Lead balls too hard? Home made ball mill media question...

[jl88]

Well I've finally started upgrading my ball mill setup. Coming from a 6lb rock tumbler (can't wait!) I have a .5hp tefc motor, rebel 17 rubber lined jar and all the other goodies required. So here's the thing. Having never seen or felt hardened lead media I'm not sure what to expect.

 

So I alloyed 1kg of antimony with 16kg of lead in my MgAl furnace (fresh pot) The lead was recycled wheel weights. I sorted the lead several times and am very confident that there was no zinc or iron in the mix, however I of course can't be 100%. It definitely got hot enough to alloy the two metals. Tested with a thermometer.

 

I estimated that the alloy would be the hardness of approximately 10% antimony. Taking into account the lead I used was already hardened. However now that I am melting the ingots into balls I have noticed that that strip along the top of the sinker mould is almost brittle. (It was cold water quenched straight from the mould and rested for 2 weeks) At the diameter of a pencil it will yield slightly and then snap... Is this too hard? Lead alone bends quite easily...

 

I am aware that 10% is on the high side for antimony. But thought it could only make a longer lasting media. Anyway let me know.

 

Thanks.

[Arthur]

Sometimes the only way is to test it! Set up the mill with a good load of balls and powder and see what happens. Try it a long way from property, a mill that size full of media will fill a large area with holes if it goes bang.

[jl88]

Thanks Arthur but I would much prefer not to destroy hundreds of dollars in equipment and upset the neighbourhood just to test my media :-D

[Col]

just run straight potassium nitrate for the initial test

[BurritoBandito]

Thanks Arthur but I would much prefer not to destroy hundreds of dollars in equipment and upset the neighbourhood just to test my media :-D

If it's too hard you're not out anything. Just recast and add more lead in the process.

[gregh]

This may sound like a stupid question, but why would it be too hard? Intuitively, one would think that the harder the media, the better the grinding action.

[MWJ]

As long as it doesn't spark, after all people use ceramic for media and that works great from what I here.

[MrB]

To hard, would be prone to cracking and shattering. I'm thinking zinc contamination, but that might just be crazy talk.

B!

[FlaMtnBkr]

Are you pouring spheres? I wouldn't think a sphere could be too hard to chip and you will just get better wear resistance. Assuming you pour it correctly and good and hot so there aren't defects. I would love to get some media that hard. Where did you get the antimony metal and was it expensive?

 

Also, a mill exploding doesn't shoot media everywhere like a shotgun. The powder,and explosion, is around the media and forces for the most part are cancelled out. It's not like a gun or grenade where the explosion is only behind the bullet to propel it to high speeds. Plus a mill jar doesn't hold that much pressure so isn't terribly powerful. It's the flame and heat that is so damaging.

 

Multiple ball mills have been filled with BP and media and ematched to see what happens. Most of the pieces are very close and pieces are not thrown much more than 15 feet for a 1 gallon jar and, I believe, a kilo of finished commercial powder.

 

Obviously you don't want a mill explosion and want to take every precaution to prevent one. But this has been tested with pretty surprising results as it didn't really act like a fragmentation grenade like most would think. But I don't believe grenades filled with HE have all that large of an effective radius.

 

Just thought I would mention it. I can find out all details of the test if anyone wants as this was done by members of FPAG a while back.

[calebkessinger]

I have been thinking of this issue and finally decided it's a non issue... the only time you're media would be beating itself to death would be in an empty jar... therefore milling itself. with anything to go in between each media it would soften the blows and the harder media will greatly improve milling! Some have more than cut their mill times in half with my media that has 12% antimony in it. This media does chip away some if loaded with nothing else in the jar. they click together like steel!! Which I think is great!!! Only time will tell for me where the perfect mixture of lead/ant. and tin is. but for now I'm pouring them with a mixture of linotype and foundry lead. when compared to soft lead it seems like comparing steel to wood.

Just my thoughts.

[jl88]

Hey guys. Damn this time difference! Okay here goes...

 

BurritoBandito: yeah if the outcome is that it is too hard I will just recast with more lead. Shouldn't be a problem as it readily melts on a hot stove top now which is nice. But if harder is better than I'd like to leave it.

 

Gregh: I'm worried as discussed bellow that it may chip or crack (although smacking them together seems like this won't happen) what I'm more worried about is that hardening to this level will negate the lead's non sparking properties...

 

FlaMtnBkr: yeah casting spheres. I am in Australia so I'm not sure if my supplier is going to be helpful to you. I used northern smelters in Queensland. They supply most metals including pure lead, antimony and tin. Also bismuth etc. it cost 58aud for 2kg delivered. Not sure if this is a good price but there were no other small quantity suppliers I could find.

 

Well thanks for the replies everyone. Looks like I will be giving it a go once it's all built :-)

[otto]

I cast a pile of media out of straight foundry type metal that's supposed to be somewhere in the neighborhood of 24% antimony. Took 'em for a spin in the tumbler just to knock off any loose bits and get 'em ready for business. Did the trick with no broken or otherwise unusable balls so I think that even at that they're not too hard. My goal was to get as hard and dense as possible without getting into ceramic/zirconia. I also ran one batch of BP with no issues.

