Mitchell Posted October 23, 2020 Posted October 23, 2020 Before you all tell at me about there already being a ball mill thread (or 2 or 3) I don't want to talk about the milk itself. I just want to talk about the jars. I have seen and heard of people making jars out of large pvc with moderate success, the pvc fails eventually. I have seen the rebel jars and know that some people swear by them. If I was looking to go the homemade route for a jar would the off work and for how long? Also if I did attempt to make a jar similar the to the hex rebel 17 what rub reused coating could I use on the inside to cut down on the noise.? Thanks in advance
justvisiting Posted October 23, 2020 Posted October 23, 2020 It's not clear what you are asking, exactly. The biggest problem with my PVC jars is the racket. The Rebel jar works just as well and much more quietly. The liner is very thick rubber, and removable. I don't think any rubber coating would last if it was used on the inside. Some people put a sound-deadening coating on star roller drums (outside). If you made your own jar in the style of a Rebel jar, you could put sound-deadening stuff on the faces on the outside. An old article on ball milling showed a drum made with beveled pieces of wood. I don't have the skills, but a guy handy with wood working could probably make a decent jar. IF you were to do that, here's an important consideration: a jar that has a larger diameter mills better. If I was designing and making my own jars, I'd want them to do the best job possible. In an experiment I did, a 'pancake' shaped jar did a MUCH better job of milling potassium nitrate than a jar that had the same volume, but was the 'usual' shape. Both jars were run on the same mill. The larger diameter 'pancake' jar did a better job, yes. But, it also did the better job at 1/3 of the RPMs the other jar turned at. 1
Arthur Posted October 23, 2020 Posted October 23, 2020 Jars come in all shapes and sizes! Usually for cheapness. Reused Whey food supplement jars made of polythene tend to be popular free choices in the UK -radiused ends and a good diameter end cap, the 5lb jar is a useful shape. My favourite jar is the jar from this; https://www.manchesterminerals.co.uk/acatalog/BEACH-2-25Kgs-TUMBLER--excl--barrel--10_020.html#SID=114 It's about six inches deep and eight inches diameter -just doesn't come "made in China cheap"
Mitchell Posted October 23, 2020 Author Posted October 23, 2020 Justvisiting - sorry if I wasn't clear. I need to make a ball mill and I already have everything I need other than the mill jar. I was asking around for ideas/inspiration on what to make a mill jar out of. The pvc idea is very simple but I have seen people say the hex shape is better because it is more efficient. Also how long did your off jar last? Did it eventually give out? Arthur - I have looked into those too but my concern is how long do they whey bottles last? The ones we have over here (US) while they seem to be pretty heavy duty, I can't see them withstanding the constant milling. To all - can anyone else confirm what just visiting had said about the pancake shaped jar. While in my mind it does make sense, has anyone else tried it?
royster Posted October 23, 2020 Posted October 23, 2020 You can glue strips of pvc in a pvc jar as seen on yt by elementalmakr, that will ensure the contents roll and not slide. I glued thin strips of wood in my harbor freigh rubber jars, together with enlarging the rollers its a mean little machine for small quantities.
justvisiting Posted October 23, 2020 Posted October 23, 2020 Mitchell, I can't prove my 'allegations', but I'll post what I wrote to a milling expert about my findings. Also, I shared my findings with the manufacturer of the hobbyist mill. It could be just coincidence, but their newer mills now have larger diameter jars. You probably won't find actual confirmation of my findings, because most pyros are more interesting in making pyro than making more work for themselves, just for the sake of learning. Here's a copy and paste excerpt from my communication on the subject: I may have posted it before, but my memory is poor. ____________________________________________________________________________ I had a situation recently with milling that I thought you'd find interesting. Working through it showed me some cool stuff, and how many guys are interested in (groan) milling details? Up until recently, my milling experiments have always been done on a 'normal' hobbyist pyro scale. I've milled the powder, nitrate, and charcoal in either PVC Sponenjars or later, the rubber-lined Rebel 17 5 litre jars. Then recently, I started working with the Pyro-Gear mill, like the one you have. We chatted a little about it before. Anyhow, my sulfur supplier closed down and I bought 99.9% sulfur pellets. When milling the sulfur, I found that it was grainy after 2 hours in the PG mill, and left specks in the (one) puck I used it in. After that, I screened it through 100 mesh, and quite a bit didn't pass, maybe 15% or so. I made another puck, and still had specks! WTF? Well, I had just switched over to milling my nitrate for 2 hours in the PG mill instead of the large one. A 250 gram PG mill load had over 2 grams fail to pass 40 mesh. I then screened the stuff through 100 mesh, to see what was what. 20 GRAMS failed to pass! Now, my testing has ground to a halt as I consider the effects of this 'lesser' degree of milling on any data I might report. I'm confining this data to a single group of tests a member asked me to do, but then I've got to have better milling to continue. Sure, I could increase the mill time, but that's too easy. I've always thought