GB2278237A

GB2278237A - Thermal cut-out device

Info

Publication number: GB2278237A
Application number: GB9310532A
Authority: GB
Inventors: Kevin Ronald Mcwilliams
Original assignee: Ceramaspeed Ltd
Current assignee: Ceramaspeed Ltd
Priority date: 1993-05-21
Filing date: 1993-05-21
Publication date: 1994-11-23
Anticipated expiration: 2013-05-21
Also published as: DE9407377U1; GB9310532D0; GB2278237B

Abstract

A thermal cut-out device for a radiant heater comprises a housing (1) incorporating at least one switch assembly, and a thermally-responsive probe assembly (2) having an end supported, and capable of articulation, in the housing and mechanically coupled with the switch assembly. A mounting bracket (6) extends from the housing in spaced relationship with the probe assembly and is adapted for securement to a radiant heater such that the probe assembly extends across at least a part of the heater. A support member (9) for the probe assembly (2) extends externally of the heater between the probe assembly (2) and either the housing (1) or the mounting bracket (6) and restrains the probe assembly (2) from articulation with respect to the housing (1). <IMAGE>

Description

Thermal Cut-Out Device This invention relates to a thermal cut-out device for a radiant heater and particularly a radiant electric heater for use in a glass-ceramic top cooking appliance.

In a radiant heater of this nature, thermal energy emitted by one or more electric heating elements or one or more infra-red lamps incorporated therein is transmitted to and through the glass-ceramic and is absorbed by a cooking utensil positioned on the surface of the glass-ceramic top. It is conventional in such heaters to include a thermal cut-out device to switch off the heater at a certain point to prevent the exposed surface of the glass-ceramic rising above a temperature which could cause damage to, or discolouration of, the glassceramic. Such a temperature is typically about 6000C.

A well known form of thermal cut-out device comprises a housing, incorporating at least one switch assembly, and a thermally-responsive elongate probe assembly having an end supported and capable of articulation in the housing and mechanically coupled with the switch assembly.

The probe assembly typically comprises a rod assembled within a tube having a different coefficient of thermal expansion from the rod, the rod and tube being secured together at an end remote from the switch assembly. Differential expansion between the rod and tube is used to actuate the switch assembly when the probe assembly reaches a predetermined temperature.

The cut-out device is mounted on the heater with the housing external of the heater and with the probe assembly traversing the heater and spaced from the heating elements or lamps. A mounting bracket, usually of strip form, is provided extending from the housing of the device and secured to the exterior of the heater. The probe assembly is supported at its free end, remote from the housing, either by means of a peripheral or internal wall of the heater or by some other support means specifically provided within the heater. The articulated mounting of the probe assembly in the housing permits accommodation of misalignment between the mounted housing and the remote support for the probe assembly. Such an articulated mounting arrangement does however make essential the use of the remote support to prevent sagging or displacement of the end of the probe assembly when the device is installed and in use in the heater.

Recent trends have been towards the use of a thermal cut-out device employing a probe assembly of reduced length, with the possibility of using the same length of probe assembly regardless of the size of heater to which it is attached. This has necessitated the provision of some form of support for the end of the probe assembly remote from the housing which could be adapted to heaters of different sizes.

It would be desirable and advantageous to provide a thermal cut-out device which could be used when required without a support for the end of the probe assembly remote from the switch housing, when installed in a radiant heater, but which at the same time would allow the existing design of articulated mounting of the probe assembly in the housing to be retained.

It is an object of the present invention to fulfil this requirement.

The present invention provides a thermal cut-out device for a radiant heater, comprising: a housing incorporating at least one switch assembly; a thermally-responsive probe assembly having an end supported1 and capable of articulation, in said housing and mechanically coupled with the switch assembly; a mounting bracket extending from the housing in spaced relationship with the probe assembly, the bracket being adapted and arranged for securement to a radiant heater such that the probe assembly extends across at least a part of the heater; a support member for the probe assembly, the support member extending externally of the heater between the probe assembly and either the housing or the mounting bracket and substantially restraining the probe member from articulation with respect to the housing.

The support member suitably has a first portion embracing the probe assembly.

The probe assembly may include a ferrule at the end which is supported in the housing, the support member in such case extending between the ferrule and either the housing or the mounting bracket.

