HEATING PIPE FOR A HOUSEHOLD APLIANCE

Abstract

 The invention relates to a heating pipe 1 for a household appliance comprising a heating device 2, wherein the heating pipe 1 has at least one outer circumferential surface portion adapted to be coated with an electrical insulation layer 11, characterized that the outer circumferential surface portion is an annular recess 24, to an arrangement comprising a heating pipe 1 and at least one heating element 4 and to a household appliance.

Description

[0001] The present invention relates to a heating pipe for a household appliance comprising an electrical heating device according to the preamble of claim 1, to an arrangement for a household appliance comprising a heating pipe and an electrical heating device, and to a household appliance.

[0002] According to heating pipes for household appliances having an electrical heating device in order to heat up water running through the heating pipe for cleaning purposes, the heating pipe has a constant outer circumferential surface. The heating device has a plurality of ring-shaped heating elements which are spaced apart from each other. In order to avoid any electrical short circuit between the heating elements and the heating pipe, the outer circumferential surface is coated over its entire length with an electrical insulation layer. An exemplary household appliance is a dishwasher or a washing machine.

[0003] It has been recognized that the insulation layer tends to instable behavior which results in cracks, delamination or a reduction of its electrical resistance. In order to avoid these disadvantages, additional process steps are necessary such as providing and adhesion layer or a brushing of the outer circumferential surface of the heating pipe before applying the insulation layer.

[0004] Therefore, the object of the present invention is to create a heating pipe for a household appliance comprising an electrical heating device, which can be produced in higher quality, an arrangement for a household appliance comprising a heating pipe and at least one electrical heating device, and an improved household appliance.

[0005] This object is solved by a heating pipe with the features of claim 1, by an arrangement with the features of claim 5 and by a household appliance with the features of claim 15. Advantageous embodiments of the invention are mentioned in the claims.

[0006] According to the invention, a heating pipe for a household appliance comprising an electrical heating device has least one outer circumferential surface portion which is adapted to be coated with an electrical insulation layer. Thereby, the outer circumferential surface portion is an annular recess, such as a groove surrounding the heating pipe.

[0007] Due to the pipe surface (shape) modification, the insulation layer shows a reduced residue stress profile and shear stress profile. Additionally, the adhesion of the insulation is improved. Regarding manufacturing, for instance, neither a brushing is necessary before applying the insulation layer, nor an adhesive layer. Further on, cutting of the heating pipe is easier, as the insulation layer needs not to be cut as well. This prevents possible short circuits. In comparison, conventional prefabricated heating pipes are provided with a continuous coating that is used for insulation, so that when these prefabricated pipes are cut to size, the coating for insulation is also separated and this can cause possible short circuits, especially at the connection ends of the cut heating pipe. Over all, the heating pipe according to the invention can be manufactured risk reduced. An exemplary household appliance in which the heating pipe is used is a dish washer or a washing machine. The heating pipe may have a cylindrical shape and may be used to heat water within a household appliance. Preferably, the heating pipe is made of steel. Steel allows an effective transfer of the heat generated by the heating device to the inside of the heating pipe to heat the water running inside.

[0008] Advantageously, the at least one annular recess is limited in axial direction by two side walls which are inclined in opposite directions to each other. If the side walls are inclined to each other, it is preferred, if in a side view, the annular recess has a V-like grooves shape or a U-like grooves shape. Thus, it is preferred, if the side walls are running away from each other in radial outwards direction. This inclined shape reduces cracks and delamination which results in improved adhesion of the insulation layer.

[0009] Preferably, the side walls are inclined in axial direction in an angle between 25 and 45 degrees, preferably between 25 and 35 degrees, more preferably 30 degrees to each other.

[0010] According to the invention, an arrangement for a household appliance comprising a heating pipe having at least one annular recess and at least one electrical heating device having at least one ring-shaped heating element. In the at least one annular recess, an electrical insulation layer is provided between a bottom of the at least one annular recess and the at least one heating element.

[0011] The electrical insulation layer between the heating pipe and the electrical heating element insulates the electrically operated heating element from the electrically conductive heating pipe so that short circuits are prevented. Exemplary, the insulation layer is a ceramic layer, for instance made of Al₂O₃. The insulation layer can be sprayed directly in the annular recess. Adhesion of the insulation can be further improved if the annular recess is cold plasma activated before.

