Ball Mill

Overview

A ball mill is a horizontal rotating grinding mill that reduces crushed ore to a fine powder suitable for mineral liberation and downstream concentration. It sits in the comminution circuit of a processing plant, typically following a SAG mill or crusher and feeding flotation or leaching. Ore and water enter as a slurry at one end and discharge as ground product at the other, the size reduction performed by a tumbling charge of steel balls.

The machine is built around a rolled-and-welded cylindrical Mill Shell closed at each end by heavy Feed Trunnion and Discharge Trunnion heads. These hollow trunnions act as the rotating journals and as the passages for feed in and slurry out. Each rides in a Trunnion Bearing, a white-metal hydrodynamic journal floated on a pressurised oil film during starting.

How it works

Rotation is delivered by the Girth Gear Drive: a two-piece ring gear bolted around the shell, driven by a pinion from the Drive Motor through a reducer. The mill turns at roughly three-quarters of its critical speed, lifting the ball charge up the rising side of the shell until it cascades and cataracts back onto the toe. Ore is ground by the combined impact of falling balls and the attrition of the rolling charge.

The shell interior is protected by a Shell Liner Set set whose profiled lifter bars also key the charge to the shell so it rises rather than slipping. As liners and balls wear, the Grinding Media charge is topped up to hold grinding power and product fineness. Ground slurry overflows through the discharge trunnion into the Discharge System, where a trommel rejects oversize and ball scats. Bearings and gear mesh are served continuously by the Lubrication System, and an auxiliary Inching Drive slowly turns the mill for liner changes and relining.