GB2429285A

GB2429285A - Temperature indicators

Info

Publication number: GB2429285A
Application number: GB0517036A
Authority: GB
Inventors: Vincent Joseph Garvey
Original assignee: Strix Ltd
Current assignee: Strix Ltd
Priority date: 2005-08-19
Filing date: 2005-08-19
Publication date: 2007-02-21
Also published as: GB0517036D0

Abstract

A cooking utensil comprises a base 4 and a thermally sensitive actuator 14 arranged in thermal contact with a peripheral wall 6 of the utensil 2. The actuator 14 is operatively coupled to an indicator 36 which may provide a visual and/or an audible effect. The actuator 14 may comprise a snap acting bimetallic actuator.

Description

- - 2429285

TEMPERATURE IND I CATORS

The present invention relates to temperature indicators and in particular to temperature indicators for cooking utensils such as pans, more particularly frying pans.

To fry food in oil in a frying pan or other pan, the oil should be preheated to about 190 C. Oil temperature can be checked before the food is fried, for example by placing a small piece of food in the oil and observing the degree of bubbling, agitation or the sound generated. This is inconvenient, however, as it requires the presence of a relatively large amount of oil in the cooking utensil and requires a certain degree of skill on behalf of the user. In addition to the above, it is sometimes desirable, for example for health reasons, to cook food without oil, for example in non- stick cookware.

To overcome this problem it has been proposed, for example in US Patent 6, 551,693 to provide the base of the cooking utensil with a region of thermochromic material which changes colour at a predetermined temperature corresponding to the desired cooking temperature. However, there are a number of disadvantages to such systems. The contrast in colour can be limited, and the range of temperatures over which the colour changes can be wide. Moreover, the precise point at which the colour change occurs may be difficult to determine and the utensil must be monitored continuously.

Another proposal, shown in US Patent 5,934,181 is to incorporate an infrared sensor in the handle of the utensil which receives infrared radiation from the base of the utensil and converts this into an electrical signal. However, this is a complicated system and one which is not well suited to the treatment which cooking utensils receive in use. For example, they are often subjected to high temperatures. Moreover they must be washed, very often in dishwashers which present a very aggressive environment.

There is thus a need for a system which can provide a clear visual and/or audible indication that a desired temperature has been reached and which can be easily detected at some distance from the utensil without the need for close monitoring.

It has been recognised by the Applicant that in any given construction of cooking utensil there is an easily determined, fixed, relationship between the temperature of the hottest point at the centre of the base of the utensil and that of the peripheral wall of the utensil.

For example, in a typical 24 cm diameter aluminium frying pan with a wall thickness of about 2.5 to 3 mm when the temperature at the centre of the pan is 190 C, the temperature at the side wall of the pan is about 110 C.

It should therefore be possible to detect the temperature of the cooking surface of the pan at the periphery of pan.

From a first aspect, therefore, the present invention provides a cooking utensil comprising a base and comprising a thermally sensitive actuator arranged in thermal contact with a peripheral wall of the utensil, the actuator being operatively coupled to an indicator.

Thus a thermally sensitive mechanical sensor can be arranged on a peripheral wall of the utensil and be coupled to an indicator such that when the actuator operates upon reaching a predetermined temperature it activates the indicator giving the user an indication that the utensil has reached the requisite temperature.

The actuator is preferably arranged in a housing to protect it from external damage.

The indicator may be a visual and/or an audible indicator. In a simple embodiment the indicator could comprise a flag, button or the like which deploys to indicate that the temperature has been reached. Thus the indicator could be mounted in the actuator housing and project therefrom on deployment. Thus, for example, the button or the like normally flush with the housing can be made to pop up into a visible position upon operation of the actuator.

Preferably the indicator is coupled to the actuator so as to amplify the movement of the actuator.

In a particularly preferred embodiment, the indicator is formed as part of, or coupled to, a pivotal lever acted on by the actuator, with the pivot axis of the lever preferably being arranged nearer the actuator than it is to the indicator to effect the necessary amplification of movement.

The actuator may comprise, for example, a shape memory alloy. Preferably, however, it comprises a bimetallic actuator, more preferably a snap acting bimetallic actuator.

The actuator is preferably of the type comprising a central leg which preferably mounts the actuator to the utensil. Examples of such actuators are shown, for example, in GB1542252.

To facilitate this mounting, a spacer may be used to space the main body of the actuator from the utensil wall. It has been found advantageous to form the spacer from a thermally conductive material such as copper or, more preferably, aluminium to improve heat transfer into the actuator. In some embodiments, the spacer may be formed integrally with the utensil wall.

