Quick BP press experiment

[Swede]

I put my electronic press pressure gauge to work today in a little experiment with the pressing of BP fresh from the mill. The gauge, from the blog:

 

Electronic gauge

 

In a nutshell, it uses a strain transducer to output a voltage proportional to the pressure applied.

 

The BP had 2% red gum milled into it. I took 50 grams of the ball mill BP, and wetted it with 75% ethanol and 25% water, 3 grams, or 6% by weight; mixed thoroughly with a spoon. Using my all-purpose 1.250" dia comet/BP pump, I pressed three separate disks that came out like hockey pucks. Each was pressed to a different level of pressure, and for this experiment, chosen somewhat by feel.

 

Puck 1 was medium pressed, 2 lighter, three the firmest. Interestingly, I would pump the press to a displayed voltage (say 5) and inititally, it would rapidly reduce to 3 as the grains compacted. Another stroke to 5, and then it would drop to 4, rather than 3, indicating harder compression. I decided to "call it" by reading what the pressure indicated after about 30 seconds of stabilization. The results:

 

Sample #----Voltage----Wet Density g/cc

1)-------------3-----------1.545

2)-------------2.5--------1.520

3)-------------5.75-------1.556

 

I was a bit surprised that the density varied as little as it did. These are wet densities, and will go down slightly when fully dry, a few %. I think what this indicates is that pressing BP to roughly 1.6 with a hydraulic press is pretty easy. Sample 3 was stroked firmly, and it didn't make it to 1.6, so if one were to simply pump until it doesn't really want to compress anymore, you're probably going to be very close to 1.6, so long as your ram or pump has a similar cross section, which was 1.250" diameter. Larger cross sections won't compact as well, smaller ones can easily generate 50,000 psi+

 

Next step is to crumble/crush the pucks, sieve, and sort them. Should be some wicked fast BP, as the charcoal was good willow. If anyone wants pics, say the word and I'll post a few.

Edited May 6, 2009 by Swede

[firetech]

Word, Swede.

[TrueBluePyro]

Pics please, I have always wanted to try and make BP "pucks", but I'm not sure if I could just use a car jack with no gauge or something, like it might work but they would never be the same cause I would never know. I did read your blog to make one, Swede, but that is a little too good for me .

 

Do you have a video as well?

[scrappy]

Pics please, I have always wanted to try and make BP "pucks", but I'm not sure if I could just use a car jack with no gauge or something, like it might work but they would never be the same cause I would never know. I did read your blog to make one, Swede, but that is a little too good for me .

 

Do you have a video as well?

 

a car jack has a set pressure relief, it won't be consistant for whistle pressing as not that much pressure is needed, but it will be ok for corning Bp consistantly, a 4 or 5 ton jack would suffice, you certainly wouldn't need a 10 or 20 ton jack, ( unless your puck die is of a large diameter )

 

your experiment is quite interesting swede, do you have an apparatus to measure the dry density ? forgive me for not looking at your link before i wrote this but do you have the comparative force in kg/voltage ?

 

Edit :- i went to get my eyes pulled out but there was nothing there

Edited May 7, 2009 by scrappy

[Swede]

Edit :- i went to get my eyes pulled out but there was nothing there

 

Haha, I tend to be very wordy with my blogging... sorry.

 

My very best guess on that transducer is 500 pounds per volt. The reason I am guessing is because the homemade amplifier has a variable gain, adjustable with a little set-screw pot. To know the exact gain, I had to measure two voltages simultaneously, the unamplified millivoltage from the gauge, and the amplified output, and from there, calculate pounds per volt. I think I am within 15% of being correct.

 

The ram has a surface area of pi*r^2 = 3.14(0.625 ^ 2) = 1.227 square inches, a 5.75 volt "pressure" should generate 2875 pounds, so the puck stabilized for 30 seconds at 2343 PSI or 162 bar. Probably on the low side for pressing BP. It certainly consolidated very well.

 

From the beginning, the plan for that thing was that it would be a "relative" device, mainly for rocket pressing. By keeping good notes, I can figure that a 4 ounce rocket with a particular tooling set needs 8 volts, for example, for good grain compacting and reliable performance.

