# A Study of Magnetic Mill Productivity
## 2 Analysis of the Latest Studies  
Modern publications present a fairly wide range of studies on industrial mills, whose principle of operation is based on moving ferromagnetic millstones in a magnetic field. Two competing technologies are mainly considered. One of them is based on creating a rotating magnetic field using a fixed inductor containing a multiphase symmetrical winding connected to a multiphase alternating current network (most often three-phase) [1; 2; 3]. The second technology is much less frequently used. Its application involves the creation of a magnetic field with the help of permanent magnets located on a rotating inductor [4]. Several directions of research into such mills are distinguished, particularly the following:  
* the development of inductor structures and working out design calculation methods [1; 5; 6];
* establishing interrelationships between the structural parameters of the mill and the course of the characteristic physical processes in its WC [2; 3; 4; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16];
* the creation and improvement of management systems [3; 6; 17; 18; 19; 20; 21; 22];
* experimental studies of grinding and/or mixing processes [1; 2; 5; 14; 19; 23; 24; 25];
* the improvement of existing and development of new technological processes that involve mills [5; 11; 20; 22; 26; 27; 28; 29]. A review of publications on the issue under study proves its relevance and highlights existing problems. For instance, [1] emphasizes the advantages of using EMMs compared to traditional ball mills as exemplified by the process of grinding copper ore. The obvious advantages of the electromagnetic method of creating a rotating field, namely the energy of the field being directly transmitted to the ferromagnetic millstones, prompted the authors of [1; 3; 6] to use it for construction of an EMM prototype. However, this approach has particular drawbacks. The inductor of such a mill consumes reactive current from the network; consequently, it will require a compensating device to maintain the power factor within acceptable limits. It is also expedient for this device to be adjustable. The phase shift angle between voltage and current will depend on the number of millstones in the WC, their size and location. In addition, in order to achieve significant values of magnetic induction in the WC and to reduce the dispersion of the magnetic field in such an inductor, its main dimensions (diameter, length) should be as small as possible. This implies using rather complex cooling systems for such inductors. In [3; 8; 18; 25] the authors take into account effects of the electromagnetic mill control system together with its cooling system, WS flow regulator, filters and separators, various purification systems, heat exchanger and WS flow recirculation system for supplementary grinding. Based on the results of the mathematical modeling of processes in such a technological complex, conclusions about efficiency of the mill are presented. A real-time control system for the energy efficiency of this mill is proposed in [19]. Moreover, the aforementioned set of equipment is used for conducting experimental studies [2; 25]. In [27], an innovative coal grinding technology for increasing the efficiency of fuel boilers is considered. This scientific paper discusses the importance of achieving the appropriate level of fuel granularity, which directly affects this indicator. Similar problems are considered in [25]. The authors study experimental results of the dry and wet grinding method, establishing the size distribution of the obtained particles, which provides an objective assessment of productivity of the technologies used. The authors of [20; 25] claim that a complex of factors acting on the substance placed in the working chamber of the magnetic mill can lead to deformation of the crystal lattice of a solid substance, a sharp increase in its chemical activity, degree of dissociation, etc.