EP4252911A1 - System for sorting metal objects - Google Patents

Abstract

The invention relates to a sorting system by magnetic separation of metallic objects, comprising: - an electromagnetic core comprising: • at least a first portion (1), • a second portion (2), • and a bottom (3), - a sorting flap arranged opposite said electromagnetic core so as to provide a circulation space for a conveyor (6) of objects to be sorted from the first portion (1) to the second portion (2), said sorting system being characterized in that the sorting flap comprises a magnetic element (4) arranged so as to form an air gap (E1) between the first portion and the sorting flap, said air gap forming a magnetic barrier opposing the passage of objects non-magnetic metallic, so that said objects are ejected from the conveyor (6), the second portion being arranged to ensure a return of the magnetic field lines towards the first portion.

Description

FIELD OF THE INVENTION

The present invention relates to a system for sorting metal objects.

STATE OF THE ART

Magnetic objects, such as iron, steel, and some magnetic stainless alloys, can be easily extracted with static magnetic fields and then recycled.

Sorting and recovery of non-magnetic metallic objects is carried out using an alternating magnetic field, producing induced electric currents in said objects, which are electrically conductive. These induced currents interact with this same surrounding magnetic field to give rise to electromagnetic forces whose direction is that of the decreasing magnetic field gradient. In magnetic separation sorting devices, these forces can be used to deflect electrically conductive objects, which are typically metallic.

A solution used today to create an alternating magnetic field is the polar wheel. This solution involves rotating a pole wheel made of alternating permanent magnets. The alternation of polarity of the rotating magnets creates a variable magnetic field that can reach several Tesla. Non-magnetic electrically conductive objects are drawn into this rotating variable magnetic field and are accelerated relative to non-electrically conductive objects.

Such a system is described in the document FR 2116430 . This system is functional for sufficiently large aluminum parts that are light and sufficiently conductive. However, the mechanical construction of said system implies a limitation of the frequency of the magnetic field. For this reason, said system does not make it possible to sort materials that are insufficiently electrically conductive and too dense, such as non-magnetic stainless steel, and it is difficult to sort materials that are very conductive and too dense, such as copper. It also has significant reliability and safety issues, particularly in the event of an emergency stop, due to the inertia of the massive pole wheel.

Another solution is to use a carpet passing over the air gap of an electromagnet powered with an alternating electric current. Such a system is described in the document WO2017/044863 . The principle is to use the swirling electric currents induced in objects in the presence of the non-homogeneous alternating magnetic field to create electromagnetic forces whose direction is the gradient of the magnetic field.

The magnetic energy E _mag of the system amounts to $${\mathrm{E}}_{\mathit{mag}}=\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.*\mathrm{H}\mathrm{B}\mathrm{V}$$

H being the magnetic excitation, B the magnetic induction and V the volume of the excited external space corresponding to the air gap. The reactive power of the system corresponds to the evacuation and then generation of this magnetic energy during each period of operation, that is to say approximately 20,000 to 100,000 times per second.

This system therefore requires very significant reactive power to create the magnetic field at the air gap, particularly for large air gaps which are not delimited.

The efficiency of such a system can be increased by reducing the size of the air gap. However, when the air gap is small, the sorting zone is also small and it therefore does not make it possible to sort large volumes of objects, nor objects of very different sizes. However, to be able to obtain an industrial application, it is necessary to sort several hundred kilograms of objects per hour with conveyor and sorting systems that can reach several meters wide.

None of these devices take into account air friction which is in fact negligible for large volume objects but is preponderant for small particles, particularly during falling or rebound phases which are typically present during sorting. by an alternating magnetic field. Air friction will influence the result of the forces experienced by the objects.

STATEMENT OF THE INVENTION

An aim of the invention is to propose a sorting device by magnetic separation of non-magnetic metallic objects making it possible to sort large volumes of products of any shape and/or size (waste, recyclable products, powders, etc.) and mixtures of objects of very different sizes. The invention also aims to sort objects into materials having very high electrical conductivity, such as copper, or very low electrical conductivity, such as non-magnetic stainless steel.

• ∘ un noyau électromagnétique comprenant :
  • ∘ au moins une première portion comportant un bobinage,
  • ∘ une seconde portion, la seconde portion étant plus large que la première portion,
  • ∘ et un fond reliant la première portion à la seconde portion,
• ∘ un volet de tri agencé en regard dudit noyau électromagnétique de sorte à ménager, entre le volet de tri et le noyau électromagnétique, un espace de circulation pour un convoyeur d'objets à trier de la première portion vers la seconde portion,

• ledit système de tri étant caractérisé en ce que le volet de tri comprend un élément magnétique agencé de manière à former un entrefer entre la première portion et le volet de tri, ledit entrefer formant une barrière magnétique s'opposant au passage d'objets métalliques non magnétiques, de sorte que lesdits objets métalliques non magnétiques sont éjectés du convoyeur,
• la seconde portion étant agencée entre le fond et une portion de l'élément magnétique du volet de tri opposée à l'entrefer pour assurer un retour des lignes de champ magnétique vers la première portion.

