US2157884A - Electric heating element - Google Patents

Electric heating element Download PDF

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Publication number
US2157884A
US2157884A US59391A US5939136A US2157884A US 2157884 A US2157884 A US 2157884A US 59391 A US59391 A US 59391A US 5939136 A US5939136 A US 5939136A US 2157884 A US2157884 A US 2157884A
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United States
Prior art keywords
tube
oxide
sheath
magnesium
deforming
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Expired - Lifetime
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US59391A
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English (en)
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Charistian B Backer
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B7/00—Insulated conductors or cables characterised by their form
    • H01B7/16—Rigid-tube 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
    • Y10T29/00—Metal working
    • Y10T29/49—Method of mechanical manufacture
    • Y10T29/49002—Electrical device making
    • Y10T29/49082—Resistor making
    • Y10T29/49087—Resistor making with envelope or housing
    • Y10T29/49092—Powdering the insulation
    • Y10T29/49094—Powdering the insulation by oxidation

Definitions

  • My invention relates to electric heating elements and more particularly to bular heating elements in which the coiled resis ance wire with its surrounding insulation is enclosed in a metallic tube or sheath.
  • the so-called Calrod element the resistance coil is surrounded by a powdered insulation material (generally magnesium oxide which has been fused and powdered), which is compacted around the resistance coil by swaging (hammering) the tube so as to reduce its diameter.
  • the insulation consists of chemically pure crystalline magnesium oxide, which is produced in place from magnesium metal by treating the metal with steam or water under very high pressure and temperature, whereby the magnesium metal is converted into magnesium hydroxide, which is further converted into magnesium oxide by heat-, ing to-dull red heat.
  • a Backer tube element is made as follows:
  • the coiled resistance wire is now inserted into the tube and held in position at both ends.
  • the assembled element consisting of the outer tube or sheath, the magnesium metal a iining and the coiled resistance wire, is now placed vertically in an autoclave nearly full of water, so that the tube is preferably covered with the water.
  • the autoclave is then closed and heated until the steam pressure is at least 15 w atmospheres, and the temperature corresponds to that of the saturated steam pressure used.
  • the hydroxide takes up about twice as large volume as the original magnesium metal, whereby the resistance coil becomes completely embedded in u the hydroxide.
  • the tube is now dried at a temperature of dull red heat in order to convert the magnesium hydroxide into oxide.
  • the center opening in the resistance coil (through which the water circulated during the conversion in the autoclave) may now be filled with any good re- 5 fractory insulation powder, or a magnesium metal wire may be inserted into the center opening and converted in the autoclave into magnesium hydroxide. Thereafter air-tight terminals are attached to the ends of the resistance wire at both 10 ends of the tube, and after a final drying operation the tube element is ready for use.
  • the magnesium hydroxide must 20 be heated to dull red heat to convert it to magnesium oxide free from water. During this drying process, which must be done at a temperature of about 600 degrees C., the magnesium oxide shrinks, as it loses its water. The result is that circumferential cracks develop in the oxide. These cracks or openings are very objectionable since they make it impossible to produce tube elements which can be flash tested with more than 1500 volts, when the tube is cold, or 800 volts, when the tube is red hot.
  • One object of my invention is to provide an improved heating element of the metalclad or sheathed type.
  • Another object of my invention is to provide a novel method of compressing or compacting the insulating material in a well-known sheathed type of heating element to increase the dielectric strength thereof.
  • a further object of my invention is to effect such compression or compacting of the insulating material, or deformation of the complete element, in a plurality of steps in conjunction with selected temperature treatments, whereby the desired compacting and deformation is effected without undue strains in the insulating material, which would otherwise develop deleterious cracks.
  • Figs. 1 to 5,.inclusive are cross-sectional views of heating elements deformed in different ways in accordance with my present invention, together with elevational views of simple dies for effecting the desired deformation in each case.
  • the tube element may be such as that designated generally by reference character I in Fig. 1, comprising the outer metallic tube or sheath 8, the coiled resistance wire 9 (initially an ordinary helical coil) and the intervening insulating material it). After the tube element has been treated in the autoclave as de-. scribed above, it is dried in a suitable drier at a temperature of from 330 to 350 degrees C. A drying period of 30 to 60 minutes is satisfactory.
  • the magnesium hydroxide loses a part of its bound hydroxide water, without being completely converted into oxide. No objectionable cracks or openings develop in the magnesium hydroxide when it is dried at only 350 degrees C. Nevertheless, it loses sufiicient water and becomes considerably softer, so that it may be easily compacted.
  • the center opening in the element is filled with insulation powder and the terminals are assembled into both ends of the tube. Then the tube is submitted to the first deforming operation by pressing it in a suitable die, so that the insulation becomes compacted, or reduced, in volume, the volume reduction in this first deforming operation may be from 15% to 25%.
  • the simplest method of deforming the tube is to press it between two flat dies ii and i2, as simply illustrated in Fig. l.
  • the tube then takes a more or less rectangular cross section, with half circular sides, as shown in Fig. 1.
  • this shape of the tube is cheaply attained, because it requires only fiat dies, and although a tube element flattened as shown in Fig. 1 is very much better in every respect than a tube which has not been deformed at all, it is not entirely satisfactory, because, if the tube is to be flattened enough to sufficiently compact the oxide at the rounded sides of the tube, the thickness of the oxide layer at the flattened sides becomes too small.
  • FIG. 2 A much better shape is shown at l3 in Fig. 2, which is more or less elliptical, rather than rectangular.
  • To deform the tube into a shape as shown in Fig. 2 requires a set of dies i4 and IS with grooves of the corresponding form, as indicated. In this shape an evenly compacted oxide is attained without-reducing the thickness of the insulation layer at any point to an objectionable degree. I have found that the shape as shown in Fig. 2 is the most desirable one, and gives a. perfect result.
  • FIG. 3 at I6 Another shape, shown in Fig. 3 at I6, also gives very good results. It is more or less square except that the sides of the square are slightly rounded, the cooperating dies i1 and i8 being correspondingly shaped, as indicated. This rounding of the sides is desirable, because in a section with straight fiat sides the fiat parts of the wall have a tendency to bulge out, when the tube is heated, and thereby destroy the good contact between the tube and the insulation.
  • FIG. 4 Another shape--approxiately semi-circularwhich may be desirable for special purposes is shown in Fig. 4 at is.
  • may be conveniently bent into hair-pin form and pressed together so as to form a return bend element of approximately circular cross section having the terminals near together at the same end of the element.
  • the cross section of such an element would be as shown in Fig. 5.
  • the tube is again put into the drier and dried for several hours at about 600 degrees C. This drying operation will convert all the magnesium hydroxide into oxide, without any cracks developing in the insulation.
  • the tube is further deformed in the same dies as used for the first deforming operation or in similar dies, as will be understood.
  • the tubes are given their final shapes as shown in Figs. 1 to 5, as the case may be, and the oxide insulation is now compacted, so that it occupies about two-thirds of the volume of the original magnesium hydroxide. This great compression of the oxide makes it extremely hard and compact, so that its dielectric strength is increased to more than the double of what it was before the deformation.
  • the deformation of a tube element may be done in a strong press by a single blow of the press. If no large press is available the deformation may also be done in a small press by stages, that is, a little at a time. If this method is used, then there is a very small lengthening of the tube, depending upon how many blows of the press are required to deform the whole length of the tube. 75
  • the swaging method is practically speaking useless for tube elements with crystalline magnesium oxide insulation (made from magnesium metal in an autoclave by the Backer insulation process).
  • the swaging method is excellent for tube elements made by the Calrod powder process. My deformation method could not be successfully used for such elements, because the resistance coil would not deform with the tube, but would have a tendency to remain circular and therefore cut through the insulation layer or reduce its thickness too much.
  • the method of making a tubular heating element comprising the steps of disposing a resistance member and moisture-containing material comprising a magnesium oxide compound surrounding said member within a metal tube or enclosing sheath, heating said material to dehydrate it to a considerable degree and initially deforming said sheath to compact said material around said resistance member and close any cracks formed therein by such dehydration, the volume reduction of said material being 15-25%, further heating said material to additionally dehydrate it and further deforming said sheath to additionally compact said material.
  • the method of making a tubular heating element comprising the steps of disposing a resistance member and insulating moisture-containing material surrounding said member within a metal tube or enclosing sheath, partially drying said material and initially deforming said sheath to compact said material around said resistance member, the volume reduction of said material being Iii-25%, further drying said material and further deforming said sheath to additionally compact said material, the. second volume reduction being of an order similar to that of the first.
  • the method of making a tubular heating element comprising the steps of disposing a resistance member and insulating moisture-containing material surrounding said member within a metal tube or enclosing sheath, drying said material at a temperature of above 300 C. for a predetermined period of time and initially deforming said sheath to partially compact said material around said resistance member, further drying said material at a higher temperature and for a longer period of time than the first-named drying, and further deforming said sheath to additionally compact said material.
  • the method of making a tubular heating element comprising the steps of disposing a resistance member and insulating moisture-containing material surrounding said member within a metal tube or enclosing sheath, drying said material at a temperature of 330 to 350 C. for a period of 30 to 60 minutes and then initially deforming said sheath to partially compact said material around said resistance member, further drying said material at about 600 C. for several hours and further deforming said sheath to additionally compact said material.
  • the method of making a tubular heating element comprising the steps of disposing a resistance member and insulating moisture-containing material surrounding said member within a metal tube or enclosing sheath, drying said material at a temperature of 330 to 350 C. for a period of 30 to 60 minutes and then initially deforming said sheath to reduce the volume of said insulating material by 15% to 25%, further drying said material at about 600 C. for several hours and further deforming said sheath to reduce the volume of said material to about twothirds of its original volume.
  • the method of making a tubular heating element comprising the steps of disposing a resistance member surrounded by hydroxide within a metal tube or enclosing sheath, partially converting' said hydroxide to oxide, initially deforming said sheath to partially compact the hydroxide and oxide, completing the conversion to oxide, and further deforming said sheath to additionally compact the oxide.
  • the method of making a tubular heating element comprising the steps of disposing a resistance member surrounded by magnesium hydroxide within a metal tube or enclosing sheath, partially converting said magnesium hydroxide to magnesium oxide, initially deforming said sheath to partially compact the hydroxide and oxide, completing the conversion to magnesium oxide, and further deforming said sheath to additionally compact the oxide.

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  • Resistance Heating (AREA)
US59391A 1935-05-21 1936-01-16 Electric heating element Expired - Lifetime US2157884A (en)

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CA204193X 1935-05-21

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US (1) US2157884A (en))
CH (1) CH204193A (en))
DE (1) DE667707C (en))
FR (1) FR806414A (en))
GB (2) GB462263A (en))
NL (1) NL43606C (en))

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2428900A (en) * 1940-10-21 1947-10-14 Wiegand Co Edwin L Electrical heating element
US2428899A (en) * 1940-10-21 1947-10-14 Wiegand Co Edwin L Electrical heating element
US2456343A (en) * 1944-12-06 1948-12-14 Tuttle & Kift Inc Electric heater and method of making same
US2591442A (en) * 1944-11-06 1952-04-01 Simplex Electric Co Ltd Method of making electric heating elements
US2662158A (en) * 1951-07-28 1953-12-08 Gen Electric Heating unit and method of making the same
US3934333A (en) * 1973-07-25 1976-01-27 Churchill John W Method of constructing bilateral heater unit
US3982099A (en) * 1973-07-25 1976-09-21 Churchill John W Bilateral heater unit and method of construction
US4125761A (en) * 1974-10-08 1978-11-14 Churchill John W Bilateral heater unit
USRE30126E (en) * 1973-07-25 1979-10-23 Bilateral heater unit
US4349727A (en) * 1973-07-25 1982-09-14 Southport Enterprises, Inc. Heater unit
US4965436A (en) * 1973-07-25 1990-10-23 Southport Enterprises Heater unit
US6414281B1 (en) 1999-07-30 2002-07-02 Watlow Electric Manufacturing Company Hot-toe multicell electric heater
US20130152382A1 (en) * 2011-12-20 2013-06-20 Shu-Lien Chen Method for making wave-shaped heating unit
CN104185315A (zh) * 2013-05-24 2014-12-03 陈树炼 波浪型电热构造及其制造方法
CN105813242A (zh) * 2014-12-31 2016-07-27 周保国 带电波纹节能电加热控制系统

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1104086B (de) * 1955-04-09 1961-04-06 Bleckmann & Co Elektrischer Rohrheizkoerper zur Erhitzung von Wasser und anderen, kesselsteinbildende Substanzen enthaltenden Fluessigkeiten ueber jenen Temperaturbereich hinaus, in dem es zur Anlagerung von Kesselstein an seinem Mantelrohr kommt
DE1136782B (de) * 1956-03-26 1962-09-20 Thermel Inc Bandartige Heizelemente, zum Beheizen zylindrischer Behaelter, Gefaesse od. dgl.
DE1565873B1 (de) * 1966-03-04 1971-04-15 Tuerk & Hillinger Kg Elektrische Heizeinrichtung
GB2011768B (en) * 1977-12-21 1982-03-17 Gen Signal Corp Electric heating units

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2428900A (en) * 1940-10-21 1947-10-14 Wiegand Co Edwin L Electrical heating element
US2428899A (en) * 1940-10-21 1947-10-14 Wiegand Co Edwin L Electrical heating element
US2591442A (en) * 1944-11-06 1952-04-01 Simplex Electric Co Ltd Method of making electric heating elements
US2456343A (en) * 1944-12-06 1948-12-14 Tuttle & Kift Inc Electric heater and method of making same
US2662158A (en) * 1951-07-28 1953-12-08 Gen Electric Heating unit and method of making the same
US3982099A (en) * 1973-07-25 1976-09-21 Churchill John W Bilateral heater unit and method of construction
US3934333A (en) * 1973-07-25 1976-01-27 Churchill John W Method of constructing bilateral heater unit
USRE30126E (en) * 1973-07-25 1979-10-23 Bilateral heater unit
US4349727A (en) * 1973-07-25 1982-09-14 Southport Enterprises, Inc. Heater unit
US4965436A (en) * 1973-07-25 1990-10-23 Southport Enterprises Heater unit
US4125761A (en) * 1974-10-08 1978-11-14 Churchill John W Bilateral heater unit
US6414281B1 (en) 1999-07-30 2002-07-02 Watlow Electric Manufacturing Company Hot-toe multicell electric heater
US20130152382A1 (en) * 2011-12-20 2013-06-20 Shu-Lien Chen Method for making wave-shaped heating unit
CN104185315A (zh) * 2013-05-24 2014-12-03 陈树炼 波浪型电热构造及其制造方法
CN105813242A (zh) * 2014-12-31 2016-07-27 周保国 带电波纹节能电加热控制系统

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Publication number Publication date
NL43606C (en))
GB462263A (en) 1937-03-05
FR806414A (fr) 1936-12-16
DE667707C (de) 1938-11-18
GB462280A (en) 1937-03-05
CH204193A (fr) 1939-04-30

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