Method for producing a tubular heating cartridge for electrical heating devices and heating cartridge

Abstract

Method for producing a tubular heating cartridge (100; 200; 300; 700) with an electric heating element located within a metal housing (20) of the heating cartridge (100; 200; 300; 700) and extending axially to a longitudinal axis of the heating cartridge (100; 200; 300; 700), wherein the heating cartridge (100; 200; 300; 700) and / or the heating element have a predetermined geometric shape with a predetermined ohmic resistance, comprising the following method steps: - providing a tubular, electrically conductive body (160; 260; 660), - processing the body (160; 260; 660) to form a heating element blank (130; 230; 630; 730) such that a tubular and deformable heating conductor track structure with a first overall length (L1) with at least a first and second conductor track end (135) and a first height (K1) is formed from the body (160; 260; 660) by introducing slots (137, 737) with opposing cut surfaces (139, 739) into the tubular, electrically conductive body (160, 260, 660), - inserting the heating element blank (130; 230; 630; 730) into the tubular metal housing (20), which has a second overall length (L2) and a second height (K2), - filling the tubular metal housing with an electrically insulating and compressible material (50; 310; 312), - compacting the filled metal housing (20) to achieve the predetermined geometric shape and the predetermined ohmic resistance of the heating element blank (130, 230, 630, 730) and / or the heating cartridge (100; 200; 300; 700) with a third total length (L3) that is increased compared to the first total length (L1) and / or a third height (K3) that is reduced compared to the first height (K1) and / or to deform the metal housing (20) to a fourth total length (L4) that is increased compared to the second total length (L2) and / or a fourth height (K4) that is reduced compared to the second height (K2).

Description

Electric heater cartridges have been known for many years. They generally have at least one tubular metal jacket, in the interior of which at least one heating conductor is arranged. In this case, the space between the heating conductor and the metal jacket is usually filled with a material which is highly thermally conductive but electrically insulating, such as magnesium oxide, in order to avoid undesired electrical contact between the heating conductor and the metal jacket. Nowadays, heating cartridges are known which have at least two lead-out leads to the heating conductor on one side of the metal jacket. However, heating cartridges are also used in which at least one supply line protrudes to the heating conductor on the respective end faces of the heating cartridge. Furthermore, heater cartridges are known in which the metal casing itself serves as one of the leads.An example of known heating cartridges and their production methods is disclosed in DE 10 2013 2012 205 A1.An essential element of these heating cartridges is the heating conductor located in the interior of the metal casing or metal housing. These electrical heating elements, with which electrical energy is converted into heat, are usually produced by providing a heating conductor material in the form of a wire and, if this wire is not used extended in any case, then bending, winding or twisting it either onto a carrier or freely to form a space curve.Apart from the problem that not every conceivable or desirable space curve can be generated in this way for such heating elements, problems arise in particular in configurations in which small heating conductor resistances have to be accommodated by high heating conductor cross sections in the narrowest space. It is namely necessary for thermal alternating loads to be maintained over long periods of time and, in addition, for process-safe unheated zones and heated zones for an electric heating device to be connected to one another, which is essential in particular at very high current loads, high surface loads and high power densities.Further electric heating devices and methods for their production are known from DE 10 2013 212 205 A1 and DE 19 17 256 A.The present invention has the object of specifying a very simple method, from a manufacturing standpoint, and thus a cost-effective method for producing a tubular heater cartridge for electrical heating apparatuses, which cartridge is also of very small construction, which is suitable for reducing the aforementioned problems. The method should ensure reproducible electrical values of the cartridge heater in the simplest possible manner, i.e. be suitable in particular for mass production.This object is achieved by a method for producing a tubular cartridge heater as set out in claim 1. Advantageous further developments of the invention are the subject of the claims which refer back to this claim 1.The method according to the invention for producing a tubular heater cartridge for electric heating devices is characterized by the following method steps:providing a tubular electrically conductive body,machining the body to form a heater blank such that the body forms a deformable heater trace structure having a first overall length with at least first and second trace ends and a first height by forming slots having opposing cut surfaces in the tubular electrically conductive body,inserting the heating element blank into the tubular metal housing, which has a second overall length and a second height,filling the tubular metal housing with an electrically insulating and compressible material,compacting the filled metal housing to achieve the predetermined geometric shape and the predetermined ohmic resistance of the heating element blank and / or the heater cartridge with a third overall length increased to the first overall length and / or a third height decreased to the first height and / or for forming the metal housing to a fourth overall length increased to the second overall length and / or a fourth height decreased to the second height.These measures ensure, on the one hand, that the heating conductor is separated from a tubular body and thus the heating conductor is suitable for mass production. In addition, this makes it