US1982689A - Magnetic core material - Google Patents

Description

Dec. 4, 1934. w. J. PoLYDoRoFF HAGNETIG .CORE MATERIAL Filed March 16, 1931 2 Sheets-Sheet l Vie/wh 2 Sheets-Sheet 2 Filed March 16. 1931 w. J. POLYDOROFF uAeNE'rIb com: MATERIAL .n m #e S .Zr 7 Z w d m M a m .M o J n. w a T. E, w. I I (Il all l. I I Il Il I Il IllO 1M M I9 mNuMwkvvlR Vvbw 1m 9 .NNNNUUMYR w n a J m f 7 .a 36@ c m /lb/ n w .N M r wox/ La A N M W 6 @4o m d L e m ,4. o E n Dec. 4, 1934.

Patented Dec. 4, 1934 UNITED STATES.. PATENT OFFICE Lacasse suonano conn Mammal.

Wladimir J. Polydoroll. Ubicato, lll., assigner to Johnson Laboratories, Incorporated. Chicago. Ill., a corporation of illinois Application March 18, 1931, Serial No. 523.112 79 Claims. (UL Pi-4l) -lhe invention relates to magnetic cores used will be small enough to permit successful operawith inductance coils and transformers employed tion in a radio circuit. in high-frequency' circuits; and said invention in- In the electrical arts. the term "apparent pervolves a new magnetic core material. anew magmeability is usually taken as the ratio of the .i net ic core, and various new methods -of producing inductance as increased by the iron. to the air- 60 said core material and said core. core -inductance, the measurement being made Hitherto. several methods o! producing a core. with a core cf a substantially closed type, de-

'suitable for frequencies of the order of signed to enclose practloalb all the lines of force 10.000 cycles per second were known. In pracof the coil. In this speciiication and in the 10;tieing these old methods. various iinely-divided claims. I have used the term "apparent permeo5 alloys with attempted insulation of each grain ability" in this sense, but I use the term eii'ecfrom the others were employed. the main object tive permeability" to indicate this same inducbeing to impart to the cores of loading coils. and tance ratio. without regard to whether the core other similar inductances used in telephone work totally or only partially surrounds and enoloses l5 at low frequencies. a high ,initial perthe ileld of the coil. 70

meability (permeability at low magnetizing inwhen a core is intended to be used for inductensity) tance variations over a wide range oi frequencies. lomes-rapidlyincrea'se with frequency, such as is employed in broadcasting'. the effective cotes'oifthe oldtype become inoperative at irepermeability must be of the order of 8. It is 29 quencies of the higher orders, such as 150 to plainly evident. therefore, that loose powdered 76 i500 k. c.. to which t range the present invention iron cannot be used to fulfill the requirements of more particularly relates. Requirements ior core a radio circuit. and that. in order to increase permeability are considerably smaller for high the permeability. the loose powdered iron should frequencies than icr the low frequencies employed be compressed into a more compact form. In 4in telephone work. and the present invention has this way. the particles may be so closely related so for an object the production of magnetic core as to produce the desired eiiective permeability. materials and cores that are suitable for use at At high frequencies. such as mentioned, the these high frequencies. Suclicores maybe concore losses are very pronoimced and may be venientlyoescribed'as commlnuted to indicate classiiied as: 1. Hysteresis losses. and 2. Eddy 80 .that the magnetic materialisiinely divided. ciment losses. Hysteresis losses mainly depend' a5 The invention will be better understoodlif refupon the' atomicdstructure of the magnetic maerencebe made. to the accompanying drawings. in terial. and are small for materials of low magwhichs i. netic coercivity. such as pure iron. Swedish iron. ligure 1 shows particles of magnetic material etc. Eddy'current losses depend upon the sur- 86 'used in'cores made in accordance with thc present tace areas of the magnetic particles. the minute 90 invention, as they appear when highly magniiled; induced currents circulating in the surface layers. Figures il and 3 show the same material in two The smaller the particles. the smaller the losses, stages ci its preparation. in imaginary crocsandfrcm this it is evident that.if several parti section: cles'are in electric contact and the paths are 40 Figures 4; c, 6, 7,. 8. 9,l lo and l1 represent thus in length, the resultant losses are 05 various shapes of magnetic cores made o! the new also increased. Therefore. insulation of the iniineiy divided material: and dividuai magnetic .particles is required, when Figures i2 and i3 digl'ammtically indicate these particles are pressed into compact masses. magnetic and electrical characteristics of cores Eddy current losses also depend on the speoinc 45 embodying the invention.A resistance of the magnetic material. an increase 10o It was shownbycurrie. U. 8. Patent No. 421367 oi. which reduces the minuto currents. Very of 1890, that, for high frequency work. magnetic oi'ten, however. an .increase of resistivity; Drocores should be made of small insulated iron duced by alloyina the metals. increases coercivity Partidos and PIM inw Buiible shopo- Inand therefore also increases hysteresil losses. so vestigation of iron powders disposed in the ileld' Dillerent magnetic powders. including various 165 of a coil operating at frequencies of the order alloys producing high initial permeability, were of 1000 kiiocycles shows that the inductance intried, the nry particle size being produced to .the .iron is of the order of 3 to 4 bymcchanical,electrolytic,orchemical processes. times. and. i .tbe particles are.of very small A preferable chemical prooess'would be the re 66 dimensions. the total losses in the. coil duction oi a suitable iron compound by hy- 110 drogen. It was round that. although pure iron has a comparatively low initial permeability. the hysteresis losses in such ironare considerably less than in magnetic alloys.

