Ball mills are rather inefficient, and typically require 10–20 kW·h of electric power to make a tonne of rawmix. The Aerofall mill is sometimes used for pregrinding large wet feeds. It is a short, largediameter semiautogenous mill, typically containing 15% by volume of very large (130 mm) grinding balls.
Cement Plant Gypsum Mill Grinding Stream Sheet 299 Vrms in pilotscale finish grinding of cement. there have been several recent studies of the energy efficiency of vrms. pilot scale results by altunet al.  indicate a potential decrease of 18% in energy consumption using a vrm compared to an existing rod mill/ball mill .