Heating element, heating module, heat treatment apparatus & method

Abstract

A heating element (10) configured to convert electric energy into heat during operation. The heating element (10) is arranged to form at least one heating zone (14) comprising at least four shanks (16), whereby each shank (16) extends between an upper end (18) of a heating zone (14) and a lower end (20) of a heating zone (14) during operation. The at least one heating zone (14) has a length, Le, of at least about 400 mm. The at least four shanks (16) are arranged in at least one non-planar configuration having a polygonal cross-section (32), whereby at least four shanks (16) are located at vertices (A, B, C, D) of the polygonal cross-section (32). Each of the at least four shanks (16) is connected to at least one adjacent shank (16) so that adjacent shanks (16) located at adjacent vertices (A-B, B-C, C-D, D-A) of the polygonal cross-section (32) are configured to conduct an electric current in opposite directions during operation.

Description

[0001] HEATING ELEMENT, HEATING MODULE, HEAT TREATMENT APPARATUS & METHOD

[0002] Field of Disclosure

[0003] The present disclosure relates to a heating element configured to convert electric energy into heat during operation. The present disclosure also relates to a heating module comprising at least one such heating element. The present disclosure further relates to a heat treatment apparatus comprising at least one such heating element or at least one such heating module. The present disclosure also relates to a method for manufacturing such a heating element or such a heating module.

[0004] Background of the Disclosure

[0005] Resistance-heated furnaces rely on the heat produced through the Joule effect within their heating elements when an electric current passes through them. Such heating elements (which are also known as resistors) may be made of metallic materials, such as iron- chromium-aluminium (FeCrAI) alloys, or ceramic materials, such as molybdenum disilicide (MoSi2).

[0006] Metallic heating elements are typically only used for temperatures up to 1200°C whereas ceramic heating elements are suitable for use in applications requiring heating element temperatures exceeding 1200°C. Molybdenum disilicide heating elements can for example be effectively utilized for heating element temperatures up to 1900°C, which makes them suitable for demanding industrial heating applications in fields such as glass manufacturing and steel production. The utilization of ceramic heating elements has however faced some limitations due to the decreasing strength and creep resistance of ceramic material at elevated temperatures, which can lead to softening and deformation of ceramic heating elements during operation.

[0007] Additionally, both metallic and ceramic heating elements may experience detrimental deformation due to electromagnetic forces resulting from the interaction between electric currents flowing through them and the magnetic fields generated around them. These electromagnetic forces can cause undesired shape changes, size variations, and movement of the heating elements away from their intended installation position. If a heating element becomes bent or twisted out of shape during operation, the risk of unintended current paths is increased and the performance and structural integrity, as well as the safety, reliability, and efficiency of the heating element may be adversely affected. Existing multi shank heating elements are often arranged to form a heating zone with a length of less than 400 mm to reduce the volume exposed to electromagnetic forces and thereby reduce deformation due to electromagnetic forces. Shorter heating elements also offer greater torsional rigidity compared to longer heating elements due to their reduced flexibility, making them more resistant to bending and twisting. However, a heating zone having a length of less than 400 mm may be insufficient for certain applications.

[0008] Description of the Disclosure

[0009] In an aspect of the disclosure, there is provided an improved heating element configured to convert electric energy into heat during operation comprising the features recited in claim 1.

[0010] The heating element is arranged to form at least one heating zone comprising at least four shanks, whereby each shank extends between an upper end of a heating zone and a lower end of a heating zone during operation. The at least one heating zone has a length, Le, of at least about 400 mm. The at least four shanks are arranged in at least one non-planar (three-dimensional) configuration having a regular or non-regular polygonal cross-section, whereby at least four shanks are located at vertices of the polygonal cross-section. Each of the at least four shanks is connected to at least one adjacent shank so that adjacent shanks located at adjacent vertices of the polygonal cross-section are configured to conduct an electric current in opposite directions during operation. The at least four shanks do not necessarily have to have the same length.

[0011] When electric current flows through a heating element during operation, it generates a magnetic field around the heating element. The direction of the magnetic field will depend on the direction of the electric current flow. Shanks conducting electric current in opposite directions will experience repulsive forces, pushing them apart. Shanks conducting electric current in the same direction will experience attractive forces, pulling them together.

[0012] In the heating element according to the present disclosure, adjacent shanks located at adjacent vertices of the polygonal cross-section will experience a repulsive force pushing them away from each other during operation. Non-adjacent shanks, such as shanks located at diagonally opposing vertices (across the polygonal cross-section) will experience an attractive force pulling them together during operation. However, since the non- adjacent shanks are located further apart than the adjacent shanks, the attractive forces experienced by non-adjacent shanks will be weaker than the repulsive forces experienced by the adjacent shanks. The net force on the shanks will push all of the shanks outwardly away from each other during operation, creating a stable configuration.

[0013] Detrimental deformation of the heating element will thereby be reduced or prevented since the shanks will be prevented from moving inwards towards each other, away from their intended installation position. This will reduce or prevent bending or twisting of the shanks and the risk of shanks coming into contact with one another during operation and creating unintended current paths. The heating element will thereby exhibit improved performance, structural integrity, safety and reliability.