A study of iron powder. reduced by hydrogen, indicates that the reduction can best be made from pure oxides Pesos. FeaOi. because these materials occur in a iinely divided state. Reduced at high temperatures in a stream oi hydrogen, the oxides are converted into pure metallic iron particles ot crystalline iorm, having plainly visible sharp edges, as seen under the microscope, the aaeotthecrystalsbeingoitheorderoiol millimeter. The apparent speciiic density of such reduced iron. when packed in a test tube. should be between 2.4 and 3.7.

AsisshowninFigureLthesecrystalsmay group together to form masses oi' the order o! .005 millimeter. these being sponge-like bodies falling ireeiy through a screen having m0-meshes.

to the inch, a variation of the temperature and the speed oi reduction producing smaller or larger particles.

Although particles smaller than those above described can easily be obtained by the aforesaid method, it h preferable. because oi their ability to be more readily compressed into compact cores. to useparticies ci substantially the described dimensions. i'or the frequency range above men- The ironpowder thus obtained is then thoroughly insulated so thateach individual particleiscoatedwithathintilmoiasoliibut not brittle. insulating substance. The particles will thus be substantially insulated from one another when they are later molded into a compressed core. Various insulating methods were tried in an eort to discover an electrical insulation that would oii'er. adequate mechanical resistance to Care should be taken to prevent the formation oi' cakesorlumps,sothattheparticleswillremain substantially loose, and each particle will be individually coated and baked. This may be accomplished by suitable agitation.

Another method oi' insulating the particles is to use a varnish capable of being oxidized, such as .four parts of China-wood oil and-one part of resin. Varnish oi this composition may be thinned out by a suitable solvent such as toluol orbensinetotherequirediiuencyandthenmixed with the iron powder. the varnish being from' 2% to.5% oitheweightoitheironaiterthe volatile matter has evaporated.

Theadvantageofsuchavarnishisthat itssuriace is oxidized very quickly, and this prevents cakingos'lumpingoitheparticles. Themixture is thenput in an oven and thoroughly baked at an elevated temperature tor several hours, thus integrating the insulating substance until a hard. yet elastic coating is obtained on the particles. It is essential oi course. to msintainthe mate- Lacasse rial in the powdered form.. The powder thu.: prepared should be appropriately tested in orde: to determine that the coatings on the particlesl are chemically stable, heat resistant and lnsoluble.

It will be understood that the materials above described for the individual insulation oi the particles are of organic nature but that equivalent inorganic or synthetic substances may, oi course, be substituted.

The insulated crystalline particles thus produced (Figure 2). are now to be bound together into a single coherent mass (Figure 3). Various binding substances. such as phenol resin. natural resin. and synthetic gums, either in liquid or dry powdered form. may be employed. and should be thoroughly mixed with' the insulated iron powder. Ii a binder in solution is used to secure the mixture, the solvent must then be thdroughly dried out. The amount of binder may vary. but in the resulting cores it should not exceed 10% o! the weight ot the iron. II the insulating substance is a China-wood oil varnish. in quantity 3% oi' the weight oi the iron. the amount of phenol resin used as a binder should be approximately 1%. so that tbe compressed core will contain. not more than 10% ci' inert materials against oi magnetic material by weight.

Cores otanydesiredshapemaybemadetrom these materials, in molds heated to a temperature oi about 100 C. `While in the molds. the mixture is subjected tonI pressure of from to tons per square inch, depending upon the shape of the core. This application ot reduces the core to approidm'ateiy tour-tenths of its initial volume. the particles being thus so closely related as to produce useful values oi' ei- !ective permeability in the resulting cores. Figures 4, l. 8. 7, 8, 9 and il indicate various shapes oi' cores'made in this way. and tor use, respectively, with solenoldal coils (Figur 4 and l0). toroidal coils (Figure 5). binocular or ligureeight coils (Figure 6) and solenoids with substantially closed magnetic fields (Figures 1. 8. 9 and 11). .The cores for use with solenoidal and binocular coils are all shown as being of circular cross-section but 'cores o! any desired form may be molded.

When a heated core is thus compreed. a considerable displacement of particles occurs. and the pressure to which it is subjected may break the insulating iilms and establish longer paths tor eddy currents. It is,l therefore, preferable that, in order to preserve the insulation of the individual particles, the insulating i'ilms should be elastic and the binding substance somewhat plastic. during compression. The plasticity of the binding substance atlfects the magnetic and electrical properties oi' the cores, and. therefore, it should be carefully controlled to produce the desired results.

