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Author: Subject: ball mill question
roXefeller
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[*] posted on 3-2-2014 at 14:51


I just finished my ball mill today while hanging out with the kids during their snow day. I used the drive from a frozen-bowl ice cream maker. It essentially turns a bowl slowly to push the product against a stationary agitator. It comes with two reductions to slow the motor to reasonable speeds. I tore it apart and mounted the motor/gears parallel to two rolling dowels and connected it with a wide gum band.
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Trotsky
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[*] posted on 4-2-2014 at 22:59


That's a good idea, but I use my ice cream maker. Home made gelato is wonderful
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roXefeller
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[*] posted on 5-2-2014 at 04:16


Eh, I can buy ice cream from the local creamery. They won't sell me pyrotechnic compositions though.:D
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Refinery
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[*] posted on 3-3-2014 at 23:03


I was thinking of making a planetary ball mill.

https://www.youtube.com/watch?v=0H0stoFw3DY

The idea is to make two different gears rotate around the center to balance out each other between to plates and bring up the rotational speed up to 300RPM.
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roXefeller
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[*] posted on 4-3-2014 at 16:41


300 seems fast, light it might throw everything to the circumference without tumbling.
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hyfalcon
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[*] posted on 4-3-2014 at 17:16


I run an 8" ball mill at 50 rpm. You don't want fast, that will glue your media to the sides of the mill jar.
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Refinery
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[*] posted on 4-3-2014 at 20:24


Please note: planetary mill. There high speeds are must. I have 6" ball mill on me and I run it at about 90RPM. The critical speed is around 120RPM and I can easily hear it when the rumbling sound stops because all media is stuck to the walls because of centrifugal forces.

My idea is to use one inbound gear and align two inner hears with bearings around an axle so when they rotate, they turn counter-clockwise 2-3 times per each revolution. Planetary mill idea is to rotate the media and material by the walls, and when the vessel turns, the media and material is ejected directly on the other wall, creating very high impact energy. Planetary mills are supposed to get 1mm particles below 10um 6-8 times faster than ordinary mills, so one could grind foil aluminium into dark pyro within 24 hours.

http://openi.nlm.nih.gov/imgs/512/358/3180689/3180689_1752-1...

If you can get the idea from this picture. The small pots contain the grinded stuff and the whole thing spins around 400RPM. The sub-gear rotation within the pot can reach even as high as 800-1600RPM.

[Edited on 5-3-2014 by Refinery]
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Refinery
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[*] posted on 5-3-2014 at 16:39


For those who understand more physics, is there any reasonable upper limits for plantary ball mill for critical speeds? For the reference picture I understand that the planetary flasks must be in critical revolution phase in order to work, but would the supporting disk have any upper limit?

planemils.jpg - 76kB
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Refinery
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[*] posted on 19-3-2014 at 10:51


For you to know, I am currently working on a planetary ball mill project. I have constructed a two-vessel structure with wooden gears and ran it for total of 2 hours now. Because I dont have lathe and other high level metalworking tools, I have hand-made the parts and therefore the tolerances are what they are. I dont have pics on hand because I forgot my camera to my workshop, but will post later. I did a 5-minute test with ballasts(I dont currently have the SS vessels, they are waiting for welding) using two plastic TCCA containers which fit into the rotating basket quite well, and the sheer centrifugal forces grinded the TCCA tablets down to powder during this time. I had to stop it because the containers were able to move few millimeters so that the metallic baskets began to grind through the walls of the baskets and there were a cloud of TCCA in the mill when I opened it. :D

The biggest problem so far is the noise. It's not just like rumbling of an ordinary ball mill, but imagine two 3-kg cylinders fixed at planetary gears to rotate at 900RPM around the planetary axis rotating about 300RPM powered by 1.2kW electric motor. :D The noise is so horrible that even when the mill is empty, I must wear protectors in my workshop. :D So sad my shop is too close to living compartments I could not leave the mill run there, so I must make some special arrangements. Well, I made a wooden coffin and simply buried the mill half-way to the ground and covered it with sandbags and installed some soundproof ventilation shaft and a fan, and now it is all quitet by 10 meters away and close it sounds like large but quiet diesel engine. :D

Waiting for some Al milling tests. Planetary mills should do the job in less than 24 hours what normal mills take weeks to do and they can't even get down to sub-micron level! :P
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roXefeller
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[*] posted on 20-3-2014 at 02:35


I imagine most of your noise is coming from gear tooth profiles and tolerances. Did you cut straight teeth or helical? Did you say that you powdered tablets in five minutes?
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[*] posted on 26-3-2014 at 20:35


I found a very reasonably priced professional ball mill at cannonfuse.com, I would check there.



