US3583887A - Magnesium oxide coating composition and process - Google Patents

Magnesium oxide coating composition and process Download PDF

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US3583887A
US3583887A US850910A US3583887DA US3583887A US 3583887 A US3583887 A US 3583887A US 850910 A US850910 A US 850910A US 3583887D A US3583887D A US 3583887DA US 3583887 A US3583887 A US 3583887A
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coating
magnesium oxide
steel
composition
coating composition
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John F Steger
Jay W Palmer
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Morton International LLC
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Morton International LLC
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/68—Temporary coatings or embedding materials applied before or during heat treatment
    • C21D1/70—Temporary coatings or embedding materials applied before or during heat treatment while heating or quenching
    • 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

  • Magnesium oxide is used extensively as a highly heat resistant separator medium and protective coating for metal surfaces. It is also used as an electrical insulator coating for metals, as a gatherer for removing impurities, such as sulfur and carbon, from thin metal sheets and particularly as a protective coating for silicon steel.
  • the electrical insulating coating is understood to be derived from coating magnesium oxide on steel, which then forms a film or coating containing Mg SiO which coating is an effective electrical insulator when annealed.
  • siliconcontaining steel is cold rolled into sheets, decarburized and thereafter coiled into convenient rolls.
  • Cold rolling develops in the steel the potential to form a grain oriented structure when the steel is later annealed.
  • the term annealed refers to a process whereby the steel is heated to about 1200 C. in an essentially pure hydrogen atmosphere (or vacuum) under programmed conditions with respect to time and temperature. This results in a growth in size of the steel grains and also in a specific grain orientation which provides the desired soft magnetic properties sought. During the annealing process, virtually all of the remaining excess carbon and sulfur content of the steel is lost. This type of annealing is known in the art as box annealing.
  • the steel so produced is in the form of a long, thin, coiled sheet which must be uncoiled and thereafter fabricated into the desired shape and size for its intended use.
  • process of fabrication which can include, for example, punching, stamping and bending, strains and stresses are introduced in the steel which impair its magnetic properties. Consequently, the strains and stress must be relieved.
  • stress relief annealing which comprises reheating the fabricated steel to a temperature of about 800 C. in a ,1
  • transformer cores are constructed from thin sheets of soft magnetic steel stacked together to form a laminated body in which each sheet is electrically insulated from its neighbor.
  • This construction vastly reduces the generation of eddy currents in the core imposed by an alternating electrical field.
  • the average density of soft iron in the core should be as large as possible and consequently the insulation on the plates should be as thin as possible to provide closer stacking of steel plates.
  • magnesium oxide is applied to steel from an aqueous suspension or slurry.
  • water volatilizes from an applied coating and can under ordinary conditions react with the iron on the surface of the steel forming current conducting iron oxides which impair the electrical insulating properties sought.
  • Areas on the surface of the steel displaying such deleterious iron oxide formations are referred to in the art as anneal patterns.
  • magnesium oxide does not form an intimately bonded tightly adherent coating which is not easily removed upon contact.
  • magnesium oxide per se fails to provide the desired high degree of required insulation and magnetic protection properties to overcome the noted defects. Accordingly, it would be desirable to provide magnesium oxide compositions for coating steel which compositions are tightly adherent and maintain suitable electrical insulating properties after box annealing and stress relief annealing, and which also preserve the desired magnetic properties of the steel after stress relief annealing.
  • magnesium oxide coating compositions containing a major proportion of magnesium oxide, and a minor proportion of the additives:
  • the invention also provides a process for coating steel sheet with an adherent, electrical insulating, corrosionresistant coating comprising in sequence applying to the surface of said steel an aqueous slurry containing the said magnesium oxide coating composition, heating to remove water therefrom, and thereafter annealing the coated steel at a temperature in excess of about 1000 C.
  • the magnesium oxide employed has a surface area in excess of about 20 square meters per gram or an iodine number (iodine adsorption valve) in excess of about 24 milligrams of iodine per gram of dry magnesium oxide.
