CA1255730A - Kettle safety fuse - Google Patents
Kettle safety fuseInfo
- Publication number
- CA1255730A CA1255730A CA000491792A CA491792A CA1255730A CA 1255730 A CA1255730 A CA 1255730A CA 000491792 A CA000491792 A CA 000491792A CA 491792 A CA491792 A CA 491792A CA 1255730 A CA1255730 A CA 1255730A
- Authority
- CA
- Canada
- Prior art keywords
- fuse
- kettle
- heating element
- safety
- temperature
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- A—HUMAN NECESSITIES
- A47—FURNITURE; DOMESTIC ARTICLES OR APPLIANCES; COFFEE MILLS; SPICE MILLS; SUCTION CLEANERS IN GENERAL
- A47J—KITCHEN EQUIPMENT; COFFEE MILLS; SPICE MILLS; APPARATUS FOR MAKING BEVERAGES
- A47J27/00—Cooking-vessels
- A47J27/21—Water-boiling vessels, e.g. kettles
- A47J27/21008—Water-boiling vessels, e.g. kettles electrically heated
- A47J27/21058—Control devices to avoid overheating, i.e. "dry" boiling, or to detect boiling of the water
- A47J27/21133—Control devices to avoid overheating, i.e. "dry" boiling, or to detect boiling of the water using a fusible material or a shape memory effect [SME] material
-
- A—HUMAN NECESSITIES
- A47—FURNITURE; DOMESTIC ARTICLES OR APPLIANCES; COFFEE MILLS; SPICE MILLS; SUCTION CLEANERS IN GENERAL
- A47J—KITCHEN EQUIPMENT; COFFEE MILLS; SPICE MILLS; APPARATUS FOR MAKING BEVERAGES
- A47J27/00—Cooking-vessels
- A47J27/004—Cooking-vessels with integral electrical heating means
Landscapes
- Engineering & Computer Science (AREA)
- Food Science & Technology (AREA)
- Fuses (AREA)
- Cookers (AREA)
Abstract
Case 2940 KETTLE SAFETY FUSE
ABSTRACT OF THE DISCLOSURE
A plastic bodied kettle having an inner brass bottom with an electric heating element supported thereby is provided with a thermo-sensitive electrical fuse for protecting the kettle by interruption of the heating element electrical supply on the occurrence of a boil-dry condition, or a "dry"
plug-in in the event that the safety thermostat fails to protect the kettle. This fuse is in addition to the safety thermostat that is normally provided, and is of particular value as a safety feature for a plastic kettle, the body of which is liable to melting or going on fire in the event that the safety thermostat should fail, with consequent safety hazard. The fuse is connected in series relation with one of the cold pins of the heating element, to assure rapid transferrence of heat to the fuse in the event of an unwonted temperature rise for the stated reasons.
ABSTRACT OF THE DISCLOSURE
A plastic bodied kettle having an inner brass bottom with an electric heating element supported thereby is provided with a thermo-sensitive electrical fuse for protecting the kettle by interruption of the heating element electrical supply on the occurrence of a boil-dry condition, or a "dry"
plug-in in the event that the safety thermostat fails to protect the kettle. This fuse is in addition to the safety thermostat that is normally provided, and is of particular value as a safety feature for a plastic kettle, the body of which is liable to melting or going on fire in the event that the safety thermostat should fail, with consequent safety hazard. The fuse is connected in series relation with one of the cold pins of the heating element, to assure rapid transferrence of heat to the fuse in the event of an unwonted temperature rise for the stated reasons.
Description
~l2557;~
Case 2940 KETTLE SAFETY FUSE
This invention is directed to an electric kettle and in particular to the provision of a fused circuit therefor.
It is well known to provide an electric Xettle with a fusing capability. In particular, in the United Kingdom it has been common practice to provide an over-current electrical fuse, which creates an open circuit upon the occurrence of an overload current. Such over-current protective fuses have generally been located in the kettle electrical receptacle, and as a consequence are not adapted to afford protection against the occurrence of overtemperature for other than that of fuse overheating due to the occurrence of an over-current.
