## How to Calculate and Solve for Mill Speed | Ball Mill Sizing

The image above represents the mill speed.

To compute for mill speed, two essential parameters are needed and these parameters are Speed Percentage (N%) and Critical Speed (Nc).

The formula for calculating mill speed:

MS = N% x Nc

Where:

MS = Mill Speed
N% = Speed Percentage
Nc = Critical Speed

Let’s solve an example;
Find the mill speed when the speed percentage is 12 and the critical speed is 10.

This implies that;

N% = Speed Percentage = 12
Nc = Critical Speed = 10

MS = N% x Nc
MS = (12/100) x (10)
MS = (0.12) x (10)
MS = 1.2

Therefore, the mill speed is 1.2 m/s.

Calculating the Speed Percentage when the Mill Speed and the Critical Speed is Given.

N% = MS / Nc

Where;

N% = Speed Percentage
MS = Mill Speed
Nc = Critical Speed

Let’s solve an example;
Find the speed percentage when the mill speed is 24 and the critical speed is 6.

This implies that;

MS = Mill Speed = 24
Nc = Critical Speed = 6

N% = MS / Nc
N% = 24 / 6
N% = 3

Therefore. the speed percentage is 3 m/s.

## How to Calculate and Solve for Shaft Power | Ball Mill Length

The image above represents shaft power | ball mill length.

To compute for shaft power | ball mill length, six essential parameters are needed and these parameters are Value of C, Volume Load Percentage (J), % Critical Speed (Vcr), Bulk Density (s.g), Mill Length (L) and Mill Internal Diameter (D).

The formula for calculating shaft power | ball mill length:

P = 7.33 x C X J X Vcr x (1 – 0.937) x [1 – 0.1/29 – 10Vcr] x s.g. x L x D2.3

Where:

P = Shaft Power | Ball Mill Length
Vcr = % Critical Speed
sg = Bulk Density
L = Mill Length
D = Mill Internal Diameter

Let’s solve an example;
Find the shaft power | ball mill length when the volume load percentage is 8, the %critical speed is 10, the bulk density is 3. the mill length is 14 and the mill internal diameter is 16.

This implies that;

J = Volume Load Percentage = 8
Vcr = % Critical Speed = 10
sg = Bulk Density = 3
L = Mill Length = 14
D = Mill Internal Diameter = 16

P = 7.33 x C X J X Vcr x (1 – 0.937) x [1 – 0.1/29 – 10Vcr] x s.g. x L x D2.3
P = 7.33 x 1 x 8 x 10 x (1 – 0.937) x [1 – 0.1/29 – 10(10)] x 3 x 14 x 162.3
P = 36.94 x [1 – 0.1/2-91] x 3 x 14 x 588.133
P = 36.94 x [1 – 0.1/4.038e-28] x 24701.609
P = 36.94 x [1 – 2.47e+26] x 24701.609
P = 36.94 x -2.475e+26 x 24701.609
P = -2.259

Therefore, the shaft power | ball mill length is – 2.259 W.