US3114196A - Method for producing magnetic core and coil assemblies with gaps in the magnetic core - Google Patents

Description

H. J. PROXMIRE 3,114,196 0 ORE AND COIL Dec. 17, 1963 METHOD FOR PR DUCING MAGNETIC C ASSEMBLIES WITH GAPS IN THE MAGNETIC CORE Filed Oct. 5, 1960 5 Sheets-Sheet l //7 Mentor. Har/yJP/vxm/hg y 7 I Dec. 17, 1963 H. J. PROXMI'RE 3,114,195

METHOD FOR PRODUCING MAGNETIC CORE AND COIL ASSEMBLIES WITH GAPS IN THE MAGNETIC CORE Filed Oct. 5, 1960 3 Sheets-Sheet 2 //7 l/GI? 5'02".

Harry J praxw/re,

y 7 W Hate/"neg.

Dec. 17, 1963 H. J. PROXMIRE 3,114,196

METHOD FOR PRODUCING MAGNETIC CORE AND COIL ASSEMBLIES WITH GAPS IN THE MAGNETIC CORE 3 Sheets-Sheet 3 Filed Oct. 5. 1960 United States Patent.

3,114,196 METHGD FOR PRUDUClNG MAGNETIC CORE AND C(lfi. ASEBEMBLEES WITH GAPS lN THE MAGNETlC CORE Harry J. Proxrnire, Fort Wayne, Ind, assignor to General Electric Company, a corporation of New York Filed (let. 5, 19%, Ser. No. cases 1 Claim. (fil. 2155.58)

This invention relates to inductive devices and to a method for producing magnetic core and coil assemblies of inductive devices with gaps adjusted to provide a predetermined value of inductance.

In many electrical applications where the inductance of the device is :a parameter in the circuit design that cannot be neglected, it is necessary to design the magnetic core and coil assembly with an inductance having a substantially constant predetermined value and it is desirable that this value be maintained within specific limits. In inductive devices, such as transformers, the magnetic core is generally comprised of two portions which form a magnetic circuit. Conventionally, to obtain a predetermined or calculated value of inductance, one or more gaps are introduced between the two portions by providing spacers which maintain the portions in spaced relation.

In the past many diiliculties have been encountered in achieving accurately spaced gaps by means of conventional spacers. Due to variations in the permeability of the iron core and irregularities in the laminations making up the core, it is difiicult to obtain a desired value of inductance by known methods for adjusting the gap of a magnetic core. Moreover, the conventional materials used as gap spacers shrink during the heat treatment of the device and thus the actual value of the inductance may vary considerably from the design value because of the shrinkage.

Another method used in the past to accurately adjust the inductance of a transformer was to provide taps in the primary and secondary windings and determine by trial and error the number of effective turns required in the windings that will provide the desired inductance for a given gap. This method required that the winding be provided with a plurality of taps. Obviously, such a method is time consuming and does not result in an economical use of materials. it is apparent, therefore, that there is a need for a method for accurately obtaining a predetermined value of inductance that can more economically be carried out.

Accordingly, a general object of the invention is to provide a method for obtaining a predetermined value of inductance in an inductive device by adjusting the gaps 'in the magnetic core that will achieve the desired results set forth above.

Another object of the invention is to provide an improved method for adjusting the gap of an inductive device so that the value of the inductance can be maintained Within predetermined limits.

In accordance with the method of the invention, a core and coil assembly is produced with gaps adjusted to provide a predetermined value of inductance. The method involves placing at least one resilient gap spacer and coil in assembled relation with the portions of the magnetic core, forcing the core portions together to compress the resilient spacer until the desired gap is obtained and then applying a means on said magnetic core for maintaining said portions of said magnetic core in rigid spaced relationship to maintain a constant gap. In a more specific aspect of the invention a thermosetting resin is applied to the magnetic core to maintain the portion in rigid spaced relationship and the proper adjustment of the air gap is determined by measuring the inductance of the core and coil assembly.

