US3150015A - Insulation for silicon steel - Google Patents
Insulation for silicon steel Download PDFInfo
- Publication number
- US3150015A US3150015A US134564A US13456461A US3150015A US 3150015 A US3150015 A US 3150015A US 134564 A US134564 A US 134564A US 13456461 A US13456461 A US 13456461A US 3150015 A US3150015 A US 3150015A
- Authority
- US
- United States
- Prior art keywords
- coating
- weight
- steel
- silica
- slurry
- Prior art date
- 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
Links
- 229910000976 Electrical steel Inorganic materials 0.000 title claims description 24
- 238000009413 insulation Methods 0.000 title description 14
- 238000000576 coating method Methods 0.000 claims description 91
- 239000011248 coating agent Substances 0.000 claims description 70
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 62
- 239000002002 slurry Substances 0.000 claims description 42
- 229910000831 Steel Inorganic materials 0.000 claims description 26
- 239000010959 steel Substances 0.000 claims description 26
- 239000000377 silicon dioxide Substances 0.000 claims description 22
- 238000000034 method Methods 0.000 claims description 10
- 101100459267 Crotalus durissus terrificus CRO3 gene Proteins 0.000 claims 1
- 238000000060 site-specific infrared dichroism spectroscopy Methods 0.000 claims 1
- 239000008119 colloidal silica Substances 0.000 description 19
- 238000012360 testing method Methods 0.000 description 16
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 14
- 239000002245 particle Substances 0.000 description 11
- KRVSOGSZCMJSLX-UHFFFAOYSA-L chromic acid Substances O[Cr](O)(=O)=O KRVSOGSZCMJSLX-UHFFFAOYSA-L 0.000 description 6
- 238000001035 drying Methods 0.000 description 6
- 239000000463 material Substances 0.000 description 6
- AWJWCTOOIBYHON-UHFFFAOYSA-N furo[3,4-b]pyrazine-5,7-dione Chemical compound C1=CN=C2C(=O)OC(=O)C2=N1 AWJWCTOOIBYHON-UHFFFAOYSA-N 0.000 description 5
- 238000004519 manufacturing process Methods 0.000 description 5
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 4
- 239000007864 aqueous solution Substances 0.000 description 4
- 238000002845 discoloration Methods 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 239000007789 gas Substances 0.000 description 4
- 238000000926 separation method Methods 0.000 description 4
- RMAQACBXLXPBSY-UHFFFAOYSA-N silicic acid Chemical compound O[Si](O)(O)O RMAQACBXLXPBSY-UHFFFAOYSA-N 0.000 description 4
- 229910052710 silicon Inorganic materials 0.000 description 4
- 239000010703 silicon Substances 0.000 description 4
- 235000012239 silicon dioxide Nutrition 0.000 description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 3
- BPQQTUXANYXVAA-UHFFFAOYSA-N Orthosilicate Chemical compound [O-][Si]([O-])([O-])[O-] BPQQTUXANYXVAA-UHFFFAOYSA-N 0.000 description 3
- 238000000137 annealing Methods 0.000 description 3
- 229910052799 carbon Inorganic materials 0.000 description 3
- 229910052804 chromium Inorganic materials 0.000 description 3
- 239000011651 chromium Substances 0.000 description 3
- 238000010292 electrical insulation Methods 0.000 description 3
- 238000003475 lamination Methods 0.000 description 3
- 238000012643 polycondensation polymerization Methods 0.000 description 3
- 229920000642 polymer Polymers 0.000 description 3
- 239000000243 solution Substances 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- 229940117975 chromium trioxide Drugs 0.000 description 2
- WGLPBDUCMAPZCE-UHFFFAOYSA-N chromium trioxide Inorganic materials O=[Cr](=O)=O WGLPBDUCMAPZCE-UHFFFAOYSA-N 0.000 description 2
- GAMDZJFZMJECOS-UHFFFAOYSA-N chromium(6+);oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[Cr+6] GAMDZJFZMJECOS-UHFFFAOYSA-N 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 238000012937 correction Methods 0.000 description 2
- 239000010408 film Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 230000001590 oxidative effect Effects 0.000 description 2
- NTHWMYGWWRZVTN-UHFFFAOYSA-N sodium silicate Chemical compound [Na+].[Na+].[O-][Si]([O-])=O NTHWMYGWWRZVTN-UHFFFAOYSA-N 0.000 description 2
- 229910019142 PO4 Inorganic materials 0.000 description 1
- 229910000676 Si alloy Inorganic materials 0.000 description 1
- 239000004115 Sodium Silicate Substances 0.000 description 1
- DBMJMQXJHONAFJ-UHFFFAOYSA-M Sodium laurylsulphate Chemical class [Na+].CCCCCCCCCCCCOS([O-])(=O)=O DBMJMQXJHONAFJ-UHFFFAOYSA-M 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 229910052910 alkali metal silicate Inorganic materials 0.000 description 1
- 239000012736 aqueous medium Substances 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 239000008187 granular material Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 229910052500 inorganic mineral Inorganic materials 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- XWHPIFXRKKHEKR-UHFFFAOYSA-N iron silicon Chemical compound [Si].[Fe] XWHPIFXRKKHEKR-UHFFFAOYSA-N 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000002609 medium Substances 0.000 description 1
- 238000003801 milling Methods 0.000 description 1
- 239000011707 mineral Substances 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 239000012299 nitrogen atmosphere Substances 0.000 description 1
- 230000035699 permeability Effects 0.000 description 1
- 235000020030 perry Nutrition 0.000 description 1
- 239000010452 phosphate Substances 0.000 description 1
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 1
- 238000006116 polymerization reaction Methods 0.000 description 1
- 235000019353 potassium silicate Nutrition 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 150000004760 silicates Chemical class 0.000 description 1
- 125000005624 silicic acid group Chemical class 0.000 description 1
- 229910052911 sodium silicate Inorganic materials 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 239000000725 suspension Substances 0.000 description 1
- 238000012956 testing procedure Methods 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
- 239000000080 wetting agent Substances 0.000 description 1
Classifications
-
- 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
-
- 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
-
- 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
- C23C24/00—Coating starting from inorganic powder
Definitions
- This invention relates to improvements in coatings for steel and relates in particular to improvements in insulating coatings for electrical grades of silicon steel strip or sheet.
- coatings as applied to electrical grades of iron-silicon alloy strip or sheet that is to be subsequently fabricated into laminated structures for use in magnetic cores for power and distribution transformers, etc., to reduce interlaminar current loss by insulating the laminations, is a standard practice in the manufacturing of such electrical steels.
- Such coatings may be either organic or inorganic, but the particular coating herein presented belongs to the latter group.
- Inorganic coatings are generally characterized by a high degre of electrical insulation and the ability to withstand stress relief annealing temperatures and atmospheres without loss of insulation quality.
- Inorganic insulating coatings may be applied to bare metal surfaces or to silicon steel strip or sheet which has been previously coated and heat treated.
- the strip material may have been coated with MgO or CaO powders which act as a separator of adjacent coil surfaces during box annealing of the strip in coiled form or all previous heat treatments may have been conducted in a continuous manner, in which event no previous coatings would have been applied.
- such previous coatings may have been stripped from the steel to avoid excessive Wear on punch and die sets used to fabricate laminations from such material.
- insulation coatings such as are presently contemplated are compatible with either the previously coated or the uncoated surfaces.
- the qualities considered desirable for such coatings include the ability to insulate or retard electrical currents before and after stress relieving anneals, the effect such coatings have on the magnetic characteristics of the steel, the adhesion qualities of the coating, and the stability of the coating to environmental conditions.
- inorganic coatings include chromium trioXide-silica (or silicate) coatings such as are revealed in United States Patent No. 1,946,146 to Kiefer et al. and 2,472,596 to Kiefer and the phosphate coatings such as are revealed in United States Patents Nos. 2,492,682 to Gilford and 2,753,282 to Perry.
- the present invention is directed to the discovery that a greatly improved chromium trioxide-silica coating may be obtained by employing particularly finegrained silica in colloidal form in place of the conventionally available granular product.
- the object of the present invention to provide an inorganic coating for electrical grades of silicon steel strip or sheet that will provide improved electrical insulating properties.
- a still further object of the persent invention is to im prove the electrical insulation between stacked laminations to reduce interlaminar electrical losses.
- the present invention is directed to the substitution of extremely fine-grained silica in colloidal form for the granulated material conventionally employed in the application of chromic acid-silica-coatings to the surface of electrical grades of silicon steel strip or sheet.
- the present invention is particularly directed to the application of a chromic acid-silica coating of from .05 to .12 mil thickness to electrical grades of silicon steel strip or sheet by passing such steel through an aqueous solution which contains from about 6 to 23%, by weight, colloidal silica, and from about 8 to 15%, by Weight, chromic acid (CrO and baking or curing the coating.
- colloidal silica may be regarded as the condensation polymerization product of silicic acid in particulate form having a particle size no greater than about 500 millimicrons.
- the conventional slurries employed for the purpose of providing CrO SiO insulating coatings are generally composed of chromic acid (CrO dissolved in Water plus milled particles of a silica or silicate, ranging in size from about .5 micron diameter to about 7 microns, or silicates may be present in solution by employing soluble alkali silicates such as water glass.
- the silica employed with the slurries used in conjunction with the present invention are only a fraction of the size of the conventional milled particles.
- the colloidal particles may be as large as 500 millimicrons diameter, but if larger particles are employed, it may not be possible to maintain them in a colloidal state, and consequently, one does not enjoy the advantages of the present process by such a practice.
- Colloidal silica is available commercially. under the trademark Ludox (E. I. du Pont de Nemours & Co., Inc., Wilmington, Delaware), which is an aqeuous colloidal silica.
- the size of the particulate silica maybe as small as 7 millimicrons diameter, but may also be obtained in 17 and millimicron sizes.
- Colloidal silica may contain particles as small as 1 millimicron diameter.
- Colloidal silica and Ludox are described in United States Patent No. 2,809,137 to John Cornelius Robinson et al.
