Non-Chemical Ball mill has hit a snag

[bswartzwelder]

I recently started to build a ball mill for crushing IC chips. My son had a discarded 30 gallong air compressor setup which had died. I cut the top and bottom out of the air storage tank and got a nice cylinder to start the project. The inside diameter is 17 7/8 inches so I bought 3 pieces of 3/16 inch thick plate steel 17 7/8 inches square to fabricate the ends. Tack welded all three plates together and painted with red steel dye for the layout portion. The bottom plate will be solid. The plate on the other end will be a circular donut about 1 1/2 inches wide. I will drill 12 holes (evenly spaced) on a circle 3/4 inch from the outside of the donut. I will then weld 12 3/8 inch bolts in the holes so they protrude towards the outside of the finished drum. The outside removable plate will have 12 evenly spaced 1/2 inch holes that will allign with the protruding bolts. Twelve nuts will secure the top in place when the unit is running. There will be a sheet rubber gasket between the donut ring and the outer front cover to seal everything.

As I said, I welded the three 3/16 inch thick plates together so I coould cut them all at once and they would all be the same. Never thought about having to cut an almost 18 inch diameter circle which is 9/16 inch thick. Could not cut them with a jig or saber saw. Sawzall barely cut through them. Got out the Porta Band and went to town. Got almost halfway around the circle when the porta band died. Found out it had plastic gears on the inside of the drive hub. Plastic gears will not take the pounding that metal gears will, so the gears are now somewhat toothless. Will have to wait until Monday to order replacement parts and then wait for their arrival. This will give me time to come up with a metod to drive the barrel. Need about 46 RPM. Have been thinking along the lines of a belt (or maybe two) which go around the drum as a method of spinning it. Will still need a motor and some more pulley speed reduction to get it down to 46 RPM or slower.

I would like to put 4 "catchers" on the inside of the drum every 90 degrees around. They will catch the "balls" and help take them to the top of the rotation where they will let them drop. Dropping from the top of the rotation should give the best crushing action but it will make it noisy. I may have to build an enclosure lined with fiberglass insulation on the inside to help deaden the noise. The enclosure would roll around on casters. Anybody with any other ideas, please feel free to share them.

 

[Harold_V]

Nothing wrong with using a belt around the OD to drive the drum. I did that with my ball mill with excellent results. I also used a variable pulley to fine tune the speed. The belt for the drum is readily visible in the attached photo.

Lose the idea of putting anything inside to lift the balls. If it's necessary, you're running the ball mill at the wrong speed, and nothing you do will make it more efficient. Run it at the proper speed and it does exactly what is required--it carries the charge and balls to the apex of the upper curve, at which time they fall to the bottom of the drum. Anything you add in the way of lifters offers the possibility of protecting the charge from proper action.

Running the ball mill to fast or too slow is not a good idea. If the charge does not drop at the appropriate time, or if it simply slides along the drum, you'll break down the charge only by attrition. That's correspondingly as hard on the ball mill as it is the charge and balls.

Harold

 

[glorycloud]

Nice ball mill Harold. What did you primarily use it for?
What materials did you process through it?

 

[Anonymous]

Lose the idea of putting anything inside to lift the balls. If it's necessary, you're running the ball mill at the wrong speed, and nothing you do will make it more efficient. Run it at the proper speed and it does exactly what is required--it carries the charge and balls to the apex of the upper curve, at which time they fall to the bottom of the drum. Anything you add in the way of lifters offers the possibility of protecting the charge from proper action.

Running the ball mill to fast or too slow is not a good idea. If the charge does not drop at the appropriate time, or if it simply slides along the drum, you'll break down the charge only by attrition. That's correspondingly as hard on the ball mill as it is the charge and balls.

