Induction heating system

Abstract

A heating system is presented comprising a magnetic device, and a power supply unit supplying electric current to the magnetic device. The magnetic device comprises at least one induction coil, and is configured and operable to generate a magnetic field and apply induction heating to a portion of an electrically-conductive target located in a magnetic field region of the induction coil. The induction heating results in creation of ejecting forces acting on molten electrically-conductive material in said portion of the electrically-conductive target causing motion of at least a segment of the molten electrically-conductive material in said portion of the electrically-conductive target. The magnetic device and / or the power supply unit is / are configured such that the magnetic field generated by the magnetic device creates retarding forces acting on the at least segment of the molten electrically-conductive material in said portion of the electrically- conductive target, to thereby damp motion of the molten electrically conductive material induced by said ejecting forces.

Description

[0001] INDUCTION HEATING SYSTEM

[0002] TECHNOLOGICAL FIELD AND BACKGROUND

[0003] The present disclosure relates to an induction heating system utilizing an induction coil.

[0004] Induction heating is known as a fast and efficient technique for heating electrically conductive materials, such as metals, by applying an alternating magnetic field and generating Joule heating.

[0005] Induction heating is widely used in industrial, medical and domestic applications, as being advantageous over traditional heating techniques (resistance heating, flame heating, ovens, furnaces, etc.). Induction heating is used also for many applications including metal surface treatment and additive manufacturing. Some of the advantages of induction heating are the ability to perform heating which is selective (i.e., only conductive materials), non-contact, flameless and having high energetic efficiency.

[0006] GENERAL DESCRIPTION

[0007] Magnetohydrodynamics (MHD) is concerned with the mutual interaction between fluid flow and magnetic fields. The relative movement of a conducting fluid and a magnetic field causes an electromotive force (e.m.f.) to develop according to Faraday's law of induction resulting in the development of electrical currents, named "induced currents". These induced currents, according to Ampere's law, give rise to a second, induced magnetic field. The combined magnetic field (imposed plus induced) interacts with the induced current density, J, to give rise to a Lorentz force, J x B. This acts on the conductor and is generally directed to inhibit the relative movement of the magnetic field and the fluid (also known as magnetic damping or magnetic braking). This ability of a conducting medium (solid or liquid) to counteract an imposed magnetic flux variation is also called Faraday-Lentz effect. Magnetic fields are routinely used to heat, pump, stir, stabilize, repel, and levitate liquid metals. Thus, metallurgical MHD finds wide industrial applications in the control of metal surfaces.

[0008] The technique of the present disclosure is particularly useful in the manufacture of metal objects by additive casting, and is therefore described below with respect to this specific application. However, the principles of the present disclosure are not limited to this specific application. Techniques of metal object production by additive casting (casting in layers) are described, for example, in WO2019053712A1, WO22243921, W02023002468, all assigned to the assignee of the present application and incorporated herein in their entirety. According to these techniques, a series of production layers are created forming a vertical stack of production layers, wherein the production layer includes also metal object layers contained within mold regions. Such manufacture utilizes heating of a metal source (e.g., a rod, a crucible) (source heating) and depositing molten metal onto object region(s) of the production layer, as well as includes heating of the object region(s) before, during and after the metal deposition (surface heating).

[0009] There is a need in the art for optimizing inductance heating processes during manufacture of metal objects, in particular but not only during manufacture by additive casting. In particular, the inventors have identified a problem of splashing / ejection forces applied to the liquid-phase metal when subjected to an alternating (AC) magnetic field aimed at heating the metal (due to eddy currents in the metal target induced by application of an AC field).

[0010] Generally, such application of ejection forces results in "blobbing" at the surface of the metal target. This may for example occur during deposition of metal drops on a surface, e.g., surface of the metal target, or in response to surface heating. In the following, the terms "metal drop" and "metal blob" are therefore used interchangeably since the principles of the present disclosure are similar being aimed at compensating or at least significantly counteracting the ejection force applied to the molten portion (drop or blob) resulting from the application of the AC magnetic field. More specifically, such ejection results from horizontally oriented forces inherently accompanying the normal operation of induction coil(s) to create a heating magnetic field (e.g., used during casting).

[0011] The present disclosure provides a heating system comprising a magnetic device, and a power supply system. The magnetic device is configured and operable to generate a magnetic field and apply induction heating to a portion of an electrically conductive target located in a magnetic field region and is also configured and operable to create retarding forces acting on at least a segment of molten electrically-conductive material in said portion of the target against ejecting forces acting on said molten electrically- conductive material as a result of the induction heating. By this, the retarding forces, acting against the ejecting forces, damp molten metal motion induced in the portion of metal target being heated by said induction heating. This is achieved by properly configuring at least one of the magnetic device and the electric current supply. In operation, a series of portions of the electrically-conductive target are treated in the above-described manner.

[0012] The magnetic device includes at least one induction coil generating the magnetic field and applying the induction heating. In some embodiments, the same induction coil is configured to cause creation of the ejecting forces and the retarding forces.

[0013] For example, the induction coil may be operable by properly supplied current, having AC and DC components (AC and a DC bias, e.g., alternating current supply having a DC offset), to cause creation of the ejecting and retarding forces, respectively.

[0014] In some other examples, the induction coil is a conductor arranged in windings, including a number M of inner windings (M>1) and a number N of outer windings (N> 1 ), where inner and outer windings are spaced between them by a gap a satisfying at least one of the following conditions: (i) a>r, r being a radius of the inner winding for M=l, and (ii) a>>b, b being a space between the inner windings for M>1. The number of the inner and outer windings may be the same or different. The induction coil may be configured such that M / N>1.

[0015] The power supply unit may be configured and operable to provide alternating current supply to the induction coil.

[0016] In some embodiments, the magnetic device comprises first and second coils arranged such that the second coil is an outer coil surrounding the first coil being an inner coil, and the outer coil is distanced from the inner coil by a predetermined gap a, the electric current supply providing alternating current to at least the inner coil which therefore operates as an induction coil to thereby apply said induction heating. For example, the inner coil is a conductor arranged in a ring of radius r, the gap a satisfying a condition a>r.

[0017] In some other examples, the inner coil is a conductor arranged in two or more windings with a space b between them, the gap a satisfying a condition a » b.

[0018] The electric current supply may provide alternating current to the outer coil. For example, the electric current supply provides the alternating current to the inner coil, which is similar to the alternating current provided to the outer coil in at least one of the following parameters and conditions: current frequency, current amplitude, current phase and current wave shape.

[0019] The electric current supply may provide direct current to the outer coil.

[0020] In some other embodiments, the magnetic device comprises: an inner induction coil operable to apply induction heating causing creation of the ejecting forces; and an outer magnetic unit surrounding the induction coil and configured to create the retarding forces created by inhomogeneous static magnetic field. To this end, the outer magnetic unit includes a plurality of permanent magnets arranged along a closed-loop path (e.g., circular path) around and spaced-apart from the inner coil (denoted “permanent magnet ring").

[0021] The induction coil may be configured with a hollow profile of at least one winding thereof, or alternatively, the induction coil may be configured with a solid profile of at least one winding thereof.

[0022] The heating system may further include a cooling system. The cooling system may be configured and operable to provide cooling of the power source, and / or cooling of the magnetic device.

[0023] Considering that at least one of the coils has at least one winding with a hollow profile, the cooling system may be configured and operable to control the flow of cooling fluid through such at least one winding having the hollow profile.

[0024] The induction coil may have a circular cross section, rectangular cross section and the like. The cross section may be symmetrical with respect to a normal pointing the heated surface (“straight cross section”). The induction coil may be configured such that at least one winding thereof has an inclined cross section with respect to a normal pointing the heated surface (“slanted cross section”). The slanted cross-section defines heating and periphery segments of, respectively, a heating portion within said heating surface and an opposite periphery portion, said heating and periphery portions having different first and second lengths LI and L2, respectively, such that L1<L2, thereby providing different respective resistances R1 <R2. The ejection forces acting on e.g., a molten metal bulb / drop in the vicinity of the inner-most winding of a coil with a slanted cross section are higher comparing the ejecting forces generated by a coil having a straight cross section of the same cross section area. According to embodiments of the present disclosure, the motion of molten metal bulbs / drops in response to such higher ejection forces is restrained and controlled.

[0025] Thus, according to one broad aspect of the present disclosure, it provides a heating system comprising: a magnetic device comprising at least one induction coil, the magnetic device being configured and operable to generate a magnetic field and apply induction heating to a portion of an electrically-conductive target located in a magnetic field region of the induction coil, said induction heating resulting in creation of ejecting forces acting on molten electrically-conductive material in said portion of the electrically-conductive target causing motion of at least a segment of the molten electrically-conductive material in said portion of the electrically-conductive target; and a power supply unit configured and operable to supply electric current to the magnetic device; wherein at least one of the magnetic device and the electric current supply is configured such that said magnetic field generated by the magnetic device creates retarding forces acting on the at least segment of the molten electrically-conductive material in said portion of the electrically-conductive target, to thereby damp motion of the molten electrically-conductive material induced by said ejecting forces.

[0026] According to another broad aspect of the present disclosure, there is provided a magnetic device for use in a heating system for heating an electrically-conductive target, the magnetic device comprising: a first inner coil configured and operable to generate a magnetic field for induction heating of a portion of an electrically-conductive target; and a second outer coil surrounding said inner coil being spaced from said inner coil by a predetermined gap a selected in accordance with at least one structural parameter of the inner coil such that when the inner and outer coils are in operation, the induction heating by the inner coil results in ejecting forces acting on at least a segment of molten electric ally -conductive material within said portion of the target and the outer coil generates a magnetic field creating retarding forces acting on said segment of the molten electrically-conductive material of the target, to thereby damp motion of the molten electrically conductive material induced by the ejecting forces.

