US2007277A - Paper covered conductor - Google Patents

Description

July 1935. J. J. KEYES 2,007,277

' PAPER COVERED CONDUCTOR Filed March 24, 1951 Ill! IIIIIIIIIIIIIIIIIL WITNESSES:

INVENTOR Jo/m J (eyes.

Patented July 9, 1935 UNITED STATES PATENT OFFICE lnghouse Electric &. Manufacturing Company,

a. corporation of Pennsylvania Application March 24, 1931,'Serial No. 524,882

8 Claims.

My invention relates to conductors and, more particularly, to conductors that are covered with fibrous or other cellulose materials.

In the winding of coils for electrical devices,

it is desirable to keep the space factor as low as possible. To this end, attempts have been made to replace the cotton, which is generally utilized for covering conductors, by very thin, strips of paper. However, none of these attempts have 10 been practicable. If, for instance, the conductor be cut, the paper. unravels to such an extent that it is difiicult to work. If, to prevent unraveling, the conductor be wrapped with a certain amount of over-lap, the thickness is not much less than cotton wrapping. On the other hand, if the paper be cemented to a bare conductor by a binding agency, in order to prevent the paper from unraveling, the wrapping will be ruptured when the conductor is bent or elongated.

In order to determine by test, what causes the paper to be ruptured, numerous samples of bare conductors were covered with paper and tested by bending and elongating the conductors. During these tests, it was found that the paper would always rupture at a point where it was not securely attached to the conductor. In other words, the rupture did not occur where the minute par ticles of the paper were securely cemented to the conductor.

Upon close inspection of those places where the paper was securely cemented to the conductor, it was found that the interstices of paper were merely enlarged wherever the conductor was bent or elongated. Because of the intimate and secure adhesion at the well-cemented portions, the conductor, when bent or elongated, carries each particle of the paper with it. In this manner, each particle of the paper is supported by the surface of the conductor and rupture of the wrapping does not take place.

This discovery suggested the desirability of utilizing a binding agency which would securely bind substantially all of the minute particles of the paper on the conductor. In order to secure periect adhesion, many'different kinds of binding agencies were tried but none would work successfully on a bare conductor because agent would not evenly adhere to it.

It is, therefore, an object of my invention to cover a conductor, having a coating, by fibrous or other cellulose materials by utilizing a binding agent, whereby the covering will stand. distortion without disruption when the conductor is deformed.

A more specific object of my invention is to the binding provide for wrapping thin strips of fibrous or other cellulose materials around an enameled conductor by utilizing a binding agent which will react with the enamel and which will penetrate the interstices of the wrapping material, thereby 5 binding substantially all of the minute particles of the wrapping material upon the enamel to cause each particle to be carried by it, with the result that the covering will stand distortion without disruption.

A further object of my invention is to provide for binding fibrous or other cellulose material upon an enameled conductor by utilizing a binding agent which reacts with the enamel and which penetrates the material in such manner as to provide a covering for the conductor which will not only increase the dielectric strength but also increase the physical strength of the enamel.

Other objects of the invention will hereinafter become apparent.

This invention, accordingly, is disclosed in the accompanying drawing and comprises the features of construction, the combination of ele-- ments and the arrangement of parts which will be exemplified in the construction hereinafter set forth and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and the objects of the invention, reference should be had to the following detailed description, taken in connection with the accompanying drawing, in which: I

Figure l is a front elevational view of a conductor-wrappmg machine which maybe utilized to wrap fibrous or other cellulose materials around a conductor.

Fig. 2 is an enlarged view of a paper-covered conductor, made in accordance with my invention, parts being broken away to show the various layers of the covering.

Fig. 3 is a cross-sectional View, taken along theline IIIIII of Fig. 2, of a paper-covered conductor, made in accordance with my invention.

