GB2285710A

GB2285710A - Liquid heating vessels

Info

Publication number: GB2285710A
Application number: GB9400571A
Authority: GB
Inventors: John Crawshaw Taylor
Original assignee: Strix Ltd
Current assignee: Strix Ltd
Priority date: 1994-01-13
Filing date: 1994-01-13
Publication date: 1995-07-19
Also published as: GB9400571D0

Abstract

An electric water or other liquid heating vessel 30 has a stainless steel body 31 onto the base of which is secured an aluminium base plate 33. A heat link 45 has one end secured to the base plate 33 and a distal end portion disposed generally perpendicularly to the plane of the base plate 33 for providing thermal connection to a bimetallic actuator of a boil dry switch of a control unit. The base plate 33 has a press-formed channel which receives an electric heater element 34. When the vessel is made, the channel is formed before the base plate is mounted to the vessel. The base is then secured in place and then sides of the channel are deformed over the element 34 to secure it (Figs 7 and 8). <IMAGE>

Description

Water Heating Vessels This invention relates to water or other liquid heating vessels of the type having a liquid receiving container made of a corrosion-resistant metal of relatively low thermal conductivity such as stainless steel and an electric water heating element which is secured in good thermal contact to the underside of a base plate formed of comparatively soft metal of higher thermal conductivity such as aluminium. The base plate is itself secured in good thermal contact with the underside of the container, for example by brazing or welding. The element may conveniently be secured to the base plate by press-fitting. Such vessels are popular, particularly in mainland Europe, because the interior of the vessel is corrosion resistant, easy to clean, and the heating element is not visible. They are hereinafter referred to as "vessels of the type described".

For safety reasons it is necessary to provide a means of disconnecting the supply of electrical current from the element in the event of the vessel overheating, as will occur if it is allowed to boil dry or if it is switched on whilst empty. Such means are known as 'switch-on-dry' apparatus and take the form of a thermally operated switch wired in series with the element. Typically the switch has contacts which are coupled to a snap-acting bi-metallic actuator which opens the contacts when overheating occurs.

A known example of a vessel of the type described is constructed by providing a stainless steel container on to which an aluminium base plate is brazed, resulting in a vessel which resembles a conventional stove-top milk pan. Before being attached to the vessel, hard wire is helically wound around the element. The element is then pressed into the aluminium base plate causing the aluminium to flow around the wire as it penetrates the base, thereby providing a thermal and mechanical connection between the element and the container.

Electrical connection is made to the so-called cold leads at each end of the heater element. Such an apparatus is described in EP-A-0031866.

As discussed previously, it is necessary to provide switch-on-dry protection for electrical water heating vessels. In this known type of vessel a discrete thermally actuated switch, is bolted to a portion of the base plate. The switch is a self-contained "off the shelf" component. This is then connected in series with the element using wires. In addition, it is necessary to provide electrical connection to a supply of current, and this may be achieved by a permanent connection or by a detachable plug/socket arrangement which has to be manually wired up during assembly of the apparatus. A cover is then placed over the lower portion of the vessel in order to support the heater element above the surface on which the vessel is placed and to enclose the electrical components.

In such arrangements it is desirable for ease of use that the vessel is not permanently wired to this main supply cable and accordingly more sophisticated vessels include a plug connector provided in a wall of the cover of the vessel for mating with a socket connector attached to the supply cable. It may also be desired to connect a steam-operated switch in series with the element in order to switch off the vessel when the water inside it starts to boil. Such switches are well known in the art and in known vessels of the type described would take the form of another discrete component in communication via a steam channel or aperture with the interior of the vessel.

A drawback with known vessels of the kind described is that, particularly with the more sophisticated arrangements, construction of the vessel can require a large number of steps. In particular, many internal electrical connections are required and these must be wired up manually. As these vessels are mass produced at high volumes, the manufacturing costs which each of these steps represent are significant.

An alternative and well known type of water heating vessel is the electric kettle or jug which employs an electric immersion heater. Such immersion heaters generally comprise a heating element located within the water receiving portion which is carried by a head adapted to be secured in a watertight manner in or adjacent an opening in a generally vertical wall of the jug or kettle. Conventionally, the heating element of the immersion heater terminates in so-called cold leads by means of which electrical connections are made to the heater. Within the vessel, the element is bent into a tortuous shape in order to obtain a sufficient length and therefore an appropriate level of heat dissipation within the available space. In addition, about half way along its length the element is connected in good thermal contact with the head.This is the so-called 'hot return' part of the immersion heater and its function is to allow a thermally operated control to be connected to the other "dry" side of the head in order to provide switch-on-dry protection. Thus, in the event of the kettle or jug boiling dry, heat from the element is conducted to the head via the hot return, which in turn causes a thermally operated switch arranged in series with the element to disconnect the electrical supply.

Most jugs and kettles are provided with an integrated control unit which is adapted to be clamped in relation to the heater head.

Such integrated control units (hereinafter referred to as "control units of the kind described") comprise, an insulating body (typically of moulded thermoplastic) having on one side terminal pins for connection to a source of electric current, and further including terminals arranged to be connected with the cold leads of a heater. The terminal pi n,S may receive a mating socket connector or may co-operate with a base unit in order to provide a device of the so-called "cordless" type. The control unit further comprises a switch-ondry mechanism comprising a switch connected in series between one of the terminal pins and one of the cold lead terminals. The switch is operated by a thermally sensitive bimetallic actuator which is mounted to the body on the opposite side to the terminal pins and which, in use, is in thermal contact with the heater.

Different types of these control units are known and various further refinements may optionally be incorporated into them. For example, the units may be arranged to form automatic direct connection with the cold tails of the heater as the unit and the head are brought into engagement. This is often achieved by providing the units with sprung contacts to ensure reliable engagement. As an additional safety precaution a back-up system may be added to the switch-on-dry protection. A known back-up system takes the form of a switch which is biased open by a spring. The switch is held closed by a push-rod of plastics material which abuts against the heater head. The material of which the push-rod is formed is chosen so that it will deform or melt in the event of the element overheating, thereby allowing the switch to open. This permanently disables the control.

In addition, it is possible to provide a steam operated control. This may be a separate unit wired to terminals in the unit, but preferably it forms an integral part of the unit. An example of a control unit of the type described incorporating these preferred refinements is disclosed in GB-A-2204450 and is commercially available as the Strix R32.

It will be seen that control units of the type described can provide, in a single component, all of the electrical and thermal interconnections required in an electric kettle or jug between the power socket and the heater head and may incorporate refinements such as a steam control. Their use, therefore, greatly simplifies the manufacture of these articles by reducing the number of assembly steps to a minimum and this, in turn, leads to significant cost savings. Unfortunately, control units of the kind described are not compatible with the known vessels of the type described and previously therefore the manufacture of such vessels has been much more complex and therefore expensive than that of electric kettles or jugs.

According to the first aspect of the invention there is provided a vessel of the type described, comprising a heat link having one end secured in good thermal contact with the base plate and the distal end extending radially to or beyond the periphery of the base plate, the distal end having a portion disposed generally perpendicularly to the plane of the base plate for providing in use thermal connection to the thermally responsive actuator of a switch of a control unit of the kind described.

Thus there is provided a water heating vessel of the type described which may incorporate a control unit of the kind described. This is a completely new departure from the prior art. The heat link serves the function of the hot return in an immersion heater system and so allows the switch-on-dry protection located within the control unit to operate in the conventional manner. The use of an integrated control unit, similar to those units used in conjunction with immersion heaters, reduces the number of assembly steps the vessel manufacturer has to carry out and minimises the number of separate parts. Cost is therefore reduced.

The heat link may take various forms. It is possible for it to be formed as an integral part of the base plate, but as this may complicate the production of the base plate it is preferably formed as a separate component of a heat conducting material. It is most convenient to use a high thermal conductivity metal since as well as conducting heat well, metals combine strength with a degree of resilience which assists in providing a simple thermal connection with a control unit. Aluminium may be used, but copper is preferred.

