Ball Milling FAQ

[DavidF]

OK, I finally finished my little round of tests with supermilling the charcoal using a 3lb rock tumbler and 304 stainless steel media. The charcoal feedstock was 10-12 mesh, willow. I cooked it in a retort. As I have said before, my goal is to make black powder from separately-milled components. 50 grams of charcoal from the same batch was used for each test. Each batch was run with half a jar of stainless media for 6 hours. 45 grams of the charcoal from each batch was used to make 300 gram batches of 75-15-10 with pre-milled potassium nitrate. The charcoal, rubbermakers sulfur, and milled potassium nitrate were run twice through 40 mesh to combine.

 

Each batch was pucked, corned, graded to 2FA size, and tested. 10 grams of +1.8g/cc. grains were used for each test. Condiment cups contained the samples, which were fused with black match with visco leaders.

 

The tests were one-offs, and not conclusive. But, I think it's safe to conclude that newbies with rock tumblers can make GOOD black powder in small amounts, with minimum outlay. The pucking and corning is not necessary. It can be replaced by screen-granulating. In that case, the flight times would go up.

 

Here are the results from this round of tests:

 

3/8" SS media- 9.5 seconds flight time, 150 gram baseball in 3" ID mortar, 10.0 gram sample

 

5/16" media- 9.8 seconds

 

1/4" media- 9.3 seconds

 

3/16" media- 8.7 seconds

 

All these results are acceptable for lift, IMO. It is interesting that my favorite 5/16" size media seems to be the 'sweet spot' when milling charcoal in a small rubber jar. Of course, these one-off results are not conclusive, and will guide me in future experiments.

[Lewjack13]

Ive used skylighters red gum method with great results

[BetICouldMake1]

Hey guys, two ball milling questions for you.

 

1: Do the weight ratings of mills refer to the total weight of jar(s)+media and material or to the total charge weight (media+material).

 

2: How efficiently would a mill mix ingredients without media, or with very little media assuming the comp to be mixed was already sufficiently ground? It seems like everything I've read is designed to optimize the mill for grinding, but if you're starting with airfloat and -100mesh sulfur and KNO3 then then really you're mixing more than milling, right? Just something I was thinking about playing around with but I would think someone has already tried it.

[OldMarine]

With fine chems a screen mixing would work as well as an empty mill jar and would be cheaper.

[Arthur]

I'd expect the weight rating of a mill to be contents of the drum. BUT read the manual or read the small print on the web description carefully before you part with money.

[BetICouldMake1]

Cheaper as in screens are cheaper than Mills or the cost of running the mill. I'm willing to pay a small price for the convenience of passive mixing.

 

 

That's what I thought too, Arthur. I've got the harbor freight 6lb tumbler but there's nothing in the manual regarding the weight. Just wondering what that motor can handle if I were to use a slightly larger but lighter jar.

[Arthur]

A TYPICAL 6lb tumbler stops at 6lb 1oz. use a 6lb tumbler with only one jar if you can, that way you get 6pounds of content in the jar.

 

When trying to use a rock tumbler there is a lot of advantage to using alumina balls or zirconia balls. Their low density means that you can still get a full jar within the weight allowance. Maybe it takes longer but it's better than using lead balls and the mill stopping.

[justvisiting]

Sulfur has a tendency to be clumpy, even though the particles are fine. I wouldn't trust a mill jar with no media to break up the clumps. Besides, running the mix through the screen is as easy as falling off a log.

As the baseball test results on the last page show, small stainless steel media can be used to make screen-mixed powder that is just as good as commercial black powder. My modified (from 45 to 73RPM) Lortone tumbler will turn one jar half full of SS media with 250 grams of potassium nitrate with no problem.

[Mumbles]

The weight rating is for rocks, and has nothing to actually do with pyrotechnics. Generally speaking it's most closely related to volume of the jar. As a very rough rule of thumb, expect the actual mass of jar + BP load + lead media to weigh approximately double the weight rating. That's not saying the motor can handle it of course. A 3lb and 6lb rock tumbler from Lortone and Chicago Electric (Harbor Freight) is the same in both models. To say that the weight rating has anything to do with legitimate capacity is misleading.

 

I would trust a screen to mix better than a rotating jar. A couple balls might help, but will be way less time efficient and not really any safer.

 

Milling definitely does more grinding even if starting from fine materials. I'd say to assume it does mostly mixing is totally false, though it does accomplish very intimate mixing. A perfectly integrating mix of commercially fine materials wont even compare to a ball milled mixture. That said, you can individually mill materials on your own and get results more similar than many will acknowledge.