- Aqueous solutions of colloidal silica and chromic acid may be made up by adding the colloidal silica in aqueous media to a prepared aqueous solution of chromic acid.
- the temperature at which such baking takes place is preferably about 1500 F. but may be as low as 1200 F. and as high as 1700 F.
- the ammeter may be adjusted so that a reading of .00 represents substantially no flow of current While a reading of 1.00 ampere represents no insulation. The readings then represent the fraction of one ampere of current permitted by the current.
- Such tests are called Franklin tests and are so referred to in the test results given in Tables I, II and III below. Since each test was conducted in an identical manner using the above procedure, the comparative results are significant. Such a test effectively measures the insulation quality of the coating whether it is applied to one or both sides of a flat rolled steel product so long as the testing from sample to sample is consistent. In the present testing, all samples were coated on both sides.
- an aqueous slurry was prepared by mixing chromic acid, Ludox (trademark for a commercially available silica in the form of a colloidal suspension in water, property of the E. I. du Pont de Nemours Co.,.Inc.), an aqueous dispersion of 30%, by weight, colloidal SiO and water in such amounts as to effect 10%, by'weight, CrO and 13%, by weight, SiO
- Water insolubility was determined by immersing samples in clear water for 48 hour periods (room temperature) and observing any discoloration of the water. If no discoloration was observable insolubility was considered excellent; a very slight discoloration was considered good, and a slight discoloration was considered lair.
- Table I The data of Table I is significant in that under the testing procedure employed, a .4 Franklin as coated (not stress relief annealed), is commercially acceptable. In addition, as indicated in Table I, the coatings were found to have good to excellent insolubility (in water) and exhibited excellent adhesion.
- Samples (3" x 8") were sheared from .018" gauge x 3" wide strip of a standard (non-oriented) (.02 C and 3.5% silicon) grade of silicon steel, part of which had been coated with an aqueous slurry made up as above, except in such proportions to effect 3.25%, by weight, CrO 13%, by weight, SiO and the balance water, and part with a slurry of 4.00%, by weight, CrO 8%, by weight, Si0 and the balance water by passing the strip continuously through the respective slurries and applying the coating by means of metering rubber rolls.
- the coating was dried as it left the coating tank and the strip was passed continuously through a furnace so as to bring it to a temperature of about 1200 F.
- the method of providing an inorganic insulating coating to fiat rolled electrical grades of silicon steel which comprises contacting the surface of said steel with an aqueous slurry that contains from about 6% to 23%, by weight, of silica having a particle size not greater than about 500 millimicrons diameter and 3% to 15%, by weight, CrO so as to leave a thin coating of said slurry on said surface, and baking said coating at a temperature of from about 1200 F. to 1700 F.
- An article of manufacture consisting of a flat rolled electrical grade of silicon steel having an insulating coating on the surface thereof that is from .05 to .12 mil in thickness and which is composed of from about 29% to 88% silica and 12 to 71% CrO said coating having been applied to said steel by contacting said steel with an aqueous slurry of said components, said silica having been present in a colloidal state, so as to leave a thin coating of said slurry on the surface of said steel and said coating having been baked at a temperature of from about 1200 F. to 1700 F.
- the method of providing an inorganic insulating coating to flat rolled electrical grades of silicon steel which comprises contacting the surface of said steel with an aqueous slurry that contains from about 6 to 23%, by weight, of silica having a particle size not greater than about 500 millimicrons diameter and 3 to 15 by weight, CrO so as to leave a thin coating of said slurry on said surface, drying said coating and baking said coatlng at a temperature of from about 1200 F. to 1700 F.
- An article of manufacture consisting of a fiat rolled electrical grade of silicon steel that has been coated by contacting the surface of said steel with an aqueous slurry which contains from 6 to 23%, by Weight, of colloidal silica, 3 to 15%, by Weight, CrO so as to leave a thin coating of said slurry on said surface, and said coating having been dried and baked at a temperature of from about 1200 F; to 1700 F.
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Chemical Treatment Of Metals (AREA)
Description
United States Patent 3,150,015 INSULATION FOR SILICON STEEL Charles D. Boyer, Natrona Heights, and Clarence L. Miller, Jr., Pittsburgh, Pa, assignors to Allegheny Ludlum Steel Corporation, Brackenritlge, Pa., :1 corporation of Pennsylvania No Drawing. Filed Aug. 29, 1961, Ser. No. 134,564 12 Claims. (Cl. 148-6.2)
This invention relates to improvements in coatings for steel and relates in particular to improvements in insulating coatings for electrical grades of silicon steel strip or sheet.
The use of coatings as applied to electrical grades of iron-silicon alloy strip or sheet that is to be subsequently fabricated into laminated structures for use in magnetic cores for power and distribution transformers, etc., to reduce interlaminar current loss by insulating the laminations, is a standard practice in the manufacturing of such electrical steels. Such coatings may be either organic or inorganic, but the particular coating herein presented belongs to the latter group. Inorganic coatings are generally characterized by a high degre of electrical insulation and the ability to withstand stress relief annealing temperatures and atmospheres without loss of insulation quality.
