Exactly. That is what makes the salt bath so attractive I also fully agree it does improve things and if you have it use it. I am not against salt baths. On contrary I am trying to see if with changes they can turn out better end result.
Where they really shined for people is in its comparison to a propane torch setup in terms of reducing unknowns. There was always that unknown of what temp were you actually applying to the case neck. Move it just a tig and it was a different temp....but what temp?? There was nonscale standard even using tempilaq. The salt bath instanty addressed this with high accuracy and consistency of temp being applied.
I do not seriously think anyone gave thought to the difference between the temp of the heat source vs the ideal temp we want the case neck brads to reach and the heat sink effects of the rest of the case in terms of how it effected heating the neck to a certain temp. There in is the issue.
We have been using both low and high temp molten salt baths in blacksmithing for heat treat annealing normalizing for some time now. It offers other benefits in this area vs brass case annealing. But it has many of the same benefits as well. Low cost. Precise control of temperature and its even and consistent in its application to the work piece.
When I went looking for support and the technical reasons for results vs other heat source annealing, frankly it was a PITA. Most annealing technical papers use ovens as they are not doing differential annealing. The info is buried in pages and pages of other techincal data etc. You had to read and wade thru it all to find the nugget you were after.
That brings up another point. I said it was annealing to temper but really its "Differential Annealing to Temper" as we are only doing that small section and decreasing to no effect as we go down the shoulder to body.
If you look at the crystaline structure of the brass in some of the microscopic images you see the are long polygonal shapes with sharp corners edges etc. When we expand the elongate but also separate from each other. Those edges lock into each other holding the tension of force. Compress them and they are being forced pressed together.
When you heat them even if its below the typical annealing temp ranges say 350-500°F. It can soften but also expand n swell those interlocking points of stress It can allow them to slip. The crystals do not change shape etc but small amount of tension. In the case of the necks release small amounts along the lateral sides and those slip joints.
For me it really helps when I can visualize what's happening.
Fact id all those studies and tech papers that speak of annealing for minutes even hours are not bogus. Obviously they are peer reviewed and were done in labs by metallurgists. At the same time we have tons of real world proof of how fast neck annealing happens using torch etc. I knew both were true so I setout to understand how. That was some time ago.
But a reloader can not be expected to spend weeks reading over studies, tech manuals, ref books, etc Buying micro vicker hardness testers etc. Outside a few geeks nuts like myself we need a cookie cutter setup Hence why salt bath was/is so exciting.
I am trying to see if I can make the high temp chloride base salts work in a lee pot or some other equally low cost setup. But it takes actually testing the hardness and looking at the structure which means paying to send it off to a lab. So its a personal nvestment for the communal benefit. Which I am good with.
Same goes for induction annealing. Building an induction setup is not costly at all. Its tuning and timer setup that is the bugger and generally cocks thing up well and good along the way.
Then we are left as we are with all of these annealers with figuring out ideal time for a given case neck mass. That will always be the thorn. Its what really was the major benefit and worth the cost of the AMP unit. IMO its where a large % of the cost overhead is tied up as its manpower heavy. If you looked at profit counting only cost of the annealer itself it would be very healthy indeed. But out in all the r&d and constant testing for proper time to reach given temper. Now that adds up to some $$. Of course it gets spread over all unit sales So in the veginning it was very much a negative return. But wity the increased vol.......
Now with the built in info and database it no longer seems the case but that has to be backed up by real testing. I want to research further to see exactly how the process on the AMP works for case testing. More out of my own curiousity. Its also protected by patent Im sure. Regardless my own *Rule 1 Violation*s would prevent me from any shenanigans.
As a community we can establish times for a given standard with trial and error. Once we have that and the relationship it will allow us to build a sort of data base. But we need a standard when it comes to induction power voltage and coil design.
I am just a curious guy that likes to work stuff like this out. I find it like others do puzzles and brain teasers.
Without a doubt I think induction is the most precise way to anneal. But I still want to give the high temp salt a go to see how close I can get. The only real downside is safety. I have suffered full thickness burns on parts of my body from past employment/career.. So I know better than most what molten liquid does to flesh.
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