DE961737C - Powdery or grainy, electrically insulating heat material for embedding electrical heating conductors - Google Patents
Powdery or grainy, electrically insulating heat material for embedding electrical heating conductorsInfo
- Publication number
- DE961737C DE961737C DES3486D DES0003486D DE961737C DE 961737 C DE961737 C DE 961737C DE S3486 D DES3486 D DE S3486D DE S0003486 D DES0003486 D DE S0003486D DE 961737 C DE961737 C DE 961737C
- Authority
- DE
- Germany
- Prior art keywords
- electrical heating
- powdery
- melted
- embedding
- electrically insulating
- 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
- 239000000463 material Substances 0.000 title claims description 23
- 238000010438 heat treatment Methods 0.000 title claims description 15
- 239000004020 conductor Substances 0.000 title claims description 12
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 claims description 4
- 239000011230 binding agent Substances 0.000 claims description 3
- PQMFVUNERGGBPG-UHFFFAOYSA-N (6-bromopyridin-2-yl)hydrazine Chemical compound NNC1=CC=CC(Br)=N1 PQMFVUNERGGBPG-UHFFFAOYSA-N 0.000 claims description 2
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 2
- 229910052782 aluminium Inorganic materials 0.000 claims description 2
- 229910000147 aluminium phosphate Inorganic materials 0.000 claims description 2
- 239000004327 boric acid Substances 0.000 claims description 2
- KZHJGOXRZJKJNY-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Si]=O.O=[Al]O[Al]=O.O=[Al]O[Al]=O.O=[Al]O[Al]=O KZHJGOXRZJKJNY-UHFFFAOYSA-N 0.000 claims description 2
- 229910052863 mullite Inorganic materials 0.000 claims description 2
- 229910052710 silicon Inorganic materials 0.000 claims description 2
- 239000010703 silicon Substances 0.000 claims description 2
- 150000004760 silicates Chemical class 0.000 claims 1
- 150000001875 compounds Chemical class 0.000 description 4
- 239000005995 Aluminium silicate Substances 0.000 description 3
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 3
- 235000012211 aluminium silicate Nutrition 0.000 description 3
- 238000010292 electrical insulation Methods 0.000 description 3
- 239000012535 impurity Substances 0.000 description 3
- NLYAJNPCOHFWQQ-UHFFFAOYSA-N kaolin Chemical compound O.O.O=[Al]O[Si](=O)O[Si](=O)O[Al]=O NLYAJNPCOHFWQQ-UHFFFAOYSA-N 0.000 description 3
- 238000002844 melting Methods 0.000 description 3
- 230000008018 melting Effects 0.000 description 3
- 238000000034 method Methods 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 239000002994 raw material Substances 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- CPLXHLVBOLITMK-UHFFFAOYSA-N Magnesium oxide Chemical compound [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 description 2
- 239000000654 additive Substances 0.000 description 2
- 239000004566 building material Substances 0.000 description 2
- 239000010431 corundum Substances 0.000 description 2
- 229910052593 corundum Inorganic materials 0.000 description 2
- 238000010494 dissociation reaction Methods 0.000 description 2
- 230000005593 dissociations Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 239000010453 quartz Substances 0.000 description 2
- 230000000996 additive effect Effects 0.000 description 1
- 239000003513 alkali Chemical class 0.000 description 1
- 239000003518 caustics Substances 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 229910010293 ceramic material Inorganic materials 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 239000004927 clay Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000007812 deficiency Effects 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 230000000887 hydrating effect Effects 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 239000000395 magnesium oxide Substances 0.000 description 1
- 238000010309 melting process Methods 0.000 description 1
- 238000005065 mining Methods 0.000 description 1
- 229930014626 natural product Natural products 0.000 description 1
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 230000001681 protective effect Effects 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 239000011214 refractory ceramic Substances 0.000 description 1
- 229910052814 silicon oxide Inorganic materials 0.000 description 1
- 230000008646 thermal stress Effects 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
- H01B3/02—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of inorganic substances
- H01B3/10—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of inorganic substances metallic oxides
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Ceramic Engineering (AREA)
