Roller Mill System
The typical roller mill system is designed to dry, pulverize, classify and deliver a number of different types of materials. From a feed ranging in size from approximately 0-40mm (½“ to 1½”), the roller mill can produce particles ranging from coarse, granular products of approximately 10%R2000 microns (90% minus 10mesh) to as fine as 0.002%R44 micron (99.998% minus 325 mesh). They can also be used to prepare feed for systems producing ultra-fine materials, such as a Raymond vertical mill, ball mill or Jet-Stream™ classifier system.
Principal of Operation
The Raymond(R) roller mill is an airswept vertical ring-roll mill with an integral classification system. A vertical shaft rotates a “spider” assembly of arms from which are suspended free-swinging journal assemblies with rolls attached. As the unit turns, centrifugal force drives the rolls against the inner surface of the vertical grinding ring. Plows, rotating with the assembly, lift feed material from the mill bottom and direct it between the rolls and the grinding ring where it is pulverized.
Air enters from below the grinding ring and flows upward, carrying fines to the classifying section. The classifier sizes the pulverized material and returns oversized particles to the grinding chamber for further processing. The mill operates under negative pressure conditions, thus minimizing mill maintenance and plant housekeeping problems, while maximizing the service life of major mechanical components.
A roller mill is most effective processing material that is 5 or less on the Mohs scale of hardness. There are a few limitations, but the most practical materials are soft to medium hard materials. Ideal applications include various clays such as fire clay, bentonite and kaolin as well as other minerals like barites, gypsum, limestone, hydrated lime, phosphate rock, talc, coal and petroleum coke. Manufactured materials such as pigments, phenolic resins or similar materials can also be processed in a roller mill system.
Raymond(R) roller mills are available in 7 sizes with grinding ring diameters ranging from 30 inches to 86 inches (760 to 2180mm). These available sizes are capable of producing a wide range of product finenesses from a wide variety of materials.
Raymond(R) Roller Mill System with Flash Drying
Practically all naturally occurring non-metallic minerals and many manufactured products contain a certain amount of free moisture. At one time it was necessary to dry these products in an independent system. The technique used by Raymond combines drying and pulverizing in the roller mill. This may make it possible to eliminate independent drying equipment reducing capital investment, processing time and handling.
Flash Drying Principles of Operation
Heated air or waste gas is delivered to the mill return air housing and introduced through air ports to the grinding zone in the mill. The air turbulence and particle size produced during the grinding process are ideal for almost instantaneous evaporation of moisture.
Feed moisture is normally limited to what can be reliably fed into the mill. Typical product moistures are 0.1 to 0.5% by weight.