WO2009051576A1 - Method for resonance excitation of the screen sieving mesh and a resonance screen for carrying out said method - Google Patents

Abstract

The invention relates to a material separation method, substantially by means of screens, and can be used in the coal, metal mining, building ant other industries. The inventive method for resonance excitation of the screen sieving mesh involves statically tensioning the sieving mesh and exposing it to frequency vibration action. The static tension of the sieving mesh is stabilised in relation to the opposite displacements of the sides thereof and the vibration action is substantially performed in the plane of the sieving mesh transversally to the above-mentioned sides thereof. The inventive resonance screen comprises a bed connected to a frame, to which the sieving mesh is attached with the longitudinal sides thereof, and at least one vibrator. The frame is designed in the form of elements which are not linked to each other and are arranged on the opposite sides of the mesh, at least one of said elements being connected to the bed by means of at least one stabilising device in the form of an elastic element located in the plane of the mesh and being provided with a vibrator.

Description

 METHOD OF RESONANT EXCITATION OF SILLING

SCREEN GRIDS AND RESONANT SCREENS FOR ITS IMPLEMENTATION

The invention relates to a method for the separation of materials, mainly on screens, and can be used in coal, mining, construction and other industries. It is known that the main way of separating materials by size is vibration screening on sieves (sieving grids) (L. A. Vaysberg, Design and calculation of vibration screens ", G.," Hedra ", 1986, p. 3).

In this case, the material to be hogged under the action of vibrations moves along the sieving nets with holes through which the necessary product is removed. Most known screens have frequencies of disturbing force far removed from resonance values. Such screens are distinguished by the simplicity of design and the stability of the oscillation parameters of the screening surface (grids) (see patents RU J \ ° N ° 2221622, 2162006, international application JVs WO 02/04778). However, in these cases, it is not possible to achieve large accelerations of the working body, which are necessary for sieving finely dispersed or wet materials.

More effective for these materials are resonant screens, in which the disturbing force has an oscillation frequency close to the eigenvalues of the dynamic screen system (EB Bratigin, abstract of a dissertation for the degree of candidate of technical sciences “Development of a vibrating transport machine with a pulse resonant drive)), Yekaterinburg , 2006). In this case, in known screens, ultimately, classical linear resonance is used, a feature of which is a very narrow range of effective disturbance frequencies (only one frequency value corresponds to an exact resonance). In the process of operation of the screen changes in the parameters of its dynamic the system due to a number of variable factors (change in the frequency of the supply current, change in the grid tension due to its drawing, change in the mass of the grid due to adhering material or its wear, reaction to interaction with the screened material, etc.). As a result, the use of additional devices is necessary to maintain resonant oscillations. For example, in the screen of patent RU N ° 2268785, a frequency converter is used in combination with an oscillation sensor that interact in a feedback mode. The Ultimate Screener ™ screen (ideal screen) uses a special adapter device that converts the original monoharmonic disturbance into a multi-frequency effect of a certain frequency range. In this case, resonance will be achieved if the natural frequency oscillations of the dynamic screen system do not go beyond this interval (see international application JCH ° WO 98/26863). Another disadvantage of linear resonance is its high sensitivity to dissipative losses, which reduces the oscillation amplitudes of the working body. At the same time, the special type of nonlinear resonance of dynamical systems, known as “parametric resonance” (see Schmidt G. ((Parametric Oscillations), translated from German under the editorship of M. 3. Litvin-Sedy, M, is known and well studied quite well). (Mir, 1978). Although the bulk of research and practical application (for example, parametric generators) of this type of oscillation relates to electrical systems, parametric resonance can also be effectively used in mechanical versions, in particular for excitation This type of oscillation distinguishes a wide range of resonant frequencies, which in non-linear screening systems can reach tens of percent of the average value, which guarantees that all possible changes in the resonant frequency that occur during the manufacture or operation of the screen are guaranteed (this non-linearity is due to the displacement of the edges of the grid under the influence of its bending and is essential only for parametric resonance.) Another advantage of parametric resonance is its low sensitivity to internal resistances of the system (with sufficient force perturbation) and higher, due to non-linearity, acceleration values for a given amplitude of oscillations. In this regard, the strength of the perturbed screening grid becomes a real limitation of the power of oscillations at parametric resonance. The present invention aims to take advantage of parametric resonance (in combination with some other factors) to generate vibrations of the working body of the screen.

