Ball mill trouble, help, please.

[hcb]

I built a ball mill to make black powder. I have a "standard" 110/220v electric motor (the kind you can buy at TSC, Horrible Freight, etc. and see on things from larger shop fans to band saws, universal mounting and such). With pulleys, I reduce its RPM and drive a 1/2" diameter steel shaft which I wrapped with black automotive hose. The steel rods (one driven, one idler) ride on pillow blocks, and both are covered in the tubing. With the diameter of the ball mill (10" for the ring, with a hexagonal enclosed area in the center, just like what I've seen the commercial folks offer (I think I've seen one for tumbling cases for reloaders)) taken into consideration, as well as the diameter of the rubber tubing, I should be hitting 60 RPM on the ball mill. It all looks fairly professional. I cast tire weights into 0.690" diameter balls...about 400+ of them, to fill the cavity 50% full (I read some articles on ball mills in general in industry which said that 50% media, 25% product, 25% air), I'm running a calculated 59# of lead balls. It's heavy.

 

It's not working well. When I fire the thing up, it begins to tumble as it should. Within about 15 minutes, the unit stopped tumbling (I could hear the racket stop). It had chewed through the rubber hose on the driven shaft. Okay, the rubber is too soft. I tried some reinforced vinyl tubing today because it felt a lot tougher than the rubber tubing. It didn't last 2 minutes (literally).

 

So, I have a motor-driven 1/2" shaft riding on pillow blocks and I need a way to get the steel shaft to friction-drive the drum. My next guess/attempt would be to try to wrap the circular end plates with some kind of electrical tape or other high-friction surface but, after two failures, I thought I'd ask others before I blindly do something else. What should I do?

 

Thanks for your time.

 

--HC

[MadMat]

After looking at you photo one thing stood out to me immediately. The driving area for your barrel is awfully small for all that weight. How wide are those ring end plates on your barrel? 1/2"? That is concentrating an awful lot of stress on the rubber tubing you covered the drive and idler rods with. I would be willing to bet if you could somehow put a nice wide ring around

the center of the hexagon barrel, thus increasing the driven area on your barrel, things would work out a lot better

Edited May 22, 2019 by MadMat

[memo]

got to agree with mat, also i fill my barrel 1/2 full , it is a rebel 17 barrel. i use about 35 lbs of lead. also i use 5/8 s rod and wrap it in hard plastic hose. i run 2 barrels side by side . for a motor i bought a totally enclose motor that is fan cooled (tefc) no sparks ! the 60 rpm is what i shoot for. looking good so far. just need to iron out a few bugs

[Piccaso]

I am a auto tech by trade so I have a lot of experience using that kind of hose. If you are using heater hose that stuff is fairly tough. Looking at your setup I am wondering if the shaft is spinning to fast and chewing threw the hose. I am in agreement with the others that making the driven surface wider would probably help but I also am wondering just how fast that shaft is being spun. What is the rpm of that motor as well as pulley sizes? The other option would be to make the drum gear driven by attaching a ring gear around the drum and cutting teeth in the shaft to drive it. This would eliminate any possibility of slippage as the weight of the drum would be sufficent to keep the teeth meshed.

[memo]

metal and sparks

[Mumbles]

Out of curiousity, which direction does your mill jar spin relative to the driven shaft?

[Arthur]

Given the drum that you have, try putting half as much in it. The weight will be less and the capacity will be less but the wear will be a lot less.

If you can remake something, make the drum wheels much wider so that they bear on much more rubber. But from the pic you may need to remake the rollers to be wider.

[justvisiting]

I admire your mechanical skills for someone of your age!

It would be great if you had a sleeve you could slide the whole thing into. Way too much weight on those 2 small areas, yup.

[hcb]

After looking at you photo one thing stood out to me immediately. The driving area for your barrel is awfully small for all that weight. How wide are those ring end plates on your barrel? 1/2"? That is concentrating an awful lot of stress on the rubber tubing you covered the drive and idler rods with. I would be willing to bet if you could somehow put a nice wide ring around

the center of the hexagon barrel, thus increasing the driven area on your barrel, things would work out a lot better

 

Thanks for the reply. Um...it's a quarter inch thick (each end cap). When I started this project I didn't know how much the lead balls would weigh (I didn't plan this thing thoroughly from start to finish and then begin work). When I realized it would be close to 60# I figured the rubber hose could handle #15. I agree with your assessment of the load being a lot. I was hoping for a better cover material for the shafts after the failure. I can do a fair number of things with metal but rolling rings is not one of them: a 1" wide piece of flat bar rolled the easy way around the end caps would help bunches. At this point, in order to widen the bearing surface, my only option I can think of would be to cut a few more profiles with void centers, in halves, and join them around the barrel and affix them to the ends...yucky.

 

--HC

[hcb]

got to agree with mat, also i fill my barrel 1/2 full , it is a rebel 17 barrel. i use about 35 lbs of lead. also i use 5/8 s rod and wrap it in hard plastic hose. i run 2 barrels side by side . for a motor i bought a totally enclose motor that is fan cooled (tefc) no sparks ! the 60 rpm is what i shoot for. looking good so far. just need to iron out a few bugs

 

Which hard plastic hose? Do you mean PVC pipe?

 

Thanks for the reply.

 

--HC

[hcb]

I am a auto tech by trade so I have a lot of experience using that kind of hose. If you are using heater hose that stuff is fairly tough. Looking at your setup I am wondering if the shaft is spinning to fast and chewing threw the hose. I am in agreement with the others that making the driven surface wider would probably help but I also am wondering just how fast that shaft is being spun. What is the rpm of that motor as well as pulley sizes? The other option would be to make the drum gear driven by attaching a ring gear around the drum and cutting teeth in the shaft to drive it. This would eliminate any possibility of slippage as the weight of the drum would be sufficent to keep the teeth meshed.

 

Thanks for the reply.

 

I agree that the shaft may be spinning too fast as the rotation of the drum and the shaft do not appear to be perfectly in sync. The motor is marked 1,625 RPM and I think the pulley sizes are 1.5" and 4" (the math came out to roughly 2.5:1 or something, in order for a 3/4" OD tube (the rubber hose) to rotate a 10" diameter ring @ 60 RPM if the input speed was 1,625 RPM).

 

Not being a jerk, trying to say it a little funny: gears ain't gonna happen. I don't have the skills or gear (how punny) to assemble such devices.

 

Tougher shaft covers would be easiest. Widening the bearing surface would be my second option.

 

--HC

[hcb]

Out of curiousity, which direction does your mill jar spin relative to the driven shaft?

 

If I understand your question correctly: the answer is that the driven pushes the area it is contacting towards the idler shaft. When testing the apparatus initially, it was rotating the opposite way such that a point on the circumference came past the idler to the driven shaft where it was propelled upwards along the long arc back to the idler. This caused the empty drum to "chatter", bouncing up and down. I re-wired the motor (per the markings on the motor) to rotate the other way and that's the way it is currently. In the photo, the pulleys rotate counter clockwise, if that makes it clearer.

 

--HC

[hcb]

Given the drum that you have, try putting half as much in it. The weight will be less and the capacity will be less but the wear will be a lot less.

If you can remake something, make the drum wheels much wider so that they bear on much more rubber. But from the pic you may need to remake the rollers to be wider.

 

Thanks for the reply. Halving the quantities is an idea I hadn't thought of. That might make it work the short term. Making the bearing surfaces wider is doable, but a pill short of re-making the whole drum...maybe...I'll think on that some more. Still hoping for some super awesome friction liner for the roller shafts. I have torn down my old plasma table and am migrating the motors/electronics to the new table (yesterday and today) and it may be a week or more, at the glacial pace I work, before I'm able to cut any new parts.

 

--HC

 

--HC

[hcb]

I admire your mechanical skills for someone of your age!

It would be great if you had a sleeve you could slide the whole thing into. Way too much weight on those 2 small areas, yup.

 

Thanks for the reply. Yeah, I'm pretty good. My daddy thinks he helped be he just mucked the project up.

 

To quote Will Smith's character in iRobot, "Gigi, you a genius!". I've been thinking inside the box. That's a great idea because it's simple and doable. A quick search shows that a 10" pipe, Schedule 30, should work perfectly (10.75" OD, 0.307" wall): should slip over my 10" parts. Betcha a dollar *nobody* has 10" pipe in Schedule 30 in captivity. But I'll see if I can find it. If I can make that work, that will solve all my "focused-load problems" and chewing through the shaft covers. On a mission now...

 

--HC

[memo]

the hard plastic hose you can buy at the hardware store, harder that rubber hose. normally clear or green.

Edited May 25, 2019 by memo

[Mumbles]

The real culprit is probably the thin edge of the jar that contact the rollers.

 

The direction the mill rotates does out additional wear on the roller covering and uses power a little less efficiently however. You generally want the powered roller to "lift" the jar and rotate away from the idle roller. Rotating into the idle roller can put extra stress on the bearings as its trying to force the jar down into the gap between the rollers.

 

I don't know if it will make a difference, but if it's simple to swap the rotation again, it might be something to try.

 

The mill looks great. Hope you get it running effectively.

[Arthur]

If you fix some 4 x 4 to the flats of the drum and trim it to the size of the end flanges you will get some 4" wide tyres without extending the mill rollers.

[Piccaso]

Open up a old electric car antenna and you will find about 3-4 feet of flexible plastic rod with gear teeth cut on one side and a gear to drive it. I think the idea about putting a pipe over it would be easier though if you can find the pipe. Trimming wood to fit was mentioned as well and is also a good idea. This site has a lot of intelligent members that come up with very creative ways of dealing with things. Let us know how it works out for you.

[BetICouldMake1]

The issue with the chatter might be related to the tubing used, which might be part of the overall problem. You need tubing soft enough to grab the jar but hard enough to not get ripped apart. Look for polyethylene tubing. McMasterCarr sells it and is kind enough to list the hardness. The stuff is super sticky but highly durable.

[MadMat]

As far as a good material, something that is both high friction or "sticky" and highly durable, I think some type of urethane would be the best you could hope for. I believe that there are two component urethane resins available and the material could be "cast" on your rollers. I know this may seem a bit involved, but you have done a great job so far. I suggest drilling a couple very small holes in your rollers in the area where you're going to cast the urethane to promote adhesion of the resin. You could either leave the holes as is, or press some pins into the holes leaving small protrusions. Alternatively, if you have access to a lathe, raising a diamond knurl on the rollers would create a good surface for adhesion of the resin. As far as a mold for casting; Plaster of Paris with wax paper creating the parting line would be an easy way to create a mold. As I said, this may seem involved, but it is doable

[Arthur]

With a mill jar as heavy as yours there is no long term solution to wear against the narrow rim. If you can widen the drum rim to 1 - 2 inches you could possible fit a small child's bike tyre to each end of the drum to enhance the grip and abrasion resistance.

[BetICouldMake1]

As far as a good material, something that is both high friction or "sticky" and highly durable, I think some type of urethane would be the best you could hope for. I believe that there are two component urethane resins available and the material could be "cast" on your rollers. I know this may seem a bit involved, but you have done a great job so far. I suggest drilling a couple very small holes in your rollers in the area where you're going to cast the urethane to promote adhesion of the resin. You could either leave the holes as is, or press some pins into the holes leaving small protrusions. Alternatively, if you have access to a lathe, raising a diamond knurl on the rollers would create a good surface for adhesion of the resin. As far as a mold for casting; Plaster of Paris with wax paper creating the parting line would be an easy way to create a mold. As I said, this may seem involved, but it is doable

Polyurethane is good. In my previous post I meant to say polyurethane tubing, not polyethylene.

[FrankRizzo]

If you live in the US, McMaster has a polyurethane tubing that's well suited to the task. https://www.mcmaster.com/catalog/125/163

 

The problem may actually be that your idler roller is too hard to turn. I use a woodworking ball bearing outfeed roller covered with a bike inner tube. Something like this: https://www.amazon.com/Roller-Bracket-Galvanized-Steel-Diameter/dp/B07S396F3C/

[snapper]

you seem to be pretty skilled in the art of making things so here are my two cents. first you need to weld a minimum of 2 inch wide bands on the ends of your drum to ride on the the drive rod to distribute the weight to prolong the drive roller covers and provide more traction in turning the drum (they should be thin but braced) for the drive rod you need to get cast round polyurethane(preferably 65-75da hardness for grip so it is not really hard) tube with the same inner diameter hole as your rod so it is a slight press fit. there is a fella that sells short lengths of it on ebay for like 20 bucks in multiple lengths and sizes, this can also help adjust your rpm a little. make sure both the drive and the slave rollers are the same diameter and the rotation of the drum is supposed to orient to contents weight over the drive roller when turning not over the slave roller. also you said you cast lead, did you add antimony to harden it? if not it will wear out very quickly.

[hcb]

Well, it's been a hot minute since I'd done anything on this. Talking with a friend a few weeks ago about building a cannon got me back on this. I rolled some 1/8" x 1.25" flat bar into a ring and welded that on each end, effectively giving me 400% more contact surface. It works now. I'm using the black, general-purpose automotive hose and it's holding up "ok". It's still super heavy and it's chewing up the hose a bit but not so much that I can't use it. I took charred willow and just threw the pieces into the mill on top of the media and let it run maybe 2 hours and got incredibly fine charcoal powder (zero pre-processing of the charred wood). I have mixed up a little straight BP with it and it works very well. I bought a cheap HF double drum rock tumbler and use it with 00 Buck lead shot to mill the BP because I want to start with smaller batches. So far, so good. Granulating the BP is being a pill so I'll go look into how to do that better.

 

Thanks for all the input on this. I'm also going to look into the polyurethane roller covers. I can't find the size I need on ebay so I'll try contacting the seller.

 

Thanks again.

 

--HC