The heat link is most conveniently provided in the form of an elongate strip, and the perpendicular surface at its distal end may simply be provided by bending the strip to the desired profile in order to locate the surface in the desired position.

Connection to the base plate may be by means of welding, brazing or bolting, but riveting is preferred since this lends itself to automated production methods, especially, as is particularly preferred, if the rivets are press formed as an integral part of the base plate.

Thus, the heat link may be provided with holes which are simply located over the rivets and the rivets are then pressed down.

The heat link may be connected to the base plate in any suitable position, but in order to keep its length to a minimum, it is preferably mounted towards the periphery of the base plate. It may be provided in direct thermal contact with the element, but this arrangement is not preferred since in heaters of the type described the underside of the element remote from the base plate is very hot in normal use and consequently direct contact with the heat link would lead to high temperatures being applied to the control unit during normal operation. It would therefore be necessary to calibrate the switch-on-dry protector switch to operate at an undesirably high temperature in order to avoid the possibility of nuisance tripping.

This can cause damage to the control unit or unwanted operation of its one-shot back-up protection means, if provided. Further, thermal expansion of the element which would take place at the very high temperatures reached during or immediately after a switch-on-dry situation (i.e. during "over shoot" heating) could cause a press-fitted element to become dislodged. It is therefore preferred that the heat link be connected to the base plate without being in direct contact with the element. This allows for a lower normal operating temperature for the heat link and a lower nominal operating temperature for the switch-on-dry protector switch.

In order further to simplify construction, the element may be arranged on the base of the vessel with the cold tails extending substantially parallel to each other and generally radially from the base plate. This allows them to make direct contact with contact terminals of a control unit of the kind described during assembly of control to heater in a similar manner to the cold tails of an immersion heater. To simplify construction even further, the element may comprise a mounting plate, arranged generally perpendicularly to the plane of the base plate, to which the control unit may be attached.Preferably the mounting plate provides connections similar to those of an immersion heater head so that by attaching the control unit to the mounting plate, electrical connection is made to the cold tails and thermal connection is made between the base plate, via the thermal link to the thermally sensitive actuator of the switch-on-dry mechanism. This thermal connection may be achieved by connecting the heat link to the mounting plate. However, since, unlike the head of an immersion heater, the mounting plate does not form a water barrier, it is possible to provide an aperture in it through which the heat link may pass, thereby allowing a direct thermal connection between the heat link and the thermally sensitive actuator of the control unit.

The invention, in a second aspect, also provides a vessel according to the first aspect of the invention further comprising a control unit of the kind described electrically connected to the cold leads of the heating element and having its bimetallic actuator arranged in thermal contact with the perpendicularly disposed portion of the distal end of the heat link.

Whilst the cold leads of the element may be wired to the control unit, they are preferably arranged for direct connection with the terminals of the control unit as described previously. This further reduces the number of production steps. The vessel may further comprise any of the preferred features discussed in relation to the first aspect of the invention. The vessel may also be provided with a cover over its lower portion, as in the prior art vessels.

Using the most basic controls of the kind described results in a vessel having a connection socket for a mains lead and switch-on-dry protection. However, by using more complex control units of the kind described it is possible to provide further advantageous features.

Thus, preferably the control unit comprises a steam operated switch arranged to disconnect the supply of electrical current to the element when water in the vessel reaches boiling point. This mechanism may be provided remotely from the body of the control unit, but this requires the use of additional connection wires.

Therefore, preferably this mechanism is provided as an integral part of the control unit. It is necessary to provide a steam path between the interior of the container and this mechanism. Therefore, depending upon the shape of the vessel and the location of the control unit, the vessel may further comprise a steam channel from the interior of the container to this mechanism.

As a further safety means, the control unit may also comprise a back-up overheat protection system of a known type, for example of the type discussed in relation to known electric kettles and jugs.

The element may be attached to the base plate of the vessel in the manner described in EP-A-0031866.

Thus, the vessel may comprise an electric element having wire helically wound around it and pressed into the base.