 

The pucks look exactly like this, amazingly hard little buggers:

 

http://www.5bears.com/firew/corn100.jpg

 

http://www.5bears.com/firew/corn101.jpg

 

To do any decent quantity of BP, I'm going to have to use a larger ram. I've got one 2.5" ID that should work well.

 

Interestingly, that puck is probably a good single grain size for some of the gigantic coastal defense cannons of the Civil War era. Maybe a little big, but not too far off.

Edited May 7, 2009 by Swede

[Swede]

Couple more pics:

 

Loading the ram; messy. When mixed, the BP should hardly appear damp. You can sense some clumpiness, but if it actually looks wet, you've got too much alcohol + water in there. 6% is a good place to start, I think, on up to 10% if you need more.

 

http://www.5bears.com/firew/bpp03.jpg

 

In the hydraulic press:

http://www.5bears.com/firew/bpp04.jpg

 

The gauge readout:

http://www.5bears.com/firew/bpp06.jpg

 

Out pops the puck:

http://www.5bears.com/firew/bpp05.jpg

 

The next step is to break these pucks and see what sort of grain strength I've got, then sieve and sort by size, and some burn tests in an aluminum channel.

 

TrueBluePyro, you definitely DON'T need a pressure gauge to press BP. With a cheapo press, simply stroke away until it feels quite compacted and you're going to be very close to the desired density. A BP ram can be made with heavy PVC and some sort of plunger to fit, although metal is tough to beat.

 

The trick is in adding *just* enough water + alcohol. Most first attempts are waaay too damp - I know mine were - and the liquid is literally flushed out the bottom of the ram, making a big mess. I think if you see a drop or two weeping out the bottom, you've got the moisture correct. If you're using red gum, the weeping goo will be red.

 

Scrappy, I forgot to mention, the dry density will have to wait until the pucks stabilize in weight and no more liquid evaporates, but that could take days, and I will probably break them before that. Since I added 6% liquid by weight, subtracting 6% of the mass of the densest puck would yield: 1.46 g/cc, assuming the dimension doesn't change, i.e. the puck doesn't shrink. Again, a bit lower than I was aiming for.

Edited May 7, 2009 by Swede

[scrappy]

very impressive !

those cute little pucks almost look edible

 

is there a specific reason you bind with red gum ? it would be interesting to know , ( perhaps you do ? ) the hardness between redgum and dextrin, and whether either would make a difference in desity when dry

 

LOL , you edited whilst i was posting, i too am impatient and wouldn't be able to refrain from an examination / post mortem, and a big yes to having the comp too damp, my first few ended up like black soup all over my press, die and everything else that was close at hand, i didn't think it was that moist,

 

edit :- in the bottom of my outer sleave i actually cut a few opposing small groves to allow any moisture to flow out freely without being too big as to let the Bp out, i notice in yours , the bottom is flat

Edited May 7, 2009 by scrappy

[Bonny]

I have never actually tested the density of my pressed BP. I press about ~1/2" thick x 3" diameter pucks (4 or 5 at a time). I use a 12 ton bottle jack and pretty much pump as hard as I can. I then wait about 10-30 minutes (depending what else I am doing) and re-pump, repeating this again awhile later. The pucks clink like china when still wet, and one corned, work great for me.

[Mumbles]

I like to get a rough idea of my density. It's pretty easy to calculate. There is probably some loss in density, but it's bound to be close. I tested this a while ago, and found the pressed product gave better results even with a much larger grain size than simple granulation. This goes against current beliefs of some though. I'll get into that in a bit though.

 

The general (sort of) consensus was that BP of density 1.7g/mL is ideal. I don't know where this came from, but it worked best for me. Lets say you have a 2.5" ID pump (who doesn't like big comets?). This has an area of 31.67 cm^2. Lets say you wanted your pucks to be 1/2" thick (1.252cm) for ease of breaking. This gives a volume of 39.65 cm^3. You would need 67.4 to fit into this volume, so weigh it out, add 4-8% water and press away. It would obviously be more convenient to calibrate for a convenient weight rather than thickness. A sharpie on your tooling is all that is needed to gauge height. This is how I've always judged density. It'd be just as easy to back calculate from pre-wetted powder if you don't want to wet each batch individually. With 8% water, the above weight would be 72.8g. Minor evaporation will not change your density any appreciable degree.