[0012] The heating device includes the at least one electrical heating element, which is supplied with electricity to generate the desired heat. The heating element may be connected to a power source by means of at least one electrically conductive trace, wherein the conductive trace may be attached to a surface of the heating pipe and may be insulated with the insulation layer.

[0013] Preferably, in one area of the at least one annular recess the insulation layer is not provided. In this uncovered area, at least on electrical connector for the at least one heating element can be positioned.

[0014] Advantageously, the insulation-free uncovered area is delimited by two inclined surfaces facing each other. An angle between 25 and 45 degrees, preferably between 25 and 35 degrees, more preferably an angle of 30 degrees to each other is preferred.

[0015] In one embodiment, the at least one annular recess is filled at least partially with the radially inner insulating layer and a radially outer sealing layer. The sealing layer surrounds the insulation layer over its entire circumferential extension and entire axial extension. The sealing acts as an impregnation of the insulation layer. Preferably, the sealing layer is applied directly on the insulation layer after the insulation layer has been coated. By means of this, there is no influence of air humidity, open pores in the insulation layer can be filled and a higher resistance and resilience in following process steps of the insulation layer can be achieved.

[0016] Preferably, the sealing layer is flush with the adjacent circumferential surfaces of the heating pipe. The sealing acts as an impregnation of the insulation layer. Preferably, the sealing layer is applied directly on the insulation layer after the insulation layer has been coated. By means of this, there is no influence of air humidity, open pores in the insulation layer can be filled and a higher resistance and resilience in following process steps of the insulation layer can be achieved.

[0017] Advantageously, the sealing layer contains phosphate. By means of this, "phosphates" can be created inside the ceramic insulation layer.

[0018] Advantageously, the at least one heating element is positioned in axial distances to the adjacent circumferential surfaces of the heating pipe. By means of this, any electrical contact between the heating element and the adjacent outer circumferential surface is prevented. For instance, the electrical insulation layer at the two ends is larger in size than the heating device arranged thereon, so that electrical contact, for example due to water drops or moisture, between the heating elements and the adjacent outer circumferential surfaces of the heating pipe and thus short circuits are prevented. Preferable the heating device comprises several heating elements, which form a heating element group and are preferably arranged at regular distances from each other. This ensures an evenly distributed heating power through evenly distributed heating elements.

[0019] Preferably, the at least on heating element is coated on the sealing layer directly as a ring. By means of this, the heating element is linked with the sealing layer directly. A preferred material for the heating element is a NiCr-alloy. The material NiCr is particularly suitable for effectively converting the electrical energy into thermal energy due to the high electrical resistance of this material. Other suitable materials are, for example, NiO + Fe3O4, TiO2, TiO2 + NiCr, AI2O3 +NiCr, Al2O3 with W, Mo, Cu or Ni; ZrO2 + Y2O3 with Ni or W.

[0020] In one embodiment, the conductive traces of the heating elements are connected in parallel. By means of this, the resistance can be reduced. Each heating element can have a single conductive trace. Alternative, one conductive tracer is assigned to several heating elements, whereby adjacent conductive traces are then connected in parallel.

[0021] In an alternative embodiment, the conductive traces of the heating elements are connected in serial.

[0022] A household appliance according to the invention comprises an arrangement that has a heating pipe having at least one annular recess and at least one electrical heating device having at least one ring-shaped heating element. In the at least one annular recess, an electrical insulation layer is provided between a bottom of the at least one annular recess and the heating device. Such household appliance can be produced in a higher quality and shows a high resistance against electrical short circuits. Exemplary household appliances are dishwashers and washing machines.

[0023] In order to enhance the area in which the water running through the heating pipe can be heated, a plurality of annular recesses is provided. The annular recesses are spaced apart from each other in axial direction, preferably in a regular distance. Heating pipe surface that are adjacent to the annular recesses, i. e. surface areas of the heating pipe between adjacent annular recesses, do not need to be prepared in particular, as in these surface areas the insulation material is not provided. These surface areas can keep their initial outer diameter.

[0024] In what follows, preferred embodiments of the present invention are explained with respect to the accompanying drawings. As is to be understood, the various elements and components are depicted as examples only, and they may be facultative and/or combined in a manner different than that depicted. Reference signs for related elements are used comprehensively and not defined again for each figure.