- Inorganic Chemistry (AREA)
- Compositions Of Oxide Ceramics (AREA)
- Conductive Materials (AREA)
Description
Pulverförmiger oder körniger, elektrisch isolierender Wärmewerkstoff zum Einbetten elektrischer Heizleiter Heizleiter werden in der Technik im allgemeinen, dann in einer Einbettmasse gelagert, wenn: die aus dem Heizleiter, seiner Einbettmasse und deren Umhüllung bestehende Heizeinheit im ganzen oder stellenweise auf eine Temperatur kommt, die im Glühgebiet liegt. Da die Heizeinheit hoch bean, sprucht wird, ist es verständlich, daß an eine brauchbare Einbettmasse mehrere Anforderungen; gestellt werden, denen, die bisher üblichen Massen, nur unvollkommen oder nur zum Teil gerecht wurden. Die Einbettmasse soll nach Möglichkeit eine gute Wärmeleitfähigkeit haben, andererseits wird aber auch im Gebiet höherer Temperaturen eine nur geringe elektrische Leitfähigkeit gefordert. Ferner soll die Masse, weder mit denn Heizleiter noch mit dessen schützenden Oxyden irgend eine Reaktion eingehen. Auch soll die Masse möglichst geringe Schwindung haben, darüber hinaus die für den späteren Verarbeitungsprozeß erforderliche Plastizität besitzen, und nicht zuletzt soll die Herstellung der Masse selbst technisch leicht durchführbar sein, wobei vor allem Wert darauf gelegt wird, daß im Gewinnungsverfahren nicht übermäßig hohe Temperaturen notwendig werden, und daß das Rohprodukt in seiner mechanischem. Härte nicht so hoch liegt, als d.aß es nur mit besonderen Zerkleinerungsmaschinen: in eine pulverige oder körnige Masse verwandelt werden kann..Powdery or granular, electrically insulating thermal material for embedding electrical heating conductors Heating conductors are generally used in technology, then stored in an investment material if: the one from the heating conductor, its investment material and its envelope existing heating unit in whole or in places on a Temperature comes, which is in the glow area. Since the heating unit is very demanding it is understandable that a useful investment material must meet several requirements; to which, the previously usual masses, only imperfectly or only for Part were fair. If possible, the investment should have good thermal conductivity on the other hand, even in the area of higher temperatures, there is only a low electrical conductivity required. Furthermore, the mass, neither with the heating conductor nor enter into any reaction with its protective oxides. Also should Mass have as little shrinkage as possible, beyond that for the later processing process have the necessary plasticity, and last but not least, the production of the mass be technically easy to carry out, whereby emphasis is placed on that excessively high temperatures are not necessary in the recovery process, and that the raw product in its mechanical. Hardness is not so high, as if it were only with special crushing machines: into a powdery or granular one Mass can be transformed ..
Da die Einbettungsmasse hitzebeständig sein muß, kommen im allgemeinen für ihrem, Aufbau nur die bekannten feuerfesten keramischen Stoffe in Frage, d. h., die Massen bestehen in ihrer Zusammensetzung in: der Regel aus den drei Stoffen Mg O, A'20, und Si 02. Diese Stoffe werden in den verschiedensten: Zusammensetzungen gebrannt oder auch ungebrannt als Einbettmassen. benutzt.Since the embedding compound must be heat-resistant, generally for their construction only the known refractory ceramic materials in question, d. That is, the masses consist in their composition as follows: as a rule of the three substances Mg O, A'20, and Si 02. These substances are in the most diverse: compositions Fired or unfired as investment materials. used.
Einbettmassen, die aus diesen Aufbaustoffen bestehen, haben aber den. Nachteil keiner oder zu geringer Plastizität. Um diesen Mangel zu beseitigen, werden sie mit geeigneten. Bindemitteln, z. B, mit Ton oder Kaolin, unter Wasserzusatz vermischt. Nachdem eine solche den Heizleiter einhüllende Masse in: den Heizmantel unter Druck eingebracht ist, findet im Anschluß daran ein Austrocknen des Heizkörpers statt, der dann betriebsfertig ist.Investment materials that consist of these building materials, however, have the. Disadvantage no or too little plasticity. To remedy this deficiency, will be them with suitable. Binders, e.g. B, with clay or kaolin, with the addition of water mixed. After such a mass enveloping the heating conductor in: the heating jacket is introduced under pressure, then there is a drying out of the radiator instead, which is then ready for use.
Dieses bekannte Verfahren hat aber mehrere Nachteile. Da die Rohstoffe der Einbettmasse durchweg beirgmännisch gewonnen werden,, läßt ihr Reinheitsgrad zu wünschen übrig; denn: sie enthalten die gängigen Verunreinigungen an Fez 0,3 und CaO sowie Alkaliverbindungen. Durch diese Zusätze wird aber die Isolierfähigkeit der Masse herabgesetzt, sie sind daher äußerst unerwünscht.However, this known method has several disadvantages. Since the raw materials of the investment are always obtained from the mountain, their degree of purity leaves something to be desired; because: they contain the common impurities of Fez 0.3 and CaO as well as alkali compounds. However, these additives reduce the insulating properties of the compound and are therefore extremely undesirable.
Da des weiteren. bei dem vorbezeichneten Verfahren, die Einbettmasse nur den, üblichen: Brenn:-ternperaturen unterworfen ist, wird aber verhindert, daß ihre Dichte den Höchstwert erreicht, so daß daher die Wärmeleitfähigkeit geringer bleibt. Die durch gängige Verunreinigungen herabgesetzte elektrische Isolierfähigkeit der Masse kann zwar wieder verbessert werden, wenn man. der Masse z. B. Kaolin zusetzt, durch das, wie, schon vorstehend erwähnt, gleichzeitig auch die Formbarkeit der Masse verbessert wird. Die auftretenden niederen Temperaturen lassen, aber die verbessernde Wirkung des Kaolins nur in beschränktem Umfang wirksam werden, da die Wirkung dieses Zusatzstoffes sich nur auf die Oberfläche der einzelnen Körner beschränkt, nicht aber auf deren Inneres einwirkt.Since further. in the case of the aforementioned method, the investment material is only subject to the usual internal temperatures, but it is prevented that their density reaches the maximum value, so that therefore the thermal conductivity is lower remain. The reduced electrical insulation capacity due to common impurities the crowd can be improved again if one. the mass z. B. adds kaolin, by, as already mentioned above, at the same time the malleability of the Mass is improved. The occurring lower temperatures leave, but the improving Effect of kaolin only to a limited extent, because the effect of this Additive is not limited to the surface of the individual grains but acts on the inside.
Im folgenden sollen nun zwei der Hauptaufbaustoffe de Dreistoffsystems oder bekannte Verbin,-Jungen aus diesen. auf ihre Brauchbarkeit für Einbettmassen näher untersucht werden.In the following, two of the main building materials of the three-component system will be discussed or known connections, boys from these. their usefulness for investment materials to be examined more closely.
Siliziumoxyd oder Quarz, das zwar als Naturprodukt, was seine Reinheit anbelangt, in seiner Güte einem erschmolzenen Produkt gleichwertig ist, ist allein schon wegen, seiner schlechtenWärmeleitfähigkeit nicht für eine Einbettmasse zu empfehlen.Silicon oxide or quartz, although being a natural product, what its purity as far as it is concerned, is equivalent in its quality to a melted product, is alone not suitable for an investment because of its poor thermal conductivity recommend.
Aluminiumoxyd Oder KoTund ist ebenso wie Quarz gegen Feuchtigkeit in hohem Grade unempfindlich und hat auch eine genügende elektrische Isolierfähigkeit. Abgesehen davon, daß seine Schmelztemperatur auch noch hoch liegt, nämlich bei 2Ioo°, ist dieses Material sehr hart, was leicht zu Beschädigungen des dünnen Heizleiters führen kann. Aus diesem Grunde dürfte Korund nicht als Hauptmasse von Heizleitern, zu befürworten sein. Man hat daher in der Technik bisher auch nur die große Härte des Korunds ausgewertet und aus diesem Material Schleifscheiben u. dgl. hergestellt.Aluminum oxide or KoTund is just like quartz against moisture highly insensitive and also has sufficient electrical insulation properties. Apart from the fact that its melting temperature is also high, namely at 200 °, this material is very hard, which can easily damage the thin heating conductor can lead. For this reason, corundum should not be used as the main mass of heating conductors, to be endorsed. So far there has only been great hardship in technology of the corundum is evaluated and grinding wheels and the like are made from this material.
Der Erfindung liegt die Erkenntnis zugrunde, daß für die Herstellung von Einbettmassen für elektrische Heizleiter überhaupt nur erschmolzene Werkstoffe in Frage kommen, und zwar nur solche, die aus mehr als. einem Grundstoff des Dreis.toffsystems erschmolzen sind. Die Einbettmasse nach der Erfindung besteht aus erschmolzenen Oxyden des Siliziums und Aluminiums, z. B. Mullit (eA12 03 - 2 S'02) oder Silimanit (A12 03 - S'02) oder anderen aus den beiden Grundstoffen erschmolzenen chearnischen Verbindungen.The invention is based on the knowledge that for the production of investment materials for electrical heating conductors only melted materials come into question, and indeed only those made of more than. a basic material of the Dreis.toff system have melted. The investment according to the invention consists of fused oxides of silicon and aluminum, for. B. mullite (eA12 03 - 2 S'02) or silimanite (A12 03 - S'02) or other Chearnic compounds melted from the two basic materials.
Die nach der Erfindung erschmolzene neue Masse weist gegenüber solchen, die aus bergmännisch gewonnenen Rohstoffen bestehen oder auch solchen, die nur einen erschmolzenen: Grundstoff des Dreistoffs.ystems erhalten, mehrere Vorteile auf. Die für ihre Erzeugung erforderliche Schmelztemperatur liegt niedriger als die Temperatur, die für die Erschmelzung jedes der einzelnen Grundstoffe erforderlich ist. Das Fertigprodukt zeichnet sich bei geringer thermischer Ion endissoziation durch entsprechend gute elektrische Isolierfähigkeit aus, was darauf zurückzuführen; ist, daß das erschmolzene Produkt überaus rein und nunmehr freu. von gängigen Verunreinigungen ist. Da die erschmolzene Masse im keramischen Sinn als tatgebrannt angesprochen werden, kann., schwindet sie bei thermischer Beanspruchung nicht. Die neue synthetische Einbettmasse kann in gleicher Weises verarbeitet werden wie die bisher gebräuchlichen. Sie wird im Anschluß an, den Schmelzprozeß einer Zerkleinerung unterworfen und dann in pulver- oder fein,-körnigem Zustand wie die bisherigen gebräuchliehen Massen weiterverarbeitet. Sie ist jedoch diesem, wie vorstehend erwähnt, qualitativ weit überlegen, zumal sie kristallin ist und die höchste Dichte hat, worauf die Güte ihrer Wärmeleitfähigkeit zurückzuführen ist. Außerdem ist sie chemisch träger und gegenüber dem früher bergmännisch gewonnenen und. verarbeiteten: Werkstoff verwitterungsbeständig. Neben, dieser Überlegenheit an, Güte erlaubt die neue Masse eine gewisse Bewegungsfreiheit, da ihre, Zusammensetzung nach Belieben verändert werden kann.The new mass melted according to the invention has compared to those that consist of mined raw materials or those that only have one melted: basic material of the three-substance system obtained, several advantages. The melting temperature required for their generation is lower than the temperature which is necessary for the melting of each of the individual raw materials. The finished product is characterized by correspondingly good dissociation with low thermal ion dissociation electrical insulation from what can be attributed to it; is that the melted Product extremely pure and now happy. of common impurities is. Since the Melted mass can be addressed as fired in the ceramic sense., it does not shrink under thermal stress. The new synthetic investment material can be processed in the same way as previously used. she will afterwards, the melting process is subjected to comminution and then in powder or in a fine, granular state, processed like the previously used masses. However, as mentioned above, it is qualitatively far superior to this, especially since it is crystalline and has the highest density, as a result of which the quality of its thermal conductivity is due. In addition, it is chemically slower and, unlike in the past, mining won and. processed: material weatherproof. Besides, this superiority on, goodness allows the new mass a certain freedom of movement because of its, composition can be changed at will.
Bei der Verarbeitung der vorbezeichneten Masse steht nichts im Wege, je nach dem Erfordernis eines der bekannten Bindemittel zuzusetzen. Empfehlenswert dürfte zwar sein, die Bindung der Masse durch ein hydratisierendes Mittel vorzunehmen:, z. B. durch Beimischen einer kleinen; Menge kaustischer Magnesia. Die hierdurch: geförderte hygroskopische Neigung der Masse kann mühelos durch einen Zusatz von Bor- oder Phosphorsäure unterbunden werden.When processing the aforementioned mass, nothing stands in the way, to add one of the known binders as required. Recommendable should be to make the binding of the mass by a hydrating agent :, z. B. by adding a small; Lots of caustic magnesia. The result: The hygroscopic tendency of the mass can be promoted effortlessly by the addition of Boric or phosphoric acid are prevented.
