Now that I’ve got all the ingredients and bits together to start making some black powder samples, I’ll need a ball mill if I want to make decent BP. The idea of the ball mill is that it grinds the chemical powders down until they are incredibly fine which allows them to mix together much better giving a much faster burn rate than in their raw state.
The principle is simple, you have a cylindrical container which is part filled with heavy lead balls (other balls could be used as long as they are also a non-sparking material). You put your powdered chemicals into the container along with the balls, and the while on its side the container is rotated, usually by the container resting between two rollers one of which is powered by a motor. This keeps the balls moving and colliding with each other, which pulverises the chemicals.
Now, I’ve not used one of these before so I will be experimenting to find the best speed of rotation, and also how long you need to mill for to get the best results. From all the reading I’ve done you are looking at a few hours milling time to get the best results.
I purchased a geared 180rpm 12v motor from eBay, which should give high torque and have no problem rotating the container (which will be quite heavy). I will probably use a belt drive from the motor to a pulley on the end of one of the rollers. This will allow me to reduce the speed further by adjusting the pulley size, to find the optimal speed.
I also purchased s heavy duty plastic container and some lead balls. My container is relatively small (about 17cm tall by 9cm diameter), but should do the job for small quantities. My lead balls are 17mm diameter and I have 50, which takes up about a third of the container. Ideally i think I should have more than this to fill it about half way, but we’ll see how I get on.
First job now was to find a way of providing a consistent 12v DC supply to the motor. It just so happens that this same week Matt, a guy I work with, had converted an old PC power supply to a lab power supply unit, which takes advantage of the existing 3.3, 5 and 12v supplies generated. Inspired by this, I decided to harness the 12v supply from a PC PSU as my power supply, which would not only be reliable but also came in a handy enclosure. Unfortunately I didn’t see Matt’s article about it until afterwards, but I had found this useful website article which detailed the PSU circuit basics.
After ripping the PSU from an old PC in my loft, I realised it didn’t have a power switch, which would be required to easily start and stop the ball mill. So I set about adding one that I had lying around. It fitted perfectly in the hole where all the old power cables came out of, and as I would only now need a single pair of cables coming out, I mounted in there with an improvised plastic plate and some screws. Following the wiring details from the article mentioned, I removed all but the cables I would need, soldered in a link on the circuit board that ensured the power remained on after pressing the power button, and generally cannibalised the innards.
I took an old cable exit grommet/sleeve from a pair of defunct hair clippers and attached this to the PSU, so that the 12v power cables could exit the unit through one of the air grilles without chaffing of damaging them. Then I rewired one of the male and female power supply connectors from inside the PC, so that the motor could be attached and detached from the PSU at will. This means I may be able to use the same PSU in fitire for other projects that require a similar supply (maybe a star roller next!).
The next step will be to build the rollers and pulley system to actually do the work, so I’m just trying to get my hands on some roller bearings and suitable materials.