[0027] According to yet another broad aspect of the present disclosure, there is provided a heating system for heating an electrically conductive target, the heating system comprising: a magnetic device comprising an induction coil configured as a conductor having a single-winding or multiple windings structure applying induction heating to a portion of the electrically-conductive target; and a power source system configured and operable to operate the induction coil by alternating current supply having a DC bias, such that said induction coil generates a magnetic field having an alternating component creating ejecting forces acting on at least a segment of molten electrically conductive material in said portion of the target, and having a static component creating retarding forces acting against said ejecting forces to thereby damp motion of the molten electrically conductive material in said at least segment of the electrically-conductive material.

[0028] According to yet further broad aspect of the present disclosure, it provides a magnetic device for use in a heating system for heating an electrically-conductive target, the magnetic device comprising: a first inner coil configured and operable to generate a magnetic field for induction heating of a portion of an electrically-conductive target, such induction heating by the inner coil resulting in ejecting forces acting on at least a segment of molten electrically- conductive material within said portion of the electrically-conductive target; and a second outer magnetic unit surrounding said inner coil being spaced from said inner coil, said second outer magnetic unit being configured to generate inhomogeneous magnetic field creating retarding forces acting on said segment of the molten electrically- conductive material of the electrically-conductive target, to thereby damp motion of the molten electrically conductive material induced by the ejecting forces. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting examples only, with reference to the accompanying drawings, in which:

[0030] Figs. 1A and IB are illustrations demonstrating a problem caused by induction heating of electrically conductive surface during metal object production by additive casting;

[0031] Fig. 2A illustrates, by way of a block diagram, the configuration and operation of a heating system of embodiments of the present disclosure for heating electrically conductive target;

[0032] Fig. 2B schematically illustrates the operational principles of the magnetic device of embodiments of the present disclosure;

[0033] Fig. 2C schematically shows exemplary configurations of a magnetic device suitable to be used in the heating system according to embodiments of the present disclosure, where the magnetic device includes an induction coil formed by inner winding(s) and outer winding(s) properly spaced from one another;

[0034] Figs. 2D-2E and 2F-2G schematically show two exemplary configurations, respectively, of a magnetic device suitable to be used in the heating system according to embodiments of the present disclosure, where the magnetic device includes an inner induction coil and an outer coil wherein the inner induction coil is configured as singlewinding unit (Figs. 2D-2E) and as multi- windings unit (Figs. 2F-2G);

[0035] Figs. 2H to 2J show more specifically the operation of the magnetic device of the present disclosure configured according to the embodiment of Figs. 2C-2F, and where the inner induction coil and the outer coil are operated by AC current supply. For simplicity, the embodiment employing an inner coil and an outer coil is illustrated, however the drawings illustrate also the operation of a single coil driven with AC power supply having inner winding / s and outer winding / s. All figures show a cut through an inner induction coil (axisymmetric view) and an outer coil (having ring-like shape); wherein Fig. 2H shows a scenario where pinching forces are acting on a metal blob located in the center of the inner induction coil; Fig. 21 shows a blob ejected by radial forces of the inner induction coil; and Fig. 2J shows a metal blob retained by the damping forces applied by the outer coil;

[0036] Fig. 2K and 2L show the results of electromagnetic simulation of the configuration described in Figs. 2H - 2J for the case where the outer coil comprises a single additional spaced turn, constituting an outer component wherein Fig. 2L is a zoom on the radial forces acting on the metal blob;

[0037] Fig. 3 shows simulation results for various sizes of a gap between the inner induction coil and the outer guard coil according to embodiments of the disclosure;

[0038] Figs. 4A and 4B show the effects of changing the polarity of the currents in the inner coil and the outer coil on the total radial force (Fig. 4A) and the heating unit temperature (Fig. 4B); the simulation results for zero gap and 20 mm gap are shown;

[0039] Figs. 5A and 5B show results of simulations where a ratio between the turns (windings) of the coils in the inner induction coil and the outer guard coil configuration is changed, wherein Fig. 5A shows the effect on the total radial force; and Fig. 5B shows the effect on heating unit temperature;

[0040] Fig. 6 shows a simulation of the influence of the metal blob height on the total radial force in the inner coil and outer coil configuration;

[0041] Figs. 7A and 7B show results of further simulations where a ratio between the turns of the inner induction coil and the outer induction coil is changed and success criteria defined, wherein Fig. 7A shows the effect on the total radial force; and Fig. 7B shows the effect on heating unit temperature;

[0042] Fig. 8 exemplifies schematically the magnetic device configured according to the embodiment of Figs. 2C-2D (the “outer guard ring” configuration) and where the inner induction coil and the outer coil are operated by, respectively, AC and DC current supply, wherein a cut through the inner induction coil (axisymmetric) and the outer guard ring is shown;

[0043] Figs. 9A and 9B illustrate the configuration and operation of the magnetic device according to another embodiment of the present disclosure, where the magnetic device includes an induction coil fed by AC and DC current supply and generating both the magnetic and retarding fields (the “AC+DC bias” configuration); Fig. 10 schematically illustrates a configuration of the magnetic device according to some embodiments of the present disclosure employing an outer magnetic unit (outer ring assembly) including an arrangement (circular array) of permanent magnets producing an inhomogeneous static magnetic field creating retarding forces (the “AC+PM” configuration);

[0044] Fig. 11 shows results of modeling the retarding forces created by the magnetic device configuration of Fig. 10;

[0045] Figs. 12A to 12C exemplify possible configuration of the windings of the induction coil suitable to be used in a magnetic device of the present disclosure, to enable improvement of heating effectivity of the electrically conductive target to a desired temperature (the “slanted cross section coil” configuration);

[0046] Figs. 13A to 13C show results of simulations of several magnetic device configurations (depicted in Fig. 13D) in which the conductor is configured with a slanted cross-section of the windings; and

[0047] Fig. 14A illustrates a configuration of non-uniform winding geometry and Figs. 14B-14C show results of simulations of several magnetic device configurations employing windings with non-uniform shapes, width, height and spacing.

[0048] DETAILED DESCRIPTION OF EMBODIMENTS

[0049] Reference is made to Figs. 1A and IB illustrating a general art inductive heating of an electrically conductive target widely used in various industrial applications. As shown, an induction coil 100 is used facing a surface of the electrically conductive target (metal object under production). For example, in an additive casting production scenario, a production metal layer is partially shown including a metal object region 140 (which is typically surrounded by a mold region, not shown in the figure). Such manufacture of the metal object by additive casting utilizes heating of a metal source and depositing a flow of molten metal (drops, a stream) onto the object region 140 of the production layer, and utilizes heating of the object region 140 up to the metal melting temperature before and / or during and / or after the metal deposition.

[0050] In general, repulsive forces (denoted by arrows in Fig. 1A) exist between the induction coil 100 and the object region 140. If the production layer is solid, the repulsive forces are not strong enough to cause any change to the metal surface of a production layer. However, when the induction coil heats the metal surface close to or above the melting temperature (e.g., prior to depositing the next drop of liquid metal), the forces turn into pressure (depending on the square of the magnetic field magnitude, as will be shown below) acting on the liquid metal pool underneath the induction coil 100, and as a result pushing of liquid metal sideways may occur, as shown in Fig. IB. In addition, the distribution of the magnetic field around the induction coil 100 is not homogenous, therefore different forces develop acting either to pinch (i.e., compress / push) the metal drops towards the center of the induction coil or to eject / splash the metal drops sideways, creating thus metal blobs above the flat metal surface of the production layer. The specific nature (i.e., pinching or ejecting) of the formed radial forces is sensitive to the precise position of the metal drop / blob under the coil.

[0051] To summarize, the movement of liquid metal, either in a shape of drops, or in a shape of deformed molten metal blobs, may originate due to one or more of the following phenomena: a) The magnetic pressure applied vertically on the liquid metal surface causing splashing / surface deforming due to the weight of the metal drops; b) Radial force applied by an induction coil (carrying an AC current) on the liquid drops / blob surface when occasional (nonideal) metal deposition results in metal drops arriving not exactly in the center of the induction coil; c) Movement, asymmetry, imperfections, or instability of the induction coil (heating coil) during deposition resulting in metal drops accumulation, thus forming a metal blob, in the regions of ejecting forces under the induction coil.

[0052] Reference is made to Fig. 2A illustrating the general principles of a heating system 200 according to embodiments of the present disclosure for heating an electrically conductive target. The heating system includes a magnetic device 110 which is connectable to a power supply unit / system 160 (including one or more power supply units) configured to provide / maintain a required current pattern in the magnetic device. The magnetic device 110 is configured and operable to generate a magnetic field B and apply induction heating to a portion of an electrically-conductive target T. The induction heating results in creation of ejecting forces Feject acting on molten electrically-conductive material in a liquid segment (drop / blob) LB of the electrically-conductive material causing motion of such segment. According to the present disclosure, the magnetic device 110 and / or the electric current supply 160 is configured such that the magnetic field generated by the magnetic device creates retarding forces Fretard acting on said segment LB, to thereby damp motion thereof induced by the ejecting forces Feject.

[0053] For simplicity, the motion damping effect was described with respect to a single portion of the electrically-conductive target. In various production scenarios, a series of portions of the electrically-conductive target are treated, e.g., while the heating system, with or without a molten metal depositor, is moved over the electrically-conductive target. The retarding forces act such that the ejection forces caused by the induction heating are counteracted and ejection / splashing of the liquid metal is mitigated or avoided. This effect is a damping of the motion of molten metal caused during the inductive heating of the surface of the electrically conductive target.

[0054] The magnetic device 110 includes at least one induction coil 100 which is operated to generate the magnetic field B and apply the induction heating. The induction coil 100 defines a heating surface by which it faces a surface of the electrically conductive target and is operated by the AC current supply, from power supply system 160. The induction coil typically has a configuration following the surface of the conductive target resulting in a fairly uniform heating of the target region.