One method of controlling the plasticity o! the binder is to mix the insulated iron powder with dry powdered phenol resin. to heat the mixture to a temperature oi' 100 degrees centigrade, the mold being heated to the same temperature. and to then press the core while in said mold.

'Another method is to mix the insulated iron powder with the phenol resin varnish, and to then press it after the major part of the solvent of said varnish has been evaporated. and while the mixture is slightly tacky.

Still another method is to add to the dry mixture of iron powder and phenol resin powder. a

minute amount of solvent so as to maire the binder semi-plastic.

Still another method is to mix the iron powder with natural resin in powdered form, and to heat the mixture until said resin becomes plastic.

Liquid binders should be avoided because. under pressure in the mold, they tend to flow aww from the iron. leaving some ot the particles unbound.

The preferable treatment after passing depends on the nature of the binder. In the case o! certain resins, the cores may be merely allowed to cool. I! condensation products are used. the cores may be baked in an oven or in a mold at an elevated temperature. until the binding material is converted by miymerization into a chemically stable product.

Ot the above described methods oi insulation. binding and compresion, 1 prefer the use of the China-wood oil resin varnish for insulation. and dry bakellte powder or bakeiite varnish as a binder. The plasticity o! the binder is eiiiciently controlled by heating the mixture to a dednite temperature and pressing it in heated molds. I also prefer to take the compressed product out o! the meldl for subsequent baking. although baking'fin the mold may be satisfactory in some cases. In either case the binder should be converted into a chemically-stable bakeiite.

One advantage of releasing the pressure. and

then heat treating the still incomplete compressed core,astorinstanceinanoven.asa nnishing operation. is that, when the binder in a plastic or softened state. the insulated magnetic particles have an opportunity to. become somewhat released and have a tendency to acquire an increased separation, which is indicated by the tact that the nnished core is slight' ly expanded. the result being a material decrease of the eddy current losses. This is par ticularly true where a very elastic insulating medium. such as a China-wood oil varnish. is employed.

Cores produced by the methods above described have satisfactory mechanical strength. are ca' pable oi' being mechanically worked like metals,

and have the following characteristics:

Bpeelilc density. 4 to 5 Specific resistance. to 50 ohms-per centimeter cube.

'millimeters will have an etl'ective permeability oi'i'rom4to5. Ac'oresimilartothatshown in Figure 6, for a binocular coil composed of two solenoids oi' the same dimensions, will have an edective permeability of about 6. The cores of Figures 7. 8. 9 and il whichare arranged to almost completely surround a solenoidal coil, have eiiective permeabilities o! approximately 8.

These values are for a frequency ol 500 kilocycles per secondand a magnetic intensity of .1 gauss. but the apparent permeability remains substantially constant for a wide band of trequencies between 1 k. c. and 500 k. c.. and a wide range o! magnetizing forces between .01 and 10 use. Figures 12 and i3 diagrammatically show the electric and magnetic characteristics ot two dilterent shapes of core.

The losses due to the core at high lrequency may be conventionally expressed in ergs per cubic centimeter per cycle at unit induction. Curve a of Figure l2 shows the core losses ot the usual toroidal core between and 45d k. c. The shape of the curve indicates that losses increase with imquency. 'Ihe curve b. being a horizontal straight line. indicates that the permeability remains substantially constant. The core loss at 200 k. c.. as indicated by the curve. is about .008 erg per cubic centimeter per cycle.

It is usual in high-frequency work to express the losses in terms o! the eiIective radio-1requency resistance oi' a coil, and the same principle may be applied to an iron core used in conjunction with an inductance. The diagram shown in Figure i3 plots factors thus derived, the measurements being made at frequencies between 300 and 1400 k. c., on a specimen core of suitable shape. 'I'he curve c represents radio-frequency resistance in ohms for an iron core et the shell type. The permeability is shown by the graph d which is a straight line. The solenoidal coil used in making these measurements was placed in the annular cavity in the core. so that the core sub-` stantiaily enveloped the field of the coil.

The inductan L o! the coil and its radiofrequency resistance R may be measured at any chosen frequency and the ratio o o le computed. It will be found that for the same core material the term es Y AR varies considerably with different shapes of core. such asshowninFigures4,5.and'l,butthat for a. given shape it remains substantially ecnstant, regardless of the inductance and resistance oi the coil by itself. The ratio u: AR may be conveniently taken aithe factor. of merit 125 ot the core. because this ratio completely indicates the effect which the core will have upon any suitable induetanee with which it is asso- Por differently shaped cores,

. il: AR

is diiierent. but for the same core with different coils. it remains substantially constant and is oi' 135 the order ot 3x10* for toroidai coils, 25x10* for solenoidal coils and 10 l0 tor a solenoid with closed magnetic field, L being stated in henrys and R in ohms. A