  • the surface area of magnesium oxide as referred to herein is determined by the standard Brunaeur-Emmet-Teller method.
  • the iodine number is approximately 1 to 1.25 times the surface area in square meters per gram.
  • the iodine number as referred to herein is determined by the following procedure:
  • V is the volume of thiosulfate equivalent to 20 ml. of the original iodine solutionbefore adsorption of iodine by the oxide; where V is the volume of thiosulfate required by the 20 ml. aliquot after adsorption; and N is the normality of the thiosulfate solution.
  • boric acids it is meant to include all of the various known boric acids, such as for example, but not limited to, metaboric acid, orthoboric acid and pyroboric acids.
  • magnesium borates it is meant to include the various known magnesium borates, such as for example, but not limited to the magnesium orthoborates, the magnesium metaborates and the magnesium pyroborates.
  • sodium borate it is meant to include all of the various known sodium borates, such as for example, but not limited to sodium tetraborate, sodium metaborate, and sodium orthoborate.
  • Silica in virtually any form and having a particle less than about 200 mesh may be employed, such as the product available under the trade name Cabosil.
  • the alkaline earth metal silicates such as for example, calcium silicate and magnesium silicate.
  • concentrations of additives range as follows:
  • the molar ratio of magnesium oxide to silica is from about 280:1 to about 2900:1, preferably from about 1000:l to 2000:1;
  • the molar ratio of boron (expressed as B 0 to silica is from about 3:1 to about 5:1, preferably from about 3 :1 to 4:1;
  • the molar ratio of magnesium oxide to sodium is from about 2000:l to about 400011 with about 2800:l being preferred.
  • the additives (silica, boron and sodium, calculated as expressed above) in the coating composition may range up to about 2 /2 mole percent and are preferably present in amounts up to about 2 mole percent, based on the total moles of MgO and additives.
  • an aqueous suspension of the above described magnesium oxide composition is prepared by mixing with Water to the desired viscosity and leveling and flow-out characteristics. Generally from about 5 to about 20 Weight percent of the magnesium oxide composition, based on water, is satisfactory to provide an aqueous slurry having the requisite viscosity and flow properties suitable for coating onto steel sheet.
  • a frit may also be prepared by fusing magnesium oxide with a boron-containing compound, a sodium compound and a silicon-containing compound as hereinbefore described. The frit may then be comminuted to a particle size less than 200 mesh and added to Water to form the coating slurry. In preparing aqueous slurries of the coating compositions, the order of addition or admixture of the various components of the composition is immaterial.
  • the coating slurry may be applied to the magnetic sheet material by any suitable means such as by immersion, brushing, or spraying. It has been found convenient to use an immersion technique whereby the steel sheet is Passed through a tank containing the coating slurry, The coated sheet thereafter is heated to drive off water and provide a dried layer of the present composition. The coated metal sheet is then coiled into a roll and placed in a furnace for box annealing as previously described. During the annealing process, the coating of this invention forms an adherent, electrically insulating, corrosion-resistant layer which also functions as a separator medium to prevent the coiled metal sheet from sticking to itself.
  • the drawing is a schematic diagram of a conventional process for coating the compositions of the present invention on steel strip.
  • a magnesium oxide composition contained in hopper 10 and water in tank 12 are fed via 13 and 13a to mixing tank 14 to form an aqueous coating suspension or slurry.
  • the aqueous coating slurry is conducted through line 18 equipped with valve 20 to coating trough 22.
  • Newly formed, hot steel sheet 23 is passed in the direction indicated by arrows over roller 24 and under roller 26 through quench tank 28 and thence over roller 25 and through coating trough 22 where it acquires a layer of the coating slurry.
  • the steel sheet coated with an aqueous slurry of the coating composition is then passed between adjustable pinch rollers 30 which regulate the coating thickness and then to heater 32.
  • heater water is volatilized from the slurry layer on the steel strip to provide an adherent coating.
  • the coated steel sheet is passed over roller 33 and coiled into suitable lengths at take-up roll 34.
