RU2457046C2 - Method of sorting loose materials, device to this end, and method of batch displacement of loose material - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to separation of loose materials and may be used in agriculture, processing, chemical and dressing industries. Batch displacement of loose material in uniformly revolving horizontal cylinder filled with loose material for 10-20% at rpm 1.5-2 times higher than critical magnitudes consists in that system ''loose material - cylinder'' changes into self-resonance motion mode. In said mode, loose material batches separate independently, one after another, from solid bulk in circle second quadrant along equipotential surface to fly in gravity field and fall on cylinder surface to impart portion of kinetic power thereto. This method is used for sizing loose material in horizontal revolving cylindrical screen wherein every batch separated from solid bulk flies to fall on screen clean surface so that previous batch has enough time to leave separation zone. Note here that loose material relative shearing motion occurs whereat minor particles PASS through screen holes while major particles leaves the surface at cylinder end. Proposed device comprises cylindrical screen secured on two rings resting on four rollers, screen rpm variator and screen holes cleaner. Batch self-resonance mode is selected by control buttons of current frequency converter built in motor supply circuit and transparent web arranged at cylinder end.

EFFECT: higher intensity and quality of separation.

3 cl, 5 dwg

Description

The method and device for sorting bulk materials can be used in the cleaning and sorting of grain and its processed products in agriculture, as well as in the chemical and enrichment industry in the separation of bulk materials.

This method is based on the use of a new portioned autoresonant type of movement of granular medium in a horizontal rotating cylindrical sieve, which allows to increase the intensity and quality of separation.

The theory and practice of using horizontally rotating cylinders (drums), sieves over the past century and to this day has considered the following main types of movement of granular medium in a cylinder: shuttle, erratic (some authors call it cascading), waterfall, mixed (a combination of the listed types of movement) and tubular (figure 1).

The main questions concerning the modes of movement of granular medium in horizontal cylinders are set forth in the works:

1. Andreev, S.E. Crushing, grinding and screening of minerals / S.E. Andreev, V.A. Perov, V.V. Zverevich. - M .: Nedra, 1980 .-- 415 p.

2. Korotich, V.I. Theoretical Foundations of Pelletizing Iron Ore Materials / V.I. Korotich. - M.: “Metallurgy”, 1966. - 151 p.

3. Olevsky, V.A. Milling equipment of concentration plants. / V.A. Olevsky. - Gosgortekhizdat, 1963.

4. Slanevsky, A.V. The classification scheme of the modes of motion of a granular medium in a rotating drum / A.V. Slanevsky, I.I. Labunina, L.G. Bernstein, A.A. Slanevsky // Cement. - 1992. - Vol. Number 3. - S. 70-77.

Here is the theoretical justification for a new batch autoresonant type of motion of the type of motion of bulk material in a uniformly rotating horizontal cylinder. For this we use the work:

5. Patrin, V.A. The stress state of a loose body in a horizontal rotating cylinder / V.A. Patrin, A.V. Patrin // Meh. and electric. S.-kh. - 2002. - No. 11. - S.11-13.

6. Malinetskiy, G.G. Mathematical foundations of synergetics / G.G. Malinetsky. - M.: Book House "Librocom", 2009. - 312 p.

It is not possible to describe the behavior of the “rotating cylinder - bulk medium” system in a deterministic way, therefore, we use bifurcation analysis and thermodynamic potentials used in synergetics and allowing us to determine and predict the behavior of the dissipative system depending on the magnitude of the force field and the physicomechanical properties of the granular medium.

The phase state of a granular medium in a rotating cylinder is described by a dynamic equation of the form

where the function (u) is the potential of the force field in the cylinder, and the point at which the derivative with respect to X is equal to the critical point or bifurcation point, where the system, depending on the combination of factors given in the brackets of equation (1), can choose another development path . In figure 1, these points are designated 1-2-3-4.

Where K _c = ω ² R / g is the centrifugal coefficient; ω, R, g are the angular velocity, the radius of the cylinder and the acceleration of gravity, respectively; ε is the degree of filling of the cylinder with bulk medium; f ₁ - coefficient of friction of the granular medium on the inner surface of the cylinder; f ₂ - coefficient taking into account the physicomechanical properties of granular medium.

The main controlling factor determining the state of the system is the number of revolutions of the cylinder, which creates a force field in which the granular medium is located. All other parameters in equation (1) can change as random phenomena, transferring the system from one state of equilibrium to another, while the form of movement of the granular medium changes. Our studies have shown that pulsating and oscillating ovals of normal stresses act on a granular medium rotating with a cylinder. At the lower point of the cylinder, the medium is compressed, at K _c = 1 the force field R = 2g, and at the upper point it is in zero gravity R = 0. The force field of a rotating cylinder makes harmonic oscillations.

In synergetics, the concept of an attractor is used - singular points of surfaces, sets in phase space, capable of attracting, controlling the state, movement of the system. In this case, the attractors is the center of the force field and equipotential surface (figure 2).

