GB2153190A - Improvements in or relating to heaters for water vessels - Google Patents

Abstract

A heater (7) consists of a metallic substrate coated with an electrically insulative ceramic material, onto which a heater track is screen printed, which is then coated with another ceramic coating. The heater (7) is cemented through an aluminium connecting component (8) into a rear wall (9) of a water jug (6) formed from a plastics material. Electrical connection tabs (12) are attached through holes (13) to portion (2) of the heater (7), and heater (7) and component (8) are flame-sprayed with pure aluminium to form an earth screen. The heater (7) may then be energised by insertion of a plug to an electrical lead through aperture (13) of the jug (6), thereby providing power to the heater track of the heater (7) via connection tabs (12). <IMAGE>

Description

SPECIFICATION Improvements in or relating to heaters for water vessels This Invention relates to a heater for a water vessel and in particular, though not exclu sively, to such a heater for utilisation in do mestic applications, such as water jugs.

Heaters which are employed in domestic applications such as jugs, kettles, etc., generaily consist of wire-wound elements which are generally relatively cheap to manufacture and therefore suitable for use in such applications.

An alternative type of heater may comprise a heater track deposited on a substantially flat substrate. However, this type of heater is usually constructed from a relatively expensive metal, such as gold, by rather complex de position techniques, thereby preventing the incorporation of such heaters in domestic applications from being commercially acceptabie.

It is therefore an object of the present invention to provide a heater for a water vessel, in conjunction with a method of constructing the same, which is relatively simple and inexpensive to manufacture, the cost thereof being at least comparable with that of a conventional wire-wound heater element.

It is another object of the invention to provide a water vessel incorporating a heater, in accordance with one aspect of the present invention, and a method of assembling the same.

According to a first aspect of the present invention there is provided a method of construction of a heater for a water vessel comprising the steps of coating a metallic substrate with an electrically insulative ceramic material, firing said coated substrate at a first temperature, screen printing a metallic heater track onto said coated substrate, firing said screen printed substrate at a second temperature, coating said screen printed substrate with said electrically insulative ceramic material, and firing said coated screen printed substrate at a third temperature.

According to a second aspect of the invention there is provided a heater for a water vessel constructed by the method set forth in the immediately preceding paragraph.

According to a third aspect of the invention there is provided a method of assembly of a heater, as set forth in the immediately preceding paragraph, in a water vessel comprising the steps of mounting said heater, via a connecting component, to a wall of said vessel, bonding electrical connections to said heater, and spraying at least said heater with a metallic substance so as to form an earth screen.

According to a fourth aspect of the invention there is provided a water vessel having a heater assembled therewithin, in accordance with the method as set forth in the immediately preceding paragraph.

The metallic substrate is preferably steel and the electrically insulative ceramic material is preferably either a vitreous enamel, such as white 106 vitreous enamel, or a glass ceramic. The heater track is preferably formed from palladium silver.

It can therefore be envisaged that the materials preferably employed in the construction of the heater, in accordance with one aspect of the invention, enable the heater to be manufactured at a substantially lower cost than known heaters of this kind, without reducing the performance thereof, thereby permitting such heaters to be utilised in domestic water vessels, such as jugs and kettles.

The water vessel, in accordance with another aspect of the invention, is preferably formed in the shape of a jug and constructed from a plastics material. In the method of assembly of the heater in the water vessel, a dental ceramic adhesive known as "Visio Dispers", which is a member of a group of resins called "Bisgma", manufactured by a German Company, is preferably employed to mount the heater into a connecting component, which is preferably aluminium and which is bonded to an inner wall of the vessel. The surface of the coated heater is preferably aquablasted to give the surface a matt finish and the heater and connecting component are then flame-sprayed with pure aluminium to provide an earth screen.

The water vessel preferably also contains two temperature sensors, one being positioned adjacent the top of the vessel to sense steam from boiling water therein and one being positioned close to the heater to detect a "boil dry" condition so as to cause the heater to be de-energised if there is no water in the vessel. The latter of these two temperature sensors may be printed adjacent the heater track on the substrate.

The invention will now be further described by way of example only with reference to the accompanying drawings, wherein: Figure 1 shows a plan view of a heater, in accordance with one aspect of the present invention, at an initial stage of construction, Figure 2 shows a plan view of a heater at a later stage of construction, Figure 3 shows a sectional view of a water vessel having a heater assembled therewithin, and Figure 4 shows another embodiment of a heater, in accordance with one aspect of the invention.