FIG. 1 is a front elevational view partially broken away of a pair of coils and a core assembled in a clamp showin the resilient spacer in assembled relation with the core portions before the clamp is tightened;

FIG. 2 shows the core and coil arrangement of FIG. 1 with a coil connected in circuit with an inductance bridge shown schematically and with the core portions being placed under compression by the clamp, the view illustrating how the gap between the core portions is adjusted against the spring force exerted by the resilient spacer in accordance with one exemplification of the invention;

FIG. 3 is a view in perspective of the core and coil arrangement of FIG. 1 partially broken away and illustrating the step of applying a thermosetting resin to the core portions in the vicinity of the gap after the desired gap has been obtained by the step illustrated in FIG. 2;

PEG. 4 illustrates the curing step of the foregoing exemplification of the invention and shows the transformer after the thermosetting resin has been applied in accordance with the step illustrated in FIG. 3, being heated in an oven to cure the thermosetting resin;

FIG. 5 is a front elevational view of an electromagnetic inductive apparatus having a shell-type magnetic core formed of E-shaped larninations and having a resilient spacer in assembled relation with the core portions to illustrate another exemplification of the invention;

FIG. 6 is a front elevational view partially broken away of the core and coil assembly shown in FIG. 5 in which the apparatus is shown connected to an inductance bridge to illustrate the step of adjusting the gap to obtain a predetermined value of inductance; and

FIG. 7 is a side elevational view partially broken away illustrating how the resin is applied to the core portions in the vicinity of the gaps according to the method of the invention.

Referring now to FIGS. 1, 2, 3 and 4 and more particularly to the perspective view of FIG. 3, the method of the present invention is illustrated in connection with a core and coil assembly 10 comprising a sintered iron magnetic core 11 and two coils 12, 13. It will be seen that the magnetic core is formed of two portions which are spaced from each other to provide a gap in the magnetic circuit and are made up of six C-type isintered iron core elements 14, -15, 16, 17, 18, 19 and 20, 21, 2-2, 23, 24, 25, respectively. The upper and lower portions of the magnetic core 11 are spaced from each other by resiilent gap spacers. In the exemplification of the invention shown in FIGS. 1-4, the resilient spacers 26, 27, are comprised of elongated strips 28, 29 of resilient material, such as rubber, neoprene and the like, which are sandwiched between two'shims 30', 31 and 32, 33, respectively. The shims 30, 31, 32, 33 are used for the purpose of maintaining the alignment of the C- shaped core elements 14, 15, 16, 17, 18, =19 and 2t}, 21, 22, 23, 24, 2:5, and for the purpose of aiding in dete'rmining the initial spacing required. Two insulating members 34, 35 provide support for the coil assemblies and also insulate the sides of the coils 12, 13 from the magnetic core 11.

A clamp 36 is used in the illustrative embodiment of the invention in the step of forcing or drawing of the portions of the magnetic core 11 against the resilient force of the spacers 26, 27 to accurately adjust the length of the gap. The clamp 36 simply comprises two parallel plates 37, 38, two clamping screws 3, 4i) and wing nuts 41, 42, the clamping screws 39, to being secured at one end to the lower plate 38. Suitable washers 4-3, 44 are provided to facilitate tightening of the wing nuts 41, 42. As shown in FIG. 1, the wing nuts 41, 42 are drawn up on the clamping screws 39, 44) so that no compressive force is exerted against the portions of the magnetic core 11.

Referring now to FIG. 2, as the wing nuts 41, 42, are drawn downward, it will be seen that upper and lower portions of the magnetic core 111 are placed under com: pression. Since this compressive force applied by the clamp is resisted by the spring force of the resilient spacers, it will be seen that very fine adjustments in the gap spacing are possible. It will be appreciated that the compressive force required to draw the portions of the magnetic core 11 together and compress the resilient spacers 26, 27 may be provided by other suitable means.

