Fireworks Chemical Milling – Fast

Written by Harry Gilliam

Topics: How to Make Fireworks

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.

Tell Me What You Think: Was this Article Helpful to You or Not?

Just leave a comment below. Thanks.

- Harry

16 Comments For This Post I'd Love to Hear Yours!

  1. Elmer Ray Hamlett says:

    Our gun shop doesn’t stock lead balls in fact they looked at me kinda strange when I asked for them! So I bought some fishing weights and they work fine!

  2. Jim says:

    I’ve used clear glass marbles for a milling medium for years. No sparks, no piezoelectricity, and a dollar a bag at the Dollar store. The only drawback I’ve noted is that they aren’t as fast as lead, due to the decreased weight of the balls.

    That’s my $0.02 worth.

  3. Shaggyman says:

    I have been using quarters for milling media. They seem to do a great job cascading around, and since they are cash, in the end they don’t cost anything at all.
    Does anyone see a potential for trouble with the silver and copper in some comps?

    • be careful with what you mill using silver/ copper although most money is now nickle/bronze,
      a lot of pyro comps may react to either of the copper/bronze or the nickle/silver
      plus using money that way is illegal (haha defacement of gvt property)
      so i would really look for published papers on the reactivity of the metals in your media,
      inert media is the best! ie LEAD/antimony/bismuth, in some rare instances steel for inert fuels, or ceramic

      but i may be wrong….this is just how i do things… as i was taught

  4. seems to me that if your kno3 is bricked then maybe using a burr mill type of grinder would work just to bring it down to manageable size..
    anyone try that?

  5. Jay Schaeffer says:

    I’ve had several of these mills over the years. I have never milled chemicals in them but just about everything else. I found with everyone I had that, over time, a large amount of milled material builds up inside the motor housing. It gets past the seal on the blade spindle. I have already shaken several tablespoons of milled material out of the motor housing. These mills have brush motors which always have some arcing. I’d be careful milling chemicals. I think an unplanned ignition is possible. I know someone who actually did have a fire problem using a blender. Not from the powdered chemical getting into the motor and igniting but from the friction where the spindle goes through the bottom. I just wanted to share this so anyone who uses this method can be aware of a possible safety issue.

  6. Kenkzak says:

    Last year I received a 5lb brick of KNO3. Never had this problem before and my screens and mortar & pestle quickly proved unequal to the task, so I went shopping.
    I found a relatively tiny food proccessor [yet bigger than a coffee mill] on closeout sale for $6. It got me through the job at hand but I rank it as a poor performer. It would reduce the load to about 1/3 powder, and 1/3 screenable with some effort. The remaining 1/3 went back in with the next load.
    I have a Black & Decker coffee mill, but my coffee is more important than my Salt Peter.. After reading this blogpost, another coffee mill is now on the horizon.

    Some folks I know use lead balls in thier tumblers and they mention that the oxidizers comes out looking a bit grey. I worry about the lead contamination in the smoke being breathed in????

  7. Tom Fay says:

    Most of the tips on blade milling reaffirmed my own experience and observations. My own particular mill is a bottom-of-the-line, Mr Cofee item. I don’t fill it beyond about 1/4″ from the rim, and I’ve found I do as well by sort of rolling it around when I run it as I would by shaking it. I’ll also give ie an occasional tap or two on the edge of the bench between depressions of the button. These techniques keep the load on the bearings from spiking, increasing the life of the unit.

    What I eventually want to do is not just get one for fuels & one for oxidizers, but one for Chlorates, one for Perchlorates, one for Nitrates, one for metallic fuels, and one for organics. The chances for cross contamination are just too great. All it takes is a few stray molecules getting with some other substance they don’t get along with, and you could at least burn the place down (perhaps spectacularly), or maybe wind up eating with your feet… by Braille.

    On to ball milling, I have a couple of questions about that. Right now, all I’ve got is one of those little Chinese rock tumblers with the rubber drums. Ceramic media seemed to rough up the interior of the jars a bit, but I was making a small batch of meal and didn’t have a good way at hand to see what kind of contamination I was incurring. This was 1/2″, spherical, porcelain stuff from CoorsTek mixed 50/50 by count with 5/8″ round brass, the idea being that the heavier brass stuff would exert more force on the working sufaces of the ceramic media. It worked according to theory, the unintended consequence being the above-mentioned erosion of the drum, plus the fact that the much harder ceramic permanently scarred the Hell out of the brass; no more nice & shiny. So are there any sources on mixed grinding media for ball mills, such as compatibility, contamination or simple size charts? Something like that would be mighty handy.

