SYSTEM FOR SORTING METAL ITEMS

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a system for sorting metal objects. STATE OF THE ART

[0002] Magnetic objects, such as iron, steel, and some magnetic stainless steel alloys, can be easily extracted with static magnetic fields and then recycled.

[0003] The sorting and recovery of non-magnetic metallic objects is carried out using an alternating magnetic field, producing induced electric currents in the objects, which are electrically conductive. These induced currents interact with the surrounding magnetic field to generate 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.

[0004] One solution used today to create an alternating magnetic field is the pole wheel. This solution involves rotating a pole wheel made of alternating permanent magnets. The alternating polarity of the rotating magnets creates a variable magnetic field that can reach several Tesla. Non-magnetic objects that conduct electricity are drawn into this rotating variable magnetic field and are accelerated relative to objects that do not conduct electricity.

[0005] Such a system is described in 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 allow the sorting of insufficiently electrically conductive and too dense materials such as non-magnetic stainless steel and has difficulty sorting highly conductive and too dense materials such as copper. It also presents significant reliability and safety problems, particularly in the event of an emergency stop, due to the inertia of the massive pole wheel.

[0006] Another solution is to use a mat passing over the air gap of an electromagnet powered by an alternating electric current. Such a system is described in document WO2017 / 044863. The principle is to use the vortex electric currents induced in objects in the presence of the inhomogeneous alternating magnetic field to create electromagnetic forces whose direction is the gradient of the magnetic field.

[0007] Magnetic energy E mag of the system amounts to E mag = 1 2 * H B V

[0008] 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 then the generation of this magnetic energy at each operating period, that is to say approximately 20,000 to 100,000 times per second.

[0009] This system therefore requires very high reactive power to create the magnetic field at the air gap, particularly for large air gaps which are not delimited.

[0010] 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 area is also small and therefore it does not allow for sorting large volumes of objects, nor objects of very different sizes. However, to achieve 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.

[0011] None of these devices take into account air friction, which is in fact negligible for large objects but is predominant for small particles, particularly during falling or bouncing phases, which are typically present during sorting by an alternating magnetic field. Air friction will influence the resultant of the forces experienced by the objects. STATEMENT OF THE INVENTION

[0012] An aim of the invention is to propose a device for sorting by magnetic separation of non-magnetic metal 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 made of materials having very high electrical conductivity, such as copper, or very low electrical conductivity, such as non-magnetic stainless steel.

[0013] To this end, the invention proposes a system for sorting by magnetic separation of metallic 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.

[0014] Such a geometry allows for optimized magnetic field distribution for the ejection of non-magnetic metal objects. In addition, the sorting system is very responsive, especially in the event of an emergency stop, and thus offers advantages in terms of reliability and safety.

[0015] Preferably, the magnetic element of the sorting flap extends parallel to the conveyor.

[0016] Advantageously, the magnetic element of the sorting shutter is in the form of a flat plate.

[0017] Advantageously, the sorting flap comprises at least one non-magnetic portion.

[0018] In some embodiments, the magnetic element has an edge arranged opposite 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 away from 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.

[0019] Preferably, the non-magnetic portion of the sorting flap comprises an ejection ramp for non-magnetic metal objects extending over the magnetic element on the side opposite the electromagnetic core, said ejection ramp being coplanar with the beveled edge of the magnetic element.

[0020] Advantageously, the beveled edge of the magnetic element is set back from a central region of the first portion in the direction of travel of the conveyor.

[0021] 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.

[0022] The surface of the at least one first portion opposite the bottom may have at least one chamfer along the air gap.

[0023] Preferably, the sorting system comprises one or more magnetic pieces 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 pieces and thus minimize the path of the magnetic field lines in the air between the sorting flap and the second portion.

[0024] 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.

[0025] 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 the non-magnetic metallic objects, and ∘ a recovery system arranged to recover the ejected non-magnetic metallic objects.

[0026] Preferably, the conveyor is a conveyor belt or a slide.