Claims (3)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DES3486D DE961737C (en) | 1943-07-08 | 1943-07-08 | Powdery or grainy, electrically insulating heat material for embedding electrical heating conductors |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DES3486D DE961737C (en) | 1943-07-08 | 1943-07-08 | Powdery or grainy, electrically insulating heat material for embedding electrical heating conductors |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| DE961737C true DE961737C (en) | 1957-04-11 |
Family
ID=7470178
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| DES3486D Expired DE961737C (en) | 1943-07-08 | 1943-07-08 | Powdery or grainy, electrically insulating heat material for embedding electrical heating conductors |
Country Status (1)
| Country | Link |
|---|---|
| DE (1) | DE961737C (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1465028B1 (en) * | 1962-11-30 | 1970-08-20 | Gen Electric | Electric resistance heating element |
| EP0035254A1 (en) * | 1980-02-29 | 1981-09-09 | Elpag Ag Chur | Electric heating equipment for ranges or cooking tops |
| DE3917869A1 (en) * | 1989-06-01 | 1990-12-06 | Guenter Kupferer | Electric surface heater - has carrier with central trough for placing heating element which can be filled with electrically insulating heat conducting material |
Citations (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE220394C (en) * | ||||
| DE453476C (en) * | 1926-04-22 | 1927-12-08 | Felix Singer Dr | Insulators for electric steam boilers |
| DE541380C (en) * | 1926-03-19 | 1932-01-06 | Berthold Redlich Dr | Process for the production of highly refractory masses and stones by firing a mixture consisting essentially of molten aluminum oxide and burnt magnesite |
| DE565889C (en) * | 1927-11-30 | 1932-12-06 | Arthur Sprenger | Process for the production of highly refractory bricks |
| DE590357C (en) * | 1931-05-19 | 1933-12-30 | Arthur Sprenger | Process for the production of highly refractory bodies |
| DE635236C (en) * | 1926-12-19 | 1936-09-12 | Felix Singer Dr Ing Dr | Process to prevent the aging of steatite, soapstone products of all kinds and other ceramic masses with magnesia components |
| DE637916C (en) * | 1928-12-25 | 1936-11-06 | Felix Singer Dr Ing Dr | Process for reducing the expansion coefficient of steatite |
| DE694635C (en) * | 1937-07-23 | 1940-08-05 | Siemens Schuckertwerke Akt Ges | Protective jacket for electrical heating elements |
| DE716928C (en) * | 1936-06-09 | 1942-02-03 | Steatit Magnesia Ag | Ceramic insulating bodies mainly containing soapstone or talc |
-
1943
- 1943-07-08 DE DES3486D patent/DE961737C/en not_active Expired
Patent Citations (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE220394C (en) * | ||||
| DE541380C (en) * | 1926-03-19 | 1932-01-06 | Berthold Redlich Dr | Process for the production of highly refractory masses and stones by firing a mixture consisting essentially of molten aluminum oxide and burnt magnesite |
| DE453476C (en) * | 1926-04-22 | 1927-12-08 | Felix Singer Dr | Insulators for electric steam boilers |
| DE635236C (en) * | 1926-12-19 | 1936-09-12 | Felix Singer Dr Ing Dr | Process to prevent the aging of steatite, soapstone products of all kinds and other ceramic masses with magnesia components |
| DE565889C (en) * | 1927-11-30 | 1932-12-06 | Arthur Sprenger | Process for the production of highly refractory bricks |
| DE637916C (en) * | 1928-12-25 | 1936-11-06 | Felix Singer Dr Ing Dr | Process for reducing the expansion coefficient of steatite |
| DE590357C (en) * | 1931-05-19 | 1933-12-30 | Arthur Sprenger | Process for the production of highly refractory bodies |
| DE716928C (en) * | 1936-06-09 | 1942-02-03 | Steatit Magnesia Ag | Ceramic insulating bodies mainly containing soapstone or talc |
| DE694635C (en) * | 1937-07-23 | 1940-08-05 | Siemens Schuckertwerke Akt Ges | Protective jacket for electrical heating elements |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1465028B1 (en) * | 1962-11-30 | 1970-08-20 | Gen Electric | Electric resistance heating element |
| EP0035254A1 (en) * | 1980-02-29 | 1981-09-09 | Elpag Ag Chur | Electric heating equipment for ranges or cooking tops |
| DE3917869A1 (en) * | 1989-06-01 | 1990-12-06 | Guenter Kupferer | Electric surface heater - has carrier with central trough for placing heating element which can be filled with electrically insulating heat conducting material |
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