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15th September 2010 01:31
Hi Alan
Thanks for the great ball mill information. I have a question regarding the mill running time.
My ballmill is homemade with a 3/4hp motor, it can run two 1 gallon jars with 30lbs of 1/2" lead balls in each.
I`m finding aggregation occuring after about 1 hour mill running time. With a material charge of 20oz per jar and an optimum 70rpm rotaion speed, the bp eventually compacts into a fairly solid mass at one end of the jar.
I am correct in assuming this aggregation signals the end of the milling process?
Regards
Col
30th June 2009 11:49
Hi Alan
Great minds think alike! I've been successfully using pedestal fan motors for years on my mills. 20 bucks at Big W gets you a relatively low speed, reasonable torue AC motor with speed controller! The first motor burn't out due to over-heating so I ripped out the blade assembly from a dead pc cooling fan & epoxied it on the the rear of the motor spindle. My motors run barely warm to touch for extensive periods now.
I notice a lot of comments on belts, bearings and pulleys. I too have had the same problems over the years and have tried many solutions, some good, others pathetic results. Here are my tips for home-brew mill-makers that have worked best for me.
Bearings: I rip out the bearings from old skateboards, scooters, rollerblades etc. they might have too small a bore for some apps but I use threaded rod from Bunnings which fits perfectly snug.
Belts: Have tried everything from small machinery V-belts, washing machine belts, O-rings etc. with mixed results. I now soley use a product called Redthane. I got it at a bearing shop for about AUD$15 per metre. It looks like surfboard leg-rope and you cut it to whatever length you need and use a tiny aluminuim joiner. I have never had a join come apart, it doesn't stretch after years of use, and it grips to almost any surface no matter what the tension.
Pulleys: The hardest one to solve! If you use Redthane as a belt, you can use almost anything for a pulley. One of my first pulleys was stolen from my son's Lego. There is also a site called smallparts.com.au where you can buy almost any little part imaginable.
Fantastic site Alan, and I hope my tips might save at least one person from going down all the Ball mill dead-ends that I did.
Guy
p.s I use a pedestal fan motor for my star roller too!
29th May 2009 17:23
Jon,
Washers and Nuts. No really - its a royal hack, truly horrible. There are two washers trapped between three nuts. I wound some cotton twine around them to improve the grip on the rubber belts. You could use a couple of different sized washers for something a bit better I guess?
If I ever rebuild it I'd probably use direct drive, the shaded-pole fan motor isn't very high RPM and the current pulley ratio is almost 1:1 anyway. I may eventually convert the current one with a flexible coupling, say a piece of PVC pipe and hose clamps to absorb any slight misalignment.
Then again, if I did build one again I'd probably build it with more guts and designed for optimum speed with 150 mm jars.
Regards,
Alan
29th May 2009 15:01
Hi Alan just looking at your ball mill and was wondering what hardware you used to make the pulleys for the drive belts?
Thanks, Jon.
21st January 2009 21:33
Andy,
Milling BP is as always a calculated risk. With Lead or Copper/Brass media it has a relatively good safety record, but remote operation is advisable. It is almost impossible to make very fast BP without milling of some kind, and the ball mill is more accessible and arguably safer than the alternatives.
Not all motors will like being speed controlled with a phase angle controller. Good point about covering the terminal block though.
Regards,
Alan
21st January 2009 14:51
Oh and on a small design note, an option which may add to functionality and electrical safety is to replace the terminal strip with a dimmer switch, this gives a true variable speed unit, no need for the fan speed controls and encloses any bare wires/screws......
21st January 2009 14:04
Nice job and nice site.....I do a fair bit with pyro and if anyone does use the mill for black powder I would advise not adding the nitrate to the mix!!!! And NEVER mill flash powders or any CHLORATE based powders....!
As for bearings, even I can buy just about any size and I'm in Thailand!!!! Good old SKF, bags of 10 are as cheap as chips just need to de-oil them first.
