Rod Grinding Mills

Rod grinding mills are rotating/tumbling mills in which comminution (size reduction) takes place with the aid of metallic rods. The length of the cylinder is typically 1.5 to 2.5 times longer than the diameter. They usually have a rod charge of 35 to 40% with size reduction being achieved by a combination of compression and attrition. As the mill turns, the rods cascade over each other in relatively parallel fashion. One of the primary advantages of a rod mill is that it prevents over-grinding of softer particles because coarser particles act as bridges and preferentially take the compressive forces. This action gives a relatively narrow size distribution and a minimum amount of extremely fine material. Rod mills can be run dry or wet but the majority are run in a wet grinding configuration.

Historically rod mills were the first stage of grinding after crushing. The current trend is to install a SAG mill in combination with ball mills. SAG mills can replace secondary and tertiary crushing as well as primary grinding. This avoids rod mills altogether and their associated costs of rod media and general maintenance costs.

- Metso Minerals, FLSmidth Minerals images.