The operating temperature of the actuator may be variable in order to vary the temperature at which the indicator operates.

In one embodiment this can be achieved by applying a force to the actuator either in or opposite its direction of operating movement to either increase or decrease its operating temperature. For example an adjustable force may be applied to a bimetallic actuator directly or indirectly, for example by a spring acting on a lever coupled to the actuator.

Preferably the coupling of the actuator to the indicator is such that the indicator is self-resetting.

This is advantageous as it does not require a user to have to remember to reset it. Where, as in the preferred embodiment, a snap-acting bimetallic actuator is employed the actuator itself will be self-resetting.

It is then sufficient for the indicator to follow the movement of the actuator. Conveniently for example the actuator may lift part of the indicator when it operates and allow the indicator to fall back down under gravity.

Alternatively a spring bias may be provided. This could be provided by a spring arranged to apply an adjustable force to the actuator to allow its operating temperature to be varied. Of course it is to be understood that for the actuator to be self-resetting its reset temperature will be above ambient temperature.

It is important that the actuator operates in response to the temperature of the base of the cooking utensil rather than extraneous heat sources, such as a gas flame, or else it may operate prematurely.

Preferably, therefore, a heat shield is provided between the actuator and the heat source. The shield may form part of the actuator housing, or an integral part of the utensil, for example the handle, or it can be formed as a separate piece of material attached to the utensil.

The shield may be formed, for example, of aluminium or stainless steel.

Another potential concern is the presence of water around the actuator. Clearly the utensil will have to be washed, especially in dishwashers, so it is preferable that the area around the actuator or the actuator housing is free-draining. Retention of water will cause the thermal sensor to heat more slowly than intended and operate too late. The provision of one or more slots or drain holes arranged to avoid the retention of water around the actuator has been found to overcome this problem.

Moreover, to ensure that there is no degradation due to corrosion it has been found advantageous to choose materials, e.g. alloys, for the actuator which are resistant to corrosion.

Hob top utensils can sometimes be placed in an oven and as such be subjected to temperatures up to 250 C.

This can result in a shift in the calibrated set point of the thermal actuator. This problem can be dealt with by using a bimeta ic actuator whose low expansion side rM) is made from Invar38% NI) and its high expansion side is made from l9Ni/7Cr/bal Fe alloy. Moreover, if during its manufacture this actuator is subjected to a temperature of at least 300 C it will remain stable even when subjected to overheating in use. This actuator construction will also be corrosion resistant.

The actuator may be mounted in any convenient location on the utensil periphery. In one arrangement, however, it is arranged adjacent a handle of the utensil which may then form part of the actuator housing.

It will be appreciated that there are a number of ways of mounting a handle to a cooking utensil. One common method used is to use two spaced apart brackets, typically rivetted to the utensil body. The brackets may be formed as part of the handle. With such an arrangement the actuator can be mounted between the brackets.

In another arrangement, a mounting boss is fixed to the utensil wall and the handle fixed to the boss. In this form of construction an outer sleeve is generally used to conceal the construction and in this case the blade can be mounted directly to the boss or to the sleeve.

Some preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a first embodiment of the invention; Figure 2 shows a modified version of the embodiment of Figure 1; Figure 3 shows the mounting arrangement of the actuator of Figures 1 and 2; and Figure 4 shows a further embodiment of the invention.

With reference to Figure 1, a cooking utensil 2, in particular a frying pan, has a base 4 with a side wall 6. Attached to the side wall 6 is a handle 8. As shown in Figure 3, the handle 8 is attached to the wall 6 through a mounting bracket 10 which is secured to the wall 6 by a pair of rivets 12.

A thermally sensitive bimetallic actuator 14 is attached to the side wall 6 of the pan by a screw or rivet 16. The actuator 14 is of the type described in GB1542252 and comprises a generally circular body 18 with a centrally released tongue 20 through which the actuator 14 is mounted to the pan wall 6. In fact, the actuator 14 is mounted on a thermally conductive spacer 22 of copper, aluminium or the like so as to accommodate the movement of the actuator in use.

The periphery 24 of the actuator 14 lies over one end 26 of a lever 28 which is pivotally mounted about a spindle 30. The spindle 30 is mounted in the side walls 32 of the handle mounting bracket 10.

The other end 34 of the lever 28 has an upstanding indicator 36 which lies below an aperture 38 formed in the upper surface 40 of the handle 8.