 

As to the red gum. The grains are much softer than dextrin or SGRS bound BP. This is why redgum is a less powerful binder than dextrin in stars, and thus easier to pulverize stars. The idea however is that because it can be wet with alcohol, the nitrate stays finely divided instead of marginally dissolved and recrystalized from the water. Some think that the nitrate soaks into the pores of the charcoal, but we'll have to agree to disagree on that theory. I could see there being a potential advantage when granulating the composition through a screen, but when pressing like this I don't think the difference would be as noticeable.

[Bonny]

The general (sort of) consensus was that BP of density 1.7g/mL is ideal. I don't know where this came from, but it worked best for me. Lets say you have a 2.5" ID pump (who doesn't like big comets?). This has an area of 31.67 cm^2. Lets say you wanted your pucks to be 1/2" thick (1.252cm) for ease of breaking. This gives a volume of 39.65 cm^3. You would need 67.4 to fit into this volume, so weigh it out, add 4-8% water and press away. It would obviously be more convenient to calibrate for a convenient weight rather than thickness. A sharpie on your tooling is all that is needed to gauge height. This is how I've always judged density. It'd be just as easy to back calculate from pre-wetted powder if you don't want to wet each batch individually. With 8% water, the above weight would be 72.8g. Minor evaporation will not change your density any appreciable degree.

 

 

Thanks Mumbles, that is a lot easier than I thought... or maybe I was just too lazy to bother.

I'll be pressing some BP in the near future and will go with the following based on your calculations:

3" pump x 1/2" puck = 3.53 in^3= 57.85 cc x 1.7 = 98.345g BP per puck + 8% water =106.2g

I don't remeber how many pucks I do at a time, but I will then calculate my total height needed including spacer disks, and press away.

 

Plus the bonus... I have completed my passfire style corning drum (hope it works) and am looking forward to not corning with a mallet etc...

[a_bab]

Last year I have finally had made my own die (2.5" diam) with the pistons made of some hard plastic, only to learn that once properly dried, breaking up the "dead pressed" pucks was just like powdering up a ceramic flower pot. And I've done this too. In about a week of drying, they really got hard. It took me more time to pound these pucks (4 of them, 4,5 ounces each), than to actually press them AND build the powder die. Aha, so that's why people make corning machines...

 

Well, the grains were rock hard, the burning speed was impressive to say the least, absolutely comparable to the commercial sample I had, but then I discovered the polverone.

 

Lady Kate wrote on her website about this, and I had to try it. Well, just to shorten up my long story: using something like 1% of CMC or MC (what I have used, "drywall glue") the resulted polverone is at least as fast as any grained stuff. So for me it doesn't pay to press my BP.

 

The die is waiting to be transformed in a comet press or something...

 

Nevertheless, the use of an electronic pressure translator is cool; it could be great for rockets.

 

Oh, one more thing. You cannot "overpress" the BP; press it as had as you can, and it'll be fine. In the end, the whole story about pressing and corning the BP is to achieve durability (strong grains) and reproductible results rather then raw performance.

 

"What is the key for amateur good BP, master Yoda?"

"Polverone, it is"

[Bonny]

"What is the key for amateur good BP, master Yoda?"

"Polverone, it is"

 

Personally I disagree here, as some mines I made using pulverone at the same weight as with my pressed and corned BP were underlifted. I also don't like pulverone as lift because I find the grains get broken up too much from all the handling. This was dextrin bound though, so maybe not as durable as your CMC bound powder. I have used pulverone as break in cannisters, but I think I might just stick to BP coated vermiculite or whatever so I have one less thing to make.

[Swede]

EXCELLENT additions to this body of knowledge. I agree, 1.6 to 1.7 is the upper limits of density for a typical bottle jack in an H-frame press. Wail away on it, you won't overcompress.

 

I've always liked Red gum vs. Dextrin. Maybe it's because I am an impatient ass and ethanol evaporates more quickly than water. I've got some CMC gum coming I'd like to try. I also think RG is more of a fuel than dextrin and makes better BP, but that theory may be BS.

 

One other way to bind is get the best of both worlds with 1% dextrin/SGRS and 1% RG. a 50:50 mix of water/ethanol should activate both sufficiently, and the ethanol will prevent the nitrate from dissolving to any degree.