The support member may comprise a plate, suitably of a metal1 having in a first portion a first aperture through which passes the probe assembly and having in a second portion a second aperture through which passes the mounting bracket.

The first and second apertures in the plate preferably have cross-sectional shapes substantially matching those of the probe assembly and the mounting bracket, respectively.

The probe assembly and first aperture in the plate may each be of circular cross-section.

The mounting bracket may be of strip form, the second aperture in the plate comprising an elongate slot.

The plate may be of any convenient shape, such as rectangular, triangular, circular or oval.

A triangular shape for the plate may be advantageous from the point of view of economy of material when the mounting bracket is of strip form, the aperture for the probe assembly being provided in the vicinity of an apex of the triangular plate and the elongate slot being provided in the vicinity of a base of the triangular plate. A plurality of triangular plates may be cut from a rectangular sheet of plate material with minimum use and wastage of material.

The plate is suitably provided as a slotted-on unit on the probe assembly and the mounting bracket.

Alternatively, the support member may comprise a bracket, suitably of metal, having a first portion with an aperture through which passes the probe assembly and having one or more second portions secured to either the housing or the mounting bracket. The one or more second portions may provide one or more flanges for securement to either the housing or the mounting bracket by means of one or more threaded fasteners.

When a said flange is provided, arranged for securement to the mounting bracket of the device, threaded fasteners may be used which also serve to secure the mounting bracket to the heater, whereby the flange is clamped between the mounting bracket and the heater.

When two said flanges are provided, arranged for securement to the housing of the device, threaded fasteners may be used which also serve to secure the mounting bracket of the device to the housing.

The aperture in the first portion of the bracket which the support member comprises, suitably has a cross-sectional shape substantially matching that of the probe assembly.

The bracket which the support member comprises suitably consists of a metal strip bent to form the first portion and the one or more second portions providing the one or more flanges.

If required, a suitable packing material, which may be of a resilient nature, may be provided between the probe assembly and the support member.

By means of the invention, a thermal cut-out construction of the prior art with a probe assembly capable of articulation in the switch housing and which previously required a support on the heater for the end of the probe assembly remote from the switch housing, can be simply and inexpensively adapted to meet the requirements for a probe assembly which, for example, does not completely traverse a radiant heater and for which a support for the free end of the probe assembly within the heater would be undesirable or impractical. It enables one standard basic form of cut-out construction to be adopted, requiring only the simple addition of the support member when a probe assembly is fitted which will receive no securement for its free end in the heater.

The invention is now described by way of example with reference to the accompanying drawings, in which: Figure 1 represents a partly-exploded perspective view of a thermal cut-out device according to the invention; Figure 2 represents a perspective view of an alternative form of support member for use in the device of Figure 1; Figure 3 represents a top plan view of a radiant electric heater incorporating the thermal cut-out device of Figure 1; Figure 4 represents a cross-sectional view of the radiant electric heater of Figure 3: and Figures 5 and 6 represent partly-exploded perspective views of further embodiments of thermal cut-out devices according to the invention.

Referring to Figure 1, a thermal cut-out device for a radiant electric heater comprises a housing 1 incorporating at least one snap-acting switch assembly (not shown) of well known form and construction. A thermally-responsive probe assembly 2, also of well known form, is provided and comprising, for example, a metal rod inside a tube of quartz or fused silica. The rod and tube of the probe assembly 2 have different coefficients of thermal expansion and are secured together at one end 3 of the probe assembly 2. The other end of the probe assembly is fixed in a metal ferrule arrangement 4 and mounted in the housing 1.

The ferrule arrangement 4 is joumalled in the housing 1, so that the probe assembly 2 is capable of articulation in the housing. This means that the end 3 of the probe assembly 2 has limited freedom of movement as indicated by the arrows 5.

The cut-out device operates in well known manner in that when the probe assembly 2 is subjected to increase in temperature, differential expansion between the rod and tube comprising the assembly causes relative linear movement therebetween, resulting in operation of the switch assembly in the housing 1 when a predetermined temperature is reached.

A metal mounting bracket 6, of strip form, is secured to the housing and is used to fix the thermal cut-out device onto a supporting dish 7 of a radiant electric heater by means of screws 8, as shown in Figures 3 and 4.