  • the coated coiled steel roll 23A is thereafter passed to annealing furnace 36, and thence to storage.
  • a steel coating composition comprising magnesium oxide, boric acid, sodium hydroxide, and silica
  • the molar ratio of magnesium oxide to silica is about 1500:l
  • the molar ratio of boric oxide to silica is about 3.521
  • the molar ratio of magnesium oxide to sodium is about 2800:1.
  • Approximately 10 to 12 Weight percent of this composition is admixed with water to form a slurry suitable for coating onto steel sheet.
  • Coiled steel sheet which was coated with this slurry and subsequently dried and thereafter box annealed according to the procedure hereinbefore described was easily unrolled. Further, the surface of the steel was relatively electrically non-conducting and resistant to attack by corrosive gases or fumes.
  • a magnesium oxide composition having the aforenoted desirable steel coating properties which comprises magnesium oxide, boric oxide, sodium tetraborate, and silica in which the molar ratio of MgO to silica is about 1500:1, the molar ratio of boric oxide to silica is about 3.5 :1, and the molar ratio of magnesium oxide to sodium is about 2800: 1.
  • EXAMPLE 1 A steel coating suspension was prepared by adding 18.0 grams of MgO (0.45 mole) to 150 ml. of an aqueous boric acid solution containing 0.00105 mole of boron expressed as B To this suspension was added 0.00016 mole of sodium hydroxide and 0.0003 mole of silica having a crystallite size of about 70 A., to yield an aqueous coating composition of about solids containing the following components in the indicated ratios:
  • Coating Composition A Molar ratio MgOzSiO 1500:1 B203 :SiO 1 MgOzNa 281221 Coating procedure
  • the resultant suspension was subjected to constant stirring and was coated onto 26 separate silicon steel sheets or plates, each sheet measuring 3.0 x 15.3 cm. by 12-14 mils in thickness.
  • the coatings were leveled and then dried in air at a temperature of about 500 C.
  • the coated, dried sheets were then stacked one upon another and annealed by heating in a hydrogen atmosphere at a temperature of 1177 C. for a period of 4.3 hours.
  • the annealed sheets were then cooled, and excess or loose magnesium oxide was scrubbed from the surface of each coated sheet by brushing in a stream of flowing water.
  • Coating Composition B Molar ratio The conductance of the coated surfaces of the sheets coated with Coating Composition A and Coating Composition B respectively was measured by means of the Franklin test.
  • Franklin test This test is widely accepted and utilized for evaluating the conductance of coated steel sheets. A detailed description is found in ASTM method A-334-52, Standard Methods of Test for Electrical and Mechanical Properties of Magnetic Materials. Briefly, the test is carried out by passing an electric current through brass contacts which cover coated areas 0.1 square inch in area. Current passing through the coating flows through the steel to a contact made directly to the steel by means of a twist drill. The resulting amperage provides a measure of the resistance encountered through the coating. Several hundred contacts are employed in obtaining readings for coating evaluation. A complete short circuit is indicated by a reading of milliamps per 0.1 square inch.
  • Coating Composition C Molar ratio MgOzSiO 1480:1 B O :SiO 4.6:1 MgOzNa 2830z1
  • the procedure of Example 1 was repeated except that the coating composition contained the following components in the indicated ratios:
  • Coating Composition D Molar ratio MgO:SiO 1480:1 B O :SiO 8.7:1 MgOzNa 2830:1
  • Coating Composition E Molar ratio MgOzSiO 1480:1 1320 18102 MgOzNa 2800:1
  • composition having the following components in the indicated ratios:
  • Coating Composition F Molar ratio MgOzSiO 1480:1 B203 I 2-3: 1 MgOzNa 2800:1
  • the coated steel plates were Observed for uniformity of coating by visual inspection. The results were as follows:
  • Coating Composition E Coating Composition F EXAMPLE 4 The procedure of Example 1 was repeated except that the ratio of MgO to sodium was varied while keeping the ratios of MgOzSiO and B O :SiO constant to provide coating compositions having the following components in the indicated ratios:
  • EXAMPLE 5 A coating composition was prepared as in Example 1, except that the molar ratio of MgOzSiO was as indicated:
  • Coating Composition 1 Molar ratio MgO:SiO 233021 B O 2SiO 3.5:]. MgO:Na 2800:1
  • Example 1 The procedure of Example 1 was followed in coating this composition onto steel plates. A control consisting of MgO with no additives was also coated onto steel plates according to the same procedure. The coated steel plates were then tested for corrosion resistance by means of the Chlorine Test for Corrosion Resistance.
