EP0131372A1

EP0131372A1 - Heating apparatus

Info

Publication number: EP0131372A1
Application number: EP84303729A
Authority: EP
Inventors: Kenneth Stockwin Frost; Alex Leopold Halberstadt; John Albert Letchford; Peter William Crossley; Robert David Smith
Original assignee: Thorn EMI Domestic Appliances Ltd; Thorn EMI Patents Ltd
Current assignee: QED Intellectual Property Ltd
Priority date: 1983-06-15
Filing date: 1984-06-04
Publication date: 1985-01-16
Also published as: EP0131372B1; DE3478559D1

Abstract

Heating apparatus includes atray (1) having a layer (2) of insulative material disposed therewithin, above which a number of infra-red lamps (7) are supported. The ends of each lamp (7) are provided with a pinch sea) (12) having an amp tag connector (14). which is connected to the respective end of a filament (9) within the lamp (7), sealed therein. Each pinch seal (12) is enclosed within a ceramic housing (10) and the heating apparatus is mounted beneath a layer of glass ceramic (25).

A plate (15) of heat-conductive material is intimately disposed between the top surface of one or more of the ceramic housings (10) and the under surface of the glass ceramic (25), so as to encourage heat from the pinch seals (12) to conduct in an upward direction towards the glass ceramic (25).

In another embodiment, a heat conductive stud (22) is intimately disposed between the glass ceramic layer (25) and the pinch seal )26). via an aperture (27) in the housing (24).

Description

This invention relates to heating apparatus and in particular, though not exclusively, to such apparatus including one or more sources of infra-red radiation.
Heating apparatus of this type is described and claimed in our copending British Application No. 8320717, wherein four quartz-halogen infra-red lamps are supported above a shallow metallic tray containing a layer of insulative material, a layer of glass ceramic material being disposed above the lamps as a hot plate for the heating apparatus, thereby forming a cooking hob.
The infra-red lamp is described in more detail and claimed in copending European Application No. 84301636.1, in the name of THORN EMI plc, wherein the lamp comprises a filament supported within a glass tube, each end of the lamp having a pinch seal with an electrical lead connected to a piece of metal foil which is in turn connected to the filament sealed into the respective end thereof, the lead being welded to an appropriate electrical connector. The pinch seal is enclosed within a ceramic housing, which is shaped to provide location of the lamp in the correct position on flanges provided either side of the metallic tray, when the lamp is incorporated within the above-mentioned heating apparatus. ;
However, the highly concentrated heat energy within the apparatus may cause the temperature of the pinch seals to rise above the preferred operating temperature thereof, which is usually at or below approximately 350°C, thereby causing oxidation of the pinch seal and thus reducing the life of the lamp.
The ceramic housing has been found to conduct heat to a limited extent from the pinch seal to the supporting flange of the metallic tray, but this may not be sufficient on its own to achieve longevity of the lamp under all operating conditions.
The object of the present invention is therefore to alleviate substantially the problem of maintaining a relatively low temperature of the pinch seals.
According to the present invention there is provided heating apparatus for mounting beneath a hot plate, said apparatus including at least one infra-red lamp, the or each lamp comprising a filament supported within a generally tubular envelope and having, at each end thereof, a pinch seal with an electrical connection to the respective end of the filament sealed therein, characterised in that said apparatus further includes means for conducting heat from said pinch seal in a substantially upward direction towards said hot plate.
Preferably, the pinch seal at each end of the or each lamp is substantially enclosed within a ceramic housing.
The means for conducting heat may include a plate of heat-conductive material intimately disposed between the top surface of the ceramic housing and the under surface of the hot plate.
A layer of a heat sink compound may also be intimately disposed between the plate of heat conductive material and the under surface of the hot plate, and/or between the plate and the upper surface of the ceramic housing.
In another embodiment , the means for conducting heat may extend into the ceramic housing through an aperture provided therein, and may take the form of a stud of suitable heat-conductive material, such as aluminium, which is intimately disposed above the upper surface of the pinch seal and the lower surface of the hot plate, the stud extending through the aperture in the ceramic housing.
In this other embodiment, means may also be provided for urging the first-mentioned means in an upward direction towards the hot plate, and these means may comprise nesiliently- mounted support member disposed between the lower surface of the pinch seal, via a second aperture in the ceramic housing, and an upwardly-sprung carrier plate which supports the heating apparatus.
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 heating apparatus illustrating two embodiments of the invention,
Figure 2 shows a plan view of heating apparatus illustrating a third embodiment,
Figure 3 shows an enlarged sectional view of the embodiment shown in Figure 2,
Figure 4 shows an enlarged sectional view of a fourth embodiment, and
Figure 5 shows a view in the direction of arrow A in Figure 4.

