Heating apparatus

Heating apparatus includes a tray having a layer of insulative material disposed in the base thereof and a number of infra-red lamps disposed thereabove. The apparatus is accommodated within a housing having a layer of glass ceramic to form a hotplate. Each end of each lamp is provided with a pinch seal enclosed within a ceramic end cap. To improve substantially dissipation of heat from the pinch seals, first apertures are provided in a hollow bar and second apertures are provided in a base plate below the pinch seals, so as to permit air to flow into the housing via the second apertures, substantially around the pinch seals, and out of the housing via the first apertures.

This invention relates to heating apparatus and in particular, though not 
exclusively, to such apparatus including one or more sources of infra-red 
radiation, as disclosed and claimed in our copending British Application 
No. 83 20717. 
In the above-mentioned applications, the sources of infra-red radiation are 
infra-red lamps, each comprising a filament supported within a quartz 
tube. The infra-red lamp is described in greater detail and claimed in 
copendiing European Application No. 84 301636.1, in the name of THORN EMI 
plc, wherein each end of the lamp has a pinch seal with an electrical lead 
connected to the filament sealed therein, 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 in the heating apparatus. 
However it is necessary to maintain the pinch seals of the infra-red lamps 
at a relatively low temperature, for example below 350.degree. C., to 
prevent oxidisation of the pinch seal, thereby prolonging the life of the 
lamp. 
A solution to this problem of maintaining a relatively low temperature of 
the pinch seal has been proposed in our copending British Application No. 
8316306, and copending British Application No. 8316304, in the name of 
THORN EMI plc, which both relate to the upward conduction of heat from the 
pinch seal towards a layer of ceramic material which forms a hot plate for 
the heating apparatus. 
The object of the present invention is to provide an alternative solution 
to the above-identified problem, which may be more convenient to implement 
in some circumstances, but which may, if desired, be used in conjunction 
with the arrangements of the aforementioned co-pending British Application 
Nos. 8316304 and 8316306. 
According to the invention there is provided heating apparatus accommodated 
within a housing, 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 housing includes a substantially 
hollow member having first apertures provided in a surface thereof, said 
member being disposed so that at least one of said first apertures is in 
contact with the ambient environment of said housing, the base of said 
housing having second apertures provided therein at least in the region 
substantially below said pinch seals, thereby permitting air to flow into 
said housing via said second apertures, substantially around said pinch 
seals, and out of said housing, via said first apertures.

Referring to the Figures, heating apparatus, as described and claimed in 
our above-mentioned copending British Application No. 83 20717, consists 
of a generally circular tray, or so-called "flan casing" 1 having a layer 
2 of insulative material, preferably one known as Microtherm, disposed in 
the base thereof and a number of infra-red lamps, one being shown at 3, 
disposed thereabove. The infra-red lamp 3 comprises a tubular quartz 
envelope 4 having a tungsten filament 5 supported therein, each end of the 
quartz envelope 4 being supported within a ceramic fibre ring 6. 
Disposed above the heating apparatus is a layer 7 of glass ceramic material 
which forms a hot plate for the apparatus, and the apparatus is 
accommodated within a housing, a base plate for which is shown at 8. 
The flan casing 1 is connected by screw fixings, 9 and 10, to a carrier 
plate 11, which is resiliently mounted to the base plate 8 by a number of 
pin and spring assemblies, such as at 12, which locate the carrier plate 
11 and exert an upward force thereon, thereby urging the heating apparatus 
upwardly towards the glass ceramic layer 2 so that the top rim of the flan 
case abuts the underside of layer 2, thus locating and retaining the 
infra-red heat generated by the lamps. 
Each end of the lamp 3 is provided with a pinch seal, one being shown at 
13, having an amp tag connector, such as at 14, which is connected to the 
respective end of the filament 5, sealed therein. Electrical leads (not 
shown) can then be connected to each amp tag connector, so as to supply 
power to the infra-red lamp 3. 
Both pinch seals 13 of the lamp 3 are enclosed within respective ceramic 
end caps, one being shown at 15, which is supported by flanges, 16 and 17, 
which are attached to the side wall of the flan casing 1. 
It is preferable that the heating apparatus consists of four infra-red 
lamps disposed substantially parallel to each other and spaced across the 
circular region above the base of the flan casing 1. It is also preferable 
that a number, such as four, flan casings, each having the lamps disposed 
thereabove, are provided below the layer of glass ceramic material, so as 
to form a cooking hob. Such an arrangement is shown in the plan view of 
FIG. 1, wherein a user-operable control panel, to control the heat 
required for cooking purposes, is shown at 18, and four flan casings, 19 
to 22, are also shown, each casing having four infra-red lamps, such as at 
23 to 26 on casing 20, associated therewith. The four flan casings, 19 to 
22, are mounted into the carrier plate 11, which is resiliently mounted to 
the base plate 8. For reasons of clarification, the top layer 7 of glass 
ceramic has been removed from the hob shown in FIG. 1. 
To prolong the life of the infra-red lamps, it is necessary to maintain the 
pinch seals of the lamp 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, 16 
and 17. 
To improve substantially dissipation of heat from the pinch seals, the 
present invention includes one or more apertures, such as at 27 and 28 in 
the base plate 8, below the region of the pinch seals. Apertures, such as 
at 29 and 30, may also be provided in the area of the carrier plate 11 
above the apertures in the base plate 8. In conjunction with the 
apertures, 27 to 30, the present invention further includes a hollow bar 
31, which is provided with perforations in the form of slot apertures, 
such as at 32 in side 34 of the bar 31, and a slot 35 in the undersurface 
of the bar 31. 
The bar 31 is disposed between the heating apparatus mounted in the carrier 
plate 11 and the control panel 18. 
End 33 of the hollow bar 31 may be open to the ambient environment of the 
hob. 
Apertures 27 to 30 are provided in the heating apparatus shown in FIG. 1 in 
regions, shown generally at 36 to 41, of the base plate 8 and, if 
required, of the carrier plate 11 below each row of pinch seals 
accommodated within their respective ceramic end caps. 
It can therefore be envisaged that relatively cool air from the ambient 
environment of the cooking hob can enter the hob, via the apertures 
provided at least in the base plate thereof, flow around the pinch seal 
regions, 36 to 41, enter the bar 31 via slot 35, and then exit from the 
hob via the slot apertures 32 in side 34 of the bar 31, thereby providing 
natural cooling of the pinch seal regions by passing a constant relatively 
cool air-flow therearound. 
In addition to apertures being provided in the base plate 8 and, if 
required, in the carrier plate 11, they may also be provided in the 
flanges, 16 and 17, which support the ceramic end caps of each lamp, 
and/or in the ceramic end caps 15 themselves. 
The perforated bar 31 may, alternatively, be disposed in extended region 
42, shown by dotted lines in FIG. 1, at the rear of the heating apparatus. 
It can therefore be seen that the present invention provides a simple and 
inexpensive technique of naturally cooling the pinch seals of the 
infra-red lamps, so as to increase substantially the life of the lamps.