Heating device

Abstract

The invention relates to a heating device (1) comprising a heating unit (3) with a number of resistance heating elements in the form of plate elements (4).

Description

[0001] HEATING DEVICE

[0002] The invention relates to a heating device comprising at least one heating register with several resistance heating elements.

[0003] Furthermore, the invention relates to a thermal processing system comprising a process chamber for an object to be processed and with a heating device which is at least partially arranged in the thermal processing system.

[0004] The electrical heating of industrial furnaces with resistance heating is well known. An electric current flows through a heating element with a corresponding electrical resistance, releasing heat. Rod-shaped heating elements are often used for this purpose. Some furnace types, such as pusher furnaces, require high energy densities. Therefore, gas heating is usually preferred for these furnaces. However, due to environmental reasons and the availability of fuel gas, efforts are being made to replace gas heating with other heating systems wherever possible.

[0005] The object of the invention is to provide a means of supplying a thermal processing plant with heating energy.

[0006] The object of the invention is achieved with the heating device mentioned at the outset, in which the resistance heating elements are designed as plate elements.

[0007] Furthermore, the object of the invention is achieved with the thermal processing system mentioned at the outset, in which the heating device is designed according to the invention.

[0008] The advantage here is that the plate elements can be used to create a heating register that offers relatively low flow resistance to the gas flowing through it. This allows the pressure loss caused by the heating register to be kept to a minimum. This, in turn, is particularly advantageous for thermal processing systems or furnaces that rely heavily on convection for heat transfer, such as hood furnaces, etc.

[0009] According to one embodiment of the invention, one, several, or all plate elements can have a meandering shape. This makes it possible to provide a higher heating output while still allowing a relatively compact design. Furthermore, this allows for easier adaptation of the heating device to the installation space in an existing thermal processing system.

[0010] To further improve these effects, according to embodiments of the invention, the meandering course may have several bends and, if appropriate, sections of the panel elements between the bends may have a parallel course. This latter embodiment, in particular, enables improved space utilization.

[0011] To better integrate the heating device or plate element into the thermal processing system, one embodiment of the invention can provide for receiving elements for fastening elements to be arranged in several or all of the bends. This enables a compact design of the heating device without the risk of accidental contact between sections of a plate element(s). This also allows for higher flow velocities in the thermal processing system.

[0012] According to one embodiment of the invention, it can be provided that the meandering course is designed as a double meander, whereby a simpler contacting of the plate elements in a single area of ​​the heating register and also an increase in the heating output per plate element can be achieved.

[0013] According to another embodiment of the invention, it can be provided that the plate elements are bent in a shovel shape, whereby the plate elements can also assume the function of a flow line in addition to the “heating” function.

[0014] According to another embodiment of the invention, beads can be arranged in at least some sections of the plate elements, which can impart improved stability to the plate elements even with small thicknesses. This can prevent or reduce the "fluttering" of the plate elements in the flow. Furthermore, they serve to improve heat transfer between the flowing medium and the plate element.

[0015] According to a further embodiment of the invention, the plate elements can have a thickness between 0.5 mm and 5 mm, which can further improve the above-described effect of low pressure loss. In addition to the aforementioned double meander design for extending the heating conductor length, another embodiment of the invention can also provide for several or all plate elements to be electrically connected in series to form a heating group.

[0016] According to one embodiment of the invention, the series-connected plate elements can be stacked one above the other, with electrical insulating elements arranged between the plate elements. This stacking again enables a compact design.

[0017] According to an embodiment variant of the invention, it can also be provided that three heating groups are electrically combined with one another in a star connection or delta connection, whereby the total heating output of the heating register can be increased.

[0018] According to one embodiment of the thermal processing system, for better transmission of the heating energy, it can be provided that the heating device is arranged in a flow channel for a gaseous medium, in particular a recirculating air channel.