However, this mode of attachment has various disadvantages. Well over half of the surface area of the element is not in contact with the base plate and therefore the flow of heat from it to the base plate is poor. Because of this the power applied to the element is limited to around 1800W to avoid overheating the element. This is a considerably lower figure than the typical 2400W which may be applied to an immersion heater. This low power input in combination with the poor heat transfer leads to the water in the vessel being heated slowly. Furthermore, winding wire around the element before pressing is inconvenient and slow.

It may also be difficult to form the element in such a shape that both cold leads project in a manner suitable for direct connection to a control unit of the type described.

It is therefore preferred for the base plate to be adapted so that the metal of which it is made (e.g.

aluminium) may be formed at least partly around the element. This leads to a greater surface area of the element being in contact with the base plate and removes the need to wind wire around the element since the shape of the base plate may hold the element in position.

Preferably the base plate has a channel provided therein to receive the element. The channel may be cast or machined but these options can lead to relatively weak and expensive base plates respectively. It is therefore preferred to press form the base plate to produce the channel, and it is particularly preferred to use aluminium for the base plate since it is comparatively easy to press.

The base plate is most conveniently cold pressed using a pressure of e.g. about 400 tons. By cold pressing it is meant that the metal is grossed without having been significantly softened by pre-heating. Cold pressing is preferred because it is simpler and less expensive than hot pressing (ie. pressing a hot, and therefore softened, piece of metal). The base plate may be pressed after being attached to the water containing part of the vessel, but this is undesirable since it may cause damage to the container. It is therefore preferred to press form the base plate before attaching it (preferably by welding or brazing) to the container.

The channel may be arranged to provide an interference fit around the element and in this case the element may simply be pressed into place and an optional further securing means such as a clamping plate may be provided. However, in order to maximise the surface area of the element which is in contact with the base plate and to more securely retain the element it is preferred that there is a further production step in which portions of the base plate adjacent the channel are pressed around or rolled over the element. The pressure required in this stage may be around 150 tons.

Thus in these most preferred embodiments the vessel has an element which is very securely attached to the base plate and which provides a better flow of heat than in the described prior art. This in itself allows water to be heated more quickly, and furthermore it allows a higher power to be safely supplied to the element, thereby allowing faster water heating.

This method of construction is itself a new departure and therefore, viewed from a third aspect, the invention provides a method of attaching an electric heating element to a base plate of a heated appliance, comprising the steps of: press-forming a channel of similar width to the diameter of the element in one face of the base plate by cold pressing; inserting the element into the channel in the base plate; and subsequently deforming portions of the base plate adjacent the channel around the element in order to secure the element in the channel.

This method of construction may be applied to provide an improved water heating vessel, and therefore, viewed from a fourth aspect the invention provides an electric water heating vessel comprising a cold pressed metal base plate secured to a water receiving container, the base plate having a channel cold pressed therein in which is received an electric heater element.

Preferably, the base plate is secured to the water receiving container by brazing. This is preferably done after the base has been pressed into shape to avoid the pressing process damaging container. Following this, the element may be inserted into the channel, which may then be deformed around the element to secure it in place.

Certain embodiments of the invention will now be described, by way of example only, and with reference to the accompanying drawings, wherein: Figure 1 is a side elevation of a water heating vessel according to a first embodiment of the invention; Figure 2 is an underneath plan view of the heating vessel illustrated in Figure 1; Figure 3 is a side elevation of a water heating vessel according to a second embodiment of the invention; Figure 4 is an underneath plan view of the vessel illustrated in Figure 3; Figure 5 is a heating element for use in the vessel illustrated in Figure 3; Figure 6 is a base plate for use in the vessel illustrated in Figure 3; Figure 7 is a partial cross section through the base plate of Figure 6, along the line VII-VII; Figure 8 is a similar view to Figure 7 showing the base plate pressed around an element.

Turning first to Figure 1 there is illustrated a water heating vessel 1 according to the first embodiment of the invention having a stainless steel container 2, which holds water which is to be boiled, on to which is brazed a base plate 3. The base plate is formed of aluminium and serves to distribute heat produced by element 4 evenly across the bottom of the container.

