SHEET-FORMED HEATER

Abstract: Sheet-shaped heater, in particular for use as a bed heater, and a water bed heater respectively. When designing such heaters it is difficult to obtain an optimal combination of properties for satisfying the different requirements imposed, inter alia with respect to reliability and safety, uniform temperature distribution and mechanical flexibility. For heat distribution the element comprises a continuous metal foil (22) in which there is formed a continuous meandering groove (20) which lies substantially at one side of the plane of the metal foil. There is no thickness reduction of the metal foil at the groove (20) formed. A heat emitting conduit, preferably a heating cable (21a-c) is tightly received in the groove, the depth thereof being substantially equal to the transverse dimension of the conduit. An outer protective layer (23) is tightly joined to the metal foil (22) and preferably to a portion of the surface of the conduit (21a-c) at that side where the groove (20) is open.

Description: Sheet-formed Heater. This invention relates to a sheet-formed heater compri¬ sing a heat emitting conduit, heat distributing parts and at least one outer protective layer. Primarely the invention is directed to such a heater for use as a bed heater, inclu¬ ding the heating of water beds. In the above specific uses very strict requirements are set to the reliability and security of the design- in par¬ ticular against electrical injury when an electrically heated element is concerned. Moreover, it is of substantial signifi¬ cance that the temperature distribution over the heat emit¬ ting surface of such elements, is as uniform as possible. An additional requirement in connection with bed heaters and water bed heaters, is that the element should have a certain degree of flexibility. It has been difficult in one and the same design of such a heater element to fulfill the above requirements to a satis¬ factory degree. Known designs have deficiencies inter alia with respect to reliable operation and life-time as well as regarding the temperature distribution. A non-uniform tem¬ perature distribution with certain portions of the element obtaining a rather strongly increased temperature during operation, leads to problems. One problem can consist there¬ in that materials included in the design may deteriorate during the life-time of the -element as a result of such heat influence. Thus, a good heat distribution has major sig¬ nificance. The invention is directed to providing a new design of such a heater element in which the requirements imposed are satisfied in combination in an optimal way. According to the invention this is obtained thereby that the heat distributing parts comprise a continuous metal foil in which there is formed a continuous meandering groove which is substantially located at one side of the plane of the metal foil and which isformed by pure folding and/or bending of the foil so that it is essentially not subjected to any thickness reduction at the groove, and that the heat emitting conduit is closely received in the groove and preferably fixed adhesively there¬ in, the depth of the groove being substantially equal to the transverse dimension of the conduit, and that an outer pro- tective layer is closely joined to the metal foil and possibly a portion of the surface of the conduit at that side where the groove is open. This solution can either be based upon electrical resis¬ tance heating or on a tube or a hose with a circulating heat medium, for example hot water. However, it is highly preferred to employ electrical heating, as hitherto has been common in bed heaters. According to the invention the heat emitting conduit in such case is a per se known electric heating cable, preferably having a double insulation. These known heating cables are normally intended for casting into floors or the like and have a very robust design which contributes substan¬ tially to the reliability of a heater element built up as stated above. Moreover, according to the invention it is preferred that an aluminum foil is employed as the metal foil mentioned. With an aluminum foil of thickness within the range 100 - 200 micrometers the necessary flexibility will be obtained. A structure based upon the present invention also has the substantial advantage that it is very material saving and thereby comparatively inexpensive in manufacture, con¬ sidered in relation to the other advantages being obtained. Finally, the sheet element according to the- invention is built up with components which to alarge extent are well adapted for a fully automatic continuous manufacturing line, which therefore is efficient. The invention shall be explained more closely below with reference to the drawing, in which: Figure 1 shows a schematic plan view of an example of a heater element according to the invention, Figure 2 shows a cross-section through an embodiment of the heater according to the invention, Figure 3 shows schematically a cross-section of another embodiment, and Figure 4 shows a similar cross-section through a third embodiment of the invention. In Figure 1 there is shown a comparatively elongate heater element 10 the longitudinal edges of which are desig¬ nated 1 and 2 respectively, whereas the transverse sides are designated 3 and 4 respectively. In meander shape there is mounted a heating cable 11 for electric resistance heating of a type known per se. It is an advantage that this hea¬ ting cable 11 is provided with a double insulation. The heating cable 11 is arranged with a number of parallel por¬ tions between the longitudinal edges 1 and 2, connected to each other alternately at one and the other side by means of end portions for example as shown at 12a and 12b. At points 8 and 9 as indicated the heating cable 11 is connected to respective supply leads 6 and 7 which together extend out of the heater through a plug connection 5 for example. By means of this plug connection the heater can be connected to for example a control and regulator unit and a current supply network. Provided that the remaining materials being included in the structure of the heater 10 are sufficiently flexible, the illustrated configuration of