Show and Tell - Ball mills.

[oldguy]

Um, a hundred pounds huh........ hmmmmmmm sounds like a lot...... wanna sell any?

 

100 lbs is not a lot running a big mill with multiple jars.

 

http://cgi.ebay.com/Zirconia-M-Grinding-Media-1-2-25-poundsd-New-Lot-B-/160597234489?pt=LH_DefaultDomain_0&hash=item2564575339

 

25 lbs for $100 w/free shipping

That is a bargain price.

Edited June 2, 2011 by oldguy

[dan999ification]

I get really good results with that type ^^^ of Zirc M media in a Harbor Freight mill. It takes 5 pounds of lead to half fill a rubber jar and only 3 pounds of Z, but it mills better in less time and there's a large increase in volume, with no caking. I believe the tubular media will perform better than balls for the kind of use we put it to - balls may work better for powdering quartz, but the kind of brittle material we use benefits from more contact between the parallel sides.

 

 

i agree my bp media are long cylinders more like bars or rollers really i run it to see if they worked before i cut them to size and they work great for bp so i didnt cut them they range from 1-3 inches and all are 12mm dia some weigh nearly 4 oz but they are useless for coarser charcoal i can make bp quicker than airfloat charcoal from mill feed with them.

dan

[Mumbles]

That's odd actually. There is a similar type of deal called a rod mill (unique name huh?). The rods run almost the entire length of the jar, and the jar is typically longer than it is wide to keep the rods oriented. These things are typically very efficient at quickly breaking down coarse material. There are less collisions, but the impact energy is greater. The efficiency drops as the particles get smaller.

 

I personally prefer a ball or roughly square cylinder (as tall as it is wide). There are people in both camps, but for what we're doing any shape performance differences can be evened out in an extra bit of milling. I'm slowly warming up to ceramics though.

[dagabu]

I'm slowly warming up to ceramics though.

 

[Mumbles]

Maybe I should clarify. I am slowly warming up to more ceramics. I've never really trusted anything but material known to come from a reputable supplier, like CoorsTec, with the milling of explosives in mind when they were made. This means high alumina materials. The surplus on ebay and other places always made me a bit uneasy for live compositions. I think time has proven that most of them are safe. It could just be a coincidence, but all the ceramic accidents that come to mind involved pretty large ceramic media. Maybe size is the key factor. There are also extenuating factors in some. One was likely caused by a leaking jar. Another was possibly caused by an undercharged mill.

[dagabu]

100 lbs is not a lot running a big mill with multiple jars.

 

http://cgi.ebay.com/...=item2564575339

 

25 lbs for $100 w/free shipping

That is a bargain price.

 

20# of the used 1/2" for $35.00 shipped. That will help load my new 12" jar

 

Make that 40# for $60.00 delivered. Sweet!

 

-dag

Edited June 2, 2011 by dagabu

[dan999ification]

That's odd actually. There is a similar type of deal called a rod mill (unique name huh?). The rods run almost the entire length of the jar, and the jar is typically longer than it is wide to keep the rods oriented. These things are typically very efficient at quickly breaking down coarse material. There are less collisions, but the impact energy is greater. The efficiency drops as the particles get smaller.

 

I personally prefer a ball or roughly square cylinder (as tall as it is wide). There are people in both camps, but for what we're doing any shape performance differences can be evened out in an extra bit of milling. I'm slowly warming up to ceramics though.

 

 

i'll look up rod mills i've never seen one. the jar is 2.5 inch dia and about 7 long, looks like something else i've accidently invented that already exists i think the reason mine doesn't fare so well with coarse c is the jar is p e t plastic and bounces quite a bit, i'll see what happens in a pvc jar soon and report back.

i should have said it makes airfloat but takes forever to get a high percentage i gave up on screening the bigger chunks out for bp uses and wait until the mill has done the work.i agree its nothing more milling wont fix.

dan.

[Mumbles]

I would actually guess it doesn't work that well because your media is horribly oversized for that jar.