11th October 2008 12:00
Bert,
Well ~10 mm balls would be useful for milling sea shells in a suitably sized mill jar.
Regards,
Alan
11th October 2008 11:58
Oh, I made a silly mistake, and did you notice that I typed "0.5~1.0mm" in the yesterday's post ? Sorry, it should be "cm"(centimeter) instead.
11th October 2008 11:50
Oh, I see. So, how do you get the chrome-steel balls?
11th October 2008 11:48
Bert,
Did you try searching on eBay? There are lots of vendors that sell the balls without the races. SKF are a massive company that wholesales bearing components world-wide, no doubt they make what you need, but you'd probably have to buy from a retailer of some description.
There is a US eBay seller called "ToolSupply" that carries just about every kind of ball imaginable, including brass which would be suitable for BP milling. I've never purchased from them, but they look promising.
Regards,
Alan
11th October 2008 11:38
Thanks! Recently, I found a bearing shop, "SKF bearings" . What do you think about it? Can I get just get chrome/stainless balls without the ball bearing?
11th October 2008 11:06
Bert,
Hello again! That media sounds like what jewellers use to rough polish articles they have made, or what reloaders use to polish their spent brass shell casings. It is great for doing just that but not very useful for milling material to a fine powder.
Often that stuff isn't used in ball mills, but rather vibration mills, I recently saw the "saturn" shaped media being used on "How its Made" in a vibratory mill for polishing Zippo-style lighters before nickel plating them.
I'd say 3/8" or 1/2" ball bearings are probably best for your sea shells. For black powder I'd use Lead fishing sinkers of a similar size which are easy to get or make - again it depends on your mill jar size. For sourcing steel balls try eBay, there are many vendors selling them, search for "Chrome Steel Bearing Balls". For 1/2" balls there are about 120 to a 1 kg, and about 280 balls to the kg for 3/8". Postage will be the killer because they are massy. You can calculate the number needed based on the spherical packing ratios and the volume of your mill jar. Get more than you need, preferably several sets.
10th October 2008 17:40
Hi again, Alan. It has been so long since the last post I made. I have a good news here, that is, I found a "goldsmith's shop", and there were plenty of good things there, including the stainless steel balls.They don't call it ball mill media, but "polishing balls". They were in the shape of balls, rods, and one in the shape of saturn(a sphere with a ring around it). Which should I choose? The bad news is, it is small. The diameter is around 0.5~1.0 mm. Can I use that?
15th August 2008 12:00
Hi Alan,Thanks for the great idea for building the ball mill, they work great.I am running the motor dirctly onto one of the shafts using a 3 inch piece of tubing (same as on the rollers)secured with zip ties,this works more reliably than the belt.Ihave also found a fan to be agood idea, my first motor melted down after running cintinuously for 5 hours.I have begun building a longer version (24 inches)running two fan motors,one direct driving each shaft.
3rd April 2008 17:33
I added it after I took the photos.
It is attached to that grey cap thing on the end of the motor output shaft. Originally it held the fan blades in place, but the original blades were far too big, so I fashioned something fan-like from a cardboard box. Its a horrible hack, but it keeps the motor sufficiently cool to allow continuous operation.
The mill looks pretty beaten up after its years of operation actually. I might take another photo of it for comparison, and the jars I now use... Would be a more accurate depiction of its current configuration.
Some BP leaked on it at one point, and the KNO3 fertilised some mould spores which took a liking to the timber. So it now has some discolouration and roughness on the base too.
3rd April 2008 17:15
But I don't see any!
1st April 2008 23:37
Bert,
Yep, mine got very hot pretty quickly, so I made a fan out of cardboard and put it on the motor shaft to blow air over the motor. That keeps it at a warm-to-the-touch temp, not stinking hot and leaving skin when you touch it temp.
Regards,
Alan
1st April 2008 23:02
Now,I am using the second lowest speed for my motor, but, it heats up very fast , and it was too hot to touch approx 70 Celsius (in 5~10 minutes). Would yours heats up that fast,that hot?
