Manufacturing process of a stabilised burner electrode

Abstract

The present invention relates to a burner electrode with an insulator and an elongated metallic rod extending section by section into or along the insulator, such as are typically used in gas or oil burners of heating systems as ignition or monitoring electrodes. According to the invention, it is proposed that the metallic rod of the burner electrode has at least one stabilizing section which is stiffened against bending moments by a cross-sectional profile that deviates from a circular and rectangular cross-section.

Description

[0001] The present invention relates to a method for producing a burner electrode comprising the steps of producing a rod-shaped metallic rod, providing an insulator and mounting the rod in or on the insulator.

[0002] During heating operation, such electrodes are exposed to the hot flames and exhaust gases of the fuel, thus subjecting them to high thermal stress. Burner electrodes are therefore made of the most heat-resistant material possible, but they still have a limited lifespan. Particularly when the rod-shaped metallic electrodes are installed horizontally in a burner for practical reasons, gravity creates a bending moment, to which the metallic electrodes, repeatedly exposed to high temperatures, yield over time because the metallic electrode material becomes increasingly softer at high temperatures.

[0003] Bending changes the position of the electrode tip, meaning that the electrode may no longer be able to fulfil its intended function, for example, to generate an ignition spark against a ground point or to generate a measurable current.

[0004] Although the metallic parts of such electrodes, or at least those exposed to high temperatures, are typically made of heat-resistant alloys, it is unavoidable that the material softens and bends over time and under high heat exposure. Even vertically mounted electrodes can easily bend and thus lead to the failure of the electrically conductive rods of the electrodes, as these typically have at least one bent tip, which is also exposed to high temperatures and transverse gravity. Bent tips of such electrodes can therefore also become increasingly tilted and eventually no longer function properly.

[0005] EP 3 617 598 A1 discloses a burner electrode with a lower shaft part, a central part adjoining the shaft part at one end, and an electrode tip adjoining the central part at the other end, wherein at least the electrode tip and at least one section of the central part adjoining the electrode tip are made of a high-temperature-resistant material. In order to create a burner electrode which has significantly improved durability and at the same time requires as little as possible of the relatively expensive, refractory material for its production, it is proposed that the central part have cavities at least along the section adjoining the electrode tip and that this section be structurally stabilized by partition walls or struts between the cavities.

[0006] FR 2 951 590 A discloses a burner electrode rod with longitudinal ribs. Geometrically shaped ribs are formed on the surface of the rod. The ribs are regularly distributed around the circumference of the rod. The ribs are formed by knurling the rod. The thickness of the ribs is between three and twenty percent of the rod diameter. The ribs are made of a malleable metal alloy resistant to the corrosion of boiler combustion gases and containing twenty-two percent chromium, five percent aluminum, and seventy-three percent iron.

[0007] DE 10 2006058 284 A1 discloses an electrode for a boiler burner, consisting of an electrode wire with a cross-sectional area, wherein the electrode wire has a first and a second longitudinal section, wherein the first longitudinal section is fastened to the burner by a holder, and wherein the second longitudinal section adjoining the first longitudinal section is designed to project freely, is under its own weight, and has its free end facing the effective area of ​​the burner. It is provided that the cross-sectional area of ​​at least the second longitudinal section has a non-circular shape with respect to an imaginary circular cross-sectional area and has its greatest section modulus against bending in the vertical direction.

[0008] IT MI20 091 540 A1 discloses an electric discharge ignition device for a boiler for space heating and the production of hot water, in particular a condensing boiler, the device comprising a pair of electrodes arranged side by side and connected to a common support element, but insulated from one another. The first electrode is connected to a power supply line and the second electrode is connected to earth. The first electrode has a body fixedly connected to an insulating element connected to the support element, and a first portion fixedly connected to this insulating element. The first electrode further has a second portion and a third outermost portion angled with respect to the second portion (10), the third portion being opposite the second electrode and arranged near a free end of the latter.The second electrode has a first portion connected to the support member and a second portion following the first.

[0009] Compared to this prior art, the present invention seeks to provide a method for producing a burner electrode that remains dimensionally stable despite exposure to high heat and the influence of gravity. This object is achieved by the method according to claim 1.

[0010] The metallic rod of the burner electrode has a stabilizing section which is stiffened against bending moments by a cross-sectional profile that deviates from a circular cross-section and deviates from a rectangular cross-section.

[0011] Deviating from a circular cross-sectional profile in the area of ​​the stabilizing section makes it possible to achieve increased stability with reduced material usage. Reducing the material usage also reduces the weight and thus the influence of gravity on the rod. In other words, the stabilizing section makes it possible to achieve greater stability against gravity-induced deformation under thermal influences while simultaneously reducing material usage.

[0012] Such cross-sectional profiles which provide stiffening against bending moments are known in the art and include a variety of profiles in which the cross-sectional area deviates significantly from the cross-section of the smallest circle encompassing the profile and is only a fraction of the relevant circular area, or which have an aspect ratio greater than 1, i.e. a maximum length of the profile measured in one direction which is greater than the dimension of the cross-section measured perpendicular to the length.

[0013] In preferred embodiments of the invention, the cross section of the profile has an area ratio of less than 3 / 4, better less than 1 / 2, preferably less than a third and in particular less than a quarter compared to the smallest circle encompassing the profile.

[0014] In preferred embodiments of the invention, the aspect ratio of the cross-sectional profile is at least 1.2, preferably at least 1.5. To avoid misunderstandings, the aspect ratio should be clearly defined here as follows: For mirror-symmetrical profiles that have (at least) two mutually perpendicular planes of symmetry, the longer dimension of the profile along one of the planes of symmetry is determined, which is then divided by the shorter dimension perpendicular to it.

[0015] For all other symmetrical or asymmetrical profiles, an aspect ratio consistent with the definition for symmetrical profiles can be defined as the length-to-width ratio of a rectangle enclosing the profile and touching it with all 4 sides, the short side of which is determined as the shortest projection of the profile cross-section onto a straight line.

[0016] An example of such a profile is a T-shaped or double-T-shaped profile, the latter consisting of two parallel, horizontally running webs or flanges in plan view and a vertical connecting web. A cross-shaped profile, consisting of a vertical web and a horizontal web crossing it, also generally exhibits greater rigidity than a round bar with a cross-section of the same area.

[0017] It should be understood that T-sections, double-T sections, and cross sections are merely examples of numerous profile shapes that effectively provide stiffening against bending moments. Most such profiles each have a specific plane in which their bending stiffness is maximum, while the bending stiffness is lower in all other planes. All of these profiles can be designed, and for standard cross-sections, are designed and dimensioned, to meet at least one of the above conditions for area ratio or aspect ratio.

[0018] In a profile composed of webs of the type described above, which can also form triangular or rectangular sections, the individual webs can also have recesses or consist of a latticework or truss structure without significantly impairing the flexural rigidity. This rigidity against bending moments is also known from numerous truss structures, especially from steel structures for bridges, whose load-bearing capacity is largely determined by steel trusses and corresponding bracing.

[0019] InIn one embodiment of the invention, the cross-sectional profile of the stabilizing section has a cross-sectional profile composed of two circular cross-sections. Such a cross-sectional profile could, for example, be formed or composed of two circular cross-sectional profiles by welding two parallel wires or rods with a circular cross-section together. In contrast, however, the previously described embodiment of the rod according to the invention can be manufactured with significantly reduced effort.

[0020] In In one embodiment of the present invention, at least the stabilizing section consists of an AlCrFe alloy.

[0021] The rod has a mounting section and a free section, the mounting section being engaged with the insulator, the free section not being engaged with the insulator, and the free section having a circular or rectangular cross-sectional profile except in the stabilizing section. The rod of such a torch electrode is very easy to manufacture. In one embodiment, a semi-finished product with a circular cross-sectional profile, i.e., a wire, can be used as the starting material. This wire then only needs to be deformed accordingly in the region of the stabilizing section so that it has a stabilizing cross-section there that deviates from the circular shape.

[0022] The free section of the rod has a longitudinal extension. For the purposes of the present application, the longitudinal extension is measured between the insulator and an end of the rod facing away from the insulator. In one embodiment of the invention, in which the rod is produced by forming and bending a semi-finished product in the form of a wire, the longitudinal extension is the length of the semi-finished product before bending and forming. In one embodiment, the stabilizing section is at a distance from the insulator, measured in the longitudinal direction of the rod, which is greater than 10%, preferably greater than 30%, and particularly preferably greater than 50% of the longitudinal extension of the free section. The choice of the exact position of the stabilizing section depends on the length, mass, and intended application of the electrode.A distance of the stabilizing section from the insulator that is greater than 30% and preferably greater than 50% of the longitudinal extent of the free section has proven optimal. In one embodiment of the invention, the distance of the stabilizing section from the insulator, measured in the longitudinal direction of the rod, is at most 80% and preferably at most 75% of the longitudinal extent of the free section.

