turtlesteve, thanks good post, I would like to hear more from you about the differences in the types of ball mills.
the ball mill
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turtlesteve
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Butcher,
Unfortunately for crushing I don't know much more than has been stated by Harold. For grinding I might be able to help, but I'm not really sure what utility this would have for this forum. In my case the milling is used prior to green forming of ceramic parts.
One other thing I might mention is that for grinding, the size of the grinding media (balls) should scale with your powder - large media for coarser powders, smaller media for finer powders. It's kind of obvious that small balls are useless at breaking up large particles, but the opposite is also bad - large balls are ineffective if you want fine powders. In extreme cases I am aware of attrition mills (which use a stirrer in a pot, kind of like a food processor) that use 0.2 mm balls to produce powders down to 40 nanometers in size.
I would assume ball size is similarly important for crushing, at least to some extent. Perhaps Harold or someone else can comment more?
Steve
Unfortunately for crushing I don't know much more than has been stated by Harold. For grinding I might be able to help, but I'm not really sure what utility this would have for this forum. In my case the milling is used prior to green forming of ceramic parts.
One other thing I might mention is that for grinding, the size of the grinding media (balls) should scale with your powder - large media for coarser powders, smaller media for finer powders. It's kind of obvious that small balls are useless at breaking up large particles, but the opposite is also bad - large balls are ineffective if you want fine powders. In extreme cases I am aware of attrition mills (which use a stirrer in a pot, kind of like a food processor) that use 0.2 mm balls to produce powders down to 40 nanometers in size.
I would assume ball size is similarly important for crushing, at least to some extent. Perhaps Harold or someone else can comment more?
Steve
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The experience I had was feeding ½"- to my ball mill. The largest balls were about 2" in diameter, with the smallest about 3/4" (I'm trusting to memory--it was long ago).turtlesteve said:
It the process of fine crushing the ore, I had a somewhat larger piece that hadn't been crushed, but it had to be included in the lot. I would guess its size about about 1½". I inserted it in the ball mill, and allowed it to run while continuously feeding the crushed material. It became well rounded, but did not crush, instead being worn down slowly. When it was reduced to less than an inch, it quickly vanished, as it was then small enough to be crushed by the balls in use. I concluded that ball size was, indeed, very important. I also assume that because I had a mixture of ball sizes, along with rollers, that I was successful in reducing the ore to a fine powder. It was fine enough for the cyanide to extract virtually 100% of the assayed content, so I considered the entire operation to be a success. I concluded that one must use reasonably large balls if the material is too coarse, so, yes, in my opinion, size is critical.
Thanks for the comments on fine grinding. I have no experience that parallels yours, but found your comments quite interesting, in particular, the idea that the mill is lined to protect against the wear I spoke of. I confess, that does make sense.
Harold
The next mill I build will be ball-less. Chuck some big chunks of rock in with the stuff straight out of the ground, maybe a few big balls but thats it. It will take longer, but will use less diesel and be alot easier to clean up. :mrgreen:
