Cryo treating a mold?

[Plugs and Muffs]

Has anyone tried cryo treating a mould? Particularly iron or steel? Liquid nitrogen is available pretty readily now. It does tighten grain structure in steel.

[nicholst55]

Just curious; what do you hope to accomplish by doing so? Seems like doing something just for the sake of doing it, to me.

[JSnover]

As far as I know it's effective on steel parts that are stressed (like barrels). It won't hurt anything and if you can get liquid nitrogen, go ahead and try it.
A proper scientific method would probably involve six identical molds, two new and two used, both of them tested before and after cryo treatment, plus one new and one used - un-treated - as a control.
The real question is how would it benefit the mold?

[longbow]

I think if you wanted to cryo treat mould material you would do it before machining but as asked above to what purpose? What "problem" are you trying to solve?

I have iron, steel, aluminum and brass moulds I have cast lots of boolits with and if treated well they don't "wear" out or change dimensionally. My moulds will outlive me. While cryo treating might improve the material qualities, what is the cost and what benefit are you looking for?

Longbow

[country gent]

Cryogenic treating converts grain structure and stress relieves materials. We had tooling done and it increased the life of it some. Barrels were done to relieve stress.

On molds the normal heat cycling also relieves stress. Done before machining would lower any warp age from machining but the size of the blocks there wont be a lot either. The other benefit of the heat cycling is it promotes the patania that helps bullets release, not sure if the cryo would do that.

Barrel stock is done in the bars before machining to make it easier then again after to relieve stress from machining. The refined grain structure makes machining easier and tooling lasts longer. The actual process raises and lowers the temp several times then a "soak" at the low end. It normally dosnt change hardness of a material, but does convert missed grain structures

[Bigslug]

I can see it maybe benefitting steel sprue plates, but as others are hinting at, what are you seeing in your mold's behavior that's making you say "We really should be freezing these things"?

With a rifle barrel, you can have stresses from hammer-forging, button rifling, chamber-to-muzzle tapering, and fluting spread out over the fairly significant length of the thing. A bullet mold being a small, homogenous cube of material, I've got to think the need for such concerns is going to be A LOT less.

[HWooldridge]

Cryo can help steel alloys because the quench converts any remaining austenite that exists at room temperature to martensite, which also assists with stress relief. Cast iron, brass and aluminum don’t share this same characteristic so I doubt any measurable gain will result - but it also won’t hurt the mold if you want to try it out of curiosity. I just don’t believe you’ll see any difference.

[parkerhale1200]

I think if you would dip the mold into that bucket, it will cool off the outside to quick, witch will give only more stress to the steel.
Possible creating micro fractures.

I think also this comes from the construction world, when things start to freeze over there is no oxidation on the iron bars or other iron (concrete poring molds)

i think cold will do the opposite of heat treating, this is by far a slower process and will soften the metal (as it heats) first before cooling down.
After the "hardening" process you would have to anneal it, i think with the extreme cold the process would be reversed.
AKA work hardening, i think this work hardening only works with aluminium and manganese (rich) steel species without going brittle.
I am looking forward to see the results and read more.

.

[Plugs and Muffs]

Good morning all;
As yet no one has answered the question. Has this been tried? It may not work, it may do nothing, there may be a 1% difference. Some of the things in my experience show that a 1% difference can count. Thomas Edison tried 1000 things to come up with a fillament for light bulbs that worked (just enough). His attitude was that he now knew 999 things now that did not work.

[JSnover]

Probably hasn't been tried because it isn't worth the time and expense to set up a proper experiment and likely offers no benefit. The molds we deal with are about as simple as they come. They're not subjected to any stress; no shear, tension, or torsion, they're not pressurized, even abrasion isn't really an issue.
If you want to try it, go ahead, you'll be the first.

[Bigslug]

Edison was trying to invent a light bulb that didn't exist at the time.

We have molds that work perfectly well with no reason to complain about them. The question then becomes how would you quantify any result if the frozen mold still works perfectly well. . .when any change could just as easily be explained by the mold getting more broken in and seasoned with additional use?

If you have a sick puppy, go ahead and freeze it - you have nothing to loose - but messing with a functional mold seems akin to tinkering with a deer rifle that already shoots half-MOA in order to get more accuracy out of it - probably won't help; more likely to hurt.

[Plugs and Muffs]

I am just a retired guy with an active mind. In a group this size of technically oriented people somebody will have access to the setup. I could have done it in my high school lab.

[HWooldridge]

Easy way to do cryo on a budget is to buy a gallon of acetone and some dry ice, which you can usually find at the local grocery. That mix will get you to -78 C degrees. Probably cost you less than forty bucks.

Liquid nitrogen would be the next step and requires more preparation for success.

[Plugs and Muffs]

Edison improved existing light bulbs and made them economically marketable. Yes, our moulds work as is. Put one under a dissecting microscope and look at the cavity, it looks like a potholed road. Look at the snipers getting hits over two miles away. The competition at 1000 yards is shooting groups 5 inches and under. They lathe turn the tips of their bullets. I am sure that the finest flint knapper in the tribe made his Folsom points with enormous skill, and it was passed down to the next 100 generations. When the Europeans showed up with trade soft steel, the transfer to that was only limited by the supply.