 

I've been collecting 8" scientific sieves in stainless of eBay for months now... it's like coin collecting, waiting for a good sieve of the correct mesh to be offered at a decent price. I'm going to stack my 10 through 50 mesh and shake away, then add a touch of graphite, and the powder should be as good as, or better than, Goex or Elephant.

 

You know what we need to do? We need to make a sticky with BP definitions as they are most commonly understood. The following terms need to be defined once and for all, eternity, amen, so we know what we are talking about.

 

1) mill powder

2) mill dust

3) Polverone

4) corned BP

5) riced BP

6) greenmix

 

I'll take a stab, and I'm sure there are other definitions that need work.

 

1) mill powder: The fine powder left over after pressing and sieving/grading. Fast & furious

2) mill dust: The BP fresh from a ball mill

3) Polverone? I've heard too many definitions.

4) Corned BP: Pressed to ~ 1.6 g/cc, broken, and sieved; sorted by grain size. Excellent stuff

5) riced BP. Typically a ball formed with mill dust and abraded against a screen to granulate. No pressing. Typical BP, good performance

6) BP created by any method other than milling.

 

Suggestions/additions?

Edited May 7, 2009 by Swede

[Bonny]

1) mill powder

2) mill dust

3) Polverone

4) corned BP

5) riced BP

6) greenmix

 

I'll take a stab, and I'm sure there are other definitions that need work.

 

1) mill powder: The fine powder left over after pressing and sieving/grading. Fast & furious

2) mill dust: The BP fresh from a ball mill

3) Polverone? I've heard too many definitions.

4) Corned BP: Pressed to ~ 1.6 g/cc, broken, and sieved; sorted by grain size. Excellent stuff

5) riced BP. Typically a ball formed with mill dust and abraded against a screen to granulate. No pressing. Typical BP, good performance

6) BP created by any method other than milling.

 

Suggestions/additions?

 

This is how I understand it:

 

1) Meal powder: fine powder from ball milling or hand mixed meal (greenmix)

2) mill dust: The fine powder left over after pressing and sieving/grading. Fast & furious

3) Pulverone/rough powder: granulated greenmix or granulated milled BP (riced)

4) Corned BP: Pressed to ~ 1.6 g/cc, broken, and sieved; sorted by grain size. Excellent stuff

5) Riced BP: made from ball milled BP granulated to size witha screen

6) Greenmix: unmilled BP mixed by hand or screen

[Swede]

Bonny, I think you are right on the mill dust vs. meal powder thing. On the others, we are essentially in agreement, I think. I kept confusing the words "mill" and "meal".

 

There is a discrepancy, though. If polverone is granulated greenmix or granulated milled BP (riced), then there are going to be huge differences in performance between the stuff that was milled, and the greenmix. I've always considered greenmix to be any BP that has never seen a mill in any form. CIA method, screening, mortar & pestle, etc.

 

These definitions over the years have morphed and changed. It'd be nice if there was a set of naming conventions where everyone is on the same page. For example, a textbook might talk about priming with "meal powder", and there is a vast difference between a greenmix powder and the BP you take from a ball mill. Definitely confusing all-around.

Edited May 7, 2009 by Swede

[Swede]

As a sort of conclusion to this little experiment, I decided to finish off the pucks by breaking and sieving them to size, followed by graphite and a comparison to Goex in terms of color and speed.

 

The first step is to break the pucks. On a large scale, this is done in big ball-mill type machines with pool balls as the media. On a smaller scale, it is easier to add a SMALL amount to a heavy duty plastic bag, and backed with a wooden board, gently break the pucks with a rubber mallet. This is one of the more dangerous operations you can do with BP. You never want to break apart too much at once, 50 to 100 grams or so, and you want no metal in the process, anywhere. Rubber, wood, plastic, all good.

 

The pucks are inserted into the heavy bag, and tapped into smaller pieces. You can feel through the bag and guess when they are about right. From there, they go into screens or sieves, as I prefer to call them when they are sorting by size.

 

I stack my sieves, with coarsest at the top, of course, and begin to shake and push the BP through.

