METHOD FOR SOLDERING HEATING ELEMENTS TO CREATE AN ELECTRIC HEATING DEVICE OR A HEATING SOURCE; CORRESPONDING ELECTRIC HEATING DEVICE

Abstract

A method for creating an electric heating source, including a body equipped with one or more housings containing mineral-insulated heating cables. The housings communicate with one or more reservoirs which accept a purely metallic solder material in solid, powder or sheet form. The device is heated in a vacuum degassing plateau, followed by a casting plateau during which the solder melts and fills the housing around the heating cables, resulting in full metal contact between the cables and the body, providing a more uniform temperature and a shorter response time to heating or cooling. Also, a heating source obtained in this manner, including an infrared faired source or an immersion heater for the heating of a liquid bath of molten metal.

Claims

1-21. (canceled)

22. A method for producing an electric heating device, or heating source, of a type comprising at least one body which incorporates at least one housing containing at least one heating resistor which constitutes a linear heating element, said method comprising the following steps: the supply or production and preparation of a body comprising: at least one housing which accommodates at least one mineral-insulated cable which constitutes said at least one heating resistor, and one or more chambers constituting casting reservoirs containing a pure solder material, introduced in the form of a solid, in a fragmented or monobloc form, wherein said casting reservoirs communicate with said housing via one or more “casting” channels, which are arranged to permit said solder material, once melted, to pass through said casting channels and fill the space in said housing surrounding said heating resistor and embed said mineral-insulated cable, at least by gravity and/or in response to a differential pressure; said casting reservoirs containing a quantity of solder material sufficient for filling said housing around said heating resistor; the heat-up of said body, particularly in a kiln, to a given temperature, in order to achieve the melting of said solder material, thereby resulting in a casting of solder via said casting channels.

23. The method as claimed in claim 22, wherein the solder material constitutes a nickel-based metal alloy, particularly from the BNi family.

24. The method as claimed in claim 22, wherein the heating element(s) incorporate exterior shielding in the form of a steel-based alloy, particularly a stainless-steel alloy.

25. The method as claimed in claim 22, wherein the heat-up step comprises a casting step which is executed under a negative pressure, and particularly under a secondary vacuum.

26. The method as claimed in claim 22, wherein the heat-up step comprises at least the following: a preliminary degassing plateau, executed for at least 5 minutes at a temperature which is lower than the melting temperature of the solder, particularly between 700° C. and 900° C., for example at 800° C., plus or minus 10° C.; a casting plateau, executed at a temperature in excess of the melting temperature of the solder and ranging from 900° C. to 1,200° C., of a duration determined in accordance with the mass to be heated, in order to achieve a temperature duration of at least 5 minutes.

27. The method as claimed in claim 22, wherein the solder material is arranged in the reservoir(s) in the form of a powder, in a quantity which represents a volume of powder determined as a function of the volume to be filled, at a ratio ranging from 1.2 to 2.0 times the volume to be filled.

28. The method as claimed in claim 22, wherein the solder is introduced in the form of at least one continuous metal part or metal foil, arranged in a volume which is situated above one or more casting channels, wherein said volume thus constitutes a casting reservoir.

29. The method as claimed in claim 22, wherein the housing(s) are produced to specific dimensions, according to the dimensions of the heating element(s), permitting a mutual clearance which ranges from 0.2 mm to 0.6 mm.

30. The method as claimed in claim 22, wherein is applied to the production of a heating plate, particularly for a semiconductor wafer; wherein the body comprises a flat support plate which is designed to accommodate an object to be heated, in the thickness of which a plurality of linear housings are formed, which receive and surround the linear heating element(s) in a substantially complementary manner; and wherein said body incorporates one or more casting reservoirs, which communicate with said housings from a position which extends transversely to the plane of said support plate.

31. The method as claimed in claim 30, wherein the support plate incorporates a functional region of oval, circular or polygonal shape, which functional region features: on one side, a support face which is designed to accommodate the wafer to be heated, and on the other side, an “internal” face, on the surface of which a plurality of grooves are cut which are substantially concentric to the functional region and, in particular, are circular or constitute one or more spirals; wherein the step for the production of the body comprises: the insertion of the heating element(s) into said grooves, the fitting and attachment on said internal face, particularly by leak-tight welding, of a counter-plate which closes said grooves, thus forming the housing(s) which enclose said heating elements.

