Immersion heater, for heating a bath of liquid metal

Abstract

Immersion heater, for heating a liquid metal bath The present invention relates to an immersion heater (4), for a liquid metal bath, with a sheath (30), which includes a distal end (34) and a proximal end (35); and with heating elements (50, 60) including a supply end (51, 61), disposed between the distal end (34) and the proximal end (35), and a free end (52, 62), disposed between the supply end (51, 61) and the distal end (34).To ensure that the immersion heater can operate at any desired power without being damaged even if the quantity of liquid metal is insufficient, the heating elements (50, 60) comprise primary heating elements (60) and secondary heating elements (50), the respective supply ends (61) of the primary heating elements (60) being arranged between the supply ends (51) of the secondary heating elements (50) and the distal end (34) of the sheath (30). Figure for the abstract: [FIG. 2].

Description

Title of the invention: Immersion heater for heating a liquid metal bath

[0001] The present invention relates to an immersion heater, for heating a bath of liquid metal, and a use of such an immersion heater.

[0002] For the needs of smelting certain metals, particularly aluminum, zinc, magnesium, or tin, it is known to use a furnace comprising a chamber or tank made of refractory material that receives a bath of molten metal, and a lid closing the chamber from the top. Immersion heaters pass through the lid, each carrying heating elements protected by a sheath, the sheath being immersed directly in the molten metal bath. When electrically powered, the heating elements allow the immersion heaters to heat or maintain the temperature of the molten metal bath. These immersion heaters can also be used in the absence of a metal bath to preheat the refractory material of the furnace, while an assembly including the heating elements and their sheath is completely immersed in the furnace air.

[0003] Given the temperatures involved, which can reach approximately 450 to 1200°C, it is critical that the heating elements, when electrically powered, be immersed in a homogeneous medium along their entire length. In other words, they should be fully immersed in the molten metal bath or, if no molten metal is present, fully immersed in air. Indeed, due to the difference in thermal conductivity between air, which is more thermally insulating, and liquid metal, which is more thermally conductive, heating the heating element while it is only half immersed in the metal bath and part of its length protrudes from the bath and is therefore exposed to air, causes rapid deterioration of the element. This is because the portion protruding into the air is susceptible to melting under the effect of the heat, since air dissipates the heat generated by the element less effectively than the molten metal bath.

[0004] One drawback of these constraints is that the furnace chamber must always be completely filled with molten metal, or completely empty, for the furnace to operate. In particular, it is not possible to supply the heating elements, especially at high power, when the furnace chamber is only partially filled with molten metal. During furnace operation, it is therefore necessary to refill the furnace with molten metal very frequently so that the bath level remains above the heating elements, ensuring that the heating elements remain fully immersed.

[0005] The aim of the invention is therefore to propose a new immersion heater capable of operating at any desired power without being damaged even if the quantity of liquid metal is insufficient.

[0006] To this end, the invention relates to an immersion heater for heating a bath of liquid metal. The immersion heater comprises a sheath, which includes a distal end and a proximal end through which a height axis of the immersion heater passes, and which is adapted to be immersed in the bath of liquid metal by its distal end. The immersion heater also includes heating elements, each heating element being arranged entirely inside the sheath and comprising: a supply end, disposed between the distal end and the proximal end and through which the heating element is connected to supply conductors, and a free end, disposed between the supply end and the distal end.

[0007] According to the invention, the heating resistors comprise primary heating resistors and secondary heating resistors, the respective supply ends of the primary heating resistors being disposed between the supply ends of the secondary heating resistors and the distal end of the sheath, along the height axis.

[0008] One idea underlying the invention is that the secondary heating elements can be electrically powered when the liquid metal bath immerses the sheath at least up to the power supply ends of the secondary heating elements, and that, when the liquid metal bath immerses the sheath up to a height intermediate between the power supply ends of the secondary and primary heating elements, the primary heating elements are electrically powered while the secondary heating elements are not. Thus, the primary heating elements, entirely below the surface of the liquid metal bath, provide the heating, while the secondary heating elements, part of which extends above the liquid metal bath, are protected by not being electrically powered.

