Looking For Advice: Ball Shell Lift Charge Is Weak

[Rushfire]

Hey Guys, I have run into an issue making the lift charge for ball shells and am wondering if anyone can point out what is going wrong? Thanks in advance.

 

So basically today I loaded a 2-1/4 inch ball shell with sand and paper to the weight of 35g, and I loaded 10g coarse granulated homemade BP into a small 2-1/4 inch tall paper dixie cup. Taped a fuse running out the dixie cup, and hot glued the shell to the cup. Loaded it into a hand rolled perfect fit mortar tube and lit. My problem is the shell only goes about 100 ft in the air and I was hoping for more around 200-300 ft. Instead of a crisp boom when the powder ignites, its more like a muffled boom.

 

My BP is the 75 15 10 blend from homemade pine charcoal, milled for 2 hours, with 1% red gum/alcohol granulated through 4 mesh screen. The powder burns up very quickly when tested by itself and when I used the same mix of fine granulated and rice hulls coated BP in the shells for my rockets they make a very loud nice burst. My rockets have all fired off excellent with a leaner mix of 60 30 10 cruising on up to about 300ft before bursting. The blue, green, red, purple, and firefly stars I have made have all turned out great. So this shell lift problem comes as a surprise to me.

 

I also tried covering the whole shell with duct tape(I didnt want to wait for paper glue tape to dry), tried reinforcing the cup with duct tape on the sides, tried using finer gran BP, but to to avail. Im thinking I might roll some tougher lift cups for a more reinforced charge and loosely packing the powder and making a core, to build up better pressure and help burn faster which would likely give it the boom I want. I could also add some flash powder to the lift charge, so there are options... It just seems odd to me that many tutorials do not require this. Maybe I could make another batch of BP milled 4 hours instead of 2 but don't think that would make much difference? Thoughts?

Edited June 27, 2016 by Rushfire

[braddsn]

Ok, first... for a 35g shell, you should need somewhere in the range of 4 - 7g of lift to hit 200-250 ft. I have never used redgum in my bp. I mill my bp in a large ball mill that turns 65 rpm's for 2 hours, and is properly "charged". I am not sure what type of ball mill you have, but if you have a small mill that is slower, you may need to mill for 4 or 5 hours. Lloyd can chime in on this, he will have the exact answer for milling duration. Second... if your bp contains ANY moisture, this drastically reduces performance. The only time I have ever had lift problems was because my granulated bp was not completely dry. It caused a major headache for me. This made me invest in a dehydrator, and I never looked back. Here is what I recommend.... use meal coated rice hulls for lift. Here is why: 1)For me, MCRH are easier to make than granulated bp. Granulating bp is about the only thing in pyro that I don't enjoy. So I don't do it anymore. HAHA! 2)It is easier and quicker to dry MCRH. 3) It works just as well, and you use the same amount!! So for example, make the same shell again, and this time try MCRH for lift. Use 5 grams with the same shell and see what happens, then adjust from there. Keep us posted!

[Rushfire]

I think my BP items should be completely dry as between the different gran sizes they are either very hard or dusty.. can the BP still contain moisture in this state? Im really not sure what rpm my ball mill is. It has 2 canisters that can handle 1 lb of BP at a time. I have some 2hr meal on hand from before, I will give it another 2 hour mill tomorrow and maybe granulate a little bit and make some fresh MCRH from the rest, see how that goes. Im glad at least that I'm not missing some kind of fundamental of shell design from the sound of it lol.

[Mixer]

Try lighting a 1 gram pile of your BP in the open - a good BP should have a very rapid burn and make a dull thump sound - leaving a large smokey grey patch with very little or no residue. If it doesn`t do this then it most likely isn`t good enough for lift in the accepted correct quantities.

[schroedinger]

Rushfire, can you pls post a picture of you mill or tell us the brand and model. Thats the only way we can help you if the mill is the problem.

 

Also you say homemade bp. I think you meant the granules.

First i would kick out the red gum, and use 2% dextrine. If possible corn the bp.

2nd what mesh did your granulss have?