possible to leave the circular cross-sectional structure of the heating conductor that is necessary in conventional heating conductor wires. Depending on the thickness of the tubular walls and depending on the cut contour, it is possible to realize almost any desired cross-sectional shapes of the heating conductor to be inserted into the cartridge heater. A wide variety of different helical structures, e.g. meandering or bifilar, can likewise be realized by this measure.According to the invention, a heating element blank which can be produced in this way in a mass-wise manner and which has a specific length and height is inserted into the interior of the tubular metal housing. Subsequently, electrically insulating material, for example insulating granules, in particular magnesium oxide granules, ceramic granules or boron nitride granules, is introduced into the tubular metal housing. Instead of this insulating granulate, however, it is also possible to fill the intermediate space between the heating element blank and the metal housing by a tubular, porous ceramic material. Likewise, an in particular porous ceramic rod can be inserted into the intermediate space of the heating element blank.During a subsequent compacting process, i.e. the tubular metal housing filled in this way is exposed to high external pressure, the insulating granulate or the porous ceramic material compresses and sinters in such a way that the ultimately desired geometric shape of the heating element blank and / or of the tubular heater cartridge with the metal housing and thus also the electrical values are adjusted to the desired final size.Within the scope of this compaction with extremely high pressures, the geometric shape of the heating element blank usually changes to an overall length which is enlarged with respect to the original heating element blank. However, the height or the diameter of the heating element blank after compaction always decreases in comparison with the height of the heating element blank previously inserted into the metal housing. The same is done with the tubular metal housing of the cartridge heater. After the compaction, the cartridge heater with its metal housing usually has an increased length, but always a reduced height or a reduced diameter. In this case, the ohmic resistance of the heating element blank or of the heater cartridge is regularly increased.The method according to the invention for producing the cartridge heater is designed in such a way that the desired geometric shape, in particular of the metal housing and its ohmic setpoint values, is achieved.It has proven expedient to close the metal housing preferably with a cover before the compression. Before the closing, it must be ensured that sufficient material to be compacted is filled into the metal housing so that no voids or poorly compacted regions are formed within the metal housing in order to achieve optimum compaction and thus good heat transfer from the heating element blank to the metal housing. In this compacting, the insulating material, usually present as granules, for example, magnesium oxide granules, is compacted or compacted more strongly from an original density of about 10% to 50%. Before or during the actual compacting, it has proven expedient to repeatedly shake the metal housing with the inserted heating element blank and the insulating material. This shaking ensures good uniform distribution of the insulating granules and high bulk density within the metal casing.It has also been found to be advantageous that, by means of the method according to the invention, the insulating granulate lies within the metal housing after compaction with an increased filling degree and the cut edges of the heating element blank are thus optimally covered there. An optimum heat dissipation from the cut edges of the heating element blank to the metal housing results.In a further development of the invention, it is provided that suitable contact connections are attached to the conductor track ends of the heating element blank, which contact connections are led out of the metal housing of the heater cartridge on the end face. In this case, the contact connections can be led out only at one longitudinal end of the cartridge heater, but also at both ends.According to a further development of the invention, the heating element blank can be produced from the plate-shaped or tubular body by means of laser cutting, water jet cutting, micro water jet cutting, etching, punching, sawing, milling, drilling, turning, grinding or the like. Particularly fine cuts and thus little material loss are possible by means of laser cutting, etching and microwater cutting.It is within the scope of the method according to the invention that the compaction is carried out in such a way that an increase in length of the heating element blank and / or of the metal housing of the cartridge heater by between, for example, approximately 1% to approximately 25% and / or a reduction in height of, for example, approximately 3% to approximately 45% is effected in each case.It is within the scope of the present invention for the heating element blank to have slots with mutually opposite cut surfaces which are arranged orthogonally to the tubular wall of the metal housing. The cut surfaces are parallel to each other. On the other hand, the slots can also be selected such that they are placed parallel to one another at an angle α or else at different angles to one another with respect to an orthogonal plane of the tubular wall of the metal housing.In addition, it is advantageously according to the invention such that the heating element blank is provided with an enlarged surface structure after its processing or after assembly, because the heating element blank after compaction has non-uniformly distributed impressions on its surfaces and also on its cut surfaces. These impressions ensure a larger heat-emitting surface of the strip heating conductor or of the heating insert. This is achieved by a positive heat flow between the heating element blank and the insulating material. Moreover, the compacting ensures a high contact pressure and a larger heat-transferring surface between the heating element blank and the insulating material, as a result of which good fixing of the entire heating cartridge and its contents is ensured. Such a good fixing is necessary because the heating cartridges are regularly exposed to vibrations, impacts and thermal alternating stresses and without this good fixing a slipping of the components located within the heating cartridge would be possible.It is within the scope of the invention that in a particular embodiment the heating element blank formed from a plate-shaped or tubular electrically conductive body is coated with a ceramic material before being inserted into the metal housing. Preferably, a porous ceramic material is provided for this coating. Such a ceramic coating of the heating element blank makes it possible during the manufacturing process of the cartridge heater to dispense with centering devices which were previously necessary during the assembly of the cartridge heater. In fact, hitherto, in the case of heating cartridges for centering the structure, it has always been necessary to ensure that the heating insert, that is to say the heating element blank, is spaced apart sufficiently from the cartridge base and from the wall of the casing housing. This has been achieved by the use of special filling machines with centring devices or ceramic spacers have been used hitherto. Within the scope of the invention, it is possible to apply such a ceramic coating to the heating element blank and subsequently to ensure good adhesion of this ceramic coating to the heating element blank by means of a temperature step, optionally by firing or annealing. In principle, it is also possible to apply a different insulating layer to the heating element blank before the insertion into the metal housing of the cartridge heater. However, a ceramic layer has proven to be particularly good.Within the scope of the present invention, only heating cartridges have been addressed up to now, which consist of a simple, metallic tube as a metal housing and are closed at the end with a cover. However, it is also within the scope of the invention to use so-called hollow cartridges as a metal housing for the heater cartridge. Such hollow cartridges are characterized by a double-walled tube, wherein the heating element blank and the above-mentioned insulating material are filled between an inner tube and an outer tube. Such heating cartridges with a double-walled, tubular metal housing are closed at the ends with an annular cover. Such heating cartridges with a double-walled tube, i.e. hollow cartridges, are especially predestined for heating cylindrical bodies, but also as continuous flow heaters for fluids or gases.The method according to the invention and a cartridge heater resulting therefrom will be explained in more detail below in connection with several exemplary embodiments. The following are shown: FIG. 1A shows a first exemplary embodiment of a cartridge heater according to the invention in a partially broken-away sectional view before the compaction, FIG. 1B shows the cartridge heater shown in FIG. 1A after the compression, FIG. 1C shows sectional views of FIG. 1A, i.e. before the compacting, FIG. 1D shows various sectional views of FIG. 1B, i.e. after the compacting, FIG. 1E shows a detailed view of FIG. 1C, FIG. 1F shows a detailed view of FIG. 1D, FIG. 1G is a detailed view of the cartridge heater of FIG. 1A in the area of a slot with cut edges running perpendicular to the metal housing, FIG. 1H is a similar view to FIG. 1G with cut edges running obliquely and parallel to one another, FIG. 1I is a similar view to FIG. 1G with cut edges inclined with respect to one another, FIG. 2A shows a second exemplary embodiment of a cartridge heater in a partially broken-away view in FIG. 5 before the compression, FIG. 2B shows the second exemplary embodiment of a cartridge heater according to the invention in a partially broken-away sectional view after the compaction, FIG. 2C shows sectional views of FIG. 2A and associated partial view according to a section D-D, FIG. 2D shows different sectional views of the cartridge heater shown in FIG. 2A after the compaction, FIG. 2C shows sectional views of FIG. 2A and associated partial view according to a section D-D, FIG. 3A shows a third exemplary embodiment of a cartridge heater in exploded view, FIG. 3B is a sectional view of FIG. 3A before the cartridge is compacted, FIG. 3C shows a sectional view of the cartridge heater of FIG. 3A after the compaction, FIG. 4 shows a tubular body from which a heating element blank according to FIGS. 1A to 1F has been separated, FIG. 5 shows a heating element blank in perspective illustration, as is used in the exemplary embodiment of FIGS. 2A to 2D, FIG. 6A shows a plate-shaped body not falling under the claimed invention, from which a heating element structure is separated, FIG. 6B shows a heating element structure which is separated out of the plate-shaped body according to FIG. 6A and does not fall under the invention FIG. 6C shows a heating element blank which is completely bent from the heating element structure of FIG. 6B and does not fall under the invention, FIG. 7A shows a perspective illustration of a further exemplary embodiment of a heating element blank, FIG. 7B shows a heating cartridge of a further exemplary embodiment in a partially broken-away view with an inserted heating element blank according to FIG. 7A, FIG. 7C shows a detailed illustration of the region E from FIG. 7B, FIG. 8 shows different sectional representations of the heating conductor according to the heating element blank of FIG. 7A with impressions introduced, FIG. 9 shows the representations A to E in FIG. 9 of the heating element blank already known from FIG. 6 during various process steps according to the method according to the invention, FIG. 10 shows a further exemplary embodiment of a heating cartridge according to the invention, which is designed as a hollow cartridge, in various views, and FIG. 11 is a view similar to FIGS. 7A, 7B and 7C, but showing the cartridge heater as a hollow cartridge.In the following description of the figures, like reference numerals designate like parts with like meaning, respectively, unless otherwise indicated.FIG. 1A shows a heating cartridge 100 for