[oldguy]

I have had a little experience with big continuous feed “rod” mills in wet ore processing. They come with their own set of problems. For them to be efficient requires a very precise drum diameter, rotation speed, rod weight, rod length, rod diameter and feed size. If any one of those factors is slightly out of kilter, rod mill efficiency drops off exponentially.

 

Ball mills are far more forgiving so long as they are properly charged.

 

With that said, with some tinkering & experimentation. I would wager a larger size PVC jar type rod mill running brass rod would be effective for pyro purposes once you had it fine tuned.

 

 

[dan999ification]

I would actually guess it doesn't work that well because your media is horribly oversized for that jar.

 

 

so you recomend smaller diameter "rods" for this type of design to crush down charcoal?

[Mumbles]

Normally the rule of thumb is 1/10th the ID of the tube or so. There is some swing room there, but I think you're pushing even that. I'd more recommend a larger diameter mill. Milling efficiency improves with diameter increase even if the total volume stays the same.

[dan999ification]

I have had a little experience with big continuous feed "rod" mills in wet ore processing. They come with their own set of problems. For them to be efficient requires a very precise drum diameter, rotation speed, rod weight, rod length, rod diameter and feed size. If any one of those factors is slightly out of kilter, rod mill efficiency drops off exponentially.

 

Ball mills are far more forgiving so long as they are properly charged.

 

With that said, with some tinkering & experimentation. I would wager a larger size PVC jar type rod mill running brass rod would be effective for pyro purposes once you had it fine tuned.

 

 

 

thanks for the info guys you learn something new every day. ive looked up rod milling and it seems like you say they can break down various ore suprising mine wont take care of c quickly

when i put this together the aim was to learn, spend nothing and use the resources i had to hand, it is a sucsess.

i came to the conclusion that the longer the media the more surface area between the media means more is getting ground at once they dont tumble just roll and fall i think the charcoal moves out of the way and has a job getting between the rollers if a larger chunk is at one end of a rod it leaves a large portion with nothing touching it as its lifted at one end and not rolling efficiently,its quiet with bp but jumps around with c in as the jar bounces back, particle size deffinatly plays a part in it, i dont know the corect ratios for effective rod milling like you say theres a lot of variables i'll look into that but i'll also wager that properly dialled in this has good potential for efficient fast milling,[bp in 3 hours already] though ballmills with short jars do have an advantage because of things not being so critical they are ready to go with most powders and you dont often have to consider very different spec media.

thanks.

dan.

[dan999ification]

Normally the rule of thumb is 1/10th the ID of the tube or so. There is some swing room there, but I think you're pushing even that. I'd more recommend a larger diameter mill. Milling efficiency improves with diameter increase even if the total volume stays the same.

 

 

so 5mm dia media it just seems so small and light to me to crush bigger items but im not in a position to argue.

i do need a larger mill this was to fill the blanks and its done its job unfortunatly i cant find a way to modify it for a bigger jar the motor wont take the weight and the speed is set if i put a bigger dia jar on it it will spin to slow for two reasons and take longer to mill anything. i dont understand how a larger jar would be more efficient because if scaled up or down it should be that scale i suppose the only parameter changing would be the weight of the media which would make a big difference.

dan

[Peret]

if a larger chunk is at one end of a rod it leaves a large portion with nothing touching it as its lifted at one end and not rolling efficiently

That's exactly the point of a rod mill. All the force at that point is on the large chunk. Since the rods can't get any closer together than the largest particle, they preferentially work down the large particles first and end up with a very uniform size. However, that uniform size isn't very small compared with a ball mill. Supposedly it's an advantage in ore processing, where you need sand rather than dust for the next stage, but not ideal for pyro.

 

As for the size of the jar improving the efficiency, that would be due to the media having further to fall in a larger jar and the energy of impact being proportional to the square of the distance dropped.

Edited June 5, 2011 by Peret

[Mumbles]

I completely agree, that 5mm is far too small to be efficient. You're finding an unfortunate aspect of ball mills, they are not infinitely scalable. There comes a point where appropriate sized media is not too effective toward milling.

