ball mill question
Posted 20 August 2017 - 02:12 PM
Dumb ass question... Would you really NEED lead media? We use lead to get the force increase that comes from the higher density, as the media cascades down. But a vibrating unit doesn't really have this cascading thing going for it. A lighter, hard, none-sparking media should work pretty ok?
On the other hand, vibrations likes to sort stuff based on density, so it might just end up layering whatever is put in to it, if the differences are to much between composition, and media. (or even between different chems in the composition)
Posted 20 August 2017 - 02:24 PM
You still need the inertia of the lead for a vibrating unit. supposedly, you will have the media moving and colliding at higher speeds, but, will it be enough to compensate the decrease in mass? In the end, it all depends of the kinetic energy of the media. From the top of my head, seems that vibrating wastes a lot more power for the same final energy in the media.
Posted 20 August 2017 - 03:20 PM
Yeah, but Baldor, in defense of the idea of lighter media, Force = mass * velocity^2... so lighter media could equate to a greater impact force.
For instance... take some media of mass 1, and say it could be accelerated to a velocity of 2. That would result in a force of 4 (arbitrary units).
Now take media of mass 0.5. A given acceleration should move it at twice the velocity of the first. Force = Mass of 0.5 * velocity(4)^2 = 8 (arbitrary units).
I wouldn't rule that out as a vague possibility. But, knowing how those vibratory polishers are driven, I still don't think it would work well, even with ceramic media. 'Real' vibratory mills are strongly motor-driven, not vibrated by 60Hz or 50Hz electromagnetic vibrators, like most of the cheap ones designed for brass-polishing. And it takes a LOT larger motor to run a vibratory mill with the same load as does a ball mill.
I'm not criticizing your opinion (which I believe is right), just listing all the physical possibilities.
Edited by lloyd, 20 August 2017 - 03:21 PM.
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Posted 20 August 2017 - 03:35 PM
Posted 20 August 2017 - 03:38 PM
You are right, simple conservation of energy. The problem is reduced to how efficient is the transfer of energy from the motor to the media, and from the media to the product being milled. In a ball mill, a lot of energy goes to the angular momentum of the individual media particles, very efficiently, which in turn is converted to friction between the media and the product. In a vibratory polisher, seems the main transfer of energy from media to product is via colision, and the same from the drum to the media.
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Posted 06 November 2019 - 07:49 PM
The optimal RPM is what you want to use. The critical speed or RPM is when the balls start to stick to the walls of the jar. You ideally want a good cascade of media.
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Posted 08 November 2019 - 03:43 AM
Correct. Just to elaborate a bit:
The critical speed is the point where the balls will stick to the inside wall due to centrifugal effects. It's used as a point of origin as it's a very precise physical effect. The optimum speed is much harder to determine, it depends on the type of mill, media, charge, phase of the moon and so on. For BP using lead ball media it should be appr 65%, but don't panic if you're a few percent off.
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