US2276973A - Insulated electric heater and method of making the same - Google Patents
Insulated electric heater and method of making the same Download PDFInfo
- Publication number
- US2276973A US2276973A US295053A US29505339A US2276973A US 2276973 A US2276973 A US 2276973A US 295053 A US295053 A US 295053A US 29505339 A US29505339 A US 29505339A US 2276973 A US2276973 A US 2276973A
- Authority
- US
- United States
- Prior art keywords
- mixture
- magnesium oxide
- wire
- borate
- magnesium
- 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 - Lifetime
Links
- 238000004519 manufacturing process Methods 0.000 title description 4
- 229960000869 magnesium oxide Drugs 0.000 description 26
- 239000000395 magnesium oxide Substances 0.000 description 26
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 description 26
- 235000012245 magnesium oxide Nutrition 0.000 description 26
- AXZKOIWUVFPNLO-UHFFFAOYSA-N magnesium;oxygen(2-) Chemical compound [O-2].[Mg+2] AXZKOIWUVFPNLO-UHFFFAOYSA-N 0.000 description 26
- 239000000203 mixture Substances 0.000 description 23
- 239000011248 coating agent Substances 0.000 description 18
- 238000000576 coating method Methods 0.000 description 18
- WYXIGTJNYDDFFH-UHFFFAOYSA-Q triazanium;borate Chemical compound [NH4+].[NH4+].[NH4+].[O-]B([O-])[O-] WYXIGTJNYDDFFH-UHFFFAOYSA-Q 0.000 description 17
- 238000010438 heat treatment Methods 0.000 description 10
- 230000009972 noncorrosive effect Effects 0.000 description 9
- 238000006243 chemical reaction Methods 0.000 description 8
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 6
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 6
- 239000008240 homogeneous mixture Substances 0.000 description 6
- 239000011810 insulating material Substances 0.000 description 6
- 239000011777 magnesium Substances 0.000 description 6
- 229910052749 magnesium Inorganic materials 0.000 description 6
- 235000001055 magnesium Nutrition 0.000 description 6
- 229940091250 magnesium supplement Drugs 0.000 description 6
- 238000000034 method Methods 0.000 description 6
- BTBUEUYNUDRHOZ-UHFFFAOYSA-N Borate Chemical compound [O-]B([O-])[O-] BTBUEUYNUDRHOZ-UHFFFAOYSA-N 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- NFMWFGXCDDYTEG-UHFFFAOYSA-N trimagnesium;diborate Chemical compound [Mg+2].[Mg+2].[Mg+2].[O-]B([O-])[O-].[O-]B([O-])[O-] NFMWFGXCDDYTEG-UHFFFAOYSA-N 0.000 description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 5
- 229910021529 ammonia Inorganic materials 0.000 description 3
- 239000007795 chemical reaction product Substances 0.000 description 3
- 238000009413 insulation Methods 0.000 description 3
- 239000011872 intimate mixture Substances 0.000 description 3
- 230000000694 effects Effects 0.000 description 2
- QGZKDVFQNNGYKY-UHFFFAOYSA-O Ammonium Chemical compound [NH4+] QGZKDVFQNNGYKY-UHFFFAOYSA-O 0.000 description 1
- ODRVIWBHHXXABI-UHFFFAOYSA-N B([O-])([O-])O.[Mg+2].[O-2].[Mg+2] Chemical compound B([O-])([O-])O.[Mg+2].[O-2].[Mg+2] ODRVIWBHHXXABI-UHFFFAOYSA-N 0.000 description 1
- 241000287828 Gallus gallus Species 0.000 description 1
- 230000009172 bursting Effects 0.000 description 1
- OSGAYBCDTDRGGQ-UHFFFAOYSA-L calcium sulfate Inorganic materials [Ca+2].[O-]S([O-])(=O)=O OSGAYBCDTDRGGQ-UHFFFAOYSA-L 0.000 description 1
- ZOMBKNNSYQHRCA-UHFFFAOYSA-J calcium sulfate hemihydrate Chemical compound O.[Ca+2].[Ca+2].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O ZOMBKNNSYQHRCA-UHFFFAOYSA-J 0.000 description 1
- 239000011507 gypsum plaster Substances 0.000 description 1
- -1 magnesium oxide ammonium borate Chemical compound 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 229910001186 potin Inorganic materials 0.000 description 1
- 239000000047 product Substances 0.000 description 1
Images
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
- H05B3/18—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor the conductor being embedded in an insulating material
-
- 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
- H05B3/40—Heating elements having the shape of rods or tubes
- H05B3/54—Heating elements having the shape of rods or tubes flexible
- H05B3/56—Heating cables
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
- Y10T428/2913—Rod, strand, filament or fiber
- Y10T428/2933—Coated or with bond, impregnation or core
- Y10T428/294—Coated or with bond, impregnation or core including metal or compound thereof [excluding glass, ceramic and asbestos]
- Y10T428/2958—Metal or metal compound in coating
Definitions
- This invention relates to insulated electric heaters and to the method of insulating suc heaters.
