How does 'airfloat' fineness relate to 100 mesh?

[ChrisPer]

I used the little blade grinder to take my charcoal, KNO3 and S to 100% passing the 100 mesh screen.

 

The charcoal is certainly very fine and fluffy!

 

Is this fine enough to now weigh out and mill the mixture, or should I go further with a few hours milling individual ingredients before mixing?

[Carbon796]

-8 or -12 would have been good enough, if your just going to ball mill it anyway.

 

What comp are you trying to make ?

[ChrisPer]

-8 or -12 would have been good enough, if your just going to ball mill it anyway.

 

What comp are you trying to make ?

Trying to beat commercial FFFg for competition muzzleloading.

[MadMat]

I make some damned good BP if I say so myself. I have an oddball screen that is somewhere between 20 and 40 mesh that I use to screen my bp components. If it passes this screen, it goes into the ball mill. The only advantage to fine grinding components before putting them into the ball mill is to reduce ball milling time, but there comes a time when you get to a point of diminishing returns. Not only do the components need to be milled extremely fine, they also need to be put into intimate contact with each other and that is also accomplished while ball milling. My two cents worth anyway!

Edited March 17, 2021 by MadMat

[ChrisPer]

Madmat, thats how I am thinking of it; fineness and intimacy. If it starts coarse and is not quickly reduced, the milling time needs to be longer.

[SharkWhisperer]

Madmat, thats how I am thinking of it; fineness and intimacy. If it starts coarse and is not quickly reduced, the milling time needs to be longer.

Agreed on all counts. That said, if you have shitty charcoal to begin with, you'll never mill it to satisfaction--the old lipstick on a pig dilemma.

 

One thing is for certain--you cannot mill BP fine enough, ever, as many will point out, but there is a point of diminishing returns. "Airfloat" is just a commonly tossed around term for very fine charcoal (or other chem); with charcoal it'll "float" when disturbed. This is not a direct evaluation of mesh size. Generally, you'll never be able to tell by touch the difference between 200 mesh anything and 600 mesh anything. It all feels like talcum powder beyond 150-200 mesh to our limited touch. And have a messy afternoon of "fun" trying to size a chem, any chem, through a 100-mesh screen. You'll be busy. My 100-mesh screen has seen precisely two uses: first when I was so sure I needed it and spent fruitless hours trying to coerce chems through it, and then again when I was screen separating titanium metal particles into different size ranges. That screen remains to pay for itself, but will probably break first. My 10-40 mesh screens see the most use. Including the approximate 30-mesh Dollar Store 11" round stainless (crummy metal, of course) flour sifter that does most of my screen mixing. And does it well. and it cost a whole buck.

 

It is a simple thing, with decent charcoal (the ultimate "decider") to beat regulated-burn-speed Goex or any other commercial BP. Easy.

 

Goex and Old Ensford and others work well at what they're designed for as BP substitutes (Pyrodex/Triple Se7ven, etc). But no way will Goex ever match burn characteristics of decent BP made from ERC, willow, paulownia, or, as our Texan friend recently educated us on--good ol' pecan wood (whooda thought it would be as fast as ERC?).

 

Goex is great at what it's designed to do. It's an expensive (and comparatively weak) alternative for hobbyists.

 

In short, "airfloat" is a generic term that refers to something that visibly floats in the air upon opening or handling. With fine charcoal, it's easy to get some floaty particles, but it doesn't really tell you the nature of the whole mix you're holding. It's a good sign, but definitely by itself is not a sign of any quantitative value.

Edited March 17, 2021 by SharkWhisperer

[ChrisPer]

Hmm, thanks SharkWhisperer.

Now I have started using my own willow charcoal I hope the batch I am about to corn will be a step in the right direction. I spent a couple of hours pre-grinding but I will see how this batch comes out and not go any further on the pre-grinding effort.

[SeaMonkey]

Willow Charcoal, if not over-cooked, will be quite soft and easily pulverized.

 

For the best possible Charcoal, no matter what wood is chosen, avoid over-cooking.

 

It is often difficult to gauge temperature without some means of measurement but

the "secret" of the most powerful BP is to never cook your char to a temperature

higher than 300 degrees Celsius or 575 degrees Fahrenheit.

 

Charcoal that lacks residual Creosote (too much Carbon) will result in a BP that

is substantially weaker than the "secret" Charcoal.

[ChrisPer]

That sounds hopeful SeaMonkey! The first batch had a tiny splash of creosote in the lid, and a few sticks still had some brown woodiness. And yes, it was quite easily pulverised except for those woody bits. Thinking of converting my classic Weber to cook in; it will hold my 8 litre soup pot which yielded about 450g /1 lb in a batch. Not sure about fuel; I would like to burn the vented gas to reduce the smoke impact, which suggests a chimney pipe, top heat. A thermometer in the heart would be good.

[MadMat]

I agree with SeaMonkey about not overcooking. I do the retort method and cook my charcoal just until the flammable gases stop being evolved. I have a small hole in the top of my retort and once the flame above that vent hole goes out, it's done. I have also found out that wood that is semi-rotted produces much hotter BP. As far as wood, I use willow and cedar. I have done extensive testing and found insignificant differences between BP made from either wood.