electrical heating devices in a partially broken-away view. Such a cartridge heater 100 can be used, for example, in medical technology, the automobile industry, laboratory and analytical technology and in packaging machines. Thanks to the possibility of being able to construct such heating cartridges 100 in very small sizes, it is possible, for example, to heat miniaturized plastic injection nozzles in heating channel technology.The cartridge heater 100 shown in FIG. 1A is depicted in a state where the cartridge heater 100 is not yet completely completed. The decisive step of the compacting yet to be explained below has not yet taken place in the illustration of FIG. 1A. However, the cartridge heater 100 already has all the components necessary for later operation. Thus, the cartridge heater 100 in FIG. 1A has a tubular metal housing 20 which is closed at its left end by a cover 21 and at its right end by a second cover 23, which is preferably made of insulating material. The cover 21 can be integrally connected to the tubular housing wall of the metal housing 20, but can also be fastened as a separate part to the metal housing 20. Within the metal housing 20, there is a heating element blank 130 with a heating conductor track structure or a heating conductor 132 which has a plurality of slots 133, 134 and 137, centered with respect to a longitudinal axis 12 or central axis. This heating element blank 130 has two meandering paths of a heating conductor path structure, which are both connected to one another via a connecting web 136 in the vicinity of the cover 21 of the metal housing 20 shown on the left. In the direction of the second cover 23, the mentioned heating conductor track structure is provided with widened conductor track ends 135, to which contact connections 40, 42 are electrically conductively connected. The contact terminals 40, 42 are guided through corresponding openings in the cover 23 and protrude to the right from the cover 23 in the illustration of FIG. 1A.The heating element blank 130 shown in FIG. 1A is separated from a metallic, tubular body by methods suitable for this purpose. FIG. 4 shows such a metallic tubular body 160 with cut lines 150 by which the heating element blank 130 can be separated from the tubular body 160. In this case, the tubular body 160 can have any length, such that a plurality of heating element blanks 150 can be separated from this tubular body 160 one after the other in accordance with the cut lines 150 introduced.In FIG. 4, slit areas 133', 134 and 137' are marked in addition to the cutting lines 150 required for producing the heating element blank 130, in which slit areas the material of the tubular body 160 is present in the illustration of FIG. 4. However, this material is separated after the slits 150 have been formed and forms cut waste. After the slot areas 133', 134', 137' have been separated out, the heating element blank 130 shown in FIG. 1A remains with the slots 133, 134 and 137.It should be noted at this point that FIG. 1A and also FIG. 4 describe a specific shape of a heating element blank 130. However, the present invention is not limited to such a configuration of the heater blank 130. Rather, there are a wide variety of variants for producing such a heating element blank 150, of which, however, only those of the claimed invention which are separated from a tubular body are omitted.For the purposes of the disclosure, express reference is hereby made to the German patent application DE 10 2019 127 753 A1 of the applicant, in which a wide variety of variants for producing a heating element blank from a plate- or tubular body are described. All variants mentioned there are likewise suitable for use within the scope of the present invention in a cartridge heater, as will be explained further, provided they can be produced by cutting them out of a tubular body.Returning again to FIG. 1A, the explained heating element blank 130 is thus inserted into the metal housing 20. This heating element blank 130 has a heating conductor track structure which is designated in FIG. 1A by a length L 1. The diameter or the height of this heating element blank 130 is marked with the reference symbol K 1. The length of the entire cartridge heater 100 is L2. The outer diameter of the heater cartridge 100 is K2. As can also be seen from FIG. 1A, an insulating material suitable for compression and suitable as a heat conductor is filled into the free space between heating element blank 130 and metal housing 20. Suitable materials for this purpose are, in particular, insulating granules, such as, for example, MgO granules, ceramic granules and also boron nitride granules.The cartridge heater 100 prepared according to FIG. 1A is subjected to a special compacting process after the filling of the insulating granulate 50 in order to allow an optimal heat conduction from the heating element blank 130 to the metal housing 20. For this purpose, the cartridge heater 100 prepared from FIG. 1A is exposed to high and high pressures from the outside. This is indicated in FIG. 1B by the arrows denoted by T. This pressure can be effected, for example, by means of rolling rolls or suitable rolling machines or suitable pressing methods, for example by means of pressing jaws. The purpose and purpose of this compacting is to ultimately produce a cartridge heater 100 having the desired electrical parameters and also the intended geometrical dimensions. The compaction is thus carried out until, on the one hand, the material 50 to be compacted has been compacted to the maximum extent in an optimum manner and the cartridge heater 100 has reached its intended final dimensions.As is particularly clear from FIG. 1B and is even more particularly clear in connection with FIGS. 1C and 1D and also 1E and 1F, the geometric dimensions of the cartridge heater 100 change critically as a result of the process of compaction. It should be noted in connection with the cross-sectional views in FIGS. 1B and 1D that for clarity, the insulating material 50 also present in the interior of the heating element blank 130 is naturally present. However, the area of the individual heating coils has been omitted intentionally in the drawing in order to be able