*Article* **Studies of a Rotary–Centrifugal Grain Grinder Using a Multifactorial Experimental Design Method**

**Andrzej Marczuk 1, Agata Blicharz-Kania 2,\*, Petr A. Savinykh 3, Alexey Y. Isupov 3, Andrey V. Palichyn <sup>4</sup> and Ilya I. Ivanov <sup>4</sup>**


Received: 26 August 2019; Accepted: 23 September 2019; Published: 27 September 2019

**Abstract:** A scientific and technical literature review on machines designed to grind fodder grain revealed that the existing designs of grinding machines—those based on destruction by impact, cutting, or chipping—have various drawbacks. Some disadvantages include high metal and energy intensity, an uneven particle size distribution of the ground (crushed) product, a high percentage of dust fraction, the rapid wear of work tools (units), and heating of the product. To eliminate most of the identified shortcomings, the design of a rotary–centrifugal grain grinder is proposed in this paper. The optimization of the grinder's working process was carried out using experimental design methodology. The following factors were studied: the grain material feed, rotor speed (rpm), opening of the separating surface, number of knives (blades) on the inner and outer rings, technical conditions of the knives (sharpened or unsharpened), and the presence of a special insert that is installed in the radial grooves of the distribution bowl. The optimization criteria were based on the amount of electricity consumed by and the performance of the rotary–centrifugal grain grinder. The quality of performance was quantified by the finished product, based on the percentage of particles larger than 3 mm in size. An analysis of the results of the multifactorial experiment allowed us to establish a relationship (interaction) between the factors and their influence on the optimization criteria, as well as to determine the most significant factors and to define further directions for the research of a centrifugal–rotary grain grinder. From our experimental results, we found that the grinder is underutilized in the selected range of factor variation. Furthermore, the number of knives installed at the second stage of the grinder, the gap (clearance) of the separating surface, and the technical condition of the knives are among the most important factors influencing the power consumption and the quality of the resulting product. A reduction in the number of knives at the first stage has a positive effect on all the selected optimization criteria; and by varying the factors in the selected range, it is possible to obtain a product corresponding to medium and coarse grinding.

**Keywords:** grain grinding; rotary–centrifugal grinder; construction optimization criteria
