# New Approach to Effective Dry Grinding of Materials by Controlling Grinding Media Actions
## 1 Introduction  
The grinding process is an essential step in different technological operations [1, 2, 3]. For example, the processes are used to increase the mineral extraction degree, obtain new building mixture properties, and accelerate chemical reactions in the mining and processing, construction, and chemical industries, etc. [4]. Among the problems present in grinding processes, the restricted possibilities of providing the required product fineness value and the high energy costs in mills can be highlighted. The reasons for these problems relate to the design features of mills and the lower grinding efficiency at finer particle sizes, caused by the increased contact area and reduced probability of effective impacts. At present, mills using grinding media in their operation procedure are commonly used in grinding processes (for example, ball, stirred, and vibration mills, etc.). Steel balls, ceramic balls, glass beads, and natural stones are typically used as the grinding media. The main function of the grinding media is transferring destruction energy from the working body of the mill to the ground particles [5]. The main factor affecting the grinding process efficiency in the considered mill type is the collision energy of the grinding media [6, 7, 8]. The grinding media collision energy is proportional to the destruction energy, which is transferred from the grinding media to the ground particles during the action of the working body. The literature analysis showed that several approaches for increasing the collision energy of grinding media have been developed to provide high product fineness and energy efficiency in the grinding process. One approach relates to increased grinding media velocities. The collision energy of grinding media is proportional to their kinetic energy, mainly depending on the grinding media velocity. The grinding media velocity increases with increased movement velocity of the working mill body. For example, increased collision energy of grinding media is achieved with increased rotational speeds of the cylindrical chamber in ball mills [9; 10; 11], oscillation amplitudes of the chamber in vibratory mills [12], and rotational speeds of the stirrer in stirred mills [13; 14]. However, there are some problems related to implementing the approach in the specified mill types. For example, in ball mills, increased chamber rotational speeds increased the grinding media concentrations on the chamber wall due to excess centrifugal force over gravitational force [15]. In vibratory mills, increased collision energy from increased amplitudes and frequencies of grinding chamber oscillation is restricted due to mill design features [16]. In stirred mills, increased collision energy from increased stirrer rotational speeds is problematic, as it also decreases the grinding media concentration in the high-kinetic-energy zone (near stirrers) [17; 18]. The next approach concerns adjusting the geometrical parameters of the mill. The geometrical characteristics for ball, vibratory, and stirred mills include chamber size, grinding media filling ratio, stirrer shape, grinding media size, and grinding media shape. Numerous studies are dedicated to investigating the effect of the specified geometric parameters on the grinding process efficiency. The investigation results showed that an increased chamber diameter decreases energy consumption in stirred mills [19], which can be explained by the increased gap distance between the chamber wall and the stirrer edge. As the grinding media filling ratio increases, the collision energy of the grinding media increases. However, an increased grinding media filling ratio resulted in decreased free space for grinding media acceleration, decreasing the collision energy of the grinding media [20; 21]. Several research works have focused on the effect of stirrer design on grinding efficiency. The investigation results demonstrated that the disk design of stirrers decreases energy consumption.