US2362034A - Shield for electrical currents - Google Patents

Description

Nov. 7, 1944. w. F. STAHL SHIELD FOR ELECTRICAL CURRENTS Filed June 25, 1941 f I Z fER/YOW METAL 6 PAPER LAM/NATIONS Patented Nov. 7, 1944 UNITED STATES PATENT OFFICE snmm) FOR ELECTRICAL CURRENTS William F. Stahl, Evanston, 111.

Application June 25, 1941, Serial No. 399,643 I (01. 174-35) 5 Claims.

This invention relates to shields for electrical currents and more particularly to laminated tubular shields wherein a layer or layers of conducting material is adapted to intercept and dissipate electro-magnetic and electro-static fields of force set up by high frequency currents.

In the radio field and in other arts wherein high frequency currents are used, it is often desirable to provide an electrically conducting shield which may be placed around the source of electrical current and will dissipate the electromagnetic and electro-static fields of force set up about the current source. Thus in radio receiving and transmitting apparatus, many of the parts of the apparatus such as coils, tubes and condensers are equipped with electricall conducting shields which extend about the parts and intercept and dissipate the fields of force generated by or emitted from the part. The shields also serve to intercept fields of force generated outside of the same. Such shields have usually been made of solid metal of low electrical resistance such as copper, brass or aluminum. This construction is heavy and expensive. A light sheet or film of the metal, on the other hand, is not self-sustaining and is readily bent or broken.

Iron and steel are ordinarily not used in such shields despite the fact that these metals are strong and relatively inexpensive. Iron, steel and other ferrous metals possess relatively high electrical resistance and hence are less efficient for intercepting and dissipating the fields of force than copper and other metals of high conductivity and low resistance. More important, how.- ever, is the fact that the ferrous metals when used as shields tend to set up magnetic fields of force as a result of the eddy currents which are created in the shield. Accordingly, instead of dissipating the fields of force, an iron or steel shield will tend to set up fields of force of its own.

In accordance with the present invention, a shield is provided in which a laminated tubular body contains a layer of ferrous metal and a layer of non-ferrous metal, the non-ferrous metal being adapted to intercept and dissipate the fields of force generated by or emitted by the current source, while the ferrous metal supports the body and further dissipates any fields of force which may be brought into contact with the same. In addition, the non-ferrous metal serves to intercept and dissipate an fields of force which the ferrous metal itself may tend to set 119.

Another feature of the invention is to provide a light weight and inexpensive base for supporting the non-ferrous metal, the base being of non-conducting or insulating material. Another feature ls to provide a laminated tubular body in which a layer of ferrous metal and a layer of. non-ferrous metal are secured to each other in electrically conducting relation.

A further feature of the invention is to provide a laminated tubular shield wherein a thin sheet of non-ferrous metal is spirally wound about a non-conducting base with the edges of the sheet being in overlapping relation to form a seam oblique to the axis of the base. The seam does not extend more than one revolution about the base. In this way, the advantages of applying a sheet to a base by spirally windin areobtained while at the same time the sheet does not extend about the base in a. plurality of revolutions which would tend to act as a coil and set up an inductance when subjected to electro-magnetic or electro-static fields of force. The invention is illustrated in the accompanying drawing in which- Figure 1 is a perspective view of a tubular shield constructed in accordance with the invention; Fig. 2 is a longitudinal sectional view taken along the line 2-2 of Fi 1; Fig. 3 is a perspective view of a modification of the shield.

Referring particularly to Figs. 1 and 2, a laminated tubular shield I0 is equipped with an outer casing II of iron or steel or other ferrous metal. The casing II may be of any suitable size and shape and is preferably of a thickness sufficient to make the casing self-sustaining without caus ing it to be excessively heavy. If desired, the casing, as shown, may be coextensive in length with the shield Ill.

Within the casing II is a thin layer I2 of copper foil or other non-ferrous metal of relatively low electrical resistance. Within the layer of copper foil I2 is a paper or other non-conducting base l3 which in turn supports another layer I4 of copper foil. The paper base may, as shown, be composed of a plurality of layers or sheets of paper I5, I6 and I! spirally wound together to form an integral tubular paper base. The layers I2 and I4 of copper or other foil may be secured to the paper base in any suitable manner, preferably by an adhesive.