[braddsn]

Rushfire, by your description of your mill, you more than likely need to be milling your bp for 4 or more hours. Try milling longer, and to answer your other question: Yes, granulated bp can look dry and dusty on the outside, but still contain moisture. 2 good ways to check for moisture: 1) Place some in a ziploc bag and place the bag in the sun. If there is moisture, it will condensate on the inside of the bag. 2) Weigh the bp, then dry for a couple days then weigh again. Continue this until the bp stops 'losing weight'.. then it is dry. A dehydrator or drying box will also make the whole process much faster. If you are fairly handy, an effective drying box can be made pretty cheap, and a good dehydrator can be had for about 30 bucks. I couldn't make it without my dehydrator.

[Rushfire]

Thanks a lot for all the good info guys. I am very confident that there would not be enough moisture in the BP to condense in plastic bag in sunlight, but there could be trace amounts of water possibly since it is quite humid where I live. I actually am quite handy with the tools and I have a ceramic heater, wood, and screen, so I'll get started on a drying box when the BP is milling. I wasn't sure if I would need a drying box, but sounds like I do.

 

Schroedinger - Thanks for the dextrin tip, I'll give it a go. Should be ok to use alcohol as a mixing solvent for dextrin? Because I like the shorter drying time than water. I got my little mill off ebay, but it is the same as the dual canister 6 pound mill from skylighter. The granules were pressed through 4 mesh screen, so I think that's 2FA.

 

I have a half pound of 2hr meal powder that I will mill another 2 hours tonight and granulate with the dex. I'll let you know how it turns out!

Edited June 27, 2016 by Rushfire

[Nessalco]

Rush, if you are going to be working with charcoal comps at all, you might consider making a drybox using small Peltier-junction dehumidifiers. They work very well to dry comps and chemicals, keep the temperature very reasonable (100F or less), and dry things quickly. It's a closed system, and the heat of the dehumidifiers is enough to raise the temperature of the box to workable levels.

 

Kevin

[MadMat]

If you use dextrin, don't go over 25% alcohol mixed with water. Higher than 25% will impede the dextrin's binding ability. Some other thoughts; how coarse is your granulation? If the grains are too big your lift performance will go down, unless you have a longer mortar tube. For that matter, how long is your tube? How close of a fit is your shell to the I.D. of the mortar? I have launched 2" shells with rather fine granulated BP and it worked just fine. If the shell fit in the tube is too sloppy, you will lose lift height. Just a few thoughts that deal with things other than BP quality.

 

BTW; I don't use any binder in my BP. I simply wet my mill dust with 20/80 alcohol/water (alcohol reduces the solubility of KNO3 in water). I then press it into pucks, let it semi-dry, corn and dry the rest of the way. My grains are more than hard enough, in fact, if I allow my pucks to dry all the way before corning, they are hard enough to "clink" like porcelain when tapped together, and are a real PITA to break up.

 

Another thought; a 35 gram projectile is rather light. My 2" shells are usually in the neighborhood of 75-100 grams. when launching a dummy shell you should try to approximate your shell weight. It may seem counter-intuitive, but you will get a lower height with too light of a shell, as the lower weight shell will have less inertia vs. wind resistance in flight.

Edited June 27, 2016 by MadMat

[Mixer]

Dextrin is the water bound binder.

 

1% Dextrin with 20% water then granulated is ideal for hard grains.

Edited June 27, 2016 by Mixer

[schroedinger]

Ok. Again a couple wrong things in this thread.

1. st don't worry about your granules not being dry. If you are using alcohol your granules will be dry in a couple hours.

2.nd if you want to granulate only with alcohol, you need 20% alcohol, overwet the comp, granulate two times, first when still quite wet and 2nd time an hour later when the comp is dried a little. This way you ensure that all resins are dissolved from the charcoal and you get a propper binding, much better then with red gum and a little bit alcohol.

3.rd if you use dextrine, use +2% and add 6-7% water/alcohol 75/15 and corn or use 10-15% for ricing.

4.th your granulationnis way to big for a 2.5" shell, you will need a something more like 4 FA.