[0055] As described further below, the same induction coil 100 (the “single coil” configurations) or an additional magnetic unit, surrounding the induction coil 100, is used to create the retarding forces as well. Such additional magnetic unit may be a coil (e.g., stand-alone coil spaced from the induction coil, or a coil implemented as extension of windings of the induction coil), or ring-like unit which carries permanent magnets (permanent magnet ring) to produce inhomogeneous static magnetic fields acting as the retarding forces.

[0056] As exemplified in Fig. 2A, the heating system 200 may also include a cooling system 180. The cooling system 180 may be used for cooling the power supply system 160, and / or may be used to supply cooling fluid to flow via hollow -profile windings of the coil(s) of the magnetic device 110, as will be described further below. Such cooling via use of hollow profile conductor is a mechanism of internal fluid cooling. Alternatively, external cooling mechanism(s) can be used, e.g., by attachment / connecting the cooling system to a passive / active heatsink, by ventilation. As indicated above, in some embodiments, the same induction coil or two coils can be used to create the ejecting forces (resulting from the induction heating) and the retarding forces acting on a drop / blob of the molten electrically conductive material.

[0057] Reference is made to Fig. 2B illustrating the effect of induction heating by the magnetic device according to some embodiments of the present disclosure. As shown, the magnetic device is configured to define spaced-apart inner coil (or inner winding(s) of the same coil) and outer coil (or outer winding(s) of the same coil) where the inner coil / winding(s) is supplied with alternating current (AC) and the outer coil / winding(s) is supplied with AC current. In the case of the inner coil and outer coil configuration, the outer coil may be supplied with DC current. The magnetic field generated by the magnetic device 110 causes creation of different forces acting on liquid segment (blob / drop) LB and differently affecting the liquid segment, depending on its position with respect to the magnetic field region - three such positions Pi, P2 and P3 being exemplified in the figure.

[0058] It should be understood that here axisymmetric geometry of the coil / coils configuration is considered and half-configuration is illustrated. When the segment LB is in position Pi, it is subjected to the retarding forces of the inner and outer coils / windings (F retard)inner and (Fretard)outer acting in the same direction; in the position P2, the segment LB is subject to counteracting ejecting forces (Fejecting)inner of the inner coil / winding(s) and retarding forces (Fretard)outer of the outer coils / windings; and in the position P3 the forces acting on the liquid segment LB are ejecting forces (Feject)inner and (Feject)outer of the inner and outer coils / windings. As mentioned above, the proper creation of the counteracting retarding forces is achieved by the configuration of the magnetic device and / or power supply thereto.

[0059] Reference is made to Fig. 2C exemplifying the single coil configuration of the magnetic device 110, which includes induction coil 100 configured and operable to generate the magnetic field and apply induction heating to a portion of an electrically- conductive target (not shown here). The induction coil 100 is a conductor arranged in windings, including a number M of inner windings (M>1) - single such inner winding Winner being shown in this specific not-limiting example having radius r, and a number N of outer windings (N>1) - single such inner winding Wouter being shown in this example. The inner and outer windings are spaced between them by a gap a which is selected to be higher than radius r, a>r, for the case M=l. In case there are more than one inner winding M>1 having a space b between adjacent inner windings (not specifically shown here), the gap a is selected to be much higher than the space b. a>>b.

[0060] Reference is made to Figs. 2D-2E and Figs. 2F-2G showing schematically two examples, respectively, of the configuration of the heating system 200 (Figs. 2D and 2F) and the magnetic device 110 (Figs. 2E and 2G) used therein, according to some embodiments of the present disclosure employing two coils. In these examples the retarding forces acting against the ejecting forces are created by using an outer coil 150 surrounding the induction coil 100 (heating coil) and being spaced from the induction coil 100 by a gap a. The outer coil 150 is at times also referred hereto as a ‘guard coil’.

[0061] When the magnetic device 110 is brought into its operation position and the heating surface is at a predetermined distance from the surface of the electrically conductive target, the heating surface of the inner induction coil 100 faces and is aligned with a first portion of the target which is to be heated, while the outer coil 150 faces and is aligned with a second portion of the target outside the portion that is to be heated; and the retarding forces created by the outer coil 150 effect the damping of the molten metal motion being formed during heating of the first portion of the electrically conductive target.

[0062] In the example of Fig. 2C, the magnetic device 110 includes the induction coil 100, which functions to apply induction heating to the portion of the electrically conductive target, and which is configured as an electrical conductor arranged in a form of a number N (N>1) of winding(s) defining the heating surface of the induction coil 100 having a substantially planar shape by which it faces a surface of the electrically conductive target during heating. Other coil shapes may be used within the scope of the present disclosure.

[0063] In the example of the two-coils configuration shown in Figs. 2D-2E, the induction coil 100 is a single-winding coil having a radius r. In this case, the outer coil 150, configured as an electrical conductor arranged in a form of a ring or as a conductor formed by a number M (M>1) of windings, is arranged around the induction coil 100 with the distance / gap a therefrom such that a>r.

[0064] In the example of the two-coils configuration shown in Figs. 2F-2G, the induction coil 100 is configured with multiple windings, N>2, with a space / distance b between neighboring windings. The surrounding outer coil 150 is arranged at the distance / gap a from the induction coil 100 such that a » b. The windings of the induction coil 100 define together the heating surface of the induction coil 100 having a substantially planar shape by which it faces a surface of the electrically conductive target during heating. The outer coil 150 is configured as an electrical conductor having a single- or multi- wingdings configuration.

[0065] The guard outer coil 150, which is actually not aimed at generating magnetic heating effect in a portion of target T to be heated (not shown in Figs. 2D-2E and 2F-2G), may be supplied with AC or DC current. The purpose of the guard outer coil 150 is to generate the magnetic field creating retarding forces acting on the molten / liquid segment (blob / drop), to thereby damp the molten metal motion formed during heating of the surface region of the electrically conductive target aligned with the induction coil 100.

[0066] The inventors have found that by configuring the above-described magnetic device 110 such that the guard outer coil 150, surrounding the main / inner induction coil 100, is distanced from the inner coil 100 by gap a (e.g., gap between the innermost winding of the outer coil 150 and the outer winding of the inner coil 100) satisfying the condition that a » b for multi-windings induction coil 100, or such that a>r for singlewinding induction coil, sufficient retarding forces are generated by the outer coil 150 to damp the molten metal motion mentioned above.

[0067] It should be understood that, generally, the relative accommodation between the inner induction coil 100 and the guard outer coil 150 (and, similarly, between the inner winding / s and outer winding / s, in the single coil configuration) may also be sensitive to such parameters as the numbers N and M, as well as width of winding(s), a working distance (i.e., height of coil above the metal target), and coil geometry and possibly also current through the coil.

[0068] Fig. 2F shows a magnetic device suitable to be used in the heating system according to an embodiment of the present disclosure, where the magnetic device includes an inner induction coil configured as a multi-windings unit and an outer coil configured as a multi-windings unit. Fig. 2G shows a cross-sectional axisymmetric view of the arrangement of the inner induction coil 100 and the outer coil 150 surrounding the induction coil 100.

[0069] In this non-limiting example illustrated in Figs. 2F and 2G, the inner induction coil 100 has a symmetric structure, including 4 tums / windings of electrical conductor having a substantially rectangular cross section, whereas the outer coil 150 includes 2 turns / windings of electrical conductor also having a substantially rectangular cross section with the gap a between the coils 100 and 150 satisfying the condition a » b. In this example, a minimal gap a of 30mm is preferred to cancel out the ejection force created by the induction coil.

[0070] It should be noted that a radius r of a central space S of the induction coil 100 is an additional design parameter which is chosen e.g., according to the required size of the metal drops being deposited.

[0071] The heating system 200 is associated with / connected to the power supply system 160 including one or more power supply units.

[0072] The magnetic device 110 including the inner induction coil 100 (carrying AC current) and the outer coil 150 surrounding the coil 100 may be of one of the following configurations:

[0073] (i) The outer coil 150 may be arranged with a number M (M>1) of windings carrying AC current, thus serving as a second induction coil. In this implementation, the coils 100 and 150 may be supplied by the same or different power supply units. The use of the same power supply, either by parallel connection or serially, may be advantageous to avoid crosstalk between the two coils.

[0074] (ii) The outer coil 150 may be arranged with a number M (M>1) of windings carrying DC current, thus serving as a source of a static magnetic field. In this implementation, the inner induction coil 100 and the outer coil 150 may be connected to and operated by different power supply units.

[0075] (iii) The outer coil 150 may be arranged with a number M (M>1) of windings configured as extension of the inner induction coil 100 carrying AC current, hence the inner and outer coils sharing the same power supply and the same excitation.

[0076] As will be described further below with reference to Figs. 9A-9B, the magnetic device 110 may include the induction coil 100 operable to serve to simultaneously apply induction heating and create the retarding forces, avoiding the need to include a dedicated outer coil. To this end, the coil 100 is provided with the alternating current supplied with a DC bias sufficient to provide the required DC current for the static magnetic field. Yet in some other embodiments exemplified further below with reference to Fig. 10, the magnetic device 110 may include an outer ring with permanent magnets arranged / distributed along the outer ring and creating strong inhomogeneous static magnetic field. This configuration advantageously creates the retarding forces without requiring any current supply.

[0077] Turning back to Fig. 2A, it is shown that the heating system 200 may be further associated with a cooling system 180. The cooling system 180 may be configured to apply a cooling field (e.g., cooling fluid) to the power supply 160. Additionally or alternatively, the cooling system 180 may be used for cooling the induction coil 100. To this end, the induction coil 100 can be configured as a hollow profile conductor, which may be used for cooling fluid running therethrough.

[0078] It should also be noted that the outer coil 150, in a configuration in which it carries DC current, may be configured as a solid profile conductor. In such configuration, the outer coil 150 may include many windings (e.g., M = 1000) of a thin wire accommodating a relatively low current (e.g., I = 5A). Heat dissipation of such coil may be arranged via a heat sink.

[0079] Reference is made to Figs. 2H to 2J exemplifying the principles underlying the technique of the present disclosure for the configuration of the magnetic device 110 including an outer coil 150 surrounding an inner induction coil 100 (e.g., Figs. 2D-2G), where the outer coil 150 is carrying alternating current. In these figures, forces acting on the liquid metal surface in the vicinity of the main / inner coil 100 are illustrated using an axisymmetric coordinate system where the axes are denoted (r, z, (|)).

[0080] A high-frequency magnetic field is generated in the inner induction coil 100 by running a high-frequency current (e.g., > 100kHz). In general, a high-frequency magnetic field induces Eddy currents in the surface of the coil 100 conductor, the currents being restricted to a thin surface layer 6 of thickness 6 = called the Penetration (or Skin) ! (Dcr / z

[0081] Depth (not shown), with m = 2nf as the angular frequency of the magnetic flux, where

[0082] <j is the electrical conductivity and is the permeability of the fluid. These Eddy currents are responsible for the central role of the induction coil 100, that of heating up to melting the electrically-conductive material in the portion of the target, e.g., in the context of additive casting in layers, of the previous solidified metallic production layer prior to additively depositing new metal drops forming the next production layer.

[0083] In the context of the present disclosure, "high-frequency" is defined as a regime where the skin depth, 6, is significantly smaller than any relevant geometric length scale, such as the characteristic dimensions of the object's surface being processed. Under these conditions, electromagnetic fields penetrate only a shallow region near the surface of the conductor, known as the skin layer. As the magnetic and electric fields decay within this skin layer, a phase difference accumulates between them, leading to the generation of a magnetohydrodynamic (MHD) pressure. The resulting force has a magnitude of22L where B is the magnetic field strength and p is the permeability of the material. This force manifests as a pressure, also with magnitude22L that acts normal to the surface of the conductor. It should be noted that the direction of this pressure is not constrained to the z-axis, but is always perpendicular to the local surface geometry of the conductor. It should be emphasized that this electromagnetic force (magnitude B2 / 2 ) affects all conducting surfaces. However, it is particularly pronounced on liquid surfaces, where the force is strong enough to induce deformation and movement due to the lower mechanical resistance of the fluid.

[0084] To this end, the phenomena of induction heating and magnetic pressure are inherent in the operation of the main / heating induction coil 100, unavoidably resulting in generation of ejection forces acting on the molten electrically-conductive material causing movement within the liquid-phase segment of the material being heated by the induction coil. The inventors have found that such undesired movement can be eliminated or significantly reduced by creating retarding forces (which can be implemented by the use of the outer ring / coil 150 (or outer winding / s of the induction coil 100) e.g., carrying high frequency AC current) to provide sufficient force / pressure to damp the lateral propelling of the metal blobs within said segment of the liquid material (e.g., metal drops during deposition).

[0085] It should be noted that when a single power supply is driving both the inner induction coil and the outer coil, in series or in parallel, the current density in the coils is rearranged in a self-consistent way. However, when two separate power supplies operate the inner and outer coils respectively, such a rearrangement does not occur, or rather the power supplies are acting against it. Possible disadvantages of using a single / common power supply for the two coils may be that no separate control on current is possible, and that there is added load on the power supply and the resonance frequency of the combined coil is reduced. This may affect the heating power as well as the maximal power, however the degree of the effects depends on the detailed properties of each coil, especially of the outer coil.

[0086] The inventors conducted simulations for the magnetic device configuration utilizing the inner induction coil and the outer surrounding coil, and found that the magnitude of the radial component of the electromagnetic force, denoted Fr, depends on the specific location of the liquid metal segment in relation to the induction coil, on the coils' geometries, and on the size of the gap a between the inner induction coil and the outer coil. As already mentioned above, the magnitude of this radial component of force is given by22LI and its direction is normal to the surface of the metal drop / blob.

[0087] Fig. 2H shows schematically a half-view of an axisymmetric induction coil 100. As shown in this example, a metal blob MB is located at the center of the induction coil 100 and is subjected to the magnetic pressure, shown as arrows pointing towards the center of the coil indicating the radial forces Frdirected normal to the surface of the blob.

[0088] The inventors have shown by simulations that in this case the resultant radial force (i.e., the sum of all radial forces Fracting on the metal blob up to a location (indicated by a dashed line in Fig. 2H) at a certain radial distance d from the induction coil's center (e.g., 20 mm in Fig. 2K) is negative, i.e., has the effect of pinching / compressing the metal blob, Fretard, which results in that the metal blob MB is substantially stationary. The inventors have found that at radial distances from the center of the induction coil larger than d, the resultant radial force is positive, i.e., directed along the positive horizontal direction towards the outer coil with the effect of moving / ejecting the metal blob, Feject.

[0089] As described above, the induction heating of the liquid metal surface is accompanied by surface movement, i.e., the movement within the liquid metal and / or movement of the induction coil. The effect of such ejecting forces Feject is shown in Fig. 21 where a metal blob MB is located farer from the center of the induction coil 100, e.g., substantially under / aligned with the coil's windings as shown in the figure. The metal blob MB is positioned in a region where the resultant radial force creates a net ejecting force Feject accelerating the movement of the metal blob towards outside a portion aligned with the induction coil. The inventors have shown by simulations that such ejecting radial force Feject at certain locations from the center of the induction coil is strong enough to cause splashing of the liquid metal (e.g., during additive casting).

[0090] Fig. 2J shows the effect of adding the outer coil 150 surrounding the inner induction coil 100 and carrying an alternating current according to some embodiments of present disclosure. Here, the outer coil 150 has a ring-like or single-turn configuration. Since in this example the outer coil 150 carries an alternating current, it creates the respective retarding and ejecting forces, (Fretard)outer and (Feject)outer, as described above. The metal blob MB, while moving as a result of the ejecting force, (Feject)inner, induced by the operation of the inner induction coil 100, becomes located in a magnetic field region of the outer coil and thus at the same time experiences the "negative" retarding force, (Fretard)outer, induced by the operation of the outer coil 150.

[0091] For a given configuration and operation of the outer coil 150 (i.e., current, number of turns), and the relative accommodation of the outer coil 150 with respect to the inner induction coil 100, i.e., distance / gap a from the inner induction coil 100 relatively to the radius r of the induction coil 100 and / or a value of distance / gap a relatively to the space between the windings of the inner induction coil), the effect of the retarding force (Fretard)outer on the metal blob induced by the operation of the outer coil 150 increases with the blob approaching the magnetic field region of the outer coil 150. As a result, the retarding force (Fretard)outer counteracts the ejecting force (Feject)inner created by the magnetic field generated by the inner induction coil 100 such that (Fretard)outer=(Feject)inner, resulting in complete damping of the metal blob's motion.

[0092] Fig. 2K shows, in an axisymmetric view, an electromagnetic and thermal simulation of the combined operation of the inner induction coil 100 and the outer ring 150 operable by AC current supply and thus functioning as outer induction coil. In this simulation, the outer coil (e.g., having ring-like or single-turn configuration) is spaced with a gap a (of about 20 mm) from the inner induction coil 100, thereby damping the "splashing / ejecting" of metal blobs (e.g., metal drops and blobs during metal deposition).

[0093] It should also be noted, and was used in this specific simulation, that the outer coil 150 may be connected in series to the inner induction coil 100, thereby enabling to use the same power supply for both coils and thus advantageously avoid crosstalk between the two coils. Fig. 2K illustrates the magnetic flux lines around the coil, the metallic target temperature, and the current density on coil windings. Fig. 2K shows, in the respective upper part of the figure, the magnetic flux lines and magnetic flux density around the coil (grey scale), the current density in the coil windings (color scale, Red-White-Blue scale), and shows, in the respective lower part of the figure, the temperature distribution and melting front inside the heated target (equi-temperature lines and color scale). The equi-temperature lines of 1150°C (melting temperature for grey cast iron) and 770°C (Curie temperature for grey cast iron) are emphasized. Fig. 2K further shows Fr arrows representing time-averaged Lorentz force contribution acting on the molten metal.

[0094] Fig. 2L shows a zoom-in on the part of Fig. 2K, showing more specifically the total forces acting perpendicular to the surface of the metal blob, acting essentially as a magnetic pressure which exerts an overall force on the blob, either ejecting or retarding, according to the blob’s position and shape.

[0095] Figs. 2K-2L add further clarification to the explanation of the combined impact of the inner component and outer component of the magnetic device provided with reference to the schematic illustration in Fig. 2J. During induction heating of the liquid metal portion, the radial force Fracting on the metal blob results in a net force, F eject, ejecting, i.e., moving, the blob in the positive horizontal direction towards the outer coil. The magnetic device 110 is configured and operable such that the retarding forces acting on the liquid / molten metal portion / segment can damp this movement of the metal blob caused by the opposite ejecting forces.

[0096] The damping effect is received in the various configurations of the magnetic device discussed herein: formed by inner induction coil and outer coil as exemplified above, or formed only by induction coil(s), or formed by inner induction coil and outer magnetic unit having a ring-like structure formed by an arrangement (circular array) of permanent magnets, as will be exemplified below). The inner component and the outer component of the magnetic device (100 and 150, respectively) are spaced apart at a distance a.

[0097] With respect to heating performance, it can be seen in Fig. 2K - the magnetic flux density norm and the temperature distribution, that the inner component and the outer component of the magnetic device (100 and 150, respectively) both contribute to heating the target, however the contribution of the inner component 100 is much more significant. The addition of the spaced-apart outer component 150 did not cause the melting of additional portions of the target.

[0098] Thus, the present disclosure provides the magnetic device configured such that the retarding forces are created by the magnetic field and act on the metal blobs / drops within the liquid-phase metal subjected to the induction heating, to thereby counteract the ejecting forces created by the induction heating. Specifically, the magnetic field also creates radial forces which can be designed (via proper selection of the value of gap a in relation to the space b between the windings of the induction coil or radius of the induction coil) to damp unwanted splashing of liquid metal during induction heating (e.g., additive metal casting).

[0099] The dynamics of the radial force Fris complex, therefore the inventors simulated it under a few simplifying assumptions, i.e., assuming for example: a rigid metal drop (i.e., simplified symmetric shape of a metal blob), free sliding of the metal blob, and no coil motion. The simulation results for various sizes of the gap a between the inner induction coil 100 and the outer ring 150 are shown in Fig. 3.

[0100] Fig. 3 shows the total radial force per azimuthal length (N / m) as a function of the metal drop position along the horizontal axis. Negative values of radial force signify a retarding radial force (i.e., directed radially along the surface of the metal blob and compressing it), whereas positive radial force signifies outward / ejecting force inducing movement of the metal blob. For all the tested gaps, including zero gap (i.e., a = b in Fig. 2E), the radial force is retarding (i.e., compressing) at the center, i.e., at radial blob position smaller than about 20 mm, the horizontal field is directed towards the center of the coil, thereby ejection / splashing of liquid metal is avoided.

[0101] Starting at metal blob position of about 20 mm, the effect of the radial force is to eject the metal blob sideways (i.e., in the positive r direction in Fig. 21, designated as F eject), as indicated by a positive peak in the radial force (e.g., at about 40 mm for zero gap). The ejecting force is largest for the outer ring distanced from the induction coil by zero gap (a = 0) and is reduced by 50% already for a gap of 10 mm. As the gap is increased, i.e., the outer coil 150 is distanced from the main induction coil 100, a new negative / retarding force is created at a certain distance from the center of the inner coil, counteracting the ejection forces. The kinetic energy E = f Fdl gained by ejection is completely offset by effect / forces created by the operation of the outer coil only for a gap above 30 mm, as indicated by the nearly equal areas under the positive and negative radial force zones for the curve of a = 30 mm in Fig. 3. For such a gap there exists a stable horizontal position, as shown in Fig. 2J, where the forces satisfy a condition (Fretard)outer=(Feject)inner. In other words, the ejecting forces created by the induction heating (by inner coil 100) are completely balanced by the retarding forces created by the outer coil 150 resulting in complete damping of the undesired metal drop / blob motion.

[0102] The inventors considered the effects of current polarity on the functionality of the outer coil, since the current in the outer coil may have a reverse polarity with regards to the inner induction coil. The simulation results for zero gap and 20 mm gap are shown in Fig. 4A. Reversing polarity causes the ejection force to be somewhat reduced for the zero gap (i.e., a = b in Fig. 2G). Reversing polarity causes the central stable retarding force zone (caused by the inner coil) to be smaller for both tested gaps and there is a slight increase in the retarding force zone of the outer coil for the 20 mm gap.

[0103] The inventors further investigated the effects of co-propagating versus counterpropagating currents in the inner and outer coils (both operating as induction coils) with respect to the heating capability of the magnetic device and the results are shown in Fig. 4B where the temperature of the metal surface without the presence of the metal blob is shown. Except for the current polarity, all other conditions (e.g., current, initial temperature, materials etc.) were kept the same. The effect of increasing the gap between the inner and outer coils reduces the maximal temperature reached for a given heating time, as can be judged from the > 10% decrease in the temperature of a heating device with 30 mm gap as compared to the same device with zero gap (for co-propagating currents).

[0104] In general, reversing the current polarity results in a drastic reduction of the coil temperature for all the tested gaps. For the outer coil with co-propagating currents, increasing the gap reduces the temperature in the center while raising the temperature in the periphery, under the outer coil. It should be noted that the temperature of the magnetic device with 30 mm coil is more uniformly distributed under the whole coil surface as compared to smaller gaps. For counter-propagating current in the outer coil, the effect is inverse. In both cases, the reduction in the heating capability of the magnetic device is considerable. It can be seen in the figure that in the counter-propagating case, an increase in temperature is obtained for an increase in the gap. This may be understood when considering that the counter-propagating loop (of the outer coil) effectively cancels out the outermost winding of the inner coil. Increasing the gap reduces this cancellation effect. However, the heating capability of the optimal counter-propagating configuration, i.e., providing the highest temperature of the surface being heated (e.g., a=30mm in the plot) is still inferior to the least potent co-propagating configuration (e.g., a=30mm in the plot).

[0105] Figs. 5A and 5B show results of the simulations where the ratio between the turns of the inner coil and the outer coil, both operating as induction coils, was changed. Fig 5A shows that adding turns to the outer coil at the expense of the inner coil extends the retarding force zone of the outer coil (see, for example, the curve for Main=2, Guard=3 where retarding radial forces extend up to about 45 mm). Fig. 5B shows that adding turns to the outer coil at the expense of the inner coil reduces and redistributes the heating power. Thus, the extending of the retarding-force zone for the case of "Main=2, Guard=3" comes at the expense of not favorable temperature distribution where the temperature peaks at 50 mm. The case of "Main=3, Guard=2" seems to be favorable both in terms of large retarding-force zone and uniform temperature distribution.

[0106] The configuration parameters mentioned above (gap a, current polarity, and ratio of the number of windings in the inner and outer coils) also affect the resistivity and operating frequency of the heating device, in case both coils are connected and operated by the same power supply, and the inter-coil crosstalk if the coils are operated by different power supplies.

[0107] In the following, the effect of the metal blob / drop height on the total radial force is presented. The results shown in Fig. 6 indicate that the higher the drop / blob, the higher the radial force applied thereon. It should be noted that the term "metal drop" in this context may relate to the height of the metal blob formed on the surface under the induction coil. There exists an equilibrium between magnetic pressure and interfacial energy, and surface tension leading to change in the wetting.

[0108] The scaling with volume shows that the repletion is weaker for smaller-height blobs, which are also further from the coils. For example, the force at r=30 mm which is acting on a 4mm high blob is only 15% of the force acting on a 10mm high blob at the same position. Figs. 7A and 7B show results of further simulations where a ratio between the turns of the inner induction coil and the outer induction coil is changed. Five turn combinations were simulated: 4 / 1 combination of an inner coil with 4 turns and a singleturn outer coil; 4 / 2 combination of an inner coil with 4 turns and an outer coil with two turns, 5 / 1 combination, 5 / 2 combination - in these combination the current flows in the clock-wise direction in both the inner coil and the outer coil, and a reversed 4 / 2 combination where the current flows in a counter clock-wise direction in the outer coil. Fig. 7A shows the effect of the turn ratio on the total radial force (N / m) acting on a metal bulb present at various locations (r-coordinate running from the center of the inner coil outward). Fig. 7B shows the effect of the turn ratio on the heating performance of the heating device, representing the temperature (deg. C) of the target (e.g., the previously- cast metal bulk in the casting in layers scenario) at various locations (r-coordinate running from the center of the inner coil outward).

[0109] It can be seen in Fig. 7A that a metal bulb, located about 27 mm from the center of the inner coil, will be effectively retarded (negative total radial force) by a magnetic device of the 5 / 2 combination and slightly less by the 5 / 1 combination. The metal bulb present at = l mm will not be retarded (positive total radial force) by the 4 / 2 combination, 4 / 1 combination and the reversed 4 / 2 combination. The heating performance of the various combinations differ significantly, as can be seen in Fig. 7B. At the position of about 27 mm from the center of the inner coil - where the most-inner turn is placed above the target surface, the temperature experienced by the target surface is significantly higher with the 5 / 2 combination, about 1900 deg. C, comparing to the 5 / 1 combination (about 1830 deg. C), the 4 / 2 combination (about 1700 deg. C), 4 / 1 combination and the reversed 4 / 2 combination.

[0110] The simulation results of Figs. 7A-7B show that the configuration and operation of the magnetic device according to various embodiments of the present disclosure can be applied to a wide range of operational needs and production scenarios.

[0111] Reference is made to Fig. 8 exemplifying the configuration of the magnetic device 110 according to the present disclosure which is configured generally similar to the above-described embodiments, i.e., includes an outer coil / ring 150 surrounding an inner induction coil 100, but in this example the outer coil 150 is supplied with DC current and creates an inhomogeneous static magnetic field B according to the Ampere's law. As already described in detail above, the application of the induction heating to liquid metal (e.g., during deposition of liquid metal drops on top of a partially liquified object surface or during heat processing up to melting of a metallic target) induces motion of metal blobs / drops sideways (e.g., due to their weight and the pressure caused by the magnetic field generated by the induction coil 100 as described above), with the result that blobs / drops are propelled through the inhomogeneous static magnetic field with certain velocity. This movement of conductive metal blobs through the static magnetic field induces magnetic damping, which results in creation of opposing retarding forces damping the motion of the molten metal blobs along the radial axis.

[0112] The inventors have roughly estimated that, under the exemplified simulation conditions, such magnetic damping might require a magnetic field of about 1 Tesla which implies a direct current of about 20fcA if a single conductor is used. Since it is technically challenging to achieve such currents, the same field may be obtained by using several conductors wound into a coil, e.g., a 10 turn coil carrying about 2C4. The main advantage of this configuration is that the outer ring 150 supplied by DC power does not heat the metallic surface (AC power is required for induction), thus the magnetic field generated by the outer coil creates retarding forces acting only as a damping force on any moving metal. In addition, the retarding / damping force is proportional to the velocity of the metal blob / drop movement, thus faster propelling blobs / drops experience higher retaining / damping force.