  • Chlorine test for corrosion resistance In this test strips of weighed Steel having 30 cm? of surface area rest against a thermocouple well located at the center of the hot Zone of a heated Vycor tube in an automatically controlled tube furnace. Helium flows through the tube at a linear velocity of 65 cm./min, The temperature is raised to 816 C. to simulate stress relief annealing conditions and minutes are allowed for equilibrium to be established after the temperature levels off. The gas is then suddenly switched to wet chlorine moving at cm./min. After 60 seconds, the flow is switched back to a 170 cm./min. fiow of helium. The system is then cooled to 315 C., samples removed, quenched in cold running water, scrubbed, dried and reweighed. The Weight loss due to iron and silicon chloride vaporization is an inverse measure of the corrosion resistance.
  • a coating composition was prepared as in Example 1 except that sodium tetraborate was used instead of sodium hydroxide and the molar ratio of MgOzSiO was 943:1 to yield a composition having the following components in the indicated ratios:
  • EXAMPLE 7 A coating composition was prepared as in Example 1 (hereinafter coating composition K) except that sodium tetraborate was used instead of sodium hydroxide and the molar ratio of MgO:SiO was 2830:1 to yield a composition having the same ratios of components as the composition of Example 5.
  • Example 1 The procedure of Example 1 was followed in coating this composition onto steel plates except that the coated plates were annealed for a period of 8.6 hours, The coated, annealed plates were tested for corrosion resistance according to the procedure described in Example 5.
  • EXAMPLE 8 A composition (hereinafter coating composition L) was prepared by fusing together magnesium metaborate, Mg(BO and SiO to prepare a frit. The frit was then comminuted and suspended in an aqueous solution containing sodium hydroxide and boric acid in such proportions to yield a composition having the same ratios of components as coating compositions I and K.
  • Example 1 The procedure of Example 1 was followed in coating this composition onto steel plates except that the coated plates were annealed for a period of 8.6 hours. The coated, annealed plates were tested for corrosion resistance according to the procedure described in Example 5.
  • coating composition M was prepared according to the procedure of Example 1 except that the molar ratio of MgO:SiO- was 283:1 to yield a composition having the following components in the indicated ratios:
  • Coating Composition M Molar ratio MgO:SiO 283:1 1320318102 3.511 MgOzNa 280021
  • the procedure of Example 1 was followed in coating this composition onto steel plates except that the coated plates were annealed for a period of 8.6 hours.
  • the coated, annealed plates were tested for corrosion resistance according to the procedure described in Example 5.
  • coating composition N A steel coating composition (hereinafter coating composition N) was prepared by admixing magnesium oxide, boric oxide, sodium tetraborate and silica in the following molar ratios:
  • Coating Composition N Molar ratio MgOISiO 148011 B O :SiO 3.511 MgOzNa 280011 Reduction in weight loss compared to grams control ment Weight loss,
  • the molar ratio of magnesium oxide to silica is from about 280:1 to about 2900:1, the molar ratio of boron expressed as (B to silica is from about 3:1 to about :1, and the molar ratio of magnesium oxide to sodium is from about 2000:1 to about 4000:1.
  • composition according to claim 1 wherein the boron compound is boric acid, the sodium compound is 10 sodium hydroxide, and the silicon-containing compound is silica.
  • a composition according to claim 1 wherein the molar ratio of magnesium oxide to silica is from about 100011 to about 2000:1, the molar ratio of boron expressed as B O to silica is from about 3:1 to about 5:1, and the ratio of magnesium oxide to sodium is about 2000:1 to 400021.
  • a composition according to claim 1 wherein the molar ratio of magnesium oxide to silica is from about 1000:1 to about 2000:1, the molar ratio of boron expressed as B O' to silica is from about 3:1 to about 4:1, and the ratio of magnesium oxide to sodium is about 2000:1 to about 4000:1.
  • composition according to claim 4 wherein the molar ratio of magnesium to sodium is about 2000Il.
  • composition according to claim 1 wherein the molar ratio of magnesium oxide to silica is about 1500: 1, the molar ratio of boric acid expressed as B 0 to silica is about 35:1, and the molar ratio of magnesium oxide to sodium is about 2800:1.
  • a process for coating steel sheet with an electrically insulating, corrosion-resistant coating which comprises in sequence forming an. aqueous slurry of a magnesium oxide composition as defined in claim 1, coating said slurry to the surfaces of steel sheet, heating the slurry coated steel to dry said coating, and thereafter annealing said coated steel sheet.
  • a process according to claim 10 wherein the slurry has a solids content of from 5 to 20 percent by weight.
  • silica has a particle size of up to 200 mesh (US. Standards Sieve Series).

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US850910A 1969-08-18 1969-08-18 Magnesium oxide coating composition and process Expired - Lifetime US3583887A (en)

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Cited By (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3765957A (en) * 1969-12-18 1973-10-16 Kawasaki Steel Co Method of forming electric insulating coating on the surface of silicon steel sheet with serpentine
US3841925A (en) * 1973-09-12 1974-10-15 Morton Norwich Products Inc Magnesium oxide steel coating composition and process
US3850683A (en) * 1973-06-12 1974-11-26 Koppers Co Inc Iron stain inhibitors
US3879234A (en) * 1971-12-22 1975-04-22 Merck & Co Inc Lithia-containing frit additives for MgO coatings
US3926688A (en) * 1973-01-30 1975-12-16 Cockerill Method of manufacturing a flat steel product having an oxidation-resistant coating
US4096000A (en) * 1973-04-11 1978-06-20 Nippon Steel Corporation Annealing separator for silicon steel sheets
US4168189A (en) * 1977-05-20 1979-09-18 Armco Inc. Process of producing an electrically insulative film
US4173502A (en) * 1976-12-09 1979-11-06 General Electric Company Method of producing silicon-iron sheet material with boron addition, and product
US4177092A (en) * 1977-01-31 1979-12-04 National Research Development Corporation Diffusing an element into a metal
US4179315A (en) * 1976-06-17 1979-12-18 Allegheny Ludlum Industries, Inc. Silicon steel and processing therefore
US4186038A (en) * 1976-04-15 1980-01-29 General Electric Company Method of producing silicon-iron sheet material with boron addition, and product
US4190469A (en) * 1977-11-09 1980-02-26 Kawasaki Steel Corporation Method for forming forsterite insulating film on an oriented silicon steel sheet
US4287006A (en) * 1978-11-28 1981-09-01 Nippon Steel Corporation Annealing separator for grain oriented silicon steel strips
US4443425A (en) * 1981-12-09 1984-04-17 Calgon Corporation Magnesium oxide composition for coating silicon steel
US4842645A (en) * 1987-05-02 1989-06-27 Kyowa Chemical Industry Co., Ltd. Rust-proofing agent, rust-proofing coating composition and coating method for preventing or inhibiting corrosion of metallic/surface
US6455100B1 (en) 1999-04-13 2002-09-24 Elisha Technologies Co Llc Coating compositions for electronic components and other metal surfaces, and methods for making and using the compositions
US20040126483A1 (en) * 2002-09-23 2004-07-01 Heimann Robert L. Coating compositions for electronic components and other metal surfaces, and methods for making and using the compositions
US20050081367A1 (en) * 2003-10-21 2005-04-21 Lauinger Geoffrey A. Method of manufacturing a media reference surface for use in a flexible data storage card
US20060210832A1 (en) * 2005-03-17 2006-09-21 Sumida Corporation Composite-type magnetic core and method of manufacturing the same

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE7407600L (enrdf_load_stackoverflow) * 1973-06-26 1974-12-27 Merck & Co Inc
ZA773084B (en) * 1976-06-17 1978-04-26 Allegheny Ludlum Ind Inc Silicon steel and processing therefor
US4102713A (en) * 1976-06-17 1978-07-25 Allegheny Ludlum Industries, Inc. Silicon steel and processing therefore
GB1597656A (en) * 1977-05-20 1981-09-09 Armco Inc Process of producing an electrically insulative glass film on silicon steel

Cited By (22)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3765957A (en) * 1969-12-18 1973-10-16 Kawasaki Steel Co Method of forming electric insulating coating on the surface of silicon steel sheet with serpentine
US3879234A (en) * 1971-12-22 1975-04-22 Merck & Co Inc Lithia-containing frit additives for MgO coatings
US3926688A (en) * 1973-01-30 1975-12-16 Cockerill Method of manufacturing a flat steel product having an oxidation-resistant coating
US4096000A (en) * 1973-04-11 1978-06-20 Nippon Steel Corporation Annealing separator for silicon steel sheets
US3850683A (en) * 1973-06-12 1974-11-26 Koppers Co Inc Iron stain inhibitors
US3841925A (en) * 1973-09-12 1974-10-15 Morton Norwich Products Inc Magnesium oxide steel coating composition and process
US4186038A (en) * 1976-04-15 1980-01-29 General Electric Company Method of producing silicon-iron sheet material with boron addition, and product
US4179315A (en) * 1976-06-17 1979-12-18 Allegheny Ludlum Industries, Inc. Silicon steel and processing therefore
US4173502A (en) * 1976-12-09 1979-11-06 General Electric Company Method of producing silicon-iron sheet material with boron addition, and product
US4177092A (en) * 1977-01-31 1979-12-04 National Research Development Corporation Diffusing an element into a metal
US4168189A (en) * 1977-05-20 1979-09-18 Armco Inc. Process of producing an electrically insulative film
US4190469A (en) * 1977-11-09 1980-02-26 Kawasaki Steel Corporation Method for forming forsterite insulating film on an oriented silicon steel sheet
US4287006A (en) * 1978-11-28 1981-09-01 Nippon Steel Corporation Annealing separator for grain oriented silicon steel strips
US4443425A (en) * 1981-12-09 1984-04-17 Calgon Corporation Magnesium oxide composition for coating silicon steel
US4842645A (en) * 1987-05-02 1989-06-27 Kyowa Chemical Industry Co., Ltd. Rust-proofing agent, rust-proofing coating composition and coating method for preventing or inhibiting corrosion of metallic/surface
US6455100B1 (en) 1999-04-13 2002-09-24 Elisha Technologies Co Llc Coating compositions for electronic components and other metal surfaces, and methods for making and using the compositions
US20040126483A1 (en) * 2002-09-23 2004-07-01 Heimann Robert L. Coating compositions for electronic components and other metal surfaces, and methods for making and using the compositions
US20050081367A1 (en) * 2003-10-21 2005-04-21 Lauinger Geoffrey A. Method of manufacturing a media reference surface for use in a flexible data storage card
US20060210832A1 (en) * 2005-03-17 2006-09-21 Sumida Corporation Composite-type magnetic core and method of manufacturing the same
EP1703527A3 (en) * 2005-03-17 2006-12-13 Sumida Corporation Composite-type magnetic core and method of manufacturing same
KR100727478B1 (ko) 2005-03-17 2007-06-13 스미다 코포레이션 복합형 자심 및 그 제조 방법
US7553562B2 (en) 2005-03-17 2009-06-30 Sumida Corporation Composite-type magnetic core and method of manufacturing the same

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DE2041051A1 (de) 1971-04-22

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