US3649372A - Reagent for forming an insulating coating on the surface of electrical steel sheets - Google Patents

Reagent for forming an insulating coating on the surface of electrical steel sheets Download PDF

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Publication number
US3649372A
US3649372A US816677A US3649372DA US3649372A US 3649372 A US3649372 A US 3649372A US 816677 A US816677 A US 816677A US 3649372D A US3649372D A US 3649372DA US 3649372 A US3649372 A US 3649372A
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United States
Prior art keywords
insulating coating
aluminum
reagent
steel sheets
electrical steel
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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
US816677A
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English (en)
Inventor
Mitsuo Imai
Hiroshi Shimanaka
Toshio Irie
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.)
JFE Steel Corp
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Kawasaki Steel Corp
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Publication date
Application filed by Kawasaki Steel Corp filed Critical Kawasaki Steel Corp
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    • 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
    • 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
    • H01F1/147—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
    • 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
    • Y10T428/26—Web or sheet containing structurally defined element or component, the element or component having a specified physical dimension
    • Y10T428/263—Coating layer not in excess of 5 mils thick or equivalent
    • Y10T428/264—Up to 3 mils
    • Y10T428/265—1 mil or less

Definitions

  • This invention relates to reagent for forming an insulating coating on the surface of electrical steel sheets and particularly to improvements on a reagent for use in a method of coating and baking phosphate solution on the surface of electrical steel sheets and providing an insulating coating having various excellent properties.
  • the insulating coating formed on the surface of electrical steel sheets is required to have a number of different properties in dependence with the magnetic property of the electrical steel sheets and the uses thereof.
  • a grain oriented silicon steel sheet for use in wound type transformers is required to have a large space factor, high interlamination resistance and high heat resistance.
  • the steel sheet is required to have an insulating coating having an excellent adhesive strength for an adhesive agent, such as epoxy resin.
  • the grain oriented silicon steel sheet for use in transformers is required to have corrosion resistance against the transformer oil and non-inflammable synthetic insulating oil.
  • a non-oriented silicon steel sheet for use in domestic electrical machines and apparatuses is required to have excellent punchability, weldability and corrosion resistance etc., more than the above mentioned properties.
  • the non-oriented silicon steel sheet for use in a motor core for refrigerators must resist against a refrigerant such as Freon gas.
  • This method makes use of a baking step under extremely strict conditions in order to produce a thin and smooth insulating coating having high corrosion resistance and insulating property, so that it is not suitable for producing industrially stable insulating coating on a mass production basis.
  • the conventional phosphate coating has the disadvantage that deterioration to the adhesion of the coating occurs when it is subjected to a stress relief annealing step and hence the coating becomes flaked off from the steel sheet, and the interlamination resistance becomes remarkably decreased, and cannot be applied to grain oriented silicon steel whose insulating property must be high.
  • An object of the invention is to obviate the above mentioned disadvantages and provide a novel reagent for forming a coating having excellent properties such as insulating property, adhesive property, corrosion resistance, space factor, heat resistance, machinability, weldability, etc., in an industrially easy manner, which can be applied effectively to the formation of an insulating film having a high break down voltage on a glass film formed on a grain oriented silicon steel sheet.
  • a feature of the invention is the provision of such an improved reagent for forming an insulating coating on the surface of electrical steel sheets which comprises an aqueous solution consisting of parts by weight of monobasic magnesium phosphate and 5 to 30 parts by weight of chromic anhydride, and 0.4 to 2.1 parts by Weight based on aluminum of aluminum nitrate and/or amorphous aluminum hydroxide.
  • the surface condition of the electrical steel sheets on which the reagent according to the invention is coated must be cleaned preliminary to the coating treatment, but it is not necessary to apply special steps such as to remove a thin oxide film formed by an annealing step on the surface of the electrical steel sheets.
  • the aluminum compounds are limited to aluminum nitrate and/or amorphous aluminum hydroxide.
  • Experimentation has shown that aluminum compounds other than aluminum nitrate and/or amorphous aluminum hydroxide or crystalline aluminum hydroxide can not attain the object of the invention.
  • the amorphous aluminum hydroxide is aluminum hydroxide gel available in the market as medical antiacid.
  • Aluminum nitrate can be aluminum nitrate nonahydrate Al(NO -9H O. It is a matter of course that an aqueous solution of Al(NO may also be used as aluminum nitrate.
  • FIG. 1 shows curves which explain the relationships between the amount of aluminum compounds added and interlamination resistances
  • FIG. 2 shows curves which explain the relationships between the amount of aluminum compounds added and adhesive properties
