CA1036659A - Molded magnetic cores utilizing cut steel particles - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
There is disclosed a magnetic core and the method of making the same. The core is formed of a plurality of microlaminations. Since each discrete microlamination is of elongated rectangular shape, soft, ductile and magnetically insulated, the cores exhibit improved permeability, lower core loss, lower exciting volt amps and exhibit improved high frequency character-istics.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
me present application is closely related to the subject matter contained in Canadian application Serial No. 207,481 filed July 21, 1974 and assigned to the assignee of the present application.
BACKGROUND OF THE INVENTION
Field Of The Invention:
The present invention relates to a magnetic core which is formed of substantially flat, elongated, rectangular particles which are termed "microlaminations".
These microlaminations are formed from plain carbon steel by cutting the same into a discretely-shaped particle (an elongated parallelopiped of generally rectangular cross-section) following which the micro-laminations are decarburized, magnetically insulated and thereafter placed in a mold and pressed to the desired density, said pressing being effective without the use of a binder for producing the finished unitary magnetic core.

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43,720 :' ~36~9 Description Of The Prior Art:
-Magnetic cores for medium and high frequencyuses are often produced from powdered metal magnetic materials or flakes, the latter being usually made by rolling powder particles to a plate-like structune. The purpose Or using powders or flakes is to provide increased temperature stability and decreased electrical losses when sub~ected to high frequency eddy currents because air gaps and insulation are present between the individual particles of the powders or the flakes, Air gaps are desirable to decrease losses but undesirable in another respect since they lower the effective perme-ability because there is a lower volume of m~gnetic material in each unit core volume.
Some of the disadvantages of the lower perme-.
ability present in powdered iron cores is overcome by ; , fabricating the cores from flakes which yield a higher density or packing factor. Significantly, the flakes ; also improved the Q factor at lower frequency. The Q
factor is defined as the ratlo of the reactance of the ; core to the effective series resistance of the core.
Generally speaking, the flakes are insulated and flat, the length and width dimensions being much larger than their thickness.
In U.S. Patent 2,689,398 to G. C. Gaut et al, , there is disclosed a method of making magnetizable com-pacts. As there set ~orth, the magnetic material in i;~ fine particulate or powder form is fed to a pair of flaking rollers where the material is flattened to a ' 30 flake thickness usually in the range between about 0.015 ., -. ~
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43,720 ... ~, ,, JL~366~9 ~ ~

and about 0.025 millimeter in thickness and transverse dimensions of from about 0.02 to about 0.5 millimeter.
Following flattening, the flaked material is mixed with silica powder to separate the flakes, and the mixture is heated to a temperature of about 900C in order to remove the strains induced during the cold worklng of the particulate material through the flaking rolls.
Advantageously hydrogen or cracked ammonia is utilized to prevent oxidation of the materials during said annealing processing. After annealing, the flakes, in the soft condition, are transferred to a separator for removing the silica and thereafter preferably the flakes are then treated to provide an oxidized surface thereon by heating in air to a temperature within the range between about 200 and 250C. The patentees found, however, that the presence of an oxide surface on the flakes is not essential. Thereafter, the flakes were charged into a -.
die of predetermined configuration and the flakes were preferably so disposed in the die to assume positions in which they lie parallel to the magnetic lines of force -; to be set up in the core during subsequent use. Punches ; were applied to the die so as to exert a pressure of -~ -between 15 to 30 tons per square inch to the faces of the flakes, thereby compressing them into the ~inal core configuration. `
Other workers in the field as typi~ied by U.S. Patent 3,255,052 to Opitz, follow essentially the same routeS namely starting with a metallic powder and thereafter rolling the same to form a flake which is ultimately utilized within a core configuration. Notably - 3 _ .
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43,720 . -1~3~65~

different with Opitz is the fact that he requires each of the individual flakes to be magnetically insulated by a ~ -plurality of coatings which coatings permit the finally configured core to be annealed at a high temperature without destroying the magnetic flake insulation. Thus, after the core was finally formed, the same was annealed at a temperature between 800 to about 950C to relieve the work strains and produce the desired magnetic char- ~
acteristic. Following heat treatment the cores were - -quenched at a rate of between about 15 and about 75~C
per minute. While Opitz is directed to a method particu-larly adapted to that material known commercially as -molyb~enum permalloy, it is stated that the process is also effective when used with other materials.
Other patentees, namely Adams et al in U.S.
Patent 2,937,964, also use molybdenum permalloy and teach a method for melting the composition as well as formulating the powder, flaking, annealing, insulating, aligning and compacting the same. This is followed by 20 another final annealing of the finished core at a i;
temperature within the range between about 600C and about 700C and the annealed core is thereafter quenched in air to room temperature.
Thus, from the foregoing practices, it becomes clear that the preferred method of the prior art was to - employ metallic particles either spheroidal or irregular in shape and flattening the same to form the individual flake-like laminates going into the core. Opitz teaches that the permeability of the magnetic core will vary 30 with the flake diameter and the core losses varies with . . , . ~ ~.. ..