In accordance with the present invention an electric kettle is provided with a thermally sensitive fuse having a predetermined operating temperature in excess of the normal operating temperature of the kettle when in a boiling condition. The fuse is connected in series relation with the electrical circuit supplying the heating element, being connected to one of the cold pins of the heating element by a solid, heavy gauge electricaL conductor possessing a good heat transfer characteristic. In operation, when ~25~;~73~
Case 2940 the kettle boils dry, or if the kettle is plugged-in when in a dry condition, in the absence of, or failure of the safety thermostat to open, the rise in temperature of the heating element beyond the usual temperature thereof associated with a water boiling condition transfers heat rapidly to the fuse element, causing it to fail and thereby create an open circuit condition for the heating element. The arrangement of the fuse element, in spaced isolation from the inner bottom of the kettle, ensures that the effects of radiant heat are minimal.
It will be understood that this fuse protection is additional to the required thermostat protection, which is the subject of safety regulation standards. However, such thermostats are not 100~
failsafe, and provision of the subject fuse provides a virtually foolproof safety back-up to the thermostat protective device, to prevent combustion of the kettle.
In the case of plastic bodied kettles, the greater safety, health and fire hazards which arise in the case of serious element overheat make the added protection of the subject fuse additionally valuable.
In selecting a suitable fuse due regard is had to ensuring that the fuse melting ("Blow") temperature exceeds normal operating temperatures by a significant amount, such as 100C, whilst also ensuring that the time required for the fuse to blow is significantly less than the time required for the plastic body of the kettle to melt or commence to burn.
In the matter of what are considered to be normal operating temperatures, evidently the normal operation of the kettle thermostat due to an overheat condition such as the kettle being plugged in while dry, or the kettle boiling dry should not cause the fuse to blow. In such an instance the temperature of 3~5~73~1 Case 2940 the fuse may rise by about 10C above normal boiling conditions.
It has been found that selection of a fuse in the range of about 190C to 220C affords a sufficient overheat margin to permit normal operation of the primary protective device, namely the safety thermostat, without a statistically large chance of the fuse being blow.
One fuse manufacturer recommends a minimum of 100C difference between normal operation of a fuse and the calibration or "blow" temperature of the fuse. Operating the fuse at less than 100C
difference from the "blow" temperature causes deterioration of the fuse and a shorter service life, whereby premature blowing occurs. The smaller the temperature difference, the shorter the working life of a fuse.
Further, it has been found that selection of a fuse operaiing in the noted temperature range of 190C to 220C assures that the fuse will blow within an operating time significantly less than the structural failure time characteristic of the kettle, namely the time required for the kettle to reach element open-circuiting failure, or in the case of a plastic kettle such as a polypropylene plastic bodied kettle, the onset of combustion of the kettle body.
It is important, in installing the subject thermal fuse, that the electrical conductor connecting the fuse element per se with the cold pin of the kettle heating element be of sufficient heat conducting capacity to ensure a low thermal gradient between heating element and fuse. This conductor is usually a rodded conductor.
Tests were carried out on a number of plastic bodied kettles to establish the possible ~;255~3~
Case 2940 existence of a self-protective function, such as element failuxe, taking place due to the occurrence of overtemperature, when malfunctioning in a boil-dry mode. However, from the limited number of such tests carried out on kettles having exterior mounted rodded elements, located beneath the kettle bottom, at no time did the element fail before the kettle body had been overheated to the extent of melting or igniting. It will be understood that in order to carry out these tests the kettle over-temperature protective safety thermostats were inactivated by b~ing short-circuited, in order to simulate their failure, which would then lead to the aforementioned boil-dry action continuing, as a consequence of that malfunction, to a destructive stage.
In kettles having the rodded heating element mounted on the water side of the inner bottom, that bottom is usually made of copper. When allowed to overheat the copper tends to melt and allow the element to open circuit.