Coressuchasthoseshowninrigures4.5. 0and'140 'l may bestatlonaryortheymaybearrangedto be movable relatively to the coil. In the latter case, movement of the core produces a gradual change or the eiiective inductance of the coil, andthus may be utilisedtohmearesonantcir- 146 cuit to various frequencies. Inductance is at a minimum when the core is virithiixitwn. correspondingtothe highestfrequencyoi'thehming range. As the core is gradually inserted into the coil. the eiiective inductance gradually increases, 150

until. when the core is all the way in, the maximum vaie -of eiiective inductance is obtained. corresponding' to the lowest frequency of the 's It has been found that with a movable type core m varies over thetuning range. as shown by curve e of'Pigure iii.l

' in radio-frequency reception it may be advan- 'tagecus to maintain this ratio constant through out the range of frequencies. The loss intro- `g duoedby the' initial portions of a homogeneous n of the core which nrst enters the coil and which will be adjacent to the air gap, in the usual case. The reduction involves a slight sacrifice of permeability in this portion. It may be conveniently called "varying .magnetic density" of the 5 eorexcurve'foil'igureisshowsthatwithsuch a' core, the factor R+AR n :is kept substantially constant, the core being so as to compensate forchanges in core losszwithtrequ'ency.

:Figure 9 is a cross section of a core with varying magnetic density. Portion 3 of said core is r of comparatively low permeability and low losses 'at high frequencies. Portion 4 is an intermediate section of the core with medium permeability and iosses.`Portion 5 is a sectiono! maximum permeability and higher losses at lower frequenlveies. These cores of varying magnetic density can be produced by subjecting separate sections to diiferent pressures. A somewhat increased of' magnetic density can be produced b'yan'additionalshapingofthecoreasshownin Figure 10. wherein the ,section 6 is of small diameter than the sections I and 8.

Another method of producing varying density istopressthecoresinmoldsoi' suchaahape that the pressure is not evenly 'distributed .throughout the core. Figure l1 shows such a core, wherein the portions D and 10 ofthe center core;due'tofrictionallossesonthewailofthe mold. 1hlave lower magnetic density than the por Btiil another method of producing varying den- "sity is to charge the mold with two or three dlfferent mixtures, in which the insulating coatings are of diiIerent thickness. Still another method to produce varying density is to use various aises ofmagneticmaterial. Asmallparticlesiseusually, produces smaller permeability and smaller losses. coax-ser particles 'producing higher perme ability with higher losses.

Cores made in quantity in the same mold in accordance with amr ot the above described 'methods l will have substantially' the same 1101811128.' dimensions and physical properties. However. smallvariations in the amount oi' magnetic 'and other materials may produce variations in magnetic and electrical properties ot the cores. 'Do obtain better uniformity. thecompleted cores may be tested and those having excess permeabilitylmay be reduced in sise by any suitable mechanical method. so as to bring them into agreement with the standards.

In cores of movable type..it is quite essential to obtain uniformity of performance.. especially1 when several cores are arranged-to operate-simultaneously and mohronously on several induct ences.l .A very careful matching oteiiectivepere' mcabilities is .required under- .theseconditiona But. in-spite of-careful matching. the intermodiate portions'of the cores may not always Droduce the same inductance variations.

To compensate for this possible misalignment, 8`5 an additional compensating pouet. such as shownl in Figure il. may be inserted in the. main cors.. a small pellet 12of magnetic material is placed-' in one end-ofthe core 9. in a suitable cavity--i3. provided to receive it. with .the core=inserted= into 'the coil to a definite intermediate position.. an adjustment of theeective permeability may: be made either -by altering' the position .of lthe pellet relatively-to the core 9 orby selecting a proper sise of pellet, and sealing it into the core: Q !,i Experience shows that this adjustment produces no substantial change in the eilective perme-A ability of the complete core.

other methods for intermediate adjustment:- are (1) toll the cavity 13 with-a suiiicient quane 109 tity of loose insulated powdered material.A and then seal the end: (2) to use a suiiicientouantity o! the insulated powderalready mixed with the sealing compound; and (Si vto use a solid core' and bore a hole at the open end. thereby: altering 105 the etlective air up. until=tho core matches thel When cores are pressed andrtaken-out oi':thc1 molds, the outer layer of particles has consider-- ably less resistivity than the interior because of 119..:

the friction of the mold walls and the consequent polishing eiiect onthe outer surface.l Thiede. crease of resistivity sometimes. is harmful at high frequencies, and continuity of the core-surnom therefore. may be broken by any suitable m'ei155,

chanical or chemical means such as sand blasting; pickling with acids. or parkerising.

The shell-type cores shown in Figures 7. 8.9 and 11 are especially advantageous in that they produce maximum permeability lwith minimum 12plosses for a solenoidal coil.4 .Coils oi thist'ype recognised a's most advantageous for high-frequency.work because of their inherent low-loss properties. The shell 14. in this type of cora-is united atone end with a c'entral core l5 betweenrli.n which and said shall. is ari-annular cavitylofor thereceptionoiasolenoidal coil. Theshelland. the 'central core m'ay be separately m'oldedfportions of the same'material as shown in-Pig'ure' 11,--

the two parts oi' the core unit being arrangedfto geheid in proper magnetic and mechanical rela;-

' 'When in theclaims I use the word maturd or the word "mature. I have reference to oxidation or polymerization, either of which can be-13 5 .considered as a forni of integration'. Also, when' I refer to the insulator as being ".maturedin situ. I mean that it is oxidized or polymer-'ized after it= is applied tothe magnetic particles.

