Magnetic shielding for induction furnace

Abstract

A shielding system for an induction furnace is provided, for heating one or more elongated elements while being conveyed through said furnace. The shielding system comprises one or more shielding tubes configured to shield the one or more elongated elements from magnetic fields induced by the furnace, the shielding system including a guiding system for guiding and holding said one or more shielding tubes. A method is also provided for heating one or more elongated elements, and for comparing the influence of heating treatments on an elongated element, by testing a portion of the element with full treatment and with treatment using the shield.

Description

Title: Magnetic shielding for induction furnaceDescriptionTechnical Field

[0001] The invention relates to the field of induction heating. More specifically it relates to installations for thermal treatment of elongated elements such as wires and control thereof.Background Art

[0002] Heating of metallic elongated elements such as wires, cords, cables etc. is required in the thermal treatment of such elongated elements.

[0003] These heat treatments include annealing, stress relief, thermodiffusion of coatings and similar processes. Homogeneous heating is necessary to obtain uniform properties along the length of the elongated element and over the cross section of the elongated element. Since the elongated elements may have lengths of several kilometres, homogeneous heating is done by conveying the elongated element through a furnace at a known speed. The furnace can be an induction coil which is highly effective for elongated elements comprising or consisting of, for example, ferromagnetic materials.

[0004] The induced magnetic field of the furnace and the speed of the elongated element determine the amount of energy received by the heated portion of the elongated element. Although the whole element is not heated up simultaneously, the whole element is submitted homogeneously to substantially the same heating treatment over its length. US 4 788 974 is a well known reference that extends the use of induction heating to elongated elements such as steel wires. The prefererred frequencies of the magnetic field is up to 50 kHz, typically between 5 to 30 kHz, This range is generally referred to as ‘mid frequent’.

[0005] However, the heating treatment needs to be controlled on some portions of the elongated element, for example for compensating for differences in different portions of material being heated (different composition, different diameter, etc.). Changing the current through the coil is possible, but not feasible in industrial conditions where the same coil is used tosimultaneously heat many elongated elements. In such cases, running different diameters side by side is not possible in that thicker wires will heat insufficiently compared to thinner wires that will be overheated. An attempt to overcome this problem is suggested in e.g. All-B-10682 / 92 wherein a cooling gas is injected into the tubes through which wires run, or wherein the wire path of wires is changed to shorten the immersion in the furnace. However, such systems are difficult to implement and lead to other problems such as oxidation of the wire surface.

[0006] It is therefore desired to provide a high control system for industrial applications that allows changing the thermal treatments to different elongated elements running side by side and / or to control the treatment along the length portions thereof.Disclosure of Invention

[0007] It is an object of embodiments of the present invention to provide a shielding system for a furnace which allows controlling the thermal treatment of an elongated element conveyed through a furnace, a method of thermal treating by induction heating and a furnace wherein the shielding system is incorporated.

[0008] In a first aspect, a shielding system for an induction furnace is provided for heating one or more elongated elements while being conveyed through said furnace. The shielding system comprises one or more shielding tubes configured to shield the one or more elongated elements from magnetic fields induced by the furnace, the shielding system including a guiding system for guiding and holding said one or more shielding tubes.

[0009] It is an advantage of embodiments of the present invention that it allows testing the influence of heating in predetermined parameters of the wire.

[0010] In some embodiments of the present invention, the one or more shielding tubes are arranged to be variably inserted over a specified length inside the induction furnace.

[0011] It is an advantage of embodiments of the present invention that different heating treatments can be applied by changing the amount of heat generated in the element, with no need of changing the current throughthe induction coils, without coolants and with no need to change the speed of the elongated element.

[0012] In some embodiments of the present invention, a plurality of shielding tubes are selectably insertable inside the induction furnace. It is an advantage that the elongated pieces can be treated simultaneously thus saving time.

[0013] In some embodiments of the present invention, one or more shielding tubes have a cut to allow inserting the elongated element. It is an advantage that the wire can be threaded inside the shielding tube, so the tube can be introduced in the coil without having to remove the wire from the furnace.

[0014] In some embodiments of the present invention, one or more shielding tubes, for example each tube, comprise or consist of an electrically conductive but amagnetic material.

[0015] It is an advantage of embodiments of the present invention that the shield can block magnetic fields from reaching inside the shield without heating to the same degree the elongated element as where no shield is present.

