Originally Posted by hanafi

hello everybody,

i'm working on the desgn of ball mill for phosphate rock grinding, i encountrer some problems with the calculation of the ball charge and the slurry charge.

according to many researchs, the ball charge should be between 30 and 40% and it's the same condition for the slurry (30 to 40%) wich means that the volume occupied is 60 to 80% of the mill volume wich i can't understand because i found that the total volume occupied shouldn't exceed 40% also!!!

any help please about the calculation of ball and slurry charge?

thank you

Hanafi,

The bulk volume occupied by the balls contains thousands, if not millions of spaces between the balls.

Typically, for spherical particles, the empty space can be as much as 40% of the bulk volume occupied by the spheres.

The slurry being of composed of small, fine particles and water will fill the space between the balls.

Take a jar, fill it with rocks.

Next pour in sand, until it is full of sand and rocks.

Next pour in water, until it is full of water, sand and rocks.

The jar was "full" after each step, but there was still space to put the next ingredient in the mix without overflowing the jar.

Do some research on the concepts of

"solid fraction", "void ratio", and "close-packed spheres".

Best regards,

Michael Thompson

Conveyor Dynamics, Inc. ■