In order to protect the actuator 14 from heat other than that conducted through the base 4 and wall 6 of the pan 2 a thermal shield 42, for example of copper, or less favourably stainless steel, is placed between the side wall 6 and the handle 8 to prevent heat being directed on to the actuator 14.

The shield 42 and the handle 8 form a housing 44 for the actuator 14 and indicator 36. A drain hole 46 is provided at the base of the shield 40 to allow any water which enters the housing 44 to drain away. Other drain holes (not shown) are arranged around the housing 44 to ensure that water can drain therefrom irrespective of the position of the utensil, for example when it is in a dishwasher.

In operation, when the pan 2 is placed on a hot plate or hob surface, heat will be conducted through the base 4 and wall 6 of the pan and thence through the spacer 22 to the actuator 14. When the actuator reaches a predetermined temperature (which bears a predetermined relationship to the temperature of the base of the pan and can be determined empirically), it will reverse its curvature with a snap action. By virtue of the interengagement of the periphery 24 of the actuator 14 and the arm 26 of the lever 28, the lever 28 will then pivot around the spindle 30 such the indicator 36 of the lever 28 projects up through the aperture 38 in the upper surface 40 of the pan handle so as to give a visible indication that the pan has reached the appropriate temperature for frying food. This position is shown in dotted lines in Figure 1.

As the spindle 30 is nearer the actuator 14 than the indicator 36, the movement of the actuator 14 (typically about 2mm) will be amplified, in this case by about a factor of three.

A spring loading may be applied to the lever 28 to bias it towards its inoperative position (shown in solid lines in Figure 1) such that when the pan temperature falls once more and the bimetallic actuator 14 resets the lever 28 will return under spring force to its restored position. However this is not essential and its own weight may be sufficient for it to fall back.

In addition to giving a visual indication of the pan reaching temperature (which may be augmented by making the indicator 36 brightly coloured, for example) the arm 34 will strike the handle to give an audible indication. Additional audible indicators may be added, for example in the form of a bell which is struck by the lever 28 as it rotates.

The embodiment of Figure 1 is arranged to operate at a single operating temperature, typically at a temperature corresponding to a temperature of about 1900 at the centre of the base 4. The embodiment of Figure 2 shows, schematically, an arrangement for varying the temperature which the actuator 14 will operate and thus at which the indicator 36 will appear.

In this embodiment, a variable spring force is applied to the lever 28 by a wire spring 50 which is mounted to a lug 52 provided on the end 26 of the lever 28, around the spindle 30. The spring 50 may be deflected to one of a number of positions against a scale 54. As the spring 50 is deflected, it increases the force of the lever 28 against the periphery 24 of the actuator 14. As such, the actuator 14 will have to reach a higher temperature than its normal operating temperature in order to overcome the spring force and operate to deploy the indicator 36. In this way, a variable temperature setting can be obtained. The spring 50 will also act to bias the indicator towards its inoperative position when the bimetal 14 resets so that the indicator is self-resetting.

The wire arm 50 may be retained in one of a plurality of positions in any number of ways, for example by friction or engagement with the scale or by being held in one of the plurality of detents provided on the handle.

Figure 4 shows an alternative embodiment of the invention.

In this embodiment, a pan 60 has a handle 62 which is attached to pan 60 through a mounting block 66 attached to the side wall 64 of the pan 60. The handle 62 is provided with a bore 68 which receives a mounting screw 70 which engages a threaded bore 72 in the mounting block 66 in order to attach the handle 62. A spacer sleeve 74 engages with a shoulder 76 provided at the forward end of the handle so as to cover and enclose the space between the handle 62 and the side wall 64 of the pan 60.

In this embodiment, a thermally sensitive bimetallic actuator 78, preferably of the type described above, is attached to the sleeve 74 through a thermally conductive spacer 80. The peripheral part 82 of the actuator is arranged under a shaft 84 which extends through the mounting block 66 and which is formed with an indicator button 86 at its upper end.

In this embodiment, therefore, when the actuator operates through thermal conduction through the pan 60 and the sleeve 74, it will push the indicator button 86 upwardly to a visible position (shown in dotted lines in the Figure) to give an indication that the pan 60 has reached the desired cooking temperature. When the bimetallic actuator 78 resets after cooling down, the shaft and indicator 84,86 will fall back down. The indicator arrangement is therefore self-resetting.

