# New Approach to Effective Dry Grinding of Materials by Controlling Grinding Media Actions
## 1 Introduction
However, the use of wing and cross types of stirrers characterized by increased energy consumption has resulted in increased collision energy [19; 22]. Regarding grinding media size, the investigation results showed that the large grinding media size increases energy consumption [23; 24]. According to the research results, the optimal grinding media-ground particle size ratio is 20:1 [25]. In addition, spherical grinding media demonstrated higher grinding performance than non-spherical ones [26; 27]. Generalizing the two approaches, we noted a problematic trend: increased grinding process efficiency increases the grinding media velocity and geometrical parameter values (especially the grinding media filling ratio). Consequently, another approach proposed in [28] aims to improve the grinding efficiency by organizing impacts from different directions, which enhances particle destruction due to the irregular shape of the particles. The authors of [28] proposed increasing product fineness as a result of particle size reduction by grinding media action in radial and axial directions. This organization of grinding media movement leads to the Rebinder effect, i.e., a decrease in particle strength due to the periodic compression and tensile stress of the particles [28]. While the grinding media movement in the radial direction is provided by the ellipsoidal rotor, the grinding media movement in the axial direction is achieved via chamber vertical vibration. As shown in Figure 1, the particle is stressed between two grinding balls (grinding media). It should be clarified that while the impact velocity of grinding ball \"1\" is greater than zero (due to the ellipsoidal rotor) before collision with the particle, the impact velocity of grinding ball \"2\" is zero in the radial direction (Figure 1a,b). Analogically, in the axial direction, while the impact velocity of grinding ball \"3\" is greater than zero (due to chamber vertical vibration) before collision with the particle, the impact velocity of grinding ball \"4\" is zero (Figure 1c,d). Thus, the particle experiences a one-sided impact from the grinding balls. Another approach has been proposed to increase general collision energy [29]. The idea of the approach is to facilitate the grinding process through the counter-collision of the grinding media (Figure 2). This is provided by the design of mills with V-shaped chambers in which the movement of the grinding media is provided due to the inclination of the chamber sections. In  
Figure 1: Scheme describing the approach of one-sided impact on the particle by grinding media: (**a**) initial position of grinding media in the horizontal direction; (**b**) particle deformation by grinding media (the particle is compressed and stretched in the horizontal and vertical directions, respectively); (**c**) initial position of grinding media in the vertical direction; (**d**) particle deformation by grinding media (the particle is stretched and compressed in the horizontal and vertical directions, respectively) [28]. Figure 2: Scheme describing two-sided impact on the particle by grinding media: (**a**) pre-compression state of the particle by grinding media; (**b**) post-compression state of the particle by grinding media [29]. this case, the one-sided impact presented in [28] changes due to the double-energy impact, increasing the general collision energy. A new approach for particle size reduction with grinding media is proposed to increase the grinding process efficiency (Figure 3). The approach essentially comprises the joint application of the last two approaches, i.e., organizing the grinding media collision in the radial and axial directions, with counter-collision of the grinding media in the radial direction (providing two-sided impact on the particles). A new mill design is developed for the proposed approach (Figure 4). The mill design includes a chamber filled with grinding media (steel balls), a vibrating table (with drive), pistons, and eccentrics with electric motors.