To this end, the invention proposes a sorting system by magnetic separation of metal objects, comprising:

• ∘ an electromagnetic core comprising:
  • ∘ at least a first portion comprising a winding,
  • ∘ a second portion, the second portion being wider than the first portion,
  • ∘ and a bottom connecting the first portion to the second portion,
• ∘ a sorting flap arranged opposite said electromagnetic core so as to provide, between the sorting flap and the electromagnetic core, a circulation space for a conveyor of objects to be sorted from the first portion to the second portion,

• said sorting system being characterized in that the sorting flap comprises a magnetic element arranged so as to form an air gap between the first portion and the sorting flap, said air gap forming a magnetic barrier opposing the passage of non-magnetic metallic objects, so that said non-magnetic metallic objects are ejected from the conveyor,
• the second portion being arranged between the bottom and a portion of the magnetic element of the sorting flap opposite the air gap to ensure a return of the magnetic field lines towards the first portion.

Such geometry makes it possible to optimize the distribution of the magnetic field for the ejection of non-magnetic metallic objects. In addition, the sorting system is very responsive, especially in the event of an emergency stop, and thus has advantages in terms of reliability and safety.

Preferably, the magnetic element of the sorting flap extends parallel to the conveyor.

Advantageously, the magnetic element of the sorting flap is in the form of a flat plate.

Advantageously, the sorting flap comprises at least one non-magnetic portion.

In certain embodiments, the magnetic element has an edge arranged facing the first portion in a direction transverse to the conveyor, said edge being beveled so as to form an inclined plane oriented in the direction of circulation of the conveyor moving away of the electromagnetic core. The sorting flap may further comprise at least one magnetic plate parallel to the beveled edge of the magnetic element, each plate being arranged opposite the first portion to form a respective air gap forming an additional magnetic barrier opposing the passage of non-magnetic metal objects.

Preferably, the non-magnetic portion of the sorting flap comprises an ejection ramp for non-magnetic metallic objects extending on the magnetic element on the side opposite the electromagnetic core, said ejection ramp being coplanar with the beveled edge of the magnetic element.

Advantageously, the beveled edge of the magnetic element is set back relative to a central region of the first portion in the direction of movement of the conveyor.

Advantageously, the second portion comprises a winding and the number of turns of the winding on the first portion is greater than the number of turns of the winding on the second portion.

The surface of the at least one first portion opposite the bottom may have at least one chamfer along the air gap.

Preferably, the sorting system comprises one or more magnetic parts arranged between the magnetic element of the sorting flap and the second portion of the core electromagnetic to guide the magnetic field in these magnetic parts and thus minimize the path of the magnetic field lines in the air between the sorting flap and the second portion.

Advantageously, the at least one first portion and the second portion are made of ferrite, and/or the magnetic element of the sorting flap is made of ferrite.

• ∘ un système de tri tel que décrit ci-dessus, et
• ∘ un convoyeur adapté pour transporter l'ensemble d'objets en direction du système de tri, ledit convoyeur étant agencé de sorte à traverser le système de tri entre le noyau électromagnétique et le volet de tri, la barrière magnétique formée par l'un entrefer entre la première portion du noyau électromagnétique et le volet de tri étant adaptée pour éjecter les objets métalliques non magnétiques, et
• ∘ un système de récupération agencé pour récupérer les objets métalliques non magnétiques éjectés.

The invention also relates to an installation for sorting a set of objects containing metal objects, comprising

• ∘ a sorting system as described above, and
• ∘ a conveyor adapted to transport the set of objects towards the sorting system, said conveyor being arranged so as to pass through the sorting system between the electromagnetic core and the sorting flap, the magnetic barrier formed by an air gap between the first portion of the electromagnetic core and the sorting flap being adapted to eject non-magnetic metallic objects, and
• ∘ a recovery system designed to recover ejected non-magnetic metal objects.

Preferably, the conveyor is a conveyor belt or a slide.

Advantageously, the sorting installation further comprises a hermetic zone arranged above at least the conveyor and the sorting flap, and a depressurization device arranged so as to create, in said zone, a movement of air adapted to orient the non-magnetic metallic objects ejected by the magnetic sorting system in a defined direction.

In some embodiments, the sorting facility includes an electromagnetic core cooling system.

