A conventional mill driven by an electric motor or turbine through a set of foot mounted reduction gearing, coupled to the top roller through a tail bar / rope coupling along with a set of crown pinions for driving the bottom rollers, has the following limitations: 1. The crown pinions and tail bar consume 10% of the total power transmitted to the mill rollers. 2. Pinion reaction at the drive end of the top roller shaft causes very high horizontal force on the top roller bearing housing, which obstructs free float of the top roller. The net result is reduction in mill extraction efficiency. 3. Since all the power is transmitted through the square end of the top roller which drives the bottom rollers through a set of crown pinions, very high levels of stresses are developed at the top roller assembly. This is the major cause of pre-mature failure of mill roller shafts and crown pinions. 4. Throughputs have to be restricted to contain the high stress level on the mill headstock and drive side top roller bearing. 5. Wear and the consequent repair of pinions, tail bar and top roller bearings after every crushing campaign is a major issue to be dealt with by the mill engineer year after year.
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