Ball mill

[loris94]

Hi! Since I decided to scale up my production I decided my ball Miller is too little (double 3lb from purocreation) so I'm making a new one.

For the structure there will be no problem since I have a Smith friend that will make a nice solid Tig welded steel structure.

The ball Mill will operate with 3 Jar (30cm id 32cm height) and the distance between the two bars will be adjustable between 15 and 25 cm to avoid any "jump" of the jar with the traction bar about 5 cm lower in height from the free bar.

So what I need to know is what are the average rpm needed (of the jar) and the motor power (I thought 0.5 hp will do).

 

Thank you very much

[loris94]

Oh I forgot media will be 2cm diameter ceramic.

[MrB]

30cm jars? i think thats 52+ rpm. 80+ rpm and it stops tumbling down.

B!

[BurritoBandito]

Here's a note that I've had stored on my phone for some time now.

 

Critical Speed = 265.45 / sqrt(Jar ID - Media Diameter)

Optimal Speed = .65 * Critical Speed

 

Both the ID and diameter of media are specified in inches.

The speeds are measured in RPM.

 

Source: Mumbles @

http://www.amateurpyro.com/forums/topic/6424-ball-mill-what-distance-between-rods/?do=findComment&comment=83049

 

Edit: I just did the math, and my answer matched the one provided by MrB. 52 RPM is optimal for your mill/media.

Edited August 30, 2014 by BurritoBandito

[MrB]

Is there a version of this formula that works with the metric system?

Just for us outside of the us i mean...

B!

[BurritoBandito]

Well, there's 2.54 cm per inch so I think it would just be:

 

Critical Speed = 265.45 / sqrt((Jar ID - Media Diameter)/2.54)

Optimal Speed = .65 * Critical Speed

 

Unless I'm missing something?

[MrB]

I dunno. Using those numbers, (ignoring media size) i come up with critical speed of 77.2, and 50.2 for optimal. While "close" it's off from what it "should" be, and i'm not sure where my math is leading me wrong. but then i was never good with #roots.

If i had an office suit installed, i'd set up an excel thingy to do the work for me... Well, anyway, it gets me in to the approximation territory. 7:20 in the morning without sleep, thats close enough.

B!

[BurritoBandito]

This is what my calculator turns up

265.45/sqrt((30-2)/2.54)*.65 = 51.967751792363

 

Edit: I could write you a ball mill calculator script if you'd like?

 

J=inputbox("Enter jar inner diameter in centimeters")

M=inputbox("Enter media diameter in centimeters")

Msgbox 265.45/((J-M)/2.54)^(1/2)*.65 & " RPM"

 

Copy the above into notepad and save as "Ball Mill.vbs". Make sure to save it as a vbs file and not a txt file.

Edited August 31, 2014 by BurritoBandito

[MrB]

Ok, that was to easy. Way to easy. Cool. Saved for the future.

 

Is there by any chance a formula for determining media size?

I know that in reality optimal media size is a constantly changing size, getting smaller as the load particle size is shrinking. I think i read about the relationship somewhere, and it's something on the order of 20:1, making our lead balls way over the top for the end of the milling process, but quite a lot to small when the process starts out with charcoal, for example.

It would be interesting to know whats "right" for any given jar.

 

B!

[BurritoBandito]

Yes, there is a formula which is contingent on the particle size of the substance being milled, but it is impractical IMO to use due to the changing particle size. According to Lloyd, 1/2" to 1" diameter media is ideal for most of the grinding we do, and the more important factor is the weight of the media. As I understand it, within the boundaries of safe materials, the heavier the better. Assuming you already have the mill and jar, you could manipulate the equation above to solve for the media diameter based off your known jar ID and RPM.

[loris94]

Thank you very much guys!

[BurritoBandito]

I got bored so I decided to rearrange the equation to solve for METRIC media diameter.

Media Diameter=-(75618.1-Jar ID*RPM^2)/RPM^2

Bear in mind that the criteria provided by Lloyd stated in my last post (weight is more important than size, and ideally were generally shooting for something between 1.27 to 2.54 cm [1/2" to 1"])