• ∘ le transport d'un ensemble d'objets métalliques dans une installation telle que décrite ci-dessus,
• ∘ l'éjection des objets métalliques non magnétiques par la barrière magnétique,
• ∘ le passage des objets non métalliques dans l'entrefer entre la première portion du noyau électromagnétique et le volet de tri.

The invention also relates to a method for sorting metal objects, comprising

• ∘ the transport of a set of metal objects in an installation as described above,
• ∘ the ejection of non-magnetic metallic objects by the magnetic barrier,
• ∘ the passage of non-metallic objects in the air gap between the first portion of the electromagnetic core and the sorting flap.

BRIEF DESCRIPTION OF THE FIGURES

• La figure 1 une vue schématique en coupe du principe d'éjection des particules conductrices avec un volet de tri faisant partie du circuit magnétique
• La figure 2 illustre un système d'éjection sur une grande largeur pour trier des grandes quantités d'objets.
• La figure 3 est une vue schématique des lignes du champ magnétique dans un système de tri de déchets selon l'invention.
• La figure 4 illustre un système de tri 4 comprenant plusieurs plaques parallèles à la surface biseautée du volet.
• La figure 5 est une vue schématique des lignes du champ magnétique dans un système de tri d'objets métalliques non magnétiques comprenant plusieurs plaques parallèles à la surface biseautée du volet.
• La figure 6 est une vue schématique en coupe d'une installation de tri de comprenant système de vide partiel.
• La figure 7 illustre un système de tri de déchets comportant des bobinages sur les deux portions et un moyen de fermeture du circuit magnétique.
• La figure 8 illustre un système de tri de déchets comportant des bobinages sur les deux portions, plusieurs plaques parallèles à la surface biseauté du volet, et un moyen de fermeture du circuit magnétique.
• La figure 9 illustre un système de tri avec plusieurs volets de tri.

Other characteristics and advantages of the invention will emerge from the detailed description which follows, with reference to the appended drawings, in which:

• There figure 1 a schematic sectional view of the principle of ejection of conductive particles with a sorting flap forming part of the magnetic circuit
• There figure 2 illustrates a wide ejection system for sorting large quantities of objects.
• There Figure 3 is a schematic view of the magnetic field lines in a waste sorting system according to the invention.
• There Figure 4 illustrates a sorting system 4 comprising several plates parallel to the beveled surface of the shutter.
• There Figure 5 is a schematic view of the magnetic field lines in a non-magnetic metal object sorting system comprising several plates parallel to the beveled surface of the flap.
• There Figure 6 is a schematic sectional view of a sorting installation comprising a partial vacuum system.
• There Figure 7 illustrates a waste sorting system comprising windings on the two portions and a means of closing the magnetic circuit.
• There figure 8 illustrates a waste sorting system comprising windings on the two portions, several plates parallel to the beveled surface of the shutter, and a means of closing the magnetic circuit.
• There Figure 9 illustrates a sorting system with multiple sorting panes.

DETAILED DESCRIPTION OF EMBODIMENTS System Overview

THE figures 1 and 2 illustrate a sorting system by magnetic separation of non-magnetic metallic objects according to the invention.

The system makes it possible to recover, for example, metal objects from waste such as metals from household or industrial waste and crushed products to be recycled such as windows, wooden pallets, cables or glass. Another application is the processing of food grains or pharmaceutical powders, which may contain undesirable non-ferrous conductive metals to be removed.

The size of said objects can vary greatly depending on the applications. The size of objects (understood as their largest dimension) can be between 0.1 mm and 10 cm in at least two directions.

The sorting system comprises an electromagnetic core comprising a first portion 1, a second portion 2 wider than the first portion, and a bottom 3 connecting the first portion to the second portion. Advantageously, the portions 1 and 2 and the bottom 3 are of essentially parallelepiped shape, assembled in a U. In certain embodiments, the portions 1 and 2 and/or the bottom can be curved and/or inclined, thus forming a core whose section can be, in an illustrative and non-limiting manner, of circular or triangular shape.

The first portion 1 of the core comprises a winding 11. In certain embodiments, the second portion 2 comprises another winding 21. Preferably, the number of turns of the winding 11 on the first portion 1 is greater than the number of turns of the winding 21 on the second portion 2. Each winding is made of electrically conducting wire. Preferably, the winding is made of copper wire having electrical insulation, or of copper tube. The number of turns and amperes of the winding, also known as the number of ampere-turns, is configured to provide a magnetic induction close to the saturation induction of the magnetic circuit, i.e. approximately 300mT for a ferrite.

Advantageously, the electromagnetic core further comprises a cooling system. Such a cooling system may, by way of illustration and not limitation, include a cooling plate, a heat sink or an inflatable seal filled with a cooling liquid, for example water.

