Grinding mill control system
Hydraulic system of Grinding Mill
To visualise what the situation is, think for a moment of a front bicycle wheel. Here the frame supports a central axle from which the wheel revolves around. In this situation, the axle is stationary and internal bearings allow the wheel to rotate freely. For a Ball Mill, turn this concept upside down and weld the wheel to the axle. So rather than the wheel rotating around the axle, the axle rotates with the wheel. Now, add 100 tonne of downward pressure to the wheel and you’ll find movement virtually impossible. And any movement which does occur resulting in excessive wear on the axle and support frame.
In the lubrication system employed in Kinsevere, four slide shoe bearings are present at each end of the Mill, and a combination of high and low pressure pumps supply these bearings with oil. High pressure pumps provide hydrostatic lubrication. Fundamentally this works by way of a constant supply of high pressure oil providing an upward force which equals the downward force of the rotating Mill to float the Mill above the bearings. Low pressure pumps provide hydrodynamic lubrication. The necessary prerequisite for this form of lubrication is velocity. Hydrostatic lubrication must be present during starting and stopping (static meaning stationary) and hydrodynamic lubrication must be present when the Mill is in operation (dynamic meaning moving).
To avoid overheating issues with the lubrication oil, the temperature is regulated by a combination of heating and cooling facilities. For heating, two movable skids (one for each end) support an oil tank storing the lubricant, with the aforementioned pumps mounted vertically on top. Heaters mounted within the tank switch on when the oil temperature falls below 30ºC, and switch off when the temperature reaches 35ºC. For cooling of the lubrication oil three chilling units provide chilled water to a heat exchanger. Circulation pumps move oil to this heat exchanger when the oil temperature exceeds 45ºC and ceases operation when the oil temperature is below 40ºC. The two systems work in tandem to regulate the oil temperature between 30 and 45ºC.
Cyclone Separator of Grinding mill
Although the Mill is effective in reducing particle size, it is not capable of ensuring all output is below this dimension. Consequently a Cyclone Separator has been installed downstream of the Mill so oversized particles can be returned to the Mill for further grinding.
The principal of operation of a cyclone separator involves a vortex of air inside a conical structure which is injected with ground ore from the Mill. As the air (infused with the ore particles of varying size) rotates upwards the vortex widens and the velocity reduces. From the reduction in velocity, heavier particles cannot overcome the effects of gravity and fall to the inner walls. Here they slide down the sides of the conical structure away from the vortex of air and fall out the bottom. The top feed of the Cyclone Separator ejects the finer, sized particles to be used in the leaching process. The bottom feed containing the heavier particles are returned to the Mill for further grinding.
Last update: February 21, 2012
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