[0016] In some embodiments of the present invention, the guiding system comprises a holder on a guide rail for holding the one or more shielding tubes.

[0017] It is an advantage of embodiments of the present invention that the shield can be operated with no need of touching it directly, avoiding potential risks of e.g. scalding.

[0018] In a second aspect, a method of adjusting the heat applied to an elongated element in a mid frequent heating installation is provided. The method comprises heating an elongated element by conveying it through at least one induction coil generating a magnetic field. The length at which the induced magnetic field interacts with the elongated element is adjusted by inserting a shield for magnetic fields between the elongated element and the induction coil surrounding it, over an insertion length. In other words, the residence time of the elongated element which is heated by induction inside the furnace is reduced by inserting a shield which shields the elongated element from the magnetic field induced in the furnace.

[0019] It is an advantage of embodiments of the present invention that different heating treatments can be applied by changing the residence time of the elongated element in the induction field, with no need of coolants and no need to change the speed of some of the elongated elements.

[0020] In some embodiments of the present invention, adjusting the heat applied to an elongated element comprises setting the insertion length of the shield for magnetic fields based on the properties of the elongated element. Multiple elongated elements with different shapes or thickness can thus be heated up in the same way, e.g. at the same temperature, by shielding predetermined elements thus adapting their residence time in the furnace. In some embodiments, the insertion length is set depending on the diameter, and / or tensile strength, and / or composition, and / or coating weight of the elongated element.

[0021] In a further aspect, a method of measuring the influence of induction heating treatment on an elongated element is provided. The method comprises:

[0022] - heating, by induction, at least one elongated element by conveying a portion thereof through at least one induction coil for a first length, obtaining a first treated portion. For example the first length may be the predetermined length of the furnace, thus obtaining a fully treated portion.

[0023] - introducing a shield for magnetic fields over a shielding length, for example a shielding length being at least 5% of the predetermined length, followed by heating, by induction, an elongated element by conveying a portion thereof through the at least one induction coil for the same predetermined length, thus obtaining a second partially treated portion

[0024] - measuring the same property on the at least one elongated element on the first (e.g. fully) treated portion and on the second, partially, treated portion, and comparing the results. The results are indicative of the amount of change to the measured property as a function of the treatment length. The first and second portions may have been treated with the shield inserted at different lengths, for example atzero length (corresponding to the fully treated portion), 5% of the predetermined length, 10% of the predetermined length, 20% or even 50% or larger. 100% of the predetermined length corresponds where the at least on elongated element is completely magnetically shielded from the induction coil.

[0025] It is an advantage that it is possible to provide two elongated element portions of the same elongated element having different thermal treatments. There is no need redirect the wire from the inside of the coil to avoid heating or to change any parameter in the energization of the furnace, allowing control of the amount of energy received by the portions accurately.

[0026] In some embodiments of the present invention, heating the at least one elongated element comprises conveying a plurality of elongated elements simultaneously through the at least one induction coil. At least one of them comprises a shield for magnetic fields inserted between the elongated element and the induction coil surrounding it, over an insertion length. It is an advantage that the elongated pieces can be treated simultaneously thus saving time.

[0027] In some embodiments, heating the plurality of elongated elements comprises conveying all the elements through the same induction coil.

[0028] It is a further advantage that the test elongated element with shielding is being conveyed under substantially the same magnetic field, optionally also the same conditions, as the rest of elongated elements, save for the presence of the shield.

[0029] The method may comprise for example measuring tensile strength on a wire length that is fully treated and on a wire length that is heated up with smaller residence time (thus, with a reduced amount of heat). The results of the tensile strength can be compared so as to obtain the influence of the heating on the tensile strength, and thus estimate the influence of other effects, such as coilability or mechanical deformation, over the tensile strength.

[0030] It is an advantage that the influence of the heating on tensile strength is approximately linear with the residence time in the furnace, that on its turn is proportional to the unshielded length .

[0031] In another aspect, an induction furnace for heating at least one elongated element by induction is provided. It includes conveying means for conveying the at least one elongated element through at least one induction coil for induction heating of the at least one elongated element along a predetermined length. It further comprises the shielding system of embodiments of the first aspect of the present invention, for selectably shielding the elongated element from the magnetic field for a portion, e.g. at least 5%, of the predetermined length. It is an advantage of embodiments of the present invention that it allows providing different heating treatments without additional cooling methods and with the same electromagnetic induction conditions. It is a further advantage that it allows testing the influence of heating in predetermined parameters of the wire.

