EP3842158A1

EP3842158A1 - Vibrating screen, especially with slotted sieve, and method for controlling the operation of the screen, especially with slotted sieve

Info

Publication number: EP3842158A1
Application number: EP20214707.0A
Authority: EP
Inventors: Piotr Czubak; Robert Klisowski; Tomasz Gawenda
Original assignee: Akademia Gomiczo Hutnicza
Current assignee: Akademia Gomiczo Hutnicza
Priority date: 2019-12-23
Filing date: 2020-12-16
Publication date: 2021-06-30
Also published as: PL432369A1; PL241072B1

Abstract

The vibrating screen, especially with a slotted sieve, is characterized in that the inverters (5) have a system for controlling the phase angle of vibrator (4) orientation, so that in the operation mode with the phase angle other than zero, the exciting force (W), being the resultant force from the forces (F) of action of the vibrators (4), acts in a plane (xc, zc) defined by a central axis (xc) perpendicular to the plane of symmetry (π) of the screen and by a central axis (zc) inclined at an angle (α) to the sieve (2) deck, with the direction of the latter being defined by the centre of gravity (C) of the screen and a point (J) lying in the plane of symmetry (π) of the screen, the point being the centre of the section connecting the axes of the vibrators (4). The method for controlling the operation of the screen is characterized in that additionally, by controlling the phase angle of vibrator (4) orientation, the direction of action of the resultant force (W) is changed such that said direction does not run in the plane of symmetry (π) of the screen and as a result, angular vibrations (β) of the screen are induced in the plane (xc, xc).

