EP0463581A1 - Self-regulating heating element for heating flowing media - Google Patents
Self-regulating heating element for heating flowing media Download PDFInfo
- Publication number
- EP0463581A1 EP0463581A1 EP91110271A EP91110271A EP0463581A1 EP 0463581 A1 EP0463581 A1 EP 0463581A1 EP 91110271 A EP91110271 A EP 91110271A EP 91110271 A EP91110271 A EP 91110271A EP 0463581 A1 EP0463581 A1 EP 0463581A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- heating element
- metal
- self
- adhesive
- adhesive layer
- 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.)
- Ceased
Links
- 238000010438 heat treatment Methods 0.000 title claims abstract description 28
- 239000000853 adhesive Substances 0.000 claims abstract description 23
- 230000001070 adhesive effect Effects 0.000 claims abstract description 23
- 229910052751 metal Inorganic materials 0.000 claims abstract description 23
- 239000002184 metal Substances 0.000 claims abstract description 23
- 239000012790 adhesive layer Substances 0.000 claims abstract description 11
- 239000000919 ceramic Substances 0.000 claims abstract description 5
- 238000007650 screen-printing Methods 0.000 claims abstract description 5
- 238000004519 manufacturing process Methods 0.000 claims description 2
- 238000000034 method Methods 0.000 description 4
- 238000003825 pressing Methods 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 2
- 230000007774 longterm Effects 0.000 description 2
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 230000006378 damage Effects 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005538 encapsulation Methods 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 238000007667 floating Methods 0.000 description 1
- 239000010410 layer Substances 0.000 description 1
- 239000002923 metal particle Substances 0.000 description 1
- 238000001465 metallisation Methods 0.000 description 1
- 239000012811 non-conductive material Substances 0.000 description 1
- 238000013021 overheating Methods 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
- 229910052709 silver Inorganic materials 0.000 description 1
- 239000004332 silver Substances 0.000 description 1
- 229910000679 solder Inorganic materials 0.000 description 1
Classifications
-
- 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—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor
- H05B3/12—Heating 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
- H05B3/14—Heating 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 the material being non-metallic
- H05B3/141—Conductive ceramics, e.g. metal oxides, metal carbides, barium titanate, ferrites, zirconia, vitrous compounds
Definitions
- the invention relates to a self-regulating heating element for heating flowing media with a metal body made of good heat-conducting metal as a heat exchanger, on the surface of which at least one disk-shaped ceramic thermistor (PTC resistor) is attached by means of a thermally and electrically conductive plastic adhesive, and also a process for the production thereof self-regulating heating element.
- PTC resistor disk-shaped ceramic thermistor
- PTC thermistors for heating flowing media.
- a heating element having the above-mentioned features is described in DE-OS-37 08 056.
- the metal body of the heating element consists of several individual bodies, in particular of two segments, each complementing a cylindrical arrangement, each with a semicircular cross section, which simultaneously serve as current leads to the PTC thermistors.
- At least one disk-shaped PTC thermistor, with its large end faces bearing the coatings, is attached to each of the two flat interfaces of the adjacent segments by means of an electrically and thermally conductive adhesive.
- a gripping bracket of the entire system is provided, for example by a rigid plastic frame. It is therefore a heating element with two-sided heat extraction.
- the adhesive strength of the polymer decreases at high temperatures in the case of plastic adhesives which are highly filled with metal particles.
- the reduction of the adhesive strength, especially at temperatures above 200 ° C, is particularly problematic in the case of high current densities, since the connection, which is reduced to many small-area contacts, is associated with local overheating of these remaining adhesive spots.
- thin-layer metallization of the PTC thermistor there is a risk of destruction of the metal assignments after prolonged cyclical temperature stress the PTC thermistor and thus also the entire heating element. This property of the plastic adhesive, which jeopardizes the long-term reliability of the heating element, cannot be influenced directly.
- the present invention is therefore based on the object of specifying a self-regulating heating element with improved long-term reliability, which can also be produced in a simplified manner.
- the ceramic component of the type specified is characterized in that a metal sieve is inserted into the adhesive layer between the PTC thermistor and the metal body.
- the method of the type mentioned at the outset for producing such a self-regulating heating element is characterized in accordance with the invention in that the adhesive layer is applied by screen printing.
- a desired pressing strength can be selected without the adhesive being displaced from the joint if the metering of the adhesive applied using the screen printing process is carried out in such a way that the applied adhesive layer is equal to the thickness of the metal sieve.