Referring to the Figure 1, heating apparatus includes a generally circular shallow tray 1, preferably made of metal, which has disposed therewithin a layer 2 of insulative material, preferably a material known as Mierotherm. The tray 1 has two extending flanges, 3 and 4, arranged on opposite sides of the rim of the tray 1, each flange having upturned end portions, 5 and 6, respectively.
A number of infra-red lamps, one being shown at 7, are disposed above the layer 2 of insulative material and are supported at each end by the flanges, 3 and 4.
Each infra-red lamp 7 is preferably a quartz-halogenated lamp comprising a tubular quartz envelope 8, within which a tungsten filament 9 is supported. Both ends of each lamp are enclosed within respective ceramic end caps, one being shown at 10, having a location tab 11. The lamps can therefore easily be inserted in apertures provided in the upturned portions, 5 and 6, on the flanges, 3 and 4.
The ceramic end cap, at each end of the lamps, encloses a pinch seal, one being shown generally at 12, having an amp tag connector, one shown at 14, or any other suitable form of male tab connector, which is connected via metal foil 17 to the respective end of the filament 9, sealed therein. Electrical leads (not shown) can then be connected to each amp tag connector, so as to supply power to each infra-red lamp.
The heating apparatus also preferably includes a thermal limiter 10, disposed between the lamps and the layer 2 of insulative material. The thermal limiter 10 is arranged to operate a microswitch 11, so as to disconnect the power to the lamps when the temperature sensed by the thermal limiter 10 reaches a threshold value.
The heating apparatus and infra-red lamp, so far described, are described in greater detail, and claimed, in the two above-mentioned copending British Application No. 8320717 and European Application No. 84301636.1.
To prolong the life of the infra-red lamps it is necessary to maintain the pinch seals at a relatively low temperature, this being achieved to a certain extent by the ceramic end caps, which conduct a limited amount of heat from the pinch seals to the respective flanges, 3 and 4.
However, to improve substantially the heat conduction away from the pinch seals the present invention provides, in a first embodiment shown on the flange 3, a respective plate of heat-conductive material, preferably aluminium, disposed above each of the ceramic end caps, one such plate being shown at 15.
As disclosed in the aforementioned British Application No. 8320717, a layer of glass ceramic (not shown) is disposed above the heating apparatus to provide a glass ceramic cooking hob and, in the present invention, the aluminium plates are intimately disposed between the top surface of the ceramic end caps and the under surface of the glass ceramic layer, thereby encouraging heat from the pinch seals to conduct in an upward direction to the glass ceramic layer.
A heat sink compound may also be provi e between, and in contact with, each aluminium plate and the glass ceramic layer, and/or between each plate and the top of each ceramic end cap thereby further improving the upwardly directed heat-conductive path. The heat sink compound has an added advantage of being relatively flexible, so as to allow a certain amount of movement, caused by expansion and contraction of the metallic tray, flanges and/or the aluminium plates.
An alternative embodiment of the present invention is shown on the flange 4, wherein each plate, such as 15, provided separately for covering each end cap is replaced by a single aluminium plate 16, which extends over all of the end caps supported on the flange 4. The plate 16 may then be covered with the heat sink compound, above which the glass ceramic layer is placed.
The plates, 15 or 16, may of course be fabricated from any suitable heat-conductive material.
Figure 2 shows a third embodiment of the heating apparatus, wherein like parts are labelled with like reference numerals with respect to Figure 1. However, the flanges 3, 4 are replaced by suitably-shaped pieces of insulative material, 18 and 19, through which the ends of each lamp extend and being shaped so that an equal portion 20 of each lamp is exposed, thereby ensuring that substantially equal amounts of heat are dissipated at the ends of all of the lamps incorporated in the heating apparatus.
To improve substantially the heat conduction away from the pinch seals, the third embodiment is provided with studs, shown at 21 and 22, which extend respectively through an aperture in each of ceramic housings, 23 and 24 of the lamp 7, each stud being in thermal contact with the upper surface of the pinch seal within each housing. The top of each stud, 21 and 22, is in contact with the under surface of a layer of glass ceramic, which is disposed above the heating apparatus,to form a hot plate therefor.
Referring now to Figure 3, wherein like parts are labelled with like reference numerals with respect to Figures 1 and 2, there is shown an enlarged sectional view of the end of the lamp 7 including the ceramic housing 23.