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the flake thickness, both increasing with increases in their respective dimensions.
Roseby U.S. Patent 1,850,181 suggests that cores may be prepared by drawing fine wire preferably of a nickel-iron alloy, of a diameter of 4 millsg - cutting the wire into small lengths, which wire is annealed, coated with an iron-phosphate, then coated with an insulating varnish and finally pressed to 10 to -15 tons per square inch into a core. In order to fill the relatively large spaces between the wire lengths, Roseby states that up to 20% of powdered iron be added to produce a more compact core. Fine wire is extremely expensive to produce, and as Roseby lndicated, the sections of wire have such a poor packing or space : .
factor that even if the nound wire sections are perfectly -arranged at least up to 20% of powdered iron should be - added to fill some of such spaces in producing a more efficient core. `~
In contrast thereto, the applicants' present ; 20 invention employs a heretofore commercially available ~ sheet material in a new and different manner and by ; forming discretely-shaped microlaminates, the several improvements and benefits of which will appear more - fully hereinafter.
SUMMARY OF THE INVENTION ` `
The material which is employed in making the microlaminations which are utilized in forming a core comprlse a plain carbon thin steel sheet preferably of that character known in the trade as AISI Type 1010 steel. The plain carbon thin steel sheet is cut into - 5 - `- -:'~ '''', 43,720 ,.-- .

:1~3~6~9 small, substantially elongated, rectangular-shaped parallelopiped particles having preferred dimensions of length, width and thickness. Following the mechanical formation of the microlaminations, they are subJected to an annealing heat treatment in which the plain carbon steel is decarburized and deoxidized to develop the required magnetic properties and at the same time the stresses are relieved which have been incurred during cold rolling of the plain carbon steel to flnish gauge as well as in the formation of the microlaminations.
Thereafter, the microlaminations are sub~ected to a coating which, in practice comprises a magnesium oxide based formulation which forms a very thin but flexible coating which adheres even after the materials have been subJected to the molding pressure to form the core. The coated ~-microlaminations are thereafter placed in a mold or die ` and magnetically aligned preferably utilizlng an iron pole piece of an çlectromagnet. Thereafter, the punches are inserted within the die and the material subJected k to the influence of pressure preferably wlthin the range between about 50 and about 100 tons per square inch to accomplish a packing factor in excess of about 80%.
` Following pressing, the consolidated core may be removed from the die and it will maintain its shape and dimensions.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a photomicrograph of a microlamina-tion taken at a magni~ication of 200X prior to annealing;

Fig. 2 is a photomicrograph of a microlamination taken at a magnification of 200X after annealing;
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~366S9 Fig. 3 is a sketch of a magnetic probe which may be employed in practicing the method of the present invention;
Fig. ~ is a sketch in cross-section of appara-tus for forming a ring core; and Fig. 5 is a photomicrograph taken at a magnifi-cation of lOOX illustrating the cross-section of a pressed core and is shown on the same sheet as Fig. l.
~ESCRIPTION OF THE PREFERR~D EMBODIMENTS - -~ . ~ . . :
The material from which the microlaminations are made is preferably a plain carbon steel normally of that type used for tin cans. mis is a low carbon steel and is recommended because of its low cost and avail-ability. The material is usually purchased in the form of "black plate", that is, the condition of the tin can steel prior to tinning. It is readily available in a ^
. : ' wide range of thicknesses usually ranging from about 0.005 to about 0.020 inch in thickness. This black plate tin can stock material is one of the lowest cost ferrous products in this thickness range. Typically the AISI Type lOlO steel will have a composition con-taining between about 0.0~% and about 0.13% carbon, about 0.30~0 and about 0.60% manganese, about 0.040%
maximum phosphorus, about 0.050% maximum sulfur and the balance essentially iron with incidental impurities.
It should be pointed out, however, that while the pre-ferred material is a plain carbon steel, such other ; ~ -materials as silicon containing steels as well as nickel-iron, molybdenum permalloy, and other magnetic alloys may be employed in practicing the present invention.

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43,720 ~ ~3~ ~ 9 It is preferred to have the steel with some degree of strength to it so that when the microlamina-tions are formed they do not become grossly distorted as will appear more fully hereinafter. Consequently, a plain carbon steel from about 0.05% to 0.15% carbon is ideally suited, for this material will have sufficient - strength and yet is sufficiently ductile that the steel ~an be readily sheared into microlamination sizes as - will be described. While exceedingly low carbon steels (more properly called "irons") can be employed, they are not recommended because of the tendency to dlstort ~;, during the microlamination formation operation. The plain carbon steel is usually purchased in the cold ;~
rolled condition and preferably has a grain size of the - order of ASTM No. 9.
:~{ Referring now to Fig. 1 of the drawings, there is shown a photomicrograph of the material as cut in its microlamination form. The grains are quite fine and are substantially elongated lndicating that the material is in its cold rolled conditlon. The cold work condition plus the carbon content of the plaln carbon steel makes this material ideally suited to the forma-tion of the substantially elongated rectangular micro-laminations which are employed in making the cores.