[0009] The invention also relates to a use of the immersion heater, in which, while the immersion heater is immersed in the liquid metal bath from the distal end of the sheath, the primary heating elements are electrically powered without electrically powering the secondary heating elements or by powering the secondary heating elements at reduced power, if the liquid metal bath immerses the sheath up to a height intermediate between the power supply ends of the primary heating elements and the power supply ends of the secondary heating elements, along the height axis.

[0010] According to other advantageous aspects of the invention, one or more of the following characteristics are provided for the immersion heater, taken individually or according to all technically possible combinations.

[0011] Preferably, the respective supply ends of the primary heating resistors are arranged at mid-height between the supply ends of the secondary heating resistors and the distal end of the sheath, along the height axis.

[0012] Preferably, the supply ends of the secondary heating resistors are at the same height along the height axis. Preferably, the supply ends of the primary heating resistors are at the same height along the height axis. Preferably, the free ends of the heating resistors are arranged at the distal end.

[0013] Preferably, the heating resistors are regularly distributed along a single circle centered on the height axis, with an alternation of secondary heating resistors and primary heating resistors around the single circle.

[0014] Preferably the secondary heating resistances are regularly distributed along a first circle centered on the height axis and the primary heating resistances are regularly distributed along a second circle centered on the height axis, distinct from the first circle.

[0015] Preferably, each heating resistance comprises: two legs, parallel to the height axis, each leg being connected with one of the supply conductors, at the supply end of the heating resistance; and an elbow, connecting the two legs together and forming the free end of the heating resistance.

[0016] Preferably, the immersion heater further comprises: a connection head, fixed to the proximal end of the sheath; a first electrical connector, carried by the connection head, the secondary heating elements being electrically connected to the first electrical connector via the supply conductors, so that the secondary heating elements are electrically supplied when the first electrical connector is electrically supplied, regardless of whether the primary heating elements are electrically supplied or not;and a second electrical connector, carried by the connection head, the primary heating elements being electrically connected to the second electrical connector via the supply conductors, so that the primary heating elements are electrically powered when the second electrical connector is electrically powered, regardless of whether the secondary heating elements are electrically powered or not.

[0017] Preferably, the immersion heater further comprises a compacted powder, which fills the sheath from the distal end, completely submerging the heating elements.

[0018] Preferably, the immersion heater further includes a temperature sensor system, which is arranged inside the sheath, coaxially with the height axis.

[0019] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the drawings as defined below.

[0020] [Fig-1] Fig. 1 is a cross-sectional view of an oven, represented very schematically, and comprising an immersion heater, represented more faithfully, according to a first embodiment of the invention.

[0021] [Fig.2] The [Fig.2] is a perspective view of the immersion heater of the [Fig.1].

[0022] [Fig.3] Fig.3 is a bottom view of the immersion heater shown in the preceding figures, where a sheath, compacted powder, and distal support were omitted.

[0023] [Fig.4] The [Fig.4] is a cross-sectional view of the immersion heater of the preceding figures, following line IV-IV shown on the [Fig.1], where the sheath and the compacted powder are shown.

[0024] [Fig.5] The [Fig.5] is a view similar to that of the [Fig.3], for an immersion heater according to a second embodiment of the invention.

[0025] [Fig.6] The [Fig.6] is a view similar to that of the [Fig.3], for an immersion heater according to a third embodiment of the invention.

[0026] [Fig.7] The [Fig.7] is a view similar to that of the [Fig.3], for an immersion heater according to a fourth embodiment of the invention.

[0027] Fig. 1 shows a furnace according to a first embodiment, with an enclosure 2, a lid 3, an immersion heater 4 and a liquid metal bath 5. In the present example, only one immersion heater is provided, but the furnace could include several identical or similar immersion heaters.

[0028] The enclosure 2, which forms a tank, contains the liquid metal bath 5 and is closed at its top by the lid 3, which is preferably removable. The liquid metal bath 5 is, for example, a bath of liquid aluminum, or of another metal, such as zinc, magnesium, or tin. The metal is preferably a non-ferrous metal, but could alternatively be another type of metal. Preferably, it is a metal whose melting point is below 1200°C. For example, the bath 5 received in the furnace is at a temperature between 450 and 1200°C to be liquid, depending on the type of metal. The enclosure 2 and the lid 3 are advantageously made of a refractory material to withstand these temperatures.

[0029] Alternatively, the oven is presented in a different form, with or without a lid. The chamber can, for example, remain open during operation.

[0030] The immersion heater 4, visible in Figures 1 to 4, defines an axis of height X4. In use, it is advantageous for the axis X4 to be vertical, or otherwise oblique to the vertical. The immersion heater 4 comprises a connection head 10, a sheath 30, a compacted powder 31, supply conductors 32, a temperature sensor system 33, and heating elements, including secondary heating elements 50 and primary heating elements 60.

[0031] The immersion heater 4 is, for example, mounted through the oven lid 3, or through another part of the oven if there is no lid. With the immersion heater 4 mounted in this way, the connection head 10 is entirely outside the oven, here above the lid 3, the sheath 30 passing through the lid 3 to extend into the oven and being immersed in the bath 5 for its distal, i.e., lower part. The immersion heater 4 is designed to heat the bath 5 by electrically supplying the heating elements, while the sheath 30 is immersed in the bath 5.

[0032] The sheath 30, shown in full in [Fig. 1] and shown in dashed lines in [Fig. 2], comprises a distal end 34 and a proximal end 35 through which the height axis X4 passes. The sheath 30 is advantageously cylindrical with a circular base centered on the axis X4, from end 34 to end 35. The distal end 34 may be rounded, as shown in the figures. Alternatively, end 34 may be flat. The sheath 30 forms a pouch, which is closed at the distal end 34, closed from end 34 to end 35, and open at end 35. In use, the distal end 34 is directed downwards while end 35 is directed upwards. The distal end 34 is designed to be immersed in the bath 5, while the proximal end 35 is designed to remain above water. The liquid metal in the bath 5 is therefore kept outside the sheath 30.The sheath 30 is intended to be in direct contact with the bath 5, at least for the part of the sheath 30 intended to be immersed in the bath 5. The proximal end 35, which is above water, is for example received in an opening provided through the cover 3, through which the immersion heater 4 passes through the cover 3.

[0033] Along axis X4, from the distal end 34 to the proximal end 35, the sheath 30 measures, for example, between 0.5 m and 1.50 m (meters). Preferably, transversely with respect to axis X4, along its entire length except at the ends 34 and 35, the sheath 30 defines a cross-section whose outer contour is circular, centered on axis X4, and which has a diameter between, for example, 28 and 170 mm, for example 55 or 75 mm.

[0034] The sheath 30 is advantageously made of a refractory material, for example a refractory ceramic, particularly one based on silicon nitride, or a metal whose melting point is significantly higher than that of the bath 5. Preferably, the material chosen is thermally conductive to transmit the heat generated by the heating elements 50 and 60 to the bath 5, and electrically insulating, given the electrical quantities involved in the elements 50 and 60, which can be achieved with a refractory ceramic. Preferably, the material chosen is resistant to corrosion that may be caused by contact with the bath 5, and facilitates the flow of the liquid metal along the sheath 30, which can also be achieved with a refractory ceramic.

[0035] The connection head 10 and the sheath 30 are fixed to each other via the proximal end 35 of the sheath 30. The connection head 10 advantageously has a through shaft X4 and is positioned beyond the end 35 of the sheath 30, opposite the end 34. The connection head 10 forms a housing, which carries a flange 11, centered on the axis X4, at the height of the end 35 of the sheath 30, and via which the immersion heater 4 is fixed to the cover 3, or to another part of the oven if there is no cover. Preferably, the connection head 10 carries two electrical connectors 12 and 13, preferably separated from each other.

[0036] Alternatively, the connecting head could be angled from the flange 11. Then, the connecting head is not necessarily centered on the axis X4.