The system further comprises a sorting flap arranged opposite said electromagnetic core. Said sorting flap comprises a magnetic element 4 arranged so as to form an air gap E1 between the first portion 1 and the sorting flap. The magnetic element of the sorting flap extends to a zone near the upper face 20 of the second portion 2.

Preferably, the magnetic element 4 of the sorting flap is made of soft ferrite, a nanocrystalline magnetic composite or an iron powder compressed with an electrical insulator. The sorting flap may also include one or more non-magnetic portions 54.

Advantageously, the magnetic element 4 of the sorting flap is in the form of a flat plate extending from the air gap E1 to a zone close to the upper face 20 of the second portion 2.

The magnetic part of the sorting flap and the core thus form a magnetic circuit comprising a circulation space for objects to be sorted between the sorting flap and the core. We thus define an entry zone for objects at the air gap E1, and an exit zone for non-metallic objects between the sorting flap and the surface opposite the second portion 2 of the core 3.

The transport of objects between the entry zone and the exit zone is carried out by a conveyor 6 passing through said circulation space. The conveyor may include a conveyor belt closed on itself and circulating between the two portions and the sorting flap. Advantageously, the magnetic element 4 of the sorting flap extends parallel to the conveyor belt.

Alternatively, the conveyor can be a slide or any other means of transporting objects.

Magnetic circuit

The magnetic element of the sorting flap 4 has an edge 14 arranged facing the first portion 1 in a direction transverse to the conveyor 6. Preferably, said edge 14 is beveled so as to form an inclined plane oriented in the direction of circulation of the conveyor away from the electromagnetic core.

In certain embodiments, the beveled edge of the magnetic element is aligned with a central region 10 of the first portion 1. In other embodiments, said beveled edge 14 is offset relative to the central region 10 of the first portion 1 forwards or backwards in the direction of movement of the conveyor 6.

In some embodiments, with reference to the figure 4 , the sorting flap further comprises one or more magnetic plates 24, 34 parallel to the beveled edge 14 of the magnetic element of the sorting flap. Each plate is arranged opposite the first portion 1 to form a respective air gap E2, E3. The number of plates 24, 34 and air gaps E2, E3 is indicated for purely illustrative and non-limiting purposes. The number of plates 24, 34 is typically between 1 and 3 and can be higher in certain embodiments.

The non-magnetic portion of the sorting flap may include an ejection ramp 54. In this case, said ramp extends over the magnetic element of the sorting flap, on the side opposite the electromagnetic core

When the edge 14 is beveled forming an inclined plane, the ejection ramp can be coplanar with the beveled edge of the magnetic element or offset in a direction in the direction of circulation of the objects or be offset in the direction opposite to the direction of the circulation of objects. For a sorting system with given dimensions, the location of the ramp is chosen so as to find a compromise between the positioning of the ramp relative to the ejection zone and good closure of the magnetic circuit.

Advantageously, the core is made of a material that conducts a magnetic field and is sufficiently low conductor of electricity in order to avoid heating by induction. Preferably, the core is made of a material having a high saturation value in magnetic field (greater than 300mT) and low magnetic losses (hysteresis cycle and by induced electric current) at the frequency of the alternating electric current applied to the windings in order to produce a high density of the magnetic field inside the core.

For example, the magnetic core may be made of a material having a relative magnetic permeability value µ _r of between 10 to 100 or even more. Advantageously, the core is made of soft ferrite, for example of the Mn-Zn CF297, 3C90 type or a material having similar magnetic properties or even a higher magnetic saturation than this material. Alternatively, the core can for example be made of a nanocrystalline magnetic composite or of an iron powder compressed with an electrical insulator. Such materials are for example marketed under the names MPP, 3F3, 3c90, Nanodust ^™ KAM or Nanodust ^™ KAH.

Preferably, the magnetic portion of the sorting flap and, where appropriate, each plate 24, 34 is made of soft ferrite, a nanocrystalline magnetic composite or an iron powder. compressed with an electrical insulator, as described for the magnetic core. The plates 24, 34 and the magnetic element 4 of the sorting flap can be made of the same material or different materials.

There Figure 3 illustrates the concentration of the magnetic field in a sorting system according to the invention. The maximum concentration of the magnetic field is located in the magnetic part 4 of the sorting flap and in the first portion 1 of the magnetic core. The maximum concentration of the magnetic field in air is located at the air gap E1. The maximum gradient of the magnetic field in the air is located in an ejection zone 18 close to the air gap E1.

Said air gap E1 then forms an immaterial magnetic barrier, opposing the passage of metallic objects, including in particular non-magnetic metallic objects.

Preferably, the surface of the first portion 1 facing the magnetic flap 4 is small, in order to increase the concentration of the magnetic field and the magnetic field gradient in an ejection zone 18 near the air gap E1.

