US2669636A - Sheathed electric heater insulating material - Google Patents

Sheathed electric heater insulating material Download PDF

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Publication number
US2669636A
US2669636A US227384A US22738451A US2669636A US 2669636 A US2669636 A US 2669636A US 227384 A US227384 A US 227384A US 22738451 A US22738451 A US 22738451A US 2669636 A US2669636 A US 2669636A
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United States
Prior art keywords
zirconium silicate
magnesium oxide
insulating material
per cent
silica
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
US227384A
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English (en)
Inventor
William T Rawles
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.)
General Electric Co
Original Assignee
General Electric Co
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 BE511468D priority Critical patent/BE511468A/xx
Application filed by General Electric Co filed Critical General Electric Co
Priority to US227384A priority patent/US2669636A/en
Application granted granted Critical
Publication of US2669636A publication Critical patent/US2669636A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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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
    • H05B3/40—Heating elements having the shape of rods or tubes
    • H05B3/42—Heating elements having the shape of rods or tubes non-flexible
    • H05B3/48—Heating elements having the shape of rods or tubes non-flexible heating conductor embedded in insulating material

Definitions

  • This invention relates to sheathed electrical heaters and particularly concerned with an improved insulating material for such heaters. It has as its principal object the provision of a heater of this character including an improved heat-refractory insulating material.
  • the sheathed heaters of the type with which the present invention is concerned are those in which a resistance conductor is enclosed in a tubular metallic sheath, and embedded in and supported in spaced relation with the sheath by a densely compacted layer of heat-refractory and heat-conducting, electrically insulating material.
  • Such a heater is shown in the accompanying drawing in which the single figure is a fragmentary view in elevation of a sheathed electric heater embodying the present invention, portions of the heater being shown in sections so as to illustrate certain details of construction.
  • the heater comprises a helical resistance conductor 19 mounted within and substantially centrally of a tubular metallic sheath H.
  • the resistance conductor Ill may be formed of any suitable material, such as a nickel-chromium alloy.
  • the sheath I l preferably is made of a suitable chrome-iron-nlckel alloy.
  • the resistance conductor It is secured at its ends to suitable terminals [3. These terminals may be formed of any suitable material, but preferably will be formed of steel. It is to be understood, however, that the conductor in, the sheath I! and terminals 13 may be made of many other suitable materials.
  • the resistance conductor Ill is embedded in and is supported in spaced relationship with reference to the sheath by a mass 12 of heat refractory and heat-conducting, electrically insulating material.
  • the mass of insulating material is in granular form and is compacted to a hard dense mass in any suitable manner, as by reducing the diameter of the sheath H after the resistance conductor, terminals, and insulating material have been assembled within the sheath. This reducing operation may be accomplished by swaging, drawing, .or rolling.
  • the heat refractory insulating material that has found wide application in such sheathed electric heaters is granular magnesium oxide, and heaters provided with this insulating material have on the whole been quite satisfactory.
  • Pure magnesium oxide has a very high initial resistance and maintains a high resistance; value throughout a very long life.
  • the granular magnesium oxide is prepared by fusing magnesium oxide and crushing and pulverizing the fused product to the desired granular size.
  • the present invention is based on the discovcry that a low cost refractory insulating material possessing satisfactory electrically insulating and heat-conducting properties and the proper compacting characteristics can be provided in the form of mixtures of zirconium silicate and magnesium oxide of particular particle sizes.
  • the term "magnesium oxide as used hereinafter is intended to include pure magnesium oxide as well as the modified commercial grades of magnesium oxide, all of which have been prepared by fusing and thereafter crushing and pulverizing the fused material tothe propergranular size.