Further tests were conducted to investigate the progression of increase in temperature of the kettle heating element, when malfunctioning with the protective thermostat fused closed, in a boil-dry condition, and the corresponding temperatures occurring in a dummy "fuse" located adjacent the gap between the ends of the heating element. The test showed that, at the power levels selected, which were slightly higher than the normal rated power levels by about 10~, the kettle element reached a glowing-red condition (680C) in approximately 90 seconds, by which time the "fuse" was at 268C, well past its failure (open-circuit) temperature of 216C. At the end of two minutes, close to the onset of ignition of the kettle plastic body, the element had reached ~2~ Case 29~0 740C and the kettle body commenced smoking, while the temperature to which the "fuse" arose has increased to over 371C, thereby demonstrating the inherent safety of the fuse temperature range selected.
05 In the case of a kettle having a 1500 watt heating element the subject fuse was found to blow in approximately 2 minutes, while the kettle commenced to burn after 3 minutes had elapsed.
The satisfactory functioning of the subject fuse is dependent in part on the conductive heat transfer characteristics of the ends of the rodded heating element. The subject tests were conducted with heating elements having cold pins ~at each end) extending about one inch into the sheath, at which location the heating element wire is attached. The use of significantly longer cold pins, say four inches long, would space the fuse correspondingly further from the heating element wire per se, thereby establishing a higher temperature differential between heat source and fuse. This in turn would necessitate the adoption of a fuse having a lower value of fuse failure temperature, if the recited "safe" time to failure was to be retained.
With a fuse in accordance with the present ~S invention positioned at a preferred location a further test was carried out, to ensure that the temperature overshoot normally experienced when the protective thermostat of the kettle is actuacted by dry operation of the kettle, would not cause the fuse to melt. It was found that by performing such a dry cut-off test, with thermostat actuation after a boil dry condition, the thermostat opened in expected fashion. However the fuse did not melt, despite the temperature of the heating element overshooting the normal maximum operating temperature.
~Z~730 Case 2940 In a further like test, simulating failure of the thermostat by providing a parallel electric shunt, the fuse melted after about 90 seconds. The temperature in the kettle rose sufficiently to cause 05 some local damage by melting, but the structural integrity of the kettle was not impaired, nor combustion thereof initiated.
In a further embodiment of the present invention, the fuse was protected from direct radiation heating by the provision of a heat shield in the form of a mica barrier interposed between the fuse and the kettle bottom. While the time required for the fuse to melt was thereby extended by some fourteen seconds, the fuse melted in desired fashion before the occurence of significant heat damage, or the onset of combustion. Evidence of extended heat deterioration in the kettle wiring was found, but no fire took place. The satisfactory functioning of the subject thermal fuse is not normally dependent upon the fuse being in any way current sensitive.
Various other tests, such as boiling dry while having the kettle inclined at an angle of 10 from the level, to as much as 30 from the level, the use of a 216C (421F) fuse, were carried out, including measurement of the temperature of the kettle plastic outer rim adjacent the crimped metal-to-plastic joint. These tests all validated the satisfactory operation of the subject thermal fuse provision, in affording the desired safety protection.
Certain embodiments of the invention are described, reference being made to the accompanying drawings, wherein:
Figure 1 is a side view in partial diametrical section of a kettle incorporating the subject thermal fuse;
~25S73~
Case 2940 Figure 2 is a view of the kettle from below, having a major portion of the bottom of the kettle removed;
Figure 3 is a view at 3-3 of Figure 2; and Figure 4 is a view similar to Figure 2 of another embodiment.
Referring to Figures 1, 2 and 3, the kettle 10 has a handle 12, a plastic body portion 14, an inner bottom 16 and an outer bottom 18. An annular rodded element 20 has one end thereof connected by conductor 22 to a terminal pin 24 of a multi-pin electrical receptacle 26. A ground conductor 28 connects a central post 30 to the ground pin 32 of the receptacle 26. A thermostat 34 contacts the kettle bottom 16, at 36, and is connected to receptacle 26 by way of conductor 38. The thermostat 34 is mounted from the central post 30 by way of a mounting strap 39.
The fuse 40 consists of conductors 42 and 46, and the fusible link 44 connected therebetween, the fuse 40 being connected between the thermostat 34 and the cold pin 48 of the element 20.
The conductor 46 is brazed or spot welded to the cold pin 48 of the element 20, in order to assure good heat transfer by conduction from the element 20 to the fuse 40.