5.th the problem is your mill. What you describe is a 2x 3lb lortone or hf mill. These are only able to make about 100 g of bp per run, not 1 lb. If you put 1 lb of bp in it, you are way overfilling it. These mills need to be modified to turn from normally 60 rpm to 90. Then you need to mill for 5 h to get a servicable powder. 2 hours is may seem fast, but it isn't.

[Arthur]

Mill a batch of powder for each of 2, 4, 6 and 8 hours granulate them all with 2% dextrin and let then dry for a week in a warm place, then perhaps another week. Pick the mill time that gives you the fastest powder.

 

Take a small sample -say 1 gram, and place i on a sheet of paper. Good fast powder leaves almost no trace slow or poorly milled powder leaves lots of black dross and char marks.

 

Personally I think (without seeing it ) that your powder is slow because your mill time is too short.

[Arthur]

A ball mill should be about 1/3 - 1/2 full of balls which are about 1/10 of the drum diameter. Usually a cheap rock tumbler will not turn this sort of load, so less lead is usual which causes the mill time to rise severely. in a badly loaded mill 12 - 24 hours per batch is not unusual.

 

ALL the charcoal should be soft and crumbly and easily crumbled by finger pressure. Hard charcoal doesn't make BP. If you still have issues try to warm separately the ingredients to dry them. Weigh out from the dried ingredients.

Edited June 27, 2016 by Arthur

[Rushfire]

Cool thanks for the info guys, much appreciated. The mill I use large lead antimony balls and that take up a little more than 1/3 the canister. The mill appears to handle the weight just fine. I'll have to take a look at modifying it to increase the rotational speed. Thanks for the info about the 4FA also!

 

I ended up getting home from work a little late last night but got some stuff done. I milled the 1/2 lb 2 hour meal I had on hand another 4 hours with 2% dextrin, so I think it should be good now, but I still need to granulate it. Dissected the ceramic heater I had to downsize it a bit, removed the "tip-over" kill switch, and framed it into a wood enclosure to fit securely to the my drying box design. Hopefully I will be able to get the dry box built and completed tonight, as well as the BP granulated. We will see what time allows for. I'll be sure to post a pic of the finished dry box.

Edited June 28, 2016 by Rushfire

[rogeryermaw]

Wow...this thing is running fast...my .02 I use no binder in my granulated bp. Binders are fuel and even if only slightly, alter the stoichiometry. Binders slow your burn. After milling, I wet with water to form a dryish dough ball like play dough. Then crumble by hand and screen to various sizes. It may seem counter intuitive, but my thought is that the lower density allows the grains to be consumed faster. I'm no master but my powder works fine.

 

As for your mill, yeah...that style of mill requires modding to increase rpm for efficient operation and those little jars are only good to 100 gram batches and require at minimum, a 4 hour cycle.

 

As for the 10% rule, I find the smaller shells can benefit from a little extra lift. Then again my 3" shells often top 200 grams. Bigger than that and it's the ounce per pound rule. I have never rolled a 4" less than 435g and some over 550g.

Edited June 29, 2016 by rogeryermaw

[Rushfire]

Well I finally finished the drying box and Im pretty satisfied with it. Modified a small ceramic heater, built it into a enclosure, built the box, cut an opening, attached the heater unit, added 3 drying racks, built and attached a lid, installed legs, and added a vent cover. Solid wood. Tested it out and it produces good airflow at what feels like around 100 degrees, which I think should be pretty good.

 

Now its time to granulate that 6 hr BP!

Edited June 30, 2016 by Rushfire

[Rushfire]

So I was in the process of wetting my BP last night for granulating and as I was slowly pouring in the water/alcohol... I had to swat a mosquito on my shoulder and dumped in way to much liquid.. ARG! So now I am waiting for it to evaporate before I can even start granulating. Dang bugs!

 

I doubt it will be dry enough when I get home tonight. It should be alright stirring on low heat in a saucepan outside right? Or is there risk of it igniting if I do that?

Edited June 30, 2016 by Rushfire

[dagabu]

Um, don't do that, yes, you will very likely start a fire and in a saucepan? Pyro has NO place inside a house!!!