At the outset, it should be noted that while a wide range of steel particles sizes and thicknesses are satisfactory, it is nonetheless preferred to con- `
trol the microlaminations to dimensions between about ;
0.05 and about 0.10 inch in length, about o.oas and about 0.05 inch in width and from about 0.002 to about ~ 43,720 1~366S9 ....
0.02 inch in thickness. Within this broad range, particu-larly satisfactory results have been obtained where the individual microlamination particle length ranges from about 0.050 to about 0. o60 inch, from about 0.010 to about 0,020 inch in width and between about 0. oo6 and about 0.013 inch in thickness. :~
The microlaminations may be formed in any number of ways and the particular manner of fashioning the microlamination is dictated solely by the overall economics of the process. Currently, the steel is cut -~
with a high speed rotary die cutter in free space or it may be slit to narrow ribbons of the width desired and then the microlaminations are severed with a rotary cutter as the narrow ribbons pass over a stationary knife edge anvil. It is obvious in this latter aspect to align the cutter and the slitter for continuous operation. In practice, good results are obtained where a single strand of Type 1010 carbon steel~ for example, about 4 inches wide is slit into a plurality of narrow ribbons, each ,~ 20 ribbon measuring approximately 0.055 lnch in width. The width of the slit ribbon thereafter forms the length dimension of the microlaminate and by advancing the ribbon at a predetermined speed into a rotating cutter ; comprising a plurality of knives which is also moving at a predetermined speed, the width dimension of the microlaminates will be determined by the speed at which the slit ribbon advances across the face of the stationary knife be~ore the material is sheared by a rotating knife.
Thus, the faster the speed of advance of the slit ribbon and the slower the cutter rotation, the greater will be _ g _ .

43,720 ~366~9 the width of the microlamination thus formed and vice versa.
In this respect, it has been found that with the sheet material in the cold worked condition with about 0.10% carbon, some burring of the microlamination -occurs upon shearing whether the same is done in free -space or against a stationary knife edge anvil. It has ~ :
been found that such burring as does occur, does not grossly affect the ultimate magnetic characteristics exhibited by the finished core. One experiment was per-formed wherein microlaminations which were formed in - the foregoing described manner were treated in acçordance with the process of the present invention and a similar batch of microlaminations was thereafter chemically polished to remove any burrs that oocurred during the manufacturing operation. Aside from this deburring operation, the two batches were processed identically from the same stock of carbon steel material into finished cores. No substantlal differences were noted in the observed magnetic characteristics between the cores formed from the deburred and the undeburred microlamina-tions especially when both cores are formed by the ;~
presently dlsclosed process.
Following the formation of the microlaminationshaving the sizes within the foregoing described ranges, it now becomes necessary to improve the magnetic charac-teristics and adJust the mechanical characteristics so that a strong, dense core with good magnetic properties may be formed therefrom. In order to do this, the micro-lamlnations produced from carbon steel must be decarburized ., - 10 - " ' :........................................................................ ~,,:

43,720 ~ 9 and deoxidized in ordeF to develop the required magnetic properties. Since the carbon has served the purpose of strengthening the steel for the formation of the micro-laminations, it is desired to remove as much carbon as - possible not only to improve the magnetic characteristics but also to soften the steel to a sufficient degree that upon the later application of pressure in order to form the core, the steel will be in its softest condition from a mechanical standpoint and therefore can be more densely packed in order to secure the requisite magnetic charac-teristics in the finished core. This is most convenlently accomplished by means of a decarburizing annealing heat treatment.
In the case of the microlaminations formed from tin plate stock, the preferred heat treatment consists of ;
heating the microlaminations to a temperature within the range between about 700C and about 800C for a period of about 4 hours. While shorter time periods can be utilized, as weli as longer time periods, it has been found sufflcient to heat the microlaminations at a temperature within the stated range for a time period of about 2 hours while employing a wet hydrogen atmosphere having a dew point preferably in excess of about ~120F. The wet hydrogen atmosphere and the temperature to which the micro-laminates are heated cooperate to effectively decarburize the steel, a nominal 0.10% carbon containing steel being decarburized to a ~alue of about 0.002% carbon within a period of about 2 hours. As little as 0.5 hour at 800C
is satisfactory. It will of course be appreciated that longer annealing times may remove additional carbon while :.

