Laboratory studies of an electromagnetic mill inductor with a power source

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The article presents the laboratory research of a prototype device for grinding and mixing materials, known as an electromagnetic mill. Studies were made of the circuit of the mill inductor, covering the analysis of the current intensity, magnetic induction and power factor during operation. The article further shows the laboratory stand and research equipment used during the measurements.

Technological advances, especially in the preparation (grinding) of raw materials and aggregates, forces the use of different, often sophisticated technological processes. They are increasingly highly energy-intensive. Therefore, designers are looking for new, high-performance methods for both obtaining the appropriate product graining [3, 8, 15, 24, 28, 30] and the appropriate methods of controlling these processes [4, 5, 14] as well as their research and modelling [7, 23 26, 27, 29]. The construction of the mill shown in this work is prototypical. In such a case it was necessary to conduct experimental research on the physical object. This was aimed at getting to know the most important electrical, magnetic, structural and operating parameters of the device under test. The electromagnetic mill is a device whose essential feature is the intensification of many processes, and through an effect on the shredded material also many force fields. Therefore, in comparison with commonly used devices, the operation of the electromagnetic mill is many times faster, depending on the application even several thousand fold faster. This also allows to obtain a series of effects of the treatment of materials impossible to achieve by other methods and with conventional equipment. The electromagnetic mill’s possibilities include [2, 12, 13, 16, 19, 25]:  dry and wet grinding of hard materials;  mixing loose, liquid and gaseous materials;  grinding elements, beans, etc.;  activation of volatile dust;  manufacture of composite materials in the process of mechanical alloying;  acceleration of chemical reactions;  obtaining high durability emulsion;  utilisation of heavy hydrocarbons  waste product of petrochemical or carbochemical processes  emulsification;  obtaining substances of relevant physical and chemical properties. 

Figure 1 shows the model of the electromagnetic mill constructed at the Lublin University of Technology and being the subject of research presented in this article. To the author’s current knowledge it is the first construction of this type of mill using an asynchronous motor stator for an inductor. This statement is based on the analysis of publications from various research centres in Poland and in the world dealing with the grinding of materials, as well as applications in patent offices [9, 10, 12, 16, 18]. For this reason an application was filed for a patent of the invention in the Polish Patent Office [22].

Based on the results obtained in the course of the studies, the following conclusions have been formed: 1. In the absence of a magnetic rotor, there is a large air gap which significantly increases the magnetic reluctance. This contributes to the reduction of magnetic induction. Induction and current versus voltage accept a linear waveform, suggesting the absence of a magnetic hysteresis; 2. A low weight of the grinding media (their small inertia) makes the milling process take place from the moment of supplying the voltage. Direct switching of the supply voltage causes the start-up current not to increase significantly, as is the case in the induction motor; 3. Magnetic induction within the process chamber of an electromagnetic mill with non-salient poles reaches values close to each other across the diameter of the chamber, which contributes to the uniform milling of the raw material in the entire working area. Changing the grinding efficiency is possible by changing the current powering the inductor. 4. The power factor in the present electromagnetic mill with non-salient poles, filled up with ferromagnetic grinding media, is 0.86. This value is much improved compared to the mills with salient poles described in the references, where the power factor was 0.2.