US3608348A - Wound magnetic core and method of forming same - Google Patents

Abstract

A WOUND CORE HAVING A PLURALITY OF TURNS OF MAGNETIC STRIP MATERIAL WITH A PREDETERMINED AMOUNT OF LOOSENESS BETWEEN THE SUPERPOSED TURNS, AND AT LEAST ONE SPACE BETWEEN ADJACENT SUPERPOSED TURNS HAVING A DEGREE OF LOOSENESS PREDETERMINATELY GREATER THAN THAT BETWEEN THE OTHER TURNS. THE SUPERPOSED TURNS OF SAID WOUND CORE ARE ROTATED IN ONE DIRECTION TO OBTAIN THE PREDETERMINED LOOSENESS AND THEN ROTATED IN THE OTHER DIRECTION TO REDISTRIBUTE A PORTION OF SAID LOOSENESS INTO A DESIRED SECTION OF THE CORE.

Description

Sept. 1971 J. a. MKEE 3,603,343

WOUND MAGNETIC CORE AND METHOD OF FORIING SAIE Filed July 7,1969 2 Sheets-Sheet 1 mvsmon JOHN B. McKEE J. B. M KEE Sept. 28, 1971 WOUND MAGNETIC CORE AND METHOD OF FORMING SAME 2 Sheets-Sheet 2 Filed July '7, 1969 22 &

FIG. 8-

FIG- 10 lllllll FIG. 13

INVENTOR JOHN B. McKEE FIG. 12

United States Patent ice 3,608,348 WOUND MAGNETIC CORE AND METHOD OF FORMING SAME John B. McKee, Glendale, Mo., assignor to Wagner Electric Corporation, Newark, N.Y. Filed July 7, 1969, Ser. No. 839,300 Int. Cl. B21c 47/02 U.S. Cl. 72-146 12 Claims ABSTRACT OF THE DISCLOSURE A wound core having a plurality of turns of magnetic strip material with a predetermined amount of looseness between the superposed turns, and at least one space between adjacent superposed turns having a degree of looseness predeterminately greater than that between the other turns. The superposed turns of said wound core are rotated in one direction to obtain the predetermined looseness and then rotated in the other direction to redistribute a portion of said looseness into a desired section of the core.

This invention relates to wound magnetic cores for induction apparatus and to a method of making such magnetic cores of the wound type.

In the past, wound cores were formed by winding a plurality of superposed turns of continuous magnetic strip material onto a rotatable mandrel into an annular or ringshaped core which was subsequently reshaped into the desired substantially rectangular form and annealed not only to relieve the stresses therein but also to impart a permanent set thereto in said desired reshaped form. After annealing, the reshaped core Was unwound and simultaneously cut into sections comprised of a desired number of turns, and such out turn sections were then rewound or repositioned in their predetermined order into an assembled finished core about a conductive coil structure.