[0019] The flow channel can also be formed by a guide vane with guide vanes, so that according to a further embodiment of the thermal processing system, it can further comprise a guide vane with guide vanes, with heating devices according to the invention arranged between the guide vanes. It is also advantageous if the plate elements of these heating devices are curved in a blade shape, so that they act like additional guide vanes.

[0020] According to another embodiment of the thermal processing plant, it can be provided that it additionally has a gas-powered heating device. By combining “electric heating” and “gas heating,” a reduction in the NOx content in the exhaust gases can be achieved during non-optimal phases, such as during holding phases with reduced burner output. With the hybrid design of the thermal processing plant, it is possible to operate these phases with reduced burner output using the heating device according to the invention and not to operate the gas burner during these phases. It is therefore also possible to reduce the total heating output of the gas burner and to provide the missing heating output via the heating device. As a result, the gas burner operates in the optimal range over longer phases, which in turn can reduce the NOx content of the exhaust gas.

[0021] According to another design variant of the thermal processing plant, it is designed as a pusher furnace, hood furnace or chamber furnace.

[0022] For a better understanding of the invention, it is explained in more detail using the following figures.

[0023] They show in a simplified, schematic representation:

[0024] Fig. 1 shows an embodiment of a heating device in an oblique view;

[0025] Fig. 2 shows an embodiment variant of a plate element of the heating device in an oblique view;

[0026] Fig. 3 shows a further embodiment of a plate element of the heating device;

[0027] Fig. 4 shows another embodiment of a plate element of the heating device;

[0028] Fig. 5 a view of the heating device in the flow direction of a material to be heated

[0029] Gases;

[0030] Fig. 6 shows a detail of a heating device;

[0031] Fig. 7 shows a further detail of a heating device;

[0032] Fig. 8 shows a section of a variant of a thermal processing plant;

[0033] Fig. 9 shows a variant of a thermal processing plant in longitudinal section;

[0034] Fig. 10 shows a section of a further embodiment of a thermal processing plant;

[0035] Fig. 11 shows a section of another design variant of a thermal processing plant.

[0036] By way of introduction, it should be noted that in the variously described embodiments, identical parts are provided with identical reference symbols or component designations. The disclosures contained throughout the description can be applied analogously to identical parts with identical reference symbols or component designations. Furthermore, the positional information chosen in the description, such as top, bottom, side, etc., refers to the directly described and illustrated figure, and these positional information must be applied analogously to the new position in the event of a change in position.

[0037] A heating device 1 is shown in Fig. 1.

[0038] The heating device 1 can be used in particular in electrically heated convection ovens or for converting ovens with burner heating into at least partially electrically heated ovens. The heating device 1 can be used, for example, in so-called upright ovens or in continuous ovens, i.e. in so-called industrial ovens. An industrial oven is defined as a space enclosed by walls in which heat is supplied to an object, in particular to allow processes to take place in the object or on its surface. The object can be a product, such as a sheet or a blank, a block, etc., or a raw material, such as a metal, etc. The process can be, for example, the melting of the object or a specific reaction in or on or with the object, such as a phase transformation, hardening of a metallic object, tempering of an object, etc.This list is merely exemplary and should not be construed as limiting. In general, the heating device 1 can be used in a thermal processing system 2 to process an object thermally, i.e., at elevated temperature, in batches or continuously. Sections of examples of thermal processing systems 2 are shown in Figs. 8 to 11.

[0039] An industrial furnace within the meaning of the invention is in particular a furnace which is used in metallurgy or in the processing of inorganic objects or objects which are or have been manufactured exclusively from inorganic raw materials.

[0040] By way of example only, it should also be noted that the heating device 1 can be used for objects made of aluminum or an aluminum alloy or generally non-ferrous metals or steel.

[0041] The heating device 1 comprises at least one heating register 3. The heating register 3 comprises or consists of several resistance heating elements. Heat is generated therein due to the electrical resistance when electric current is passed through. Since this principle is known per se, reference is made to the relevant prior art to avoid repetition.

[0042] The resistance heating elements are designed as plate elements 4 or sheet metal elements. Such a plate element 4 is shown in Fig. 2.

