During operation, the material is fed into this vortex along an engineered tangent circle and accelerates. Strong velocity gradients near the jet cause the suspended particles of the material to collide with each other and reduce themselves by attrition and collision. Size reduction is the result of the high-velocity collisions between particles of the process material itself. No grinding media is involved. The jet fluid exits through an outlet at the center of the chamber either from top and draws the micronized the particles with it to the cyclone collection system. Heavier oversized particles are held in the grinding chamber by centrifugal force, until micronized to a desired size.

Feed particle size is critical, restricted by the size of the feed injector. For mills of 200-300 mm, the feed size can be a maximum of 1.5 mm. For smaller-size mills, the feed size is correspondingly finer.

There are several factors, both operational and physical, which affect the fineness of the end product, such as feed rate, nozzle size, nozzle pressure, nozzle angle, airflow rate, feed particle size, chamber diameter and width, and product outlet diameter. All of these variables can be adjusted during operation, but it is more likely that once operation has begun, only feed rate will be varied to meet the required particle-size distribution.

Actually the spiral jet milling process is not governed only by the jet mill itself. It is a process involving different machines and components which need to be properly integrated and controlled. These accessories include a source of fluid energy, a feeder, a cyclone separator, a dust collector etc.