Annealer

[hounddawg]

It's not my theory of time. It is the copper Institute of America's table for annealing of 70/30 brass. But you are right the entire thickness needs to be brought to temperature, it just is not as slow as what you are making it out to be.

Brass (70/30) has a thermal conductivity of around 120, in comparison the thermal conductivity of water is about .598, air is .024 and silver is 419. 60/40 brass is about 96 because of the difference of the alloy. Your cake batter analogy would be a slurry of water and solids with gas bubbles being formed as it bakes so I would guess the TC would probably be around .3 - .5. Just guessing but it would be very low regardless.

edit - if you want to cut down the time to bake a potato take a aluminum rod and insert it into the potato to transfer heat and bake the potato from the outside in and from the inside out at the same time

Bottom line is heat is transferred very quickly throughout a piece of brass. Not as fast as silver, gold, or aluminum but PDQ. Thankfully for our purpose a full anneal is not needed, some stress relief is sufficient.

If you want more of a anneal a flash anneal can be provided by a AMP because it is able to time the anneal down to the millisecond and uses a tightly focused magnetic field to do so. Something that cannot be accomplished with flame. The AMP's Aztec software takes the test case up to the melting point to determine how much energy needs to transfer to heat the mass and alloy of the case being tested to achieve a flash anneal of the neck/shoulder. The test case is unusable after the test but then you can dial in the number provided for future anneals of that brand and lot number afterwards.

I have not noticed any difference either in chronograph numbers, accuracy or case life since switching to the AMP from my Annealeez so for me I don't find the "perfect" anneal really worth the money from that standpoint. It is however fast and convenient and I have no plans to sell mine.

edited at 6 PM EST to make it a bit more readable

 

[markr6754]

@WendyJ
This is the unit that I use. I had a manual 2 torch unit that I used in the past, but switched to this Burstfire Annealer and Case Prep Center and greatly improved my annealing and my brass processing.
Since purchasing my unit the developer released a new articulating torch holder that greatly improved the process for my short .300 Blackout cases.

https://burstfireguns.com/collections/burstfire

 

[hounddawg]

This is the unit that I use. I had a manual 2 torch unit that I used in the past, but switched to this Burstfire Annealer and Case Prep Center and greatly improved my annealing and my brass processing.
Since purchasing my unit the developer released a new articulating torch holder that greatly improved the process for my short .300 Blackout cases.

https://burstfireguns.com/collections/burstfire

Nice! A good price and all made in the USA as a bonus, I like the 4 station prep center also

 

[Unclenick]

Thickness matters because the temperature is not instantly uniform throughout the brass. As you say, it takes time for the core of a sample to approach its surface temperature. In steel annealing, the general rule of thumb for an oven, where the heat source is self-convecting hot gas, is to allow one hour per inch of thickness for the core to be close enough to temperature. This is called heat-soaking. The value of 70:30 brass thermal effusivity (a measure of the ability of a material to exchange heat with its surroundings) is about 1.6 times greater than 4140 steel. In addition, the thermal diffusivity of brass (a measure of how quickly heat will move within the brass once it gets there) is about 1.3 times greater. From those numbers, I would expect brass to need about half as much soak time as steel does per inch of thickness to heat-soak. That may seem like too little difference looking at the thermal conductivity alone, but what happens is the greater conductivity drops the temperature more at the interface with the hot gas or other heat sources, so a chunk of the speed advantage is self-limiting. Then you have to work out from the specific heat capacity and density of the material, how much heat has to move to make a given temperature change. That's what those numbers do.

All that is part of what makes induction heating attractive. The heat is generated internally in the metal. Exact uniformity depends on uniform field strength from the coil at different places in the metal, but, generally speaking, with the right coil, you can make the heat more uniform throughout the piece during a given exposure time. On the other hand, case neck brass is so thin, that the temperature drop to the core is less significant than it is with a thick piece of metal. Based on the rule of thumb we looked at, 25 seconds for a 0.014" neck wall in an oven, and less with the torch, which won't allow as much of a gas temperature gradient at the surface.

As we've been over before, in ascending order of the combination of time and temperature required to achieve them, the stages of annealing are:

1 Recovery
2 Recrystallization
3 Grain Growth

To stress-relieve to prevent case splitting, all you need is recovery. This is using heat to provide triggering energy that allows dislocated atoms to find their way back into the crystal lattice. But there is a complication: The more numerous and extreme (greater work hardening) the dislocations are, the less time and temperature it takes to initiate this process. For example, a 50% work-hardened piece of brass requires about ten times longer exposure to a given temperature for recovery than a 90% work-hardened piece does. Same for recrystallization (for which it is believed recovery is a required pre-cursor). So when you target a particular temperature for a particular amount of time for highly work-hardened brass, it can stress-relieve all your very hard brass completely and do practically nothing to your half-hard brass.

As a practical matter, this means that if you set up your annealing time and temperature to anneal a very hard case and use it for every load cycle, for most of those cycles, it won't do anything. When the work hardening finally builds back up enough over several load cycles for that time and temperature combination to start recovery again, the brass will go back to the stress-relieved state, and you have to start re-working-hardening it over again. So it won't be the same hardness every load cycle. It will, instead, go through a series of hardnesses during which each piece with the same load history will track each other's degree of hardness, but they won't be the same as they were on the previous cycle or will be on the subsequent cycle.

If you want the brass the same every load cycle, you have to find a time and temperature combination great enough to get recovery completed after one load cycle, then repeat every load cycle. Just be aware that any other piece of brass you anneal at that time and temperature that starts with a greater degree of work hardening will go further in that time and temperature, so its hardness won't match the other brass, either.

 

[hounddawg]

edited for politeness

question for the Metal God and Nick - The test samples used in the studies I have quoted are normally 1 inch wide, 1/8 th inch thick, and 6 inches long. How many seconds do you think it would it take for that piece of brass to be heated through in a 800F lab furnace.

 

[Metal god]

I have no idea and FWIW My name is based in heavy metal music not actual metal , steel or brass lol .

 

[hounddawg]

well read the section on annealing

https://www.ampannealing.com/articles/40/annealing-under-the-microscope/

Just my opinion and some hillbilly shade tree theory here but in my non scientific experiments I feel that the torch methods that have been used for years is sufficient to equalize the plastic /elastic deformation of case necks is all that is really needed.

The AMP will make the metal softer than the torch method, no doubt. However as I said earlier I saw no difference on the chronograph, the paper, or the life expectancy of my cases when I switched from flame to AMP. If my Amp died tomorrow i would buy that unit that markr6754 posted above

 

[Wendyj]

And all of this is why I want to send it off and get it done. LOL. You all lost me at how much the guy charged me to do it before.

 

[hounddawg]

might want to make a post over on the Accurate Shooter reloading forum. I am pretty sure one of the regulars there does annealing and neck turning as a cottage business. Can't recall his name but a search there might pull it up

 

[Unclenick]

Hounddawg,

Based on my post, three minutes and forty-five seconds for your 1/8" plate. But, again, that's in an oven without a fan; natural convection only. One of the good things about a torch is the hot gas is blowing on the work, and that makes heat transfer to the surface faster. If a 0.014" thick neck were in an oven, my earlier calculation suggests it would take 25 seconds for natural convection to soak it, but with a torch blowing hot gas on it, the core would reach temperature faster. Moreover, you can allow the torch to slightly overheat the outer surface without damage, and that will drive adequate heat into the core faster, too. The practical result is the flame works just fine.

My original purpose in going into detail in my previous post was simply to point out there is no one right annealing time and temperature for achieving a particular level of annealing for brass that doesn't all have the exact same degree of work hardening. On the other hand, that begs the question: is there any reason to reach an exact degree of annealing? I think people assume that even with matching as-sized neck diameters, bullet pull will vary directly with neck hardness. It should not. This is because the modulus of elasticity is the same at all brass hardness levels. So, theoretically, if you anneal the brass enough that it won’t split, but don’t anneal it so much that you lower its yield point so much that a bullet stretches it past its elastic range, all annealing levels within those parameters should produce the same bullet pull if the necks are the same thickness and are sized to the same diameter. On the other hand, increasing work hardening raises the yield point, so a neck bushing that made a neck -0.002” smaller than the bullet when it was first reloaded, may only get it down to -0.001” when it gets hard enough. That mechanism will change bullet pull if the degree of annealing isn't consistent. But if you can achieve consistent neck diameter, merely annealing within the not-too-soft and not-too-hard Goldilocks zone should all produce the same bullet pull.

The bottom line, as I am seeing it, is that achieving an exact level of annealing is for the resizing operation’s consistency, rather than directly for the neck's grip on the bullet. That means that if you can resize to consistent neck diameters regardless of brass hardness within the Goldilocks zone, then you will have consistent bullet pull over a range of degrees of annealing.

 

[hounddawg]

well Nick try sticking a .308 case neck into a torch flame for 25 seconds and see what happens At most convection will cause a heat transfer increase of around 30%.

When I was using a torch about 3- 5 seconds in the flame seemed about right. I used some 450 templaq on the case body to make sure the heat did not get too far down when setting my times. The Annealeez worked fine but with short cases like 6BR and 6.5 Grendel the plastic on the wheels would start to melt and major problems occured. For longer cases like the .223 and .308 it worked like a champ.

Heat transfer is way more complicated however. The greater the delta T the faster the transfer which means as the two objects near equilibrium the slower the rate of transfer.

The newer annealing machines use metal wheels which not only cures the melting situation but also acts as a heatsink for the case body. That's a win - win



Anyway read the AMP article I linked it goes into detail on the time vs temp in the annealing process and they use split cases for their test samples. Thankfully from all evidence I can find a stress relief or mild anneal of the neck is all that we need as shooters

 

[Unclenick]

I think the context is maybe getting a little confused. The heat soaking numbers, including the 25 seconds, are for something placed in an oven that is operating at the desired annealing temperature. Not for a torch flame thousands of degrees above the needed annealing temperature. The one flame situation I can think of that takes that sort of time is metallurgist Fred Barker’s candle flame method.

"…Candle-flame method: Hold case body in fingertips, place case neck in flame and twirl case back & forth until case body is too hot to hold, then slap case into wet towel; wipe soot off neck & shoulder with dry paper towel or 0000 steel wool."

Fred Barker, Precision Shooting Magazine (RIP), July 1996, pp. 90-92

The candle flame is able to heat the metal enough to get a highly work-hardened neck through recovery to prevent splitting (indeed, recovery can actually be done in boiling water, but it takes weeks rather than seconds at that temperature). But it isn’t hot enough to do more, so it is very safe.

 

[hounddawg]

I think the context is maybe getting a little confused. The heat soaking numbers, including the 25 seconds, are for something placed in an oven that is operating at the desired annealing temperature. Not for a torch flame thousands of degrees above the needed annealing temperature. The one flame situation I can think of that takes that sort of time is metallurgist Fred Barker’s candle flame method.

just for reference a normal plumbers torch using propane maxes at about 2000F. I set the times by putting a stripe of 450 Templaq about 1/4 inch below the shoulder then increasing in flame time until the Templaq melted. Then I backed it off a bit on the time. Nothing real scientific but it worked well enough. No major case failures of any kind other than some Hornady .204's I oversized when learning had necks separate. Some of my .308 cases have 25+ reloadings on them, no neck splits or other problems

If memory serves it was about 5 seconds for .223, a couple of seconds longer for .308, .260 Rem, and 6.5 Grendel. I tried using IR thermometers on the neck but all I got was flame temp

 

[Metal god]

I've been staying out of this not to muddy the waters but .... haha . I don't believe a case or piece of brass that is work hardened more then another . Will not be stress relieved the same as each other if brought to the same temp for the same duration of time . This is the first I've heard of this and it would seem to indicate no machine or hand and torch can ever get each piece of brass the same as the next or last .

Maybe I read it wrong but I took what you said UN to say if one piece of brass from the same lot was fired and resized 3 times and another was fired and resized 20 times they could never be the same hardness as each other again ?

I literally did that with some Remington brass I have . I have maybe 500 pieces with varying firings . One day I just annealed them all to have them all relatively the same hardness . Now I'm hearing that was a waist of time because they are all still just as inconsistent as they were before annealing ?

 

[hounddawg]

neither did I until this

https://thefiringline.com/forums/showthread.php?t=610013&highlight=prep

 

[jetinteriorguy]

Maybe my take on this isn’t correct, but it would seem the final diameter of the neck has more influence on tension than the degree of hardness. So the best solution would be annealing first then neck sizing, given that the necks are all turned to produce the same thickness.