[0043] A sheet metal, as defined by the invention, is a metal product whose width and length are much greater than its thickness. Accordingly, a plate element 4 is understood to be a flat piece of metallic material, uniformly thick throughout, subject to tolerances, defined on two opposite sides by a flat surface that is larger than its thickness.

[0044] It should be noted at this point that all or several of the resistance heating elements of the heating device 1 can be of identical design. Although this is the preferred embodiment of the heating device 1, it is possible within the scope of the invention for different plate elements 4 to be installed in the heating device 1. These can be arranged within the same heating device 1 or, if multiple heating devices 1 are present in a thermal processing system 2, in different heating devices 1. The difference can lie in a plate thickness 5, in a current-carrying length, in the number of bends, in the material, etc., or in combinations thereof.

[0045] In the following, only one plate element 4 is described in detail. However, the explanations can be applied to other or all plate elements 4 of the heating device 1.

[0046] The embodiment of the plate element 4 shown in Fig. 2 is a preferred one. However, the plate element 4 can also look completely different. For example, in its simplest form, the plate element 4 can be a straight, flat bar. In the preferred embodiment, however, the plate element 4 has a meandering shape with bends 6 (also referred to as apex regions) and sections 7 between the bends 6. The specific number of bends 6 and, accordingly, sections 7 shown in Fig. 2 is not to be understood as restrictive. The specific number can depend, among other things, on the desired overall heating output and / or the installation situation of the heating device 1. For example, a plate element 4 can have between two and 50, in particular between 6 and 45, for example between ten and 40, such bends 6.The sections 7 can extend at an angle to one another such that a distance 8 between the sections 7 increases starting from the respective bend 6. In a preferred embodiment, however, it can be provided that - as shown in Fig. 2 - the sections 7 of the plate elements 4 have a mutually parallel course between the bends 6.

[0047] The distance 8 between the sections 7 can be between 1 mm and 50 mm.

[0048] A width 9 of the sections 7 can be between 2 mm and 100 mm, in particular between 10 mm and 60 mm.

[0049] The plate thickness 5 can be between 0.5 mm and 5 mm, in particular between 1 mm and 2 mm. The plate elements 4 are thus relatively thin, so that they have low flow resistance. Reference is made to Fig. 5, which shows the heating device 1 in the flow direction (perpendicular to the plane of the paper).

[0050] The total length of a plate element 4 in the direction of current flow can be between 100 mm and 3 m.

[0051] The plate element 4 can be manufactured by appropriately forming a straight blank. It is also possible for the plate element 4 to be cast into the desired shape. However, the plate element 4 is preferably cut from a sheet metal using a cutting process, for example, with a laser or a water jet.

[0052] The plate element 4 comprises or consists of at least one metallic material. For example, it can consist of a Kanthal alloy, a Nikrothal alloy, or an Inconel alloy.

[0053] 3 and 4 illustrate by way of example, the meandering course of the plate element 4 can also be designed differently. For example, instead of the round bends 6, right-angled transitions 10 can be provided between the sections 7, as shown in Fig. 3. Furthermore, the meandering course can be designed as a double meander (Fig. 4), so that, for example, the two electrical connection areas of the plate element 4 are arranged next to one another. To form the heating register 3, the plate elements 4 can be arranged in a receiving element, such as a frame element 11, as shown by way of example in Figs. 1, 5 and 6. In principle, the plate elements 4 can be connected to the receiving element in a wide variety of ways or can be arranged in or on it. The receiving element can, for example, be provided with groove-shaped recesses into which the plate elements 4 can engage.If necessary, these recesses can be designed with undercuts.

