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Ball mill media


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#41 MrB

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Posted 16 March 2017 - 12:02 PM

The smaller media mills more efficiently (when each ball is heavy-enough to give the desired impacts), not because of the smaller space, but because there are more contact-points in a mass of small balls than in a mass of large ones.

 

Smaller media is most effective, as long as it's heavy enough to break whatever you are milling. There is something of a relationship where larger media is more effective at larger particles of the same material and as the size is reduced, you gain efficiency with smaller media.

Pretty much, there is a optimum size for everything.

At least that is my understanding. Again, i have been wrong before.

I'm using 10mm lead balls cast from mainly wheel-weights, with some added tin scraps, and water quenched when cast. Not really compared the media to anything else, but it works.

B!



#42 lloyd

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Posted 16 March 2017 - 01:12 PM

"There is something of a relationship where larger media is more effective at larger particles of the same material and as the size is reduced..."

-------------

Not for a given "friability".  Small media works as well on a given substance, almost regardless of the particle size, until you get into 'large chunks'.  But usually, 'chunky stuff' like lump charcoal is broken down into manageable particles before being ball milled.

 

Sure... if the pieces are larger than the spaces between the balls, you create an efficiency deficit.  But not much, if they're smaller.

 

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Edited by lloyd, 16 March 2017 - 01:13 PM.

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#43 Boophoenix

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Posted 16 March 2017 - 06:50 PM

I use ½" hardened lead in my 6" mill jar as well as in my larger one and achieve excellent results. Dave Forster has used smaller stainless media with good results but it requires longer milling times.



I'm not certain longer times are always required.

You are correct Dave does mill for a decent amount of time, but a lot of that is to keep his tests standardized as that is what he started at originally. He did do some time testing and saw better results with longer times, but I don't recall the media used.

At some point ya have to ask is the added mill time necessary for the end use since the gains are going up way slower than the length of time. For wicked rockets yes maybe. For lift not really. For a good break could be debatable.

My personal belief is to mill with as little time as is necessary to get the result you want. I'm sure Dave won't mind correct me if I'm recalling anything incorrectly. We've had more than a couple of lengthy conversations about milling and media.

#44 MrB

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Posted 16 March 2017 - 06:53 PM

Sure... if the pieces are larger than the spaces between the balls, you create an efficiency deficit.  But not much, if they're smaller.

 

Never thought about it quite like that. But yeah, that may well be where the perceived milling efficiency comes from. But i don't think stuff doesn't need to be quite as large as you indicate. If you have a 5mm space between the balls, and 3mm material to be milled, then your going to remove a lot of impacts simply since there isn't room for more then 1 particle in every "hole". It would quickly become under-filled as well.

 

And 3mm stuff still isn't what i would consider "chunky" to start with. I wonder how much difference rod-milling does in comparison to ball milling.

 

At some point ya have to ask is the added mill time necessary for the end use since the gains are going up way slower than the length of time. For wicked rockets yes maybe. For lift not really. For a good break could be debatable.

 

There is always a point of diminishing returns. To some extent it comes down to what is "good enough" for the individual setting the standard.

B!



#45 PeteyPyro

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Posted 20 May 2017 - 02:42 PM

I used to cast my own bullets in .451(45 Colt), .356 (.38 spl. & .357 mag., and .429 (44 spl. & mag.). I found that I could take a piece of disposable pine and drill 5/8" holes about 5/8" deep, and ladle my hardball alloy mix into the holes, then split the wood, to get decent ball media. Not spherical, but close enough. I tried to use .356 balls, cast for my 36 caliber Naval BP revolver, but they were a tad too small.
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#46 lloyd

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Posted 20 May 2017 - 02:58 PM

Petey,

 

I've made molds in many ways, but the simplest and quickest was to make tubular aluminum foil molds (around a dowel), GENTLY embed them in dry sand (gently, so as to prevent them from being collapsed), and cast long rods of lead, which I subsequently just cut to length with bolt cutters.  The 'funnel' that forms upon cooling was simply cut off and re-melted for the next batch.