32. The method as claimed in claim 31, wherein the preparation of the body includes the deposition of the solder material in one or more casting reservoirs which are temporarily affixed to the counter-plate, or forming a fixing base and/or infeed for the conductors of the heating elements.

33. The method as claimed in claim 30, wherein the support plate is formed of a material which is selected from the following: an austenitic stainless steel, a martensitic stainless steel, a type 304 or 316 or 321 or 310 stainless steel, according to the AISI standard, a nickel-based alloy, a nickel-based alloy of the nickel-chromium type, a titanium metal or alloy, or a copper-based alloy.

34. The method as claimed in claim 22, wherein the method is applied to the production of an immersion heater for the heating of a liquid bath, particularly of molten metal; wherein the body comprises a casing which is designed to be totally or partially immersed in the liquid to be heated, incorporating a housing which is enclosed in a leak-tight manner vis-à-vis said liquid; wherein said housing incorporates one or more linear insertion channels, which receive and enclose the heating element(s) in a substantially complementary manner, and feature at least one insertion end for the introduction of the heating elements; and wherein the casting reservoir(s) are formed by the extension of said insertion ends, or are connected to said insertion ends.

35. The device as claimed in claim 34, wherein the casing which constitutes the body comprises a shell of a ceramic base material, particularly of the silicon nitride, silicon carbide or aluminum oxide type, which forms a leak-tight barrier between the insertion channel and the liquid to be heated.

36. The method as claimed in claim 22, wherein the method is applied to the production of a faired infrared source, particularly for the execution of the welding of one or more thermoplastic parts, wherein the body comprises at least one linear or two-dimensional “fairing” part, incorporating one “functional” surface, the shape of which is defined in order to produce a weld bead in the form which said heating source is intended to produce, wherein said fairing part incorporates, in its thickness, one or more linear grooves which accommodate and surround the linear heating element(s) in a substantially complementary manner; and wherein said body comprises one or more casting reservoirs, which communicate with said housings from a position which extends transversely to the plane of said support plate.

37. The method as claimed in claim 36, wherein the fairing part incorporates one or more grooves which surround the heating element(s), on a different surface, described as the “internal” surface, which faces in a different direction to the functional surface (typically an opposing surface); and wherein the opening of said grooves receives the solder material prior to the casting step, such that said solder material castings into said grooves during the casting step, wherein said grooves thus constitute the housing in which the solder material secures or embeds said heating elements.

38. The method as claimed in claim 36, wherein at least one fairing part is produced by a direct metal laser additive manufacturing process, or “Direct Metal Laser Sintering”, primarily employing a cobalt-chromium alloy, specifically comprising: between 60% and 65% cobalt and between 26% and 30% chromium.

39. The method as claimed in claim 36, wherein the heating element(s) selected have an external diameter equal to or less than 2 mm.

40. A heating device produced by a method as claimed in claim 22.

41. A heating device constituting a heating plate, produced by a method as claimed in claim 30, wherein the support plate comprises at least two independent heating elements.

42. The device as claimed in the claim 41, wherein the device comprises at least one “interior” heating element, forming at least one spiral, and at least one “peripheral” heating element forming a circular loop or a number of spiral loops, which surrounds said interior heating element, particularly in a planar arrangement, and which are parallel to the support surface and, for example, mutually coplanar.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0084] Further particular features and advantages of the invention proceed from the detailed description of one form of embodiment, which is not provided by way of limitation, and from the attached drawings, in which:

[0085] FIG. 1: shows an organigram which illustrates production steps of the method, according to an exemplary form of embodiment;

[0086] FIGS. 2 to 9 illustrate a first exemplary form of embodiment of the invention, involving a heating plate for the treatment of semiconductor wafers:

[0087] FIG. 2: shows a perspective photo illustrating a finished heating plate, according to the first exemplary form of embodiment;