There is a method of resonant excitation of screening grids of a screen, including static tension of the screen and vibrational impact on it with a frequency close to resonant, and this effect is directed mainly from the plane of the screen, the screen itself is fixed to the screen frame rigidly, and maintaining a given frequency of oscillation is provided by a frequency converter interacting with an oscillation sensor (see patent RU N ° 2268785, IPC B 07 V 1/40, 1/42, 1/28) - prototype. One of the disadvantages of the prototype is the difficulty of maintaining an oscillation frequency close to the resonant one (the value of which varies within certain limits due to the variability of a number of operational factors), for which the known method uses a frequency converter interacting with an oscillation sensor, which reduces the reliability of its operation. Further, the known method, as noted above, is characterized by the excitation of linear resonance, in which the acceleration of the grid has a limited value (for a given amplitude of oscillation), which can complicate the sieving of sticky materials. At the same time, during intense vibrations even in the linear resonance mode, when the acceleration of oscillations from the plane of the grid significantly exceeds the acceleration of gravity, the scattered material practically cannot move along the grid. This leads to the fact that predominantly particles are sieved, the sizes of which are much smaller than the size of the mesh cell in the light, while the probability of sifting particles close in size to the cells becomes small (it is necessary to "directly" get into the mesh hole).

The basis of the invention (method) is the task of improvement a known method of resonant excitation of screening grids, in which, due to a change in the modes of some operations, it became possible to ensure the operation of the screen in parametric resonance mode, which leads to powerful nonlinear grid vibrations in a wide range of disturbing frequencies, which will simplify the screen design and increase the separation efficiency of bulk materials, including wet with increased stickiness.

The problem is solved in that in the known method of resonant excitation of the screening grid, providing for its static tension and vibrational impact with a frequency close to the resonant, according to the invention, the static tension of the screening grid is stabilized with respect to opposing displacements of its edges, and the vibrational effect is performed mainly in the plane of the screening grid transversely referred to its edges. In addition, the specified vibrational effect can be carried out by means of different frequency sources.

Also known is a resonant sieve, including a bed, a frame mounted with shock absorbers, screen cloths (screening mesh) fixed to the frame, a device for changing the angle of inclination of the frame, a feed chute, a vibrator mounted on a beam attached to the side of the frame, between the vibrator and a spring is installed by the beam, the rigidity of which, together with the stiffness of the shock absorbers in the direction of the frame oscillation vector and the mass of the frame, are connected by a certain mathematical relationship, and the vibrator windings are connected to the mains supply through a frequency converter, configured to change the frequency of the electric current, and an oscillation sensor mounted on the frame connected to a frequency converter control device, the output of which is connected to a frequency converter control channel, and the frequency converter control device is configured to operate in two modes: manual mode settings for frame vibrations and the mode of automatically maintaining specified frame vibrations (see patent RU JCH ° 2268785, IPC B 07 V 1/40, 1/42, 1/28) - prototype. The disadvantage of this device is the need to maintain the oscillation frequency close to the resonant one (the value of which varies within certain limits due to a number of operational factors), for which purpose a frequency converter is provided in its design that interacts with the oscillation sensor, which complicates the design of the device, reduces the reliability of its operation and accuracy sifting.

The basis of the invention (device) is the task of improving the known device for the resonant excitation of screening grids, in which, due to design changes, it became possible to ensure the operation of the screen in parametric (nonlinear) resonance mode, which will improve the separation efficiency of any bulk materials, including wet ones, (sticky) materials without sticking, and also improve sieving accuracy.

The problem is solved in that in a known resonant screen having a frame connected to a frame to which a screening grid is attached with longitudinal edges, at least one vibrator, according to the invention, the frame is made in the form of parts not connected to each other on opposite sides of the grid, moreover, at least one of the mentioned parts is connected to the bed by means of at least one stabilizing device, made in the form of an elastic element located in the plane of the grid, and sleep Bjena vibrator.

In addition, vibrators mounted on different parts of the frame have different disturbance frequencies.

In addition, a limit stop is installed under the net. The invention is illustrated by graphic materials, where in FIG. 1 shows a rumble in plan, FIG. 2 is a cross-section A-A, and FIG. 3 is a view B with options for arranging vibrators.

The device includes a screening mesh 1, fixed by longitudinal edges to parts of the frame 2, which are separate relative to each other, and which are connected to the frame 5 by means of stabilizing devices - elastic elements, for example, closed pneumatic cylinders 3 located in grid planes 1. On parts of the frame 2, vibrators 4 with an axis 6 of unbalance rotation are installed. Under the grid along its entire length with a gap to it, an emphasis 7 is installed, made in this particular case in the form of three rods. The rods can be lined with soft material, such as rubber, or entirely made of stretched rubber cords. The implementation of the method of resonant excitation of screening grids of the screen is provided by the claimed resonant screen.