- An object of this invention is the provision of an insulated electric heater unit, the insulation of which is a dense homogeneous mixture of materials which are non-corrosive and have high electrical resistivity.
- a further object of this invention is the provision of a method of insulating electric resistor wires of the heater type, whereby a hard, dense, non-corrosive insulating coating isformedabout the wire. 4
- Fig. 2 is an enlarged view in section of the element of Fig. 1, taken along the line II---II.
- any of the wellknown metallic resistor units may be employed, and particularly the metallic heating wires it, as illustrated in the drawing, such as are utilized.
- the heating units of electric roosters, strip heaters, hot plates and the like All of these elements should be so insulated as to prevent oxidation thereof and to electrically insulate them from the apparatus in which they are employed, while permitting the heat developed therein to fiow therefrom.
- this invention provides for utilizing the reaction products of a mixture of materials as the insulating material i! for embedding the heating wire i therein as illustrated in the drawing.
- the materials employed for forming the insulating material comprise a mixture of magnesium oxide and ammonium borate.
- the magnesium oxide and the ammonium borate are thoroughly mixed, with the ammonium borate constituting from to 50% by weight of the mixture, after which sufllcient water is added to the resulting mixture to give it a creamy, mud-like consistency so that it can be poured.
- the amount of water employed to give the mud-like consistency to the mixture will vary depending upon the grade of magnesium oxide employed, but inall cases should be'so limited to that quantity which gives the mud-like consistency to the mixture. Where an extremely pure grade of magnesium oxide is utilizedfit is preferred to make the mixture in a 1:1 ratio by weight of magnesium oxide and ammonium borate. For the impure grades of magnesium oxide, smaller quantities within the range of 25%, to 50% by weight of the ammonium borate can be employed giving a mixture having a ratio ranging between 1:1 and 2:1 by weight of the magnesium oxide to the ammonium borate.
- the magnesium oxide and ammonium borate formed into the mixtur having a mudlike consistency
- it is applied to the wire to be insulated in any of the well known manners for completely embedding the wire.
- the mixture can either be poured directly about the wire or it can be extruded about the wire, or films of the mixture can be applied to both sides of a heating element to envelop it.
- the mixture, as applied has a mudlike consistency it will set about the heating wire or unit in a manner similar to the setting of plaster of Paris. In this form, the embedded heating wire can be moved without danger to the applied coating.
- the embedded article is placed in any suitable furnace and subjected to a baking treatment at a temperature of not, less than (3., and preferably between 120 C. and C., it being found that such baking effects a reaction upon the components of the mixture constituting the coating.
- This reaction between the magnesium oxide and ammonium borate is accompanied by the evolution of ammonia and moisture from the mixture, and gives a resulting product comprising a uniform, intimate and homogeneous mixture of magnesium oxide and magnesium borate.
- magucs oxide ters flint are employed in 112:3 ratio.
- the in sulating coating comprising the urifiorm and homogeneous mixture of magnesimo oxide, mu magnesium box-ate, either by itseli or with the potters flint as herelnbeiore descri ed, is quite dense and extremely hard. Further, it is found that the resulting reaction product good thermal conductivity, an extremely high elem trlcal resistivity and the desired characteristic of being non-corrosive.
- the ulstiou will not crack when subjected to the extreme changes in temperature as are cncountred irl bursting the iormeduult'as a heating element, nor is it affected by the humidity of the atmosphere in which it is operated, the insulating coating being free of decrepitation.
- the method of insulating electric resistor wires of the heater type comprising the steps oi, embedding the wire in a mixture of magnesium oxide and ammonium borate having a ratio of between 1:1 and 2:1 and sufficient water to give the mixture :1 mud-like consistency, letting the mixture set in position about the wire, and heating the mixture while in position about the wire to effect a reaction between the magnesium oxide and ammonium borate whereby ammonia is evolved and a hard, dense, noncorrosive coating of intimately mixed magnesium oxide and magnesium borate is formed about the wire.
