A single-jar rolling ball mill (often called a drum mill or jar mill) operates on a completely different principle than the high-energy vibratory or planetary mills we've discussed. It is a low-energy, long-duration milling solution. Instead of high-frequency vibration, it relies on the gravity-driven cascading motion of grinding media inside a rotating horizontal jar.

In a rolling ball mill, the jar is placed on two or more motorized rollers. As the rollers turn, the jar rotates, and the grinding balls are lifted by centrifugal force and friction until they reach a certain height, after which they "cascade" or fall back down onto the sample. (1) Impact: Occurs at the "toe" of the charge where balls fall. (2) Attrition/Shear: Occurs between the sliding balls and the jar wall. (3) Critical Speed (nc): This is the most vital parameter. If the jar rotates too slowly, the balls just slide (no grinding). If it rotates too fast, centrifugal force pins the balls to the wall (no grinding). The ideal operating speed is typically 65% to 80% of the critical speed.

References:

1. M. V. C. Machado, et al., Experimental and Numerical Study of Grinding Media Flow in a Ball Mill, Chemical Engineering Technology, 2017, 40, 1835-1843
2. D. Li, et al., Numerical study on the effect of drum on the flow behavior of binary-size particles in rotating drums, Powder Technology, 2021, 386,  108-119