However, for reasons to be explained hereafter, before the cut-out device is fixed to the heater, a support member 9 for the probe assembly 2 is added. Such support member comprises a metal plate 10, of any suitable shape but conveniently rectangular, as in Figure 1, or triangular as in Figure 2. The support member 9 is provided with a circular aperture 11 and a slot-shaped aperture 12. The support member 9 is slotted onto the cutout device with the probe assembly 2 passing through the aperture 11 and the mounting bracket 6 passing through the aperture 12. In its final intended position, the support member 9 is located with the ferrule 4 of the cut-out device inserted through the aperture 11 therein. The apertures 11 and 12 in the support member 9 are dimensioned so as to fit as closely as is reasonably practicable, the ferrule 4 and bracket 6. Once in place, the support member 9 prevents or minimises movement of the end 3 of the probe assembly in the directions indicated by the arrows 5. If required, packing material (not shown) of suitably resilient nature may be applied between the ferrule 4 and/or bracket 6 and the walls of the apertures 11, 12 in the support member 9.

Referring now to Figures 3 and 4, a radiant heater is shown mounted under a glassceramic cooking top 13. The heater comprises a supporting dish 7 containing a layer of thermal and electrical insulation material 14 on which are arranged electric heating elements 15. A peripheral wall 16 of thermal insulation material is provided and also a terminal block 17 for making electrical connection to the heating elements 15. Such a heater is well known in the art.

When the thermal cut-out device of Figure 1 is mounted on the heater and secured by the screws 8, the probe assembly 2 passes through an aperture in the wall of the heater supporting dish 7 and an aperture in the peripheral wall 16 and terminates midway across the heater with its end 3 unsupported by the heater. This is the reason for the provision of the supporting member 9. In the absence of the supporting member 9, the end 3 of the probe assembly could be undesirably displaced on account of the articulated arrangement of the ferrule 4 in the housing 1. The supporting member 9 prevents or minimises such displacement and obviates the need for a support for the end 3 of the probe assembly 2 to be provided inside the heater.

The articulated arrangement of the probe assembly 4 in the housing 1 of the cut-out device was originally and specifically designed for probe assemblies which were intended to extend completely across the heater and with the free end of the probe assembly supported by the peripheral wall 16. The present invention allows the same basic form of construction to be used for a cut-out incorporating a probe assembly of reduced length whilst eliminating the need for a support inside the heater for the free end of the probe assembly.

In the heater of Figures 3 and 4, the heating elements 15 are shown as being of coiled wire form. However other forms of heating elements could be added or substituted, such as metal strip or ribbon elements or infra-red lamps such as halogen lamps.

Figures 5 and 6 show thermal cut-out devices with alternative arrangements of support members. The basic thermal cut-out device shown in these Figures is the same as that shown in Figure 1 and the same reference numerals are used for parts common to those in Figure 1. In Figure 5, however, a support member 9 is provided in the form of a bracket consisting of a metal strip bent to provide a first portion 18 and a second portion 19 in the form of a flange. The first portion 18 has an aperture 20 for receiving the ferrule 4 of the probe assembly 2. The flange portion 19 is provided with two holes 21 which, when the support member 9 is fitted to the cut-out device, align with the holes 22 in the device mounting bracket 6. When so fitted, the flange 19 of the support member 9 overlies the bracket 6 of the device.

When the thermal cut-out device is fitted to a radiant heater, in like manner as shown in Figures 3 and 4, the screws 8 used to secure the device to the heater pass through the holes 22 in the mounting bracket 6, through the holes 21 in the flange 19 of the support member 9, and into the heater. The support member 9 is thereby secured and clamped between the heater and the device mounting bracket 6.

If desired, a shorter flange 19 may be provided on the support member 9, as indicated by the dotted line 23. The support member 9 may then be secured to the mounting bracket 6 of the device by means of a screw 24 passing through a hole 25 in the mounting bracket and a hole 26 in the flange 19.

In Figure 6, a further alternative form of support member 9 is shown in the form of a bracket comprising a metal strip bent to provide a first portion 27 and second portions consisting of two flanges 28. The first portion has an aperture 29 for receiving the ferrule 4 of the probe assembly 2. The flanges 28 are provided with holes 30 by means of which the support member is secured to the housing 1 of the thermal cut-out device, using the same screws 31 which secure the device mounting bracket 6 to the housing 1.

