	​	NaNO2 – Sodium Nitrite​	7%​	£8.00​
​	​	​	​	​
​	​	​	Total​	£130.80​
​	​	​	​	​
Reference document regarding melting points of the above salts for guidance.​	​
http://pubs.acs.org/doi/pdf/10.1021/je00032a022​	​
​	​	​	​	​
It takes about 250g of salt mix for the pot so do your sums before ordering too much. As the salts are hydroscopic you need to keep them in a dry place. I use a Kilner kar for the spare salt and put the Lee pot, complete with contents in a ziplok bag once cool.​

 

[pinkfoot1]

I have pics and diagram but will get them up here later...

 

[Alantoo]

Comprehensive, thank you. I look forward to the photos.

Not that I see it as being any sort of a problem, but why did you go for 500˚C rather than 400˚C?

Alan

 

[pinkfoot1]

Comprehensive, thank you. I look forward to the photos.

Not that I see it as being any sort of a problem, but why did you go for 500˚C rather than 400˚C?

Alan

1. To move further away from lower, potentially more variable results

2. To minimise dip time

3. To minimise any effect of heat loss in the salts to approach 1. above