[0027] Advantageously, the sorting installation further comprises a sealed zone 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 suitable for orienting the non-magnetic metallic objects ejected by the magnetic sorting system in a defined direction.

[0028] In some embodiments, the sorting facility includes an electromagnetic core cooling system.

[0029] The invention also relates to a method for sorting metal objects, comprising ∘ the transport of a set of metallic 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

[0030] 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. figure 2 illustrates a wide-width ejection system for sorting large quantities of objects. figure 3 is a schematic view of the magnetic field lines in a waste sorting system according to the invention. The figure 4 illustrates a sorting system 4 comprising several plates parallel to the beveled surface of the shutter. The 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 shutter. The figure 6is a schematic sectional view of a sorting installation including a partial vacuum system. The figure 7 illustrates a waste sorting system comprising windings on both portions and a means of closing the magnetic circuit. The figure 8 illustrates a waste sorting system comprising coils on both portions, several plates parallel to the beveled surface of the shutter, and a means of closing the magnetic circuit. The figure 9 illustrates a sorting system with multiple sorting panels. DETAILED DESCRIPTION OF EMBODIMENTS System Overview

[0031] THE Figures 1 and 2 illustrate a system for sorting by magnetic separation of non-magnetic metallic objects according to the invention.

[0032] The system can be used to recover, for example, metal objects from waste such as metals in household or industrial waste and shredded products for recycling such as windows, wooden pallets, cables or glass. Another application is the processing of food grains or pharmaceutical powders, which may contain unwanted non-ferrous conductive metals that need to be removed.

[0033] The size of said objects can vary greatly depending on the application. The size of the objects (understood as their largest dimension) can range from 0.1 mm to 10 cm in at least two directions.

[0034] 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 essentially parallelepiped in shape, assembled in a U. In certain embodiments, the portions 1 and 2 and / or the bottom may be curved and / or inclined, thus forming a core whose section may be, in an illustrative and non-limiting manner, circular or triangular in shape.

[0035] 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 conductive wire. Preferably, the winding is made of copper wire comprising electrical insulation, or of copper tube. The number of turns and amperes of the winding, also called 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.

[0036] Advantageously, the electromagnetic core further comprises a cooling system. Such a cooling system may, by way of illustration and without limitation, comprise a cooling plate, a heat sink or an inflatable seal filled with a cooling liquid, for example water.

[0037] 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 an area close to the upper face 20 of the second portion 2.

[0038] Preferably, the magnetic element 4 of the sorting flap is made of soft ferrite, a nanocrystalline magnetic composite or a compressed iron powder with an electrical insulator. The sorting flap may further comprise one or more non-magnetic portions 54.

[0039] Advantageously, the magnetic element 4 of the sorting flap is in the form of a flat plate extending from the air gap E1 to an area close to the upper face 20 of the second portion 2.

[0040] The magnetic part of the sorting flap and the core thus form a magnetic circuit comprising a space for the circulation of objects to be sorted between the sorting flap and the core. This defines an entry zone for the 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.

[0041] The transport of objects between the input zone and the output zone is carried out by a conveyor 6 passing through said circulation space. The conveyor may comprise 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.

[0042] Alternatively, the conveyor can be a slide or any other means of transporting objects. Magnetic circuit

[0043] The magnetic element of the sorting flap 4 has an edge 14 arranged opposite 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.

[0044] In some 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 forward or backward in the direction of travel of the conveyor 6.

[0045] 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 may be higher in certain embodiments.

[0046] The non-magnetic portion of the sorting flap may comprise 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.

[0047] When the edge 14 is beveled forming an inclined plane, the ejection ramp may be coplanar with the beveled edge of the magnetic element or offset in one direction in the direction of circulation of the objects or be offset in the opposite direction to the direction of circulation of the 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.

[0048] Advantageously, the core is made of a material that conducts a magnetic field and is sufficiently low in electrical conductivity to avoid induction heating. Preferably, the core is made of a material with a high magnetic field saturation value (greater than 300 mT) and low magnetic losses (hysteresis cycle and induced electric current) at the frequency of the alternating electric current applied to the windings in order to produce a high magnetic field density inside the core.

