25 replies to this topic

[willd]

I've finally managed to get a press and some sieves, what mesh size would you recommend for lift and what mesh size is best for breaks.

Thanks.

[Yugen-biki]

I use 2-7mm BP granules for lift. For break I let the stuff I coat determin the size (2-7mm would do just fine here to).

I have found out that when you are using green powder as lift charge the mesh is more important. Something like 2-3mm grains were the best for me. But when the quallity of the BP got better the size didn?t matter as much.

[Phoenix]

Passfire suggest that when making polverone you should granulate through a 1/4" screen. When the grains are dry, you sieve them through a 1/8" screen. Everything that falls through is lift, and everything that stays on top is burst.

I use <2mm grains of pressed powder for lift (on shells of 40mm and less), and BP coated rice crispies or vermiculite for burst. I've only ever fired one shell larger than that (70mm) for which I used 2-6mm grains to lift.

[EDIT] Got my screen size wrong.

Edited by Phoenix, 26 April 2004 - 05:34 PM.

[Yugen-biki]

Ooops! I forgot to specifie the size of the shells I use. The smallest are 2" (50mm)and the biggest are 3" (70mm).

I tried mixing some lose BP powder with BP granules to lift my 2". I`t worked OK.
To big granules may work worse then lose powder when fireing small shells (like 2"). Specially when green powder or likewise are used.
I have done tests with my BP using granules of 2-7mm size. And they work good for 3" spherical shells. I have a mixed size of 2-7mm, and the biggest granules are 7mm and the smallest 2mm. Give or take one mm. Leaving me a average of something like 4-5mm.

This is no exact science. More like "try and error" science. But guide lines are good to have.

[pritch]

So could anybody tell me what mesh sizes I should get and where I could purchase them?

Im a beginner and just want some good powder for propellant and some good powder for blast. I just don't understand when you say 1/4 inch screen for example. Is that what I would ask for? Sorry for being ignorant :

[Phoenix]

1/4 inch screen means that the (square) holes in the screen are 1/4" by 1/4."

4 mesh screen has four holes per linear inch, or 16 holes per square inch. since the wires do have a thickness, these holes will not actually be 1/4 of an inch, but a little less. A 100 mesh screen has 100 holes per linear inch, 10,000 holes per square inch.

For sorting BP grains you can probably use kitchen sieves, or home made screens. I found two different sizes; one had holes that were about 0.75mm, and one had holes that were about 2mm. I got a peice of metal and drilled 6mm holes in it for a larger sieve. Having cracked up and dried my pressed BP, I sieved it through the 6mm one first. Any that stayed on top of that got re cracked. What fell through got sieved through the 2mm one. What stays in this usually gets cracked up again, (hence I dont bother with the 6mm one) but I sometimes use it for larger stuff. What falls through the 2mm one is seived in the .75mm one. everything that stayes in this is general purpose lift. Everything that falls through is corning dust, which I use as good quality meal for cracker fuse or burst.

I have just bought a new set of screens off Steve (Hint, hint; that's one place to get them), so I am likely to optimise all this soon, but the above has worked so far.

I have not really had any experience using fine screens for sorting particle sizes, so I'll leave that to someone who has, but for mixing I have found the .75mm kitchen sieve to be fine. 20-40 mesh are probably good for mixong too.

[phildunford]

Dan williams has some useful advice on BP and screen sizes at

dan

Traditionally the size (say 60 mesh) is the number of wires per inch, but th hole obviously varies with the thickness of the wire (and it's the hole you need!).

Now the hole size is sometimes specified in mm.

Look at the big suppliers of ceramic chemicals - most of them do seives or the material.

[pritch]

Thanks for the information. I've been reading up and i've allready wrote a cheque out for steve

Now I am just going to decide tomorow whether I buy a ball mill or make one if I can find the bits. May as well order the 137 grain 11.5 mm lead balls from suttlers now.

[Creepin_pyro]

Has anyone tried polishing their granules? I've been compressing meal pucks, and then attacking them to granulate. After some calculations, I've worked out an average density of 1.31g/cm3 - I've seen 1.4g/cm3 listed as the optimal - is this correct? I wanted to try polishing the grains - just to see if I could, and how it would effect performance. After tumbling on their own for a little while, I could see no visible smoothing, or change in performance. Anyone bothered giving this a go?

[paul]

For polishing the blackpowder grains are tumbled with some graphite. But it has no advantages to the hobby pyro because this only makes them less sensitive to moisture etc....

You safe a lot of work if you don?t polish them....


Edit: There is a smoothing. But to get good results you have to fill in a lot of grains, not only 20g.. Then the grains will lost their sharpness. But why should someone do that

Edited by paul, 27 April 2004 - 12:50 PM.

[Phoenix]

Polishing grains is mainly of advantage for people using BP for muzzle loading firearms, and possibly blasting (though BP blasting is pretty rare today) so that the grains flow more easily, making them easier to measure out from a powder flask and pour down the barrel or bore hole.

However, polishing them with graphite does make the burn slower. Considering that how easily the BP flows is not really an issue in fireworks, and that many people strive for fast burning powder, the only reason you are likely to want to polish your BP (other than for the challenge) is to protect it from moisture, with is not usually a problem either.

[chim-chim]

Pheonix, Paul,

Thanks,
You just saved me some work.
I was going to polish a batch w/ graphite, just to see what, if any advantage it gives.

Moisture resistance isn't a big advatage here.

Tuesday : Plentiful sunshine. Hot. High near 95F. Winds WNW at 10 to 15 mph,
Dewpoint: 53? Barometer: 1016.8 mb Humidity: 33%

And the dry season is coming.

[pritch]

Ive just found a very good guide to mesh sizes and uses. Mayb someone can verify if it really looks useful or not.
http://members.aol.c...aqs/bptypes.htm

[sasman]

I am about to make a new batch of BP and am intrested in Polishing the grains after i have corned it..I have found an old batch of powder that i have kept in an airtight drum...The grains varied from 4 mesh to 30 + mesh..I half filled my Hexagonal Milling Jar with this BP i added a few grams of Graphite..and left it to run for a few hours..

I have noticed some of the larger grains 4 to 8 mesh...were smoother with no jagged edges there was a slight sheen to the larger grains but overall the powder did not shine like i was hoping..Any ideas how long i should tumble the powder for?.

[sasman]

eh

Edited by sasman, 22 July 2007 - 09:43 PM.