GB2374783A - Self regulating heating element - Google Patents
Self regulating heating element Download PDFInfo
- Publication number
- GB2374783A GB2374783A GB0030623A GB0030623A GB2374783A GB 2374783 A GB2374783 A GB 2374783A GB 0030623 A GB0030623 A GB 0030623A GB 0030623 A GB0030623 A GB 0030623A GB 2374783 A GB2374783 A GB 2374783A
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- resistive
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- metal oxide
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Classifications
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/20—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater
- H05B3/22—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater non-flexible
- H05B3/24—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater non-flexible heating conductor being self-supporting
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01C—RESISTORS
- H01C17/00—Apparatus or processes specially adapted for manufacturing resistors
- H01C17/06—Apparatus or processes specially adapted for manufacturing resistors adapted for coating resistive material on a base
- H01C17/065—Apparatus or processes specially adapted for manufacturing resistors adapted for coating resistive material on a base by thick film techniques, e.g. serigraphy
- H01C17/06506—Precursor compositions therefor, e.g. pastes, inks, glass frits
- H01C17/06513—Precursor compositions therefor, e.g. pastes, inks, glass frits characterised by the resistive component
- H01C17/06533—Precursor compositions therefor, e.g. pastes, inks, glass frits characterised by the resistive component composed of oxides
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01C—RESISTORS
- H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
- H01C7/06—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material including means to minimise changes in resistance with changes in temperature
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/10—Heater elements characterised by the composition or nature of the materials or by the arrangement of the conductor
- H05B3/12—Heater elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material
Abstract
An electrically resistive heating element exhibiting constant resistivity and resistance from ambient to preset operational temperature and increase in resistivity and resistance above preset operational temperature comprises successive layers of different metal oxides deposited on an electrically conductive metal substrate the layers of metal oxides having both different composition and degrees of oxidation on an electrically conductive metal substrate such that the combined characteristics of different metal oxides result in desired overall characteristics. The element may be adapted for use in a water heating arrangements such as kettles, coffee percolators and heated jugs.
Description
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This present invention relates to electrical heating elements for use in domestic
liquid heating appliances which,, by virtue of their configuration, construction and the . l inherent properties of the materials used, will not continue to heat up beyond a predetermined limiting temperature when electrical power is applied to them, even under overload or unusual operating conditions.
In this respect such elements exhibit a self-controlling property and function by virtue of the characteristics of the materials utilised. The method of construction and the configuration, a property which is not available from conventional liquid heating elements and consequently renders them safer for use in domestic appliances than conventional elements.
Conventional electrical *qoid heating elements of the tubular sheathed variety or
screen printed type do not have any self-regulating properties and when connected to an electrical power source will continue to heat up with increasing rise in temperature until they fail by burning out and self-destruct.
The safe use of these conventional elements in domestic appliances is achieved by combining them with some form of temperature sensitive control device which effectively cuts off the electrical supply when a predetermined temperature level has been reached Generally these temperature sensitive control devices Incorporate bimetals In various configurations and rely on the ability of the bimetallic components to deflect at or around a predetermined temperature to provide a mechanical action which "makes"or"breaks"the electncal supply contacts thus interrupting the electncal power supply to the elements concerned Whilst such temperature sensitive bimetallic and other similar control devices are widely used and produced to high quality standards they are generally mechanical devices, and like all mechanical mass produced devices subject to the probability of ailure, this failure probability Increasing wfth increased usage
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The operational failure of such temperature sensitive control devices will result in y the over-heating and self-destruction of the associated elements, with potentially catastrophic results for users of the domestic appliances incorporating such items.
Electrical heating elements are available which have self-controlling characteristics and are manufactured from various compositions of barium titanate, where the resistance increases by several powers of ten when the temperature is raised to the vicinity of the Curie Point, also known as the"switching"temperature.
However, such heating elements have several basic disadvantages which currently severely limit their widespread application and usage, some of which are set out as follows.