[0113] Reference is made to Figs. 9A and 9B exemplifying the configuration of the magnetic device 110 according to yet another embodiment of the present disclosure. As already described above, e.g., with reference to Fig. 2A, the magnetic device 110 is configured to generate the magnetic field and apply induction heating (thus causing creation of ejecting forces), F eject, and also to cause creation of the retarding forces, Fretard, which compensate or at least significantly reduce the ejection forces acting on metal blob / drop caused by the induction heating.

[0114] As exemplified in Fig. 9A, this can be achieved by providing in the magnetic device 110 only the induction coil(s) 100 with no outer component, where the induction coil is operable to serve simultaneously for generating the magnetic field providing induction heating effect and creation of the retarding forces (the “AC+DC” configuration). To this end, power supply to the induction coil 100 includes AC component (required by the induction coil 100 to generate the magnetic field sufficient to implement induction heating and achieve the melting temperature of the metal target) supplied with a DC bias, for example a DC offset, sufficient to provide the required DC current for creating the static magnetic field inducing creation of retarding forces. Such combined AC+DC current configuration is shown in Fig. 9B. As shown, the metal blob located in the magnetic field region of the induction coil 110 (being within the surface region of the electrically conductive target aligned with the induction coil) experiences simultaneously ejecting / movement forces due to the alternating magnetic field and a sufficient retaining / damping force due to the static magnetic field resulting from the DC offset.

[0115] This can advantageously be implemented using one power supply, or alternatively the output of separate AC and DC power supplies can be combined.

[0116] For example, if the induction coil 100 requires ~ 1 kA and the required DC current for the static magnetic field comes up to 3-4kA, one can use the same power supply that will provide the required DC offset. Embodiments of the present disclosure are not limited by the DC biasing technique that is used.

[0117] Reference is made to Fig. 10 that schematically illustrates a configuration of the magnetic device according to some embodiments of the present disclosure employing an outer magnetic unit (outer ring assembly) which includes an arrangement (circular array) of permanent magnets producing an inhomogeneous static magnetic field creating retarding forces (the “AC+PM ring” configuration).

[0118] In this configuration, the magnetic device 110 includes an outer magnetic unit 150 which surrounds the inner induction coil 100 and includes an array / arrangement of permanent magnets PM distributed along a closed-loop path (for example, circular, ellipsoid or another closed-loop shape) around the inner coil 100. In the description below, such outer magnetic unit is at times referred to as "outer ring" or "outer ring assembly".

[0119] The permanent magnets outer ring PM may comprise NdFeB and / or N35 magnets. The plurality of permanent magnets PM are arranged in a spaced-apart relationship along a ring-like path. It should be understood that the type of permanent magnets, and / or number of magnets, and / or spatial arrangement of magnets may vary according to the requirements of specific application. The permanent magnets may be arranged within a frame 157.

[0120] As also exemplified in the figure, a cooling element / mechanism may be provided being implemented as a cooling ring 158 located adjacent to the PM arrangement and thus facing the inner induction coil 100. The cooling ring 158 may be accommodated between the outer magnetic unit and the induction coil. The cooling ring 158 is preferably made of a non-ferromagnetic but conductive material (e.g. aluminum) such that the cooling ring 158 provides shielding for the outer ring assembly from the inductive heating of the inner coil 100.

[0121] Fig. 11 shows the results of modeling an exemplary configuration based on an outer ring assembly 150 including permanent magnets PM. The field lines of the inhomogeneous static magnetic field are shown entering into a ferromagnetic substrate representing the ferromagnetic production layer.

[0122] Comparing for example the scenario illustrated in Fig. 2K showing the temperature beneath the outer component 150 being above the Curie temperature Tc, the material of the production layer under the outer ring assembly 150 shown in Fig. 11 is ferromagnetic. In the scenario illustrated in Fig. 11, the liquid metal region is found at smaller radial distances, i.e., under the induction coil (not shown here). In other words, the liquid segment (drop / blob) LB is modeled as moving on top of a ferromagnetic substrate having a temperature T lower than the Curie temperature Tc, the ferromagnetic substrate being magnetized by the static magnetic field produced by the outer ring assembly 150. The penetration of the static magnetic field lines into the ferromagnetic material of the production layer contributes to produce stronger retarding forces acting to retard the liquid metal drop LB being ejected by the magnetic field of the induction coil.

[0123] However, it should be noted that the material of the production layer may not be ferromagnetic. In these embodiments, the retardation of the ejected liquid drop LB will be reduced but still relies on the inhomogeneous static magnetic field developing above the surface of the production layer.

[0124] Referring now to Figs. 12A-12C, a possible configuration of the induction coil 100 is exemplified, aimed at optimizing the heating properties of the coil. These figures exemplify the induction coil 100 in which the conductor is configured with a tilted / slanted cross-sections 120 of the windings, shown in this specific non-limiting example as being in the form of tilted parallelogram. This tilted / slanted configuration provides a required resistance difference condition Ri <R2 between the resistance Ri of a heating portion lOOh of the coil 100 (the portion by which the coil faces the target being heated) and the resistance R2 of an opposite periphery portions lOOp of the coil's conductor.

[0125] According to the parallelogram- shape cross-section example of the pancake-type configuration of the induction coil / conductor 100, the winding is configured such that the above-described difference in the resistance (RI<R2) for the near-target heating portion lOOh and the periphery portion lOOp is achieved by configuring and orienting the cross-section 120 of the winding to provide a first circumferential length Li of the neartarget heating portion lOOh of the conductor shorter than a second circumferential length L2 of the periphery portions of the conductor, i.e., Li < L2.

[0126] The two opposite sides of the parallelogram cross-section 120 define a near-target heating segment 120h and a periphery segment 120p of, respectively, the near-target heating portion lOOh and periphery portion lOOp, which are substantially parallel to the heating surface of the coil (and to the metallic target MT). To this end, the cross section 120 of the winding has an axis and is oriented such that said axis is inclined with respect to a normal axis to the heating surface of the coil at a certain tilt angle a. The other parallel sides of the parallelogram 120 are inclined at said tilt angle a with respect to the normal axis to the heating segment. The tilt angle may be in a range 5° < |a| < 85°.

[0127] The provision of the slanted / tilted orientation of the cross-section of the winding results in that the near- target heating portion 120h of the winding has a length Li smaller than a length L2 of the periphery portion 120p of said winding. In response to electric current through the coil 100, magnetic fields generated in the far facet - the periphery portion lOOp - also contributes to heating the metallic target MT. However, the heat generated due to magnetic fields generated in the near facet - heating portion lOOh - is considerably higher. Hence, the winding of the coil 100 is configured such that the heating portion 120h has the first resistance Ri smaller than the second resistance R2 of the periphery portion 120p, such that, when the induction coil 100 is operated (i.e. electric current passes therethrough), the heating portion 120h of the winding has an electric current density Ji higher than an electric current density J 2 in the periphery portion 120p of the winding. The first resistance Ri is preferably at least 10% smaller than the second resistance R2. The inventors have found that the induction coil configured with electrical conductor satisfying the condition of Ri < R2 provides an improved heating effectivity of the metallic target MT to a desired temperature as compared to the conductor having the same resistance for all portions of the windings. The inventors realized that such difference in resistances between the heating portion lOOh and the periphery portion lOOp is beneficial for the intended use of heating the metal target MT since it makes the heating portion lOOh, which is close to the surface being heated (metal target MT), favorable to the current. The improved heating efficiency provides for shortening of the heating time of the metallic target to the desired temperature under given electric current, and / or for use of smaller value of the electric current to heat the metallic target to said desired temperature and / or for producing sharper temperature profile on the target being heated.

[0128] It should be noted that, generally, the use of the tilt / slant feature in the planar- type winding, while providing the required resistance difference between the heating and peripheral portions, affects the total resistance of the coil. This is taken into consideration to properly select the electric current parameters supplied to the coil. More specifically, the adverse effect of slanting the coil winding is an increase in AC resistance, which means more voltage is required to drive the coil at a given current, and in increase in coil inductance, meaning that for a given power supply the resonant frequency decreases, resulting in less inductive heating; this can be addressed by adequate redesign of the power supply's capacitor bank.

[0129] As described above, the electrical conductor of the induction coil 100, as well as that of the outer coil 150, may be configured with a hollow profile allowing the flowing of a cooling fluid therethrough.

[0130] An example of such a hollow conductor (for the induction coil 100 having slanted / tilted configuration of its windings) is shown in Figs. 12B and 12C also showing specially designed inlets and outlets for the cooling fluid. In general, the induction coil 100 may include at least one cooling fluid inlet and at least one cooling fluid outlet.

[0131] Fig. 13A exemplifies a design / configuration of a magnetic device 110 of the present disclosure including an inner induction coil 100 and an outer coil 150, both configured with tilted / slanted cross-sections of the windings. In the non-limiting example of Fig. 13A the inner induction coil 100 has four windings and the outer coil 150 has three windings, thus this configuration will be referred to as “flat slanted 4+3” configuration where “flat” indicates that all near-target heating segments 120h (as defined above with reference to Fig. 12A) form a single flat surface above the target. In this embodiment, the outer coil 150 is connected in series with the inner induction coil 100 (in other words, the windings of the outer coil are constituted by extension of the windings of the inner coil), thereby enabling use of the same power supply and same excitation.

[0132] In this simulation, both coils are supplied with 1500A at a frequency matching the system’s resonance.

[0133] Looking at the bottom part of Fig. 13A, simulating the temperature of the target substrate, it can be seen that the contribution to heating of the substrate by the outer unit 150 is not insignificant. It is shown that the temperature of the area beneath outer unit 150 is above the Curie temperature line and near the melting temperature line.

[0134] The inventors simulated the design of Fig. 13A and some of its variations to study the performance of the magnetic device 110 in terms of its heating efficiency and retardation efficiency. For each configuration of inner induction coil 100 and outer coil 150 a heating profile is the radial temperature profile at steady state, being mainly an indication of heating power. The force profile effected by the magnetic fields of the simulated magnetic device 110 is constructed by integrating electromagnetic forces on a liquid metal drop at a given position. Positive force indicates ejection and negative force indicates retarding.

