RU2028836C1 - Screening method - Google Patents

Abstract

FIELD: loose material separation. SUBSTANCE: method comprises steps of charging a material on an upper portion of an inclined roll-type screen, having rolls, longitudinally arranged along a motion direction of the material; imparting to rolls a rotation in the same direction with a rate, increasing or decreasing according to a rotation sign or with the same revolution number of each successive roll relative to a previous one. EFFECT: enhanced efficiency. 1 cl, 4 dwg

Description

 The invention relates to the separation of bulk materials by size and can be used in the mining industry and the industry of non-metallic building materials, mainly for the separation of sand and gravel mixtures into sand and gravel and fractionation of gravel and crushed stone.

 The most widely used method of screening on vibrating screens. Depending on the type of vibration exciter, they are divided into gyration, inertial, self-balancing and resonant.

 The disadvantages of the method of screening on vibrating screens - the complexity of repair and maintenance, significant weight, the complexity of the design of the used screens.

 Working elements of vibrating screens are sieves. Usually used metal, rubber, polyurethane sieves. The disadvantages of metal sieves (wire mesh) include a short service life, significant replacement costs. Perforated solid sieves, as well as rubber reinforced and rubber solid sieves, are of high cost, limited live section, low specific productivity, complexity of installation and repair. Polyurethane sieves have a high cost, require the installation of a special sowing pad, have a low specific productivity, are difficult to repair. A common disadvantage is the inability to clean the sieves when clogging and sticking the cells, which leads to a decrease in productivity and screening quality.

 A known screen including a bed, supports, on which cylindrical grates are pivotally mounted. One of the supports is installed in the bed with the possibility of reciprocating movement, and the hinges in the grid-irons are installed with the possibility of axial movement.

 A disadvantage of the known device is the possibility of jamming particles of material, the sizes of which correspond to the width of the gap between adjacent grates, which leads to a decrease in duty cycle, lowering the efficiency and productivity of screening.

 The closest in technical essence to the claimed method of screening is a method of separation of materials by size, implemented on a roll sieve.

 A known method of screening is to feed the source material onto an inclined roll sieve with rolls longitudinally arranged along the material moving, on which the size of the starting material is classified, and then unloading the fractionated material into bins located under the roll sieve. Roll sieve is a block of inclined rollers of variable cross section, decreasing from top to bottom.

 The roll working bodies are informed of the rotational movement with the same angular velocity so that each subsequent roller rotates in the opposite direction as compared to the previous one.

 The disadvantage of this method is the low productivity, due to the fact that to prevent jamming of material particles between adjacent rollers rotating towards each other from the side of the working surface, their slotted holes are blocked, which leads to a decrease in the duty cycle of the roller sieve and, accordingly, a decrease in productivity. The opposite direction of rotation in the working area causes partial removal of grains from the slotted holes, which also leads to a decrease in productivity.

 The purpose of the screening method is to increase productivity due to more efficient use of the screening surface and increase the throughput of the roll sieve.

 This goal is achieved by the fact that the roll working bodies, longitudinally located along the movement of the material, forming a roll sieve, inform rotation in one direction so that each subsequent roll rotates with less, or more, or with the same compared to previous roll speed.

 In FIG. 1 shows a device for implementing the method, side view; in FIG. 2 - the same, top view; figure 3 is a diagram of the interaction of particles with one of the working rolls; figure 4 is a diagram of the interaction of the initial sand-gravel mixture with roller working bodies.

 The device comprises cylindrical roll working bodies 1 mounted on a frame 2. The gaps between the rolls are constant and correspond to the size of the boundary grain of the separated fractions. The frame 2 is pivotally connected to the jacks 3, providing the ability to change its spatial position. A feed device 4 is used to supply the starting material. The over-sieve product is removed by conveyor 5, and the under-sieve conveyor 6.