the heating cable 11 will to a large extent make possible bending thereof about trans¬ verse axes, so that the complete element may for example easily be rolled together in its longitudinal direction. During such bending or rolling the heating cable 11 which is relatively stiff per se, will quite simply be subjected to torsional twist along the straight portions, which can be taken up by the cable structure without any problem. The location of the connecting points 8 and 9 and the remaining arrangement makes it possible to manufacture the meander-shaped heating cable 11 and in particular a suppor¬ ting foil therefor, in a continuous manner to unlimited lengths By cutting to suitable lengths heaters of different sizes can then easily be assembled. The cross-section of Figure 2 may be regarded as lying in the longitudinal direction of an element as shown in Figure 1, whereby three parallel heating cable portions 21a, 21b and 21c are comprised by the cross-section. These heating cables 21a - c are supported or carried by an aluminum foil 22 in which grooves have been formed, as shown for example at 20, for the various portions of the heating cable. Thus, this groove has the same configuration as shown for the heating cable 11 in Figure 1, from side to side and over the whole length of the metal foil 22. The groove has generally the same cross-sectional shape as the heating cable and a depth corresponding approximately to the diameter or trans¬ verse dimension of the heating cable. Accordingly, the different portions of the heating cable will lie substantially at one side of the plane defined by the foil 22 having its main portions located between the various portions of the groove 20. Over the aluminum foil 22 there is applied a protective layer 23 which is closely joined to the foil 22 and preferably to those portions of the heating cable which faces the open side of the groove 20. Therefore, the pro¬ tective layer 23 will lie generally smooth and flat over the whole surface as illustrated in the figure. It is of signi¬ ficance to avoid air spaces between the foil 22 and the layer 23, since the heat emission is intended primarily to take place through the layer 23, i.e. in a direction upward in Figure 2. The very simple embodiment shown in Figure 2 is intended inter alia for mounting in building structures, in particular for the purpose of room heating. Possibly in such case the protective layer 23 can consist of a stiff plate, for example in the form of a wall panel or a ceiling panel or another form of.building plate. The joint between the metal foil 22 and the protective layer, possibly the sheet 23, conveniently can take place by means of an adhesive, in particular a heat curing adhesive. The heating cable can alsobe mounted in the groove 20 by means of an adhesive joint during a preceding manufacturing step. In the preferred embodiment with flexibility as explained above, the protective layer 23 is preferably formed by a flexible material, in particular a synthetic plastic material. The forming of the groove 20 in the metal foil, in par¬ ticular aluminum foil 22, must be carried out in such a way that the foil at no point is subjected to any significant thickness reduction,- which might make the element less reli¬ able throughout an extended operational life-time. The for¬ ming of the groove is effected by means of forming methods as known per se, in several steps based upon a pure folding or bending so that the foil thickness is essentially main¬ tained without change. This does not mean that the foil at certain portions cannot be folded or bent for example to double foil layers. With the aluminum foil 22 discussed here there is obtained a very good heat distribution from the heating cable throughou the whole surface of the heater element, the foil 22 extending across the whole of this surface substantially to the edges 1, 2, 3 and 4 as shown in Figure 1. Figure 3 shows an embodiment particularly intended for use as a bed heater. Here there are shown three cable por¬ tions 31a, 31b and 31c arranged in grooves in an aluminum foil 32. Thus, cable portion 31a lies in a groove 30. On the upper side there is provided a protective layer 33 simi¬ lar to the layer 23 in Figure 2. Moreover, on the underside there is applied another protective layer 34 which like the layer 33 can consist of a suitable flexible synthetic plastic material. Layer 34 is mainly attached to the bottom portions of the groove 30 so that the intermediate portions of the layer 34 extend freely between the groove portions spaced from the foil 32. Thereby an air chamber is formed, for example as shown at 39a and 39b. These air chambers or spaces have a very favourable effect by insulating against heat transport downwardly in the structure as shown in Figure 3. As mentioned in connection with Figure 2 the heat emission is intended to be essentially upwardly through the above first or upper protective layers, 23 and 33 re¬ spectively (Figure 3) . As a particular modification one could contemplate pro¬ tective layers 23 and 33 respectively, as discussed above, consisting of metal foil similar to the described foils 22 and 32. Such a structure would imply that the element is to be included in a -more composite assembly, for example com¬ prising an outer building panel in some form, as mentioned above in connection with Figure 2. In this respect it is a great advantage that the upward surface of the structures of Figures 2 and 3 is substantially planar, i.e. with the groove and the heating cable portions lying broadly below the general plane defined by the metal foils 22 and 32. The above specific embodiment with metal foils 32 and 33 at both sides of the heating cable, is particularly inte¬ resting when the heating cable is not based upon electric resistance heating, but is a plastic hose or a plastic tube for circulating hot water. In such a case the metal foil enclosure of the plastic hose- will inter alia have the advantage that it is very difficult for air to diffuse through the plastic material wall from the outside. Finally Figure 4 shows a more composite structure in which in addition to a metal foil 42 with grooves 40 and heating cable portions 41a, 41b and 