Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
  • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
  • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
  • H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
  • H01F1/14—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys
  • H01F1/147—Alloys characterised by their composition
  • H01F1/14766—Fe-Si based alloys
  • H01F1/14775—Fe-Si based alloys in the form of sheets
  • H01F1/14783—Fe-Si based alloys in the form of sheets with insulating coating
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F27/00—Details of transformers or inductances, in general
  • H01F27/24—Magnetic cores
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
  • H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
  • H01F41/0206—Manufacturing of magnetic cores by mechanical means

Definitions

• This invention relates to coatings for ferrous material and, more particularly, an improved magnesium oxide/ magnesium hydroxide coating for grain oriented silicon steel, and the material coated by such process.
• the first function of the coating is to provide separation of the various turns or layers of the coiled material to prevent their sticking or welding together during high temperature anneals.
• a second function is that of aiding in the chemical purification of the ferrous material to develop the desired optimum magnetic characteristics of such material.
• the third function of the coating is to form on the surface of the ferrous material a refractory type coating which will provide electrical insulation of one layer of ferrous material from the next, for example, during its use as a core in a transformer.
• magnesium oxide and/or magnesium hydroxide are, in general, applied to the ferrous material in the form of a suspension of magnesium oxide and/or magnesium hydroxide in water.
• the suspension comprises a quantity of magnesium oxide in water and is mixed sufficiently for the desired application, the magnesium oxide being hydrated to an extent dependent on the character of the oxide used, the duration of mixing and the temperature of the suspension. Therefore, the term magnesium oxide coating is with reference to a coating of magnesium hydroxide which may include magnesium oxide which has not been hydrated.
• portions of an annealing separator of magnesium oxide can, during a heat treatment at suitable temperatures, be caused to react with silica particles on or near the surfaces of previously oxidized silicon-iron sheet stock to form a glass-like coating, which coating is useful as an interlaminary insulator in the use of silicon-iron in electrical apparatus, e.g. m the cores of transformers.
• the steel In the production of silicon steel for the magnetic cores of transformers, the steel is generally annealed to provide optimum grain growth and grain orientation which develops the magnetic properties of the silicon steel.
• This anneal is usually carried out in a hydrogen atmosphere at temperatures ranging from approximately 950 to 1500 C. from about 2 to about 50 hours.
• This anneal also aids in purifying the steel, aided by the coating placed on the steel.
• a portion of the magnesium oxide coating reacts with the silica on the surface of the silicon steel to form a glass-like coating of magnesium silicate.
• This glass-like coating provides electrical insulation during the use of the silicon steel in electrical apparatus, e.g., in the cores of transformers.
• This invention relates to an improved MgO/Mg(OH) coating which forms a superior insulating glass film when applied to silicon steel surfaces which have been previously oxidized.
• an improved MgO/Mg(OH) coating which forms a superior insulating glass film when applied to silicon steel surfaces which have been previously oxidized.
• one such method of oxidation which may be employed is taught in US. Pat. 2,385,332, discussed above. More particularly the invention concerns coatings containing magnesium oxide/magnesium hydroxide and organic or inorganic lithium bearing compounds which when applied to silicon sheet steel imparts unexpected and improved insulation qualities to the silicon steel after the final high temperature anneal.
• Representative members of the class of organic and inorganic lithium bearing compounds includes the followmg:
• lithium acetate lithium borate such as lithium metaborate, lithium metaborate hydrate, lithium pentaborate, lithium tetraborate and lithium borohydrate lithium chromate lithium fluoride lithium hydroxide lithium lactate lithium nitrate lithium phosphate lithium silicate lithium sulfate lithium zirconate lithium zirconium silicate lithium hydroxide monohydrate lithium carbonate lithium acetylsalicylate lithium metaaluminate lithium aluminum hydride lithium amide lithium antimonide lithium orthoarsenate lithium azide lithium benzoate lithium bromide lithium bromide, dihydrate lithium carbide lithium bicarbonate lithium chlorate lithium chlorate hydrate lithium perchlorate lithium perchlorate .trihydrate lithium chloride lithium chloride monohydrate lithium chloroplatinate lithium bichromate dihydrate lithium dichromate lithium citrate lithium fluosilicate lithium fluosulfonate lithium formate monohydrate lithium gallium hydride lithium gallium nitride lithium metagermanate lithium hydride lithium iodate lithium iodine
• lithium compounds which have a relatively high weight percent of lithium are preferred for use in the instant invention since the anion portion of the lithium compound (assuming it to be a salt) would ordinarily serve no purpose. Itshould be emphasized, however, that any lithium compound (or mixtures of such compounds) may be utilized to obtain the advantageous function here involved since the key to this function is the presence of the lithium atom or ion.
• Analysis of the composition of the glass film formed according to the practice of this invention reveals a novel film containing predominately well crystallized MgO, magnesium silicate and lithium.
• the concentration of the lithium bearing compound calculated as Li with. respect to the amount of the MgO employed in the coating is not critical and may vary from about 0.1 to about 30 weight percent of the magnesium oxide. A satisfactory concentration for most 4 practical purposes (calculated as Li O) has been found to be from about 0.2 .to 12.5 weight percent of MgO. It should be noted that the particular grade of MgO to be utilized is not critical and any commercially available MgO may be employed in the practice of the invention.
• the lithium-MgO/Mg(OH) coatings of the invention a may be applied to the grain-oriented silicon steel using techniques conventionally employed in the coating of these materials.
• a continuous strip of the ferrous material is passed through a bath containing the MgO/Mg(OH) suspension and then through a drying furnace.
• MgO/Mg(OH) exclusive of lithium additive
• amount of MgO/Mg(OH) (exclusive of lithium additive) that is applied to the silicon steel in the practice of this invention is similar to those amounts that heretofore had been employed in MgO/Mg(OI-I) coatings and in general will vary from about 0.020 to 0.060 ounce of MgO per square foot of steel surface.
• the manner and time at which the lithium compounds are combined with the magnesium oxide is not critical. As described by the various examples set forth below, these procedures include adding the lithium compound to a magnesium material, such as magnesium basic carbonate or Mg(OH) prior to their conversion to the magnesium oxide; blending the lithium material with the MgO or Mg(OH) adding the lithium compound separately during coating slurry make-up; or mixing the lithium material in the water used for coating slurry make-up prior to the addition of the MgO powder.
• a magnesium material such as magnesium basic carbonate or Mg(OH)
• the annealing of the silicon steel that has previously been coated with the coating composition of the invention may be carried out in a reducing atmosphere at temperatures ranging from approximately 950 to 1500 C. for from about 2 to. 50 hours using techniques well known to the art.
• EXAMPLE 1 A slurry containing about 1 lb. MgO/gal. concentration was made up by mixing 60 g. of a commercial grade MgO with 6 g. of a reagent grade lithium caarbonate, and then addingSOO ml. of deionized water in a Waring blendor for one minute. The resulting slurry was coated on strips of silicon steel (size 3 mm. x 30.5 mm.) at a coating weight of 0.038 oz./ft. dried at 250-275 C., and
• Additive (MgO basis): Resistance 0% 3.7 ohms-cmfi.
• EXAMPLE 2 A slurry containing about 0.5 lb. MgO/gallon concentration was made up by mixing 30 g. of a commercial grade MgO with 0.3 g. of a reagent grade lithium carbonate. and then adding 500 ml. of deionized water in a Waring blendor for one minute. The slurry was coated on silicon steel strips and tested in the same manner as described in Example 1. Franklin test results show:
• EXAMPLE 3 60 g. of a commercial grade magnesium oxide was added to a Waring blendor containing 500 ml. of deionized water. 4.8 g. of a reagent grade lithium hydroxide was then added and mixed thoroughly for one minute. The slurry was coated on silicon steel strips and tested in the same manner as described in Example 1. Franklin test results showed:
• EXAMPLE 6 60 g. of a commercial magnesium-oxide, 3 g. of lithium metaborate and 500 ml. of deionized water were added simultaneously into a Waring blendor and mixed to form a smooth coating slurry. This slurry was coated on silicon steel strips and tested in the same manner as described in Example 1. Franklin test results show:
• EXAMPLE 7 60 g. of a commercial magnesium oxide and 6 g. of lithium acetate (LiC H O -2H O) were thoroughly mixed and added to 500 ml. of deionized water in a Waring blendor. The resulting slurry was coated on strips of silicon steel and tested in the same manner as described in Example 1. Franklin tests on the surfaces show:
• EXAMPLE 8 60 g. of a commercial magnesium oxide, 0.6 g. of lithium sulfate and 500 ml. of deionized water were mixed in a Waring blender. The slurry was coated onto strips of silicon steel in the same manner as described in Example 1. Franklin tests show:
• Lithium lactate Li C H O 5 0. 73 15. 0 l0 1. 46 38. 3 Lithium tetraborate "i 8: 6,? (Ll2B407.5H20) 10 1. 15 2g?) Lithium phosphate (2LiaPO .1/2H 0)- ⁇ g 7 Lithium silicate (LizSiOa) 6;; Lithium zirconate (Li2Zl03) m Lithium zirconium silicate 1 0. 14 12. 9 (2Li O .Z1O2.Sl02). 6 0. 70 11. 8 1 0. 12 3. 8 Lithium diehromate (LiZCrZO'l-HZO) 5 0.60 12. 4 10 1. 20
• a method of producing an electrical insulating film on magnetic silicon steel which comprises applying a coating composition consisting essentially of a material selected from the group consisting of MgO, Mg(OH) and mixtures thereof and at least one lithium compound to surface oxidized silicon steel and annealing said silicon steel at an elevated temperature, said lithium compound being present at from about 0.1 to about 30 weight percent of magnesium oxide calculated as U 0.
• lithium compound is selected from the group consisting of lithium carbonate, lithium hydroxide, lithium fluoride, lithium borate, lithium acetate, lithium sulfate, lithium oxide, lithium lactate, lithium phosphate, lithium silicate, lithium zirconate, lithium zirconium silicate, lithium dichromate, and lithium nitrate.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Chemical & Material Sciences (AREA)
• Dispersion Chemistry (AREA)
• Chemical Treatment Of Metals (AREA)

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Cited By (26)

• 1970
  • 1970-08-17 US US64644A patent/US3697322A/en not_active Expired - Lifetime
• 1972
  • 1972-07-11 BE BE786123A patent/BE786123A/fr unknown

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