[0037] The heating resistors 50 and 60 are arranged entirely inside the sheath 30, between the distal end 34 and the proximal end 35. In the present example, six resistors 50 and six resistors 60 are provided. However, a different number of resistors 50 and / or a different number of resistors 60 could be provided.

[0038] Advantageously, each heating element 50 and 60 consists of an individual resistive filament, which may be coiled. For each element 50 and 60, the resistive filament has a shape and is made of a material that enables it to generate a significant amount of heat by Joule heating when an electric current flows through the element 50 or 60. For example, the resistive filament is made of a metal alloy with high resistivity and a high melting point, such as a nickel-chromium alloy. Nickel-chromium alloy is a high-performance material for producing the Joule heating effect while being resistant to high temperatures, including temperatures that would even exceed the temperature required for the bath 5.

[0039] The supply conductors 32 are made of a material and / or have a cross-section that makes them electrically more conductive than the resistors 50 and 60. For example, each conductor 32 is formed by a conductive metal bar, or by a conductive metal braid. The material chosen is advantageously a high-conductivity metal alloy. Since the conductors 32 are much more conductive than the resistors 50 and 60, no heat or negligible heat is generated by the conductors 32 during use.

[0040] Preferably, each secondary heating resistance 50 can be described as an elongated heating resistance, compared to the primary heating resistances 60, which can be described as shortened heating resistances.

[0041] Each secondary heating element 50 comprises a supply end 51, visible in [Fig. 2], and a free end 52, visible in [Fig. 3]. The free end 52 is disposed near the distal end 34 of the sheath 30, preferably as close as possible to the distal end 34. The supply end 51 is disposed between the distal end 34 and the proximal end 35 of the sheath 30. In other words, the free end 52 is disposed between the supply end 51 and the distal end 34. The end 51 is provided to be disposed inside the enclosure 2, under the cover 3. In other words, each heating element 50 is provided to be entirely inside the furnace.

[0042] Preferably, the resistive filament of the heating element 50 forms successively a first leg 53, a bend 54, and a second leg 53. The legs 53 are visible in Figures 2 and 4, while the bend 54 is visible in Figure 3. The first leg 53 is parallel to the axis X4 and extends from the supply end 51 to the free end 52. The bend 54 extends from the first leg 53 to the second leg 53, connecting the two legs 53 together at the free end 52, by making a half turn. The second leg 53 is parallel to the axis X4 and distant from the first leg 53. The second leg extends from the free end 52 to the supply end. Overall, the secondary heating element 50 advantageously has a general U-shaped form. Each leg 53 advantageously has the same height, along the X4 axis, and are arranged at the same height, along the X4 axis, relative to each other.

[0043] Preferably, the supply ends 51 of the secondary heating resistors 50 are at the same height along the height axis, that is to say, are in the same plane P51 orthogonal to the axis X4. Along the axis X4, the plane P51 is located between the cover 3 and the end 34.

[0044] In particular, the end of each leg 53 at the level of the supply end 51 is at the same height along the axis X4. Preferably, the free ends 52 of the secondary heating resistors 50 are at the same height along the height axis X4, that is to say, are in the same plane P52 orthogonal to the axis X4, distinct from that of the supply ends 51. In particular, the end of each leg 53 at the level of the free end 52 is preferably at the same height along the axis X4, so that all the elbows 54 are at the same height.

[0045] In relation to each other, the two legs 53 and the elbow 54 of the same resistance 50 are advantageously arranged in a plane which is orthoradial with respect to the axis X4, that is to say a plane which is perpendicular to a ray from the axis X4.

[0046] As can be clearly seen in Figures 3 and 4, the resistors 50 are preferentially distributed around the axis X4, in particular along a circle C50 centered on the axis X4. In other words, the resistors 50 are arranged in a cylinder with a circular base, centered on the axis X4, the base of which is the circle C50. In particular, each leg 53 is supported by the cylinder.

