WO2019070539A1

WO2019070539A1 - High-throughput electrodynamic sorter

Info

Publication number: WO2019070539A1
Application number: PCT/US2018/053602
Authority: WO
Inventors: James R. NAGEL; David COHRS; Raj Rajamani
Original assignee: University Of Utah Research Foundation
Priority date: 2017-10-05
Filing date: 2018-09-28
Publication date: 2019-04-11

Abstract

An electrodynamic sorting assembly (100, 200) with an embedded magnetic core (104) is disclosed. The core (104) is excited by a high- frequency electrical current to produce a time-varying magnetic field (107) above a small gap (106) of air. When a conductive particle passes through the magnetic field (107), electrical eddy currents are induced throughout the volume resulting in a repulsive force away from the gap (106). The ensuing trajectories (109a, 109b) can vary as a function of electrical conductivity, mass density, and physical geometry, thereby providing mechanisms for rapid sorting in accordance with such properties. The magnetic core (104) is specifically oriented upright against gravity so that particles pass over the top of the gap (106) rather than feed directly into it. Multiple magnets may also be coupled together in parallel for increased throughput.

Description

HIGH-THROUGHPUT ELECTRODY AMIC SORTER

GOVERNMENT SUPPORT

[0001] This invention was made with government support under Grant DE- AR0000411 awarded by the Department of Energy. The government has certain rights in the invention.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of and priority to United States Provisional Application No. 62/568,403, filed October 5, 2017, titled "High-Throughput

Electrodynamic Sorter," the entirety of which is incorporated herein by this reference.

FIELD OF THE INVENTION

[0003] The invention relates to magnetic separation. In particular, the invention relates to eddy current separation.

BACKGROUND

[0004] There are many occasions in scientific and industrial applications where materials need to be sorted. For example, the food industry may wish to purify grain products by removing stray particles of metal that accumulate during the grinding process. In the scrap recycling industry, mixed metal streams (e.g., aluminum, zinc, and copper) accumulate in large quantities and need to be separated according to their basic elemental components. Mixed metal alloys (e.g., Al-6063 and Al-380) are also common products that potentially increase in value when separated from other similar alloys.

[0005] For many applications, separation relies on the inherent magnetic properties of the material being separated. For example, magnetic separation is a process that uses permanent magnets to extract ferromagnetic materials from nonmagnetic metals and other nonmetallic fluff. In a related process called eddy current separation (ECS), the motion of a permanent magnet is used to induce electrical eddy currents throughout the volume of a conductive particle. Those currents then react to the applied magnetic field by forcibly dragging the particle along the direction of motion. ECS can be very effective, for example, at removing conductive, nonmagnetic metals from other nonmetallic fluff.

[0006] To separate nonmagnetic metals even further down to their elemental components, scrap recyclers will often utilize an array of technologies. For example, density separation is a common technique that relies on Earth's gravity to sort metals according to their inherent mass density. This can be quite effective at separating relatively low-density metals like aluminum (2.72 g/cm³) from high-density metals like copper (8.96 g/cm³). Other technologies may employ arrays of sensitive metal detectors followed by pneumatic j ets to shoot them away from other nonmetallic fluff This can be an effective method for extracting small, awkward bits of metal that traditional ECS tends to miss. Some systems may perform a direct analysis of elemental composition through X-ray fluorescence (XRF). Such a system may be well-suited for identifying various alloys of aluminum and then sorting them accordingly. Even hand-sorting can be a viable option in some circumstances.

[0007] Despite the vast array of available technologies to choose from, most processes suffer from inherent limitations on their sorting capabilities. For example, ECS tends to struggle when operating on very small particles (e.g., 1.0 cm and below).

Density separation cannot differentiate between metals of similar mass density (e.g., copper, zinc, nickel, and tin). XRF -based methods have limited throughput since each particle must be analyzed and sorted individually. Hand sorting cannot easily distinguish between particles of similar color (e.g., aluminum and zinc), nor can it effectively meet throughput needs on very small geometries (e.g., 1.0 cm and below).

