US3792233A - Heating element - Google Patents

Heating element Download PDF

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Publication number
US3792233A
US3792233A US00254034A US3792233DA US3792233A US 3792233 A US3792233 A US 3792233A US 00254034 A US00254034 A US 00254034A US 3792233D A US3792233D A US 3792233DA US 3792233 A US3792233 A US 3792233A
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United States
Prior art keywords
outs
cut
heating element
heating
electric current
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Expired - Lifetime
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US00254034A
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English (en)
Inventor
A Anthony
K Dembinski
L Dupont
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Bpifrance Financement SA
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Agence National de Valorisation de la Recherche ANVAR
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01L—CHEMICAL OR PHYSICAL LABORATORY APPARATUS FOR GENERAL USE
    • B01L7/00—Heating or cooling apparatus; Heat insulating devices
    • B01L7/54—Heating or cooling apparatus; Heat insulating devices using spatial temperature gradients
    • 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
    • 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 heating element is formed of refractory material resistant to oxidation, in the general shape of a parallelepiped. It has, in a direction perpendicular to two opposite surfaces, a nonhomogeneous structure such that when one of the two surfaces concerned is brought to a sufficiently high temperature to become electrically conducting, the other remains at a sufficiently low temperature to be thermally and electrically practically non-conducting.
  • the structure is adapted to withstand movements due to differences in expansion.
  • the element is made either of entirely or partially stabilized zirconia or of a definite compound of the pyrochlore type based on zirconia, of the formula Zr T O T being a metal, especially a rare earth. It has holes and cut-outs formed in the mass of the element in a direction substantially perpendicular to that which unites said two opposite surfaces.
  • the ratio hollow/solid is within a range of about 0.1 to 3.
  • the invention relates to a heating element of the type formed of a refractory material resistant to oxidation, with melting point above 2,500C, and generally known as resistors.
  • the heating element according to the invention is characterised by the fact that it is of general shape close to that of a parallelopiped and that it has, in a direction perpendicular to two opposite surfaces, a nonhomogeneous structure such that when one of the two surfaces concerned is brought to a sufficiently high temperature to become electrically conducting, the otherremains at a sufficiently low temperature to be practically non-conductive of electricity, the said structure being adapted to support the movements due to differences of expansion.
  • the invention consists, apart from the above-said features, of certain other features which are used, preferably at the same time and which will be more explicitly considered below.
  • FIGS. 1, 2 and 3 show respectively in perspective for the first and in elevation for the two others, three modifications of the first embodiment of the heating element according to the invention.
  • FIGS. 2a and 3a are views of FIGS. 2 and 3 along the lines 2a 2a and 3a 3a.
  • FIGS. 4, and 6 show in elevation three modifications of a second embodiment of a heating element according to the invention.
  • FIGS. 4a, 5a and 6a are views along the lines 4a--4a, 5a5a and 6a-6a of FIGS. 4 to 6.
  • FIGS. 7 to 10 show in perspective assemblies of several heating elements according to the invention.
  • FIG. 11 shows in elevation a fourth modification of the above-said first embodiment.
  • FIGS. 12 and 13 lastly, show respectively in elevation and in view and partial section along the lines XIII- XIII of FIG. 12, a fourth modification of the abovesaid first embodiment.
  • the general shape of the said heating element which is made of a refractory material resistant to oxidation of the type used for the manufacture of resistors, is parallel-epipedic or close to that of a parallelopiped. It has, consequently, the general shape of a brick of which the length L is greater than the height H, itself greater than the thickness E.
  • the difference in temperature between the two faces F, and F is such that the resistance of thecool face is at least times higher than the resistance of the hot face.
  • the supply of electric current to the heating element is effected at the level of the two ends of the element taken in the sense of the length, for example by means of platinum contacts.
  • the constituant material of the elements according to the invention is partially or entirely stabi lised zirconia in its form stable at hightemperature that is to say its cubic form. 7
  • the elements according to the invention can also be constituted of a definite compound of the pyrochlore type based on zirconia, of the formula Zr T O T being a-metal, preferably a rare earth;
  • this absence 'of homogeneity due to which the transmission of heat from face 1 to face 2 is sufficiently limited for the face F to remain at a temperature at which it is not conducting, is obtained by holes and cut-outs formed in the mass of the heating element in the direction substantially perpendicular to that which connects the faces F, and F, the ratio cavity/solid, when the constituent material of the element is partially or entirely stabilised zirconia, being selected around 0.l-0.2 to 3.
  • the arrangement and configuration of the above-said holes and cut-outs are selected so that when the constituent material of the element which is situated in the vicinity of the face F, is brought to the temperature from which it becomes conducting, the electric current only passes in fact in the vicinity of the said face F,.
  • FIGS. 1, 2 and 3 there are shown three modifications of this first embodiment.
  • the heating element denoted as a whole by 1, comprises a plurality of the holes 2 as shown, as well as cut-outs 3 in the form of a slot along a broken line comprising parts parallel to a certain length, at 30, to the face F,, as well as parts 3band 3c of a general shape substantially perpendicu lar to the face F, the assembly being such that the said face F, is connected to the cold face F, by parts 4 of the element which, as a result of the selection of the cutouts 3, are of relatively slight cross-section. Due to this constitution, the transmission of heat from the face F, to the face F is very much reduced.
  • the positioning of the parts 3a is selected so that the thickness of the element at the level of the face F,, through which thickness the electric current passes, is relatively slight.
  • this thickness denoted by D, in the Figure, as well as that of the parts 4 denoted by D is of the order of 1-3 to 5-10 mm.
  • the heating element 1 may be advantageous to arrange the heating element 1 so that the temperature reached by the face F, is progressive over at least a part of its length.
  • the progression occurs in the direction increasing along the arrow F,.
  • the holes and cut-outs 8, 9, 10 are arranged between two holes 5 at the level of which are provided current lead-ins, not shown. Moreover, again as in the case of FIG. 1, the distribution of the holes and cut-outs 8, 9 and 10 is advantageously, as shown, selected so that there is obtained a temperature gradient in the direction of the arrow F, analogous to that described with regard to FIG. 1.
  • cut-outs 20 perpendicular to the face F, as shown and of length H from 0.5 to 3cm.
  • the cut-outs 20 are provided at the level of the parts 4.
  • the element thus constituted offers good thermal and electrical insulation, good power-temperature ratio, good suspending possibilities, especially at the level of the holes 5, good elasticity, good resistance to forces of expansion and a large heating surface.
  • the element according to this embodiment comprises, as that of FIG. 11, a heating face F, of constant temperature in the useful part.
  • This element comprises two large cut-outs 20 of general direction parallel to F, forming a thickness D, of a heating surface F, (D, respects the above-mentioned criteria) and connected to the face F, by two cut-outs 21 of general direction perpendicular to F,, except a part 21a situated in the vicinity of the cut-outs 20 and oriented at about 45.
  • the cut-outs 21 open on the face F
  • the element is hence formedof three parts 22, 23 and 24 comprising respectively cavities 25, 26 and 27 of which the first and third serve for the housing of the current lead-ins (not shown and very accesible due to this construction), the second having the purpose of lightening the whole of the structure.
  • the part inclined at45 of the cut-outs 210 forms a screen and ensures the heat insulation of the heating surface F,.
  • cut-outs 34 of general direction perpendicularto the face F, and situated in the mass of the element between the cut-outs 20 and the cavities 25, 26 and 27, these cut-outs 34, through their arrangement and situation which are apparent from the Figure, ensuring good conduction of the current and localising possible fissures caused by mechanical forces capable of being due to thermal thock and to centering of the constituant material;
  • cut-outs 35 provided in the vicinity of the ends of the elements, perpendicular and open on the face F, these cut-outs playing the role of a heat shield and of releasing forces of expansion.
  • the face F is cut-out along for example two cavities 37 and 38 which give it a T and a U profile shown in FIG. 13 by means of which a better behaviour in operation is achieved.
  • the element according to this modification has not been also lightened as the preceding ones, the ratio cavity/solid being much less.
  • it is of rapid and easy manufacture by reduction in the cutouts which are selected so that the propagation of fissures is avoided. It is well understood that it is by reason of the higher weight that the points of suspension are multiplied.
  • the constituent material of the element is zirconia with 4 percent of lime the temperature of the face F, will be 1,200K when F, is at 2,200K.
  • the element 1 there is conferred on the element 1 the above-said nonhomogeneous structure along a direction substantially perpendicular to the facesF, and F, by making the said element comprise a part A of'low porosity, less than percent comprising especially the face F, which is intended to become conductive, this part with low porosity being combined with apart B of high porosity,
  • the part with low porosity can be constituted by stabilised zirconia similar to that constituting elements 1 in the embodiments of FIGS. 1 to 3.
  • the part of high porosity in which the pores play the role of cut-outs in the modifications of the preceding embodiments can be constituted by the same material as the part of dense porosity, or again of a more economical material such as ZrO -AI O, eutectic, alumina or another refractory without chemical interaction with the zirconia.
  • the part of low-porosity which comprises the face F will have a density of the order of 4.5 and the porous part comprising the face F will have a density of the order of 2.
  • part A is attached to the part B, for example by projection, by having recourse to techniques using a plasma torch.
  • FIGS. 4, 5 and 6 three possible modifications for the constitution of the elements 1 constructed according to this second embodiment.
  • FIGS. 4 and 6 are symmetrical with respect to a median plane in the direction of the length of the element.
  • FIG. 4 There are distinguished in FIG. 4 holes 5 similar to those of FIGS. 1 to 3, and in FIG. 6 attached parts 13 also forming holes 5.
  • the current lead-ins not shown are placed against the corresponding surfaces of the parts A, at the level of the holes 5.
  • the part A can be arranged as is shown in FIG. 5, by conferring on it a diminishing cross-section in the direction of the arrow f, which indicates the direction of increasing temperatures.
  • the element shown in FIG. 5 comprises a hole T for suspension.
  • FIGS. 4a, 5a and 6a show cross-sections of the elements of FIGS. 4 to 6.
  • the heating elements according to the invention are distinguished by excellent behaviour in operation of long duration.
  • FIGS. 7 to 10 there are shown several possibilities for the constitution of the furnaces.
  • FIG. 7 firstly there is shown an arch-shaped furnace with horizontal axis, constructed by means of elements 1 with a trapezoidal cross-section of the type of those shown in FIG.2.
  • the various elements 1 rest on one another without it being necessary to resort to individual connections.
  • the current lead-ins 6 are arranged as in the case of FIG. 1. There is shown the conductive wires connecting the current lead-ins 6 to the electrical current source.
  • the elements 1 used for the construction of the furnace with rectangular cross-section as shown in FIG. 8 are of the type of that of FIG. 1.
  • the three elements 1 constituting the sealing of the furnace are held in place by a mechanical suspension, preferably by a refractory steel fixing.
  • the three furnaces which have just been described have a heating cavity with a horizontal axis.
  • FIG. 10 shows a modification with a vertical axis.
  • elements 1 of the type of that shown in FIG. 1, spacing elements 17 being provided between the elements.
  • the uniting of the elements 1 and 17 to one another is obtained by means of a shaping enclosure, containing and guiding the whole into good position.
  • Heating element formed of refractory material resistant to oxidation, in the general shape of a parallelepiped, adapted to be heated by electric current supplied through electric contacts cladding said element, and having in a direction perpendicular to two of its opposite surfaces, a nonhomogeneous structure such that when one of said two surfaces is brought to a sufficiently high temperature by said electric current to become electrically conducting, the other remains at a sufficiently low temperature to be thermally and electrically practically non-conducting, said structure being adapted to withstand movements due to differences in expansion. 2.
  • Heating element formed of refractory material resistant to oxidation, in the general shape of a parallelepiped, adapted to be heated by electric current supplied through electric contacts cladding said element, and having in a direction perpendicular to two of its opposite surfaces, a nonhomogeneous structure such that when one of said two surfaces is brought to a sufficiently high temperature by said electric current to become electrically conducting, the other remains at a sufficiently low temperature to be thermally and electrically practically non-conducting, said structure being adapted to withstand movements due to differences in expansion, constructed of at least partially stabilized zirconia, comprising holes and cut-outs formed in the mass of the element in a direction substantially perpendicular to that which unites said two opposite surfaces of which one is intended to be brought to a sufficient temperature to become electrically conducting, the ratio hollow/solid being selected in a range of about 0.1 to about 3.
  • Heating element according to claim 2 wherein the ratio hollow/solid is in the vicinity of unity.
  • Heating element according to claim 2 wherein the shape and the distribution of the holes and cut-outs are such that, on one hand the two opposite surfaces of which one must be brought to a sufficient temperature to be electrically conducting are connected to one another by portions of relatively slight cross-section and that, on the other hand, the electric current is obliged to pass through the surface of .which the'temperature is brought to a sufficient value for it to become conducting.
  • Heating element according to claim 4 wherein the distribution of the holes and cut-outs is selected so that the temperature reached by the surface through which the electric current passes is progressive along this surface.
  • Heating element according to claim 4 wherein the distribution of the holes and cut-outs is selected to that the temperature reached by the surface through which the electric current passes is uniform along this surface.
  • Heating element formed of refractory material resistant to oxidation, in the general shape of a parallelepiped, adapted to be heated by electric current supplied through electric contacts cladding said element, and having in a direction perpendicular to two of its opposite surfaces, a non-homogeneous structure such that when one of said two surfaces is brought to a sufficiently high temperature by said electric current to become electrically conducting, the other remains at a sufficiently low temperature to be thermally and electrically practically non-conducting, said structure being adapted to withstand movements due to differences in expansion wherein along a direction substantially perpendicular to the assembly of the two opposite surfaces first part is formed of stabilized zirconia of density of the neighborhood of 4.5 and that the second part is formed of one of the materials comprising zirconia, eutectic zirconia A1 0 and alumina alone, the density of this second part being in the vicinity of 2.
  • Heating element according to claim 9 wherein the first part comprises a section decreasing in the direction of the length of the heating element.
  • Heating element according to claim 1 wherein the surface through the electric current passes is divided into lamellae, parallel to one another, by cut-outs perpendicular to the said surface in the direction of the length of the element.
  • Heating element according to claim 1 wherein the heating surface comprises hollows giving it a T and U structure, along a section perpendicular to the direction of the length.
  • Heating element according to claim 1 formed of a definite compound of the pyrochlore type based on zirconia, of the formula Zr T O where T is a metal, comprising holes and cut-outs formed in the mass of the element in a direction substantially perpendicular to that which unites said two opposite surfaces of which one is intended to be brought to a sufficient temperature to become electrically conducting, the ratio hollow/solid being selected in a range of about 0.1 to about 3.

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  • Chemical & Material Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Clinical Laboratory Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
  • Resistance Heating (AREA)
  • Surface Heating Bodies (AREA)
  • Laminated Bodies (AREA)
  • Compositions Of Oxide Ceramics (AREA)
US00254034A 1971-05-19 1972-05-17 Heating element Expired - Lifetime US3792233A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
FR717118236A FR2138230B1 (enrdf_load_stackoverflow) 1971-05-19 1971-05-19

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US3792233A true US3792233A (en) 1974-02-12

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US00254034A Expired - Lifetime US3792233A (en) 1971-05-19 1972-05-17 Heating element

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US (1) US3792233A (enrdf_load_stackoverflow)
JP (1) JPS5438734B1 (enrdf_load_stackoverflow)
FR (1) FR2138230B1 (enrdf_load_stackoverflow)
GB (1) GB1391203A (enrdf_load_stackoverflow)
NO (1) NO135158C (enrdf_load_stackoverflow)
SE (1) SE385428B (enrdf_load_stackoverflow)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4541898A (en) * 1981-05-25 1985-09-17 Ngk Insulators, Ltd. Method for heating
US4906821A (en) * 1985-09-18 1990-03-06 Commissariat A L'energie Atomique Resistor for the treatment of materials

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2373206A1 (fr) * 1976-12-02 1978-06-30 Anvar Nouvel element chauffant en oxyde refractaire et son procede de fabrication
US4998008A (en) * 1989-10-31 1991-03-05 Walther Menhardt Heating element
KR0140505B1 (ko) * 1991-01-31 1998-06-01 볼프강 마우스, 지그프리트 나스 불균일하게 전기 가열되는 벌집형 본체

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1543714A (en) * 1923-02-03 1925-06-30 Westinghouse Electric & Mfg Co Heat-treating furnace
US1588641A (en) * 1923-07-13 1926-06-15 Westinghouse Electric & Mfg Co Electric heat-treating furnace
US1719888A (en) * 1925-10-10 1929-07-09 Gen Electric Electric furnace
US2358406A (en) * 1942-04-20 1944-09-19 Lichtgarn Fred Electrical device
US3032635A (en) * 1960-10-03 1962-05-01 August L Kraft Heater and utilization system for converting small quantities of fusible solids

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1543714A (en) * 1923-02-03 1925-06-30 Westinghouse Electric & Mfg Co Heat-treating furnace
US1588641A (en) * 1923-07-13 1926-06-15 Westinghouse Electric & Mfg Co Electric heat-treating furnace
US1719888A (en) * 1925-10-10 1929-07-09 Gen Electric Electric furnace
US2358406A (en) * 1942-04-20 1944-09-19 Lichtgarn Fred Electrical device
US3032635A (en) * 1960-10-03 1962-05-01 August L Kraft Heater and utilization system for converting small quantities of fusible solids

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
New Zirconia Materia in a New Material Preview, March 1951, p. 81 *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4541898A (en) * 1981-05-25 1985-09-17 Ngk Insulators, Ltd. Method for heating
US4906821A (en) * 1985-09-18 1990-03-06 Commissariat A L'energie Atomique Resistor for the treatment of materials

Also Published As

Publication number Publication date
JPS5438734B1 (enrdf_load_stackoverflow) 1979-11-22
NO135158B (enrdf_load_stackoverflow) 1976-11-08
NO135158C (enrdf_load_stackoverflow) 1977-02-16
GB1391203A (en) 1975-04-16
DE2224503A1 (de) 1972-12-21
FR2138230A1 (enrdf_load_stackoverflow) 1973-01-05
FR2138230B1 (enrdf_load_stackoverflow) 1973-05-11
SE385428B (sv) 1976-06-28
DE2224503B2 (de) 1976-09-23

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