GB2166330A - Improvements in or relating to electric heating units - Google Patents

Abstract

An electric heating unit, suitable for use in a cooker hob, has at least one infra-red heating element, for example a tungsten filament lamp (4). To reduce the risk of over-heating of the terminal connections (11, 19, 22, 23) of the heating element, the terminal connections are thermally-connected to a heat sink (13) and, in addition are so arranged that ambient air can circulate freely around them. <IMAGE>

Description

SPECIFICATION Improvements in or relating to electric heating units This invention relates to electric heating units and has particular but not exclusive reference to heating units for incorporation in electric hobs and the hobs of electric cookers.

It has been proposed, in such units, to use sources of infra-red radiation as the heat sources and tungsten filament lamps have been suggested as suitable sources. Tungsten filament lamps operate at high temperatures and this results in the heating-up of the terminal connections of the tubes.

It is, therefore, an object of the present invention to provide an electric heating unit which, when used with sources, for example tungsten filament lamps, of infra-red radiation are less prone to over heating of the terminal connection.

According to the present invention, an electric heating unit comprises at least one heating ele ment having terminal connections exposed to cool ing by ambient air and connected by a thermally conducting path to a heat sink.

A preferred embodiment of the invention com prises a plurality of tungsten filament lamps ar ranged in spaced relationship each lamp having terminal connections exposed to cooling by am bient air and connected by heat conductive paths to at least one heat sink.

The lamps may be of tubular form with terminal connections at each end, the lamps being sup ported above a base of thermally insulating mate rial contained in a metal pan to which the or each heat sink is secured in heat conducting manner.

Each terminal assembly may include a contact portion part at least of which is contoured to ac commodate thermal expansion of the portion.

Each terminal portion may be electrically con nected to a terminal bolt by which the portion is supported from the heat sink or one of the heat sinks.

Each bolt may be electrically insulated from its associated heat sink.

By way of example only, an embodiment of the invention will now be described in greater detail with reference to the accompanying drawings of which: Figure 1 is a plan view of part of the embodi ment, and Figure 2 is a side elevation partly in section and on a slightly larger scale of the embodiment.

The embodiment which is suitable for use as a heating unit in an electric hob comprises a dish shaped pan 1 of metal, for example mild steel.

Seated in the pan support 1 is a bed 2 of a ther mally insulating material, for example Microporous ceramic fibre. The peripheral region 3 of the bed 2 is slightly raised and contoured at diametrically op posite regions to support in spaced parallel posi tions four tungsten halide filament lamps 4 of tubular form as can be seen from Figure 1. The up per surface of the bed 2 may be coated with a heat reflective material.

Seated upon the lamps is a collar 5 of generally annular form with chordal portions 6 whose lower surfaces are also contoured to extend downwardly between the lamps 4 to assist in retaining the latter in the spaced positions shown.

Extending from a housing 7 secured to the pan 1 by means of a bracket 8 is a heat sensor 9 of tubular form. The sensor lies just above the tubes 4 and comprises a metallic tube containing a rod of iow thermal coefficient of expansion which is operatively connected to an electric switch contained in the housing 7. The purpose of the sensor will be explained below.

Each of the lamps 4 has a tubular envelope of a material permeable to infra-red radiation. Each contains a tungsten filament connected at each end to an electrically conducting strip that is sealed in the "pinched" end of the tube as indicated at 10.

Each strip may be molybdenum or other suitable metal with which an effective seal to the glass envelope can be achieved. The strips terminate in outer contact positions 11 and each has a corrugated portion 12.

Located below the pan 1 at positions immediately beneath the chordal portions 6 are rectangu lar metallic plates 13 each secured to the pan base by bolts 14. As can be seen from Figure 2, the plates are cranked upwardly and each has a downwardly-extending strengthening flange 15 round most of its periphery, the inner edges 16 of the plates 13 being plain and fitting beneath the recessed edge portion 17 of the pan 1.

Along the outer edges of the plates 13 are formed four holes in which are located the lower ends of four electrically-insulating spacers 18 of generally cylindrical form in whose bores are located terminal bolts 19. The spacers are stepped externally to form seats 20 which rest upon the plates 13. The lower projecting ends of the spacers locate in cup-shaped spacers 21, the bolts 19 passing through apertures in the bases of the spacers.

The upper ends of the bolts 19 pass through holes in the contact portions 11. Connector tags 22 are secured to the upper ends of the bolts by nuts 23.