1st April 2008 19:09
Wow!Thanks for your looooooooonnnnnnnnngggggggg reply!
1st April 2008 10:46
Bert,
Wow, you ask a lot of questions... I like that, really I do! It is how us Humans learn, but much of what you ask is learnable online or at a library. I'll share what I've learnt with anyone, but I sense you are trusting me literally and not doing too much sanity checking or alternative thought on what I am telling you. That's the worst thing anyone can do, for all you know I have no idea what I am talking about and could be leading you into injuring yourself!
My general advice for all things applies to ball mills as much as any other geeky endeavour:
- Common sense first!
- Keep you distance from something with a lot of stored energy in any form.
- PPE is not optional (and absolutely mandatory for situations of significant stored energy or toxic emissions).
- Do the research and the maths before spending a lot of time/money on something. The internet is a modern geek's blessing.
- However, never be afraid to do empirical experiments, even on hopelessly inefficient or simplified systems. Be Sceptical of everything. Much advice out there is for efficient or optimal designs, many things will work sufficient for your purposes even hopelessly "wrong" according to the texts. I guess this really means "trust no one", in the sense that common wisdom is often completely wrong or comes from a position of differing interests.
- Optimise after getting basic operation. Spending days of inaction waiting for a perfect device is pretty pointless. Most physical principles of the universe can be demonstrated by very crude equipment, just look how far the pioneers got with only a fraction of the technology and knowledge we have now.
- That said, never compromise safety for expediency.
Anyway, to answer your questions specifically:
I'd go 3/8" for that jar, but its more often a question of what you can get cheap. I am not sure how to calculate the optimal size.
Lifter bars can help a lot if there is media slippage. I've used jars with and without lifters. Most of my jars don't have lifters and are just a random plastic jar of roughly the right diameter to fit the rollers. Hexagonal drums are another option.
I look at it this way, if you are doing it commercially, or even as an amateur on a large scale then its worthwhile optimising everything. For a smaller mill that won't be frequently used then almost anything will work, but it might take a while. Many amateur pyrotechnicians use rock tumblers (which are vastly under-powered and too slow to be efficient mills) to make usable BP, it just takes longer and can't process as big of a batch as a Sponenburgh mill.
To grind eggshells to a talc-like consistency takes about 1 day for me with a somewhat undercharged mill running chrome steel balls for media. I put them in fairly coarse "gritty" straight from a few seconds in a coffee grinder. Because it is "food" for my bird, I obviously don't use lead media. Sometimes I use ceramic too, which works fine but takes a little longer because the media masses less.
Sea shells are somewhat denser calcite and aragonite crystalite phases (bound in a protein matrix) than hen egg shells. Egg shells are primarily calcite and are less well mineralised than most marine animal shells, so they will be marginally softer. Keep some coarse material from the original charge out of the mill and compare it with material sampled from the mill periodically, this will tell you how well and fast your mill is processing the charge.
I'd pick the Steel balls, because I won't have to cut up the steel rods! Rod mills I haven't experimented with, but I could see the rods getting tangled up pretty easily, depending on their size relative to the mill drum and charge. Balls and short cylinders I understand much better and have tooled around (extraction screens, etc). Bearing balls, cut up rods, fishing sinkers, hex nuts, ceramic pyramids and beads, etc. It all works.
Most importantly though, the media type should be matched to the charge. Lead can't be used for "pure" chemicals or anything you are likely to feed to a living organism. However Lead is really the only well-studied and generally safe choice for black powder processing. Some experience is available on Copper-clad Lead and Brass for BP, even non-sparking Stainless Steel alloys, but Lead is much easier to work with, as it can just be cast into media forms at quite a low temperature. Ceramic media is well studied for metal and single-chemical milling, but there is plenty of accident reports for its use with live compositions. Its best to dedicate a media and drum set to each particular type of charge, cleaning media and the drum is nearly impossible unless the charge is water soluble.