a 'pancake'-shaped mill jar would provide better 'fall' in a small diameter mill, and thus, better milling. Now was my opportunity to quantify this, in an obvious way. I made a pancake jar out of PVC fittings, and a bit of tape. The OD of the pancake jar was just shy of 6 1/2". The jar was made to prove a point, and fabbed up from scraps. I put wire 'guides' on either side of the tippy jar to keep it centered on the rollers. Wow, this took the RPMs from 75 down to 25! It was like watching paint dry, seeing it run. I thought about the chart you posted on Pyrobin about mill RPMs with different jar sizes. I then consoled myself by thinking that maybe the fact that I was achieving the same number of inches of travel, with greater 'fall', with the same amount of the same media, would have to make some improvement. Anyhow- it did. Using the same load of media and powder with the new jar for the same milling cycle time caused ALL the potassium nitrate to pass 40 mesh. Then I ran the pancake batch through 100 mesh. Only 0.45 gram sat on the screen. Using this new jar (or a better-made version of it) ALONE solves my problem to my satisfaction, at least as far as the nitrate is concerned. Tomorrow I will test the new jar with sulfur. As I've said before, I think charcoal is better milled by 'rubbing', and your interpretation of milling in general is by 'impacts'. By looking at this scenario, I can see where we can both be right. Black powder is a 3 component mixture, with 85% of the mixture being hard, crystalline substances, and only one- the charcoal- something that can be worn down, rather than smashed. But the wearing down and the smashing both have to happen when milling BP. Breaking it down, as I have, starts to show this- I think! I'm very excited to tell you about these preliminary results. It strengthens your 'impact' position, but still allows me to have my theory about what the charcoal component needs (or would prefer), if ground separately, to make the fastest powder. I've let Ken know of my results too. I'm just happy to add something to the community pot of knowledge that I think is fairly important. I'll apply what I've found in my future BP testing, which requires proper milling, mainly so that I can mimic the performance of my larger mill without running the huge electricity-sucking motor and large batch size. I'd especially be interested in what you think about my 'inches of travel' way of looking at things." Also, I don't understand this: "Also how long did your off jar last? Did it eventually give out?" My 'pancake' jar was made of PVC. I'd expect it to last as long as any other PVC jar of the same diameter. I used it to diagnose the issue. I believe my findings would be very useful to those that have a 'curiouser than usual' interest in milling efficiency
Mitchell Posted October 23, 2020 Author Posted October 23, 2020 That is very interesting for sure! When I am making up mill jars I will have to try making a pancake and see for myself if I can get the same results you did. Thanks a lot!
royster Posted October 24, 2020 Posted October 24, 2020 Can someone shed more light on the pancake jar? I make my pancakes round mostly, i figured its a round jar?
Mitchell Posted October 24, 2020 Author Posted October 24, 2020 (edited) So what I am taking it as(you can correct me if I'm wrong) is a ball mill jar that has a large diameter compared to the length of the jar. An over exxagerated example is this. Picture an 8 inch diameter mill jar that is only 1 or 2 inches wide Edited October 24, 2020 by Mitchell 1
justvisiting Posted October 24, 2020 Posted October 24, 2020 Exactly. I'm not making the point that the diameter has to be larger in relation to the length, really. I'm making the point that the diameter has to be greater to do better milling. The generally accepted shape of milling containers is not the shape that promotes the most efficient milling, if one only considers how the available mill jar volume is used. With a pancake shaped jar, a small test run can be done that will produce the same results as powder milled in a much larger mill. With the Harbor Freight rubber jars, MUCH more time is required, due in great part to the small diameter. This is an issue that seems to have gotten almost no attention, or it hasn't gotten enough attention- IMO. IIRC, there are rubber jars of the shape I describe available online.
justvisiting Posted October 24, 2020 Posted October 24, 2020 This is what I'm talking about. Yes, it's expensive. I'm sure the concept can be copied cheaply enough.
Mitchell Posted October 25, 2020 Author Posted October 25, 2020 It is only an 8 inch diameter jar.... That would be very doable to make that same style. What RPM would be ideal for something like that. Is there a formula that I have seen people calculating stuff with in the past?
Mitchell Posted October 25, 2020 Author Posted October 25, 2020 (edited) Also take a look at this motor. This seems like an awesome price for a TEFC motor.' https://www.ebay.com/itm/IRON-HORSE-MTR-P33-1AB18-MOTOR-33HP-115V-W-WORLD-WIDE-HDRF206-30-1-GEAR-XLNT-/322366675326 It also already has a 30 to 1 reducer built in to bring it to 60 RPM. That's described as the sweet spot for most jars correct?? Edited October 25, 2020 by Mitchell
Mumbles Posted October 26, 2020 Posted October 26, 2020 The formula for critical RPM is 265.35/sqrt(mill ID - media diameter). Both the ID and diameter are in inches. This is the RPM that media will stick to the walls of the jar. Typically, we shoot for about 65% of that value. For that particular jar with 1/2" media, you'd want to shoot for about 67rpm
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