[0049] For example, the magnetic core may be made of a material having a relative magnetic permeability value µ r of between 10 and 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 may for example be made of a nanocrystalline magnetic composite or of compressed iron powder with an electrical insulator. Such materials are for example marketed under the names MPP, 3F3, 3c90, Nanodust ™ < KAM or Nanodust ™ < KAH.

[0050] Preferably, the magnetic portion of the sorting flap and, if applicable, each plate 24, 34 is made of soft ferrite, a nanocrystalline magnetic composite or a compressed iron powder with an electrical insulator, as described for the magnetic core. The plates 24, 34 and the magnetic element 4 of the sorting flap may be made of the same material or different materials.

[0051] 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 the 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.

[0052] Said air gap E1 then forms an immaterial magnetic barrier, preventing the passage of metallic objects, including in particular non-magnetic metallic objects.

[0053] Preferably, the surface area of ​​the first portion 1 opposite 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 in proximity to the air gap E1.

[0054] The surface 10 of the first portion opposite the bottom may comprise one or more chamfers 17a, 17b arranged on the angles between the surface 10 and the faces of the coil carrier. Said chamfers extend along the air gap and make it possible to reduce the surface of the first portion opposite the sorting flap and thus increase the concentration of the magnetic field around the air gaps E1. Such chamfers also prevent saturation of the magnetic element in the edges of the first portion 1.

[0055] The magnetic element of the sorting flap extends to an area 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 in proximity to the air gap E1 for a given power.

[0056] 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 the ramp from bending under the effect of this attractive force.

[0057] The second portion 2 ensures a return of the magnetic field lines towards the first portion 1. It preferably comprises a wide surface in order to distribute the magnetic field in a uniform and weak manner, 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.

[0058] 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. Furthermore, the geometry of the magnetic parts 9 allows the passage of the conveyor, and non-ejected objects transported on the conveyor under the flap.

[0059] The system parameters are chosen with the aim of reducing the reluctance R of the magnetic circuit, i.e. the ratio of the length l of the magnetic circuit and the product of the permeability µ and the surface S: R = l μ ∗ S

[0060] 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.

[0061] 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 zones, the surface S is the section in which the lines of the magnetic field pass. Said surface S corresponds to the upper surfaces of the first portion 1 and the second portion 2 arranged opposite the sorting flap.

[0062] In the first zone, the length l corresponds to the sum of the lengths of the first portion 1, the bottom, the second portion 2 and, where applicable, the plates 23, 24 and / or the magnetic parts 9 in the direction of the magnetic field lines. In the second zone, the length is the length of the sorting flap.

[0063] In the third zone, the length l corresponds to the width of the air gap. In the fourth zone, the length lis 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.

[0064] The magnetic permeability of the material µ is expressed by the product of the vacuum permeability µ 0 and the relative permeability µ r: μ = μ 0 * μ r µ 0 is a universal constant, the magnetic constant (or vacuum magnetic permeability), 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 higher the magnetic permeability of an element, the lower the reluctance in this element. However, a higher relative magnetic permeability would cause the saturation value in the magnetic field to drop too much and would involve a loss of energy leading to significant heating.

[0065] The number of ampere-turns that sizes the magnetic circuit is given by Hopkinson's law: F = N . I = R . φ 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.

[0066] 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 S and magnetic permeability µ of the four respective zones Rtotale = R 1 + R 2 + R 3 + R 4 Or R 1 is the magnetic reluctance of the magnetic core, R 2 is the magnetic reluctance of the magnetic element of the sorting shutter, R 3 is the reluctance of the ejection zone, and R 4 the reluctance in the return or loop zone of the magnetic field.

[0067] Among these four zones, the third zone and fourth zone concern a magnetic field in the air.

[0068] Due to the high relative magnetic permeability, typically between about 10 and 100, in the magnetic circuit, the reluctance in this circuit is small and can be neglected compared to the reluctance in the third and fourth zones in which the magnetic field is in air.

