Effects of filling degree and viscosity of slurry on mill load orientation

In wet milling, the presence of a pool plays a key role in governing the transport of material in the mill. It also contributes in lowering the power drawn to the mill. And in the process, grinding efficiency could be altered. Understanding the pool formation in a tumbling mill and its interrelation to slurry filling is the main focus of this work.To this end, a mixture of water and glycerol was prepared with appropriate concentrations to mimic viscosities ranging from 1 to 60 mPa s. A transparent mill (552 × 180 mm), made of Perspex material and filled with 10 mm balls, was used for the tests. Ball filling and mill fractional speed were kept constant respectively at 20% and 60% while slurry filling was varied from 0% to 300%. Using a high speed video camera, the motion of the charge was captured. The movies were then analysed frame by frame and the angular positions of the media shoulder, the media toe as well as the pool of slurry were measured. The orientation of the load under the different conditions was in this way determined.Preliminary results show that there exists a definite trend between pool angle θpool and slurry filling U. A power function of the form θpool = C · Uk appears to be a good description of the relationship where C and k are fitting parameters. It was also found that, within the range investigated, viscosity has little to no effect on the load behaviour.

Figure optionsDownload as PowerPoint slideHighlights
► The general behaviour of a laboratory mill was explored with focus on slurry pool.
► Media charge orientation is not substantially affected by the presence of slurry.
► At constant viscosity, media shoulder angle stays within ±6° about the average.
► More cataracting is consistently observed for low slurry viscosities.
► A power function is found to correlate well slurry toe position and slurry filling.