[0032] In some embodiments, the shielding system is adapted to shield at least 10%, for example at least 13%, 15%, 20%, 25%, 50%, or 100% of the predetermined length.

[0033] In some embodiments, the at least one induction coil is configured for induction heating of a plurality of elongated elements simultaneously, wherein the induction coil is adapted for conveying each elongated element through the same predetermined length of the furnace, wherein one or more shields are provided for selectably shielding one or more of the elongated elements being less than all the elongated elements of the plurality. It is an advantage that it allows comparison between different wires under the same conditions except for the heating conditions.

[0034] In some embodiments, the shielding tube comprises a longitudinal cut along the whole length of the tube thereby transforming the tube to a sleeve. It is an advantage that the wire can be slid into the sleeve through the longitudinal cut, so the sleeve can be introduced in the coil without having to thread the wire through the shield that would necessitate that the wire should be cut.

[0035] In some embodiments, the shield comprises conductive material being non-magnetic, so that alternating magnetic fields generate eddy currents on the exterior of the tube thus rejecting the magnetic field inside the tube. It is an advantage of embodiments of the present invention that the shield can block magnetic fields from reaching inside the shield without heating significantly. The shielding tube may comprise metallic material, e.g. copper, copper alloys, aluminium, aluminium alloysor the like.

[0036] In some embodiments, the furnace comprises a plurality of adjacent and sequential induction coils, further comprising a guiding region of the at least one elongated element traversing sequentially all the induction coils, so that each induction coil forms a section of the predetermined length of the guiding region, wherein the shield for magnetic fields provides shielding of at least one section. In some embodiments, a gap is provided between at least two adjacent and sequential induction coils. The shield provides shielding for magnetic fields of a segment, up to the gap or including a portion thereof. It is an advantage of embodiments of the present invention that the shield can be left in the furnace for long periods of time without risk of damaging it.

[0037] As the shielding system and method allow to optimise the required input of electrical energy to the mid frequent induction furnace, it reduces overall electricity usage, thereby contributing to less emission of green house gasses.

[0038] Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims.

[0039] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.Brief Description of Figures in the Drawings

[0040] FIG 1 illustrates the basic working principle of the shielding system.

[0041] FIG 2 shows how the shielding system can be integrated with a furnace.

[0042] FIG 3 and FIG 4 show a block diagram of favourable methods of providing heat treatment using the shielding system of embodiments of the present invention.

[0043] The drawings are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes.

[0044] Any reference signs in the claims shall not be construed as limiting the scope.

[0045] In the different drawings, the same reference signs refer to the same or analogous elements.Mode(s) for Carrying Out the Invention

[0046] The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.

[0047] Furthermore, the terms first, second and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

[0048] Moreover, the terms top, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.

[0049] It is to be noticed that the term “comprising”, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifyingthe presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. The term “comprising” therefore covers the situation where only the stated features are present and the situation where these features and one or more other features are present. The term “consisting” is limited to the stated features.

[0050] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in other embodiments.

[0051] Similarly it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

[0052] Where in embodiments of the present invention reference is made to “elongated element”, reference is made to’ anything that has a length that is much larger than the dimensions of the cross section perpendicular to that length dimension. The cross section of the elongated element will show a minimum calliper size that is called the ‘thickness ‘t” and a maximum calliper size that is called ‘width ‘w”. Width and thickness can beof about the same size, for example the width is less than ten times the thickness, or even less than five or two times the thickness. When the thickness is equal to the width the wire can have a constant diameter, e.g. the cross section can be a circle or a Reuleaux polygon, for example a Reuleaux triangle. The length dimension of the wire may for example exceed at least 104 times the width.

[0053] An induction furnace includes at least one induction coil including a plurality of windings, and encloses a region through which the elongated element is conveyed or moved through. When active, an alternating current flows through the windings and that generates an alternating magnetic field within the coil for induction heating. The alternating magnetic field in the coil generates alternating eddy currents in ferromagnetic material, that heat the element through the resistance of the ferromagnetic material.

[0054] Where reference is made to a ‘coil’ or ‘induction coil’, reference is made to a plurality of windings, usually provided as a single unit, which carry current in the same direction. Therefore, an induction furnace can include many sequential coils connected between them, even if a series connection is provided between them via a connection. In some cases, the coils are connected so that they provide current travelling in opposite directions, thus they provide magnetic fields in opposite directions, to reduce voltage buildup as noted below.

[0055] Induction furnaces can be used for example to provide heat treatment of elongated elements such as wires (also bars, cables, etc.). These treatments include annealing, stress relief, thermodiffusion, etc. Induction furnaces work best with high magnetic permeability materials such ferromagnetic materials such as cobalt, iron, nickel and alloys thereof for example steel. Where in embodiments of the present invention reference is made to ‘furnace’, reference is made to the part of the installation for heating. The mid-frequent heating installation includes the furnace and may comprise other systems such as mid frequent current supplies cooling systems, safety shielding, etc....

[0056] One or more elongated elements can be inserted inside of, and conveyed through, the coil. Usually many elongated elements can be heated, travelling next to each other within a respective channel, usually a ceramic channel. Rather than having a single coil per elongated element, usually all channels are surrounded by the same coil (or each coil, if many are used).

[0057] The element or elements are conveyed through the coil at a known speed. The speed and the length of the coil determine the residence time of the elongated element inside the coil and thus the amount of energy received from the alternating magnetic field. The induced alternating eddy currents generates the heat inside the elongated element by resistance heating. Of course also the magnitude and frequency of the alternating magnetic field will also influence the heat generated inside the elongated element. For some applications, it is desired that the elongated element receives a variable amount of heat along its length for example to modulate some properties of the elongated element along its length. Alternatively, it may be desired that different elements should receive a different amount of heat than others even if conveyed simultaneously through the furnace. For example when different diameter elongated elements run through the same coil. Or when the wires of equal diameter have different properties due to a difference in composition for example a different amount of carbon in the specific case of steel. However, changing the conveying speed or providing cooling is cumbersome and / or gives inaccurate results.

[0058] The present invention relates to shielding of one or more elongated elements from the magnetic field generated by an induction coil during induction heating, for controlling the heating of the elongated element. The shielding can be applied in a simple way to accurately control the amount of heating without changing the conditions of the rest of furnace and without redesigning the furnace.

[0059] The shielding is interposed between the windings and the elongated element, for preventing the alternating magnetic field induced by the coil from reaching the elongated element, for at least a portion of the furnace. Thus, the residence time of the elongated element can be controlledwithout removing the elongated element from the coil, but by shielding the element from the magnetic field, thus preventing heating of the element.

[0060] In a first aspect, the present invention provides a shielding system for an induction furnace. The system includes a shielding sleeve or hollow tube that can be introduced inside, slid into the furnace, so that the wall of the tube separates the winding of the coil from the elongated element, shielding the elongated element from the magnetic field generated within the coil. The shielding system includes a guiding system for holding and guiding the shielding tube, so the shielding tube can be inserted into, slide into the furnace and isolate or shield the elongated element from the magnetic field generated by the coil over a specified length or shielding length. The shielding tube has a certain length. The shielding tube may be not, partially or completely inserted into the furnace. Notable is that the part of the shielding tube that is not inside the furnace has no influence on the heating, only the part that is inside the furnace reduces the heating length.

[0061] A simple shielding system is shown in FIG 1 . The figure shows a detail of a furnace including a coil 7 for induction heating of one elongated element ‘W. The channel 10 formed by the inside wall of the induction coil may be resistant to heat, and it may comprise a ceramic material. The channel 10 also holds a shielding tube 3, and serves as a guide to the tube 3. The tube 3 is sized so it slidingly fits inside the coil while allowing sufficient room for the elongated element W.

[0062] In some embodiments, the shielding tube can be inserted and removed from the induction furnace, for example by sliding it within the channel. For example the outer diameter may be in the order of few mm less than the inner diameter of the channel. As an indication of the scale, the present invention not being limited thereto, some experimental shielding tubes were made with a diameter of 8 mm and a wall thickness of 1 mm.

[0063] The shielding tube comprises non magnetic, electrical conducting material. For example, the shielding tube may be a tube comprising copper. For example, the tube may be a copper tube of a high purity (soft) Cu, such as the material used for making the induction coils.