The major disadvantage lies with the inherent property of almost all the compositional variations of barium titanates, in that the resistivity of such materials is not constant over the temperature range from ambient to the"switching"temperature, or Curie Point, but reduces progressively with increasing temperature before increasing to a high value The consequence of this is that elements manufactured from such compositions will have operational resistances which reduce significantly from that measured at ambient temperature, to that just prior to the"switching"temperature, or Curie Point, a reduction which can be as high as half the original resistance This presents the domestic appliance manufacturers with the problem of using such elements and deciding which ambient resistance to produce such elements to, In order to maximise the power output In explanation of this, consider the use of a conventional element in a domestic kettle operating with a single phase 230 volt a c supply The maximum current allowed for 230volt appliancesis 13 amps and by Onm's La\ this defines the
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maximum power output of such appliances to circa 3 kilowatts, and consequently / the minimum resistance of the heating element employed to 17.7 ohms.
In general the resistance of such elements increases slightly with increase in operating temperature by 1-2%.
Consequently the generation of heat by the element and transfer of this energy to the water is a maximum when the temperature is at a minimum and only slightly reduced from this as the boiling point is reached.
The same power and current limitations apply to barium titanate elements such that the minimum resistance of 17.7 ohms would need to be at a temperature near the "switching" or Curie Point, resulting in a higher resistance at ambient temperature.
Assuming a resistance decrease over the appropriate temperature range of, say, 25%, a typical barium titanate element would need to be produced with an ambient resistance of 23.6 ohms.
Using Ohm's Law It can be shown that at the start of the water heating cycle the thermal energy available is only 2.24kw, rising to 3kw only when the boiling point is reached.
This is the opposite of that required by the domestic appliance manufacturers and an example of the resistance-temperature characteristic of a barium titanate
composition with the Cune POint "switching" temperature at 1200C IS shown In Fig 1 Fig 1
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A second disadvantage with barium titanate elements arises from the method used / to produce them. Barium titanates derive their particular temperature/resistance properties mainly from the characteristics of the grain boundaries between the individual particles making up the bulk matrix of any particular piece.
Accordingly, objects made of barium titanates are produced by pressing together the required amount of fine powder particles of the appropriate composition in a press, usually with a binding agent, to the appropriate size and shape of the required finished object and then sintering the pressed mass in a furnace at the requisite temperature to produce a homogeneous product.
Whilst this is an adequate manufacturing process it may result in products which are not fully dense from the pressing stage, and therefore do not exhibit uniform operating characteristics or have residual stresses from the sintering stage, which may result in cracking and failure during subsequent thermal operational cycles.
The present invention seeks to overcome, or very substantially reduce, the problems previously described by providing an electncal liquid heating element which has the required self-controlling characteristic, in that the resistance increases by powers of ten when the operating temperature IS raised to a predetermined limit, but additionally has a nearly constant resistivity and resistance In the temperature range from ambient to the predetermined operational limit In accordance with a first aspect of the present invention there IS provided a supporting substrate which may be comprised of an electncally conductive metal or metal alloy, or an electncally insulating matenal with an electrically conductive layer applied onto an area of It a thermally sprayed resistive metal oxide deposit applied to an appropriate area of one surface of the conductive substrate Oí to 3r appropriate area of the electrically conductive layer situated onto one suffac o'ar
electrically irsulating Substrate a contact area disposed over me malt) rit zu
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thermally sprayed electrically resistive metal oxide deposit such that an electric current may be passed from the contact area on one side through the thickness of the thermally sprayed resistive metal oxide deposit to the conductive metal substrate, or the conductive layer applied to the Insulating substrate, on the other, electrical connection being made firstly to the contact area and secondly to the conductive metal substrate, or the conductive layer applied to one surface of an insulating substrate, and that heat is generated within the volume of the thermally sprayed resistive metal oxide deposit matrix as a result of the passage of said electrical current.
The contact layer may be comprised of any electrically conductive material such as copper, nickel, aluminium gold, silver, brass or conductive polymers, applied by means of flame spraying, chemical vapour deposition or magnetron sputtering techniques, electrolytic or chemical processes, or a solid piece held in place with adhesives, mechanical pressure or magnetic means.
Such contact layer is smaller In area than the metal oxide deposit so as to leave a distance between the outer edge of the metal oxide deposit and the corresponding outer edge of the contact layer, sufficient to prevent an electric current passing directly from the contact area to the conductive substrate or conductive layer on an Insulating substrate when a voltage IS applied between contact and substrate For the conductive contact layer the thickness should be such that It wttf carry the
maxImum current required and allow It to distribute evenly over the whole of Its surface such that the current passing through the thermally sprayed metal oxide deposit from contact to substrate IS uniform in density for each unit area of the metal oxide
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This provision ensures that the. heat energy generated within the volume of the resistive metal oxide is uniformly distributed, producing a uniform temperature over the appropriate area of the supporting substrate without any localised hot spots.