[0069] The previous equation can therefore be simplified: Rtotale = R 3 + R 4

[0070] We therefore seek to shorten the length of the field in these areas in the air, by bringing the air gap as close as possible to the upper surface of the second portion 2.

[0071] Reluctance R 3 of the ejection area is linked to the geometry of the system and can hardly be modified.

[0072] Concerning the fourth return zone or loop 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.

[0073] One possibility to reduce the reluctance on the return path (looping) is to add magnetic parts 9 on the air gap, for example rollers, possibly discontinuous, which allow both to guide the magnetic field in a path with high magnetic permeability. In addition, these parts 9 can perform a mechanical movement facilitating the passage of non-conductive and non-ejected elements.

[0074] Limiting the magnetic field in the air and optimizing the passage of the magnetic field through magnetic elements of the system helps to reduce the required reactive power.

[0075] The core geometry takes into account the magnetic field in order to obtain a magnetic field zone that is most concentrated in the ejection zone of the metallic objects. This avoids right angles, particularly around the ejection zone, in order to avoid saturation of the magnetic field in these angles. Application of a magnetic field

[0076] 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 shutter, and the air gap E1. Such an electric current typically has an intensity of approximately 2400 A.turns, distributed for example over 20 turns at 120 A 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 air gap E1. 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.

[0077] The frequency is chosen based on the size and size distribution of the objects to be sorted. It typically ranges from 20 to 35 kHz and can go up to 150 kHz. Generally, higher frequencies are used when the objects to be sorted are smaller, and lower frequencies for larger objects to be sorted. However, a high frequency implies significant heating and electrical losses. Inductance and capacitance will therefore be taken into account to determine the operating frequency. Sorting process

[0078] When a non-magnetic metallic object is placed in a unidirectional magnetic field on one axis whose value increases on a second axis perpendicular to the first axis, swirling electric currents within the object are induced. The interaction of these 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 metallic object in an area of ​​strong magnetic field is greater than the force on the object in an area of ​​weaker magnetic field. The magnetic field gradient involves a resultant of the forces that pushes the metallic object in the direction of decreasing magnetic field.

[0079] The electric currents induced in objects depend on the electrical conductivity of the material, their shape and surface area, and also on the frequency of the magnetic field. Induced electric currents have the same frequency as the applied magnetic field, and a skin effect occurs within the object. The higher the frequency of the alternating magnetic field, the more electric current will flow along the surface of the object.

[0080] For fine particles, this effect prevents the induced electric current from being canceled by the induced electric current flowing in the opposite surface. Increasing the frequency of the magnetic field thus facilitates the ejection of fine particles because the forces are not attenuated by the cancellation of the induced electric currents.

[0081] When a set of objects to be sorted is transported to the air gap by the conveyor 6 towards the first portion 1, such a swirling electric current occurs in the non-magnetic metal objects approaching the air gap. A metal object can thus be ejected in a direction depending on the gradient of the magnetic field.

[0082] 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 down the 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 direction for ejection. For example, the position of the beveled edge of the sorting flap, and, if applicable, the ejection ramp, can be adjusted by optimizing the width of the air gap and the positioning of said ramp relative to the ejection zone according to the gradient of the magnetic field near the air gap.

[0083] Metal objects ejected at the air gap are, if necessary, guided by the ejection ramp to a metal object recovery system. Non-metallic objects are not ejected at the air gap and can be recovered from the conveyor in a later step. Sorting facility

[0084] Sorting and ejecting small objects, for example with a cross-section of 2mm × 2mm and a thickness of 0.1mm, involves other technical constraints due to air friction. The electromagnetic forces acting on small objects are, below a certain size depending on the weight and geometry of the particles, negligible compared to the air friction forces. The weak movement imposed by these electromagnetic forces is therefore not a sufficiently discriminating factor for sorting and ejecting these objects which all follow a more or less random (non-deterministic) movement depending on their density, their air penetration coefficient and the random air movements in the sorting area.

