Chemical milling, that is, reducing the particle size of powdered chemicals is part of fireworks making. No matter how find and free flowing chemicals are when you first buy then, many of them can and will turn to stone like blocks over time. And as you can read from the little lesson above, they can quickly solve otherwise intractable pyrotechnic formulation problems that you will run into over and over.
Reducing particle sizes is commonly done with thumb and forefinger, screening, blade milling, ball milling, and more exotic and expensive alternatives. Each has its pros and cons.
A blade mill is a cheap chemical grinding mill, available everywhere, and incredibly efficient and fast. They are not suited for grinding large quantities of stuff, but for a pound or less of a single chemical, they are hard to beat. They mill faster, and are quick and easy to clean up. Bigger, ball mills have a place, too. Eventually, you will want to have both.
A spinning blade-type coffee grinder is what I use. They’re cheap, and available at Walmarts everywhere in several models. My advice is to get three. One for oxidizers, one for everything else, and a backup. Look for simplicity. Higher cost is a waste of money. Cheap and simple is best. Avoid tops that are tricky to get on and off, or having locking mechanisms on them.
How to use a blade mill. Use them this way and they will last and last: Put your chemicals into the mill. Put the top on, and holding the mill in your hands, off the table, turn the mill on and off intermittently for a few seconds at a time while you shake the mill at the same time to really circulate the material around inside.
How to burn out your mill. Turn it on and leave it on for a few minutes. It’s simple and foolproof. You can reliably burn it out every time this way. The most common reason blade mills burn up is the way they are used. I have two (out of 3 purchased originally) that have been used regularly for nearly 15 years. Cost me $12 each at Walmart.
The secret is not to leave them running very long. I run mine for very short periods, 15-30 seconds max, shaking the grinder at the same time it is on. Then I shut it off, and repeat the process *IF I HAVE TO*. Which I almost never do. I don’t get much additional reduction in particle size after 30 seconds of milling.
How to grind a lot of chemicals fast: I can blade mill a pound of potassium nitrate rocks into fine fluffy powder in 5 minutes or less. Just use small batches in your mill. Be sure and shake the mill at the same time you’re milling the powder. It speeds up the process and you can actually hear the coarse particles getting smaller. Don’t try and put too much in at a time. Smaller batches mill up faster. Bigger batches bog the mill down and slow the process.
Cleaning blade mills: Dump and tap as much powder out as you can get out that way. Then use a paintbrush to get down into the mill and the top to remove the rest. Remove everything you can see. The tops can usually be run through a dishwasher, but be sure they’re completely dry before reuse. The base unit with the motor cannot be submerged, but you can certainly use a damp cloth on the inside of them.
Lifetime of a blade mill: Mills used for oxidizers will break sooner. The corrosive action of the oxidizer dust will eventually kill the little mill. Not to worry. You have a spare.
Milling fuels and oxidizers together. You can only do this once. If you survive the first attempt, you will certainly never do it again. Depending on the reactivity of the particular chemicals you’re trying to mill together, your injuries may range from bad burns to death. Never attempt to blade-mill oxidizers and fuels together.
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