GB2319154A

GB2319154A - Mounting heating element in liquid heating apparatus

Info

Publication number: GB2319154A
Application number: GB9620552A
Authority: GB
Inventors: James Henry Sharples
Original assignee: Pifco Ltd
Current assignee: Pifco Ltd
Priority date: 1996-10-02
Filing date: 1996-10-02
Publication date: 1998-05-13
Also published as: GB9620552D0

Abstract

An element module (1) for a heating apparatus, such as an electric kettle, comprises a planar heating element (5) which is intended to close an opening defined in a wall of a vessel of said apparatus such that after attachment it is integrated into the body of the vessel. The module (1) comprises an annular carrier (8) for the heating element (5) and retains control means (6,7) for the element (5) in a working relationship therewith. Means (22) are also provided for attachment of the module (1) to the apparatus around the periphery of the element (5) whereby the element (5) can be sealed against the periphery of the opening. Preferably, the control means (6, 7) comprise at least one control device (6) which is mounted in a spring loaded working relationship against a surface of the element (5).

Description

IMPROVEMENTS TO HEATING APPARATUS The present invention relates to an element module for use in a heating apparatus, in particular but not exclusively in water heating apparatus such as an electric kettle.

Conventionally, an electric kettle comprises a vessel in a lower portion of which a sheathed coiled wire electrical element is located. The element and accompanying electrical control circuitry are usually mounted on a side or base wall of the vessel. Typically the element passes through an aperture in the side wall and projects into the vessel. Suitable sealing means are used to ensure a water-tight joint between the element and the wall of the vessel to prevent leakage of water in use.

Such sheathed coiled wire elements are now being replaced by more modern planar elements which typically comprise a thick film printed circuit. Various methods have been proposed for the integration of such an element into heating apparatus comprising a vessel for heating liquid. Problems arise because typically such vessels are made of plastics material that would be damaged by use of the element if it were to be placed in direct contact with the vessel itself. For example, domestic kettles now have bodies made of polypropylene or similar plastics materials which would be unable to withstand the element temperatures required during normal operation to boil water without sustaining considerable damage were the element to be placed in direct contact therewith.

However, even after the element has been connected to the apparatus various control devices must be coupled to the element for safety reasons. Typically such devices comprise a temperature sensitive control switch, which is used to disconnect the electrical power supply to the element if its temperature rises above a first temperature threshold indicative of a boil dry or dry boil condition, and a thermal fuse, which is used to disconnect the element from the power supply permanently if its temperature rises above a second higher threshold temperature indicative of a fault in the apparatus.

Typically these control devices are attached to the apparatus in a working relationship to the element after connection of the element to the apparatus itself. The apparatus is then subjected to several quality control checks to ensure that the apparatus is water tight and the element and the various control devices are operating correctly.

It will be appreciated, therefore, that the production of a heating apparatus comprises several separate, successive operations which are typically completed on a production line. However, such a production line is comparatively expensive to operate. It would be advantageous if a pre-assembled and fully tested element module could simply be mounted into a vessel to produce such a heating apparatus.

The object of the present invention is to address the aforementioned disadvantage with a view to overcoming or substantially mitigating same by the provision of such an element module.

According to a first aspect of the present invention there is provided an element module for a heating apparatus comprising a planar element adapted for closing an opening defined in a wall of a vessel of said apparatus, a electrical control means for the element, and a annular carrier for the element and the control means, the carrier comprising means for retaining the control means in a working relationship with the element, and means for attachment of the module to the apparatus around the periphery of the element whereby the element can be sealed against the periphery of said opening.

Preferably, the carrier comprises an annulus with radial webs adapted to provide a housing for the control means.

Preferably also, the carrier is provided with a peripheral lip with an outline similar to that of the element and against which the periphery of the element can bear.

Preferably also, the carrier is provided with clips for the retention of electrical wiring.

Preferably also, the carrier and the element are each provided with a plurality of peripheral lugs which can bear against one another to retain the element in the carrier between the lip and its lugs.

Preferably also, at least one control device is mounted in a spring loaded working relationship against a surface of the element, the spring loading additionally acting to spring load the peripheral lugs of the element into contact with the peripheral lugs of the carrier prior to attachment of the module to a heating apparatus.

Preferably also, the means for attachment of the module to the apparatus project outwardly from the carrier to a greater radial extent than the lip whereby on attachment of the module to the apparatus, the element is moved against the spring-loading so that its peripheral lugs move out of contact with those of the carrier and its periphery moves into close contact with the lip.

Preferably also, a sealing means is provided for sealing the periphery of the element to the opening defined in the wall of the vessel of the apparatus to which the module is to be attached, whereby on attachment of the module to the apparatus the element is held peripherally between the sealing means and the peripheral lip of the carrier.

Preferably also, the means for attachment of the module to the apparatus comprise brackets through which screw means can be located for attachment of the module to a heating apparatus.

Preferably also, the planar element comprises a thick film resistive track applied to the surface of a planar substrate.

According to a second aspect of the present invention there is provided a liquid heating apparatus provided with an element module according to a first aspect of the present invention, a sealing means being provided around the periphery of the opening which the element closes and against which the element is held peripherally by the carrier.

Preferably, the element module is secured to the apparatus by a plurality of screws located around its periphery.

The present invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is an exploded perspective view of an element module according to the first aspect of the invention; Fig. 2 is a side view of the module shown in Fig. 1 when assembled; and Fig. 3 is a schematic cross-sectional view of part of of the module combined with a vessel to form a heating apparatus according to the second aspect of the present invention, and showing schematically the structure of a control device.

A heating apparatus for liquids, such as a domestic kettle, typically comprises a vessel having base and side walls and accommodates an electrical element. It is intended that the element module 1 of the present invention can be mounted so as to close an opening 2 in a wall 3 of such a vessel 4 so that after attachment to the vessel 4 it is integrated into the body of the vessel to make an entire heating apparatus capable of being used for heating liquids.

The module 1 comprises a planar electrical element 5 and control devices, such as devices 6 and 7 as shown in Figs. 1 and 3, which are retained in a working relationship with the element 5 via a carrier 8.

It is envisaged that the element 5 will comprise a thick film resistive track (not shown) applied to one surface 9 of a planar metal substrate 10, typically a stainless steel plate. However, it will be appreciated that the invention is not limited to such elements, the carrier 8 being capable of adaption to accommodate other planar elements. In the present case, however, the resistive track is applied to the surface 9 of the substrate 10 which is to be located outside of the interior of the vessel 4 and which therefore faces the carrier 8. The control devices 6 and 7 are thus retained by the carrier 8 in close proximity to the element 5.

The control devices 6 and 7 can be of any suitable type as appropriate for the particular application of the element module 1. Typically, such a device 6 comprises a temperature sensitive control switch 11, which is used to disconnect the electrical power supply to the element 5 if its temperature rises above a first temperature threshold indicative of a boil dry or dry boil condition. The device 7 may comprise a thermal fuse (not shown), which is used to disconnect the element from the power supply permanently if its temperature rises above a second higher threshold temperature indicative of a fault in the apparatus. However, it is advantageous for the present invention, as will be described, if at least one of the control devices 6, 7 is mounted in a spring loaded working relationship against the surface 9 of the element 5.

As shown in Fig. 3, in the present example, the carrier 8 comprises a housing 12 for the control device 6 which accommodates a spring 13 by means of which the temperature sensitive switch 11 is retained against the surface 9 of the element 5.

The carrier 8 itself generally comprises an annulus 14 which is provided with a plurality of radial webs 15 which are appropriately adapted to provide the housing 12 and a housing 16 for the devices 6 and 7 respectively.

Alternatively, the webs 15 could be adapted simply to provide fixing means such as posts to which conventional control means can be attached by screws, rivets, bolts or the like.

The annular form of the carrier 8 enables an air space to be left below the element 5 to insulate wiring and other components of the heating apparatus, such as a base covering, from the element 5. The annulus 14 and the webs 15 are also both adapted to define U-shaped channels 17 to act as clips for the safe retention of wiring associated with the element 5 and the control devices 6 and 7.

The annulus 14 has an diameter slightly smaller than that of the element 5 but it is provided with a peripherally projecting lip 18 with an outline, typically circular, similar to that of the element and against which the periphery of the element 5 can bear.

In order to retain the element 5, the annulus 14 is provided with a plurality, for example three, equidistantly spaced peripheral lugs 19 which project longitudinally and radially outwards from the lip 18. The element 5 is also provided with three similarly spaced lugs 20. In this way, by manoeuvring the element 5 so that its periphery is located adjacent the lip 18 and turning it so that its lugs 20 bear against the lugs 19 it can be retained by the carrier 8.

It will be appreciated that such retention of the element 5 by the carrier is fairly loose but it provides a sufficient means for supporting the element during testing of the module, transit, and subsequent assembly of a heating apparatus incorporating same. However, the retention of the element 5 is greatly improved if the at least one control device 6 is mounted in a spring loaded working relationship against the surface 9 of the element 5, as mentioned above. Such a spring loading has the effect of spring loading the lugs 20 of the element 5 against the lugs 19 of the carrier 8 so that the element 5 is retained by the carrier 8 by a form of bayonet fixing.

Preferably, the second control device 8 also comprises a means (not shown), such as a fuse pin, which is mounted in a spring loaded working relationship against the surface 9 of the element 5. This improves the retention of the element 5 by the carrier 8.

However, in the assembled heating apparatus, it is not intended that the element 5 will be retained in this way, rather that the element 5 will be retained between the lip 18 and a sealing means 21 provided around the periphery of the opening 2 in the wall 3 of the vessel 4.

