16 10 2014 Explanation of the mill sizing procedure

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MILL SIZING EXPLAINATION By the Bond method 1 Work index (base) These data are normally defined in laboratory SG Specific gravity of ore 2 Efficiency factors 2a EF1: Kind of process If dry process = 1,3 If wet process = 1

2b EF2: Open circuit correction Required product in % Passingof Bond separation size in µ EF2

50 1,035 60 1,05 70 1,1 80 1,2 90 1,4 92 1,46 95 1,57 98 1,7 2c EF3: Mill diameter correction

2d EF4: Feed size correction where Wib is Work index base, Pf is the 80% Passing dimension in the feed Po is the 80% Passing dimension in the O'flow

www.themininggrindingoffice.com If Po < 75µ in wet process and 15µ ≤ Po ≤ 75µ, then apply the correction factor 2e EF5: Product fineness correction 2f EF6: Reduction ratio correction if Pf/Po < 6 3 Work index corrected

where Wic = work index corrected 4 Specific energy (estimated) 5 Production target Data defined by the plant 6,7 Power required

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16 10 2014 Explanation of the mill sizing procedure

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where P = power in kW, Q = Production target in t/h and σ = efficiency in % 8 Mill diameter The mill diameter is calculated with a mill power formula. Few formulas can be used at the discretion of the user. The most famous being the Bond formula where C = 1 if overflow mill and 1,16 if grate mill, J =volume load in %, Vcr = % of critical speed Sg = bulk density of the ball charge in t/m3 L = mill length Di = mill internal diameter

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