[0008] One recent development that avoids many such problems is a process known as electrodynamic sorting (EDX). Like eddy current separation, EDX relies on a time- varying magnetic field to induce forces in conductive particles. However, rather than utilize the motion of heavy, permanent magnets, EDX excites a stationary electromagnet with an alternating electrical current. As particles pass through the magnetic field, induced eddy currents cause marked deflections in accordance with such properties as conductivity, density, and even geometry.

[0009] The advantages offered by EDX technology are numerous. Because the system relies on alternating electrical current rather than a rotating drum of permanent magnets, EDX can generate much higher frequencies of magnetic excitation. While ECS is generally limited to the range of 1.0 kHz and below, EDX can reach as high as 50 kHz and beyond. Such high frequencies allow EDX to act on particles down to 1.0 mm and below in length. The tunability of frequency also allows metals to be sorted by either density or conductivity, thereby filling two niches with the same machine. The solid- state nature of the electromagnet further improves reliability due to the removal of fast- moving mechanical parts. SUMMARY

[0010] While EDX provides numerous advantages over conventional ECS, conventional systems suffer from at least three potential limitations. A first limitation stems from the gapped nature of the magnetic toroid that introduces a bottleneck through which material must be fed. This tends to place heavy limitations on throughput, thereby preventing EDX from processing on the scale required by modem industrial recycling (typically many tons per hour). A second limitation arises from the geometry of scrap material itself, which often manifests as thin, flaky particles. When fed into a gapped magnetic toroid, flaky particles tend to orient themselves along the minimum cross- sectional area with respect to the applied magnetic field. This reduces the deflection forces experienced by such particles, thereby lowering the effectiveness of EDX as a sorting process. A third limitation arises when magnetic particles accidentally enter the magnetic gap and disrupt operation of the system. While conductive, nonmagnetic particles tend to repel away from the applied magnetic field, magnetic particles (most notably steel and iron) may instead get pulled directly in. This can cause numerous problems for the drive electronics and overall consistency of an EDX system.

[0011] Described herein are embodiments of an EDX process that provides throughput on the scale required by typical scrap recycling facilities (e.g., 1-5 tons per hour). In certain embodiments, the process can also function on the thin particle geometries prevalent in scrap material streams. The embodiment can furthermore, in certain embodiments, be robust against clogging by magnetic particles that attract towards the magnet rather than repel away.

[0012] At least one embodiment relates to an electrodynamic sorting system with high throughput, improved reliability, and greater sorting efficiency. A magnetic core is wound with insulated conductive wire (e.g., copper) and excited by an alternating electric current. The core is open at one end to create an air gap for magnetic field to propagate into the surrounding space. The core geometry may, for example, be shaped somewhat like the letter "U" and oriented in an upright posture. A thin, non-conducting plate may be placed over the gap of the magnet while a suitably-paced conveyor belt feeds material over the top. As material passes through the magnetic field, electrical eddy currents are induced in conductive particles. Depending on the frequency and magnitude of the applied magnetic field, particles will accelerate with varying intensities in accordance with their electrical conductivity, mass density, and physical geometry. Particles with large mass density, low electrical conductivity, improper geometry, or some combination thereof, tend to pass through the magnetic field without significant reaction and thus follow a free-falling kinematic traj ectory. Particles with very low mass density, high electrical conductivity, ideal geometry, or some combination thereof, are deflected strongly in the magnetic field and follow an altered kinematic traj ectory. With the appropriate placement of a mechanical splitter, particles are sorted into distinct collection bins.

[0013] An upright orientation of the magnetic core provides one or more benefits. One benefit is that flattened particle geometries tend to naturally orient themselves along maximum cross-sectional exposure to the applied magnetic field. This causes flat particles to deflect much more intensely than could otherwise be achieved by dropping them directly through the gap as in conventional EDX processes.

[0014] Another advantage is the improvement in throughput it provides. When feeding particles directly into a gap, as in conventional EDX processes, the gap width places an upper limit to how much material can be processed over a given time interval. If the gap is oriented upright and rotated, the throughput is instead determined by the thickness of the magnetic core, which can more readily be designed according to desired size parameters. The nature of the configuration further allows several magnets to stack together in parallel with relative ease, thereby greatly improving scalability of the system. The separation process also tends to function more efficiently with a conveyor belt as in certain embodiments described herein, as opposed to relatively slower conveyance systems in conventional EDX processes. The disclosed systems can thus increase throughput even further.