 

Milling works my grinding material between cascading media. Thus the more collisions you can get, the faster milling you get. A larger diameter mill, even with the same volume, will have more collisions, by virtue of a deeper media load, per rotation than a smaller diameter.

[dan999ification]

That's exactly the point of a rod mill. All the force at that point is on the large chunk. Since the rods can't get any closer together than the largest particle, they preferentially work down the large particles first and end up with a very uniform size. However, that uniform size isn't very small compared with a ball mill. Supposedly it's an advantage in ore processing, where you need sand rather than dust for the next stage, but not ideal for pyro.

 

"thats why it takes so long to get air float when there are still larger pieces left"

 

As for the size of the jar improving the efficiency, that would be due to the media having further to fall in a larger jar and the energy of impact being proportional to the square of the distance dropped.

 

i was going to add that to my last post but didnt want to rely on what i think i know.

thanks for clearing things up understanding makes way for improvement and i like to know how and why things work or dont.

dan.

Edited June 5, 2011 by dan999ification

[dan999ification]

I completely agree, that 5mm is far too small to be efficient. You're finding an unfortunate aspect of ball mills, they are not infinitely scalable. There comes a point where appropriate sized media is not too effective toward milling.

 

i had a homer simpson "doh" moment when i left the computer 1/10 would be fine in a 6ft dia jar but not a small scale like mine

 

Milling works my grinding material between cascading media. Thus the more collisions you can get, the faster milling you get. A larger diameter mill, even with the same volume, will have more collisions, by virtue of a deeper media load, per rotation than a smaller diameter.

 

i get ball milling, charge, media load, critical speed, jar dimension but this to me is new teritory since it does its job differently, im just trying to work out how it makes bp in 3hrs i even "tested" some to be sure i wasnt misleading myself it is lift quality,though ive seen recently 4 and 6 inch shells lifted and broken with unmilled bp, made me wonder if we put too much effort in.

dan.

[Peret]

i get ball milling, charge, media load, critical speed, jar dimension but this to me is new teritory since it does its job differently, im just trying to work out how it makes bp in 3hrs i even "tested" some to be sure i wasnt misleading myself it is lift quality,though ive seen recently 4 and 6 inch shells lifted and broken with unmilled bp, made me wonder if we put too much effort in.

It's normal to mill good BP in three hours with a properly loaded ball mill - that is, half full of media and not overcharged with comp. I believe it may be possible to break larger shells with unmilled powder, and maybe even to use it for lift since they prefer a slow burning powder, but trust me, ball milling makes a big difference that's well worth the effort. I offer this video in evidence - the second fuel has been ball milled (only for two hours, because I was in a hurry) but it made all the difference.

 

http://www.youtube.com/watch?v=FzeXiaAlLmY&feature=player_embedded

[oldguy]

Peret, should have ran the last one another 5 seconds.

Ball milling does make a HUGE differance in most comps.

[Peret]

Peret, should have ran the last one another 5 seconds.

Ball milling does make a HUGE differance in most comps.

Yeah, Mrs P was on the camera and it took off so fast, she lost it.

 

I shot another unmilled rocket that day, and it burned in place without lifting at all.

[dan999ification]

Peret, should have ran the last one another 5 seconds.

Ball milling does make a HUGE differance in most comps.

 

 

agreed.

[oldguy]

There is sure one hell of a big differance between schedule 80 & normal 6 inch PVC pipe.

[dagabu]

I gots me a big ole 12" ball mill jar all glued up and drying in 90° heat. The test cap goes on tomorrow and a 10psi test will tell if the welds will hold or not.

 

-dag

[oldguy]

Waiting for a look see picture

[dagabu]

Waiting for a look see picture

 

I put it on the rollers and it has a very interesting wobble to it... Seems that someone needs to check their saw for square.

 

I found two good sized air pockets, I need to dig out an opening and fill them so the pressure check will now be Wednesday.

 

This thing is a monster!

 

-dag