WO2009101081A1

WO2009101081A1 - Electric heating element

Info

Publication number: WO2009101081A1
Application number: PCT/EP2009/051507
Authority: WO
Inventors: Roberto Colombo
Original assignee: I.R.C.A. S.P.A. Industria Resistenze Corazzate E Affini
Priority date: 2008-02-12
Filing date: 2009-02-10
Publication date: 2009-08-20
Also published as: ITRM20080077A1

Abstract

An electric heating element for heating water in a household appliance consists of an electrical resistor inserted into a profiled base of a support fixed in a hole made in one of the vertical walls of the tank for heating the water in the household appliance, preferably in a low vertical position close to a water discharge pipe, in order to occupy a very limited space and to avoid the accumulation of lime-scale close to the heating element.

Description

ELECTRIC HEATING ELEMENT Field of the invention

The present invention relates to an electric heating element for heating water used by a household appliance, and to its use in a household appliance such as a washing or laundry machine, a dishwasher, or a steam generator. State of the art

Household appliances such as washing machines or dishwashers use electrical devices to heat the water which is used for washing clothes or dishes, respectively. The heating devices contain electrical resistors which are placed at the bottom of the water container to allow the water to be heated even for those cycles requiring a small quantity of water. Therefore, washing drums or compartments are equipped with an area for collecting water at the bottom where, in the presence of even a small quantity of water, the electrical resistor is however completely immersed in the water. This is provided to prevent overheating caused by the element heating up without being covered by water.

A vertical cross-section of a state-of-the-art washing machine equipped with a shielded electric resistor 30 inserted into a recess placed at the bottom of the tank of the washing machine is shown in figure 1. Washing machines with electrical resistors of this type have certain disadvan- tages. In use, lime-scale mixed with lint may often deposits around the heating element, thus reducing the heat exchange and increasing the risk of corrosion. The resistor also needs to be fixed to a metal support, to ensure its mechanical stability, especially during the spin cycle of washing machines, with the risk of creating rust spots. For this type of electrical resistors, the tank needs to have a spe- cific space large enough to ensure that, during the operating cycle, the resistor is always covered with water, in order to prevent overheating. These electrical resistors further need to be well inserted into the tank (supported by a non-visible metal bridge) and secured thereto by means of a suitable tightening torque to ensure that no water leaks occur outside the tank. Therefore, a need for an innovative heating system which allows to overcome the aforesaid problems is felt. Summary of the invention The main object of the present invention is to provide a heating element that over- comes the disadvantages listed above.

A further object of the invention is particularly directed to the use of an electric heating element having compact dimensions which does not require any large spaces or housings, and which may be placed in a position in the household ap- pliance where it remains in contact with the water during the operation.

Therefore, the present invention suggests to achieve the above-discussed objects by providing an electric heating element for heating water in a household appliance, particularly a washing machine, a dishwasher, or a steam generator, which in accordance with claim 1 comprises: - a thin, metal supporting element having a base with a first side, referred to as the internal side, intended to be placed in contact with the interior of a tank of the household appliance containing the water to be heated, and a second side, referred to as the external side, on the part of the base opposite the internal side, and intended to be positioned on the external part of said tank, when mounted to the household appliance,

- an electrical heating resistor, fixed on the external side of the supporting element,

- sealing means to prevent fluids from flowing between the external side and the internal side, - a metal heat-dissipation disc interposed between the electrical heating resistor and the supporting element, said heating element being intended to be fixed to a vertical wall of the tank so that the supporting element is vertically arranged along the wall. According to a further aspect of the invention, a household appliance is provided, particularly a washing machine or a dishwasher or a steam generator, which in accordance with claim 7 comprises a tank for containing water to be heated, an electric heating element having the features described above for heating the water, the heating element being placed at a lower area of the tank, vertically fixed into an opening obtained in a vertical wall of the tank itself. In virtue of the new embodiment of the heating element, which is more compact and almost flat, or in any case greatly flattened, combined with the feature of being flat-mounted against a wall orthogonal to the horizontal base of the tank containing the water at the lower area of the household appliance, there are several advantages with respect to the state of the art.

Lime-scale, as well as lint in the case of washing or laundry machines, is less likely to accumulate around the heating element, and moreover tends to self- remove due to the thermal dilatation of the heating element surface in contact with the water, and to the force of gravity itself. In addition, the position chosen for the heating element causes these residues to be dragged towards the bottom of the tank, with the advantage of minimising the danger of overheating and corrosion of the resistor. Especially for laundry machines, in the embodiment in which the heating element is fixed at and above the inlet of the water discharge pipe, the lime-scale that detaches from the heating element, along with any lint, directly enters the discharge pipe and are eliminated from the household appliance.