The objects of my invention may be accomplished broadly by wrapping thin strips of paper around an enameled conductor and utilizing an alcoholic solution of shellac as a binding agent. The alcoholic solution of shellac is found to re- 50 act, to a certain extent, with the outer surface of the enamel and thus produce a composite binding agent which securely binds the paper upon the conductor. In fact, the paper is so closely bound upon the outer surface of the 5 .enamel as to constitute almost an integral part tion of the enamel and the paper provides a cov-.

ering which can withstand more distortion without disruption than the enamel itself canstand. In fact, it is observed that the paper not only increases the dielectric strength of the enamel but also increases the physical strength. This improvement, results from the novel action of the binding agent which intimately unites the fibrous covering, having considerable strength, with the enamel which is rather brittle because of the fact that the enamel is a material baked on the conductor. To determine whether or not an enameled wire for a conductor meets the requirements or specifications requisite for magnet coils and armature windings, the enameled wire is given an elongation test. If the enamel cracks or peels off, while being elongated, before the wire breaks, it is not only considered'unsatisfactory but also useless and of no value whatsoever, because one defect, however small, is sufficient to cause a short circuit, with the result that the entire magnet coil or armature winding is damaged. In order to meet the required specification, the enamel must securely adhere to the wire up to the breaking point of the wire, which generally occurs between 25 to 36% elongation, depending upon the physical properties of the wire. Therefore, when a thin strip of paper is adhesively bound over the enamel, it must likewise, in order to meet the rigid requirements of the winding operations, withstand an elongation up to the breaking point of the wire.

As heretofore pointed out, when the paper is applied in accordance with my invention, it not only withstands an elongation up to the breaking point of the wire, but also increases the physical strength of the enamel, so that the combination' of the enamel and the paper provides a composite covering which can be more distorted without rupture than the enamel itself. Hence, the effect is mutual in that the paper and the enamelreinforce each other. As is well known in the art, paper by itself can withstand only 1% to 3% elongation, because the elongation occurs only at the weakest portion, being the place where the paper eventually breaks, while the stronger portions do not elongate at all, thus making the total elongation, with respect to the entire length of the paper, very small.'

Should the minute particles of the paper be insecurely cemented to the conductor, the 'minute particles will not, when the wire is being elongated, be uniformly carried along by the enamel, with the result that the paper will soon break or rupture at the point of the greatest stress concentration. However, when all of the minute particles of the paper are securely adhering to the enamel, the paper may be elongated up to the breaking point of the wire, because, in this case, each minute particle of the paper is carried by each corresponding minute part of the enamel, with the result that the interstices of the paper are merely enlarged, but not up to the point of rupture of the fibressince thestresses' are evenly distributed through all the fibres of the paper.

In magnet coils and notably in diamonditself, withstand this abuse, particularly in the diamond-shaped armature windings, where the wire must withstand a certain amount of pounding, scraping, and twisting in order that the wire may be properly formed, and arranged in the armature slots. If it were not forthis fact, the enameled wire itself would be adequate because it possesses sufiicient dielectric strength to electrically insulate the adjacent turns of the wire. Consequently, the paper is primarily put on to protect the enamel from peeling off, while incidentally the paper likewise insures additional dielectric strength. In diamond-shaped armature windings, the wire is bent back very sharply at the apex of the windings and it is at this point where the paper, if it is not securely cemented to the enamel, is most likely to rupture. Therefore, if the paper covering for the wire cannot be elongated up to the breaking. point of the wire or cannot withstand the severe bending encountered in the formation of diamond-shaped armature windings, the paper covering is useless and of no value whatsoever for this particular application.

Moreover, it is not necessary to overlap adjacent turns of the paper in order to secure a good covering, as has heretofore been necessary. Good results are attained when the paper is applied to the conductor with a very slight overlap or with no lap at all. In this way a very thin covering, never before attained, can be produced.

It will be readily understood that the method of wrapping a conductor with but a slight overlap or no overlap at all effects a great saving of paper. Also, the speed at which the paper may be applied is considerably greater than that by the old method, wherein a lap joint was necessary.

Referring now to the drawing, Fig. 1 designates, generally, a machine which may be utilized to wrap a covering on a conductor, in accordance with my invention. In view of the fact that the structural features and the mode of operation of this machine are explained in my copending application Serial No. 524,881, entitled Core-wrapping machines, filed March 24, 1931, and assigned to the assignee of this invention, it is deemed sufiicient in this application to state; generally, the manner in which it operates.

In explaining the operations of the machine, ll designates a supply of enameled wire or conductor which is to becovered by fibrous or other cellulose material. However, I do not limit my invention to covering of an enameled conductor. Any type of coating which will react with an alcoholic solution of shellac will serve as well as enamel. The primary function of a coating, such as enamel, is to provide means for securely binding every particle of the paper to the conductor.