Turning to the Figure 4 embodiment a mica barrier 50 shields the fuse 44 from direct radiation from the element 20.- However, this was found to have little influence upon the operation of the thermal fuse.
In place of receptacle 26, a cord 52 in permanent wired relation is shown, having its conductors.54, 56, 58 connected to the respective components as in the Figure 1 embodiment.
Case 2940 KETTLE SAFETY FUSE
This invention is directed to an electric kettle and in particular to the provision of a fused circuit therefor.
It is well known to provide an electric Xettle with a fusing capability. In particular, in the United Kingdom it has been common practice to provide an over-current electrical fuse, which creates an open circuit upon the occurrence of an overload current. Such over-current protective fuses have generally been located in the kettle electrical receptacle, and as a consequence are not adapted to afford protection against the occurrence of overtemperature for other than that of fuse overheating due to the occurrence of an over-current.
In accordance with the present invention an electric kettle is provided with a thermally sensitive fuse having a predetermined operating temperature in excess of the normal operating temperature of the kettle when in a boiling condition. The fuse is connected in series relation with the electrical circuit supplying the heating element, being connected to one of the cold pins of the heating element by a solid, heavy gauge electricaL conductor possessing a good heat transfer characteristic. In operation, when ~25~;~73~
Case 2940 the kettle boils dry, or if the kettle is plugged-in when in a dry condition, in the absence of, or failure of the safety thermostat to open, the rise in temperature of the heating element beyond the usual temperature thereof associated with a water boiling condition transfers heat rapidly to the fuse element, causing it to fail and thereby create an open circuit condition for the heating element. The arrangement of the fuse element, in spaced isolation from the inner bottom of the kettle, ensures that the effects of radiant heat are minimal.
It will be understood that this fuse protection is additional to the required thermostat protection, which is the subject of safety regulation standards. However, such thermostats are not 100~
failsafe, and provision of the subject fuse provides a virtually foolproof safety back-up to the thermostat protective device, to prevent combustion of the kettle.
In the case of plastic bodied kettles, the greater safety, health and fire hazards which arise in the case of serious element overheat make the added protection of the subject fuse additionally valuable.
In selecting a suitable fuse due regard is had to ensuring that the fuse melting ("Blow") temperature exceeds normal operating temperatures by a significant amount, such as 100C, whilst also ensuring that the time required for the fuse to blow is significantly less than the time required for the plastic body of the kettle to melt or commence to burn.
In the matter of what are considered to be normal operating temperatures, evidently the normal operation of the kettle thermostat due to an overheat condition such as the kettle being plugged in while dry, or the kettle boiling dry should not cause the fuse to blow. In such an instance the temperature of 3~5~73~1 Case 2940 the fuse may rise by about 10C above normal boiling conditions.
It has been found that selection of a fuse in the range of about 190C to 220C affords a sufficient overheat margin to permit normal operation of the primary protective device, namely the safety thermostat, without a statistically large chance of the fuse being blow.
One fuse manufacturer recommends a minimum of 100C difference between normal operation of a fuse and the calibration or "blow" temperature of the fuse. Operating the fuse at less than 100C
difference from the "blow" temperature causes deterioration of the fuse and a shorter service life, whereby premature blowing occurs. The smaller the temperature difference, the shorter the working life of a fuse.
Further, it has been found that selection of a fuse operaiing in the noted temperature range of 190C to 220C assures that the fuse will blow within an operating time significantly less than the structural failure time characteristic of the kettle, namely the time required for the kettle to reach element open-circuiting failure, or in the case of a plastic kettle such as a polypropylene plastic bodied kettle, the onset of combustion of the kettle body.
It is important, in installing the subject thermal fuse, that the electrical conductor connecting the fuse element per se with the cold pin of the kettle heating element be of sufficient heat conducting capacity to ensure a low thermal gradient between heating element and fuse. This conductor is usually a rodded conductor.