A further advantage is the fact that a need for providing a metal support to fix the heating element to the tank is suppressed, with consequent savings in production costs and reduction of corrosion risk.

Furthermore, the solution in accordance with the invention results in energy saving since it is no longer necessary to provide the traditional housing at the bottom of the tank where the heating element is to be accommodated. This leads to a reduction in the quantity of water contained in the washing tank during the operation, with a consequent saving in terms of the quantity of heat to be input. Since the heating element is appropriately attached to the wall of the tank, e.g. with screws or quick fastening devices, there is no need to apply a tightening torque to fix the heating element to the wall, which operation is always potentially critical, especially when the wall to which the heating element is fixed is made of plastic. A hermetic seal of the heating element against the humidity present at the low area of the household appliance is ensured by using MgO with silicone. In virtue of the arrangement of the heating element, an NTC (Negative Temperature Coefficient) temperature sensor may be directly placed on the casing of the heating element to measure the water temperature. Brief description of the Drawings

Further features and advantages of the invention will become more apparent from the following detailed description of preferred though not exclusive embodiments of a heating element for household appliance which is illustrated by way of non- limitating example with the aid of the accompanying drawings, in which: Figure 1 shows a section along a longitudinal plane of a state-of-the-art household appliance;

Figure 2 shows a section along a longitudinal plane of a household appliance in- eluding the heating element according to the invention;

Figure 3 shows an axonometric view of a heating element in accordance with the invention in another household appliance;

Figure 4 shows an enlarged sectional view of detail A in Figure 2;

Figure 5 shows an enlarged sectional view of detail B in Figure 4 in a variant in accordance with the invention.

Detailed description of preferred embodiments of the invention With particular reference to Figure 2, a household appliance is diagrammatically depicted, which could be, for example, a washing or laundry machine or a dishwasher. Without departing from the scope of the invention, it could also be an- other household appliance of a similar type, in which water needs to be heated. The washing machine 1 includes a wash tank 4 and a diagrammatically shown, rotating basket 5. At the bottom of the washing machine 1 the inlet 3 of a discharge pipe is arranged for discharging the water from the wash tank 4, the external wall of which is made, for example but not necessarily, of plastic. At the inlet 3, where the diameter of the discharge pipe is generally larger, a heating element 2 fixed to the vertical wall of the tank 4 is arranged.

With particular reference to Figure 4, the vertical wall of the tank 4 has a hole or opening 6 in which the supporting element 7 for the heating element 2 is inserted, consisting of a metal sheet, for example made of stainless steel or another equivalent metal, appropriately shaped. The base 8 of the supporting element 7 is advantageously, but not necessarily, circularly shaped in its plan view, with a size corresponding to that of the hole 6 in which the supporting element 7 is inserted and fixed by using known fastening means, not shown in the figure. These could be, for example, screws, clamps or other conventional fastening means or quick- release means. The base 8, when viewed in diametral section, is flat in shape, but may also be made in the shape of a spherical cap with a very large radius of curvature. In addition, the curvature may be either concave or convex in shape. The left-hand side of the vertical wall of the tank 4, with reference to the arrange- ment shown in figure 4, contains the wash water 9, while on the right-hand side there is the external access side for assembling or carrying out maintenance or repairing operations on the heating element 2.

The supporting element 7 incorporates a heat sink 20 on its external side, advan- tageously made of aluminium or equivalent heat conducting material, for a better heat distribution. The heat sink 20 is appropriately fixed to the surface of the supporting element 7, for example by means of brazing.

The heating element 2 comprises the electrical resistor 21 fixed in turn on the external side of the heat sink 20. The electrical resistor 21 , shown in Figure 4 by way of mere example, may have various shapes. Its shape and volumes are such that it may be contained inside the heating element 2. In this variant, the electrical element is folded in the shape of a circle, but it may also be coil-shaped or may be made with any other equally compact shape. In order to shield the resistor and other electrical parts of the heating element from humidity, MgO is used together with silicone, which form an electrical insulation while allowing the heat produced by the resistor to pass through.

Depending on needs, the external part of the heating element 2 may have other components needed for the correct operation of the heating element, such as a thermostat and a temperature fuse to allow a controlled shut-off in the event of an overload.

