The grinding mill’s rotational speed directly determines the movement of the grinding media inside the mill and the grinding efficiency. At low speeds, the balls are lifted relatively low, and under their own gravity, they roll down from the top of the ball load in a cascading motion. At this speed, the impact force of the balls is small, but the grinding effect is strong; the ore is mainly ground and crushed, resulting in low grinding efficiency.
At higher speeds, the balls are lifted higher. After reaching a certain height, the balls detach from the mill and fall along a parabolic trajectory, entering a cascading motion. At the point of impact, there is a significant impact force, and the ore is mainly crushed by impact, resulting in the highest grinding efficiency.
When the mill speed exceeds a certain limit (very high speed), the balls rotate with the mill and do not fall, entering a centrifugal state. At this point, the balls have little impact force, and the grinding effect is also small, causing the grinding process to stop.