Having thus described my invention what AI 144) claim is: A

l. A compressed comminuted magnetic material having individuallyvinsulated particles and a.. substantially constant permeability forv a band of radio frequencies at least one octave wide. 2. A c comminuted magnetic material having individually-insulated particles and a substantially constant permeability for a band of fr'eccliuencies between 1 kilocycle andto kilo.-

es. i

n lor an inductance rrequeneyoieiiokilocyclea thespaceimmedilttely s. A comminutsd magnetic material having individually-insulated particles and a substantially constant permeability at frequencies ci from 800 to i400 kllocycles.

4. A' compressed comxnlnuted magnetic material having individually-insulated particles and a substantially constant permeability for a range oi magnetic intensities between .0i and l gauss.

d. A compressed comminuted magnetic material having individually-insulated particles. and an apparent permeability o! the order of Il and a resistivity ranging from to 50 ohms per centimeter cube.

core loss ot the order meter per cycle at unit quency o! the order o! 200 kilocycles.

'1. A compressed toroidal comminuted magnetic core having individually-insulated particles and a factor of merit of the order of 3x10 at a frequency of 500 kilocycles. A

8. A compressed cylindrical comminuted magnetic core having individuallydnsulated particles and a'ractor of merit of the order o! 25x10* at a AD. A- .compressed comminuted magnetic core unit. having individually-insusted particles and includingacore andashellofthesamema adaptedto receive between them a solenoidal coil, said core unit having an eil'ective permeabilityot the order of 8 and a (actor of merit of the order o! 10x10* at a frequency of 500 kiiocycles.

l0. A compressed comminuted magnetic core having magnetic density varying along its magnetic path, adapted to vary the inductance of a aolenoidal coil while maintaining the ratio o! inductance to resistance substantially constant.

1l. A compressed comminuted magnetic core containing varying quantities of magnetic materialalongitsmagneticpatn. adaptedtovary the inductance of a soienoidal coil while maintaining the ratio of inductance to resistance substantially constant.

varyingm magnetic density along its magnetic pa 13. A compressed comminuted magnetic core coil, said core having varying magnetic included in said path. l

le. Aecompressed comminuted magnetic core having magnetic density varyini! along its magnetic path in such a manner as to compensate for changes in core losses with frequency, to thereby maintain the factor oi merit substantially con' 1b. A compressed commlnuted magnetic core having insulated particles and having an apparent permeability oi not less than 'l and a resistivity ci at -lcast 10 ohms centimeter cube. and having an internal porin adapted to adlustablyoccupythespacewithinacoil. andan external portion adapted to adjustably occupy surrounding said coil, and forming a magnetic circuit containing an air le. A compreed -comminuted'magnetic core having insulated particles and having an apparentpermeabilityoi notlessthan'landaresistivity ot at least l0 ohms per centimeter cube.

- Lacasse internal portion adapted to ad- Justably occupytbe space within a solenoidal coil. and an external portion adapted to adlustably occupy the space immediately surrounding laid coil. said two portions being united at one end, and forming a magnetic circuit containing an air comminuted magnetic core and hlvlll In internal within a sclenoidal coil. and an external portion adapted to adlustably occupy the space immediately surrounding said coil. said two portions being united at one end. said magnetic core having varying magnetic density along its magnetic path.

18. A compressed comminuted magnetic core comprising a central portion and a shell portion surrounding the central portion and forming an annular gap between said two portions. which gap is adapted to receive a solenoidal coil, said core having sections o! varying magnetic density along its magnetic path.

19. A compressed comminuted magnetic core having a tapered portion and having dltl'erent 100 degtees o! magnetic density along its magnetic Pl 20. A compressed magnetic core carrying at one end a standardizing magnetic mass.

21. A compressed magnetic core having at one end a cavity for the reception oi a standardizing magnetic mass.

22. The process ot a compressed comminuted magnetic core, which consists in varying the cross-section o! the magnetic circuit o! said core at a desired portion.

23. The process ci standardizing a comprmed comminuted magnetic core, which consists in varying the cross-section of the magnetic circuit' ot said core, at a point adjacent to an air gap.

A24,'lheprocessoi f .1 comminuted magnetic core, which consists in the cross-section of the magnetic circuit oi' said core, at a point adjacent to an air gap, where such variation produces least eilect on the eilective permeability ot the complete core.

26. A com comminuted magnetic core having individually-insulated particles and a broken outside surface which incrmes the resistivity o! the surface layer.

26. A powdered magnetic material o! low coer- I civity. consisting o! particles approximating in sire .005 millimeter. the particles being substantially insulated by thin nlms of insoluble heat-resisting material.