The center of the force field lies on a vertical diameter, at a distance from the axis of rotation of the cylinder, equal to: -R / K _c . For all K _c <1 outside the circle, and for K _c > 1 inside the circumference of the cylinder. It is necessary to take into account the thickness of the grain layer in the cylinder. Each elementary layer has its own value R _c , therefore, its centers of lines of force on a segment of vertical diameter.

Equipotential surfaces have equal accelerations and equal potential energy for all its points. Equipotential surfaces have a cross-sectional view of the concentric circles conducted any radius from the center of the force field, described by the equation y ² -x ² + 2yg / w ² + C = 0.

The bulk medium with a cylinder is a kind of energy transformer, in which the kinetic energy K continuously transitions from the cylinder surface to the potential energy P of the bulk medium at the upper point, which again turns into kinetic E _{into an} incident or flowing stream, where there is a relative shear flow, redistribution particles in size, useful work is done A. Part of the energy is spent on friction, deformation of particles, the temperature of the system rises, its entropy ST grows.

The energy transformation in the system can be represented as a thermodynamic potential

K → P → E _vn = A + ST.

The bifurcation diagram in figure 1 shows the dependence of the state of the grain medium and the type of its movement in a horizontal rotating cylinder on the magnitude of the main control factor - the centrifugal coefficient. The diagram is based on experimental data obtained in a laboratory setup with a cylinder diameter of 700 mm and a length of 250 mm. The diagram shows that the internal energy of the grain medium with increasing speed increases to a tubular form of motion, at which E _in = 0.

The energy transformation in the tubular form of motion stops. In local areas between the bifurcation points, there are minima of the internal energy E _ext1-2 = min, in which the system has a standard equilibrium state. This phenomenon can be explained by the fact that, following the principle of least action (Maupertuis law) mSV = min, the system, using autoregulation, switches to optimality due to symmetry in the motion paths of individual particles and the entire mass, tends to a state with a minimum potential energy, where m - mass, V - velocity, S - particle path. The photographs clearly show the circulation of individual particles along constant symmetrical trajectories in compliance with the law of cyclicity.

A further increase in the energy transferred to the grain medium in front of each bifurcation point leads to loss of stability, symmetry breaking, fluctuations, both internally generated by the system itself, particles move to higher motion trajectories, and external fluctuations, load changes, physical and mechanical properties of the grain vibration etc.

At bifurcation points 1-2-3-4, the instability of the system leads to a catastrophe for the choice of new development directions that are sometimes so unexpected, as can be seen from the bifurcation example, at point 3, when the system begins to tear off and feed grain to the cylinder surface in portions from the solid-state part of the granular medium with uniform rotation. In this case, resonant oscillations appear in the system. Such bifurcation points are called the “Poincare catastrophe” and are found in the vast majority of dynamics problems.

At each bifurcation point, the derivative, with a certain combination of variables in equation (1), becomes equal to zero. A system from an unstable position can follow two development paths to a new, more stable equilibrium position. In this case, at point 1, the system can take a shuttle or erratic mode of movement depending on the state of the cylinder surface f and load ε, at point 2, the determining parameters are load ε, at point 3, a combination of internal pulsations of the force field and “external noise” - fluctuations in the drive system. As experiments have shown, the batch type of movement has a high degree of stability and occurs with a gradual increase in cylinder speed, and with a reverse decrease, starting from the tubular form of movement of the granular medium. As can be seen from the bifurcation diagram, in a batch type of motion, the granular medium has maximum internal energy, in addition, each portion of the grain, as it were, throws itself onto a clean sieve surface, the previous portion has time to slide out of the separation zone.

Preliminary experiments showed a high intensity of the separation process with a portioned autoresonant form of grain movement in a cylindrical sieve.

The loss of connection and the separation of each portion from the rising solid-state part of the granular medium occurs along an equipotential surface passing through the center of rotation of the cylinder.

One of the creators of the catastrophe theory, Rene Tom showed that if the number of control parameters does not exceed four, then in typical situations only seven elementary catastrophes are possible [6].

It should be noted that in the system under consideration, the bifurcation points, or the transition points of the granular medium into a new type of motion, are not constant, but depend on a combination of variables in equation (1) and slide along the abscissa axis. Theoretically, the grain medium should have passed into a tubular form of motion at K _c = 1. As can be seen from the diagram in our experiments, this happens when K _c = 2.

A device for implementing the method of sorting granular medium in a batch autoresonant mode of motion includes a cylindrical sieve 1 with punching holes mounted on two rings 2 (Fig. 3), which are supported by four rollers 3, two of which are leading. On top of the cylinder are two restrictive rollers 4, which limit the displacement of the cylinder in the vertical direction. To reduce noise in the cylinder drive and increase the transmitted force from the drive rollers, as well as to limit the cylinder from axial displacement, grooves 5 are made in the rings (Fig. 4), in which the V-belts 6 are stacked and rigidly fixed to the ring with the ring on the reverse flat side . In the leading, driven and upper restrictive rollers, grooves are made for the V-belt, so that when rotating the cylinder is in contact with the metal rotating parts only through the rubberized V-belt.