41c, a first or upper protective layer 43 of plastic material and a second or lower protective layer 44 also of plastic material, there is additionally provided a metal foil 45 between the foil 42 and the layer 43. Foils 42 and 45 as well as the layer 43 are tightly joined to each other over the whole surface for making possible a good heat distribution and heat emission upwardly. Concerning the direction of heat emission mentioned, i. e. upwardly, this discussion is of course based upon the orientation of the element as shown in Figures 2, 3 and 4 of the drawings. This is the orientation which is of interest in the primary field of application, namely as a bed heater. It is obvious, however, that the orientation of such a heater element can be completely as desired, and then the direction of heat emission will vary correspondingly. For example when used as a ceiling heater the element will be oriented upside down in relation to what is shown in Figures 2, 3 and 4, i.e. so that the heat emission takes place in a direction down¬ wardly. As to the plastic materials which can be used in the pro¬ tective layers, it will be near at hand to an expert to se¬ lect suitable qualities. For example PVC can be employed, preferably with additives which make the material self- extinguishing. Also more rubber-like materials may be employe in particular when it is desired to obtain a high degree of flexibility. In the case of aluminum foil it is an advantage to employ pure aluminum being annealed for a maximum of bending capabi¬ lity. The forming of grooves etc. as described, should be effected in such a manner that the aluminum foil will not be¬ come hard because of tensioning. This consideration will be more or less automatically taken into account in the forming as described above, based substantially on a pure bending and/or folding. As far as joining methods are concerned there may also in addition to adhesive connections as discussed, be employed heat sealing, possibly high frequency sealing of the plastic foils included in the structure of the heater element. As a practical example of dimensions and capacities of a heater element based on this invention, the following is quoted : Effective width: Approximately 30 cm Effective length: Approximately 1 m Number of meanders of the heating cable: 26 Electric power: 400 W. Obviously by varying dimensions, heating cable resis¬ tance per unit length, arrangement of the meander shape of the heating cable and so on, it is possible to adjust the total power as well as power per unit area of the element within wide limits depending upon the field of application aimed at.

Claims: C l a i m s : 1. Sheet-shaped heater comprising a heat emitting conduit, heat distributing parts and a least one outer protective layer, characterized in that the heat distributing parts comprise a continuous metal foil (22, 32, 42) in which there is formed a continuous meandering groove (20, 30, 40) which is located substantially at one side of the plane of the metal foil and which is formed by pure folding and/or bending of the foil so that it is essentially not subjected to any thickness reduction at the groove (20, 30, 40) , that the heat emitting conduit (21a-c, 31a-c, 41a-c) is closely received in the groove (20, 30, 40) and preferably attached therein by an adhesive, the depth of the groove being sub¬ stantially equal to the transverse dimension of the conduit (21a-c, 31a-c, 41a-c) and that an outer protective layer (23, 33) is closely joined to the metal foil (22, 32, 42) and possibly to a portion of the surface of the conduit (21a-c, 31a-c, 41a-c) at that side where the groove (20, 30, 40) is open. 2. Heater according to claim 1 based upon electric resistance heating, characterized in that the conduit is a per se known electrical heating cable (21a-c, 31a-c, 41a-c) , preferably being provided with a double insulation. 3. Heater according to claim 1 or 2, characterized in that the metal foil is an aluminum foil. 4. Heater according to claim 1, 2 or 3, characterized in that a second outer protective layer (34, 44) is provided at the opposite side in relation to said first protective layer and attached to the metal foil (32, 42) at the groove (30, 40) so that there is formed an air space (39a-b, 49a-b) between the foil and the second protective layer at the portions between the adjacent parts of the groove (30, 40) 5. Heater according to any one of claims 1 - 4, characterize in that the groove (11) is arranged with a number of parallel portions which together constitute the main part of the total length of the groove, and which extend nearly over the whole width of the heater element (10) , with end portions (12a, 12b) which alternately connect the parallel portions (11) at one and the other end thereof. 6. Heater according to claim 5, characterized in that the protective layer or layers (23, 33, 43, 34, 44) consist of a flexible material, for example a plastic material. 7. Heater according to any one of claims 1 - 6, characterized in that between the metal foil (42) with grooves (40) and said first protective layer (43) there is provided a second, generally plane metal foil (45) being joined tightly to the protective layer and the grooved metal foil respectively, possibly also to a portion of the surface of the conduit (41a-c) . 8. Heater according to any one of claims 1-7, characterized in that a connector (8, 9) for supply conduits (6, 7) is placed at least at two end portions of the groove located at the same side edge (2) of the heater element (10) . 9. Heater according to any one of claims 3-8, characterized in that the aluminum foil (2, 32, 42) has a thickness in the range from 100 to 200 micrometers. 10. Heater according to claim 1, based upon heating with circulating hot water, characterized in that the conduit is a tube of plastic material and that the outer protective layer preferably comprises a metal foil being applied with a maximum of contact or enclosure against that portion of the plastic tube which is not enclosed by the groove (Figures 3 and 4) .

Inventors: WESSELTOFT PER, WESSELTOFT, PER
Applicants: WESSELTOFT AS, PER WESSELTOFT A/S
Application year: 1986
Main classification: H05B3
IPC codes: H05B3