[0088] FIG. 3: shows a sagittal section diagram, illustrating a production step for the heating plate according to FIG. 2,

[0089] FIG. 4: shows a similar diagram illustrating a subsequent step,

[0090] FIG. 5: shows a similar diagram illustrating a subsequent step,

[0091] FIG. 6: shows a similar diagram illustrating a subsequent step,

[0092] FIG. 7: shows a diagram illustrating an alternative to FIG. 4,

[0093] FIG. 8: shows a diagram illustrating an alternative to FIG. 5,

[0094] FIG. 9: shows a diagram in an axial view, illustrating the routing of heating elements within the bed of the heating plate.

[0095] FIGS. 10 to 14 illustrate a second exemplary form of embodiment of the invention, involving an annular infrared source for the welding of thermoplastic materials:

[0096] FIG. 10: shows a perspective view illustrating the infrared source and its heating element, shown in a transparent view,

[0097] FIG. 11: shows a perspective view for the separate illustration of the heating element, in the form which it assumes in the interior of the infrared source,

[0098] FIG. 12: shows a transverse sectional view of part of the annular part of the source, which illustrates a production step,

[0099] FIG. 13: shows a similar illustration of a subsequent step to FIG. 12,

[0100] FIG. 14: shows a similar illustration of a subsequent step to FIG. 13,

[0101] FIG. 15: illustrates an alternative to FIG. 13.

[0102] FIGS. 16 to 18 are longitudinal section diagrams illustrating a third exemplary form of embodiment of the invention, involving an immersion heater for the maintenance of the temperature of a melt bath:

[0103] FIG. 16: illustrates a production step,

[0104] FIG. 17: shows a similar illustration of a subsequent step to FIG. 16,

[0105] FIG. 18: shows a similar illustration of a subsequent step to FIG. 17,

[0106] FIG. 19: shows a transverse section diagram, illustrating the immersion heater according to FIG. 18,

[0107] FIG. 20: shows a transverse section diagram, illustrating the immersion heater according to FIG. 18, in a variant in which the casing comprises three heating elements.

DESCRIPTION OF FORMS OF EMBODIMENT

Heating Plate

[0108] FIG. 1 illustrates production steps of the method, according to a preferred form of embodiment. FIGS. 2 to 6 provide a more detailed illustration of the application of this method in a first exemplary form of embodiment of the invention, involving a heating plate 1 for the treatment of semiconductor wafers.

[0109] The method involves the production of an electric heating device or heating source, of a type comprising at least one body 11 incorporating at least one housing 190 which encloses at least one mineral-insulated heating resistor (shielded or otherwise), forming a linear heating element 191.

[0110] As illustrated in FIG. 1, in a preferred form of embodiment this method comprises the following steps: [0111] EA: supply, or production, and preparation of a body comprising: [0112] at least one closed housing, which encloses said at least one heating resistor, and [0113] one or more casting chambers or reservoirs 180 containing a solder material 8 in powdered form.

[0114] This reservoir communicates with said housing via one or more “casting” channels 181, wherein said reservoirs are arranged to permit said solder material, once melted, to pass through said casting channels and fill said housing 190 around said heating resistor 191, by gravity and/or in response to a differential pressure and/or by capillary action; [0115] EB: heat-up of said body, particularly in a kiln, to a specific temperature, in order to achieve the melting of said solder material 8.

[0116] In greater detail, step EA comprises the following operations, preferably, but not necessarily, in the following order: [0117] E1: production of the body (in this case: the plate 111 and the counter-plate 112), [0118] E2: formation of the housings 190 and of the casting reservoir(s) (in this case: the base 13 and its interior 180) [0119] E3: insertion of the heating elements (191, 192) and thermocouples (71, 172); [0120] if necessary, closure of the bed by welding 1119, [0121] E4: filling of the casting reservoirs 180 with the powdered solder material 8, in a specific quantity required to ensure the filling of all accessible volumes within the housings 190, between the heating elements 191, 192 and the body (the bed 11), and between the thermocouples 171, 172 and the body.

