Abstract
A ceramic heating resistor to be arranged in a tubular element of an electrical heating element for heating a fluid, preferably air, wherein the heating resistor can be produced by sintering a green body comprising at least one ceramic raw material. The heating resistor includes an electrically insulating component and an electrically conducting component, and the electrically insulating component forms a matrix in which the electrically conducting component is accommodated. An electrical heating element for heating a fluid, preferably air, comprising including at least one tubular element, through which a fluid flows or can flow, and to a device for heating a fluid, preferably air, including at least one such heating element.
Claims
1-14. (canceled)
15. An electrical heating element for heating a fluid, comprising at least one tubular element through which a fluid flows or can flow, and a ceramic heating resistor disposed in the tubular element, the heating resistor being produced by sintering a green body, comprising at least one ceramic raw material, and comprising an electrically insulating component and an electrically conducting component, and the electrically insulating component forming a matrix in which the electrically conducting component is accommodated, characterized in that the heating resistor comprises an arrangement of two open helicoid bodies having a respective central screw axis, the screw axes of the helicoid bodies being parallel to one another and the helicoid bodies being helically wound inside one another in a contactless manner, the central screw axes of the helicoid bodies being oriented substantially parallel to the central axis of the tubular element, the helicoid bodies being connected to one another in an electrically conducting manner in the region of one end of the helicoid arrangement and designed as separate connecting electrodes at an opposing further end of the helicoid arrangement, an electrically insulating element being disposed in at least one central cavity formed by the open helicoid bodies along the screw axes of the open helicoid bodies, the electrically insulating element having a tubular, rod-shaped or sectionally tubular and rod-shaped design, and the cross-sectional surface of the tubular element, in terms of shape and size, being only insignificantly larger than the maximum cross-sectional surface of the heating resistor.
16. The electrical heating element according to claim 15, wherein the ratio of the radial helix thickness to the axial helix width of at least one helicoid body of the ceramic heating resistor is at least 2:1.
17. The electrical heating element according to claim 15, wherein the ratio of the inside diameter to the outside diameter of at least one helicoid body of the ceramic heating resistor is a maximum of 1:2.
18. The electrical heating element according to claim 15, wherein at least one helicoid body of the ceramic heating resistor has a variable axial helix width, and in particular a radially increasing axial helix width.
19. The electrical heating element according to claim 15, wherein at least one helicoid body of the ceramic heating resistor has a variable axial helix width along the screw axis thereof.
20. The electrical heating element according to claim 15, wherein at least one helicoid body of the ceramic heating resistor has a variable distance between adjoining turns along the screw axis thereof.
21. The electrical heating element according to claim 15, wherein the electrically conducting component of the ceramic heating resistor is at least partially formed of a metal alloy of the silicide type.
22. The electrical heating element according to claim 15, wherein the electrically insulating component of the ceramic heating resistor is formed at least of a mineral of the silicate type, a ceramic of the oxide type, and/or an arbitrary combination thereof.
23. A device for heating a fluid, comprising at least one electrical heating element according to claim 15.
24. The electrical heating element according to claim 21, wherein the metal alloy of the silicide type is molybdenum disilicide.
25. The electrical heating element according to claim 22, wherein the electrically insulating component of the ceramic heating resistor is formed at least of feldspar, feldspathoids or other substances forming silicate glass.
26. The electrical heating element according to claim 22, wherein the electrically insulating component of the ceramic heating resistor is formed at least of aluminum oxide.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] Further advantages, features and details of the invention will be apparent from the claims and the following description of preferred embodiments based on the drawings, in which identical or functionally equivalent elements are denoted by identical reference numerals. In the drawings:
[0040] FIG. 1 shows a schematic illustration of a heating resistor according to the invention in a side view;
[0041] FIG. 2 shows a sectional view of the heating resistor of FIG. 1 along line A-A from FIG. 1;
[0042] FIG. 3 shows a sectional view of the heating resistor of FIG. 1 along line B-B from FIG. 2;
[0043] FIG. 4 shows a view from above onto the connecting region of the heating resistor of FIG. 1, with a viewing direction along the longitudinal axis;
[0044] FIG. 5 shows a view from above onto the connecting side of the heating resistor of FIG. 1, with a viewing direction along the longitudinal axis opposite to FIG. 4;
[0045] FIG. 6 shows a longitudinal sectional view of a schematic arrangement of the heating resistor in the sectional image according to FIG. 2 in a tubular element;
[0046] FIG. 7 shows an isometric view of a heating element according to the invention comprising a heating resistor according to the invention (not visible in this view);
[0047] FIG. 8 shows a longitudinal sectional view of a heating element according to the invention according to FIG. 7;
[0048] FIG. 9 shows a hot air hand-held device comprising a heating element according to the invention (not visible in this view); and
[0049] FIG. 10 shows an automatic welding machine for the overlapping welding of planar plastic materials comprising a heating element according to the invention (not visible in this view).
DETAILED DESCRIPTION OF THE INVENTION
[0050] The illustration of FIG. 1 shows an exemplary embodiment of a heating resistor 1 according to the invention. The heating resistor 1 is essentially formed of an arrangement of a first helicoid body 2 and a second helicoid body 3, which are helically wound inside one another in a contactless manner, and the screw axes of which coincide. The arrangement of the two helicoid bodies thus corresponds to a type-1 double helix, which is also referred to as a double-threaded screw. The shared screw axis of the helicoid bodies 2, 3 also forms the preferred longitudinal axis of the heating resistor 1. The helicoid bodies 2, 3 have an identical design, however are twisted with respect to one another by an angle an angle in a plane perpendicular to the screw axis, so that the two helicoid bodies 2, 3 extend around one another in a contactless manner. For this reason, the center of the arrangement of the two helicoid bodies 2, 3 is hollow, which is resulting from configuring the two helicoid bodies 2, 3 as open helicoid bodies. The central cavity 21 is cylindrical, the cylinder axis of symmetry corresponding to the shared screw axis of the two helicoid bodies 2, 3. At the two longitudinal-side ends 4, 5 of the arrangement of the two helicoid bodies 2, 3, these are each continued parallel to one another by integral moldings along the shared screw axis. On one longitudinal side of the arrangement of the two helicoid bodies 2, 3, the respective integral moldings at the helicoid bodies 2, 3 are connected to one another in an electrically conducting manner in a connecting region 22. At the longitudinal-side end 4 of the arrangement of the two helicoid bodies 2, 3 which is located opposite the connecting region 22, the respective integral moldings are implemented as separate connecting electrodes 6, 7, wherein the connecting electrode 6 belongs to the first helicoid body 2, and the connecting electrode 7 belongs to the second helicoid body 3.
[0051] FIG. 2 shows the heating resistor 1 as a sectional image along line A-A of FIG. 1, and FIG. 3 shows this as a sectional image along line B-B of FIG. 2. In the illustrated exemplary embodiment, the inner radius r as well as the outer radius R and the radial thickness d.sub.r=R−r of the helices (see FIG. 5 in this regard) of the two helicoid bodies 2, 3 are constant across the entire axial length of the arrangement of the two helicoid bodies 2, 3. The axial width b.sub.a, which is to say the thickness of the helices based on a direction parallel to the shared screw axis of the arrangement of the two helicoid bodies 2, 3, is likewise identical in all helices of the two helicoid bodies 2, 3, and increases with the radial distance from the shared screw axis of the two helicoid bodies 2, 3, apart from the respective rounding at the outer radial edge of the helices.
[0052] The illustration in FIG. 4 shows the heating resistor 1 of FIG. 1 in a top view onto the longitudinal-side end 5 of the arrangement of the two helicoid bodies 2, 3 including the connecting region 22, and the illustration in FIG. 5 shows the opposite longitudinal-side end 4 including the two separate connecting electrodes 6, 7 as well as the inner radius r and the outer radius R.
[0053] FIG. 6 shows a schematic longitudinal sectional illustration of the heating coil 1 of FIG. 1 according to the sectional image of FIG. 2 in a tubular element 8 of a heating element. The tubular element 8 has a hollow-cylindrical design in the exemplary embodiment shown here, and the inner radius of the tubular element 8 is only slightly larger than the outer radius of the arrangement of the two helicoid bodies 2, 3 of the heating resistor 1 disposed in the interior of the tubular element 8. In this way, the heating resistor 1 can be inserted without difficulty into the tubular element, wherein sufficient clearance is still present in the radial direction to compensate for manufacturing tolerances, and additionally it is ensured that the heating resistor and the inner side of the tubular element 8 cannot make contact as a result of thermal expansion during operation of the heating resistor 1. The tubular element 8 is made of a heat-resistant, electrically insulating, ceramic material, preferably a silicate ceramic or an oxide ceramic, such as aluminum oxide.