It is preferable but not necessary to make that area of the contact layer to which the external power supply point is to be fixed thicker than the remaining areas to assist In the even distribution of the current.
The supporting substrate may be comprised of any electrically conductive metal or metal alloy, or electrically insulating material and of a sufficient thickness to provide dimensional stability for the element system during production and subsequent operational use.
In the case of liquid heating elements utilised in kettles, heating jugs, etc, the substrates are generally circular in configuration and may vary in size from 80mm diameter to 130mm diameter or larger, having thicknesses in the range of 0. 7mm to 4.00mm The thermally sprayed resistive metal oxide deposit is comprised of successive layers of different metal oxides having both different compositions and degrees of oxidation such that the combined charactenstlcs of the various different metal oxides result In the thermally sprayed resistive metal oxide deposit exhibiting an effectively constant resistivity and resistance over the temperature range from ambient to a predetermined operating temperature limit and increase In resistivity and resistance by powers of ten at temperatures above the predetermined
operational temperature limit, the rate of ! ncreas) ng restst ! V) ty and resistance being greater than the rate of temperature increase The property of the thermally sprayed resistive metal oxide deposit, whereby the "es'stty and resistance increase by powers of ten a temperatures above a pre
"jerm'ned operational lmtng temperature cnfevec : by mak'ng one or more of
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the successive layers of different metal oxides comprising the prementioned / resistive metal oxide deposit from one of a variety of ferro-electric materials which have crystalline structures of the perovskite type and of the general formula 'A. B. 03', where'A'may be a mono-, D1-, or trivalent cation, and'B'may be a penta- tetra-, or trivalent cation, and 03 is the oxygen anion.
Such mixed metal oxides of the prementioned types are also generally known as oxygen-octahedra-ferro-electrics, and the characteristics of these materials, such as initial resistivity, variation of resistivity with temperature and Curie Point, or "switching" temperature, may be varied by variations in composition.
Barium titanates are the most well known, researched and widely used form of the oxygen-octahedra-ferro-etectrics and is utilised in the forthcoming example of an element type which is the subject of this present invention.
All the oxygen - octahedra - ferro-electric metal oxides exhibit the characteristic of reducing resistivity with increasing temperature up to the Curie Point, or"switching" temperature, and this is compensated for in the element type which is the subject of the present invention by making one or more of the successive layers of the different metal oxides comprising the prementioned resistive metal oxide deposit from metal oxides which exhibit the characteristic of increasing resistivity and resistance with increasing temperature It IS known that metal alloys comprised of the nickel-chrome type when oxidised and thermally sprayed exhibit the required charactenstlc of increasing resistivity/ resistance WIth Increasing temperature, generally as descnbed In patents EU302589, US5039840 and PCT/GB96/01351 Such nickel-chrome type metal alloys may be oxidised to the required degree as a precursor operation, pnor to being thermally sprayed as one or more lavers of the
or r, ay bE, oxiclised ic) reSistive metal oXide jeposlt 3S described In GB2344042 or rìay be ox, dlsed to : f- é. ;
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required degree during the thermal spraying operation, generally as described in patents EU302589, US5039840 and patent application No PCT/GB96/01351.
In order that the prementioned thermally sprayed resistive metal oxide deposit exhibits the characteristic of a constant resistivity and resistance over the temperature range from ambient to a predetermined operating temperature limit, the rate of increase of resistivity with temperature of the one or more layers of thermally sprayed resistive metal oxide deposit comprised of oxides produced by the processing of alloys of the nickel-chrome type should closely match the rate of decrease of resistivity with temperature of the one or more layers of the oxygenoctahedra-ferro-electric oxides over the same temperature range.
Accordingly a second aspect of this present invention provides an electrically resistive liquid heating element having the properties of effectively constant resistivity and resistance over an operating temperature range from ambient to a predetermined limiting temperature and thereafter an increase of resistivity/ resistance with temperature at values above the limiting temperature by powers of ten preventing the element from exceeding the predetermined limiting temperature by any amount other than that small temperature rise due to thermal momentum, and that such properties are achieved from a combination of different metal oxides as previously described and that In exhibiting a temperature limiting property the element has a self-control ling characteristic by the inherent properties of the different metal oxides comprising the thermally sprayed resistive metal oxide deposit applied to the prementioned supporting substrates It IS a second aspect of this present invention that the resistance In ohms of the electrical element described in the first aspect will be dependent upon the resistivity of the several layers of the different metal oxides compo. seing the thermattv sorayed
res ! s''/e rneta ! oxlde deposit, the number anc ; C ck l f the severa ! tayers of the
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different metal oxides and the. area of the thermally sprayed resistive metal oxide / deposit comprised of several layers of different metal oxides.