43,720 1~366$9 ;
shorter times may result in higher residual carbon con- ;
tent. The carbon content after the annealing should be less than 0.01%. Good results have been obtained when -~
the wet hydrogen atmosphere is maintained for a time period of about 2 hours at temperatures of from 700C
to 800C. Thereafter, and without any intermediate -cooling, the annealing heat treatment is continued;
however, the atmosphere is changed to dry hydrogen which has the effect of deoxidizing the microlaminations and -thereby improving the overall magnetic characteristics as wlll be set forth hereinafter. While it has been ;
usual to heat treat plain carbon steels in so-called "forming" gas, such type of atmosphere must be eliminated -and ~or that matter any other oxidizing atmosphere that produces an oxide on the steel cannot be used since the oxide thickness adversely affects the packing factor of the finished core material. Annealing temperatures in excess of about 800C should be avoided since the micro-laminations may tend to weld together. While success has been attained where the microlaminations are annealed in ~;~ flat trays in a box-type furnace, it will of course be recognized that for mass production, a rotary furnace can be employed or a duplex zone furnace can be employed so long as the materials are decarburized and deoxidized and any stresses resulting from cold rolling as well as in ~-the formation of the microlamination are substantially reduced during the annealing heat treatment operation. ~
Referring now to Fig. 2, there is illustrated - ;
the microstructure of a microlamination after annealing for 2 hours at 745C employing a hydrogen atmosphere ~ .',, ~ . . . : : . ,. . . . . :

43,720 ~36~5~

having a dew point of about +120F followed by an addi-tional 2 hours at the same temperature but having a dry hydrogen atmosphere of about -40F. In Fig. 2 it will -be seen that the grains are substantially equiaxed and have grown to about ASTM size 7. This ~ grain size is preferred from the magnetic characteristic view-point.
After the annealing operation, the micro- ~-laminations must be electrically insulated in order to develop the required core loss characteristics in the finished product. In this respect, it has been found that a very thin and flexible coating whose integrity will withstand the molding pressure and retain the inter-laminar resistance is required. However, the coating must be applied after annealing since attempts to apply such a coating prior to annealing usually results in insufficient decarburization and instead of deoxidizing, the surface of the steel may actually result in an ; oxidation of the steel surface, thereby resulting in an adverse effect on the magnetic characteristics which are developed within the microlamination. A typical example ; of a suitable insulation coating is a magnesium base formulation, preferably one which is devoid of an oxygen containing radical. It has been found that a water slurry containing between about 6% to 8~ magnesium methylate has fulfilled all of these characteristics.
Greater concentrations of magnesium methylate can be employed. A container is filled with the magnesium methylate solution and the annealed microlaminations are deposited, as by sifting, uniformly on the surface - ~ ~
--43,720 ~:
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1~36~i5~ ::
of the fluid. Characteristically, they will float momentarily due to the surface tension of the fluid and ; -~
then sink to the tank bottom. In the process, the coated microlaminatlons with a substantially uniform adherent coating of magnesium methylate are then removed from the tank and the coating ls air dried. Magnetic - ; `
means may be associated with the tank, for example, a lifting magnetic means will greatly aid in removing the ~
coated laminations from the tank. The air dried coat- -ings have sufficient adhesion to the surface of the microlaminations that the miçrolaminations may be readily handled normally without destroying the integrity of the coated surface.
The magnetically insulated microlaminations are - next placed into a mold in an orderly "brick wall" type arrangement and preferably are arranged in such a way that the elongated rectangles are aligned in an easy flux path in the pre~erred direction for ultimate use. In the case of a simple ring core, the microlaminations would be !' . .
; 20 aligned with the flat faces being in a circumferential dlrection. This alignment may be most readily accom-plished by applying to the die an electromagnet contain-ing an iron pole piçce, which is referred to as a magnetic probe.
Referring now to Fig. 3, such a magnetic probe ; is depicted which essentially consists of an electro-magnet which may be energized from any convenient source of electricity. More particularly, the magnetic probe is shown generally at 10 and comprises a coil electro-magnet 12 which is energized from a suitable source of ` -43,720 1~36659 -~3 electricity ~4 in a circuit which contains a switch 16 which may be closed as required to energize the electro-magnet. The electromagnet is connected to a steel hol~ing chuck 18 which carries an iron pole piece 20.
As the chuck is rotated within the die and periodically -energized by closing the switch 16 the more or less loosely disposed microlaminations are aligned in a cir-cumferential direction. Alternatively, it has been found that by slowly pouring the laminations into the - 10 mold and mechanically distrlbuting the same while apply-ing a source of sonic or ultrasonic mechanical energy to -~
the die is also surprisingly effective for aligning the microlaminates in the preferred direction with better packing density also taking place. After the mold is filled to the predetermined height, or by weight, if desired, the magnetic probe is removed and an annular -~
punch i5 inserted and a ring core is pressed in the manner known to the art.
Referring now to Fig. 4, a typical punch and die arrangement for such pressing of a ring core is illustrated embodying a double action uniaxial press.
In Fig. 4, there is shown, in sectional elevation, a ring core mold designated generally at 30 whlch com-prises an outer die member 32 having a centrally disposed opening 3~contained therein, an annular bottom punch 36 and an annular top punch 38 which are aligned within the central opening ~rof the die member 32. Prior to the assembly of the bottom punch 36, and the top punch 38, a core bar 40 which fits centrally of the annular top punch 38 and the annular bottom punch 36 respectively, ::
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43~720 ~;
r ~ ' ~ ~36659 is inserted and centered so as to form the desired dimen- -sion for the inside diameter of the ring core. The aligned microlaminations 42 which have been aligned hereto~ore by use of the magnetic probe as illustrated in Fig. 3~ are confined within the space between the die member 32~
core bar 40~ the bottom punch 36 and the top punch 38.
Thereafter, this assembly is sub~ected to uniaxial pres-sure by means of a double action press (not shown) or by means of a single action press, exerting a force within -the range between about 50 and about 100 tons for cores of from 1 to 3 inches outside diameter. While the tonnage of the press is exemplary only, it will be understood that sufficient pressure of at least 50,0Q0 psi be exerted on the microlaminates so as to obtain a packing factor or density which is within the range between about 80% and 100% of theoretical density. As will be more fully set forth hereinafter, the packing factor will have a sub- ; , stantial effect on the observed magnetic characteristics of the molded ring core, the higher the better.
It will be appre¢lated that while the f~re-going illustrates thç manufacture of a simple ring core, cores of varying complexity can be made by compacting the - microlaminations in conventional powder metallurglcal dies and presses. The parts so made may be of very com-plex shape with holes of various geometries so long as the cross-section parallel to the pressing direction contains no reentrant angles. The process is essentially scrap-less and can be automated for rather high production rates. It will of course be appreciated that hydrostatic as well as isostatic pressing can also be employed in the :

43,720 ,_ .

3ti6~9 manner well known to form the core of the required geometry.
In order to more clearly demonstrate the present invention, reference may be had to the following. A
simple ring core was formed designed to have a 1-3/4 inch outside diameter and 1 inch inside diameter. AISI Type 1010 steel, having a thickness of about o.oo8 inch, was employed and cut into microlaminations each averaging about 0.055 inch in length and about 0.013 inch ln width.
They were heated to a temperature of 745C in an atmos-phere of wet hydrogen having a dew point of about +120F
for a time period of 2 hours and thereafter the atmosphere was changed to dry hydrogen having a dew point of less than about -40F, the annealing in dry hydrogen at a temperature Gf 745~C being continued for an additional

2-hour period. The microlaminations were cooled while -~
under the influence of the hydrogen atmosphere. There-after, a 7% magnesium methylate formulation contained in water was employed and the microlaminates deposited on the surface of the tank containing the solution. Upon sinking to the bottom, they were removed from the tank with a magnet and air dried. The microlaminations were assembled in the shape of a ring core and aligned by employing the magnetic probe as described in Fig. 3, which magnetic probe was manually rotated within the die cavity (core bar 40 being withdrawn) at the rate of about 10 revolutions per minute with the switch mechanism periodically being opened and closed several times to energize and deenergize the magnet. A plurality of cores were made employing various molding pressures to establish .: .
-. . . . , :

43,720 -1~36659 `:
a range of packing factors. These cores were then com- ;
pared with commercial magnetic cores manufactured by a well-known flake iron process with the results set forth hereinafter. The flake iron cores were quite expensive as compared to the cost of the microlaminate core.
Table I

Losses Molding Molding Pres- Packing dc AC - 60 Hz Force Tons sure psi Factor % H=50 Oe B@H=ioo Oe PC/lb 15 kG
~ .
100 124,000 96.1 15.0 kG 16.8 kG 6.5 W/lb - ---87,000 92.9 13.1 14.8 6.4 ~ -62,000 89.0 12.3 13.9 6.0 Commercial Cores (Flake Iro~) 77.5 6.o __ 5.0 @ 10 kG
In Table I there are listed the molding force and pressure, -~
the packing factor and some DC as well as AC magnetic characteristics of cores having the indlcated packing factors in comparison with commercial cores made by the flake iron process. It is interesting to note that the DC properties obtained by the present in~ention more than exceed double that of the commercial cores made from the flake iron process. In this respect, it is seen that as the packing factor goes up, the flux density also increases both at a field intensity of 50 oersted -and at 100 oersted. As would be expected by reason of the greater deformation and the larger amount of stress that was employed in securing the more dense packing factors, the core loss increases slightly from a core loss of 6 watts per poupd at 15 kilogauss and 60 hertz, up to a value of 6.5 watts per pound where the packing factor has been increased from 89% to about 96.1%. On the other hand, with a magnetizing force of 10 kilogauss - 18 - ;

