United States Patent [19]
`Miller
`
`[54]
`[75]
`
`ELECTRICAL STEEL LAMINATION
`Inventor: Robert F. Miller, New Kensington,
`
`-
`
`Pa.
`
`[73]
`
`[21]
`[22]
`[51]
`[52]
`
`Assignee: Allegheny Ludlum Steel Corporation,
`Pittsburgh, Pa.
`Appl. No.: 73,812
`Filed:
`Sep. 10, 1979
`Int. Cl* ....................... B32B 15/18; H01F 27/24
`U.S. Cl. .................................... 428/216; 336/219;
`428/415; 428/416; 428/433; 428/436; 428/450;
`428/457; 428/460, 428/471; 428/469
`Field of Search ............... 428/433,436, 415, 539,
`428/471, 416, 460,457, 450, 216; 336/219
`References Cited
`U.S. PATENT DOCUMENTS
`7/1951 Compton .....
`2,561,462
`---------------- 336/219
`7/1962 Ashe ............
`3,045,133
`----- 336/219
`3,160,509 12/1964 Schaefer ............................... 336/219
`
`[58]
`
`[56]
`
`[11]
`[45]
`
`4,277,530
`Jul. 7, 1981
`
`
`
`3,533,861 10/1970 Foster .................................. 336/219
`3,554,966
`1/1971
`Jones .....
`... 336/219
`3,670,278
`6/1972 Foster ...
`... 336/219
`3,924,022 12/1975 Schroeter .
`336/219
`4,032,673
`6/1977 Schroeter ............................. 336/219
`Primary Examiner—Ellis P. Robinson
`Attorney, Agent, or Firm—Vincent G. Gioia; William J.
`O'Rourke, Jr.
`ABSTRACT
`[57]
`A laminated article for electrical applications is dis
`closed which comprises at least two sheets of electri
`cally isolated electrical steel each having a thickness of
`less than 0.020 inch, and an adhesive between adjacent
`sheets bonding the adjacent sheets to one another with
`out creating significant compressive stress in the plane
`of the sheets. The adhesive is characterized by substan
`tially instantaneous bonding at a temperature less than
`750° F.
`
`17 Claims, No Drawings
`
`Am. Honda v. IV II - IPR2018-00442
`PET_HONDA_1006-0001
`
`

`

`1
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`4,277,530
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`' ELECTRICAL STEEL LAMINATION
`
`BRIEF SUMMARY. OF THE INVENTION
`
`The present invention relates to a laminated article
`and, more particularly, to an adhesively bonded electri-
`cal‘steel lamination for electrical applications. The lami-
`nated article of the present invention may be used in
`electrical devices such as transformers, generators or
`electric motors.
`A continuing objective in the use of electrical steels in
`electrical applications is to reduce the energy loss asso-
`. ciated,with magnetization of the electricalvsteel sheet. It
`has been disclosed in the prior art, such as US. Pat. No.
`2,561,462, that employingthinner gage electrical steel
`sheets for such use is desirable. The reason for the desir-
`ability of thinner gage electrical steel sheets in electrical
`applications is that a thin gage reduces the path over
`which magnetically induced eddy currents may flow.
`At the present time a large proportion of the electri-
`cal steel sheet produced for applications, such as elec-
`tric power transformers, falls within a thickness range
`of from 0.010 to 0.015 inch (0.025 to 0.040 mm). It ap-
`pears that the lower limit for conventional sheet thick-
`ness of electrical steel sheet is, to a large extent, deter-
`mined by the manufacturing considerations of the con-
`sumer of these materials who fabricates the electrical
`device from the electrical steel sheet. Thin gage electri-
`cal steel sheet, such as 0.010 inch siliconsteel strip and
`0.002 inch amorphous strip material, is, understandably,
`more susceptible to damage during handling and fabri-
`cation. Also, the thinner gage electrical sheet often
`requires additional labor in the fabrication of various
`electrical devices. In summary, it is well known that
`more energy efficient devices such as transformers may
`be made by decreasing the thickness of the electrical
`steel strip, however, manufacturing considerations have
`placed, a practical lower limit on the thickness of the
`strip which may be economically and successfully fabri-
`cated into electrical devices.
