RogueRose
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Ball Mill design for multiple containers & multi-size & use of inert gas usage
I've seen a number of designs for ball mills and some use what seems like an awefully large motor for one mill (like 1/2 to 3/4 hp). I want to build
one that will accept a number of containers - like gallon paint cans - maybe up to 6 or so if possible. I also would like to be able to use quart and
pint paint cans for smaller milling jobs.
I have seen mills that have a drive wheel located above the mill container that pressed down on the container and turns it. I think this won't be
easy for a multi container setup.
My idea was to have two parallel shafts/rods/pipes that connect to a vertical board/wall that has a ball bearing for each of the shafts (so say 4
total). One of the shafts will extend through the wall and will have a pulley or a gear for power transfer to turn that shaft.
I was thinking that the drive shaft might work best as something like a 2-4" diameter PVC pipe with a metal shaft running through it. I plan on
wrapping the PVC in something like duct or Gorilla tape or maybe some very thin silicone (like the silicon baking sheets that are maybe 1-1.5mm
thick). This should give the drive shaft grip on the milling containers. I don't know what other options there are for this or if there are better
alternatives - any ideas on that?
As far as the non-drive shaft, I was thinking that using lots of small ball bearings all along the shaft maybe every 4" or so - this way those would
spin independently of the entire shaft which may be important if turning multiple size containers. I think it may be necessary to add the silicone
sheet or tape to these as well which would allow them to turn with the spinning container (it would probably be more quiet as well).
The biggest question I have is with the multiple size containers. If the gallon is turning at optimum speed will the small ones be turning slower or
faster or would they be the same?? I'm thinking slower??
As far as the drive mechanism I plan on a simple motor with a pulley. There will be a 3 level pulley on either the motor or the drive shaft to allow
for different speeds. I guess another alternative would be to use a multi-speed motor or use something like a PWM or a router speed controller
(depends on the type of motor used).
Finally I am kind of concerned about the containers. I will probably line the outside with a tape or silicone pad (probably tape as it may adhere
better) which will help deaden any sound. I'm considering adding some in/outlets for injecting something like nitrogen or argon into the vessel to
purge as much air/O2 as possible as it seems that oxidation of fine powders is one of the biggest enemies of this process.
This brings me to another issue - what gas would be best to use? N2? Argon? CO2? One of the most popular uses seems to be powdering things like
nitrates, chlorates, oxides, metals like Al and Mg. The metals are the main reason I am considering adding the gas vents.
What I am concerned about is once the milling is done and the container is opened can the metal spontaneously oxidize/combust? If that is a
possibility, is there something that should be done? I know that adding something like stearic acid (at a VERY low %) to Al will help coat the Al to
prevent oxidation. Would putting the container in the fridge/freezer prior to opening reduce any risk of fire?
Well, I think those are the biggest concerns I have for the mill ATM but any comments and suggestions are welcome.
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Dr.Bob
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Most of these questions are likely already answered on the energetics part of this forum. You might want to look there. Also, be aware to never
reuse any container for non-compatible materials, like Al and any oxidant, that can be very bad. Worse yet, don't ever mill mixtures of chemicals,
always mill each one separately, and then mix them. Yes, there are exceptions for experts and certain mixes, but the experts will know what those
are and why it is OK. Even experts blow up occasionally doing that.
Inert gas is best done at the beginning and end of the process, hard to do during the process. CO2 is NOT an inert gas around metals, but argon is
ideal, and N2 would be better than nothing. Depends on the chemical if you need it. But be careful, read the warnings in the energetics area and
learn from experienced people, if they are old, then likely have not made many dumb mistakes.
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RogueRose
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Quote: Originally posted by Dr.Bob  | Most of these questions are likely already answered on the energetics part of this forum. You might want to look there. Also, be aware to never
reuse any container for non-compatible materials, like Al and any oxidant, that can be very bad. Worse yet, don't ever mill mixtures of chemicals,
always mill each one separately, and then mix them. Yes, there are exceptions for experts and certain mixes, but the experts will know what those
are and why it is OK. Even experts blow up occasionally doing that.
Inert gas is best done at the beginning and end of the process, hard to do during the process. CO2 is NOT an inert gas around metals, but argon is
ideal, and N2 would be better than nothing. Depends on the chemical if you need it. But be careful, read the warnings in the energetics area and
learn from experienced people, if they are old, then likely have not made many dumb mistakes. |
Lots of good points, thank you. I was planning on keeping the chemicals separately that is why I wanted to make a mill that can handle multiple
containers at one time.
Just out of curiosity is it possible to mill black powder (not in separate components) - not that I would do it - I had read some people saying that
they do this. I have heard of adding water to the black powder and grinding it with a mortar and pestle, some people have stated adding some kind of
alcohol (not sure if it was meth/eth/iso) and milling/grinding. The person stated 7-10% moisture by weight for this process.
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Fulmen
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Regarding motor sizing: These motors (1/2HP+) are chosen for several reasons, partly due to the availability (broken washing machines etc) but mostly
due to the needed starting torque. A 6" lead-filled jar weights a lot, and many AC-motors suffer from low starting torque.
As for milling black power, it's the only practical route to commercial grade BP at home. The mill media must be soft and non-sparking (lead or
possibly bronze), and you have to take the risk of an explosion into account.
We're not banging rocks together here. We know how to put a man back together.
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Bert
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Mood: " I think we are all going to die. I think that love is an illusion. We are flawed, my darling".
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Lloyd Sponenbergh's book has rules of thumb for answering your rotational speed questions-
http://www.rocketsaway.com/pyrotechnics_ball_mill_theory_spo...
And see post #163 here about a black powder method NOT requiring milling all ingredients at the same time.
http://castboolits.gunloads.com/showthread.php?104979-Here-i...
Some guy wrote it.
[Edited on 6-1-2016 by Bert]
Rapopart’s Rules for critical commentary:
1. Attempt to re-express your target’s position so clearly, vividly and fairly that your target says: “Thanks, I wish I’d thought of putting it
that way.”
2. List any points of agreement (especially if they are not matters of general or widespread agreement).
3. Mention anything you have learned from your target.
4. Only then are you permitted to say so much as a word of rebuttal or criticism.
Anatol Rapoport was a Russian-born American mathematical psychologist (1911-2007).
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Fulmen
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Lloyd book is the obvious starting point for anyone interested in making a ball mill, he was the one that popularized their use for pyrotechnic use.
We're not banging rocks together here. We know how to put a man back together.
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NedsHead
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aga and I had a good go at making ball mills here https://www.sciencemadness.org/whisper/viewthread.php?tid=61... my completed mill is on the following page, it could take multiple smaller drums
easily or the rollers made longer to take more drums and a pillow block bearing placed in the centre to support a longer roller
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Fulmen
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The CIA /precipitation method described in the castboolits thread is well known and produces a decent powder for pyrotechnic use. It's however not
anywhere near commercial grade and would be a poor substitute for many uses such as firearms. In order to get real BP you will need to mill all the
constituents together before pressing the powder to a density of appr. 1.7g/cm^3.
We're not banging rocks together here. We know how to put a man back together.
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