to explain the present invention and the structure of the heating cartridge in a better manner.Both the heating element blank 130 and the entire heating cartridge 100 extend to a length L 3 or L 4, respectively. On the other hand, both the heater blank 130 and the heater cartridge 100 undergo a height change, namely a height reduction to the height K3 of the heater blank 130 and to a height K4 of the metal casing 20. The opposite cover 23 undergoes a change in thickness. The slots 133, 134 and 137 also vary in width. Thus, the slots 133, 134 are widened between the meandering course of the heating conductor track structure, as the two detailed representations show detail A in FIG. 1C before the compaction and in FIG. 1D after the compaction. The slots 133, 134 become wider, while the slot 137, which is worked parallel to the longitudinal axis 120 in the heating element blank 130, becomes narrower. The slot width of this longitudinal slot 137 is indicated in the sections B-B of FIG. 1C and D-D in FIG. 1D with the width indications b1, b2. A change in thickness, namely an increase in thickness, also experiences the cross section of a heating conductor of the heating element structure of the heating element blank 130 due to the compression, as the reference symbols A 1, A 2, A 3 and A 5 in FIGS. 1C and 1D show. A change in thickness also occurs in the wall of the metal shell 20 as indicated by reference numerals A4 and A6 in FIGS. 1C and 1D.FIGS. 1E and 1F show the change in thickness of the cross sections of the heating element conductor structure of the heating element blank 130 again enlarged.In FIG. 1G, the metal housing 20 of the heating cartridge is shown enlarged in the region of a slot 133 of the heating element blank 130. The heating conductor 132 is shown in detail with two coils shown in section, which are separated by the slot 133. The heating conductor 132 has an upper surface 137 and a lower surface 138 that is closer to the longitudinal axis 12. The two surfaces 137 and 138 are parallel to each other and also parallel to the inner wall of the tubular metal housing 20, and the cut surface 139 connecting the two surfaces 137 and 138 is parallel to the opposite cut surface of the heating conductor 132. Both cut surfaces 139 are parallel to a cut surface F which is oriented orthogonally to the tubular wall of the metal housing 20. The right angle is indicated by the reference sign α in FIG. 1G. The cut surfaces 139 are formed by being separated from the aforementioned tubular body.FIG. 1H shows another exemplary embodiment in which the cut edges are not arranged parallel to the surface F, but are oriented parallel to one another. The angle α of the cut edges 139 is now approximately 130°. As can be seen, the cut edges 139 of the mutually opposite heating conductors 132 are aligned parallel to one another.A third exemplary embodiment of how the cut edges or cut surfaces 139 can be aligned with one another is shown in FIG. 1I. Here, the cut surfaces 139 are not aligned parallel to one another, but obliquely to one another. The cut edge 139 shown on the left in FIG. 1I has the cut angle α as in FIG. 1H. The opposite cut surface has an angle of -α to the surface F.In principle, cutting angles α can be selected which are aligned between 15° and 165° with respect to the cutting plane F. Cutting angles of 30° to 150° are more advantageous, and cutting angles of 60° to 120° are particularly advantageous. By the oblique selection of these cutting angles relative to the cutting plane F, the surface of the cutting surfaces 139 is enlarged and thus the load on the cutting edges during compacting is also reduced.FIGS. 2A, 2B, 2C and 2D show a second exemplary embodiment of a cartridge heater 200 according to the invention. This cartridge heater 200 differs substantially from the cartridge heater 100 described above in the use of a differently configured heating element blank 230. The heating element blank 230 is now equipped with a bifilar heating conductor structure, but, as shown in the detailed illustration of FIG. 5, is again separated out of a tubular metallic tubular body 260 by suitable separating methods. Suitable separation methods are, for example, laser cutting, water jet cutting, micro water jet cutting, etching, punching or sawing.FIG. 5 again shows the parting or cutting lines 250 necessary for producing the heating element blank 130 and those regions 234' and 240 which represent cut waste after severing from the tubular body 260. FIG. 5 shows the widened conductor track ends 235 and the heat conductor tracks 232 of the heating element blank 230. The heating conductor track structure shown in FIG. 5 has a U-shaped connecting web 236, at which the incoming heating conductor winding reverses again.The illustration of FIG. 2A shows this heating element blank 230 inserted into the metal housing 20 with a slot 234 running in a spiral shape, the two conductor track ends 235 electrically connected to the contact connections 40, 42, the connecting web 236 and the heat conductor track structure 232. The heating element blank 230 is in turn surrounded in this way by insulating granules to be compacted. FIG. 2A shows the cartridge heater 200 prior to compaction.FIG. 2B shows the cartridge heater 200 shown in FIG. 2A after compaction has been completed. The height reductions from K1 to K3 of the heating element blank 130 and of the metal housing 20 are again set from K2 to K4. The resulting changes in length of the heating element blank 230 and of the metal housing 20 are marked in FIG. 2B again by the reference symbols L 3 and L 4.FIGS. 2C and 2D again show details in this respect. The changes in cross section of the heating conductor track structure of the heating element blank 230 are marked with the reference numerals A 7 to A 12.FIGS. 3A, 3B and 3C show a third exemplary embodiment of a cartridge heater 300. This cartridge heater 300 differs in a significant point from the two aforementioned exemplary embodiments, namely in the realization of the material to be compacted within the metal housing 20.As FIG. 3A shows in a perspective illustration, the heating cartridge 300 has the already known metal housing 20 with the two covers 21 and 23. However, an