Bulk density of meal powder?

[Fulmen]

I need to design a new press die for BP, and for the life of me I can't find any notes on the density of the meal. I know I could just add some length to be sure, but I was hoping I could fit two dies on top of each other so I really want the dies to be as compact as possible.

[OldMarine]

Your final density is the only real consideration besides the amount of pressure your press can generate. Make dies that can allow you to generate the pressures needed and fill them up. Your final pucks should end up around 3/8" thick at 1.7 grams/cc. Different charcoals behave differently and deliver varied results based on the starting load.

I gave up on corning my powder as I really didn't see much benefit for the labor required.

[Fulmen]

I know that, what I don't know is how long the die must be to fit the loose meal before pressing. I want the dies to be as short as possible so I can stack them and press more than one puck at the time.

My press is only 5ton, if I assume I need 150kg/cm^2 to get a density of 1.7 the die can't be more than 3", a 3/8" puck would then be appr 50grams. Making a few pounds will be slow work, so I'm looking at ways to speed things up a bit.

First thing is to press more than one puck per die. Layering powder between plastic disks should work I guess, but there is still a limit to how tall such a stack can be before the powder starts binding in the die. A height equal to 1/2-1x the diameter of the die should be OK I think. But I might even be able to fit two such dies in the press, allowing me to press up to a pound at a time in theory.

 

For pyro I agree that you can drop the corning, I always used CIA-BP in the past so even milled and wet-granulated would be an improvement. But I also want some BP for shooting which do require proper BP.

[Shadowcat1969]

Well your meal powder density out of the mill will probably vary, depending on the charcoal you use. Some are quite a bit less dense than others at a given mesh size and that would translate to a difference in your finished BP as well.

 

You'll probably need to figure the actual finished weight of a puck of your powder at 1.77 gm/cm^3, if it is actually 50 grams, then whatever volume 50 grams of your mill dust fills will be what you need, minimum.

 

I also have given up corning for pyro use, but I understand the need for shooting. I would also suggest that you should work your plans into milling several batches of BP, integrate all the mill dust from the batches together and use the overall powder to make your pucks. You will want to have identical performance between your loads and if you use different batches of mill dust for one pressing vs. another you could end up with something way overpowered for a load. I'd probably mill myself up a good 20 - 50 pounds of powder and get it integrated, depending how much you actually shoot, then you won't ever have to re-calibrate your loads. I'd also say to press and corn as close to the same conditions (temp, humidity, etc) as possible and, of course store all your powder together.

 

And a last note, when I was pressing I would use aluminum disks cut from soda cans to separate pucks in the die and press up to 8 or 10 at a time. The wore out fairly quickly (dimples and perforations would appear) but they are quite easy and cheap to make.

[Fulmen]

I know it's impossible to get an accurate number, I just need a ballpark figure so I don't make it too short. I can't run the mill just yet, and I'd like to have the die ready by the time I do.

 

Getting a consistent product is never easy, the first thing would be to make a large uniform batch of charcoal. I don't know if it's necessary to blend the meal as well or if it's enough to mix up the finished powder. I'll have to do some tests. Aluminum disks form cans is a great idea, thanks.

[Fulmen]

Guess I'll have to do what I usually do: Wing it and see what happens

[Mumbles]

I did some cursory tests a number of years ago on performance vs density. Anyway, I found that with just body weight pressure, I got between 1.3 to 1.4 g/cc. This was milled willow bp. Hopefully that gives you a ballpark figure. It's not a fluffy bulk density, but hopefully helps a little.

[Fulmen]

Thanks, I think I'm good. Just finished casting the pistons now, I didn't have polyester so I used epoxy. Should be strong enough :-)

I've added 2,5x the final volume just to be sure, I think I can stretch my press enough to accommodate two if I have to.

[DavidF]

I don't claim any expertise in making pucks but I'll share, based on my limited experience. I just finished making a few pucks. I moisten, screen, and temper my (screen-mixed) dust. My pucks are 2" diameter, and pressed to 1/2" thick. This gives a density of +1.8. Each load of moistened powder weighs 51.0 grams. When a puck worth of powder is spooned into the sleeve and rapped on the table a few times to level it, the depth is about 1 3/4". After pressing they weigh about 48 grams.

[dagabu]

I don't claim any expertise in making pucks but I'll share, based on my limited experience. I just finished making a few pucks. I moisten, screen, and temper my (screen-mixed) dust. My pucks are 2" diameter, and pressed to 1/2" thick. This gives a density of +1.8. Each load of moistened powder weighs 51.0 grams. When a puck worth of powder is spooned into the sleeve and rapped on the table a few times to level it, the depth is about 1 3/4". After pressing they weigh about 48 grams.

 

After they are dried or before? I assume that the water is not squeezed out at pressing?

[DavidF]

Dave, they weigh about 48 grams before they are dried. 8% of the batch weight of water is spritzed in to the mix. I screen and temper, screen and temper, through 20 mesh both times. About 75% of the water is squeezed out during pressing. The last gram or so per puck evaporates easily from the corned, graded powder. The method works just as well as Kyle Kepley of Passfire said it would. He said more water makes better, drier pucks. And it's true. He actually uses 10% water, not 8%. He gave me permission to blab and theorize about it on FW, but there was so little interest I gave up talking about it.

 

I did read recently that 2 pyros advocate pressing BP pucks dry. All I can say to that is- try it once! Then try using water. Hint: if you try it dry, make sure you have a good shield, lots of extra pressing force, and balls the size of grapefruits. In my single test, the dry-pressed puck was .615" thick, and incompletely consolidated at 5 tons of force. The wet-pressed pucks made with several different charcoals were all as smooth as silk, perfectly consolidated, and .490-.500" thick. All pucked corned wet-pressed powders tested match or beat Goex in baseball tests. They were also pressed at 5 tons of force.

 

Before somebody mentions it, yes, I think it's a good idea to increase the potassium nitrate content to end up with closer to 75-15-10. I'm not doing it yet, only because I started with 75-15-10 exactly, and I don't want to deviate in the middle of testing.

[dagabu]

Sweet! Do you use any paper to catch the water or just let it collect on the plate?

[DavidF]

Actually, it's a pretty Mickey Mouse setup. I won't bother describing exactly how I do it, because I just cobbled the 'pucker' up out of junk Please don't make me show it! The water starts oozing out around 3 tons, but a lot better at 4. I leave it at 4 until it goes back down to 3, and wipe up the water around it. I crank it up to a little more than 5 tons of force, and let it go down to 5. Meanwhile I am getting the next weighed amount ready. It's needed to weigh it, but I'm testing stuff, so I do. It's under pressure for only a couple of minutes. But it's only one puck, too.

 

A 300 gram batch (+25 grams water) I pucked and corned today weighed 305-306 grams as a stack of pucks that add up to 3.15". They are 2" diameter. 300 grams is my test batch size. Almost 2/3 ends up as 2FA when corned. The paper towel I use to wipe up the water potassium nitrate solution is pretty damp after pressing the pucks.

[dagabu]

Stacked pucks in the pump?

[DavidF]

No. I thought a math geek might want to calculate the density of my pucks based on the info I gave. So I provided the height