    My other question has to do with the use of vibratory media in ball mills. I was at Harbor Freight & saw some triangular, ceramic media about 3/4″ corner to corner, about 1/4″ thick. There were smaller and larger sizes, but all had the same basic proportions. Would using these buy me any particular advantage in performance or economy? (Not in this little machine, of course.)

    Thanks, TF.

    • HEGilliam says:

      Tom,

      First, for you and for everyone else reading your post… I have a very strong bias against ceramics for *mixed* pyro compositions.

      I am aware that there are probably “safe” ceramics and unsafe ones. I have alumina media from Coors, and their piezo electric activity in the 5 gallon mill bucket in my cement mixer looked like a blue firestorm! I have absolutely no doubt that those media would cause a batch of black powder to explode so fast it would make your head spin.

      I am aware that some ceramics do not produce piezo-electric sparks. But how do one really know, until one uses them? “They all LOOK the same–white, heavy things…hmmm, did they send me right ones?” I personally ain’t willing to be the guinea pig.

      Ceramics are fantastic for any *individual* chemical I have ever milled, from caked oxidizers to even titanium turnings. Great results.

      But if you are milling black powder or any other mixed comp, I would only recommend non-sparking lead or brass (there are other alternatives, but these are the easiest to get hold of).

      (I am sure this will provoke naysayers — I’ve been in this argument before. The argument goes like this: “well I have been using ceramics for 5 years and never had an explosion.”

      Which is kinda like “I have been driving for five years without wearing a seatbelt, and haven’t been killed, yet.” )

      All of these milling media are heavy. Their weight will make quick work of most rock tumbler motors (the cost of ball mills appears to be proportionate to their size and horsepowder–duh!)

      I dunno about them triangles. I am a simple country boy. We only had round balls when I was a pup. And bothering to mix media begins to sound complicated to my lazy, simple nature. I am lazy, and I am impatient. I just wanna do the least work to get the job done right.

      Here’s my formula for successful ball milling of excellent black powder.
      - Open ye mill jarre
      - Fill half of the jar with lead balls (.50 caliber are nice)
      - Fill 1/4 with rough mixed BP chemicals–leave 1/4 empty
      - Cap it, and turn the mill on.
      - Go do whatever I damn well please for 2-4 hours, or 8 or 10 (but 2-4 will do it).
      - Come back and retrieve finished black powder

      Works perfectly every time. I dunno about them triangle thingys–I might worry about them starting to lose their shape or something. I got enough worries. Hell, it took me 5 years to get over my phobias of the millenium bug!

      • love the .50 call ball but…..
        but i found some GREAT .78cal grapeshot for milling! (grapeshot is the size of a quarter)
        most blackpowder gun stores may have these behemoths on clearance
        used for hunting buffalo i bought 100 of these for around 15 dollars.
        these are great for cannons and for milling almost anything

  8. Left's Mixing Shed says:

    I have used coffee mills and agree that they work well, especially for small quantities. For larger quantities, a kitchen blender works equally well and you can allow it to run for a much longer time. The key is not to overfill. About 1/3 full works well. If you are really patient, you can find inexpensive blenders on sale at discount stores for surprisingly low prices. I bought two on two separate occasions for $17-$20 about four years. When using a blender, it often helps to guide the powder into the vortex using a wooden or plastic spatula. Avoid touching the spinning blades. Shaking the blender while it is working is another good trick. The different speed settings on a blender are very helpful, and it’s very easy to clean a blender. You also can buy spare parts. If you want to experiment a little, buy a cheap blender and experiment by milling some KNO3 or KClO4 at different speeds with different levels of filling. Heck – you probably can experiment using NaCl and your wife’s kitchen blender! It won’t take long for you to figure out how to do it.

  9. ron roessel says:

    Harry- I absolutely love your writing style and your articles. VERY informative and enjoyable to read. Please don’t change that style. I wait for them almost as bad as a junkie waiting for his next fix. Kinda like a pyro in mid-March…too much snow to get to the launch site and too many goodies to light. Hoping to be able to make it to the next pyro convention. Play safe. Ron.

    • HEGilliam says:

      Ron,

      The kindness of your words is exceeded only by your taste in writing! Thanks.
      Go outside and LIGHT something!

  10. Don says:

    This was needed information. I had the identical problem but thought it was my digital scale and the proportions of oxidizer and smoke powder. The cheap coffee mill is a new idea to me so off we go to get two of them. Thanks.

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