[0085] In order to sort such small objects, we therefore 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 sealed and / or depressurized zone 66. This zone 66 is arranged above at least a portion of the conveyor and the sorting flap. In this hermetically sealed and / or depressurized zone 66, 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. Even a weak electromagnetic force is then a discrimination factor and makes it possible to sort objects of all sizes. Sorting system comprising several air gaps

[0086] One or more air gaps can be adapted to sort objects of different sizes and very different grain sizes.

[0087] In some embodiments, with reference to 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.

[0088] 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 respective magnetic elements 4b, 4c.

[0089] In 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.

[0090] 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.

[0091] The succession of the first portions 1a, 1b, 1c aims to give momentum to the ejected objects when they begin to experience air friction.

[0092] 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. This produces 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 of small dimensions, that is to say, the largest dimension of which is less than approximately 10 cm.

[0093] 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 settings make it possible to eject objects of very different size, weight or shape into each ejection zone corresponding to the respective air gaps. Such a configuration can be envisaged for example when the mixture of objects to be sorted is of a very inhomogeneous composition.

[0094] 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 passes. The spacings and the size of said magnetic circuits are defined according to the size and speed of movement of the objects, the density and the intensity of the magnetic field.

[0095] 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 comprise an ejection zone adapted to sort bulky objects, an ejection zone for sorting stainless steel objects, and an ejection zone for sorting small objects or other objects with distinct properties.

[0096] 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 remove the magnetic objects before the mixture of objects passes into the sorting system.

[0097] 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

[0098] FR 2116430 WO2017 / 044863

Claims

1. System for sorting metal objects by magnetic separation, comprising : • an electromagnetic core comprising : ∘ at least one first portion(1) comprising a winding (11), ∘ a second portion (2), the second portion being wider than the first portion, ∘ and a base (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) to the second portion (2), said sorting system being characterized in that the sorting flap comprises a magnetic element (4) arranged 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 metal objects, so that said non-magnetic metal 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.

2. A system as claimed in claim 1, in which the magnetic element (4) of the sorting flap extends parallel to the conveyor (6).

3. 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.

4. A system according to one of the preceding claims, in which the sorting flap comprises at least one non-magnetic portion (54).

5. 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 bevelled so as to form an inclined plane oriented in the direction of conveyor travel away from the electromagnetic core.

6. A system according to claim 5, in which the sorting flap further comprises at least one magnetic plate (24, 34) parallel to the bevelled edge (14) of the magnetic element, each plate being arranged opposite the first portion (1) to form a respective air gap (E2, E3) forming an additional magnetic barrier opposing the passage of non-magnetic metal objects.

7. System according to one of claims 5 or 6 in combination with claim 4, wherein the non-magnetic portion of the sorting flap comprises an ejection ramp (54) for non-magnetic metal objects extending over the magnetic element on the side opposite the electromagnetic core, said ejection ramp being coplanar with the bevelled edge of the magnetic element.

8. System according to one of claims 5 to 7, in which the bevelled edge (14) of the magnetic element is set back from a central region (10) of the first portion (1) in the direction of travel of the conveyor (6).

9. A 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.

10. 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.

11. A 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 magnetic field lines in the air between the sorting flap and the second portion.

12. 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.

13. System according to one of the preceding claims, in which the magnetic element (4) of the sorting flap is made of ferrite.

14. Equipment 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 to pass through the sorting system between the electromagnetic core and the sorting flap, the magnetic barrier formed by the air gap (E1) between the first portion of the electromagnetic core and the sorting flap being adapted to eject non-magnetic metal objects, and ∘ a recovery system designed to recover ejected non-magnetic metal objects.

15. Equipment according to claim 14, in which the conveyor (6) is a conveyor belt or slide.

16. Equipment 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 to create, in said zone, an air movement adapted to orientate the non-magnetic metal objects ejected by the magnetic sorting system in a defined direction.

17. Equipment according to one of claims 14 to 16, comprising an electromagnetic core cooling system.

18. Process for sorting metal objects, comprising ∘ transporting a set of metal objects in an equipment according to one of claims 14 to 17, ∘ ejection of non-magnetic metal objects through 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.