[0015] Yet another advantage can be improved effectiveness of the sorting process itself. By orienting the magnet upright and passing particles over the top of the magnet, particles must overcome the force of gravity before any physical deflection actually occurs. This introduces a nonlinear threshold effect wherein particles essentially do nothing significant until the magnetic repulsion exceeds the gravitational weight. In contrast, a free-falling particle that passes through an EDX magnet, as in conventional EDX systems, will always experience some net acceleration in direct proportion to the force applied.

[0016] In a second embodiment, the magnetic core is embedded directly within the conveyor belt assembly. A low-friction buffer plate (such as a fluoropolymer or other known low-friction material known in the art) is then placed between the top of the magnet and the underside of the conveyor belt. This allows smooth physical contact to occur between the magnet and the belt. Such a configuration is strongly resilient against clogging when exposed to magnetic materials. Any magnetic particles attracted to the gap are simply swept away by the conveyor belt, thus ensuring a smooth, uninterrupted flow of material.

[0017] In a third embodiment, the conveyor belt assembly and magnetic core are tilted (i.e., so that the conveyor tilts downward rather than being horizontal). In so doing, the force of gravity against the particles on the conveyor belt is reduced by the cosine of the tilt angle, thus improving the deflection of high-density metals (e.g., copper, brass, and zinc). It can also be used to offset the backward component of the force vector experienced by material that enters the magnetic field.

[0018] In another embodiment, multiple magnetic cores are placed in parallel to widen the lane width (e.g., to work in conjunction with a wider conveyor belt). To ensure a continuous magnetic field profile over the gaps, flux bridges of magnetic material may be used to connect the gaps together and fill the space between cores. Balancing inductors may also be placed in series with the coil windings to ensure a consistent flow of electrical current across each core.

[0019] In a further embodiment, the gap of the magnetic core is formed with an asymmetric profile. By introducing an asymmetry, the gap may be placed closer to the edge of the conveyor belt and closer to the mechanical splitter. Doing so frees up significant volumes of space for particles to reach the splitter with unobstructed traj ectories.

[0020] In a final embodiment, a cooling system is integrated into the magnetic core assembly. One configuration uses fans to force air across the cores and dissipate heat. Alternatively, or additionally, if air-cooling is not sufficient, the cores may be immersed in a liquid coolant which is circulated to a radiator.

[0021] Other features and aspects of the invention will become apparent by consideration of the following detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a side view representation of an improved electrodynamic sorting (EDX) unit.

[0023] FIG. 2 is a side view representation of another embodiment of an improved EDX unit in which an electromagnet assembly is integrated with a conveyor belt.

[0024] FIG. 3 is a side view representation of portions of an electromagnet assembly. [0025] FIG. 4 is a side view representation of portions of another electromagnet assembly having an asymmetric gap.

[0026] FIG. 5 is a simplified electric circuit for the drive electronics of the electromagnet assembly.

[0027] FIG. 6 is a simplified electric circuit for the drive electronics of another electromagnet assembly.

[0028] FIG. 7 is a side view representation of portions of another electromagnet assembly including balancing inductors.

[0029] FIG. 8 is a perspective view of a parallel assembly of multiple magnetic cores.

[0030] FIG. 9 is a side view representation of an improved EDX unit with a cooling system.

[0031] FIG. 10 is a side view representation of an improved EDX unit with a tilted conveyor belt and electromagnet assembly.

[0032] FIG. 11 is a side view representation of an improved EDX unit with an inclined/slanted conveyor belt and a tilted electromagnet assembly.

[0033] FIG. 12 is a side view representation of an improved EDX unit with a curved/parabolic conveyor belt and a tilted electromagnet assembly. DETAILED DESCRIPTION

[0034] It will be understood that the present disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

[0035] FIG. 1 depicts a side-view for one embodiment of an electrodynamic sorting (EDX) unit 100. The unit includes a feeder 101, such as a vibratory feeder, configured to receive a mixed feedstock of unsorted material 102, a conveyor belt 103, an

electromagnet core 104, wire coils 105 for exciting the core 104, a gap 106 formed in the top of said core, a magnetic field 107 projected above said gap during operation of the core 104, a plate 108 covering the top of said gap, two kinematic trajectories 109a and 109b resulting from operation of the unit 100, a mechanical splitter 110, and two collection bins 111a and 111b. [0036] The initial feedstock of unsorted material 102 is typically categorized into two distinct sets, indicated by the white circles 102a and dark circles 102b.