 The rotation of the roller working bodies is communicated from the electric motors 7 through the gears 8. One motor can be used to communicate the movement to one or more rolls. Brushes 9 are provided for cleaning the working surfaces of roll working bodies. For cleaning gravel from adhering sand and clay particles, the device can be provided with a wash water supply system and a number of nozzles mounted above the roll sieve (not shown).

 When dividing the source material into several fractions, the device is multi-tiered. The number of tiers K = n-1, where n is the number of fractions. The values of the gaps between the rolls in each tier are equal to the size of the boundary grain of the fractions shared on each tier.

 PRI me R 1. Implementation of the method for separation into fractions of materials with a particle size of more than 3 ... 5 mm The source material, for example unfractionated gravel, is fed through a loading device 4 to the screening surface of the screen formed by roll working bodies 1 mounted on frame 2 with gaps corresponding to the grain size of the boundary grain of the separated fractions. The diameters of the roller working bodies depend on the size of the source material and can vary widely. The separation of the source material by size is carried out on a roll sieve. The angular velocity of each subsequent roll in the direction of rotation is greater than that of the previous one.

When supplying the source material to the sieve, part of the grains of the source material comes into contact with the working surface of one of the roll working bodies. The following forces act on a particle: gravity mg; centrifugal inertia force m ρω ² ; Coriolis inertia force 2mω S; normal force N; friction force fN.

= g cos β -

;
нормальная сила равна N = 2m

+ +mgsin β- m ρω², где

- скорость частицы при перемещении ее относительно криволинейной поверхности валкового рабочего органа;
ω- угловая скорость валкового рабочего органа;
m - масса частицы;
ρ- радиус-вектор частицы;
β- угол между вектором силы тяжести и вектором относительной скорости частицы.The differential equation of motion of a particle on a site has the form:

= g cos β -

;
normal force is N = 2m

+ + mgsin β- m ρω ² , where

- the speed of the particle when moving it relative to the curved surface of the roll working body;
ω is the angular velocity of the roll tool;
m is the mass of the particle;
ρ is the radius vector of the particle;
β is the angle between the gravity vector and the relative particle velocity vector.

 The equation is written for a material particle without taking into account its shape, which determines the peculiarities of the interaction of the particle with roller working bodies.

gcosβ< f

, до площадки, для которой удовлетворяется условие gcosβ =

, где происходит отрыв частицы от рабочего органа, либо, если первоначально в момент первого контакта выполнялось условие gcosβ >

, частица скатывается в зазор между смежными валками. Частицы материала крупностью d меньше величины зазора между валками δ проходят в него и удаляются конвейером 6. Частица, крупность которой d > δ, войдет во взаимодействие с двумя смежными рабочими органами. В этом случае суммы проекций сил, действующих на зерно гравия в направлениях, перпендикулярных площадкам n₁ и n₂, принадлежащим смежным валковым рабочим органам, контактирующим с частицей, могут быть записаны в виде:
N₁= 2m

+ mgsinβ - mρω $\genfrac{}{}{0ex}{}{\text{2}}{\text{1}}$ - N

cos2β - N₁f sin 2β
N₂= 2m

+ mgsinβ - mρω $\genfrac{}{}{0ex}{}{\text{2}}{\text{2}}$ - N

cos2β - N₂f sin 2β

=

Анализ уравнений показывает, что при ω₂>ω₁ величина N₂ > N₁. Отсюда следует, что сила трения между первым по направлению вращения валком и частицей гравия меньше, чем между вторым валком и той же частицей. Это обстоятельство приводит к тому, что зерно гравия затягивается в пространство между валками с меньшей силой, чем выносится из него, что полностью исключает возможность заклинивания зерен между валками. Пара сил N₁f₁ и N₂f₂ создает момент, под действием которого частица приобретает вращательное движение, благодаря чему трение скольжения материала по поверхности валкового рабочего органа заменяется на трение качения.Depending on the position of the site of contact of gravel with a roll working body, determined by the angle β, it can either be transported by a roll working body

gcosβ <f

to the site for which the condition gcosβ =

, where the particle detaches from the working body, or if, initially at the moment of the first contact, the condition gcosβ>