It is known from empirical work with flame sprayed metal oxides described in the prementioned patents that the resistive properties of the different metal oxides derive mainly from the grain boundary effects at the junctions between successive oxidised metal particles, and that the smaller the size of the oxidised particles the greater the number in any given volume of the thermally sprayed resistive metal oxide deposit the greater will be the resistivity of the thermally sprayed resistive metal oxide deposit, and consequently the smaller the volume required to achieve the optimum resistance for a liquid heating element designed to produce a given output of heating energy from conventional single phase domestic electrical supply.
It is similarly known from empirical work that the thermally sprayed resistive metal oxide is comprised of"lines"of interconnecting metal oxide particles which act as current carrying mechanisms, and that the greater the number of such"lines"of inter-connecting metal oxide particles the higher is the current carrying capacity of any thermally sprayed resistive metal oxide deposit comprised of such"lines". Such "tines"of interconnecting metal oxide particles may be considered as resistive wires in parallel and consequently the overall resistance of the thermally sprayed resistive metal oxide deposit IS the sum of all the resistances of the parallel lines of inter- connecting metal oxide particles which in turn will be dependent upon the area of the thermally sprayed resistive metal oxide deposit to which a contact area, as mentioned in the first aspect, is disposed, and additionally the size of the metal oxide particles comprising the current carrying lines Utilising the previously described first and second aspects of the present invention It 's possible to determine by calculation ìhe dimensions and relatIonship between tnd
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various components comprising'the type of electrical liquid heating element which is the subject of this present invention utilising the following basic procedures.
For the purpose of this example it is assumed that a typical electrical liquid heating element IS required to produce 2.5 kilowatts of heating energy from a conventional domestic single phase electrical supply of 230 volts with maximum current of 13 amps.
From considerations of Ohm's Law a power output of 2500 watts at 230 volts requires a current of 10.87 amperes with an element having a minimum resistance of 21.16 ohms.
Such an element will utilise a metal substrate 110mm diameter with a thermally sprayed resistive metal oxide deposit 80mm diameter applied to It and a contact area 70mm diameter disposed over it. The metal substrate will be comprised of 2mm thick aluminium plate, such material having excellent electrical and thermal conductive properties.
Empirical work has shown that for water to boil at the surface of such a metal substrate the metal-liquid interface temperature must be a minimum of 101 C and uniform over the whole of the 11 Omm diameter metal surface.
Using the values of density, specific heat and thermal conductivity for aluminium It IS possible to calculate the operating temperature of the thermally sprayed resistive metal oxide deposit necessary to generate 2500 watts of thermal energy with a liquid-metal Interface temperature of 101 C as being 160 C In order that the element exhibits the required self-controlling charactenstices it should not exceed a temperature more than 10 C above the operating level to allow for variations in operating conditions of such liquid heating elements Consequently the safe maxmm operating temperature of the element may be fi < ed at 1700e
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Examination of the tabulated properties of the various oxygen-octahedra-ferro- electric metal oxides enables a suitable composition to be chosen, having a Curie Point,"switching"temperature, at or close to 170 C. Such bibliographic sources will also detail the ambient resistivity and rate of decrease of resistivity with temperature over the temperature range from ambient to the maximum safe operating temperature of 170 C.
Utilising the data of ambient resistivity and rate of decrease of resistivity with temperature of the chosen oxygen-octahedra-ferro-etectric metal oxide, the required ambient resistivity and rate of increase of a second metal oxide may be calculated such that a combination of the oxygen - octahedra - ferro-electric metal oxide and the second metal oxide provide the thermally sprayed resistive metal oxide deposit with the properties required and previously described of constant resistivity over the operating temperature range and a very rapidly increasing resistivity with increase in temperature above the predetermined safe limit.
Utilising details of the ambient resistivities of the two component oxides and their rate of change of resistivity with temperature and the design heating area of the thermally sprayed resistive metal oxide deposit, the overall thickness of said thermally sprayed resistive metal oxide deposit may be calculated Similarly, the same details will enable the proportion of the different oxides within the total t'ckness of the thermally sprayed resistive metal oxide to be determined As a mathematical Illustration of the preceding aspects of the present invention and prementloned combinations of different oxides an element construction is envisaged which utilises a combination of barium titanate and oxidised NtCrFe alloy
, ..,. . psnt apptfcation No 98210206 6'ib ! shed as GB2344042 rìere IS a oaflum titanate composition with a Cut 2 POInt,'switching'temperature r 0'7Q'C which from empirical work and b < o' ; graph) ca data has an ambient
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resistivity of circa 4000 ohm cms, a rate of decrease of resistivity with temperature ,/, circa 40%, giving a resistivity at 160-170 C of 2400 ohm cms.
Similarly, as stated in patent application 9821020. 6 published as GB2344042, it is known that an alloy of 75% Ni, Cr 15% and Fe 10%, when oxidised to circa 15%, has an ambient resistivity circa 24000 ohm cms increasing with temperature by 25% to give a resistivity at 160-170 C circa 30, 000 ohm cms.
The combination of the several layers of the prementioned two different oxides comprising the thermally sprayed resistive metal oxide deposit are considered as resistances in series, and the overall prescribed element resistance of 21. 16 ohms is comprised of the resistance of the barium titanate component, defined as Ri, added to the resistance of the oxidised NtCrFe alloy, defined as R2, such that
21 16 ohms = R10hms + R2 ohms [1]
The conductive area of the thermally sprayed resistive metal oxide deposit is defined by the contact area disposed over it and established as having a diameter of 70mm and area of 38 5cm2 by calculation.
The resistances Ri and R2 of the two oxides comprising the resistance of the thermally sprayed resistive metal oxide deposit may be defined In terms of the +thicknesses and areas as set out In equation [2]
Resistance R = Resistivity p x Thlcknes : [2]
Area A Consequently, equation [1] may be re-wntten In the form
Ai A2 Where pi, t1 and Ai are respectively the resistivity, thickness and area or tne banurr titanate component of the oxide deposl and p2, t2 and A2 are respectlxely the reslSlivlty, thickness an (J areii O''he oXlcllsed NICrF ('comper- Î' : c, - T. 32""-
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thermally sprayed resistive metal oxide deposit, the areas Ai and A2 are equal and have the value of 38. 5cm2 as defined by the contact area.
For the element to have the same effective overall resistance for the intended operating temperature range of ambient to 1600C equation [3] should have the same value for both temperature points and may consequently be re-written inserting the resistivity values for each oxide component at the respective upper and lower temperatures of ambient and 1600C as equations [4] and [5], where:
and
The solution to equations [4] and [5] gives a relationship between the thickness of the barium titanate component t1 and the NiCrFe oxide component t2 where
Substituting the values of t1 or t2 into either of equations [4] or [5] gives values for t1 of 0 0783cms and t2 of 0 0209cms respectively, with a total thickness for the thermally sprayed resistive metal oxide deposit of
Thus it is claimed that a liquid heating element may be produced In accordance with the preceding aspects of this present invention which h3s an effectively constant resistivity over an operational range from ambient to a predecermined limiting upper temperature and which also has a self regulating propetv \/hereby the resistivity Increases by powers of ten above the predetermined IIfT'1 g temperature by virtue of the Inherent properties of the different metal oxides Comp@sing it, the configura-
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tion of one oxide with respect to a second and the constructional techniques employed to manufacture such liquid heating elements.
Whilst the preceding mathematical example set out assumes that only one alternative and second metal oxide is required to combine with the chosen oxygenoctahedra-ferro-electric oxide, with the appropriate resistivity and rate of resistivity increase at the predetermined operational limiting temperature, it is envisaged that at other limiting temperatures and operational temperature ranges, combinations of two or more metal oxides may be required to balance the properties of the chosen oxygen-octahedra-ferro-electric oxide or oxides.
The degree of oxidation and methods of combining metal oxides deriving from different metals or alloys is substantially as set out in patent application No 9821020.6 published as GB2344042.
