# Ball vs Rod vs Roll Mills



## Anonymous (Mar 7, 2010)

Hi guys, I'm trying to figure out the differences in Ball mills, Rod mills and roll mills, does it make a difference which type I use? I'm looking at fine gold in hard rock. K


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## aussco999 (Mar 8, 2010)

dalmatiangirl61:

In the order you have listed; a ball mill can fine grind down to <400 mesh if needed, a rod mill will efficiently grind to 150/200 mesh range, and a roll mill can do a +/- 100 mesh. The ball and rod mills are similar in appearence, as a large rotating lined cylindrical tube filled with either metal balls or long rods used as the grinding medium. In some cases, they can be used interchangable, but not with a mix of balls and rods. Both ball and rod mills can be operated either wet or dry, and in a batch or a continuiously mode. There are also few variations to the a ball mill, such as a SAG or pebble mill.

A roll mill is two opposing rotating hard-faced rollers, one mounted stationary and the other under heavy spring tension. The material to be ground is fed between the rollers and is nipped crushed by pressure tension, versus the crushing abrasion of the ball/rod mills. The roll mill can also be operted wet or dry.

Also, in between the grinding capabilities of the ball and roll mills, there are hammer, chain, cage, impact and air mills, all capable of medium to fine grinding, depending on the feed material. And, on soft feed materials, a shredder mill (variation on the roll mill), can be used. The choice of which style of grinding mill to use largely depends on the friability of the material to be ground and the liberation point need to extract the valuables. I hope this general information on the different types of grinding mills will be helpfull to you.

Good luck on your projects,

John


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## Anonymous (Mar 8, 2010)

Hi John, thanks for the reply. Design I understood, just did not know they produced different fineness of material. I guess I'll build a small ball mill, seems like an easy enough project. The large ball mills I've seen looked like material was fed thru one hollow shaft, and exited thru a hole in drum with screens, is this how all are designed, or are there variation? I see a couple of small ball mills on ebay right now, 10K each, ouch. K


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## Anonymous (Mar 8, 2010)

Another question, what are ball mills lined with? Would Rhino-liner work, or do I need to glue a 1/4" thick pad of rubber to the inside of the drum, and hope it holds. K


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## qst42know (Mar 8, 2010)

You can line the outside for quieter operation but you want hard against hard on the inside. 

The balls are like hammers and the drum is the anvil. If you could see inside the balls would look much like a surfers wave curl almost reaching the top and falling in an arch and striking at the bottom of the drum. It's the continuous pounding that does the work.

Though I hate to mention it, clothes in a laundromat dryer take the same path but a dryer will not take the abuse as a ball mill.


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## aussco999 (Mar 10, 2010)

dalmatiangirl61:

This post might be a little long winded since there are volumes of books written on the different types and operation of the various mills, so the more specific your question, the more detailed the answer.

My expertise is mostly in hard rock mining and the recovery of metals, including the crushing and grinding of the ore. I’ve also spent a few years in assay labs, and running start-up pilot plants. My current gold project is a pilot plant with a maximum capacity of 300 TPD, and we will be using some form of a mill to fine grind the ore.

Fine grinding is more complicated than throwing some balls into a rotating drum and hoping for the best. You need to know as much about the material to be ground, as the system needed to do the grinding. For example, the ore I’m now working with is a mix of quartz/hematite/pyrite and is very friable. The free gold liberates at 80 mesh, down to about 20 micron. Most of the micron gold is associated with the pyrites, and lab testing has determined fine grinding to 200 mesh will liberate the pyrites to achieve a +90% gold recovery.

Regarding your question about the large ball mills, they are all continuous feed systems. Ore is feed into the mill through the trunnion bearing opening on one end and after a predetermine grind time, is discharged out the other end. An open-circuit grinding system sends the discharge to the next procedure, while a closed-circuit mill has some form of screen/grate system on the discharge end to send the over-sized material back to the mill for regrinding.

The small mill you are interested in building would probably be a “batch” mill, meaning the material would just stay in the mill until you have reached your desired grind size. The longer the residual grind time, the finer the grind. On large mills, dry grinding require about 30% more power than wet grinding. 