[0047] As shown in [Fig. 2], at the supply end 51, each leg 53 is connected to one of the supply conductors 32. In other words, each heating element 50 is electrically connected to two of the supply conductors 32, via their respective supply end 51. Each supply conductor 32 connects the heating element 50, inside the sheath 30, to the connection head 10, passing through the proximal end 35 of the sheath 30.

[0048] During use, for each resistance 50, the two supply conductors 32 are brought to a different electrical potential, thus inducing the passage of electric current in the resistance 50 concerned, producing heat by Joule effect in the resistance 50.

[0049] The electrical connector 12 of the connection head 10 is intended to be connected to an external power supply. When electrically powered by the external power supply, the connector 12 provides electrical power to the secondary heating elements 50 so that they heat the bath 5, whether or not the primary heating elements 60 are electrically powered. For this purpose, each heating element 50 is electrically connected to the connector 12 via two of the supply conductors 32, without being connected to the other connector 13.

[0050] Each primary heating element 60 comprises a supply end 61, visible in [Fig. 2], and a free end 62, visible in Figures 2 and 3. The free end 62 is disposed near the distal end 34 of the sheath 30, preferably as close as possible to the distal end 34. The supply end 61 is disposed between the distal end 34 and the proximal end 35 of the sheath 30, being disposed between the free end 62 and the proximal end 35 of the sheath 30. In other words, the free end 62 is disposed between the supply end 61 and the distal end 34.

[0051] Preferably, the resistive filament of the resistor 60 successively forms a first leg 63, a bend 64 and a second leg 63. The legs 63 are visible in Figures 2 and 4, while the bend 64 is visible in Figures 2 and 3. The first leg 63 is parallel to the axis X4, extends from the supply end 61 to the free end 62. The bend 64 extends from the first leg 63 to the second leg 63, connecting the two legs 63 together at the free end 62, by making a half turn. The second leg 63 is parallel to the axis X4 and distant from the first leg 63. The second leg 63 extends from the free end 62 to the supply end 61. Overall, the primary heating resistance 60 advantageously has a general "U" shape, similar to that of the resistance 50.Each leg 63 advantageously has the same height along the X4 axis, and they are arranged at the same height, along the X4 axis, relative to each other.

[0052] Preferably, the supply ends 61 of the primary heating resistors 60 are at the same height along the height axis, that is, are in the same plane P61 orthogonal to the axis X4. In particular, the end of each leg 63 at the supply end 61 is at the same height along the axis X4. Preferably, the free ends 62 of the primary heating resistors 60 are at the same height along the height axis X4, that is, are in the same plane P62 orthogonal to the axis X4, distinct from that of the supply ends 61. In particular, the end of each leg 63 at the free end 62 is preferably at the same height along the axis X4, so that all the bends 64 are at the same height.

[0053] Advantageously, planes P52 and P62 are provided to be at the same height along the X4 axis, or almost at the same height, as shown in Figures 1 and 2. In other words, the free ends 52 and 62 of the heating elements 50 and 60 are almost at the same height, being positioned at the distal end 34 of the sheath 30. Advantageously, the immersion heater 4 comprises a distal support 39, here discoid in shape, and disposed inside the sheath 30 at the distal end 34, holding the heating elements 50 and 60 in position, by their ends 52 and 62, relative to the sheath 30. Thus, the distal support 39 is traversed by planes P52 and P62.

[0054] Alternatively, planes P52 and P62 could be located further apart. In particular, plane P52 could be at the same level as plane P61.

[0055] Along the X4 axis, the plane P61 is provided to be positioned between the plane P51 and the planes P52 and P62. In other words, the respective supply ends 61 of the primary heating resistors 60 are positioned between the supply ends 51 of the secondary heating resistors 50 and the distal end 34 of the sheath 30, along the X4 axis. In other words, the resistors 60 are shorter than the resistors 50, and therefore do not extend as high as the resistors 50 from the distal end. 34, along the X4 axis. The height difference between the ends 51 and 61 is expected to be significant; that is, preferably, the respective supply ends 61 of the primary heating elements 60 are positioned midway between the supply ends 51 of the secondary heating elements and the distal end 34 of the sheath 30, along the X4 height axis. Alternatively, instead of being midway, the ends 61 could be positioned at one-quarter of the height or three-quarters of the height, or somewhere between these two extremes. The portion of the sheath 30 extending from plane P51 to the proximal end 35 is a non-heating section, which preferably contains no heating elements, but essentially the supply conductors 32.