It is a third aspect of this present invention that the different oxides of different compositions comprising the thermally sprayed resistive metal oxide deposit may be applied to the supporting substrate in a variety of ways and using different techniques One first methodology can be to deposit the metal oxides produced from the NiCrFe or similar alloys as one complete layer, thermally sprayed to the required calculated thickness, area and configuration, subsequently followed by the application of the appropriate oxygen-octahedra-ferro-electric oxide component, thermally sprayed to the required calculated thickness, area and configuration, to produce the required combined properties and characteristics of the liquid heating element concerned Alternatively, the reverse of this first methodology may be utilised, whereby the
oxygen-octahedra-ferro-electnc oxide component Is firstly applied to the suoporting substrate followed by the seconc component metal oxide
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An alternative third methodology can be to apply the different metal oxides as alternate and successive layers until the required thickness of the thermally sprayed resistive metal oxide deposit is reached.
The thermal spraying operation required to apply the different oxides to the supporting substrate may be achieved using any of a variety of techniques ranging from flame spraying, where the heat source is provided by the combustion of oxygen and various hydrocarbons, plasma equipment, high velocity oxy fuel, and wire spraying.
For particular compositions of the oxygen-octahedra-ferro-electric oxides, other deposition techniques may be utilised and incorporated and these may include chemical and physical vapour deposition techniques.
It is a fourth aspect of this present invention that the configuration of the liquid heating element precedingly described may be of any shape appropriate to the end use of said liquid heating element ranging from square, rectangular or rhomoidal with re-entrant or projecting areas as determined by design, calculation or usage.
A further aspect of this present invention IS embodied in the procedures used in the deposition of the layers of the different oxides comprising the thermally sprayed resistive metal oxide deposit, that such liquid heating elements may be manufactured within close tolerance limits for the required final operating resistance
Claims (15)
1. Forms of self-controlling electrically resistive heating elements for use in domestic and other appliances which involve the heating of liquids for food preparation such as kettles, heating jugs, coffee percolators and the like, which will not continue to heat up beyond a predetermined limiting temperature when electrical power is applied even under overload or unusual operating conditions and exhibit a self-controlling property and function by virtue of the characteristics of the different metal oxides utilised in their construction whereby the combination of one type of metal oxide having a positive temperature coefficient of resistance with a second metal oxide which substantially increases in resistivity and resistance at temperatures above the pre-determined operational temperature limit provide a heating element having a constant resistance from ambient to the pre-determined operating temperature and a very substantial increase in resistance at the pre-mentioned operational temperature limit such that the power output decreases rapidly to a fraction of that produced below the operational temperature limit, consequently the elements will not exceed the operational temperature limit and require no external devices or controls to provide this self-controlling property as with current conventional heating elements of the tubular sheathed variety or screen printed types.
2. Heating elements of the type described in claim 1 whereby the construction consists of a conductive metal substrate, or an insulating substrate to which is applied an electrically conductive layer, and onto the said substrate the two different resistive metal oxides are applied as two layers in intimate contact with successively the conductive substrate and each other and to the upper surface of one of the resistive oxide layers is applied an electrically conductive contact layer such that when a voltage is applied between the conductive substrate and the contact layer a current flows through the resistive metal oxide layers generating heat within them by virtue of their resistance (generally as described in PCT/GB01/05148).
3. Heating elements of the type and configuration described in claims 1 and 2 whereby the different resistive metal oxide layers and electrically conductive layers may be applied to the appropriate substrate by any means and method ranging from thermal deposition, whereby powders of metal oxides are passed through a heat source comprising a plasma arc or the combustion of oxygen and hydrocarbon gases to soften them prior to Impact onto the substrate, such methodology being known generally as thermal spraying, or electrolytic processing, or hot isostatic pressing utilising powder compression and sintering combinations or chemical or vapour deposition techniques.
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4. Elements of the type and configuration described in claims 1 to 3 wherein one of the resistive metal oxide layers is one of a variety of ferro electric materials having crystalline structures of the perovskite type and of general formula A B. 03 where'A'may be a mono - 01 or trivalent cation and'B'may be a penta, tetra or trivalent cation and Os is the oxygen anion and generally known as oxygen-octahedr-ferro electric materials whereby the characteristics of initial resistivity and variation of resistivity with temperature and"switching"temperature of Curie Point may be varied by variations in composition as described in PCT/GB01/05148.