[marnor]

By reading this reply you will maybe see the worst english you have never saw before and i apologize for it and i hope you will understand it :s

Hey last time i was asking on discord what was the less dangerous milling media and i was advised to took brass media so i was looking for some brass rod and i dont know now if i must take brass (64%Cu+36%Zn) or (UZ39 = 59%Cu+39%Zn+2%Pb)

 

I would like to know too if it is possible to make aluminium powder with a ball mill or if its far too dangerous.

I look some that ball mill it with glass marble and open the jar every 8 hour , some grinding it with stainless steel and open the jar every 4 hour.

If i understood you must open the jar for avoid a massif oxydation (that heat the powder) and let it oxyde "slowly".

But i saw this information on some blog and on youtube so i dont trust it so much, and nobody speak about using brass media (i think it can react with aluminium and oxyde it but i am not sure :s )

I know its many question but if someone can answer my question i will be greatful.

[Arthur]

Marbles (well the glass ones) make small gritty fragments of glass that sensitise any mixture more than is reasonable, there is an incident report on here relating to a mill explosion where glass marbles were used. Good materials include antimony hardened lead, brass, and some ceramics. When milling single ingredients stainless steel, may be good. Purely for incorporating mixtures, I've even heard of hard wooden balls being used.

 

Once it's brass it doesn't matter what particular brass alloy! Lots of pyro was invented before brass alloys could be determined to 5 significant figures!

 

The method used commercially for fine metal powders isn't popularly known, and many people have tried to replicate all of the named and numbered materials with little success. I know of two significant mill fires when supposedly skilled people milled metals.

[marnor]

thx for your answer.

I thinks i will stay on brass (whatever the composition) and order aluminium powder if i need some ^^

[R7T]

I have a question about ball mill media, I would like to mix lead balls with lead cylinders for a better grind. I read about this somewhere and they said it gave better results combing the 2 different shapes/sizes.

The problem I have is locating the lead cylinders, everywhere else has the lead balls in stock but I can not find the cylinders anywhere.

If anyone knows where I can find these I would really appreciate it.

 

Thanks

[Arthur]

I doubt the value of mixing balls and cylinders, though I've no data to prove this opinion. Look for several sizes of balls -most sizes are available, in ceramic or lead.

 

When the mining industry used ball mills they would fill the drum with media then, as the balls eroded, they would put more balls in the drum. This had the effect of keeping the drum full of a mix of sizes of balls.

 

Read the book on ball milling for better info with experimental data to back up their assumptions.

[Download]

Anyone got any tips for precrushing magnalium before ball milling? Some of the chunks are very hard and when they finally break into smaller pieces they go anywhere. I have to wonder if there's an easier way than a hammer.

[BetICouldMake1]

Anyone got any tips for precrushing magnalium before ball milling? Some of the chunks are very hard and when they finally break into smaller pieces they go anywhere. I have to wonder if there's an easier way than a hammer.

 

There are guys that use a quality blender to reduce initial size (ninja or vitamix). A cheaper blender will work, but expect to burn out your motor in a hurry. Obviously, as with milling MgAl, exercise caution.

[justvisiting]

When I had to pre-crush phenolic resin prior to ball-milling, I used my rocket press. I took pieces the size of limes and put them in a sleeve that sat in a plastic test cap. I used a piece of 3" diameter aluminum as the crusher. Magnalium is brittle like phenolic resin, so it should work similarly.

[Hext]

Excellent thread, this was incredibly helpful to me when I was making my ball mill.

 

Thank you.

[Mitchell]

To all, does this seem like a good deal for a ball mill motor? It is TEFC and already pregeared down to 60 RPM

 

https://www.ebay.com/itm/IRON-HORSE-MTR-P33-1AB18-MOTOR-33HP-115V-W-WORLD-WIDE-HDRF206-30-1-GEAR-XLNT-/322366675326

[BetICouldMake1]

It's not a terrible price but not really much cheaper than you would pay for a comparable new motor, and you can certainly find them cheaper. I picked up my 1/3hp TEFC motor on amazon for about $60 shipped. As for the geared reduction keep in mind that the target rpm is the speed of the jar, not the speed of the motor shaft. To determine that speed you need to do to pully calculations based on the the OD of your jar and roller shaft. The easiest way to get the correct speed is to use pullies on your motor shaft and drive shaft. This has the added benefit of increasing torque on the roller pully. Since the Jar OD is constant and your roller OD is likely predetermined based on your build, you can buy appropriate sized pullies to get your target rpm.

[slohand637]

Just wondering if anyone else has tried this; I dont have a tumbler ball mill, but I do have a vibratory brass polisher for bullet reloading. For an experiment, I dumped the media, poured in some marbles (I know its a big no no but this was just a test on charcoal) added some ground charcoal and turned it on for any hour. It was quite noisy, but it produced perfect air float charcoal powder.