It can clearly be seen from Figure 3 that the stud 22 is intimately disposed between the under surface of layer 25 of glass ceramic material and the top surface of pinch seal 26 which is enclosed within the housing 23, via an aperture 27 in the housing. The stud 22 is fabricated from any suitable heat-conductive material, preferably aluminium, thus providing a good heat-conductive path from the pinch seal 26 to a region of the glass ceramic layer 25 which is relatively cool.
The embodiment shown in Figure 3 also includes a support member 28, which is mounted to a carrier plate 29 by means of a screw fixing 30 and which is in contact with the under surface of the pinch seal 26, via a second aperture 31 in the ceramic housing 23.
The carrier plate 29, which supports the tray 1, is resiliently mounted to a base plate 32 by a number of pin and spring assemblies, such as at 33, which locate the carrier plate 29 and exert an upward force thereon, thereby urging the heating apparatus upwardly towards the glass ceramic layer 25 so that the top of the tray 1 and the insulative material 19 abuts the underside of the layer 25, thus locating and retaining the infra-red heat generated by the lamps.
It can therefore be envisaged that the pin and spring assembly 33 also urges the support member 28, which is mounted on the carrier plate 29, upwardly, thereby urging the pinch seal 26 into good thermal contact with the stud 22, which in turn is urged into good thermal contact with the glass ceramic layer 25.
To optimise heat conduction, the stud 22 may be cemented into the aperture 27 and/or a heat conducting cement may be provided between the pinch seal and the stud and between the stud and the glass ceramic layer. Support member 28 may also be cemented into aperture 31.
The support member 28 may be formed from a stud of similar shape and size as stud 22 or, alternatively, it may be in the form of a leaf spring, supported by the carrier plate 29 and in contact with the pinch seal 26 via a slot aperture provided in place of circular aperture 31.
The stud 22 and support member 28 may have a cross-section which is circular or any other suitable shape, so as to provide optimum thermal conduction.
It may be preferable to mount all of the support members, which are provided in a common line on each side of the heating apparatus shown in Figure 2, on to a strip plate which is then mounted onto the carrier plate 29, thereby allowing easier fitting of the apparatus into the base plate 32 to form a cooking hob. A limited amount of heat may be conducted downwardly via the support member 28, but since the carrier plate 29 is preferably metallic and therefore most likely to be much hotter than the region of the ceramic layer in contact with the stud 22, downward heat conduction should be discouraged.
Figures 4 and 5 show a fourth embodiment of the invention, wherein the stud 22 has been replaced by an elliptically-shaped ring 34, made from a suitable heat-conductive material, which may be secured above the pinch seal 26, in thermal contact therewith, by means of slots 35 and 36 provided either side of an aperture 37, which extends across the top of the housing 23.
The advantage of this second embodiment is that the ring 34 provides a measure of extra resilience for the glass ceramic layer 25, which is mounted above, and in contact with, the top portion of the ring 34, and thus aids in reducing manufacturing tolerances.
In Figure 4, it can be seen that the heating apparatus is provided with a flange 38, as in the embodiment shown in Figure 1, to support the ceramic housing 23, the housing having a locating flange 39 at the end thereof to provide positive location of the housing 23 on the supporting flange 38. The flange 38, which is fixed to the side of the tray 1, is therefore also urged upwardly by the pin and spring assembly 33, thereby urging the ring 34 upwardly into contact with the ceramic layer 25.
Figure 5 shows a view in the direction of arrow A in Figure 4, indicating the end face of the housing 23, within which the pinch seal 14 is contained, and illustrating the ring 34 in contact with the ceramic layer 25 and the top of the pinch seal 26.
A beat-conducting cement may, of course, be provided between the contacting surfaces of the pinch seal and the ring and of the ring and the ceramic layer.
The portion of the housing 23 which has been cut out to form the aperture 37 may be replaced after insertion of the ring 34 into its position in contact with the pinch seal 26, thereby aiding in maintaining good contact between the ring and the pinch seal.
Instead of incorporating an amp tag connector within the pinch seals of each lamp, it may be preferable to join a high temperature flexible cable directly to an outgoing wire from the pinch seal.
It may be clearly envisaged that any suitable combination of the features shown in the above-identified embodiments may be employed in the heating apparatus.
The Figures show a single coil tungsten filament accommodated within each lamp, but it may however be preferable to employ a coiled coil tungsten filament, which generally possesses substantially greater resilience to mechanical shock than single coil filaments.
It can therefore be envisaged that the present invention provides a heat conductive path extending upwards from the ceramic housing, enclosing each pinch seal of the infra-red lamp, towards the glass ceramic layer, thereby forming an efficient heat sink for each pinch seal, so as to reduce the temperature thereof and consequently to prolong the life of the lamp.