5. Elements of the type and configuration as described in claims 1 to 4 inclusively whereby the second resistive metal oxide is produced from nickel- chrome type metal alloys which may be oxidised to the required degree as a precursor operation prior to being applied in layer form to the substrate or maybe oxidised to the required degree during the application operation and which exhibit the required characteristic of increasing resistivity/resistance with increasing temperature generally as described in Patents EU302589,
US5039840, PCT/GB96/01351, GB2344042 and PCT/GB01/05148.
6. Elements of the type and configuration as described in claims 1 to 5 inclusively whereby the resistive metal oxide portion of the element may comprise firstly a layer of resistive metal oxides derived from metal alloy or the nickel-chrome type applied to the substrate and secondly a layer of the oxygen-octahedra-ferro electric oxide material to which is deposited a final electrically conductive contact layer as described in PCT/GB01/05148.
7. Elements of the type and configuration as described in claims 1 to 6 inclusively whereby the resistive metal oxide portion of the element may comprise a layer of the oxygen-octahedra-ferro electric oxide material applied firstly to the substrate and secondly a layer of resistive metal oxides derived from alloys of the nickel-chrome type to which is deposited a final electrically conductive contact layer as described in PCT/GB01/05148.
8. Elements of the type and configuration as described in claims 1 to 7 inclusively whereby the resistive metal oxide portion of the element may be comprised of alternate layers of the oxygen-octahedra-ferro electric material and resistive metal oxide derived from alloys of the nickel-chrome type as required by element usage and to the top surface of which is deposited a final electrically conductive contact layer as described in PCT/GB01/05148.
9. Elements of the type and configuration as described in claims 1 to 8
Inclusively whereby the oxygen-octahedra-ferro electric materials may have ambient resistivities in the range 100-100,000 ohm cms and the resistive metal oxides derived from alloys of the nickel-chrome types have ambient resistivities in the range of 2,000-80, 000 ohm cms.
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10. Elements of the type and configuration as described In claims 1 to 9 inclusively whereby for a design of known heating area and operating power level the relative thicknesses of the different resistive oxides of the oxygen- octahedra-ferro electrical materials and those derived from alloys of the nickel-chrome type may be derived by calculation from a knowledge of the resistivities of the materials to be utilised.
11. Elements of the type and configuration as described in claims 1 to 10 inclusively whereby the area of the finally applied electrically conductive contact layeris made smaller by 2%-5% than the area of the combined resistive oxide layers so as to leave a resistive peripheral track thus ensuring that when a voltage is applied between the conductive substrate and the contact layer the current flow is directly through the resistive oxide from contact to substrate and not laterally from contact edge to substrate which may cause short circuiting of the resistive path.
12. Elements of the type and configuration as described in claims 1 to 11 inclusively whereby the conductive substrate may be comprised of any electrically conductive metal or metal alloy comprised of aluminium, copper, mild steel or stainless steel or of any type of electrically insulating material comprised of plastic, ceramics, glass or composites of the same to which is applied an electrically conductive layer to which a contact may be made.
13. Elements of the type and configuration as described in claims 1 to 12 inclusively whereby the finally applied contact layer may be comprised of any type of electrically conductive material to which a contact may be made.
14. Elements of the type and configuration as described in claims 1 to 13 inclusively whereby the techniques utilised to apply the final electrically conductive contact layer to the resistive oxide layer may comprise any form of thermal deposition, electrolytic deposition, adhesion utilising glues or solders, mechanical attachment or chemical and physical vapour deposition.
15. Elements of the type and configuration as described in claims 1 to 14 inclusively whereby the element may have any size, shape or form for which a mathematical equation may be derived.