[0054] Such a tubular element 8 is an integral part of a heating element 9 shown in the isometric three-dimensional illustration in FIG. 7, wherein the tubular element 8, as in FIG. 6, comprises a heating resistor 1, which is not visible in FIG. 7. FIG. 8 shows a simplified schematic longitudinal sectional view of such a heating element 9 comprising a heating resistor 1 in the interior of the tubular element 8. In addition to a tubular element 8 and a heating resistor 1, the heating element 9 comprises a cover disk 10, a connecting piece 11 and an attachment and clamping means 15 in the form of a rod that extends along the central longitudinal axis of the heating element 9 and is made of an electrically insulating, heat-resistant ceramic material. The connecting piece 11 comprises two outer electrical contacts 12, which in the interior of the heating element 9 respectively transition into one of the two inner electrical contacts 13, wherein each of the inner electrical contacts 13 electrically contacts one of the two connecting electrodes 6, 7 of the heating resistor 1 in the interior of the tubular element 8. The connecting piece 11 moreover includes four cut-outs 14, through which air is able to flow from the exterior space into the interior of the heating element 9, flow around the heating resistor 1 in the tubular element 8, and flow through cut-outs 16 in the cover disk 10 out of the interior of the heating element 9 again. The attachment and clamping means 15 extends both through the entire tubular element 8, and thus also through the heating resistor 1 and through the connecting piece 11 and the cover disk 10. The attachment and clamping means 15 carries the heating element 1 and is implemented with appropriate supports on the outside of the connecting piece 11 and the cover disk 10 so as to brace the entire arrangement made up of the connecting piece 11, the heating resistor 1 and the cover disk 10 in the axial direction. This also serves to limit the thermal expansion of the heating element 1 in the axial direction. In the heating resistor 1 shown in the longitudinal sectional view in FIG. 8, the connecting region 5 of the two helicoid bodies 2, 3 has to be configured differently than in the heating resistor 1 shown in the illustrations in FIG. 1 to FIG. 5, so that the attachment and clamping means 15 can also extend in a rectilinear manner through this region. For this purpose, the heating resistor 1 can, for example, include an appropriate feedthrough for the attachment and clamping means 15 in the connecting region 5.
[0055] FIG. 9, by way of example, shows a hot air hand-held device 17 as a variant embodiment of a device according to the invention for heating a fluid, and in particular air. In the case of the hot air hand-held device, a heating element according to the invention, such as the heating element 9 shown in the illustrations in FIG. 7 and FIG. 8, is disposed in the heating tube 18.
[0056] FIG. 10 shows an automatic welding machine 19 for the overlapping welding of planar plastic and/or bitumen sheets as a further example of a variant embodiment of a device according to the invention for heating a fluid, and in particular air, wherein the material layers to be welded together are at least partially plasticized in at least one connecting region by way of a hot air flow. In the case of the automatic welding machine, a heating element according to the invention, such as the heating element 9 shown in the illustrations in FIG. 7 and FIG. 8, is disposed in the heating tube 20.
LIST OF REFERENCE NUMERALS
[0057] 1 heating resistor [0058] 2 first helicoid body [0059] 3 second helicoid body [0060] 4 first end [0061] 5 second end [0062] 6 first connecting electrode [0063] 7 second connecting electrode [0064] 8 tubular element [0065] 9 heating element [0066] 10 cover disk [0067] 11 connecting piece [0068] 12 outer contacts [0069] 13 inner contacts [0070] 14 cut-outs for air to enter [0071] 15 attachment means/clamping means [0072] 16 cut-outs for air to exit [0073] 17 hand-held hot air device [0074] 18 heating tube [0075] 19 automatic welding machine [0076] 20 heating tube [0077] 21 central cavity [0078] 22 connecting region