The device operates as follows.

When you synchronously turn on the vibrators 4, installed on opposite sides of the screening grid 1, counter forces occur in the plane of the grid. Since the pneumatic cylinders 3 stabilize the tension of fastening the mesh to the bed 5 of the relative oncoming approach of its edges, and the mesh itself is rigid in its plane, these forces are transmitted to the mesh and change its tension with the frequency of rotation of the unbalance vibrators 4. If this frequency is close to resonance, then as a result of such fluctuations in tension there is a parametric resonance, which leads to instability of the transverse (from the plane) movement of the grid. The bandwidth of the resonant frequencies depends on the ratio of the amplitude of the oscillations of the grid tension to its initial tension, which may be sufficient to ensure constant resonance with natural deviations of the parameters of the dynamic system during the operation of the screen. Vibrators 4 can be installed with a vertical arrangement of the axis of rotation 6 of the unbalance (Fig. For), because as a result of instability, the presence of disturbances from the grid plane is not necessary. For a faster increase in transverse vibrations, it is possible to install vibrators 4 with an inclined axis (Fig. 36 and c). The same mode can be provided by one vibrator due to the inertial resistance of the masses of fastening of the opposite side of the grid, and in the case of rigid fastening of the opposite side, due to the rigidity of this fastening.

The arising powerful vibrations of parametric resonance ensure the disintegration of the adhered grains of the scattered material (screening of wet materials) and prevent the mesh from sticking. In the case of rotation of the unbalances of the vibrators installed on different parts of the frame with different frequencies (the difference is small in comparison with the frequency), beats will occur, including a periodic change in the oncoming and incidental effects of the vibrators on the grid. Parametric resonance arises during the oncoming action, and in the case of the incidental action, the grid oscillates in its plane. In the latter case, the scattered material slides along the grid, which ensures high sieving accuracy in accordance with the grid parameters. In general, the material, as it moves along the grid, will be sequentially subjected to both the powerful influence of parametric resonance and is in conditions of optimal sieving.

In the case when a blank grid will be subjected to parametric resonance, the size of the amplitude of its transverse vibrations increases until it hits the stops 7. Impacts of the grid into the stops lead to a loss of vibration energy, which prevents a further increase in the amplitude. This protects the mesh from tensile and bending overloads.

The inventive device for implementing the proposed method can also work in linear resonance mode with vertical, horizontal or mixed oscillations of the grid. For this, the vibrators must be installed with the transverse to the longitudinal edges of the grid axis of rotation of the unbalance. With vibrators with directional perturbation, vertical or horizontal vibrations of the grid will take place, with circular perturbations, the mixed mode will be performed.

The design does not exhaust the possibility of a device for implementing the proposed method. For example, pneumatic cylinders can be replaced by springs or other elastic elements, for example springs or rubber cords lying in the plane of the grid, suspension of loads is possible (the concept of “lying in the grid plane” means that the elastic elements act in the plane of the grid, the elements themselves can be placed differently Thus, for example, springs can be installed in a perpendicular plane, but act, that is, deform, in the grid plane). The general requirement for stabilizing devices is that they must have a sufficiently low rigidity so that the tensile forces in them change little during deformations arising from working displacements of the longitudinal edges of the mesh.

Possible embodiments of the device using one or more vibrators.

A possible embodiment of the device, in which one of the parts of the frame is rigidly attached to the frame of the screen, and the other with the help of elastic elements.

The experimental studies fully confirmed the expected results, in particular, it was possible to perform dry sieving of materials that were previously sifted only in the wet screening mode with subsequent drainage, and in other cases, to increase the specific (on lm screening surface) screening productivity by 2.5 - 3 times.

Claims

CLAIM 1. The method of resonant excitation of the screening screen mesh, including the static tension of the latter and vibrational impact on it with a frequency close to the resonant, characterized in that they stabilize the static tension of the screening network relative to the opposing displacements of its edges, and the vibration effect is performed mainly in the plane of the screening screen transversely to its edges. 2. The method according to p. 3. A resonant screen, including a bed connected to a frame, to which a screening grid is attached with longitudinal edges, at least one vibrator, characterized in that the frame is made in the form of unconnected parts located on opposite sides of the grid, and at least at least one of the mentioned parts is connected to the bed by means of at least one stabilizing device - an elastic element located in the plane of the grid and equipped with a vibrator. 4. The screen according to claim 1, characterized in that the vibrators installed on the various parts of the frame mentioned above have different disturbance frequencies. 5. The screen according to claim 1, characterized in that a restrictive stop is installed under the grid.