The diameter of the cylindrical sieve in an experimental grain cleaning plant is 700 mm. The front end wall 7 is made of glass to monitor the regime of movement of bulk material in the cylinder. The back wall is made of plexiglas in the form of sectors 8 with a hole in the center through which bulk material is fed. Between the rear end wall and the surface of the sieve there is an adjustable gap - X, through which large impurities K are removed immediately from the cylinder. Small ones go through the holes of the sieve. The gap is changed by moving along the cross of sectors 8.

The drive of the cylindrical sieve is carried out from the electric motor 9 through a V-belt transmission 10. The belt is tensioned by moving the electric motor along the frame.

To smoothly change the cylinder speed both in the direction of increasing and decreasing, we used a current frequency converter in the power circuit of the electric motor.

To clean the holes of the sieve from the particles, kapron washers 11, mounted on a swinging spring-loaded roller 12, were used. The degree of pressing of the washers is regulated by the nut 13. The washers roll over the surface of the cylindrical sieve and squeeze stuck particles out of the holes. The washers along the entire circumference have a sharp edge, which facilitates the washer getting into the elongated hole of the sieve.

The device operates as follows. The processed material is fed into the cylindrical sieve through the charging device 14. Using the control buttons of the current frequency converter and the transparent end wall of the cylinder, an autoresonant batch mode of granular medium movement is established, which is stable when the degree of filling the cylinder with grain in the range of 10-20% and revolutions exceeding critical 1.5-2 times.

The features of the separation process in this mode and its advantages over the known ones are as follows:

1. The separation process occurs on a large sieve surface in the 3rd and 4th quadrants of a circle.

2. Bulk material always falls on a clean sieve surface, as the previous portion has time to leave the separation zone.

3. Particles falling onto the surface of the sieve have a normal component of velocity to the hole of the sieve, which facilitates their passage through the hole.

4. The separation process proceeds with fast shear flows and large relative displacements compared to conventional sieves, which provides a high speed of redistribution of particles by size inside the granular medium, as is the case with gravitational separation methods, but in contrast to them in the proposed method “quantity cycles "rise-fall can be adjusted, make unlimited.

5. The autoresonant mode of movement allows you to save energy on the cylinder drive, since portions of grain falling on the surface of the sieve in the 3rd quadrant of the circle have a speed higher than the sieve and give part of the energy to the sieve, creating a torque that matches the direction of rotation sieve.

The technological process of working a cylindrical sieve in the autoresonant batch mode is shown in Fig.5. The degree of filling of the cylinder is set by the ratio of the gap between the end wall and the sieve and the amount of granular medium supplied to the cylinder per unit time.

Claims (6)

1. A batch method of moving granular medium in a uniformly rotating horizontal cylinder with a degree of filling with granular medium in the range of 10-20% and revolutions exceeding critical by 1.5-2 times, characterized in that the system "granular medium - cylinder" goes into autoresonant mode of motion, in which in the second quadrant of the circumference the portions of the granular medium independently tear off one after the other from the solid part along the equipotential surface and fly in the field of gravity, then fall in the 3rd and 4th quadrants rhnost cylinder, giving him some of the kinetic energy. 2. A method of sorting granular materials by particle size in a horizontal uniformly rotating cylindrical sieve with punching holes, characterized in that a portioned autoresonant mode of movement is used to separate the granular medium into fractions, in which each portion, torn from the solid part of the granular medium, flies and falls on a clean sieve surface so that the previous portion has time to leave the separation zone, while there is a rapid relative shear flow of the medium, during which the shallow particles pass through holes, and large particles come off the surface at the end of the cylinder. 3. A device for implementing the method of sorting granular medium according to claim 2 in a batch autoresonant mode of motion, comprising a cylindrical sieve with punch holes, mounted on two rings that are supported by four rollers, two of which are leading, a device for smoothly changing the speed of the sieve and a device for cleaning sieve openings, characterized in that the search and tuning for a portioned autoresonant mode of movement is carried out using the control buttons of the current frequency converter included in the electric electric power supply of the electric motor and a transparent partition in the end of the cylinder. 4. The device according to claim 3, characterized in that two V-belts are used to drive the cylinder, rigidly fixed around the circumference of the rings with the flat back, and grooves are made in the leading and driven support rollers to the size of the V-belt, so that the cylinder rests on the rollers through V-belt. 5. The device according to claim 3, characterized in that the flow of granular medium into the cylindrical sieve is through a hole in the center of the rear end wall of the cylinder, and the removal of a large fraction through an adjustable gap between the end wall and the surface of the sieve, while the performance and degree of filling of the cylinder with bulk medium is regulated by the ratio of the amount of grain supplied to the cylinder and the gap. 6. The device for cleaning holes in the sieve according to claim 3, characterized in that they use nylon washers assembled on a swinging spring-loaded shaft, while the washers have the ability to roll over the cylinder surface, squeezing out stuck particles in the holes of the sieve, and the degree of pressing the washers on the surface sieves are adjusted by changing the stiffness of the spring.

Images