During the initial winding of the strip material, a certain degree of looseness or slack between the superposed turns thereof was provided by the well-known method of inserting sacrificing material, such as nylon thread, paper, or other shims or spacers, between the superposed turns, or by predeterminately crimping the strip material itself. Such looseness in the core was, of course, provided in an attempt to compensate for excessive stress imparted to the out turn sections upon the subsequent reassembly thereof about the coil structure so that the finished core of the reassembled cut turn sections on the coil structure approximated the size, shape and position of the annealed core prior to the unwinding and cutting of said turn sections. One of the disadvantageous or undesirable features of such past cores and methods of assembly thereof was that it was virtually impossible to obtain the correct or desired amount of slack in each core which is necessary for proper reassembly of the cut turn sections thereof because of the great variance in the thickness of the strip material, the variance in the tension used to initially wind the strip material, and the variance in the slidability between the turns of the strip material. Too much slack between the adjacent turns of said past cores was undesirable since it increased the means length of each turn and made the core larger than necessary or desired. Another disadvantageous or undesirable feature of the previous cores and the previous methods of imparting slack or looseness to the core was that a substantially uniform space factor was usually provided between the superposed turns. For instance, those skilled in the art have found from experience that such a uniform space factor is satisfactory only within a stack height range approximating one-half inch to three-fourths of an inch of superposed turns. Within this range, the adjacent ends of the successive cut 3,668,348 Patented Sept. 28, 1971 turn sections would abut each other or so closely approximate each other as to form a butt joint which afforded the core desirable magnetic characteristics and a low destructability factor. The reason for such approximate stack height range is, of course, that the out turn sections within such range are not overstressed when rewound into finished position about the coil structure; however, as the stack height increased, the out turn sections were stressed in excess of a desired amount as they are rewound into finished position about said coil structure. Therefore, due to the overstressing in the reassembly of the cut turn sections, another disadvantageous or undesirable feature was that said cut turn sections would not return to their annealed shape resulting in a gap between the adjacent ends of the out turn sections, and as the stack height increased in excess of the range, said gaps became progressively larger which, of course, adversely affected the magnetic characteristics and destructibility factor of the core. Still another disadvantageous or undesirable feature was that as the stack height increased in excess of the range, the end or yoke portion of the core in which the gaps are formed built up; therefore, the stack height of the core in said yoke became appreciably greater than that in an adjacent leg portion, and this was due to the inability of the out turn sections to return to their annealed shape upon the aforementioned overstressing thereof during as-.

bility thereof was adversely affected. Furthermore, still another disadvantageous or undesirable feature was that a spongy core would also slump appreciably when support mg its own weight to further depart from the desired substantially rectangular configuration.

The principal object of the present invention is to provide a wound core and a method of making such wound core which overcomes the aforementioned disadvantageous and undesirable features of the past wound cores and the past methods of forming wound cores, as well as other disadvantageous and undesirable features thereof, and this and other advantageous and desirable features of the present invention will become apparent in the specification which follows.

Briefly, the present invention includes a wound core having the looseness between the adjacent superposed turns of magnetic strip material predetermined in progressively increasing amounts in a direction from the inner perimeter toward the outer perimeter of said core. Another aspect of the invention provides at least one space gap selectively provided at a desired position in the stack height of said turns having a degree of looseness greater than that between the other of said turns. The invention also includes a method of winding a plurality of superposed turns of magnetic strip material to form an annular core substantially without slack between said turns, rotating said turns to obtain predetermined slack distribution in progressively increasing amounts in a direction from the inner perimeter toward the outer perimeter of said core throughout at least a portion of the core.

In the drawings which form a part of the specification and wherein like numerals refer to like parts wherever they occur:

FIG. 1 is a diagrammatic view illustrating the winding of magnetic strip material into a wound core;

FIG. 2 is an enlarged elevational view of the wound core of FIG. 1 illustrating the displacement of the outer turn to predetermine the core outside diameter and the amount of slack to be inserted into said core;

FIG. 3 is an elevational view showing the core of FIG. 2 with the turns thereof in their adjusted unwound positions upon rotation of the core turns in a direction opposite the winding direction;

FIG. 4 is a greatly enlarged fragmentary view taken from FIG. 3 illustrating the predetermined space factor or slack distribution between the adjacent superposed core turns in their adjusted unwound positions;

FIG. 5 is a partial sectional view of the wound core showing a tool for rewinding the core turns in the winding direction;

FIG. 6 is a greatly enlarged fragmentary view illustrating the predetermined space factor or slack distribution between the adjacent superposed core turns and also the space gaps provided in said core upon the rewinding of said core turns in the winding direction onto the tool;

FIG. 7 is an elevational view of the core with the turns thereof in their rewound positions upon the rewinding of said turns onto the tool;

FIG. 8 is an elevational view of another wound core embodying the present invention in which the outer turn is wound to a predetermined diameter and the inner turn thereof is slightly greater than a preselected inner diameter of said core;

FIG. 9 is an elevational view showing a finished wound core placed in a press for the shaping thereof;

FIG. 10 is an elevational view illustrating the shaping of the finished wound core into the desired rectangular shape by the press;

FIG. 11 is a greatly enlarged fragmentary view taken from FIG. 10 illustrating the redistribution of the space gaps into the corners of the shaped core;

FIG. 12 is an elevational view illustrating the annealed and out turn sections which are unwound from the shaped core; and

FIG. 13 is a partial sectional view of the conductive winding structure linked by a magnetic core made in accordance with the present invention.

Referring now to the drawings and in particular to FIG. 1, magnetic strip material 1, such as grain oriented silicon steel strip, is drawn from a supply spool 2 thereof in a winding direction shown by the directional arrow onto a driven, rotatable, annular mandrel or arbor 3 forming a wound core 4 of superposed, spirally wound turns 5, and a desired turn tension is maintained during winding by passing said strip material through an adjustable tensioning device, such as opposed rollers 6 in a manner well known in the art. The leading end of the strip material is bent at 5a as said strip material is lead onto the arbor 3 from the supply spool 2, and, of course, the tensioning of the strip material 1 during winding produces the desired effect of substantially eliminating slack or space between the turns 5 of the initially wound core 4. In one aspect of the invention, the diameter of the arbor 3 substantially conforms to the desired inside or window diameter or perimeter for the wound core 4, and said core is wound to a predetermined stack height of turns 5 afiording a desired or predetermined cross-sectional turn area and also the desired pounds of strip material 1 for the particular core size. As mentioned above, the inside diameter of the wound core 4 is maintained to the desired predetermined diameter, and upon winding the predetermined stack height of turns 5, the outside diameter or perimeter of said core is predeterminately undersized. When the pre determined stack height of turns 5 is so wound on the arbor 3 to form the desired core 4, the strip material is severed by cutters 7 in a manner well known in the art, and said core is removed from said arbor.

After the initial winding of the core 4, the free end 8 of the outside turn 9 of said core is then displaced or set-ofl. a predetermined distance or amount S relative to the next adjacent turn 10, as shown in FIG. 2, and such displacement represents the predetermined amount of looseness or slack to be subsequently inserted or placed in the core and is substantially equal to the difference between the undersized outside perimeter or circumference of said core as wound and the predetermined outside perimeter or circumference desired in the finished core. In other words, the outside diameter or perimeter of the core 4 as initially wound on the arbor 3 was predeterminately undersized, as mentioned hereinbefore, so that the displacement S of the free end 8 of the outer turn 9 relative to the next adjacent turn 10 not only predetermines the amount of slack to be inserted into said core but also adjusts or increases the outside diameter to the predetermined dimension desired for the finished core. In order to maintain the outside turn free end 8 in its displaced position, the outside turn 9 is restrained or is connected by suitable means, such as the tape 11, to the adjacent turn 10; however, albeit not shown, such connection could, if desired, be accomplished by other means, such as spot welding or clamping, or the initially wound core could be placed in a retaining ring having the desired outside diameter of the finished core. It should be noted that the bent or free end 5a of the inside turn 13 of the coil is unrestrained against movement relative to its next adjacent turn 14.