[0023] In a further embodiment, the stabilizing section has a longitudinal extent of 16 cm or less, preferably 10 cm or less, and particularly preferably 7 cm or less. In one embodiment, the stabilizing section even has a longitudinal extent of 5 cm or less. This reduces the manufacturing effort for the rod. For example, during production by forming a semi-finished product with a circular or rectangular cross-section, only a small part of the semi-finished product needs to be formed, for example, squeezed. In one embodiment, the stabilizing section has a longitudinal extent of 1 cm or more, and preferably 1.5 cm or more.

[0024] In a further embodiment, the free section of the metallic rod has at least two segments angled relative to one another, with the transition between the two segments being arranged in the stabilizing section. In one embodiment, the free section has exactly two segments. The individual segments are preferably straight. If the stabilizing section with the non-circular cross-section is located in the region of the angle, i.e., the transition between the two segments angled relative to one another, stabilization of the metallic rod of the burner electrode can be achieved in a simple manner.

[0025] The metal rod of the torch electrode is manufactured by forming a semi-finished product with a circular or rectangular cross-sectional profile. The forming takes place exclusively in the stabilizing section.

[0026] InIn one embodiment of the invention, the rod consists of an AlCrFe alloy.

[0027] Such alloys are particularly heat-resistant and can still be plastically deformed with reasonable effort.

[0028] In In one embodiment, the forming process is carried out by stamping, squeezing, or drop forging. This, of course, requires a material that is sufficiently plastically deformable.

[0029] According to another embodiment, the burner electrode is manufactured using a metal spraying process.

[0030] Finally, according to one embodiment of the invention, the rod of the burner electrode has at least one section along which the rod is partially curved. This curvature then divides the rod into two segments. The curved section does not necessarily have to include the stabilizing section, although this is preferred. Preferably, the curvature is limited to one plane of curvature.

[0031] It goes without saying that a corresponding electrode is generally installed such that the plane of maximum bending stiffness, i.e., the plane in which the metallic rod generally has its greatest extension, runs parallel to the direction of gravity. This means that the bending moment generated by gravity acts in a direction in which an electrode with the cross-sectional profile according to the invention exhibits its maximum stiffness. In this way, the rod is less susceptible to the bending elements that occur, and the service life of the electrode, to the extent that it is limited by bending due to the effects of gravity, is significantly increased.

[0032] The electrode manufactured according to the invention has the advantage that the metallic rod offers significantly greater resistance to the bending moments caused by gravity than is possible with conventional electrodes in the form of a round rod. It should be noted that the special profile shape, which deviates from a circular or rectangular cross-section, in particular the aforementioned preferred profile shapes of a T, double T, or even a cross, can significantly increase the flexural rigidity in at least one direction.

[0033] These effects are further amplified when individual sections or web electrodes are formed by struts, a framework or the like.

[0034] Further advantages, features, and possible applications of the present invention will become clear from the description of preferred embodiments and the accompanying figures. In the figures, identical elements are designated by identical reference numerals. They show: Figure 1a perspective view of the metal rod of a burner electrode, Figure 2several sectional views and the position of the cuts of the Figure 1 metal rod, Figure 3 a perspective view of the metal rod of another burner electrode, Figure 4 several sectional views and the position of the cuts of the Figure 3 illustrated metal rod Figures 5 -7 three variants of a further embodiment of a metal rod Figure 8 several sectional views and the position of the sections of the Figure 5 shown metal rod, Figures 9 and 10 further variants of a metal rod of a burner electrode, Figure 11 several sectional views and the position of the sections of the Figure 10shown metal rod, Figure 12 a side view of a burner electrode according to the invention and Figure 13 a side view of a rod of a further variant of the burner electrode according to the invention and Figure 14 a cross-sectional view through the rod from Figure 13 .

[0035] The embodiments of the Figures 1-11 are not part of the invention.

[0036] The burner electrode according to Figure 1, more precisely the electrode rod of such a burner electrode, has a shaft in the lower area designated by 5, while the upper section is designated by 6, and in the embodiments shown here is curved or angled. The shaft 5 serves as an assembly section and is inserted into a ceramic insulator in the fully assembled burner electrode. The metallic rod consists of a material with good electrical conductivity, in particular metal. In the embodiment shown, the rod has an indicated double-T profile in its upper section 6, which in the sectional views of the Figure 2 is shown in more detail.

[0037] The tip 4 of the rod is designed to generate an ignition spark when subjected to a sufficiently high voltage pulse, which ignites the fuel of a burner, ie gas or oil. The shaft 5 of the burner electrode in Figures 1 and 2has a square cross-section. The cross-section of the bar is flattened in an upper section 6 by pressing or forging and indented laterally.