, the particle rolls into the gap between adjacent rolls. Particles of material with a particle size d less than the gap between the rollers δ pass into it and are removed by conveyor 6. A particle with a particle size d> δ will enter into interaction with two adjacent working bodies. In this case, the sum of the projections of the forces acting on the gravel grain in directions perpendicular to the pads n ₁ and n ₂ belonging to adjacent roll working bodies in contact with the particle can be written in the form:
N ₁ = 2m

+ mgsinβ - mρω $\genfrac{}{}{0ex}{}{\text{2}}{\text{1}}$ - N

cos2β - N ₁ f sin 2β
N ₂ = 2m

+ mgsinβ - mρω $\genfrac{}{}{0ex}{}{\text{2}}{\text{2}}$ - N

cos2β - N ₂ f sin 2β

=

An analysis of the equations shows that for ω ₂ > ω _{1 the} quantity N ₂ > N ₁ . It follows that the friction force between the first roll in the direction of rotation and the gravel particle is less than between the second roll and the same particle. This circumstance leads to the fact that the gravel grain is drawn into the space between the rollers with less force than is removed from it, which completely eliminates the possibility of jamming of the grains between the rollers. A pair of forces N ₁ f ₁ and N ₂ f ₂ creates a moment under the action of which the particle acquires a rotational motion, due to which the sliding friction of the material on the surface of the roll working body is replaced by rolling friction.

 Material with a particle size d> δ rolls along inclined grooves formed by adjacent rolls onto conveyor 5. The speed of transportation of material particles depends on the angle of inclination of the longitudinal axes of the working bodies in the vertical plane, which is regulated by jacks 3, as well as the friction forces between the surface of the rolls and particles processed material, for example gravel grains.

Since the rolling friction coefficient is less than the sliding friction coefficient, and the normal force is not constant and varies within 0 ≅N ≅mg, to ensure the transportation of gravel grains along inclined grooves formed by adjacent rotating rolls, the angle of inclination of their longitudinal axes is 15. ..20 ^about . (For static screening angle of at least 30 is selected ^to provided the rinsing water supply. Transportation gravel particle size is 5 ... 70 mm on the fixed ramp is carried out at an angle of ^about 35-45).

1,8 d_max, где D - диаметр валкового рабочего органа; d_max - максимальная крупность частиц обрабатываемого материала.The diameters of the roller working bodies, it is desirable to choose so that the condition D

1.8 d _max , where D is the diameter of the roll working body; d _max - the maximum particle size of the processed material.

, что приведет к транспортированию некоторых из них поперек валковых рабочих органов за пределы валкового сита.The need to fulfill this condition is caused by the fact that otherwise the condition gcosβ <f

, which will lead to the transportation of some of them across the roll working bodies outside the roll sieve.

.When D ≅ 1.8 d _max in order to avoid transportation of material across the rolls, the frame should be rotated in a plane perpendicular to the longitudinal axes of the rolls in the direction opposite to their rotation by an angle of 5 ... 10 ^o (depending on the ratio)

.

 PRI me R 2. The implementation of the method for the separation of sand and gravel sand-gravel mixture (ASG), the water content from 5 to 40%. The source material (ASG) through the loading device 4 is fed to the screening surface of the screen formed by roll working bodies 1 mounted on the frame 2 with gaps corresponding to the size of the boundary grain (3 ... 5 mm). The diameters of the roll organs are selected in the same manner as in example 1. Separation of the ASG into sand and gravel is carried out on a roll sieve. In this case, the angular velocity of each subsequent in the direction of rotation of the roll is less than the previous one.

 Air-dry, wet and wet sand-gravel mixtures, the moisture content of which is in the range of 5 ... 40%, form a dense mass in which particles of material are interconnected by the forces of molecular attraction between the grains and the water enveloping them.

