*The F. Bond rod mill*

Currently, the use of grinding rods is not very widespread among the Ukrainian producers. Still, this type of grinding media is used and we consider it appropriate to consider the F. Bond calculation, which we are talking about in series of articles.

**RWi **is the rods grinding work index. It is applied for the energy input calculation (kW*h/t), that is needed to grind one ton of material in the rod mill.

Rod mills are used in the grinding of material (on the whole, the ore), the size of which is -13,2 +3,2 mm. In practice, this method is applied for the energy input calculation to engineer first grinding stage in the ball mills at the ore mining and processing enterprises.

The formula used for calculation the **RWi** index is as follows:

where D is the size hole of classification sieve (µm);

G_{c } – material grindability at the rod mill (g/r);

F_{80} and Р_{80} – the mesh size whereby 80% of material is sieved in starting material and industrial product, respectively.

Grindability (Gc) means the quantity of sieved material, that is reseived during one rotation of the F. Bond mill.

As in crush process engineering, the results of **RWi** calculation serve to determine which type of equipment will be most effective in the specific case of grinding (the rod or grinding balls 90-12 mm are used as a grinding material).