wayneinkeywest on tue 16 dec 03
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=20
father's spirit kicked me in the butt and said=20
"you can do it cheaper", so I started thinking.
I often have access to electric clothes dryers that=20
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=20
the center of a clothes dryer tub, along the axis,=20
so that as the drum rotated, so would the inner=20
drum. In it I could fasten a set of metal "vanes"=20
to the walls to aid in the tumbling. Loading and=20
unloading could be accomplished by sliding out=20
the smaller drum from the larger one=20
and unscrewing the lid. A plastic=20
five gallon bucket sold with pool chlorine tablets in it=20
would be just the thing, I think, for the little bits I=20
would process. It's water tight, too, as is.
Question is, how fast does an "off the shelf"=20
ball mill drum rotate? Anyone? Comments welcome
on or off list.
Dave Finkelnburg on tue 16 dec 03
I believe all this is in the archives.
The minimum speed at which a ball mill will "centrifuge" or cease to
grind because the balls just keep going around stuck to the wall by the
force of rotation pushing them there is given by the formula: N =
54.19/square root of R, where N is Revolutions per Minute, and R is the
radius of the mill in FEET. You want to run your mill at 50 to 80 percent
of this critical speed. This is from the book "Extractive Metallurgy" by
Joseph Newton, although you can derive the formula easily from first
I would attempt to run the mill without flights (lifters) to start, just
to see what will happen. If the wall is too smooth, the lifters will help,
but with reasonable wall roughness and high enough speed you will get
tumbling of the balls, and that's what does the grinding. Lifters are a
pain to install and maintain and most small ball mills work fine without
By the way, the mill will wear out -- there is some wear on the walls
from the grinding action -- so you may want to check your ball mill from
time to time.
Good luck with your excellent project!
----- Original Message -----
Subject: ball mill question
Question is, how fast does an "off the shelf"
ball mill drum rotate?
wayneinkeywest on tue 16 dec 03
Once again, my apologies to all. I did not dig far enough back
into the archives to find the answer on my own.
> I believe all this is in the archives.
Paul Herman on tue 16 dec 03
Those companies want a lot alright.
In the spirit of your dad, figure a way to do it with a ceramic jar,
instead of plastic. You can buy one, for probably under a hundred
dollars. Or you can throw one, like I did a long time ago. It's still in
use, and shows no sign of wearing out. This is a place where plastic
ain't good enough.
A considerable difference is that with a ceramic jar, the balls grind
against the jar, not just against each other. I'd bet it does the job
twice as fast, and surely would last longer.
As Dave from Idaho pointed out, the RPM depends on the inside diameter.
If you make a jar, throw it thick (like one inch) out of white
stoneware, and keep the opening plugged as it turns. You are a Potter,
Non Illigitum Carborundum,
Great Basin Pottery
423-725 Scott Road
Doyle, California 96109 US
>Subject: ball mill question
>Date: Tue, Dec 16, 2003, 2:43 PM
> Never having seen a ball mill, I was,er, um, stunned
> at the price various companies wanted.