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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..."

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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.

 

Lloyd


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!





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