- two disk-shaped PTC thermistors with a thickness of approximately 0.8 mm, the large end faces of which are each approximately 2 cm2 in size, are fastened between the two individual segments of a cylindrical aluminum heat exchanger using a silver conductive adhesive.
- PTC thermistors with a reference temperature of 220 ° C and a nominal voltage of 14 V can be used.
- the metal screen can preferably be wider-meshed than the metal mesh usually used for the screen printing of ceramic components.
- the curing as already known from DE-PS-31 51 109, can also be done by applying a voltage to it System.
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Ceramic Engineering (AREA)
- Thermistors And Varistors (AREA)
Abstract
Description
Die Erfindung betrifft ein selbstregelndes Heizelement zum Erwärmen strömender Medien mit einem aus gut wärmeleitendem Metall bestehenden Metallkörper als Wärmeübertrager, an dessen Oberfläche mindestens ein scheibenförmiger keramischer Kaltleiter (PTC-Widerstand) mittels eines thermisch und elektrisch leitfähigen Kunststoffklebers befestigt ist und ferner ein Verfahren zur Herstellung dieses selbstregelnden Heizelementes.The invention relates to a self-regulating heating element for heating flowing media with a metal body made of good heat-conducting metal as a heat exchanger, on the surface of which at least one disk-shaped ceramic thermistor (PTC resistor) is attached by means of a thermally and electrically conductive plastic adhesive, and also a process for the production thereof self-regulating heating element.
Die Verwendung von Kaltleitern zum Aufheizen strömender Medien ist bekannt. Ein Heizelement, das die obengenannten Merkmale aufweist, ist in der DE-OS-37 08 056 beschrieben.The use of PTC thermistors for heating flowing media is known. A heating element having the above-mentioned features is described in DE-OS-37 08 056.
In der genannten Offenlegungsschrift besteht der Metallkörper des Heizelementes aus mehreren einzelnen Körpern, insbesondere aus zwei sich zu einer zylinderförmigen Anordnung ergänzenden Segmenten mit jeweils halbkreisförmigem Querschnitt, die gleichzeitig als Stromzuführungen zu den Kaltleitern dienen. Mindestens ein scheibenförmiger Kaltleiter ist mit seinen die Belegungen tragenden großen Stirnflächen an jeder der beiden ebenen Grenzflächen der benachbarten Segmente mittels eines elektrisch und thermisch leitenden Klebers befestigt. Zur Unterstützung des Klebers ist eine umklammernde Halterung des gesamten Systems, beispielsweise durch einen starren Kunststoffrahmen, vorgesehen. Es handelt sich also um ein Heizelement mit zweiseitiger Wärmeauskopplung.In the aforementioned publication, the metal body of the heating element consists of several individual bodies, in particular of two segments, each complementing a cylindrical arrangement, each with a semicircular cross section, which simultaneously serve as current leads to the PTC thermistors. At least one disk-shaped PTC thermistor, with its large end faces bearing the coatings, is attached to each of the two flat interfaces of the adjacent segments by means of an electrically and thermally conductive adhesive. To support the adhesive, a gripping bracket of the entire system is provided, for example by a rigid plastic frame. It is therefore a heating element with two-sided heat extraction.
Elektrisch und thermisch leitfähige Klebstoffe für höhere Betriebstemperaturen sind beispielsweise in der US-PS 3 898 422 beschrieben. Allerdings wird dort das PTC-Heizelement nur einseitig an das aufzuheizende Objekt mit einem solchen Klebstoff angeklebt, während die zweite Seite des PTC-Heizelementes über eine Klemmfeder kontaktiert wird.Electrically and thermally conductive adhesives for higher operating temperatures are described, for example, in US Pat. No. 3,898,422. However, the PTC heating element is only glued to one side of the object to be heated with such an adhesive, while the second side of the PTC heating element is contacted via a clamping spring.
Alle bisher bekannten möglichen Verbindungen der Kaltleiter mit dem Wärmeübertrager weisen neben einer Reihe von Vorteilen auch Nachteile auf. Lötverbindungen sind hinsichtlich thermischer Ausdehnungseffekte nicht flexibel genug, während großflächige Klemmkontaktierungen oftmals zu einer problematischen Stromverteilung auf der Oberfläche des Kaltleiters führen. Auch bei Verwendung der Klebetechnik treten zwei grundsätzliche Probleme auf.All previously known possible connections of the PTC thermistor to the heat exchanger have disadvantages in addition to a number of advantages. Solder connections are not flexible enough with regard to thermal expansion effects, while large-area terminal contacts often lead to problematic current distribution on the surface of the PTC thermistor. Two fundamental problems also arise when using adhesive technology.
Einerseits muß während des Aushärtens des Klebers in der Montage auf eine exakte Fixierung und Ausrichtung der Teile des Heizelementes zueinander geachtet werden, da sonst ein nachfolgendes Umspritzen der Heizelemente mit Kunststoff nicht mehr möglich ist. Bereits bei Versetzungen der Teile zueinander um einige hunderstel Millimeter besteht die Gefahr, daß beim fertigen Heizelement die empfindlichen Kaltleiter nicht vollständig abgedichtet sind. Hinzu kommt, daß durch sehr aufwendige spezielle Halterungen versucht werden muß, den Kaltleiter während des Aushärtens zu fixieren, ohne daß dabei durch Druck auf die Klebestelle der dünnflüssige Kleber aus der Klebefuge herausgepreßt wird. Ein solches fixiertes, aber 'schwimmendes' Aushärten wird durchgeführt, um ein Herumfließen des leitfähigen Klebers um den PTC, und damit die Gefahr eines Kurzschlusses zu vermeiden. Es wird zusätzlich dadurch erschwert, daß die notwendige Fixierungsvorrichtung in einem relativ kleinen Ofen zum Aushärten Platz haben soll.On the one hand, care must be taken during the curing of the adhesive in the assembly to ensure that the parts of the heating element are precisely fixed and aligned with one another, since a subsequent encapsulation of the heating elements with plastic is no longer possible. Even if the parts are offset by a few hundredths of a millimeter, there is a risk that the sensitive PTC thermistor will not be completely sealed in the finished heating element. In addition, very complex special brackets must be used to try to fix the PTC thermistor during curing without the thin adhesive being pressed out of the adhesive joint by pressure on the adhesive point. Such a fixed, but 'floating' hardening is carried out in order to avoid the conductive adhesive flowing around the PTC and thus the risk of a short circuit. It is further complicated by the fact that the necessary fixing device should have space for curing in a relatively small oven.
Bei Verwendung der Klebetechnik ist ferner in Betracht zu ziehen, daß bei hochgradig mit Metallpartikeln gefüllten Kunststoffklebern bei hohen Temperaturen die Haftfestigkeit des Polymers abnimmt. Die Verminderung der Haftfestigkeit, vor allem bei Temperaturen oberhalb von 200° C, ist besonders im Falle hoher Stromdichten problematisch, da die auf viele kleinflächige Kontakte verminderte Verbindung mit örtlicher Überhitzung dieser verbleibenden Haftstellen einhergeht. Besonders bei Dünnschichtmetallisierung des Kaltleiters besteht nach längerer zyklischer Temperaturbelastung die Gefahr der Zerstörung der Metallbelegungen des Kaltleiters und damit auch des gesamten Heizelementes. Diese die Dauerzuverlässigkeit des Heizelementes in Frage stellende Eigenschaft des Kunststoffklebers ist nicht direkt beeinflußbar.When using the adhesive technology, it should also be taken into account that the adhesive strength of the polymer decreases at high temperatures in the case of plastic adhesives which are highly filled with metal particles. The reduction of the adhesive strength, especially at temperatures above 200 ° C, is particularly problematic in the case of high current densities, since the connection, which is reduced to many small-area contacts, is associated with local overheating of these remaining adhesive spots. Especially with thin-layer metallization of the PTC thermistor, there is a risk of destruction of the metal assignments after prolonged cyclical temperature stress the PTC thermistor and thus also the entire heating element. This property of the plastic adhesive, which jeopardizes the long-term reliability of the heating element, cannot be influenced directly.
Der vorliegenden Erfindung liegt daher die Aufgabe zugrunde, ein selbstregelndes Heizelement mit verbesserter Dauerzuverlässigkeit anzugeben, das auch vereinfacht herstellbar ist.The present invention is therefore based on the object of specifying a self-regulating heating element with improved long-term reliability, which can also be produced in a simplified manner.
Zur Lösung dieser Aufgabe ist das keramische Bauelement der eingangs angegebenen Art dadurch gekennzeichent, daß in die Kleberschicht zwischen dem Kaltleiter und dem Metallkörper ein Metallsieb eingelegt ist.To solve this problem, the ceramic component of the type specified is characterized in that a metal sieve is inserted into the adhesive layer between the PTC thermistor and the metal body.
Das Verfahren der eingangs angegebenen Art zur Herstellung eines solchen selbstregelnden Heizelementes ist erfindungsgemäß dadurch gekennzeichnet, daß die Kleberschicht im Siebdruckverfahren aufgetragen wird.The method of the type mentioned at the outset for producing such a self-regulating heating element is characterized in accordance with the invention in that the adhesive layer is applied by screen printing.
Beim Aushärten ist es nun möglich, den Kaltleiter starr an die Oberfläche der Metallkörper zu pressen. Dabei kann eine gewünschte Preßstärke gewählt werden, ohne daß der Kleber aus der Fuge verdrängt wird, wenn die Dosierung des im Siebdruckverfahren aufgetragenen Klebers so erfolgt, daß die aufgetragene Kleberschicht gleich der Dicke des Metallsiebes ist.When hardening, it is now possible to rigidly press the PTC thermistor onto the surface of the metal body. A desired pressing strength can be selected without the adhesive being displaced from the joint if the metering of the adhesive applied using the screen printing process is carried out in such a way that the applied adhesive layer is equal to the thickness of the metal sieve.
Bei einer vorteilhaften Ausführungsform der Erfindung werden zwei scheibenförmige Kaltleiter mit einer Dicke von ca. 0,8 mm, deren große Stirnflächen jeweils ca. 2 cm² groß sind, mittels eines Silberleitklebers zwischen den beiden Einzelsegmenten eines zylinderförmigen Wärmeübertragers aus Aluminium befestigt. Es können beispielsweise Kaltleiter mit einer Bezugstemperatur von 220° C und einer Nennspannung von 14 V verwendet werden. Das Metallsieb kann vorzugsweise weitmaschiger als die üblicherweise für den Siebdruck keramischer Bauelemente verwendeten Metallgewebe sein.In an advantageous embodiment of the invention, two disk-shaped PTC thermistors with a thickness of approximately 0.8 mm, the large end faces of which are each approximately 2 cm² in size, are fastened between the two individual segments of a cylindrical aluminum heat exchanger using a silver conductive adhesive. For example, PTC thermistors with a reference temperature of 220 ° C and a nominal voltage of 14 V can be used. The metal screen can preferably be wider-meshed than the metal mesh usually used for the screen printing of ceramic components.
Es wurden Dauerversuche durchgeführt, bei denen das Heizelement durch einminütiges Aufheizen und darauf folgendes anderthalbminütiges, beschleunigtes Abkühlen bis unter 40° C zyklisch belastet wurde. Dabei zeigte sich eine deutliche Überlegenheit der Heizelemente mit dem erfindungsgemäß eingelegten Metallsieb, die darauf zurückzuführen ist, daß selbst bei Ablösung der Kleberschicht aufgrund der hohen thermischen Belastung immer noch genügend Kontaktfläche des Metallsiebes zu einer sicheren Stromleitung zur Verfügung steht. Die überraschend hohe Beständigkeit der Kontaktsicherheit kommt unter anderem auch durch eine leichte strukturelle Federwirkung des Metallsiebes zustande. Durch das Pressen während des Aushärtens des Klebers entsteht eine Vorspannung, die auch im Falle des Ablösens der Kleberschicht hilft, einen sicheren Kontakt aufrecht zu erhalten.Endurance tests were carried out in which the heating element was cyclically loaded by heating it for one minute and then accelerating it for one and a half minutes to below 40 ° C. This showed a clear superiority of the heating elements with the metal sieve inserted according to the invention, which can be attributed to the fact that even when the adhesive layer is detached due to the high thermal load, there is still sufficient contact area of the metal sieve for a safe power line. The surprisingly high stability of the contact reliability is due, among other things, to the slight structural spring action of the metal sieve. Pressing while the adhesive is curing creates a pretension, which also helps to maintain a secure contact even if the adhesive layer is removed.
Wird die Vorrichtung zum Pressen der Teile während des Aushärtens aus nichtleitenden Materialien hergestellt, so kann bei Kaltleitern mit Bezugstemperaturen oberhalb 180° C die Aushärtung, wie an sich bereits aus der DE-PS-31 51 109 bekannt, auch durch Anlegen einer Spannung an das System erfolgen.If the device for pressing the parts during the curing process is made of non-conductive materials, then in PTC thermistors with reference temperatures above 180 ° C, the curing, as already known from DE-PS-31 51 109, can also be done by applying a voltage to it System.
Claims (3)
dadurch gekennzeichnet,
daß in die Kleberschicht zwischen dem Kaltleiter und dem Metallkörper ein Metallsieb eingelegt ist.Self-regulating heating element for heating flowing media with a metal body made of heat-conducting metal as a heat exchanger, on the surface of which at least one disk-shaped ceramic thermistor (PTC resistor) is attached by means of a thermally and electrically conductive plastic adhesive,
characterized,
that a metal sieve is inserted into the adhesive layer between the PTC thermistor and the metal body.
dadurch gekennzeichnet,
daß die Dicke des Metallsiebes gleich der Dicke der Kleberschicht ist.Self-regulating heating element for heating flowing media according to claim 1,
characterized,
that the thickness of the metal screen is equal to the thickness of the adhesive layer.
dadurch gekennzeichnet,
daß die Kleberschicht im Siebdruckverfahren aufgetragen wird.A method of manufacturing a self-regulating heating element according to claim 1,
characterized,
that the adhesive layer is applied by screen printing.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE4020466 | 1990-06-27 | ||
| DE4020466 | 1990-06-27 | ||
| DE4021130 | 1990-07-03 | ||
| DE4021130 | 1990-07-03 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| EP0463581A1 true EP0463581A1 (en) | 1992-01-02 |
Family
ID=25894512
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP91110271A Ceased EP0463581A1 (en) | 1990-06-27 | 1991-06-21 | Self-regulating heating element for heating flowing media |
Country Status (1)
| Country | Link |
|---|---|
| EP (1) | EP0463581A1 (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4210197C1 (en) * | 1992-03-28 | 1993-06-09 | Tuerk & Hillinger Gmbh, 7200 Tuttlingen, De | Self-regulating electric heating device using positive temp coefficient elements - has holes drilled in surface of each heat dissipation element before bonding to surface of positive temp coefficient element. |
| DE4225990C1 (en) * | 1992-08-06 | 1993-08-05 | Tuerk & Hillinger Gmbh, 7200 Tuttlingen, De | Mfg. electrical heating device with PTC elements - joined to heat removing elements by conductive adhesive in inner region but by non-conductive adhesive at outer edges |
| WO1994004872A1 (en) * | 1992-08-17 | 1994-03-03 | Rapa Rausch & Pausch Elektrotechnische Spezialfabrik Gmbh | Oil-burner nozzle connection |
| AT401682B (en) * | 1995-01-23 | 1996-11-25 | Vaillant Gmbh | GAS-FIRED COMBINATION CIRCUIT HEATER |
| DE102019107546A1 (en) * | 2019-03-25 | 2020-10-01 | Webasto SE | Method for contacting a heating element and heating element |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3708056A1 (en) * | 1987-03-12 | 1988-09-22 | Siemens Ag | Heating element for heating flowing media |
| DE3730195A1 (en) * | 1987-09-09 | 1989-03-30 | Eltra Gmbh & Co Kg | Electric heater with positive temperature coefficient |
-
1991
- 1991-06-21 EP EP91110271A patent/EP0463581A1/en not_active Ceased
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3708056A1 (en) * | 1987-03-12 | 1988-09-22 | Siemens Ag | Heating element for heating flowing media |
| DE3730195A1 (en) * | 1987-09-09 | 1989-03-30 | Eltra Gmbh & Co Kg | Electric heater with positive temperature coefficient |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4210197C1 (en) * | 1992-03-28 | 1993-06-09 | Tuerk & Hillinger Gmbh, 7200 Tuttlingen, De | Self-regulating electric heating device using positive temp coefficient elements - has holes drilled in surface of each heat dissipation element before bonding to surface of positive temp coefficient element. |
| DE4225990C1 (en) * | 1992-08-06 | 1993-08-05 | Tuerk & Hillinger Gmbh, 7200 Tuttlingen, De | Mfg. electrical heating device with PTC elements - joined to heat removing elements by conductive adhesive in inner region but by non-conductive adhesive at outer edges |
| WO1994004872A1 (en) * | 1992-08-17 | 1994-03-03 | Rapa Rausch & Pausch Elektrotechnische Spezialfabrik Gmbh | Oil-burner nozzle connection |
| US5679276A (en) * | 1992-08-17 | 1997-10-21 | Rapa Rausch & Pausch Elektrotechnische Spezialfabrik Gmbh | Foil electrical connector for an oil burner nozzle |
| AT401682B (en) * | 1995-01-23 | 1996-11-25 | Vaillant Gmbh | GAS-FIRED COMBINATION CIRCUIT HEATER |
| DE102019107546A1 (en) * | 2019-03-25 | 2020-10-01 | Webasto SE | Method for contacting a heating element and heating element |
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