Differentiation between these sets may be drawn by electrical conductivity, mass density, physical geometry, or any appropriate combination thereof. Example mixtures may include, but are not limited to, specific metal combinations like copper and brass, copper and aluminum, aluminum and zinc, or aluminum and titanium. Other mixtures may even be more loosely defined; for example, metals mixed with nonmetals, aluminum alloys mixed with various non-aluminum metals, or even flaky particles mixed with wires. The goal is to separate 102a from 102b by placing each particle into its corresponding bin.

[0037] The unsorted feedstock 102 is initially fed to the vibratory feeder 101 where it distributes across the width of the conveyor belt 103. As material 102 drops onto the moving conveyor belt 103, it accelerates up to a constant horizontal velocity before passing over the electromagnet core 104. The electromagnet core 104 is simultaneously excited by an alternating electric current through the coils 105, which projects a magnetic field 107 directly above the gap 106. As conductive particles pass through the magnetic field 107, electrical eddy currents are induced throughout their volumes. Particles from the first set 102a are unaffected by or less affected by the magnetic field 107 and subsequently drop along a first trajectory 109a. Particles from the second set 102b are relatively more affected by the magnetic field 107, thereby experiencing a force that propels them up and away from the magnetic gap 106. Deflection by the induced eddy currents causes material to traverse the longer and higher kinematic traj ectory 109b. A mechanical splitter 110 is placed between the two traj ectories for separation into the corresponding bins 1 1 l a and 1 1 lb (or other suitable container and/or additional conveyor belts). The near bin 11 la is commonly referred to as the drop bin, and all materials landing in the drop bin are simply referred to as drops. Likewise, the far bin

1 1 lb is commonly referred to as the throw bin, and all materials landing in the throw bin are referred to as throws.

[0038] With continuing reference to FIG. 1, it will be noted that the mechanical splitter 1 10 includes a suitable adjuster 1 12 that is movable in height, angle, and/or horizontal distance away from the core 104. The conveyor belt 103 is likewise adjustable in horizontal velocity. The alternating current which excites the magnetic core 104 is also adjustable in frequency and amplitude.

[0039] The interface between the magnetic core and the conveyor belt is achieved through the use of a thin, insulating plate 108. The plate 108 is oriented in parallel to the conveyor belt 103 and couples with the edge of the conveyor belt 103 to receive material 102. The plate 108 is ideally made as thin as possible (e.g., less than 3 mm, less than 2 mm, or even more preferably less than 1 mm) to reduce losses in intensity of magnetic field 107 due to distance away from the magnetic gap 106. The plate 108 is also preferably constructed out of an insulating material to avoid any significant excitation of eddy currents within. The plate 108 is further preferably constructed out of a low-friction material (e.g., fluoropolymers) to avoid slowing particles as they slide over the top of the gap.

[0040] FIG. 2 depicts a modified embodiment of another EDX unit 200. Except as noted below, the EDX unit 200 shares many characteristics with the EDX unit 100, and like reference numbers are intended to refer to like components. In this embodiment, rather than place the magnetic core 104 at the end of the conveyor belt 103 and couple it with the thin plate 108, the core 104 is instead embedded directly within a modified conveyor belt assembly 201. Such a configuration may use the addition of two extra belt pulleys 202 or other conveyance components known in the art to properly wrap the belt 103 around the body of the core 104. The core 104 is elevated to very close proximity (or even direct physical contact) with the underside of the conveyor belt 103 in order to reduce distance between the core 104 and unsorted material 102 passing over the core 104. Material 102 then feeds over the top of the gap 106 in a similar manner as described earlier and separates into the desired bins 102a and 102b.

[0041] With continuing reference to FIG. 2, the conveyor belt 103 is ideally constructed as thinly as possible while still maintaining mechanical integrity; for example, 5 mm or less, 3 mm or less, 2 mm or less, or more preferably 1.0 mm or less. The nearest pulley 202 to the magnetic gap 106 is also likely to experience some excitation by the nearby magnetic field 107 and is thus preferably constructed out of low-conductivity /low-permeability material(s). The height of the core 104 is also adjustable for optimal contact with the conveyor belt 103.