`The prior art discloses coatings for electrical steel
`sheets used in electrical applications. For example, US.
`Pat. No. 3,160,509 discloses the use of a high tempera-
`ture insulative refractory coating, specifically chromic
`oxide, which is tightly adherent to the surface of silicon
`steel strip material and serves as an annealing separator
`for the silicon steel..U.S. Pat. No. 3,670,278 pertains to
`a glass coating applied at relatively high bonding tem-
`peratures onto the surface of sheets of electrical steel
`which hold the sheet in tension to reduce magnetostric-
`tion and strain sensitivity and thereby reduce the noise
`level in a transformer employing such sheets. Also, US
`Pat. No. 4,032,673 discloses the use of irradiation cur-
`able solventless organic resins as an additional coating
`to improve the insulating characteristics of oriented
`silicon steel having an underlying inorganic insulating
`coating. However,
`there is a need for adhesively
`bonded electrical steel laminations in which the adhe-
`sive does not Create significant compressive stress in the
`plane of the sheets and in which the adhesive bonds at
`temperatures less than about 750° F.
`,
`. Accordingly, a new and. improved electrical steel
`sheet is desired which combines the improved electrical
`properties of very thin electrical steel sheet with the
`practical manufacturing economy of fabricated thicker
`sheets.
`.
`The present. invention may be summarized as provid-
`ing a new and improved laminatedarticle for electrical
`
`2
`applications comprising at least two sheets of electri-
`cally isolated electrical steel each having a thickness of
`less than 0.020 inch,land an adhesive between adjacent
`sheets bonding the adjacent sheets to one another with-
`out creating significant compressive stress in the plane
`of the sheet. The adhesive is characterized by substan-
`tially instantaneous-bonding at a temperature less than
`750° F. In a preferred construction, the adhesive layer
`of the laminated article of the present invention exhibits
`a bond strength of at least 1,000 pounds per square inch
`as measured in uniaxial tension.
`An objective of the present invention is to provide a
`laminated electrical steel article which combines the
`
`low energy loss characteristics and advantages of using
`thinner sheets of silicon steel, with the inherent manu-
`facturing economies of handling and processing thicker
`electrical steel articles. In particular, the silicon steel
`sheets in the composite article of the present invention
`are bonded at a temperature below about 750° F. with
`sufficient strength to permit the composite article to be
`subjected to routine processing operations, including
`coiling, shearing, mitering,
`trimming and punching,
`without causing the composite article to delaminate.
`Simultaneously, the adhesive bonding of adjacent sheets
`does not create undesirable stresses in the plane of the
`sheets.
`‘
`
`An advantage of the present invention is that the use
`Of thinner sheets may become commercially accepted
`without requiring modification of conventional manu-
`facturing processes and operations.
`A primary objective of the present invention is to
`provide a laminated silicon steel article comprised of
`multiple sheets of electrically isolated silicon steel
`bonded at a relatively low temperature with an adhe-
`sive which does not create significant compressive
`. stress in the plane of the sheet which could impair the
`electrical and magnetic properties of the laminated arti-
`cle.
`
`Another advantage of the present invention is to
`provide the ability to utilize thinner sheets of electrical
`steels in conventional magnetic manufacturing pro-
`cesSes for making transformers, electric power motors,
`generators and the like, in order to reduce the energy
`loss associated with the magnetization of thicker electri-
`cal steel sheets.
`A further advantage of the present invention is to
`proVide a laminated electrical steel article bonded by an
`adhesive which is compatable with the high tempera-
`ture operating environments of electric transformers
`such as about 100° C. above ambient temperature in
`which such articles may be employed. Specifically, the
`adhesiveused in the laminated article of the present
`invention does not decompose in such environment to
`contaminate dielectric oils used in typical devices, and
`further withstands prolonged exposure to such oils at
`elevated temperatures without degradation, decompoSi-
`tion or delamination.