Although in the accompanying drawings a thermal cut-out device is shown in which the probe assembly 2 includes a metal ferrule 4, the invention is equally applicable to probe assemblies without such a ferrule. With such assemblies it may be preferable to provide a cushion of resilient packing material, eg in the form of a sleeve or washer, between the probe assembly 2 and the support member 9.

Claims

1. A thermal cut-out device for a radiant heater, comprising: a housing incorporating at least one switch assembly; a thermally-responsive probe assembly having an end supported, and capable of articulation, in said housing and mechanically coupled with the switch assembly; a mounting bracket extending from the housing in spaced relationship with the probe assembly, the bracket being adapted and arranged for securement to a radiant heater such that the probe assembly extends across at least a part of the heater; a support member for the probe assembly, the support member extending independently of the heater between the probe assembly and either the housing or the mounting bracket and substantially restraining the probe member from articulation with respect to the housing.

2. A thermal cut-out device according to Claim 1 in which the support member has a first portion embracing the probe assembly.

3. A thermal cut-out device according to Claim 1 or 2, in which the probe assembly includes a ferrule at the end which is supported in the housing, the support member extending between the ferrule and either the housing or the mounting bracket.

4. A thermal cut-out device according to Claim 1, 2 or 3, in which the support member comprises a plate having in a first portion a first aperture through which passes the probe assembly and having in a second portion a second aperture through which passes the mounting bracket.

5. A thermal cut-out device according to Claim 4, in which the plate comprises a metal.

6. A thermal cut-out device according to Claim 4 or 5, in which the first and second apertures in the plate have cross-sectional shapes substantially matching those of the probe assembly and the mounting bracket, respectively.

7. A thermal cut-out device according to Claim 6, in which the probe assembly and the first aperture in the plate are each of circular cross-section.

8. A thermal cut-out device according to Claim 6 or 7, in which the mounting bracket is of strip form and the second aperture in the plate comprises an elongate slot.

9. A thermal cut-out device according to any of Claims 4 to 8, in which the plate is rectangular, or triangular, or circular, or oval in shape.

10. A thermal cut-out device according to Claim 9, as dependant upon Claim 8, in which the plate is triangular in shape, the aperture for the probe assembly being provided in the vicinity of an apex of the plate and the elongate slot being provided in the vicinity of a base of the plate.

11.A thermal cut-out device according to any of Claims 4 to 10 in which the plate is provided as a slotted-on unit on the probe assembly and the mounting bracket.

12. A thermal cut-out device according to Claim 1, 2 or 3, in which the support member comprises a bracket having a first portion with an aperture through which passes the probe assembly and having one or more second portions secured to either the housing or the mounting bracket.

13. A thermal cut-out device according to Claim 12, in which the one or more second portions in the bracket which the support member comprises, provide one or more flanges for securement to either the housing or the mounting bracket by means of one or more threaded fasteners.

14. A thermal cut-out device according to Claim 13, in which a said flange is arranged for securement to the mounting bracket by threaded fasteners which also serve to secure the mounting bracket to the heater, whereby the flange is clamped between the mounting bracket and the heater.

15. A thermal cut-out device according to Claim 13, in which two said flanges are arranged for securement to the housing by threaded fasteners which also serve to secure the mounting bracket to the housing.

16. A thermal cut-out device according to any of Claims 12 to 15, in which the bracket comprises a metal.

17. A thermal cut-out device according to any of Claims 12 to 16, in which the aperture in the first portion of the bracket which the support member comprises has a cross sectional shape substantially matching that of the probe assembly.

18. A thermal cut-out device according to any of Claims 13 to 17, in which the bracket which the support member comprises consists of a metal strip bent to form the first portion and the one or more second portions providing the one or more flanges.

19. A thermal cut-out device according to any preceding Claim, in which a packing material is provided between the probe assembly and the support member.

20. A thermal cut-out device according to Claim 19, in which the packing material is resilient in nature.

21. A thermal cut-out device constructed and arranged substantially as hereinbefore described with reference to the accompanying drawings.

22. A radiant electric heater provided with a thermal cut-out device according to any preceding Claim.