 

Keep in mind that forcing BP to dry will precipitate the KNO3 out and cause it to crystallize, making it even slower...

[Rushfire]

Um, don't do that, yes, you will very likely start a fire and in a saucepan? Pyro has NO place inside a house!!!

 

Keep in mind that forcing BP to dry will precipitate the KNO3 out and cause it to crystallize, making it even slower...

Well no it would be outside on a electric burner. And it wouldn't be to dryness, just to where it isn't a free flowing liquid. Still a no go?

Edited June 30, 2016 by Rushfire

[dagabu]

Still

 

Well no it would be outside on a electric heater. And it wouldn't be to dryness, just to where it isn't a free flowing liquid. Still a no go?

 

Still a no-go.... It's kind of a rule, no heating of Black Powder! It's even recommended that you dont dry it directly in the sun (KNO3 crystallizes) and in a stainless steel bowl, the sun can (and has!) light off comp, BP and stars just because of the bowl curvature and the shiny surface!

 

The ONLY acceptable way to dry BP is to use air, rice it out on kraft paper and leave it in the shade in a breeze, move it around every once in a while to expose more of the surface to the breeze.

[Rushfire]

Still

 

 

Still a no-go.... It's kind of a rule, no heating of Black Powder! It's even recommended that you dont dry it directly in the sun (KNO3 crystallizes) and in a stainless steel bowl, the sun can (and has!) light off comp, BP and stars just because of the bowl curvature and the shiny surface!

 

The ONLY acceptable way to dry BP is to use air, rice it out on kraft paper and leave it in the shade in a breeze, move it around every once in a while to expose more of the surface to the breeze.

Dang, that is surprising to me, it seems so inflammable when wet. But you have way more experience than I do. Is there like some kind of flash temperature BP reaches even when completely saturated in water that it can ignite?

[MadMat]

After your "slop" dries, you may have to put it back in the ball mill. By soaking the KNO3 and drying it, probably too slowly, it will recrystallize into larger crystals. This will slow your burn rate down, a lot. By all means, try it out first after drying, you might get lucky. If it burns slow, then you know what you have to do. I don't want to instill paranoia, but any where that solution (yes after all that water was added you made a solution of KNO3) went other than staying in the mass of BP, some potassium nitrate was lost

 

One other thing in case you haven't read it yet; add around 20% alcohol to your water. The solubility of potassium nitrate goes down dramatically in a mixture of water and alcohol. You don't really want to dissolve the KNO3 when wetting your BP.

Edited June 30, 2016 by MadMat

[Rushfire]

After your "slop" dries, you may have to put it back in the ball mill. By soaking the KNO3 and drying it, probably too slowly, it will recrystallize into larger crystals. This will slow your burn rate down, a lot. By all means, try it out first after drying, you might get lucky. If it burns slow, then you know what you have to do. I don't want to instill paranoia, but any where that solution (yes after all that water was added you made a solution of KNO3) went other than staying in the mass of BP, some potassium nitrate was lost

 

One other thing in case you haven't read it yet; add around 20% alcohol to your water. The solubility of potassium nitrate goes down dramatically in a mixture of water and alcohol. You don't really want to dissolve the KNO3 when wetting your BP.

I tested a small pile of the dried powder this morning that I scraped off the sides of the bowl last night, and it made a nice instant poof. No sparks at all just a flash. So hopefully it should be ok. And yeah, I used 20% so good there. Might try rigging up my lab vac and vacuum evaporate the excess water tonight.

[MadMat]

Vacuum evaporation would be a great idea. I have a vacuum pump myself. Vacuum evaporation does get cold, so, if you can warm it up, that will help.

[schroedinger]

Vacuum evaporation would be a great idea. I have a vacuum pump myself. Vacuum evaporation does get cold, so, if you can warm it up, that will help.

No, vacuum is expensive an ineffective due to the cooling of the material. Heating it is also very ineffective in a vakuum, since it insulates very well.

 

Bp will be dry after two days open drying, thats fast enought. All these drying technics, won't help at all, if you don't have a good mill. You don't need a drying box unless you can only produce at festivals like the pgi and need to stop and burn everything after a week.