With the outside and next adjacent turns 9, 10 so connected, the-core 4 is rotated in a direction opposite to the winding direction indicated by the arrow to distribute the slack effected by the displacement S of the outer turn 8 throughout said core, as shown in FIGS. 3 and 4. In other words, a rotative force is applied onto the outside turn 9 to initiate the rotation of the interconnected outside and next adjacent turns 9, 10 of the core 4 in the direction opposite to the arrow and continued rotation effects a partial and successive unwinding and realignment of the superposed turns 5 radially outwardly toward new or adjusted positions commensurate with the adjusted outside diameter of the core 4 which was established upon the predetermined displacement of the outside turn free end 8, and at the same time, the slack occasioned upon the predetermined displacement of said outside turn free end is distributed in a substantially uniform manner or substantially equal amounts between each of the adjacent superposed turns 5 in their adjusted positions. For instance, as the core 4 is being rotated, the outermost of the turns 5 move radially outwardly in succession; therefore, as core rotation progresses, the successive radially outward movement of said turns effects a greater mass for rotation and such a greater mass effects a greater inter-turn friction or drag opposing rotation. The increasing drag opposing the mass of said turns 5 being rotated effects a progressively varying tensioning force which controls the substantially uniform manner in which the slack is inserted into the core. For instance, during the initial rotation of the core 4, there is very little drag since the mass of the turns 5 being rotated, i.e., those turns which have been unwound radially outwardly to their adjusted positions, is quite small compared to the rest of the mass of the core turns which are substantially stationary; therefore, the outermost of said turns are unwound rather tightly in their adjusted positions with respect to each other, but as the mass of the radially outer turns 5 being rotated increases upon further rotation, the drag thereof is also proportionally increased to eifect successively greater distances between adjacent turns in a radial direction from the outer toward the inner perimeter of the core 4. In other words, the increasing drag occasioned upon the successive unwinding movement of the turns 5 radially outwardly toward their adjusted positions effects a space factor or radial distance between each adjacent turn which increases incrementally in a radial direction from the outside toward the inside perimeter of the core, as shown greatly exaggerated in FIG. 4; therefore, due to the incrementally increasing space factor, the predetermined amount of slack is inserted or distributed between each adjacent turn in substantially equal or uniform amounts throughout the stack height 5. It should be noted that while the outside diameter of the core 4 was adjusted to the desired dimension, the distribution of the predetermined amount of slack into said core does not appreciably increase or adjust the predetermined inside perimeter or diameter as wound on the arbor 3.

A winding tool 15, FIG. 5, is provided with a round disc or base portion 16 having a circumference and diameter substantially equal to the desired predetermined inside circumference and diameter of the core 4. With the predetermined amount of slack uniformly distributed throughout the core 4 and turns 5 thereof in their adjusted positions, as previously described, the disc portion 16 of the tool is inserted into the inside perimeter or window portion of the core 4 into interfering or driving engagement with the inner turn 13 of said core. As shown in FIG. 5, the tool 15 may be provided with a slot 16a in the periphery of the tool disc 16, and the free end 5a of the inside turn 13 is inserted into restraining or driving engagement with said slot to drivingly engage said tool with said inside turn; however, other means, such as an expanding tool or a power-driven tool or the like, are contemplated to effect such driving engagement.

Rotation of the tool 15 in the winding direction with the free end 5a of the inner turn 13 restrained in the tool slot 16a applies a rerotative force on said inside turn to effect a partial and successive rewinding and alignment of the turns 5 from their adjusted positions radially inwardly toward new or rewound positions about the disc portion 16 of said tool which defines the desired or predetermined inside perimeter of the core 4. For instance, as the tool 15 is being rotated, the innermost of the turns 5 move radially inwardly in succession toward the inner turn 13 in its rewound position, and as such rotation progresses, the successive radially inward movement ofsaid turns effects a greater mass for rotation and such increasing mass for rotation effects an increasing inter-turn friction or drag; therefore, due to the proportioned relationship between the increasing mass and drag, a progressively varying or increasing tensioning force is established which controls the space factor and distribution of the slack between the adjacent turns in their rewound positions. During the initial rotation of the tool 15, there is very little drag since the mass of the turns 5 being rotated, i.e., those turns which have been rewound radially inwardly to their rewound positions, is quite small compared to the rest of the mass of the core turns which are substantially stationary; therefore, the innermost of said turns are rewound on said tool rather tightly in their rewound positions with respect to each other, but as the mass of the rewound turns increases, the drag thereof is also proportionally increased to effect successively and incrementally greater distances between each of said adjacent rewound turns in a radial direction from the inner perimeter toward the outer perimeter of the core 4. In other words, the increasing drag occasioned upon the successive rewinding movement of the turns 5 radially inwardly toward their rewound positions efiects a space factor or radial distance between each adjacent rewound turn which increases incrementally in a radial direction from the inside perimeter toward the outside perimeter of the core, as shown in FIG. 6; therefore, since the space factor between each adjacent rewound turn is increased incrementally in the radially outward direction, it is apparent that the predetermined amount of slack is redistributed between each adjacent rewound turn in an increasing manner or in progressively increasing amounts also in the direction from the inner perimeter toward the outer perimeter of the core 4.