43,720 1~36659 :~:

the commercial core made by the flake iron process exhibited a watt loss of 5 watts per pound. However, it was impossible to energize the commercial core to 15 kilogausses and consequently it may be concluded that the 15 kilogauss core loss would be far in excess of the core loss figures set forth in Table I.
As was stated hereinbefore, the microlaminates have particular utility when their magnetic character-istics are employed in medium range frequency applica-tions. In order to demonstrate these outstanding magnetic characteristics, reference is directed to ~
Table II which lists a comparison of the core loss, the . :
exciting volt amps and the permeability over a range of frequencies of from 400 Hz to 2000 Hz for microlaminated cores which were sub~ected to a molding pressure of a ~ `
124 kpsi (identified as "Micro") and which produced a packing factor of about 96.1% in comparison with a commercially obtained flake iron core in which the molding pressure was unknown, but which had a packing factor of 77.5%.

-- . . . . . .. - ~ . : - .- .-~ 43,720 .

1~36~
Table II -Medium Frequency Magnetic Properties Pc/lb Pa/lb ~u .:
- Frequency B - kG Mlcro Flake Micro Flake Micro Flake 400 Hz .50.2 - 0.20.52 - 1.16 259 - 144 :~
o . 66 - 0.81.59 - 3.92 357 - 175 22.00 - 2.94.64 - 13.4 498 - 202 47.0 - 9.114.0 - 56.o 653 - 187 :- -1000 Hz ,50.57 - o.681.3 - 3.0 256 - 142 --~ .. -11.9 - 2.34.1 - 10.0 349 - 173 26.6 - 7.612.2 - 34.o 492 - 200 ~
4 22 - 24 37 - 139 639 - 190 ~.: .
1500 Hz .50.97 - 1.02.1 - 4.5 252 - 146 13,2 - 3.56.6 - 15.0 346 - 177 211.2 - 12.019.4 - 51.0 471 - 200 ^ .
4 38 - 38 60 - 209 616 - 191 ; :
2000 Hz .5 1.3 - 1.3 3.0 - 6.o 249 - 146 1 4.7 - 4.8 9.0 - 19 338 - 177 4 55 - 54 85 - 282 586 - 190 i~
The test results set forth in Table II clearly indicate that while there is a slight improvement with varying flux densities at a frequenoy of 400 and 1000 hertz insofar as the core loss is concerned, above about a ;~
1000 hertz the core loss is substantially identical between the product produced in accordance with the teachings of the present invention and with the com- :
mercially available flake iron core. However, when the aspects of the exciting volt amps, which is designated ;
Pa/lb9 are compared at the same flux densities and the same frequencies it becomes abundantly clear that the present process produces an outstanding improvement in :
the exciting VA or as it is sometimes referred to as . :. .
the apparent watt loss. To substantially the same effect, the AC permeability at medium frequencies with varying flux densities clearly shows the outstanding improvement obtained by employing the teachings of the 43,720 1~36~5~

present invention. It is believed that these outstandingmagnetic characteristics are in part due to the fact that employing the teachings of the present invention a higher density or greater packing factor, in addition to other benefits, is attained in the core so produced. :
Reference is directed to Fig. 5 which is a photomicrograph of the cross-section of the microlaminates after the same have been preseed into a ring core con-figuration in accordance with the teachings of the present invention. The essentially orderly brick wall alignment as is shown in Fig. 5 is believed to be indica-tive of the improved packing factor realized and provides an easy flux path in the preferred direction. This in part is due to the fact that during the annealing treat-ment not only is the carbon reduced to the indicated low - levels whieh thereby improves the ductillty and lowers the strength allowing for compression to attain a much higher packing factor, but in addition, the amount of strains which are actually induced to the molded ring core in accordance with the teachings of the present invention result in lower residual stresses thereby imparting the improved magnetic characteristics as is set forth hereinbefore.
An alternative embodiment involves the aspect of a bonded core and thereby results in a change in the magnetic insulative coating employed in the present invention. Typically, the microlaminations are formed in the same manner as described hereinbefore and annealed for the purpose of decarburizing and deoxidizing the microlaminations. However, at this particular .