Description

The subject matter of the invention is a vibrating screen, especially with a slotted sieve, and a method for controlling the operation of the screen, especially with a slotted sieve, applicable, inter alia, in the mining, metallurgical and cement and lime industry, in the processing of mineral resources and waste, and especially in the production of high-quality refined mineral aggregates, for sieving regular grains from irregular grains.
How effective is the separation of regular grains from irregular grains on screens with slotted sieves in industrial conditions depends, inter alia, on the graining range and shape of the classified aggregate, on the type of sieves and the dynamics with which the screen operates and which is influenced by many parameters of its operation.
A screen is known from Polish patent description PL160340B1 , which is characterized in that extreme vibrators are arranged in a jointed manner on two opposite walls of the riddle, the walls being parallel to each other and perpendicular to the plane of the sieve, in such a way that the lines of action of exciting forces intersect in the centre of gravity of the riddle or are vibrated relative to its axis. In addition, a central vibrator is arranged above or below the riddle, in the axis of the riddle. In the screen of the invention, the shafts of the extreme vibrators rotate at the same speed and can operate concurrently and counter-currently, being synchronized. In the screen of the invention, the extreme vibrators are switched on simultaneously and then a central vibrator is switched on. The synchronization thus obtained makes the extreme vibrators cause the screen to circulate in a horizontal plane, while the central vibrator causes it to circulate in a vertical plane.
From another Polish patent description PL167019B1 , a vibrating screen is known, flexibly suspended from a support suspension and equipped with a cuboidal riddle with stretched sieves and drive vibrators. The screen is characterized in that two vibrators, called side vibrators, are attached to the front and rear wall of the riddle, each vibrator having a different exciting force and a different rotational speed and operating on the basis of self-synchronization. The side vibrators induce a flat vibrating movement which takes place in a vertical plane, the plane perpendicular to the surface of the sieve, and is generated longitudinally relative to the riddle. In another variant of the solution, the screen can also be equipped with one side vibrator, attached to the front wall of the riddle and inducing a flat non-linear movement. In addition, the screen is equipped with two identical rotary vibrators arranged on a basis such that their transverse axes of symmetry, perpendicular to the axes of rotation of the vibrators attached to the front and rear wall of the riddle, pass through the centre of gravity of the entire riddle. These vibrators force vibrations in a plane perpendicular to the previous vibration plane and intersecting at an acute angle with the sieve plane. As a result of the overlap of vibrating component movements, a non-linear, elliptical resultant movement is obtained. The operation of the screen is as follows. The side vibrators are actuated simultaneously, which causes their dynamic synchronization. The directions of rotation of these vibrators may be the same or opposite, which causes different trajectories of the vibrating sieve. The rotary vibrators, which can rotate in the same or opposite directions, are then activated.
The screen disclosed in US Patent US6513664B1 is also able to operate using elliptical vibrations. The screen has three inertial vibrators. Two counter-rotating vibrators are arranged symmetrically on a transverse beam connecting the sides of the riddle in such a way that their axes of rotation are parallel to the plane of symmetry of the screen, with the centre of gravity of the screen lying in said plane, and the direction of action of the resultant exciting force, in the operation mode with synchronized vibrators, passes through the centre of gravity of the screen obliquely to the sieve deck. The third vibrator is arranged on a transverse beam such that its axis of rotation is perpendicular to the plane of symmetry of the screen and the resultant force acts in that plane. Each vibrator is made up of unbalanced masses mounted on two ends of the shaft, driven by the rotor of an electric motor. Each electric motor is connected to a regulator of rotational speed. The sieve of the screen is mounted on the riddle, the riddle supported by means of flexible supports on a non-deformable foundation. The operation of the screen can be controlled by means of a controller which runs an implemented program, the program making it possible to select one of two operation modes of the screen: a linear vibration mode, with two counter-rotating vibrators being actuated, or an elliptical vibration mode in the plane of symmetry of the screen, by switching on the third vibrator. Elliptical vibrations are forced in a similar way by the screen described in Chinese patent description CN101690931B .
The objective of the invention is to develop a screen and a method for controlling its operation such that the screen, in addition to providing an optimal grain toss indicator, can also cause a change in the nature of grain movement, by giving the grains a variable trajectory and causing them to rotate in two axes. This increases the likelihood that flat grains, especially the larger ones, will be tossed and, as a result of rotation, will fall with their minimum projection area into the sieve slots, leading to a greater grain separation efficiency. In addition, the optimum toss indicator will enable difficult grains wedged in the meshes (slots) of the sieves to unwedge and to be transported to the oversize of the screen.
The screen comprises a riddle, the riddle arranged by means of flexible supports on a rigid base and with at least one sieve deck arranged in the riddle, with two inertial counter-rotating vibrators suspended to the sieve deck and arranged symmetrically, in such a way that the axes of rotation of the vibrators are parallel to the plane of symmetry of the screen, with the centre of gravity of the screen lying in said plane, and the direction of action of the resultant exciting force, in the operation mode with synchronized vibrators, passes through the centre of gravity of the screen obliquely to the sieve deck, and in addition, the vibrators are connected, via known means of drive transmission, to electric motors equipped with regulators of rotational speed, being inverters. The essence of the vibrating screen, especially with a slotted sieve, is that the inverters additionally have a system for controlling the phase angle of vibrator orientation, so that in the operation mode with the phase angle other than zero, exciting force W, being the resultant force from the forces of action of the vibrators, acts in a plane defined by two central axes: a central axis perpendicular to the plane of symmetry of the screen and a central axis inclined obliquely to the sieve deck, with the direction of the latter being defined by the centre of gravity of the screen and a point lying in the plane of symmetry of the sieve, the point being the centre of the section connecting the axes of the vibrators.
It is preferred that the vibrators are suspended from the screen in such a way that the oblique inclination of the central axis to the sieve deck is in the range from 30° to 45°.
It is also preferred that the spacing between the flexible supports is symmetrical relative to the centre of gravity of the screen and does not exceed 0.6 of the length of the screen.
It is further preferred that the distance from the point, which is the centre of the section connecting the axes of the vibrators, to the centre of gravity of the screen is greater than 0.25 of the length of the screen.
The essence of the method for controlling the operation of the screen, especially with a slotted sieve, realized in such a way that the amplitude and speed of screen vibrations acting in its plane of symmetry are adjusted by changing the rotational speed of the vibrators, is that by controlling the phase angle of vibrator orientation, the direction of action of the resultant force is changed such that said force does not run in the plane of symmetry of the screen and as a result, angular vibrations of the screen are induced in the plane defined by the central axis perpendicular to the plane of symmetry of the screen and by the central axis inclined obliquely to the sieve deck, the direction of the latter being defined by: the centre of gravity of the screen and a point lying in the plane of symmetry of the screen, the point being the centre of the section connecting the axes of the vibrators.
The vibrating screen and the method for controlling the operation of the screen of the invention are presented in more detail in the implementation example and illustrated in the drawing, in which Fig. 1 shows a general view of the screen in perspective, Fig. 2 shows a simplified view of a physical model of the screen in the plane of symmetry π , and Fig. 3 shows a fragment of sectional view (A-A) of the screen, parallel to the plane of action of the exciting forces, for an instantaneous position of the vibrators.
The screen (Fig. 1, Fig. 2) has a riddle 1, in which the deck of the slotted sieve 2 is arranged. The riddle 1 is arranged by means of a flexible support 3 on a rigid base. The spacing between the supports is 0.6 of the length of the screen and is arranged symmetrically relative to centre of gravity C of the screen. Two counter-rotating inertial vibrators 4 are arranged, in an upper arrangement, on the common beam connecting the sides of the riddle, the vibrators driven by electric motors equipped with regulators 5 of rotational speed, which are inverters equipped with a system for controlling the phase angle Δϕ of vibrator 4 orientation. The vibrators 4 are arranged symmetrically, in such a way that their rotational axes are parallel to each other and are parallel to the plane of symmetry π of the screen, with centre of gravity C of the screen lying in said plane. Point J, also lying in the plane of symmetry π and being the centre of the section connecting the axes of the vibrators 4, together with centre of gravity C of the screen define the direction of central axis z_c, inclined at an angle α=30° to the deck of the slotted sieve 2. Central axis z_c and central axis x_c, the latter being perpendicular to the plane of symmetry π, define the plane in which exciting force W acts, which is the resultant force from the forces F of action of the vibrators 4 (Fig. 3). The distance from point J to centre of gravity C of the screen is 0.25 of the length of the screen.
The method for controlling the operation of the screen is that in order to adjust the speed with which the material being screened is transported along the sieve 2 deck, the forcing frequency is controlled by changing the rotational speed of the vibrators. With synchronized vibrators (ϕ₁=ϕ₂), exciting force W (W=W_z), acting along central axis z_c, pulsatorily changes its value and sense and induces only linear vibrations of the screen in the plane of central axes z_cy_c to cause transport of the feed as in a classic screen. In order to induce vibrations in the plane of central axes z_cx_c, the phase angle Δϕ= |ϕ1 - ϕ2| of vibrator 4 orientation is controlled by means of inverters 5, equipped with a system for controlling the phase angle of vibrators 4. With the phases of the vibrators 4 having been varied by said controlling, resultant force W coming from the vibrators induces additional angular vibrations β of the screen. This is related to the fact that the direction of action of resultant exciting force W, being variable in terms of value, does not pass through centre of gravity C of the screen, but passes beside it, acting in plane z_cx_c, along axis ξ of a variable direction. As the moment of resultant exciting force W acts on arm r, angular vibrations β of the screen in plane z_cx_c are induced, aimed at tossing and rotating the grains. This increases the likelihood of them falling into the slots of the sieve 2 with their minimum projection area and effective sieving (separating) of flat or elongated (irregular) grains from regular (cubic) grains. Depending on the fraction being sieved and the sieve mesh (slot) size being used, the screen operation parameters are adjusted by controlling the forcing frequency and phase angle Δϕ of vibrator 5 orientation. The greater the angle between varied phases Δϕ, the greater arm r of resultant force W and the greater the amplitude of angular vibrations β.
In another embodiment of the screen, the vibrators 4 are suspended from the screen such that central axis z_c is inclined to the sieve 2 deck at an angle α=45°. As a result of increasing the angle α of inclination of central axis z_c, the component of the screen vibrations is increased, said vibrations causing a change in the trajectory of grain movement, at the expense of the component of vibrations causing grain transport along the sieve deck.
The solution being the subject matter of the invention makes it possible to force axial vibrations in the plane of symmetry π of the screen and angular vibrations β of the vibrator in a plane perpendicular to the plane of symmetry π of the screen, without the need to install on it additional devices to force vibrations.