Anyone else experiment with a vibratory polisher?

Just wondering if anyone else has tried this; I dont have a tumbler ball mill, but I do have a vibratory brass polisher for bullet reloading. For an experiment, I dumped the media, poured in some marbles (I know its a big no no but this was just a test on charcoal) added some ground charcoal and turned it on for any hour. It was quite noisy, but it produced perfect air float charcoal powder.

Anyone else experiment with a vibratory polisher?

[Arthur]

Never tried a vibratory mill, BUT I know they are used in the precious metal quarrying industry.

[SharkWhisperer]

Just wondering if anyone else has tried this; I dont have a tumbler ball mill, but I do have a vibratory brass polisher for bullet reloading. For an experiment, I dumped the media, poured in some marbles (I know its a big no no but this was just a test on charcoal) added some ground charcoal and turned it on for any hour. It was quite noisy, but it produced perfect air float charcoal powder.

Anyone else experiment with a vibratory polisher?

Just wondering if anyone else has tried this; I dont have a tumbler ball mill, but I do have a vibratory brass polisher for bullet reloading. For an experiment, I dumped the media, poured in some marbles (I know its a big no no but this was just a test on charcoal) added some ground charcoal and turned it on for any hour. It was quite noisy, but it produced perfect air float charcoal powder.

Anyone else experiment with a vibratory polisher?

Interesting. Never considered that or heard of anybody trying it before. What quantity of charcoal did you add? How big of charcoal chunks did you vibrate for an hour? What would be estimated max volume capacity?

 

That's a metal container, I'm guessing? If it's appropriate stainless, I'd be less concerned about sparking (marbles aside, though I've never seen/experienced a marble spark), but maybe more concerned about localized heating from that rapid vibration, or perhaps more frictional events/time than with a ball mill. Ultimately it's the friction of comps rubbed/pounded between balls in a mill that do the crushing, but temp rises would be expected to be negligible in a mill. Would be super cool to check the temp periodically with a handheld infrared meter to check temps.

 

I wouldn't even consider doing a complete BP mix in that unless tested extensively--single comps to be screen mixed or briefly milled might be great, but then what would the advantage be over a coffee grinder for smaller volumes? I'd also guess that if your container is metal, that your milling media might be degraded much faster in the vibrational cleaner from repeated micro-slamming against a hard metal surface.

 

Interesting though.

[SharkWhisperer]

Never tried a vibratory mill, BUT I know they are used in the precious metal quarrying industry.

But you're talking about a massive beast for crushing ore, no? Not a small unit for polishing brass. Similar mechanics but likely highly divergent parameters at their scales.

 

One limitation I could envision with the small vibratory unit is that your crushing media (and crushing field) would be limited to the bottom surface of your vessel because the milling media won't be lifted and dropped like a ball mill. So it's easy to envision that any chems added higher than the media layer would stay atop (and uncrushed) as the smaller particles fell towards the surface. Unless the whole damned thing was filled with media, but the motor probably wasn't designed for those weights.

 

With brass, your cartridges are submerged aren't they? It's not a dry polishing, right? Maybe you could do BP suspended in IPA, but then you'd have the same problem of comp settling by density (KNO3 on the bottom, charcoal on top)...

 

Anyways, sounds interesting, but would guess it's only useful for small quantities (half marble height; above this nothing is smacking together or grinding against container wall). Not sure I see the benefit over a coffee grinder for single chems or a mill for complete BP (or larger volumes of single chems). If it's all you have, it's all you have. Definitely better than a mortar/pestle, but not sure it'd be very practical for the chem quantities used in functional pyro?

 

But an interesting idea, for sure.

[slohand637]

To answer a few questions:

 

-The container is PE plastic.

-Brass is always polished dry.

-The bowl is designed to slowly turn over the media.

-I have a couple of blade grinders and they work well, but still dont produce a fully powdered, talc like product. This vibratory does it completely and rather quickly.

-I am a retired mechanical engineer who focused on mechanic design, automation and robotics. In my career I actually did some designing of monstrous vibratory polishers that were up to 20 feet tall snd 50 feet long, but with the right media ((usually ceramic) were used to polish fine China.

-I am a totally competent fabricator and builder, and have half the stuff to build a rotary tumbler in my shop. The only reason I tried this is, Im limited due to an elbow surgery, and I already had the vibratory polisher.

-I have used hardwood lump charcoal and homemade Easter red cedar in it. I do a pre-mill in a food processor.

 

One observationI have used half inch balls in it to this point. It seems that with the vibratory action, smaller media may be more effective.