US3324532A

US3324532A - Method of making encased magnetic core

Info

Publication number: US3324532A
Authority: US
Current assignee: CBS Corp
Publication date: 1967-06-13
Anticipated expiration: 1984-06-13

Description

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y June 13, 1967 l METHOD OF MAKING ENCASED MAGNETIC CORE originan Filed sept. 14, 1960 W17' figa l l E 8 gj.. 16.5 210. 11 1o l 14 157i /eg Q9 Mm 0 1B 10B 50 U 'fm 60 1611 l!!! 321% [245 Q 66B m- Et I 65B E0 l 16 1m il', n mi ffl .6. MB 66B y s" I n v M \44//1 mi 415/; m 161 l' INVENTOF 1M PLV Q.

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Z'G Bt; ATTORNEYS 3,324,532 METHOD F MAKING ENCASED MAGNETIC CORE .lohn W. Cook, Shady Side, Md., assignor, by mesne assignments, to Sprague Electric Company, a corporation of Massachusetts Original application Sept. 14, 1960, Ser. No. 55,890. Di-

vvided and this application June 8, 1965, Ser. No.

1 Claim. (Cl. 29-155.56)

vThis is a division of application Ser. No. 55,890 filed Sept. 14, 1960, and now abandoned.

This invention relates to encasing toroidal magnetic cores of the smaller variety known as bobbin cores, and it more particularly relates to enclosing bobbin cores in a tube on which the core is wound.

.The tape used in bobbin vmagnetic cores is extremely thin, fragile and strain-sensitive being only a fraction of a mil in thickness. It is wound upon bobbins which must be resistant to high temperatures in the neighborhood of 1000 C.`because the tape must be annealed at these temperatures after winding to adjust its magnetic properties to optimum values. These bobbins have, therefore, usually been made of ceramic material which is an effective insulator as well as being resistant to the high annealing temperatures. After annealing, the tape has been sealed within the flanges of the bo-bbin, for example, by wrapping an adherent tape about the periphery of the flanges. ExtremeV care must be taken in this enclosing 'process or` any other -that is yconducted after annealing because any stress transmitted to the tape no matter how slight will disturb the critical adjustment of its magnetic properties accomplished during annealing.

An object of this invention is to provide a method of encasing a -bobbin-type core which minimizes the transmission of forces to the core after annealing.

Another object is to provide such a method of encasing cores with materials whi-ch are resistant to heat thereby permitting enclosure of the core prior to annealmg.

In accordance with this invention a hollow toroidal shell formed entirely of material of tubular structure is enclosed around a magnetic core. The formed shell extends radially outwardly from both ends of the tubular structure -and substantially laterally parallel to it from at least one end. These extensions formed from both endsextend closely adjacent each other to substantially enclose a magnetic winding disposed about the tubular structure within the shell, and the adjacent ends of the shell are joined by a sealing means to tightly seal the winding within the shell.

Novel features and advantages of the present invention will become apparent to one skilled in the art from a reading of the following description in conjunction with the accompanying drawings wherein similar reference characters refer to similar parts and in which:

FIGURE 1 is a View in elevation of one embodiment of this invention;

FIGURES 2-5 are cross-sectional views in elevation of the embodiment shown in FIGURE l throughout successive stages of fabrication;

FIGURES 6-9 are cross-sectional views in elevation of another embodiment of this invention throughout the successive stages of fabrication;

FIGURE 10 is a cross-sectional view in elevation of still -another embodiment of this invention; and

FIGURE l1 is a cross-sectional view in elevation of a further embodiment of this invention.

In FIGURES 1-5 is shown an encased magnetic core 10, which includes a toroidal casing 12, formed entirely of material of tubular structure 14 as indicated by its initial tubular form shown in FIGURE 2. The material of tubular structure 14 is, for example, a heat-resistant nonferromagnetic material such as stainless steel which is extremely strong and resistant to high annealing tem- .peratures A magnetic winding 16 made, for example,

of thin magnetic tape 0.000125 inch thick is wound about tubular structure 14.

FIGURE 3 shows how a forming die 18 is utilized to deform the ends of tubular structure 14 radially outwardly and then substantially laterally parallel as indicated in the lower portion of FIGURE 3 which has been formed in this manner to provide one half 20 of toroidal shell 12. After the forming operation indicated in FIG- URE 3 is completed, the two halves 20 of toroidal shell 12 substantially enclose tape winding 16 within it. The ends 22 extending from both ends oftubular structure 14 are spaced a slight distance from each other to break the electrical circuit about the shell. Since shell 12 is made of heat-resistant stainless steel, it can be exposed to high annealing temperatures vwithout destroying it.

