grinding chemicals

[CrashLanding]

Hi,

 

I understand I should pass most of my pyrotechnic ingredients through a 100 mesh screen before mixing. I then mix by passing the composition through a 40 mesh screen. I don't pass airfloat charcoal or metal through a screen, I diaper mix it later. Most ingredients don't need to be ground first. But some do. These include potassium nitrate and parlon. The problem I am having is mostly with these two chemicals, but today I found another, barium carbonate. Red Gum seems to pass at first and then fails to pass as if some of it is not as well ground. Some of these ingredients seem to clog a 100 mesh screen because I quickly get to the point that I can't get any more to pass through the screen, but using a fresh 100 mesh screen allows some more to pass. I have already burned out a Hamilton beach coffee grinder grinding PN. Parlon especially seems never to get small enough to pass through the 100 mesh screen no matter how long I grind. With PN and Parlon I need a large amount but can only grind a small amount at a time because of the size of the mill, and because overfilling the mill seems to prevent grinding. So I got a ball mill with ceramic media. I grind for 8 hours and the parlon especially still seems never to go through the screen. I am spending far too much time grinding these few ingredients. Tonight for example I tried to pass barium carbonate through a 100 mesh screen. I needed 67 grams. This stuff seems to be an incredibly find powder. Yet it doesn't want to pass through the screen. I tried grinding some with a coffee grinder, but it didn't seem to help. I spent about 90 minutes and got only 41 grams. My question is this. Is there an easier way to grind these chemicals ? Do I need to pass them all through a 100 mesh screen ? Is there a document I can read which lists these ingredients and tells me how best to grind them, and if I need to pass them through a 100 mesh screen ?

Edited May 18, 2017 by CrashLanding

[lloyd]

Crash,

In commercial production, we never use anything finer than 60-mesh, and only that for 'pre-screening' chemicals before mixing. All our mixing is done with 40-mesh or 20-mesh.

 

Except for parlon, which always has coarse particles in it, all our other chemicals are obtained as fine powders. Pre-screening before mixing is done primarily to sort out the occasional 'rock' (foreign materials) and to break up any lumps that may have formed.

 

I don't understand why you're not running air float through your screens. Even the best charcoal may contain a large particle or two. Diapering charcoal makes no sense at all. (???) It's as safe to screen as any chemical you possess.

 

Lloyd

[CrashLanding]

Hi Lloyd,

 

Thank you for your quick reply. I was not very clear about airfloat charcoal. I have not been putting it through a 100 mesh screen because it is already finer than that and never seems to have lumps. The only thing I seem to accomplish is getting a 100 mesh screen dirty. It is the metals I do not put through screens at all because I have heard they can become stuck in a screen. Also, most, like 400 micron flake aluminum for example, are already finer than the 100 mesh screen and never have lumps. The way I have been mixing is this. First I have been putting everything except charcoal and metals through a 100 mesh screen. Then I pour the ingredients onto a piece of craft paper (except metals) in long parallel lines and I then diaper mix it briefly to start the mixing process. Then I put it all through a 40 mesh screen 4 to 5 times to mix it. Then I add the metal(s) if any and diaper mix them in.

[lloyd]

Crash,

If you're using screens larger than the particle sizes to mix the comp, and you're NOT actually "classifying" metals, you won't have any real problem with metals sticking. Diaper the whole mess together, then screen.

 

Commercially, we even do this with flash powder -- but I wouldn't recommend to most amateurs to screen flash. For star comps, it's efficient, and safe-enough to not be an issue (so long as you don't attempt to scrape materials through the screen).

 

Lloyd

[Mumbles]

Since you're grinding the nitrate, I think the nitrate may be benefiting from passing through the 100 mesh screen, but you might be wasting your time with everything else. I will second Lloyd's recommendation of a 60 mesh, if you happen to have one. Personally I give my compositions a pass through a 60 mesh screen after an initial mixing and just discard anything coarser than that, replacing if necessary. For a colored star, the coarse material was almost exclusively material from parlon and red gum. The parlon I'd save for people who did acetone binding of stars. The red gum material was often not actually entirely red gum. It was pieces of bark, sand, dirt, etc. that I wouldn't want in my composition anyway. The stars burn just fine if you leave that stuff in there, but can be more ashy, and leave an incandescent tail in the case of parlon. 60 mesh seemed to be about the cut off between behaving this way and not, but finer wont hurt anything except for your yield. It has the added benefit of mixing the comp pretty well while doing the removal. When you get used to it, you know about how much you're going to lose from every batch. I don't remember the exact amounts anymore, but I feel like parlon was around 8-10% and red gum was probably 4-6%.

 

Some materials don't like to go through screens as easily on their own, as when they're mixed into a comp. This is why I screen post-mixing. I think this might be the issue you're having with the barium carbonate. All the BaCO3 I've ever encountered has been a very fine powder. I've heard of some coarse Strontium carbonate on the market, but never encountered it personally.

 

Apparently people have had success in reducing the parlon size by milling. The mentions I was able to quickly just fine mostly are using stainless steel. That's not to say other media wont work, just giving all the information. I suspect they're also using larger, 1 gallon sized jars.

[CrashLanding]

Thank you for the information. It is very helpful. The barium carbonate was the strangest stuff I tried to pass through a 100 mesh screen. It looks so fine, like baby powder, but doesn't want to pass. I am tempted to look with a microscope to see what is actually happening. Since asking this question I have put barium carbonate, red gum and parlon through a 60 mesh screen and it is making life a lot easier. I think the finest moment in mixing a comp is passing it through the 40 mesh screen because it glides through it so easily, and the mixing is so effective.