[0064] The present invention is not limited thereto, and it may comprise other metals such as aluminum, or any other alloy such as for example brass or bronze as long as it complies with the conductivity and magnetic permeability requirements. Thus, when submitted to very large alternating magnetic fields, the alternating magnetic flux inside the tube drops as eddie currents are generated in the wall of the shielding tube that counter the alternating magnetic field inside the tube.

[0065] The shielding tube can be variably inserted over a specified length inside the induction furnace. For example, it can be introduced over a shielding length of at least 5% of the predetermined length. This, in effect, reduces the time in which the elongated element interacts with the magnetic field (or residence time), thus reducing the heating of the element. Changing the residence time changes similarly the amount of heat in usual working conditions, e.g. while operating under the Curie temperature of the material of the elongated element.

[0066] FIG 2 shows a mid-frequent (MF) table 100 including a shielding system 101 and the furnace 106, with at least one induction coil with many channels, e.g. ceramic channels, or channels made with heat insulating materials, and / or materials which are heat resistant as shown in FIG 1 . These channels allow homogeneous induction heating of a plurality of elongated elements, one per channel. The shielding system 101 comprises at least one shielding tube 3 and a table 103 including a guide rod 104 and a holder 105 for holding the tube. The holder may allow handling of the tube 3 with no need to touch it, since during use the tube may heat up to uncomfortable or even scalding temperatures.

[0067] The shielding system 101 may be placed upstream of the furnace 106, at the entry of the induction coil system 102 including an induction coil, through which the elongated element are introduced in the furnace 106 for heating. As the shielding system 101 can be made short, this leaves enough room for other devices 107, such as roller guides and so on. However, the present invention is not limited thereto, and the shielding system can be placed downstream of the furnace, as long as a portion of the predetermined length of the furnace can be shielded.

[0068] The furnace 106 may include several sequentially disposed induction coil systems, so that the elongated element may travel inside several sequential induction coils. For example, the element may pass through the first induction coil system 102 and enter the following induction coil, e.g. present in an adjacent induction coil system 108. The residence time of the elongated element through the furnace (e.g. through the first induction coil in the first system 102) can be adapted, by limiting exposure to the magnetic field in the coil. This is done by introducing the shielding tube 3 to the desired length into the corresponding channel.

[0069] The MF table may be adapted to heat 15 or more, e.g. 30, e.g. 60 or even more elongated elements. For example, the induction coil may be wide enough to fit all these along the coil, and each of them being inside substantially the same magnetic field. They may cross the induction coil in a respective channel. One, some or all of the channels may be selectively shielded. Thus, the table may include shielding tubes which are selectably insertable inside the induction furnace. The shielding system shown in FIG 2, for example, includes shielding tubes 3 at specified positions. The specified length at which a tube is inserted inside the furnace, in some embodiments of the present invention, can be varied, so the length at which the elongated element interacts with the magnetic field can be varied, thus effectively changing the residence time of the corresponding elongated element inside the furnace.

[0070] The furnace length is a predetermined length which the elongated element traverses inside the furnace, in particular including the distance surrounded by windings of the coil. In general, the furnace length is the distance traversed by the elongated element while being exposed to heatinducing magnetic fields. However, the present invention provides a shielding over a specified distance, so the wire is exposed to heatinducing magnetic fields in a total length smaller than the furnace length. Thus, the elongated element does not need to be led outside the coil, or the current through the coil does not need to be changed in order to modulate the amount of heat delivered to the elongated element.Moreover, heating and heat transfer can be accurately controlled with no need of additional coolants or the like.

[0071] The specified length to which the tube is inserted in the furnace may be around 5% of the predetermined length of the furnace or more. For example, the specified shielding length may be at least 10%, for example at least 13%, 15%, 20%, 25%, 50%, or 100% of the predetermined length. The residence time can be controlled by controlling the shielding length and the speed at which the elongated element is conveyed through the furnace 106.

[0072] The MF table 100 of FIG 2 is used for simultaneous heating of a plurality of elongated elements. The induction coil is adapted for conveying each elongated element through the same predetermined length. Since it is possible to select which elongated element or elements are shielded, it is possible to run simultaneously several treatments with tailored heating for each elongated element, increasing flexibility of the line. This allows compensation of the differences of different elongated elements, so that all of them receive effectively the same heating energy. For example, elements with different diameters, or different composition (e.g. steels with different composition, such as different carbon amounts), or different coatings, or even different thermal or mechanical history (e.g. different tensile strength) could all receive the same net energy, for example, while using the same conditions of heating: same induction coil, same current in the induction coil, same conveying speed, etc. This could be used to adjust the temperature, for example so all the elements reach the same temperature despite having different properties, shape, size, and / or composition. This is enabled by providing a specified shielding length on those elements that require less exposure to the magnetic field to generate the same heating as other elongated elements, while still providing simultaneous treatment to all of them.

[0073] In some embodiments, the tube includes a longitudinal cut or slot so the elongated element, usually a wire, can be threaded inside the tube even if the wire is already installed and ready to be conveyed inside the furnace. In some embodiments, the tube is a closed tube. In this case it would berequired to insert the wire through the tube in the same way as it is inserted through the coil (e.g. through the channel through the coil).

[0074] In particular, the tube may be sized so as to cover a section of the predetermined length covering a whole induction coil. In other words, the tube may reach the border between two induction coils, e.g. between two induction coil systems 102, 108. For example, a gap may be provided between two adjacent (and sequential) induction coils. The tube may be inserted to a specified length equal to the induction coil, up to the gap.

[0075] If the shield covers a whole coil, e.g. reaches the gap, it has been found that the shielding tube can be left inserted in the tube for long periods of time, even days, with no risks of deposition of material in the channel.

[0076] An induction furnace including the shielding system in accordance with aspects of the present invention allows exposing each elongated element to a different heating with no need to change the current magnitude through the induction coil(s). Rather than doing so by e.g. changing the speed of the elongated element or adding cooling elements, they change the amount of EM energy received by the elongated element by introducing shielding tube at different specified lengths. This way the tube wall is between the elongated element and the coil winding. The shielding system (shielding tube, guiding system) can be added to existing furnaces with only minor adaptations.

[0077] In a further aspect, the present invention provides a method of controlling induction heating of an elongated element with no need of reducing or increasing the current through an induction coil. The method comprises shielding the elongated element with a tube, or sleeve, introduced so that the tube contains the elongated element and the coil contains the tube. This insertion reduces the amount of net heating energy transferred to the element being heated. Thus, thermal treatment may be shortened at will, and its influence in properties can be easily decoupled from other influences (e.g. deformation). The method may be carried out by any of the embodiments of the first aspect of the present invention.

[0078] The insertion length is a specified length chosen in accordance with the heating requirements. For example, a plurality of elongated elements withdifferent characteristics may be treated simultaneously in the induction furnace using the same coil(s). If the same thermal treatment is desired, it is necessary to compensate for these differences in the characteristics of the elongated materials. This way, the materials being heated can reach the same temperature even if they are very different. These parameters are heavily material dependent and dependent of the geometry, porosity, coating, even mechanic treatment history. Shielding at a specified length reduces the amount of magnetic field reaching the elongated material, thus reducing the heating of the shielded material. This allows controlling the heating received by each elongated material, by adding shielding in those elements that require less EM energy to heat up to the same temperature as the other elements, less sensitive to the induction.

[0079] FIG 3 is a flowchart with an embodiment of the method. The method comprises providing 301 a shielding tube including a highly conductive and non-magnetic material, for example a metal (as explained above), and inserting 302 it into the furnace, in particular inside the induction coil, in particular for example inside the channel through which the elongated element is conveyed through the coil. The insertion is done up to an insertion distance. This distance can cover 5% of the predetermined length of the furnace, or more, for example 13% or 20% or 25%, up to the whole length of the furnace (100% of the predetermined length).

[0080] The method optionally comprises covering 303 a whole induction coil (so the field generated by windings with the current flowing in the same direction does not reach the elongated element). This allows keeping the process running for long term safely.

[0081] The method can be used for providing an elongated element with a length portion that had the thermal treatment with no shielding, and another length portion with the shielding tube inserted. However this is not the only option, and a plurality of elongated elements can be treated simultaneously while some of them are shielded.

[0082] In a further aspect, the present invention provides a method of measuring the influence of the thermal treatment on a property of the elongated element.

[0083] In a particular embodiment, as shown in FIG 4, the measurement is done on the same wire (or other elongated element). A shielding tube is provided 301 as before. A first length portion of the wire is thermally treated by heating 401 by conveying it through a first length, for example the whole furnace length (thus, without shielding in), and a first sample is taken 402. This may include performing a test or measurement of a physical characteristic of the elongated element. Then the shielding tube is inserted 302 in the furnace up to a length, e.g. an insertion length, surrounding the elongated element (for example following embodiments of the method of the previous aspect) and, after a short stabilisation period, a thermal treatment by heating of a second length portion of the wire is performed 403. Subsequently, a second sample is taken 404 of the length second portion. The properties of first and second sample are compared 405. As before, when the shielding tube is inserted, it can cover 303 the whole length of and induction coil, e.g. up to the region between two coils, e.g. two coils arranged so their currents flow in opposite directions.

[0084] It is noted that the comparisons may be performed between two portions of the elongated element which received different heating processes, in general, for example two portions wherein the first portion is heated with the shield introduced up to a first length and the second portion is heated with the shield introduced up to a second, different, length. For example, one of the portions can be conveyed through the furnace while the shield is inserted to a length, and the other portion is conveyed while the shield is not inserted at all, i.e. the insertion length is zero, so the other portion is fully treated.

[0085] It is also possible to compare the properties of two different elongated elements, one having received a full treatment through the whole furnace predetermined length (with no shielding) and a second having received a thermal treatment with the shield inserted. This can be done as a first approximation, however, there are other factors (such as diameter, coiling, etc.) that cannot be accounted for in this comparison.

[0086] The method can be applied to the measurement of the tensile strength. The influence of the thermal treatment can be considered linear. Forexample, a portion of the elongated element can be thermally treated and shows a value TS of tensile strength. A second portion of the elongated element may be thermally treated after introducing a shielding of a specified length of X% of the predetermined length. The amount of heat applied to the wire will be reduced accordingly without change of speed or additional coolants or the like. In this case, the tensile strength of the second portion would be TS+Delta, that is it has increased with a value Delta. This Delta is proportional to X. A change in tensile strength of the wire has an impact on the properties of the final products made of the wire.

[0087] The shielding tube can be introduced for a specified length of at least 5%, for example at least 10%, for example at least 13%, 15%, 20%, 25%, 50%, at least 100% of the predetermined length of the furnace.

[0088] If the method is carried out on a furnace with a plurality of sequential coils, in some embodiments the method comprises shielding one of the induction coils completely. This coil may be the starting coil at the ingress of the furnace, if there is more space than at the egress. This has been already explained relative to embodiments of the first aspect. The tube may cover the coil up to the point wherein the magnetic field of one coil changes direction due to the direction of the current at the other coil; as indicated above, this place may be a gap between the two sequential coils.

[0089] It is an advantage that the method can be carried out for extensive periods of time since the shielding tube can be left inside the furnace for even days without risk.

[0090] In a further aspect, the present invention provides a furnace. The furnace may integrate a shielding system as in embodiments of the first aspect.

[0091] Embodiments of such furnace are shown in FIG 1 and FIG 2. The induction furnace may be linked to conveying means for conveying the at least one elongated element through at least one induction coil. The conveying means may be external to the present invention. The furnace may comprise a controller including connections to the furnace and the conveying means, and may be programmed for controlling both the speedof the elongated element and the current through the coils, so as to control the heating of the elongated element and the thermal treatment.

[0092] As shown in the previous figures, the furnace includes a shielding system with one or more tubes insertable within the at least one induction coil for selectably shielding the elongated element from the magnetic field for a specified length, being at least 5% of the predetermined length. The furnace also includes a guiding system for holding and guiding the tube. This system can be provided as a table. It is an advantage of embodiments of the present invention that the furnace allows carrying out any of the methods of the previous aspects. In particular it allows providing different heating treatments without additional cooling methods and with the same electric conditions. It is a further advantage that it allows testing the influence of heating in predetermined parameters of the wire. In some embodiments, some elongated elements are shielded for a specified distance, while others are shielded for a different distance, the distances being chosen taking into account at least the geometry and composition of the elongated elements, so that every elongated element receives the same thermal treatment, for example the same net heat energy. A furnace with the same electric conditions and conveying conditions can be obtained for the simultaneous treatment of many elongated elements, while providing different heating conditions to some of them (different length for which effective heating is provided).