 

Yes, they had a 'nip' on each end, but that smoothed-out in just a few dozen minutes of milling with a little waste media like a bit of sanded sawdust. (I added a few tablespoons-full of sharp sand to the sawdust before milling, then with clean sawdust to clean-up their surfaces and prepare them for product milling).

 

Lloyd


Edited by lloyd, 20 May 2017 - 02:59 PM.

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#47 saltflat

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Posted 12 June 2017 - 04:32 PM

I bought some from woodys rocks here in missouri. Reasonable price and they are hardened



#48 lloyd

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Posted 12 June 2017 - 04:51 PM

You'll be good with Caleb's media.  He does a good job.

 

Lloyd


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#49 PeteyPyro

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Posted 08 July 2017 - 07:50 PM

I got my newest .50/.58 caliber hard cast, high antimony (12%?) alloyed lead balls from hqhandcast, or maybe handcasthq, on Etsy. They are some of the roundest and hardest alloy ones I've seen, but somewhat pricey. I used to hand cast my handgun bullets, but got rid of all my Lee moulds years ago. I've noticed shrinkage in my old balls, and I'm only 60~ish <grin>. But seriously, it seems the charcoal really eats away at even the hardened lead over many, many runs.
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#50 PeteyPyro

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Posted 08 July 2017 - 08:02 PM

On second thought, these are probably too pricey and too nice to use just for media. Lloyd's right about Caleb's ball mill media, and I defer to him, since he 'wrote the book' on this ...(literally!)
Peter

#51 Baldor

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Posted 23 July 2017 - 04:03 AM

I'm having difficulties finding good media in Europe. I can only find aluminium ceramic, and after reading other threads, decided against it. I found one supplier for antimonium alloyed lead, but it's expensive, too big for my jars, and the shipping is still more expensive. Casting is out of the equation for now, I can get all the lead I need, but will be soft and I'm not in the mod for casting with 28ºC plus and high humidity.

 

I thought about using fishing sinks, but are soft, and the hole in the middle will only help with cross contamination.

 

I work with small bathes, 1300ml jars, about 100mm diameter.

 

I can get 2m 10mm diameter AISI-304 stainless steel for less than 5€ plus shipping. Since I´m purchasing other materials shipping is not a problem. I can cut this bars to make cylindrical media, I will be wasting a lot of material with every cut, but it's cheap, and my time is free. What do you think? Will 20mm long cylinder be Ok, or can I make them longer? Should I get bigger diameter media, say, 12mm, for this jar?



#52 lloyd

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Posted 23 July 2017 - 05:54 AM

For 100mm i.d. jars, about 12mm is close to optimum.  Cylindrical media should be close to 'square' -- that is, the length should be about the same as the diameter.

 

De-burr freshly-cut metal media by milling an abrasive for a time.  Carborundum powder mixed with water works well.  Charge the jar 1/2 full of media, and use only 1/8 volume of the jar charge of the grit (a normal 'material charge' would be 1/4 the gross volume of the jar).  "Undercharging" with material tends to exacerbate media wear, and this case, that's exactly what we're trying to accomplish!

 

Mill until all the sharp corners are smoothed.  Further rounding and 'easing' of the corners will occur with time.

 

Thoroughly clean the jar and the media of any abrasive residue before using on your chemicals.

 

Lloyd


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#53 Baldor

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Posted 23 July 2017 - 07:12 AM

Thanks.

 

I'm thinking of using a "disposable" paint can for  deburring the media, to avoid damaging the good jars.80 grade will be Ok for deburring, or do you think I will need a finer one?



#54 lloyd

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Posted 23 July 2017 - 08:03 AM

Almost any grit coarser than 200-mesh would work, but the coarser the better at the beginning, because that's when you want the fastest wear.  Yes, 80mesh, or even 50mesh would be just fine.

 

The grit WILL be milled finer, and the process is self-limiting.

 

Lloyd


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