More BP Pressing; CMC gum

[Swede]

As a sort of follow-up to the other BP corning experiment, I decided to try a puck using CMC gum.

 

CMC gum is pretty amazing stuff. A pinch of gum + water creates a gelatinous gooze that is amazingly thick, and sticky. To properly do this experiment, I would have normally ball milled the gum right into the BP, but instead I screened some CMC gum and added 2% to a 15 gram BP sample, and thoroughly mixed it in by hand. This was wet with about 80/20 water/isopropanol, about 8% or 1.2 grams.

 

Right away, I noticed something different... the liquid, where it contacted the fluffy BP, formed some pretty stout balls that had to be crushed to distribute the liquid evenly. Lesson: on large batches, use an atomizer or spray bottle.

 

The BP was significantly clumpier than earlier samples using dextrin or red gum, but with a bit of manipulation, it was stirred in correctly.

 

The press was loaded, and this time I went for 9 volts, which should have created a pressure of 3543 PSI or 244 bar, significantly higher than the previous tests. It showed. The wet density of the puck was 1.75 g/cc, with an estimated dry density of 1.64 g/cc. There was just enough liquid in there to weep a bit at the bottom of the ram.

 

The puck is strong and dense. Overall, handling of the CMC gum was not much different from dextrin or red gum. All that awaits now are breaking the puck, grain strength observations, and burn tests.

 

If I were going to mill CMC gum right into a BP batch, I'd screen it first, as the batch of gum I had contained some dense, larger particles that even in a mortar and pestle were hard to crush. I guess it all depends upon the purity of your gum. I'd also make sure everything is BONE DRY, or you'll end up with a giant ball when you open your mill jar!

 

It does look promising, so far. Hopefully it will make exceptional grains with good burn characteristics.

Edited May 12, 2009 by Swede

[qwezxc12]

Swede,

 

Sounds good. You may find that 2% is more binder than you need. I think Danny Creagan found that over 1.5% and the burn speed of the BP began to be adversely affected. CMC makes tough BP grains - best of luck breaking those pucks up!

 

For lift grains I've settled on this hybrid process, halfway between corning and pressing pucks:

1.5% CMC milled in with standard 75:25:10 Alder charcoal meal, dampened with 18-22% water/alc.

Dampened meal is pressed in 2.5" puck in my 6-ton press, approximate max pressure in this press should be ~2440 lbs/in²... I press probably about half this pressure; basically just to consolidate the puck and get the moisture thoroughly distributed.

The wet puck is then corned through a -8ish screen while damp.

 

After drying the CMC grains are very hard and durable. I screen the lift grains and get approximately 60% 4-12mesh, 35% 12-24mesh, and <5% +24mesh. I use the largest grade for lifting 4-8in shells, the 12-24mesh for lifting comets and 3in shells, and the +24mesh for piping fire and other misc uses.

 

I use 2% Red Gum BP for breaking can shells now - it's considerably faster than water bound BP.

[Swede]

I can see now how CMC gum has a real potential for making tough grains. The problem with this experiment was that the gum was not correctly distributed, and I found that out when I broke the puck. Portions of it were really soft and crumbly, and I thought "This stuff's no good" but then I encountered nodules within the puck that were really hard.

 

Obviously, it needs to be milled into the BP, but it does look like an excellent additive for pressing BP in lieu of red gum, which is significantly more expensive. And I think it's going to be stronger than dextrin.

[Swede]

A quick burn test = excellent. I can see no difference between the CMC BP and the red gum BP.

 

I know it's nothing terribly new, but it is nice to have an option for BP in addition to dextrin or red gum. It definitely needs to be milled into the BP along with the normal ingredients for correct dispersion.

 

Further, I think this would be a good binder for BP rockets, although they would take days at a minimum to dry in a non-humid environment, especially when the size of the rocket increases. I get the feeling that CMC is a more flexible, less brittle binder than many, and that would be a good thing for a BP rocket.

[qwezxc12]

I think one of it's best properties is that it has equivalent or superior binding properties compared to dextrin at a much lower %; I thought that 1.5% of CMC was superior in binding that 5% of dextrin, without affecting the burn speed.

 

I've not tried it for binding star comps, though... anyone tried that?

[a_bab]

I would only work for pressed stars, as CMC can take so much water, that once the water evaporates the left structure is full of voids, leading to a very fast burning and ligt stars.

 

This property CMC or MC makes it great for polverone; the granules are both strong and porous, hence a good burning speed is easily achieved.

[FREAKYDUTCHMEN]

Swede, why do you use a binder in your pressed BP?

[Swede]

Swede, why do you use a binder in your pressed BP?

 

Good question. The thing that brought me to APC last year was my search for alternative propellants for muzzleloading guns and firearms. I've always been a sucker for pyrotechnics, and was a kewl in my youth, and was amazed at what amateurs were producing, so it got me jazzed and back into pyrotechnics, in a safe manner this time.

 

Anyway, to answer your question, I was always impressed by both the density and grain strength of Goex and similar. If you take Goex FFG and handle it, it does not fracture into smaller fragments and dust, and I want my BP to behave the same way, even though for pyrotechnics, such grain strength is probably not necessary.

 

The pressed BP I made without any binding additives breaks down with handling. Maybe it was my technique, I don't know. I do know that the pucks and grains with RG or similar produces BP as close as I can make it to Elephant or Goex. It's just a personal thing, I guess. If I sieve BP to 10 mesh, I want it to remain at 10 mesh, not turn into a mix of 10 + finer.

[a_bab]

I also wondered why using a binder for pressing the BP rather than for ricing it.

 

If really strong grains are what you're after, the composition should be well wetted. Just a "bit" less water and the puck crumbles back to meal very easily. I'd say, just use the standard way: simply add something like 4-5 ml of water for every 100 g of meal. Press it as hard as you can (several sessions/puck). Once well pressed it will start dripping the extra water. These pucks are rock hard. And hard to crush too... The granules feel like little ceramic shards betweel the fingers, and they barely leave black marks when abused.

[Swede]

I'll try a few without binders. Thanks for the inputs!

[Arthur]

I've just been given a puck of BP -it's about an inch DIAMETER and possibly 4 inches LONG which I find funny! (I expected it to be wide and flat) Was made by a friend who has a 30tonne press, who simply presses with 4% moisture max.

 

He made several of these esp the slow gold, so his work is OK. The bullet hit was done by a pro SFX person, but the kid enjoyed himself!

 

 

Edited May 19, 2009 by Arthur

[FREAKYDUTCHMEN]

I have much better results with 5% water and 5% alcohol than only with water.

[Arthur]

My piont being that though a binder is needed for ricing/granulating powder, pressure is sufficient for pressed and corned pucks. Yes you need lots more pressure to make pucks dry, but you can do! I fancy thin picks that break easily for safety, but I've never pressed any pucks.

 

On mate has a die set that makes the shape of charcoal briquettes, He bags up the BP briquetes into a BBQ charcoal bag!

[Swede]

On mate has a die set that makes the shape of charcoal briquettes, He bags up the BP briquetes into a BBQ charcoal bag!

 

Oh man, I've got an image, and it isn't pretty. What if someone (a wife, a neighbor) finds those "BBQ Briquettes" and decides to fire up the grill? I just hope they are safely stored and labeled. Otherwise, it's a clever "stealth" idea.