Classifications

• • 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
  • 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
• • 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
  • H01F1/20—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 particles, e.g. powder
  • H01F1/22—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 particles, e.g. powder pressed, sintered, or bound together
  • H01F1/24—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 particles, e.g. powder pressed, sintered, or bound together the particles being insulated
• • 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
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/27—Web or sheet containing structurally defined element or component, the element or component having a specified weight per unit area [e.g., gms/sq cm, lbs/sq ft, etc.]
  • Y10T428/273—Web or sheet containing structurally defined element or component, the element or component having a specified weight per unit area [e.g., gms/sq cm, lbs/sq ft, etc.] of coating

Definitions

• This invention relates to compositions suitable for application to ferrous metal surfaces to produce insulating coatings thereon, the processof applying the compositions and the product produced therewith.
• the laminations In preparing laminations of magnetic material for the building of magnetic cores therefrom, it is necessary that the laminations be provided with electrical insulation between one another in order to minimize eddy currents and to achieve low losses.
• the insulation should preferably be an extremely thin film integral with the surfaces of each lamination to provide for a high space factor.
• the insulating material applied to laminations should withstand the elevated temperatures which are encountered in strain annealing cores after assembly in order to improve their efficiency. Temperatures" encountered in stress re-' lieving occasionally reach 1200 C. and are rarely less than 600 C.
• the insulation for the magnetic sheet material be capable of withstanding bending
• Magnetic material is usually cut or punched after the insulating material is applied thereto, and thereafter'the cut or punched magnetic material may be bent or wound in order to produce a predetermined core structure. Additionally, the assembled cores may be subjected to machining or grinding, and, in some cases, etching with acids in order to' remove burrs and the like.
• the insulation resistance frequently drops to values of the order of 0.15 to 0.5 ohmper square centimeter. Often the phosphate film is disrupted during twisting and the resistance is zero.
• an interlaminar resistance of at least one ohm per square centimeter is necessary tolimit eddy current loss in the core to a workable value.
• the lack of adherence and abrasion re- 'sistance as evidenced by decrease of resistance dered refractory such as magnesia, alumina, or v silica flour to the phosphoric acid before application to ferrous metal does not materially improve the insulating film produced.
• the ohmic re sistance' of the films is not significantly greater than that produced with the phosphoric acid alone.
• the adherence of the phosphate films is not better when embodying such refractory solids.
• the object of this invention is to provide a tenaciously adherent insulating film possessing, high ohmic resistance on ferrous metal surfaces.
• a further object of the invention is to provide a composition composed of phosphoric acid and a silica hydrogel capable of producing adhered films of high ohmic resistance on ferrous material by heat treatment.
• aqueous compositions are prepared containing a relatively high phosphoric acid concentration and a substantial amount of a silica hydrogel substantially all of whose particles are from 1 to 20 microns in diameter.
• compositions of the present invention are composed of 100 parts by weight of orthophosphoric acid, from 5 to 55 parts by weight of a silica hydrogel composed of particles substantially all of which are in the range of from 1 to 20 microns in diameter and from 7 to 15 parts by weight of water for each part of the silica hydrogel, the maximum amount of water not exceeding 600 parts by weight.
• the composition may be conveniently prepared by admixing 100 parts by weight of aqueous orthophosphoric acid solution having more than 50% orthophosphoric acid by weight and from 60 to 200 parts by weight of an aqueous silica hydrogel dispersion, prepared as will be described hereinafter, containing from to by weight of silica in the form of particles substantially all of which are from 1 to microns in diameter.
• a silica hydrogel suitable for the practice of the present invention is made by mixing sodium silicate, preferably having a ratio of from 3 to 3 /2 SiOz groups per NazO group, with sulphuric acid.
• the proportions of sulphuric acid and the sodium silicate are approximately equimolecular, an excess of acid being preferred.
• the mixture whichis known as a hydrosol, is permitted to age, for example, in tubs holding several hundred pounds of the hydrosol. From 3 to 5 hours aging results in a gellation of th hydrosol to a colloidal hydrogel of the desired consistency, and the hydrogel is emptied from the tubs and broken into small lumps as by passing over a screen.
• the metal and applied coating are heat-treated at a temperature of from 300 C. to 950 C. for a length of time sufficient to drive off the water and to cause a reaction of the composition ingredients with the metal surface to take place.
• the precise nature of the reaction is not known but smooth homogeneous coating less than one-quarter of a mil in thickness results.
• the time of the reaction need only be a few seconds at temperature of 700 C. and higher. At lower temperatures, the reaction may be somewhat longer.
• Several minutes heat treatment at temperatures from 650 C. to 950 C. has given good results in practice. It is preferred to maintain a relatively low oxidizing or inert atmosphere in the furnace to prevent undue oxidation and the formation of rust.
• compositions which have been applied to silicon iron laminations 13 mils thick The following examples set forth compositions which have been applied to silicon iron laminations 13 mils thick.