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Amos
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[*] posted on 27-3-2014 at 07:04


If you continue having trouble with your ball mill, your grinding media may be lining up in a way that disrupts the grinding process. Upon adding a plastic bar along the inside diameter of my canister; this kept the balls from lining up and greatly sped up the process.
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[*] posted on 18-2-2016 at 16:02


Here is another critical speed calculator for wanna be metallurgists and a ball size calculator https://www.911metallurgist.com/blog/top-ball-size-grinding-... and more https://www.911metallurgist.com/blog/EQ
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[*] posted on 18-2-2016 at 16:26


Will something like this work as a ball mill if I use alumina balls: http://www.ebay.com/itm/ROLLING-STONES-MODEL-635-ROCK-TUMBLE...
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[*] posted on 19-2-2016 at 06:06


I had the exact same rock tumbler, when I started milling things, which I got at a yard sale for $3 IIRC. I used it to make 10-15g of flake aluminum powder at a time suitable for flash powder for small firecrackers in 4 days or so from aluminum sandings. Stainless Steel sling shot ammo was used as grinding media. Used to make small batches of black powder with it too. Eventually (after about 10-12 batches) the drive wheel got worn down to the point that it wouldn't drive the drum anymore (I assume all the aluminum dust on the drum and wheel accelerated the wearing). I assume the rubber drive wheel could have been replaced, but it wasn't a great setup anyway. It was too small and the drum couldn't be sealed well at all; there was a big gap where the two pieces of the drum fit together which I sealed with tape as best I could and ran the mill on an incline so the powder was less likely to escape. I built a mill with a PVC drain pipe drum after that which was much better in every way.



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[*] posted on 19-2-2016 at 06:15


I would be concerned that alumina may not have the mass to grind much in such a small ball mill, +1 for building your own ball mill to the specifications you need
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[*] posted on 19-2-2016 at 06:50


If you are going to re purpose a rock polisher, larger diameter is always better. 6" ID and up drums will make for much shorter working times when grinding Al powders.

Alumina works, given a large enough Dia. mill jar and larger pieces of media, but heavy media like ball bearings works much faster.




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[*] posted on 20-2-2016 at 01:39


Hmm... looks like I might have to build a ball mill.

I am very curious about United Nuclear's, but every time I check, they are sold out.
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[*] posted on 1-3-2016 at 06:19


I built home made ball mill and I used washing machine motor.
the motor was overheated after few days of running however I used a fan to cool it down.
I think washing machines motors are not suitable to work for continues operation!!
any better suggestions ?

[Edited on 1-3-2016 by ecos]
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James Ikanov
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[*] posted on 1-3-2016 at 08:14


Perhaps the motor from a dryer?

I might be off, but I would consider the work load more comparable between a ball mill and a dryer than a washing machine and a ball mill.

If nothing else works, then perhaps you could consider putting your motor on a timer, so it has enough time to cool down occasionally? Even one of those "I'm going on vacation but want the lights to flick on/off for a few hours" type deals that plug into the wall could probably be had fairly cheap, if you're using out the wall current.




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[*] posted on 1-3-2016 at 09:54


the washing and dryer motors are "universal motors"

from wiki:

Quote:

negative aspect is that these motors may only be used where mostly-clean air is present at all times. Due to the dramatically increased risk of overheating, totally-enclosed fan cooled universal motors would be impractical, though some have been made. Such a motor would need a large fan to circulate enough air, decreasing efficiency since the motor must use more energy to cool itself. The impracticality comes from the resulting size, weight, and thermal management issues which open motors have none of.


It is a headache to reduce the speed of the universal motor using pulleys since it has average speed of 10,000 RPM. Mine has 16,000 RPM

I am thinking to use fan motor (induction motor), I am not sure yet if it is the right choice or not !!! :(
at least induction motors has better power efficiency but I am not sure about overheating.
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[*] posted on 1-3-2016 at 13:09


Trotsky: If you ever scale your ball mill up, here are some great materials I use that you might like too. The belt would be the rubber inner tube from a child's bicycle, with a diameter of 20 inches. One roller would be a PVC tube coated in this rubber too, and the other would just be inverted wheels from scrapped furniture. (The wheeled type used for patios and workshops)
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[*] posted on 1-3-2016 at 19:00


Quote: Originally posted by ecos  
the washing and dryer motors are "universal motors"

Snip

It is a headache to reduce the speed of the universal motor using pulleys since it has average speed of 10,000 RPM. Mine has 16,000 RPM

I am thinking to use fan motor (induction motor), I am not sure yet if it is the right choice or not !!! :(
at least induction motors has better power efficiency but I am not sure about overheating.


Most dryers have an induction motor. See the one I extracted a few days ago. Unfortunately one of its bearings is worn out. Its a pity as its a nice size (smaller than than many I see) for a mill.

Yes getting the rpm geared down is pain. I prefer a belt reduction system as its more tolerant of build tolerances.

With a universal motor you can probably use a triac phase controller to adjust the rpm or even better an adjustable dc power supply.

WP_20160302_01_29_05_Pro.jpg - 1.3MB
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[*] posted on 1-3-2016 at 20:12


I have the weirdest old electric stirrer from the 60s or older, which has a controllable rpm. Pretty big score, also considering how durable and strong the motor is.
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[*] posted on 2-3-2016 at 01:15


I think dryers and washing machines motors are not designed to work for 11 days continuously without stop!

in their work , they run for certain point then stop again and so on, this is not as stressful as running for days without stop.

I am thinking that a fan motor or air pump motor will be the best solution since their normal work is to run for long time !

I am still thinking about better solution !

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