If one does not have a ball mill there is another option for grinding coarse potassium nitrate into a free flowing, fine powder. Coffee and spice grinders work well for grinding small batches of individual chemicals.
Even though I have a ball mill, there are times when the coffee grinders come in handy for pulverizing smaller batches of chemicals. I have some Parlon, most of which will pass through a 40-mesh screen, but which has some larger particles as well. I’ll take those larger bits and run them through the coffee grinder in order to reduce them to smaller particles.
Warning: Dedicate one grinder for use on oxidizers, and another one for use on fuels such as charcoal. We don’t want fires or explosions when we’re grinding chemicals. Never grind complete or mixed compositions such as black powder in a coffee grinder.
I have found two kinds of coffee grinders: blade-grinders and burr-mills. Don’t get a burr-mill; they don’t work as well as blade-grinders. The blade-grinders have a stainless steel blender type blade that spins at high speeds in the bottom of the material cup, chopping the material into small bits in the process.
I have purchased many of the smaller, less expensive, blade-type coffee grinders. But here’s the warning: they really don’t last too long if you mill chemicals for a minute or two at a time. To use them, mill your chemicals in pulses of a few seconds at a time. I’ve found that shaking them while pulse-grinding gives me the fastest results.
The Kitchenaid blade mill has a larger hopper, and a larger, more powerful motor, and is rated to be used often. I’m hoping that it will last longer than the $13 WalMart models I’ve been using.
I put a half-cup, 4.6 ounces, of 12-mesh potassium nitrate into its hopper, pressed down on its lid to start it, and pulse-milled the powder for just under a minute, shaking the grinder now and then in the process.
Quite a bit of fine powder started to accumulate on the inside top of the clear lid as it milled. I dumped the ground chemical onto my 100-mesh screen, and used a fine paint brush to clean off any that was clinging to the inside of the hopper or the lid.
About three-fourths of this milled powder would pass through the 100 mesh screen, and I set aside that which wouldn’t to be ground again with the next batch.
Granular potassium nitrate can be dried if necessary, and ground easily with a ball mill or with a coffee blade mill, so that it passes through a 100-mesh screen and is ready to be used in pyrotechnic compositions.