Still having issues with BP clumping in mill

[deepdixie]

Fellow pyro's,

 

I am having a difficult time milling my BP. I have read nearly every thread on APC dedicated to the topic, and still can't figure out why I am having issues with my powder clumping inside the mill.

 

I have to stop the mill about once an hour to run the powder through a 40 mesh screen to declump it. After milling for 5-6 hours, I wet granulate my BP. The end product is adequate for my needs, but probably would be even hotter if not for the clumping in the mill, and it sure is a nuisance having to stop the mill at least five time to declump during a mill run.

 

My chemicals are pure and dry. I store multiple dessicant packs in each chemical storage container. I only mill during periods of cooler temperatures when the humidity is relatively low. I make 180 gram batches in each jar, and add 3.5% Dextrin only prior to the last 30 minutes of milling time. Some say that clumping is a sign that the powder is adequately milled, but I am seeing clumping after only 1 hour of milling time.

 

Here is the mill I am currently using. The base and rollers are a Thumler's Tumbler, Model AR-12. I decided against using the 15 lb. jar that came with it and instead have been using two 6 lb. jars. The jars are filled half full with antimony hardened lead balls. I purchased an aftermarket 1/30hp. 3000rpm High Speed motor and installed it. She turns at 75 rpm now, which I believe to be optimal, after all the research I have done on the subject. The mill jars feel warm to the touch when I stop the mill, as they are positioned relatively close to the motor. Could this heat be a cause for the clumping?

 

I'm sorry if this is a worn out, tired topic for many of you who are far more experienced than myself. I thought I would have the milling process perfected by now, but it seems this is not so.

 

 

Edited February 4, 2016 by deepdixie

[lloyd]

My chemicals are pure and dry. I store multiple dessicant packs in each chemical storage container. I only mill during periods of cooler temperatures when the humidity is relatively low. I make 180 gram batches in each jar, and add 3.5% Dextrin only prior to the last 30 minutes of milling time. Some say that clumping is a sign that the powder is adequately milled, but I am seeing clumping after only 1 hour of milling time.

----------------

I must argue against your premise that the chemicals are (actually) dry. Having dessicant packs in a container is no guarantee of dryness. First, those packs may be water-saturated and require re-charging. You did not describe how you ensured that THEY were operating properly.

 

Second, there may be so much moisture in your nitrate and charcoal so that the dessicants cannot cope with it, even if they were properly charged before use.

 

The only way to ensure your chemicals are dry is to oven-roast them (and the dessicants) long enough to drive off all moisture except for the waters of crystallization. The charcoal actually seems to exacerbate the problem more than the nitrate, but both must be scrupulously dry. It takes more time and effort to dry materials than it seems it should, and gas ovens take MUCH longer to accomplish it than do electrics, because of the water product of combustion from gas.

 

You cannot accomplish proper drying except by performing repetitive weighing experiments during the process. When the weight does not diminish by even a tiny fraction of a percent over a few hours' of heating, THEN the materials are dry. Diminishment of weight is the classical method for determining when a chemical is properly dried.

 

I have 'been at this for a while' ("wrote the book", as it were, on milling! <G>_), and I can say almost unequivocally that moisture is your problem.

 

LLoyd

Edited February 4, 2016 by lloyd

[deepdixie]

Thanks Mr. Lloyd!

 

I have read your book. I benefitted from it greatly, and appreciate your vast contributions to the field of pyrotechnics. I was hoping that you would reply.

 

I use Crystal Cat Litter (Silica Gel) wrapped in coffee filters as my makeshift Dessicant packs. Every six months or so I discard the currently used packs and replace them with new packs. Perhaps in this climate here in the Deep South 6 months may even be a bit of a stretch for the non-stop use of Dessicant packs, in an outdoor storage building. I have been considering re-activating the packs every three months or so in the oven, for say 24 hours at 220 degrees. Perhaps this may help some with moisture issues.

 

I buy all my chemicals commercially prepared and wrapped in air tight containers. I'm sure this is no guarantee of their actual dryness. There is no telling what they were exposed to prior to being packaged for sale. I have never oven dried or tested any individual chemicals prior to milling to test for moisture. After reading your reply, it would make sense that the chemicals may indeed contain some moisture which may be causing my milling problems. I may very well have to start oven drying the chemicals prior to placement in the ball mill. I appreciate your input. It makes sense that slight amounts of moisture in my chems could be the problem. Your advice is noted and I will bear this is mind when weighing/preparing chemicals for the next mill run.

 

DeepDixie

Edited February 4, 2016 by deepdixie

[lloyd]

I use Crystal Cat Litter (Silica Gel) wrapped in coffee filters as my makeshift Dessicant packs

-------------

Hmmm... there's no particular evidence that the silica gel in cat litter is properly 'charged' to begin with. Silica gel can absorb liquid water FAR above its ability to absorb vapor from the air.

 

I think the strategy of thoroughly drying the chemicals before milling (or even storage) and also charging the silica gel will probably pay dividends.

 

Lloyd

[deepdixie]

Would it be best to oven charge my newly made fresh from the store Cat Litter Silica packs before placement in my pyro containers?

 

I'll take your advice and oven dry my BP chems from now on before milling, given the issues I have been having. I reckon I could settle for mediocre BP, as I have now (even w/ using Willow Charcoal), or I could have some super hot BP by adequately drying the chems before milling.

Edited February 4, 2016 by deepdixie

[lloyd]

Would it be best to oven charge my newly made fresh from the store Cat Litter Silica packs before placement in my pyro containers?