insulating rod 312 is now inserted into the interior of the heating element blank 230 and an insulating tube 310 is additionally inserted between the metal housing 20 and the outer periphery of the heating element blank 230. The insulating rod 312 and the insulating tube 310 may each be made of, for example, a porous ceramic material. In addition, according to FIG. 3B, insulating granulate 50 is filled into the space that is still remaining, as described above, in order to avoid any dead space, i.e. space filled with air, as far as possible. The interior space of the cartridge heater 300 filled in this way is subsequently subjected to a compaction process, which is again indicated by the arrows P in FIG. 3C. The previously described changes in length and height are again obtained for the cartridge heater 300 thus completed. The same applies to the heater blank 230.While in the previous exemplary embodiments it has been assumed in each case that the heating element blank 130, 230 has been separated from a tubular body 160, 260, it is not within the scope of the invention claimed if the heating element blank is separated from a plate-shaped material. This non-claimed approach is illustrated in FIG. 6A, which illustrates, for example, a metallic plate of copper material or the like in side view, together with FIGS. 6B and 6C. Such a plate can also be separated from a wound metal strip.A heating conductor track structure is separated from the plate-shaped body 660 of FIG. 6A, for example, as is illustrated in FIG. 6B. This heating conductor track structure has two line sections 632 running in meandering fashion, which are connected to one another in the middle via a connecting web 636. In each case on the left and right, the two sections 632 have conductor track ends 635. An alternative embodiment of the connecting web is shown in dashed lines in FIG. 6C and is provided with the reference numeral 636'. This variant shown in dashed lines has the advantage that the heating element blank 630 can also be separated from a tubular body.The heating conductor track structure produced in this way is then bent multiple times in order to form a heating element blank 630 according to FIG. 6C. For this purpose, a U-shaped bending is carried out in the region of the connecting web 636, so that the two sections 632 lie one above the other. These two sections with the meandering heating conductor profiles are then bent over toward one another about the longitudinal axis 620, resulting in the profile of the entire heating conductor track structure and thus of the heating element blank 630 shown in FIG. 6C.Another embodiment of a cartridge heater according to the invention will be explained in conjunction with Figs. 7A, 7B and 7C. FIG. 7A shows a heating element blank 730 in a perspective view, which is formed similarly to the heating element blank 230 in FIG. 2A. However, the individual heating coil or the heating conductor 732 of a winding is now selected to be significantly wider in the direction of the longitudinal axis 12 than in the example of FIG. 2A. This heating element blank 730, however, likewise has a U-shaped connecting web 736, the already mentioned heating conductor 732 and the slots 734 lying between the individual turns of the heating conductor 732. The heating element blank 730 has two conductor track ends 735, to which the contact connections 40, 42 are connected.The heating element blank 730 thus configured is inserted, according to FIG. 7B, into a tubular metal housing 20, from which the contact terminals 40, 42 protrude in the manner already explained. As can be seen clearly in the partially broken-open plan view of FIG. 7B, compressible material 50 is filled between the metal housing 20 and the heating element blank 730, it being assumed that in the illustration of FIG. 7B the compaction of this material 50 and the associated dimensional changes of the heating cartridge 700 have already taken place.The detail marked with the reference symbol E in FIG. 7B is shown in FIG. 7C in an enlarged manner. The reference numerals already explained continue to apply. The heating conductor 732 has the two surfaces 737 and 738 which are parallel to each other and left and right of it cut surfaces 739. The cut surfaces 739 are parallel to one another in this exemplary embodiment. The already compacted material 50 is marked with the reference sign 50. It can be clearly seen in FIG. 7C that both the surfaces 737 and 738 and the cut surfaces 739 have an enlarged surface due to the compaction, in that irregularly distributed impressions 770 are provided on these mentioned surfaces. These impressions significantly improve the efficiency of the cartridge heater, i.e. the heat transfer from the heating element blank 730 via the compacted material 50 is ideally passed on to the metal housing 20.In FIG. 8, four different variants of impressions are shown. The impressions are marked with the reference number 770. Depending on how much the pressure P is set during the compacting of the pre-assembled cartridge heater, the impressions 770 are less or more pronounced. In addition, the type and configuration of the depressions 770 also depends on which compressible material 50 is filled into the metal housing 20 of the cartridge heater 700. It has been found that particularly strong impressions 770 are achieved during compacting if MgO granules are selected. When compacting porous ceramic material, in particular ceramic tubes or ceramic rods, the impressions are formed to be significantly smaller.It should be noted for the method according to the invention for producing the described heating cartridges 100, 200, 300 that the compaction is effected in such a way that an increase in length of the heating element blank 130, 230, 630 and / or of the metal housing 20 of between approximately 1% and approximately 15% and / or a reduction in height of the heating element blank 130, 230, 630 and / or of the metal housing 20 of in each case approximately 5% to approximately 25% is obtained.An important advantage of the method according to the invention is that, due to the use of a heating element blank 130, 230, 630, 730 which has been separated from a tubular metallic body 160, 260, 660, the cut edges which are produced in this case contribute optimally to the heat transfer to the metal housing 50 as a result of the compacting. After the compacting, highly compacted insulating material is applied to these cut edges, which promotes good heat transfer from the heating element blank 130, 230, 630, 730 to the metal housing 50. Moreover, due to the fact that the heating element blank 130, 230, 630, 730 according to the invention can have almost any cross-sectional shape in contrast to conventional heating wires, it can be designed to be very variable in order to enable optimum heat transfer.It should be noted that in the case of the heating cartridges according to the invention, the tubular metal housing and the heating element blank are mounted parallel to one another, that is to say have the same direction of extent. In this case, the cut surfaces can be arranged wholly or partly at right angles to the outer jacket of the tubular metal housing. It is also possible to arrange the surfaces of the heating element blank which are not processed by cutting entirely or partially parallel to the outer jacket of the metal housing. Finally, it is also possible to design the tubular metal housing as an electrical return conductor for the heating element or to provide a plurality of heating circuits for the heating element.Referring now to Figures 9A-9E, various production steps are illustrated for making a cartridge heater 600 as contemplated by the present invention. In this case, the heating element blank 630 already known from FIG. 6C is again shown in a perspective view in FIG. 9A. The connecting web 636' is formed in an arc shape and runs at least approximately concentrically about the central axis 12.In the exemplary embodiment shown in FIG. 9E, this heating element blank 630 is covered with an insulating coating, in the present case a ceramic coating 650. Only the conductor track ends 635 are not provided with this coating 650. Porous ceramic material is particularly suitable as the coating 650. Due to the coating 650 of the heating element blank 630, the heating element blank 630 can be inserted into the metal housing 20 without centering aids. The conductor tracks of the heating element blank 630 are thus insulated from the metallic housing 620. This is illustrated in FIG. 9C. The metal housing 20 is provided on the left and right with the housing base 21 and the housing cover 23. In this case, the material 50 to be compacted is filled into the interior of the metal housing 20. In a subsequent processing step, the cartridge heater 600 thus prepared is subjected to the described compaction process. This is illustrated in FIG. 9D. As explained, the elongation of the metal shell 20 achieved with the compacting and the diameter elongation of the metal shell 20 are shown in FIG. 9D.FIG. 9E shows the cartridge heater 600 again in perspective.FIG. 10 shows a further embodiment of a cartridge heater according to the invention. FIG. 10A shows the associated perspective illustration of the individual components, FIG. 10B a sectional view before the compaction and FIG. 10C a sectional view after the compaction of the cartridge heater.In this exemplary embodiment, the metal housing 20 of the heating cartridge 1000 is designed as a hollow cartridge. This means that the tubular metal housing 20 has a central inner tube 22. This inner tube 22 and the tubular metal housing 20 are aligned concentrically with the longitudinal axis 12. The heating element blank is inserted into the space between the metal housing 20 and the inner tube 22. In the exemplary embodiment of FIG. 10A, this heating element blank 230 is a heating element blank 230 as has been explained in connection with FIGS. 2A to 2D. This heating element blank 230 in turn has two conductor track ends 235, to each of which a contact connection 40, 42 is connected. As can be seen from FIG. 10B, after the heating element blank 230 has been inserted into the intermediate space between the metal housing 20 and the inner tube 22, compacting material 50 is again introduced. The cartridge heater 1000 is closed on its side shown on the left in FIG. 10B by an annular housing base 21 and on its opposite end by an annular housing cover 23.In a subsequent method step, which is illustrated in FIG. 10C, the cartridge heater 1000 is subjected to a compaction step. For this purpose, a so-called calibrating pin is expediently inserted into the cavity of the inner tube 22. This calibrating mandrel is provided with the reference sign 52 and rests closely and flatly against the inner wall of the inner tube 22 before the actual compacting process, so that this inner tube 22 cannot narrow during the subsequent compacting process. After the actual compacting process, the calibrating mandrel 52 is removed, so that the finished cartridge heater 1000 can be slid onto a cylindrical body, if necessary, in order to heat the latter.A final embodiment is illustrated in conjunction with Figures 11A, 11B and 11C. The already known reference numerals are used further. The heater blank in FIG. 11A corresponds to the heater blank 730 of FIG. 7A. This heating element blank 730 is now inserted, similar to the embodiment shown in FIG. 10, into a double-walled metal housing, i.e. into a tubular metal housing 20 with an inner tube 22 on the inside. The detail E according to FIG. 11C again shows the compacted material and the surface structure achieved on account of the compaction, with impressions 770 in the line sections 732 of the heating element blank 730.List of reference characters12 Longitudinal axis 20 Metal housing 21 Housing base 22 Inner tube 23 Housing cover 40 Contact connection 42 Contact connection 50 Compressible material 52 Calibration mandrel 100,200,300,600,700 1000 Heating cartridge 130, 230, 630, 730 Heating element blank 132, 232, 632, 632 Heating conductor 132, 232 Heating conductor region 133,134,137,234,734 Slot 133', 134', 137' Slot region 135, 235, 635, 735 Conductor track end of the heating conductor 136,236,636,636',730 U-shaped end of the heating conductor 230 137, 737 First surface of the heating element blank 138, 738 Second surface of the heating element blank 139, 739 Cut surfaces of the heating element blank 140, 240 Cut waste 150, 250 Cut line 160, 260, 660 Tubular or plate-shaped body 310 Insulating tube 312 Insulating rod 312' Compacted material 632, 732 Sections 650 Coating, in particular ceramic coating 770 Impressions b1, b2 slot width A1-A12 surfaces B-B cut C, D, E detail D-D cut F K1 height of the heating element blank before compaction K2 height of the heating cartridge before compaction K3 height of the heating element blank after compaction K4 height of the heating cartridge after compaction K5 thickness of the heating conductor before compaction K6 thickness of the heating conductor after compaction L1 length of the heating element blank before compaction L2 length of the metal housing before compaction L3 length of the heating element blank after compaction L4 length of the heating cartridge after compaction L5 distance between two heating conductor connections before compaction L6 distance between two heating conductor connections after compaction the compacting P pressure α angle

Claims

Method for producing a tubular cartridge heater (100; 200; 300; 700) having an electrical heating element lying within a metal housing (20) of the cartridge heater (100; 200; 300; 700) and extending axially to a longitudinal axis of the cartridge heater (100; 200; 300; 700), wherein the cartridge heater (100; 200; 300; 700) and / or the heating element have a predetermined geometric shape with a predetermined ohmic resistance, comprising the following method steps: - providing a tubular, electrically conductive body (160; 260; 660), - processing the body (160; 260; 660) to form a heating element blank (130; 230; 630; 730) such that the body (160; 260; 660) a tubular and deformable heating conductor track structure having a first overall length (L1) with at least one first and second conductor track end (135) and a first height (K1) is formed by introducing slots (137, 737) with mutually opposite cut surfaces (139, 739) into the tubular, electrically conductive body (160, 260, 660), - inserting the heating element blank (130; 230; 630; 730) into the tubular metal housing (20), which has a second overall length (L2) and a second height (K2), - filling the tubular metal housing with an electrically insulating and sealable material (50; 310; 312), - compressing the filled metal housing (20) to achieve the predetermined geometric shape and the predetermined ohmic resistance of the heating element blank (130, 230, 630, 730) and / or of the heating cartridge (100; 660); 200; 300; 700) having a third overall length (L3) increased in relation to the first overall length (L1) and / or a third height (K3) decreased in relation to the first height (K1) and / or for forming the metal housing (20) to a fourth overall length (L4) increased in relation to the second overall length (L2) and / or a fourth height (K4) decreased in relation to the second height (K2).Method according to Claim 1, characterized in that the metal housing (50) is closed with at least one cover (23, 24) before the compacting.Method according to either of Claims 1 and 2, characterized in that the at least first and second conductor track ends (135; 235; 635) or contact connections (40, 42) provided with them are led out of the metal housing (20) on the end face.Method according to one of Claims 1 to 3, characterized in that the body (160, 260, 660) for forming the heating element blank (130, 230, 630, 730) is processed by means of laser cutting, water jet cutting, microwater jet cutting, etching, punching, drilling, milling, turning or sawing.Method according to one of Claims 1 to 4, characterized in that the heating conductor track structure is formed at least in sections in meandering fashion.Method according to one of Claims 1 to 5, characterized in that the heating conductor track structure is formed in a bifilar manner.Method according to one of Claims 1 to 6, characterized in that insulation granules (50), in particular MgO granules, ceramic granules and boron nitride granules, or porous ceramic material (310, 312) is used as material (50, 310, 312) for the compacting.Method according to one of Claims 1 to 7, characterized in that the compaction is carried out in such a way that an increase in length of the heating element blank (130; 230; 630; 730) and / or of the metal housing (20) by between approximately 1% and approximately 15% and / or a reduction in height of in each case approximately 5% to approximately 25% is effected.Method according to one of Claims 1 to 8, characterized in that the heating element blank (130; 630; 730) is coated with an insulating layer, in particular a porous ceramic layer, before insertion into the tubular metal housing (20).Method according to one of Claims 1 to 9, characterized in that a double-walled hollow tube is used as the metal housing (20).A cartridge heater (100, 200, 300, 700) manufactured according to any one of claims 1 to 10.The cartridge heater (100, 200, 300, 700) of claim 11, characterized in that the heater blank (130, 230, 330, 730) has slots (137, 737) with opposing cut surfaces (139, 739) that are arranged orthogonally to the tubular wall of the metal housing (20).The cartridge heater (100, 200, 300, 700) of claim 11, characterized in that opposing cut surfaces (139, 739) are arranged parallel to each other at an angle (α) to the tubular wall of the metal housing (20).The cartridge heater (100, 200, 300, 700) of claim 13, characterized in that opposite cut edges (139, 739) are opposite each other at different angles (α, -α) to the tubular wall of the metal housing (20).The heater cartridge (100, 200, 300, 700) according to any one of claims 12 to 14, characterized in that the heating element blank (130, 230, 330, 730) in the fully assembled and compacted state has impressions (770) on its surfaces (137, 237) and on its cut surface (139, 739).Cartridge heater according to one of claims 11 to 15, characterised in that its metal housing (20) is designed as a double-walled tube (20) with an inner tube and an outer tube (22).The cartridge heater according to any one of claims 11 to 16, characterized in that the heater blank (130; 230; 330; 730) is coated with an insulating layer.

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