Inorganic insulating coatings may be applied to bare metal surfaces or to silicon steel strip or sheet which has been previously coated and heat treated. For example, the strip material may have been coated with MgO or CaO powders which act as a separator of adjacent coil surfaces during box annealing of the strip in coiled form or all previous heat treatments may have been conducted in a continuous manner, in which event no previous coatings would have been applied. Also, such previous coatings may have been stripped from the steel to avoid excessive Wear on punch and die sets used to fabricate laminations from such material. In any event, insulation coatings such as are presently contemplated are compatible with either the previously coated or the uncoated surfaces.
The qualities considered desirable for such coatings include the ability to insulate or retard electrical currents before and after stress relieving anneals, the effect such coatings have on the magnetic characteristics of the steel, the adhesion qualities of the coating, and the stability of the coating to environmental conditions.
Commercially available inorganic coatings include chromium trioXide-silica (or silicate) coatings such as are revealed in United States Patent No. 1,946,146 to Kiefer et al. and 2,472,596 to Kiefer and the phosphate coatings such as are revealed in United States Patents Nos. 2,492,682 to Gilford and 2,753,282 to Perry. The present invention is directed to the discovery that a greatly improved chromium trioxide-silica coating may be obtained by employing particularly finegrained silica in colloidal form in place of the conventionally available granular product.
It is, therefore, the object of the present invention to provide an inorganic coating for electrical grades of silicon steel strip or sheet that will provide improved electrical insulating properties.
It is a further object of the persent invention to provide an improved chromium trioXide-silica coating for ice electrical grades of silicon steel strip or sheet that will provide improved electrical insulating properties.
A still further object of the persent invention is to im prove the electrical insulation between stacked laminations to reduce interlaminar electrical losses.
Other objects and advantageous features of the present invention will be obvious from the following description and claims.
In general, the present invention is directed to the substitution of extremely fine-grained silica in colloidal form for the granulated material conventionally employed in the application of chromic acid-silica-coatings to the surface of electrical grades of silicon steel strip or sheet. The present invention is particularly directed to the application of a chromic acid-silica coating of from .05 to .12 mil thickness to electrical grades of silicon steel strip or sheet by passing such steel through an aqueous solution which contains from about 6 to 23%, by weight, colloidal silica, and from about 8 to 15%, by Weight, chromic acid (CrO and baking or curing the coating. For the purpose of the present invention, colloidal silica may be regarded as the condensation polymerization product of silicic acid in particulate form having a particle size no greater than about 500 millimicrons.
The conventional slurries employed for the purpose of providing CrO SiO insulating coatings are generally composed of chromic acid (CrO dissolved in Water plus milled particles of a silica or silicate, ranging in size from about .5 micron diameter to about 7 microns, or silicates may be present in solution by employing soluble alkali silicates such as water glass. The silica employed with the slurries used in conjunction with the present invention, are only a fraction of the size of the conventional milled particles. The colloidal particles may be as large as 500 millimicrons diameter, but if larger particles are employed, it may not be possible to maintain them in a colloidal state, and consequently, one does not enjoy the advantages of the present process by such a practice. Colloidal particles may be as small as l millimicron diameter. Colloidal silica is not obtained by milling conventional sources of SiO but is obtained by the controlled con densation polymerization of silicic acids. Colloidal silica therefore, as presently referred to, is not a milled mineral such as is employed in the conventional silica slurries, but is a polymer of silicic acid (presumably a polymer of monosilicic acid).
The condensation polymerization of silicic acid tends to form amorphous spherical polymers which are in a colloidal state in the liquid medium in which they are created. So long as the polymerization is discontinued before the particles grow to exceed 500 millimicrons in diameter they will continue to exist in the colloidal state.
Colloidal silica is available commercially. under the trademark Ludox (E. I. du Pont de Nemours & Co., Inc., Wilmington, Delaware), which is an aqeuous colloidal silica. The size of the particulate silica maybe as small as 7 millimicrons diameter, but may also be obtained in 17 and millimicron sizes. Colloidal silica may contain particles as small as 1 millimicron diameter. Colloidal silica and Ludox are described in United States Patent No. 2,809,137 to John Cornelius Robinson et al.
Aqueous solutions of colloidal silica and chromic acid may be made up by adding the colloidal silica in aqueous media to a prepared aqueous solution of chromic acid.
Slurries that contain less than about 3%, by weight, CrO or 6%, by weight, colloidal silica, will not effect continuous coatings with satisfactory insulating properties, particularly in the stress relieved or annealed condition.
High concentrations or thick slurries, i.e. those that contain more than about 23%, by weight, silica or 15%, by weight, C10 are difficult to apply to a sheet or strip surface and leave voids or uncoated areas which adversely affect the insulating properties of the coat.
Silicon steel (preferable in strip form) is passed through the solution or slurry preferably at room temperature, and the slurry is preferably metered onto the steel surface by rubber rolls so that a thin film of the silica-chromic acid is deposited on the strip surface, so that when the film is dried it has a film thickness of between .05 to .12
mil.