-----------

Absolutely. You don't know how 'charged' the silica gel was before it was packaged (in paper bags, maybe?). You don't know how long it sat in outdoor warehousing, or on store shelves. It could be wet.

 

Silica gel is only an effective dehumidifier when freshly 'charged'. It's purpose as cat litter is to absorb LIQUID water, which is not the same as absorbing humidity in the gaseous form.

 

Lloyd

[deepdixie]

Thanks.

 

I will charge my brand new homemade packs of Silica in the oven from now on before use. I will also oven dry my BP chems individually before Milling. After reading your above replies, and considering that my mill is optimized, moisture in the chems could be the only cause to the maladies afflicting my BP milling process. The storage of chems in hot, humid Deep South is proving rather tricky.

[lloyd]

I don't recall if there's an indicator in that cat litter gel. In dedicated dessicant gels, there is usually a color indicator that is brightly one color when fully re-charged, and a dingy and dull color when moisture has been absorbed.

 

In any case, a couple of hours in a shallow tray at 220F in a DRY oven will desiccate it well. If you have the choice, transfer it while still hot to an airtight metal container, so 1) the atmosphere won't begin to use it, and 2) the heat of the material won't damage the container. Lidded paint cans work well for this sort of work, and you _can_ cook it in them, too, but it will take longer, if not layered thinly while baking.

 

One last thing Dixie (from a southern boy, m'self)... Ned Gorski has decided that about a couple of hours' milling in an optimized mill is about as good as it gets. That wasn't my finding when I was preparing the book, and I think it depends very much on the diameter of the jar (because longer falls result in more energetic milling).

 

But Ned's a very sharp guy (and a PGI Grand Master). If he says it works, then I believe him.

 

Lloyd

Edited February 5, 2016 by lloyd

[deepdixie]

I couldn't afford stocking up on the made-for-the purpose high dollar Dessicant packs, given all the uses I have for them. So I did the research and settled for the homemade packs made with Cat Litter. I will make sure that they are adequately dried before any future use with the storage of chems, finished BP, Stars, etc.

[Mumbles]

Have you thought about getting some of silica with the indicator, and mixing it in with what you have? It doesn't have to all indicate to be able to tell. I was just doing a quick check on Amazon, and you can get a quart of indicating silica gel for about $12-15. You can cut this down to probably 10-20% indicator.

 

This is really common in all the chem labs I've worked in. We use calcium sulfate (drierite) for most common tasks. It's actually easier to tell when the desiccant is spent when it's sitting against a background of white non-indicating material.

[Arthur]

Sometimes doing pyro safely requires that you spend the money on tools and preparation. Somewhere to dry ingredients, something to dessicate ingredients seem like good start points.

 

Dessicant like silica gel has a finite capacity before it is full of water, then it may be dried itself, in an oven, and reused. As Mumbles says indicating silica gel changes colour as it absorbs water and says clearly when it needs regenerating. Don't assume that all youtube instructions are correct cat litter likely isn't all silica gel.

 

Silica Gel takes time to remove moisture from other goods, and again takes time in an oven to lose that water to the atmosphere.

Edited February 5, 2016 by Arthur

[deepdixie]

Great idea Mumbles! I just purchased a quart of the Indicating Silica Gel Beads. I will mix these in at a rate of 10-20% with the Crystal Cat Litter in my makeshift coffee filter and twist tie dessicant packs.

[FloridaCracker]

You can get silica gel that contains an indicator that is used for drying flowers and available at Hobby Lobby and similar craft stores. I believe it comes in 5 lb bags and around $12. And hobby lobby has a 40% off one item coupon that is always on their website which makes it a lot cheaper.

 

There wouldn't be tons of indicator if you mixed it but in my experience the indicator change at about the same rate which should mean all the silica gel has about the same moisture content so as long as there are a few indicators throughout you should know when it needs to be changed and dried out.

 

Also, there are definitely some cat litters that are all silica gel and it seems like I remember seeing one that already had an indicator or at least had some beads that were dyed for a splash of color for the consumer that is wowed by bright colors.

[deepdixie]

 

 

 

I have 'been at this for a while' ("wrote the book", as it were, on milling! <G>_), and I can say almost unequivocally that moisture is your problem.

 

LLoyd

 

 

 

 

 

 

I oven dried both my Charcoal and my Nitrate for about 3 hours each at 200 degrees. This morning I loaded up the mill, and after three hours milling time, I checked the powder. There was absolutely no clumping or caking whatsoever! I had a very dry, free flowing powder.

Edited February 13, 2016 by deepdixie

[lloyd]

Hooray!

Lloyd

[deepdixie]

Methinks, even with my relative inexperience in BP production, that the chems I purchase are most likely exposed to all sorts of less than ideal conditions during the many transactions and changing of hands that are made before the product is finally repackaged and sold in 5 or 10 lb. lots for retail sale. After oven drying my Nitrate (540g before drying), I discovered that post-drying I only had 532 g. of material left. After oven drying my Willow Charcoal, (108g before drying), I discovered that I only had 101g. of powder left after drying. Clearly a large amount of moisture had contaminated my Potassium Nitrate and Charcoal. I will now be oven drying the chems prior to milling, as for me this has now proven to be the only way to ensure that I have completely dry chems that will not clump in the mill.

 

Clumping issues solved for me, I do believe. Thanks to all ya'll who posted and provided much needed and sought after advice.

Edited February 13, 2016 by deepdixie