Tests were carried out on a number of plastic bodied kettles to establish the possible ~;255~3~
Case 2940 existence of a self-protective function, such as element failuxe, taking place due to the occurrence of overtemperature, when malfunctioning in a boil-dry mode. However, from the limited number of such tests carried out on kettles having exterior mounted rodded elements, located beneath the kettle bottom, at no time did the element fail before the kettle body had been overheated to the extent of melting or igniting. It will be understood that in order to carry out these tests the kettle over-temperature protective safety thermostats were inactivated by b~ing short-circuited, in order to simulate their failure, which would then lead to the aforementioned boil-dry action continuing, as a consequence of that malfunction, to a destructive stage.
In kettles having the rodded heating element mounted on the water side of the inner bottom, that bottom is usually made of copper. When allowed to overheat the copper tends to melt and allow the element to open circuit.
Further tests were conducted to investigate the progression of increase in temperature of the kettle heating element, when malfunctioning with the protective thermostat fused closed, in a boil-dry condition, and the corresponding temperatures occurring in a dummy "fuse" located adjacent the gap between the ends of the heating element. The test showed that, at the power levels selected, which were slightly higher than the normal rated power levels by about 10~, the kettle element reached a glowing-red condition (680C) in approximately 90 seconds, by which time the "fuse" was at 268C, well past its failure (open-circuit) temperature of 216C. At the end of two minutes, close to the onset of ignition of the kettle plastic body, the element had reached ~2~ Case 29~0 740C and the kettle body commenced smoking, while the temperature to which the "fuse" arose has increased to over 371C, thereby demonstrating the inherent safety of the fuse temperature range selected.
05 In the case of a kettle having a 1500 watt heating element the subject fuse was found to blow in approximately 2 minutes, while the kettle commenced to burn after 3 minutes had elapsed.
The satisfactory functioning of the subject fuse is dependent in part on the conductive heat transfer characteristics of the ends of the rodded heating element. The subject tests were conducted with heating elements having cold pins ~at each end) extending about one inch into the sheath, at which location the heating element wire is attached. The use of significantly longer cold pins, say four inches long, would space the fuse correspondingly further from the heating element wire per se, thereby establishing a higher temperature differential between heat source and fuse. This in turn would necessitate the adoption of a fuse having a lower value of fuse failure temperature, if the recited "safe" time to failure was to be retained.
With a fuse in accordance with the present ~S invention positioned at a preferred location a further test was carried out, to ensure that the temperature overshoot normally experienced when the protective thermostat of the kettle is actuacted by dry operation of the kettle, would not cause the fuse to melt. It was found that by performing such a dry cut-off test, with thermostat actuation after a boil dry condition, the thermostat opened in expected fashion. However the fuse did not melt, despite the temperature of the heating element overshooting the normal maximum operating temperature.
~Z~730 Case 2940 In a further like test, simulating failure of the thermostat by providing a parallel electric shunt, the fuse melted after about 90 seconds. The temperature in the kettle rose sufficiently to cause 05 some local damage by melting, but the structural integrity of the kettle was not impaired, nor combustion thereof initiated.
In a further embodiment of the present invention, the fuse was protected from direct radiation heating by the provision of a heat shield in the form of a mica barrier interposed between the fuse and the kettle bottom. While the time required for the fuse to melt was thereby extended by some fourteen seconds, the fuse melted in desired fashion before the occurence of significant heat damage, or the onset of combustion. Evidence of extended heat deterioration in the kettle wiring was found, but no fire took place. The satisfactory functioning of the subject thermal fuse is not normally dependent upon the fuse being in any way current sensitive.
Various other tests, such as boiling dry while having the kettle inclined at an angle of 10 from the level, to as much as 30 from the level, the use of a 216C (421F) fuse, were carried out, including measurement of the temperature of the kettle plastic outer rim adjacent the crimped metal-to-plastic joint. These tests all validated the satisfactory operation of the subject thermal fuse provision, in affording the desired safety protection.
Certain embodiments of the invention are described, reference being made to the accompanying drawings, wherein:
Figure 1 is a side view in partial diametrical section of a kettle incorporating the subject thermal fuse;
~25S73~
Case 2940 Figure 2 is a view of the kettle from below, having a major portion of the bottom of the kettle removed;
Figure 3 is a view at 3-3 of Figure 2; and Figure 4 is a view similar to Figure 2 of another embodiment.