`
`60
`
`These and other objectives and advantages of this
`invention will be more fully understood and appreci-
`ated with reference to the following description.
`
`DETAILED DESCRIPTION
`
`65
`
`The electrical steel sheets, or silicon steel-sheets, used
`in the laminated article of the present invention are
`ferrous base metal sheets, or preferably an iron silicon
`alloy containing up to about 6% silicon, by weight, and
`more preferably containing about 3% silicon. The elec-
`
`Am. Honda V. IV 11 - IPR2018-00442
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`PET_HONDA_1006—0002
`
`Am. Honda v. IV II - IPR2018-00442
`PET_HONDA_1006-0002
`
`

`

`,
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`35
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`40
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`
`’. 3
`, trical sheets of the present invention are typically grain
`oriented ‘silicon steel sheets having a thickness of less
`than about 0.020 inch. However, non-oriented grades of
`.. silicon steel, amorphous metal strip materials and nu-
`merous other electrical alloys may be employed in the 5
`laminated article of this invention, particularly for ap-
`plications wherein the use of thinner gage strip materi-
`als yield improved watt loss characteristics.
`In accordance with the present invention, a laminated.
`article, or composite structure,
`is provided by adhe— lo
`sively bonding two or more sheets of electrical steel. As
`will be explained in more detail below, the resulting
`composite structure has the physical and mechanical
`integrity required for conventional fabrication and suc-
`cessful performance in an electrical device, and the 15
`electrical and magnetic properties which are far supe-
`rior to any known single sheet of electrical steel of a
`thickness comparable to the total thickness of the com-
`‘posite structure.
`The adhesive which is used to bond adjacent sheets of 20
`electrical steel in the laminated article of the present
`invention must be characterized by substantially instan-
`taneous bonding at a temperature below about 750° F.
`Such adhesive also provides adequate bond strength
`when used along thin glue lines. In particular, for steel 25
`strip having a thickness of less than about 0.020 inch, the
`stacking factor of the laminated article of the present
`invention as well as for the electrical device manufac-
`‘ tured with the laminated article of the present invention
`should exceed at least 90%, and more preferably should 30
`exceed 95%. To obtain a stacking factor of greater than
`90%, the adhesive layers should have a total thickness
`of leSs than 10% of the total article thickness. Relatively
`high stacking factors, i.e., in excess of 95%, may be
`necessary in order to maximize the amount of electrical
`steel which is employed in the finished device. It will be
`understobd by those skilled in the art that stacking fac-
`tors less than 90%, and perhaps as low at 75% may be
`. tolerable for certain laminated articles such as amor-
`phous strip materials.
`'
`The‘strength of the bond between adjacent sheets of
`electrical steel in the laminated article of the present
`invention must be sufficient to permit subsequent han-
`dling and fabricating operations. The laminated article
`of the present invention is intended to be shipped to a
`manufacturer of electrical devices. Therefore, it is un-
`derstandable that the laminated article will be coiled,
`sheared, ledge trimmed, mitered, and punched as it
`passes through typical operations used in the manufac-
`turing of electrical devices such as transformers. There-
`fore, the bond strength of the adhesive layer between
`adjacent sheets must be sufficient to permit such han-
`dling and fabrication without causing the composite
`article to delaminate. For example, it has been found
`that a bond strength of at least about 1,000 pounds per 55
`square inch may be sufficient to bond silicon steel sheets
`to permit subsequent manufacturing operations without
`causing delamination. However, for such sheets bond
`strengths in excess of 2,000 psi are preferred. Such bond
`strength should be measured in uniaxial tension.
`The laminated article of the present invention is in-
`tended to be manufactured into electrical devices such
`as transformers which typically use dielectric oils at
`elevated temperatures during operation. The adhesive
`. in the laminated article of the present invention should 65
`retain its bond strength in such operating environment.
`Also, in cases where the intended use is for electric
`power transformers, the bonding adhesive should not
`
`4,277,530
`
`4
`contaminate the dielectric, oils used in these devices.