[0014] The inventors have surprisingly found that by configuring a heating element having at least four shanks and at least one heating zone with a length of at least 400 mm, so that, during operation, each of the at least four shanks is connected to at least one adjacent shank so that adjacent shanks are arranged to electromagnetically repel one another enhanced electromagnetic stability will be promoted.

[0015] Such a heating element has the ability to heat large areas and is due to its length less prone to damage or breakage.

[0016] Furthermore, the hereinabove or hereinafter described inventive heating element eliminates the need to secure the shanks of the heating element using one or more clamps along the length of the shank to prevent it from moving away from its intended installation position during operation. This reduces costs, and simplifies installation, maintenance, and repair work, which in turn reduces downtime, and minimizes stress points on the heating element, and also decreases the risk of damaging the heating element.

[0017] Additionally, the hereinabove or hereinafter described inventive heating element will essentially maintain its shape and structural integrity even if it is used to conduct a high electric current.

[0018] According to an embodiment, the at least one heating zone has a centre axis, and the at least four shanks are arranged in parallel, or essentially in parallel, to the centre axis.

[0019] According to an embodiment, the at least four shanks are arranged so that the vertices of the polygonal cross-section intersect a perimeter of an ellipse or a circle.

[0020] According to an embodiment, the heating element is arranged to form a plurality of alternating peaks and valleys, such as a plurality of alternating U-shaped peaks and valleys. According to an embodiment, the heating element is arranged to form a plurality of adjacently arranged heating zones during operation.

[0021] According to an embodiment, the at least one heating zone is configured to provide omnidirectional heat radiation, i.e. to distribute heat evenly and radially.

[0022] According to an embodiment, the at least one heating zone consists of four shanks or an even number of shanks greater than four, such as six shanks, eight shanks, ten shanks, twelve shanks, or more. According to an embodiment, the at least one heating zone comprises a maximum of four shanks, a maximum of six shanks, a maximum of eight shanks, a maximum of ten shanks, or a maximum of twelve shanks. Each shank may be located at a vertex of the polygonal cross-section. Four shanks may be arranged to form at least one non-planar configuration having a quadrilateral cross section, such as a square, rectangular, rhombus, or parallelogram cross-section. According to embodiments, six shanks may be arranged to form at least one non-planar configuration having a hexagonal cross-section or eight shanks may be arranged to form at least one non-planar configuration having an octagonal cross-section. According to embodiments, ten shanks may be arranged to form at least one non-planar configuration having a decagonal crosssection or twelve shanks may be arranged to form at least one non-planar configuration having a dodecagonal cross-section.

[0023] According to an embodiment, the heating element comprises a plurality of terminals, i.e. two or more terminals, each comprising a first end that is configured to be connected to a heating zone, and a second end that is configured to be connected to an electric power source. A plurality of terminals may be connected to an electric power source individually, or in one or more groups. The first end of a terminal may be connected to a heating zone by welding using any suitable welding technique. The second end of a terminal may comprise a contact-improving surface, such as an oxide-layer-free surface, or a contactimproving coating.

[0024] According to an embodiment, the heating element and / or the plurality of terminals comprise(s) one of the following ceramic materials: a silicide, molybdenum disilicide (MoSi?), molybdenum disilicide alloyed with tungsten (W), chromium (Cr) or aluminium (Al), molybdenum disilicide containing oxides. The physical properties of a silicide, such as MoSi?, for example its high temperature strength, thermal stability and fracture toughness at elevated temperature, can be improved by alloying with tungsten (W) or aluminium (Al). Optionally, the heating element and the plurality of terminals comprise or consist of the same material. According to an embodiment, the heating element has a diameter, D, which may be at least about 0.5 mm, or at least about 1 mm, or at least about 2 mm, or at least about 3 mm, or at least about 4 mm, or at least about 5 mm, or at least about 6 mm, or at least about 7 mm, or at least about 8 mm, or at least about 9 mm, or at least about 10 mm, and up to about 3mm, or up to about 4 mm, or up to about 5 mm, or up to about 6 mm, or up to about 7 mm, or up to about 8 mm, or up to about 9 mm, or up to about 10 mm, or up to about 11 mm, or up to about 12 mm, or up to about 13 mm, or up to about 14 mm, or up to about 15 mm, or up to about 16 mm, or up to about 17 mm, or up to about 18 mm, or up to about 19 mm, or up to about 20 mm, or up to about 21 mm, or up to about 22 mm, or up to about 23 mm, or up to about 24 mm, or up to about 25 mm.

[0025] According to an embodiment the heating element has a diameter, D, and comprises at least one of the following :

[0026] - a shank centre-to-centre distance, a, of about 25 mm to about 250 mm, or about 30 mm to about 200 mm, or about 40 mm to about 150 mm, or about 50 mm to about 120 mm, or about 60 mm to about 110 mm, or about 70 mm to about 100 mm, or about 80 mm to about 90 mm,

[0027] - at least one heating zone having a length, Le, of about 400 mm< Le< about 2000 mm, or a length, Le, of at least about 450 mm, or at least about 500 mm, or at least about 600 mm, or at least about 700 mm, or at least about 800 mm, or at least about 900 mm, or at least about 1000 mm, or at least about 1100 mm, or at least about 1200 mm, or at least about 1300 mm, or at least about 1400 mm, or at least about 1500 mm, or at least about 1600 mm, or at least about 1700 mm, or at least about 1800 mm, or at least about 1900 mm, and up to and including about 1950 mm, or about

[0028] 1900 mm, or about 1800 mm, or about 1700 mm, or about 1600 mm, or about 1500 mm, or about 1400 mm, or about 1300 mm, or about 1200 mm, or about 1100 mm, or about 1000 mm.

[0029] The present disclosure also concerns a heating module comprising at least one heating element according to any of the embodiments described herein. The heating module also comprises at least one support structure and the at least one heating element is mounted on, or suspended from, the at least one support structure. The at least one heating element may be supported from above by attachment to a surface of the at least one supporting element, such as by hanging the at least one heating element from a lower surface of the at least one support structure. Optionally, the heating module may comprise insulation material, which may be connected to the at least one support structure, by mechanical joining and / or gluing for example. The at least one support structure and / or the insulation material and may provide electrical insulation and / or thermal insulation and / or resistance to chemicals and / or resistance to heat and / or resistance to thermal degradation.

[0030] According to an embodiment, the at least one support structure comprises at least one of the following : refractory material, such as a refractory brick or a refractory castable, ceramic material, ceramic fibre, metallic material. The insulation material may comprise ceramic fibre insulation material, such as vacuum-formed ceramic fibre insulation.

[0031] According to an embodiment, the heating module comprises at least one clamp and the at least one heating element is / are clamped to a surface of the at least one support structure using the at least one clamp. The at least one clamp may comprise at least one of the following : a U-shaped clamp, a T-shaped clamp, an L-shaped clamp, an open or closed circular, oval, square or rectangular clamp. The at least one clamp may comprise ceramic material. According to an embodiment the at least one clamp is used only to clamp the heating element at the upper part of the heating element i.e. at the upper 30% or the upper 20%, or the upper 10%, or the upper 5% of the length of the heating element, or at the top of the heating element, thereby securing the top of the heating element in position while permitting the remainder of the heating element to remain unsecured i.e. unclamped.

[0032] The present disclosure further concerns a heat treatment apparatus comprising at least one compartment configured to receive at least one object that is to be heat-treated. The heat treatment apparatus comprises at least one heating element or at least one heating module according to any of the embodiments described herein. Optionally, the at least one compartment at least partly surrounds the at least one heating element or the at least one heating module.

[0033] The present disclosure also concerns a method for manufacturing a heating element configured to convert electrical energy into heat during operation or a heating module comprising such a heating element. The method comprising arranging the at least one heating element to form at least one heating zone having a length, Le, of at least about 400 mm and comprising at least four shanks, whereby each shank extends between an upper end of a heating zone and a lower end of a heating zone during operation. The method also comprises arranging at least four shanks in at least one non-planar configuration having a polygonal cross-section whereby at least four shanks are positioned at vertices of the polygonal cross-section and connecting each of the at least four shanks to at least one adjacent shank so that adjacent shanks located at adjacent vertices of the at least one non-planar configuration are configured to conduct an electric current in opposite directions during operation.

[0034] The method optionally comprises at least one of the following :

[0035] - arranging the at least four shanks in parallel, or essentially in parallel, to a centre axis of the at least one heating zone,

[0036] - arranging the at least four shanks so that the vertices of the polygonal cross-section intersect a perimeter of an ellipse or a circle,

[0037] - arranging the heating element to form a plurality of alternating peaks and valleys, such as a plurality of alternating U-shaped peaks and valleys,

[0038] - arranging the heating element to form a plurality of adjacently arranged heating zones during operation,

[0039] - arranging four shanks in at least one non-planar configuration having a quadrilateral cross-section, such as a square, rectangular, rhombus, or parallelogram cross-section,

[0040] - arranging six shanks in at least one non-planar configuration having a hexagonal cross-section,

[0041] - arranging eight shanks in at least one non-planar configuration having an octagonal cross-section,

[0042] - providing a plurality of terminals comprising a first end that is configured to be connected to a heating zone, and a second end that is configured to be connected to an electric power source,

[0043] - providing a heating element and / or a plurality of terminals comprising one of the following ceramic materials: a silicide, molybdenum disilicide (MoSi?), molybdenum disilicide alloyed with tungsten (W), chromium (Cr) or aluminium (Al), molybdenum disilicide containing oxides,

[0044] - providing a heating element having a diameter, D, and arranging the heating element to comprise at least one of the following : o a shank centre-to-centre distance, a, of about 25 mm to about 250 mm, o at least one heating zone having a length, Le, of about 400 mm< Le < about 2000 mm,

[0045] - suspending at least one heating element from at least one support structure, using at least one clamp for example,

[0046] - clamping at least one heating element to at least one support structure using at least one clamp,

[0047] - clamping at least one heating element to at least one support structure using at least one a U-shaped clamp, a T-shaped clamp, an L-shaped clamp, an open or closed circular, oval, square or rectangular clamp, - clamping at least one heating element to at least one support structure using at least one clamp comprising ceramic material,

[0048] - connecting at least one clamp to an overlying surface or to at least one support structure by at least one of: mechanical joining and / or gluing and / or welding,

[0049] - connecting a first end of a terminal to a heating zone by welding,

[0050] - arranging each shank to extend in a vertical direction during operation,

[0051] - welding ceramic material to form a heating element.

[0052] The steps of a method according to any embodiment of the disclosure may be carried out in any suitable order and not necessarily in the order recited in the claims. A plurality of steps may be carried out at the same time. Part of a step may be carried out before carrying out at least part of at least one other step.

[0053] All embodiments of the disclosure and particular features mentioned herein may be taken in isolation or in combination with any other embodiments and / or particular features mentioned herein (hence describing more particular embodiments and particular features than disclosed herein) without departing from the disclosure of the disclosure.

[0054] Definitions

[0055] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains.

[0056] The term "shank" is intended to mean a part of a heating element that contributes to the overall heat distribution and performance of the heating element, such as an elongated part of a heating element.

[0057] The term "during operation" is intended to mean during the time the at least one heating element is being used convert electric energy into heat.

[0058] The term "the at least four shanks are arranged in at least one non-planar configuration having a polygonal cross-section, whereby the at least four shanks are located at vertices of the polygonal cross-section," is intended to mean that the at least four shanks are not confined to a single (two-dimensional) plane but arranged to form one or more three- dimensional configurations. The cross-sectional shape of the, or each, three-dimensional configuration has a polygonal outline. The polygonal cross-section must have four or more vertices and does not therefore include a three-sided or triangular cross-section. The term "the at least four shanks are arranged in parallel, or essentially in parallel, to the centre axis of the at least one heating zone" is intended to mean that a minimum of four shanks are either positioned : i) in parallel to the centre axis, i.e. in such a way that the at least four shanks extend alongside each other, maintaining a consistent distance apart and do not intersect an imaginary line that runs through the centre of the at least one heating zone, serving as a reference point for the arrangement, or ii) essentially parallel to the centre axis, i.e. in such a way that there are one or more deviations from such a parallel arrangement. The one or more deviations are small enough so as not to significantly affect the performance of the heating element or heating module. For example, two shanks may be considered to be "essentially parallel" if they are within about 40 mm, or within about 30 mm, or within about 20 mm, or within about 10 mm, or within about 5 mm, or within about 2 mm, or within about 1 mm from a parallel arrangement over a length of about 400 mm.

[0059] The term "at least four shanks are located at vertices of the polygonal cross-section" is intended to mean that four shanks, more than four shanks but not all of the shanks, or all of the shanks of the heating element are located at vertices of the polygonal cross-section.

[0060] The term "adjacent shanks" is intended to two shanks of the same heating element that are situated next to each other along the electric current path without any additional shank therebetween.

[0061] The term "adjacent vertices" is intended to mean two vertices of the same polygonal crosssection that have no additional vertex of that polygonal cross-section located between them.

[0062] The term "support structure" is intended to mean a load-carrying arrangement.

[0063] The term "clamp" is intended to mean at least one mechanical fastener, such as a brace, band, or clasp.

[0064] As used herein, the term "comprises" will take its usual meaning in the art, namely indicating that the component includes but is not limited to the relevant features (i.e. including, among other things). The term "comprises" also includes references to a component "consisting of" the relevant feature(s) or material(s). Wherever the word 'about' is employed herein in the context of amounts, such as distances, lengths, diameters, etc., it will be appreciated that such variables are approximate and as such may vary by ±10%, or ±5% or ±2%, or ±1% from the actual numbers specified herein.

[0065] Description of the Figures

[0066] Figure 1: schematically shows a heating element according to the prior art having a heating zone with a length of less than 400 mm,

[0067] Figure 2: schematically shows a heating element according to the prior art having four shanks and a heating zone with a length of less than 400 mm,

[0068] Figure 3: schematically shows a cross section of a heating element according to the prior art,

[0069] Figure 4: schematically shows a perspective view of a heating element according to an embodiment of the disclosure,

[0070] Figure 5: schematically shows a heating module according to an embodiment of the disclosure,

[0071] Figure 6: schematically shows a cross-section through four shanks of a heating element according to an embodiment of the disclosure,

[0072] Figure?: schematically shows a heating element according to an embodiment of the disclosure,

[0073] Figure 8: schematically shows a cross-section through eight shanks of a heating element according to an embodiment of the disclosure,

[0074] Figure 9: schematically shows a cross-section through six shanks of a heating element according to an embodiment of the disclosure,

[0075] Figure 10: schematically shows a plan view of a heat treatment apparatus according to an embodiment of the disclosure, and Figure 11: schematically shows four plan views of at least four shanks arranged located at the vertices of polygonal cross-sections according to embodiments of the disclosure.

[0076] All of the drawings have not necessarily been drawn to scale and the dimensions of certain features may have been exaggerated for the sake of clarity.

[0077] Examples

[0078] Figure 1 shows a prior art heating element 1 comprising a plurality of shanks 2 forming a heating zone having a length, L. The short length of the shanks 2 minimizes the volume of heating element material subjected to electromagnetic forces during operation, thereby reducing the risk of deformation. Additionally, the short shanks 2 possess high torsional rigidity which enhances their resistance to bending and twisting. However, the limited length of the heating zone may render this design unsuitable for applications requiring an extended heating zone.

[0079] Figure 2 shows another prior art heating element 1 featuring four shanks 2 interconnected by connections 3 and arranged in a bellows-type, four-shank configuration. The symmetrical geometry of this configuration offers advantages in plug design, as it significantly reduces the risk of plug 4 cracking due to thermal fluctuations. As with the configuration shown in Figure 1, short length of the shanks 2 minimizes the volume of heating element material subjected to electromagnetic forces during operation, thereby reducing the risk of deformation and their high torsional rigidity enhances their resistance to bending and twisting. Nevertheless, the limited length of the heating zone may still be insufficient for some applications.

