How to Measure a Ball MillFebruary 1, 2005 By: Stephanie vL Henkel, Sensors Sensors
The gold that lies in the Carlin Trend of Nevada consists of tiny particles trapped in complex ores. The ratio of ore to gold is 200 tons to 1 oz., and the first step toward extracting that ounce is to pulverize the ore in a ball mill. The business part of these contrivances is an immense steel cylinder containing steel balls. Chunks of ore are loaded in and the cylinder rotates. As the mix of ore and steel cascades against the cylinder's inner wall, the ore is broken into ever-diminishing pieces. Needless to say, this operation is tough on the mills as well as the ore. When the personnel at one facility wanted to find out if their mill had settled on its foundations enough to distort the machine frame and cause bearing misalignment, they brought in experts in the field of metrology and inspection services. And the experts brought in the FARO Laser Tracker. Using a laser beam reflected from a movable target placed on the equipment to be evaluated, the system measures points that lie within 115 ft. of the sending/receiving unit. A SuperADM feature lets the Laser Tracker reacquire an interrupted beam without returning to a reference point. The measuring "envelope" is ±360° horizontal and +80°/–50° vertical; point accuracy is 10 μm ±0.8 μm. After setting up the base tracker on a tripod, the operator touches or drags the target reflector along the surface of interest. The laser projects a beam onto the reflector and receives a split reflection. Using the angle between the beams and the distance to the target, the tracker's software triangulates and records the position of each point measured. Measurements at 40 points on the mill produced a digitized image accurate to ±0.005 in. that revealed most of the points to be within 0.040 in. of where they belonged.
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