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Author: Subject: ball mill question
Trotsky
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[*] posted on 1-6-2013 at 01:01
ball mill question


I recently made myself a pseudo ball mill, consisting of a large pill bottle wrapped in wire, the ends twisted tight around each other, inserted in an electric drill. I control the speed with another bit of wire, one wrap around the trigger and twisted around each other, tighten the twists to speed it up, loosen to show it. Pretty basic and chintzy.

However it works.

1) are lead balls required? I threw in some pennies and socket heads. It seems to be doing the trick. Do they offer any benefit over random hard chunks of metal?

2) how long do you usually mill aluminum for? I intend to use it in a potassium permanganate enhanced ammonal blend for bullet initiation.

3) will it all mill down or do you call time after some point and remove any larger chunks that remain? I have little powder so far but many tiny flakes, very tiny flakes. However there are also some larger pieces that don't seem to be milling down despite 24+ hours. I only have it running at night when I'm home, so I get about 12 hours a day. Four days should be 48 hours, I know, but the wire I used to hold it at first broke off at some unknown point on days two and three.


Thanks!
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Ral123
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[*] posted on 1-6-2013 at 01:11


How long will that drill last? Let me give you a hint, it's not made to work for days.
How do you expect to mill aluminium with lead balls?
In what scale do you plan the madness of mixing AN/KMnO4?
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Dornier 335A
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[*] posted on 1-6-2013 at 06:54


It takes about a week to mill the aluminium. You don't have to remove anything. Here is a good instruction.
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Hennig Brand
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[*] posted on 2-6-2013 at 08:15


Nice tutorial. Milling time varies though and is dependent on several factors. I have a homemade ball mill that uses a 1/2 hp induction motor and 4" PVC sewer pipe as a drum. It can mill 1/2 pound or so of aluminum sandings down to powder, that works well in small salutes mixed with KClO4 or KClO3, in about 2 days. I put a lot of steel balls in the drum. I used 3/8" steel slingshot ammunition because it was readily available. I think I put about $50 worth in the drum, at 5 dollars per pack of 75 that works out to 750 3/8" steel balls. It would have been nice to have larger media, at least half inch or so in diameter. A larger drum size is also much better for milling aluminum. I have materials for a 6" drum and an 8" drum but just never got around to building them. I found a nice piece of 8" PVC on the side of the road when the city had some streets dug up replacing sewer lines. I found a supplier for end caps, and quickly realized that the price of fittings go up very quickly as the pipe size increases. An end cap for 4" is about $5, for 8" about $20. Anyway, I am sure once I get the right motor and media, etc, I will be able to mill aluminum very quickly with the 8" drum.

Milling time also varies greatly depending on how fine a product you desire. The following was taken from Wikipedia.

Taken from Wikipedia:

"Bond Work Index

In the 1930s through early 1950s, Bond developed a new theory of comminution that introduced an index, called the 'Bond Work Index', which relates power consumption in crushing and grinding to the feed and product size distribution.[1] His theory and index were introduced in a widely cited 1952 journal article.[2] Bond called his theory the "third theory of comminution", counting those of Peter von Rittinger and Friedrich Kick as the first and second. This term and the terminology of "laws of comminution", as in "Rittinger's law", "Kick's law", and "Bond's law", are sometimes used in the field, along with those of subsequent researchers including Walker and Hukki.[3][4][5] Whereas Rittinger's theory held that the work done in breaking rock is proportional to the new surface area produced (that is, inversely proportional to the diameter of the product particles), and Kick's theory held that the work done is directly proportional to the reduction ratio (ratio of feed particle diameter to product particle diameter), Bond's theory held that the work varies inversely as the square root of the product particle diameters. Bond's theory and index brought a greater measure of openness to the calculations for selecting the type, size, and power ratings for ore milling equipment"


Example using Bond's theory:

Work is proportional to 1/ (Product Diameter) ^0.5 - 1/ (Feed Diameter) ^0.5

Going from say 1mm sandings to 100 mesh (149 micron) product gives 50.3
Going from 100 mesh (149 microns) to 625 mesh (20 micron) product gives 141.7

These values are not actual values of work but are only used to make a comparison between the energy required to mill to the 2 different sizes. Efficiencies were assumed to be equal in both cases and the constants were excluded.

