BP, presses, and pucks

[Swede]

I'm a rank noob with pyro, and am enjoying the journey tremendously so far. This appears to be an exceptionally kind forum - thank you all.

 

I did execute a search on the topic of pressing BP to improve its qualities, but got a lot of hits, and many were confusing to me.

 

I produced a nice BP batch recently using the alcohol precipitation method, and it seems fairly brisk. I do have a ball mill, and am going to start using it. I am also exceptionally fortunate to have my own machine shop, so I look forward to making much of my own tooling. This means I can produce things like star pumps, dies, etc to good accuracy, for use in my hydraulic press.

 

Can someone explain the basics behind BP pressing? I am picturing a female cavity, into which you insert your BP, with perhaps some added dextrin, and a finely fitted male piston. Install the widget into your press, and have at it. Out pops a disk of BP. True?

 

I am concerned about safety. Is it possible for the BP to ignite under pressure? And if it does, given the circumstances (piston over BP cavity) where would the gas go? It seems a bit scary to me, but I'd like to give it a try.

 

Thank you all! I look forward to a fun new hobby!

[JCrewPyros]

Check this out (=

 

I asked the same question

 

http://www.apcforum.net/forums/index.php?showtopic=2395

 

I don't believe it is a matter of how hard you press it... It boils down to getting the BP Pucks to the right density...

 

If I am wrong please please someone chime in...

[Mumbles]

Yes, some very basic testing I did pointed to a density of around 1.7g/mL to be about optimal. It's the time tested standard.

 

Most dies are a steel or PVC pipe with a good fitting rammer. Some prefer to use a "nipple" of sorts on the bottom so that the BP disk is recessed. By nipple I mean a short disk the diameter of your die. The rammer is generally made from metal, plastic, or wood. Some here have had good results with Ultra high mol weight HDPE.

 

You will want to take your prepared meal, and dry it. It makes calculation of the water needed easier. You will want to add 8-10% water by mass to the powder and evenly distribute it. The addition of dextrin or other binders is recommended in order to produce solid grains, although the pressing by itself produces very solid particles. I am not saying that it can't happen, but I have never heard of wet BP being ignited while pressing it into a powder die. The most dangerous part, by far is breaking up the powder cakes into the granules. Some break them up while still wet but I am unsure how wet breaking it up vs allowing them to dry compares.

 

In the unlikely case that it ignites, and assuming a solid press base and press, my guess is that it would either blow out the sides of the die, or go out past the rammer.

[Swede]

Thanks for the info, guys. JCrew, I read your question and I'm thinking we have similar goals. It's annoying that we can't simply "see" how it's done, but since we are all separated by distance, we go by descriptions instead. Known density is a good goal. Now we just need to figure out the best way to implement it. I'm thinking of a cavity that has a rim, meaning the BP cannot be compressed any further. If 1.7 g / cc is the goal, if we have a 1 cc cavity, we load it with 1.7grams, and press until the ram reaches the stop. Hold it there for a while, release. Sound good?

[Mumbles]

I would be worried about pinching fuel on the rim. It's just as easy to machine calibration grooves on your ram. A millimeter high or low certainly wont hurt anything.

 

Depending on what kind of pressing apparatus you have it may not be as easy as compress to the stop and leave it sit for a bit. It's common with weaker presses, such as bench vices for instance, to compress somewhat and have to leave it for several minutes. You can then compress it more as it settles. You have the right idea with letting it sit though. It can expand back out if you simply compress and let it out. It will certainly be quite solid, but not quite as accurate of density.

[Swede]

Hi Mumbles, I've got one of the cheaper manual hydraulic shop presses. I understand now, I believe. A mechanical rim wouldn't work because the fluffy BP would be spilled over it prior to pressing. Using either an indicator or some sort of calibrated markings would work, as you mentioned. Thank you for your help, I'll try to work on some press tooling today.

[JCrewPyros]

Yeah I am thinking markings or a pressure gauge would work... Mark at the PAT event said that he would crank his up to 8000lbs and let the pressure slowly fade on its own... then crank it back to 8000 again... and rinse and repeat a few times... he was also pressing huge pucks... something like 2inches thick and 5 inches wide...

[Bonny]

Most dies are a steel or PVC pipe with a good fitting rammer. Some prefer to use a "nipple" of sorts on the bottom so that the BP disk is recessed. By nipple I mean a short disk the diameter of your die. The rammer is generally made from metal, plastic, or wood. Some here have had good results with Ultra high mol weight HDPE.

I have used ABS and PVC pipe as powder dies, re-enforced with gear (hose) clamps.As for the pistons, mine are UHMW and they work well using a 3" die set and 12 ton bottle jack. Solid nylon or PVC would also be fine I'm sure. I use 10% water and max out the press, then wait about 10 minutes and repeat. Pucks over 1" think are rock solid...clinkiing like china when dry.

I am going to try the passfire multi puck set up as soon as I get a warm day to do it outside. In that case I will be re-cranking the jack 2 more times after initial compression. I think I should be able to press close to 1kg (wet weight) in a shot.

[Swede]

I did a micro-test today - I took my skylighter-ingredients ball-milled BP, talc-fine, with 3% dextrin... added water/ETOH 50:50 to form a dough. The bulk I screened immediately to dry, but I took maybe 20 grams and loaded it into a tool-steel die with an aluminum piston that fitted well. PUMP PUMP PUMP on the handle, and the water/etoh oozed out all over the place. What came out of the die - a slug 1/2" diameter by 1/2" tall. The 20 grams made 5 or 6 of these little pills.

