Discussion:
First project - Ball Mill - LONG
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aborza
2003-07-31 13:33:07 UTC
Permalink
Thanks for the comment Lloyd,

But darn, I'm disappointed.

I want to be at the top of "The Very Best" re: a 1/2 gallon ball mill for
the making of best quality Meal/Pulverone and BP rather than in the middle
of good. I want to try to match or beat the "oomph" of commercial BP for
lift and break purposes. I know that I will have to experiment with
varieties of Charcoal, pressing, corning, etc. but wish to have the mill as
a constant at the highest level.

I have already purchased 302 stainless as well as brass media (both are .5")
and will make up some lead media soon.

Where did I go wrong?
'Sounds like you did your homework!
Keep in mind that the speed issue does not require precision. The optimum
speed will vary considerably with different materials and weights of
media.
The calculations you've done will drop you right in the middle of the
'good'
range.
LLoyd
My first pyro project is underway. I have a suitable AC motor on hand. I
have purchased media. I have purchased a mill jar. I am now about to
order
the sheaves, bearings, etc. to complete my ball mill. I have made some
calculations a la Sponenburgh and would appreciate a check out to be
sure
I
have not screwed up. I would like the fastest milling possible with the
jar
and media I have.
From Sponenburgh the RPM of the jar should be based on the ID of the jar
and
the OD of the media. Mine are 6.75" and .5" respectively. So...
RPM = (.65) (265.45)/ SQRT (jar id - ball od)
RPM = (.65) (265.45)/ SQRT (6.75 - .5)
RPM = 69
1750/69 = 25.36:1
The drive shaft will be rubber covered and .75" OD and the mill jar will
be
7.25/.75 = 9.66666:1 or 9.67:1
Since I need overall gearing of 25.36:1 and drive shaft to jar gearing
is
25.36/9.67 = 2.623:1
A 2" sheave has a 1.85" pitch diameter and a 5" sheave has a 4.85" pitch
diameter (using an A belt). Using those sheaves the gear ratio the gear
4.85/1.85 = 2.623:1
total gearing = (2.63)(9.67) = 25.43:1 and
ball jar RPM = 1750/25.43 = 68.8 RPM
Also, drive and roller shaft separation should be about .75 of jar
diameter.
So
Roller separation = (.75)(7.25) = 5.44"
Is all the above right? Any suggestions?
Thanks
aborza
2003-07-31 18:49:52 UTC
Permalink
I suppose that in my 6.75" mill jar 3/4" media (302SS, brass, lead) would
get me done in 2-3 hours with the same quality that 1/2" media would get me
in 3-4 hours. Right?

If so, it is only a matter of a little time and not quality and that is fine
with me.

Thanks
Within a fairly wide range of efficiencies, you'll make perfectly good
('best') black powder. The only thing that will change is the time it
takes
to mill it.
Since you're using 1/2" media, I'd guess you'll get good BP in 3-4 hours
in
a 6" jar. Both brass and 302SS are heavy enough to do the job well.
LLoyd
Joe 123
2003-08-01 16:24:41 UTC
Permalink
Backwards, smaller balls less time finer "grind". Big balls longer time
course grind. for a given material. It has to do with surface area and
volume, void, weight, contact, etc. The ideal situation would be a bunch
of balls varing in size from 1/4 inch to 1 inch and the bulk being 1/2 inch.
platinum balls @ 21.45 g/cc would kick butt. lead is 11.34 g/cc. Ofcourse
this all means nothing unless you know what you want to grind. Harder
substances require heavier hard media, soft stuff require lighter for same
effect. Big balls are heavier so they can put more energy into the grind
but will take way longer due to less contact sites. Smaller balls have
greater contact with in a given volume or less void space. Big balls have
greater void space than small balls. Cylindars are good because they have
even greater contact area. I would imagine that the less void you have in
the media per volume of media the more work you will achieve out of you
mill. Ive seen mills that use long cylindars that are almost the length of
the mill jar so as to not be able to turn sideways thus all energy is
transmitted along the length of the cyclindar. they just keep rolling over
each other.

Big balls will be good for breaking big stuff to smaller stuff. Like
charcoal. You get even more work when you have lift bars for any given size
ball.

BTW I just made my first batch of charcoal with my new electric oven. I
will post a thread describing it soon. Kicks butt. I reached 650F in less
than 1 hr and was done in 2.5 hours had to back down ofcourse to 550F. I
waited one hour to cool but when I open the lid the stuff on bottom started
glowing red like embers. Too hot still.

