Science behind "green" vs "milled" BP?

[Norwest]

Hi,

 

Can someone point me to an article, book or thread that explains the science behind the speed and other combustion characteristics of "green" vs. milled BP? Thinking of extensively milling the individual components of BP and then mixing and screening together. There seems to be quite a bit of "folklore" around the speed of different preps of BP. The discussions around charcoal source are also quite varied and anecdotal. I do respect individuals empirical experiences but there seems to be quite a variety of countering opinions out there. I did check out the Skylighter article where they tested different BP preps in a baseball cannon but I could not tell by the article if they tested any "green" preps. At this point I am not comfortable ball milling black powder mix at my property due to space and proximity challenges. As a scientist I am always striving to understand phenomenon and come up with alternative and new solutions.

 

Thank you,

 

Norwest

Edited August 19, 2015 by Norwest

[Arthur]

In the days of military BP powders were separately milled to size then they were mixed in the incorporating mill. As incorporating was dangerous I'm sure they needed the process or they wouldn't have used it.

[pyrokid]

In the old days of huge BP production, they made extensive use of wheel mills, which had the capability of working damp. I think ball mills did find some use back then, however primitive their implementation was.

 

I know some guys here experimented with mill-less BP for use in lift, and experienced some success. Hopefully they'll chime in.

 

Something to try is milling some sulfur with charcoal, sulfur with saltpeter, charcoal with saltpeter, to give a better degree of integration than what would be possible by simply screening the individual airfloat components together.

[rogeryermaw]

https://www.youtube.com/watch?v=rmtK2BgmGCw

 

this is not only a great watch, but, early on, it actually adresses some of the science behind the answer to your question.

 

the factor with the biggest impact is your selection of charcoal. it is based on density. the lower the density of your charcoal, the faster it will burn. when you pyrolize, the volatile chemicals that escape the wood leave small pockets of empty space that, through milling, become impregnated with nitrate. this more intimate mixing allows for much faster reaction.

Edited August 19, 2015 by rogeryermaw

[PIL]

In green meal the potassium nitrate particles ,sulfur and charcoal are 'separate'. Inside a ball mill, point-to-point impact against the balls pushes nitrate and sulfur into charcoal pores while pulverizing.

To replicate the results I tried using 'R-Candy Method'.It works.

First pulverize the charcoal and sulfur together in 3:2 ratio. Next add 1 part water to one part nitrate and heat the nitrate solution on an electric stove . When the solution boils, add the charcoal-sulfur mixture and dextrin .Don't worry about charcoal floating above, STIR and boil GENTLY.It will be dough-like when most of the water have evaporated. If you end up with a bowl of crumbs, add water and boil again. Finally drop the hot dough onto a cold metal plate.

This method is RISKY! Wear full PPE and make NO MORE THAN 100g at a time.

Edited August 20, 2015 by PIL

[Norwest]

Thanks for the responses. The video from Chris Bishop was very informative and entertaining. Looks like he has several other lectures on Youtube. Has anyone heard of cacao/spice stone grinding mills being used to make BP? They are designed for wet milling but perhaps they could also be used to dry mill. I assume this may be safer than a ball mill? These can be had for around $200.00 http://www.amazon.com/Premier-2-0l-Tilting-Wet-Grinder/dp/B0030MS1XI.

 

Norwest

[Arthur]

With the number of ball mills round the world turning out fireworks compound and the (some but) few incidents, in my personal opinion ball mills are the usual method, use with caution.

[rogeryermaw]

that grinder looks as though it may use a spinning blade. if this is the case, it has the potential to spark as they will undoubtedly be steel.

 

the cia method (hot solvent) of production not only scares the shit out of me (super flammable powder on a hot plate/stove? no sir!!) but, from the reports i've read only produces b.p. in quality between milled and green mix. i'm only guessing but it may be due to the recrystallization of the nitrate producing crystals larger than the fine flour made by milling.

Edited August 20, 2015 by rogeryermaw

[Mumbles]

While the idea that charcoal pores get filled with nitrate and sulfur has always been one of the more prevailing theories, recently it's come to be understood as simply an old wives tale. Ian von Maltitz' book reiterates that there is no considerable hosting of other materials, and the milling process simply provides an fine particle size, and intimate grinding. For it to even be remotely possible, the sulfur and nitrate would need to be ground to a level an order of magnitude or more finer than the charcoal to fit inside of grains. Considering that the charcoal comes out with a particle size on average single digit microns, this idea has little merit. Additionally, much of the cellular and porous structure is broken down upon milling.

 

I was looking at some of the various melangers, and they work kind of interestingly. The bowl spins, not the wheels. I'm not sure how this would work, or if there would be any sort of safety issues with motors, bearings, etc. If you can't comfortably mill BP, I wouldn't try these either just in case.

 

If you read about the wheel milling process, it seems they go much slower. The powders are individually milled, and then added damp to the wheel mill and allowed to run. This essentially kneeds the ingredients together achieving a very intimate mixture.

 

Assuming you can mill the individual components fine enough, that you could make something by simply mixing. I'm one of the people working on these mill-less lift powders. A good quality charcoal helps as well. The mill-less thing, which I have been working on, does work on some of these principles. It also can work via increased confinement of the lift charge. The mill-less burst works more by flash coating the polverone.

 

I think I've posted the link to the WPAG mill-less lift article before, but here it is again. http://wpag.us/learn/How%20To%20Make%20Black%20Powder.pdf It works, though you may need to use more of it. I'd consider it more of a starting point if you were interested in trying to develop something like this.

[rogeryermaw]

very enlightening mumbles, thank you!

[Norwest]

Thanks for the info and article Mumbles. Where does one get one of those special round cutters? Is it kitchen tool or is it a hardware item? I assume the blades need to made out of non sparking material? Also I was wondering what you meant by "flash coating the pulverone"?

 

Thanks,

 

Norwest

[Mumbles]

That's a good question. I'm honestly not entirely sure. I think it might be a pasta cutter, like this one. http://www.amazon.com/Eppicotispai-Stainless-Steel-Rolling-Cutter/dp/B00J2RB524/ref=sr_1_8?ie=UTF8&qid=1440382476&sr=8-8&keywords=pasta+cutter

 

What I meant by the flash coating polverone is about what it sounds like. Polverone is granulated un-milled black powder. It's most commonly used as a flammable filler in cylinder shells. If you coat the granules with flash powder, it increases the burn rate and power up to the level that it allows you to use it as a burst. This technique is pretty common using black powder coated rice hulls in order to boost the size of the burst in ball shells.

[dagabu]

I am only using screen mixed BP nowadays, the 75:15:10 typical ratio using ERC yields the same overall power (rocket thrust) as I got with milled, pucked and riced BP using hard wood charcoal. TR uses a screen mix as well, it works well for him too.