In a method of construction of a heater, in accordance with one aspect of the present invention, Figure 1 shows a substrate of steel, which has been machined or punched out from a steel sheet to provide a circular portion 1 and a protruding portion 2, through which a number of holes, shown generally at 3, are machined or punched.

The substrate is then coated, for example by dipping, with an electrically-insulative ceramic material, which is preferably either a vitreous enamel, such as white 106 vitreous enamel, or a glass ceramic, to provide a coating thereof on the substrate. The coated substrate is then fired at a temperature of approximately 820"C.

A heater track, which is shown at 4 in Figure 2, preferably fabricated from palladium silver or any other suitable cermet thick film ink, is then screen printed onto the fired substrate in any desirable configuration and the screen printed substrate is then fired at a lower temperature of approximately 700 750"C. A temperature sensor 5, the function of which will be described hereinafter, may also be screen printed at any suitable location adjacent to the heater track 4 on the substrate.

The screen printed, fired substrate is subsequently coated with the ceramic material to provide a second coating thereof and then fired once more at a still lower temperature of approximately 650-700"C.

As an alternative to dipping the substrate into the ceramic material, the substrate may be coated by screen-printing, spraying, electrophoresis, or high voltage electrostatic spraying.

To increase substantially the power density of the heater, a heater track may be screen printed onto both surfaces of the substrate.

It can therefore be seen that one aspect of the present invention provides a substrate heater utilising less expensive materials and easier construction than those used in the manufacture of known substrate heaters, thereby permitting the heater to be employed in domestic applications, such as jugs or kettles.

Referring now to Figure 3, there is shown a water jug 6, which is preferably fabricated from a suitable plastics material, within which a heater 7, in accordance with the present invention, is assembled.

The heater 7 is cemented through an aluminium connecting component 8, which is bonded into a rear wall 9 of the jug 6, so that circular portion 1 of the substrate, upon which the heater track 4 is screen printed, extends into interior region 10 of the jug 6 and protruding portion 2 of the substrate extends into an exterior back region 11 of the jug 6.

Prior to assembly of the heater 7 in the water jug 6, the surface of the heater 7, which is coated with the ceramic material, is aquablasted to give it a matt finish, so that an earth screen, in the form of pure aluminium which is flame-sprayed thereonto, can adhere to the surface. Preferably, both the -heater 7 and the component 8 are flame-sprayed with the pure aluminium.

The heater 7 is cemented into the component 8 by a dental ceramic adhesive, which is preferred for health safety reasons. One such adhesive is called "Visio Dispers", which is a member of a group of resins known as "Bisgma" resins. Electrical connection tabs.

one being shown at 12, are then attached, either by bonding or mechanical attachment for example, through holes 3, to portion 2 of the heater disposed within the region 11. The heater 7 is subsequently tested for insulation to British Standard specifications.

The heater 7 may then be energised by insertion, through aperture 1 3 in the rear of the jug 6, of a plug (not shown) connected to a lead, thereby providing power to the heater track 4 of the heater 7, via connection tabs 12.

In addition to the heater 7, the jug 6 also preferably contains two temperature sensors, one shown at 1 4 located adjacent the top of the jug 6 and one shown at 1 5 located as close as is permissible to the heater 7. Temperature sensor 1 5 may, in fact, be constituted by the temperature sensor 5, which is screen printed on the substrate adjacent to the heater track 4, as shown in Figure 2.

The sensors 1 4 and 1 5 are preferably negative temperature co-efficient thermistors or silicon sensors. Sensor 1 4 is positioned so as to sense steam produced by boiling water within the jug 6 and sensor 1 5 is positioned so as to sense a "boil dry" condition when the heater 7 is energised whilst there is no water in the jug, both sensors being respectively arranged to operate a relay (not shown) to de-energise the heater 7.

The substrate illustrated in Figure 4 shows a heater track 1 7 and a looped track 18, part 1 9 of the looped track 1 8 being a temperature sensor track and part 20 being a conductor track, which is preferably fabricated from substantially the same material as the heater track. The sensor track 1 9 is preferably made from a high negative or positive temperature coefficient thermistor type cermet ink, such as ESL nickel 2554 or ESL NCT 2414.