In view of the foregoing, the amount of slack distributed between the adjacent rewound turns and the space factor therebetween is, of course, less than that between the other turns 5 of the core 4 which are still in their adjusted positions; therefore, slack take-up is occasioned upon the successive radially inward movement of the turns 5 from their adjusted positions to their rewound positions creating a slack or space gap, indicated generally at 17 in FIG. 7, which can be selectively positioned and maintained at any diameter of the stack height of the turns 5 as desired. During the successive rewinding of the turns 5 into their rewound positions on the tool 15, the slack gap 17 moves radially outwardly, and when said slack gap approaches a desired diameter or preselected point in the stack height of the turns 5, the operator can retain or maintain said slack gap at said preselected point or diameter of the stack height by temporarily inserting a clamp or spacer, or other such restraining means, into said slack gap or by holding or pressing the side edges of the adjacent turns on the radially inner and outer sides of said slack gap with his fingers or other restraining object. In this manner, the slack gap 17 is positioned at the preselected stack height, and thereafter continued rotation of the tool 15 will again initiate the successive rewinding of the turns 5 from their adjusted positions toward their rewound positions adjacent the slack gap 17 to redistribute the remaining slack in the core 4 in the progressively increasing manner, as described above. Although only one slack gap 17 is described, the operator can split up or distribute the slack in the slack gap 17 into other smaller slack gaps, such as that shown at 17a, at several preselected points or diameters in the stack height of the turns 5 in the same manner as previously described wherein said space gaps 17, 17a divide the stack height of said turn into turn groups indicated generally at 18, 19 and 20. The space gaps 17, 17a are inserted into the core 4 at various preselected diameters thereof to provide re-indexing or new reference points or diameters which effect and insure a desirable and tight-fitting core upon the assembly thereof with a conductive winding structure, as discussed hereinafter.

Referring now to FIG. 8 in another aspect of the invention, another core 104 is wound in substantially the same manner and has substantially the same component parts as the previously described core 4 with the following exceptions. The arbor 3 of FIG. 1 on which the core 104 is wound is provided with a diameter or circumference which is slightly greater than the preselected inside diameter or perimeter of the core 104; therefore, the inside diameter or perimeter of said core as originally found is slightly oversized and the outside diameter or perimeter thereof is wound to the predetermined or desired perimeter of the finished core. In order to maintain the outside turn free end 8 in its wound or predetermined position, the outside turn 9 is restrained or is connected by suitable means, such as the tape 11, to the next adjacent turn 10; however, albeit not shown, such connection could, if desired, be accomplished by other means, such as spot welding or clamping, or the initially wound core could be placed in a retaining ring having the desired or predetermined outside perimeter of the finished core.

In this aspect of the invention, the operator may elect to rotate the turns 5 of the core 104 from the inside diameter thereof by the use of the tool 15 wherein the disc portion 16 thereof is provided with a perimeter which defines the predetermined or desired inside perimeter of said core, as previously mentioned. With the turns 5 of the core 104 positioned as originally wound substantially without slack therebetween, the disc portion 16 of the tool 15 is inserted into the inside perimeter or window portion of the core 104 for driving engagement with the inner turn 13 of said core wherein the free end 5a of the inside turn 13 is inserted into restraining or driving engagement with the disc slot 16a of said tool; however, other means, such as an expanding or power-driven tool or the like, are contemplated to effect such driving engagement, as previously mentioned.

