US2118924A

US2118924A - Coil and method of making coils

Info

Publication number: US2118924A
Application number: US49700A
Authority: US
Inventors: Fred E Henderson
Original assignee: Western Electric Co Inc
Current assignee: AT&T Corp
Priority date: 1935-11-14
Filing date: 1935-11-14
Publication date: 1938-05-31
Anticipated expiration: 1955-05-31

Description

F. E. HENDERSON COIL AND IBTHOD OF MAKING COILS Filed NOV. 14, 1935 //vv-ro/? E E HENDERSON ATTORNEY May 31, 1938. I

Patented May 31, 1938 UNITED STATES PATENT OFFICE COIL AND METHOD OF MAKING COILS Application November 14, 1935, Serial No. 49,700

6 Claims.

This invention relates to coils and a method of making coils and more particularly to coils having interleaving cellulose acetate sheets.

Investigation has shown that the failure of coils in service is due in many cases to electrolytic cor rosion caused by moisture gaining access to ionizable substances in the coil. This permits an electrolytic current to flow due to the difference in potentials in the several parts of the coil. For this reason it has been proposed to hermetically seal coils to exclude moisture therefrom.

Objects of the present invention are to provide non-corrodible coils and a method of making such coils.

In accordance with one embodiment oi the invention the use of corrosive substances in a coil is avoided by winding the coil with enameled wire and interleaving the layers of the coil with cellulose acetate sheets. A mechanical seal is then formed at the ends of the coil by compressing the ends of the projecting sheets, to prevent the ingress of ionizable substances.

A complete understanding of the invention may be had by reference to the following description taken in conjunction with the accompanying drawing, in which Fig. 1 is an elevational view partly in section showing a coil embodying the invention;

Fig. 2 is a similar view of a coil with the ends compressed, and

Fig. 3 is a perspective view of the coil shown in Fig. 2.

Referring now more in particular to the drawing, Fig. 1 shows a coil having a conductor wound in a plurality of layers 4 of convolutions, each layer being wound upon a sheet of cellulose acetate 5. The outer layer is also covered with a sheet of cellulose acetate overlapped on the periphery of the coil and the overlapping portions may be coalesced by the application of a solvent.

Cellulose acetate is free from ionizable substances and in order that there will be no ionizable substances in the coil, the conductor is insulated with a material which contains no ionizable substances. This insulation may comprise a treated silk insulation of a type disclosed in Lewis et a1. Patent 1,980,413, November 13, 1934, or it may comprise the usual enamel commonly used for insulating electrical conductors. Since all the materials entering the coil are free from ionizable substances, the coil may be exposed to moisture without forming any electrolytes which would cause corrosion as the result of electrolytic currents flowing therein due to the diiference in potential in various parts of the coil.

It has been a common practise heretofore to hermetically seal electrical coils in order to exclude moisture therefrom. This is quite important where the coil contains ionizable substances or in the case where the surrounding atmosphere is heavily laden with ionizable substances. However, when a coil is made of materials which are free from ionizable substances, it is not essential to seal the coils to prevent the ingress of moisture. In many cases even where the atmosphere contains substantial quantities of ionizable substances it is suflicient to form a mechanical seal not completely impervious at the ends of the coil to prevent the infiltration of such substances into the coil.

In winding a coil in accordance with this invention the ends of the cellulose acetate sheets extend axially beyond the ends of the coils. The ends may then be crushed under a high pressure to firmly compact the projecting material against the ends of the coil as shown at B in Fig. 2. It has been found that a coil will withstand extremely high end pressures and a pressure on the order of 6000 pounds per square inch may be applied to the ends of the coil without damage to the coil.

This high pressure so thoroughly compacts the projecting ends of the cellulose acetate sheets against the ends of the coil that the compacted ends present a smooth, plane surface. The ends thus formed, while they do not hermetically seal the coil, form a sufficient seal to prevent corrosion of a coil even'in an atmosphere containing substantial amounts of corrosive material.

For use in some locations the coil may be used in the form shown in Fig. 1, although in general it is desirable to press the ends of the interleaving sheets both for the reason above given and also on account of space requirements.

The coils are preferably wound in multiple on a long mandrel and each layer of convolutions of the conductor is wound on a sheet of cellulose acetate having a thickness of less than one mil and as wide as the group of coils being wound. When the last layer of convolutions has been wound a covering layer 1 of cellulose acetate sheet is applied. After the coils are removed from the mandrel the cellulose acetate sheets between the coils are cut to separate the coils into individual units. Cellulose acetate sheets of the requislte thinness is available on the market. This material may contain ingredients other than pure cellulose acetate provided that they consist solely of non-ionizable substances and the term cellulose acetate" as used in the appended claims is to be understood to have tlrls meaning.

It will be understood that the nature and embodiment of the invention herein describedds merely illustrative, and that many changes and modifications may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A coil free from ionizable substances comprising layers of convolutions of a conductor insulated with an insulating material free from ionizable substances, cellulose acetate sheet material interleaving said layers and projecting laterally therefrom, the projecting ends of the sheet material being mechanically compacted without mutual adhesion against the ends of the coil to form a mechanically crushed but non-united barrier at the coil ends to close the ends and retard the entry of ionizable substances into the coil.

2. A coil free from ionizable substances comprising layers of convolutions of a conductor interleaved with cellulose acetate sheets extending beyond the ends of the coil, the projecting ends being closely compacted but not united against the coil ends to form a dense unbonded barrier for minimizing the entry of ionizable substances at the ends of the coil.

3. A coil free from ionizable substances comprising a conductor insulated with enamel and wound in layers of convolutions, cellulose acetate interleaving sheets between said layers and extending beyond the ends of the coil, the projecting ends of said sheets being mechanically crushed against the coil ends without being joined to form a dense uncoalesced barrier at the coil ends for retarding the entry of ionizable substances to the coil.

4. A method of making a coil which comprises winding each layer of convolutions of a conductor on a sheet of cellulose acetate, said sheets projecting beyond the ends of the coil, and mechanically compacting the projecting portions of the sheets against the coil ends without causing mutual adhesion of the sheets to form a mechanically crushed but non-united barrier at the coil ends for impeding the entry of ionizable substances into the coil.

5. A method ofmaking a coil of non-ionizable materials which comprises winding each layer of convolutions of a conductor on a sheet of cellulose acetate, the ends of said sheets projecting beyond the ends of the coil, and subjecting the coil to a high endwise pressure to mechanically crush and compact without mutually adhering the projecting portions of the sheets against the coil to form adense uncoalesced barrier to minimize the entry of ionizable materials into the coil.

6. A method of making a coil which comprises winding each layer of convolutions of a conductor on a sheet of cellulose acetate, covering the outer layer with a sheet of cellulose acetate, the ends of said sheets projecting beyond the ends of the coil, and subjecting the ends of the coil to an endwise pressure for the purpose of mechanically compacting without coalescing the projecting ends of the sheets to provide a mechanically crushed but not integrally united barrier at the coil ends the coil.

FRED E. HENDERSON.