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Rotary seed sorters used for wheat processing show some functional advantages in eliminating persistent contaminants, especially due to the more aggressive treatment applied to the processed material. The objective of this paper was to design a new constructive subassembly that would increase the performance of rotary sorters used for extracting various contaminants from seeds. By testing a pilot stand that reproduces the operation of a professional equipment and developing mathematical models that fits the main operating parameters, it was possible to identify the new characteristics needed to improve cylindrical sieves and to optimize the functioning of this equipment. REZUMAT Sortatoarele rotative utilizate în procesarea grâului, prezintă unele avantaje funcționale în eliminarea contaminanților persistenți, în special datorită tratamentului mai agresiv aplicat materialului procesat. Obiectivul lucrării a fost acela de a crea un nou subansamblu, care să crească performanțele echipamentelor rotative de extragere a contaminanților din semințe. Prin testarea unui stand pilot care reproduce fidel funcționarea unui echipament profesional și prin modelarea matematică a principalilor parametri de funcționare ai acestuia, s-au putut identifica noile caracteristici necesare pentru îmbunătățirea sitelor cilindrice, precum și optimizarea modului de funcționare a acestor echipamente. INTRODUCTION Axial and tangential rotary wheat separators, are considered to be most suited sorters when processing wheat that is fixed in different conglomerations or when the contamination with leaf and light straws is relatively high. Rotary sorters can be integrated successfully in the pre-cleaning section, before silo loading, when larger perforated sieving sheets are usually used, or at the cleaning section before milling, when smaller perforated sieving sheets are preferred. Equipment that uses rotary motion for separation are less used than vibrating sorters due to their increased complexity, however they can bring important improvements to the separation process, especially for crops that have high contamination, high humidity, or when contaminants are stuck to the seeds. Compared to other treatment methods, separation by rotation has the advantage of producing a more aggressive treatment of wheat, allowing easier release of the grain when caught into conglomerations. However, the process involves some disadvantages related to the fact that separation achieved by rotation is usually breaking up the straws, resulting in a reduction of the contaminating particles volume and a worse impurity retention (Casandroiu T., 1993; Bracacescu C. et al., 2016). Păun A. et al., (2018) studied the design and installation of cylindrical sieves combined with countercurrent suction and separation using a rotary seed separator for the elimination of large contaminants (e.g. straw). These large contaminants cause problems for the separation process, because they do not come out easily through the perforations of the sieves’ outer wall, affecting the cleaning process. Jianbo, Y. et al., (2018), have tested rotary sieve speeds, assessing quantifiable losses associated with the increasing of rotational speeds. Vol. 62, No. 3 / 2020 INMATEH – 250 Another important parameter, namely the cylindrical diameter, was researched by Shi X. et al., (2018), Yuan J. et al., (2018), and Krzysiak Z. et al., (2020), for establishing relationships between the increase in diameter in relation to the separation efficiency and average axial grain speed. Mathematical modelling for the evaluation of various cylindrical sieves parameters have been intensively studied in order to optimize their efficiency (Naumenko M. et al., 2018; Badretdinov I. et al., 2020; Voicu Gh. et. al., 2008), bringing improvements to the design and construction, and obtaining superior quality of the grains. An element which has to be taken into account when using rotary separators on an industrial scale is the high technological complexity. They must have increased efficiencies, while allowing ease of maintenance at low costs, otherwise the performance of this equipment is greatly influenced by too frequent repairs. Our goal was to assess an experimental rotary wheat sorter functioning, identify all the working issues that may arise during operation and propose some design improvements related to the main identified shortcomings. In addition, a number of observations made by farmers using these cleaning systems has been considered. MATERIALS AND METHODS A pilot experimental stand has been used to test the seed rotary sorters performances, varying a series of parameters to succeed in simulating the operating conditions of a similar industrial equipment. The analyses performed on the experimental stand have been associated with the theoretical calculation of the rotary sorters, in order to determine which design specifications could be improved to increase equipment performances. All the important