[0122] The heat-up step EB comprises the following operations: [0123] E5: preheating in a kiln, for the achievement of a uniform temperature within the entire assembly, to a temperature which is lower than the melting temperature of the solder material. Optionally, preheating incorporates a degassing plateau, which is executed under a secondary vacuum, either throughout or during a final part of preheating. [0124] E6: casting heating, to a temperature which exceeds the melting temperature of the solder material, for a specific time period, in order to permit the filling of all accessible volumes within the housings, between the heating elements and the body. Melting is executed under a secondary vacuum, i.e. at a pressure lower than 10.sup.−3 mbar (1 microbar).

[0125] The method further comprises a post-casting step EC. This particularly comprises, either in this order or in another order: [0126] E7: a control step, comprising a heat-up test to the service temperature, or close to the service temperature, and including a temperature uniformity control. [0127] E8: a finishing step, particularly involving re-machining for the achievement of the requisite dimensional tolerances. [0128] a preliminary degassing step E5, executed at a temperature below the melting temperature of the solder for at least 5 minutes, particularly in excess of 750° C. and/or below 850° C.; [0129] a casting plateau E6, executed at a temperature in excess of the melting temperature of the solder, and of a specific duration, according to the mass to be heated, in order to achieve a sustained temperature for at least 5 minutes and, for example, for less than 30 minutes.

[0130] According to a particular feature, the preliminary degassing plateau E5 is executed, for example, at a temperature close to 800° C., to a margin of 20° C. or even 10° C., and for a duration of the order of 15 minutes.

[0131] According to a further particular feature, the casting plateau E6 is executed, for example, at a temperature between 940° C. and 1,040° C. for a duration of the order of 10 minutes.

[0132] The solder material 8 constitutes a nickel-based metal alloy, in this case selected from the BNi family.

[0133] The heating element(s) 191, 192 incorporate exterior shielding in the form of a steel-based alloy, in this case stainless steel, for example of type 304L under the terms of the AISI standard (issued by the American Iron & Steel Institute).

[0134] The solder material is arranged in the reservoir(s) in the form of a powder, in a quantity which represents a volume of powder determined as a function of the volume to be filled, at a ratio ranging from 1.2 to 2.0 times the volume to be filled, where this ratio is calculated for a powder comprising between 20% and 45% voids.

[0135] The housing(s) are preferably produced to specific dimensions, according to the dimensions of the heating element(s), permitting a mutual clearance which ranges from 0.2 mm to 0.6 mm between the exterior surface of each heating element and the wall of the housing which accommodates the latter. A particularly satisfactory compromise is thus achieved, which permits the achievement of sufficient enclosure, whilst promoting the casting of material by capillary action.

[0136] FIG. 2 illustrates an example of a heating plate 1 of this type. It comprises a body 11 which constitutes a bed, in this case a circular bed. The support surface 111a of this bed 11 is generally flat, and is employed as a work surface for the production of semiconductors.

[0137] According to requirements, this bed may incorporate the various known devices and arrangements, whether in whole or in part. For example, it may be traversed by air intake ducts, which permit the maintenance of the semiconductor wafer on the support surface by means of aspiration via these ducts. The bed may also incorporate a cooling system of a known type or, for example, a tubular or channel system. Holes may also be provided for the accommodation of a mobile support system for the wafer, described in English as “lift spin”. The surface of the bed may also be provided with an anti-slip channel, or with “gas line” protection, to protect the edge of the wafer which overshoots the bed against deposition.

[0138] On its opposite side, which faces downwards during use, the bed 11 is secured to a base 13, in this case in the center of the bed. This base, which may not be present in other versions, depending upon requirements for the production machine concerned, is employed here as a fixing support for the bed, and protects the various electrical conductors 199, 179 which are routed to the bed 11. The device 1 is illustrated here with a central base 13, but may also be executed differently, with lateral bases or with no base at all, in which case a direct outlet is arranged on the underside of the bed.

[0139] FIGS. 3 to 6 illustrate certain production steps in greater detail, according to a preferred version. FIG. 3 illustrates the heating plate 1 in an inverted position, in order to permit a casting by gravity. The bed 11 is already provided with its housings 190, which are formed in a support plate and in which the heating elements are inserted, in this case two linear heating elements 191 and 192 which can be controlled in a mutually independent manner from one another. The housings are constituted, for example, by grooves which are machined into the support plate 111, and which run along its internal surface 112a.

[0140] In a preferred version illustrated here, the support plate 111 comprises two independent heating elements 191, 192, i.e. which are capable of being controlled in an independent manner from one another. Optionally, the bed may comprise only a single heating element, or may comprise more than two, for example three or four heating elements.

[0141] FIG. 9 illustrates a preferred example of the arrangement of heating elements. A first interior heating element 191 forms a spiral with a plurality of turns, in this case about its point of origin at the center of the bed 11. A second peripheral heating element 192 forms a circular or oval loop (or, optionally, a plurality of spiral loops) which surrounds the interior heating element 191. In the present example, the two heating elements are each arranged in a parallel plane to the support surface 111a, and are mutually coplanar.

[0142] By the separate and differing control of the two heating elements 191 and 192, it is thus possible to execute the separate regulation of heating in the central region and the peripheral region, for example to take account of their mutually differing thermal losses. It is thus easier to achieve a uniform temperature over the entire support surface 111a of the bed.

[0143] In the present example, the bed 11 further comprises optional thermocouples 171, 172, which themselves are inserted in housings within the support plate 111 and are preferably embedded by casting. They permit localized temperature control, and the adjustment of heating by the various heating elements 191, 192.

[0144] The heating elements and thermocouples are powered and connected by means of conductors 199 and 179 respectively. According to the position of the heating elements and thermocouples, their conductors may traverse the bed via a radial groove 181a in the counter-plate 112. They exit, for example, via the base 13, in this case traversing the casting reservoir 180.

[0145] As illustrated in FIG. 3, in a preferred version and regardless of the number of heating elements, a counter-plate 112 is fitted to the internal surface 111b of the support plate 111, and thus closes the housings 190. The counter-plate 112 is welded 1119 to the support plate 111 in a leak-tight arrangement over its entire perimeter and, in this case, is fitted thereto by interlocking with a flange 1110, constituting a skirt which projects from the support plate about its internal surface 111b.

[0146] Clearance between the support plate 111 and the counter-plate 112 is calibrated exactly by means of bosses which project from the surface of one or other thereof, the thickness of which is determined to ensure the requisite clearance around the heating elements 191, 192 in their housings 190. The dimensions of the two plates are preferably adjusted such that a flatness tolerance not exceeding 0.6 mm is achieved between the latter.

[0147] In this case, the device 1 comprises a single casting reservoir which is formed, for example, by a space 180 arranged in a vertical cylinder which projects upwards and forms a base 3. Alternatively, or in combination, a number of casting reservoirs may be employed, for example welded in different positions above the bed, possibly on a temporary basis.

[0148] As can be seen from the figure, the casting reservoir 180 constitutes a separate volume from the housing 190, with which it communicates via an opening which is narrow in comparison with the greatest cross-section of the housing which is to be filled. This reservoir thus extends in a perpendicular direction to said greatest cross-section.

[0149] The casting reservoir 180 communicates with the various housings via casting channels. By way of an example, in this case, said casting channels comprise a space 180 which is arranged between the counter-plate 112 and the top of the heating elements, together with the internal surface 111b of the support plate 111. Alternatively, or in combination, they may also comprise grooves 181b which interlink the different housings, in this case in a radial arrangement.

[0150] The right-hand section of the figure illustrates the support plate 111 only, with its housings 190, but prior to the insertion of the heating elements 191, 192 and the closure of the housings by the counter-plate 112.

[0151] The left-hand section of the figure illustrates the bed, with its heating elements and thermocouples in place, already closed and fitted to its base 13, for example by welding.

[0152] As illustrated in FIG. 4, once the assembly is complete and leak-tight, solder material 8 is inserted into the casting reservoir 180 in powdered form.

[0153] As illustrated in FIG. 5, further to the degassing E5 and the heat-up of the melt material E6, the powdered solder 8 has melted and filled the casting channels 181 and the housings 190, in this case by gravity only, thus constituting a continuous material element 82 which embeds the heating elements 191, 192 in the material of the bed 11. This solder 82 thus permits the secure fixing of the heating elements, and provides continuous material contact thereof with the plate 111 of the bed 11, thus delivering excellent thermal conduction.

[0154] FIG. 6 represents the heating plate 1, restored to its operating position, for example for inspection and finishing. The dash-dotted lines on either side illustrate the peripheral zone of the bed, which will be removed in the final machining step, and incorporating in this case the positioning skirt 1110.

[0155] FIGS. 7 and 8 illustrate an alternative, in which the solder is introduced in the form of one or more metal foils 81. These metal foils are selected with a specific thickness, in order to deliver the requisite volume for the filling of the housings 190 between the heating elements and the bed. They are arranged in the volume situated between the bed 111 and the counter-plate, above the casting channels 181, 181a, such that the latter are covered.

[0156] They are trimmed, as required, to ensure the coverage of all the casting channels. FIG. 7 illustrates the pre-casting step, where the foil 81 is in place and the bed is closed. FIG. 8 illustrates the post-casting step, where the melted solder 82 has embedded the heating elements by engaging with the walls of the grooves 190.

[0157] Optionally, these foils may incorporate a part which is arranged in the interior of the grooves which constitute the housings 190, and which is thus interposed between the bed 111 and the heating elements 191, 192. This part is preferably of a thickness which is smaller than the definitive spacing to be achieved between the heating elements and the walls of their housing/groove 190. Preferably, another part of these foils projects beyond, or is arranged above, the housings 190, in the volume which constitutes the casting reservoir 180, in order to deliver a total quantity of solder which is sufficient to ensure the filling of the housings.

Faired Infrared Source

[0158] FIGS. 10 to 14 illustrate a second exemplary form of embodiment of the invention, which will only be described with respect to its differences. In this example, the heating source 2 is an infrared source for the welding of thermoplastic materials.

[0159] As illustrated in FIG. 10, the infrared source comprises a body 21, the shape of which corresponds to the weld which it is to execute: in this case, an annular bead of width W2 and internal diameter D2. This body incorporates fixing lugs 21, which permit the fixing thereof in its service position. This body 21 forms a fairing element, having a functional surface 21a, which is continuous over the entire emission zone. In this example, this functional surface 21a is a flat surface which, in FIG. 10, is illustrated facing upwards.

[0160] This fairing 21 is heated by a linear heating element 291, supplied by conductors 299, illustrated in isolation in FIG. 11. This heating element 291 is secured to an “internal” surface 21b of the fairing, opposite the functional surface 21a and, in this case, is wound on said internal surface in a spiral having three turns.

[0161] The fairing 21 is illustrated in FIGS. 12 to 14, in a partial sagittal sectional view at the section line AA indicated in FIG. 10.

[0162] FIG. 12 illustrates the fairing with the heating element 291 in place. In this case, the functional surface 21a is flat, and is turned to face the bottom of the figure. The internal surface 21b, on the opposite side, incorporates three grooves, which are mutually parallel, and parallel to the path of the weld bead, arranged here in a spiral. The base of each groove thus constitutes the housing 290 which accommodates the linear heating element 291. The depth of the groove is greater than the diameter of the heating element 291, and leaves a space above the latter which is enclosed by the walls of the groove. This space thus forms a trench, which constitutes a casting reservoir 280.

[0163] As illustrated in FIG. 13, the powdered solder 8 is then introduced into this trench 280 via the longitudinal opening of the groove. In this form of embodiment, the powdered solder fills the opening of the housing, which can thus be considered to be closed around the heating element.

[0164] As illustrated in FIG. 14, further to the heat-up step EC and the casting step E6, the solder has been melted, and has flowed by gravity to the base of the housing 280 and around the heating element 291, wherein this space thus constitutes the casting channels 281 for the method. After cooling, the solidified solder thus forms a continuous material element 82 which embeds the heating element 291 in the fairing material 21, thus ensuring its secure attachment and optimizing thermal conduction.

[0165] FIG. 15 illustrates an alternative arrangement for the introduction of solder, wherein said solder is introduced in the form of a continuous metal element 81. By way of an example, the groove on the left-hand side of the figure contains, above the heating element 291, a solder tape or wire in the form of a continuous element 81. A further example can be seen on the right-hand side of the figure, where a number of contiguous grooves are covered by a single continuous element, in this case a single tape or foil 81 which covers two turns of the heating element 291.

Immersion Heater

[0166] FIGS. 16 to 20 illustrate a third exemplary form of embodiment of the invention, involving an immersion heater 3 for the maintenance of the temperature of a liquid bath of molten metal. The metal may be, for example, tin, zinc, magnesium or aluminum.

[0167] For example, for the production of components by shell-mold casting or lost pattern casting, for example engine blocks, a bath of this type may be maintained continuously at 800° C., for example using two to four immersion heaters per bath, of respective power rating 10 kW to 25 kW.

[0168] FIG. 16 shows a longitudinal section of the body 31 which constitutes a casing in the form of a thermowell, in which a linear heating element 391 has been inserted, connected by a conductor 399. The casing 31 has an interior volume in the form of, for example, a circular or oval cylinder. Over the height of the heating element, this interior volume thus constitutes the insertion channel which accommodates the heating element 391, and thus assumes the role of the housing 390 of said heating element. The upper part of the insertion channel forms the insertion opening, and extends above this heating element, thus assuming a greater volume which, in this case, constitutes the casting reservoir 380. The parts below this upper part may thus be considered to form the casting channels 381.

[0169] As illustrated in FIG. 17, this reservoir 380 is then filled with powdered solder 8, in quantities which are calculated and tested to ensure the enclosure of the heating element.

[0170] As illustrated in FIG. 18 and FIG. 19, further to the heat-up step EC, the liquefied solder has filled the housing 390 around the heating element 391, thus constituting a continuous metal cladding 82 between the surface of the heating element 391 and the interior wall of the body 31.

[0171] FIG. 20 illustrates a variant of an immersion heater of this type, in which a number of heating elements are arranged in a single casing 31, in this case three heating elements 391, 392 and 393 which are supplied, for example, with the three phases of a three-phase voltage. In this case, each of these is arranged in a common region of the volume, wherein this region forms the housing 390 and constitutes a common insertion channel for the heating elements. Alternatively, the housing may also be constituted by a number of distinct regions, which are entirely separate or which only communicate over part of their length, thus constituting a number of distinct insertion channels.

[0172] By the improvement of heat transfers within the immersion heater, energy efficiency is improved and the thermal gradient between the interior and the exterior is reduced, thus further permitting an improvement of the reliability and the service life of the immersion heater.

LIST OF REFERENCE SYMBOLS—NOMENCLATURE

[0173] 1 heating plate [0174] 11 body—bed [0175] 110 support plate flange [0176] 111 support plate [0177] 111a, 111b support surface, internal surface [0178] 112 counter-plate [0179] 1119 leak-tight weld for closure of the bed [0180] 13 base [0181] 171, 172 thermocouples [0182] 179 thermocouple conductors [0183] 190 housings—grooves [0184] 191, 192 heating elements [0185] 199 heating element conductors [0186] 180 casting reservoir [0187] 181 casting channels [0188] 181a (casting channel) disk space between the support plate and the counter-plate [0189] 181b (casting channels) radial inter-groove channels [0190] 182 degassing flues [0191] 2 faired infrared source body, fairing part [0192] 21a, 21b functional surface, internal surface [0193] 290 housing—hollow and base of grooves [0194] 291 heating elements [0195] 299 heating element conductors [0196] 280 casting reservoir—opening of grooves [0197] 281 casting channels—groove trench [0198] 3 immersion heater [0199] 31 body—casing [0200] 381 casting channels—insertion ends [0201] 380 casting reservoir—opening of casing [0202] 390 housing—insertion channels [0203] 391, 392, 393 heating elements [0204] 399 heating element conductors [0205] 8 powdered solder material [0206] 81 foil solder material [0207] 82 solder material after melting