Ball lead screws are used to change the rotary motion to linear motion, and torque to thrust, and vice versa. These are a power screw with a train of ball bearings riding between the screw and the nut in a recirculating track. It has a rounded shape to conform to the balls. It converts torque into linear motion through direct sliding friction. It is very similar to a regular nut and bolt combination.
The ball mill, an intermediate and fine size reduction device, is a tumbling drum with a 40% to 50% filling of the balls. The material that is to be grounded fills the voids between the balls. Very large tonnages can be grounded with these devices because they are very effective material handling devices. The feed can be dry with less than 3% moisture or slurry can be used containing 20% to 30% water by weight. Ball mills are employed either primary or secondary grinding applications. In primary applications, they receive their feeds from crushers, and in secondary applications, they receive their feed from rod mills, autogenous mills. Ball mills are sometimes used in single stage grinding, receiving crusher product. The circuits of these mills are often closed with classifiers at high circulating loads.