I would like to see the test info from the lead example. Other studies have shown it takes 5-8 seconds at 500c to anneal a brass neck (see https://ballisticrecreations.ca/salt_home/annealing-knowledge-centre/annealing-lit-review/)That is not true. They have done studies using 1000°F molten lead It took a piece the thickness and size of a cae neck fully submerged 19 seconds to reach equal temp to the bath. Actually they used it heated from 650 in steps up to 1200. The higher the temp the shorter the time to reach equalibrium.
Not directed at anyone here but a genrral observation. People want salt bath to be the answer as its cheap its easy to do. It addresses the heat consistency issues of propane torch. But it just does not work as people think. It does do some stress relief. The beginning part of recovery phase of annealing. But there is no way it can work. 3/4 of the case is acting as a huge heat sink pulling heat off the neck. It takes a fully submerged piece so no cooling or heat sink effect 19 second. Thats way too long. A neck submerged case would take much longer.
The one way it might work is switching out the 50/50 blend of nitrate based salts for a 50/50 blend of chloride based salts. This would allow 1600°F.
Consider for a second that the flame on a propane torch, the outer part of the light blue tip where it almost goes clear, is around 2000°F. That is why it works so effectively. It overwhelms the thermal conductivity ability of the brass. Heats way fast than it can absorb.
We have to have sonething that heats super fast that it overcomes/overwhelms the thermal conductivity of brass which is one of the highest.
Low temp; molten salt bath does improve the cases and will make them last longer but they are not annealed to a factory state nor to a ideal hardness. I also think they will continue to get harder just at a reduced rate. So its not a complete failure just under performing.
What we are actually doing or our goal is not to just anneal the case neck; that has no frame or specificity. Its also why there is so much confusion because people throw around terms that are not correct or specific trying to describ things.
What we are doing same as the factory on the final neck annealing is known as "Temper Annealing" or "Annealing Temper" Ior Annealing to Temper" the last is most correctly descriptive. We are annealing to a specific hardness range , state also known as temper. There is an entire standardized list of anneal temper states in various industries.
I have wanted to lay out all the data with the carious referenced data studies lab reports etc but its a immense amount of work. I felt I would likely get frustrated when people tried to refute it with nothing more than "it works for me" or similar without any real tech support for thier position.
The AMP guys knew this before they ever bothered to test it as they have to have more time into annealing research than me. Otherwise I very much doubt they would have reported the results. The results where the shoulder lost more piint in hardness from its starting point than the neck also maje sense on the long soak time and is fully explained in the annealing science of work hardened copper alloys.
Hey I can be wrong but some of this but the studies and technical articles from metalugists that are suppose to be experts in this field support it.
Again salt bath does have a positive effect but its a small one. Believe me I wish it worked just as well. I would not be spending the hours tweaking things and studying schematics to build an induction annealer. What you really pay for with AMP is testing that developed the program to test and chose the correct anneal time or there manual testing to give the correct time.
IMO, that's where the real critical part is. Knowing that [email protected]/mass formula for each case.
Questions I have always had, but haven't taken the time to figure out:
1. How long does it take heat to transfer from both sides of the neck thru the entire .015" (for example)?
2. How is the zinc affected since its melting point is <800f?
It seems that SBA gets us to the temps needed to anneal the brass without as much error as a flame. Since we are looking for consistency, even a partial annealing (assuming it doesn't fully anneal) would still be what we are looking for.
All this to say, I'm not sure how Hot Lead Annealing cannot somehow anneal the brass when a temp/time is what we are after. Simple mechanical or chemical engineering tables should allow us to compute the time it takes 500c heat to transfer thru the neck. Then further help us compute how much time it takes to transfer the heat up the shoulder and case body.