`Further, the bond should not degrade or decompose
`upon 'exp‘Osu‘re to such'environment at elevated temper~
`aturesover prolonged operating periods.
`, The adhesive bonding of two or more sheets of elec-
`trical steel with an adhesive, such as that used in the
`laminated article of the present invention, requires that
`special attention be taken to avoid cXcessive residual
`stresses. It is well known that the presence of compres-
`sive stresses acting parallel to the sheet rolling direction
`in the case of grain oriented silicon steel cause severe
`degradation of both magnetostriction and watt
`loss
`characteristics. Residual stresses are generally removed
`in conventional single-sheet practice by a high tempera-
`ture stress relief annealing operation. A high tempera-
`ture stress relief anneal typically ,1400° F. and above
`cannot be applied to the composite structures Of the
`present invention because exposure to such high tem-
`peratures would cause the adhesive to melt, resulting in
`delamination of the article.
`The particular adhesive chosen'to bond the electrical
`steel sheets in the laminated article of the present inven-
`tion should exhibit certain characteristics. In particular,
`the adhesive should be thermoplastic,
`i.e., have the
`ability to soften at elevated temperatures on the order of
`300° to 600° F. Thermoplasticity is the common prop-
`erty of a variety of plastics and resins which facilitates
`the application of the adhesive to the sheets in the arti~
`cle of the present invention. The adhesive should also
`have the ability to adhere to a smooth or glassy surface.
`The adhesive should be characterized by rapid curing.
`In this regard, it has been found to be beneficial for the
`adhesive is characterized by substantially instantaneous
`bonding at a temperature of less than 750° F. As ex-
`plained above in more detail, the adhesive must demon-
`strate adequate bond strength when used along thin
`glue lines. Also, as explained in more detail above, the
`adhesive should be resistant to attack in dielectric oils at
`such elevated operating temperatures.
`It is known that exposure to high temperatures may
`have an adverse affect upon the magnetic properties of
`silicon steel strip material. For this reason, as well as for
`practical manufacturing reasons, the adhesive utilized
`to bond strip materials should not require high curing
`temperatures. To minimize degradation of electrical
`f properties, the adhesive of the present invention should
`bond, substantially instantaneously at a temperature
`below about 750° F. Such relative low bonding temper-
`ature requirement for the adhesive is critical in instances
`where amorphous strip material
`is bonded because
`amorphous strip materials recrystallize when exposed
`to temperatures above about 750° F. ‘
`.
`Exemplary materials which may be used. to adhe-
`sively bond electrical steel sheets in the laminated arti-
`cle of the present invention include phenolic adhesives
`which are characterized by rapid curing without libera-
`tion of by—products, such as acetic acid which is liber-
`ated during the curing of silicon rubber adhesives. Cer-
`tain high strength, flexible epoxy adhesives which ex-
`hibit the properties listed above may also be employed.
`A specific material which may be used to bond the
`electrical steel sheets is PA‘44459‘ adhesive, a product
`manufactured and sold by 3M Company of St. Paul,
`Minnesota. PA-4459 is a clear, amber colored synthetic
`resin based adhesive which utilizes ‘a ketone-alcohol
`solvent.
`,
`.
`‘
`
`.
`
`Curvature of silicon steel sheets bonded into the lami-
`nated article of the present invention must be minimized
`
`Am. Honda V. IV 11 - IPR2018-00442
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`PET_HONDA_1006-0003
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`Am. Honda v. IV II - IPR2018-00442
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`

`

`4,277,530
`5
`to prevent the creation of harmful residual stress in the
`sheets. Bonded electrical steel composites of two or
`more sheets may be treated as a single, uniform sheet of
`multiple thickness for purposes of calculating residual
`stresses. The stresses encountered during bending of the
`composite steel sheet may be calculated from the fol
`lowing equation:
`-
`Equation I
`
`5
`
`where:
`
`.
`
`10
`
`15
`
`20
`
`R=radius of curvature at To (the service tempera
`ture),
`a=coefficient of thermal expansion (12×10-6/°C.),
`T=bonding temperature of the colder sheet,
`To =service temperature,
`AT=temperature differential between the sheets at
`the time of bonding, and
`d=thickness of an individual sheet of the bonded
`pair.