Anyway, it takes 141.7/50.3 =~ 2.8 times as much energy to go from 100 mesh to 625 mesh than it does to go from 1mm to 100 mesh.

So as you can see a large amount of work is required to mill material down to a small particle size.


Attachment: Comminution Theory.pdf (967kB)
This file has been downloaded 4690 times


[Edited on 2-6-2013 by Hennig Brand]




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Trotsky
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[*] posted on 2-6-2013 at 12:26


I dunno how long it'll last, it barely gets warm after 12 hours, brushes will probably wear out quick though, I don't think it's brushless.


Your tubes turn like they're rolling, right? I have mine set up to flip end over end. It, turning real slow. As fast as I can set it so the pieces aren't just stuck to the ends
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Trotsky
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[*] posted on 2-6-2013 at 12:47


Oh for size of material, I'm planning on filling a pill bottle with the material. I'm not sure offhand how much that'll weigh
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Hennig Brand
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[*] posted on 2-6-2013 at 13:05


Not exactly sure who is talking to who, but we are all on the same subject so hey.

Yes, the drum rolls on rollers. The electric motor drives one of the rollers via a belt and pulley.
I have 3 strips of the same PVC piping, PVC glued (solvent welded) to the inside of the drum. These lifters greatly increase the tumbling effect of the balls and material to be milled in the drum. I don't remember the exact speed, but I remember looking it up and then changing pulley sizes 2 or 3 times to get the right rotational speed for the size of the drum. Balls should tumble inside the drum, not be glued to the side by excessive centrifugal force from excessive speed. Too little speed is bad also, balls don't climb sides enough and milling/grinding action is slower.

BTW, like the tutorial author I also add some fast burning charcoal (like is used for hot black powder) to the aluminum sandings before milling. I think I was using 5-10% charcoal.

I use a bench top belt sander to sand some aluminum scrap down to sandings.

I haven't made any aluminum powder in a while because I bought a bunch a while back.


[Edited on 2-6-2013 by Hennig Brand]




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Ral123
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[*] posted on 2-6-2013 at 16:34


Here's a tutorial for easy to make mill. It will grind quite hard materials with hard ceramic balls.
http://www.youtube.com/watch?v=58PBInYuJWU
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Trotsky
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[*] posted on 5-6-2013 at 10:27


How do you collect the shavings from the sander? Mine just flung them all over the place.
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Hennig Brand
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[*] posted on 6-6-2013 at 06:30


I set the whole thing in a box with the sander on an incline. Some was lost but most was recovered. If you use too much force it destroys the sanding belts quickly and at the same time results in more contamination of the aluminum sanding with grit from the belt. I was going to set something up that put a constant light pressure on the scrap, as it was fed into the sander, but never got around to it. Some sort of system exploiting gravity or a spring(s) was the idea, which would allow the system to just be monitored instead of applying pressure by hand. I think it took me about 45 fun filled minutes to get a half pound or so of aluminum sandings the last time.



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testimento
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[*] posted on 11-7-2013 at 22:44


Can one use hardened steel balls(not stainless) for milling aluminium? I plan to use PVC or stainless steel as the mill material, but SS balls are so sick priced in my country that I have to go for normal steel balls or something else. Even gave a thought for small rocks. :D
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[*] posted on 14-7-2013 at 04:46


I have seen ball mills for as little as $40 on Craigslist.

In that case it was about 18 inches diameter with 2 drive rollers. I believe it was somebody's ex-rock polisher.

I have also seen other rock polisher - same geometry as ball mills - on Craigslist, but more expensive, e.g. $100.

For grinding media, if you can live with steel, the old type with the ball. Most of them have about a .700 diameter steel ball, coated with rubber.

It may impart some impurities to the media being milled.


On to the ir-relevant section. I know one guy with a larger ball mill. He uses concrete balls to process low-yield gold ore. Processes about 20 tons a day, grinds it from rock to powder. Must be noisier than heck.

The guys at
http://goldrefiningforum.com/

are also interested in ball mills, they always have some active threads about them. Varying in size from smaller to humongous.