Joe
Post by aborza
I suppose that in my 6.75" mill jar 3/4" media (302SS, brass, lead) would
get me done in 2-3 hours with the same quality that 1/2" media would get me
in 3-4 hours. Right?
If so, it is only a matter of a little time and not quality and that is fine
with me.
Thanks
Within a fairly wide range of efficiencies, you'll make perfectly good
('best') black powder. The only thing that will change is the time it
takes
to mill it.
Since you're using 1/2" media, I'd guess you'll get good BP in 3-4 hours
in
a 6" jar. Both brass and 302SS are heavy enough to do the job well.
LLoyd
Lloyd E. Sponenburgh
2003-08-01 20:29:11 UTC
Permalink
Post by Joe 123
The ideal situation would be a bunch
of balls varing in size from 1/4 inch to 1 inch and the bulk being 1/2 inch.
Well... almost. Unless the milling media is totally wear-resistant, it's
not good to have various sizes of media, because the larger balls tend to
mill the smaller balls.

If it were possible to have a medium that could not be abraded by itself, in
theory the idea would work... but it would drastically change 'fill-factor'.
Post by Joe 123
Smaller balls have
greater contact with in a given volume or less void space. Big balls have
greater void space than small balls.
Most of what you said in your post was right on. But this is an error.
Spheres in a mass occupy approximately 60% solid and 40% voids -- regardless
of the size of the spheres.

Ive seen mills that use long cylindars that are almost the length of
Post by Joe 123
the mill jar so as to not be able to turn sideways thus all energy is
transmitted along the length of the cyclindar. they just keep rolling over
each other.
Yep... rod mills.
Post by Joe 123
Big balls will be good for breaking big stuff to smaller stuff. Like
charcoal.
Yep
Post by Joe 123
You get even more work when you have lift bars for any given size ball.
Not necessarily; If the surface of the jar is rough enough to prevent the
media from sliding, you'll get just as good a cascade angle without lifters
as with them. It's more an issue of speed than anything else. Lifters are
most often necessary when milling wet, or for materials with high lubricity.
Post by Joe 123
BTW I just made my first batch of charcoal with my new electric oven. I
will post a thread describing it soon. Kicks butt. I reached 650F in less
than 1 hr and was done in 2.5 hours had to back down ofcourse to 550F. I
waited one hour to cool but when I open the lid the stuff on bottom started
glowing red like embers. Too hot still.
O.T.... but I think 650F is WAY too hot; 'drives out all the volatiles,
leaving pure carbon (which is way slower than good charcoal in BP)

LLoyd
m***@iprimus.com.au
2003-08-01 23:46:20 UTC
Permalink
to source good parts for a ball mill try looking for an old photocopy
machine, they have everything form spindles/shafts bearings, bushes,
rubber sleeves, motors, fuses, swirtches, sprockets, toothed fan
belts, potentiometers :) etc. and it cost my nothin, just grabbed it
from an old graveyard.
Chuck S.
2003-08-11 12:46:44 UTC
Permalink
Sheez. Just buy a rock polisher for $30 and be done with it. Good for small
amounts of grinding.
Old Dog
2003-08-12 16:22:22 UTC
Permalink
Post by Chuck S.
Sheez. Just buy a rock polisher for $30 and be done with it. Good for small
amounts of grinding.
Not so good, really. Not when you compare the results to the products of real
ball-milling.

I think it's the superficial similarity of polishers to ball mills that makes
people think of using them. See, you've got a jar full of "stuff" and you're
using a motor to power it, and some way to transfer power from the motor to the
jar to rotate it. But if you ever SAW the two working side by side, you would
immediately see that there is a VAST difference.

You're not trying to "polish" anything with a ball mill, you're trying to
"pulverize" it! The different application of physics mostly requires different
(much higher) RPM's and different (much heavier) jar loads, and that naturally
means stronger motors and belts or gears to transfer that higher power to the
heavy mill jar, and stronger support for the jar itself. There is also some
minimum jar diameter below which you are just not going to get very efficient
milling.

IMHO, about the only thing that can be used from a Lortone is the mill jar
itself. The larger rubber Lortone jars do make very nice mill jars for some
applications, because they don't seem to develop or hold static charges, they
are "ribbed" on the inside (so you get good tumbling action, not just media
sliding along the walls), and they don't make anywhere near as much noise. The
lids are designed to withstand a lot of pounding from heavy loads and to hold
liquids, so they don't come apart or leak powder either if assembled correctly.

-Rich

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