To determine the precise gap spacing that will provide the predetermined value of the inductance, the gaps are progressively adjusted as the force exerted by the clamping means is increased. The value of the inductance is measured while these adjustments are made. The coil 13 is connected in an alternating current inductance bridge circuit 46 shown schematically in FIG. 2. The bridge circuit 46 includes a decade type of inductance switch 47 that provides predetermined value of the inductance against which the inductance of the core and coil assembly is compared, a galvanometer 4S and a switch 49. Thus, while the gap is being adjusted, the actual inductance readings for a given adjustment are compared against the predetermined standard value provided by the decade inductance switch 47. When the two values of inductance are substantially equal, as shown by the galvanometer readings, the desired gap has been obtained.

After the desired gap is obtained by the preceding step, the next step of the invention involves applying to the magnetic core 11 a means for maintaining the core portions of magnetic core 11 in rigid space relationship.

Preferably, as shown in FIG. 3 thermosetting resin 51 is applied to the core 11 in the vicinity of the gaps so that upon curing the resin will form a rigid connection between the portions of the core 11 and maintain the portions in rigid spaced relation. The thermosetting resin 51 may be applied by means of a caulking gun 52, only a portion of which is shown. In this illustrative embodiment of the invention, a heat curable polyester resin, propylene glycol ma'leate adipate was used. The resin was cured for a period of two hours at a temperature of 125 degrees centigrade. Resins containing polymerizable acrylic acid type of esters have good bonding properties. However, it will be appreciated that many other types of resins, such as the epoxy resins, may be used. Further, it will be appreciated that the portion of the core 11 may also be maintained in rigid spaced relationship by clamping frames and other mechanical means.

In FIG. 4 the core and coil assembly .10 and clamp 36 are shown in an oven 52 heated by the electrical element 53. Whether or not a heating step is required in a practice of the invention will depend upon whether the thermosetting resin employed requires heating to effect a cure. If the resin used is curable at room temperature, the curing step, obviously, becomes unnecessary. In the hereinafter described exemplification of the invention, a polyester resin having anaerobic curing characteristics was used, and consequently it was not necessary to heat the core and coil assembly.

Referring now to FIGS. 5, 6 and 7, the method of the present invention is illustrated in connection with a reactor 55. The reactor 55 is comprised of a coil 56 wound on a spool 57 and a magnetic core 58 formed of two oppositely disposed stacks of E-shaped laminations 59, 60. The laminations are firmly held together by a clamping member 61 substantially channel-shaped and formed with two tabs 62, 63 at each end. Resilient spacers 64, 65 are interposed between the ends of the outer legs of lamination stacks 59, 60.

As shown in FIG. 5, the reactor 55 is loosely held in a clamp 36 which is identical to the clamp 36 of FIGS. 1-4, like reference numerals being used to identify cor responding parts. The clamp 36 consists of the two parallel plates 37, 38, the two clamping screws 39, 4t secured to the bottom plate 38, and the wing nuts 41, 42. In the view shown in FIG. 6, the reactor 55, the tabs 62, 63 of the clamping member 61 are folded over, and the two stacks of laminations 59, 60 are under compression. Further, there is shown in FIG. 6 a schematic circuit diagram of an inductance bridge which is substantially the same as the circuit shown in FIG. 2. Like reference numerals are used to identify the corresponding components of the circuits.- The proper value of the inductance is determined by adjusting the gaps until the galvanometer indicates that the values of inductance of the predeter mined standard value set on the decade inductance switch 47 and the inductance of the reactor 55 are substantially equal.

The terminals of the bridge circuit 46 were connected across an alternating current supply of four volts at 3500 cycles per second. When the predetermined value of the inductance was obtained, a small amount of resin was introduced into the aperture 67 formed in the clamping member. The resin 66 is attracted by capillary action between the clamping member 61 and the lamination stacks 59, 69 so that when the resin is cured to an infusible and insoluble mass, the two lamination stacks will be held in rigid spaced relationship.