In that manner, the contact portions 11 are supported firmly above the plates 13.

When energised via conductor leads secured round the bolts 19 and inside the connector tags, the filaments of the lamps 4 are raised to a high temperature at which a substantial part of the emitted radiation is in the infra-red band. The major parts of the lengths of the filaments and the tubes are confined within bed 2 and the collar 5 and heat emitted by those parts thereby contained.

However, some heat is transmitted along the filaments to the strips sealed in the pinched tube ends and thus to contact portions 11.

The construction described above is designed to dissipate as much as possible of the heat transmitted to the terminal assemblies comprising the contact portions 11, bolts 19, tags 22 and nuts 23.

As is apparent from Figure 2 the terminal assemblies are spaced apart from each other and from the adjacent collar 5 and pan 1. Thus, ambient air can circulate freely round the assemblies in direct contact with the latter and a proportion of the heat is carried away by radiation and convection. In addition, heat is transmitted along the bolts 19 and the spacers 18 and 21 to the plates 13 which con stitute heat sinks of extended surface area.

The result is that the terminal assemblies remain relatively cool. Any expansion of the contact portion 11 is accommodated by the corrugations 12.

The heating unit described above is intended for use in a hob or cooker and is usually located beneath a hob plate of ceramic material or glass that is permeable to infra-red radiation. The unit is also provided with a suitable circuit enabling a user to control the heat output of the unit.

The heat sensor 9 is exposed to radiant heat emitted by the lamps 4 and acts as a thermal limiter to prevent overheating of the unit. The rod and tube act in the well known manner to operate an electric switch in the housing 7. The switch is connected in the power supply to the unit and when a predetermined temperature is sensed, the switch operates to terminate the supply of power to the unit.

It will be appreciated that the invention is applicable to other forms of infra-red heating elements and to heating units other than those incorporating infra-red heating elements, for example the heating elements may be conventional sheathed or open resistance wires or tapes.

The hob or electric cooker hob may also incorporate one or more infra-red heating units and at least one unit having a conventional sheathed or open heating element.

Claims (9)

CLAIMS 1. An electric heating unit comprising at least one heating element having terminal connections exposed to cooling by ambient air and connected by a thermally conducting path to a heat sink. 2. An electric unit comprising a plurality of tungsten filament lamps arranged in spaced relationship each lamp having terminal connections exposed to cooling by ambient air and connected by heat conductive paths to at least one heat sink. 3. A unit as claimed in claim 2 in which the lamps are of tubular form with terminal connections at each end, the lamps being supported above a base of thermally insulating material contained in a metal pan to which the or each heat sink is secured in heat conducting manner 4. A unit as claimed in claim 3 in which each terminal assembly includes a contact portion part at least of which is contoured to accommodate thermal expansion of the portion. 5. A unit as claimed in claim 4 in which each contact portion is electrically connected to a terminal bolt by which the portion is supported from the heat sink or one of the heat sinks. 6. A unit as claimed in claim 5 in which each bolt is electrically insulated from its associated heat sink. 7. An electric unit substantially as herein described with reference to and as illustrated by the accompanying drawings. New claims or amendments to claims filed on 30 July 85 Superseded claims 1-7 New or amended claims:

1. An electric heating unit comprising at least one infra-red heating element having terminal connections exposed to cooling by ambient air and connected by a thermally conducting path to a heat sink.

2. A unit as claimed in claim 1, in which the heating element is a filament lamp.

3. A unit as claimed in claim 2, in which the heating element is a tungsten filament lamp.

4. An electric heating unit comprising a plurality of tungsten filament lamps arranged in spaced relationship, each lamp having terminal connections exposed to cooling by ambient air and connected by heat conductive paths to at least one heat sink.

5. A unit as claimed in claim 3 or claim 4, in which the or each lamp is of tubular form with terminal connections at each end, the lamp being supported above a base of thermally insulating material contained in a metal pan to which the or each heat sink is secured in heart conducting man- ner.

6. A unit as claimed in claim 5, in which each terminal connection includes a contact portion part part at least of which is contoured to accommo- date thermal expansion of the portion.

7. A unit as claimed in claim 6, in which each contact portion is electrically connected to a terminal bolt by which the portion is supported from the heat sink or one of the heat sinks.

8. A unit as claimed in claim 7, in which each bolt is electrically insulated from its associated heat sink.

9. An electric heating unit substantially as herein described with reference to and as illustrated by the accompanying drawings.