[0080] If longer shanks 2 were used in the configuration shown in Figure 2 to create a heating zone, operational issues would arise due to electromagnetic forces as will be explained below.

[0081] Figure 3 illustrates a cross-section of heating element 1 with the same configuration as in Figure 2, but with an extended heating zone having a length of at least 400 mm. The arrows in Figure 3 represent the electromagnetic forces acting on the shanks 2 of the heating element 1 during operation. Attractive forces occur between the two lower connections 3, as well as between opposing pairs of shanks 2 since electric current flows in the same direction in those parts of the heating element 1. Simultaneously, the adjacent shanks 2 of the heating element 1 repel each other in diagonally outward directions as indicated by the arrows shown in Figure 3. If a heating element 1 is configured as in Figure 2 but with an extended heating zone and freely suspended from a plug 4 during operation, deformation of the heating element 1 will occur due to the action of electromagnetic forces as illustrated in Figure 3. The electromagnetic forces will namely lead to undesirable shape changes, dimensional instability, and displacement of the heating element 1 from its intended installation position. The heating element 1 may become bent and twisted, and an unintended current path may be formed. These electromagnetic effects compromise the performance, structural integrity, safety, reliability, and efficiency of the heating element 1.

[0082] To address this issue, prior art solutions include limiting the length of a heating zone of a heating element 1, or using flat, two-dimensional heating elements, which may either be mounted like panels on a furnace wall or suspended from a plug 4 or the furnace ceiling, preferably with their central shanks 2 stapled to the plug 4 or the furnace ceiling for added stability.

[0083] The present disclosure provides a heating element configuration that minimizes deformation caused by electromagnetic forces, thereby enabling a heating element having at least one extended heating zone to be freely suspended from a plug or a furnace ceiling without compromising its performance, structural integrity, safety, reliability, or efficiency.

[0084] The disclosure is illustrated by way of the following examples, which are not intended to be limiting on the general scope of the disclosure.

[0085] Figure 4 shows a heating element 10 configured to convert electric energy into heat during operation according to an embodiment of the disclosure. The heating element 10 is arranged to form a heating zone 14 having a length, Le, of at least about 400 mm and consisting of four shanks 16 that are arranged in parallel to the centre axis of the heating zone 14, whereby each shank 16 is configured to extend vertically between an upper end 18 of the heating zone 14 and a lower end 20 of the heating zone during operation.

[0086] The at least four shanks 16 of a heating element 10 according to the present disclosure do not necessarily have to be arranged in parallel to a centre axis of a heating zone 14, but the closer the at least four shanks 16 are to a parallel alignment, the stronger the repulsive forces between them will be.

[0087] In the illustrated embodiment, the heating element 10 has a circular cross-section. The heating element 10 may comprise or consist of one of the following ceramic materials: a silicide, molybdenum disilicide (MoSi?), molybdenum disilicide alloyed with tungsten (W), chromium (Cr) or aluminium (Al), molybdenum disilicide containing oxides. Such ceramic materials have a high melting point, and good oxidation and corrosion resistance in various atmospheres, including nitrogen, hydrogen, and reducing environments.

[0088] A ceramic heating element 10 according to any of the embodiments of the present disclosure may be used to achieve a heating element temperature of at least 1200°C, or at least 1300°C, or at least 1400°C, or at least 1500°C, or at least 1600°C, or at least 1700°C, or at least 1800°C.

[0089] In the illustrated example, the four shanks 16 are arranged to form a plurality of alternating U-shaped peaks and U-shaped valleys, whereby the upper ends of two adjacent shanks 16 are connected via a connection 34 to form a U-shaped peak at an upper end 18 of the heating zone 14 and the lower ends of each pair of adjacent shanks 16 shanks are connected, via connections 34, to form a U-shaped valleys at the lower end 20 of the heating zone 14. The highest part of the U-shaped peak constitutes the upper end of 18 of the heating zone 14 and the lowest part of the U-shaped valleys constitutes the lower end of 20 of the heating zone 14. The connections 34 are configured to conduct electric current between the shanks 16 and constitute parts of the heating element 10.

[0090] The four shanks 16 are arranged in a non-planar configuration having a square crosssection, whereby each of the four shanks 16 is located at a vertex of the square crosssection. Each of the at least four shanks 16 is connected to at least one adjacent shank 16 so that adjacent shanks 16 located at adjacent vertices of the square cross-section are configured to conduct an electric current in opposite directions during operation.

[0091] The heating element 10 comprises two terminals 26 each comprising a first end 28 that is configured to be connected to the heating zone 14, and a second end 30 that is configured to be connected to an electric power source to form an uninterrupted circuit for the flow of electric current. The second end 30 of each terminal 26 may comprise a contactimproving surface or coating.

[0092] A terminal 26 may comprise the same material as the heating element 10. A terminal 26 may have a larger diameter than the heating element 10. A terminal 26 does not necessarily have to have a uniform diameter. For example, at least part of a terminal 26 may have a conical profile. A heating element 10 according to the present disclosure does not have to be mounted on a floor, wall or roof of a heat treatment apparatus, such as a furnace or ladle, but may be used in hanging applications.

