US3504327A - Heater element - Google Patents

Heater element Download PDF

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Publication number
US3504327A
US3504327A US774576A US77457668A US3504327A US 3504327 A US3504327 A US 3504327A US 774576 A US774576 A US 774576A US 77457668 A US77457668 A US 77457668A US 3504327 A US3504327 A US 3504327A
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United States
Prior art keywords
layer
layers
core
metal
oxide
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Expired - Lifetime
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US774576A
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English (en)
Inventor
Rene Clement
Maurice Ducos
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Societe de Fabrication dElements Catalytiques
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Sfec
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    • 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
    • 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

Definitions

  • An electrical heater element comprises an electrically conducting core.
  • a purality of superimposed layers cover said cores; the layers are made alternately of refractory compounds and of a metal capable, after melting, of wetting the two adjacent oxide layers.
  • the metal has a melting temperature lower than the working temperature of the heater.
  • the present invention relates to heater elements more particularly of the type used, for example, in electrical ovens.
  • heater resistors consist either of refractory metals, or of intermetallic compounds, or of carbides, the substance generally used being silicon carbide.v
  • the resistors which are generally in the shape of rods or cylinders, are prepared from powder by moulding and by extrusion with a plastic binder. The rough parts are then increased in density by high temperature heat treatment, often in a protecting atmosphere (argon, nitrogen, hydrogen) to prevent the grains from being oxidized.
  • argon, nitrogen, hydrogen a protecting atmosphere
  • an electrical heater element comprising an electrically conducting core, a plurality of successive layers covering said core, said layers being alternately of refractory compounds and of a metal capable of wetting the adjacent oxide layer.
  • iFIG. 1 shows in longitudinal section one example of a heater element according to the invention
  • FIG. 2 shows a transverse section of the element in its coated parti and FIG. 3 shows a modification in longitudinal section.
  • FIG. l shows a cylindrical graphite core 1, with a reduced diameter in the central region thereof.
  • the core is coated, except for its ends, which are clear for the purpose of making electric connections, with a deposit consisting of alternate layers of refractory material 2 and of metal 3 whose melting temperature may be less than the working temperature of the heater.
  • a metal layer 4 formed at the ends of the element ensures good electric contact between the graphite core and the electric connection collars.
  • FIG. 2 shows a transverse section of the element in its coated part. It shows the successive concentric deposits of refractory oxide 2 and of metal 3 on the graphite core.
  • the refractory layers consist of oxides or oxide compounds, with a melting point higher than l600 C; for example, aluminium oxide, zirconium oxide (stabilized with lime or yttrium oxide), chromium oxide, spinel of magnesia (AlzOg-MgO), zirconium silicate, etc. may be used.
  • the iirst refractory layer need not be formed of a single oxide layer but of several superposed thin layers of different oxides With expansion coecients of increasing value to form an expansion gradient between the graphite core which is subject to little expansion and the metal layer which, in general, has an expansion coetlicient greater than 15 0X 10-7.
  • the nature of the metal has to be carefully chosen, for its vapour pressure, at the working temperature of the heater element must not exceed 10 millimetres of mercury, since a high vapour pressure would result in the destruction of the outer oxide layer.
  • the metal may be chosen, for example, from among the following: iron, nickel, cobalt, copper, chromium, silicon, titanium or their alloys.
  • the metal or alloy has to be chosen for its capacity of wetting the neighbouring oxide layers; it has been found that alloys containing a certain amount of titanium, such as, for example, nickel-titanium or copper-titanium, wet alumina layers perfectly. This characteristic allows the metal layers to spread out well between the oxide layers in a continuous and tight deposit. If the metal fails-to wet adjacent oxide deposits, it runs together, after melting, into small islands which leave large pores through which oxygen from the air can penetrate to oxidize the graphite core.
  • titanium such as, for example, nickel-titanium or copper-titanium
  • the number of layers is not limited and that, to secure a better seal, three or more layers of oxide or of refractory compounds may be used.
  • the metal layer may be cornpressed by elastic membranes in isostatic compression.
  • the graphite bar has a diameter of about 2O mm. and is 250 mm. long. It is reduced in its middle part over a length of about 8O mm. to a diameter of 3 mm. This operation can be easily performed, for example on a lathe, by choosing a fine grain, easily machined graphite.
  • a layer of alumina is deposited on the reduced portion, the layer thus formed extending over some 10 mm. on the larger diameter ends.
  • This alumina layer is then sprayed with a layer of copper (66%)-titanium (33%) alloy, care being taken that this metal deposit should not extend beyond the alumina layer underneath, for the metal would short-circuit the graphite.
  • a third layer of alumina is then deposited to cover the first two layers completely.
  • a silver-copper a1- loy is sprayed over a length of about l0 to 15 mm. on the graphite to ensure electrical contacts.
  • the middle part very quickly glows red.
  • the temperature reaches 1500" C. This temprature can be safely sustained or even exceeded up to 1700 C.
  • the shape of the bar is immaterial. It may be, for example, prismatic or parallelipedic.
  • the heating element according to the invention is substantially improved, as to the admissible working temperature and the useful life thereof, if an additional layer of an oxidizable substance, for example a layer of molybdenum, tungsten,
  • niobium or tantalum is provided between the graphite core 1 and the refractory material 2.
  • this intermediate layer has probably the effect of compensating the difference between the thermal expansion coefficients of the graphiteand of the layers superimposed thereupon, this being due to the fact that this intermediate layer is so selected that its expansion coefficient has a value which is comprised between that of the graphite expansion coeicient and that of the oxide layer expansion coefficient. Also a layer of carbide is thus formed.
  • a silver-copper alloy covers the end portions of the graphite core for providing electric connections.
  • Another effect of the intermediate layer is that it traps air oxygen which might have penetrated between the protective layers.
  • the metal layer or layers interposed between the oxide layers may be advantageously so selected so as to reduce supercially at high temperature the oxide layers.
  • aluminium layers may be used to separate alumina layers which they reduce in part and on which aluminium is perfectly spread out.
  • FIG. 3 shows by way of example a bar 10 of graphite 280 mm. long and having a 20 mm. diameter.
  • the graphite core has its diameter reduced to 3 mm. in its intermediate portion over some 80 mm.
  • a molybdenum coating 11 is projected on the core 1, this coating extending up to some mm. from the ends of the core.
  • An aluminium layer 12 is formed on the molybdenum layer.
  • an alumina layer 13 is formed on the aluminium layer 12 and a further aluminium layer 14 is formed on layer 13.
  • An electrical heater comprising:
  • a heater as claimed in claim 1 wherein said element comprises a cylindrical core, having a restricted center portion covered with said layers, and two metallized end portions.
  • a plurality of successive layers covering said core said layers being alternately of refractory and metal selected from the group comprising iron, nickel, cobalt, copper, chromium, silicon, titanium and aluminium, wherein a further metal layer lis interposed between said core and said successive layers, said further'layer being of an oxidisable metal having an expansion coecient comprised between the expansion coeicients of said core andthe layer adjacent thereto, and a melting point higher than 2500 C.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
  • Resistance Heating (AREA)
US774576A 1965-06-14 1968-11-01 Heater element Expired - Lifetime US3504327A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
US774576A US3504327A (en) 1965-06-14 1968-11-01 Heater element

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
FR20613A FR1447293A (fr) 1965-06-14 1965-06-14 Nouveaux éléments chauffants et procédé de fabrication de ces éléments
US55726966A 1966-06-13 1966-06-13
US774576A US3504327A (en) 1965-06-14 1968-11-01 Heater element

Publications (1)

Publication Number Publication Date
US3504327A true US3504327A (en) 1970-03-31

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US774576A Expired - Lifetime US3504327A (en) 1965-06-14 1968-11-01 Heater element

Country Status (5)

Country Link
US (1) US3504327A (OSRAM)
DE (1) DE1565812A1 (OSRAM)
FR (1) FR1447293A (OSRAM)
GB (1) GB1157891A (OSRAM)
NL (1) NL6608212A (OSRAM)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3890521A (en) * 1971-12-31 1975-06-17 Thomson Csf X-ray tube target and X-ray tubes utilising such a target

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1200352A (en) * 1911-09-05 1916-10-03 William S Hadaway Jr Electric resister.
US1736745A (en) * 1927-03-19 1929-11-19 Lohmann Hugo Electrical heating body and method of manufacturing the same
US1788146A (en) * 1928-04-30 1931-01-06 Carroll H Boyles Resistance unit and method of producing the same
US2385702A (en) * 1942-09-24 1945-09-25 Carborundum Co Electrical resistor
US3348929A (en) * 1962-04-16 1967-10-24 Metalurgitschen Zd Lenin Protecting carbon materials from oxidation

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1200352A (en) * 1911-09-05 1916-10-03 William S Hadaway Jr Electric resister.
US1736745A (en) * 1927-03-19 1929-11-19 Lohmann Hugo Electrical heating body and method of manufacturing the same
US1788146A (en) * 1928-04-30 1931-01-06 Carroll H Boyles Resistance unit and method of producing the same
US2385702A (en) * 1942-09-24 1945-09-25 Carborundum Co Electrical resistor
US3348929A (en) * 1962-04-16 1967-10-24 Metalurgitschen Zd Lenin Protecting carbon materials from oxidation

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3890521A (en) * 1971-12-31 1975-06-17 Thomson Csf X-ray tube target and X-ray tubes utilising such a target

Also Published As

Publication number Publication date
GB1157891A (en) 1969-07-09
FR1447293A (fr) 1966-07-29
DE1565812A1 (de) 1970-03-19
NL6608212A (OSRAM) 1966-12-15

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