Harold

bswartzwelder,
The ball mill that I built was a beast.Just over 22 inches in diameter,1/4 steel,with huge slugs,pucks,and balls. I used a lifter bar in my ball mill,and it works pretty well.It is raised off of the drum to allow the material to remain at the bottom,while the media was being lifted to drop point.Once finished,I ran it with cover off,and fine tuned the "drop point" by lowering my lifter bar,until the media dropped on to the "sweet spot".The reason I chose to do it this way,was because,once my mill was finished,I was limited to a number of sheaves to adjust the speed,and I was unaware of what an adjustable sheave was.I love my ball mill,because I designed it,cut almost every piece of metal myself,and built the entire thing.It is my pride and joy,but............from an industry standpoint,it is as slow as mollasses running uphill.Utilizing the exact same setup,but switching to variable sheaves,I could literally grind 10 times the material,in any given amount of time.
The main problem with using a lifter bar is this,with every rotation of the drum,the media is lifted and dropped only one time.When not using a lifter bar,and using the rotational force to lift the media,and material to an apex,everything is being lifted and dropped constantly.Nothing is ever sitting idle at the bottom of the drum,waiting to be raised by the lifter bar.Also,using a lifter bar ONLY works when the drum is turning slower than a non-lifter drum.In the words of GSP "Go for the gusto" use variable speed sheave,and lose the lifter bar.
Here's a list of them on ebay
http://www.ebay.com/sch/i.html?_nkw=variable+sheave&_sacat=0&LH_BIN=1&_sop=10&_odkw=variable+speed+pulley&_osacat=0&_trksid=p3286.c0.m270.l1313

 

[rusty]

My mill is now 3 years old, uses a lifter bar.

The job currently under way, the mill is abrading silver contacts loose from the buss bars.


I'm with Harold on this lose the idea.

[youtube]http://www.youtube.com/watch?v=IaDd34paaQU&list=UUisCclhYzYd2NOSEm1AyTdg&index=1&feature=plcp[/youtube]

 

[jack_burton]

Rusty- what kind of motor is this?

 

[ericrm]

what size of ball is the best to use?is the bigger the better or is there a magic size ball who doest the trick like one or 2 inch ball?

 

[Anonymous]

what size of ball is the best to use?

It depends on what you want to accomplish.Sometimes you have to try different media,and watch the results.

 

[Smack]

Rusty, looks like yours could go about 3x as fast.

 

[bswartzwelder]

Unfortunately, I already had the lifter bars installed when I made the post. They are simple 3/16 inch thick by 2 inches wide pieces of plate steel and unfortunately they were welded full length to the barrel on both sides. I will continue with the design from here. If I have to remove them in the future, I'll think of a way either cutting or grinding. The part to fix the band saw was ordered today and might be here in time for the weekend. I'll keep everyone informed. I may just cut an end cover out of plexiglas so that I can fine tune the speed. I found an equation for the critical speed and it said that typically ball mills run at 65% to 75% of the actual calculated critical speed. For mine, that would work out to 46 RPM. Thanks Harold, for the idea of the variable speed pulley. I'll order one soon.

 

[Harold_V]

Nice ball mill Harold. What did you primarily use it for?
What materials did you process through it?

The ball mill was built to run a specific product, which, in this case, was a complex gold ore that assayed over 300 ounces/ton. I received the ore crushed to ½"-.

The ball mill is (was) a continuous feed---so ore was constantly introduced, along with lime, and water. How much water was introduced dictated how long the material spent in the mill. A set of classifier bars in the discharge prevented anything of size from being ejected, then the discharge was classified twice. First time was at the top, where small nuggets were trapped on a coarse screen, then again at the bottom of the chute, where a fine screen trapped finer gold and tiny bits that were not crushed fine. Very little had to be returned to the mill, simply be controlling the water rate.

The ball mill was a resounding success, and contained no lifters. There's a formula for calculating proper operating speeds for a ball mill. If the formula is observed, as in my case, a ball mill is far more efficient.

Harold

 

[Harold_V]

what size of ball is the best to use?is the bigger the better or is there a magic size ball who doest the trick like one or 2 inch ball?

Size of the ball will be dictated by the size of the charge. What you'll quickly come to understand is that if the balls are too small, they don't crush. They will, however, slowly abrade the pieces until they're to a critical size, at which time they'll fracture and be crushed fine. That's not a very good way to operate a ball mill.

My mill had a varied size charge of balls and rods. I had balls up to 2" in size, and everything down to about 3/4". All were just commercial balls, from ball mills, but well used. Many of them start life as large as 6" in diameter, but are slowly abraded.

