847,281. Ball-and-ring mills. BABCOCK & WILCOX Ltd. Dec. 3, 1958 [Dec. 6, 1957], No. 37997/57. Class 59 In a ball-and-ring mill having an upper non-rotary grinding ring and a lower rotary grinding ring disposed within a casing, the upper ring is urged towards the lower ring by means of a plurality of hydraulic power devices mounted outside the casing …