- All insulated electric heater comprisin n combination, a resistor wire and a. coating of is sulating material disposed thereon, said co, ing comprising a hard, dense, non-corrosive lam terlsl having a high electrical resistivity comprising an intimate and homogeneous l. ture of magnesium oxide and magnesium as essential binding elements thereof.
- An insulated electric heater comprising combination, a. resistor wire and a coating insulating material disposed thereon, said lug comprising arr-intimate and homogeu mixture or magnesium oxide and magnesium rate formed by effecting a reaction between hesium oxide and ammonium borate in the or between 1:1 and 2:1, the coating being u and non-corrosive.
- An insulated electric heater comprislzo combination, a resistor wire and a coat insulating material disposed thereon, said c ing comprising a hard, dense, non-corrosive serial having a high electrical resistivity sisting of an intimate and homogeneous oi potters flint, magnesium oxide and 1 s5 nesium borate, the magnesium oxide and r uesium borate being present as essential clcmenm in the coating and binding the no" mogeneously distributed potters flint.
- An insulated electric heater comprising in combination, a resistor wire and a coating of insulating material disposed thereon, said coating comprising an intimate and homogeneous mixture 01 .potters flint, magnesium oxide and magnesium borate, the magnesium oxide magnesium borate having been formed by etfectlng a reaction between magnesium oxide and ammonium borate in the presence of the potters flint, the ratio of the ammonium borate, mag nesium oxide and potters flint being 1:2:3, coating being dense and non-corrosive.
Landscapes
- Resistance Heating (AREA)
Description
March 17, 1942. H, D. HOLLER I 2,276,973
INSULATED ELECTRIC HEATER AND METHOD OF MAKING THE SAME Filed Sept. 15, 1939 kg, N 10 WITNESSEZ: INVENTOR lib/4e! [fa/Z22:
Patented Mar. 17, 1942 INSULATED ELECTRIC HEATER AND METHOD OF MAKING THE SAME Homer D. Holler, Export, Pa., aasignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania 1 Application September 15, 1939, Serial No. 295,053
7 Claim.
This invention relates to insulated electric heaters and to the method of insulating suc heaters.
In producing insulated electric heaters, it has been found to be diiiicult to provide an insulation of uniform homogeneous composition which is capable of withstanding the high temperatures sometimes encountered in service while having the characteristic of being non-corrosive. It has also been diiilcult to insulate the heater elements, theexisting methods requiring considerable care in practicing the steps thereof, while the results are not always uniform.
An object of this invention is the provision of an insulated electric heater unit, the insulation of which is a dense homogeneous mixture of materials which are non-corrosive and have high electrical resistivity.
A further object of this invention is the provision of a method of insulating electric resistor wires of the heater type, whereby a hard, dense, non-corrosive insulating coating isformedabout the wire. 4
Other objects of this invention will become apparent from the following description when taken in conjunction with the accompanying drawing, in which Figure 1 isa side view of a resistor element embodying the teachings of this invention; and
Fig. 2 is an enlarged view in section of the element of Fig. 1, taken along the line II---II. In practicing this invention, any of the wellknown metallic resistor units may be employed, and particularly the metallic heating wires it, as illustrated in the drawing, such as are utilized. in the heating units of electric roosters, strip heaters, hot plates and the like, All of these elements should be so insulated as to prevent oxidation thereof and to electrically insulate them from the apparatus in which they are employed, while permitting the heat developed therein to fiow therefrom.
In order to satisfactorily insulate such heating wires, this invention provides for utilizing the reaction products of a mixture of materials as the insulating material i! for embedding the heating wire i therein as illustrated in the drawing. The materials employed for forming the insulating material comprise a mixture of magnesium oxide and ammonium borate. In making the mixture for applying to the wire to be insulated, the magnesium oxide and the ammonium borate are thoroughly mixed, with the ammonium borate constituting from to 50% by weight of the mixture, after which sufllcient water is added to the resulting mixture to give it a creamy, mud-like consistency so that it can be poured. The amount of water employed to give the mud-like consistency to the mixture will vary depending upon the grade of magnesium oxide employed, but inall cases should be'so limited to that quantity which gives the mud-like consistency to the mixture. Where an extremely pure grade of magnesium oxide is utilizedfit is preferred to make the mixture in a 1:1 ratio by weight of magnesium oxide and ammonium borate. For the impure grades of magnesium oxide, smaller quantities within the range of 25%, to 50% by weight of the ammonium borate can be employed giving a mixture having a ratio ranging between 1:1 and 2:1 by weight of the magnesium oxide to the ammonium borate.
With the magnesium oxide and ammonium borate formed into the mixtur having a mudlike consistency, it is applied to the wire to be insulated in any of the well known manners for completely embedding the wire. Thus the mixture can either be poured directly about the wire or it can be extruded about the wire, or films of the mixture can be applied to both sides of a heating element to envelop it. Regardless of the method employed for enveloping or embedding the heating wire in the mixture of magnesium oxide and ammonium borate, it is found that where the mixture, as applied, has a mudlike consistency it will set about the heating wire or unit in a manner similar to the setting of plaster of Paris. In this form, the embedded heating wire can be moved without danger to the applied coating.
In order to produce the finished insulating coating about the wire, the embedded article is placed in any suitable furnace and subjected to a baking treatment at a temperature of not, less than (3., and preferably between 120 C. and C., it being found that such baking effects a reaction upon the components of the mixture constituting the coating. This reaction between the magnesium oxide and ammonium borate is accompanied by the evolution of ammonia and moisture from the mixture, and gives a resulting product comprising a uniform, intimate and homogeneous mixture of magnesium oxide and magnesium borate.
In a particular embodiment of this invention,
a material which is inert with respect to the reaction between the magnesium oxide and ammonium borate is included in the mixture to add strength to the resulting insulating coating and to reduce the cost per pound for insulation. Potin the chemical reaction between the mesh lzl. and 2:1 oif moriiuru borate whether or is present in the l I ammonium borate, magucs oxide ters flint are employed in 112:3 ratio.
When the flint, magnesium. oxide or; mouiuin borate is mixed with water to I" mud-like consistency sud applied to and treated in the warmer P re do scribed, it is found that the no part gnesium oxideand ammonium borate but iu the resulting insulating costing, uniformly distributed therein and aids in giving added strength to the reaction products of the magnesium oxide and ammonium borste, the resulting insulating coating consisting of a uniform, and homogeneous mixture of flint, maguesium oxide and magnesium hora-rte.
Upon examination, it is found that the in sulating coating comprising the urifiorm and homogeneous mixture of magnesimo oxide, mu magnesium box-ate, either by itseli or with the potters flint as herelnbeiore descri ed, is quite dense and extremely hard. Further, it is found that the resulting reaction product good thermal conductivity, an extremely high elem trlcal resistivity and the desired characteristic of being non-corrosive. in addition to the foregoing desired characteristics, the ulstiou will not crack when subjected to the extreme changes in temperature as are cncountred irl bursting the iormeduult'as a heating element, nor is it affected by the humidity of the atmosphere in which it is operated, the insulating coating being free of decrepitation.
Although this invention has been described with reference to a particular embodiment thcreof, it is, 01' course, not to be limited thereto ex= cept insofar as is necessitated by the scope oi the appended claims.
I claim as my invention:
l. The method of insulating electric resistor wires of the heater type comprising the steps oi, embedding the wire in a mixture of magnesium oxide and ammonium borate having a ratio of between 1:1 and 2:1 and sufficient water to give the mixture :1 mud-like consistency, letting the mixture set in position about the wire, and heating the mixture while in position about the wire to effect a reaction between the magnesium oxide and ammonium borate whereby ammonia is evolved and a hard, dense, noncorrosive coating of intimately mixed magnesium oxide and magnesium borate is formed about the wire.
2. The method of insulating electric resistor e wire in a mixture oi mug .esiui simonium boraie barbie a ratio .1: cud 32:1 and sulilcieu'l; water u mud-dike consistency, in.
sitiou about the wire, and We while in position about the are of st least C. to dri J ,esctiori between the magnesium:- oxide u borate whereby ammonia is cvo :2. hard, dense, non-corios1ve coating oi mutely mixed magnesium oxide and magncsiujze bursts is formed about the wire.
, All insulated electric heater comprisin n combination, a resistor wire and a. coating of is sulating material disposed thereon, said co, ing comprising a hard, dense, non-corrosive lam terlsl having a high electrical resistivity comprising an intimate and homogeneous l. ture of magnesium oxide and magnesium as essential binding elements thereof.
4. An insulated electric heater comprising combination, a. resistor wire and a coating insulating material disposed thereon, said lug comprising arr-intimate and homogeu mixture or magnesium oxide and magnesium rate formed by effecting a reaction between hesium oxide and ammonium borate in the or between 1:1 and 2:1, the coating being u and non-corrosive.
5. An insulated electric heater comprislzo combination, a resistor wire and a coat insulating material disposed thereon, said c ing comprising a hard, dense, non-corrosive serial having a high electrical resistivity sisting of an intimate and homogeneous oi potters flint, magnesium oxide and 1 s5 nesium borate, the magnesium oxide and r uesium borate being present as essential clcmenm in the coating and binding the no" mogeneously distributed potters flint.
6. An insulated electric heater compri" combination, a resistor wire and a cos. of insulating material disposed thereon, said coat lug comprising an intimate and homogeneous mixture of potters flint, magnesium oxide and magnesium borate, the magnesium oxide and magnesium borate having been formed by e'llfecting a reaction between magnesium oxide ammonium borate in the ratio of between 1:1 and 2:1, the coating being dense and non-corlOSlVe.
7. An insulated electric heater comprising in combination, a resistor wire and a coating of insulating material disposed thereon, said coating comprising an intimate and homogeneous mixture 01 .potters flint, magnesium oxide and magnesium borate, the magnesium oxide magnesium borate having been formed by etfectlng a reaction between magnesium oxide and ammonium borate in the presence of the potters flint, the ratio of the ammonium borate, mag nesium oxide and potters flint being 1:2:3, coating being dense and non-corrosive.
HOMER D. HOLLEB.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US295053A US2276973A (en) | 1939-09-15 | 1939-09-15 | Insulated electric heater and method of making the same |
| DES142291D DE737885C (en) | 1939-09-15 | 1940-09-16 | Isolation for electrical heating conductors |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US295053A US2276973A (en) | 1939-09-15 | 1939-09-15 | Insulated electric heater and method of making the same |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| US2276973A true US2276973A (en) | 1942-03-17 |
Family
ID=23136014
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| US295053A Expired - Lifetime US2276973A (en) | 1939-09-15 | 1939-09-15 | Insulated electric heater and method of making the same |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US2276973A (en) |
| DE (1) | DE737885C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4302508A (en) * | 1972-02-28 | 1981-11-24 | Emerson Electric Co. | Silicon carbide elements |
-
1939
- 1939-09-15 US US295053A patent/US2276973A/en not_active Expired - Lifetime
-
1940
- 1940-09-16 DE DES142291D patent/DE737885C/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4302508A (en) * | 1972-02-28 | 1981-11-24 | Emerson Electric Co. | Silicon carbide elements |
Also Published As
| Publication number | Publication date |
|---|---|
| DE737885C (en) | 1943-07-28 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US3477058A (en) | Magnesia insulated heating elements and methods of production | |
| US2375058A (en) | Electrical heating element and process for producing the same | |
| US2276973A (en) | Insulated electric heater and method of making the same | |
| GB528718A (en) | Improvements in and relating to a method of manufacturing electric heating elements | |
| US2292065A (en) | Magnesium oxide insulation | |
| US2022314A (en) | Electrical resistor and its manufacture | |
| US2091107A (en) | Electric heating element and method of making the same | |
| US1742259A (en) | Electrical resistor, conductor, and the like | |
| JPH0338715B2 (en) | ||
| US2357072A (en) | Electrical insulating compositions | |
| US3592771A (en) | Tubular heating elements and magnesia insulation therefor and method of production | |
| JPS6021448B2 (en) | Electrical insulating material for burying metal heater wires and method for manufacturing the same | |
| US2873342A (en) | Electric heating | |
| US1528388A (en) | Resistor for electric heating | |
| US2477121A (en) | Resistive device | |
| US2125075A (en) | Electrical heating element | |
| US2012897A (en) | Process for increasing the electri | |
| US1125615A (en) | Embedding material for electrical heating units. | |
| US2363130A (en) | Electrical heating element | |
| US1318838A (en) | Inx co | |
| DE693516C (en) | Process for the manufacture of radiators for electric cooking and heating devices | |
| US848954A (en) | Process of making resistance devices. | |
| US1125616A (en) | Embedding material for electrical heating units. | |
| JPS6029195Y2 (en) | Sea heater | |
| AT141158B (en) | Method of manufacturing electrical radiators with heating resistors. |