The surface 10 of the first portion opposite the bottom present may include one or more chamfers 17a, 17b arranged on the angles between the surface 10 and the faces of the carrying the windings. Said chamfers extend along the air gap and make it possible to reduce the surface of the first portion facing the sorting flap and thus increase the concentration of the magnetic field around the air gaps E1. Such chamfers also avoid saturation of the magnetic element in the edges of the first portion 1.

The magnetic element of the sorting flap extends to a zone close to the surface 20 of the second portion 2 and is thus arranged so as to create a magnetic field return towards the second portion 2. The path of the magnetic field is favored in the magnetic element of the sorting flap. The path of the magnetic field in the air is thus minimized. The magnetic element of the sorting flap is thus an integral part of the magnetic circuit. Such an arrangement makes it possible to increase the magnetic field and the gradient of the magnetic field in the ejection zone near the air gap E1 for a given power.

The magnetic field exerts an attractive force between the magnetic circuit in the core and the sorting flap. It is therefore necessary to provide mechanical support for the ejection ramp to prevent bending of the ramp under the effect of this force of attraction.

The second portion 2 ensures a return of the magnetic field lines towards the first portion 1. It preferably comprises a large surface in order to distribute the magnetic field uniformly and weakly, the magnetic flux remaining constant. In addition, the second portion 2 extends close to the magnetic element 4 of the sorting flap in order to minimize the extent of the magnetic field in the air.

Advantageously, as illustrated in the Figure 7 and the figure 8 , one or more magnetic parts 9 are arranged between the magnetic element of the sorting flap and the second portion 2 of the electromagnetic core. Said magnetic parts are arranged to guide the magnetic field and thus minimize the path of the magnetic field lines in the air between the sorting flap and the second portion 2. In addition, the geometry of the magnetic parts 9 allows the passage of the conveyor, and non-ejected objects transported on the conveyor under the shutter.

The parameters of the system are chosen with the objective of reducing the reluctance R of the magnetic circuit, that is to say the ratio of the length l of the magnetic circuit and the product of the permeability µ and the surface S: $$R=\frac{L}{\mathrm{\mu }\ast S}$$

In the sorting system, four reluctance zones can be distinguished. The first zone corresponds to the magnetic core with, where appropriate, magnetic parts 9 and/or plates 23, 24. The second zone is the magnetic part of the sorting flap. In these zones, the surface S corresponds to the section of each respective part.

The third zone is the ejection zone, and the fourth zone corresponds to the zone above the second portion 2, ensuring the return or looping of the magnetic field. In the third and fourth zone, the surface S is the section through which the magnetic field lines pass. Said surface S corresponds to the upper surfaces of the first portion 1 and the second portion 2 arranged opposite the sorting flap.

In the first zone, the length / corresponds to the sum of the lengths of the first portion 1, the bottom, the second portion 2 and, where appropriate, the plates 23, 24 and/or the magnetic parts 9 in the direction of the magnetic field lines. In the second box, the length is the length of the sort pane.

In the third zone, the length / corresponds to the width of the air gap. In the fourth zone, the length / is the distance between the second portion 2 and the sorting flap plus, where applicable, the distances between the plates 23, 24 and the magnetic part of the sorting flap.

The magnetic permeability of the material µ is expressed by the product of the vacuum permeability µ ₀ and the relative permeability µ _r : $$\mathrm{\mu }={\mathrm{\mu }}_0*{\mathrm{\mu }}_{\mathrm{r}}$$

µ ₀ is a universal constant, the magnetic constant (or magnetic permeability of vacuum), which is 4π × 10 ^-7 H/m. In air, the relative magnetic permeability µ _r is approximately equal to 1. The material of the magnetic circuit typically has a relative magnetic permeability of 10 to 100. The stronger the magnetic permeability of an element, the greater the reluctance in that element is weak. However, a higher relative magnetic permeability would lead to an excessive drop in the magnetic field saturation value and would involve a loss of energy leading to significant heating.

ϕ étant le flux d'induction magnétique. Ledit flux correspond à l'induction magnétique dans une surface donnée. Dans la zone d'éjection, on cherche à augmenter le flux magnétique ϕ sans diminuer la surface concernée, afin de pouvoir trier une certaine quantité et un certain volume d'objets.The number of Ampere-turns which dimensions the magnetic circuit is given by Hopkinson's law: $$F=\mathrm{NOT}.I=R.\varphi$$

ϕ being the magnetic induction flux. Said flux corresponds to the magnetic induction in a given surface. In the ejection zone, we seek to increase the magnetic flux ϕ without reducing the surface concerned, in order to be able to sort a certain quantity and a certain volume of objects.