[0038] The constriction or flattening is referred to here as longitudinal web 1 in reference to a double-T profile.

[0039] In the shaft region, which is exposed to less high temperatures than tip 4, and the upper region adjacent to tip 4, the cross-sectional profile is compact with an aspect ratio of 1.

[0040] The ratio of the area of ​​the cross-sectional profile in these sections to the area of ​​the smallest circle enclosing the profile is slightly less than 1 / 2. The metal rod 5 thus has a significantly increased flexural rigidity in the plane in which the upper section of the electrode is also bent or curved relative to the lower shaft area.

[0041] The curvature or bending of the upper section of the rod relative to the lower shaft part 5 is provided because the electrode is intended for a vertical arrangement next to a burner surface, so that the shaft 5 can maintain a greater distance from the burner surface.

[0042] In other variants, where the electrode is mounted in a horizontal orientation, a corresponding curvature of the upper section relative to the shaft is not provided.

[0043] Figure 3 and the cross-sectional views according to Figure 4 show another metal rod which, starting from a circular cross-section in the shaft area 5, was reshaped in the upper section to a cross-section that roughly corresponds to an "8". This increases the cross-section similar to the indicated double-T profile of the embodiment according to Figures 1 and 2 the flexural rigidity in a plane corresponding to the longitudinal center plane of the "8" profile.

[0044] In contrast to the embodiments of the Figures 1 -4 , which are pressed or forged from solid bars, are in the Figures 5 - 11 Embodiments are shown as they can be produced using powder metallurgy.

[0045] Figure 5 shows such an embodiment with a double-T profile of the electrode rod, with two transverse webs 2, 3 and a longitudinal web 1a, 1b connecting the transverse webs. Figure 6 In the cross-sectional views shown, it can be seen that the longitudinal web 1b in the upper section is significantly longer or higher than the longitudinal web 1a in the area of ​​the shaft 5, so that the aspect ratio H / B in the upper section is twice as large as in the shaft area.

[0046] The cross-sectional ratio defined in claim 2 is also less than 30% in the upper section of the electrode rod and more than 40% in the area of ​​the shaft 5, whereby this would also mean an improved flexural rigidity compared to a square solid profile.

[0047] The Figures 6 and 7 each show an electrode rod with the same basic shape as in Figure 5 , whereby only the longitudinal web was thinned to save material and weight, whereby in the case of the Figure 6 the longitudinal web of the double-T profile has 6 circular recesses in the upper section and in the case of Figure 7 was replaced by a short, rod-shaped longitudinal bar. Figure 8 shows again the cross sections of the designs of the Figures 5 - 7 , where the cross section B-B in the case of Figures 7 and 6 is limited to only one or a few positions along the upper section.

[0048] The longitudinal web has a lower height a in the lower part and is designated 1a there, while the height h in the upper part of the electrode section 6 is approximately twice the height a and the connecting web is designated 1b there.

[0049] Further embodiments of powder metallurgically produced electrode rods are described in the Figures 9 - 11 Here too, the profile is double-T-shaped, but constant over the entire length of the electrode rod, including the shaft and upper section, and with the exception of the electrode tip. In the variant in Figure 10 The longitudinal or connecting web of the double-T profile is replaced by a framework of bars that runs in a zigzag pattern between the upper and lower flanges or transverse webs 2, 3. In this case, the external dimensions of the profile are constant over the entire length of the section 10 shown up to the tip 4.

[0050] In the side view according to Figure 11cThis results in a truss or lattice construction between the crosspieces 2, 3. The cross section according to the line AA in Figure 11c is in Figure 11a and the cross section according to line BB in Figure 11c is in Figure 11b Since the truss band has a smaller cross-section at every point of the section shown than in the embodiment of the Figures 1 - 4 , the area ratio to the smallest circumscribed circle of the profile is significantly smaller than ½ while the aspect ratio is approximately 1.

[0051] Alternatively, the profile could simply be T-shaped or cross-shaped, although these profile shapes also provide increased flexural rigidity if they are installed in such a way that the force of gravity acts in the direction of the largest cross-sectional dimension.

[0052] In the corresponding complete electrodes, the lower section of a shaft 5 is housed in a ceramic sleeve as an insulator, and the electrode additionally has an electrical contact at the lower end. The upper section of the electrodes is designed differently, as shown in the figures above. The recesses in the longitudinal webs of some embodiments are intended to reduce the weight and the material required for the electrode, while still producing an electrode that is stable and better resistant to bending forces, even under strong heating.

[0053] Figure 12 shows a burner electrode 20 with an electrical ceramic insulator 21 and an elongated rod 22 made of an AlCrFe alloy. In the variant from Figure 14Only the metallic rod 22 is shown, and the ceramic insulator 21 is omitted from this illustration. In both variants, the rod 22 is made of a semi-finished product with a circular cross-sectional profile, i.e., a wire. This wire is curved in a transition section 23, so that two straight sections 24, 25 of the wire are connected by the transition section 23 and are bent relative to each other by the transition section 23.

[0054] If one imagines that the burner electrode 20 is installed with its segment 25 aligned vertically, it is immediately clear that the force of gravity acting on the segment 24 tries to deform the rod 22, ie, to straighten it. To make the rod 22 more stable against the influences of gravity, the rod has a stabilizing section 29. In the variant from Figure 12the stabilizing section 29 coincides with the transition section 23, ie the transition section 23 is reshaped. In the variant from Figure 13 the stabilizing section is arranged within the straight segment 25 of the rod 22.

[0055] In the stabilization section 29, the rod 22 is deformed in such a way that the cross-sectional profile in this area deviates from the circular shape of the original wire used as a semi-finished product. Figure 14 For illustrative purposes, shows an example of a cross-sectional view along the line AA of bar 22 from Figure 13 . By embossing, the wire is deformed in such a way that it has a cross-sectional profile in the stabilizing section 29 that corresponds to Figure 8a ). For this purpose, the bar has been stamped so that it has an upper chord 26 and a lower chord 27 and a recess 28 between these two chords.

Claims

1. A method for producing a burner electrode (20), comprising the steps of: producing a rod-shaped metallic rod (22), providing an insulator (21), and mounting the rod in or on the insulator, wherein the rod has a mounting section and a free section, wherein the mounting section is in engagement with the insulator, and the free section is not in engagement with the insulator, characterised in that the free section, except in a stabilising section (29), has a circular or rectangular cross-sectional profile, wherein producing of the rod is effected either a) by the steps of: providing a rod-shaped metallic semi-finished product with a circular or a rectangular cross-sectional profile, and reshaping the semi-finished product into the rod in the stabilising section such that in the stabilising section the cross-sectional profile deviates from the circular or rectangular cross-sectional profile of the semi-finished product and is stiffened against bending moments, or b) by the step of metal spraying the rod such that in the stabilising section it has a cross-sectional profile deviating from a circular or rectangular cross-section and is stiffened against bending moments.

2. The method according to claim 1, characterised in that the reshaping is embossing, swaging or die forging.

3. The method according to any one of the preceding claims, characterised in that the free section has a longitudinal extent, wherein the stabilising section (29) is spaced from the insulator (21) by a distance which is larger than 10%, preferably larger than 30% and particularly preferably larger than 50% of the longitudinal extent of the free section.

4. The method according to any one of the preceding claims, characterised in that the stabilising section (29) has a longitudinal extent of 16 cm or less, preferably of 10 cm or less and particularly preferred of 7 cm or less.

5. The method according to the preceding claim, characterised in that the free section has two, preferably straight, segments (24, 25) angled with respect to one another, wherein a transition between the two segments is preferably arranged in the stabilising section.

6. The method according to any one of the preceding claims, characterised in that the area of the cross-sectional profile of the stabilising section is less than half, preferably less than one third, and in particular less than one quarter of the area of a circular cross-section whose diameter is equal to the diameter of the smallest circle enclosing the profile.

7. The method according to any one of the preceding claims, characterised in that the cross-sectional profile of the stabilising section deviates from a cross-sectional profile composed of two circular cross-sections.

8. The method according to any one of the preceding claims, characterised in that the area of the cross-sectional profile of the stabilising section has an aspect ratio of at least 1.2, preferably of at least 1.5.

9. The method according to any one of the preceding claims, characterised in that the cross-sectional profile of the stabilising section is symmetrical with respect to a plane of symmetry defined by the largest diameter.

10. The method according to any one of the preceding claims, characterised in that the c ross-sectional profile of the stabilising section is a T-profile or a double-T-profile.

11. The method according to any one of the preceding claims, characterised in that the cross-sectional profile of the stabilising section is a double-T-profile with two transverse webs and a connecting web, wherein the spacing of the transverse webs and thus the height of the connecting web varies in the longitudinal direction of the rod.

12. The method according to any one of the preceding claims, characterised in that at least the stabilising section consists of an AlCrFe alloy.

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