The rock-polisher type are about 10 inches diameter. The gold-mine type are about 4 meters diameter.
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[*] posted on 4-1-2014 at 06:15


Would it make the mill more efficient to make the drum from high strength steel instead of PVC tube? With this, when the balls tumble inside, they will also adhere between the drum and not only with other balls, and afaik this should create additional power.

I'm planning of using 250w motor to drive 160mm drum of steel or PVC at 180-240rpm with 1000pcs of 8mm steel balls and pre-grind the aluminium with blender.

Would it improve the effect to use some form of solvent, like ethanol or oil to adhere the aluminium?

Second, how fine should the powder get? I'd like to procceed all the way down to 1-10mic scale with few days of milling.
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[*] posted on 4-1-2014 at 07:24


Man where has this thread been, I had a lot of questions 2 months ago when I was building my ball mill, anyway I've answered almost all of them my self now, I still have 1 question, how fast is too fast? I'd be running it, and then it I would come back about 30 mins later, and it would act like a centerfuge, the contents would be on the outside of the container and it would make a lot less noise, (because no grinding was happening). I assume that all grinding affects cease as soon as this happens, the moter is from an electric mixer and there is no way to slow it down. Oh, one more question, would a smaller vessel prevent this action? Thanks.



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Dornier 335A
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[*] posted on 4-1-2014 at 07:56


180 rpm sounds way too fast. This is what it should look like inside:


[Edited on 4-1-2014 by Dornier 335A]
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Zyklon-A
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[*] posted on 4-1-2014 at 08:33


I think mine spins faster than 180 rpm, it's about 3 inches in diameter, maybe more?
Is there a formula to calculate how fast it can go based on the diameter of the vessel, and the density/weight of the powder and balls? Maybe some other factors as well, I don't know much about physics




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[*] posted on 4-1-2014 at 14:45


An upper limit on the angular velocity would be given by w=sqrt(g/r), where w is the angular velocity, g is acceleration due to gravity, and r is the radius of the ball mill. At this angular velocity the balls will not fall down at the top of the mill. Thus, for a 5 cm radius ball mill, the maximum angular velocity is about 14 radians per second, or 133 rpm.



As below, so above.
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confused
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[*] posted on 4-1-2014 at 18:55


no first hand experience, but from a web search found that it should be 60%-75% of the mill's critical speed

Nc =76.6(D-0.5)

Nc is the critical speed,in revolutions per minute,
D is the mill effective inside diameter, in feet.

https://sagmilling.com/tools_millspeed

[Edited on 5-1-2014 by confused]
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testimento
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[*] posted on 4-1-2014 at 23:35


So for 160mm OD 150mm ID mill would ideally work at 110RPM.

But how is the mill drum material? Will harder be better? I can do it from PVC or steel. Or does it matter at all?
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[*] posted on 5-1-2014 at 02:07


harder would be better but you might want to avoid any materials that might be spark or might produce alot of static

but people usually use pvc
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[*] posted on 5-1-2014 at 02:35


I dont think the sparking or static would be a problem, since the container will be airtight and aluminium does not react with plain steel - it needs oxidized iron. I have heard that using ceramic or SS media is required, but I see that this is necessary when manufacturing commercial, high grade powders, but for my use, in salutes, I don't wanna pay 5-10 times the cost of SS or special media.
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[*] posted on 5-1-2014 at 03:35


Here's what I use in my mill jars.

http://www.ebay.com/itm/310091049786?ssPageName=STRK:MEWAX:I...
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[*] posted on 5-1-2014 at 04:37


I use the alumina ball too.
20mm is OK for a small rock tumbler (with increased rpm), but not very effecient, for Oxidizers OK.

Ball milling aluminium does not pay off imho. It does not mill very well and takes too long, it's just not worthwhile.

Magnesium or magnalium maybe, if you dare to.
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[*] posted on 5-1-2014 at 07:01


I use a plactic container,
thanks for your help guys.




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testimento
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[*] posted on 5-1-2014 at 07:48


Lucky for you Americans to get everything delivered to your door in two days. Try to order something to this forsaken land of mine, and the only quick thing here is the state force. :D That should be a good enough indicator that any aluminium that is finer than 0.1mm at foil form is classified explosive and therefore illegal so milling is only option.
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