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Abstract
Charge motion is of prime importance in the efficiency of comminution in tumbling mills. Since direct observation of charge shape and its motion in an industrial mill is not possible, a combination of analytical and physical studies was used to determine charge trajectory. Software packages, which predict charge motion such as the GMT (Grinding Media Trajectory) only consider the outermost layer of charge (single ball) and ignore the interactions of grinding elements. In this research, the measured charge trajectory in a 1 m-diameter mill with a transparent end, called a model mill, was compared with that of the GMT. Four types of polyurethane rings were accurately machined to scale down the liners’ arrangements at two industrial mills. To explore various charge shapes and trajectories, the model mill was operated at 55, 70, and 85% of critical speed for five levels of mill filling (10, 15, 20, 25, and 30% by volume). The angular displacement of the toe, toe departure, shoulder, and charge impact point were determined from the photographs taken from the model mill. New relationships to predict charge shape and charge impact points were introduced to modify the GMT results. The relationships were validated by the model mill using the new liner of the Sarcheshmeh copper complex SAG mill. The relative error of prediction was found to be 1.1%. The results indicated that when the lifter face angle increased from 7 to 30°, the distance between the charge impact point and the toe decreased from 52 to 31° for 25% filling. This meant increasing the probability of charge impacting the toe not the liner which favored more efficient comminution practice. After converting AG mills to SAG mills on account of liner profile change, a 31% increase in throughput (from 419 to 548 t/h) in addition to a 4% decrease in product size (from 516 to 496 µm) was realized which was a significant contribution to plant performance improvement.

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	All Years to Access Full-Text Export citations A METHOD TO PREDICT SHAPE AND TRAJECTORY OF CHARGE IN INDUSTRIAL MILLS By M Maleki Moghaddam, M Yahyaei, S Banisi Published in International Mineral Processing Congress (IMPC) at 2012 Direct link: http://kmpchemmat.ir/pii/41479 Abstract Charge motion is of prime importance in the efficiency of comminution in tumbling mills. Since direct observation of charge shape and its motion in an industrial mill is not possible, a combination of analytical and physical studies was used to determine charge trajectory. Software packages, which predict charge motion such as the GMT (Grinding Media Trajectory) only consider the outermost layer of charge (single ball) and ignore the interactions of grinding elements. In this research, the measured charge trajectory in a 1 m-diameter mill with a transparent end, called a model mill, was compared with that of the GMT. Four types of polyurethane rings were accurately machined to scale down the liners’ arrangements at two industrial mills. To explore various charge shapes and trajectories, the model mill was operated at 55, 70, and 85% of critical speed for five levels of mill filling (10, 15, 20, 25, and 30% by volume). The angular displacement of the toe, toe departure, shoulder, and charge impact point were determined from the photographs taken from the model mill. New relationships to predict charge shape and charge impact points were introduced to modify the GMT results. The relationships were validated by the model mill using the new liner of the Sarcheshmeh copper complex SAG mill. The relative error of prediction was found to be 1.1%. The results indicated that when the lifter face angle increased from 7 to 30°, the distance between the charge impact point and the toe decreased from 52 to 31° for 25% filling. This meant increasing the probability of charge impacting the toe not the liner which favored more efficient comminution practice. After converting AG mills to SAG mills on account of liner profile change, a 31% increase in throughput (from 419 to 548 t/h) in addition to a 4% decrease in product size (from 516 to 496 µm) was realized which was a significant contribution to plant performance improvement.