GB2133959A - Vessels for heating liquids - Google Patents

Abstract

A jug or kettle having a thermoplastic body 10, a heating element assembly 12, switch assembly 13 and a two-part metal heat shield with insulating means to protect the body in the event of overheating of the element 23. The heat shield comprises a dished member 51, 52 and an upstanding member 60 insulated from the element head 21 and the body by seals 53A, B of the insulating means and a spacer 54 provided by a clamping ring 22. The dished member 50 is a push fit in the body, and the member 60 has flanges 63, 65 to engage the body. <IMAGE>

Description

SPECIFICATION Vessels for heating liquids This invention concerns vessels for heating liquids, which vessels are of the kind comprising a hollow body having a lower portion which is constructed from a plastics or other material which will melt or otherwise lose its structural integrity at or below a red hot temperature, and further comprising an electrical immersion heater having a head mounted on the hollow body, an electrical resistance heating element disposed within the vessel and mounted on the head so as to provide a "hot spot" on the head, and a thermal cut-out located in the head in thermal contact with the hot spot so as to be responsive to overheating of the element to switch off or otherwise interrupt the electrical power supply to the element. Such vessels are hereinafter referred to as being "of the aforementioned kind".

It is known to provide in such vessels a metal tray which rests on the bottom wall of the body immediately below the heating element, with the intention of protecting the body, to some extent, from thermal damage in the event of the heating element bending or becoming displaced towards the bottom, but such trays do not provide effective protection. For instance, if the thermally responsive device fails, it is possible for the element to overheat to such an extent that the body melts and starts to burn in spite of the presence of the protective metal tray or like insert below the element.

If the vessel is in the form of a kettle, the kettle body can be arranged so that it is very difficult to empty the vessel, by trapping a certain quantity of liquid within the body, in an endeavour to ensure that there is always a minimum amount of liquid in the vessel which minimum amount is sufficient to cover the element. However this minimum amount of quantity may be boiled away if the thermal cut-out or other protective device fails to operate, and thereafter the element will overheat.

Similarly it is possible to provide, at considerable extra cost, a supplementary safety device, e.g. a switch off device responsive to the level of liquid in the vessel, in order to try and protect the element, but likewise such devices can become inoperative, e.g. due to a build-up of scale or other deposits within the vessel, and again the element can overheat if the safety cut-out or other thermally sensitive device fails to operate.

We have tried, experimentally, reducing the thickness of the element wire to reduce the burnout time of the element so as to reduce the period during which the vessel body is heated if the thermally responsive device fails. However, reducing the thickness of the element wire seriously reduces the service life of the element and makes the element unacceptably prone to failure in normal use of the vessel.

What is needed is means to protect or otherwise prevent the body from starting to burn in the event of the vessel being operated with insufficient liquid in the vessel.

According to the present invention there is provided a vessel of the aforementioned kind wherein the element is disposed within a metal surround comprising a lower part which is disposed substantially between the element and the base of the vessels body, and an upstanding part which substantially surrounds the head of the immersion heater; wherein the head comprises a main panel, to which the element is secured, a flange of the periphery of the main panel, and a cylindrical externally threaded extension which extends through apertured portions of the upstanding part and the hollow body; and wherein thermal insulating means is interposed between the flange and said apertured portions.

It has been found that the head remains in its correct orientation even if overheating is prolonged to the extent that the extension becomes heated to a temperature above the temperature at which the body melts or softens to a plastic state.

The insulating means preferably comprises an insulating part of rigid or semi-rigid form interposed radially between the extension and the apertured portion of the body and said insulating part preferably has a higher melting or softening temperature than the body. The insulating means in combination with the provision of the metal surround in the vessel gives sufficient protection to the body to prevent the latter starting to burn, even when element wire of at least usual thickness is employed.In particuiar the head is securely located in the vessel and is supported in cantilever manner upon that portion of the body which is afforded thermal protection by the upstanding part and the insulating means, so that even during overheating the immersion heater is reliably supported to withstand the cantilever loads caused by the element, thereby substantially preventing displacement of the immersion heater.

The dished member is preferably a push fit in the body and has a sharp brim which engages the body to obviate rattles and displacement of the dished member, and preferably has feet so that most of the dished member is held clear of most ol the interior surface of the body to minimise the conduction of heat from the dished member to the body.

The brim is preferably arranged so as to hinder the flow of liquid from the space between the body and the dished member as the vessel is emptied, so that a small amount of liquid will usually remain as a thermal buffer between the lower portion and the bottom of the body.

The heat shield member preferably includes locating means which comprises at least one flange which engages or is proximal to interior surface of the body, and preferably includes extensions which extend both laterally, to overlap upstanding portions of the dished member, and upwardly to above the level of the highest part of the immersion heater.

The insulating part may comprise a cylindrical collar or ring, or may comprise one or more extensions of a clamping ring which is engaged around the extension.

The invention will be described further by way of example with reference to the accompanying drawings, wherein: FIGURE 1 shows a vertical cross section through a lower part of a vessel constructed in accordance with the invention; and FIGURE 2 is a plan diagram of said lower part.

The vessel is substantially similar to that described in our co-pending Application No.

8119895 with reference to FIGURE 4 of that Application.

The aforementioned application discloses a vessel in the form of a water heating jug having a plastics body on which is mounted an electrical heating element assembly together with a switch assembly and a steam responsive mechanism for actuating the switch assembly when the liquid in the vessel boils. The switch assembly includes a boil dry cut-out which is responsive to overheating of the heating element. Within a lower portion of the body is a metal tray which rests on the bottom of the body and is disposed immediately below a heating portion of the heating element.

