US2285952A - Electric heater insulating material - Google Patents

Electric heater insulating material Download PDF

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Publication number
US2285952A
US2285952A US287334A US28733439A US2285952A US 2285952 A US2285952 A US 2285952A US 287334 A US287334 A US 287334A US 28733439 A US28733439 A US 28733439A US 2285952 A US2285952 A US 2285952A
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US
United States
Prior art keywords
lime
silica
per cent
weight
around
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
US287334A
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English (en)
Inventor
Oliver G Vogel
Navias Louis
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.)
EDISON GENERAL ELEC APPLIANCE
EDISON GENERAL ELECTRIC APPLIANCE COMPANY Inc
Original Assignee
EDISON GENERAL ELEC APPLIANCE
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 BE441872D priority Critical patent/BE441872A/xx
Application filed by EDISON GENERAL ELEC APPLIANCE filed Critical EDISON GENERAL ELEC APPLIANCE
Priority to US287334A priority patent/US2285952A/en
Priority to GB12097/40A priority patent/GB536795A/en
Priority to FR867202D priority patent/FR867202A/fr
Application granted granted Critical
Publication of US2285952A publication Critical patent/US2285952A/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
    • 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

Definitions

  • This invention relates to electric heaters, more particularly to electric heaters of the sheathed type, and it has for its object the provision of a heater of this character having improved insulating material.
  • this invention is particularly applicable to sheathed heaters having a resistance conductor enclosed in a metallic sheath, and embedded in and supported in spaced relation with the sheath by a densely compacted layer of heat refractory and conducting, electrically insulating material.
  • a heater is described in the United States patent to Charles C. Abbott, dated February 1, 1921. It is to be understood, however, that this invention is not limited to the specific sheathed heater disclosed in this patent, but has more general application to sheathed heaters.
  • the heat refractory insulating material that has found wide application in sheathed electric heaters is granular magnesium oxide, and heaters provided with this insulating material have, in the main, been quite satisfactory. Pure magnesium oxide has a very high initial resistance and maintains a high resistance value throughthe electrical resistance of the heaters falls rather rapidly with use.
  • silica-lime ratio in the insulation such that the silica neutralizes the effects of the lime by combining with it and the magnesium oxide to form.
  • silicates of lime and magnesia Silica should be present in the proper amounts before the magnesium oxide is fused so as to prevent the segregation of any free lime in the fused mass as it cools, that is, to prevent the presence of any uncombined lime.
  • the heater comprises a helical resistance conductor Ill mounted within and substantially centrally of a tubular metallic sheath II.
  • the resistance conductor I0 may be formed of any suitable material, such' as a nickelchromium alloy.
  • the sheath ll preferably will be made of a suitable chromium-iron-nickel al loy.
  • the resistance conductor I0 is secured at its ends to suitable terminals l2. 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 l0, the sheath H and terminals I2 may be made of many other suitable materials.
  • the resistance conductor I0 is embedded in and is supported in spaced relation with reference to the sheath by a mass I3 of heat refractory and heat conducting, electrically insulating material.
  • the mass of insulating material is in granular form and is compactedto 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 with the sheath. This reducing operation may be accomplished by swaging, drawing or rolling.
  • the mass of insulating material I3 is formed of granular magnesium oxide which is treated by fusing the material, crushing it and pulverizing it to the desired granular size.
  • commercialmagnesium oxides have more or less lime present, and the presence of this lime is very detrimental to the heater in that it reduces materially the insulating resistance of the heater with use, and increases its reactivity to moisture. and also to heated metal.
  • the resistance conductor [0, the metallic sheath II and the metallic terminals I? are attacked by the insulating mass 13.
  • a silica-lime ratio is established in the magnesium oxide to counteract the detrimental eifects of lime; and the ratio should be established before the magnesium oxide is fused so that no free lime will precipitate out when the magnesium oxide cools from fusing.
  • the presence of the silica reduces materially the reactivity of the insulation i3 to metals, and to moisture, and it maintains the electrical resistance through a very long useful life.
  • Silica has a tendency to reduce the initial electrical resistance of the magnesium oxide at high temperatures and, therefore, the amount used must be controlled, but within fairly wide limits. A little of the initial electrical resistance, however, may be sacrificed because of the other outstanding benefits obtained from the presence of silica, an important one of which is the maintenance of the resistance.
  • the magnesium oxide have a limited maximum lime content. It is desirable that this maximum lime content should not be above around per cent by weight, and preferably it should be below around 2.5 per cent by weight; and it is preferable that the maximum silica content be not greater than around 25 per cent by weight.
  • the ratio of silica to lime should be at least as great as 1 to 1, although this minimum ratio may be around 2 to 3.
  • the ratio of silica to lime may range from 2 to 3 to 2 0 to l; but the silica content should not in any case be below around 1 per cent nor' above around 25 per cent by weight.
  • the silica content should range from around 1 to 2 per cent by weight.
  • the preferred silica-lime balance should be as follows: for any lime content of around 0.5 per cent or less by weight, the silica content should range from about 1 to 2 per cent by weight; and for any lime content ranging from around 0.5 per cent up to about 5 per cent by weight, the ratio of silica to lime should range from 2 to 1, to 3 to 1.
  • the silica content may be as great as 25 per cent by weight which is a ratio of silica to lime of to 1; if the lime content be around 1.5 per cent by weight, a silica content of 25 per cent by weight may be used, which gives a ratio of silica to lime of around 1'7 to 1; for a lime content of .75 per cent by weight, the silica content may be as high as per cent by weight which gives a ratioof silica to lime of to 1; and. ii. the lime content be around .05 per cent by weight, the silica content may be as high as 1 to 2 per cent by weight, or in the ratio of 20 to 1, to- 40 to 1.
  • ing material for said resistance element comprising fused magnesium oxide having present before being fused a controlled silica-lime content
  • the percentage of silica ranging from 1 to 2 per cent by weight when the lime content is around 0.5 per cent or less by weight, and in a ratio of. silica to lime of around 2 to 1 to 3 to 1 when the lime content ranges from around 0.5 per cent to 5 per cent by weight.
  • Electrically insulating and heat conducting material for a sheathed electric heater that is provided with a metallic sheath and a resistance conductor within the sheath embedded in and supported in spaced relation with reference to the sheath by the electrically insulating and heat conducting material comprising a mass of fused magnesium oxide which before being fused has present a predetermined lime-silica content. said lime content not exceeding about 5% by weight and the silica content not exceeding about 25% by weight.
  • an electric heater provided with a metallic casing and a metallic resistance element in said casing, electrically insulating and heat conducting material adapted to be inserted in the casing to embed the resistance element and hold it in spaced relation with reference to the casing comprising, fused magnesium oxide having present before being fused a controlled silica-lime content, the ratio of the silica to lime being not less than around 2 to 3, but when the lime content is less than around 0.5 per cent by weight. then the silica content being not less than around 1 per cent by weight.
  • an electric heater provided with a metallic casing and a metallic resistance element within said casing, electrically insulating and heat conducting material adapted to be inserted in the casing to embed and support the resistance element and hold it in spaced relation to the casing, said material comprising fused magnesium oxide which has present before being fused'a controlled silica-lime content, the ratio of the silica to lime being not less than around 2 to 3 and not greater than around 20 to 1 where the lime content ranges from about 0.5 to around 5 per cent by weight, and said lime content being not greater than around 5 per cent by weight and said silica content not greater than around 25 per cent by weight.
  • a mass of fused magnesium oxide adapted to be inserted in said casing for embedding said resistance element and holding it in spaced relation with reference to said. casing, said fused magnesium oxide having present before being fused a controlled silica-lime content, the ratio of silica to lime ranging from 2 to 3 to 20 to 1;
  • said resistance element consisting of fused magnesium oxide having present before be-- ing fused a controlled silica-lime ratio, the proportion of silica being sumciently great to prevent the presence of free lime in said magnesium oxide after being fused.
  • an electric heater provided with a metallic sheath and a metallic resistance conductor in said sheath, electrically insulating and heat conducting material adapted to be inserted in the sheath to embed the resistance conductor and hold it in spaced relation with reference to the sheath, said material comprising granular magnesium oxide which has been fused, cooled and then crushed into granular form, and said magnesium oxide having a controlled silica to lime ratio, the silica being present before fusing in suflicient quantities to prevent the segregation of free lime in said magnesium oxide when it cools after fusing.