Claims

Vibrating screen, especially with a slotted sieve, comprising a riddle, the riddle arranged by means of flexible supports on a rigid base and with at least one sieve deck arranged in the riddle, with two inertial counter-rotating vibrators suspended to the sieve deck and arranged symmetrically, in such a way that the axes of rotation of the vibrators are parallel to the plane of symmetry of the screen, with the centre of gravity of the screen lying in said plane, and the direction of action of the resultant exciting force, in the operation mode with synchronized vibrators, passes through the centre of gravity of the screen obliquely to the sieve deck, and in addition, the vibrators are connected, via known means of drive transmission, to electric motors equipped with regulators of rotational speed, being inverters, characterized in that the inverters (5) additionally have a system for controlling the phase angle of vibrator (4) orientation, so that in the operation mode with the phase angle other than zero, the exciting force (W), being the resultant force from the forces (F) of action of the vibrators (4), acts in a plane (x_c, z_c) defined by a central axis (x_c) perpendicular to the plane of symmetry (π) of the screen and by a central axis (z_c) inclined at an angle (α) to the sieve (2) deck, with the direction of the latter being defined by the centre of gravity (C) of the screen and a point (J) lying in the plane of symmetry (π) of the screen, the point being the centre of the section connecting the axes of the vibrators (4).
The vibrating screen according to claim 1, characterised in that the vibrators (4) are suspended from the screen in such way that the central axis (z_c) is inclined to the sieve (2) deck at an angle (α) being in the range from 30° to 45°.
The vibrating screen according to claim 1, characterised in that the spacing between the flexible supports (3) is symmetrical relative to the centre of gravity (C) and does not exceed 0.6 of the length of the screen.
The vibrating screen according to claim 1, characterised in that the distance from the point (J), which is the centre of the section connecting the axes of the vibrators (4), to the centre of gravity (C) of the screen is greater than 0.25 of the length of the screen.
Method for controlling the operation of the screen, especially with a slotted sieve, the method being that the amplitude and speed of screen vibrations acting in its plane of symmetry are adjusted by changing the rotational speed of the vibrators, characterized in that by controlling the phase angle of vibrator (4) orientation, the direction of action of the resultant force (W) is changed such that said direction does not run in the plane of symmetry (π) of the screen and as a result, angular vibrations (β) of the screen are induced in the plane (x_c, z_c) defined by the central axis (x_c) perpendicular to the plane of symmetry (π) of the screen and by the central axis (z_c) inclined at an angle (α) to the sieve (2) deck, the direction of the latter being defined by the centre of gravity (C) of the screen and a point (J) lying in the plane of symmetry (π) of the screen, the point being the centre of the section connecting the axes of the vibrators (4).