Salt Bath Annealing - AMP Study

[Shinbone]

While it might be intended as marketing, it fits the legal definition of libel, which is actionable.

Further, lots of salt bath users have publicly said the method works for them, so the author arguing that the libelous statement is true will not be a successful defense.

JMHO

 

[oldduc]

AMPs definition of "annealing" may not be what is really necessary for accuracy. Text book "metallurgy" is not necessary to achieve useful results, in my experience. I have been salt bath annealing for about one year and have been pleased with the results. I anneal at 525C for 6 seconds, and after annealing the cases are noticeably and significantly softer than before annealing and the pressure required for seating bullets is lessened and very uniform. That is all I require. I have no quarrel with AMP, but them purporting that they are the only ones capable of "annealing" a cartridge case sounds to me like unnecessary and egotistical marketing. If you've got $1,850 to spend on an AMP setup, go for it. I don't, and that's about two years worth of reloads for me. As usual, YMMV! (posted on another thread)

 

[riflewoman]

Im not promoting AMP in fact I made my own induction machine. With regards to
" if induction annealing allows precise control of time and temperature thus allowing annealing at a very high temperature."
Well most of the home made units are using timers that have a 0.01 second resolution so accurate and consistent timing is not a problem. They also have a very consistent power supply so being able to reach a certain temperature for a given time repeatability is very good.
As to what the factories do I know that ADI induction anneal a friend in the Rifle club used to work there in quality control. It was done on a production line imagine all the cases upright all next to each other traveling on some sort of belt. They just passed by a induction element.
Do they the factories and AMP reach higher temperatures I dont know at this point I have a friend with a amp so perhaps some tests with tempilaq will reveal that secret. At the moment I use 750 tempilaq and set the time to make a change in that but in a dark room show no sign of any heating. It will most often show a sign on the cases but not always despite having reached the 750 mark.

Even Tempilaq has a “time at temperature” requirement to melt. So while the case is putting energy in to melt the tempilaq it might be significantly hotter. Best bet is a pyrometer.

 

[David101]

Even Tempilaq has a “time at temperature” requirement to melt. So while the case is putting energy in to melt the tempilaq it might be significantly hotter. Best bet is a pyrometer.

Yes I agree I actually have another induction machine that is able to do the job faster. However look at it like if it is a very fast rise time in temperature even though the off time can be set very precisely. The measurement cant be made that quickly.
So I have gone for a slightly longer anneal time at about 4.3 seconds for a 308. I have tried 700 and 750 on the cases at the same time to get an idea of exactly that type of thing.
If you want to get a really nice anneal mark it is easily done but the temperature will be hotter I have watched many cases in a dark room at different levels of heating from a slit pink for a fraction of a second to a full on red glow.
I am pretty convinced that adjusting the setting so that the Tempilaq (what ever temp you want to select ) changes state colour and no colour change is seen in the brass in a dark room. I am happy with that it is something that is very consistent and I feel I have not overdone anything but it has made a difference in the brass.

The difference was not so noticeable in my 308 probably because of custom chamber and neck bushing die along with competition shell holder to minimize any shoulder bump.
Butt is was a different story with some of the 223 brass I had one or two firings and the necks could not be sized there was just no tension in the necks. A quick anneal and they were like new.

A lot of the home made jobs get a bit creative with auto feeders and such. Good on the people that made them. They are working well and suit the persons needs. But I basic model can be made cheaply and relatively easily. I process my brass most often in lots of 50 cases to anneal those cases using a simple trap door under the case on my unit 10 seconds a case would easily be achievable. I can actually feed it nearly continuously, so 50 cases is 81/2 minutes. A clean process no real setup time no need to quench they cool very quickly.

 

[Webster]

Yes I agree I actually have another induction machine that is able to do the job faster. However look at it like if it is a very fast rise time in temperature even though the off time can be set very precisely. The measurement cant be made that quickly.

Everyone wants to make it more complicated than it is. As long as you don't get the cases to hot and make the necks to soft so you loose tension you are getting benifits. I have done metallurgical failure analysis my entire career and I choose to use a torch. 5 seconds is what I have settled on. The cases may have almost the same hardness as before annealing. I don't care, they are stress relieved. I get long case life, good neck grip and my varmint hunting rifle can shoot 1/4" groups. What more could you ask for?

Copper, gilding metal and cartridge brass are all annealed in the same temperature range. Slight differences in the low and top temperature for annealing depended whose data base your looking at.

 

[dcali]

This seems entirely reasonable to me. I think people would be surprised by how bad thier annealing techniques are when put under a microscope. This is one reason (of several) that I don't do it. The time/temperature/hardness relationship for small thin samples for very short times is very hard to nail down. You won't find any literature on it. I've tried. It's not out there publicly.

As for bagging on competitor, I'm not sure who that competitor would be. They're just saying why their machine is better than a salt bath. Again, totally reasonable. (Note the part at the end that says, in effect, "If you can't afford ours, buy a torch based competitor's. Just don't play around with salt baths." Hardly a cynical jab at business rivals.)

If one is to anneal, I honestly can't see a reason for not using an AMP to anneal, other than the hefty price tag. They're literally the only product on the market who has tested and published their results, and it does exactly what they says it does. There are plenty of reasons to believe that torches and salt/lead baths would create inconsistent results.

Whether or not you need that level of precision is an entirely different discussion. The main critique of their machine in my opinion is that their target annealed state is totally arbitrary. If a torch and a drill does what you want, that's all you need. If you want repeatable hardness, nobody has stepped up to challenge AMP.

I've got no dog in this fight. I don't own their machine (or anyone else's), and I have no intention of buying one.

Edit: The interesting thing here is that I can't think of what the mechanism would be that would prevent the neck from annealing while allowing the rest of the case to. Perhaps its corrosion or some sort of chemical reaction that insulates the neck as it heats quickly, where as the rest of the case avoids that. Just speculating. It's an interesting phenomenon. A head scratcher. I suspect it has something to do with the rate of heat transfer into the case.

 

[Qtip]

Edit: The interesting thing here is that I can't think of what the mechanism would be that would prevent the neck from annealing while allowing the rest of the case to. Perhaps its corrosion or some sort of chemical reaction that insulates the neck as it heats quickly, where as the rest of the case avoids that. Just speculating. It's an interesting phenomenon. A head scratcher. I suspect it has something to do with the rate of heat transfer into the case.

I agree, it is hard to understand why the neck does not soften, while the case does.

 

[ChrisNZ]

My engineering friend has a possible explanation for this. Here are his thoughts:

Firstly, you cannot end up with a very soft shoulder from "over-annealing" with salt without the neck brass being equally annealed. There seems to be plenty of evidence that a salt bath approach does usefully soften/stress relieve the neck to the point where neck tension/seating pressure is more consistent. The fact that a plier crush test shows the neck will deform far more easily after the salt bath shows that something has changed significantly. The Vickers testing is probably revealing a degree of surface hardening while the underlying brass is actually annealed.

He suggests that a deformation test would be useful indicator, eg laying the case neck on a V block and measuring how much force was required to deform the neck say 10 thou.

 

[dcali]

I would buy that if they didn't section the cases before testing, and there isn't really a way the surface would be hardened that I'm aware of. I wouldn't rule out testing error, but I can't think of what that would be.

The best I can come up with is that the neck pulls some cruft that was floating on the surface of the salt down into the molten salt and it gets trapped around the neck area, insulating the metal well enough that the rest of the case goes dead soft before heat transfers to the neck. That's not a terribly satisfying explanation, and I've never even tried salt bath annealing, so I'm reaching here.

 

[rardoin]

While it might be intended as marketing, it fits the legal definition of libel, which is actionable...snip...
JMHO

Actionable against who??? The 'Salt Bath Annealing Corporation'? They are just reporting results of their testing. Libel would involve intentional misrepresentation of the truth with the purpose of harm to an individual/company.

 

[riflewoman]

He suggests that a deformation test would be useful indicator, eg laying the case neck on a V block and measuring how much force was required to deform the neck say 10 thou.

A better approach is to squeeze the case neck overva suitable mandrel and measure the permanent deformation. Easier to control and measure. Take a 6mm with a .262 neck. If you took a .223 mandrel in the neck and squeezed it shut in a small vise with smooth jaws, so your total stack would be .223 + (.262-.243) = .241. Measure the resulting diameter after the pressure is released. Let’s say with new brass you get .246 or .005 springback. Your cases that have been fired 3 times read .251 or .010 springback. Depending on the case wall, the total stack squeezed and the hardness of the brass it will be different, but for any metallurgical state it should be consistent and repeatable. After you “anneal” you might find you get .007 springback and that might be enough.