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  • Resistance Heating (AREA)
US287334A 1939-07-29 1939-07-29 Electric heater insulating material Expired - Lifetime US2285952A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
BE441872D BE441872A (en, 2012) 1939-07-29
US287334A US2285952A (en) 1939-07-29 1939-07-29 Electric heater insulating material
GB12097/40A GB536795A (en) 1939-07-29 1940-07-24 Improvements in electric resistance heaters
FR867202D FR867202A (fr) 1939-07-29 1940-09-16 Perfectionnements aux éléments chauffants

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US287334A US2285952A (en) 1939-07-29 1939-07-29 Electric heater insulating material

Publications (1)

Publication Number Publication Date
US2285952A true US2285952A (en) 1942-06-09

Family

ID=23102443

Family Applications (1)

Application Number Title Priority Date Filing Date
US287334A Expired - Lifetime US2285952A (en) 1939-07-29 1939-07-29 Electric heater insulating material

Country Status (4)

Country Link
US (1) US2285952A (en, 2012)
BE (1) BE441872A (en, 2012)
FR (1) FR867202A (en, 2012)
GB (1) GB536795A (en, 2012)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3088906A (en) * 1959-12-07 1963-05-07 Norton Co Cathode bar for aluminum reduction cell
US3621204A (en) * 1969-04-29 1971-11-16 Dynamit Nobel Ag Electrical heating element with fused magnesia insulation
JPS4921737A (en, 2012) * 1972-06-21 1974-02-26
US4681862A (en) * 1985-03-19 1987-07-21 Tateho Kagaku Kogyo Kabushiki Kaisha Electrically insulating filler for sheathed heaters

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3088906A (en) * 1959-12-07 1963-05-07 Norton Co Cathode bar for aluminum reduction cell
US3621204A (en) * 1969-04-29 1971-11-16 Dynamit Nobel Ag Electrical heating element with fused magnesia insulation
JPS4921737A (en, 2012) * 1972-06-21 1974-02-26
US4681862A (en) * 1985-03-19 1987-07-21 Tateho Kagaku Kogyo Kabushiki Kaisha Electrically insulating filler for sheathed heaters

Also Published As

Publication number Publication date
GB536795A (en) 1941-05-27
BE441872A (en, 2012)
FR867202A (fr) 1941-10-07

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