27. A powdered magnetic material consisting oi particles approximating in sine .005 millimeter, the particles being substantially insulated -by thin films o! chemically-stable and pressure-resis-ting material of organic nature.

28. A powdered magnetic material, the particles whereof are approximately .005 millimeter in size and are substantially insulated by an organic material matured in situ.

29. A powdered magnetic material, the particles whereof are small enough to pass through a screen of 400 meshes per inch and are substantially insulated by an organic material matured in situ by heat treatment. 1

30. A powdered magnetic material. the particles whereof are substantially insulated by an oxidized varnish.

31. A powdered magnetic material. the particles whereotaresub'stantially insulated byanoxldiaed 150 varnuhwhichiseitheorderoiwaoitheweight ot the mido material.

82. A powdered magneticmaterial. the particles whereof are substantially insulated by an oxidised China-wood oil varnish.

38. The process oi insulating powdered magnetic material. which consists in coating the particles o! said material with a iiuent organic substance. and maturing the coatings by heat treatment while maintaining the material in the powdered form. t

84. The process oi insulating powdered magneticmaterial. which consists in coating the particles o! laid material with a uent oxidizing organic substance. and maturing the coatings by heat treatment while maintaining the' material in the powdered form.

85. The process oi insulating powdered magnetic material. which consists in coating the par ticlea ot said material with a iiuent China-wood oilvarniah,andmatuiingthecoatingsbyheat treatment while maintaining the material in the powdered form. 436.1"heprocesso!insulatingpowderedmagnneticmaterial.whichconsistsincoatingtheparticles of said material with iilms of a quick-oxidizing iiuent substancefand completing the oxidation ofsaid films by heat treatment. while maintaining-the material in the powdered form.

Il. Theprocessoi'makingacommin'utedmagnetic core. which consists in coating magnetic particleswithorganicinsulatingiilmamixingthe coatedparticlwithablndingmateriaLsoiteningaaidblndlngmatexialtorenderitplastic.and

` mbiectingtheentiremassiopreesureinamold whilesaidbinderisstillplastic.

88. 'Ihe process ci producing a comminuted magnetic core, whichconsistsincoating magnetic particleswith organic insulating nlmamixinga "binderwiththelnsulatedparticlestoproducea coherent mass. placing said coherent mass in a mold,renderingaaidmassplastic.andthensub iectingsaidmasstoapressureotirom5to25tons peraquareinch.depend.ingupontheshapeofthe core. to thereby reduce it to the desired volume.

39. The process o! producing a comminuted magnetic core, which consists in coating magnetic particieswith elastic insulating mms, mixing a -phenolic resin binder with the insulated par- -ticlestoprcducea.coherentmass.placingsaidcoherentmassinamold,subiectlngsaidmass.while at a temperature approximating loo C.. to a pressureot i'rcmbtotcnspersquareinch. dependingupontheshapeotthecoxatotherebyreduce ittothe dedredvolumaandthenbakingthecompressed core to thereby convert thephenolic resin binder into a chemically-stable bakelite.

4o. A magnetic material including magnetic particles, China-wood oil varnish and a phenolic resin.saidchina-woodoilvarnishbeinginquan titynotmorethan 8% oi the weight oi'the mate rial. and said phenolic resin being in quantity not more than 1% of the weight of said material.

4l. The process oi insulating powdered magnetic 'materiaL which consists in coating the particlesci said material with an organic substance, and then integrating the substance oi said coatings while maintaining the material in the powdered iorm. c

42. The process oi insulating powdered mag- `neticmaterial, whicheonsistsincoatingthe particles-o! saidmaterialwithaiinent organic substance. and then treating the coatings oi.' said substance to render them insoluble. while maintaining thematerial in the powdered form.

.hydrogen the 43. The process oi producing insulated magnetic particles, which consists in coating said particles with an organic substance. and sub- Jeeting said coated particles te heat treatment until the organic substance is so matured' as to constitute insulating elastic nlms on said particles.

44. 'the process ot making a core oi com minuted magnetic material, which consists in coating 'the particles oi said material with an 'elasticinsulating substance. mixing said insulated particles with a binder, compressing the mix,- ture in a mold. removing the molded compressed core and treating said core to release the compression oi said elastic subtance while the binder is in a softened state.

46. The process oi producing a magnetic core ot comminuted magnetic material. which consista in coating the particles of saidmaterial with an organic insulating substance dissolved in a solvent. evaporating said solvent while agitating the mixing said particles after the coating is dry with a binder. and subjecting saidmixturetoheatand pressurein amold at a temperature suiiicient to seiten said binder. i 100 46. The process oi producing a magnetic core o! comminuted magnetic material. which consists in coating the particles of said material with a iluent insulating substance containing volatile matter, evaporating the volatile matter 105 while the particles are being coated and agitated. and continuing the agitation until the particles arecoatedwithadryeiasticlmmixinga binder with said insulated particles, subjecting V themlxturetoheatandpressureina mold atllo a temperature suiiicient to soften the binder. removing the core from the mold and subjecting the core to treatment which slightly. increases its dimensions and materially reduces its electrical losses.