Fig. 1

schematic representation of an inventive heating pipe carrying heating elements of a heating device in a side view;

Fig. 2

section of figure 1;

Fig. 3a

the heating pipe shown in figures 1 and 2 in a front view;

Fig. 3b

a detail of the figure 3a;

Fig. 4

a manufacturing step of the heating pipe in a side view; and

Fig. 5

a schematic representation of another embodiment of an inventive heating pipe in a side view

[0025] Terms used in the specification such as "axial" and "radial" are referred to the longitudinal axis x of a heating pipe 1, which preferably has a cylindrical shape.

[0026] Figure 1 shows a schematic representation of an axial section of an inventive arrangement 10 comprising a heating pipe and heating elements 4 of a heating device. The arrangement 10 can be installed in a household appliance such as a dish washer or a washing machine in order to heat cold water running through the heating pipe 1 for washing (cleaning) purposes.

[0027] The heating device comprises a first annular heating element group 3 consisting of four ring-shaped heating elements 4, for instance.

[0028] The heating element groups 3surrounds the heating pipe 1. Between the heating elements 4 and the heating pipe 1 a layer-composition 11, 20 is arranged which will be explained in more detail in Figure 2.

[0029] The heating elements 4 of the heating element group 3 is arranged at a fixed axial distance 6 from each other, which may, for example, be at least one seventh of a width 7 (extension in axial direction of the heating pipe 1) of an individual heating element 4. The heating elements 4 themselves have a strips-like shape and are put around the layer-composition 11, 20. As can be seen in Figure 3b, the heating elements 4 are formed as an opened ring having two ends spaced apart and facing each other.

[0030] Figure 2 shows a section of Figure 1 with a single heating element group 3 with four heating elements 4 exemplary for all heating element groups 5 provided on the heating pipe 1.

[0031] As illustrated, the heating element group 3 is positioned in a groove-shaped area of the heating pipe 1. In particular, the annular heating element group 3 is arranged on a layer-composition 11, 20 which is positioned in an annular recess 24 of the heating pipe 1, wherein each heating element 4 is coated directly on the radially outer layer 20.

[0032] The annular recess 24 is provided on the outer side of the heating pipe 1. The annular recess 24 has two inclined side walls 21, 22 which are delimiting the annular recess 24 in axial direction (longitudinal direction of the heating pipe 1). The side walls 21, 22 are inclined opposite to each other, preferably they are inclined in an angle 23 of 30 degrees each in axial direction.

[0033] The annular recess 24 in the heating pipe 1 is filled with a radially inner electrical insulation layer 11, for example of Al₂O₃, and with a radially outer sealing layer 20, for instance of phosphate. However, as explained with reference to Figures 3a and 3b, one area 33 of the annular recess 24 is uncovered. The layers 11, 20 are thus filled in the annular recess 24 that the outer circumferential surface of the sealing layer 20 is coaxial with adjacent outer circumferential surfaces 25 of the heating pipe 1. The insulation layer 11 has a greater radial extension than the sealing layer 20. The axial end sides of the insulation layer 11 and of the sealing layer 20 are inclined to each other according to the side walls 21, 23 of the annular recess 4 in the same angle, which is preferably (but not limited to) 30 degrees.

[0034] The sealing layer 20 terminates at a first end 26 of the annular recess 24 at a first distance 27 from a first end 28 of the heating element group 4 comprise the respective heating elements 4 in other axial direction, the sealing layer 20 terminats at an opposite second end 29 of the annular recess 24 at a second distance 30 from a second end 31 of the heating element group 4. The distances 27, 30 are at least one sixth of the width 7 of a heating element 4, such that a sufficient distance is thereby ensured to prevent a short circuit.

[0035] As can be seen in Figures 3a and 3b, the insulation layer 11 and thus the sealing layer 20 are interrupted in circumferential direction. Thus, the insulation layer 11 and the sealing layer 20 are opened rings in circumferential direction. Thus, an uncovered area 33 of the annular recess 33 is provided. The uncovered are 33 can extend over the entire length of the annular recess 24. Alternatively, a plurality of uncovered areas 33 are provided, which are spaced apart from each other by strips of the layer-composition 11, 20 (not shown). In this case, each uncovered area 33 would be prepared for one electrical component such as a connector.

[0036] What is also shown in Figures 3a and 3b is that the heating elements 4 are also "opened rings". They have a strips-like shape and are positioned on the sealing layer 20 in such a way that their opposite ends are positioned in a distance to the uncovered area 33. The uncovered area 33 has such a size an electrical component such as an electrical connector 35 can be positioned in it.