[0056] In the case of [Fig. 1] given by way of example, the resistors 60 are entirely below the surface of the bath 5, while a proximal part of the resistors 50, including the supply ends 51, are above the surface of the bath 5. In other words, the surface of the bath 5 is at a height intermediate between the planes P51 and P61, along the axis X4. In other words, the sheath 30 is immersed by the bath 5 up to a height intermediate between the ends 51 and 61. In this case, it is advantageous to electrically supply the resistors 60, particularly at high power or maximum power, so that they heat the bath 5, without electrically supplying the resistors 50, in order to avoid any risk of damage, since the resistors 50 are partially submerged.The heating elements 50 can optionally be electrically powered at a reduced power to heat the air contained in the oven above the bath 5, at the same time as the bath 5 is heated.

[0057] Alternatively, in the same situation, it is also possible to choose to electrically supply the heating elements 50 at a reduced power to heat the air contained in the oven above the bath 5, at the same time as the bath 5 is heated, in particular without supplying the elements 60. Alternatively, it is also possible to supply the elements 60, at reduced power, or at full power.

[0058] However, if the furnace contains more liquid metal, the surface of the bath 5 can rise above the plane P51. In this case, all the heating elements 50 and 60 are entirely below the surface of the bath 5. In other words, the bath 5 immerses the sheath to a height greater than that of the ends 61 and 51, along the axis X4. In this case, at least the heating elements 50 can be electrically powered to heat the bath 5. Depending on the application and installation, the heating elements 60 can also be provided with power to contribute to the heating, or not.

[0059] In relation to each other, the two legs 63 and the elbow 64 of the same resistance 60 are advantageously arranged in a plane which is orthoradial with respect to the axis X4, that is to say a plane which is perpendicular to a ray from the axis X4.

[0060] As can be clearly seen in Figures 3 and 4, the resistors 60 are preferentially distributed around the axis X4, in particular along a circle C60, distinct from the circle C50 and centered on the axis X4. In other words, the resistors 60 are arranged in a cylinder with a circular base, centered on the axis X4, the base of which is the circle C60. In particular, each leg 63 is supported by the cylinder C60.

[0061] Here, circle C50, coaxial with circle C60, is expected to have a diameter smaller than circle C60. In other words, the resistors 60 are arranged around the resistors 50.

[0062] As shown in [Fig. 2], at the supply end 61, each leg 63 is connected to one of the supply conductors 32. In other words, each heating element 60 is electrically connected to two of the supply conductors 32, via their respective supply end 61. Each supply conductor 32 connects the heating element 60, inside the sheath 30, to the connection head 10, passing through the proximal end 35 of the sheath 30.

[0063] During use, for each resistance 60, the two supply conductors 32 are brought to a different electrical potential, thus inducing the passage of electric current in the resistance 60 concerned, producing heat by Joule effect in the resistance 60.

[0064] The electrical connector 13 of the connection head 10 is intended to be connected to a different external power supply than that of connector 12, or at least to be able to be activated independently of that for connector 12. When electrically supplied by the external power supply, connector 13 provides electrical power to the primary heating elements 60 so that they heat the bath 5, whether or not the secondary heating elements 50 are electrically powered. For this purpose, each heating element 60 is electrically connected to connector 13 via two of the supply conductors 32, without being connected to the other connector 12. Preferably, either the heating elements 50 or the heating elements 60 are powered, but not both.

[0065] Advantageously, the compacted powder 31 fills the sheath 30 from the distal end 34 to a plug 38, sealing the sheath 30 near the proximal end 35. The plug 38 is traversed by the supply conductors 32. Between the plug 38 and the distal end 34, the compacted powder 31 completely saturates the heating elements 50 and 60, as well as the ends of the conductors 32 connected to the elements 50 and 60. The heat produced by the elements 50 and 60 is thus diffused to the sheath 30 by heat conduction through of the compacted powder 31. The compacted powder is therefore advantageously chosen for its thermal conductivity, allowing for efficient heat dissipation, while also being electrically insulating. For example, the compacted powder 31 is boron nitride.

[0066] The temperature sensor system 33, visible in Figures 1 and 4, is advantageously located inside the sheath 30. Preferably, the sensor system 33 is arranged coaxially with the axis X4. Preferably, the sensor system 33 comprises one or more temperature sensors. A first temperature sensor is, for example, located between the ends 51 and 52, to measure the temperature at the heating elements 50. A second temperature sensor is, for example, located between the ends 61 and 62 to measure the temperature at the heating elements 60. The temperature sensor system 33 is designed to control the temperature of the immersion heater 4, inside the oven, in order to regulate the power supply to the heating elements 50 and / or 60.

[0067] According to a second embodiment shown in [Fig. 5], the secondary resistances 50 and primary resistances 60, instead of being regularly distributed along two separate circles C50 and C60, are distributed along a single circle C50' centered on the axis X4. The distribution of the resistances 50 and 60 along the circle C50' shown in [Fig. 5] is then similar to the distribution of the resistances 50 along the circle C50 shown in Figures 1 to 4. In the case of [Fig. 5], all around the circle C50', an alternation of resistances 50 and 60 is advantageously provided. In certain situations, this can improve the efficiency of the heat diffusion generated by the resistances 50 and 60 to the bath 5. In this second embodiment of [Fig.[5], the immersion heater 4 is otherwise identical to that of Figures 1 to 4, except possibly for the dimensions of the sheath 30 and the elements it contains, as well as for the cap 38 and the distal support 39, which are modified accordingly. In this embodiment of [Fig. 5], it is also advantageously provided that the free ends 52 and 62 are exactly at the same height along the X4 axis, unlike the embodiment of Figures 1 to 4.

[0068] According to a third embodiment shown in [Fig. 6], the secondary heating elements 50 and primary heating elements 60 are each oriented in a respective plane parallel to the axis X4, but which is neither orthoradial nor radial with respect to the axis X4. In particular, this plane is oblique with respect to the orthoradial or radial plane. Preferably, all heating elements 50 and 60 are provided with the same oblicity, as is the case in [Fig. 6]. This improves the radial compactness of the immersion heater. This principle can be applied to the case where all heating elements 50 and 60 are supported by the same circle C50' shown in the [Fig.6], or in a case where the resistances are distributed according to several circles as shown in figures there 4.

[0069] We have seen that, for the embodiment shown in Figures 1 to 4, the resistors 50 and 60 are, in pairs of resistors 50 and 60, distributed on the same radius from the axis X4. In other words, each resistor 50 is radially aligned with one of the resistors 60. According to a fourth embodiment shown in [Fig. 7], it can be foreseen, on the contrary, that the secondary resistors 50 and primary resistors 60, respectively distributed on the circles C50 and C60 as in the embodiment of Figures 1 to 4, are offset, the resistors 50 with respect to the resistors 60, around the axis X4. In other words, in pairs of resistors 50 and 60, each resistor 50 is offset around the X4 axis relative to the nearest resistor 60, rather than being radially aligned with said resistor 60. In this example, the resistors 50 and 60 can be oriented along respective orthoradial planes as in the embodiment of figures 1 to 4.Alternatively, the resistors could be oblique, as in the embodiment of [Fig.6].

[0070] Any feature described for one of the above embodiments can be applied to any other embodiment described above, as far as technically possible.

Claims

Demands

1. Immersion heater (4), for heating a liquid metal bath (5), the immersion heater (4) comprising: • a sheath (30), which includes a distal end (34) and a proximal end (35) through which a height axis (X4) of the immersion heater (4) passes and which is capable of being immersed in the liquid metal bath (5) by the distal end (34); and • heating resistors (50, 60), each heating resistor (50, 60) being arranged entirely inside the sheath (30) and comprising: • a supply end (51, 61), disposed between the distal end (34) and the proximal end (35) and through which the heating resistor (50, 60) is connected to supply conductors (32), and • a free end (52, 62), disposed between the supply end (51, 61) and the distal end (34);in which the heating resistors (50, 60) comprise primary heating resistors (60) and secondary heating resistors (50), the respective supply ends (61) of the primary heating resistors (60) being arranged between the supply ends (51) of the secondary heating resistors (50) and the distal end (34) of the sheath (30), along the height axis (X4), characterized in that the free ends (52, 62) of the heating resistors (50, 60) are arranged at the distal end (34).

2. Immersion heater (4) according to claim 1, wherein the respective supply ends (61) of the primary heating elements (60) are arranged mid-height between the supply ends (51) of the secondary heating elements (50) and the distal end (34) of the sheath (30), along the height axis (X4).

3. Immersion heater (4) according to any one of the preceding claims, wherein: • the supply ends (51) of the secondary heating resistors (50) are at the same height (P51) along the height axis (X4); and / or • the supply ends (61) of the primary heating resistors (60) are at the same height (P61) along the height axis (X4); and / or • the free ends (52, 62) of the heating resistors (50, 60) are strictly at the same height along the height axis (X4).

4. Immersion heater (4) according to any one of the preceding claims, wherein the heating elements (50, 60) are regularly distributed along a single circle (C50') centered on the height axis (X4), with an alternation of secondary heating elements (50) and primary heating elements (60) around the single circle (C50').

5. Immersion heater (4) according to any one of claims 1 to 3, wherein: • the secondary heating elements (50) are regularly distributed along a first circle (C50) centered on the height axis (X4); and • the primary heating elements (60) are regularly distributed along a second circle (C60) centered on the height axis (X4), distinct from the first circle (C50).

6. Immersion heater (4) according to any one of the preceding claims, wherein each heating element (50, 60) comprises: • two legs (53, 63), parallel to the height axis (X4), each leg (53, 63) being connected with one of the supply conductors (32), at the supply end (51, 61) of the heating element (50, 60); and • an elbow (54, 64), connecting the two legs (53, 63) together and forming the free end (52, 62) of the heating element (50, 60).

7. Immersion heater (4) according to any one of the preceding claims, further comprising: • a connection head (10), fixed to the proximal end (35) of the sheath (30); • a first electrical connector (12), carried by the connection head (10), the secondary heating elements (50) being electrically connected to the first electrical connector (12) via the supply conductors (32), so that the secondary heating elements (50) are electrically supplied when the first electrical connector (12) is electrically supplied, regardless of whether the primary heating elements (60) are electrically supplied or not;and • a second electrical connector (13), carried by the connection head (10), the primary heating resistors (60) being electrically connected to the second electrical connector (13) via the supply conductors (32), so that the primary heating resistors (60) are electrically powered when the second electrical connector (13) is electrically powered, regardless of whether the secondary heating resistors (50) are electrically powered or not.

8. Immersion heater (4) according to any one of the preceding claims, further comprising a compacted powder (31), which fills the sheath (30) from the distal end (34), completely submerging the heating elements (50, 60).

9. Immersion heater (4) according to any one of the preceding claims, further comprising a temperature sensor system (33), which is disposed inside the sheath (30), coaxially with the height axis (X4).

10. Use of the immersion heater (4) according to any one of the preceding claims, wherein, while the immersion heater (4) is immersed in the liquid metal bath (5) from the distal end (34) of the sheath (30), a supply of electrically the primary heating resistors (60) without electrically supplying the secondary heating resistors (50) or supplying the secondary heating resistors (50) at reduced power, if the liquid metal bath (5) bathes the sheath (30) up to an intermediate height between the supply ends (61) of the primary heating resistors (60) and the supply ends (51) of the secondary heating resistors (50), along the height axis (X4).

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