Depending on the type of mill, liners on large mills are made of replaceable hard metal alloys such as Cr-Mo, Ni-Cr iron, Cr-Mo steel and Mn steel. Flint and pebble mills normally use a ceramic liner. There is a new mill with a rubber liners, but that system has not caught on well in the industry yet. Maybe the Rhino spray liner would work in a small batch mill, but not with continuous use, and the textured surface would be difficult to clean. (IMHO)

On a past project, testing to determine the proper grind size was needed, so we built a small batch rod mill (about 16” dia X 4’ long), using a Reeves drive for variable speed control, with a mix of 1” to 2” diameter solid rods, on a front, down tilting stand. The rods and ore were loaded into the mill through a sealed bolt-on front plate for grinding, and the front down tilting stand allowed for easy rod removal and clean up. With the mix of rods, and the mill running over night, we got a dry grind of < 200 mesh on about 20 Kgs. of minus ¼” ore. That’s a 86 times reduction. Remember, longer grind time, finer grind. Also, a rod mill is a bit quieter than a ball mill, but not by much.

Although I don’t participate in second hand gold recovery (jewelry, sweeps, computers, etc), I enjoy reading how everyone else “mines” their gold, and some of the forum’s chemistry might be applicable to a future project. But, if you need any more info on crushing or grinding equipment, just ask.

Good luck with your project,

John


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## Palladium (Mar 11, 2010)

Very fine piece of information John.


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## Anonymous (Mar 11, 2010)

Thanks John, that answered my questions well. I'm headed to the scrap yard tomorrow to see if I can find some 16" to 24" thick walled pipe, 4 foot long would be perfect. Not quite sure how I'm going to power it, vari-drive would be simple, but I'm going with antique gas engines, I think. What type of ore? I have no idea :roll: . Its a friends mine, the ore is a reddish brown color, not real hard, separates in layers with quartz? (shiny crystals), looking at the crystals with a magnifying glass there are lots of gold blobs in the quartz, blobs, no crystaline structure. In a nutshell what I'm thinking of doing is setting up a display on mining for the touri,( crusher, ball mill, concentrating table) and processing the ore from my friends mines, for a cut :mrgreen: . Still trying to figure out the legal issues, if doing the display is going to cause too many problems I'll probably set it all up in a shipping container behind the house. K


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## KHUMBU (Jun 1, 2017)

i might have seen this so late , but i would still want to know the type of mill that you would recommend for hard rocks and works for small scale miners, especially in Zimbabwe


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## ashir (May 22, 2019)

I am going to start a medium scale refinery to recycle medium to high grade ewaste
I was looking for ball mill to grind incinirated stuff
But ball mill produce too much noise that industrial area not allowing to use it. What about roller mill ? I see this in a video that posted gaurave in a post ! 


Any recomendation?


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## g_axelsson (Jun 7, 2019)

I would suggest that a ball or rod mill should be lined on the inside. All commercial ones I've seen in mining operations have been rubber lined on the inside. The grinding action should be between rods or balls, if the drum is part of the grinding surface it will be worn through quite fast.

Göran


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## ashir (Jun 10, 2019)

g_axelsson said:


> I would suggest that a ball or rod mill should be lined on the inside. All commercial ones I've seen in mining operations have been rubber lined on the inside. The grinding action should be between rods or balls, if the drum is part of the grinding surface it will be worn through quite fast.
> 
> Göran



Thanks göran
But i can not understand your concept. 
If rubber will be used inside ball mill then there will no fraction to crush material, rubber will not provide hard surface. This is the one ball mill that i own, 

Its deal such as
Directly put material to be crushed and put the balls and run. Its a high grade iron sheet with 2 cm width. It produce so much noise . I wabt your more guide


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## rickzeien (Jun 10, 2019)

Grinding in a ball mill is not the results of the ball media striking the wall of the mill with a particle in between. 

A properly run ball mill grinds the particles between the ball media. 

It must be run at sub critical speeds for this milling action to occur. 

Excess noise is usually the fault of running the mill at super critical speeds. (It also causes premature war to the drum wall or liner if so equipped)

Here is a video and an article that will walk you through the working principles. 