features identified in theory were varied when testing the experimental stand. This allowed identifying important characteristics to be considered when designing new equipment and legitimate certain improvements on the installation design, in order to streamline the main shortcomings. Figure 1 shows the experimental stand that is in the custody of INMA Bucharest for evaluation and for improving its specifications. During operation, the wheat containing different types of contaminants of known dimensions and quantities, is introduced in one of the feeding inputs (5), provided with a quantity dosing flap. The rotating sieve drive motor (1) drives the sieve (2) unidirectional by means of an axis of rotation (4). The sieve is automatically cleaned by the brush (3) during the rotation preventing wheat or impurities to get trapped in the sieve holes. Impurities will be collected in the impurity collection trays (6), which will allow the analysis of the separation of the masses of impurities along the sieve, this being an important element in the evaluation processes. Total mass of clean wheat is then stored in a special tray (7), while the angle of inclination of the sieve is varied by means of the hydraulic jack (9). The equipment is equipped with a start/emergency stop button (8). Fig. 1 Rotary wheat separators pilot experimental stand (1) drive motor, (2) sieve, (3) brushes, (4) axis of rotation, (5) feeding inputs, (6) impurity collection trays, (7) clean wheat tray, (8) start / emergency stop button, (9) hydraulic jack The row material inserted into the rotating cylindrical sieve, was composed of mixtures of wheat and other contaminating seeds, free and in conglomerations, driven gravitationally from the feeder when lifting the hopper retainer. The impurities separated by the wheat grains fall into the collecting chambers through the sieve holes, as long as the clean material advances along the length of the sieve. Vol. 62, No. 3 / 2020 INMATEH – 251 The material advancement is made either by the sieve inclination at a customizable angle, either by the rotational speed imposed to the sieve. The mixture of seeds introduced inside the cylindrical sieve, acquires a rotational movement, along with the rotating sieve and a translational movement along the length of the sieve. The advancement of the seeds inside the equipment takes place conditioned by the rotating sieve inclination angle. This is one of the equipment adjustable parameters which generates the speed of advancement of the processed material and might be varied depending on the level of seed contamination. These movements allow the mixture to separate into fractions, so that the small seeds come out through the sieve holes, while the big seeds move along the sieve, towards the end of the cylinder, being collected separately. Depending on the angular velocity of the sieve (ω), the following outcomes are drawn towards the movement of the seed mass, illustrated by the following three distinct cases. Case A when high rotation speeds are applied to the sieve (Ω = ω; ω˃˃), (where Ω is the angular speed of the absolute movement of the seed), it is observed that seed mass adheres to the inner surface of the cylindrical sieve and rotates with it (Fig.2a). In this case the separation process does not take place, and the speed at which this phenomenon occurs is called the critical speed of the sieve (relative rest phase); Case B when applying angular velocities lower than the critical speed (Ω = ω), the seed mass adheres to the surface of the cylindrical sieve, rotating with it up to detachment point DP1 (where normal reaction N = 0), after which they detach and a sliding process begins following a parabolic trajectory up to landing point – LP1, point of contact with the sieve, (Fig.2b); Case C when applying low angular velocities to the cylindrical sieve, the seed mass slides in the opposite direction to the movement, rotating around the cylindrical sieve rotation axis, with an angular velocity Ω ˂ ω. The mass of seeds, being driven in rotational motion with an angular velocity Ω ˂ ω, causes some of the seeds to pass through the sieve holes, while the rest of the seeds detach and begin to fall after a parabolic trajectory until the landing point – LP2, (Fig.2c). Fig 2a Fig 2b Fig 2c Fig. 2 The movement of the seed mass inside the sieve, depending on the angular velocity of the sieve Case A (Fig.2a) when high rotation speeds are applied to the sieve; Case B (Fig.2b) when applying angular velocities lower than the critical speed (Ω = ω); Case C (Fig.2c) when applying low angular velocities to the cylindrical sieve However, angular velocities from the cylindrical sieve are depending on the mass of seeds entering the process, being observed that a very high intake of seeds would block or negatively affect the separation. A problem identified in practice is that as the volume of seeds introduced for processing increa

INCREASING THE PERFORMANCE OF CYLINDRICAL SEPARATORS FOR CEREAL CLEANING, BY USING AN INNER HELICAL COIL