Rotation of the tool 15 in the winding direction with the inner turn free end a restrained in the tool slot 16a applies a rotative force in the inside turn 13 to effect a partial and successive rewinding and alignment of the turns 5 from their originally wound positions radially inwardly toward new or rewound positions about the disc portion 16 of said tool which defines the predetermined inside perimeter of the core 104. For instance, as the tool 15 is being rotated, the innermost of the turns 5 move radially inwardly in succession toward the inner turn 13 in its rewound position, and as such rotation progresses, the successive radially inward movement of said turns elfects a greater mass for rotation, and such increasing mass for rotation eifects an increasing inter-turn friction or drag; therefore, due to the proportioned relationships between the increasing mass and drag, a progressively varying or increasing tensioning force is established which controls the space factor and distribution of the slack between the adjacent turns in their rewound positions. For instance, during the initial rotation of the tool 15, there is very little drag since the mass of the turns 5 being rotated, i.e., those turns which have been rewound radially inwardly to their rewound positions, is quite small compared to the rest of the mass of said core turns which are substantially stationary; therefore, the inner most of said core turns are rewound onto said tool rather tightly in their rewound positions with respect to each other, but as the mass of the rewound turns increases, the drag thereof is also proportionally increased to effect successively and incrementally greater distances between each of said adjacent rewound turns in a radial direction from the inner perimeter toward the outer perimeter of the core 104. In other words, the increasing drag occasioned upon the successive rewinding movement of the turns 5 radially inwardly toward their rewound positions effects a space factor or radial distance between each adjacent rewound turn which increases incrementally in a radial direction from the inside to the outside perimeter of the core 104, as shown in FIG. 6; therefore, since the space factor between each adjacent rewound turn is increased incrementally in the radially outward direction, it is apparent that the predetermined amount of slack is distributed between each adjacent rewound turn in an increasing manner or in progressively increasing amounts also in the direction from the inner perimeter toward the outer perimeter of the core 104.

As previously mentioned, the core 104 was originally wound with a substantially solid stack height of turns substantially without slack therebetween; therefore, in view of the insertion of the slack into the core 104, it is apparent that the radially inward and successive movement of the turns 5 from their originally wound positions toward their rewound positions effects a slack gap therebetween, as indicated generally at 17 in FIGS. 6 and 7, which can be selectively positioned and maintained at any diameter of the stack height of turns, as desired. During the successive rewinding of the turns 5 into their rewound positions onto the tool 15, the slack gap 17 moves radially outwardly, and when said slaok gap approaches a desired diameter or preselected point in the stack height of the turns 5, the operator can retain or maintain said slack gap at said preselected point or diameter of the stack height by temporarily inserting a clamp or spacer, or other such restraining means, into said slack gap or by holding or pressing the side edges of the adjacent turns in the radially inner and outer sides of said slack gap with his fingers or other restraining object. In this manner, the slack gap 17 is predeterminately positioned at the preselected stack height, and thereafter continued rotation of the tool 15 will again initiate the radially inward and successive rewinding of the turns 5 from their originally wound positions toward their rewound positions adjacent to the slack gap 17 to distribute the remaining slack throughout the core 104 in the progressively increasing manner, as previously described. Although only one slack gap 17 is described, the operator can split up or distribute the slack in the slack gap 17 into other smaller slack gaps, such as shown at 17a, at several preselected points in the stack height of turns 5 in the same manner previously described wherein said space gaps 17, 17a divide the stack height of said turns into turn groups indicated generally at 18, 19 and 20. The space gaps 17, 17a are inserted into or provided in the core 104 at the various preselected diameters thereof to provide reindexing or new reference points which effect and insure a desirable and tight-fitting core upon the assembly thereof with a conductive winding structure, as discussed hereinafter.

The finished wound cores 4, 104- as shown in FIG. 7, having the predetermined amount of slack inserted thereinto and distributed predeterminately throughout the turns 5 of said core according to any of the methods set forth hereinabove is then deformed into the desired rectangular shape by any one of several Well-known shaping methods. In FIG. 9, for instance, the finished core 4 or 104 is placed in a press 21 having opposed stationary sides 22', 23 and opposed movable sides 24, 25, and a window block 26 is placed in the window or inner diameter of said core. Opposed forces F F are then applied by suitable means (not shown) on the movable press sides 24, 25 to deform the core 4 into the desired rectangular shape, as shown in FIG. 10, and as shown in FIG. 11, the slack previously inserted between the adjacent turns 5 and in the space gaps 17, 17a is repositioned into each of the four corners of the shaped core 4 or 104 to predeterminately create reindexing or reference points 27, 27a in the stack height of the turns 5 to facilitate the reassembly of said core onto a conductive winding element, as discussed, hereinafter. The forces F F are then removed from the movable press sides 24, 25, and the shaped core 4 or 104 is removed from the press 21 and placed in an annealing furnace (not shown) to relieve stresses in said shaped core and impart a permanent set thereto, as well known in the art.

After being removed from the annealing furnace and cooled, the shaped core 4 or 104 may be linked with a preformed winding structure, in accordance with one method, by first unwinding the strip material 1 of said shaped core and cutting through said strip material at preselected spaced intervals to provide a plurality of cut turn sections, as is also well known in the art. FIG. 12 shows a plurality of nested out turn sections 31, 32 and 33 each having a preselected length equal to approximately one 'and a half turns of the shaped core 4. These cut turn sections of strip material may then be linked with an insulated conductive winding element or structure 34, as shown in FIG. 13. To assemble the out turn sections 31, 32, 3-3 on the winding structure 34', it is, of course, necessary to spread said cut turn sections as they are being rewound about one side of said winding structure, and as the stack height of said out turn sections is built up about said winding structure, excessive spreading of said out turn section could effect permanent distortion thereof which, of course, would adversely affect the desirable butt jointing of the adjacent ends of said out turn Sections and impart a spongeness or stack height build-up in one of the leg or yoke sections of the assembled core 4. However, the slack gaps 17, 17:: which define the reindexing points 27, 27a prevent such stack height build-up in the assembled core 4 by providing a predetermined amount of slack between the turn groups 18, 19 and 20 wherein the first turn of each group provides a new reference or indexing point about which the other turns of said group are assem bled without regard to any stack height build-up which may have been present in the assembly of the turns of the previously assembled group. In other words, the provision of the reindexing points 27, 27a not only minimizes the possibility of tolerance build-up or stack height build-up in each of the turn groups 18, 1Q, 20 upon the assembly of the individual out turn sections 30, 31, 32 thereof but also minimizes the cumulative affect of said turn groups with regard to such stack height build-up, and thereby desirable closeness with regard to the butt-jointing of the adjacent ends of said out turn sections is enhanced.

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

1.--A method of making a wound transformer core from a continuous strip of magnetic material comprising the steps of: spirally winding a plurality of superposed turns of said strip material into an annular stack height of turns substantially without slack therein, said stack height being wound to a predetermined outer perimeter and having an inner perimeter in excess of that predeterminately desired, moving the inner turn of said stack height'relative to its next adjacent turn toward a displaced position defining the desired predetermined inner perimeter and providing a predetermined amount of slack for distribution in said stackheight, applying a rotative force on the inner turn of said stack height to effect substantially successive rotative movement of at least a portion of said turns radially inwardly toward rewound positions about said inner turn and simultaneously distribute the slack between each of the adjacent turns in their rewound positions in progressively increas ing amount from the inner perimeter toward the outer perimeter of said stack height.

2. A method according to claim 1, comprising the additional step of restraining two selected adjacent turns in said stack height to establish a slack gap therebetween having an appreciably greater amount of slack than that distributed between the other adjacent turns in their rewound positions upon the rotation of said turns in response to the applied rotative force.

3. A method of making a wound transformer core from a continuous strip of magnetic material comprising the steps of: spirally winding a plurality of superposed turns of said strip material into an annular stack height of turns substantially without slack therebetween, said stack height having a predetermined outer perimeter and an inner perimeter wound predeterminately in excess of that desired, drivingly engaging a tool having a perimeter defining the desired predetermined inner perimeter of said stack height with the inner turn thereof, the difference between the wound inner perimeter of said stack height and the tool perimeter defining the amount of slack for distribution in said stack height, driving said tool to apply a rotative force on said inner turn to effect substantially successive rotative movement of said inner turn and at least a portion of the other of said turns radially inwardly toward rewound positions about said tool perimeter and simultaneously distribute the slack between each of the adjacent turns in their rewound positions in incremental amounts progressively increasing from the inner perimeter toward the outer perimeter of said stack height.

