GB2264214A - Heating element assembly for liquid heating - Google Patents

Abstract

An electric heating element assembly 10 comprises a heating element 12 supported by a base 14 of a non-electrically conductive material which is adapted to engage with a hole in a container wall 24 via seal 26 such that at least part of the base 14 is in communication with the container's interior. The base 14 has connections 16 adapted for engagement with a cover member and electrical control parts 32 engaging with the electrical connections 16 and optionally being provided with a metallic waterproof sheath 28 covering at least that part of the base 14 which is inside the container. <IMAGE>

Description

HEATING ELEMENT ASSEMBLY This invention relates to a heating element assembly especially for a container of water, for example, a kettle or a washing machine.

Known electric heating element assemblies normally comprise a heating element which is usually sheathed so as to avoid direct contact with the surrounding water, the element being secured to and supported in a coiled or looped configuration by a metal backplate. This metal backplate is provided with a plurality of pins some of which serve to locate the backplate in relation to a plastic control cap and some of which serve as electrical connections for the heating element itself. One further use for the metal backplate is to provide one spot thereof in direct contact with the heating element so as to act as a heat transfer point to a bimetallic strip acting as a thermostat.

One problem with such an arrangement is that the plastics plug to which the element is to be attached is required to be formed in two parts. A base part which is located adjacent to and locates with the metal backplate and an upper plug part which locates over and, in some configurations, encloses the first part and is attached thereto thereby enclosing the control parts located therein. These control parts will be the thermostatic control mechanism, for example, the bimetallic strip and the associated connections and electrical connections for the heating element itself.

It will be understood that the backplate is provided with a watertight seal to the container wall so that water in the container will not escape therefrom. As the backplate is in contact with the water it is also important that the backplate should be water resistant, relatively inert and resistant to temperature. The requirement for the plate to be relatively inert is so as to avoid any poisoning of the water in the container during use. Furthermore as the backplate is used as a thermal transfer medium to a bimetallic strip or other similar temperature measuring device as a cut-out it is important that the plate should be resistant to changes in temperature whilst at the same time permitting good heat transfer between the heating element and the backplate. For this reason the backplate is commonly made out of metal.

Unfortunately a metal backplate requires a large degree of assembly time and also difficult operations such as welding or brazing to ensure adequate seals and contacts are made.

Plastics would be preferable to construct the backplate with suitable provision for electrical and thermal contacts.

However, plastics which are inert i.e. will not dissolve on contact with water and/or temperature resistant are relatively expensive and are thus not commonly used.

It is an object of the present invention to provide an electric heating element assembly utilising a backplate of plastics material to support the heating element and fulfil the functions of the previously mentioned upper plug part whilst at the same time overcoming difficulties inherent in previous known constructions.

With this object in view, in a first aspect the present invention provides an electric heating element assembly comprising a heating element having extending therefrom a plurality of electrical connections, characterised in that the element and the connections are supported by a base of a nonelectrically conductive material which is adapted to engage with a hole in a container wall such that at least part of the base is in communication with the container's interior, the base having connection means adapted for engagement with a cover member and electrical control parts engaging with the electrical connections and optionally being provided with a waterproof sheath covering at least that part of the base which is in communication with the container's interior.

Preferably the base plate is formed of a plastics material moulded so as to provide support for the element's electrical connections and/or the control parts.

In a preferred embodiment a waterproof sheath is provided on the base and preferably takes the form of a relatively thin metal sheet formed around the base member. The sheet is preferably of stainless steel in order to match known stainless steel element designs. The waterproof sheath forms no part of the thermal link to the thermal switch or switches e.g. the bimetallic strip. Such thermal connection may be for example by way of a clamping arm as described in our copending United Kingdom Patent Application No.9125038.1 or may be by way of thermal contact with one end of the heating element's sheath as described in our co-pending United Kingdom Patent Application No. GB-A-2257341, the disclosures of both of which references are incorporated herein by reference.