The present embodiment likewise includes a moulded plastics body 10 having secured thereto a heating element assembly 12, a switch assembly 13 and a steam responsive mechanism 14, only part of which is indicated in broken lines.

The heating element assembly 12 includes a heating element having two cool end portions 25 which extend downwards to a low level heating portion 23.

In the present invention the vessel is provided with a metal surround comprising a heat shield member 60 and a dished member 50. The latter comprises a substantially flat lower portion 51 located parallel to the bottom 1 7 of the body 10 by feet 56, and an upstanding portion 52. The latter has a sharp brim 52A which is a push fit in the body, so as to hinder water leaving a space 59 when the vessel is tilted to pour water. A cut-out 58 is provided adjacent the member 60 to admit water to the space 59. The members 50 and 60 are formed from aluminium sheet, or, preferably, thin stainless steel sheet. A mounting aperture is provided in a portion of the member 60, and sealing means, in the form of ring seals 53A, B, is provided to abut both sides of said portion around the aperture in the member 60.The latter has lateral extensions 61 which overlap the portion 52; a vertical extension 62 providing a top flange 63 which rests on an internal ledge surface 64 in the body; and a bottom flange 65 close to the bottom 1 7. The flange 63 serves as locating means, and the flange 65 may abut the bottom 17 to serve also as part of the locating means, for the heat shield member.

A slightly larger diameter mounting aperture is provided in a portion of a sidewall'15 of the body.

A flange 20 around a main panel of a head 21 of the heating element assembly 12, and a clamping ring 22 are arranged to clamp the sidewall 15, the member 60 and the sealing means 53A, B therebetween as shown, whereby to support the element assembly and the member 60 on the wall 1 5, so that the element is supported in cantilever manner.

The sealing means forms part of thermal insulating means which further comprises an insulating part in the form of a narrow cylindrical extension 54 of the ring 22 or a narrow insert ring, which part 54 is disposed as a thermal shield radially between the wall and an externally threaded cylindrical extension 55 of the head 21, which extension 55 extends through the apertures, the sealing means and the insulating means for engagement by the clamping ring.

The heating portion 23 is interrupted by an intermediate part 26 which is raised slightly relating to the heating portion and is secured to the main panel of the head 21 to produce a hot spot 24, and within the switch assembly 1 3 there is a thermally responsive device which is actuable by the hot spot 24 reaching a predetermined temperature to interrupt the supply of eiectricity to the heating element, in known manner.

Referring to FIGURE 2, it can be seen that the three feet 56 are angularly offset from raised protuberances 66, provided to support the heating portion 23, in the event of the heating portion 23 being distorted by heat. Also, the bottom flange 65 has substantially the same dimensions as the bottom portion of the cut-out 58 whereby to shield the bottom 1 7 from heat radiated from the portion 23 and the head 21.

During assembly of the vessel, the dished member 50 is pushed into the bottom of the body 10 so that the cut-out 58 leaves the mounting aperture free from obstruction; and then the element assembly together with the sealing means and heat shield member 50 in situ upon the extension 55 are simply insulated into the vessel and easily manoeuvred to insert the extension into the mounting aperture ready to accept the ring 22.

The seals 53A, B and the insulating means may be made from any suitable materials of low thermal conductivity (compared with brass) and relatively high melting point (compared with the body material). For example, the seal 53A may be of a heat resistant soft silicone rubber material, the ring 53B may be of a harder nitrile rubber material of lower melting point, and the ring 22 and extension 54 of a hard plastics material of a lower melting point than the silicone rubber material. If a separate insert ring is employed, the ring may be of stainless steel or ceramic material.

The inside surfaces of the surround are preferably polished to reflect heat back to the element under boil dry conditions, and a perforate reflective lid may be provided on the pan.

In this embodiment approximately 30% of the upstanding portion is disposed above the level of the heating portion 23 of the heating element.

The two-part surround and the insulating means described are inexpensive to make and particularly simple to fit; do not give rise to secondary problems such as rattles and softening and distortion of the body; gives ample protection for the body especially the portion on which the immersion heater is supported, as described, substantially in cantilever manner; and enables durable element wire 60 (e.g. of 28 gauge instead of 30 gauge) to be employed.

Claims (7)

1. Avessel-ofthe aforementioned kind wherein the element is disposed within a metal surround comprising a lower part which is disposed substantially between the element and the base of the vessels body, and an upstanding part which substantially surrounds the head of the immersion heater; wherein the head comprises a main panel, to which the element is secured, a flange at the periphery of the main panel, and a cylindrical externally threaded extension which extends through apertured portions of the upstanding part and the hollow body; and wherein thermal insulating means is interposed between the flange and said apertured portions.

2. A vessel as claimed in Claim 1 wherein the insulating means is constituted, at least partially, by sealing means providing seals between the flange and the upstanding part and between the upstanding part and the apertured portion of the hollow body.

3. A vessel as claimed in Claim 1 or 2 wherein the upstanding part is in the form of a heat shield member comprising at least one flange, spaced apart from the apertured portion, which engages or is proximal to the interior surface of the body.

4. A vessel as claimed in Claim 1, 2 or 3 wherein the lower part is in the form of a dished member, which is a push fit in the body has a peripheral upstanding portion substantially surrounding the element, and has a brim which engages the body.

5. A vessel as claimed in Claim 4 as appended to Claim 3 wherein the heat shield member includes extensions which extend laterally from the apertured portion to overlap the upstanding portions of the dished member.

6. A vessel as claimed in Claim 5 wherein the upstanding part has a flange at the bottom of an extension which projects downwards through a cut-out in the dished member.

7. A vessel substantially as hereinbefore described with reference to the accompanying drawings.