[0042] FIG. 3 depicts a side view of the electromagnet assembly 300, which includes the magnetic core 104 and the wire coils 105 (e.g., insulated copper wire) wound around the core 104. As shown, the core 104 includes an open-air gap 106 at the top. The coils 105 are excited with an alternating electric current to induce a corresponding magnetic field 107 directly above the gap 106. Wire bobbins 301 may also be used to efficiently contain the coils 105 around the core 104. [0043] The preferred geometry of the magnetic core 104 is similar to the shape of the letter "U" and is thus referred to as a U-core. The legs of the U are used as mounts for the coils 105 while the top of the U is capped with magnetic tips 302 that converge toward one another and toward the air gap 106. The horizontal base of the U-core need not be coiled with any wire, but may simply serve as a bridge for magnetic flux to flow between the two legs. In some embodiments, the gap 106 is formed by cutting the core 104 to form the gap 106.

[0044] The tips 302 around the gap 106 play an important role in shaping the magnetic field profile 107. Ideally, the tips 302 should project some height (e.g., 1-2 cm) above the coils 105 and then narrow in tip width at the top. The exact dimensions of the tips 302 will have significant impact on several important parameters. In particular, they affect the overall intensity of the magnetic field 107 for a given drive current, the general projection of the field 107 into the space beyond the gap 106, and the overall inductance of the circuit in accordance with the total energy carried by the magnetic field 107 throughout the system. Large-sized particles of scrap metal will generally utilize greater tip width and a larger gap to project the field into a greater volume of space above. Smaller-sized particles will generally utilize smaller tip width and a smaller gap so as to focus the field into a smaller volume of space.

[0045] FIG. 4 shows an embodiment of an electromagnet assembly 400 where the gap 401 is formed with an asymmetric profile. That is, the tips 402 do not form mirror images of each other about a vertical axis extending through the center of the core 104. One purpose of the asymmetry is to place the magnetic field 107 closer to the edge of the conveyor belt 103 (e.g., the right edge of the core 104 as shown in FIG. 4). This is done to open up a greater volume of space for particles to fall into and get separated by the splitter.

[0046] FIG. 5 shows a simplified electric circuit diagram 500 that may be utilized for the drive electronics around the core. The drive voltage source V can be any form of high-power electronic circuit driven by some periodic signal with variable frequency f and variable amplitude. The coiled wires 105 around the magnetic core 104 will manifest as large inductors with two distinct inductances Li and L2. Due to the internal losses of the coils 105 and the core 104, some significant resistances Ri and R2 will also present themselves in series with the inductances Li and L2.

[0047] With continuing reference to FIG. 5, it is noted that the two coils 105 around the core 104 are preferably wired in a parallel configuration. The reason for this configuration is that it reduces the total voltage drop across the coils 105. To illustrate, assume the two coils 105 are identically wound such that Li = L2 = Lo. If the coils 105 are connected in series, then the series inductance between them evaluates to L_s = 2 Lo. Given a peak drive current lo throughout the circuit, the voltage drop VL across the coils satisfies |V_S| = 2nfL_s|Io|. In contrast, if the inductors are connected in parallel, then the parallel inductance L_p across the coils would satisfy L_p = Lo/2, or L_p = L_s/4. To maintain consistent current density, however, the peak drive current must then be doubled to 2Io. The voltage drop V_p across the parallel configuration thus satisfies |V_P| = 2nf(L_s/4)|2Io| = |Vs|/2. Thus, we have reduced the voltage drop by a factor of two at the expense of increasing net current by two as well.

[0048] With continuing reference to FIG. 5, we could theoretically divide the circuit into n parallel segments rather than just two. In such a case, it can be shown that net the voltage drop across the coils also reduces by a factor of 1/n. The trade-off is that total drive current must simultaneously increase by a factor of n in order to maintain consistent current density throughout the cores.

[0049] With continuing reference to FIG. 5, it is further noted that the large inductive reactance of the circuit creates a large impedance against drive voltage when excited at high frequency. A capacitance C is thus inserted in series with the inductors Li and L2 to produce a resonant RLC circuit. The resonant frequency fo of the circuit is then given by

1

o⁼ 2 IZ where L is the equivalent inductance of the parallel configuration. When the circuit is excited at the frequency f = fo, the capacitive reactance cancels out the inductive reactance, thus leaving some real resistance R to impede current flow throughout the coils 105.

[0050] The choice of frequency f depends heavily on particle geometry and the properties by which materials are sorted. In general, larger particles will respond to lower frequencies of excitation while smaller particles may respond to greater frequencies. For example, scrap metals in the order of 1-2 mm in length may respond to frequencies in excess of 50 kHz to sort effectively. In contrast, scrap metals on the order of 20-40 mm may need as little as only 1.0 kHz. Excitation at either extreme is generally limited only by the quality of electronic drive circuitry and power dissipation. [0051] To further increase throughput of the EDX system, it is often desirable to connect many cores in parallel. However, even if all coils are wound with perfect consistency, there is still no guarantee that the inductances will be identical. For example, parasitic coupling to any nearby metallic objects can slightly vary the inductance of a given coil. This is generally undesirable, as it causes some of the coils to draw more current than the others and produce inconsistent magnetic fields across the gaps.

[0052] One way to enhance consistency is to deliberately add or subtract a small amount of inductance at the end of each coil until impedance is balanced at resonance. FIG. 6 depicts the schematic representation of such an embodiment. The variable inductors L3 and L4 are placed in series with the main coil inductances Li and L2.

Inductance may then be added or subtracted as to balance the total series inductance along each coil.

[0053] FIG. 7 shows one example of an electromagnet assembly embodiment 700 that utilizes balancing inductors L3 and L4 around the magnetic assembly 300. A small toroid 701 of magnetic material is wound with an extra length of copper wire 702 extending from the wire coils 105. Adjustments to the inductance may then be achieved by either adding or subtracting turns from the windings around the small toroid 701. Smaller loop areas in the toroid 701 allow for finer adjustments in inductance but may also use more turns to reach a desired outcome. The array of balancing inductors can then repeat indefinitely to as many coils as desired.

[0054] FIG. 8 depicts a parallel assembly 800 of two magnetic cores 801a and 801b. The legs of each core are wound independently with coils of wire in a parallel configuration and balanced accordingly. If desired, the partem may continue to any suitable number of parallel cores for further increases in lane width and throughput. To maintain continuity across the top of the assembly 800, small flux bridges 802 and 803 of magnetic material may be inserted between the cores 801a and 801b. Adding the flux bridges has the desired effect of creating an uninterrupted projection of magnetic field 107 over the parallel assembly 800. The flux bridges 802 and/or 803 may be attached to the magnetic cores 801a and 801b or may be integrally formed with the cores 801a and 801b as a result of the particular manufacturing process used to form the cores.

[0055] With continuing reference to FIG. 8, also shown is a cross-sectional view of the flux bridges 802 and 803 attached between the cores 801a and 801b. The top flux bridges 802 around the gap are cut with a conformal geometry and extend just down to the top of the wire coils 105. The bottom flux bridge 803 is likewise cut to a conformal shape with the base of the core and extends up to the bottom of the wire coils 105. The flux bridges 802 and 803 may be bonded to the cores 801 a and 801b using a strong, nonconductive adhesive (e.g., epoxy). The space between the flux bridges 802 is kept as small as possible (e.g., less than 1.0 cm), allowing just enough space for the wire coils 105 that carry electrical current.

[0056] When operating an electromagnet at high frequency and high current, it is common for a significant amount of power to dissipate in the form of heat. The two primary sources of this heat are the magnetic core 104 and the coil wiring 105. If the core 104 is constructed out of an electrically conductive material, eddy currents tend to build up inside the core and generate heat in the form of Ohmic losses. The wiring used in the coils 105 is also subject to some Ohmic loss, which may be significant at the large values of current typically used by an EDX system. In both cases, the problem is often exacerbated by the high frequencies of excitation which only further increase Ohmic losses.

[0057] To help mitigate heating within the core 104, it may be desirable to choose a material that has low electrical conductivity with relatively high magnetic permeability. Some materials that satisfy this requirement are NiZn ferrites and MnZn ferrites.

Unfortunately, the magnetic saturation of such materials is often somewhat limited (300- 600 mT, typically), thereby forcing a tradeoff between electrical conductivity and magnetic saturation. For example, many forms of electrical steel have magnetic saturation as high as 2.0 T. However, such materials might also possess a relatively high conductivity (1.0 MS/m typically). For this reason, it is common to slice the electrical steel magnets into thin laminations, thereby limiting the amount of self-induced eddy currents that may flow.

[0058] Even with various countermeasures in place, it is still common for thermal heating to pose a concern. In such a scenario, it may be desirable to incorporate some form of active cooling system into the electromagnet assembly 300. To that end, FIG. 9 depicts a preferred embodiment of an EDX unit 900 including a cooling assembly.

Except as noted, the EDX unit 900 shares many characteristics with the other EDX units described herein, and like reference numbers are intended to refer to like components. The electromagnet assembly is associated with a pneumatic duct 901 with cooling fans 902 placed at either or both ends. The fans blow a channel of air 903 across the electromagnet assembly, thereby dissipating heat through convective cooling. Alternatively, or in addition, if air is insufficient for heat transfer, the cooling assembly 900 may be filled with a liquid coolant. The coolant may be pumped throughout the electromagnet assembly and then to a radiator for more aggressive cooling.

[0059] FIG. 10 depicts a tilted embodiment of an EDX unit 1000. Except as noted below, the EDX unit 1000 shares many characteristics with the other EDX units described herein, and like reference numbers are intended to refer to like components Due to the relatively high mass density of certain metals (e.g., copper, brass, and zinc), it can often be difficult to generate sufficient magnetic field intensity to overcome gravitational weight and provide effective separation of trajectories 109a and 109b. When the flow of material is tilted, however, the vector component of weight that is perpendicular to the conveyor belt 103 gets reduced by the cosine of the tilt angle 1001. Thus, it may sometimes be useful to rotate the conveyor belt 103 so as to provide greater kinematic deflection and therefore better separation for a given intensity of the magnetic field 107.

[0060] FIG. 1 1 shows another embodiment of an EDX unit 1 100 configured for tilting the flow of material 102. Rather than rotate the entire conveyance assembly, the lower pulley 1 102 may be proj ected out beyond the upper pulley 1101. The magnetic core 104 is then placed underneath the inclined segment 1103 of the conveyor belt 103 and rotated to match the angle of inclined segment 1 103. To prevent material from tumbling over the sudden drop-off, the upper pulley 1101 may require a substantially larger radius than the lower pulley 1102. Or, alternatively, the upper pulley 1 101 may be replaced with several small rollers along an arc, thus providing a gradual transition in angle for material to follow with minimal tumbling.

[0061] FIG. 12 shows another tilted embodiment of an EDX unit 1200 with a parabolic arc 1201 used in place of the straight, inclined plane 1103. The parabolic arc 1201 is shaped to match (or approximately match) the free-falling trajectory of feed material 102. Doing so tends to greatly diminish the gravitational weight of feed material 102 such that even relatively small repulsive forces can significantly deflect heavy materials.

[0062] Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of one or more independent aspects of the invention as described.

Claims

1. An electrodynamic sorter system, comprising:

an electromagnet assembly including an electromagnet core and coils for exciting the core, the electromagnet core including a gap and being configured to generate a magnetic field above the gap when excited; and

a conveyor assembly arranged to feed particles over the gap of the electromagnet and into the generated magnetic field to thereby enable sorting of the particles based on differential interaction of the particles with the magnetic field.

2. The system of claim 1 , further comprising a splitter configured to separate particles according to separate kinematic traj ectories as the particles move beyond the gap of the electromagnet core.

3. The system of claim 2, wherein the splitter is adjustable in height, angle, and distance relative to the conveyor assembly.

4. The system of claim 2 or claim 3, further comprising one or more bins and/or conveyor belts positioned beyond the splitter to receive particles after passing over the gap.

5. The system of any one of claims 1 through 4, further comprising a tunable, variable-frequency drive circuit for exciting the electromagnet core, optionally tuned to a frequency within a range of about 1 -100 kHz.

