18 replies to this topic

[Potassium chlorate]

I have 6 kilos of brass "pellets" for milling between 1 and 1½ kilo of composition. This seems very sufficient for making BP.

Are there any equations for this? I know that there are for the volume of the jar vs the volume of the milling media and composition, but the mass?

[BrightStar]

Are there any equations for this? I know that there are for the volume of the jar vs the volume of the milling media and composition, but the mass?

Probably not... As I understand it, the volumetric guidelines are based on the mechanical action of the media and composition in the mill. The idea is create a continuous flowing wave in the barrel, rising to about 2/3s of the ID in height for the optimum milling effect. This action is only slightly dependent on the mass of the components, much more on the fill level and mill speed.

If you're milling barium nitrate, you can use a charge 50% greater in mass than if grinding potassium nitrate due to it's higher density. Milling charcoal, much less.

[Arthur Brown]

IMO the drum should be 1/2 to 2/3 full of media then you fill the interstices with ingredients. so Just cover the balls, However that's purely volumetric, makes no concern for the density of the powder or it's particle size which affects it's bulk density when mixed with media. This also infers that the media is spherical and not cylindrical.

Also these estimations make no concern for the density of the media from lightweight ceramic through steel & brass to lead.

With ingredients the bulk density varies hugely, for example charcoal: BBQ lumpwood makes a dense charcoal while willow, pine etc make a much frothier charcoal with very low density.

IMO the mill and various ingredients are too complex an operation to have accurate figures easily.

[digger]

There are empirical equations for milling in Perry's chemical engineers handbook. I will see if I can dig em out next week.

[Potassium chlorate]

There are empirical equations for milling in Perry's chemical engineers handbook. I will see if I can dig em out next week.

That would be very nice of you.

[Mumbles]

Something could probably be derived to determine optimal media and optimal composition load (assuming BP) from the jar volume. There isn't a correlation between media mass and composition, as has already been pointed out, density matters greatly. There is a factor of three difference between the lightest ceramic and lead. Now, I'd never use that kind of ceramic for BP, but the high alumina stuff that is suitable still requires about 2.5x less than lead by mass despite occupying the same volume.

[Potassium chlorate]

The 6 kilos of brass pellets have a density of about 6 g/cm^3. They fill up a 1 litre plastic box very well.

[dr thrust]

what are brass pellets?, shape?, size these are important factors as well, i use 12mm brass round bar 15mm-20mm long

Edited by chris m, 23 May 2010 - 01:42 PM.

[Potassium chlorate]

what are brass pellets?, shape?, size these are important factors as well, i use 12mm brass round bar 15mm-20mm long

The Swedish word for it would be "kutsar". I didn't find that word in English, so I called it "pellets". A "kuts" is a massive cylinder with (at least the ideal one) the same length as diameter.

But OK, " round bars" it is. Mine are about the same size as yours, maybe a little bigger in diameter. Can check that later.

Edited by Pyroswede, 23 May 2010 - 01:57 PM.

[dr thrust]

talking about round bar, i did reading a description of a "bar mill" where the media was indeed a collection of round bars just under the length of the milling jar i wonder how effective these are?

[Potassium chlorate]

talking about round bar, i did reading a description of a "bar mill" where the media was indeed a collection of round bars just under the length of the milling jar i wonder how effective these are?

Probably pretty effective. In the old gun powder factories, they didn't use ball mills at all first. They used very large massive drums crushing the particles over and over again.

Edited by Pyroswede, 23 May 2010 - 02:37 PM.

[BrightStar]

Probably pretty effective. In the old gun powder factories, they didn't use ball mills at all first. They used very large massive drums crushing the particles over and over again.

In simple terms, media that provides a relatively larger contact area such as cylindrical ceramic or bar stock generally mills faster for 'rough grinding'. For the finest particle size spherical media prevails, as the smaller contact area and higher contact pressure will ultimately grind finer.

There's some indication that small ball mills may never produce optimal BP though. In milling BP, we are not only grinding but 'incorporating' the ingredients and the heavy granite wheel mills of old proved excellent at this.

Edited by BrightStar, 23 May 2010 - 02:50 PM.

[dr thrust]

i see , thanx for the speedy reply!
ill pick up some round stock, and try it just out of interest, sounds an issue so it may be a "quiet option"?

[Arthur Brown]

The quiet option often includes the use of a rubber mill jar!

I suspect that there will be methods and details that create different mesh cut ratios of product after different times, and I suspect that if we were trying to make a living at pyro we'd need to study this for electricity economy.

Rods go faster to medium mesh but balls go to finer ultimate sizes, etc......

However in real pyro hobby life we don't have enough choice of mill jars, media material size and shape etc to make a valid study of milling efficiencies under different conditions.

[Potassium chlorate]

I checked my "kutsar" now, and they're 15 mm in diameter and between 10 and 20 mm in length, although most of them are 15 mm long, that is "real" "kutsar".