Fluid energy grinding or jet milling
Using fluid energy for grinding is a unique method of breaking solids into fine particles. Mills powered by fluid energy have no moving parts. Grinding is achieved by pressurized elastic fluids such as air or steam, which cause the particles to collide with force sufficient enough to break them into smaller particles. Fluid energy grinding delivers micron and submicron products with a much narrower particle size distribution than can be obtained with other types of grinding operations. In addition, many other functions -- such as classification, dehydration of wet materials, of fine particles with liquids or solids, blending, drying, and some chemical reactions ? can be performed simultaneously. This article outlines several different types of jet mills and discusses the practical and theoretical aspects of fluid energy grinding.
Jet mills grind continuously, reducing solids to particle sizes in the low-micron to submicron range. The material to be pulverized -- which can range from heat-sensitive soft waxes, ores, and crystals to hard abrasives [Table I] -- is exposed to streams of elastic fluid in the mill. This fluid, usually compressed air, compressed gas, or super-heated steam, is introduced through specially designed nodes that convert the fluid energy into velocity. The solid particles are then swept into the violent turbulence created by these sonic or supersonic velocity streams, and collide with and pulverize one another. The mill grinds and classifies simultaneously by using the principle of centrifugal force.