To this end and to facilitate generally the securement of the module 1 to the vessel 4, the carrier 8 is provided with a plurality of spaced brackets 22 through which screws 23 can be located for attachment of the module to the vessel 4. The brackets 22 project outwardly from the annulus 14 adjacent to but to one side of the lip 18, and to a greater radial extent. In order to accommodate the screws 23, the vessel 4 is provided with a similar plurality of spaced posts 24 around the exterior periphery of the opening 2. However, the posts 24 are spaced slightly from the edge of the opening 2 to allow for location of the sealing means 21.

Hence, in order to attach the module 1 to the vessel, the sealing means 21 is located around the opening 2, the brackets 22 of the module 1 are aligned with the posts 21 and the module 1 is then simply screwed down tightly to the vessel. This operation causes the periphery of the element 5 to come into direct contact with the sealing means 21 and, as the screws 23 are tightened, the element 5 is moved against the spring-loading of the device 6 so that its peripheral lugs 20 move out of contact with those 19 of the carrier 8 and its periphery is forced into close contact with the lip 18. Hence, in the assembled heating apparatus the element 5 is held peripherally between the sealing means 21 and the peripheral lip 18 of the carrier 8.

As both the carrier 8 and the sealing means 21 are in contact with the element 8, it is important that they are made of a heat-resistant material. It is also important that they are resilient and can accommodate expansion and bowing of the element 8 which is likely to occur during use of the apparatus so as to prevent any liquid leakage from the vessel around the periphery of the element 8.

Preferably, therefore, the carrier 8 is made of a glassloaded nylon and the sealing means 21 comprises a silicone rubber. The sealing means 21 preferably comprises a preformed strip or advantageously an O-ring in the correct dimensions to be located around the opening 2 but it could be formed in situ from a liquid, paste or foam.

Thus, the element 5 becomes an integral part of the body of vessel 1 without actually touching the vessel 4 at any point. This is important if the vessel 4 is made of a plastics material such as polypropylene which is incapable of withstanding normal operating temperatures of the element 5.

As the element module 1 is pre-assembled prior to attachment to a vessel 4, it can be tested and supplied as a complete pre-assembled unit containing all the controls and electrical parts necessary for satisfactory operation of a liquid heating apparatus without the need for many subsequent assembly and testing steps after attachment to the vessel 4.

Claims

1. An element module for a heating apparatus comprising a planar element adapted for closing an opening defined in a wall of a vessel of said apparatus; an electrical control means for the element; and an annular carrier for the element and the control means, the carrier comprising means for retaining the control means in a working relationship with the element, and means for attachment of the module to the apparatus around the periphery of the element whereby the element can be sealed against the periphery of said opening.

2. A module as claimed in Claim 1, wherein the electrical control means comprises at least one control device which is mounted in a spring loaded working relationship against a surface of the element.

3. A module as claimed in Claim 1 or Claim 2, wherein the carrier comprises an annulus with radial webs adapted to provide a housing for the control means.

4. A module as claimed in any one of Claims 1 to 3, wherein the carrier is provided with a peripheral lip with an outline similar to that of the element and against which the periphery of the element can bear.

5. A module as claimed in Claim 4, wherein the carrier and the element are each provided with a plurality of peripheral lugs which can bear against one another to retain the element in the carrier between the liD and its lugs.

6. A module as claimed in Claim 5, wherein the electrical control means comprises at least one control device which ' is mounted in a spring loaded working relationship against a surface of the element, which spring loading additionally acts to spring load the peripheral lugs of the element into contact with the peripheral lugs of the carrier prior to attachment of the module to a heating apparatus.

7. A module as claimed in Claim 6, wherein the means for attachment of the module to the apparatus project outwardly from the carrier to a greater radial extent than the lip whereby on attachment of the module to the apparatus, the element is moved against the spring-loading so that its peripheral lugs move out of contact with those of the carrier and its periphery moves into close contact with the lip.

8. A module as claimed in any one of Claims 1 to 7, wherein the means for attachment of the module to the apparatus comprise brackets through which screw means can be located for attachment of the module to a heating apparatus.

9. A module as claimed in any one of Claims 1 to 8, wherein the carrier is provided with clips for the retention of electrical wiring.

10. A module as claimed in any one of Claims 1 to 9, wherein the planar element comprises a thick film resistive track applied to the surface of a planar substrate.

11. A liquid heating apparatus comprising a vessel defining an opening which is closed by an element module as claimed in any one of Claims 1 to 10.

12. A heating apparatus as claimed in Claim 11, wherein a sealing means is located around the periphery of the opening and against which sealing means the element is held peripherally by the carrier.

13. A heating apparatus as claimed in Claim 11 or Claim 12, wherein the element module is secured to the vessel by a plurality of screws located in a spaced relationship around its periphery.

14. An element module for a heating apparatus substantially as described herein with reference to any one of the accompanying drawings.

15. A liquid heating apparatus comprising and element module substantially as described herein with reference to any one of the accompanying drawings.