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Size grinding mills with Bond's Third Theory and the Rowland-Kjos EF corrections: specific energy, net and gross power, mill dimensions and operating work index.
This calculator sizes grinding mills with Bond's Third Theory of Comminution (1952): W = 10·Wi·(1/√P80 − 1/√F80), where W is the specific energy in kWh/t, Wi the Bond work index, and F80/P80 the 80%-passing feed and product sizes in µm. The base energy is corrected multiplicatively with the Rowland & Kjos (1978) efficiency factors EF1 to EF8 (dry grinding, open circuit, mill diameter, oversized feed, fineness, the two reduction-ratio corrections and the rod-mill circuit factor). Only EF3, the mill diameter factor, can fall below 1.0: EF3 = (2.44/D)^0.2 gives a credit for mills larger than 2.44 m, down to 0.915 at 3.81 m and above. EF4 and EF5 are not allowed below 1.0.
Net power is W×throughput; gross power applies a 95% drive efficiency. Mill dimensions are estimated by inverting the Hogg & Fuerstenau power formula P = 15.23·D^2.5·L·φc·ρap·(J − 1.065·J²)·sin(α), with the charge-volume term valid for fillings up to about 40%. The operating work index back-calculates Wi from measured plant power, throughput and sizes, for comparison against laboratory grindability results.
Every formula is anchored to published references and covered by unit tests, including a hand-calculated power case (a 5.5 × 8.5 m ball mill at 72% critical speed and 38% filling draws ≈ 4,289 kW net) that the dimension estimator round-trips.
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