Ball Mill Comminution
Ball mills work in a different way than AG or SAG mills. Ball mill attrition depends on nipping the ore particles. A rule of thumb is the ball size required to nip the largest particles is about 15-20 time the particle size. A 4 inch ball (very large for a typical ball mill) would be able to process 5-7mm.
If you feed with larger particles, they will comminute at a slower rate. Too many and they will plug your circuit.
Prediction of the 4 inch particle can only be determined by knowing the expected quantity being held up in the mill. Otherwise you are trying to make you ball mill act as a SAG mill. SAG mill comminution can take these large particles. Its breakage evolution is done at the base (toe) of the mill where the ore kidney changes direction near the toe of the charge. More than 95% of the rock is broken in the lower kidney section where pressure is maximized between rock and balls. In a ball mill this is not the case.
We can model the breakage rate of any size particle in any mill. The ball size also needs to be known as does the end slot size that retains the smallest ball size. Thus, you need to know:
1. Ball size distribution in equilibrium
2. Ball mill size
3. Ball mill liner configuration
4. Ore particle size distribution
5. Ore strength by size distribution
6. Tonnage throughput desired
7. Mill speed
8. Slurry properties
9. Size of balls classified as too small to be retained = exit grate size
10. Retained ore mass
11. may have missed some. ■
Re: Ball Mills To Do The Job Of A Crusher
Your questions without any details necessary to engineer a product:
1. Will the large particles damage the mill? Answer: No
2. Will the crusher do a better job? Answer: for your application most likely it will
3. Can your circuit work? Answer: depends on the product you desire, throughput, power available, ball size used, ball liner used and other attributes. ■
Re: Ball Mills To Do The Job Of A Crusher
Mr Nordell is right and another factor is that efficiency of a crusher is much higher than of a mill - that is the reason behind the High Pressure Grinding Rolls development. You can grind whatever you want in the Ball Mill but the efficiency will be very low and therefore expensive ■
Re: Ball Mills To Do The Job Of A Crusher
Please note that this is a project to help very small miners become self sufficient and to avoid using and spilling mercury into the environment. Efficiency is something we do do without as these small miners are limited by law to only mill 15 tons/day.
We want to be able to build something that is scalable, to this end we are to purchase locally manufactured ultra small mills, something that can use a 1 HP motor, say a mill that would handle 30 Kg. of ore and have it run with a small genset. 30 Kg. of ore x 20 hours/day = 600 Kg. If a small miner can process 3 tons he would need 5 of these mills, 6 tons = 10 mills and so on. We want to keep it this small as this would be easily accepted among the indigenous population.
As you can see our mills are very inefficient but yet they are effective for our purpose.
The local manufactured mills are just cylindrical bodies with 4" balls, we might have to have one mill operate with 4" balls to do the job of a crusher and when we get to about -1 mm we can then have another mill in series that could operate with smaller media to get to approx. 150 to 200 mesh. Another way would be to be able to build a more efficient (multi-compartment) mill, something that is not yet locally manufactured.
The logic that we are trying to follow is to eliminate a crusher and keep this project very simple as if it has more than one or two components the local population will not accept it.
Is there software out there to be able to do CFD modelling of ball mills? I am looking for something that is not expensive or downright free.
I would appreciate your comments. ■
Re: Ball Mills To Do The Job Of A Crusher
Rodsallick
Talk to Collin Spann from Sandvik(he previously worked for Svedala) - he has the right experience with crushers and Mills and you should get the answer to the question
Colin Spann
Manager, Mining and Construction
Sandvik New Zealand Ltd
Ph: +64 (0)9 273 5888
Fax: +64 (0)9 273 5899
Mobile: +64 (0) 275 927 468
Email: colin.spann@sandvik.com ■
Re: Ball Mills To Do The Job Of A Crusher
Dear Rodsallick,
You have not offered details on the product you are trying to grind. As you may know the cement industry does compartmentalize grinding media into axial zones that each contain successively smaller grinding media. Usually, two stages.
I believe your 1 kw drive would not rotate the mill.
Have you ever worked with grinding media and gem stone tumbling mills? Why not just build the little bugger and trial the scheme you want to apply? Surely, this is more cost effective than doing in with Discrete Element Breakage (FEA integrated with DEM)) code coupled with CFD (viscous fluid) to convect the ore out.
See our website demonstrating rock breakage and also reference SAG 2001 and 2006 papers that give you understanding of my words. The cost will be too high to trial various mill details with sufficient particle sizes sets. We have modelled many kinds of mills and crushers with great success.
We do model very large mills (40 ft Cadia), vertical mills, gyratory, roll and cone crushers with our grain (rock) breakage code. To go from 4" down to 0.10 inch (40:1 particle size range) will take many days to model.
In the past, a typical model might take about 40-60 days in a batch mode to obtain reasonable answers on comminution performance with resulting size distribution. I will be far less costly to build a mill of your expectations and apply our patented mill liner configuration. You must understand the starting size.
I suggest you start with something large than 1 kW and scale down. Since I am skeptical, I would start with 10 kW to save a lot of fanfare in trials. Think of the ratio of ore size to mill size. Think of the mill size to support ore and balls. A 200T grinding mill such a Cadia uses about 20,000 kW. The mill size scales exponentially. Read the literature on sizing ball and SAG mills. You will need to understand the difference in grinding process between the two. In essence, I believe you will need a minimum of two mills, on for breaking big 4" rock and one for find grinding. Also read the literature on find grinding. ■
Re: Ball Mills To Do The Job Of A Crusher
You might try a stamping mill as the first stage to break the 4" rock to a manageable size for fine grinding. ■
Re: Ball Mills To Do The Job Of A Crusher
Dear Rodsallick,
The best our company can do is size reduction from 30 mm to a 200-300 micron (P90),
yet there is a possibility to go for a second mill run..
Lowest production capacity is about one ton/hour with 70 kW drive.
It would be quite useful if you provide more details
Ezry Akkerman
Cyclotec@gmail.com
Cyclotec Ltd ■
Re: Ball Mills To Do The Job Of A Crusher
Without knowing what kind of rock you are crushing, I would recommend you try a laboratory size jaw crusher. They are in the range of small Hp you are describing, and they will probably take a 4" lump down to 1/2" (or maybe smaller if you shim the gap down)
There are usually a number of used units available at a good price. I don't ever remember buying a new jaw crusher because the old ones last so well and you can keep rebuilding them.
Our experience with full size production units on various materials is good as long as the material is fairly hard and the fines don't pack. If you are going to buy a used unit and it is still connected up run a sample of material through it. You will find out more in 15 minutes by doing this than the software will ever tell you. ■
Ball Mills to Do the Job of a Crusher
I am working with small miners, we are looking at providing these miners with small crushers and then small ball mills. The crushers would crush from about 4" to -1/4" and then this would be fed to a ball mill.
My question is about the elimination of the crushers and feed the ball mills with the 4" material. Is this possible?
Could we ruin the mill? I do not think so.
What is the approx. time that a ball mill would take to mill/crush material from 4" to 1/4"?
If x is the amount of time it takes a ball mill to reduce ore from -1/4 to 200 mesh what % of x would it take to reduce material from 4" to -1/4"?
I would appreciate your comments. ■