où R₁ est la reluctance magnétique du noyau magnétique, R₂ est la reluctance magnétique de l'élément magnétique du volet de tri, R₃ est la reluctance de la zone d'éjection, et R₄ la reluctance dans la zone de retour ou bouclage du champ magnétique.The _total reluctance R of the sorting system is the sum of four reluctances for the four zones of the sorting system, each reluctance being given by equation (1) with the parameters length l , surface area S and magnetic permeability µ of the four respective zones $$\mathit{Rtotal}=\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">R</figure-callout>}1+\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">R</figure-callout>}2+\mathrm{<figure-callout\; id="3"\; label="R"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">R</figure-callout>}3+{\mathrm{<figure-callout\; id="4"\; label="R"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">R</figure-callout>}}_4$$

where R ₁ is the magnetic reluctance of the magnetic core, R ₂ is the magnetic reluctance of the magnetic element of the sorting flap, R ₃ is the reluctance of the ejection zone, and R ₄ the reluctance in the return zone or looping of the magnetic field.

Among these four zones, the third zone and fourth zone concern a magnetic field in the air.

Due to the high relative magnetic permeability, typically between about 10 and 100, in the magnetic circuit, the reluctance in this circuit is low and can be neglected compared to the reluctance in the third and fourth zone in which the magnetic field is in the air.

The previous equation can therefore be simplified: $$\mathit{Rtotal}=\mathrm{<figure-callout\; id="3"\; label="R"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">R</figure-callout>}3+\mathrm{<figure-callout\; id="4"\; label="R"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">R</figure-callout>}4$$

We therefore seek to shorten the length of the field in these zones in the air, by bringing the air gap as close as possible to the upper surface of the second portion 2.

The reluctance R 3 of the ejection zone is linked to the geometry of the system and can hardly be modified.

Concerning the fourth return or looping zone of the magnetic field, the distance between the magnetic core and the magnetic element of the sorting flap presents a minimum distance allowing non-ejected objects to be evacuated. It is therefore imposed by mechanical considerations. However, the sorting system is preferably designed so that the surface S of this zone is as large as possible.

One possibility of reducing the reluctance on the return path (looping) is to add magnetic parts 9 on the air gap, for example rollers, possibly discontinuous, which make it possible to guide the magnetic field in a path with strong magnetic permeability. In addition, these parts 9 can perform a mechanical movement facilitating the passage of non-conductive and non-ejected elements.

Limiting the magnetic field in the air and optimizing the passage of the magnetic field through magnetic elements of the system makes it possible to reduce the reactive power required.

The geometry of the core takes into account the magnetic field in order to obtain an area of magnetic field most concentrated in the ejection zone of metallic objects. Right angles are thus avoided, particularly around the ejection zone in order to avoid saturation of the magnetic field in said angles.

Application of a magnetic field

When the electromagnetic core is powered by an electric current generator applying an alternating electric current to the windings 11, 21, an alternating magnetic field is established in the core, the magnetic element 4 of the sorting flap, and the air gap E1. Such an electric current typically has an intensity of approximately 2400A.turns, distributed for example over 20 turns at 120A each. This current creates a magnetic field of between 0.3 and 0.4 T in a ferrite core and approximately 0.1 T in the E1 air gap. The number of wires and therefore turns is limited by the space in the installation, the heating due to the electric current, and possible overvoltage problems.

The frequency is chosen according to the size and size distribution of the objects to be sorted. It is typically between 20 and 35 kHz and can go up to 150 kHz. Generally speaking, higher frequencies are applied when the objects to be sorted are smaller, and lower frequencies for larger objects to be sorted. However, a high frequency implies heating and significant electrical losses. The inductance and capacitance will therefore be taken into account to determine the operating frequency.

Sorting process

When a non-magnetic metallic object is placed in a unidirectional magnetic field on one axis that increases in value on a second axis perpendicular to the first axis, swirling electric currents within the object are induced. The interaction of said swirling electric currents with the magnetic field generates electromagnetic forces (known as the Lorentz force) perpendicular to the lines of constant magnetic field value. The force exerted on the metal object in an area of strong magnetic field is greater than the force on said object in an area of weaker magnetic field. The magnetic field gradient involves a resultant force that pushes the metallic object in the direction of the decay of the magnetic field.

The electric currents induced in objects depend on the electrical conductivity of the material, their shape and surface, but also on the frequency of the magnetic field. The induced electric currents have the same frequency as that of the applied magnetic field, and a skin effect occurs in the object. The higher the frequency of the alternating magnetic field, the more electric current will flow on the surface of the object.

For fine particles this effect prevents the induced electric current from being canceled by the induced electric current circulating in the opposite surface. By increasing the frequency of the magnetic field, this facilitates the ejection of fine particles because the forces are not attenuated by the cancellation of the induced electric currents.

