Grinding & Classification Circuits

Grinding & Classification Circuits 2017-04-04T06:57:16+00:00
  • To participate in the 911Metallurgist Forums, be sure to JOINLOGIN
  • Use Add New Topic to ask a New Question/Discussion about Grinding.
  • OR Select a Topic that Interests you.
  • Use Add Reply = to Reply/Participate in a Topic/Discussion (most frequent).
    Using Add Reply allows you to Attach Images or PDF files and provide a more complete input.
  • Use Add Comment = to comment on someone else’s Reply in an already active Topic/Discussion.

Equation to calculate grinding mill ball size (3 replies and 1 comment)

6 months ago
sajid 6 months ago

My grinding mill has length and diameter of 4.57 m. the maximum size of the balls selected is 77 mm, as there are two or three kinds of ball sizes to select the second ball size. are there any formula or equation that i can calculate the ball size.


Alex Doll
6 months ago
Alex Doll 6 months ago
2 likes by Helena Russell and David

Ball size is usually dictated by the size of the feed material you are grinding, and only minimally dependent on the dimensions of the grinding mills.

There are two equations commonly used to estimate the ball size, first is Azzaroni's equation and second is  Bond's equation.  Both predict a single size of ball to recharge an operating mill (there are different equations for the range of ball sizes for the first charge of a new mill).

The two equations are in Jaime Sepulveda's 'MolyCop tools' software as:

d = 6.06 (F80)^0.263 (ρ Wi)^0.4 (N D)^-0.25

d = 1.354 (F80)^0.5 [ρ Wi / (Nc D^0.5)]^⅓

where d is the make-up ball size in mm, F80 is feed size in µm, ρ is ore density (specific gravity) in t/m³, Wi is metric Bond work index for ball milling, N is mill rotation speed in rev/min; Nc is rotation speed as % of critical, and D is the mill diameter in US feet.

You'll get different answers from the two equations; just pick a size between the two and you should be close enough.

5 months ago

thanks for valuable information. i already calculated it for the first charge. but now i need calculation for the second charge. if you could give me some guideline it would be appreciated.

Maya Rothman
6 months ago
Maya Rothman 6 months ago

To maybe complement Alex's great answer see

6 months ago
David 6 months ago

Use the Social Share Bar on the Left. Tell everyone you can about It's FREE & GOOD.

Please join and login to participate and leave a comment.

BUY Laboratory & Small Plant Process Equipment

We have all the laboratory and plant equipment you need to test or build/operate your plant.

ENTER our Mining Equipment' Store

We Sell EQUIPMENT for all types of Mineral Treatment PROCESSES and Laboratory Testing needs

Have a Mineral Processing QUESTION?

Come in, ask your question

911Metallurgist Community Forums

Talk to other metallurgists and be helped.


We can IMPROVE ALL PLANTS / Mineral Processing Engineering & LABORATORY Ore Testing

911Metallurgy Engineering

Contact us for process engineering, metallurgical investigations, plant optimization, plant troubleshooting, needs. WE “FIX” METALLURGY.