Priority Applications (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB0030623A GB2374783A (en) | 2000-12-15 | 2000-12-15 | Self regulating heating element |
| AU2002223863A AU2002223863A1 (en) | 2000-11-21 | 2001-11-21 | A method of producing electrically resistive heating elements having self-regulating properties |
| PCT/GB2001/005148 WO2002043439A1 (en) | 2000-11-21 | 2001-11-21 | A method of producing electrically resistive heating elements having self-regulating properties |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB0030623A GB2374783A (en) | 2000-12-15 | 2000-12-15 | Self regulating heating element |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB0030623D0 GB0030623D0 (en) | 2001-01-31 |
| GB2374783A true GB2374783A (en) | 2002-10-23 |
Family
ID=9905163
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB0030623A Withdrawn GB2374783A (en) | 2000-11-21 | 2000-12-15 | Self regulating heating element |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2374783A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2445464A (en) * | 2007-01-04 | 2008-07-09 | 2D Heat Ltd | A self-regulating electrical resistance heating element |
| GB2460833A (en) * | 2008-06-09 | 2009-12-16 | 2D Heat Ltd | Self-regulating electrical resistance heating elements |
| WO2017151965A1 (en) * | 2016-03-02 | 2017-09-08 | Watlow Electric Manufacturint Company | Heater element having targeted decreasing temperature resistance characteristics |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5185063A (en) * | 1990-02-22 | 1993-02-09 | Valmet Paper Machinery Inc. | Method of and apparatus for cutting a lead-in strip of a paper web |
| GB2344042A (en) * | 1998-09-29 | 2000-05-24 | Jeffery Boardman | Method of producing resistive heating elements on an uninsulated conductive substrate |
-
2000
- 2000-12-15 GB GB0030623A patent/GB2374783A/en not_active Withdrawn
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5185063A (en) * | 1990-02-22 | 1993-02-09 | Valmet Paper Machinery Inc. | Method of and apparatus for cutting a lead-in strip of a paper web |
| GB2344042A (en) * | 1998-09-29 | 2000-05-24 | Jeffery Boardman | Method of producing resistive heating elements on an uninsulated conductive substrate |
Cited By (18)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2445464B (en) * | 2007-01-04 | 2010-10-27 | 2D Heat Ltd | A self-regulating electrical resistance heating element |
| WO2008081167A3 (en) * | 2007-01-04 | 2008-11-13 | 2D Heat Ltd | A self-regulating electrical resistance heating element |
| GB2445464A (en) * | 2007-01-04 | 2008-07-09 | 2D Heat Ltd | A self-regulating electrical resistance heating element |
| RU2464744C2 (en) * | 2007-01-04 | 2012-10-20 | 2Д Хит Лимитед | Self-controlled heating element with electric resistance |
| AU2009259092B2 (en) * | 2008-06-09 | 2013-04-04 | 2D Heat Limited | A self-regulating electrical resistance heating element |
| CN102047752A (en) * | 2008-06-09 | 2011-05-04 | 2D热度有限公司 | A self-regulating electrical resistance heating element |
| GB2460833B (en) * | 2008-06-09 | 2011-05-18 | 2D Heat Ltd | A self-regulating electrical resistance heating element |
| WO2009150454A1 (en) * | 2008-06-09 | 2009-12-17 | 2D Heat Limited | A self-regulating electrical resistance heating element |
| GB2460833A (en) * | 2008-06-09 | 2009-12-16 | 2D Heat Ltd | Self-regulating electrical resistance heating elements |
| JP2019516207A (en) * | 2016-03-02 | 2019-06-13 | ワットロー・エレクトリック・マニュファクチャリング・カンパニー | Heater element as a sensor for temperature control in transient systems |
| WO2017151960A1 (en) * | 2016-03-02 | 2017-09-08 | Watlow Electric Manufacturing Company | Heater element as sensor for temperature control in transient systems |
| WO2017151965A1 (en) * | 2016-03-02 | 2017-09-08 | Watlow Electric Manufacturint Company | Heater element having targeted decreasing temperature resistance characteristics |
| US10544722B2 (en) | 2016-03-02 | 2020-01-28 | Watlow Electric Manufacturing Company | Virtual sensing system |
| US10648390B2 (en) | 2016-03-02 | 2020-05-12 | Watlow Electric Manufacturing Company | System and method for axial zoning of heating power |
| US10724417B2 (en) | 2016-03-02 | 2020-07-28 | Watlow Electric Manufacturing Company | Dual-purpose heater and fluid flow measurement system |
| US10760465B2 (en) | 2016-03-02 | 2020-09-01 | Watlow Electric Manufacturing Company | Heater element having targeted decreasing temperature resistance characteristics |
| US10934921B2 (en) | 2016-03-02 | 2021-03-02 | Watlow Electric Manufacturing Company | Heater element as sensor for temperature control in transient systems |
| EP4047193A1 (en) * | 2016-03-02 | 2022-08-24 | Watlow Electric Manufacturing Company | Heater element having targeted decreasing temperature resistance characteristics |
Also Published As
| Publication number | Publication date |
|---|---|
| GB0030623D0 (en) | 2001-01-31 |
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Legal Events
| Date | Code | Title | Description |
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| COOA | Change in applicant's name or ownership of the application | ||
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |