US3186066A

US3186066A - Method of making magnetic cores

Info

Publication number: US3186066A
Application number: US158208A
Authority: US
Inventors: Jr James I Metzger
Original assignee: Wagner Electric Corp
Current assignee: McGraw Edison Co
Priority date: 1961-12-11
Filing date: 1961-12-11
Publication date: 1965-06-01
Anticipated expiration: 1982-06-01

Description

Junejl, 1965 J. I. METZGER, JR 3,186,056

METHOD OF MAKING MAGNETIC CORES Filed Dec. 11, 1961 2 Sheets-Sheet l Moan/rat.

James I. M512 45;? J2.

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June 1, 1965 J, 1. METZGER, JR

METHOD OF MAKING MAGNETIC CORES 2 Sheets-Sheet 2 Filed Dec. 11, 1961 FIG.5

FIG.4

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United States Patent '0 3,186,066 METHOD F MAKING MAGNETIC CORES James I. Metzger, Jr., St. Louis, Mo., assignor to Wagner Electric Corporation, St. Louis, Mo., a corporation of Delaware Filed Dec. 11, 1961, Ser. No. 158,208 3 Claims. (Cl. 29-15557) The present invention relates to a method of making magnetic cores. More particularly, the present invention relates to an improved method of making curved or wound-type magnetic cores from magnetic strip material.

Curved or Wound-type magnetic cores are usually formed by flatwise bending and assembling magnetic strip material to form an assembly of nested layers such as by Winding magnetic strip material onto a mandrel to form a coil. The strip material may be wound into a coil having approximately the same size and shape it is to have in the finally assembled apparatus, or it may be wound into a coil which must be formed to the desired shape. The coil is then annealed in the well-known manner to relieve stresses in the strip material and impart a permanent set thereto. The annealed coil is subsequently assembled with a conductive Winding structure to form a finished core.

As is well known to those skilled in the art, it is usually necessary in the manufacture of curved cores to provide spaces or a certain degree of looseness between turns in a portion of the annealed coil prior to its as sembly with a conductive winding structure. Such looseness permits the annealed coil to be assembled with the conductive winding structure without inducing excessive stresses in the magnetic material. For example, where an annealed coil is to be unwound and successive portions linked with a winding structure to form a finished core, the abovementioned looseness of turns is needed so that each of the turns in the finished core has substantially the same size, shape, and position it had in the annealed coil and Without having excessive stresses in magnetic material. Also, in cores having butt joints, such looseness permits the tight closing of the joints during assembly.

Various well-known forms of spacer means have been employed and these include metal shims, powder, and burnable materials such as string and paper. The use cost of material and handling, as well as additional storage space. Also, the use of burnable spacer means such as string or paper often results in contamination of the atmosphere by fumes or burnt particles about the annealing oven or at other work stations where the 'coil is handled. There is also danger in the case of liquid dielectric submerged induction apparatus of the contamination of the liquid dielectric by such burnt particles unless great care is taken. a

In accordance with the present invention, the use 0 the abovementioned spacer means in the manufacture of magnetic cores is not required and the abovementioned disadvantages can be avoided. In accordance with one aspect of the present invention, an improved method of making a magnetic core is provided which includes the steps of forming deformations in magnetic material,

assembling the strip material into an assembly of nested layers having spaces between layers-in a portion of the I assembly as a result of the deformations, and substantially removing the deformations in the material in that portion of the assembly to provide the desired spaces or looseness between layers in another portion of the assembly. a I It is therefore an object of the present mvention to provide an improved method of making a magnetic core I of the abovementioned spacer means requires additional wherein the abovementioned disadvantages of employing separate spacer means can be avoided.

Another object is to provide a new and improved method of making a curved magnetic core without the necessity of employing separate spacer means and wherein undesirable stresses in the core material are avoided.

Still another object is to provide a new and improved method of making a non-circular Wound-type magnetic core, which method is relatively simple and efiicient.

Still another object is to provide an improved method of making a generally rectangular wound-type magnetic core without the necessity of employing separate spacer means and wherein the core produced thereby has a relatively high space factor.

These and other objects and advantages of the present invention will become apparent from the following description and accompanying drawings in which:

FIG. 1 is a diagrammatic elevational view illustrating the processing of magnetic strip material and the winding thereof into a coil,

FIG. 2 is a fragmentary perspective view of the magnetic strip material indicated at 10a in FIG. 1,

FIG. 3 is a front elevational view illustrating a coil of strip material formed in the manner shown in FIG. 1, and in position for annealing,

FIG. 4 is a front elevational view of the coil of strip material shown in FIG. 3, but after it has been annealed,

FIG. 5 is a view illustrating a step in one method of linking an annealed coil of strip material with a preformed winding,

FIG. 6 is a cross-sectional view of a preformed winding linked by a magnetic core made in accordance with the present invention,

FIG. 7 illustrates a modified manner of annealing a coil of strip material, and

FIG. 8 illustrates a coil annealed in the manner indicated in FIG. 7.

Referring now to the drawings and particularly to FIGS. 1 and 2, magnetic strip material 10, such as grain oriented silicon steel strip, is first processed and thereafter successive portions are flatwise curved or bent and assembled together in nested relation. As shown, the magnetic strip material 10 is provided with deformations as it is drawn from a supply spool 14 by passing it through a metal forming mechanism 15 which is shown as including a pair of similar

deforming rollers

16 and 18 mounted for rotation on a standard 20 fixed to a base or floor 22. Preferably, the strip material 10 is passed between the

rollers

16 and 18 as it is wound onto a mandrel 24 supported for rotation by a standard 26 fixedly mounted to the base 22. As indicated by the arrows in FIG. 1, mandrel 24 is rotatable in a clockwise direction by any suitable-driving meanswhile the two

rollers

16 and 18 are rotated in opposite directions with respect to each other as the strip material passes therebetween.

The rollers are preferably rotated by the strip material itself asthe material is wound onto the mandrel, although the rollers may be driven by auxiliary driving means which may be synchronized with the rotation of the mandrel.- e

valley-like depressions 34.. The strip material is thus shown undulated or corrugated by the rollers 16..and

. embodiment.

18,'the undulations orcorrugations being exaggerated in the drawing for clarity of illustration. The bosses 32 extend outwardly of the plane of the strip material and entirely across the width of the strip in the illustrated Preferably, the metal forming mechanism 15 imparts similar equally spaced bosses or continuous undulations substantially throughout all of the strip material used in making a magnetic core.

The mandrel '24 is shown generally rectangular in shape and has an outer periphery which, in this case, substantially defines the inner periphery that the finished core is to have. The thus far processed strip material a is flatwise spirally wound around the mandrel until the a desired amount of material has been transferred'thereto.

The wound coil of corrugated strip and mandrel 24 may then be removed from the standard 26. In order to prevent unwinding of the coil, suitable retaining means turns of the coil, these spacesbeingindicated at '36. In

forming the corrugated strip material 10a around 'the mandrel it has a tendency to flatten out, especially as it is bent aroundthe corners and the opposite short ends of the mandrel. Thus, the spaces 36 between turns will be substantially greater in the-opposite longer sides or

legs

38 and 40 than in the opposite short sides or

ends

42 and 44.

The coil of corrugated strip material, as seen in FIG. 3, may now be further processed to remove the corrugations or bosses, as well as spaces 36 between layers in the longer sides thereof, to thereby provide the desired looseness or space between turns at the ends or corners of the coilf This may be done by applying opposing forces to the opposite longer sides of the coil to flatten the layers in the sides, for example, vby placing the coil, while on the mandrel, in a press to compress the coil sides, and then annealing thecompressed coil.

' However, the corrugations and spaces between layers in the sides of the coil are preferablyremoved with the corrugated strip material at a temperature sutficient to soften the material, and this is preferably accomplished during the strain-relief annealing treatment. The-wound coil of corrugated strip material 10a on mandrel 24' is preferably annealed with one of its longer sides above the other as illustrated in FIG. 3. As shown, the longitudinal axis of the coil, which is indicated by a broken line 46, is parallel to a horizontal base 48, while" the transverse axis, indicated by a broken line 49, is normal to the base. The base 48 may be a steel supporting plate used to transport the coil into an annealing oven, the base being disposed in the oven horizontally or parallel to the floor of the oven. The coil of strip material is annealed byheating it to a suitable temperature which may be about 1600" F.

The coil is under compression in the annealing oven due to the force of gravity acting on the mass thereof.

In addition to the weight of the strip material in the coil,

any additional forces, such as the weight of a. compression plate 50 and/or any other compressive force applied thereto, will, of course, contribute to the total compressive force'acting' on the coil. Depending on the size of the coils, a suitable number of such wound coils may be placed in the annealing oven together, each. in the position shown in FIG. 3. .These coils may be disposed in rows with coils in each row stacked one upon the other. 7

During the annealing process, the strip material becomes supple and the deformations and spaces between the layers in the

sides

38 and 40 are readily removed as the layers are flattened and forced relatively tightly against one another in the sides due to the forces of gravity. The coil after it has beenysuitably'annealed is illustrated in FIG. 4. It is seen that the layers of strip material in the longer sides of the annealed generally rectangular coil are straight and in close contact engagement with one another and with the longer sides tightly against the mandrel. The spaces 36, which were present in the longer sides 38 and 40 before annealing, as shown in FIG. 3, are absent after annealing, as shown in FIG. 4. It will be noted however, that there are suitable spaces 51 between layers at the short ends and adjacent the corners of the coil. The spaces 51 are principally a result of the removal of space from the sides of the coil during annealing. Thus, supporting the coil in the annealing oven under compression or with pressure on the sides removes the deformations in the strip material and effects the transfer of spaces from the sides to the ends and corners of the coil.

Because the corrugations or bosses 32 in the strip material 10a in the preferred embodiment extend across the full width of the material, the forming thereof does not undesirably stress or tear the material, and such corrugations are subsequently readily removed.

While a particular pre-winding processing of magnetic strip material has been shown in the drawings by way of illustration, it will be apparent to those skilled in the art that other forms of deformations and methods of forming them may be employed. For example,

" spacing of assembled layers.

As previously mentioned herein, by providing suitable spaces between layers'in the ends or adjacent the corners of the annealed coil, such as spaces 51 in FIG.

4, the coil can be readily assembled with an inductive winding structure without introducing undesirable stresses therein. 7

The annealed coil, after it is removed from the annealing oven and cooled, may be linked with a preformed winding structure, in accordance with one method, by first unwinding the coil and cutting through the strip material at spaced intervals toprovide a plurality of sections. FIG. 5 shows a plurality of nested

sections

52, 54 and 56, each section having a length equal to approximately two turns of the coil. These sections of strip material may then be linked with an insulated conductive winding structure, such as indicated at 58 in FIG. 6. The winding structure 58 represents a winding structure of a transformer and includes a pre-formed primary winding 60 and a divided pre-formed secondary winding 62, the windings forming a window- 64. The sections of strip material, starting with the innermost section 52, are successively threaded through the window 64 of the winding structure, each being collapsed around closed magnetic core having turns substantially the same size, shape, andrelative position as they had in the annealed coil. In this instance, the core has a plurality of butt joints 66 bridged by an adjacent unbroken layer. The winding structure shown in FIG. 6 is linked by two such cores, one being shown in phantom.

Because of the looseness or space between turns in the annealed coil shown in FIG. 4, the abovementioned steps of unwinding the coil and threading the successive sections thereof through the window of the windingstructure can be accomplished without inducing excessive stresses in the strip material. Also, the resulting core will have tight butt joints and the lamination layers in same manner as the pre-annealed coil of corrugated strip material shown in FIG. 3, and like reference numerals are used in the drawings to denote like parts. In FIG. 7, the coil is provided with restraining means for limiting its lengthwise dimension, which dimension is along the longitudinal axis 46, during the subsequent processing of the coil. As shown in FIG. 7, a rectangular frame or clamp 70 extends around the center of the coil and encircles the opposite short ends thereof. The frame 70 includes two opposite parallel metal side plates 72 (one shown) and two opposite metal end plates 74, the plates being connected at their ends such as by Welding. The side plates 72 extend parallel to the longitudinal axis 46 and maintain the end plates 74 in fixed relation to each other.

The coil may then be annealed with the longer sides of the coil under pressure such as by placing the coil in the annealing oven while in the position shown in FIG. 7, which is the same coil position previously described in connection with FIG. 3. During annealing, as strip material softens, the compressive forces resulting from the force of gravity effects the removal of the corrugations in the strip material and the transfer of strip material and spaces from the longer sides to the corners and ends of the coil. In this case, however, since the frame limits the lengthwise dimension, the resulting annealed coil has a configuration which more closely approaches a true rectangle. The annealed coil is illustrated in FIG. 8, and as seen therein, has substantially straight ends, indicated at 76 and 78, with the desired spaces indicated at 80 be tween layers at or adjacent each of the corners of the coil.

By limiting or restraining the lengthwise dimension of a coil having spaces between layers in the sides thereof, such as by frame 70, the over-all length of the core will be somewhat shorter and the space factor will be high. Various types of frames for this purpose are, of course, possible. For example, in some cases a pair of end plates, such as plates 74, may be clamped against their respective coil ends by one or more surrounding conventional banding straps. Also, where a number of coils are placed in the annealing oven together, such restraining means may conveniently include a plurality of frames, such as shown in FIG. 7, connected together.

The annealed coil shown in FIG. 8 may be linked with a conductive winding structure in any suitable manner. For example, this annealed coil may be assembled with a conductive winding in the manner previously described in connection with the coil shown in FIG. 4.

While the invention has been described in detail, it is to be understood that the description is intended as illustrative rather than limiting as various modifications are possible within the scope of the invention which is defined in the appended claims.

What is claimed is:

1. The method of making a wound type magnetic core from a strip of magnetic material having a predetermined length and thickness and a width greater than the thickness thereof, said strip being defined in thickness by a pair of opposed surfaces and in width by a pair of opposed side edges which respectively intersect with said surfaces, comprising the steps of forming a plurality of spaced ridges each continuously extending entirely across the Width of said strip and substantially normal to said side edges to predeterminately shorten the length of said strip and prevent deleterious stretching of said strip in a direction substantially normal to said surfaces,

winding the shortened length of strip into a closed coil having a plurality of superposed layers of said strip, said coil having opposed side and end portions with adjacent superposed layers in at least one side por-.

tially remove said ridges fromthe adjacent superposed layers thereof by the force of gravity and lengthen said adjacent superposed layers thereof to predeterminately provide spacing between adjacent superposed layers in another portion of the coil, uncoiling the strip from said annealed coil and cutting the strip into a plurality of sections,

and subsequently assembling said sections with an inductive winding to form said magnetic core.

2. The method of making a wound type magnetic core for a preformed inductive winding from a strip of magnetic material having a predetermined length and thickness and a width greater than the thickness thereof, said strip being defined in thickness by a pair of opposed surfaces and in width by a pair of opposed side edges which respectively intersect with said surfaces, comprising the steps of transversely bending said strip successively in different directions to produce a plurality of parallel alternating ridges and valleys substantially throughout the entire length of said strip with each extending substantially normal to said side edges continuously across the entire width of said strip to predeterminately shorten said strip and prevent deleterious stretching of said strip,

winding the shortened strip onto a mandrel to form an oblong generally rectangular closed coil having -a plurality of superposed layers of said strip, the coil having opposed relatively long sides and opposed relatively short ends with substantially all of the layers in at least said opposed sides spaced from each other by said ridges and valleys,

annealing the coil by positioning said coil While on the mandrel in an annealing oven on one of said sides with the other of said sides above said one side, and Weighting said other side, so that said ridges and valleys are substantially removed and the layers in said sides are lengthened by the force of gravity while in the oven to provide spacing between layers in said ends of the coil,

unwinding said annealed strip from the mandrel,

and reassembling the annealed strip into a coil sur rounding a portion of a preformed inductive winding to form said magnetic core. 3. The method of making a wound type magnetic core from a strip of magnetic material having a predetermined length and thickness and a width greater than the thickness thereof, said strip being defined in thickness by a pair of opposed surfaces and in width by a pair of opposed side edges which respectively intersect with said surfaces, comprising the steps of forming a plurality of alternating ridges and valleys in said strip each extending normal to said side edges and continuously across the entire width thereof to predeterminately shorten the length of said strip and prevent deleterious stretching of said strip in a direction normal to said surfaces,

winding the shortened strip onto a rotating generally rectangular mandrel to form a closed coil of a plurality of superposed layers of said strip having opposed sides and opposed ends with the layers in said sides of said coil spaced from each other by said ridges and valleys but with said ridges and valleys in the strip at the corners of the coil being substantially removed as a result of bending the strip around the corners of the mandrel during the winding of the strip thereon,

