GB2288110A

GB2288110A - Heater or temperature sensor using a layer of metal matrix compound

Info

Publication number: GB2288110A
Application number: GB9506523A
Authority: GB
Inventors: Helmut Nechansky
Original assignee: Electrovac AG
Current assignee: Electrovac AG
Priority date: 1994-03-30
Filing date: 1995-03-30
Publication date: 1995-10-04
Anticipated expiration: 2015-03-30
Also published as: AT408299B; GB2288110B; CH689530A5; ITUD950053A1; FR2718317A1; ITUD950053A0; FR2718317B1; GB9506523D0; ATA67994A; IT1280150B1; DE19510989A1

Description

i 2288110

Description:

The present invention relates to a component combination for electric hotplates, igniters, temperature sensors or the like, which comprises an electric resis- tance element, an electrically insulating layer and a heat-transfer plate.

in principle, such a component combination is present in every hitherto customary hotplate or cooking plate in which a heating spiral is provided underneath a heat-transfer plate, which spiral is separated from the heat-transfer plate by an insulating air gap. The transfer of heat from the heating spiral to the air and from the air to the heat-transfer plate is relatively poor, which is why considerable heat losses are to be observed is in these constructions.

Attempts have therefore been made to replace the air gap by a layer of a solid insulation material.

However, the cast metal materials generally used as heat-transfer plates can, in respect of their thermal expansion properties, be matched to solid insulation materials only poorly, so that a component combination having an insulation layer consisting of a solid has hitherto been virtually impossible because of the occurrence of great thermal stresses.

It is an object of the present invention to improve this type of constructions in terms of heat technology.

To achieve this object, it is proposed according to the invention that the heat-transfer plate consists at least partly, preferably completely, of a metal matrix compound (MMC) material.

This material, which is known in another context, inter alia for the production of chip housings in electronics, comprises a reinforcing material impregnated or infiltrated with a matrix metal. The selection of the reinforcing component and the metal allows the properties of these composite materials to be influenced as desired with regard to mechanical and also thermal properties.

This also makes it possible to achieve matching of the thermal expansion properties of the heat-transfer plate to those of an insulation material.

Therefore, according to a preferred embodiment of the invention, the electrically insulating layer in component combinations of the type mentioned in the introduction comprises an electrically insulating solid and no longer of air, in particular with the material of the MMC plate and the material of the electrically insulating layer having coefficients of thermal expansion which are essentially matched to one another.

This component combination makes it possible to use a thin-layered structure, preferably based on silicon, as resistance element.

In practice, an insulation material is applied to is the heat-transfer plate or in depressions thereof, the dimensions of the insulation material corresponding essentially to those of the resistance element. The consumption of insulation material is thereby kept low, which has a favourable effect on the costs of the combi- nation elements produced.

A further embodiment of the invention can comprise the insulating layer being constructed as an insulation plate integrated, except for one side, into the heat-transfer plate, in which insulation plate the resistance element is applied, e.g. laid on or soldered on.

Heat-transfer plate and insulator can thereby be produced jointly. The integration of the insulation plate is best carried out by means of a metal compound which is formed in the course of the infiltration of the reinforcing material with the matrix metal. The infiltration is preferably carried out in such a way that the metal is cast around the reinforcement, so that a surface layer of the matrix metal is formed.

A further embodiment of the invention can comprise all resistance elements and the strip conductors (4) for the supply of electricity being arranged on a common insulation layer.

The process costs can thereby be reduced and 0 process steps can be saved.

As a further embodiment of the invention, it can be provided for the strip conductors for the resistance element to consist of a metal layer cast onto the insula tion layer.

On the other hand, however, the insulation layer can also be provided with groove-shaped depressions which are filled with the matrix metal during the infiltration process and can be used as supply and outlet leads.

This makes it possible for the surface of the MMC body to be subsequently worked up, with the metal remaining in the grooves serving as electrical supply and outlet leads.

Supply and outlet leads for the resistance element can, in a further embodiment of the invention, be produced by local removal of a surface metal layer which originates from the casting of metal around the MMC material occurring at the same time as the metal infiltration of the latter. 20 in a further embodiment of the invention, the reinforcement present in the MMC material is an oxide, carbide and/or nitride ceramic, e.g. silicon carbide, aluminium nitride, beryllium oxide, aluminium oxide, boron nitride or carbon, and/or a metal, e.g. molybdenum, having a higher melting point than the matrix metal. The metallic component of the MMC material can, in an embodiment of the invention, comprise one or more metals selected from the group consisting of aluminium, iron, nickel, cobalt, silicon, copper, molybdenum or alloys of the same.

The MMC material has metal-filled channels which, for example, connect opposite sides of the plate with one another. During the metal infiltration these drilled holes or channels are filled with the metal and then form heat-conducting bridges by means of which a more rapid removal or dissipation of the heat in the desired direction occurs.

According to another variant of the invention, the material of the electrically insulating layer is preferably an oxide, carbide and/or nitride ceramic, for example aluminium nitride, aluminium oxide or beryllium oxide, or a heat- resistant, electrically insulating plastic, such as polybenzimidazole (PB1).

Apart from the silicon thin-layer structures, the resistance element used can also be, according to a further variant, an element based on a PTC or NTC ceramic. These types of ceramic are materials having temperaturedependent conductivity values and can be advantageously used for this purpose.

A further feature of the invention can comprise the resistance element being constructed as a heating element.

The conductor strips can here be produced in a is known way, e.g. by photolithography, etching, action of a laser beam, or the like.

In a further embodiment of the invention, the heat-transfer plate can be provided with a sealing ring.

The heat-transfer plate can thereby be installed in a heat-insulated manner.

In the use of the component combination of the invention as a cooking plate, the surface layer of the heat-transfer plate advantageously has a layer for increasing the mechanical strength on the side opposite the heating elements. It is also possible to provide a layer for improving the smoothness and for intensifying the contact with the article to be heated which is placed on top.

The component combination of the invention can be produced by putting together its constituents individually or the combination of heat-transfer plate and insulator can be prefabricated and the resistance element can be applied subsequently, e.g. laid on or soldered on.

One embodiment of a hotplate or cooking plate of the invention is shown in the accompanying drawings which serve to illustrate the invention.

Fig. 1 shows a component combination of the invention from below; Fig. 2 shows a section along the line II-II of f; is Fig. 1.

Fig. 3 shows a further embodiment of a component combination of the invention from below and Fig. 4 shows a section along the line IV-1V in Fig. 3.

Fig. 1 shows a component combination of the invention in the form of a disc-shaped hotplate 7 in a view from below, based on its use position. The hotplate 7 consists of a heat-transfer plate 1 and rectangular insulation plates 2 arranged in a star pattern on the underside thereof, with the insulation plates being integrally let into depressions in the underside of the heat- transfer plate 1 except for one side.

The heat-transfer plate 1 comprises a metal matrix compound material MC), while the insulation layers comprise an electrically insulating solid, for example an oxide, carbide and/or nitride ceramic such as aluminium nitride, aluminium oxide or beryllium oxide, or a heat-resistant, electrically insulating plastic, such as polybenzimidazole (PB1), on the surfaces of which facing away from the heat-transfer plate 1 there are applied.planar resistance elements 3.

The MMC material can contain as reinforcement, for example, an oxide, carbide and/or nitride ceramic, for example silicon carbide, aluminium nitride, beryllium oxide, aluminium oxide, boron nitride, or carbon and its metallic component can comprise, for example, one or more metals selected from the group consisting of aluminium, iron, nickel, cobalt, silicon, copper, molybdenum or alloys thereof. The metal matrix compound of the heattransfer plate 1 and the insulation plates 2 here have coefficients of thermal expansion which are essentially matched to one another, so that thermal stresses can be avoided. As reinforcement, it is also possible to use a metal, e.g. molybdenum, which has a higher melting point than the matrix metal.

The MMC material can be provided, prior to the metal infiltration, with drilled holes or channels 9, as is indicated in Figs. 2 and 4, which, for example, connect two or more sides with one another. During the metal infiltration, these drilled holes or channels are filled with the matrix metal and are then thermally conductive bridges by means of which a more rapid dissipation or removal of the heat occurs in directions which can be determined by the arrangement of the drilled holes or channels.

The resistance elements 3 are here made of a thin-layer structure based on silicon, but it is also possible to use other suitable thin-layer materials. As can be seen from Figs. 1 and 2, the insulation plates 2 and the resistance elements 3 have approximately equal dimensions, with the insulation plates 2 continuing into is insulation strips 8 which are to extend radially against the strip conductor 4, on which insulation strips 8 there run conductor bridges 41 connected to the annular and the central strip conductor 4. The way in which the resistance elements 3 are applied to the insulation layers 2 can vary, for instance by laying on or soldering on. on the surface of these insulation plates 2 there are located the resistance elements 3 which are constructed as heating elements. The heating elements 3 are supplied with power via strip conductors 4 which comprise the metal of the MMC material, are arranged on insulation strips and are - constructed as supply and outlet leads, with the heating elements 3 being connected in parallel.

However, the resistance elements can also be based on a PTC or NTC ceramic, whereby the known properties of the ceramic can be utilized for temperature stabilization.

For better installation of the hotplate 7 into a support arrangement, such as a cooker plate or the like, and for better thermal insulation thereof, the heattransfer plate 1 has an inset sealing ring 5. This can be co-manufactured in the production of the plate or can be set in later.

Fig. 2 shows a section through the plate 7 of Fig. 1 along the line II-II. It can be clearly seen that the insulation plate 2 is arranged in a depression of the P heattransfer plate 1, whereby it is, apart from one side, integrated into the MMC plate. The heating element 3 is connected to the electric supply and outlet leads 4 arranged on the insulation strips 8.

Fig. 3 and Fig. 4 show a further embodiment in which components corresponding to Figs. 1 and 2 are provided with the same reference numbers. Unlike Figs. 1 and 2, the heat-transfer plate 1 bears a continuous insulation layer 10 on which the strip conductors 4 or conductor bridges 41 and the heating elements 3 are arranged.

The strip conductors or conductor bridges 4 for the heating elements 3 are produced by local removal, for instance by etching or the like, of a surface metal layer is which originates from the casting of metal around the MMC material occurring at the same time as the metal infiltration of the MMC material. As an alternative thereto, it is also possible for depressions, for example grooves, to be provided in the insulation layer 10, which depress- ions are filled with the matrix metal during the infiltration process and can be used as supply and outlet leads, since after this process the surface of the MMC body can be worked off, with the metal remaining in the grooves serving as electric supply and outlet leads. The heat-transfer plate 2 can either consist entirely of the metal matrix compound material, as shown in Figs. 1 and 2, or it can have only a core 111 of such a material, which core is imbedded in the matrix material, as shown by way of example in Figs. 3 and 4. 30 For household use, the heat-transfer plate 1 has a surface layer 6 on the side opposite the side having the insulating layers 2, which surface layer serves to increase the mechanical strength, to increase the smoothness and intensify the contact, i.e. to increase the heat transfer, with the articles placed on top, such as cooking vessels and the like. The sealing ring 5 which is provided for the insulating installation of the hotplate can likewise be seen.

The component combination of the invention is more compact than the previous elements, since it has no air gap and can get by with comparatively small heating and insulation elements. It shows extremely small heat losses, which ensures more rapid heating and a more userfriendly service.

The combination of the invention can be used, with the same advantages, as an igniter, for example for airbags or the like, and also as a temperature sensor.

1 #1 A

Claims

Patent clains:

Component combination for electric hotplates, igniters, temperature sensors or the like, comprising an electric resistance element, an electrically insulating layer and a heat-transfer plate arranged on top of one another, characterized in that the heat-transfer plate (1) consists at least partly, preferably entirely, of a metal matrix compound (MMC) material.
2. Component combination according to Claim 1, 10 characterized in that the electrically insulating layer (2;10) comprises an electrically insulating solid.
3. Component combination according to Claim 2, characterized in that the material of the MMC plate (1) and the material of the electrically insulating layer is (2;10) have coefficients of thermal expansion which are essentially matched to one another.
4. Component combination according to any one of Claims 1 to 3, characterized in that the resistance element (3) comprises a thin-layer structure, preferably based on silicon.
5. Component combination as claimed in any one of Claims 1 to 4, characterized in that the insulating layer (2) has-dimensions corresponding essentially to those of the resistance element (3).
6. Component combination as claimed in Claim 5, characterized in that the insulating layer (2) is constructed as an insulation plate which is integrated, except for one side, into the heat- transfer plate (1), on which insulation plate the resistance element (3) is applied, e.g. laid on or soldered on.
7. Component combination according to any one of Claims 1 to 5, characterized in that all resistance elements (3) and the strip conductors (4) are, for them to be supplied with electricity, arranged on a common insulation layer (10).
8. Component combination according to any one of Claims 1 to 7, characterized in that the insulation layer (2;10) is provided with grooveshaped depressions which are filled with metal during the infiltration process and can be used as electric supply and outlet leads.
9. Component combination according to any one of Claims 1 to 8, characterized in that the strip conductors (4) for the resistance element (3) comprise a metal layer cast onto the insulation layer (2;10).
10. Component combination according to Claim 9, characterized in that the strip conductors (4) are produced by local removal of a surface metal layer which originates from the casting of metal around the MMC material at the same time as the metal infiltration of the MMC material.
11. Component combination according to any one of Claims 1 to 10, characterized in that the MMC material contains as reinforcement an oxide, carbide and/or is nitride ceramic, for example silicon carbide, aluminium nitride, beryllium oxide, aluminium oxide, boron nitride, or carbon and/or a metal, e.g. molybdenum, having a higher melting point than the matrix metal.
12. Component combination according to any one of 20 Claims 1 to 11, characterized in that the metallic component of the MMC material comprises one or more metals selected from the group consisting of aluminium, iron, nickel, cobalt, silicon, copper, molybdenum or alloys thereof.
13. Component combination according to any one of Claims 1 to 12, characterized in that the MMC material has metal-filled channels (9) which, for example, connect opposite sides of the plate with one another.
14. Component combination according to any one of 30 Claims 1 to 13, characterized in that the material of the electrically insulating layer (2;10) is an oxide, carbide and/or nitride ceramic, for example aluminium nitride, aluminium oxide or beryllium oxide, or a heat-resistant electrically insulating plastic, such as polybenz- imidazole (PBI).
15. Component combination according to any one of Claims 1 to 14, characterized in that the resistance element (3) is an element based on a PTC or NTC ceramic.
16. Component combination according to any one of Ii Claims 1 to 15, characterized in that the resistance element (3) is constructed as a heating element.
17. Component combination according to any one of Claims 1 to 16, characterized in that the heat-transfer plate (1) is provided with a sealing ring (5).
18. Component combination according to any one of Claims 1 to 17, characterized in that the heat-transfer plate (1) is provided on the side opposite the heating elements with a layer (6) for increasing the mechanical strength or for increasing the smoothness and intensifying the contact with an article to be placed on top.