47. The process otmakinga core ci' comminuted magnetic material. which consists in lnsulating the individual particles o! said magnetic material, mixing the insulated particles with' an unmatured binder. binding said insulated par- 12D ticles together under pressure. and then'releasing the pressure and completing the' maturing o! said unmatured product.

48.1heprocessoimakingacoreoicomminuted magnetic material, which. consists in in- 125 sulating the individual particles o! said magnetic material, mixing said lnsulatedparticles with fa binder, landing 4said insulated particles together under pressure in a mold-to produce the core. removing said core from the mold in order to 123 release the pressure, and heat treating said core to slightly increase its dimensions and to materiallyreduceits electrical losses.

49. The processfoi decreasing the electrical losses oi' a material made from ilnely- 135 divided insulated magnetic particles. which consistsintreatingthematerialtosecure apermanent increase in its physical dimensions.

50. Powdered iron, chemically reduced as by hydrogen. the greater portion ci the particles 14a thereof being small enough to pass through a screenoimmeshesintheinchandbeingsubstantially insulated by an oxidized varnish.

5l. Powdered iron, chemically reduced as by hvdrogen. the particles thereof being small 1:5 enoughtopassthroughascreen ci 40o meshs totheinchandbeing insulatedbyanoxidired` China-wood oil varnish. 'y

62. Powdered iron. chemically reduced as by particles thereof being small 150 `'emug'h-tc pass through-a screen of 400 meshes and being substantially insulated by hydrogen. B11011811 to pas! 'to the inch and being substantially insulated by s''-chemicallystable `and presume-resisting materialof'organionatin'e.

M. Powdered iron. chemically redwed as by hydrogen. the particles whereof are substantially insulated by an elastic'substanoe which is of the order of 8% of the weight of'the powdered iron. .Powdered iron. chemically reduced as by hydrogen.consistmg of particles approximating iii-slss .005 millimeter. the particles being substantially insulated by thin nlms of insoluble, elastic material.

'56. Powdered iron,'chemically reduced as by hydrogen, consisting of particles approximating in sise .005 millimeter. the particles being substantially insulated by thin mms of organic ma terial chemically changed in situ.

51. A powdered magnetic material of low coercivity. consisting of particles approximating in size .005 millimeter. the particles being substantially insulated by thin illms of heat-resisting material.

58. A magnetic material including magnetic particles small enough to pass through a screen of 400 meshes to the inch, and a chemically-converted insulating organic substance in quantity of the order of 3% of the weight of the material.

59. Compressed magnetic material including individually-insulated magnetic particles of such dimensions and so closely related that said material has a factor of merit ranging from 3x10* to 25x10* at a frequency of 500 kllocycles in cores of various shapes.

s0. Compressed magnetic material including individually-insulated magnetic particles of such dimensions and so closely related that said materia! has an apparent permeability of the order of 8. and a factor of merit ranging from 3x10* to 25x10* at a frequency of 500 kilocycies in cores of various shapes.

61. Compressed magnetic material including individually-insulated magnetic particles oi' such dimensions that the majority of the particles will pass through ascreenhavlng 400meshestothe inch and so closely related that said material has a factor of merit ranging from 3 x 10' to 25x 104 at a frequency oi 500 kilocycles in cores of various 62. Compressed magnetic material including individually-insulated magnetic particles of such dimensions that the majority of the particles will pass through a screen having 400 meshes to the inch and so closely related that said material has an apparent permeability of the order of 8. and a factor of merit ranging from 3x10. to 25 x10-i at a frequency oi 500 kilocycles in cores of various shapes.

63. The process of producing a magnetic core of comminuted magnetic material, which consists in coating the' particles of said material with 'an organic insulating substance dissolved in a solvent. evaporating said solvent while agitating the particles, heat treating the insulated particles, mixing said particles with a binder after thecoatingisdryandsubiectlngsaidmixtureto heat and pressure in a mold at a temperature sumcient to soften said binder.

64. The process o! insulating powdered magnetic material. which consists in particles of said material with a iluent organic substance and then treating said co'atings to mature the same while maintaining the material in the powdered form.

d5. A compressed comminuted magnetic core unit having individually-insulated particles' and including a core and a shell of the same material adapted to receive between them a solenoidal coil. said core unit having a i'sctor of merit of the order of .111x104 at a frequency of 500 kilocycles.

The process of improving the electrical characteristics of a compressed comminuted magnetic core including a binder. andparticies lnsulated by an elastic substance. which consists in rendering the binder plastic and releasing the compression so as to produce an increase in the physical dimensions o! the core before the binder is solidiiied.

t1. The process of decreasing the electrical losses of a compressed comminuted magnetic body including bonded particlesinsulated by an elastic substance. which consists in maintaining the binder in a plastic conditon and releasing the compression so as to produce an increase in the physical dimensions of the body before the binder is matured.

68. The process of decreasing the electric losses of a compremed comminuted magnetic core including bonded particles insulated by an elastic substance, which consists in rendering the binder plastic and releasing the compression so as to produce an increase in the physical dimensions of the core before the binder is matured.