[0135] It should be noted that in their simulations, the inventors considered various alternative configurations of the “flat slanted 4+3” design of Fig. 13A, in particular, the following configurations (depicted in Fig. 13D): (1) “slanted 4+2” where the outer coil 150 includes 2 windings only; (2) “flat slanted 4+3” - the design shown in Fig. 13A; (3) “ slanted 4+3 straight” where the cross sections of the inner induction coil 100 is slanted and the cross section of the outer coil 150 resembles that of Fig. 2G or Fig. 2K, i.e., no tilted / slanted configuration;) (4) “slanted 4+3 vertical” where the windings of the outer coil 150 (3 windings) are arranged in a solenoid-like vertical arrangement; and (5) “slanted 4+3 inverse” which is the structure shown in Fig. 13A where the direction of the current in the outer coil 150 is inversed. A reference configuration comprising only a 5- windings inner coil 100 was also considered.

[0136] Figs. 13B and 13C show the results of simulations of the reference configuration, “flat slanted 4+3” design of Fig. 13A and its variations (1) to (5). Fig. 13B shows the heating profile of various configurations as a function of the radial coordinate. The temperatures shown are the temperatures of the metal surface below the magnetic device 110 obtained at “infinite” time and are used here as a “figure of merit” to compare the heating power of various configurations. It can be seen that the highest temperature of the metal surface within the area of interest (r-coordinate around 27mm + / - 5mm, indicative of the deposition zone in the additive metal casting scenario discussed above) is reached by configuration (2) - the “flat slanted 4+3” design of Fig. 13A. Configurations (4) and (5) reach the slightly lower temperatures yet above 1100 deg. C, while configurations (1) and (3) did not reach 1100 deg. C. The heating performance of the reference - with only the inner coil 100 - is about 800 deg. C.

[0137] Fig. 13C shows the radial force profile of the various configurations. It can be seen that, compared to the reference and configurations (1), (3)-(5), configuration (2) - the “flat slanted 4+3” design of Fig. 13A, advantageously provides a larger integral of negative forces, indicative of larger retarding force, as compared to the integral of positive forces, indicative of the ejecting force.

[0138] Fig. 14A illustrates a configuration of non-uniform winding geometry and Figs. 14B-14C show the results of simulations of several magnetic device configurations employing windings with non-uniform shapes, width, height and spacing. Coils with such non-uniform winding geometry may be manufactured using 3D printing techniques known in the art.

[0139] Fig. 14A exemplifies a design / configuration of a magnetic device 110 including an inner induction coil 100 and an outer coil 150, both configured with tilted / slanted cross-sections of the windings, and also including non-uniform winding cross-sections in their width (e.g., 100-1 and 100-2 vs. 100-3 and 100-4), height from the substrate (e.g., h6 > hl > h2, h3, h4, h7 and h8), spacing (e.g., si s3 s4), spatial position (e.g., 100-5 and 150-3), shape and size.

[0140] The inventors considered such non-uniform designs to achieve various goals. These include: the motivation to make the inner windings of the inner induction coil 100 thicker (e.g., 100-1 and 100-2) in order to improve water cooling of the coil, especially at the most-inner windings of the inner unit 100); and the motivation to raise some inner windings (e.g., 100-1) above the otherwise flat surface of the slanted coil to make place for the “pinched” blob of liquid metal, thereby reducing its splashing outwards from the inner induction coil 100 region.

[0141] It should be noted that in the embodiments where non-uniform width of the windings is used, the cooling liquid’s entry / exit points along the coil windings are properly considered to optimize efficient cooling.

[0142] A base design of the inner induction coil 100 includes four windings, 100-1, 100-2, 100-3, and 100-4, where windings 100-1, and 100-2 are non-uniform, and winding 100-1 in addition to being thicker than the windings 100-3 and 100-4, is also raised above the inner induction coil 100 flat surface (defined by the near-target heating segments of windings 100-3 and 100-4 forming a flat surface above the target). A full design of the inner induction coil 100 includes also an inner extra winding, 100-5, located well above the induction coil 100 flat surface.

[0143] The base design of the outer coil 150 includes two windings, 150-1 and 150-2. A full design of the outer coil 150 includes also an outer extra winding, 150-3, located above the outer coil 150 flat surface (defined by the near-target segments of windings 150-1 and 150-2).

[0144] The inner component 100 and the outer component 150 of the non-uniform winding geometry may be realized as a single coil or two coils.

[0145] Figs. 14B and 14C show the results of simulations of the following configurations of the magnetic device 110 based on the windings’ designations of Fig. 14A: (i) “full” configuration including windings 100-1, 100-2, 100-3, 100-4, and 100-5 of the inner induction coil 100 and windings 150-1, 150-2, 150-3 of the outer coil 150, (ii) “base” configuration (depicted in the figures by legends “minimal”) including windings 100-1, 100-2, 100-3, 100-4, of the inner induction coil 100 and windings 150-2, 150-3 of the outer coil 150, (iii) “base + inner extra” configuration (depicted in the figures by legends “inner”) including windings 100-1, 100-2, 100-3, 100-4, and 100-5 of the inner induction coil 100 and windings 150-1, 150-2 of the outer coil 150, and (iv) “base + outer extra” (depicted in the figures by legends “outer”) including windings 100-1, 100-2, 100-3, 100-4, of the inner induction coil 100 and windings 150-1, 150-2, 150-3 of the outer coil 150. A reference configuration of an inner coil 100 having 5 windings in a flat arrangement was also considered. Fig. 14B shows the heating profile of the various configurations as a function of the radial coordinate. It can be seen that the “full” configuration (i) wins, i.e., the more windings there are, the better is the heating power of the magnetic device 110.

[0146] Fig. 14C shows the radial force profile of the various configurations. It can be seen that configuration (iii), “base + inner extra”, contributes the most to ejection (i.e., has the largest integral of positive forces), while configuration (iv), “base + outer extra”, contributes the most to retardation (i.e., has the largest integral of negative forces), and is therefore likely to succeed in completely retarding the splashing of liquid metal during manufacturing. This “winning” of configuration (iv) in retardation may be rationalized, since, compared to other simulated configurations, this configuration (iv) provides an extra winding in the outer coil 150 while the inner induction coil 100 stays with the base number of windings. The simulations show that the retarding force of the “full” configuration is marginal.

[0147] In some embodiments of the present disclosure, the heating system is incorporated within a molten metal deposition system of an additive casting machine (additive casting machines and methods as described, for example, in WO2019053712A1, WO22243921, W02023002468). Embodiments of the heating system of the present disclosure may serve to heat the surface of a previously-casted object region before, during and / or after the additive deposition of molten metal. Embodiments of the heating system of the present disclosure may be movable over the area of the object region. Embodiments of the heating system of the present disclosure may be physically coupled to a molten metal depositor and moved together with the depositor over the area of the object region.

[0148] In some embodiments of the heating system of the present disclosure, both the inner component and outer component - realized as a single coil or two coils - may be physically coupled to a molten metal depositor and moved together with the depositor over the area of the object region. In other embodiments of the heating system of the present disclosure, one or both of the inner component and outer component are coupled to the molten metal depositor during its operation, and are further capable of operating - heating the surface underneath, while not attached to the depositor. The molten metal to be deposited undergoes melting and / or heating by dedicated heaters (“source heaters”) that operate above and / or near the heating system of embodiments of the present disclosure. Thus, the landing position of the molten metal with respect to the heating system, as well as other parameters (e.g., drop size and shape) may vary due to various inaccuracies, irregularities, and errors, attributed e.g., by system elements as movement elements, heaters, depositor / s and their influence on other elements and materials present in their vicinity.

[0149] Embodiments of the present disclosure were discussed in the context of additive casting and the sequential addition of molten metal to a target to be heated. With respect to the radial views discussed above, the sequential addition of molten metal is considered at r=0, and the target to be heated was exemplified at various distances (various values of r). It should be understood that these measures / values are not limiting the present disclosure and other design parameters may be used.

[0150] Embodiments of the present disclosure were discussed in the context of additive casting and the sequential addition of metal drops to a target to be heated. However, the present disclosure is not limited to the described production scenarios. For example, embodiments of the present disclosure may be applied to damp motion of metal blobs in response to surface heating, even when no new molten metal is added.

[0151] Embodiments of the present disclosure were discussed in the context of liquid metal (grey cast iron) and heating. However, the present disclosure is not limited to damping motion of liquid metal (blobs) formed in response to heating. Embodiments of the present disclosure may be applied to damp motion of metal or metallic particles that are present in an area neighboring the heating system.

[0152] Embodiments of the present disclosure were discussed mainly with reference to surface heating using coils with a closed-loop shape, e.g., circular. Coils with ellipsoid shape may also be used, as well as coils with non-symmetrical closed-loop shapes. Closed-loop shapes are particularly useful for damping motion of electrically conductive molten material such as molten metal bulbs and drops, as the acting forces under system jittering, inaccuracies and imperfections may cause the molten blob / drop to move in various directions. Coils with symmetrical closed-loop shapes facilitate rotational operation of the heating unit along the heating path. Depending on specific system requirements, non-closed-loop coils may also be used. Embodiments of the present disclosure referring to inner coil and outer coil were discussed mainly with reference to inner coil and outer coil having the same closed-loop shape, but this is not necessarily so.

[0153] Embodiments of the present disclosure referring to a heating system having a single coil arranged as the inner and outer components, two coils constituting separately the inner component and the outer component, but this is not necessarily so. More than two coils may be used to constitute the inner and outer components, with the required alterations and modifications.

[0154] Embodiments of the present disclosure were discussed mainly with reference to surface heating using coils with substantially planner shape, e.g., “pancake” coils. However, the present disclosure is not limited to the illustrated coil configurations. For example, helical coils, spherical-helical coils and coils of other shapes may be used.

[0155] As used throughout the specification, the terms "metal" or "metallic" refers to any metals and / or metallic alloys which are suitable for melting and depositing, for example, ferrous alloys, aluminum alloys, copper alloys, nickel alloys, magnesium alloys, and the like.

[0156] Embodiments of the present disclosure were discussed mainly with reference to additive casting of metal. The present disclosure is not limited to this application and can apply for the additive casting of other materials. Further, the present disclosure is not limited to additive manufacturing and may apply to other applications involving induction heat treatment.

[0157] Embodiments of the present disclosure were discussed mainly with reference to applications involving moving one or more heating units over a surface. Embodiments of the present disclosure are not limited to these applications. For example, embodiments of the present disclosure are applicable to the use of stationary heating unit / s and a moving surface (e.g., a drum). Thus, the heating system according to embodiments of the present disclosure is configured and operable to provide a relative displacement between the heating system and the target. Embodiments of the present disclosure are further applicable for using stationary heating unit / s for heating stationary targets.

[0158] While certain features of the present disclosure have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the present disclosure.

Claims

CLAIMS:

1. A heating system comprising: a magnetic device comprising at least one induction coil, the magnetic device being configured and operable to generate a magnetic field and apply induction heating to a portion of an electrically-conductive target located in a magnetic field region of the induction coil, said induction heating resulting in creation of ejecting forces acting on molten electrically-conductive material in said portion of the electrically-conductive target causing motion of at least a segment of the molten electrically-conductive material in said portion of the electrically-conductive target; and a power supply unit configured and operable to supply electric current to the magnetic device; wherein at least one of the magnetic device and the power supply unit is configured such that said magnetic field generated by the magnetic device creates retarding forces acting on the at least segment of the molten electrically-conductive material in said portion of the electrically-conductive target, to thereby damp a motion of the molten electrically conductive material induced by said ejecting forces.

2. The heating system according to claim 1 , wherein the induction coil is a conductor having a single-winding or multiple windings structure, said power supply unit being configured and operable to provide alternating current supply having a DC bias to said induction coil, such that said magnetic field has an alternating component resulting in said ejecting forces and has a static component inducing said retarding forces.

3. The heating system according to claim 1 , wherein the induction coil is a conductor arranged in windings, including a number M of inner windings (M>1) and a number N of outer windings (N>1), said inner and outer windings being spaced between them by a gap a satisfying at least one of the following conditions: (i) a>r, r being a radius of the inner windings for M=l, and (ii) a>>b, b being a space between the inner windings for M>1.

4. The heating system according to claim 3, wherein the number of the inner and outer windings is the same or different.

5. The heating system according to claim 3, wherein the induction coil is configured such that M / N>1.

6. The heating system according to any one of claims 3 to 5, wherein the power supply unit is configured and operable to provide alternating current supply to the induction coil.

7. The heating system according to claim 1, wherein said magnetic device comprises a first coil, operable as said induction coil, and a second coil, the first coil and the second coil being arranged such that the second coil is an outer coil surrounding the first coil being an inner coil, and the outer coil is distanced from the inner coil by a predetermined gap a, the electric current supply providing alternating current to at least the inner coil which therefore operates as the induction coil to thereby apply said induction heating.

8. The heating system according to claim 7, wherein the inner coil is a conductor arranged in a ring of radius r, the gap a satisfying a condition a>r.

9. The heating system according to claim 7, wherein the inner coil is a conductor arranged in two or more windings with a space b between them, the gap a satisfying a condition a>>b.

10. The heating system according to any one of claims 7 to 9, wherein the power supply unit provides alternating current to the outer coil.

11. The heating system according to claim 10, wherein the power supply unit provides an alternating current to the inner coil, which is similar to the alternating current provided to the outer coil in at least one of the following parameters and conditions: current frequency, current amplitude, current phase and current wave shape.

12. The heating system according to claim 7 to 9, wherein the power supply unit provides direct current to the outer coil.

13. The heating system according to claim 1, wherein the magnetic device further comprises an outer magnetic unit surrounding said induction coil, the outer magnetic unit being configured and operable to generate an inhomogeneous magnetic field creating said retarding forces.

14. The heating system according to claim 13, wherein the outer magnetic unit comprises a permanent magnet ring formed by a plurality of permanent magnets arranged in a spaced-apart relationship along a ring-like path around the induction coil.

15. The heating system according to any one of claims 1 to 14, wherein the induction coil has a hollow profile of at least one winding thereof.

16. The heating system according to any one of claims 1 to 14, wherein the induction coil has a solid profile of at least one winding thereof.

17. The heating system according to any one of the preceding claims, further comprising a cooling system.

18. The heating system according to claim 17, wherein the cooling system is configured and operable to provide cooling of the power supply unit.

19. The heating system according to claim 17 or 18, wherein the cooling system is configured and operable to provide cooling of the magnetic device.

20. The heating system according to any one of claims 2 to 16, further comprising a cooling system configured and operable to provide cooling of the magnetic device, wherein the induction coil has a hollow profile of at least one winding thereof, and the cooling system is configured and operable to control a flow of cooling fluid through said at least one winding having the hollow profile.

21. The heating system according to any one of claims 7 to 12, further comprising a cooling system configured and operable to provide cooling of the magnetic device, wherein at least one of the inner coil and the outer coil has a hollow profile of at least one windings thereof, the cooling system being configured and operable to control a flow of cooling fluid through said at least one winding having the hollow profile.

22. The heating system according to any one of claims 13 to 16, further comprising a cooling system configured and operable to provide cooling of the magnetic device, said cooling system comprising a cooling ring accommodated between the outer magnetic unit and the induction coil.

23. The heating system according to claim 22, wherein the cooling ring is made of an electrically conductive material configured to provide shielding of the outer magnetic unit from the induction heating of the induction coil.

24. The heating system of any one of the claims 1 to 23, wherein said induction coil is configured such that at least one winding thereof has a cross-section defining a heating segment and a periphery segment of, respectively, a heating portion within said heatingsurface and an opposite periphery portion, said heating portion and periphery portion having different first and second lengths Li and L2, respectively, such that LI<L2, thereby providing different respective resistances RI<R2.

25. A heating system for heating an electrically conductive target, the heating system comprising: a magnetic device comprising an induction coil configured as a conductor having a single-winding or multiple windings structure applying induction heating to a portion of the electrically-conductive target; and a power source system configured and operable to operate the induction coil by alternating current supply having a DC bias, such that said induction coil generates a magnetic field having an alternating component creating ejecting forces acting on at least a segment of molten electrically conductive material in said portion of the electrically-conductive target, and having a static component creating retarding forces acting against said ejecting forces to thereby damp motion of the molten electrically conductive material in said at least segment of the electrically-conductive material.

26. A heating system according to any of claims 1 to 25, wherein said electrically- conductive material in said portion of the electrically-conductive target is molten metal.

27. A heating system according to any of claims 1 to 26, wherein said portion of the electrically-conductive target comprises electrically-conductive material additively added to said portion of the electrically-conductive target.

28. A heating system according claim 27, wherein said electrically-conductive material in said portion of the electrically-conductive target comprises molten electrically-conductive material generated in said portion of the electrically-conductive target in response to said induction heating which is provided before, during and / or after the electrically-conductive material is added.

29. A heating system according to any of claims 1 to 26, further configured and operable to provide a relative displacement between the heating system and said target.

30. A heating system according to claim 29, wherein the heating system is movable over said electrically-conductive target.

31. A heating system according claim 30, further configured and operable to generate said magnetic field and apply said induction heating while moving said heating system over a series of portions of an electrically-conductive target.

32. A magnetic device for use in a heating system for heating an electrically- conductive target, the magnetic device comprising: a first inner coil configured and operable to generate a magnetic field for induction heating of a portion of an electrically-conductive target; and a second outer coil surrounding said inner coil being spaced from said inner coil by a predetermined gap a selected in accordance with at least one structural parameter of the inner coil such that when the inner and outer coils are in operation, the induction heating by the inner coil results in ejecting forces acting on at least a segment of molten electrically-conductive material within said portion of the electrically-conductive target and the outer coil generates a magnetic field creating retarding forces acting on said segment of the molten electrically-conductive material of the electrically-conductive target, to thereby damp motion of the molten electrically conductive material induced by the ejecting forces.

33. The magnetic device according to claim 32, wherein said outer coil operates by alternating current supply.

34. The magnetic device according to claim 33, wherein said inner coil operates by alternating current supply which is similar to said alternating current supply of the outer coil in at least one of the following parameters and conditions: current frequency, current amplitude, current phase and current wave shape.

35. The magnetic device according to claim 32, wherein said outer coil operates by direct current supply.

36. The magnetic device according to any of claims 32 to 35, wherein the inner coil and the outer coil are arranged in parallel.

37. The magnetic device according to any of claims 32 to 35, wherein the inner coil and the outer coil are serially arranged.

38. A magnetic device for use in a heating system for heating an electrically- conductive target, the magnetic device comprising: a first inner coil configured and operable to generate a magnetic field for induction heating of a portion of an electrically-conductive target, such induction heating by the inner coil resulting in ejecting forces acting on at least a segment of molten electrically- conductive material within said portion of the electrically-conductive target; anda second outer magnetic unit surrounding said inner coil being spaced from said inner coil, said second outer magnetic unit being configured to generate inhomogeneous magnetic field creating retarding forces acting on said segment of the molten electrically - conductive material of the electrically-conductive target, to thereby damp motion of the molten electrically conductive material induced by the ejecting forces.

39. The magnetic device according to claim 38, wherein the outer magnetic unit comprises a permanent magnet ring formed by a plurality of permanent magnets arranged in a spaced-apart relationship along a ring-like path around the induction coil.

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