The media should be compatible with the charge - that kinda common sense. Non-corrosive chemicals can be milled with raw steel/iron media, but in general I'd avoid steel media except for chrome/stainless steel, even they will stain things and corrode is left uncleaned or damp with many common chemicals.
I wouldn't use a tin can for a mill jar. Not only would it be enormously loud compared to a polymer one, but it would rapidly loose its inner tin coating and rust away quite quickly. PVC water pipe makes very robust jars, hard rubber makes quiet ones. Any old plastic jar the right size works in a pinch.
Milling metal takes a long time (it doesn't scale down well). I use ceramic media for that, so not only does the metal get "stamped" by the media collisions, it also gets abraded a bit (until it clogs with fine metal dust). I've generally used atomised Aluminium, shavings or swarf which is already pretty small, some people report good success with cross-cut paper shredders fed with Aluminium cooking foil. For Magnalium I used granular material, probably -10 mesh, from busting up bulk Magnalium with a hammer. Magnesium I only tried once and feel somewhat lucky I got away with it without incident when I hear of other rather nasty experiences.
All I can say about milling metal is that you should be extra careful with it. Metal flash-fires are extremely energetic and can cause as much damage by their radiated light than direct flame contact. Lloyd's Magnesium accident (not milling, just mixing using a mill) is a case in point. He was severely sunburnt by the shortwave light, but didn't even loose his body hair.
Regards,
Alan
31st March 2008 21:03
If you have steel rods and steel balls of same diameter, what will you choose as media for grinding?
Sardine can or PVC tubing,which is more durable to use as the jar?
Thanks a lot.
31st March 2008 20:33
How long would you take to grind eggshells into powder?
I am currently grinding sea shells.
31st March 2008 17:52
My jar was 3.5" diameter, and have four lifter bars around the inside of the jar. What is the optimal media size for this jar?
Each lifter bar was 1cm wide, 0.4cm high.Would it be too big for me?
Can lifter bars increase the efficiency of the mill enormously?
I wonder how can I grind aluminium? What must I do to prepare the aluminium ready for ball milling?
30th March 2008 21:44
Bert,
My mill is quite a bit slow for its size about 65 RPM, it should run near 100 RPM.
Ball mills are typically run at about 75-90% of the critical speed. The critical speed is the speed at which the media simply centrifuges right around against the walls. Smaller mills need to run faster, the critical speed is about 42/sqrt(diameter in metres). So, for a 4" jar (100 mm) the critical speed is about 140 RPM. Normal speed for good efficiency would be about 100-120 RPM.
Efficiency increases with diameter too, so larger jars tuning slower can be more efficient than smaller jars going quicker. There is some optimal media size, but I'm not sure how to calculate it. Even just intuitively it is easy to see that the media shouldn't be too large or too small. 3/8" is about right for a small 4" mill, 1/2" is better for your "average" amateur 6" mill. I've used 1/4" fishing sinkers in 3" jars which actually seems a little large.
Remember that even the massive, optimised commercial mills for processing cement clinker are lucky to be even 2% efficient! The other 98% of the input energy (typically Megawatts) just heats up the charge and media.
Regards,
Alan
30th March 2008 15:08
How fast do your ball mill's container turn?
I used the fastest speed of the fan, and used no reduction gear, and I get about 70 rpm. Is it too fast?
30th March 2008 15:05
Thanks for your help!
I sticked some inner tube in the motor shaft , like you put some tape around it, and it works.
During the construction, I used a lot of inner tube and contact adhesive,and the work paid for me.It's worth it.
Thanks.
30th March 2008 02:35
Bert,
Mine slipped a little at first too, I wrapped some twine and tape around my motor shaft to give a better grip on the belt and a centring "mound", belts run "up-hill" so convexity on the contact surface tends to keep them centred without flanges. A larger pulley on the roller so there is some reduction will help enormously. My current belt is about 8 mm wide.
Like me, you are using very non-ideal materials to build this device, so it is anticipated that it may not work very well. Some fiddling will be required no doubt, but the basic mechanics don't really change.
Regards,
Alan
30th March 2008 00:34
No,no. I mean, the belt slips at the driver pulley(actually,no pulley like the one in your picture).
How wide was your belt is? Mine was slightly more than 1cm.
29th March 2008 22:19
Try a tensioning idler pulley, or direct drive. Otherwise, increase the size of the pulley on the roller and use a wider belt.
29th March 2008 21:28
I made a belt with inner tube, and I hook it up. But, it has a problem, that is, when loaded with a 300g media, it slips and does not turn, but the motor continued to turn and turn, without obvious speed change.I have made sure that the belt is tight, and now I can do nothing to fix this problem. And, it slips at the shaft of the motor. What can I do?
28th March 2008 11:46
Bert,
I'd say try it and see!
You can probably cut a piece from an inner tube that doesn't need to be glued at all. Its a Torus after all, you can make any length between its cross-sectional circumference to its outer circumference by cutting it differently. Obviously oblique cuts will give you oddly shaped bands, but you may be able to arrange the motor to roller distance to match one of the three "square" options.
You can always try direct drive eliminating the belt all together. Most cheap fan motors are shaded pole devices which have a fairly low speed. Unfortunately they also have a pretty low torque, so this may not work. Fan motors are probably the worst choice possible really, but I used one for mine because of the very small scale of my mill (and it worked fine because it isn't a shaded pole motor, its a capacitor-start squirrel-cage induction motor). A short flexible coupling can be made between the motor and the roller with some tubing and hose clamps to absorb vibration and compensate for any slight alignment errors.
Regards,
Alan
28th March 2008 00:06
Sorry to interrupt, but I have some problems regarding the materials.
Can I make my own belt by using inner tube? How long will it last? I cannot find such belt like yours.
Which is better? Contact adhesive or rubber cement?
27th March 2008 22:36
Bert,
Threaded rod can be cut with a hacksaw fitted with a suitable blade. Best to put a nut on it first so you can screw the nut off over the cut and clean up any damage to the thread.
Real bearings are the best bet, you don't want the bearings to overheat and fail or wear and become sloppy. You can get bearings for inline skates fairly cheaply, even from places like Big-W. They are suitable for smaller toy mills like this.
Regards,
Alan
27th March 2008 21:43
Haha! Everyone think I was crazy, because I bought 2 meter screw(with no screw heads, and it has screw threads all over the screw).I have to cut it to smaller pieces by using a saw since the "bolts and nuts" shop doesn't have any machine to cut it.
I made sleeve bearings by using aluminium foil to wrap tightly on the screw surface, and tighten it with two nuts at both ends.I use two piece of wood, make two holes on each piece, and put the bearing into the holes. It was almost frictionless!
26th March 2008 23:10
Bert,
You mean the input material for the mill?
I dunno, "sugary" granular stuff at worst. Sometimes lumpy charcoal, takes a bit longer but it will break it down to airfloat eventually. Screening and roughing stuff down to a reasonable size can't hurt.
Regards,
Alan
26th March 2008 18:49
Finally, the last question. Until now, how fine was the material ground?Air float?0.05mm?
26th March 2008 11:47
Bert,
You don't really need to fix the roller to the bearing inner race, unless it is a very sloppy fit. Mine was friction fit, but I tightened a nut to either side of the inner race to stop is sliding. The nuts were just small enough to not touch the outer race of the bearing (stationary) and still bear against the inner race. The bearings I used have seals on the cages which are slightly inlaid compared to the inner race.
The optimal media charge for a ball mill is roughly half-full. The charge itself should be just sufficient to completely intercalate with the media and *just* over half fill once milled. For fine unmilled charge material this is a little more than just covering the media when shook into the spaces around the media. It isn't extremely critical, and somewhat less media or somewhat more charge will only marginally reduce the efficiency. Too much charge or media will rapidly reduce the efficiency though, and too little charge tends to wear the media more quickly. Optimum speed is also important.
If you have more than just a passing interest in ball milling then I recommend you get Lloyd Sponenburgh's book Ball Milling Theory and Practice for the Amateur Pyrotechnician. There is also much information available online in various journals. Ball milling is big business, commercial mills are used on massive scales and use enormous amounts of power, as such they are a well-studied science to optimise their operation.
Regards,
Alan
26th March 2008 01:06
Hi again.
How many steel balls you use for the mill? What is the size?How long do you grind it(to get the powdered material)?
25th March 2008 20:46
Hmm, I have one more question, that is, how do you fix the bearing to the roller? It has screw threads on its surface!
25th March 2008 10:27
Bert,
For grip you can try rubber hose over the rollers. I used PVC, which isn't very successful, but by putting rubber bands on the mill jars it gives a reasonable grip. Unfortunately they quickly perish, but they are cheap to replace and will generally last a batch.
Belts present a bit of a problem. It also depends on what pulleys you are using which kind of belt will match your mill. I use turn table belts which I got from Dick Smith Electronics in a pack of assorted sizes. For larger mills you'd probably use belts designed for car engines or drill presses and other assorted machine shop machines. Worst case you can laminate inner tube or rubber gloves or something with RTV or even tyre repair kits. Doubt it would last long, but it beats string which tends to rapidly fray and tangle up in everything.
Media used depends on the Charge. For pyrotechnic compositions use Lead! Fishing sinkers are relatively expensive for the Lead they contain and have holes, but are easily available. Musket balls are fairly traditional, or you can cast your own with a musket ball mould (or even just some holes drilled in a piece of timber, there is no need for media to be spherical and molten Lead will just char *dry* timber). Nothing else but Lead is really well tested enough to be considered safe, except perhaps brass or copper which is just more expensive, harder to get and annoying to work with (and is dangerous with some compositions).
If you are just milling separate chemicals then hex nuts work quite well. They work on metals softer than them, but loose their Zinc coating quickly. For oxidisers they will rust very quickly. Screws and bolts may work, but aren't "convex" and will probably fill with unmilled material quickly. Ball bearings are ideal for milling separate chemicals and metals, but will also rust if not kept dry and clean.
Regards,
Alan
24th March 2008 23:20
Hi Alan.
I have built a similar ball mill like yours, using a 40W electric fan motor.It seems like the roller do not provide a good grip for the container to turn.How can I improve it?
Where can I buy a small belt for this machine?(give me some examples)
Can I use screws or nails as grinding media, since screws and nails are cheap here and I can't find any shop which sells steel balls and bearings.
Thanks.
10th March 2008 17:49
Cecilia,
I don't know if a ball mill would work well for pulping plant fibres? At least not on a small scale, I suspect it would tend to cease up. Although I'd imagine it might be superior to pulping in a blender which would tend to chop up and shorten the fibres.
I've pulped scrap paper before in a kitchen blender with excess water, then reformed the pulp into different things (like rocket cones, or used it as an additive to blackmatch slurry to make it more robust). I'd imagine this would work for your paper making as well.
Other than that I don't know much about making paper, other than I believe chemicals (hydroxide + sulfide or acidic sulfite) are used to break down the lignin and leave just the cellulose. I've never tried boiling up plant material in such a brew, does it just fall apart? Commercially the timber is chipped first, which must limit the length of the fibres? Sounds like a rather smelly process, especially for Kraft...
Regards,
Alan
8th March 2008 00:10
Hi Alan, I am so glad I found your website. I am a fellow geek in so much as I love computers, steam driven machinery and thinking up different ways to do things but I am NOWHERE NEAR as talented as you and would not know where to start making projects like yours. I am in awe of the ball mill you made as it would be PERFECT for my experiments with making paper out of assorted fibrous plants. I was wondering how much you'd charge for one, and if you ever make them for other people?
Cecilia (Melbourne)
22nd September 2010 23:35
Dave wrote...