 

They were hard as a rock! It took forever to grate them through a seive, but the resulting pile of granular powder looks very good. When it's thoroughly dry, I'll unscientifically compare the pressed vs. the unpreeed BP from the same batch.

 

I've saved one of the pills, and I'll weigh it and calculate its density.

[Arthur]

When properly pressed and dried the pucks should chink like porcelein and be very hard. The pressing physically pushes the ingrediebts into close contact so the reaction happens best. When the pucks are whole they burn slowly. When they are re broken (Corned) the powder is selected by grain size to have speeds and power suited to different purposes.

 

Has anyine ever made pucks really thinly so that they break with a light pressure rather than hammer blows. I was thinking of getting a powder die with several metal shim inserts so that a 3inch puck an inch high was actually made with four or five layers then the layers could be broken by hand.

[InRainbows]

Arthur, you could press one puck, then put in a thin border, a wooden or plastic plug, and then press your next one, rinse, repeat. Or just put in calculated meal, border, meal, border, then press, but doing them all at the same time would yield bad results.

 

It would require a press a little too strong to work optimally, I would think.

[Mumbles]

I wouldn't say that it would give bad results pressing them all at once. It really depends on how much you're doing at once. Yes, if you're pressing a 6" stack of cakes it will probably end poorly. But if there will be 4 3/8" stacks in a 4" die there should be no problems.

[Swede]

Results of the press test... pure luck, if 1.7g/cc is the goal. Base 13.26mm, height, 10.33mm = 1426 cubic millimeters, or 1.42 CC. Weight = 2.4 grams, for a density of 1.69 g/cc.

 

http://www.5bears.com/firew/bp029.jpg

 

Those little micropucks are HARD. I managed to screen them through a sieve, and the resultant powder was fast, definitely the fastest that I have ever produced.

 

http://www.5bears.com/firew/bp029a.jpg

 

This is the third batch I've made while exploring the basic methods of making BP. Far and away the best has been a 4 hour ball-milling with brass media. Second (and I think it's very useful powder) is the alcohol precipitation method. A distant third is a moist greenmix.

 

The performance of the pressed powder vs. the unpressed seems very close. Is it really worth the trouble to press, or is this done just to get grains sorted by size?

[justanotherpyro]

I break up my pucks while they are wet. It makes the process much much easier than letting them fully dry. After sizing out the grains I reliably get good quality lift.

[FREAKYDUTCHMEN]

Is it possible to press the BP to a even higher density than 1.7 g/cc?

With the result that the BP haves a lower burnrate?

[Bonny]

The performance of the pressed powder vs. the unpressed seems very close. Is it really worth the trouble to press, or is this done just to get grains sorted by size?

I think the main benefits of pressing are consistency (a very good thing) and much harder grains. This way they don't get crushed while loading and handling etc...

 

@FREAKYDUTCHMEN: I think increasing the density past 1.7 will slow the burnrate. I think someone had posted some test results of different densities.

[Mumbles]

Yes, I did tests at simply riced, 1.4, 1.7, and 2.0 density. 2.0 density was the max I could get it to. 1.7 did have the best burning characteristics. I was testing them by shooting wooden plugs from a 1" mortar and timing them. 5 runs each and averaged. I can't get the webpage I posted my results on to come up, but 1.7 was the best followed by 1.4, 2.0 and riced.

 

It probably would have been more scientific if I could have gotten them all to the same grain size. The 2.0 pellets were harder so I probably had more trouble breaking them up and may have ended up larger grained. It's a test I'd like to redo now that I have appropriately sized screes to get good size fractions.

[FREAKYDUTCHMEN]

Thank you guys, that was what I liked to know.

Now I know it's necessary to calculate before i start pressing.

[Stinger]

Hi all

 

I was thinking about pressing BP, too.

I want to make a wooden frame for the press, since I cant

weld metals, so I am forced to make a wooden frame.

 

Which wood should I take?

 

This is the BP I want to press:

 

http://www.youtube.com/watch?v=ZRO0COye04o

 

Stinger

[Mumbles]

Use a hard heavy wood such as oak or yellow pine. I have no idea what is commercially available in Germany, so I can't give very good advice.

[Swede]

FDM, for reference, the 1.7 g/cc I got was with a 12 ton hand-pumped hydraulic press almost identical to this one. I pumped it up until it felt very firm, and really had very little more to give, being a hand-press. Unless you have a pretty serious machine, it may be hard to get denser than 1.7

 

http://www.use-enco.com/ProductImages/4852326-11.jpg

[BPinthemorning]

I think i have the same press you do. Mine looks like that, but with a few differences. it works. It was way worth the 20 bucks I spent for it. In the states, it is easy to get a press for really cheap. Look at the Pep boys auto sale adds in the paper. Like I said, 20 bucks is an awesome deal.

[Bonny]

FDM, for reference, the 1.7 g/cc I got was with a 12 ton hand-pumped hydraulic press almost identical to this one. I pumped it up until it felt very firm, and really had very little more to give, being a hand-press. Unless you have a pretty serious machine, it may be hard to get denser than 1.7

 

http://www.use-enco.com/ProductImages/4852326-11.jpg

I'm curious, how much does the frame flex with that press using a 12ton jack? I have a homemade press that is built more rigid and it still flexes.

[BPinthemorning]

I have had absolutely no flex when I crank it...

[Bonny]

I have had absolutely no flex when I crank it...

Interesting...the material must be heavier than it appears in the pic. My press is very narrow with a heavy wall 2" sq. tube as the top it is visibly bent.Are you giving the jack full power?