  • FIG. 3 shOWS a graph which explains the relationships between the amount of aluminum compounds added and baking times at 450 C.
  • FIG. 4 is a diagrammatic illustration of a circuit arrangement for measuring break down voltage of an insulating coating formed on the surface of an electrical steel sheet by a reagent according to the invention.
  • chain line curve a, full line curve 11 and dotted line curve 0 show the relation between the amount of aluminum salts added and interlamination resistances of insulating coatings formed on the surface of electrical steel sheets.
  • the interlamination resistances of the insulating coatings each having a thickness of 0.8 to 1.2 1. were plotted in function of the amount of aluminum in the aluminum salts.
  • this steel sheet is uniformly coated with an aqueous solution containing 100 cc. of water, g. of Mg(H PO and 3 g. of CrO and added with various amounts of aluminum salts.
  • the insulating coatings thus obtained are baked in a furnace at a temperature of 450 C. for one minute.
  • the curves a and b show changes of the interlamination resistances in dependence with additions of aluminum hydroxide A1(OH) and aluminum nitrate nonahydrate Al(NO -9H O, respectively, the more the amount of aluminum is present, the higher the interlamination resistance becomes.
  • the curve 0 shows the change of the interlamination resistance of a grain oriented silicon steel sheet covered with a heat resistance glass film on which is formed an insulating coating with the aid of a reagent containing aluminum nitrate nonahydrate Al(NO -9-H O. As seen from the curve 0, in this case the interlamination resistance be comes considerably increased. But, the correlation between the interlamination resistance and the amount of aluminum salt added is substantially the same as that shown by the curves a and b where the reagent is directly coated on the abovementioned steel sheet.
  • the solubility of the amorphous aluminum hydroxide in an aqueous solution of the monobasic magnesium phosphate is comparatively small.
  • more than 6 g. of amorphous aluminum hydroxide cannot be dissolved into 100 cc. of aqueous solution of the monobasic magnesium phosphate containing 12 g. of chromic anhydride.
  • the amount of baked on aluminum of aluminum compounds added in accordance with the invention is limited to 0.4 to 2.1 parts by weight.
  • FIG. 2 shows the relation between the amount of aluminum compounds added and adhesive properties of the insulating coating.
  • FIG. 2 was plotted from the re sults obtained by measuring the adhesive properties of the insulating coatings formed by reagents comprising cc. of water, 20 g. of Mg(H PO.;) 0 to 6 g. of CrO and O to 8 g. of aluminum nitrate.
  • the addition of Al(NO -9H O causes an improvement of the adhesive property of the insulating coating and the addition of CrO is effective to further improve the adhesive property of the insulating coating.
  • C1-C serves not only to improve the adhesive property of the insulating coating, but also to improve the corrosion resistance of the insulating coating.
  • Cr0 it is necessary to add more than 5 parts by weight of Cr0 with respect to 100 parts by Weight Of Mg(H PO Moreover, CrO is effective to make the insulating coating smooth and vitreous.
  • Al(OH) it is possible to make its solubility higher by decreasing the pH of the reagent, while when using Al(NO CrO is capable of prohibiting the above mentioned reaction between the steel sheet surface and the reagent coated thereon and hence preventing occurrence of the spot patterns.
  • pulverized heat resistant substance such as colloidal silica, mica or surface active agent may be added to the reagent according to the invention.
  • the insulating coating formed by the reagent according to the invention and having a thickness of 0.3 to 2.5 may have excellent properties such as adhesive property, interlamination resistance etc.
  • the insulating coating having a thickness less than 0.3 is low in interlamination resistance and inferior in corrosion resistance, while the insulating coating having a thickness more than 3.0;/. becomes opaque viridescent in color and flaky in shape, so that the insulating coating is liable to be flaked away from the surface of electrical steel sheets.
  • a reagent according to the invention again to the insulating coating which has been formed on the steel sheets and baked to obtain an insulating coating having a thickness which could not be obtained by one treatment, thus providing an insulating coating having an extremely high interlamination resistance and adhesive property.
  • the composition, concentration and baking temperature of the reagent reapplied to the insulating coating may be the same as those of the reagent applied at the first time.
  • the reagent according to the invention after having been coated may be baked at a comparatively low temperature for a short time. If the baking temperature is lower than 300 C., the insulating coating thus baked becomes hygroscopic. It has been found out that if the insulating coating is baked in a furnace at a temperature of 300 to 600 C. for 30 to 120 seconds the insulating coating thus baked becomes non-hygroscopic and is particularly adapted for use in various electrical fields.
  • FIG. 3 shows relationships between baking times at 450 C., for example, and amounts of aluminum compounds added. FIG. 3 was plotted by observing the surface condition of a steel sheet having a thickness of 0.5 mm. and coated with a reagent comprising 100 cc.
  • the use of Al(NO as the aluminum compounds can decrease the baking time by the order of to seconds.
  • the grain oriented silicon steel sheet for use in a large type transformer has recently been coated with an insulating coating adopted by steel sheet makers without being subjected to the varnish baking step.
  • Such silicon steel sheet is required not only to have a high interlamination resistance, but also to have a high break down voltage.
  • the insulating coating formed by the reagent according to the invention has a remarkably improved break down voltage as compared to other phosphate coatings and hence can be applied to the grain oriented silicon steel sheet for use in the large type transformers.
  • FIG. 4 shows a circuit arrangement for measuring the break down voltage.
  • a grain oriented silicon steel sheet coated on the surface thereof with glass film is further subjected to be coated on the glass film with the reagent according to the invention and baked thus providing an insulating coating having a thickness of 2a.
  • the thus treated sheet is annealed at a temperature of 800 C. in an N; atmosphere.
  • the break down voltages of the insulating coating thus obtained and measured by the circuit arrangement shown in FIG. 4 are shown in the following table.
  • 1 designates a 220 v. alternating current supply source, 2 a voltage regulating transformer, 3 an ammeter, 4 a resistor, 5 a circuit breaker, 6 a voltmeter, 7 an electrical steel sheet to be tested, 8 an insulating coating formed by a reagent according to the invention, 9 a measuring electrode having a diameter of 20 mm. and made of brass and 10 a measuring drill rod.
  • the addition of the aluminum compound serves to remarkably improve the break down voltage of the insulating coating.
  • the insulating coating formed on the surface of electrical steel sheets by the reagent according to the invention has various properties other than those described above, which read as follows.
  • the insulating coating provides a colorless glass-like film which is lustrous and beautiful in appearance and so hard that it is difiicult for it to be scratched.
  • the insulating coating has an excellent corrosion resistance and prevents formation of rust and has an excellent antichemical property and is stable against Freon gas and not damaged by transformer oil and punching oil.
  • the insulating coating is not flaked oil from the steel sheet when subjected to the stress relief annealing step and thus maintains a relatively high interlamination resistance even after the annealing step.
  • the insulating coating does not contain any organic compound and hence has a good weldability and does not cause blow holes after being subjected to a TIG-arc welding.
  • An electrical steel sheet containing 1.2% by weight of silicon and having an insulating coating formed thereon by the reagent according to the invention could be punched through by a punching die made of steel and having a clearance of 40,14 to obtain discs over one hundred and ninety thousand punchings until burr formed along the periphery of the disc obtained reaches to a height of 100
  • Such number of punching is about two times larger than that'of the electrical steel sheet coated with conventional phosphate insulating coating and then baked.
  • aluminum sulfate is used as a soluble aluminum compound, aluminum sulfate is not decomposed at a temperature less than 1,000" C. so that 80.; radical remains in the coating thus deteriorating its corrosion resistance and not improving its insulating property and adhesive property.
  • AlCl is also soluble in the magnesium phosphate, but the reagent containing AlCl when in contact with the steel sheets, immediately begins to react with them and spot-like patterns of tribasic phosphate are produced throughout the surface of the coating. Thus, after the steel sheets have been subjected to the baking step the coating is bad in appearance, corrosion resistance and adhesive property and cannot be used as an insulating coating.
  • the monobasic magnesium phosphate contains a free phosphoric acid
  • a portion of added amorphous aluminum hydroxide reacts with the free phosphoric acid to produce aluminum phosphate with the result that the desired film properties cannot be obtained.
  • the monobasic magnesium phosphate contains free phosphoric acid, the above mentioned spot-like patterns of tribasic phosphate are liable to be produced on the coating so that it is preferable to make the amount of the free phosphoric acid in the monobasic magnesium phosphate as small as possible.
  • a reagent for forming an insulating coating on the surface of electrical steel sheets comprising an aqueous solution consisting of parts by weight of monobasic magnesium phosphate and 5 to '30 parts by weight of chromic anhydride, and 0.4 to 2.1 parts by weight based on aluminum of aluminum nitrate and/or amorphous aluminum hydroxide.
  • a method of forming an insulating coating on the surface of electrical steel sheets comprising the steps of coating the surface of an electrical steel sheet with an aqueous solution consisting of 100 parts by weight of monobasic magnesium phosphate and 5 to 30 parts by weight of chromic anhydride, and 0.4 to 2.1 parts by weight based on aluminum of aluminum nitrate and/or amorphous aluminum hydroxide to form an insulating coating on the surface of the electrical steel sheets, and baking the insulating coating thus obtained in a furnace at a temperature of 300 to 600 C. for 30 to seconds.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • General Chemical & Material Sciences (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Inorganic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electromagnetism (AREA)
  • Dispersion Chemistry (AREA)
  • Power Engineering (AREA)
  • Chemical Treatment Of Metals (AREA)
  • Inorganic Insulating Materials (AREA)
  • Soft Magnetic Materials (AREA)
US816677A 1968-10-28 1969-04-16 Reagent for forming an insulating coating on the surface of electrical steel sheets Expired - Lifetime US3649372A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP43078036A JPS4812300B1 (xx) 1968-10-28 1968-10-28

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US (1) US3649372A (xx)
JP (1) JPS4812300B1 (xx)
BE (1) BE740885A (xx)
DE (1) DE1954216B2 (xx)
FR (1) FR2021764A1 (xx)
GB (1) GB1218678A (xx)
SE (1) SE348009B (xx)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3909313A (en) * 1972-09-29 1975-09-30 Nippon Steel Corp Method for forming an electric insulating film having excellent punching property and heat resistance on an electrical steel sheet
DE2545578A1 (de) * 1974-10-11 1976-04-22 Armco Steel Corp Ueberzugsloesung fuer die direkte bildung von isolierueberzuegen auf elektrostahl
WO2012045593A1 (de) 2010-10-07 2012-04-12 Thyssenkrupp Electrical Steel Gmbh Verfahren zum erzeugen einer isolationsbeschichtung auf einem kornorientierten elektro-stahlflachprodukt und mit einer solchen isolationsbeschichtung beschichtetes elektro-stahlflachprodukt
RU2463384C1 (ru) * 2011-03-16 2012-10-10 Алексей Иванович Гончаров Способ получения электроизоляционного покрытия трансформаторной стали

Families Citing this family (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS554451Y2 (xx) * 1974-07-01 1980-02-01
US4032366A (en) * 1975-05-23 1977-06-28 Allegheny Ludlum Industries, Inc. Grain-oriented silicon steel and processing therefor
US4316751A (en) * 1980-04-14 1982-02-23 Hooker Chemicals & Plastics Corp. Electrical resistance coating for steel
ES8203984A1 (es) * 1980-07-01 1982-04-01 Bnf Metals Tech Centre Un metodo de depositar un revestimiento de conversion a basede oxido de aluminio hidratado sobre un sustrato de aluminiomagnesio,estano o zinc.
IN158643B (xx) * 1982-05-12 1986-12-27 Westinghouse Electric Corp
US4544408A (en) * 1983-04-18 1985-10-01 Sermatech International Inc. Thixotropic alumina coating compositions, parts and methods
DE102010054509A1 (de) 2010-12-14 2012-06-14 Thyssenkrupp Electrical Steel Gmbh Verfahren zur Herstellung eines kornorientierten Elektrobands
WO2020013304A1 (ja) * 2018-07-11 2020-01-16 Ｎｅｘｔ Ｉｎｎｏｖａｔｉｏｎ合同会社 絶縁層形成方法、絶縁層付部材、抵抗測定方法及び接合型整流素子

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3909313A (en) * 1972-09-29 1975-09-30 Nippon Steel Corp Method for forming an electric insulating film having excellent punching property and heat resistance on an electrical steel sheet
DE2545578A1 (de) * 1974-10-11 1976-04-22 Armco Steel Corp Ueberzugsloesung fuer die direkte bildung von isolierueberzuegen auf elektrostahl
WO2012045593A1 (de) 2010-10-07 2012-04-12 Thyssenkrupp Electrical Steel Gmbh Verfahren zum erzeugen einer isolationsbeschichtung auf einem kornorientierten elektro-stahlflachprodukt und mit einer solchen isolationsbeschichtung beschichtetes elektro-stahlflachprodukt
KR20130117789A (ko) * 2010-10-07 2013-10-28 티센크루프 일렉트리컬 스틸 게엠베하 방향성 전자 강판 제품에 절연 코팅을 형성하기 위한 방법 및 절연 코팅으로 피복된 전자 강판 제품
RU2580778C2 (ru) * 2010-10-07 2016-04-10 Тиссенкрупп Илектрикел Стил Гмбх Способ изготовления плоского изделия из электротехнической стали и плоское изделие из электротехнической стали
KR101896046B1 (ko) 2010-10-07 2018-09-06 티센크루프 일렉트리컬 스틸 게엠베하 방향성 전자 강판 제품에 절연 코팅을 형성하기 위한 방법 및 절연 코팅으로 피복된 전자 강판 제품
RU2463384C1 (ru) * 2011-03-16 2012-10-10 Алексей Иванович Гончаров Способ получения электроизоляционного покрытия трансформаторной стали

Also Published As

Publication number Publication date
BE740885A (xx) 1970-04-01
FR2021764A1 (xx) 1970-07-24
DE1954216A1 (de) 1970-05-14
GB1218678A (en) 1971-01-06
DE1954216B2 (de) 1971-05-13
SE348009B (xx) 1972-08-21
JPS4812300B1 (xx) 1973-04-19

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