It will be appreciated that with the aforementioned constructions, particularly in embodiments which include the waterproof sheath, the plastics material need not necessarily be of the previously high quality, i.e. low toxicity and high temperature performance, as it is not in direct contact with the water in the container. Furthermore, when used the metal or other inert sheathing material is not required to be of substantial construction since it does not provide any part of the structural integrity of the element assembly.

This type of construction enables an element to be assembled relatively easily when compared with previous arrangements and in particular leads to an easier assembly of the element into the container. Preferably such assembly can be done by inserting the heating element assembly through a hole into the container. This differs from the heretofore known constructions which require the heating element to be placed in the container with its backplate in contact with the container wall and then matched with control elements or members brought into contact therewith from the outside of the container.

In a particularly preferred embodiment of the invention therefore the base is moulded of a plastics material to conform to a hole provided in the side of a container, the plastics base being assembled or moulded directly around the exposed ends of a heating element and provided with integral electrical connections and a thermal contact point, a surface of the base being provided with suitable engagement points to allow electrical or thermal connection to these items and being provided with means for engaging with a cover member attached thereover and containing within it electric connection control parts which are brought into engagement with the said electrical connections provided in the base.

In such an embodiment it will be understood that the control elements, i.e. the bimetallic strip and electrical connections, are assembled directly onto the base or head of the element assembly prior to its connection to the container.

Such fine construction is easier to accomplish with the element away from its site of use and therefore provides substantial advantages during the construction phase.

The invention will be described further by way of example with reference to the accompanying drawings in which: Fig. 1 is a side-sectional view of a first embodiment of the invention; and Fig. 2 is a side-sectional view of a second embodiment of the invention.

Referring firstly to Fig. 1, a first embodiment of the invention is referred to generally by the reference numeral 10. In this embodiment a heating element 12 is attached to a base member 14 moulded of a plastics material and arranged so that electrical connections 16 to the heating element 12 project therethrough. The base 14 is provided with an upstanding peripheral wall 18 which serves to provide a plugtype engagement between the base 14 and a hole 22 arranged in a container wall 24.

The container (not shown fully), for example an electric kettle, would normally be required to hold therein a quantity of water and accordingly a sealing member 26 is provided around the upstanding wall 18 and in engagement with the container wall 24 so as to provide a watertight seal. In order that the seal is extended to the plastics material of which the base 14 is formed, a thin sheath-forming covering sheet 28 of, for example, stainless steel, is arranged substantially around the base 14 and extending between the base 14 and the sealing element 26.

In this way contact is prevented between the water held in the container and the plastics base thus allowing the base to be constructed of relatively low quality plastics and overcoming any toxicity problems inherent with such contact.

The sheath 28 is provided with a hole 30 to permit the heating element 12 to project therethrough, which hole 30 is sealed around the element, for example by brazing or a similar method.

In alternative embodiments it may be possible to dispense with the sheath 28 altogether, though in this case it is preferred to use a higher quality, physically and chemically inert and non-toxic plastics base material (e.g.

polyphenylsulphide). In such embodiments where the base 14 is not used with a waterproof sheath 28, in order to provide the required degree of sealing for the interior of the container, the element-base connection is preferably provided with a sealing element e.g. a rubber compression seal, examples of which are well known in the art.

The exposed part of the base 14 projecting through the hole 22 in the container wall is adapted to engage with a control assembly indicated generally by the reference numeral 32. In this embodiment it is intended that the control assembly 32 should be of conventional construction, i.e.

normally two-part, and is thus not shown in detail for clarity. Briefly, such an assembly would contain a first substantially rigid base member usually of plastics and adapted to be frictionally or otherwise held against the base 14. The first base member is provided with a plurality of holes or slots allowing the electrical connections 16 from the heating element 12 to project therethrough and to engage with an upper cover part. A bimetallic strip would normally be located between the cover part and the first base member so as to be held in thermal contact with the heating element 12 either by known conventional means or by the two methods described in our co-pending aforementioned United Kingdom patent applications.

It will be appreciated that the construction described allows an electric heating element to be provided which has the required structural integrity whilst overcoming the weight and expense problems normally associated with a metal backplate.

In a further embodiment of the invention as shown in Fig.

2, further advantages of the use of a plastics base will become apparent. In this modified embodiment referred to generally by the reference numeral 40, a heating element 42 of a construction generally similar to that heretofore known is attached at one end to a plastics base 44 pre-moulded for location in a hole in a container wall 46. The container can be, for example, an electric kettle or an electric washing machine.

In order to provide a watertight seal between the plastics base 44 and the container wall, a resilient sealing member 48, for example of rubber, is provided therebetween.

Additionally, in order to provide a waterproof cover between the plastics base 44 and liquid, e.g. water, held in the container, a thin sheath 50, for example, of metal, is preferably provided and is arranged around that part of the base 44 which protrudes through the container wall 46.

That part of the base 44 which is located substantially outside the container wall 46 is arranged to seal thereto around the sealing member 48 and is additionally provided with a plurality of engagement points to provide electrical connections between the heating element and an external supply of electricity. Furthermore the base is also provided with connections for attachment of a bimetallic strip or similar temperature sensitive switch arranged to be in thermal contact with the heating element in the container. A cover plate 52 is adapted to be either a frictional fit over the base or alternatively provided with fixing means such as screws or nuts and bolts for its retention thereto.

It will be understood that in this embodiment the control elements are located directly on the base 44 and are assembled prior to positioning of the cover plate 52. Thus the element can be assembled substantially away from the container wall 46 and prior to insertion of the heating element assembly through the container wall 46. This offers substantial advantages over the heretofore known construction techniques.

The invention is not confined to the foregoing details and variations may be made thereto within the scope of the invention.

Claims (14)

CLAIMS:

1. An electric heating element assembly comprising a heating element having extending therefrom a plurality of electrical connections, characterised in that the element and the connections are supported by a base of a non-electrically conductive material which is adapted to engage with a hole in a container wall such that at least part of the base is in communication with the container's interior, the base having connection means adapted for engagement with a cover member and electrical control parts engaging with the electrical connections.

2 An electric heating element assembly according to claim 1, wherein the base is provided with a waterproof sheath covering at least that part of the base which is in communication with the container's interior.

3. An electric heating element assembly according to claim 1 or claim 2, wherein the base is formed of a plastics material moulded so as to provide support for the element's electrical connections and/or the control parts.

4. An electric heating element assembly according to any one of claims 1 to 3, wherein the waterproof sheath is provided on the base and takes the form of a thin metal sheet configured around the base.

5. An electric heating element assembly according to any preceding claim, wherein the connection means of the base are adapted for engagement with electrical control parts which comprise a temperature sensitive switch in thermal contact with the heating element.

6. An electric heating element assembly according to claim 5, wherein the said thermal contact is by virtue of a clamping arm, one end of which is attached to the heating element and the other end of which contacts the temperature sensitive switch.

7. An electric heating element assembly according to any one of claims 1 to 5, wherein the said thermal contact is by virtue of direct thermal transfer between a sheath of the heating element and the temperature sensitive switch.

8. An electric heating element assembly according to any preceding claim, wherein the electrical control parts are located directly on the base.

9. An electric heating element assembly according to any preceding claim, wherein the base includes an upstanding peripheral wall which allows the base to be plugged into the hole in the container wall.

10. An electric heating element assembly according to claim 9, further comprising a sealing member provided around the upstanding wall and in engagement with the wall of the container so as to provide a water-tight seal.

11. An electric heating element assembly according to claim 1, wherein no waterproof sheath is provided on the base, and wherein the connection between the heating element and the base is provided with a water-tight sealing element.

12. An electric heating element assembly substantially as described herein with reference to Figure 1 or Figure 2 of the accompanying drawings.

13. An electric heating appliance fitted with an electric heating element assembly according to any one of claims 1 to 12.

14. An appliance according to claim 13 which is an electric kettle or an electric washing machine.