Salt Bath Annealing

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  • JeepHammer

    SHOOTER
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    Aug 2, 2018
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    SW Indiana
    I'm gong to throw the safety disclaimer in right up front,
    You saw the burn on the right index finger, just about one drop of salt size...
    Or just a touch on the rim of the melter size.

    Without knowing in particular WHY he addressed some of the issues in annealing.
    Time & Temp being the first two.

    Electro-magnetic induction annealing often is simply too fast.
    There are three stages to cartridge brass annealing, and Time AT Temp is a big one.

    When you see flame annealing by amateurs, it's almost always a pin point 'Jet' torch WAY overheating the OUTSIDE of the case,
    While if you see a video of factory annealing with flame, you see a ROW of gas nozzles that diffuse the flame,
    Lower heat, and the brass takes TIME to travel over the row of nozzles.

    Heat saturation is another issues 'Immersion' annealing solves.
    With the primer knocked out, the salt gets INSIDE the case allowing for a much more uniform annealing.
    Just jet blasting the outside of the case doesn't allow for a uniform heating.
    This keeps the brass from Delaminating, you don't cook the brass in layers and you won't see it separate as much.
    Anyone that's had a case separation knows what a huge pain in the butt that is to remove case neck/shoulder from the chamber, and this helps avoid that.

    The other thing he showed was the salt line on the case body, and below it the HAZ. (Heat Affect Zone)
    When you see a VERY distinct line on the brass, no transfer zone hardly at all, that brass usually cracks sooner, almost always on that line.
    That is the heat stress line in the brass, hard to soft, and from full hard to dead soft it will crack much sooner.
    Ask any welder about pre-heating & controlling cooling of a weld to keep it from cracking if you don't believe diffusing HAZ isn't a requirement.

    The three steps of annealing are,
    1. Stress Relief.
    When chrystal structure of the brass breaks, it breaks in slivers/shards much like glass or rock.
    Those slivers/shards have sharp edges which dig in and jack chrystals/grain apart, like a wedge splitting wood.
    The HEAT allows the Chrystal/grain structure to open up and release the slivers/shards to somewhat realign.
    This take a BUNCH of the preload, or strain, or stress off the grains.

    2. The second step is absorbing the small bits, when enough heat energy AND TIME are introduced,
    The smaller 'Dust' and slivers/shards are recombined with the chrystals, or align fully in the grain.

    3. The third step is absorbing the slivers/shards and 'Dust' back into the chrystals, growing the Chrystal size.
    This is where it can go bad all at once when things are too hot.

    Cartridge brass has a very specific Chrystal size and grain spacing for best function.
    Under standard inspection magnification (called a micrograph), the Chrystal grain pattern can have too big of chrystals (mono-chrystaline)
    Or they can be too small, too many for a given inspection count for a given area (micro-chrystaline).

    An example of a micrograph, the diamond shape is a punch mark for hardness testing.

    cdb81757-0e6b-459a-a5dd-3187943f90db-original.jpg



    Too big, too much heat for too long and it all looks to be one big blob and it fractures/fails catastrophically.
    Too small, and it fails from lack of cohesion, it cracks.

    This guy wasn't using stupid high temps, so he had TIME for the heat to saturate and do the work,
    This guy had a media that applied heat evenly inside & out, so very uniform annealing,
    And he kept the time reasonable to keep the HAZ in check but allow a HAZ wide enough to do its job.

    Without scientific micrographs & scientific hardness testing there is no way to tell if his annealing is 'Perfect' or not,
    Getting a specific cross sectional density and a specific chrystal size & grain spacing, but he's REAL close since he's getting much more consistent brass resizing.
    --- consistency being the name of the game in hyper accurate shooting,
    And the brass WILL live longer (more reloads) since the stress is relieved.

    It's not going to do much for case head separation, but other than not running stupid hot loads is going to do much for that with any given brass lot, and your brass properly fitting the chamber so it doesn't stretch a stupid amount in the first place.
    The better the case fits any particular chamber the more variables you eliminate in your shooting, and the longer your cases last.
     
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