Chapter 7 - Tubular Ball Mills

Abstract

The usual objective of reducing the size of run-off mine ore pieces is to separate the mineral of interest contained in the ore body from associated gangue minerals. As only crushing does not liberate a mineral, further size reduction is usually required. This is achieved by grinding the crushed ore in tubular mills. This chapter draws attention to the working and usage of these tubular ball mills. In tubular mills, a grinding media, such as steel balls, rods or hard pebbles, impart the forces required for size reduction. On rotating a mill charged with rocks and grinding media, the entire charge rises against the perimeter of the mill in the direction of motion. This chapter explains in detail the various components of the mills illustrating the functioning of these components. The energy of impact by the steel balls on the rock particles will depend on the height from which the rocks fall and the angle at which the impact occurs. The size reduction that follows will depend on the charge characteristics, such as mass, volume, hardness, density and size distribution, the characteristics of the grinding media, the speed of rotation of the mill, and slurry density. The capacity of a ball mill depends on its dimensions, the type of mill, the speed at which the mill rotates, the mill loading, the product size required from a given feed size, the work index, the mill shaft power, and the specific gravity of the rock. The chapter also discusses the mill power estimation.