When included, an NTC temperature sensor may be directly positioned onto the casing of the heating element 2, in a position that is very easy to be achieved, with an improvement as compared to the state-of-the-art, which generally arranges it on the resistor itself inside the tank of the household appliance. This arrangement allows to save on production costs for the heating element 2. For a better hydraulic seal on the wall of the tank 4 there is a structural element, for example an annular ridge 23, having a shape corresponding to the periphery of the supporting element 7, for optimising the contact between the heating element 2 and the wall of the tank 4. Advantageously, there is also a separate sealing element, for example an O-ring 24 between the supporting element 7 and the wall 4. Other equivalent sealing elements may be used instead of or in addition to the O- ring 24. To allow a better positioning and an optimal fixing of the heating element 2, an annular flange 8' is provided around its peripheral area. The heating element 2 is connected by known means to the electric power line 22 when it is mounted to the household appliance on which it is used. With particular reference to Figure 3, an alternative embodiment of the heating element 2, incorporated in a steam generator 10 is shown. This is a device that produces steam by channelling it through the outlet 13 once the heating element 2 has brought the water contained therein to the boil. In this alternative embodiment, the heating element 2 is fixed to a vertical side wall 15 of the steam generator 10. In this case, all the lime-scale that forms during the operating cycle is deposited on the bottom 1 1 of the steam generator container or tank, allowing for easier cleaning of the steam generator 10. The external shape of the heating element 2 is advantageously circular, but it may also be differently shaped. The means for fastening the heating element 2 to the wall 15 are also the same as those indicated for the above-described variant of the invention, or other equivalent and ap- propriate fastening means may be also used.

The heating element in accordance with the invention provides a solution with a particularly compact volume that offers certain advantages of use with respect to the state-of-the-art solutions when it is mounted to the household appliances. A particular advantage is that should the heating element 2 be only partially im- mersed in or touched by the water, due to the fact that the steam generator 10 is not completely full of water, then when the water begins to boil in the area close to the heating element 2, air bubbles are formed. The bubbles produce a turbulent movement of the water which causes the level 14 of the water to practically raise in that area, thus allowing to keep the heating element 2 immersed, resulting in a more efficient heat exchange during the operation.

With particular reference to Figure 5, a detail of a variant of the heating element 2 in accordance with the invention is shown, where the same elements described in the previous embodiments are indicated with the same reference numbers. The heating resistor 21 is inserted into an extruded tubular element 25, for example made of aluminium, which also has a pipe 26, obtained in the extruded element itself, for the flow of fluid. The pipe 26 thus runs alongside the electrical resistor 21 for its entire length, or part thereof. This solution allows to create an optimal heat conductivity between the electrical resistor 21 and the pipe 26, and to use part of the heat produced by the electrical resistor 21 to also heat the fluid flowing through the pipe 26.

In an advantageous solution for a steam generator, the pipe 26 of the heating element 2 directly communicates with the outlet 13 (by means of pipes not shown in the figures), and the steam produced in the steam generator 10 is channelled thereto, thereby producing overheated steam.

Claims

1. An electric heating element (2) for heating water in a household appliance, in particular a laundry machine, a dishwasher, or a steam generator, comprising

- a thin, metal supporting element (7) having a base (8) with a first side, referred to as the internal side, intended to be placed in contact with the interior of a tank of the household appliance containing the water to be heated, and a second side, referred to as the external side, on the part of the base (8) opposite the internal side, and intended to be positioned on the external part of said tank, when mounted to the household appliance, - an electrical heating resistor (21 ), fixed on the external side of the supporting element (7),

- sealing means (24) to prevent fluids from flowing between the external side and the internal side,

- a metal heat-dissipation disc (20) interposed between the electrical heating re- sistor (21 ) and the supporting element (7), said heating element (2) being intended to be fixed to a vertical wall of the tank so that the supporting element (7) is vertically arranged along the wall.

2. A heating element (2) according to claim 1 , wherein the base (8) is circularly shaped in its plan view.

3. A heating element (2) according to claim 2, wherein the base (8) has a flat or spherical cap section shape.

4. A heating element (2) according to claim 3, wherein there is an annular flange (8') in the peripheral area.

5. A heating element (2) according to any one of the preceding claims, wherein there is a pipe (26) for the passage of steam running alongside the electrical heating resistor (21 ), adapted to produce overheated steam.

6. A use of a heating element (2) having the characteristics described in any one of the claims 1 to 5 in combination with a household appliance (1 , 10), said heating element being fixed into an opening (6) made in a vertical wall of the tank (4) of the household appliance (1 , 10), intended to contain the water to be heated in use, in an area such that one internal side thereof is in contact with said water in use.

7. A household appliance (1 , 10), in particular a washing machine or a dishwasher or a steam generator, comprising a tank (4) for containing water to be heated, an electric heating element (2) having the characteristics described in any one of the claims 1 to 5 for heating the water, the heating element (2) being placed at the lower area of the tank (4), where the heating element (2) is vertically fixed into an opening (6) obtained in a vertical wall of the tank.

8. A household appliance according to claim 7, wherein the heating element (2) is arranged in a position in the household appliance such that it remains at least partially immersed in water in use.

9. A household appliance according to claim 8, wherein the heating element (2) is arranged in a position above a pipe (3) for discharging the water from the household appliance.