Grinding course materials to smaller size (without powdering)?

[Extrarius]

For some of the formulations I'm working with for impact initiation, I need a course, hard material to (according to common theory) help with the creation of "hot spots" within the mixture in order to aid ignition.

 

For example, ground glass is often mentioned as one such material. I'd like to make my own, but I'm not sure how to do so effectively - I'd like to create an end product that has rather homogeneous particle sizing, but I want the particles to be rather large (compared to common milled materials in the 0-100μm range) . For this reason, standard ball milling doesn't seem appropriate, but nothing else comes to mind.

 

Glass isn't the only material I'd like to process this way - there are several porous materials that I'd like to reduce in size without eliminating the pores (ex expanded perlite, activated carbon, silica gel, lava rock, etc).

 

Is there an easy way to accomplish this?

[schroedinger]

Do i understand sou right, you wan't to mill some materials, but just to a quite coarse materials size?

 

If yes, you are propably best of with short millihg times and sizing screens, or better with a mill that sizes itself.

The two easiest self sizing mills will be stamp and ball mills.

 

Don'T know about your area, but maybe have a look at ebay as stamp mills can often be gotten quite cheap of farmers. And there are also cheap new modells.

 

A ball mill for your purpose wan'ts to have large media. Propably using a ceramic media, as these a lightweight. And need's a sizing opening. Have a look at industrial ball mills to understand twe way how they work.

 

Alternative you could work witch batch processes and screens. This could be done with nearly every type of mill, ranging from mortar and pestle, over blender type mills to ball mills. Just blend for a short time and then size. For glass and a blender type mill maybe try milling it under water

[Arthur]

Ball milling probably IS the best method, it produces a mix of particle sizes from which you can sieve the cut you want, just don't mill for too long or it will all be fines.

 

Rod mills make a narrower range of sizes but are harder to operate and a rod crash means new rods.

[Col]

Apart from the lava rock all the other items (expanded perlite, activated carbon, silica gel etc) could be reduced in a old food processor. It best to use a low speed and the pulse function until it breaks down a bit.

Edited February 13, 2014 by Col

[Extrarius]

I've considered trying to line my ball mill with several layers of screen, with all but the innermost a very large size (and the innermost the size I'm targeting), so that as it mills, the "right" sized particles could fall to the outside of the mill where they (theoretically) won't be milled any more. I don't yet have a proper ball mill (I bought the book and a 3/4 hp motor, but haven't yet had time to assemble anything), but I can try this in my horribly inefficient "made from what I had" ball mill (5 gal bucket directly mounted to a 5 rpm motor, and I use the 5 gal bucket as the 'driving bar' by putting milling jars inside it).

 

Another thing I've been thinking about is building a "screw-type" mill. Not sure of the correct name, but I'm thinking about the old mechanical pencil sharpeners with two 'screws' moving around the tip to shave it down. Moving the screws relative to each other should allow reasonable size selection, I'd think. Any idea on where I might find a 'grinding screw' like that (aside from taking apart a mechanical pencil sharpener)?

[shouldnoteatindat]

is this thing that you are trying to mill down flammable by itself? if its not i suspect there is some sort of a kitchen prodect that would work for say grinding dry corn or something like that.

 

http://www.ebay.com/itm/Premium-Cast-Iron-Victoria-Corn-Grinder-For-Wheat-Grains-or-Use-As-A-Nut-Mill-/161218428452

[Mumbles]

What sizes of material are you looking into? This will take some of the fun out of it, but you can buy fairly accurately sized sand for a variety of purposes that might work.

 

As far as mechanically reducing particle size relatively accurately, a hammer mill or jet mill are probably your best bet. They often come with sizing screens, so the material you want passes out before being ground too much. I don't think of ball mills as being all that selective in size. Hammer and Jet mills are not exactly what I'd consider OTC though. There are cheap mills on Ebay from time to time.

 

The other thing you might want to consider if you want a little coarser material, is something like a grain mill. There are a few different types, but they all generally work by crushing the grain between rollers or spinning plates or something like that. The one I'm thinking of has two rollers with a rough surface that pulls the material between the rollers and crushes them as it passes. You can do multiple passes with successively closer distances between the rollers to get it finer with better control and throughput. There are smaller versions sold for grinding coffee, commonly called burr type mills.

[Extrarius]

I'm not sure on exactly what sizes I'll need, but for the ground glass, at least, I'm thinking probably a little larger than "regular" sand particles. I have several types of sand (course pool filter sand, regular play sand, fine paving sand, plus pure silica that is around 400 mesh), but even the coursest is a little smaller than I think I'll need. Actually, after drying some silica gel litter for use as desiccant, I think it'll serve the purpose well because it is very rough, hard, probably piezoelectric (I'm guessing they don't waste the energy to turn it into amorphous silica). It might be a problem that it is a desiccant (hygroscopic by definition), but I figure I can find something else to fill the pores with that won't interfere with combustion (maybe even dissolve a fuel and/or oxidizer in a water, soak it, evaporate the water, and then dip in a liquid fuel or oxidizer).

 

Thank you shouldnoteatindat and Mubles for the idea of a grain mill. I've looked into burr mill coffee grinders before, which I don't think would suit this purpose at all, but a burr mill for grain looks like it'd work perfectly!