 

[michaelbz]

The shoulder and upper body can be softer than the neck after heat treatment because they have different amounts of cold work. New unstressed grains will nucleate at lower temperature with higher amounts of cold work.

The only problem with the study is the declaration that brass necks are ideal at Hv 95-100. They offer no proof for that. Case grip is far more dependent on average brass thickness than Hv. Thickness, Hv, lubrication(friction), Seating depth, and Button size all impact case grip, hence, I doubt there is an ideal Hv. You just want it to be consistent with proper lot control.

If you accept AMP's criteria that necks have to be Hv100, then they have proven a 500-550C Salt bath will not work because you will reduce the strength of the case body due to dwell time and thermal conductivity of brass. I cannot fathom why people have a problem with that part of the experiment.

A flame system with a regulator and a full size grill tank will give an excellent reproducible flame, hence, for me, an AMP machine is unnecessary. If I started a custom ammo or brass restoration business I would consider an AMP or a similar system.

 

[Alexander-M]

Partial quote>

. . . The only problem with the study is the declaration that brass necks are ideal at Hv 95-100. They offer no proof for that. . .

Perhaps they consider the second sentence of this statement (in their report) to substantiate their claim:

"We can say with some certainty that optimum annealed neck hardness is 95 HV – 100 HV. This also happens to be the neck hardness of most virgin Peterson, Lapua and Norma brass."

Of course, that would be for brand new, unfired brass, and whether optimal for performance is not clear, as you suggested.

Alex

 

[oldduc]

Partial quote>


Perhaps they consider the second sentence of this statement (in their report) to substantiate their claim:

"We can say with some certainty that optimum annealed neck hardness is 95 HV – 100 HV. This also happens to be the neck hardness of most virgin Peterson, Lapua and Norma brass."

Alex

The hardness of virgin brass necks is primarily an artifact of the manufacturing process. I have not read that Peterson, Lapua, and Norma claim that to be the optimum state of brass for reloading.

 

[6MT]

The hardness of virgin brass necks is primarily an artifact of the manufacturing process. I have not read that Peterson, Lapua, and Norma claim that to be the optimum state of brass for reloading.

I agree. I've found all virgin Lapua brass to yeild almost meaningless results on the first firing. After proper prep, the second firing is when I pay close attention to the results.

 

[dcali]

When I was in college, we were told of a satellite that was being designed. The satellite had large solar panels that folded up. Once it was in orbit, they would unfold.

The engineers designed and built a spectacular shock obsorbtion system to keep the fragile panels from breaking on deployment. Dampers, springs, etc. Very impressive. (This is not a trivial thing to do when it must operate in the extreme environments of space). Lots of design and testing went into it. And it was great.

Then someone asked, “hey- do we even need these? I’m pretty sure the arrays will survive without them”. And they would. Nobody had done the analysis to figure that out.

Now is this story true? I don’t know. But it happens over and over again in the engineering world - I’ve seen it more than a few times with my own eyes. And I can’t help but wonder if that’s what’s happening with the AMP.

(By the way, I’m still not satisfied as to why the necks aren’t annealing. If it’s the initial state, it wouldn’t be so sudden.)

 

[David101]

Sounds a bit like the American Pen designed for the Astronauts so that it would work in zero gravity. Millions of dollars were spent huge amount of development time. Meanwhile the Russians gave their Astronauts a pencil.

 

[Richard Coody]

Like most things in reloading whatever works for you. I have used a geraud for years. Happy with the results. Do i sometimes question my consistency. Sure

if you need to know your technique is consistent then get the AMP.

if what you are doing works for you then stick with it.

No sense in arguing about what is the best way to anneal.

 

[memilanuk]

No sense in arguing

If it wasn't for arguing, half (at least!) of the posts on this (or any other) forum wouldn't exist!

 

[rwj]

If it wasn't for arguing, half (at least!) of the posts on this (or any other) forum wouldn't exist!

I minimize arguing as it rarely seems to produce positive outcomes. I do offer, and read this forum for, countering viewpoints. They permit each person to decide their direction from an informed position That’s my theory and I’m sticking to it!