  • zirconium silicate alone has poorer electrically insulating properties than magnesium oxide, in mixtures of zirconium silicate and magnesium oxide of the above proportions, these poorer electrically insulating properties are offset by the better heat-conducting properties of the zirconium silicate so that heater elements containing such mixtures were completely satisfactory, both from the heat conductivity and electrical insulating standpoints. .In
  • the silica may be substituted for up to 60 per cent by weight of the zirconium silicate.
  • the silica content of the total refractory mixture may be up to 40 per cent by weight.
  • a powder mixture consisting of 7 parts zirconium silicate and 3 parts crystalline fused magnesium oxide of the above-mentioned particle sizes was loaded into a sheathed unit employing the standard technique described, for example, in Oakley et a1.
  • the loaded unit was prepared for a reduction in cross-sectional area by rolling in the standard manner after first being sealed by means of washers crimped into the end of the tubular sheath.
  • the units were thereafter rolled to compact the powder and checked for elongation, degree of compaction, or hardness of the compacted material, reproducibility, and position ofrthe helical resistance elements.
  • the zirconium silicate or mixture of zirconium silicate and silica comprises the principal portion.
  • the magnesium oxide in the proportions employed permits the proper compaction of the granular mixture which cannot be obtained with either pure zirconium silicate or mixtures of zirconium silicate and silica. It is essential that the magnesium oxide have a grain size larger than the particle sizes or average particle sizes of the zirconium silicate and silica.
  • the improved compacting characteristics result from the fact that the magnesium oxide is more easily crushed during the rolling or swaging operations performed on the sheathed unit and because of its cubic crystal habit, it breaks down in all directions with equal ease to fill in between the particles of the zirconium silicate or mixtures of zirconium silicate and silica and effect a satisfactory compacting of the entire mixture.
  • the mixtures of the present invention are particularly characterized by the absence of any binder, such as clay or the like, frequently employed for the purpose of bonding together poorly compactible granular insulating materials ordinarily as a result of a partial sintering or fusing of the clay or similar binder.
  • binder such as clay or the like
  • Such binders are undesirable in the sheathed units with which the present invention is concerned due to their poor electrical characteristics.
  • the primary function of the magnesium oxide is that of a binding action without fusion. This binding action results solely from the compacting characteristics of the magnesium oxide and its ability to disintegrate during the reducing operation and fill the voids between the zirconium silicate or zirconium silicate and silica particles.
  • a binder-free granular, refractory, heatconductive, embedding and electrically insulating material for sheathing electrical resistance elements comprising a mixture of (a) from about 20 to 40 per cent, by weight, granular fused magnesium oxide of a particle size such that at least about 22 per cent is retained on a SO-mesh screen and all passes through a 40-mesh screen, and (b) from about 60 to by weight, of at least one material of the class consisting of (1) zirconium silicate and (2) mixtures of zirconium siilcate and silica, said material (b) being of a particle size less than 80 mesh with at least 80 per cent thereof being of a particle size less than 100 mesh.
  • the insulating material of claim 1 consisting of to 40 per cent magnesium oxide, to 70 per cent zirconium silicate and up to per cent silica.
  • the insulating material of claim 1 consisting of 30 per cent fused magnesium oxide, per cent fused zirconium silicate and 20 per cent silica.
  • a sheathed electrical heating element including an embedding material comprising a 0mm pressed, binder-free, granular mixture of 20 to 40 per cent granular fused magnesia, balance at least one granular material of the group consisting of 1) zirconium silicate and (2) mixtures of zirconium silicate and silica of a particle WILLIAM T. RAWLES.

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US227384A 1951-05-21 1951-05-21 Sheathed electric heater insulating material Expired - Lifetime US2669636A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
BE511468D BE511468A (en, 2012) 1951-05-21
US227384A US2669636A (en) 1951-05-21 1951-05-21 Sheathed electric heater insulating material

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US227384A US2669636A (en) 1951-05-21 1951-05-21 Sheathed electric heater insulating material

Publications (1)

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US2669636A true US2669636A (en) 1954-02-16

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US227384A Expired - Lifetime US2669636A (en) 1951-05-21 1951-05-21 Sheathed electric heater insulating material

