Operation of SAG Mills The processing capability of a SAG mill is greatly affected by ore geology and operating variables within the mill. The key issues broadly can be classified into two categories: field of breakage and charge motion, and flow through the grate and pulp lifters.
Since the different operating conditions cause different behaviour in the SAG mill charge levels, the FOPTD approximation is not satisfactory. Therefore, the SAG mill was modelled as an integrator for rock and grinding media. The in-flows are the mill feed and the ball addition. The out-flows are from rock charge breakage and ball charge wear.
mill operation as the operating parameters vary. The SAG mill power draw model of Austin (using the calibration by Doll, 2013) is used to predict the process power draw at the mill shell, Pshell, and the efficiency losses for the drive's mechanical components based on Doll (2012) are used to determine the motor output power, P.
operating SAG mills (it is not intended for design, but could help with it). Even if the mill total load is a key variable and can be indi-rectly measured with bearing pressure measurements, it was decided to discard it as an input variable. The main reason is that this kind of model must be useful to relate independent input vari-
The traditional operation of SAG mills relies on the operator to adjust the manipulated variables to maintain the target mill load and power draw. Changes to the ore hardness, feed size or ore specific gravity require an alert operator to adjust the variables while keeping up with all the other demands in the plant.
Besides being a function of the geometric variables, such as mill diameter, mill length, grates openings, and pebble ports size; the power equation is also function of all the operational variables selected for this study. The applied force is a function of the mass inside the mill and it is composed of balls, ore and water.
Similar to the impeller design affecting pump capacity, the pulp lifter design affects the discharge capacity (or mill throughput) of AG and SAG grinding mills. Generally, the discharge from AG/SAG mills consists of one or both of the following components: slurry (water and finer particles) and pebbles (20-100 mm).
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