During construction the element 4 has hard wire helically wrapped around it and the wire wrapped element is then pressed into the aluminium base plate 3 with sufficient force to cause the aluminium partially to flow around the element and wire, thereby providing a mechanical and thermal connection between the element and the base plate. (The wire is not shown in the diagram for purposes of clarity). At each end of the heating element there are provided cold leads 6 and 7 which provide electrical connection to the element in a manner well known in the art.

Also connected to the base plate 3 is the heat link 8. This is in the form of an elongate copper strip which projects radially from the base plate and is bent upwards generally to follow the side wall of the container 2.

Attached to the lower portion of the side wall of container 2 adjacent the heat link is a mounting plate 9. The mounting plate has projecting from it three studs 10 (only two shown) which are used to connect a control unit 11 to the vessel. Also provided on the mounting plate are a pair of electrical terminals 12 and 13 which are connected via wires 14 and 15 to the cold leads 6 and 7 respectively of the element 4. These terminals project from the mounting plate in a manner which mimics the way in which the cold leads project from the dry side of the head of an immersion heater.

The control unit 11 is shown in phantom. It is clamped to the mounting plate 9 by three screws which pass through holes in the control unit and are received in threaded bores in the studs 10 of the mounting plate 9. The control unit 11 is of a type which is well known in the context of electric water heating jugs or kettles.

Between the mounting plates 9 and the control unit 11 there is sandwiched a portion of the heat link 8.

The purpose of this heat link is to provide a thermal contact between the base plate 3 and the parts of the control unit 11 which, when used in conjunction with an immersion heater, will be arranged to be in thermal contact with the immersion heater head. It will be noted that there is a dimple portion 16 in the heat link 8 which provides the heat link with a convex surface at that point. The purpose of this to mimic the dry side of an immersion heater head opposite where the heat return is connected. The dimple engages a bimetallic actuator which forms part of the thermally actuated switch-on-dry protection apparatus within the control unit 11. It will be seen that the mounting plate 9 and associated components serve to mimic the mechanical, thermal and electrical contacts found on the head of a conventional heater head.Therefore a suitable connection to known immersion heater control units is provided.

As the control unit 11 is of a known design it will not be described in detail here, but for completeness its basic features will be identified. The illustrated control unit is described in detail in GB-A-2204450 and available from Strix Limited in the R32 Control. It has three connector pins 17, 18 and 19 to which a socket connector and mains lead may be connected. Pin 19 is for connection to earth and the control unit 11 provides a direct connection between this and mounting plate 9 via the connecting lugs. This serves to earth the vessel 1. Pins 17 and 18 provide for connection to the line and neutral supplies. These are connected via switch means within the control unit to terminals 12 and 13 on the mounting plate.

The control unit provides three types of control.

One of these is the thermally actuated switch-on-dry protection which comprises a pair of contacts which are opened and closed by the action of a snap-acting bimetallic actuator 20 mounted on the exterior of the control unit in contact with the dimple portion 16 of the heat link 8. The control unit 11 is also fitted with a back-up protection system which comprises a plastics rod 21 projecting from the control unit and abutting an upper portion of the heat link 8. The heat link presses the rod 21 into the control unit against a biasing spring and this serves to close a pair of switch contacts within the control unit 11. In the event of serious overheating (i.e. in the event of failure of the switch-on-dry protection means), the rod 21 will melt, thereby allowing the switch contacts to open and thereby disconnecting the supply of current from the element 4.

Finally, the control unit 11 is provided with a steam operated control 22 arranged to switch off the water heating vessel when the water in it has boiled. It incorporates a further bimetallic actuator coupled to a switch within the control via an over centre lever mechanism. In order for this to operate it is necessary to provide a steam channel between the interior of the container 2 and the actuator of the steam operated control 22. Such a channel could be provided within a moulded plastics handle and base unit (not shown).

Figure 2 shows the vessel 1 from beneath and shows the form of the element 4 and the connections between it and the mounting plate 9.

In use, the vessel is operated in the same manner as a conventional water heating jug or kettle. Thus, after being filled with water and connected to the supply of current the steam operated control is reset by a lever provided on the handle and base unit (not shown). This allows electric current to flow to the element 4 which heats the water via the base plate and the bottom of the container 2. In normal operation, as the water heats up, steam will pass via a steam channel to the actuator of the steam operated control 22, and when the water boils the steam operated control 22 will disconnect the supply of current from the element 4.

However, should the vessel 1 be switched on without water being present within the container 2 then the steam operated control will not operate. As the element starts to warm up, heat will be transferred via the base plate 3 and heat link 8 to the snap-acting bimetallic actuator 20 in the control unit. When this reaches a preset temperature, typically about 135"C this will act to disconnect the element. Should this switch-on-dry mechanism fail, the temperature will continue to rise to a point where the heat link 8 becomes sufficiently hot to cause the rod 21 to deform or melt. The rod will therefore cease holding the biasing spring against which its acts in compression, and this will cause a set of contacts to open and thereby disconnect the element permanently.

The second embodiment of the invention is illustrated in Figures 3 to 8. The views of this embodiment in Figures 3 and 4 correspond to those of the first embodiment in Figures 1 and 2 respectively. The second embodiment is a water heating vessel 30 formed from a stainless steel container 31 which is identical to container 2 and has a base plate 33 brazed to its bottom surface. However, the method of attaching the heating element 34 to the base plate 33 is significantly different.

Figure 6 illustrates the base plate 33 in a condition in which it is ready to be attached to the container 31. This occurs before the element 34 is connected to the base plate 33. The base plate is formed from an aluminium disc which is about 5 mm thick, somewhat thicker than the base plate of the first embodiment. It has formed in it an element receiving channel 35 which extends from a point cn the circumference of the disc, via a re-entrant path to a second point on the circumference adjacent the first.

This channel is of substantially the same width as the diameter of the element which is to be used. The sides of the channel are provided by a combination of thinning the plate material at the base of the channel and raising upstanding portions 36 at its edges. The base plate 33 is formed by cold pressing a flat 5mm disc of aluminium. A die is used which has recesses corresponding to the sides of the channel with projections on either side of the recesses. These force the aluminium from the channel and from a region outside the channel walls to form the upstanding portions 36.

It will be appreciated that most of the pressing force is concentrated in the region of the channel. As a consequence of providing the upstands 36, recesses 37 surround the outer walls of the channel 35. The pressing operation also provides three rivets 38 which project from the base plate near where the channels meet the circumference.

Once the base plate 33 has been provided in the form illustrated in Figure 6, it is ready to be brazed on to the bottom of container 31. This is then ready to have the electrical components added.

In order to prepare the heater element 34 for insertion into the base plate it is necessary to bend it into a shape as illustrated in Figure 5 which matches the shape of the element receiving channel 35. It will be noted that the end portions of the element are arranged to project beyond the outside diameter of the container 31.

The next stage in the preparation of the element is to secure to it the mounting plate 40. This is a circular disc which lies in a plane at right angles to the plane of the element 34. It is provided with two holes in which the ends of the element 34 are located and brazed into place, leaving their cold leads 41 and 42 projecting beyond the mounting plate. The mounting plate is also provided with three projecting studs 43.

The purpose of the mounting plate, as in the previous embodiment, is to mimic the action of the head of an immersion heater. Thus, the studs are arranged to provide mechanical connection to a control unit 50 and the cold leads provide electrical connection thereto.

The mounting plate also has a dimpled portion 44 in order to make thermal contact with the bimetallic actuator of the switch-on-dry mechanism within a control unit. On the other side of the dimpled portion of mounting plate 40 there is attached by riveting or brazing a copper strip which forms the heat link 45.

This is bent so that at the opposite end there is provided a portion 46 which lies in the plane of the element, the purpose of which is for connection to the base plate 33. To this end, three holes 47 are provided in this portion for cooperation with rivets 38.