When a set of objects to be sorted is transported towards the air gap by the conveyor 6 towards the first portion 1, such a swirling electric current is produced in the non-magnetic metallic objects approaching the air gap. A metallic object can thus be ejected in a direction depending on the gradient of the magnetic field.

In addition, gravity, possible friction with air and/or solid objects such as the ejection ramp, and air currents may exert other forces that can slow ejected objects or change their trajectory and must be taken into account for the design of the sorting system. The geometry of the sorting system must then be adapted to the additional forces exerted on the objects, ensuring that the gradient of the magnetic field is close to its maximum value in the ejection zone of the objects, and that the direction of said gradient is oriented in the desired ejection direction. For example, it is possible to adjust the position of the beveled edge of the sorting flap, and, where appropriate, the ejection ramp by optimizing the width of the air gap and the positioning of said ramp relative to the ejection zone in function of the gradient of the magnetic field near the air gap.

The metal objects ejected at the level of the air gap are, where applicable, guided by the ejection ramp towards a metal object recovery system. Non-metallic objects are not ejected at the air gap and can be recovered on the conveyor in a later step.

Sorting facility

Sorting and ejecting small objects, for example with a section of 2mm × 2mm and a thickness of 0.1mm, involves further technical constraints due to air friction. The electromagnetic forces which act on small objects are, below a certain size depending on the weight and geometry of the particles, negligible compared to the friction forces of the air. The weak movement imposed by these electromagnetic forces is therefore not a sufficiently discriminating factor to sort and eject these objects which all follow a more or less random (non-deterministic) movement depending on their density, their coefficient of penetration into the air and random air movements in the sorting area.

In order to sort such small objects, we try to reduce or eliminate air friction. For this purpose, a sorting installation for particles may comprise, with reference to the Figure 6 , a hermetically closed zone 66 and/or under depressurization. This zone 66 is arranged above at least part of the conveyor and the sorting flap. In this hermetic zone 66 and/or under depressurization, air friction is at least partially eliminated, resulting in a free fall movement in a vacuum where all the objects then follow exactly the same trajectory. A strength Even weak electromagnetic radiation is then a discrimination factor and makes it possible to sort objects of all sizes.

Sorting system including several air gaps

One or more air gaps can be adapted to sort objects of different sizes and very different particle sizes.

In some embodiments, with reference to the figures 4 And 5 , several air gaps E2, E3 are formed between the first portion 1 of the core and plates 14. 24 parallel to the beveled edge of the air gap E1.

In other embodiments, with reference to the Figure 9 , the core may comprise several first portions 1a, 1b, 1c and several second portions 2a, 2b, 2c. In this case, an air gap is formed between the first portion 1a and the edge 14 of the magnetic element of the sorting flap, and other air gaps E2b, E3c are formed between the first portions 1b, 1c and the magnetic elements 4b, 4c respective.

In the embodiments comprising additional air gaps E2, E3, E2b, E3c, the passage of the magnetic field in the air is limited for each air gap as described for the air gap E1.

In reference to the Figure 5 , a strong gradient of the magnetic field in the air is located in a respective zone around each air gap. The air gaps E2, E3, E2b, E3c thus each form an additional magnetic barrier opposing the passage of non-magnetic metallic objects.

The purpose of the succession of the first portions 1a, 1b, 1c is to give momentum to the ejected objects when they begin to experience air friction.

In certain embodiments, the air gaps E1, E2, E3 or E1a, E2b, E3c are arranged at a distance of a few centimeters between them. As an illustrative and non-limiting example, the air gaps are arranged at a distance of approximately 5 cm between the middle of each air gap. We thus obtain a succession of electromagnetic forces ensuring a stronger and more constant trajectory. Such an arrangement is useful in order to compensate for the effects of air friction when all the objects to be sorted are small, that is to say whose largest dimension is less than approximately 10 cm.

In other embodiments, several air gaps E1, E2, E3 or E1a, E2b, E3c are arranged at a distance of several tens of centimeters. Such an embodiment makes it possible to create a respective ejection zone for each air gap. Each ejection zone can thus have different settings. Such adjustments make it possible to eject objects of very different size, weight or shape in each ejection zone corresponding to the respective air gaps. Such a configuration can be considered for example when the mixture of objects to be sorted is of a very inhomogeneous composition.

Another embodiment of a sorting system comprises several magnetic circuits arranged in series through which a common means of transport such as a conveyor 6. The spacings and size of said magnetic circuits are defined according to the size and speed of movement of the objects, the density and intensity of the magnetic field.

It is thus possible to create a sorting installation comprising several ejection zones adapted to sort objects according to their shape, size and material. For example, such an installation may include an ejection zone suitable for sorting bulky objects, an ejection zone making it possible to sort stainless steel objects, and an ejection zone making it possible to sort small or large objects. other objects with distinct properties.