In the illustrative embodiment of the invention shown in FiGS. 5-7, a res-in 6 comprising a polymerizable acrylic acid ester having anaerobic characteristics was used. Such polymerizable compositions which can be used are fully described in U.S. Patent No. 2,628,178Burnett et al. These resinous compositions readily penetrate between adjoining surfaces by capillary action and then rapidly polymerize t-o form a solid infusible bond between the surfaces because of the absence of air. By using an anaerobic synthetic resin it is possible to eliminate the heating step since the curing of such resins can be readily etlected without the application of heat.

The method of the present invention provides the distinct advantage over other known methods for producing magnetic core and coil assemblies with gaps adjusted to provide a predetermined value of inductance of the rated value in that more precise adjustments are rendered economically feasible even in such difiicult magnetic core structures such as the sintered iron core type of transformer illustrated in FIGS. 1-4. The method of this invention makes it possible to maintain the rated inductance within very close limits. As an example, with the method of the present invention it was possible to maintain the primary inductance of the core type of transformer illustrated in FIGS. 1-4 within two percent of the predetermined value for factory assembled transformers. When methods of the prior art were employed for adjusting the gap, inductance could only be main tained within twenty percent of the rated value. To obtain a value of inductance within two percent of the design value by the trial and error method of employing multiple taps in a winding, it was found that approximately ten taps were required above and below the nominal voltage rating or a total number of twenty taps. Thus, the multiplicity of taps required rendered this method impractical and uneconomical from a manufacturing standpoint. Moreover, it will be appreciated that the gap obtained in accordance with the invention is not dependent upon the spacer material or the mechanical structure of the unit when a resin has been used to bond the core. Thus, the method of the present invention insures the gap will be permanently maintained at its preset spacing during the service life of the device. Further, it will be apparent that the present method eliminates the need for providing multiple taps in the windings of an electromagnetic inductive device to which in the past were used to fix the value of the inductance.

While I have illustrated embodiments of my invention in connection to two different types of core structures, it will be understood that my invention is not limited to use with such core constructions. My method of producing magnetic core and coil assemblies may be used with any magnetic core in which a gap is formed between portions of the core which can be drawn together to compress a resilient spacer interposed between the portions.

Although I have shown and described herein particular embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the inven tion. Therefore, it is aimed in the appended claim to cover all such changes and modifications as fall Within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

A method of producing a magnetic core and coil assembly with a gap adjusted to provide a predetermined value of inductance for the assembly, said magnetic core comprising a plurality of C-shaped core elements oppositely disposed with respect to each other, said method comprising: assembling the C-shaped core elements with a resilient gap spacer sandwiched between two essentially rigid spacers of nonmagnetic material in the gap between the G-shaped core elements, placing the C-shaped core elements in a clamp to adjustably draw the core elements toward each other against the gap spacers, connecting the coil assembly in circuit with an inductance bridge for determining the inductance of said core and coil assembly,

adjusting the clamp to draw said core elements progressively toward and away from each other against the spring force of the resilient gap spacer until the predetermined value of inductance is obtained, applying a thermosetting resin to the core portions in the vicinity of the gap, curing said thermosetting resin to an infusible state to rigidly bond said core elements thereby to maintain the gap therebetween substantially constant, and removing said core and coil assembly from said clamp.

References Cited in the file of this patent UNITED STATES PATENTS 2,055,175 Franz Sept. 22, 1936 2,165,055 Kafka July 4, 1939 2,180,759 Kneisley Nov. 21, 1939 2,318,095 Putman May 4, 1943 2,319,775 Mitter-maier May 18, 1943 2,367,591 McAllister Jan. 16, 1945 2,445,408 Root July 20, 4948 2,550,127 Specht Apr. 24, 1951 2,558,110 Stein June 2 6, 1951 2,586,320 Ford Feb. 19, 1952 3,043,919 Tannenbaum et a l. July 10, 196-2

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