I used both to design and build my ball mill. I will post some pictures soon. 

https://youtu.be/L6sgGXXYdEU

https://www.911metallurgist.com/blog/ball-mill-critical-speed

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## Shark (Jun 10, 2019)

Speed is most critical...here is a way to help get your speed right and the best description I have ever found for it...

https://www.sagmilling.com/tools_millspeed


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## rickzeien (Jun 10, 2019)

Shark said:


> Speed is most critical...here is a way to help get your speed right and the best description I have ever found for it...
> 
> https://www.sagmilling.com/tools_millspeed


I was on that site as well. I wound up using a gearbox that would reduce the speed to slightly faster than critical speed. 

Then I put a variable drive unit on it to set the proper speed. 

Also it has a 60:1 gearbox that is behind the motor. 

https://drive.google.com/a/group11elements.com/file/d/18DVhcmBBhNVj3Qq0LhVG2Nckm66JOiRc/view?usp=drivesdk


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## Shark (Jun 10, 2019)

rickzeien said:


> Shark said:
> 
> 
> > Speed is most critical...here is a way to help get your speed right and the best description I have ever found for it...
> ...



I can't see the page, I get a "you need permission" page in it's place.

The big thing for me was the description.



> The "Critical Speed" for a grinding mill is defined as the rotational speed where centrifugal forces equal gravitational forces at the mill shell's inside surface. This is the rotational speed where balls will not fall away from the mill's shell.



Once I understood what that meant, setting up a ball mill seemed easier for me, and quieter.


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## rickzeien (Jun 10, 2019)

This link should work.

https://drive.google.com/file/d/1-fmVCe_1GQFmHRQqkvjoGcTZRkszEq83/view?usp=drivesdk

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## Shark (Jun 10, 2019)

Worked great that time. Thanks, that is a sweet setup, and I think the speed controller is the only way to go to maintain the correct speed using different sized ball media. It will be interesting to see your whole operation up running.


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## ashir (Jun 11, 2019)

I am still confused. 
People here are also experts while the person prepare ball mill is also famous here as expert, 
I talked to him with respect to discussion here, he said there is no way to reduce noise, while he is not understanding the concept of ball mill as mentiond here. Can any body guide me to modify me ball mill so that it start working on principle of grinding within balls, not with ball and mill wall. 
What changes should i do in my ball mill? 
Another thing is , i noticed that my ball is curvy, while many ball mills are round! Is there no diffrence in working principle of round and curved mill?


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## rickzeien (Jun 11, 2019)

Here is a company that builds six sided ball mills. Perhaps they could enlighten you on the principles of their mill. 

I read briefly that their ball media is designed fall into itself so it sounds like the grinding occurs in the ball media also. 

http://unitednuclear.com/index.php?main_page=product_info&products_id=364

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## kurtak (Jun 11, 2019)

A cement mixer works VERY WELL as a ball mill - at least it works "very well" for milling incinerated IC chips & I have used it as well to mill incinerated plastic pin sockets

There has been discussions in the past claiming a cement mixer wont work because the speed is not right for lifting the balls to provide the "crushing" action in the mill

That's just not true

A ball mill needs two things to happen in the milling

1) it needs the balls to lift so that they crash down on the material for a "crushing" action on the material

2) it needs the balls to roll in the bottom of the mill to provide a "grinding" action on the material

Both things can be done in a cement mixer

With a cement mixer you can get more - or less of ether one of these actions depending on the stage of the milling & which one of those actions you want to happen between start (crushing) of milling & end (grinding) of milling

It's a matter of adjusting the angle of the cement mixer to get it to do the task you are wanting at any given time in the milling process

By adjusting the angle of the drum you can get mostly crushing - or some crushing & some grinding - or mostly grinding

:arrow: http://goldrefiningforum.com/phpBB3/viewtopic.php?f=38&t=25489&p=270739&hilit=cement+mixer#p270739

I love my cement mixer - it was a cheap investment for the job

Kurt


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## rickzeien (Jun 11, 2019)

Based on your needs and your situation I think Kurt has proposed a great solution for your milling needs. 

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