[country gent]

improvements come from experimentation and testing. Modern manufacturing processes have improved almost everything in use, with tighter tolerances, better finishes and being able to use better materials. Materials consistency has improved also.

I think the the edm processes used in mould making would make big improvements in quality and use. A couple carbon electrodes turned under sized .010 and then used to "burn" the cavities in would be very accurate give a very fine finish and be repeatable. It would also allow for much finer detail in the cavities.

The cryro genic is a final "fine tune" of a part or a staring point to aid machining.

Dry ice in a styrofoam cooler soak the blocks in a baggie for several hours and then remove allow to warm and repeat the process several times over a few days. See if you see any improvement. The actual process isnt expensive to have done either.

We had a deep freeze at work that was at -60* used for shrink fits and to stiffen rubber when it had to be machined. We would also rough in tooling ( vee blocks angle plates ) then over a week or so insert into freezer for the shift and removed when shift ended. When done the parts ground in and finished much faster since they warped was much less they also seldom needed touched up after the first few uses.

[Plugs and Muffs]

Thank you sir.
Bear in mind I saw references how to refrigerate assembly of parts in the World Book Encyclopedia from the 1950's. My father was employed by Pratt and Whitney to photograph cryogenic processes in the 1950- 1960 time frame. I am interested in the serendipitous aspects. Dig for fishing worms; strike gold.

[15meter]

As Country Gent stated, it's not just a dunk in liquid nitrogen for a couple of minutes and you have a miraculous metallurgical transformation. It is a fairly complex set up that has specific time cycles to go through.

I worked with a company that did cryo treating of gages. It was pretty involved, based on size of part and type of steel. It did work to improve tool longevity and tool dimensional stability.

Interesting idea, I'm not sure the effort will give measurable results.

But go for it and report back if you have documentable results.

[longbow]

Not trying to dissuade you from trying something new and I have little doubt that you are correct that cryo treating material before machining a mould may well result in better material properties and probably better machining but first look at the boolits that mould is producing and how rough is the surface? Not likely near as rough as the mould surface due to surface tension and instant freezing of the lead as it fills the mould.

Of more concern (I think anyway) are variablilities in the alloy density inside the boolits, dross inclusions and air bubbles. Swaging takes care of most of that so the next logical move is to swage bullets. A cast boolit is unlikely to ever meat the consistency of swaged bullets.

Then, as you mention, lathe turned bullets which are made from either rolled or swaged bar stock.

In short, I doubt a cast bullet will be improved much if any by having a better surface finish than we have now in our moulds. As 15meter said "I'm not sure the effort will give measurable results."and in the end that is what matters.

An easy test to run would be to buy swaged bullets and cast boolits with the same profile and weight, weight sort and size the cast boolits then shoot side by side at whatever long range you want and record results. I am betting the swaged bullets will be at least somewhat more accurate because they will be more homogenous and consistent than the best cast boolit. The best machined mould no matter how smooth will still be producing boolits with minor cast insconsistencies, voids, density variations no matter how smooth the surface is.

Again, there is certainly no harm in trying if you want to put the time, effort and money into it. You may be on to something but I will need to see consitently measurable better results that are useful to me before I'd be spending a significant amount of money on that mould.

It may make a difference to a competitive target shooter/benchrest shooter but will it to a casual shooter or hunter?

If you carry on and cryo treat a mould then test for accuracy please post results. If you are right we may all benefit!

Longbow

[405grain]

Plugs and Muffs: It's a matter of cost vs rewards. What we have now works fine, and has for over 100 years. The added expense and effort to cryo treat a set of mold blocks would very likely result in no change in the finished bullets. Those shooters that choose to have a more refined surface finish on their lead alloy projectiles can achieve that by swaging. Excellent results are already achieved using brass, aluminum, and iron molds, and though cryogenic treatment may offer benefits in strength and durability for high strength steel alloys in heavily loaded applications, it would most likely have no actual benefit on bullet molds. You're more than welcome to try this process if you like, but as a University level engineer with over 30 years experience I can tell you that the difference between a bullet cast in a quality set of molds, and those same molds that have been cryogenic treated will be virtually nothing. Proper care of molds, good alloy selection, and good casting technique already produce bullets that are capable of excellent performance. I don't wish to rain on your parade, especially someone that just joined the forum, but there's a lot of people here that are helpful, have lots of experience, and are willing to give good advise. Without experimenting there wouldn't be innovation, so go ahead and try new things to see how they work. If you feel strongly about your ideas, then prove the doubters wrong, and learn new things along the way. I've tried unconventional stuff when bullet casting - some worked, and others didn't, but all of it was worth trying.

[Rickf1985]

Thank you sir.
Bear in mind I saw references how to refrigerate assembly of parts in the World Book Encyclopedia from the 1950's. My father was employed by Pratt and Whitney to photograph cryogenic processes in the 1950- 1960 time frame. I am interested in the serendipitous aspects. Dig for fishing worms; strike gold.

If you live in a dairy farming area just take your mold and a small heavy plastic container and visit a couple dairy farms. You could probably get one of them to donate some nitrogen for a 20.00 bill. They will always have it on hand to keep the bull sperm frozen.