The copper sheet of foil I4 is spirally Wound about the inside surface of the paper base I3 with the edges of the sheet overlapping to form a seam I8 oblique to the axis of the tubular base. The seam l8 extends about the tubular base less than a single revolution. Similarly, the sheet of copper foil I2 is wound about the outside of the paper base and forms a seam which does not extend completely about the base.

The spiral winding of thin sheets of copper or other non-ferrous metal about a tubular base to form a laminated structure, is described and set forth in detail in my copending application, Serial No. 397,197, filed June 9, 1941, for Shield for high frequency electrical currents and my copending application Serial No. 397,198, filed June 9, 1941, for Laminated tubular bodies and method of forming the same, which has matured to Patent No. 2,354,556, dated July 25, 1944. Accordingly, the method of preparing such spirally woundtubular bodies will not be described in detail herein.

Adjacent one end of the tubular shield Ill are a pair of spade bolts [9 and which are equipped with flattened surfaces 2| and 22 respectively extending along the outside of the casing II on opposite sides thereof. Rivets 23 and 24 or other suitable means extend through the plates 2| and 22 respectively and also through casing H and the layers l2, l3 and M, the rivets serving to secure the spade bolts l9 and 20 to the shield and also to bring the casing H into electrically conducting relation with the sheets l2 and M of non-ferrous metal. The other ends 25 and 26 of the spade bolts l9 and 20 respectively are threaded to provide studs for the mounting of the shield.

The shield assembly thus includes, as shown, a substantially cylindrical tubular base ii of paper or other non-conducting material. Thin sheets l2 and M of copper or other non-ferrous metal extend about the outer and inner surfaces respectively of the tubular base, the sheets being spirally wound about the base and having their edges in overlapping relation to form seams oblique to the axis of the base. The casing ll of the ferrous metal extends about and encloses the base l3 and the sheets l2 and [4. If desired, the casing ll may be closed at one end and, if so constructed, may be equipped with a layer of non-ferrous metal on the inside of the closure portion.

In the modification of the invention shown in Fig. 3, the tubular shield is of square cross section but is otherwise constructed in a manner analogous to that shown in Figs. 1 and 2. The tubular base 32 of rectangular cross-section may be equipped with layers of foil of a non-ferrous metal extending about the inner and outer surfaces of the base just as the non-conducting base I3 of Fig. 2 is arranged. The inner layer of foil 33 is spirally wound about the inside of the tubular paper base 32 with the edges of the sheet of foil in overlapping relation forming a seam 34 oblique to the axis of the base 32. The seam 34 is preferably on only one of the rectangular sides of the tubular base and extends in a single plane. The layer of foil extending about the outside of the tubular base is similarly arranged. The iron or steel casing 35 is of square cross-section and snugly receives the base. Spade bolts 36 and 31 are attached to the casing 35 and the base 32.

The term tubular is used herein in its broad sense and is intended to include hollow sleeve-like bodies of circular, polygonal, rectangular or other cross-section construction.

The shield may be assembled in any suitable manner. Preferably the base of paper or other non-conducting material is provided with the layers of non-ferrous metal foil to form the laminated structure described and set forth in my copending applications referred to heretofore. This laminated structure may then be inserted in the tubular casing of ferrous metal.

One method of forming a. shield of the construction set forth herein is to provide a tubular base or body which is self-sustaining, but is nevertheless collapsible, and to wind a strip of metal foil about the base, the foil being wound at an angle as in spiral winding. Upon the layer of foil may be placed a layer of paper laminations. Preferably, the paper is in the form of gummed tape or the like and is spirally wound about the metal foil. If desired, the strips of gummed tape and metal foil may be wound simultaneously about the tubular base. In forming the structure shown in Figs. 1 and 2, a. second layer of metal foil is wound at an oblique angle about the laminated paper layer and, if desired, thi foil may be applied simultaneously with additional strips of gummed tape which are spirally wound to form a laminated tubular body about the outer layer of metal foil. The adhesive on the gummed tape may secure the first layer of metal foil to the intermediate layer of tape. Similarly, adhesive may be used to secure the outer layer of metal foil to the intermediate layer of tape.

