SAG MILLS CHOOSING METHODS. II. The working index of F. Bond in grinding

Last year, we affected one rather interesting topic – use of the energy indices in the grinding process design. We had planned to consider three calculation methods. Having studied this issue in more detail, we’ve decided to cover this topic in more detail. We will try to briefly, but as informative as possible, describe the methodology for providing the fifteen generally accepted laboratory tests types.

All those methods based on the F. Bond works, who as early as the 1950s put forward his famous theory (in narrow circles it is called the «third theory»). F. Bond claimed, during the grinding process designing, it is necessary to calculate the specific energy spent on reducing the material initial particles size to the required size after grinding.

General view of the Bond theory equation has the following form:

Where: E is the specific energy of particle size reduction for 1 ton of material, kW * h / t;

Wi – Bond’s working index;

P_80 – the mill feed size, 80% passes the control sieve;

F_80 – the product size at the output, 80% passes the control sieve.

What does the term “F. Bond’s Working Index” mean?

The “F. Bond’s Working Index” is a grinding parameter expressing the material resistance to crushing or grinding. In numerical terms, the working index measured in kW * h \ t. So, this indicator shows the energy amount needs to be spent on grinding the one short ton of material.

Depending on the method (stage) of crushing/grinding, the F. Bond’s Working Index divided into:

1. The crushing index (CWi);
2. The work index grinding rod(RWi);
3. The grinding ball index (BWi).

In the next article, we will reveal in detail the methodology for the indicated indices calculation, and make calculations at specific examples.