Dry grinding mill is a unit operation designed to break a solid material into smaller pieces. There are many different types of grinding mills and many types of materials processed in them. The grinding of solid matters occurs under exposure of mechanical forces that trench the structure by overcoming of the interior bonding forces. After the grinding, the state of the solid is changed the grain size, the grain size disposition and the grain shape. Mechanical impact mills utilize rotating hammers, pins or beater bars to accelerate and impact particles against another hard surface or other particles. More advanced impact mills use an internal air classifier to control the maximum particle size.