Referring to Figures 1, 2 and 3, the kettle 10 has a handle 12, a plastic body portion 14, an inner bottom 16 and an outer bottom 18. An annular rodded element 20 has one end thereof connected by conductor 22 to a terminal pin 24 of a multi-pin electrical receptacle 26. A ground conductor 28 connects a central post 30 to the ground pin 32 of the receptacle 26. A thermostat 34 contacts the kettle bottom 16, at 36, and is connected to receptacle 26 by way of conductor 38. The thermostat 34 is mounted from the central post 30 by way of a mounting strap 39.
The fuse 40 consists of conductors 42 and 46, and the fusible link 44 connected therebetween, the fuse 40 being connected between the thermostat 34 and the cold pin 48 of the element 20.
The conductor 46 is brazed or spot welded to the cold pin 48 of the element 20, in order to assure good heat transfer by conduction from the element 20 to the fuse 40.
Turning to the Figure 4 embodiment a mica barrier 50 shields the fuse 44 from direct radiation from the element 20.- However, this was found to have little influence upon the operation of the thermal fuse.
In place of receptacle 26, a cord 52 in permanent wired relation is shown, having its conductors.54, 56, 58 connected to the respective components as in the Figure 1 embodiment.
Claims (5)
1. An electric kettle having a heating element therein, electric current supply conductor means connected to the ends of said element, a safety thermostat in said supply conductor means and thermal fuse means having a melting temperature thereof in excess of the temperature reached by said fuse means during normal functioning of the kettle, said electrical current conducting means connecting said fuse means in effective heat transfer relation with one end of said heating element, in series electrical relation therewith, to conduct electrical current thereto during normal operation, said fuse being subject to receive heat from said heating element through said current conducting means during sustained overtemperature operation of the element at a rate sufficient to increase the temperature of the fuse to cause the fuse to melt and interrupt said electric current supply prior to the initiation of a fire hazard condition by said heating element to the kettle.
2. The kettle as set forth in claim 1, said kettle having a plastic body susceptible to combustion upon prolonged overtemperature operation of said heating element.
3. The kettle as set forth in claim 1, said fuse having a melting point in the range of 175°C - 370°C.
4. The kettle as set forth in claim 2, said electrical current conducting means connecting said fuse means with said heating element being of sufficient heat conducting capacity to provide a low temperature gradient between said heating element and said fuse.
5. The kettle according to claim 1, 3 or 4 wherein said fuse means is in series relation with said safety thermostat.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000491792A CA1255730A (en) | 1985-09-27 | 1985-09-27 | Kettle safety fuse |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000491792A CA1255730A (en) | 1985-09-27 | 1985-09-27 | Kettle safety fuse |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1255730A true CA1255730A (en) | 1989-06-13 |
Family
ID=4131487
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000491792A Expired CA1255730A (en) | 1985-09-27 | 1985-09-27 | Kettle safety fuse |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1255730A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1995034188A1 (en) * | 1994-06-09 | 1995-12-14 | Strix Limited | Liquid heating vessels |
| WO2010149600A1 (en) * | 2009-06-24 | 2010-12-29 | Nestec S.A. | Thermo-fuse for a pump of a beverage machine |
-
1985
- 1985-09-27 CA CA000491792A patent/CA1255730A/en not_active Expired
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1995034188A1 (en) * | 1994-06-09 | 1995-12-14 | Strix Limited | Liquid heating vessels |
| GB2299454A (en) * | 1994-06-09 | 1996-10-02 | Strix Ltd | Liquid heating vessels |
| GB2299454B (en) * | 1994-06-09 | 1997-12-03 | Strix Ltd | Liquid heating vessels |
| WO2010149600A1 (en) * | 2009-06-24 | 2010-12-29 | Nestec S.A. | Thermo-fuse for a pump of a beverage machine |
| CN102802478A (en) * | 2009-06-24 | 2012-11-28 | 雀巢产品技术援助有限公司 | Thermo-fuse for a pump of a beverage machine |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |