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US2629065A - Overwound filament - Google Patents

Overwound filament Download PDF

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Publication number
US2629065A
US2629065A US27122A US2712248A US2629065A US 2629065 A US2629065 A US 2629065A US 27122 A US27122 A US 27122A US 2712248 A US2712248 A US 2712248A US 2629065 A US2629065 A US 2629065A
Authority
US
United States
Prior art keywords
core
coil
filament
tungsten
cathode
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
Application number
US27122A
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English (en)
Inventor
Hampton J Dailey
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
CBS Corp
Original Assignee
Westinghouse Electric Corp
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Priority to BE488975D priority Critical patent/BE488975A/xx
Application filed by Westinghouse Electric Corp filed Critical Westinghouse Electric Corp
Priority to US27122A priority patent/US2629065A/en
Priority to GB10478/49A priority patent/GB669912A/en
Priority to DEW1639A priority patent/DE818536C/de
Application granted granted Critical
Publication of US2629065A publication Critical patent/US2629065A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
    • H01J1/02—Main electrodes
    • H01J1/13—Solid thermionic cathodes
    • H01J1/15—Cathodes heated directly by an electric current

Definitions

  • This invention relates to overwound filaments for use particularly as cathodes for electron discharge devices...
  • the basic defect of the ordinary tungsten cathode is the rapid burning up thereof, especially at a mid-part of the same. It is an unavoidable circumstance that end portions of a cathode will be cooled by heat conduction therefrom by the lead-in connections whereas the mid-portion of the cathode does not correspondingly suiier from this reduction in operating temperature. Due to the temperature existing at the mid-portion of the usual fila ment or cathode being higher than at the end portions in development of the desired average cathode temperature, the rate of evaporation of. the emissive material is much greater at the mid-portion.
  • the cathode suiiers from the vicious cycle of becoming thinner and hotter at its mid-portion during use until it finally erodes to the point of use lessness orbreakage.
  • An object of the present invention is to provide a tungsten filament wherein evaporation is substantially prevented.
  • Another object of the invention is to obtain a greater than double electron emission per watt of filament power over conventional tungsten filaments.
  • an object of the invention is to provide a filament which is equally usable in high power, high voltage electron discharge devices or tubes and which, when so used, has longer life and increased emissivity over prior art conventional filaments.
  • Yet another object of the invention is to provide an emissive wrapping on a tungsten core in such manner that heating current suiiers 2 substantially no change due to evaporation oc--v curring, in the wrapping, and in. which evaporation will not materially reduce tube life.
  • an object of the invention istoretain the benefits oi sturdiness of tungsten wire for filament use.
  • a further object of the invention is to obtain rapid heat interchange from the tungsten core of my improvedfilament to the emissive wrapping thereon andla consequential 'loweringof necessary operating temperature for thesaid core.
  • FIGs 1 and 2 are side elevations of two forms of filaments embodying my invention
  • Figure .3 is a longitudinal section of a portion of a filament showing the invention. in its simplest form and before alloying heat. has been applied;
  • Figure 4 is an enlarged view in section of a part of the showing of Figurev 3, but before alloying has been efiected;
  • Figure 5 is a sectional view similar to Figure 4,, but after alloying has been effected;
  • Figure 6 is an. elevation of a portion of a filament ofmodified constructionv utilizing overwindings of difierentdiameters.
  • Figure '7 is an enlarged longitudinal section of a portion of the filament of liigure 6..
  • a filamentary metallic core of material which becomes incandescent by fiow of electrical current therethrough.
  • An acceptable example is tungsten wire of 0.011 inchdiameter foroperation with current in the range of 4 to 6 amperes. Wound tightly upon this core this a helical coil H the convolutions of which are in tangential engagement each with the next adjacent one, thereby obtaining a closed coil which preferably extends along the core at least for the length thereof where emission is desired, and for which purpose the said cell is preferably a material which is electron emissive when heated.
  • tantalum or an alloy of tungsten and tantalum are given as satisfactory examples for coil materials to be used in conjunction with the example given above of tungsten core.
  • the diameter of the coil wire is preferably less than the diameter of the core, so example of a satisfactory coil wire may be given for use with the mentioned tungsten core, of tantalum wire having a diameter of 0.002 inch.
  • the most economical mode of manufacture is to wind the tantalum wire directly upon the tungsten coil in long lengths and cut off such length thereof as needed for any particular filament.
  • the severed length of the overwound core is attached in place upon the supporting posts or lead-in wires M of the electron discharge tube or device, and a current is then applied thereto for rendering the core highly incandescent to a degree of temperature approximating 2400 K. to 3000 K. which will obtain an alloying r welding unification of the convolute portions of the coil where in engagement with the core due to the tight winding of the coil on the core.
  • This alloying or weldin is indicated in Figure as accomplished at l5. There is no alloying or welding of the convolutions to each other since the tangential engagement of the convolutions with each over is at a distance from the incandescent core.
  • the alloying of the coil to the core is evidenced in a gradual change in filament characteristics over an approximate period of forty-eight hours of applied current to the filament. For instance, where an initial current of about 4.8 amperes is used to heat the core to incandescence, the current drawn as alloying progresses will rise and will reach approximately 5.1 amperes in the period mentioned, showing that the alloying has been accomplished. Alloying of the coil to the core will cause the core to operate at a lower temperature. At the desired operating temperature of 2400 K. of the tantalum coil, its resistivity is 92.85 x ohm-centimeters. Throughout the temperature range of 2400 K.
  • the highest practical emission efliciency for a pure tungsten filament is approximately 6-7 milliamperes per watt of filament power.
  • the limitation, to use of a tungsten filament with higher temperature and correspondingly higher emission, resides in the relative high evaporation rate or erosion of the tungsten at temperatures of 2500 K. and above. The evaporation reduces the cross section of the wire, thus causing hot spots and early burnouts at the points of reduced cross section in the prior art filaments.
  • the coil or wrapping of tantalum traps products of tungsten evaporation within the closed spaces l6 formed by the convolutions so that the vapor pressure due to the evaporation that occurs is confined to those spaces and operates to deter or prevent further evaporation. Since the wrapping or coil carries little of the heating current, evaporation of material from the coil or erosion of the coil at its outer or exposed portions will not affect the heating current. With a coil or wrapping of tantalum operated at approximately 2400 K, the electron emission per watt of filament power is substantially 20 milliamperes per watt or roughly three times that of a prior art pure tungsten filament.
  • a core [0a as shown in Figure 2 of in creasing diameter toward the mid-portion of the length thereof.
  • a core may be of tungsten and otherwise be of the character of core previously described.
  • said core Illa may be over-wound or wrapped with a coil of tantalum wire alloy of tungsten and tantalum, or other emissive material or materials as heretofore described, with the convolutions tightly Wound upon the core and in tangential engagement with each other.
  • a cathode comprising a metallic cylindrical core adapted to be heated by flow of current therethrough, and an overwound coil of wire on said core, said coil being of different chemical constituency from said core and having a continuous-spiral portion of its convolutions in contact with and alloyed directly to said core substantially throughout the length of said continuous-spiral portion, and said cathode having a greater outside diameter at its middle than at its ends.
  • a cathode comprising a metallic cylindrical core adapted to be heated by flow of current therethrough, said core having a greater outside diameter at its middle than at its ends, and an over-Wound coil of wire on said core, the wire of said coil having substantially uniform di ameter throughout its length and the convolutions of said coil having greater diameter midway of the length of said coil than at the ends thereof in conformity with the diameters of the core where the coil is over-wound.
  • a cathode comprising a metallic cylindrical core adapted to be heated by flow of current therethrough, and an overwound coil of wire of difi'erent chemical constituency from and on said core the convolutions whereof are in contact with and alloyed directly to said core, and the convolutions midway of the length of said coil being formed of wire of greater diameter than the wire forming the convolutions at the ends of said coil.

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  • Solid Thermionic Cathode (AREA)
US27122A 1948-05-14 1948-05-14 Overwound filament Expired - Lifetime US2629065A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
BE488975D BE488975A (it) 1948-05-14
US27122A US2629065A (en) 1948-05-14 1948-05-14 Overwound filament
GB10478/49A GB669912A (en) 1948-05-14 1949-04-20 Improvements in or relating to cathodes
DEW1639A DE818536C (de) 1948-05-14 1950-04-14 Kathode, insbesondere fuer Elektronen-Entladungsgeraete

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US27122A US2629065A (en) 1948-05-14 1948-05-14 Overwound filament

Publications (1)

Publication Number Publication Date
US2629065A true US2629065A (en) 1953-02-17

Family

ID=21835821

Family Applications (1)

Application Number Title Priority Date Filing Date
US27122A Expired - Lifetime US2629065A (en) 1948-05-14 1948-05-14 Overwound filament

Country Status (4)

Country Link
US (1) US2629065A (it)
BE (1) BE488975A (it)
DE (1) DE818536C (it)
GB (1) GB669912A (it)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2810107C1 (ru) * 2022-10-06 2023-12-21 Общество с ограниченной ответственностью "Торговый Дом "ХИММЕД" Катодолюминесцентная лампа цилиндрического типа

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE972442C (de) * 1952-05-27 1959-07-23 Siemens Ag Halterung fuer eine Kathode fuer elektrische Entladungsgefaesse

Citations (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1190412A (en) * 1914-02-19 1916-07-11 Radio Telephone & Telegraph Company Electrode for devices for varying electrical resistance.
US1777253A (en) * 1926-04-06 1930-09-30 Philips Nv Oxide cathode
US1946603A (en) * 1929-05-09 1934-02-13 Electrons Inc Cathode for electrical discharge devices
US2015417A (en) * 1930-12-13 1935-09-24 Rca Corp Cathode
GB486138A (en) * 1937-01-19 1938-05-31 Gen Electric Co Ltd Improvements in electrodes for high-pressure metal vapour electric discharge devices
US2141933A (en) * 1937-11-18 1938-12-27 Gen Electric Cathode
US2175345A (en) * 1935-07-12 1939-10-10 Gen Electric Electric gaseous discharge device
US2241345A (en) * 1938-06-24 1941-05-06 Westinghouse Electric & Mfg Co Electron emissive cathode
US2297454A (en) * 1940-01-20 1942-09-29 Berger Hermann Cathode
US2329118A (en) * 1941-07-12 1943-09-07 Gen Electric Electrode for electrical discharge devices
US2363028A (en) * 1941-12-16 1944-11-21 Carl J Warnke Cathode filament
US2371205A (en) * 1943-10-30 1945-03-13 Coiled

Patent Citations (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1190412A (en) * 1914-02-19 1916-07-11 Radio Telephone & Telegraph Company Electrode for devices for varying electrical resistance.
US1777253A (en) * 1926-04-06 1930-09-30 Philips Nv Oxide cathode
US1946603A (en) * 1929-05-09 1934-02-13 Electrons Inc Cathode for electrical discharge devices
US2015417A (en) * 1930-12-13 1935-09-24 Rca Corp Cathode
US2175345A (en) * 1935-07-12 1939-10-10 Gen Electric Electric gaseous discharge device
GB486138A (en) * 1937-01-19 1938-05-31 Gen Electric Co Ltd Improvements in electrodes for high-pressure metal vapour electric discharge devices
US2141933A (en) * 1937-11-18 1938-12-27 Gen Electric Cathode
US2241345A (en) * 1938-06-24 1941-05-06 Westinghouse Electric & Mfg Co Electron emissive cathode
US2297454A (en) * 1940-01-20 1942-09-29 Berger Hermann Cathode
US2329118A (en) * 1941-07-12 1943-09-07 Gen Electric Electrode for electrical discharge devices
US2363028A (en) * 1941-12-16 1944-11-21 Carl J Warnke Cathode filament
US2371205A (en) * 1943-10-30 1945-03-13 Coiled

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2810107C1 (ru) * 2022-10-06 2023-12-21 Общество с ограниченной ответственностью "Торговый Дом "ХИММЕД" Катодолюминесцентная лампа цилиндрического типа

Also Published As

Publication number Publication date
GB669912A (en) 1952-04-09
DE818536C (de) 1951-10-25
BE488975A (it)

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