• Example I A composition was prepared by admixing 10 gallons of 75% phosphoric acid and 100 pounds of silica hydrogel suspension containing 11 pounds by weight of silica proper. This mixture formed a stable suspension of coating consistency. Rolls of 13 mil thick sheet silicon iron 14 inches wide were roller-coated with the suspension, a total of 9600 pounds of silicon iron being coated, and passed into an oven having an atmosphere at a temperature of 760 C. The sheets were in the oven for approximately 1 minutes. The sheets were found to be uniformly coated with a hard film of insulating refractory. The sheets were tested with a C-clamp tester whose construction and operation are described in detail in the Horstman et a1. Patent 2,354,123, issued July 18, 1944. The tester at no time indicated a resistance of below 100 ohms per square centimeter, and indicated infinity resistance for nearly all the spots tests on sheets produced. Such resistance was recorded even when the tester was twisted several times.
• Example II A composition was prepared by admixing:
• Parts Water 100 Phosphoric acid '70 Silica hydrogel dispersion (11% S102) 70 The composition was applied to silicon iron laminations in the proportion of one gallon to 320 square feet of surface. composition were baked at 700 C. for 15 seconds. The coatings so produced were extremely adherent and indicated infinity resistance.
• Example III A composition was prepared by mixing:
• Example IV A composition was prepared by admixing:
• Example V A composition was prepared by admixing the following:
• compositions of this invention have numerous advantages.
• the aqueous compositions are highly stable and will not precipitate, or deteriorate even on long-continued storage, as for several weeks. They do not contain flammable solvents, such as are present with ethyl silicate compositions, and, therefore, are safe for use with any type of furnace.
• the compositions may be diluted indefinitely with water without breaking; therefore, the thickness of the applied coatings may be controlled readily by the amount of water added.
• Silicon iron laminations coated with the insulating film derived on heat treating the compositions of this invention on their surfaces are refractory at elevated temperatures. Tests of magnetic cores produced therewith which were annealed at 700 C. showed that practically no laminations stuck together after the annealing operation.
• a composition suitable for applying to fer-. rous metal to produce on the metal after heat treatment tenaciously adherent insulating coatings having a high ohmic resistivity composed of, in combination, 100 parts by weight of orthophosphoric acid, from 5 to 55 parts by weight of a silica hydrogel having from to 15% by Weight of silica, the hydrogel composed of particles substantially all of which are in the range of from 1 to microns in diameter, and from 7 to not more than 15 parts by weight of water for each part of the silica hydrogel, the maximum amount of water not exceeding 600 parts by Weight, all combined as an aqueous dispersion.
• a coating composition in the form of an aqueous dispersion composed of parts by weight of aqueous orthophosphoric acid having more than 59% phosphoric acid and from 60 to 200 parts by weight of an aqueous silica hydrogel dispersion containing from 10% to 15% by weight of silica, the hydrogel particles substan-- tially all of which are from 1 to 20 microns in diameter.
• the steps comprising applying to the surface of the ferrous metal a composition composed of 100 parts by weight of ortliophosphoric acid, from 5 to 55 parts by weight of a silica hydrogel composed of particles substantially all of which are in the range of from 1 to 20 microns in diameter, and from 7 to not more than 15 parts by weight of Water for each part of the silica hydrogel, the maximum amount of water not exceeding 600 parts by weight, the composition being applied to provide from /2 to 5 pounds of the silica in the hydrogel for each 300 square feet of metal surface, and heat-treating the ferrous metal and applied composition at a temperature of from 300 C. to 950 C. to drive off the water and cause a reaction of the composition with the ferrous metal to take place to provide the adherent film.
• a composition composed of 100 parts by weight of ortliophosphoric acid, from 5 to 55 parts by weight of a silica hydrogel composed of particles substantially all of which are in the range of from 1 to 20 microns in diameter, and from 7 to not more
• Magnetic sheet material comprising a body composed of ferrous magnetic metal and a surface film composed of an adherent refractory coating, the coating being derived by applying to the surface of the ferrous metal a composition composed of 100 parts by weight of orthophosphoric acid, from 5 to 55 parts by weight of a silica hydrogel composed of particles substantially all of which are in the range of from 1 to 20 microns in diameter, and from 7 to not more than 15 parts by weight of water for each part of the silica hydrogel, the maximum amount of water not exceeding 609 parts by weight, the composition being applied to provide from to 5 pounds of the silica in the hydrogel for each 300 square feet of metal surface, and heat-treating the ferrous metal and applied composition at a temperature of from 300 C. to 950 C. to drive ofi the water and cause a reaction of the composition with the ferrous metal to take place to provid the adherent fihn.
• a composition composed of 100 parts by weight of orthophosphoric acid, from 5 to 55 parts by weight of a silica hydrogel

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Dispersion Chemistry (AREA)
• Power Engineering (AREA)
• Materials Engineering (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Paints Or Removers (AREA)
• Soft Magnetic Materials (AREA)
• Silicon Compounds (AREA)

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Cited By (17)

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Citations (6)

• 1947
  • 1947-12-11 US US791168A patent/US2554250A/en not_active Expired - Lifetime
• 1948
  • 1948-11-10 GB GB29243/48A patent/GB680325A/en not_active Expired
  • 1948-12-09 FR FR976367D patent/FR976367A/fr not_active Expired

Patent Citations (6)

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