 

[hounddawg]

Maybe my take on this isn’t correct, but it would seem the final diameter of the neck has more influence on tension than the degree of hardness.

your take is absolutely correct in that the hardness has nothing to do with the elasticity of the metal. Elasticity is at the molecular level. The mixture of protons and electrons that compose brass act like little magnets when the meatl is stretched. Heat treating does not affect the elasticity, but it does allow the crystiline structure to realign itself which affects the springback when sizing and seating.

I linked Damon Cali's article earlier in this thread it explains exactly what occurs during the sizing and seating process and why a bit of softening goes a long way when deforming the metal assuring the plastic/elastic deformation is uniform

 

[Unclenick]

It has no effect on the modulus of elasticity, but it does change how far something stretches before it passes the yield point, where it starts to bend plastically rather than elastically, or before it breaks (see below).

I don't believe a case or piece of brass that is work hardened more then another . Will not be stress relieved the same as each other if brought to the same temp for the same duration of time .

Start by having a look at the graph on this student material on the third and last page of this simple summary of 70:30 brass (aka, C260, C2600, and Cartridge Brass) annealing. The graph shows plainly how much faster and further the harder samples soften at 400°C (752°F) than the less hard samples do.


Next move on to this much more detailed paper about cartridge brass recrystallization. It covers the whole annealing process briefly and has many tables of the hardness differences over time at different temperatures. Page 12 has good graphs showing the yield point drop with an increase in annealing (shortening of the elastic range). Page 16 has graphs of the time and temperature exposure combinations in units of 10³/T(K^-1) where you can see a 50%-work-hardened piece takes nearly ten times longer to recrystallize than a 75%-work-hardened piece does. In other places, the paper also has good tables and graphs showing the shortening of the percent elongation at break with the hardness.

Something the AMP people got right was the need for a micro-Vickers hardness tester to discern the differences. It is also important to note there is a limit to softness imposed by higher temperature, and if you look at the paper's page 15 plot of 300°C (572°F) in the upper right, you see that even after 1000 minutes (16⅔), there is considerable hardness difference for every piece, with the ones that started with the most work hardening becoming the softest. The last plot, though, shows only about a ⅓ difference in hardness after 60 minutes at 550°C (1022°F). Indeed, that smaller difference appears to be established at about 6 minutes.

Anyway, the constancy of the modulus of elasticity is, I think, key. That's what determines how hard the brass tries to spring back in opposition to being stretched by the seating of the bullet, as long as you stay in the brass's elastic range. When you consider the circumferential stretch of a .308 case mouth with 0.305" as-sized case neck ID, which is only 1% of its circumference, you realize that staying inside the elastic range is pretty easy to do over a pretty wide range of hardnesses.

 

[hounddawg]

some interesting info Nick, I have often wondered myself why brass with varying degrees of work hardening seem to group more consistently after annealing. I think you may have found the explanation

My own little non scientific experiment came after 300+ never annealed Lapua .260 Remingtons with varying amounts of firings on them became mixed together. They worked fine before the mix up when all the cases in any box of loads had the same number of firings. But after the mix up when I had cases with X number of firings mixed with cases with X+2 firings, X + 4 firings etc etc I was getting large vertical spreads. At 800 yards one or two would end up in the 8 or even 7 ring out of 20 rounds. When I annealed those cases the "what the heck "flyers went away

 

[Metal god]

Start by having a look at the graph on this student material on the third and last page of this simple summary of 70:30 brass (aka, C260, C2600, and Cartridge Brass) annealing. The graph shows plainly how much faster and further the harder samples soften at 400°C (752°F) than the less hard samples do.

Ok , that's actually the opposite of what I understood your post to mean . As far as I can tell it does not matter how work hardened a piece is because the VERY work hardened piece will soften faster then the less work hardened piece actually catching up to the softness of the less work hardened piece . Resulting in them being more the same then different when annealed for the same amount of time to the same temp 750*+ ?

I thought you were saying ( just making this up as an example ) No mater how hot or how long , if case A is at 100 and case B is at 50 . If you anneal case B to now be 25 and anneal case A the same as case B ( time and temp ) , Case A will only be at 75 now because case B was only changed 25 points .

Now I understand it to mean case A will soften much faster then case B resulting in them actually ending up much closer in softness even though they were annealed for the same duration to the same temp ?

It also seems to indicate as long as you get the brass to 750* as I recommended and understood to be the sweet spot for stress relieving you should be GTG regardless ??