4. A method according to claim 3, comprising slot means in said too], said slot means being connected with the free end of said inner turn prior to the driving engagement of said tool with said inner turn.

5. A method according to claim 3, comprising the additional step of limiting the movement of a selected one of said turns relative to the next adjacent turn thereto in its rewound position to establish a slack gap between said selected one turn and said next adjacent turn thereto in its rewound position separating the turns in their rewound position from the other turns in said stack height, said slack gap defining an appreciably greater amount of slack than that distributed between any other two adjacent turns in their rewound positions.

6. A method according to claim 3, comprising the step of connecting the outer turn of said stack height with its next adjacent turn against displacement to main- 10 tain the predetermined outer perimeter of said stack height.

7. A method of making a wound transformer core from a continuous strip of magnetic material comprising the steps of: connecting one end of said strip material with a rotatable arbor having a perimeter predeterminate ly in excess of the desired inner perimeter of said core, rotating said arbor to spirally wind thereon a plurality of superposed turns of said strip material into a stack height of said turns having a predetermined outer perimeter, severing the other end of said strip material from the supply thereof when said stack height of turns is wound to its predetermined outer perimeter, removing said stack height of turns from said arbor and connecting said other end of the outer turn of said stack height to its next adjacent turn against displacement to maintain the predetermined outer perimeter of said stack height, engaging a tool having a perimeter defining the desired inner perimeter of said stack height with said one end of the: inner turn of said stack height, the difference between the perimeter of the inner turn of said stack height wound on said arbor and the perimeter of said tool predeterminately defining the entire amount of slack for distribution between the turns of said stack height, driving said tool to apply a rotative force on said one end of said inner turn effecting substantially successive rotative movement of said inner turn and at least a portion of the other of said turns radially inwardly toward rewound positions about the perimeter of said tool and simultaneously distributing a portion of said slack between each of the adjacent turns in their rewound positions in incremental amounts progressively increasing from the inner perimeter toward the outer perimeter of said core.

8. A method according to claim 1, comprising shaping the core to a predetermined shape having yoke and leg members, and annealing said core to relieve stresses therein.

9. A method according to claim 1, comprising the step of restraining the rewinding movement of at least one turn relative to its next adjacent turn in said stack height to establish a slack gap therebetween having a greater amount of distributed slack than that distributed between any of the other adjacent turns in their rewound positions during the rotation of said turns to their rewound positions, shaping the core to a predetermined shape having opposed yoke and leg members, and annealing said core in its predetermined shape to relieve stresses therein.

10. A method of making a wound transformer core from a continuous strip of magnetic material comprising the steps of: spirally winding a plurality of superposed turns of said strip material into an annular stack height of turns substantially without slack therein, one of the inner and outer perimeters of said stack being predeterminated, moving one of the inner and outer turns of said stack relative to its next adjacent turn toward a displaced position to predeterminately define the other of the inner and outer perimeters and provide a predetermined amount of slack for distribution in said stack height, and rotating at least a portion of said turns of said stack toward rewound positions about said inner turn to simultaneously distribute the slack between each adjacent turn in their rewound position in progressively increasing amounts from the inner perimeter toward the outer perimeter of said stack.

11. A method according to claim 10, comprising the step of restraining the movement of at least one turn relative to its next adjacent turn to establish a slack gap therebetween having a greater amount of slack than that distributed between the other adjacent turns in their rewound positions during the rotation of said turns toward their rewound positions.

12. A method according to claim 11, comprising shaping the core to a predetermined shape having yoke and 2 leg members, and annealing said core to relieve stresses 3,223,955 12/1965 Olsen et a1. 29--605 therein. 3,406,600 10/1968 Minick 29-426 References Cited UNITED STATES PATENTS 5 RICHARD J. HERBST, Pnmary Examlner 2,282,854 5/ 1942 Driftmeyer 2960S US. Cl. X.R. 3,200,476 8/ 1965 Olsen et al. 29605 29605

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