# Ball mill electric motor



## Dwf (Jul 17, 2020)

Hello everybody,

I have a ball mill that my brother made. It’s a 24” drum by 36” long. It’s powered by a gas engine that runs a hydraulic motor. 
It works really well, but I’d like to convert it to an electric motor. The whole setup is in my shop, and the engine is a bit noisy. I have the ball mill inside an insulated box, so it’s actually not to bad. I think the engine would over heat if I built something around it. 
My question is, does anyone have or have seen a ball mill of this size with an electric motor? The hydraulic motors are old, and don’t have any ratings printed on them, so I’m not sure what I need for HP and torque?

Thanks!


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## butcher (Jul 18, 2020)

I am unsure if you are wanting to run the hydraulics off of an electric motor or replace the gas engine and hydraulics...

An electric motor of less horsepower will do the work of a higher horsepower gas engine.
View attachment EngineReplace_Horsepower_0617_rev1118 (1).pdf


to put an electric motor on the hydraulic system you would not need as large a horsepower motor.


If doing away with the gas and hydraulics you should look into gearing

To turn a drum the motor does not need to be a large horsepower if you use gearing to reduce the load on the motor.

Take a look at cement mixers we can use a smaller horsepower motor to drive a small pully which turns a larger pully tied to a small gear driving a big drum gear...

You can use a gear reduction (similar to a transmission) along with your smaller horsepower motors)...


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## Dwf (Jul 18, 2020)

Thanks for the reply. 
I guess I should have been more clear. 
I want to do away with the whole hydraulic system. 
No oil messes, and it takes up more room. 
Yeah, I was thinking about the gear reduction. Most of the electric motors I’ve looked at are around 1700 rpm, which is way to fast. The hydraulic motors are running at about 105-110 rpm. 
Still curious what I’d need. I’d like to get something with more power than I need, so it doesn’t have to work very hard, and lasts longer. 
I’m not very familiar with how the calculations work, but it seems like a 5hp motor, geared down from 1700rpm to around 110rpm, would have a lot of torque.


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## rickzeien (Jul 18, 2020)

First thing you need to do is calculate your critical speed. Then you can calculate the speed of your gear reducer and motor. I have a ball mill a little larger than yours. I use a 3HP motor at 1750 RPM and a 40:1 gear reducer. 

Here is an article to get you started. 

https://www.911metallurgist.com/blog/ball-mill-critical-speed#:~:text=The%20Theoretical%20Critical%20Speed%20(Cs,Critical%20Speed%20of%20that%20mill.

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## Dwf (Jul 18, 2020)

Perfect! Thanks!
That’s what I was hoping for, someone that has an operational ball mill to give me an example of what is actually working, not what should in theory work. 
Thanks again!


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## Smack (Jul 19, 2020)

Rick, your mill is only turning at roughly 45 rpm?


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## rickzeien (Jul 19, 2020)

Smack said:


> Rick, your mill is only turning at roughly 45 rpm?


Yes. Many people run their home built mills at to fast a speed. Here is a site that does the calculations for you and a video that demonstrates mill grinding performance at various speeds.

(The inside diameter is the measurement used to calculate the speed)

I actually run at a lower speed as I also have a speed controller on the motor. 

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

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## Smack (Jul 24, 2020)

Yep, I used the same calculation and then loaded my mill with media and ran it, then with media and material and ran it and noticed that it behaved differently with material in it.


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## rickzeien (Jul 24, 2020)

Smack said:


> Yep, I used the same calculation and then loaded my mill with media and ran it, then with media and material and ran it and noticed that it behaved differently with material in it.


When it was loaded did the RPM stay the same or did it slow down. 

If the load transferred to the motor causes it to slow down that could account for the change. 

The calculation says to run at a percentage of critical speed. This percentage accounts for other variables. Wet or dry, larger or smaller media (I used a mixture of sizes) , if what your grinding is brittle or soft. 

Then you can run faster or slower up to that critical speed. This is why I added a speed controller to my mill.

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