 

My screens for this experiment were 10, 20, 40 and 60 mesh. At the bottom is a piece of newspaper to collect the dust that makes it through. Each size is captured and labeled. For example, everything retained by the #20 sieve is labeled >20, meaning the grain size is greater than 20 mesh. Another way to label it would be everything that falls through the 20, but is captured by the 40, becomes 20-40 mesh. However you want to do it, be consistent. For this experiment, I just used small "dixie" cups to hold the samples.

 

Here are the >10 and >20 samples:

http://www.5bears.com/firew/bpp09.jpg

 

When completed, I laid out small samples and photographed them like so:

http://www.5bears.com/firew/bpp11.jpg

 

I then added a minute amount of graphite, which in theory creates an easier flow, and darkens the grains. The former definitely works, but as far as darkening, I saw little effect. The only way to check is to compare the samples with commercial BP, in this case, Goex. A picture of the >40 mesh with Goex 3F and Goex 2F BP. The Goex 3F was lighter colored, more gray, than my sample, while the 2F seemed darker:

http://www.5bears.com/firew/bpp13.jpg

 

In terms of grain size, the 20-40 mesh was somewhere between the 2F and the 3F.

 

Interestingly, the leftover dust had a tendency to clump which was cured immediately with the addition of graphite. There is further evidence that graphite may help dissipate static, but I am not 100% sure on that.

 

As far as the speed of the burn, I could see no difference between the Goex and the 20-40 mesh, but further tests will have to wait.

 

The grain strength was excellent. Vigorous handling of the coarser BP produced no breakage and almost no dust. The >10 mesh would be a great lift for larger mortars, I'm guessing, while the >40 mesh stuff would be fine for shell burst, perhaps in conjunction with a boost of whistle, FP, or KP.

 

If a dark, shiny black is what you're after, I'd get a hard density of 1.6 or greater, and perhaps lampblack would be better than graphite, but the coloration is purely cosmetic, IMO.

 

One last thought - if you are buying screens for BP sorting, I'd go 5, 10, 15, 20, 30, 40. Anything finer than 40 approaches dust, and is a waste of time, IMO.

[Swede]

One last post, then I'll stop talking to myself!

 

The weights, or distribution of the various grain sizes:

 

10M = 11.19

20M = 17.40

40M = 8.67

60M = 4.43

Dust = 7.22

 

total: 48.91 grams, loss of 1.09 grams.

 

This distribution varies with technique, but I've noticed that a press, break, and sieve operation makes a lot of dust. Note that most of the grains ended up 10-20 mesh, then they fall off, until we reach the dust, which spikes a bit. This dust is excellent for prime or anything that calls for a quality, fine-grained BP.

 

Oddly enough, in the dixie cup samples, this morning there were about 10 dead winged ants in the BP, but they were ONLY in the 40 mesh stuff. How weird is that? It's almost like I sieved ant eggs that then hatched! But how the hell could they have survived 3,000 PSI? I should have taken a picture.

Edited May 12, 2009 by Swede

[Arthur]

http://www.pyroguide.com/index.php?title=Gunpowder_Grades

 

May be of some interest. Lots of things on that site, most of it collated from elsewhere.

[Bonny]

This distribution varies with technique, but I've noticed that a press, break, and sieve operation makes a lot of dust.

 

According to the Passfire article (corning drum I think) - if the BP is corned wet it will result in less milling dust than if fully dried beforehand. Not sure if that only applies to the corning drum, but I don't see why it would be different...breaking up the grains is breaking up the grains.

[andyboy]

Not going to be to long winded and I apologise if it's been said before, but here are some of my thoughts on these matters.

 

 

 

I always let the BP sit still in the press for a while so that it can compact "on it's own" for a while before pressing further, the BP seems to resist beeing pressed fully in one go, it needs it's rest so to speak.

 

 

 

After the pucks come out I break them up emediatly, no resting at this stage. As a_bab stated, when dry these suckers stand up to hammer blows (if one would be so foolish as to use a hammer).

 

 

 

1,7 grams is optimal in my experience as well as many pyros with a lot more experience.

 

 

 

Overwetting makes it harder to compress unless you have slits in the bottom of your die to let the water out, your pucks will fall apart when taking them out of the die. A little water goes a long way when pressing, just make sure it is evenly distributed. I go with 2-3% and still se water oosing out when pressing.