Classifications

• • 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
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/73—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals characterised by the process
  • C23C22/74—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals characterised by the process for obtaining burned-in conversion coatings
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
  • H01B3/002—Inhomogeneous material in general
  • H01B3/006—Other inhomogeneous material
• • 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
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S428/00—Stock material or miscellaneous articles
  • Y10S428/90—Magnetic feature

Definitions

• Electrically insulating coating for strand annealed magnetic silicon steel is composed of an aqueous mixture of (1) reaction product of chromium nitrate and sodium chromate, (2) phosphoric acid and (3) colloidal silica.
• the present invention relates to coated magnetic sheet material and a method of making the same. More particularly, the invention concerns refractory coating material which is applied to such sheet material, and especially to strand annealed silicon steel strip, and serves as a permanent insulating coating in the use of the metallic sheet material in laminated electrical structures.
• the forms of magnetic sheet material with which the invention is concerned include strip material such as used in wound transformer cores, and cut or punched laminations forming stacked transformer cores or other electrical apparatus.
• strip material such as used in wound transformer cores, and cut or punched laminations forming stacked transformer cores or other electrical apparatus.
• compositions of magnetic sheet materials which may be effectively coated in accordance with the invention are silicon steel (typically containing about l5% silicon), nickel-iron alloys, common iron, and other ferromagnetic materials.
• the invention is particularly applicable to silicon steel strip which has been subjected to a grain growth and purification anneal treatment wherein the steel is heated in the form of a single strand, as distinguished from coiled or stacked form, in a suitable furnace through which the strand may be continuously passed during the heat treat- .ment.
• the application of insulating coatings in general to the steel sheet prior to the annealing treatment has the disadvantage in a strand anneal procedure that the presence of the insulating coating tends to delay the purification of the steel during the strand anneal, e.g., by hindering removal of sulfur from the steel, and consequently the strand anneal process is not as rapid as it might be in the absence of such coatings.
• the prior types of inorganic insulating coating such as magnesium hydroxide require relatively high curing temperatures, e.g., over 1000 C., to produce final coatings of the requisite hardness, electrical insulating and other properties.
• a further object of the invention is to provide an improved insulating coating composition for the above purposes which requires relatively low curing temperatures.
• Still another object of the invention is to provide an insulating coating composition which is particularly adapted for use on electrical steel sheet material treated by a strand anneal process.
• the present invention in one of its aspects relates to an insulating coating composition
• an insulating coating composition comprising a mixture of water soluble salt of trivalent chromium, a water soluble chromate salt, phosphoric acid, a finely divided refractory material selected from the group consisting of colloidal silica and colloidal alumina, and water.
• the chromium and chromate salts are initially mixed together to form a reaction product which is then mixed with the remaining ingredients of the mixture.
• the foregoing insulating mixture is deposited on the surfaces of silicon steel strip which has been subjected to a strand anneal process for producing the desired magnetic texture and removing undesired impurities therein.
• a strand anneal process is disclosed in detail, for example, in Fitz et al. Pat. 2,986,485, and the disclosure of that patent is incorporated herein by reference.
• the strand anneal process which may be carried out on a continuous basis, comprises the steps of heating silicon steel material for about 5 to 60 minutes (preferably about 15 minutes) at a temperature of about 950 to 1050 C., and thereafter heating the material at a temperature of about 1175 to 1250 C.
• the annealing treatment is preferably carried out in a reducing atmosphere in the furnace, such as in hydrogen or other reducing gases.
• a reducing atmosphere in the furnace such as in hydrogen or other reducing gases.
• the thus annealed steel strip which previous to the anneal had not been provided with an insulating coating, is then coated with the abovedescri'bed mixture, and the latter is then dried by heating or otherwise cured to form a hard, tightly adherent, highly insulating coating on the steel surfaces.
• a particular coating mixture found eminently satisfactory for the purposes of the invention has the following composition, shown in a preferred and a range of proportions in percent by Weight:
• the hydrated compound thus obtained as the reaction product of chromium nitrate and sodium chromate is then added first to the phosphoric acid, and as the water is added the mixture is stirred until the precipitate dissolves.
• the colloidal silica is then added to the solution to produce the coating bath.
• the mixture thus produced is a green liquid with a specific gravity of 1.23 and a pH of about 2.
• the coating solution is applied to the strand annealed steel material in any suitable manner such as by dipping, spraying, brushing or other methods. Typically, the steel strip, which has been allowed to cool to room temperature, is dipped into the coating bath, allowed to drain 30 seconds, and then baked in an oven at 250 C. for about 1 minute.
• the coating thus produced was smooth, hard and tightly adherent and did not craze appreciably on bending of the coated sheet material. It was characterized by excellent electrical insulation properties, had minimal effect on watt-loss and permeability properties, while improving magnetostriction properties. It was found by test, for example, that such a coating deposited in an amount of .05 oz./sq. ft. on the steel sheet provides a Franklin insulation value of about .00 ampere, it being known by those skilled in the art that any Franklin value below .20 ampere is satisfactory for transformer use, and that the lower this value the better the insulating quality.
• chromium nitrate has proved satisfactory for use in the above mixture
• other water soluble salts of trivalent chromium may be used, such as chromium acetate, chromium sulfate, and chromium chloride or other chromium halogen salts.
• water soluble chromate salts other than sodium chromate may be used, such as potassium chromate, magnesium chromate, and calcium chromate.
• the colloidal silica which may be used in the described mixture is in the form of an aqueous solution containing SiO in an extremely finely divided form made by an ion exchange technique.
• Colloidal silica is available commercially under the trademark of Ludox, a product of E, I. du Pont de Nemours & Company, which is an aqueous colloidal sol containing approximately 30% Si with less than 0.5% Na O as a stabilizer.
• Ludox a product of E, I. du Pont de Nemours & Company
• colloidal silica which is a dispersion in water of alumina particles which are sufficiently finely divided to provide a colloidal sol in water.
• a colloidal form of alumina available commercially which may be used is sold under the trademark Baymal, a product of E. I. du Pont de Nemours & Company. This is a white, freeflowing powder consisting of minute fibrils of boehmite (AlOOH) alumina and which disperses readily in water to yield a colloidal sol. Further detailed descriptions of this material and colloidal sols thereof and methods of making them are set forth in the patent to Bugosh 2,915,475. In general, for the purposes of this invention a concentration of -50 grams per liter of water of the finely divided colloidal alumina has been found suitable, with a range of 30-40 grams/liter affording optimum results.
• a suitable composition for, use in such a process is as follows, in percent by weight:
• the drying stage temperature may vary in. a range of about 200 C. for 3 minutes to about 300 C. for about /2 minute.
• composition of the finally produced coating which is transparent and pale green in color, is not presently known and cannot be definitely ascertained, and it is accordingly referred to herein simply as the cured product of the mixture of ingredients as above described.
• insulating coating is particularly applicable for use on strand annealed silicon steel material, it is not limited to such use. It will be found of advcantage, for example, for coating such steel or other metallic material where rela tively low curing temperatures are or must be used.
• an improved insulating coating composition which has excellent electrical insulating properties, may be deposited in thin and tightly adherent layers to the steel surface, which does not contribute to electrical loses or other unfavorable electrical properties in the coated steel material, and which is applied easily in a continuous operation.
• the very tenacious adherance of the insulating coating is especially noteworthy in view of the very smooth surfaces which characterizes strand annealed steel, as distinguished from steel annealed in coiled or stacked form as in conventional processes, and which ordinarily make it difiicult for conventional insulating coatings to firmly adhere thereto.
• An insulating coating composition comprising an aqueous mixture of (l) the phosphoric acid soluble, water-Washed precipitate formed by stirring the aqueous mixture of a water soluble salt of trivalent chromium and awater soluble chromate salt, (2) phosphoric acid, and (3) a finely divided refractory material selected from the group consisting of colliodal silica and colloidal alumina.
• a composition as defined in claim. 1, comprising in percent by weight of about .5 to 10% of said precipitate, about 15 to 30% posphoric acid, about 10 to 40% of said finely divided refractory material, and about to 70% water.
• a composition as defined in claim 2 comprising about 1% of said precipitate, about 27% phosphoric acid, about 30% colloidal silica, and about 42% water.
• An insulating coating composition comprising a mixture of (1) a water soluble salt of trivalent chromium, (2) a water soluble chromate salt, (3) phosphoric acid, (4) a finely divided refractory material selected from the group consisting of colloidal silica and colloidal alumina, and (5) water.
• a composition as defined in claim 4 including in percent by weight 2 to 10% chromium nitrate, 2 to 10% sodium chromate, 15 to 30% phosphoric acid, 20 to colloidal silica, and 15 to water.
• a composition as defined in claim 8 including about 1% of said precipitate, about 27% phosphoric acid, about 30% colloidal silica, and about 42% water.
• Magnetic sheet material having thereon a thin, tightly adherent coating composed of the cured product of the mixture defined in claim 1.
• coated magnetic sheet material which comprises providing on the surface thereof a mixture as defined in claim 1, and heating the same at a temperature of between 200 C. and 300 C.
• coated magnetic sheet material which comprises providing on the surface thereof a coating mixture as defined in claim 7, and heating the same at a temperature of between 200 C. and 300 C.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Chemical & Material Sciences (AREA)
• General Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Manufacturing & Machinery (AREA)
• Chemical Treatment Of Metals (AREA)
• Manufacturing Of Steel Electrode Plates (AREA)
• Heat Treatment Of Sheet Steel (AREA)
• Soft Magnetic Materials (AREA)

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Cited By (26)

Families Citing this family (2)

• 1968
  • 1968-04-26 US US724636A patent/US3562011A/en not_active Expired - Lifetime
• 1969
  • 1969-03-24 GB GB05216/69A patent/GB1248127A/en not_active Expired
  • 1969-04-19 DE DE19691919997 patent/DE1919997A1/de active Pending
  • 1969-04-25 JP JP44031522A patent/JPS4817581B1/ja active Pending
  • 1969-04-25 FR FR6913198A patent/FR2007031A1/fr not_active Withdrawn

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