I also ran a large number of rollers from large bearings. They varied in size, too, but not greatly. About 7/8" diameter by about 1½" long to 3/4" diameter and an inch long.

The charge was adequate for the feed, in my case, but I added a couple large pieces of ore (hadn't been crushed), which remained in the mill for several hours (make that a few days). Again, once down to a particular size, they were rapidly eliminated, but the process getting them worn down was very slow. It is for that reason I suggest that a ball mill be made to operate at the proper speed. They're way too noisy to be allowed to run unnecessarily. I could not be in the same room with the ball mill without ear protection when it was operating.

Harold

 

[glorycloud]

300 Oz of Au per ton = NICE!

Thanks for sharing Harold! 8)

 

[ericrm]

thank you harold for the answer ,steel ball are realy expensive so knowing will save me much needed money

 

[rusty]

thank you harold for the answer ,steel ball are realy expensive so knowing will save me much needed money

Only Harold could tell us how many pounds of balls it took to make his mill functional, I'm guessing no less than 200 lbs. The drum would have been at least half full.

 

[ericrm]

if it realy take that much ball ,i think i will look to find some cheaper ball,
do you think that a steel tube(full)cut in section could do the trick?

 

[rusty]

if it realy take that much ball ,i think i will look to find some cheaper ball,
do you think that a steel tube(full)cut in section could do the trick?

This is why we amateurs use a lifer bar, it allows us to use less balls to achieve the same goal.

When your refining on a toll basis your working against the clock, we have the luxury of ownership.

Owning a continuous feed ball mill would be the ultimate toy, with the amount of feedstock I acquire in one years time this is exactly what a mill like Harold's would be just another toy in my shop. I could not justify having a continuous fed mill like this over my lowly mill with a lifter bar and a half dozen balls.

My mill may not grind the same pounds per hour that Harold's mill would have, for example if I load 60 lbs of IC's into my mill at 5:00 PM you can bet there is nothing left of those chips come morning other than a very finely milled powder.

Harold's mill in the same time period may have milled 400 lbs and I may have well over estimated on the amount.

 

[kuma]

Hi all , how are tricks?
I hope all is well! :mrgreen:

Lose the idea of putting anything inside to lift the balls. If it's necessary, you're running the ball mill at the wrong speed, and nothing you do will make it more efficient. Run it at the proper speed and it does exactly what is required--it carries the charge and balls to the apex of the upper curve, at which time they fall to the bottom of the drum. Anything you add in the way of lifters offers the possibility of protecting the charge from proper action.

Giggles! Just when you think that you have something sussed in your mind , ........ :shock:
Once again Harold , thank you for the heads up!
Wishing you all the best and sending my kindest regards ,
Chris :mrgreen:

 

[Harold_V]

thank you harold for the answer ,steel ball are realy expensive so knowing will save me much needed money

Only Harold could tell us how many pounds of balls it took to make his mill functional, I'm guessing no less than 200 lbs. The drum would have been at least half full.

By weight, no, as I never weighed the charge, but I kept the ball level slightly below the bottom trunnion of the right hand end of the mill. The entire assembly was tilted downhill to the right, with the discharge trunnion smaller in size than the intake trunnion. I would estimate the drum was probably 40% full at the most.

I was fortunate to have a used equipment dealer near me when I built the ball mill. They had a small assortment of well used balls. I do not recall the price, but they were affordable. They are nothing more than castings, often with traces of the runner still attached. Doesn't matter, not for the purpose.

Harold

 

[Harold_V]

300 Oz of Au per ton = NICE!

Thanks for sharing Harold! 8)

Nice, it was! The gentleman that owned the ore gave me several samples, some of which would likely assay well over 1,000 ounces/ton. I posted pictures of them some time ago. One of the samples is sawn---exposing a large percentage of the surface as gold.

Remember---this was an ore--not a concentrate. He informed me that he could have purchased some that assayed over 600 ounces/ton. I processed for him only one time. He was quite old then. Indications were that he had purchased the ore from miners that were (my assumption) high-grading from the mine where they worked. I was given very little in the way of information, aside from the fact that the ore came from Colorado, sold from a residence in Grand Junction.

Harold