Substantiation of rational parameters of the root crops separator with a rotating inner separation surface

The aim of the paper is to justify the design and rational parameters of the secondary post-treatment separator of potato heap in the form of a truncated cone with a rotating internal separating surface which ensures the separation of potato tubers from soil lumps commensurate with them. Based on the analysis of works devoted to the process of potato heap separation, including on inclined surfaces, as well as the analytical calculations, it was concluded that it is possible to create a device for separating potato tubers from soil lumps in the form of a rotating truncated cone with an internal separating surface. As a result of the research, the design of the secondary post-treatment separator of potato heap in the form of a rotating drum in the form of a truncated cone with a separating roller. Laboratory and field tests have shown that with appropriate adjustments, separation of up to 80% of soil impurities commensurate in size with potato tubers is provided. Introduction The plans for the implementation of food security most countries have defined the nomenclature of strategically important crops, among which the potato always occupies one of the leading positions (Devaux and Ortiz, 2014; FAO, 2018). A need for significant financial investments, significant labor costs in the cultivation and harvesting especially on heavy wetlands limit the production of this crop in a number of soil and climatic zones (Abhilash et al., 2016). At the same time, the use of even the most advanced technologies and methods of storage does not guarantee the safety of the crop if the quality of the stored products does not meet agricultural requirements (Ebrahem et al., 2011). Among the agrotechnical indicators, the most important are the presence of soil impurities and damaged tubers in the similar heap which inevitably leads to the loss of a significant part of the crop if the agrobiological background is unfavorable (Agu et al., 2015; Khamaletdinov et al., 2018). This state of affairs is largely due to the fact that in modern potato harvesters the main way to separate potato tubers from impurities is the separation of potato heap on bar elevators in thickness after the preliminary destruction of soil lumps to pass sizes (Bishop and Monder, 1983; Gao et al., 2010; Klindtworth and Sonnen, 2014; Fomin, 2018). In this case, the magnitude of the Ac ce pt ed p ap er external forces applied to the tuber formation is limited by the condition of damage to the tubers. However, on heavy and waterlogged soils, the impact of forces in the range of allowable values is insufficient to destroy the bulk of lumps, which leads to an increased soil content, and with an increase in the impact forces leads to injury to tubers (Mathew and Hyde, 1997; Mollah et al., 2018). Despite numerous works devoted to the development of separating bodies, the principle of work is the use of the difference in the characteristics of potato tubers and soil particles, such as hardness, specific gravity, elasticity, friction coefficients of sliding and rolling, aerodynamic properties, the ability to absorb and reflect rays and others, the task of creating devices for separating potato tubers from soil lumps commensurate with potato tubers remains unresolved (Klindtworth and Sonnen, 2014; Agu et al., 2015; Khasanov et al., 2018). Materials and methods Research design The analysis of physical and mechanical characteristics of potato heap components shows that the greatest difference of separation characteristics is observed in the rolling angles of tubers and soil lumps (Zangeneh et al., 2015; Jamróz et al., 2018). Figure 1 shows the density distribution of the angles of rolling the tubers of potato varieties Nevsky and lumps of soil is loam type indicating the presence of minor areas of overlap of this symptom. It is no coincidence that currently the most promising for the separation of commensurate in size potato tubers and soil particles are devices that operate on the principle of an inclined finger slide. At the same time the proposed constructive solutions based on the division on this basis have a number of drawbacks. First, the components of the heap move when separating towards each other (in the counterflow), and secondly, the adjustment parameters (angles, kinematic modes of operation, elasticity of the fingers, etc.) are determined based on the average physical and mechanical characteristics of the heap components, which does not allow these devices to ensure complete separation of root crops from soil lumps. Thus, the authors propose the design of the separator in the form of a flexible Ac ce pt ed p ap er moving infinite tape in the form of a body of rotation, for example, a truncated cone, the design scheme of which is shown in the Figure 2. Mathematical model Taking into account the shape and kinematics of the interacting surfaces, let’s consider the moving components of the heap in a cylindrical coordinate systemr, j, z. Polar radius r determines the distance to the centre of mass of the components from the rotation axis of the cone Оz. The point of contact of the interacting surfaces is on the ray passing perpendicularly through the axis Оz and the centre of component mass. The deviation of the radius r from the vertical is determined by the polar anglej. The movement along the axis of rotation of the cone is estimated by the coordinate z. The radial acceleration of the center of mass of the component is determined by , trasversal acceleration – , respectively the velocities and accelerations along the axis Оz are equal to and . The component with the mass m is affected by the following forces: gravity G=mg, the normal reaction N and the friction force fN, where f is the coefficient of friction of the component on the cone surface. After projecting all the acting forces on the cylindrical coordinate axes, taking into account the inertial component of the point mass, the system of differential equations of component motion is as follows: