Principle of OperationBowl Mill is driven by AC motor, coupled with flexible coupling to the worm shaft. The worm shaft drives worm gear, mounted on the Main Vertical Shaft. A bowl mounted on the top of the shaft rotates at a speed of 40 to 65 rpm. For a particular mill the speed is constant .Integral coolers are provided in the mill base with circulating water for removing heat from the oil. External lube oil systems are also used for cooling the oil in the gear box, which consists of a motor driven pump, cooler and filter. To prevent coal entering in to the Gear case, an air sealing system is provided.Hot primary air for drying and carrying pulverized coal, enters through insulated Mill side and Liner Assembly. Tramp Iron, pyrites and stones coming in the mill with raw coal move out of the bowl and being heavy, fall into the mill side and linear assembly. These are scraped and dumped in the pyrite hopper assembly through the Tramp Iron and Spout valve.The journal assembly consisting of Grinding Rolls is mounted on Separator Body. Grinding force is applied by pressure spring adjustment. The roller assembly can be moved up and down depending upon the roll condition and coal bed. Separator Body consisting of linear assemblies deflects the air stream to the center of bowl.Mill is equipped with the stationery classification with adjustable vanes for adjustment of coal fineness. The coarser particles in the in the pulverised coal are separated in the classifier and returned back to the bowl for further grinding.Mill Discharge Valves mounted on the Separator top consist of Flap type closure plates operated by pneumatic Cylinders, which can be tilted out of the path of coal stream. This is used to isolate the mill from Boiler during maintenance.