It is also preferable to conduct the coated steel when in strip form after drying continuously through a furnace to bake the coating. The temperature at which such baking takes place is preferably about 1500 F. but may be as low as 1200 F. and as high as 1700 F.
The dried and baked coating as applied will, of course, be composed of chromium trioxide and silica in approximately the same ratio as these chemicals are present in the slurry or solution. Consequently, the applied coating will be composed of from about 29 to 88%, by weight, silica and 12 to 71% by weight, chromium trioxide.
It is both desirable and preferable to dry the coating soon after its application to obtain a more uniform and evenly coated strip product. However, such drying would not be essential, since the coating would naturally dry during the baking or curing of the coated surface. Drying is conveniently accomplished by directing a stream of warm air onto the surface of the coated metal as it emerges from the coating tank.
In evaluating coatings such as are applied by the method of the present invention for their electrical insulating properties, it is conventional practice to contact both sides of the coated strip with one or more opposing electrodes between which an electric current is passed (see the instrument of U. S. Patent No. 2,982,912 to Mitchell, designed for this purpose). A measurement of the current with and without the intervening coating reflects the amount of resistivity oifered by the coated sample. The pressure applied by the electrodes is of importance, and in the test examples given below, was 900 pounds per square inch of electrode contacting area. The electric current flow between the electrodes is measured by an ammeter. At .5 volt potential, the ammeter may be adjusted so that a reading of .00 represents substantially no flow of current While a reading of 1.00 ampere represents no insulation. The readings then represent the fraction of one ampere of current permitted by the current. Such tests are called Franklin tests and are so referred to in the test results given in Tables I, II and III below. Since each test was conducted in an identical manner using the above procedure, the comparative results are significant. Such a test effectively measures the insulation quality of the coating whether it is applied to one or both sides of a flat rolled steel product so long as the testing from sample to sample is consistent. In the present testing, all samples were coated on both sides.
To conduct the tests, an aqueous slurry was prepared by mixing chromic acid, Ludox (trademark for a commercially available silica in the form of a colloidal suspension in water, property of the E. I. du Pont de Nemours Co.,.Inc.), an aqueous dispersion of 30%, by weight, colloidal SiO and water in such amounts as to effect 10%, by'weight, CrO and 13%, by weight, SiO
Samples (.014" gauge x 3 x 8") of an uncoated standard grade silicon steel strip (.02% carbon and 3.50% silicon) and of grain oriented silicon steel strip (.002 carbon and 3.50% silicon) which exhibited an extremely thin glass-like coating (less than .05 mil) which resulted Table 1 Franklin insulation tests (900 lbs./in.
As annealed As at 1,4.75 F. Type strip coated, in cracked Insolubility Adhesion amp. gas, amp.
.002 C, 3.25 Si (ori- 30 .22 Very good.... Excellent.
cnted). .02 3.25 Si (stand- .18 .31 Excellent-... Do.
Water insolubility was determined by immersing samples in clear water for 48 hour periods (room temperature) and observing any discoloration of the water. If no discoloration was observable insolubility was considered excellent; a very slight discoloration was considered good, and a slight discoloration was considered lair.
Z Adhesion was determined by bending samples over a radius of their gauge and observing any separation of the coating from the sample. If there was no observable separation at the bend, adhesion was considered to be excellent; very slight separation was considered good, and a small amount of visible separation was considered fair.
The data of Table I is significant in that under the testing procedure employed, a .4 Franklin as coated (not stress relief annealed), is commercially acceptable. In addition, as indicated in Table I, the coatings were found to have good to excellent insolubility (in water) and exhibited excellent adhesion.
Samples (3" x 8") were sheared from .018" gauge x 3" wide strip of a standard (non-oriented) (.02 C and 3.5% silicon) grade of silicon steel, part of which had been coated with an aqueous slurry made up as above, except in such proportions to effect 3.25%, by weight, CrO 13%, by weight, SiO and the balance water, and part with a slurry of 4.00%, by weight, CrO 8%, by weight, Si0 and the balance water by passing the strip continuously through the respective slurries and applying the coating by means of metering rubber rolls. The coating was dried as it left the coating tank and the strip was passed continuously through a furnace so as to bring it to a temperature of about 1200 F. for a time of about 30 seconds. Stress relieving anneals were conducted while employing various non-oxidizing atmospheres as well as still air, since the atmospheres conventionally employed vary and such atmospheres do affect the insulating qualities of inorganic coatings. Test results of the insulating properties are shown in Table II below:
Table II [Franklin insulation tests (900 lbs./in.
Coating, percent As ann., As ann., As ann., As ann., AS l,550 F. l,550 F. 1,550 F. 1,550 F. coated in cracked in forrnin nitroin still (H0, 810; gas ing gas gen air Coating, percent Insolubllity Adhesion 3. 25 13 Good Good. 4. 00 8 Excellent Fair.
As shown by Table II, the lower concentration slurries still provide good insulation properties particularly in the as coated and still air heat treated conditions, but do not exhibit the insolubility and adhesion properties of the heavier slurries.
The test results reported in Table III below were obtained from samples (about 3" x 7 sheared from .014" gauge x 12" wide coated strip (MgO separator coating applied prior to box annealing) of an electrical grade of silicon steel (about .002% carbon, 3.50% silicon and the balance essentially iron) which was coated with the aforementioned slurry (13%, by weight, colloidal silica, by weight, CrO and the balance water), by passing the strip continuously through the slurry and applying the coating by means of metering rubber rolls. The slurry contained a small amount (about 1%, by weight) of a wetting agent (Wetanol, an aqueous solution containing about 2%, by weight, modified sodium lauryl sulfate, trademark of Glyco Products Company, New York, N.Y.) The coating was dried as it left the coating tank and the strip was passed continuously through a furnace so as to bring it to a temperature of about 1500 F. for a time of about one minute. Comparative samples from similar strip (MgO coated) which was coated in an identical manner but while employing a conventional slurry of 1.8%, by weight, CrO 5.3%, by weight, Na O, 16.6%, by weight SiO (as sodium silicate), and balance water. The latter tests were conducted for the purpose of comparison. Stress relieving anneals were conducted While employing various non-oxidizing atmospheres as well as still air, since the atmospheres conventionally employed vary and such atmospheres do affect the insulating qualities of inorganic coatings.
Table III [Franklin insulation tests (900 lbs./in.
As ann.,
1,475" F. in forming amp.
As ann., ,475 F. m nitrogen, amp. a
1,475 1 in cracked gas, amp.
As coated, amp.
Coating Magneto- Electrical properties striction Coating WPP at KB 10H .ilLat fi igi rii f iiyi 1322; iiiii ii s sbdium silicate) Slog, 76.3% iiirn-A Franklin value of 0 amp. represents perfect insulation; 8. value of 1.0 amp. represents a dead short. or no insulation.
Test results shown by Table III show the coating of the present invention to provide superior insulation to the conventional coating. The improvements are particularly observable from the as coated material but also may be seen in the material stress-relief annealed in the presence of a nitrogen atmosphere and still air. Table III also shows the electrical properties of the resulting coated material. It may be observed that the watt loss (WPP) of the samples coated in accordance with the present invention is less at 15 KB and the permeability is higher at 10 H than the samples coated with the commercial coating. Also, there is shown to be less change in dimensions when magnetized in the material coated in accordance with the present invention. Hence, the present coating not only provides superior electrical insulation, but also provides excellent adhesion, is insoluble in water and does not interfere with the electrical properties of the steel to which it is applied.
We claim:
1. The method of providing an inorganic insulating coating to flat rolled electrical grades of silicon steel which comprises contacting the surface of said steel with an aqueous slurry that contains from about 6% to 23%,
6 by weight, of colloidal silica and 3% to 15 by weight, CrO so as to leave a thin coating of said slurry on said surface and baking said coating.
2. The method of providing an inorganic insulating coating to fiat rolled electrical grades of silicon steel which comprises contacting the surface of said steel with an aqueous slurry that contains from about 6% to 23%, by weight, of silica having a particle size not greater than about 500 millimicrons diameter and 3% to 15%, by weight, CrO so as to leave a thin coating of said slurry on said surface, and baking said coating at a temperature of from about 1200 F. to 1700 F.
3. The method of providing an inorganic insulating coating to flat rolled electrical grades of silicon steel which comprises contacting the surface of said steel with an aqueous slurry that contains from about 6% to 23%, by weight, colloidal silica and 3% to 15%, by weight, CrO so as to leave a dry weight coating of said slurry on said surface of from .05 to .12 mil thick and baking said coating at a temperature of from about 1200 F. to 1700 F.
4. A composition for the coating of electrical grades of flat rolled steel comprising an aqueous slurry consisting of from 6 to 23%, by weight, of colloidal silica, 3 to 15%, by weight of CrO and the balance Water.
5. A composition for the coating of electrical grades of flat rolled steel comprising an aqueous slurry consisting of from 6 to 23%, by weight, of silica having a particle size not greater than about 500 millimicrons diameter, 8 to 15%, by weight CrO and the balance water.
6. An article of manufacture consisting of a flat rolled electrical grade of silicon steel that has been coated by contacting the surface of said steel with an aqueous slurry which contains from 6 to 23%, by weight, of colloidal silica, 3 to 15 by weight, CrO so as to leave a thin coating of said slurry on said surface, and said coating having been baked at a temperature of from about 1200 F. to 1700 F.
7. An article of manufacture consisting of a flat rolled electrical grade of silicon steel having an insulating coating on the surface thereof that is from .05 to .12 mil in thickness and which is composed of from about 29% to 88% silica and 12 to 71% CrO said coating having been applied to said steel by contacting said steel with an aqueous slurry of said components, said silica having been present in a colloidal state, so as to leave a thin coating of said slurry on the surface of said steel and said coating having been baked at a temperature of from about 1200 F. to 1700 F.
8. The method of providing an inorganic insulating coating to flat rolled electrical grades of silicon steel which comprises contacting the surface of said steel with an aqueous slurry that contains from about 6 to 23%, by weight, of colloidal silica and 3 to 15%, by weight, CrO so as to leave a thin coating of said slurry on said surface, drying and baking said coating.
9. The method of providing an inorganic insulating coating to flat rolled electrical grades of silicon steel which comprises contacting the surface of said steel with an aqueous slurry that contains from about 6 to 23%, by weight, of silica having a particle size not greater than about 500 millimicrons diameter and 3 to 15 by weight, CrO so as to leave a thin coating of said slurry on said surface, drying said coating and baking said coatlng at a temperature of from about 1200 F. to 1700 F.
10. The method of providing an inorganic insulating coating to flat rolled electrical grades of silicon steel which comprises contacting the surface of said steel with an aqueous slurry that contains from about 6 to 23%, by weight, colloidal silica and 3 to 15%, by weight, CrO so as to leave a dry weight coating of said slurry on said surface of from .05 to .12 mil thick, drying said coating and baking said coating at a temperature of from about 1200 F. to 1700 F.
11. An article of manufacture consisting of a fiat rolled electrical grade of silicon steel that has been coated by contacting the surface of said steel with an aqueous slurry which contains from 6 to 23%, by Weight, of colloidal silica, 3 to 15%, by Weight, CrO so as to leave a thin coating of said slurry on said surface, and said coating having been dried and baked at a temperature of from about 1200 F; to 1700 F.
12. An article of manufacture consisting of a flat rolled electrical grade of silicon steel having an insulating coating on the surface thereof that is from .05 to .12 mil in thickness and which is composed of from about 29 to 88% silica and 12 to 71% CrO said coating having been applied to said steel by contacting said steel with an aqueous slurry of said components, said silica having been present in a colloidal state, so as to leave a thin coating of said slurry on the surface of said steel and said coating having been dried and baked at a temperature of from about 1200 F. to 1700 F.
References Cited in the file of this patent UNITED STATES PATENTS 2,030,601 McDonald Feb. 11, 1936 2,909,454 Neish Oct. 20, 1959 3,013,897 Cupery et al. Dec. 19, 1961 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No Q 3., 150 ,015 September 22, 1964 Charles D, Boyer e1; alo It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.
Column 3, line 54,, for "current", second occurrence, read coating insulation Signed and sealed this 24th day of November 1964,
(SEAL) Attest:
ERNEST W. SWIDER EDWARD J BRENNER Attesting Officer Commissioner of Patents
Claims (1)
1. THE METHOD OF PROVIDING AN INORGANIC INSULATING COATING TO FLAT ROLLED ELECTRICAL GRADES OF SILICON STEEL WHICH COMPRISES CONTACTING THE SURFACE OF SAID STEEL WITH AN AQUEOUS SLURRY THAT CONTAINS FROM ABOUT 6% TO 23%, BY WEIGHT, OF COLLODIAL SILICA AND 3% TO 15%, BY WEIGHT, CRO3 SO AS TO LEAVE A THIN COATING OF SAID SLURRY ON SAID SURFACE AND BAKING SSID COATING.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US134564A US3150015A (en) | 1961-08-29 | 1961-08-29 | Insulation for silicon steel |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US134564A US3150015A (en) | 1961-08-29 | 1961-08-29 | Insulation for silicon steel |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| US3150015A true US3150015A (en) | 1964-09-22 |
Family
ID=22463927
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| US134564A Expired - Lifetime US3150015A (en) | 1961-08-29 | 1961-08-29 | Insulation for silicon steel |
Country Status (1)
| Country | Link |
|---|---|
| US (1) | US3150015A (en) |
Cited By (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3421949A (en) * | 1964-08-12 | 1969-01-14 | Hooker Chemical Corp | Composition and process for producing an electrically resistant coating on ferrous surfaces |
| US3506499A (en) * | 1964-03-16 | 1970-04-14 | Yawata Seitetsu Kk | Method of surface-treating zinc,aluminum and their alloys |
| US3657080A (en) * | 1968-09-25 | 1972-04-18 | M & T Chemicals Inc | Mist suppression in electroplating solutions |
| US3856568A (en) * | 1971-09-27 | 1974-12-24 | Nippon Steel Corp | Method for forming an insulating film on an oriented silicon steel sheet |
| US3993510A (en) * | 1975-05-21 | 1976-11-23 | The United States Of America As Represented By The Secretary Of The Navy | Thixotropic chemical conversion material for corrosion protection of aluminum and aluminum alloys |
| US4099990A (en) * | 1975-04-07 | 1978-07-11 | The British Petroleum Company Limited | Method of applying a layer of silica on a substrate |
| US4238534A (en) * | 1975-08-22 | 1980-12-09 | Kawasaki Steel Corporation | Method for forming a heat-resistant coating on an oriented silicon steel sheet |
| US4362782A (en) * | 1980-09-25 | 1982-12-07 | Westinghouse Electric Corp. | Low temperature cure interlaminar coating |
| US4462842A (en) * | 1979-08-13 | 1984-07-31 | Showa Aluminum Corporation | Surface treatment process for imparting hydrophilic properties to aluminum articles |
| US20100310764A1 (en) * | 2005-09-28 | 2010-12-09 | Snecma | Method of protecting a cmc material thermostructural part made of ceramic matrix composite material against wear, a coating, and a part obtained by the method |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2030601A (en) * | 1934-04-20 | 1936-02-11 | Victor Chemical Works | Rustproofing composition and method of coating iron and steel |
| US2909454A (en) * | 1957-12-04 | 1959-10-20 | United States Steel Corp | Process for producing core-plated electrical steel strip |
| US3013897A (en) * | 1959-03-20 | 1961-12-19 | Du Pont | Silica coating composition, process of coating metal therewith and article produced thereby |
-
1961
- 1961-08-29 US US134564A patent/US3150015A/en not_active Expired - Lifetime
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2030601A (en) * | 1934-04-20 | 1936-02-11 | Victor Chemical Works | Rustproofing composition and method of coating iron and steel |
| US2909454A (en) * | 1957-12-04 | 1959-10-20 | United States Steel Corp | Process for producing core-plated electrical steel strip |
| US3013897A (en) * | 1959-03-20 | 1961-12-19 | Du Pont | Silica coating composition, process of coating metal therewith and article produced thereby |
Cited By (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3506499A (en) * | 1964-03-16 | 1970-04-14 | Yawata Seitetsu Kk | Method of surface-treating zinc,aluminum and their alloys |
| US3421949A (en) * | 1964-08-12 | 1969-01-14 | Hooker Chemical Corp | Composition and process for producing an electrically resistant coating on ferrous surfaces |
| US3657080A (en) * | 1968-09-25 | 1972-04-18 | M & T Chemicals Inc | Mist suppression in electroplating solutions |
| US3856568A (en) * | 1971-09-27 | 1974-12-24 | Nippon Steel Corp | Method for forming an insulating film on an oriented silicon steel sheet |
| US4099990A (en) * | 1975-04-07 | 1978-07-11 | The British Petroleum Company Limited | Method of applying a layer of silica on a substrate |
| US3993510A (en) * | 1975-05-21 | 1976-11-23 | The United States Of America As Represented By The Secretary Of The Navy | Thixotropic chemical conversion material for corrosion protection of aluminum and aluminum alloys |
| US4238534A (en) * | 1975-08-22 | 1980-12-09 | Kawasaki Steel Corporation | Method for forming a heat-resistant coating on an oriented silicon steel sheet |
| US4462842A (en) * | 1979-08-13 | 1984-07-31 | Showa Aluminum Corporation | Surface treatment process for imparting hydrophilic properties to aluminum articles |
| US4362782A (en) * | 1980-09-25 | 1982-12-07 | Westinghouse Electric Corp. | Low temperature cure interlaminar coating |
| US4425166A (en) | 1980-09-25 | 1984-01-10 | Westinghouse Electric Corp. | Low temperature cure interlaminar coating |
| US20100310764A1 (en) * | 2005-09-28 | 2010-12-09 | Snecma | Method of protecting a cmc material thermostructural part made of ceramic matrix composite material against wear, a coating, and a part obtained by the method |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US3856568A (en) | Method for forming an insulating film on an oriented silicon steel sheet | |
| US3583887A (en) | Magnesium oxide coating composition and process | |
| CN105980584B (en) | Grain oriented electrical steel flat steel product containing insulating coating | |
| US3150015A (en) | Insulation for silicon steel | |
| US4347085A (en) | Insulative coatings for electrical steels | |
| US3948786A (en) | Insulative coating for electrical steels | |
| US3996073A (en) | Insulative coating for electrical steels | |
| JPS6253589B2 (en) | ||
| CN111302366B (en) | Magnesia for grain-oriented electromagnetic steel sheet annealing isolating agent | |
| US3138492A (en) | Insulating coating for magnetic steel | |
| US3841925A (en) | Magnesium oxide steel coating composition and process | |
| CN114381584B (en) | Insulating coating liquid for oriented silicon steel surface, oriented silicon steel plate and manufacturing method thereof | |
| JPS61257483A (en) | Crystal grain oriented silicon steel and stress coating thereto | |
| US4425166A (en) | Low temperature cure interlaminar coating | |
| KR930002940B1 (en) | Insulative coating composition for electrical steels | |
| CN111961359A (en) | Insulating coating liquid for improving magnetism of oriented silicon steel and preparation method and application method thereof | |
| US2809137A (en) | Insulating coating for magnetic sheet material and method of making the same | |
| CN112831200A (en) | Coating for chromium-free oriented electromagnetic steel sheet, preparation method thereof and preparation method of chromium-free oriented electromagnetic steel sheet with coating | |
| GB1587981A (en) | Coating solution formagnetic steels | |
| US2215295A (en) | Surface insulation for magnetic sheet steel | |
| JPH04323382A (en) | Formation of insulated film grain-oriented silicon steel sheet containing no p and cr compound | |
| CN101812683A (en) | Insulating coating liquid for oriented silicon steel of anti-adhesion sheets and coating process thereof | |
| US3582409A (en) | Method of producing potassium silicate glass coating for ferrous magnetic sheet stock | |
| US2790739A (en) | Method of coating core plates and composition therefor | |
| US4207123A (en) | Coatings for reduced losses in (110) [001] oriented silicon iron |