[0037] The uncovered area 33 is delimited in circumferential direction by two surfaces 37, 39. As the insulation layer 11 is covered entirely with the sealing layer 20, these inclined surfaces 37, 39 are provided by the sealing layer 20. Similar to the side walls 20, 21, the inclined surfaces 37, 39 are inclined in opposite direction to each other, preferably in an angel of 30 degrees.

[0038] In Figure 4, a manufacturing step of the inventive arrangement 10 is shown. According to Figure 4, an "endless" heating pipe 1 is provided carrying several heating element groups 3, 5. In a pipe zone between the adjacent heating element groups 3, 5 and thus in a pipe zone which is free of any layer-composition 11, 20, the endless heating pipe 1 is divided along a separation plane 41 into several arrangements 10 with a required length.

[0039] As illustrated in Figure 5, in one embodiment several heating element groups 3, 5 are provided on one heating pipe 1. The heating element groups 3, 5 are arranged at an axial distance 8 from each other, which may, for example, be at most one seventh of a width 9 of a heating element group 3, 5.

[0040] The invention relates to a heating pipe 1 for a household appliance comprising a heating device 2, wherein the heating pipe 1 has at least one outer circumferential surface portion 10 adapted to be coated with an electrical insulation layer 11, characterized that the outer circumferential surface portion is an annular recess 24, to an arrangement comprising a heating pipe 1 and at least one heating element 4 and to a household appliance.

Reference signs

[0041] 

1

heating pipe

3

heating element group

4

heating element

5

heating element group

6

axial distance between adjacent heating elements

7

width of a heating element

8

axial distance between adjacent heating element groups

9

width of heating element group

10

arrangement

11

insulation layer

20

sealing layer

21

side wall

22

side wall

23

angle

24

annular recess

25

outer circumferential surfaces

26

first end of annular recess

27

first distance

28

first end of heating element

29

second end of annular recess

30

second distance

31

second end of heating element

33

uncovered area

35

connector

37

inclined surface

39

inclined surface

41

separation plane

x

axial / longitudinal axis of the heating pipe

Claims

1. Heating pipe (1) for a household appliance comprising an electrical heating device (3, 5), wherein the heating pipe (1) has at least one outer circumferential surface portion adapted to be coated with an electrical insulation layer (11), characterized that the outer circumferential surface portion is an annular recess (24).

2. Heating pipe (1) according to claim 1, wherein the at least one annular recess (24) is limited in axial direction by two side walls (21, 22) which are inclined in opposite directions to each other.

3. Heating pipe (1) according to claim 2, wherein the side walls (20, 21) are inclined in an angel (23) between 25 degrees and 45 degrees each in axial direction.

4. Heating pipe (1) according to any of the preceding claims, wherein a plurality of annular recesses (24) is provided which are spaced apart from each other in axial direction.

5. Arrangement (10) for a household appliance, comprising a heating pipe (1) according to one of the preceding claims having at least one annual recess (24) and at least one electrical heating device (3, 5) having at least one ring-shaped heating element (4), wherein an electrical insulation layer (11) is provided between a bottom of the at least one annular recess (24) and the heating device (4, 5).

6. Arrangement (10) according to claim 5, wherein in one area (33) of the at least one annular recess (24) the insulation layer (11) is not provided.

7. Arrangement (10) according to claim 6, wherein in circumferential direction the uncovered area is delimited by two inclined surfaces (37, 39) facing each other.

8. Arrangement (10) according to claims 5, 6 or 7, wherein a sealing layer (20) surrounds the insulation layer (11) over its entire circumferential and axial extension.

9. Arrangement (10) according to claim 8, wherein the sealing layer (20) is flush with adjacent circumferential surfaces (25) of the heating pipe (1).

10. Arrangement (10) according to claim 8 or 9, wherein the sealing layer (20) contains phosphate.

11. Arrangement (10) according to any of the preceding claims 5 to 10, wherein the at least one heating element (4) is positioned in axial distances (26, 28) to the adjacent outer circumferential surfaces (25) of the heating pipe (1).

12. Arrangement (10) according to any of the preceding claims 5 to 11, wherein the at least on heating element (4) is coated on the sealing layer (20) directly in a ring shape.

13. Arrangement (10) according to any of the preceding claims 5 to 12, wherein the heating elements (4, 5) are connected via electrically conductive in parallel.

14. Arrangement (10) according to any of the preceding claims 5 to 12, wherein the heating elements (4, 5) are connected via electrically conductive in serial.

15. Household appliance comprising an arrangement (10) according to any of the claims 5 to 13.

Drawing