GB2304468A

GB2304468A - Use of heat transfer tape with thermal controls for kettles etc

Info

Publication number: GB2304468A
Application number: GB9517094A
Authority: GB
Inventors: R A O'neill; Kevin Edwin John
Original assignee: Otter Controls Ltd
Current assignee: Otter Controls Ltd
Priority date: 1995-08-21
Filing date: 1995-08-21
Publication date: 1997-03-19
Anticipated expiration: 2015-08-21
Also published as: DE69607630D1; GB2304468B; EP0846329B1; DE69607630T2; WO1997007319A1; EP0846329A1; HK1001850A1; CN1200194A; AU6826696A; GB9517094D0

Abstract

Thermal controls for electric kettles and the like commonly have a bimetallic switch-operating element juxtaposed in heat transfer relationship with the heating element of the kettle, and a heat sink compound in grease or paste form is commonly introduced between the bimetallic element and the heating element. The heat sink compound is relatively costly and is messy and difficult to apply with precision in an automatic manufacturing process. To overcome these problems which have plagued the industry for many years, the present invention proposes to use a pad or patch of self-adhesive heat transfer tape rather than the heat sink compound, such heat transfer tapes previously having been used only in the electronics industry for heat sinking of power transistors and the like.

Description

IMPROVEMENTS RELATING TO THERMAL CONTROLS This invention concerns improvements relating to thermal controls and more particularly concerns thermal controls for electrically powered liquid heating vessels such as kettles, jugs, pots, pans, urns, laboratory and industrial equipment and the like.

It is well known to provide a thermal control for the electric heating elements of electric kettles, hot water jugs and the like, the control serving to protect the heating element and the appliance against the effects of the appliance being switched on inadvertently without sufficient liquid in the appliance or being allowed to boil dry. It is likewise well known to employ bimetallic elements as thermally-responsive actuators in such controls, the bimetallic elements being customarily arranged to open a set of electrical contacts so as to disconnect the heating element from its power supply in response to a sensed overtemperature condition. Exemplary thermal controls employing bimetallic elements as switch actuators are disclosed in GB 1401954, GB 1470366, GB 2117568, GB 2176055, GB 2194099 and WO 92/16003.

Snap-acting bimetallic elements have been developed to overcome the problems of arcing between switch contacts and contact erosion which occurs when switch contacts are opened slowly. Many different forms of snap-acting bimetallic elements are known, but all are generally characterized by a dished configuration which can move into an opposite curvature with a snap-action.The dished configuration, however, gives rise to a problem as regards transferring heat efficiently from the heating element into the bimetallic element, and to meet this problem it has been common to provide a portion of the heating element, or more precisely the heating element head plate, with a curved configuration complementary to that of the bimetallic element so that the heating element and the bimetallic element nest together in relatively good thermal contact; such an arrangement is disclosed in GB 2176055 for example. In this connection, the foregoing reference to the heating element head plate will be understood to refer to the common heating element configuration in which the heating element proper, that is to say the part which heats up when the heating element is powered, is mounted to a head plate which serves for the mounting of the heating element in a vessel.The heating element proper is commonly of a tubular sheathed wire wound configuration with a mineral insulator packed into the tubular sheath, and commonly has a so-called hot return portion which is affixed to the heating element head plate on the wet side thereof, that is to say the side which will be in contact with the liquid being heated, the hot return portion defining on the opposite, dry side of the element head plate a location having a temperature approximating to that of the heating element proper which serves as the location whereat the bimetallic element senses the heating element temperature.

In addition to configuring the element head plate to conform to the dished configuration of the snapacting bimetallic element, it has furthermore been conventional to employ a heat sink compound as a heat transfer medium between the heating element head plate and the bimetallic element. The heat transfer compound is a grease, conventionally silicone based, with proprietary filling to enhance its thermal conductivity. The heat transfer compound is relatively costly and is difficult to handle economically or automatically. It is difficult to remove once applied and tends to lose its efficiency over time as the oils in the grease slowly dry out.

The material has to be applied at the time when the heating element and its bimetallic protective control are assembled together, which means that it generally falls to the manufacturers of electric kettles, hot water jugs and the like, who have the task of assembling the heating element and its control to the vessel body, to apply the heat sink compound.

Appliance manufacturers generally do not have the skill to apply optimum amounts of heat sink compound in optimum positions and this leads to excessive use of heat sink compound and impairment of the performance of the element protector control.

The present invention resides in the realization that the solution to the abovementioned problems arising out of the use of grease type heat sink compound, which problems have beset the industry for many years without any solution being forthcoming, is to use self-adhesive heat transfer tape, such as is commonly used in the electronics industry for assembling electronic components to heat sinks, instead of the grease compound.

According to the present invention, therefore, a control for a liquid heating apparatus which incorporates a bimetallic switch-actuating element arranged to be juxtaposed with the liquid heating apparatus in thermal transfer relationship therewith further includes a patch of heat transfer tape adhered to that surface (the facing surface) of the bimetallic element which is to face the liquid heating apparatus in use.

The present invention also extends to a liquid heating apparatus provided with a control as aforesaid and with the patch of heat transfer tape sandwiched between a surface of the apparatus, particularly though not exclusively the dry side of a head plate of an electrically powered heating element of the apparatus, and the facing surface of the bimetallic switch-actuating element of the control.