This assembly of element, heat link and mounting plate is then attached to the base plate on the vessel 30. Figure 7 shows a cross section of a part of the element receiving channel 35 ready to receive the element. The element 34 is located within the channel 35 and portion 46 of the heat link 45 is located over the rivets 38. Pressure is then applied to the base plate to form the upstands 36 around the element.

Figure 8 shows a corresponding view to Figure 7 after this has been done. It will be seen from this Figure that the aluminium base plate is in physical contact with a large proportion of the surface area of the heater element 34 and therefore provides a good thermal connection between these two components. The pressing action also serves to rivet the heat link firmly in place.

It will be appreciated that any conventional control unit 50 (illustrated in phantom) may be connected to the mounting plate in the same manner as if the vessel had an immersion heater. As in the previous embodiment, the control is clamped to the mounting plate 40 by screws which are received in studs 43 and direct electrical connection is automatically made by terminals within the control unit to the cold leads 41 and 42. A snap-acting bimetal on the outside of the unit makes thermal contact with the dimple portion 44 of the mounting plate 40 in order to provide thermal contact via the heat link 45 to the base plate 33, therefore allowing the switch-on-dry protection to operate. The vessel is completed by the addition of a moulded cover over the lower portion and control unit which may also provide a handle having an operating lever disposed therein.

The details of the operation of the control unit and the manner in which the vessel is used are the same as for the first embodiment and therefore will not be described further.

Claims

Claims

A A vessel of the type described, comprising a heat link having one end secured in good thermal contact with the base plate and the distal end extending radially to or beyond the periphery of the base plate, the distal end having a portion disposed generally perpendicularly to the plane of the base plate for providing in use thermal connection to the thermally responsive actuator of a switch of a control unit of the kind described.
2. A vessel as claimed in claim 1, wherein the heat link is formed as a separate component of heat conducting material.
3. A vessel as claimed in claim 1 or 2, wherein the heat link is in the form of an elongate strip having a bent portion to form the perpendicular surface at its distal end.
4. A vessel as claimed in any of claims 1, 2 or 3, wherein the heat link is riveted to the base plate.
5. A vessel as claimed in any preceding claim, wherein the heat link is mounted towards the periphery of the base plate.
6. A vessel as claimed in any preceding claim, wherein the heat link is connected to the base plate without being in direct contact with the element.
7. A vessel as claimed in any preceding claim, wherein cold tails extend from the element substantially parallel to each other and generally radially from the base plate.
8. A vessel as claimed in any preceding claim, wherein the element comprises a mounting plate, arranged generally perpendicularly to the plane of the base plate, to which the control unit may be attached.
9. A vessel as claimed in claim 8, wherein the mounting plate has an aperture through which the heat link passes.
10. A vessel as claimed in any preceding claim further comprising a control unit of the kind described electrically connected to the cold leads of the heating element and having its bimetallic actuator arranged in thermal contact with the perpendicularly disposed portion of the distal end of the heat link.
11. A vessel as claimed in claim 10, wherein the cold leads of the element are arranged for direct connection to the terminals of the control unit.
12. A vessel as claimed in claim 10 or 11, wherein the control unit comprises a steam operated switch and there is provided a steam channel from the interior of the container to the steam operated switch.
13. A vessel as claimed in any preceding claim, wherein the metal of which the base plate is made is formed at least partly around the element.
14. A vessel as claimed in claim 13, wherein the base plate has a channel provided therein to receive the element.
15. A vessel as claimed in claim 13 or 14 wherein the base is formed by cold pressing.
16. A vessel as claimed in claim 15 wherein the portions of the base plate adjacent the channel are rolled over the element.
17. A method of attaching an electric heating element to a base plate of a heated appliance, comprising the steps of: press-forming a channel of similar width to the diameter of the element in one face of the base plate by cold pressing; inserting the element into the channel in the base plate; and subsequently deforming portions of the base plate adjacent the channel around the element in order to secure the element in the channel.
18. An electric water heating vessel comprising a cold pressed metal base plate secured to a water receiving container, the base plate having a channel cold pressed therein in which is received an electric heater element.
19. A vessel substantially as hereinbefore described with reference to Figures 1 and 2 or 3 to 8 of the accompanying drawings.