Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D9/00—Electrolytic coating other than with metals
  • C25D9/04—Electrolytic coating other than with metals with inorganic materials
  • C25D9/08—Electrolytic coating other than with metals with inorganic materials by cathodic processes
  • C25D9/10—Electrolytic coating other than with metals with inorganic materials by cathodic processes on iron or steel
• • 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
  • H01B3/02—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of inorganic substances
• • 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
  • H01B3/02—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of inorganic substances
  • H01B3/025—Other inorganic material
• • 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
  • 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
  • H01F1/16—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 in the form of sheets
  • H01F1/18—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 in the form of sheets with insulating coating

Definitions

• the present invention relates to coated metallic sheet materials and to the method of producing the same. More particularly, the invention concerns electrically insulating coatings for magnetic sheet material and to an improved process for applying such coatings.
• magnetic sheet material with which the invention is principally concerned include strip material such as used in wound transformer cores, and cut or punched laminations forming stacked transformer cores and other electrical apparatus.
• a particular magnetic sheet material which may be effectively coated in accordance with the invention is magnetic silicon steel which in 'a conventional composition contains about 3% silicon, 12% manganese, .03% carbon, .01% sulfur, and 01% phosphorus, it being understood, however, that the composition of the magnetic silicon steel used in practicing the present invention need not correspond to the specified values.
• the sheet material In the process of treating the magnetic sheet materials to adapt them for use in transformers or other electrical devices, the sheet material is generally wound in the form of a roll or cut and arranged into a plurality of stacked sheets, and placed in these forms in an annealing furnace for the purpose of developing the magnetic properties of the sheet material.
• the adjacent surfaces of the magnetic sheet material are in contact with each other over comparatively large areas with the result that at the elevated temperatures employed for developing the magnetic qualities of the material, the adjacent laminations or turns of the material tend to stick together unless some means is provided for separating the surfaces during the heat treatment.
• an insulating barrier to be provided between the adjacent laminated sheets of the magnetic material in order to reduce the eddy current losses in the core formed by the sheet material in its use in a transformer, motor or the like.
• Coating compositions used in the past to provide interlaminar insulation for the above purposes have been subject to various drawbacks, including the tendency to rub oil on contact, the lack of uniformity in thickness with resultant poor space factor, the introduction of contaminants such as carbon into the metal being coated, or the lack of adequate insulation qualities after the high temperature annealing treatment.
• the invention in its broad aspects provides a method of producing an insulating coating on the surface of a magnetic silicon steel body which comprises the deposition of an adherent metal hydroxide coating on the surface of the silicon steel body by electrolyzing an aqueous solution of a water soluble metal salt from which insoluble 3,054,732 Patented Sept. 18, 1962 hydroxides are deposited on the silicon steel body forming the cathode.
• the silicon steel body thus coated with a thin adherent metal hydroxide coating is then subjected to elevated temperatures during which the hydroxide deposit is converted to a refractory insulating coating.
• Particularly preferred compounds for forming the insulating coatings are water soluble calcium and magnesium salts, e.g., calcium nitrate or magnesium nitrate, from 0 which the insoluble calcium hydroxide or magnesium hydroxide may be deposited in accordance with the invention.
• the conventional high temperature annealing treatment of silicon steel strip on which the hydroxide coatings are applied as described results in the formation of a silicate film at the interface of the hydroxide deposit and the metal surface due to the reaction between the hydroxide and the silicon in the iron.
• This silicate film which is a glass-like, highly insulating layer, serves in the final assembly of the silicon steel laminations as interlaminar insulation to reduce eddy current losses.
• the remaining hydroxide deposit decomposes to yield the corresponding refractory oxide, e.g., calcium oxide, which separates the strips during pack annealing and thus prevents sticking of the strips to one another.
• Soluble salts of other refractory producing metals may be employed, notably those of aluminum and manganese, as, for example, aluminum nitrate, manganese sulfate and manganese nitrate.
• Mixtures of the various salts mentioned above may also be used in preparing the solution to be electrolyzed;
• the concentration of the soluble salt in the aqueous solution is not critical and may vary widely from a very small value, say, 0.1 molar, up to a saturated solution. A satisfactory concentration for most practical purposes has been found to be about 0.8 molar. This Value, of course, will vary depending on the particular salt, the solution temperature, and other factors.
• Example I An 0.8 molar solution of Ca(NO was electrolyzed in an electrolytic bath, using a silicon-iron sheet 5% inches wide x 6 inches long as the cathode and platinum as the anode. In the experiment, 8 volts were applied across the terminals with a current density of amps./ft. the electrolyzing period being for 30-60 seconds. In this and the other examples described herein, the spacing of the electrodes was 3 inches. Using the above procedure, adherent coatings of Ca(OH) ranging in thickness from .05 to .20 mil were obtained on a number of samples of silicon-iron sheets.
• the Franklin insulation values mentioned herein were determined by the standard Franklin test for determining the value of insulation of coatings of the described type, and in this test readings of 1 ampere represent no surface insulation and 0 ampere represent perfect insulation.
• Example 11 A 1.2 molar solution of Mg(NO was electrolyzed, using stainless steel of 18% chromium, 8% nickel, remainder iron as the anode and a silicon-iron sheet as the cathode, the applied voltage being 3.8 volts with a current density of 75 amperes per square foot. The solution was electrolyzed for 50 seconds, and a coating of Mg(OH) of 0.4 mil thickness was deposited on the silicon steel sheet. The Franklin insulation values of several samples after annealing for 8 hours at 1175 C. in
• Example III Silicon-iron sheet material was successfully coated with a mixture of Ca(OH) and Mg(OH) by electrolyzing a number of solutions containing various amounts of Ca(NO and Mg(NO Best results were obtained where the weight ratio of Mg(NO to Ca(NO did not exceed 1 to 10.
• An aqueous solution containing a l to 20 weight ratio of Mg(NO to Ca(NO) was electrolyzed at a current density of 70 amperes per square foot, and a coating mixture of Ca(OH) and Mg(OH) was depositedin a thickness of about 0.3 mil per side after a period of 60 seconds.
• Example V Using a platinum anode and a silicon-iron Sheet as cathode, a saturated solution of MnSO; was electrolyzed for 45 seconds, thereby obtaining a 0.15 mil deposit of white Mn(OH) on the cathode. A current density of 70 amps/ft. was used. Upon drying the coating, it turned black, apparently forming Mn The amount of coating material deposited in a given period depends on such factors as the current density, the concentration of the solution, and the size and spacing of the electrodes. Accordingly, suitable variation of these factors provides a means for readily controlling the coating thickness to obtain the desired results.
• the mechanism of the deposition by the described electrolyzing process apparently involves the discharge of hydrogen ions at the cathode, which results in an increased hydroxyl ion concentration at the surface of the cathode.
• soluble salts of calcium are present in the solution, calcium hydroxide will precipitate on the cathode forming an adherent coating.
• the oxygen is evolved in this reaction at the anode and results from the oxidation of hydroxyl ions at the anode.
• the hydrogen is evolved at the cathode.
• solid Ca(OH) powder may be added if desired to the solution to neutralize the nitric acid. Such addition will serve not only to keep the pH 4 constant but also to keep the concentration of the Ca(NO at its original value.
• inert anodes are preferred for use in the present process, such as platinum, anodes of other materials may be used provided they do not contaminate or otherwise unfavorably afiect the coating deposited on the cathode.
• Aluminum for example, could be satisfactorily employed as anode material in coating Silicon steel for electrical purposes.
• the hydrogen ions are depleted by reaction with the nitrate ions, thus making the solution basic and resulting in the deposition of Mg(OH) on the cathode.
• the mechanism of the present electrolyzing process is not simply the migration (electrophoresis) of charged particles to the cathode for deposition of a coating thereon.
• the subject process involves not only the electrolyzing of the soluble salt but also a subsequent chemical reaction, as indicated above, to provide the necessary conditions for forming and precipitating the insoluble hydroxide and depositing it on the surface of the metal cathode sheet. It appears that the excellent adherence as well as the uniform thickness of the deposited coating is very likely due to the very small particle size of the hydroxy compound as it precipitates out of the solution.
• the method of producing electrically insulated magnetic silicon steel sheet material which comprises electrolyzing an aqueous solution consisting essentially of at least one com-pound selected from the group consisting of water soluble salts of calcium, magnesium, manganese, and aluminum, with the silicon steel sheet material be ing arranged as the cathode in said solution, for forming and depositing an adherent coating of the hydroxide of the cation of said compound on said silicon steel sheet material, removing the thus coated silicon steel sheet material-from said solution, and heating said coated sheet material at elevated temperature to react said hydroxide with the silicon in said sheet material for forming a refractory insulating coating comprising a silicate compound on the surfaceof said sheetmaterial;
• the method of producing electrically insulated magnetic silicon steel sheet material which comprises electrolyzing an aqueous solution consisting essentially of at least one compound selected from the group consisting of Water soluble salts of calcium, magnesium, manganese, and aluminum, with the silicon steel sheet material being arranged as the cathode in said solution, for forming and depositing an adherent coating of the hydroxide of the cation of said compound on said silicon steel sheet material, removing the thus coated silicon steel sheet material from said solution, and heating said coated sheet material at about ll75 C. to react said hydroxide with 5 the silicon in said sheet material for forming a refractory insulating coating comprising a silicate compound on the surface of said sheet material.
• Electrically insulated magnetic sheet material comprising a magnetic silicon steel sheet having thereon a thin, tightly adherent coating of the reaction product of the silicon in said sheet material and a water insoluble metal hydroxide deposited on said sheet material by electrolysis of an aqueous solution of at least one compound selected from the group consisting of water soluble salts of calcium, magnesium, manganese, and aluminum, said reaction product comprising a permanent, electrically insulating, refractory layer composed of a silicate com- 6% pound firmly bonded to the surface of the silicon steel sheet material.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Inorganic Chemistry (AREA)
• Dispersion Chemistry (AREA)
• Power Engineering (AREA)
• Metallurgy (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Electrolytic Production Of Metals (AREA)
• Soft Magnetic Materials (AREA)
• Chemical Treatment Of Metals (AREA)
• Other Surface Treatments For Metallic Materials (AREA)

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Cited By (19)

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Citations (5)

• 0
  • DE DENDAT1249049D patent/DE1249049B/de active Pending
• 1959
  • 1959-03-05 US US797344A patent/US3054732A/en not_active Expired - Lifetime
• 1960
  • 1960-02-17 GB GB5624/60A patent/GB922521A/en not_active Expired
  • 1960-02-27 ES ES0256100A patent/ES256100A1/es not_active Expired

Patent Citations (5)

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