Furthermore, the invention also extends to a method of assembling a control as aforesaid or a liquid heating apparatus as aforesaid provided with such a control, the method including the step of adhering a patch of heat transfer tape to the facing surface of the bimetallic switch-actuating element of the control.

Thermal controls for liquid heating apparatuses are also known in which the bimetallic switchactuating element of the control is mounted behind a thermally-conductive mounting plate or cover plate, formed of aluminium for example, and one such control is disclosed in WO 92/16003. In a modification of the control, the liquid heating apparatus and the method of assembly above recited, a patch of heat transfer tape is adhered to the bimetallic element of such a control as is just mentioned so as to enhance the conduction of heat from the mounting plate to the bimetallic element, and/or is adhered to the facing surface of the mounting plate, that is to say that surface of the mounting plate which faces the liquid heating apparatus in use.

Whilst the preference is to adhere the heat transfer tape to the bimetallic element of the control, and/or to the mounting plate of such a control as is discussed immediately above, it would be possible for the heat transfer tape to be adhered instead to the surface of the liquid heating apparatus, particularly but not exclusively to the dry side of the head plate of an electrically powered heating element of the apparatus, at a location where it will be effective to enhance the transfer of heat from the apparatus to the bimetallic element of the control. The present invention also extends to this modification, though such a modification is not presently preferred since it places the onus upon the appliance manufacturer to fit the patches of heat transfer tape, whereas it is considered to be preferable that they do not have this task, It is a relatively simple matter to modify the automatic production apparatuses that are used for the manufacture of bimetallic controls for liquid heating apparatuses so that a patch of heat transfer tape is automatically adhered to the facing surface of the bimetallic element. The control with the patch applied would then be shipped to the appliance manufacturer who would then assemble it into the appliance without the need to apply a heat transfer grease.

As aforementioned, heat transfer tape is readily available, having been used heretofore in the assembly of electronic components such as power transistors to their heat sinks. It can be cut to shape to suit whatever configuration of bimetallic element is employed in the control. Heat transfer tape is available in a range of thicknesses and the selection of an appropriate tape thickness to suit a particular application is a simple matter. Suitable heat transfer tape is available from Warth International Ltd. of East Grinstead, Sussex, England whose products include SemrexTM heat transfer material which has a 99% carbon composition and a thermal conductivity approaching that of silicone grease.

The present invention is particularly, though not exclusively, applicable to the X1 control manufactured by us, this control being substantially as described in GB 2194099 with particular reference to Figures 3A, 3B and 3c of the drawings thereof. An exemplary embodiment of the present invention, which requires no further description, is such an X1 control having a patch of SemrexTM heat transfer tape of appropriate thickness adhered to the facing surface of the bimetallic element of the control.

Having thus described the present invention by reference to particular examples, it is to be appreciated that modifications and variations are possible without departure from the spirit and scope of the invention as set forth in the appended claims.

For example, whereas the invention has been described in connection with the application of bimetallic controls for liquid heating vessels, further application of the invention for example to controls incorporating PTCR (positive temperature coefficient of resistance) elements might be possible.

Claims

CLAIMS:

1. The use of heat transfer tape, rather than a heat sink compound in grease or paste form, for enhancing the thermal transfer capability between an apparatus and a thermal control for the apparatus.

2. A control for a liquid heating apparatus, said control including a bimetallic element arranged to be juxtaposed with the liquid heating apparatus in thermal transfer relationship therewith, and a pad or patch of heat transfer tape adhered to that surface of the bimetallic element which is to face the liquid heating apparatus in use.

3. A control for a liquid heating apparatus, said control including a bimetallic element arranged to be juxtaposed with a mounting plate or cover plate which in turn is to be juxtaposed with the liquid heating apparatus in thermal transfer relationship therewith, and a pad or patch of heat transfer tape adhered to that surface of the mounting plate or cover plate which is to face the liquid heating apparatus in use and/or sandwiched between the bimetallic element and the mounting plate or cover plate.

4. A liquid heating apparatus provided with a control as claimed in claim 2 or 3.

5. A liquid heating apparatus provided with a control incorporating a thermal sensor in heat transfer relation with a surface of the apparatus, and a pad or patch of heat transfer tape provided between the thermal sensor and the said surface of the apparatus.

6. A liquid heating apparatus as claimed in claim 5 wherein the pad or patch of heat transfer tape is adhered to a surface of the thermal sensor.

7. A liquid heating apparatus as claimed in claim 5 wherein the pad or patch of heat transfer tape is adhered to a surface of the apparatus.

8. A liquid heating apparatus as claimed in any of claims 5 to 7 wherein said thermal sensor comprises a bimetallic element.

9. A liquid heating apparatus as claimed in any of claims 4 to 8 wherein the control is arranged so that the thermal sensor thereof is operatively juxtaposed with the head plate of an electric heating element of the apparatus.

10. A method of assembling a thermally-responsive control to a liquid heating apparatus, said method including the step of adhering a pad or patch of heat transfer tape to a surface of the apparatus which is to be juxtaposed with a thermally-responsive sensor of the control and/or to a surface of the control and/or of the sensor thereof which is to be subject to heat conducted from the liquid heating apparatus.