[0054] In the embodiment shown, however, the plate elements 4 are stacked on top of one another or, depending on the installation position, suspended in an arrangement next to one another in the frame element 11. For this purpose, according to one embodiment, the plate elements 4 can be provided with receiving elements 12 for fastening elements 13 (also referred to as holding elements) of the frame element 11. The receiving elements 12 can be designed as receiving lugs, which are arranged, for example, in the apex regions of the bends 6, as shown in Fig. 2. In this case, each bend 6 can preferably be provided with such a receiving element 12, so that the plate element 4 can be connected to the frame element 11 at each bend 6. For connection or attachment, the frame element 11 can have rod-shaped fastening elements 13, wherein these fastening elements 13 protrude through openings in the receiving elements 12 of the plate elements 4.In other words, the plate elements 4 can be threaded onto the frame element 11, as can be seen, for example, in Fig. 5 or Fig. 6. The rod- or bar-shaped fastening elements 13 can be held by end plates 14 of the frame element 11.

[0055] The receiving elements 12 of the plate elements 4 can also be designed differently, as can be seen, for example, from Fig. 11.

[0056] Preferably, the receiving elements 12 are formed integrally with the rest of the plate elements 4.

[0057] For the stacked arrangement of plate elements 4, insulating elements 15 are provided between the plate elements 4. The insulating elements 15 can be arranged extending through the receiving elements 12, for which purpose the openings in the receiving elements 12 can be designed accordingly large. In the preferred embodiment, the insulating elements 15 are sleeve-shaped, so that the fastening elements 13 can be arranged extending through the insulating elements 15. Thus, the insulating elements 13 can achieve not only the electrical insulation between adjacent plate elements, but also the electrical insulation from the frame element 11 (or generally from the receiving element for the plate elements 4).

[0058] The insulating elements 15 can be made of materials known for electrical insulating elements 15, with the restriction that these materials must also withstand the temperatures in the thermal processing system 2. For this reason, the insulating elements 15 are preferably designed as ceramic elements.

[0059] As can be seen from Fig. 5 and Fig. 6, two structurally different, sleeve-shaped insulating elements 15 can be used, which can be inserted into one another. This can simplify the assembly of the heating device 1 and the centering of the plate elements 4.

[0060] For the preferred assembly of the heating device 1, the frame element 11 can be provided in a first step, which, however, does not yet have an end plate 14 on at least one side. A first insulating element 15 is then placed on each of the fastening elements 13. These first insulating elements 15 are supported on one of the end plates 14 and provide electrical insulation to this / these end plate(s) 14. A first plate element 4 is then pushed on so that the fastening elements 13 protrude through the receiving elements 12. This plate element 4 is centered using second insulating elements 15, which have a cylindrical extension that can be received by the first insulating elements 15, as best shown in Fig. 6. The further construction of the heating register 3 is achieved by repeating these steps.

[0061] In principle, the electrical contacting of the plate elements 4 can be made on opposite sides of the heating device 1. In the preferred embodiment, however, these connections are arranged on the same side of the heating device 1. In particular, so-called connection lugs 16, 17 can also be provided or arranged for this purpose and connected to the plate elements 4. For electrical connection on only one side, plate elements 4 designed as double meanders, for example, can be used.

[0062] According to another embodiment, it can also be provided that several or all plate elements 4 of a heating device 1 are electrically connected in series to form a heating group 18. In the embodiment of the heating device 1 shown in Fig. 1, it has three such heating groups 18. The heating groups 18 can also be arranged on the same frame element 11, e.g., separated by intermediate plates 19 (see Fig. 5).

[0063] To form the series connection of the plate elements 4, metallic current connecting elements 19 are provided alternately (at the beginning and end of a plate element 4) in the end regions of the plate elements 4. These elements conduct the electrical current from a plate element 4 in a first level to a plate element 4 in the subsequent level. The heating group 18 is therefore traversed by the electrical current in a zigzag pattern.

[0064] The power connection elements 19 are also preferably sleeve-shaped. They can have cylindrical extensions on one or both sides, which can be accommodated by adjacent insulating elements 15. The power connection elements 19 can also have a centering effect for centering the plate elements 4.

[0065] As can be seen in Fig. 2 with reference to a section 7, according to one embodiment of the heating device 1, it can be provided that beads 20 are arranged or formed in the plate elements 4, at least in individual sections 7, in particular in all sections 7. The beads 20 can be produced by forming the sections 7. The beads 20 can have a depth of between 0.5 mm and 3 mm.

[0066] All plate elements 4 of a heating device 1 can be connected in series. However, to increase the overall heating output, one embodiment variant can provide for the heating device 1 to have three heating groups 18, as shown in Fig. 1. These three heating groups 18 can be electrically combined with one another in a star connection or delta connection. Reference is made to Fig. 7, which shows a star connection of the three heating groups 18. Electrical connections 21 to 23 for the three phases P1, P2 and P3 can be seen, as well as a star point connection 24. These electrical connections 21 to 23 then form the connection to a power supply unit 25 (see Fig. 1), via which the heating register 3 can be supplied with power.

[0067] A thermal processing system 2 can have one heating device 1 or several heating devices 1, depending on the required heating output. For example, a thermal processing system 2 can have between one and 20 heating devices 1. As already explained above, the heating device 1 is used in a thermal processing system 2 to warm up or heat a gaseous medium, such as circulating air. The energy is then introduced into the object to be heat-treated via this gaseous medium.

[0068] A first embodiment of the thermal processing system 2 is shown in detail in Fig. 8. This comprises a process chamber 26 for accommodating at least one object to be processed. The thermal processing system 2 further comprises at least one of the heating devices 1 according to the invention (preferably several). The heating device 1 can be arranged within the process chamber 13 and / or outside the process chamber 13 and at least partially surrounding it. The at least one heating device 1 can be arranged in a flow channel 27, at least partially, preferably entirely, within a housing 28 of the thermal processing system 2. In the embodiment shown, the thermal processing system 2 is a so-called pusher furnace.

[0069] The flow channel 27 can be completely separated from the process chamber 26, for example via a gas baffle 29.

[0070] The thermal processing system 2 may also include further components corresponding to the state of the art, which, however, are not further mentioned in this description. A person skilled in the art will arrange them accordingly in the thermal processing system 2 as needed.

[0071] The gaseous medium to be heated can be selected or composed depending on the thermal process in the thermal processing system 2. This is also known to the person skilled in the art, so further discussion is unnecessary.

[0072] In general, the heating device 1 is preferably used in thermal processing systems 2 with an energy density of at least 0.5 W / cm 2 , especially between 0.5 W / cm 2 up to 25 W / cm 2 , is used. The energy density depends on the flowing medium, in particular the type of medium, the speed of the medium, and the temperature of the flowing medium.

[0073] Fig. 9 shows a section of another embodiment of a thermal processing system 2. This is designed in the form of a bell furnace. As with the pusher furnace or generally in the thermal processing system 2, a fan 30 or a turbine can be provided to circulate the gaseous medium in the process chamber 26. The heating device 1 can be arranged in the flow channel 27 formed centrally and above the fan 30.

[0074] The heating device 1 or one or more additional heating devices 1 can also be arranged in a differently designed flow channel 27. For example, a guide vane for a medium to be circulated is shown in Fig. 10. The guide vane has guide vanes 31, between which flow channels 27 are formed. The guide vanes 31 are curved accordingly in order to achieve a corresponding flow pattern.

[0075] Plate elements 4 of the heating device 1 are now arranged between the guide vanes 31, or between at least some of the guide vanes 31. As can be seen from Fig. 10, the plate elements 4 are curved in a blade-like manner. In particular, they at least approximately replicate the curvature of the guide vanes 31, whereby the plate elements 4 also contribute to flow guidance and not just to heating the gaseous medium.

[0076] In the embodiment of the thermal processing system 2 according to Fig. 10, the plate elements 4 are arranged upright between the guide vanes 31, so that the meandering course extends in the vertical direction. In contrast, Fig. 11 shows that the plate elements 4 can also be arranged horizontally. This Fig. 11 also shows, as already explained above, that the plate elements 4 can also look or be designed differently than that in Fig. 2. Here, too, it is possible to stack several plate elements 4 vertically on top of one another and to electrically insulate them from one another with insulating elements 15. The stack can again be held together by fastening elements 13, as already explained above.

[0077] This design variant also makes it possible to illustrate the variability and adaptability of the heating device 1 to a wide variety of conditions in existing thermal processing systems 2.

[0078] The heating device 1 can be arranged or operated alone, in a group of several heating devices 1, and / or in a hybrid application with at least one gas burner for heating a gaseous fluid. In addition to the illustrated examples of "pusher furnace" and "hood furnace," the thermal processing system 2 can also be a chamber furnace or, generally, preferably, a furnace system with convective heating, such as convection furnaces for continuously moving belts or roller-hearth furnaces.

[0079] The embodiments show possible design variants of the heating device 1 or the thermal processing system 2, whereby it should be noted at this point that combinations of the individual design variants are also possible.

[0080] For the sake of clarity, it should finally be pointed out that in order to better understand the structure of the heating device 1 or the thermal processing system 2, these are not necessarily shown to scale.

[0081] Reference symbols Heating device Thermoprocessing system Heating register Plate element Plate thickness Bend Section Distance Width Transition Frame element Receiving element Fastening element End plate Insulating element Terminal lug Terminal lug Heating group Power connection element Bead Connection Connection Connection Star point connection Power supply unit Process chamber Flow channel Housing Gas baffle Fan Guide vanes

Claims

Patent claims 1. Heating device (1) comprising at least one heating register (3) with several resistance heating elements, characterized in that the resistance heating elements are designed as plate elements (4).

2. Heating device (1) according to claim 1, characterized in that one, several or all plate elements (4) have a meandering course.

3. Heating device (1) according to claim 2, characterized in that the meandering course has several bends (6).

4. Heating device (1) according to claim 3, characterized in that sections (7) of the plate elements (4) between the bends (6) have a mutually parallel course.

5. Heating device (1) according to claim 3 or 4, characterized in that receiving elements (12) for fastening elements (13) are arranged in several or all of the bends (6).

6. Heating device (1) according to one of claims 2 to 5, characterized in that the meander-shaped course is designed as a double meander.

7. Heating device (1) according to one of claims 1 to 6, characterized in that the plate elements (4) are bent in a shovel shape.

8. Heating device (1) according to one of claims 1 to 7, characterized in that beads (20) are arranged in the plate elements (4) at least in sections (7).

9. Heating device (1) according to one of claims 1 to 8, characterized in that the plate elements (4) have a plate thickness (5) between 0.5 mm and 5 mm.

10. Heating device (1) according to one of claims 1 to 9, characterized in that several or all plate elements (4) are electrically connected in series to form a heating group (18).

11. Heating device (1) according to one of claims 1 to 10, characterized in that the plate elements (4) connected in series are arranged stacked one above the other, with electrical insulating elements (15) being arranged between the plate elements (4).

12. Heating device (1) according to one of claims 1 to 11, characterized in that three heating groups (18) are electrically combined with one another in a star connection or delta connection.

13. Thermal processing system (2) comprising a process chamber (26) for an object to be processed and with a heating device (1) which is arranged at least partially in the thermal processing system (2), characterized in that the heating device (1) is designed according to one of claims 1 to 12.

14. Thermoprocessing system (2) according to claim 13, characterized in that the heating device (1) is arranged in a flow channel (27) for a gaseous medium, in particular a recirculating air channel.

15. Thermal processing plant (2) according to claim 13 or 14, characterized in that it further comprises a guide vane with guide vane blades (31), and that heating devices (1) according to one of claims 1 to 12 are arranged between the guide vanes (31).

16. Thermal processing plant (2) according to one of claims 13 to 15, characterized in that it additionally comprises a gas-operated heating device.

17. Thermal processing plant (2) according to one of claims 13 to 16, characterized in that it is designed as a pusher furnace, hood furnace or chamber furnace.

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