As shown, the enameled conductor is drawn, first, through a container l6 which is provided with a binding agent, such, for example, as an alcoholic solution of shellac. In order to secure perfect adhesion between the paper and the enamel, it is necessary to have the alcoholic content of the binding agent of such value as to cause the solution to adhere to the enameled conductor as it is drawn through the container.

For the purpose of insuring an even and continuous coating of shellac before it is wrapped, the conductor is drawn through a wiping device 11 provided on the top of the container.

After the conductor leaves the wiping device, it is immediately drawn into cooperative relation to a wrapping head 20. Generally stated, the wrapping head comprises means for withdrawing a strip of covering material from a rotatively mounted supply source and wrapping it around the conductor as it travels through the head. After the covering material is wrapped upon the conductor, and immediately upon its leaving the wrapping head, it may be subjected to a wiping action, thereby being pressed closely upon the surface of the conductor. As the finished product leaves the wrapping head, it is wound upon a takeup reel 22. 7

Referring to Figs. 2 and 3 of the drawing, 25 represents, generally, a bare conductor provided with a coating 26 of enamel. The coating immediately surrounding the enamel is an alcoholic solution of shellac and is represented by the numeral 21. As shown, the paper covering 28, which is helically wrapped over the shellac, is so closely bound around the enamel as to constitute almost an integral part of it. In this manner, the paper is securely attached to the enamel and will stand distortion without disruption.

In order to cause the shellac to penetrate the paper and thereby secure perfect adhesion between the covering material and the enamel, it is found that better results can be attained with certain kinds of covering materials especially those having relatively small interstices, if they are heated in a bake oven. However, good results are attained without heating if a very thin soft paper, having relatively large interstices be utilized.

While the illustrated example constitutes a practical embodiment of my invention, I do not limit myself strictly to the exact details herein illustrated, since the structure may be considerably varied without departing from the spirit of the invention, as defined in the appended claims.

I claim as my invention:

1. An. article of manufacture comprising, in combination, an enameled conductor, a covering having a fibrous base for the conductor, and a binding agent comprising an alcoholic solution of shellac to bind the covering upon the enamel, the binding agent having characteristics which enable it to adhere to the enamel and to penetrate the interstices of the covering, thereby binding substantially all of the minute particles of the covering upon the. enamel to cause each particle, when the wire is bent or elongated, to be carried by each particle of the enamel to which it is attached, with theresult that the covering will stand distortion without disruption.

2. An article of manufacture comprising, in

combination, an enameled conductor, a paper covering comprising a fibrous base for the conductor, and a binding agent comprising an alcoholic solution of shellac to bind the covering upon the enamel, the binding agent having characteristics which enable it to adhere to the enamel and to pentrate the interstices of the covering, thereby so binding substantially all of the minute particles of the covering upon the enamel as to cause each particle, when the wire is bent or elongated, to be carried by each particle of the enamel to which it is attached, with the result that the covering will stand distortion without disruption.

3. The method of covering an enameled conductor comprising applying an alcoholic solution of shellac over the enamel and covering the solution by wrapping thin strips of fibrous material around the conductor.

4. The method of covering an enameled conductor comprising applying an alcoholic solution of shellac over the enamel and covering the solution by wrapping thin strips of paper, comprising a fibrous base, around the conductor.

5. The method of covering an enameled conductor comprising applying an alcoholic solution of shellac over the enamel, covering the solution by wrapping thin strips of fibrous material around the conductor and heating the conductor to cause the shellac to penetrate the fibrous material.

6. The method of covering an enameled conductor comprising applying an alcoholic solution of shellac over the enamel, covering the solution by wrapping thin strips of paper, comprising a fibrous base, around the conductor and heating the conductor to cause the shellac to penetrate the paper.

7. The method of covering an enameled conductor comprising applying an alcoholic solution of shellac over the enamel, covering the solution by wrapping thin strips of fibrous material around the conductor and wiping the wrapping material and conductor in the wrapping direction.

8. The method of covering an enameled conductor comprising applying an alcoholic solution of shellac over the enamel, covering the solution by wrapping thin strips of fibrous material edgeto -edge around the conductor and subjecting the wrapping material and conductor to a wiping action in the wrapping direction during the wrapping operation.

JOHN J. KEYES.

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