Claims

1. Heating apparatus for mounting beneath a hot plate (25) said apparatus including at least one infra-red lamp (7), the or each lamp (7) comprising a filament (9) supported within a generally tubular envelope (8) and having, at each end thereof, a pinch seal (12) with an electrical connection (14) to the respective end of the filament (9) sealed therein, characterised in that said apparatus further includes means (15) for conducting heat from said pinch seal (12) in a substantially upward direction towards said hot plate (25).

2. Heating apparatus as claimed in claim 1 wherein said pinch seal (12) at each end of the or each lamp (7) is substantially enclosed within a ceramic housing (10).

3. Heating apparatus as claimed in claim 2 wherein said means (15) for conducting heat includes a plate (15) of heat-conductive material intimately disposed between an upper surface of the ceramic housing (10) and an under surface of the hot plate (25).

4. Heating apparatus as claimed in claim 3 wherein each ceramic housing (10) has a respective plate (15) associated therewith.

5. Heating apparatus as claimed in claim 3 wherein at least two adjacently-disposed ceramic housings (10) have a common plate (16) associated therewith, said plate (16) substantially extending over the upper surfaces of said ceramic housings (10).

6. Heating apparatus as claimed in any one of claims 3 to 5 wherein a layer of a heat sink compound is intimately disposed between an upper surface of said plate (15) and the under surface of said hot plate (25).

7. Heating apparatus as claimed in any one of claims 3 to 6 wherein a layer of a heat sink compound is intimately disposed between a lower surface of said plate (15) and the upper surface of said ceramic housing (10).

8. Heating apparatus as claimed in Claim 2 wherein said neans (22) for conducting heat extend into said ceramic housing (24) through an aperture (27) provided therein.

9. Heating apparatus as claimed in Claim 8 and further including means (28) for urging ₃aid first-r ationed means (22) in a substantially upward direction towards said hot plate (25).

10. Heating apparatus as claimed in Claim 8 or 9 wherein said first-mentioned means (22) comprises a stud (22) of heat-conductive material, intimately disposed between an upper surface of said pinch seal (26) and a lower surface of said hot plate (25), said stud (22) extending through the aperture (27) in said ceramic housing (24).

11. Heating apparatus as claimed in Claim 9 or 10 wherein said means (28) for urging said first-mentioned means (22) comprises a resiliently-mounted support member (28) disposed below said pinch seal (26).

12. Heating apparatus as claimed in Claim 11 wherein said support member (28) is in contact with a lower surface of said pinch seal (26), via a second aperture (31) provided in said ceramic housing (24).

13. Heating apparatus as claimed in Claim 8 wherein said means (22) comprises a ring (34) of heat-conductive material, said ring (34) being in thermal contact with an upper surface of said pinch seal (26) and a lower surface of said hot plate (25).

14. Heating apparatus as claimed in Claim 9 wherein said means (28) for urging said first-mentioned means (22) comprises a leaf-spring mounted below said pinch seal (26) so as to urge said pinch seal in a substantially upward direction.

15. A cooking hob including a hot plate (25), having one or more heating apparatus, as claimed in any preceding claim, mounted therbeneath.