69. The process of improving the electrical characteristics of a compressed comminuted magll netic body including bonded particles insulated by an elastic substance, which consists in rendering the binder plastic and releasing the compresion so as to produce increased separation of the magnetic particles before the binder is solidified.

'10. The process of completing a moulded and compressed magnetic core having an elastic substance between the particles of said core, which consists in releasing the pressure in said core to thereby permit said elastic substance to separate 120 contacting particles of said core.

11. The process of making a magnetic material. which consists in coating magnetic particles with organic insulating iilins, mixing the coated par ticles with a binding substance, softening said '125 binding substance to render it plastic, and sub- Jecting the mixture to pressure while the binder is still plastic.

'12. The process oi decreasing the electrical loses of a compressed comminuted magnetic core -130 including a binder. which consists in rendering the binder plastic and thereby releasing the compression so as'to produce an increase in the physical dimensions of the core before the binder is solidied.

'13. The process of producing a comminuted magnetic core, which consists in coating magnetic particles with insulating films, mixing a binder with the insulated particles, placing said mixture o in a mold. subjecting said mixture while the' i binder is in a plastic condition to a pressure of from Ito 25 tons per square inch.- depending upon the shape oi' the core. to thereby reduce it to the desired volume. and then treating the core outside of the mold to permit it to expand so as to reduce its electrical losses.

'14. Compressed magnetic material including minute magnetic particles, characterized in that substantially all of said magnetic particles are 150 capable of passing through a l0-mesh screen and are insulated. and that the compressed material has an apparent permeability oi' not less than 'l and a resistivity oi at least l0 ohms per centimeter cube.

'15. Compressed magnetic material including insulated magnetic particles o! such dimensions and so closely related that said compressed material has an apparent permeability of not less than 'l and a resistivity of at least 10 ohms per centimeter cube.

76. Compressed magnetic material including magnetic particles approximating in size .005 millimeter. said particles being insulated and so closely related that said compressed material has an apparent permeability o! not less than 7 and a resistivity oi' at least l0 ohms per centimeter cube.

77. A compressed comminuted magnetic core containing magnetic particles line enough to pass through a screen having 400 meshes to the inch, said core having an eii'ective permeability of not less than 4 and a resistivity of at least l0 ohms per centimeter cube.

1,ess,eeo

78. The lprocess ot producing a Ioomxninuted magnetic core. which consists in individually insulating nneiy divided magnetic particles with organic ilims, mixing said insulated particles with a powdered binder. placing said mixture in a mould. subjecting said mixture to pressure while the binder is in a plastic condition to `thereby .reduce said mixture to the desired volume. and

WLADDIIR J. POLY'DOROFF.

CERTIFICATE or comisarios.

Patent No. 1,982,689. December 4, 1934 WLADIHIR J POLYDOROFF.

It is hereby certified that error appears in the printed specification oi the above numbered patent requiring correction ae follows: Page 3, first column, line 10, for "passing" read pressing; and that the said Lettere Patent should be read with this correction therein that the same may confor-r to the record of the case in the Patent Office.

Signed and sealed this 31st day of March, A. D. 1936.

Leslie Frazer (Seal) Acting Commissioner of Patents.

so 12s capable of passing through a l0-mesh screen and are insulated. and that the compressed material has an apparent permeability oi' not less than 'l and a resistivity oi at least l0 ohms per centimeter cube.

'15. Compressed magnetic material including insulated magnetic particles o! such dimensions and so closely related that said compressed material has an apparent permeability of not less than 'l and a resistivity of at least 10 ohms per centimeter cube.

76. Compressed magnetic material including magnetic particles approximating in size .005 millimeter. said particles being insulated and so closely related that said compressed material has an apparent permeability o! not less than 7 and a resistivity oi' at least l0 ohms per centimeter cube.

77. A compressed comminuted magnetic core containing magnetic particles line enough to pass through a screen having 400 meshes to the inch, said core having an eii'ective permeability of not less than 4 and a resistivity of at least l0 ohms per centimeter cube.

1,ess,eeo

78. The lprocess ot producing a Ioomxninuted magnetic core. which consists in individually insulating nneiy divided magnetic particles with organic ilims, mixing said insulated particles with a powdered binder. placing said mixture in a mould. subjecting said mixture to pressure while the binder is in a plastic condition to `thereby .reduce said mixture to the desired volume. and

WLADDIIR J. POLY'DOROFF.

CERTIFICATE or comisarios.

Patent No. 1,982,689. December 4, 1934 WLADIHIR J POLYDOROFF.

It is hereby certified that error appears in the printed specification oi the above numbered patent requiring correction ae follows: Page 3, first column, line 10, for "passing" read pressing; and that the said Lettere Patent should be read with this correction therein that the same may confor-r to the record of the case in the Patent Office.

Signed and sealed this 31st day of March, A. D. 1936.

Leslie Frazer (Seal) Acting Commissioner of Patents.

so 12s

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