# Ball mill pics



## scwiers (Aug 3, 2008)

I'm attaching some pictures, with explanation.

Basically, I'm guessing that I've run this thing for a total of 100 hours. In that time, I've pulverized probably 600 lbs. total of electronics. I had the tumbler and hoops built by a local welder, but did the rest myself.

Catalytic biscuit goes 'fast'. The first time I ran it, it brought 150 lbs. of biscuit down to <50 in an afternoon.

PC board takes much, much longer. I guess, I'm looking into processing just straight ceramic components, off the PC board, or with PC board kept to an absolute minimum.

When starting a batch of PC board, I make sure that the pieces are about the size of playing cards, or smaller. I load 150 lbs. or so into the tumbler, and add another 70 lbs. large ball bearings, steel machine screws, etc.

After running for 36 Hours or so, I empty the contents onto a chicken-wire sieve. All the larger pieces of steel, plastic, and PC board get pulled out, at this point, as long as their components are removed. Otherwise, back into the mill. The stuff that goes through the sieve goes immediately into my trash-can shaker (not shown), 100 mesh. If it doesn't go through the sieve, back into the machine.

I can't stress enough how important it is NOT TO BREATHE ANY OF THE DUST produced by this thing, when emptying it. This isn't so much of a problem when running it, because there's a gasket on the lid. I wear an air mask whenever I'm near this thing, but even so, I had a startle when at my last Dr. visit, my blood Pb and As levels came up 2x normal. Now, I'm more cautious than ever. Ear plugs are required equipment, too.

Here are some specs, all approx:

tumbler dimensions: 30" x 20". The individual sides of the prism are stitch-welded from 28" x 10" plates. I had to reinforce the hoops with little spokes made from scrap pipe, because the hoops kept breaking at the vertices. The hoops are cushioned by 4 belts (I forget the size).

tumbler material: 3/32" steel plate **CORRECTION: 3/16" plate 

Weight, entire unit with motor, bed, empty: approx 150 lb.

Weight, full and running: 350 lb

shafts: 1" diameter

chain, pulley, and sprockets: chosen to give a steady 1 RPS of the main drum. Faster than that, and the machine acts up, breaking belts, or bouncing. [corrected, thanks Carlos - not 1 RPM !!]

rollers: 3" diameter; mounted on 4 pillow blocks. I needed to put on an additional bearing where the shaft comes directly from the large pully wheel, because the 1" shaft repeatedly sheared off right at this point. So the power really doesn't go directly go to the chain where the pulley is attached.

motor: 1/3 HP 120 v. ; the motor is mounted with a pair of door hinges.


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## NuggetHuntingFool (Aug 3, 2008)

Interesting. I'd like to fashion my own someday.

I might consider buying a really cheap one until I can build a large one.


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## skippy (Aug 4, 2008)

Well done - I'm impressed!

Scwiers, maybe a little garlic every day will help keep your As levels in
check. Stay safe. 

http://www.newscientist.com/channel/health/mg19726385.100-garlic-combats-arsenic-poisoning.html


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## skippy (Aug 4, 2008)

Also, its one thing to wear a mask when you're opening and emptying the mill jar, but if the dust settles around your work area, migrates into your house, etc, then you still may have a problem. I remember reading 
a paper about incineration, I can't remember if it was about escrap or not, but the message was control the dust, control the problem. 

Maybe build some sort of box where you the emptying operation is contained would further reduce dust in your workspace.


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## AuMINIMayhem (Aug 6, 2008)

she's a beaut! Thumbs up!


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## scrapdealer (Sep 2, 2008)

Inspired by SCWIERS interesting little ball mill above I decided it was time to build one to process our com boards and electronics bits & pieces. 
Based on the same concept here are a few photos of our mill. I put a 3 phase, 2 HP motor on the mill but it is not overly happy running at 45 RPM full of material and steel balls, I will upgrade to a 5 HP motor. 
Notice the wood under the feet, that's to try and stop it walking around the shop. It certainly needs bolting down to the floor..! 
I also decided to put on a central loading and discharge door so we can drop material into a bin or wheel barrow.


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## scwiers (Sep 2, 2008)

hey scrapdealer, now that's a pro-looking ball mill--are those hoops solid material, or channel stock? I'd sure appreciate a play-by-play on how you built the thing.