As in the earlier embodiment the sleeve 74 may be provided with one or more drain openings to allow water which may enter the sleeve to escape thereby preventing corrosion of the actuator its mounting. Also, the sleeve 74 may be adapted so as to make thermal contact with the pan over a greater surface area to improve heat transfer into the actuator 78. It may, for example, have a tongue which extends over an area of the pan wall 64.

In the embodiments described above, the actuator is preferably made with a low expansion side made from Invar (38w Ni) and its high expansion side made from 19 Ni/7Cr/bal Fe alloy.

- 10 - It will be appreciated that various changes may be made to the embodiments described without departing from the scope of the invention.

For example, other forms of bimetallic actuator or thermally sensitive actuator may be used than those disclosed For example, a shape memory alloy may be used instead of a bimetallic actuator. Also, any other form of thermally sensitive mechanical actuator could be used.

In addition, it is not essential that the actuator 14 be located adjacent the handle 8. The actuator 14 and indicator 36 could be positioned in a housing elsewhere on the periphery of the utensil, for example displaced 90 or 180 from the handle.

The present invention is applicable to both coated (i.e. non-stick) and traditional non-coated cookware.

Claims

- 11 - Claims 1. A cooking utensil comprising a base and comprising a

thermally sensitive actuator arranged in thermal contact with a peripheral wall of the utensil, the actuator being operatively coupled to an indicator.
2. A cooking utensil as claimed in claim 1 wherein the indicator provides a visual and/or an audible effect.
3. A cooking utensil as claimed in claim 2 wherein the indicator comprise a flag, button or the like.
4. A cooking utensil as claimed in any preceding claim wherein the actuator is mounted in a housing and indicator is mounted in the housing so as to be deployable therefrom.
5. A cooking utensil as claimed in any preceding claim wherein the indicator is coupled to the actuator so as to amplify the movement of the actuator.
6. A cooking utensil as claimed in any preceding claim wherein the indicator is formed as part of, or coupled to, a pivotal lever acted on by the actuator.
7. A cooking utensil as claimed in any preceding claim wherein the actuator comprises a bimetallic actuator, preferably a snap acting bimetallic actuator.
8. A cooking utensil as claimed in claim 7 wherein the actuator is of the type comprising a central leg which mounts the actuator to the utensil.
9. A cooking utensil as claimed in any preceding claim wherein the actuator is spaced from the wall of the utensil by a thermally conductive spacer.

- 12 -
10. A cooking utensil as claimed in any preceding claim comprising means to vary the operating temperature of the actuator.
11. A cooking utensil as claimed in claim 10 wherein said means comprises means for applying a variable force to the actuator.
12. A cooking utensil as claimed in claim 11 comprising a variable force spring acting on a or the lever coupled to the actuator.
13. A cooking utensil as claimed in any preceding claim wherein a heat shield is provided between the actuator and an extraneous heat source.
14. A cooking utensil as claimed in claim 13 wherein said shield extends between a handle and the utensil wall below the actuator.
15. A cooking utensil as claimed in any preceding claim wherein the area around the actuator is free-draining.
16. A cooking utensil as claimed in any preceding claim wherein said actuator is made from materials which are resistant to corrosion.
17. A cooking utensil as claimed in any preceding claim wherein said actuator comprises a bimetallic actuator (grM) whose low expansion side is made from InvarA(389 NI) and its high expansion side is made from l9Ni/7Cr/bal Fe alloy.
18. A cooking utensil as claimed in any preceding claim wherein the actuator is arranged adjacent a handle of the utensil.

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19. A cooking utensil as claimed in claim 18 wherein the indicator is arranged to protrude from the handle.
20. A cooking utensil as claimed in claim 18 or 19 wherein the handle is attached to the utensil body by a mounting brackets and wherein the actuator is mounted between the mounting brackets.
21. A cooking utensil as claimed in claim 18 or 19 wherein a mounting boss is fixed to the utensil wall and the handle fixed to the boss, and the actuator mounted to the boss.
22. A cooking utensil as claimed in claim 21 comprising an outer sleeve arranged around the boss, and wherein the actuator is mounted, instead, to the sleeve.
23. A cooking utensil as claimed in any preceding claim wherein said indicator is self-resetting.
24. A cooking utensil as claimed in claim 23 wherein said actuator comprises a snap-acting bimetallic actuator.
25. A cooking utensil as claimed in claim 23 or 24 wherein the indicator is arranged to reset under gravity.
26. A cooking utensil as claimed in claim 23 or 24 comprising a spring bias for resetting the indicator.
27. A cooking utensil as claimed in claim 26 wherein said spring bias is provided by means to vary the operating temperature of the actuator.