[braddsn]

Im betting your barium carbonate has the slightest amount of moisture, and its simply clogging the screen. All the barium carb i have ever seen is at least - 325. No reason to ever screen it.

[CrashLanding]

I had thought it could be moisture in the barium carbonate that was making it resist the screen. Is that a problem ?

 

I should mention that I think an incandescent tail sounds like a good thing.

[lloyd]

Crash, it can be moisture, but even scrupulously-dried barium carbonate tends to 'blind' screens. (FWIW, 'blinding' is the industry's term for clogging up a screen.) Some chemicals just beg to be mixed with other constituents before they'll screen well.

 

When I read 'incandescent tail', I read "unwanted sparks, insufficient to make a full, rich tail". That's an interpretation based on my having seen a lot of stars that shed some few sparks they weren't supposed to shed.

 

Brad, without regard to its form 'out of the barrel', in commercial production, everything gets re-screened at mixing time; everything. As a rule, every 'fireworks grade' chemical will have a few lumps here and there, a few particles out of size-range, and often a few pieces of extraneous matter.

 

Screening eliminates all those defects, and delivers a much better-incorporated mixture than any other method.

 

Lloyd

[MadMat]

It seems to me that there might be some dangers to grinding prilled ammonium nitrate. I was just given some (thanks Chuck!) and want to try it out for rockets. I've found a few formulas utilizing ammonium nitrate and would like to get this stuff to at least 40 mesh. Any suggestions?

[lloyd]

Mat,

There's not much danger in milling AP and AN. But ALL ball milling should be done behind a suitable barricade, such that, if an explosion were to occur, nothing would be damaged (nor people hurt) except for the mill, itself.

 

Lloyd

Edited May 22, 2017 by lloyd

[MadMat]

So, I'm correct in assuming that grinding AN in a blender is a bad idea?

[lloyd]

I responded to this by PM, too. I don't have enough experience grinding AN to know, for sure.

 

I DO use it in some special low-smoke stage effects, but I've never had an accident with it (in a ball mill).

 

ANY substance that has the potential to explode should be milled (ground, whatever) behind a suitable barricade.

 

Lloyd

[braddsn]

Ok Lloyd, I think I see what you are saying... so commercially you guys screen everything before ever using it? For me, I don't screen any chemicals separately. When I get new chems, they go in airtight containers until they are ready to use, then I simply mix my comp (be it red, green, TT, etc) in a big mixing bowl. Once it's mixed very well, I dump it all onto a large (24x24) 40 mesh screen, and screen mix it all together. I know some fellas screen their chems individually to remove the unwanted trash, but I just don't have time for it usually. That stuff usually ends up sitting on top of the screen when I mix the final comp. Funny side note... when I started doing pyro, I did all kinds of experimenting. One of the first things I did was make some stars from comp that I had just mixed in a bowl, because I hadn't invested in screens yet. The burn time on stars that were bowl-mixed as opposed to screen-mixed was pretty drastic. The bowl-mixed stars burned much slower, and of course not nearly as pretty.

[lloyd]

Well, Brad, "almost".

 

There are some substances (like the barium carbonate we've been discussing) that just don't screen well by themselves. So very often, we'll mix a couple-three fuels, and screen them together, just to make the screening process go more easily.

 

With some things like red gum, we'll always screen it separately. In the case of red gum, it's because the stuff comes full of trash, bugs, large particles, bark, etc.

 

Lloyd

[DesertCatUSN]

I have some ammonium nitrate that is caked up hard (somehow moisture snuck in the sealed container). Do I just:

 

a). grind it up to get the right size for mixes again, but then it has a high moisture content still,

. use hot air or gently "bake" to get the moisture out,

c). put it under vacuum and possibly the water could boil off,

d). use some dehydrating agent like drierite on it or,

e). none of the above - please provide safe alternative

 

I also have some other chemicals that have the same problem, and obviously the chemical type is key to what you can do, but is there a general procedure for getting rid of moisture once it contaminates a chemical, that is safe and efficient.

 

Appreciate some wise guidance. Cheers, Roger

[lloyd]

First, DO break it up into no larger chunks than 1/4". Then you can gently bake it dry IF it got wet.

 

However, some oxidizers (and AN is one of them) tend to slowly re-crystallize and agglomerate even if kept dry. This may be all that has happened.

 

To assure yourself of that, powder some fairly fine (say 40-mesh). Take a carefully measured 100g of it to a drying oven at not more than 175F for about 8 hours. While it's still hot, weigh it again. If you've lost any significant amount of moisture, you'll see it in the differences.

 

Because I don't wish to expose something as hygroscopic as AN to the atmosphere when I'm doing such an exercise, I do the following:

 

I have a stainless steel bowl with a pyrex glass cover I use for such experiments (a SS cover would work, too). I accurately weigh the clean bowl and lid before beginning, and record that. I tare the scale with the bowl on it, and accurately weigh 100g of the suspected-wet material into the bowl. Then I proceed with drying.

 

Of course, my scale won't remember the tare-weight of the bowl and lid after 8 hours, but I have it recorded. When I come back after drying, I expect to see the tare weight of the bowl and lid PLUS 100 grams, and minus any lost water.

 

It takes longer to describe than to do!

 

Lloyd

[DesertCatUSN]

Thanks Lloyd! Great stuff as always. I didn't know about the recrystallization. I'm pretty sure that's what happened because it's a sealed container from the supplier - unopened. I take it that means I can just pulverize it gently to the size I need? Thanks again.

Roger