Fast Air Cooled

[hollywood63]

So I was out coating a batch of boolits and as I'm sitting there waiting for the timer to go off. I was looking at the fan set on high that is cooling off the last batch that came out of the oven and was thinking . Its not water dropping but I was cooling them from 400 to room temp in maybe 5-8 minutes. Is there any noticeable hardening happening cooling down that fast?

Just a ponderin that's all

[shoot-n-lead]

Nah, that is still air cooled.

If ya' wanta harden them some...water drop'em.

[dragon813gt]

No effect on hardness that way. They need to be dropped in water immediately to harden them.

[Scorpius]

No effect on hardness that way. They need to be dropped in water immediately to harden them.

Wonder what liquid nitrogen would do for a fast cooling and hardness.
Just curious.


Sent from my iPhone using Tapatalk

[shoot-n-lead]

Wonder what liquid nitrogen would do for a fast cooling and hardness.
Just curious.


Sent from my iPhone using Tapatalk

Probably shatter them.

[sqlbullet]

Faster cooling = harder bullets....to a point.

Imagine the lead is a lattice, and the antimony and tin are balls of different sizes/colors. When your alloy is fully melted the balls are equally distributed around the lattice. As the metal cools you have migration, wherein the balls try to clump together. When the metal air cools, the balls can migrate into relatively large clumps, which larger sections of pure lead lattice. This migration occurs even after the metal is "solid" but not yet cool, which is why you can remove any hardness from quenching by heating the bullets to 350°-400°F and then allowing them to cool in place.

When you cool the alloy quickly, the antimony and tin have far less time for migration. And the faster you cool, the less migration. HOwever, once you reach a rate of cooling that effective preserves a uniform distribution, faster cooling won't do much.

You will see diminishing returns in 96/3/1 above a BHN of 24. What I mean by that is you will have to cool orders of magnitude faster to see a difference, and even then the difference will be only a few more points. The hardest I have ever tested was 29.5 for this alloy. This was cast from a 700°F pot, and water dropped straight from the mold. The bullets were Lee 175 grain .401 tumble lube. This hardness was the average of 10 picked at random from a batch of 30. I didn't record the temp in the garage that day, but it was below freezing.

On the opposite side of very fast cooling, we have difference in room temp cooling rates It will not make a meaningful difference. Further, it will be very non-uniform as the bullets exposed directly to the moving ambient temp air will cool differently on one side than the other, and bullets further back in the grid will be exposed to air pre-warmed by the bullets before them.

[hollywood63]

Faster cooling = harder bullets....to a point.

Imagine the lead is a lattice, and the antimony and tin are balls of different sizes/colors. When your alloy is fully melted the balls are equally distributed around the lattice. As the metal cools you have migration, wherein the balls try to clump together. When the metal air cools, the balls can migrate into relatively large clumps, which larger sections of pure lead lattice. This migration occurs even after the metal is "solid" but not yet cool, which is why you can remove any hardness from quenching by heating the bullets to 350°-400°F and then allowing them to cool in place.

When you cool the alloy quickly, the antimony and tin have far less time for migration. And the faster you cool, the less migration. HOwever, once you reach a rate of cooling that effective preserves a uniform distribution, faster cooling won't do much.

You will see diminishing returns in 96/3/1 above a BHN of 24. What I mean by that is you will have to cool orders of magnitude faster to see a difference, and even then the difference will be only a few more points. The hardest I have ever tested was 29.5 for this alloy. This was cast from a 700°F pot, and water dropped straight from the mold. The bullets were Lee 175 grain .401 tumble lube. This hardness was the average of 10 picked at random from a batch of 30. I didn't record the temp in the garage that day, but it was below freezing.

On the opposite side of very fast cooling, we have difference in room temp cooling rates It will not make a meaningful difference. Further, it will be very non-uniform as the bullets exposed directly to the moving ambient temp air will cool differently on one side than the other, and bullets further back in the grid will be exposed to air pre-warmed by the bullets before them.

That makes perfect sense Wasn't really looking to get any hardness increase was just thinking what if any was happening. Thanks for the input folks

[paul h]

I had debated using an iced brine mixture for water dropping to see if it made harder bullets than ~60F or whatever the temperature of the garage is when I cast. Then again, I don't really want to run salty bullets through my bore

[rwadley]

Dry ice in water

[runfiverun]

the speed they are cooled is what does the hardening not the water itself.

[Yodogsandman]

Wait for winter and put snow in the water. Ice cubes in the summer.

[runfiverun]

I try for a more consistent mixture of @ 65-f water and a consistent mold temperature.
I don't need maximum hardness but I want harder than ww alloy.
but it's nice to have it as close as possible from batch to batch.

[swheeler]

Raise the boiling point of the water with antifreeze to get hardest bullets for that alloy, 50-50 water to antifreeze. You are trying to stop the steam forming bubbles on the surface of the bullets which insulates them, slowing cool down.

[el34]

All of my boolit alloy is mixed to produce either 12.5BHN for almost everything or 16BHN for special cases. After PC the boolit hardness will be the original alloy hardness.

[Hickory]

Just a little note;
Water will carry away heat 7.2 times faster then air will at the same tempeture.
Some worthless information I picked up milking cows in my youth.