`The passage of adhesively bonded electrical steel
`strip over rolls having a relatively small radius of curva
`ture may also result in severe damage to the composite
`article. The minimum radius of rolls tolerable in the
`processing of the bonded strip material of the present
`invention may be calculated by setting the value of
`stress to be less than the yield strength of the material
`and solving Equation I, above, for the tolerable radius
`of curvature. For example, for a bonded strip of grain
`oriented silicon steel with thickness equal to 0.022 inch
`and a yield strength of 35,000 psi, the minimum tolera
`ble roll radius would be about 11 inches.
`The primary utility of forming laminated articles of
`electrical steel sheets is the provision of a material
`which is ideally suited to the conventional manufacture
`of commercial electrical devices, such as transformers.
`The composite articles of the present invention are
`bonded at sufficient strength to insure that they are
`highly resistant to delamination during subsequent
`forming operations. Furthermore, such composite arti
`cles possess electrical and magnetic properties far supe
`rior to those of a single sheet of electrical steel of equal
`thickness. The following examples describe the prepara
`tion of electrical steel laminated articles of this inven
`tion and illustrate the electrical and magnetic properties
`obtained.
`
`or=maximum stress acting on a sheet, either tensile
`or compressive,
`‘.
`.
`E=Young's modulus of the sheet in the direction
`parallel to the resulting stress,
`d=sheet thickness of the bonded structure, and
`R=radius of curvature.
`Due to the stress-sensitive nature of silicon steels it is
`desirable to insure that significant compressive stress is
`not created in the plane of sheets. In this context, the
`magnitude of compressive stresses should be limited to
`a maximum value less than about 1,000 psi in the service
`condition. More particularly, the sum of, or total resid
`25
`ual compressive stresses acting in the plane of the
`bonded sheet, whether coated or not, should be below
`about 1,000 pounds per square inch. It will be under
`stood that residual compressive stresses may be im
`parted by a variety of mechanical, chemical and struc
`30
`tural sources. Such sources include the adhesive, the
`substrate coatings, curvature of the strip, thermal stress,
`strip shape, temperature differentials during bonding,
`curing of the adhesive, thermal expansion differentials
`between the sheet and a coating, and the like. It is the
`35
`total residual compressive stresses acting in the plane of
`the sheet which could adversely affect the properties of
`the lamination and, therefore, should be held below
`about 1,000 psi.
`As mentioned above, stress could be created by cur- 40
`vature of the article. The minimum radius of curvature
`produces the maximum stress and the magnitude of
`EXAMPLE 1
`stress depends on the final thickness of the adhesively
`Ten panels of high tension coated grain oriented
`bonded composite. For example, consider a bonded
`silicon steel were adhesively bonded into pairs using a
`composite article comprised of two individual grain- 45 thermoplastic resin, specifically 3M Company PA-4459
`orinted electrical steel sheets each having a thickness
`adhesive. Magnetic tests were performed on the indi
`equal to 0.011 inch. Young's modulus in the rolling
`vidual sheets and on the sheets taken as pairs before
`bonding. The panels, 26 inches by 12 inches, were press
`direction of the sheet is about 17×106 psi. The total
`composite article thickness is slightly greater than 0.022
`bonded with the thermoplastic resin at a temperature of
`50
`350°F. (175° C) for two minutes under a load of 250 psi
`inch. The minimum radius of curvature allowable to
`(2 MNm-?) using a 0.001 inch (0.025 mm) glue line
`prevent residual stresses in excess of 1,000 psi may be
`thickness. The stacking factor exceeded approximately
`calculated from Equation I as R=187 inches. Radii of
`95% for each laminated article. The bonded electrical
`curvature smaller than 187 inches result in excessive
`steel composite articles were tested magnetically, sub
`residual stresses present in the composite sheet when
`jected to various cutting operations, then examined for
`the strip is constrained to lie flat, as in a transformer.
`delamination and tested for electrical isolation of the
`For the purposes of this specification, excessive residual
`individual electrical steel sheets. Table I below lists the
`stresses are those in excess of 1,000 pounds per square
`pertinent magnetic test data.
`TABLE I
`The conditions which may result in small radii of
`60
`curvature could arise from improperly flattened sheet
`when used as the starting material for bonding. Another
`cause of curvature may be due to temperature differen
`tials between the sheets as they are being bonded. The
`radius of curvature of a bonded pair of sheets of equal
`65
`thickness resulting from temperature differentials may
`be calculated from the following equation:
`
`inch.
`
`*
`
`.
`
`.
`
`.
`
`Equation II
`
`. . . . . .
`
`.
`
`-
`
`-
`
`Individual.
`Sample
`l
`2
`3
`4
`
`Gate
`(inches)
`.01.08
`.0109
`,0108
`.01.10
`
`Pairs of Sheets
`Before
`After
`Individual
`Bonding Bonding
`Sheets
`Pair WPP at WPP at
`WPP atº
`17 KG Sample 17 KG 17 KG
`,692
`.682
`.682
`.708
`
`1 & 2
`
`.746
`
`.789
`
`3 & 4
`
`.760
`
`,861
`
`Am. Honda v. IV II - IPR2018-00442
`PET_HONDA_1006-0004
`
`

`

`4,277,530
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`7
`
`TABLE I-continued
`
`Individual
`- Sheets
`WPP at“
`17 KG
`.667
`.682
`.668
`.721
`.950
`.938
`
`Gate
`Individual
`(inches)
`Sample
`.0109
`5
`.0108
`6
`.0107
`7
`.0107
`8
`.0131
`9
`.0136
`10
`‘Watts per pound at 17,000 gauss
`
`Pairs of Sheets
`Before
`After
`Bonding
`Bonding
`Pair WPP at WPP at
`Sample
`17 KG
`17 KG
`
`5 & 6
`
`7 & 8
`
`.729
`
`.767
`
`9 & 10
`
`1.000
`
`.842
`
`.879
`
`1.114
`
`The watt loss measured on samples from Table I
`tested as pairs before bonding is somewhat greater than
`the average for the two panels tested as individual
`sheets. This increase is believed to result primarily from
`variations in the path of magnetic flux which occur
`when the sheets are tested as pairs and cannot occur
`when the sheets are tested individually. This gives rise
`to local areas of the sheets which operate at'signifi-
`cantly higher magnetic inductions than the average.
`Watt losses increase with the square of the magnetic
`induction, and therefore increase the total watt loss
`measured. Testing the sheets as pairs before bonding
`does not cause a degradation of the electrical sheet, but
`reflects more accurately the watt losses which might be
`experienced in service where several laminations are
`operating at an average induction.
`The bonded laminated articles for the above example
`were less than 5% thicker than the total thickness of the
`individual panels. The minor additional thickness was
`due to the thin, 0.001 inch, glue line. A small increase in
`the watt losses of the bonded electrical sheets occurred,
`ranging from 5 to 16% above that Of the pairs tested
`before adhesive bonding. This increase is due in part to
`the increased sample weight used to calculate the mag-
`netic induction, and partially due to minor undesirable
`stresses present in the bonded composite.
`Samples of the laminated articles of this example
`were subsequently sheared and slit from the electrical
`steel composites. The sheared and slit samples exhibited
`no delamination of the individual, bonded electrical
`sheets. Continuity tests made on the samples cut from
`the bonded composite article showed that electrical
`isolation of the sheets was maintained, since no short
`circuit path had been created between the adjacent
`electrical steel sheets.
`
`EXAMPLE II
`
`Eighteen additional, 24' inch>< 10 inch, panels of con-
`ventional grain oriented silicon steel were adhesive
`bonded using the technique described above for Exam-
`ple 1. Samples 11 through 16 were finish coated with a
`high tension coreplate. Samples 17 through 24 were
`finish‘coated with a conventional phosphate glass core-
`plate applied over a mill glass, magnesium silicate, coat-
`ing. Samples 25 through 28 had a mill glass base coating
`only. By way of explanation, silicon steels may be gen-
`erally coated with an annealing separator, such as mag-
`nesia, prior to a high temperature annealing operation.
`The reaction product of magnesia with silica on the
`strip surface is primarily comprised of forsterite,
`Mg28i04. Such forsterite layer, is usually called the base
`coating. The term “coreplate” refers to a finish coating,
`typically a phosphate glass based material, which is
`applied to the strip over the base coating, or to a bare
`strip surface in which the base. coating has been re-
`
`10
`
`15
`
`20
`
`25
`
`3O
`
`35
`
`45
`
`50
`
`55
`
`60
`
`65
`
`8
`moved. High tension coreplates generally are finish
`coatings which place the underlying strip in biaxial
`tension to reduce watt losses, lessen strain sensitivity
`and improve magnetostriction. It should be understood
`that the electrical steel sheets in'the laminated article of
`the present invention should be electrically isolated by
`a coating. Such coating may be those discussed herein.
`Alternatively, the adhesive layer may not only bond the
`sheets, but may also serve as the electrically isolative
`coating. Table II below summarizes the magnetic test
`data taken on these samples prior to and following adhe-
`sive bonding.
`TABLE II
`'
`Pairs of Sheets
`Before
`After
`Individual
`Bonding
`Bonding
`Sheets
`Individual
`Gage
`WPP at
`Pair WPP at WPP at
`
`Sample
`(inches)
`17 KG
`Sample
`17 KG
`17 KG
`11
`.0134
`1.000
`12
`.0133
`.970
`13
`.0135
`.902
`14
`.0142
`.998
`15
`.0138
`.911
`16
`.0136
`.945
`17
`.0112
`.790
`'18
`.0112
`.802
`19
`.0113
`.760
`20
`.0109
`.798
`21
`.0115
`.840
`22
`.0130
`.901
`23
`.0125
`.911
`24
`.0113
`.821
`25
`.0105
`.841
`26
`.0103
`.857
`'
`27
`.0100
`.860
`
`28 1.630 .0106 1.010 27 & 28 .950
`
`
`
`ll & 12
`
`1.010
`
`13 & 14
`.
`15 & 16
`
`17 & 18
`
`19 & 20
`
`21 8c 22
`
`23 & 24
`
`25 & 26
`
`
`
`1.000
`
`.962
`
`.812
`
`.792
`
`.891
`
`.879
`
`.872
`
`
`
`1.079
`
`1.098
`
`1.022 ‘
`‘
`1.196
`
`1.342
`
`1.158
`
`1.000
`
`1.588
`
`The data in Table II above illustrate the utility of high
`tension finish coatings as substrates for electrical isola-
`tion of bonded laminations. The electriCal steel compos-
`ites may exhibit a radius of curvature which places the
`inner-electrical steel sheet in a compressive stress state.
`In the case where adhesives are used to create the bond
`between the sheets in the composite article, compres-
`sive stresses may also be introduced in the electrical
`steel sheet by the setting or curing of the adhesive itself.
`I High tension finish coatings, such as those employed on
`samples 11 through 16, counteract the undesirable com-
`pressive stresses and limit the increase in watt loss asso-
`ciated with bonding.
`.
`Conventional phosphate glass coreplate is less suc-
`cessful as a finish coating for electrical steels employed .
`in electrical steel laminated articles. Such bonded com-I
`posites do counteract some undesirable residual stresses
`in the electrical steel sheet, and in general provide ex-
`cellent electrical insulation, as do high tension coatings,
`which prevent eddy current flow between adjacent
`laminations.
`
`The watt loss increase following bonding of the elec-
`trical steel sheets in Example II was greatest in samples
`25 through 28 where the surfaces of the electrical steel
`sheets were coated only by a mill glass. This phenome-
`non is believed to be due to the relatively poor suppres-
`sion of residual stresses by mill glass coatings.
`'
`It should also be noted that samples sheared and slit
`from the electrical steel composites listed in Table II
`showed no delamination of the individual sheets ire-
`spective of the type of electrical steel coating employed.
`
`Am. Honda V. IV 11 - IPR2018-00442
`
`PET_HONDA_1006-0005
`
`Am. Honda v. IV II - IPR2018-00442
`PET_HONDA_1006-0005
`
`

`

`4,277,530
`10
`4. A laminated article as set forth in claim 1 wherein
`the total residual compressive stresses acting in the
`plane of the sheet are less than 1,000 pounds per square
`inch.
`5. A laminated article as set forth in claim 1 wherein
`the strip material is amorphous.
`6. A laminated article as set forth in claim 5 wherein
`the amorphous strip material has a thickness of less than
`about 0.006 inch.
`7. A laminated article as set forth in claim 3 wherein
`the thickness of each iron-silicon steel sheet is greater
`than about 0.006 inch.
`8. A laminated article as set forth in claim 1 wherein
`the adhesive layer is resistant to attack in dielectric oils.
`9. A laminated article as set forth in claim 8 wherein
`the adhesive layer is resistant to attack in dielectric oils
`at elevated operating temperatures.
`10. A laminated article as set forth in claim 1 wherein
`the adhesive layer thickness is less than 10% of the total
`composite thickness.
`11. A laminated article as set forth in claim 1 wherein
`the adhesive layer thickness is less than 5% of the total
`composite thickness.
`12. A laminated article as set forth in claim 1 wherein
`the electrically isolative coating is selected from the
`group consisting of phosphate glass, magnesium silicate,
`and phosphate glass over magnesium silicate.
`13. A laminated article as set forth in claim 1 wherein
`the electrically isolative coating is a high tension coat
`
`10
`
`15
`
`20
`
`9
`EXAMPLE III
`Four electrical steel composite samples generated in
`Example II above were thermally flattened in a box
`furnace in air by placing the bonded panels on a flat bed
`plate having a radius of curvature greater than 900
`inches (23 meters), and heating or annealing, the panel
`for ten minutes at a temperature of 400°F. The samples
`were allowed to air cool on removal from the furnace
`and were magnetically tested. The results of magnetic
`testing are given in Table III below.
`TABLE III
`After
`Bonding
`WPP at
`17 KG
`1.098
`1,022
`1.196
`1.342
`
`After
`Flattening
`WPP at
`17 KG
`,995
`.972
`,828
`.805
`
`Before
`Bonding
`WPP at
`17 KG
`!.000
`.962
`.812
`.792
`
`Pair
`Sample
`13 & 14
`15 & 16
`17 & 18
`19 & 20
`
`No delamination of the individual electric steel sheets
`occurred as a result of the flattening operation. As can
`be seen from the data in Table III, the watt losses of all
`25
`bonded specimens after thermal flattening approached
`those measured prior to bonding. The advantage of
`high tension finish coatings is dependent upon the ex
`tent of undesirable stresses in the composite structure
`which are tolerable. Providing that curvature and bond
`30
`ing stresses can be adequately relieved by the above
`described flattening operation most coatings may be
`suitable for electrical steel sheets.
`-
`Whereas, the particular embodiments of this inven
`tion have been described above for purposes of illustra
`35
`tion, it will be apparent to those skilled in the art that
`numerous variations of details may be made without
`departing from the invention.
`I claim:
`1. A laminated article for electrical applications com
`40
`prising:
`at least two sheets of electrical steel strip material,
`each having a thickness of less than 0.020 inch,
`each sheet being electrically isolated by a coating,
`a thermoplastic adhesive layer having a thickness less
`than or equal to 0.001 inch between adjacent
`sheets, bonding the adjacent sheets to one another
`with a bond strength of at least 1,000 pounds per
`square inch as measured in uniaxial tension, with
`out creating significant compressive stress in the
`50
`plane of the sheets, said adhesive characterized by
`substantially instantaneous bonding at a tempera
`ture of less than 750° F.
`2. A laminated article as set forth in claim 1 wherein
`the electrical steel is an iron-silicon