[0093] Figure 5 schematically shows a perspective view of an omnidirectional heating module 12 comprising the heating element 10 shown in Figure 4.

[0094] The heating module 12 comprises a support structure 22 and the heating element 10 is suspended from the support structure 22. In the illustrated embodiment, the support structure has a circular cross-section. A support structure 22 may have any suitable uniform or non-uniform cross-section. The heating element 10 is namely clamped to a lower surface 24 of the support structure 22 using a U-shaped clamp 25. No other clamps are necessary to restrain the heating element 10 during operation. Any number of heating elements 10 may be clamped to a support structure 22.

[0095] At least one clamp 25 of a heating module 12 according to any of the embodiments of the disclosure may be pressed into the heating module's support structure 22, such as to a depth of up to 10 cm, up to 5 cm, up to 3 cm, up to 2 cm or up to 1 cm. According to an embodiment, a surface 24 of a support structure 22 may comprise a groove or opening for receiving at least one clamp 25.

[0096] The heating zone 14 is configured to radiate heat omnidirectionally during operation, i.e. radially outwards from the longitudinal axis of the heating module 12. Such a design ensures uniform, efficient and consistent heat distribution across a desired space, optionally reaching all parts of a surrounding space. This is beneficial for applications such as industrial process equipment where consistent temperature profiles are crucial.

[0097] Figure 6 schematically shows a cross-section 32 through the four shanks 16 of the heating element 10 shown in Figures 4 and 5.

[0098] The four shanks 16 form the vertices A, B, C, D of a square. During operation, electric current flows downwards into and along the shank 16 located at vertex A in a direction into the plane of the paper, along the connection 34 that extends between the lower ends of the adjacent shanks 16 located at vertices A and B, and upwards along the shank 16 located at vertex B in a direction out of the plane of the paper. The electric current then flows along the connection 34 that extends between the upper ends of the adjacent shanks 16 located at vertices B and C and downwards along the shank 16 located at vertex C in a direction into of the plane of the paper. The electric current then flows along the connection 34 that extends between the lower ends of the adjacent shanks 16 located at vertices C and D and upwards along the shank 16 located at vertex D in a direction out of the plane of the paper where it flows out of the heating element 10.

[0099] The shanks 16 located at the diagonally opposing vertices A and C of the square crosssection 32 conduct electric current in the same direction during operation (i.e. downwards into the plane of the paper). The shanks 16 located at the diagonally opposing vertices B and D conduct electric current in the opposite direction during operation (i.e. upwards out of the plane of the paper).

[0100] Each shank 16 generates a magnetic field around it due to the electric current flowing through it. The shank 16 located at vertex A generates a magnetic field that pushes the shank 16 located at vertex B away. Likewise, the shank 16 located at vertex B generates a magnetic field that pushes the shank 16 located at vertex A away. The shanks 16 located at vertices B and C, vertices C and D, and vertices D and A interact in the same way.

[0101] The magnetic fields generated around the shanks 16 located at diagonally opposing vertices A and C, and vertices B and D, cause those shanks 16 to experience an attractive force that pulls them closer together. However, the shanks 16 located at diagonally opposing vertices, i.e. at vertices A and C, and at vertices B and D, are further apart than the shanks 16 located at adjacent vertices, i.e. at vertices A and B, B and C, C and D, and D and A, so the attractive forces between them are weaker than the repulsive forces that push the shanks 16 located at adjacent vertices away from each other. The net effect is that all of the shanks 16 experience repulsive forces that push the shanks 16 away from each other outwardly, which creates a stable configuration.

[0102] The magnitude of the repulsive forces between shanks 16 located at adjacent vertices, A- B, B-C, C-D, and D-A, may be selected by adjusting the electric current strength and the shank centre-to-centre distance, a. Stronger electric currents lead to stronger magnetic fields and more significant repulsion. A smaller shank centre-to-centre distance, a, intensifies the interaction between magnetic fields, while a greater shank centre-to-centre distance, a, reduces the effect. The desired repulsive forces can therefore be achieved by selecting a suitable electric current and a suitable shank centre-to-centre distance, a, for a particular cross-section geometry. The specific cross-section geometry will determine how evenly the repulsive forces are distributed.

[0103] A suitable shank centre-to-centre distance, a, for adjacent shanks 16 located at adjacent vertices A-B, B-C, C-D, D-A of the cross-section may be about 25 mm to about 250 mm. If a heating element 10 as shown in Figures 4 and 5 is freely suspended from a plug 24 during operation, the adjacent shanks 16 will repel each other electromagnetically during operation. The electromagnetic forces will cause the heating element 10 to naturally adopt a geometry resembling a prolate spheroid, effectively reducing the risk of twisting and short-circuiting. As a result, deformation will be minimal and the electromagnetic forces acting on heating element 10 will not compromised its performance, structural integrity, safety, reliability, or efficiency.

[0104] Figure 7 schematically shows a heating element 10 that is arranged to form two adjacently arranged heating zones 14, whereby each heating zone 14 comprises four shanks 16. Each group of four shanks 16 forms a non-planar configuration having a square cross-section. At least one of the connections 34 at the upper end of the heating zones 14 may be clamped to a support structure 22 of a heating module 12.

[0105] Figure 8 schematically shows a cross-section 32 through the eight shanks 16 of the heating element 10 shown in Figure 7. Magnetic fields around the shanks 16 interact to create net repulsive forces that push the shanks 16 of each heating zone 14 outwardly away from each other during operation as described with reference to Figure 6.

[0106] Figure 9 schematically shows a cross-section 32 through six shanks 16 of a heating element 10. The six shanks 16 form the vertices of a hexagon. Each of the shanks 16 is connected to at least one adjacent shank 16 via at least one connection 34 so that adjacent shanks 16 located at adjacent vertices of the hexagonal cross-section 32 are configured to conduct an electric current in opposite directions during operation. Magnetic fields around the shanks 16 interact to create net repulsive forces that push the shanks 16 of each heating zone 14 outwardly away from each other during operation as described with reference to Figure 6.

[0107] A polygonal cross-section 32 of a heating element 10 according to the present disclosure need not necessarily have interior angles of the same size and / or a shank centre-to centre distance, a, of the same magnitude throughout the polygonal cross-section 32 as long as the desired net effect that all of the shanks 16 experience repulsive forces that push the shanks 16 away from each other is achieved.

[0108] Figure 10 schematically shows a plan view of a heat treatment apparatus 36 according to the present disclosure which comprises an omnidirectional heating module 12. The heat treatment apparatus 36 comprises a compartment 38 configured to receive at least one object that is to be heat-treated, which surrounds the omnidirectional heating module 12.

[0109] A plurality of heating elements 10 or a plurality of heating modules 12 according to the present disclosure may be configured to heat different parts of a compartment 38, or different compartments 38 of a heat treatment apparatus 36, to different temperatures by independently controlling individual heating elements 10 or heating modules 12, or adjusting the electric power supplied to one or more specific heating elements 10 or heating modules 12.

[0110] According to an embodiment, the shape of a heating element 10 or a heating module 12 is adapted to conform to the geometry of a surface of at least one object that is to be heat treated in a heat treatment apparatus 36 so that a homogeneous irradiation of the surface of the at least one object may be achieved.

[0111] Figure 11 schematically four plan views of at least four shanks arranged so that the vertices of the polygonal cross-sections 32 intersect the perimeter of an ellipse.

[0112] A heating element 10 according to any of the embodiments of the disclosure may be manufactured by arranging the heating element 10 to form at least one heating zone 14 having a length, Le, of at least about 400 mm and comprising at least four shanks 16, whereby each shank 16 extends between an upper end 18 of a heating zone 14 and a lower end 20 of a heating zone 14 during operation. The method also comprises arranging the at least four shanks 16 to form at least one non-planar configuration having a polygonal cross-section 32 and positioning at least four shanks 14 at vertices A, B, C, D of the polygonal cross-section 32. The method further comprises connecting each of the at least four shanks 16 to at least one adjacent shank 16 so that adjacent shanks 16 located at adjacent vertices A- B, B-C, C-D, D-A of the at least one non-planar configuration are configured to conduct an electric current in opposite directions during operation.

[0113] Options and examples for a given aspect, feature or parameter of the disclosure should, unless the context indicates otherwise, be regarded as having been disclosed in combination with any and all options and examples for all other aspects, features and parameters of the disclosure. For example, any feature disclosed with respect to the heating element 10 may be regarded as having been disclosed in a heating module 12, a heat treatment apparatus 36, or a method for manufacturing a heating element 10 or heating module 12, and vice versa.

Claims

Claims1. A heating element (10) configured to convert electric energy into heat during operation, whereby the heating element (10) is arranged to form at least one heating zone (14) comprising at least four shanks (16), whereby each shank (16) extends between an upper end (18) of a heating zone (14) and a lower end (20) of a heating zone (14) during operation, characterized in that the at least one heating zone (14) has a length, Le, of at least about 400 mm, the at least four shanks (16) are arranged in at least one non-planar configuration having a polygonal cross-section (32), whereby at least four shanks (16) are located at vertices (A, B, C, D) of the polygonal cross-section (32), and each of the at least four shanks (16) is connected to at least one adjacent shank (16) so that adjacent shanks (16) located at adjacent vertices (A-B, B-C, C-D, D- A) of the polygonal cross-section (32) are configured to conduct an electric current in opposite directions during operation.

2. A heating element (10) according to claim 1, characterized in that the at least one heating zone (14) has a centre axis and the at least four shanks (16) are arranged in parallel, or essentially in parallel, to the centre axis.

3. A heating element (10) according to claim 1 or claim 2, characterized in that the vertices (A, B, C, D) of the polygonal cross-section (32) intersect a perimeter of an ellipse or a circle.

4. A heating element (10) according to claim 1 or claim 2, characterized in that the heating element (10) is arranged to form a plurality of alternating peaks and valleys, such as a plurality of alternating U-shaped peaks and valleys.

5. A heating element (10) according to any preceding claim, characterized in that the heating element (10) is arranged to form at least one heating zone (14) comprising : four shanks (16) arranged in a non-planar configuration having a quadrilateral crosssection, such as a square, rectangular, rhombus, or parallelogram cross-section, or six shanks (16) arranged in a non-planar configuration having a hexagonal cross-section, or eight shanks (16) arranged in a non-planar configuration having an octagonal crosssection.

6. A heating element (10) according to any preceding claim, characterized in that the heating element (10) comprises a plurality of terminals (26) each comprising a first end (28) that is configured to be connected to a heating zone (14), and a second end (30) that is configured to be connected to an electric power source.

7. A heating element (10) according to any preceding claim, characterized in that the heating element (10) and / or the plurality of terminals (26) comprise(s) one of the following ceramic materials: a silicide, molybdenum disilicide (MoSi?), molybdenum disilicide alloyed with tungsten (W), chromium (Cr) or aluminium (Al), molybdenum disilicide containing oxides.

8. The heating element (10) according to any preceding claim, characterized in that the least one heating element (10) has a diameter, D, and the heating element (10) comprises at least one of the following : a shank (16) centre-to-centre distance, a, of about 25 mm to about 250 mm, at least one heating zone (14) having a length, Le, of about 400 mm< Le< about 2000 mm.

9. A heating module (12) comprising at least one heating element (10) configured to convert electric energy into heat during operation, whereby the heating module (12) comprises at least one support structure (22), characterized in that the heating module (12) comprises at least one heating element (10) according to any preceding claim mounted on, or suspended from the at least one support structure (22).

10. A heating module (12) according to claim 9, characterized in that the at least one heating element (10) is hung from a lower surface (24) of the at least one support structure (22).

11. A heating module (12) according to claim 9 or claim 10, characterized in that the heating module (12) comprises at least one clamp (25), such as a U-shaped clamp, a T-shaped clamp, an L-shaped clamp, an open or closed circular, oval, square or rectangular clamp, and the at least one heating element (10) is clamped to a surface of the at least one support structure (22) using the at least one clamp (25).

12. A heat treatment apparatus (36) comprising at least one compartment (38) configured to receive at least one object that is to be heat-treated, characterized in that the heat treatment apparatus (36) comprises at least one heating element (10) according to any of claims 1-8, or at least one heating module (12) according to any of claims 9 -13. A heat treatment apparatus (36) according to claim 12, characterized in that the at least one compartment (38) at least partly surrounds the at least one heating element (10) or the at least one heating module (12).

14. A method for manufacturing a heating element (10) configured to convert electrical energy into heat during operation or a heating module (12) comprising at least one such heating element (10), characterized in that the method comprises:- arranging the heating element (10) to form at least one heating zone (14) having a length, Le, of at least about 400 mm and comprising at least four shanks (16), whereby each shank (16) extends between an upper end (18) of a heating zone (14) and a lower end (20) of a heating zone (14) during operation, arranging at least four shanks (16) in at least one non-planar configuration having a polygonal cross-section (32), whereby at least four shanks (16) are positioned at vertices (A, B, C, D) of the polygonal cross-section (32), and connecting each of the at least four shanks (16) to at least one adjacent shank (16) so that adjacent shanks (16) located at adjacent vertices (A-B, B-C, C-D, D-A) of the polygonal cross-section (32) are configured to conduct an electric current in opposite directions during operation.

15. A method according to claim 14, characterized in that the method optionally comprises at least one of the following : arranging the at least four shanks (16) in parallel, or essentially in parallel, to a centre axis of a heating zone (14), arranging the at least four shanks (16) so that the vertices (A, B, C, D) of the polygonal cross-section (32) intersect a perimeter of an ellipse or a circle, arranging the heating element (10) to form a plurality of alternating peaks and valleys, such as a plurality of alternating U-shaped peaks and valleys, arranging four shanks (16) in at least one non-planar configuration having a quadrilateral cross-section, such as a square, rectangular, rhombus, or parallelogram cross-section, arranging six shanks (16) in at least one non-planar configuration having a hexagonal cross-section, arranging eight shanks (16) in at least one non-planar configuration having an octagonal cross-section, providing a plurality of terminals (26) each comprising a first end (28) that is configured to be connected to a heating zone (14), and a second end (30) that is configured to be connected to an electric power source,providing a heating element (10) and / or a plurality of terminals (26) comprising one of the following ceramic materials: a silicide, molybdenum disilicide (MoSi?), molybdenum disilicide alloyed with tungsten (W), chromium (Cr) or aluminium (Al), molybdenum disilicide containing oxides, providing a heating element (10) having a diameter, D, and arranging the heating element (10) to comprise at least one of the following : o a shank (16) centre-to-centre distance, a, of about 25 mm to about 250 mm, o at least one heating zone (14) having a length, Le, of about 400 mm< Le< about 2000 mm.- suspending at least one heating element (10) from at least one support structure (22),- hanging at least one heating element (10) from a lower surface (24) of the at least one support structure (22),- clamping at least one heating element (10) to the at least one support structure (22) using at least one clamp (25),- clamping at least one heating element (10) to at least one support structure (22) using at least one of the following : a U-shaped clamp, a T-shaped clamp, an L-shaped clamp, an open or closed circular, oval, square or rectangular clamp,- clamping the at least one heating element (10) to at least one support structure (22) using at least one clamp (25) comprising ceramic material, connecting at least one clamp (25) to the at least one support structure (22) by at least one of: mechanical joining and / or gluing and / or welding, connecting a first end (28) of a terminal (26) to a heating zone (14) by welding, arranging each shank (16) to extend in a vertical direction during operation, welding ceramic material to form a heating element (10).

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