. annealing said coil by supporting said coil and mandrel in an annealing oven on one of its sides with the other side above said one side and with restraining means adjacent the ends of the coil to prevent layers in the ends of the coil from moving away from the mandrel so that said ridges and valleys are substantially removed and the layers in said sides are lengthened while in the oven by the 'force'of gravity to provide spacing between layers at-the corners of the coil,

' removing the c'oil'and mandrel from the annealing oven and uncoilingthe annealed strip from the mandrel, and reasseinbling the annealed strip around a portion of a preformed inductive winding to form raj-magnetic core having substantially straight'opposedsides and ends.

7 i s References'Cited by'th'e Exa'miher UNITED STATES PATENTS 705,935 7/02 Lee et a1. 336-213 X 2,305,650 12/42 Vienneau 29-15557 2,907,967 10/59 Smith 29-15557 X 2,969,585 1/61 Smith 29-15557 3,027,628 4/62 Wilk et a1. 29-155.57

JOHN F. CAMPBELL, Primary Examiner.

Claims

2. THE METHOD OF MAKING A WOUND TYPE MAGNETIC CORE FOR A PREFORMED INDUCTIVE WINDING FROM A STRIP OF MAGNETIC MATERIAL HAVING A PREDETERMINED LENGTH AND THICKNESS AND A WIDTH GREATER THAN THE THICKNESS THEREOF, SAID STRIP BEING DEFINED IN THICKNESS BY A PAIR OF OPPOSED SURFACES AND IN WIDTH BY A PAIR OF OPPOSED SIDE EDGES WHICH RESPECTIVELY INTERSECT WITH SAID SURFACES, COMPRISING THE STEPS OF TRANSVERSELY BENDING SAID STRIP SUCCESSIVELY IN DIFFERENT DIRECTIONS TO PRODUCE A PLURALITY OF PARALLEL ALTERNATING RIDGES AND VALLEYS SUBSTANTIALLY THROUGHOUT THE ENTIRE LENGTH OF SAID STRIP WITH EACH EXTENDING SUBSTANTIALLY NORMAL TO SAID SIDE EDGES CONTINUOUSLY ACROSS THE ENTIRE WIDTH OF SAID STRIP TO PREDETERMINATELY SHORTEN SAID STRIP AND PREVENT DELETERIOUS STRETCHING OF SAID STRIP, WINDING THE SHORTENED STRIP ONTO A MANDREL TO FORM AN OBLONG GENERALLY RECTANGULAR CLOSED COIL HAVING A PLURALITY OF SUPERPOSED LAYERS OF SAID STRIP, THE COIL HAVING OPPOSED RELATIVELY LONG SIDES AND OPPOSED RELATIVELY SHORT ENDS WITH SUBSTANTIALLY ALL OF THE LAYERS IN AT LEAST SAID OPPOSED SIDES SPACED FROM EACH OTHER BY SAID RIDGES AND VALLEYS, ANNEALING THE COIL BY POSITIONING SAID COIL WHILE ON THE MANDREL IN AN ANNEALING OVEN ON ONE OF SAID SIDES WITH THE OTHER OF SAID SIDES ABOVE SAID ONE SIDE, AND WEIGHTING SAID OTHER SIDE, SO THAT SAID RIDGES AND VALLEYS ARE SUBSTANTIALLY REMOVED AND THE LAYERS IN SAID SIDES ARE LENGTHENED BY THE FORCE OF GRAVITY WHILE IN THE OVEN TO PROVIDE SPACING BETWEEN LAYERS IN SAID ENDS OF THE COIL, UNWINDING SAID ANNEALED STRIP FROM THE MANDREL, AND REASSEMBLING THE ANNEALED STRIP INTO COIL SURROUNDING A PORTION OF A PREFORMED INDUCTIVE WINDING TO FORM SAID MAGNETIC CORE.