As an alternative to a relay, a triac may be employed, however this type of device may not be capable of dissipating a sufficient amount of heat to permit efficient operation of the heater.

The jug 6 preferably also includes a useroperable on/off button 16, so that the heater 7 may be de-energised before the water within the jug 6 reaches boiling point, if required.

The jug 6 may further include a re-set button (not shown), to re-commence operation of the heater 7, and/or an indicator (also not shown), such as a neon light, to indicate that there is no water in the jug, either on detection of a "boil dry" condition by the sensor 1 5 or on initial energisation of the heater 7.

It may be advantageous to provide the substrate with a number of apertures to aid in reducing the amount of hard water salts, such as calcium, which could form on the surface thereof and possibly also to improve convection current circulation within the vessel.

It can therefore be seen that another aspect of the present invention provides a water vessel, preferably in the form of a jug, incorporating a substrate heater, the cost of which is at least comparable with that of such a vessel incorporating a conventional wirewound heater element, whilst having the advantages of the heater being relatively compact and easy to clean.

The present invention is not limited to the described method of assembly of the heater within the jug and alternative methods may be envisaged by those skilled in the art.

The heater, in accordance with the present invention, may of course be utilised in alternative domestic applications, such as room heaters, cookpots, clothes press, etc.

Claims (20)

1. A method of construction of a heater for a water vessel comprising the steps of coating a metallic substrate with an electrically insulative ceramic material, firing said coated substrate at a first temperature, screen printing a metallic heater track onto said fired, coated substrate, firing said screen printed substrate at a second temperature, coating said fired, screen printed substrate with said electrically insulative ceramic material, and firing said coated screen printed substrate at a third temperature.

2. A method of construction as claimed in Claim 1 wherein said metallic substrate is formed from steel.

3. A method of construction as claimed in Claim 1 or 2 wherein said electrically insulative ceramic material is a vitreous enamel.

4. A method of construction as claimed in Claim 1 or 2 wherein said electrically insulative ceramic material is a glass ceramic.

5. A method of construction as claimed in any preceding claim wherein said metallic heater track is fabricated from a cermet thick film ink.

6. A method of construction as claimed in claim 5 wherein said cermet thick film ink is palladium silver.

7. A method of construction as claimed in any preceding claim wherein said third temperature is substantially lower than at least said first temperature.

8. A heater for a water vessel constructed in accordance with the method of construction as claimed in any preceding claim.

9. A method of assembly of a heater, as claimed in Claim 8, within a water vessel, comprising the steps of mounting said heater, via a connecting component, to a wall of said vessel, attaching electrical connections to said heater, and spraying at least said heater with a metallic substance so as to form an earth screen.

1 0. A method of assembly as claimed in Claim 9 wherein said heater is mounted to said connecting component with a dental ceramic adhesive, said component being bonded to said wall.

11. A method of assembly as claimed in Claim 9 or 10 wherein said heater is mounted so that a portion thereof extends through said wall into an outer region of said vessel, said portion having said electrical connections attached thereto.

1 2. A method of assembly as claimed in Claim 9, 10 or 11 wherein said heater is aquablasted prior to being sprayed, so as to provide a matt finish to the surface thereof, tc which said metallic substance is capable of adhering.

1 3. A method of construction as claimed in any one of Claims 9 to 1 2 wherein said metallic substance is pure aluminium.

14. A method of construction as claimed in any one of Claims 9 to 1 3 wherein said heater and said connecting component are sprayed with said metallic substance.

1 5. A water vessel having a heater assembled therewith in in accordance with the method of assembly as claimed in any one of Claims 9 to 14.

1 6. A water vessel as claimed in Claim 1 5 wherein said vessel is in the shape of a jug.

1 7. A water vessel as claimed in Claim 1 5 or 1 6 including a first temperature sensor arranged to sense steam from boiling water within said vessel and to de-energise said heater on sensing of said steam.

18. A water vessel as claimed in Claim 15, 1 6 or 1 7 including a second temperature sensor arranged to detect a "boil dry" condition, wherein said heater is energised when no water is present in said vessel, and to deenergise said heater on detecting said condition.

1 9. A heater for a water vessel substantially as herein described with reference to Figures 1 and 2 of the accompanying drawings.

20. A water vessel substantially as herein described with reference to Figure 3 of the accompanying drawings.