After annealing, the opening into enclosure 12 is sealed by a material which is insulating such as a cement 25 or tape. A suitable cement is a polymerizing organic material such as an epoxy resin, and various types of Iadherent types of tape, such as plastic, may be used. The very slight separation or spacing 24 between ends 22 minimizes the strength requirements of the sealing material, and sealing substances which lare relatively fluid during application can therefore be dependably utilized.

FIGURES 6-9 illustrate :another embodiment of this invention in which the tubular structure is composed of two cooperating

portions

14A and 14A-1. This pair of

tubular structures

14A and 14A-1 respectively have radial and substantially lateral and parallel extensions 20A and 20A-1 to form the shell 12A shown in FIGURES 8 and 9. These

tubular structures

14A and 14A-1 are formed, for example, of a nonferromagnetic material such as the aforementioned stainless steel which is formed in the previously described manner, or they may be fabricated of molded or cast material, such as, a heat-resistant die cast alloy.

In FIGURE 7 a magnetic winding 16A is shown wound about tubular structure 14A. This magnetic winding 16A is, for example, an ultrafine magnetic wire which is, for example, either a round lwire having a diameter of approximately 0.003 inch, or similar wire subsequently flattened to provide dimensions, of approximately 0.003 by 0.003 inch. The utilization of wire instead of tape facilitates winding within a partially enclosed structure, and it unexpectedly permits the winding operation to be made completely automatic because wires can be provided in substantially great lengths in contrast with tape which can only be handled in limited lengths. Furthermore, Wire can be manipulated automatically without damage, which is practically impossible with tape which must be carefully manipulated by hand to avoid tearing or creasing. Furthermore, wire can exhibit satisfactory magnetic properties in a core in spite of the previously widelyaccepted theory that opposing fields `would be set up which would interfere with its proper operation in a magnetic core. In fabrication, both ends of the wire would be welded to the core before and after it is wound to secure it in place.

FIGURE 8 shows how tubular structure 14A-1 is forced into engagement within tubular structure 14A to provide an extremely rigid casing for magnetic winding 16A.

Tubular structures

14A and 14A-1 may be formed with great precision to dimensions which provide an intimate engagement between them when engaged in the manner shown in FIGURE 8. When both

tubular structures

14A and 14A-1 made of a heat-resistant material such as stainless steel, the enclosed core 12A shown 1?` in FIGURE 8 can be annealed and then sealed `by cement 25A as shown in FIGURE 9. Another cement seal 26A seals the opposite ends of

tubular structures

14A and 14A-1 if necessary. However, it is possible to make only one tubular half such as 14A of heat-resistant material lwhich can withstand the annealing temperature, and then subsequently enclose the core after annealing by insertion within it of a tubular structure 14A-1 which is made of a material such as plastic which cannot withstand annealing temperatures.

This situation is shown in FIGURE 10 where casing half 14B-1 is made of a strong moldable plastic such as polystyrene which is inserted within a stainless steel tubular structure 14B to bring its ends 22B-1 into close proximity to ends 22B of structure 14B. Since structure 14B-1 is made of a nonconductive material, it can be brought directly into contact with tubularv structure 14B `with no space between ends 22B-1 and 22B. This further facilitates their joinder by cement 25B. Another cement seal 26B is also applied to the unformed end 28B-1 of tubular structure 14B-1 to insure that there is no break in the closure if necessary. Even though tubular structure 14B-1 is applied after winding 16B is annealed, there is no undue danger of damaging the magnetic characteristics of the winding, since itis` protected by the extended end 20B which partially encloses it; and the application of plastic tubular structure 14B-1 is not likely to induce any troublesome stresses and strains in the/far stronger tubular structure 14B of stainless steel.

FIGURE 11 illustrates a toroidal shell 22C made of a heat-resistant tubular structure 14C of stainless steel upon which a winding 16C of magnetic `wire is wound. Tubular structure 14C is U-shaped in cross section, and cooperating tubular structure 14C-1 which is., for example, made of plastic similar to 14B-1, therefore, need only include a radially extending ange 30C whose end 4 22C-1 contacts end 22C of tubular structure 14C. Cement seals 25C and 26C fully seal toroidal shell 22C by application to both mating ends of tubular structures 14C and 14C-1.

What is claimed is:

A method for encasing an ultra-tine magnetic winding comprising the steps of applying said winding about a tube of refractory `ductile metal, forming both ends of said tube into a curved shape extending toward the other end of said tube and about the periphery of said magnetc winding and spaced apart to form a narrow separav tion to form a toroidal shell of said tube which encloses without touching the .magnetic Winding, heating the enclosed magnetic winding within the toroidal shell, adjusting the magnetic properties of the winding by annealing, and applying a non-conducting sealing material to said separation in the fluid state to tightly enclose said mag netic winding.

References Cited UNITED STATES PATENTS JOHN F. CAMPBELL, Primary Examiner.

R. W. CHURCH, I. CLINE, Assslam Examiners.