 

Bottom line: you'll be fine.

[dagabu]

Hey guys. Damn this time difference! Okay here goes...

 

BurritoBandito: yeah if the outcome is that it is too hard I will just recast with more lead. Shouldn't be a problem as it readily melts on a hot stove top now which is nice. But if harder is better than I'd like to leave it.

 

Gregh: I'm worried as discussed bellow that it may chip or crack (although smacking them together seems like this won't happen) what I'm more worried about is that hardening to this level will negate the lead's non sparking properties...

 

FlaMtnBkr: yeah casting spheres. I am in Australia so I'm not sure if my supplier is going to be helpful to you. I used northern smelters in Queensland. They supply most metals including pure lead, antimony and tin. Also bismuth etc. it cost 58aud for 2kg delivered. Not sure if this is a good price but there were no other small quantity suppliers I could find.

 

Well thanks for the replies everyone. Looks like I will be giving it a go once it's all built :-)

 

No worries there, you cannot make lead or its alloyable metals to cause a spark. Really, there is no such thing as too hard a casting as long as it holds together without chipping while making comps like BP.

[jl88]

Too easy. Well I have slammed two of these balls together several times and can't get a chip or dint... Damn there hard lol.

 

Then I performed a very scientific test involving a 4lb hammer and the sidewalk. I could not get one to break apart or chip. Just deform some what (flatten) i am surprised how much difference a relatively small amount of antimony can make. My previous media with no hardening flattens like a pancake with one or two hits.

 

Thanks again guys. Looks like I'm good to go.

[Arthur]

For your first two mill loads I'd still suggest that you test the system by trying a batch through it, probably in work hours when neighbours are almost expecting noises.

 

Load 1 would be Pot Nitrate, load 2 would be charcoal, if it was my job. Then I'd open it carefully and look for broken balls or bits of metal that you are not expecting.

Given both runs milled well with no "wreckage" then I'd weigh out the ingredients for BP, and see how much the mill wants to cover the balls nicely. I'd set it running and take a sample every hour or so to see what mill time is needed, bigger mills with deeper media tend to take less time.

[jl88]

Mmm... 17kg (37lbs) of 14mm hardened lead balls. Fills the rebel 17 drum JUST over half. I know they are a little bigger than half inch but I NEVER want to have to make them again lol and I assume they will last my pyro career. Tested several of them and none crack under a hammer. But will mill them by themselves to smooth out all slight mould marks. Then run a few test runs with solo chemicals.

[MrB]

But will mill them by themselves to smooth out all slight mould marks.

No point. Those marks will go away anyway.

Nice batch.

B!

[calebkessinger]

I have decided to mill all that I make for 2 hours to get any loose lead off. With a new mold there is hardly any of this but as the mold wears you get more and more build up around the spru and maybe around the seam if you get crap stuck where the mold comes together.

They turn a really nice color like blued steel. I wouldn't roll them by themselves too much more or they will just beat themselves to death!

 

Oh, just for what its worth, For those just pouring wheel weight and calling that Hard lead. Then saying the molds last forever. Ha,

It might be harder than pure lead but what I'm pouring is stupid hard I have destroyed 1 aluminum mold for every 200 lbs made. My lead is a mix of linotype and monotype. Then water dropped. Lead of this sort will Age and Work Harden, It clacks like ball bearings when smacked together and should only get harder.

Just some observations.

Edited December 31, 2014 by calebkessinger

[Bobosan]

You could also try corn cob or walnut shell media to break them in.

 

 

[MrB]

You could also try corn cob or walnut shell media to break them in.

for "cleaning" i use bentonite, as in kitty litter, and it cleans up the balls nicely. But i don't "break in" new casted media. Seams like a waste to me, but of course, that depends on how much you expect to knock off the balls through the first milling. From his picture above it didn't look significant.

 

IOh, just for what its worth, For those just pouring wheel weight and calling that Hard lead. Then saying the molds last forever. Ha,

It might be harder than pure lead but what I'm pouring is stupid hard I have destroyed 1 aluminum mold for every 200 lbs made.

Wheel weights are hard enough for the purpose, but i keep trying to get some linotype just to get it some better yet. I didn't know it ate molds tho. Any idea on how / why? I use a rather crappy casted mold intended to make round sinkers for fishing purposes that i modified to my liking. As you said, the mold hasn't any significant signs of wear. Just curious, thats all. The mold was dirt cheap, and the mods were simple enough, i can replace it if it should start wearing, but it would be nice to know why, and if there is anything one can do about it.

 

Cheers.

B!

[Bobosan]

for "cleaning" i use bentonite, as in kitty litter, and it cleans up the balls nicely. But i don't "break in" new casted media. Seams like a waste to me, but of course, that depends on how much you expect to knock off the balls through the first milling. From his picture above it didn't look significant.

 

There is a significant difference where the flat sprue area is cut and rounded. Fresh media was a sharp edged sprue. The balls really don't need a break in but have found small pieces of lead during fresh media break ins.

 

The mold seam lines are smoothed also. Again, all that could be done with a "live" mill run using fresh cast media, however, there exists a possibility of small lead pieces in the milled material. More of an aesthetics issue than a practical one.

Edited December 31, 2014 by Bobosan