[SharkWhisperer]

That sounds hopeful SeaMonkey! The first batch had a tiny splash of creosote in the lid, and a few sticks still had some brown woodiness. And yes, it was quite easily pulverised except for those woody bits. Thinking of converting my classic Weber to cook in; it will hold my 8 litre soup pot which yielded about 450g /1 lb in a batch. Not sure about fuel; I would like to burn the vented gas to reduce the smoke impact, which suggests a chimney pipe, top heat. A thermometer in the heart would be good.

There is also such thing as undercooked charcoal. If hard pieces remain in the centers, you may have undercooked your coals. The value of volatile chem retention vs the basic charcoal (cellulose and lignin mostly) relationships and microscopic physical traits remains the topic of several disputes.

 

Lately, I'm using the second half of a huge collection of weeping willow charcoal that equals any speed I've ever gotten from ERC, and absolutely beats the pants off of Goex burn rate, at any/every particulate size range. Beating Goex is not difficult. It is not meant to burn as fast as possible, and it would be essentially impossible to guarantee that maximum burn rate because of charcoal availability and variations. However, commercial BP is corned and pucked and is denser, but this also slows burn rate versus the usual pyro wet-granulated of the same size range. Some fireworkers do press/puck/corn their BP (it's not hard; just equipment investment), but it seems that most don't. The practical implication is will you be able to load a sufficient mass of homemade less-dense BP vs commercial? Probably, but you should keep this in the back of your mind.

 

For charcoal storage, please remember that charcoal is super hygroscopic and will happily suck all the moisture out of the sky, affecting burn characteristics and mass-equivalents in compositions. My retorted willow sticks are put into a contractors bag (or doubled up ziplock gallon bags) and beaten to crumbles with a flat-faced dead-blow hammer (an orange plastic one from HF that I use to ram BP motors). A little less messy than using a coffee grinder. You already know charcoal gets everywhere. Once powdered, its potential for making an even huger mess is large. To each their own. But all of my "in use" charcoal (aka powdered to usable dust or crumbles) is oven dried (I use low, 200F for a few hours) to drive off all remnant water and then is stored in airtight containers with color-indicating silica bead packets. If your charcoal contains 20% water, and it can hold a lot of occult water and still behave like dry charcoal, then your actual carbon content will probably vary from batch-to-batch using the same component ratios. Such variations probably won't make huge differences when your charcoal is used in some star comps or gerbs, but with a firearms propellant you absolutely need to minimize batch variability so you have get consistent and repeatable precision. If making smaller batches, they will vary from batch-to-batch, maybe not noticeable in a rocket motor, but definitely in a chrono'ed lead sabot from a firearm. Like the commercial BP manufacturers do, consider combining many of your hotter batches together so you are assured that you have an adequate amount of BP with well-defined burn characteristics.

 

You're gonna get a small chuckle when you develop your BP making skills and for the first time watch Goex lose badly in a side-by-side comparison with your homemade BP.

 

Not incidentally, there is a new vendor on this site who was selling Paulownia charcoal, reputed historically to be amongst the very best woods for making the hottest BP. Though I haven't compared this charcoal yet, I couldn't pass the temptation to order some for future evaluation--it is sometimes difficult to find hot pyro charcoals, which is why most make their own.

 

Oh, and if you're still doing the paint can on the Weber grill, just flip the can upside down and the released gasses will ignite like a vigorous jet flame (after most of the water has been off-gassed) and assist your cook... Else could probably ignite emitted gasses with a long lighter if can is upright or on its side.

Edited March 17, 2021 by SharkWhisperer

[ChrisPer]

Mmm. I have got a decent little pile of paulownia wood, sawn ready to cook...maybe three two-gallon pots, enough for quite a bit of powder... and about the same of willow deadfall sticks waiting to bark and cut.

 

First time I put a qas ring down on the bricks beside the house, vented pot of wood on top, and enclosed it all in clay roof tiles as an oven. It worked very well but the smoke was offensive and pervasive.

[SharkWhisperer]

Mmm. I have got a decent little pile of paulownia wood, sawn ready to cook...maybe three two-gallon pots, enough for quite a bit of powder... and about the same of willow deadfall sticks waiting to bark and cut.

 

First time I put a qas ring down on the bricks beside the house, vented pot of wood on top, and enclosed it all in clay roof tiles as an oven. It worked very well but the smoke was offensive and pervasive.

The smoke will ignite and burn without issue if you ignite it. Noxious vapor problem solved.

 

Paulowonia is invasive all over the NC/SE of USA, so access should become less and less of an issue, if you know what you're looking for. Proven paulownia farms are plentiful, and they're happy to sell you their scraps--the biggest cost consideration is the volume (like balsa) because it is very light (non-dense), so a few pounds make a a big box. Grow your own, or be satisfied with Walmart ERC chips or whatever grows in your neighborhood. There is simply no part of the USA that does not grow, in bounty, wood that is perfectly suitable for making hot BP...