steve harrison on thu 18 dec 03
Hi Wayne,
All ball mills turn at a speed between 64% and 87% of the critical
speed of the diameter of the inside of the mill.
The critical speed is the speed that will be fast enough to 'stick' the
balls to the walls by centrifugal force. This can be calculated from a
simple formula.
There fore small mills turn fast and big mills turn slower.
There is a lot more to it than that, but that is the general theory.
I have written a book called "Thoroughly Modern Milling"
Which is all about how to build a ball mill. In it, I canvas the
possibility of using plastic drums as well as throwing your own
porcelain jar. etc.
Best wishes
Steve Harrison
Hot & Sticky Pty Ltd
5 Railway Pde
Balmoral Village
NSW 2571
Australia
http://ian.currie.to/sh/Steve_Harrisons_books.html
On Wednesday, December 17, 2003, at 09:43 AM, wayneinkeywest wrote:
> Never having seen a ball mill, I was,er, um, stunned
> at the price various companies wanted.
>
> Thinking about how a ball mill does what it does, my
> father's spirit kicked me in the butt and said
> "you can do it cheaper", so I started thinking.
>
> I often have access to electric clothes dryers that
> have burned out elements, but still turn just fine.
> Even a used one that still works is only $25-50 here.
>
> I thought about mounting a small plastic drum in
> the center of a clothes dryer tub, along the axis,
> so that as the drum rotated, so would the inner
> drum. In it I could fasten a set of metal "vanes"
> to the walls to aid in the tumbling. Loading and
> unloading could be accomplished by sliding out
> the smaller drum from the larger one
> and unscrewing the lid. A plastic
> five gallon bucket sold with pool chlorine tablets in it
> would be just the thing, I think, for the little bits I
> would process. It's water tight, too, as is.
>
> Question is, how fast does an "off the shelf"
> ball mill drum rotate? Anyone? Comments welcome
> on or off list.
>
> Wayne Seidl
>
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