Also, nifty way to keep the mill on track with those guides along the roller.

Man, I want to find out lot's more about your setup. Let me know how the side trap works for you. Probably, I should thing about the same, esp. for unloading. The trick, as always, will be to keep the dust down when dumping...

A++.

Cheers,

SamW


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## Shecker (Sep 2, 2008)

Have any of you tried wet grinding? For mineral sources no one does dry grinding because of the health risks of fine silicon powder. I am sure they also health risks for other fine air born powders -- such things as
ultramicrospicpneumococcosis (Meaning very fine air borne particular pneumonia). Remember these boards are just as loaded with potential biological hazards as a dollar bill.

Randy in Gunnison


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## scrapdealer (Sep 2, 2008)

Hi there Scwiers, yes the tyres are solid made of some 3" x 1" flat we had rolled. 2" angle iron pieces welded to the tyres and the mill. 
There was some 12" wide x 6mm plate from a job we had finished that was used for the actual mill. The shafts are 3" dia and we just machined them down to suit the bearings.
The tyre guides were made from some wide flanged steel tube and welded to the shafts, on a larger machine, however it would be wiser to machine them as one piece from large diameter steel. The center trap was from memory of some aluminium dross processing mills when I worked down in Malaysia a few years back. The mills were primitive but actually did the job quite well. Just get a high sided wheel barrow or bin to dump it out, keep downwind and wear a mask.
I have just been rolling some oxidized shredded aluminium in it today to clean the material up and give the mill a test run. The steel balls will be ready tomorrow so then I can really get going with the com scrap. 
I recon the mill has cost equivalent of US$ 300 to put it together including machining, rolling the tyres and labor cost. So its payback time in the next few days....! Will keep you posted how well it performs.


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## goldsilverpro (Sep 2, 2008)

From experience, I feel that, with too fast a speed, the balls will tend to slide around the perimeter of the drum, due to excess centrifugal force (grinding action), whereas, with a slower speed, they tend to drop (pounding action) from the apex. With too slow a speed, the balls drop too early, from too short a distance. The "critical speed" calculation proves this out.

Here's the formula for critical speed of a ball mill, from my copy of the "Chemical Engineer's Handbook, fifth edition, pp *8*-26.". The critical speed (as I understand it) is where, at the top of the mill, the centrifugal force equals the force on the ball due to gravity. Therefore, for any speed less than the critical speed, the balls will drop at some point, as they approach the top.

Critical RPM = 76.6/(square root of the diameter of the mill, in feet)

For dry grinding, they recommend a speed of 70 to 75% of the critical speed. This can be increased by 5%, if the mill is unbaffled.


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## scwiers (Sep 2, 2008)

OK.

10" sides, so a diameter of 20" = 1.67' 

1.67' sq rt = approx. 1.29

Plug 'n chug: 76.6/1.29 = 59.38 RPM critical.

Well, darn. All I wanted was build a nice ball mill with 10" edges turning around 60 RPM and lookie, if it don't turn out the way the numbers say it should.


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## goldsilverpro (Sep 2, 2008)

The formula is for a round mill and I've never used a hexagonal one. Neglecting material thickness, the diameter of one with 10" sides, from flat to flat, is 16". From corner to corner, it is 22". I don't know what the effective diameter, for our purposes, is. I would guess 18", for a 2" ball. For 75% of the critical speed, that would be 47 RPM @ 18" diameter. For a 17" effective diameter, it is 48 RPM. For 16", it is 50". For 19", it is 46 RPM. For 20", it is 45 RPM.


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## scwiers (Sep 2, 2008)

Goldsilverpro:
my mill--a hexagonal prism as you point out--has 'edges' of 10", so it's 20" across from vertex to vertex--just picture two equilateral triangles touching 'apex to apex'.

Faces are 2 x (sq. rt of 75) apart (base 5", hypotenuse 10")

= approx. 2 x 8.67 = approx. 17.3"

In any case, I appreciate the source from the mining book. Practically speaking, when I run it, it'll do me good to slow it down a tad--maybe loading it down more full fully will have the desired effect.

Thanks again,
Sam


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## buynselljewelry (Nov 29, 2008)

is there a write up for the processing of milled material?

thanks


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