Advantageously, the installation further comprises a system for sorting magnetic objects comprising magnets, arranged upstream of the sorting system according to the invention, in order to evacuate the magnetic objects before the mixture of objects passes through the sorting system.

In some embodiments, the sorting flap may be energized by an alternating current source to form an active part of the magnetic system. In this case, the alternating current source is synchronous with the current source supplying the windings and oriented in the same direction.

REFERENCES

• FR 2116430
• WO2017/044863

Claims (18)

Sorting system by magnetic separation of metal objects, comprising: • an electromagnetic core comprising: ∘ at least a first portion (1) comprising a winding (11), ∘ a second portion (2), the second portion being wider than the first portion, ∘ and a bottom (3) connecting the first portion to the second portion, • a sorting flap arranged opposite said electromagnetic core so as to provide, between the sorting flap and the electromagnetic core, a circulation space for a conveyor (6) of objects to be sorted from the first portion (1) towards the second portion (2), said sorting system being characterized in that the sorting flap comprises a magnetic element (4) arranged so as to form an air gap (E1) between the first portion and the sorting flap, said air gap forming a magnetic barrier opposing the passage of non-magnetic metallic objects, so that said non-magnetic metallic objects are ejected from the conveyor (6), the second portion being arranged between the bottom and a portion of the magnetic element of the sorting flap opposite the air gap to ensure a return of the magnetic field lines towards the first portion. System according to claim 1, in which the magnetic element (4) of the sorting flap extends parallel to the conveyor (6). System according to one of the preceding claims, in which the magnetic element (4) of the sorting flap is in the form of a flat plate. System according to one of the preceding claims, in which the sorting flap comprises at least one non-magnetic portion (54). System according to one of the preceding claims, in which the magnetic element has an edge (14) arranged opposite the first portion (1) in a direction transverse to the conveyor (6), said edge (14) being beveled so to form an inclined plane oriented in the direction of circulation of the conveyor away from the electromagnetic core. System according to claim 5, in which the sorting flap further comprises at least one magnetic plate (24, 34) parallel to the beveled edge (14) of the magnetic element, each plate being arranged facing the first portion (1 ) to form a respective air gap (E2, E3) forming an additional magnetic barrier opposing the passage of non-magnetic metallic objects. System according to one of claims 5 or 6 in combination with claim 4, in which the non-magnetic portion of the sorting flap comprises an ejection ramp (54) for non-magnetic metallic objects extending on the magnetic element of the side opposite the electromagnetic core, said ejection ramp being coplanar with the beveled edge of the magnetic element. System according to one of claims 5 to 7, in which the beveled edge (14) of the magnetic element is set back relative to a central region (10) of the first portion (1) in the direction of circulation of the conveyor (6). System according to one of the preceding claims, in which the second portion comprises a winding and the number of turns of the winding on the first portion is greater than the number of turns of the winding on the second portion. System according to one of the preceding claims, in which the surface (10) of the at least one first portion opposite the bottom has at least one chamfer (17a, 17b) along the air gap. System according to one of the preceding claims comprising one or more magnetic parts (9) arranged between the magnetic element of the sorting flap and the second portion of the electromagnetic core to guide the magnetic field in these magnetic parts and thus minimize the path of the lines magnetic field in the air between the sorting flap and the second portion. System according to one of the preceding claims, in which the at least one first portion (1) and the second portion (2) are made of ferrite. System according to one of the preceding claims, in which the magnetic element (4) of the sorting flap is made of ferrite. Installation for sorting a set of objects containing metal objects, comprising ∘ a sorting system according to one of the preceding claims, and ∘ a conveyor (6) adapted to transport the set of objects towards the sorting system, said conveyor being arranged so as to cross the sorting system between the electromagnetic core and the sorting flap, the magnetic barrier formed by an air gap (E1) between the first portion of the electromagnetic core and the sorting flap being adapted to eject non-magnetic metallic objects, and ∘ a recovery system designed to recover ejected non-magnetic metal objects. Installation according to claim 14, in which the conveyor (6) is a conveyor belt or a slide. Installation according to one of claims 14 or 15 further comprising a hermetic zone (66) arranged above at least the conveyor and the sorting flap, and a depressurization device arranged so as to create, in said zone, an air movement adapted to orient the non-magnetic metallic objects ejected by the magnetic sorting system in a defined direction. Installation according to one of claims 14 to 16, comprising a cooling system for the electromagnetic core. Process for sorting metal objects, comprising ∘ the transport of a set of metal objects in an installation according to one of claims 14 to 17, ∘ the ejection of non-magnetic metallic objects by the magnetic barrier, ∘ the passage of non-metallic objects in the air gap between the first portion (1) of the electromagnetic core and the sorting flap.

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