When such material is fed to the screen, the source material, which is a spontaneously indestructible mass, lies on the surface of the roller working bodies and overlaps the screening cracks of the screen. In this case (without taking into account the rotation of the rolls), sand particles due to molecular adhesion forces can be held on the surface of the roll at an angle β≥70 ^about .

Particles of material interacting directly with the roller rotating with an angular velocity ω ₂ due to the adhesion forces between the working surface of the roller working body, they are carried out from the sieving gap. These particles, in turn, interact with the particles of material in contact with them and, due to the forces of molecular cohesion, carry them along.

Particles of material interacting directly with the roller rotating with an angular velocity ω ₁ are transported by it in the direction of the screening slit, involving adjacent particles in the movement. Under the action of this pair of forces, the material rotates in the half-space formed by the cylindrical surfaces of the roll working bodies, the destruction of bonds between individual particles and their intensive mixing.

Since the angular velocity ω ₁ > ω ₂ , the material is drawn into the gap between adjacent rolls at a higher speed than is removed from it. Thus, particles of the starting material, for example, ASG, the size of which is smaller than the size of the screening slit, are forcibly transported through it and get to the conveyor 6. Particles of material, the size of which is larger than the size of the boundary grain, roll along the inclined grooves formed by adjacent rolls to the conveyor 5, as described in example 1. Cleaning of the working surfaces of the rolls from small particles, such as grains of sand, is carried out by brushes 9.

 PRI me R 3. The implementation of the method for the separation of sand and gravel sand-gravel mixture (ASG) with a water content of from 0 to 5% and more than 40%. Sand and gravel mixtures with a water content of up to 5% (dry mixes) are characterized by flowability, and with a water content of more than 40% (liquid) - by fluidity. In this state, the material can pass spontaneously through the sieving slots. Nevertheless, in order to increase the speed of passage of particles through the openings of the sieve, to prevent clogging of the sieve slots, to replace the sliding friction of the particles of material on the surface of the roll working body with rolling friction, and also to ensure uniform sieving of the material on all sieving slots, the roll working bodies are informed of rotation direction with equal angular velocities. The source material is fed to the screen and, as described in example 2, rotates between adjacent rolls. Since the friction coefficient of dry (up to 5% moisture) and liquid (with a water content of more than 40%) material is much lower than that of wet material, the process of mixing is less intense, and the transporting function of the roll working bodies decreases. Nevertheless, the screening process is effective due to the properties of the starting material — fluidity or flowability.

 Particles of material, the size of which is smaller than the boundary grain, pass into the sieve slot partially under the influence of its own weight, partly due to the friction forces between the material particles and the roller working body, and get onto conveyor 6 (for dry material) or tray 6 (for flooded material), and larger particles, rolling along the inclined grooves formed by the surfaces of the rolls, fall on the conveyor 5.

 In contrast to the known device, where the rolls rotate in opposite directions and both contribute to the removal of particles of material from the screening gap due to the action of friction between the particle and the surface of the working body, which reduces the speed of passage of particles through the slot hole of the roller sieve, in a device that implements the proposed method , roller working bodies rotate in one direction. One of the rolls transports the particles of material that are in contact with it in the direction of the screening slit, and the other from it, which makes it possible to increase the speed of passage of the particles of material through the gap between adjacent rolls. In addition, in the known device, screening slots between adjacent rollers, the surfaces of which rotate towards each other, are blocked to prevent jamming of material particles between them. Since the proposed method is implemented on a device where all the rolls rotate in one direction, the need to block part of the slots is eliminated, which allows a significant (almost two-fold) increase in screening performance with the same dimensions of the device.

Claims (1)

 METHOD OF DRAWING, including loading the source material onto the upper part of an inclined roll sieve from rotating rolls longitudinally arranged in the direction of the material movement, material classification and separate removal of the over-sieve and under-sieve product, characterized in that the rolls are told to rotate in one direction with increasing or decreasing along rotation speed or with the same speed of rotation of each subsequent roll relative to the previous one.

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