[0093] At least one induction coil is configured for induction heating of a plurality of elongated elements simultaneously. The coil, rather than a cylinder with a circular cross section, may be an elongated shape with an elongated cross section, closer to a rectangle. This allows a plurality (e.g. 30 or more, e.g. 60 or more) of elongated element to be laid out next to each other. This way, each elongated element may be conveyed through the same predetermined length. One or more shielding tubes are provided on a table, for selectably introducing some of these into the furnace, thus shielding some of elongated elements.

[0094] As explained earlier, the furnace may have channels (e.g. ceramic tubes) inside the coil or coils, extending the whole predetermined length of thefurnace. The shield tubes slidingly fit the channel. The guiding system may include also guides e.g. guiding rods attached to the furnace, and may include holders for handling the shielding tube with no need to directly touch it. These may be included in a table as an extension of the MF table.

Claims

Claims1 . A shielding system (101 ) for an induction furnace (100) for heating one or more elongated elements (W) while being conveyed through said furnace, characterised in that the shielding system comprises one or more shielding tubes (3) configured to shield the one or more elongated elements from magnetic fields induced by the furnace, the shielding system including a guiding system (10, 104, 105) for guiding and holding said one or more shielding tubes in or out of said induction furnace.

2. The shielding system according to claim 1 wherein the one or more shielding tubes are arranged to be variably inserted over a specified length inside the induction furnace.

3. The shielding system according to claim 1 or 2 for heating a plurality of elongated elements and wherein a plurality of shielding tubes are selectably insertable inside the induction furnace.

4. The shielding system according to any one of claims 1 to 3 wherein one or more shielding tubes have a longitudinal cut over the whole length of the tube.

5. The shielding system according to any one of claims 1 to 4 wherein the one or more shielding tubes comprise an electrically conductive but amagnetic material.

6. The shielding system according to any one of claims 1 to 5 wherein the guiding system comprises a holder (105) on a guide rail (104) for holding the one or more shielding tubes.

7. A method of adjusting the heat applied to an elongated element in an induction heating installation comprising heating an elongated element by conveying it through at least one induction coil generating a magnetic field, further comprising adjusting the length at which the induced magnetic field interacts with the elongated element by inserting (302) a shield for magnetic fields between the elongated element and the induction coil surrounding it, over an insertion length.

8. The method according to claim 7, wherein adjusting the heat applied to an elongated element comprises setting the insertion length based on the properties of the elongated element.

9. The method according to claim 8, wherein the insertion length is set depending on the diameter, and / or tensile strength, and / or composition, and / or coating weight of the elongated element.

10. A method of measuring the influence of induction heating treatment on an elongated element, comprising- heating (401 ) by induction at least one elongated element by conveying a portion thereof through at least one induction coil for a first length being at least the length of the furnace, thus obtaining a first treated portion,- positioning (302) a shield for magnetic fields over a shielding length,- heating (403) by induction an elongated element by conveying a portion thereof through the at least one induction coil for a second length being different from the first, thus obtaining a partially treated portion,- measuring (402, 404) the same property on the at least one elongated element on the first treated portion and on the partially treated portion after heating with the introduced shield, and comparing (405) the results.11 . The method according to claim 10 wherein heating the at least one elongated element comprises conveying a plurality of elongated elements simultaneously through the at least one induction coil, wherein at least one of them comprises a shield inserted between the elongated element and the induction coil surrounding it, over an insertion length.

12. The method according to claim 11 wherein heating the plurality of elongated elements comprises conveying them through the same at least one induction coil.

13. The method according to any one of claims 10 to 12 wherein measuring the same property comprises measuring tensile strength.

14. An induction furnace for heating at least one elongated element by induction, the furnace comprising conveying means for conveying the at least one elongated element through at least one induction coil for induction heating of the at least one elongated element along a predetermined length, further comprising the shielding system of any one of claims 1 to 6 for selectably shielding the elongated element from the magnetic field for a portion of the predetermined length.

15. The induction furnace according to claim 14 wherein the at least one induction coil is configured for induction heating of a plurality of elongated elements simultaneously and over the same predetermined length of the furnace, wherein one or more shields for magnetic fieds are provided for selectably shielding one or more of the elongated elements and less than all the elongated elements of the plurality.

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