43,720 1~36~S9 ~uncture, especially where the finished magnetic core product is to be used in a motor rotor, for example, or in a relay which involves mechanical stresses due elther to rotation or to impact, it may be desirable to form a highly bonded core of these materials and in that respect it is preferred to change the character of the magnetic insulative film which is applied to the ;~
microlaminations.
In this respect~ it has been found that a magnetically insulative bonding material which may be fired at a temperature of between about 900C and about -1200C can be employed. It has been found that both sodium silicate and potassium silicate work well, it being understood that other magnetically insulative coatings can be employed within the teachings of the .: .
present invention. One characteristic difference between the bonding material which also acts as a magnetically ;
insulative film and that of, for example, magnesium methylate is the fact that the bonding magnetically insulative coating wlll of necesslty be somewhat thicker than the magneslum methylate film whlch has been described ;
heretofore. Consequently, since the bonding magnetically insulative coating is somewhat thicker, it would be expected that the packing factor would be somewhat lower and thereby result in an adverse effect on the magnetic characteristics. While this is true, some of the adverse effect on the magnetic characteristics can be compensated for by reason of the fact that the bonding magnetic insulative film is usually heated to a sufficiently high temperature following the pressing of . .; ; ~, , , ~ , ~ 43,720 ~366S9 the microlaminate core that any residual stresses which are induced during the pressing operation are relieved and as a result, the overall magnetic characteristics are not seriously adversely affected by utilizing the bonding magnetically insulative coating material as con-trasted to the magnesium film which has been described hereinbefore.

~a~
More specifically, microlaminations~which have been made in accordance with the teachings set forth hereinbefore~were coated with a potassium silicate coating~the potassium silicate coating having a density between about 25 and about 45 Baume. Such a product~
commercially sold under the tradename Kasll #l by the Philadelphia Quartz Company~is a potassium silicate of 25 Be. This product was admixed with an equal propor-tion of water by volume and the microlaminations were coated in the same manner as the application of the magnesium methylate Upon air drying, the microlamina-tions were assembled and aligned in the ring core con-figuration and pressed utilizing the same pressures as - heretofore described. Following pressing of the ring core, it exhibited a packing factor between 80 and 85%.
The ring core was placed in an annealing furnace and heated to a temperature of 900C for a period of time sufficient to fuse the applied potassium silicate coating within microlaminate core to provide a strong, tough~integral core structure. Upon cooling to room temperature, and testing, the bonded core exhibited magnetic characteristics of approximately the same magni-tude as those in the unbonded core whose data is set - ~ ~

43,720 _~ . "''"'' lQ3f~6~9 :~ :
forth hereinbefore in Table I.
From the foregoing, it can be seen that the -present invention teaches that small elongated rectangu-lar steel particles cut from thin carbon steel sheets and processed to yield the required magnetic properties can be pressed to form quality cores. These cores have magnetic properties superior to commercially available -cores molded from flake iron or powders. The primary -benefit of this invention is improved permeability, -lower core loss, lower exciting VA, lower processing cost and lower material costs than commercially avail-able flake iron cores. The magnetic characteristics especially at higher frequencies are far superior to those exhibited by commercially available flake iron cores.
Other binders may be advantageously employed -~
in the manufacture of magnetic cores of this invention.
Thus, the microlaminations, after insulation with a magnesium methylate may be admixed with an air setting binder such as shellac. Thereafter the microlamina-tions are aligned into thè core configuration and pressed and held, with or without heating, until the binder has hardened or set. In this modification, the binder content should be kept to a minimum in order to obtain the highest packing factor.
Likewise, a thermal setting resin such as an epoxy resin having an anhydride hardener may be admixed with the insulated microlaminations and while the mixture is pressed, sufficient heat to attain a temper-ature of about 200C is applied to cure the resin.

43,720 ~(~36659 While such binders are effective for improving the strength of the finished configuration, the cores -~3 '~ formed without the use of a binder ~ass2~ remarkable strength and would be preferred for many applications.

.. . .
~ ' :

Claims (31)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. The method of producing magnetic core components for use in electrical apparatus, the steps comprising severing microlaminations from thin, flat strips of ferrous alloys, said microlaminations being substantially of elongated rectangular shape, annealing said microlaminations in decarburizing and deoxidizing atmospheres to improve the magnetic characteristics by reducing carbon to less than 0.01% reducing the oxygen to low values and relieving stresses, applying a thin elastic electrical insulation to the microlaminations, assembling a plurality of the microlaminations within a mold of predetermined configuration, aligning the microlaminations into a desired orientation, and thereafter pressing the aligned microlaminations into the solidified configuration of the desired core component.

2. The method of claim 1 in which the mate-rial from which the microlaminations are formed is an iron alloy having a carbon content between about 0.05%
and about 0.15%.

3. The method of claim 1 in which the micro-laminations each have dimensions within the range between about 0.05 and about 0.10 inch in length, about 0.005 to about 0.05 inch in width and from about 0.002 to about 0.02 inch in thickness.

4. The method of claim 1 in which the micro-laminations are annealed at a temperature between about 700°C and about 800°C.

5. The method of claim 4 in which the micro-laminations during annealing are heated to said tempera-ture for a time period of up to about 4 hours.

6. The method of claim 4 in which the micro-laminations are decarburized during the initial portion of the annealing cycle.

7. The method of claim 4 in which the anneal-ing atmosphere during decarburization consists of hydrogen having a dew point in excess of +120°F.

8. The method of claim 7 in which the decar-burization treatment is followed by a treatment in hydrogen having a dew point of less than -40°F.

9. The method of claim 7 in which the decar-burization annealing takes place for a period between about 0.5 and about 2 hours.

10. The method of claim 1 in which the annealed microlaminations are coated in a slurry con-taining at least about 6% by volume of a magnesium formulation for forming an electrically insulative coating thereon.

11. The method of claim 1 in which the microlaminations are insulated with a coating of magnesium methylate.

12. The method of claim 1 in which the micro-laminations are magnetically aligned and thereafter hydrostatically pressed into the desired configuration.

13. The method of claim 1 in which a binder is admixed with the microlaminations prior to pressing and set during pressing.

14. The method of claim 1 in which a binder is admixed with the microlaminations and set after pressing.

15. The method of claim 1 in which a magnetic coil with a pole piece is disposed within the mold con-taining loose microlaminations and said magnetic coil is energized prior to compressing said microlaminations for aligning the same into a predetermined configuration.

16. In the method of making a molded magnetic core, the steps comprising, forming a plurality of substantially elongated, flat, rectangular-shaped microlaminations from a plain carbon steel containing from about 0.05% to about 0.15% carbon, annealing the microlam-inations to improve the magnetic characteristics thereof, electrically insulating said microlaminations, assembling said microlaminations into a preformed configuration while aligning the same into a desired orientation and thereafter pressing said microlaminations into high space factor core having the mold configuration.

17. The method of claim 16 in which a mag-netic field is employed to align the microlaminations into said configuration and with a desired orientation.

18. The method of claim 17 in which the microlaminations are subjected to sufficient pressure during pressing to provide at least an 85% packing factor in the core.

19. The method of claim 18 in which the assembled aligned microlaminations are subjected to a static pressure of at least 50,000 psi.

20. A molded magnetic core comprising, a plurality of ferrous base metal microlaminations formed of substantially flat, elongated, rectangular platelets, each of said platelets having been stress-relieved, decarburized, deoxidized and insulated from one another, the microlaminations being aligned in a predetermined orientation and pressed into the desired configuration, the pressed core exhibiting a packing factor in excess of 85%.

21. The core of claim 20 in which the micro-laminations are essentially parallelopiped in shape and have dimensions within the range between about 0.05 and about 0.10 inch in length, about 0.005 and about 0.05 inch in width and from about 0.002 and about 0.02 inch in thickness.

22. The core of claim 20 in which the micro-laminations are molded into the preferred configuration and include a binder.

23. The core of claim 20 in which the platelets after decarburizing have a carbon content of less than about 0.01% by weight.

24. A microlamination suitable for use in molded magnetic components comprising, a substantially flat, elongated, rectangular steel particle having dimen-sions including from about 0.05 and about 0.10 inch in length, about 0.005 and about 0.05 inch in width and from about 0.002 and about 0.02 inch in thickness, a carbon content of less than about 0.002% by weight, are substantially stress-free and having an electrically insulating coating covering the surface of the micro-laminations.

25. The microlamination of claim 24 in which the carbon content of the steel from which the micro-lamination is formed is within the range between about 0.07% and about 0.13% by weight.

26. In the method of making a molded magnetic core, the steps comprising, forming a plurality of sub-stantially elongated, flat, rectangular-shaped microlamina-tions from magnetic alloys, heat treating the microlamina-tions to improve the magnetic characteristics compared to those characteristics exhibited by the alloy in the "as-severed" condition, electrically insulating the micro-laminations, assembling the insulated microlaminations into the desired configuration of the core and thereafter sub-jecting the microlaminations to sufficient pressure to form a molded core exhibiting a packing factor in excess of 85%.

27. A molded magnetic core comprising a plurality of magnetic alloy microlaminations, each of said microlam-inations having been heat treated to improve the magnetic characteristics thereof, and electrically insulated from one another, the microlaminations being substantially aligned in a predetermined orientation and pressed into the desired configuration, the pressed core exhibiting a packing factor in excess of 85%.

28. A microlamination suitable for use in molded magnetic components comprising a magnetic alloy in the form of an elongated parallelopiped of rectangular cross-section, the microlamination having been heat treated to improve the magnetic characteristics compared to the "as-severed" mag-netic characteristics of the alloy and having an electrically insulating coating covering the surface of the microlamina-tion.

29. The method of claim 26 in which each of the microlaminations has dimensions within the range between about 0.05 and about 0.20 inch in length, about 0.005 and about 0.05 inch in width and from about 0.002 to about 0.02 inch in thickness.

30. The method of claim 27 in which each of the microlaminations has dimensions within the range between about 0.05 and about 0.20 inch in length, about 0.005 and about 0.05 inch in width and from about 0.002 to about 0.02 inch in thickness.

31. me method of claim 28 in which each of the microlaminations has dimensions within the range between about 0.05 and about 0.20 inch in length, about 0.005 and about 0.05 inch in width and from about 0.002 to about 0.02 inch in thickness.