The shield may be formed as a tubular body of circular cross section and may be readily converted into a polygonal tubular body by passing the shield over a mandrel of appropriate polygonal cross section. The inner tubular base may then be withdrawn from the body and the outer paper layer may also be removed.

The product which is formed by these operations contains two layers of metal foil, each wound at an angle as in spiral winding, the lay- I ers being separated by a layer of laminated paper, and each of the layers being adhesively secured to each other to form a unitary body. This product may then be inserted in the iron or steel casing to form the shield shown in Figs 1 and 2.

In forming the shield shown in Fig. 3, the metal foil is wound on the tubular bMe, and laminations of paper are applied to the foil, after which the tubular base is collapsed and the product consisting of a tubular body of paper with a foil layer on the inner side thereof may be inserted in the casing to form the shield.

The product shown in Fig. 4 may be made by the method described in connection with the construction of Figs. 1 and 2, the circular product being converted into one of rectangular cross section by passing-it over a suitable mandrel.

When the shield is to be used, it is placed about the current source in such a manner that the copper foil intercepts and dissipates the electro-magnetic and electro-static fields of force generated by the current source. Thus when the shield is to be used with a coil, it is merely placed over the coil, the fields of force emanating from the coil are intercepted by the layer or layers of copper or other non-ferrous metal. Any fields of force which are not dissipated by these layers are intercepted by the iron or steel casing which also acts, although less efliciently, to dissipate the fields of force. At the same time, the copper layers effectively dissipate any magnetic fields of force which may be set up in the iron or steel casing. By reason of the spiral winding of the sheets of copper with the seam extending less than one revolution about the tubular base, a simple structure is provided which eflectively avoids the setting up oi the inductance currents in the shield.

The spade bolts and Ill may be used to mount the shield in an assembly. The shield may be of any suitable size and shape and may readily be adapted for the various types of current source with which it is to be used.

While there have been shown and described certain embodiments of the invention, it is to be understood that it is capable of many modincations. Changes, therefore, in the construction and arrangement of the parts may be made without departing from the spirit and scope oi the invention as disclosed in the appended claims.

I claim:

1. A self-sustaining shield for electrical currents, comprising a rigid tubular casing of ferrous metal, a pair of spaced tubular sheets of non-ferrous metal of low electrical resistance disposed within said casing, a carrier for said tubular sheets which is of nonconducting material and to which each of said tubular sheets is adhesively secured, and means for electrically connecting said sheets of non-ferrous metal with said tubular casing.

2. A self-sustaining shield for electrical currents, comprising a rigid tubular casing of ferrous metal, a pair of spaced tubular sheets 01 non-ferrous metal of low electrical resistance disposed within said casing, and a carrier for said tubular sheets which is of non-conducting material and to which each of said tubular sheets is adhesively secured.

3. A self-sustaining shield for electrical currents, comprisin a rigid tubular casing of ferrous metal, a tubular sheet of non-ferrous metal of low electrical resistance disposed within said casing and adjacent thereto, a second tubular sheet of non-ferrous metal of low electrical resistance within said first-mentioned tubular sheet and spaced therefrom, a supporting tubular sheet of insulating material disposed between said tubular sheets, and layers of adhesive securing said tubular sheets of non-ferrous metal to said insulating sheet, said insulating sheet being of suflicient rigidity to maintain said firstmentioned sheet of non-ferrous metal snugly against said rigid casing.

4. A shield as set forth in claim 3 in which said tubular sheets are spirally wound.

5. A self-sustaining shield for electrical currents, comprising a rigid tubular casing of ferrous metal, a tubular sheet of paper within said casing, a tubular sheet of copper adhesively secured to the outer side of said paper sheet and supported in position adjacent said casing by said paper sheet, tubular copper sheet within said paper sheet and adhesively secured thereto, and means for connecting said casing and said copper sheets with ground potential.

WILLIAM F. STAHL.

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