6. The system of any one of claims 1 through 5, further comprising a vibratory feeder for applying particles to the conveyor assembly.

7. The system of any one of claims 1 through 6, wherein the electromagnet assembly is coupled to an adjustable height mount that enables adjustment of the height of the electromagnet assembly relative to the conveyor assembly.

8. The system of any one of claims 1 through 7, wherein the electromagnet assembly is embedded within the conveyor assembly.

9. The system of claim 8, wherein an upper portion of the electromagnet core is placed in direct contact with an underside of a conveyor belt of the conveyor assembly.

10. The system of claim 9, wherein the upper portion of the electromagnet core is topped with a low-friction material.

11. The system of any one of claims 1 through 9, wherein the conveyor assembly includes a conveyor belt and a plurality of rollers upon which the conveyor belt is moveable.

12. The system of claim 11, wherein at least one of the plurality of rollers is formed of a rigid, nonconducting material.

13. The system of claim 12, wherein the at least one roller formed of a rigid, nonconducting material is a roller closest to the electromagnet core.

14. The system of any one of claims 1 through 13, wherein the conveyor assembly and/or electromagnet assembly are arranged so that the particles pass over the gap at an angle tilted downward from the horizontal.

15. The system of claim 14, wherein a conveyor belt of the conveyor assembly, or one section of the conveyor assembly, is tilted such that the particles travel toward the gap at a downward angle.

16. The system of claim 14 or claim 15, wherein at least a portion of a conveyor belt feeding toward the gap is curved such that it curves downward from the horizontal.

17. The system of claim 16, wherein the electromagnet core is contacted to the curved portion of the conveyor belt.

18. The system of any one of claims 1 through 17, wherein the electromagnet core has a U-like shape.

19. The system of any one of claims 1 through 18, wherein the coils include two or more coils connected in parallel electrically.

20. The system of any one of claims 1 through 19, the electromagnet assembly further comprising one or more balancing inductors.

21. The system of claim 20, wherein the one or more balancing inductors includes a wound toroid of magnetic material connected in series with a coil of the electromagnet assembly.

22. The system of any one of claims 1 through 21, wherein the electromagnet assembly includes a plurality of electromagnet cores.

23. The system of claim 22, wherein the electromagnet cores are coupled to one another with flux bridges.

24. The system of any one of claims 1 through 23, wherein the electromagnet core is formed from one or more of NiZn ferrite, MnZn ferrite, and electrical steel, including laminated electrical steel.

25. The system of any one of claims 1 through 24, further comprising a cooling system in fluid communication with the electromagnet assembly and configured to assist in cooling the electromagnet assembly via circulating air and/or liquid coolant.

26. The system of any one of claims 1 through 25, wherein the gap is asymmetrical.

27. A method of electrodynamically sorting a mixed material, the method comprising:

providing an electrodynamic sorter system as in any one of claims 1 through 26;

feeding a stream of mixed material to the conveyor assembly such that the mixed material is passed over the gap of the electromagnet core and such that particles within the stream interact with the generated magnetic field and continue on at least two differential trajectories based on their interaction with the magnetic field; and

separately collecting material passing along the at least two differential traj ectories, resulting in corresponding streams of separated material.

28. The method of claim 27, wherein the mixed material includes both ferrous and non-ferrous materials.

29. The method of claim 27 or claim 28, wherein separation into the at least two different trajectories is based on one or more of electrical conductivity, mass density, and physical geometry.

30. The method of any one of claims 27 through 29, wherein the mixed material comprises a mixture selected from the group consisting of: copper and brass, copper and aluminum, aluminum and zinc, aluminum and titanium, metals and nonmetals, aluminum alloys mixed with non-aluminum metals, and flaky particles mixed with wires.

31. An electrodynamic sorting apparatus, comprising:

an electromagnet core embeddable within a sorting assembly, the electromagnet core including a gap and conductive coils, the conductive coils enabling excitation of the core by electrical current to produce a time-varying magnetic field above the gap,

wherein the core is oriented upright such that particles passing over a top side of the core pass over the gap rather than into the gap, and particles passed over the gap of the electromagnet and into the generated magnetic field are sortable based on differential interaction of the particles with the magnetic field.