Roller Mill made for finer grinding
Principle of operation
The Raymond® fine grinding roller mill is an air-swept vertical pendulum mill with integral classification. A vertical shaft rotates an assembly of grinding journals / rolls inside the grinding zone. As the unit turns, centrifugal force drives the rolls against the grinding ring. Feed material enters the mill from the top of the grinding zone and moves down to the mill bottom by gravity. It is then lifted by plows from the mill bottom to the nip area of the grinding rolls and ring where the grinding occurs. The plows rotate about the center shaft together with the journals rolls assembly. The ground material is discharged into the process airstream.
The airstream flows through nozzles beneath the bull-ring carrying the pulverized material upward to the dynamic classifier where the coarse particles are separated and returned to the grinding zone, while acceptable materials exit the mill to product collection in a cyclone or a baghouse.
With the conventional roller mill design, when fine grinding, the classifier tails (rejected particles) are also quite fine and can be easily entrained into the airstream. However, the fine grinding roller mills are designed with a separate path for the coarse reject material to travel back to the grinding zone in such a way that particle short circuiting is avoided.