BP Granulating / Granulation techniques

[nordicwolf]

I started in this hobby doing fountains and am heading toward rockets now. For fountain mixes it started with screen-mixed BP 75/15/10 but now I think I have settled on 60:40 ball milled mix. Fast enough to eject microstars to a respectable height, slow enough for decent duration.

 

I like to reduce the dust when pressing and am trying various methods. I wonder what others have used successfully. I have tried the following:

 

60:30 - once screen mixed I put comp in ziploc baggie, added HOT water and kneaded into a ball, screen granulated the ball (12 mesh), let dry. This results in decent granules that break with the slightest pressure. It reduces poofs of dust when pressing but there is still some dust

 

60:40 - ball milled. Fresh out of mill, this mix is the speed I like. To reduce dust, I did the HOT water mix described above only to discover that really sped up the comp. I have granules but they are much hotter than before.

 

75:15:10 - ball milled. For this I tried the "2% dextrin Liquor" approach described elsewhere. I had a 500g batch of BP, so I made 10g dextrin to 68.75g water (mimicking the 20g/137.5g for a 1kg batch). I had trouble dissolving the dextrin in the water, plus my dextrin (from one of the respected suppliers) is not white but rather amber in color. IS there such a thing as White Dextrin? Is it better for this? Where do I get it? Anyway, I heated up the water and the dextrin dissolved more readily, so I added it to the BP already in a baggie. However I was not able to make a ball out of these proportions. Not enough liquor in my opinion. So the best I could do was screen mix the kneaded damp comp 6 times through a 12 mesh screen. In the end I got a good yield of -20mesh granules and a small amount of -12+20 granules. Very little dust. I have not pressed a rocket with this yet but plan to use it for the 3/4"x3.75" cohete tubes and Econo tooling.

 

75:15:10, 60:35 - with these, given the charcoal was ERC, I used denatured alcohol to screen granulate. This did not work at all. I had read that ERC has binders in it that work with denatured alcohol to form granules, but that was not the case for me. I wound up with powder maybe a bit less fine and dusty than when I started. FYI it is this 75:15:10 I granulated with alcohol that I later used above in the dextrin liquor example.

 

60:15:15:10 - this batch is still in progress. I ball milled 60:15:10, the 15 being ERC. Rather than try the dextrin liquor, I added +2% dextrin into the mill, so I got out a nice powder consisting of 60:15:10:2. Once milling done, I added 15 of 80 mesh hardwood from one of the pyro suppliers. I am screen mixing this now and have a few more iterations to go. With this mix I hope to knead a ball using (room temperature) water as necessary, and then screen granulate through 12 or 8 or 4 mesh. I do not use lift (not yet), so I may just stick with 12 mesh granulation and see what I get.

 

[justvisiting]

Nowadays, I'm a fan of using water-dampened propellant in my rockets. It keeps the dust down and facilitates consolidation. I wax my tubes, because the damp propellant has a tendency to pull the tube down a bit. For 75-15-10 nozzleless rockets, I use 2 1/2% water, screened in by passing twice through 16 (or so) mesh. For 60-30-10 nozzled rockets, I use 3 1/2% water. The use of water allows for much lower pressures when loading. The rockets I make are 1lb and 3lb, so this damp, non-granulated powder is not a problem to load. For smaller rockets, it could be very annoying to make it go down the tube. In that case, a person could 'pre-densify' the propellant by pressing light pucks with the damp propellant and breaking it down through a 12 mesh screen into granules. It's a fair amount of work, and the propellant needs to be stored tightly sealed to keep the moisture in.

 

For end burners, I've taken the milled 75-15-10 and spritzed it with 8% by weight of water, screened in. I pass the damp powder through a 20 mesh screen and dry it in thin layers to produce a free-flowing, non-dusty powder.

 

For both kinds of rockets, I've used 2% paraffin wax dissolved in Coleman Fuel to granulate, after moistening to a shiny ball consistency. The propellant is then dried away from sparks until it doesn't smell of naphtha any more. Of course, that involves using expensive and flammable solvent. But it works well. When using wax in the propellant, waxing the tubes is unnecessary. Many folks would say waxing the tubes is unnecessary anyway, but I like to do it.

 

All my rockets using these propellants are long-spindled, not Cohete-style.

 

The story about ERC having properties that allow straight alcohol binding is just that- a story. Almost all of us that have tried it agree that it makes a dusty, barely held together granulate that falls apart if you look at it the wrong way. It's a waste of alcohol and time- in my opinion. Most denatured alcohol has a high percentage of methyl alcohol (methanol, methyl hydrate) in it. The fumes are explosive and toxic, FYI.

 

Many of us have experienced CATOs when using dextrin to granulate rocket propellant, especially if the propellant is well dampened before granulating. I'm talking about 'regular' (yellow) dextrin, used for rockets with long bores, like standard BP tooling produces. I've never used white dextrin.

 

My methods are not necessarily typical, but they make reliable rockets, which is very important to me.

[nordicwolf]

Thanks for the info. Interesting about the CATOs, but I hope since I will be using universal hybrid tooling for 1# full length tubes and the cohete style for 3/4" 3.75" tubes the risk of CATO using that 75:15:10 dextrin granulated fuel is reduced.

 

Not sure what to do with the 60:30:10. That is for a 4 oz 1/2" ID x 5" motor. I have standard core burner tooling I was going to use with that, probably nozzled as I think the rammer is intended for that. Given it is 1/2" ID I appreciate the comment about dampened comp perhaps being difficult to drop down a narrower tube. Will have the think about this. Thanks!

[dagabu]

Yeah, try a nozzle to up the pressure and use a longer spindle to utilize the slower fuel.