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BE (1) BE511468A (en, 2012)

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2916594A (en) * 1957-08-05 1959-12-08 Gen Electric Electric heating
US2962683A (en) * 1957-10-18 1960-11-29 Gen Electric Electric heating units and methods of making the same
US3087134A (en) * 1958-10-08 1963-04-23 Wiegand Co Edwin L Electric heater assembly
US3192059A (en) * 1963-06-28 1965-06-29 Harbison Walker Refractories Volume stable refractory and method of making same
US3457092A (en) * 1966-10-25 1969-07-22 Norton Co Granular electrically insulating material of magnesia and fused zircon
DE1902433A1 (de) * 1968-02-01 1969-08-28 Gen Electric Elektrisch isolierende,feuerfeste Masse
US3621204A (en) * 1969-04-29 1971-11-16 Dynamit Nobel Ag Electrical heating element with fused magnesia insulation
US3658587A (en) * 1970-01-02 1972-04-25 Allegheny Ludlum Steel Electrical insulation coating saturated with magnesium and/or calcium ions
FR2306509A1 (fr) * 1975-04-03 1976-10-29 Eichenauer Fritz Masse d'enrobage granuleuse ininflammable pour fils electriques de chauffage helicoidaux
US4689443A (en) * 1984-12-21 1987-08-25 U.S. Philips Corporation Armored cable having mineral insulation
US4697069A (en) * 1983-08-22 1987-09-29 Ingo Bleckmann Tubular heater with an overload safety means
US20190074112A1 (en) * 2017-09-05 2019-03-07 Hyundai Motor Company Sheath heater

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1359400A (en) * 1920-06-22 1920-11-16 Cutler Hammer Mfg Co Electric heater
US1952119A (en) * 1931-04-21 1934-03-27 Titanium Alloy Mfg Co Refractory cement

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1359400A (en) * 1920-06-22 1920-11-16 Cutler Hammer Mfg Co Electric heater
US1952119A (en) * 1931-04-21 1934-03-27 Titanium Alloy Mfg Co Refractory cement

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2916594A (en) * 1957-08-05 1959-12-08 Gen Electric Electric heating
US2962683A (en) * 1957-10-18 1960-11-29 Gen Electric Electric heating units and methods of making the same
US3087134A (en) * 1958-10-08 1963-04-23 Wiegand Co Edwin L Electric heater assembly
US3192059A (en) * 1963-06-28 1965-06-29 Harbison Walker Refractories Volume stable refractory and method of making same
US3457092A (en) * 1966-10-25 1969-07-22 Norton Co Granular electrically insulating material of magnesia and fused zircon
DE1902433A1 (de) * 1968-02-01 1969-08-28 Gen Electric Elektrisch isolierende,feuerfeste Masse
US3621204A (en) * 1969-04-29 1971-11-16 Dynamit Nobel Ag Electrical heating element with fused magnesia insulation
US3658587A (en) * 1970-01-02 1972-04-25 Allegheny Ludlum Steel Electrical insulation coating saturated with magnesium and/or calcium ions
FR2306509A1 (fr) * 1975-04-03 1976-10-29 Eichenauer Fritz Masse d'enrobage granuleuse ininflammable pour fils electriques de chauffage helicoidaux
US4101760A (en) * 1975-04-03 1978-07-18 Firma Fritz Eichenauer Refractory granular embedding composition for electric heating coils
US4697069A (en) * 1983-08-22 1987-09-29 Ingo Bleckmann Tubular heater with an overload safety means
US4689443A (en) * 1984-12-21 1987-08-25 U.S. Philips Corporation Armored cable having mineral insulation
US20190074112A1 (en) * 2017-09-05 2019-03-07 Hyundai Motor Company Sheath heater
US10622121B2 (en) * 2017-09-05 2020-04-14 Hyundai Motor Company Sheath heater

Also Published As

Publication number Publication date
BE511468A (en, 2012)

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