US2588173A - Method of making magnetic cores - Google Patents

Description

March 4, 1952 G. G. SOMERVILLE 2,588,173

METHOD OF MAKING MAGNETIC CORES Filed Aug. 24, 1948 Inventor: Gareth. G, Semen/Hie His Attorney Patented Mar. 4, 1952 METHOD OF MAKING MAGNETIC CORES Gareth G. Somerville, Pittsfield, Mass, assignor to GeneralElectric Company, a corporation of N ew York Application August 24, 1948, Serial No. 45,833

1 Claim.

This invention relates to magnetic cores and more particularly to improvements in wound cores and the method of making the same.

Conventionally, magnetic cores for induction devices are constructed of punched or cut laminations which are stacked one above he other to form the core structure. This methodhas the inherent disadvantage of being limited to cores which have laminations of substantial thickness since it is difiicult to satisfactorily punch or out very thin magnetic materials. By very thin is meant materials having a thickness of less than 3 mils. One of the only ways cores formed of such thin layers can be satisfactorily constructed is by winding them from strip material. Since a rolled steel having a most favorable magnetic direction in the direction of the grain may be used in forming such a core, substantially lower core losses may result due to the fact that the flux flows continually along the path of least magnetic losses. After the core has been wound and properly annealed, it is often necessary to cut the core to allow for the mounting of the associated coils. It is the common practice to cut the core in half, by any suitable means, and after the coils are mounted to orient the two halves in adjacent abutting relationship to one another. The use of a butt joint increases the reluctance of the core by allowing the formation of an air gap between the two core halves. If the two core halves are maintained in intimate magnetic contact by means of lapped joints, the reluctance of the magnetic core is decreased since there is no unbridged air gap present.

In accordance with this invention, there is provided a preferably wound magnetic core having two halves which are lap-jointed together and the use of butt joints is completely eliminated. This is accomplished by using a method of construction which allows the strips of conventionally coated magnetic material from which each half of the core is constructed to be interleaved one with the other.

It is an object of this invention to provide a new and improved magnetic core.

Another object of this invention is to provide a novel method of making a magnetic core.

A further object of this invention is to provide a new and improved magnetic core formed in two overlapping interleaved parts.

Still another object of this invention is to provide a new and improved magnetic core which utilizes a plurality of lapped joints and thereby achieves lower magnetic reluctance.

A further object of this invention is to provide a lap-jointed magnetic core of very thin layers of magnetic material whose method of construction eliminates the use of punches and dies.

The invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claim.

In the drawing, Fig. l is a perspective view of an induction apparatus having a core constructed in accordance with this invention. Fig. 2 illustrates the first step in the method of making a core in accordance with this invention. Fig. 8 is a perspective view, and Fig. 4 a front elevation illustrating successive steps in the method of making the core shown in Fig. 1. Fig. 5-is a front elevation of an alternative method of core construction.

Referring now to the drawing, there is shown in Fig. 1 an electromagnetic induction apparatus I having a core 2 constructed in accordance with this invention and having mounted on it the coils 3 and l which may serve as the primary and secondary of a transformer. The first step in the method of constructing core 2 is shown in Fig. 2, wherein a continuous strip of magnetic material 5 is wound on a rotatable axle or mandrel 6 which has a substantially rectangular shape. It should be noted that a plurality of magnetic strips may be wound simultaneously on the mandrel 6, so that for each rotation of the mandrel 6, a plurality of layers is formed. In Fig. 2, it can be seen that the rectangular shape of the mandrel 6 is imparted to the core as it is wound, thus forming the sides 1 and 8 and the ends 9 and I0. As the core 2 is wound upon the mandrel 6 to form a closed loop, spacers H may be placed between individual layers or groups of layers of the core material, as shown at the ends 9 and Ill. The cross-sectional height of the spacers II, or the thickness of each spacer times the number of spacers used, should be such as to be approximately equal to the cross-sectional height 01', as is generally known in the art, the build of the core 2. It has been found advantageous to wind 3 or 4 convolutions of the core 2 before inserting a spacer I I; the spacer being of a thickness equivalent to the combined thickness of the convolutions plus approximately 10%.

After the core 2 has been wound on the mandrel 6, it may be placed in a clamp to accentuate its rectangular shape. It is then annealed at a high temperature in a protective atmosphere which is generally hydrogen. This annealing process not only reduces the strains present in the steel due to rolling and winding, but it also one half of the core 2, the coil 3 is wound and on the remaining half is wound the coil 4.

In finally assembling the core 2, the two halves l3 and M are brought into intimate magnetic contact by interleaving each layer or group of layers and achieving a plurality of lapped joints by placing the layers of the core in the spaces which were provided by the spacers II. The induction device I is permanently clamped as a unit by any suitable means, such as a clamping band 15, which may be wound around the periphery of the core 2 and spot welded at the point I6.

Fig. 5 shows an alternative method of winding a core I! which eliminates the use of separate spacer material and achieves the spacing between layers of the core by crimping the continuous strip of magnetic material or by winding it back upon itself at each end, as shown by I8. Thus, when the core is out, small U-shaped pieces of magnetic material may be removed leaving spaces similar to those provided by the spacers II in Fig. 1. Separate means not illustrated in the drawing may be provided to crimp or bend the magnetic strips back upon themselves. In Fig. 5, each successive layer of magnetic material is shown bent back upon itself at both ends of the core 11. In actual practice, it has been found most convenient to wind at least three layers of the strip material simultaneously and these three layers are bent back upon themselves.

While there have been shown and described particular embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the invention and, therefore, it is aimed in the appended claim to cover all such changes and modifications as fall within the true spirit and scope of the invention.

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

The method of making a wound core having a plurality of lapped joints which comprises winding a strip of magnetic material into a closed loop having any desired number of layers, crimping said magnetic material back upon itself during the winding operation so as to cause successive layers of said closed loop to be separated at two diametrically opposite zones of said loop by an amount equal to at least the thickness of one of said layers, the crimped portions of said magnetic material all being aligned with respect to a plane extending transversely through said loop cutting through said closed loop and through all of the crimped portions of said loop along said plane, removing the resulting crimped portion halves and interleaving the ends of the layers of the loop sections thus formed to produce a core having a plurality of lapped joints. 1

GARETH G. SOMERVILLE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,797,807 Swendsen Mar. 24, 1931 1,933,140 Gakle Oct. 31, 1933 1,992,822 Granfield (A) Feb. 26, 1935 2,142,066 Eppelsheimer Dec. 27, 1938 2,330,824 Granfield (B) Oct. 5, 1943 2,387,099 Vienneau Oct. 16, 1945 2,393,439 White Jan. .22, 1946 2,456,461 Dunn Dec. 14, 1948 2,478,030 Vienneau Aug. '2, 1949 2,489,625 Dornbusch Nov. 29, 1949 2,516,164 Vienneau July 25, 1950

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