US2546395A - Method of making electrical connectors - Google Patents

Description

March'27, 1951 D. c. HUBBARD METHODYOF MAKING ELECTRICAL CONNECTORS 2 Sheets-Sheet 1 Filed Nov. 7, 1945 IN V EN TOR.

W L /M m 9 March 27, 1951 c HUBBARD 2,546,395

METHOD OF MAKING ELECTRICAL CONNECTORS Filed Nov. 7, 1945 2 Sheets-Sheet 2 INVENTOR.

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Patented Mar. 27, 1951 UNITED STATES PATENT OFFICE METHOD OF MAKING ELECTRICAL CONNECTORS poration of Missom'ii Application November 7, 1945, Serial No. 627,141

The present invention relates to electrical connectors and methods of making them, and is particuiarly concerned with electrical connectors of the split-bolt type which are used for securing together two conductors, such as a transmission line conductor and a tap wire.

One of the defects of the connectors of this type of the prior art is that pressure which is exerted upon the conductors by the connectors of the prior art is such that it causes the soft conductor'material to flow out from under the gripping surfaces of the connectors of the prior art. This makes such connectors loose, even though they have been initially tightened, and, being loose, they become pitted or burned, and the sparking which results from the looseness of the connector is a source of radio interference.

One of the objects of the invention is the provision of an improved connector of the type last described and an improved method of making these connectors which combines the advantages of low cost, rapid volume production, high strength, marked saving in metal, and improved construction.

Another object of the present invention is the provision of an improved split-bolt connector which has a greatly increased contactarea so that the pressure per unit area on the conductor canbe reduced to such an extent that there is no longer any marked tendency for the soft metal of the conductors to flow out from under the clamping surfaces, yet provides adequate pressure for a sound electrical contact.

Other objects of the invention will be apparent from the following description and the accompanying drawings, in which similar characters of reference indicate similar parts throughout the several views.

Referring to the two sheets or drawings accompanying the specification,

Fig. l is a side elevational View of a split-bolt connector embodying the invention applied to tmvo conductors.

Fig. 2 is an end elevational view with the conductor shown in section.

Fig. 3 is a vertical sectional view taken on the plane of the line 3--3 of Fig.

Fig. 4 is a horizontal sectional view taken on the plane of the line 4-4 of Fig. 1 looking in the direction of the arrows.

Fig. 5 is a view perspective of the spring clamping member.

Fig. 6 is a top plan view of the assembly of Fig. 1..

Fig. 7 is aplan view of a blank which is formed 1 Claim. (Cl. 27)

'2 in the first step of the method of making connectors of Figs. 1 to 6.

Fig. 8 is an end view of the blank of Fig. 7.

Fig. 9 is .a side elevational view of the blank of Fig. 7.

Fig. 10' is a top plan view showing the blank after it has been acted upon in the next step of the making of these connectors which consists in the formation of a suitable head and hood flanges.

Fig. 11 is an end elevational view of the metal member or Fig. 10.

Fig. 12 is a side elevational view of the metal member of Fig. 10.

Fig. 1'3 is an end elevational view of the partially completed split-bolt showing its condition after the next step in its formation, which consists in the bending of the metal member of Fig. 10 to the shape of Fig. 13..

Fig. 14 is a bottom plan view of the metal member of Fig. 13.

Fig. 15 is a side elevational view of a split-bolt after it has been subjected to the fourth operation during which a thread is coined on the legs of the bolt.

Fig. 16 is a bottom plan view of the split-bolt of Fig. 15.

Fig. 17 is a side elevational view of the splitbol't of Fig. 15.

The present application relates to an improved construction of a split-bolt connector which is covered by my prior application, Serial No. 624,497, filed October '25, 1945, entitled Electrical Connectors, executed October 16, 1945, and which has since matured into U. '8. Patent No. 2,471,957, granted May 31, 1949.

The present application is particularly concerned with the provision of an improved method of manufacture of such split-bolt connectors which have, up to this time, involved a great many different machining operations which make I connectors of this type relatively expensive.

In order to illustrate the present method of manufacture it is necessary to illustrate first the construction of the connector which is to be made.

Referring to Figs. 1 and 2, Ill indicates the line conductor and H a tap-oii wire which is secured to the line conductor ill by means of a split-bolt connector indicated in its entirety by the numeral 12.

The split-bolt connector 12 preferably comprises three parts, the split-bolt "'13, the nut 14, and the spring clamping member I5. The splitbolt 13 and the nut 14 maybe made of any suitable metal, such as brass, copper, aluminum, annealed duronze, Duralumin, or other suitable alloys, the metal used depending upon the type of conductors with which it is to be employed.

The nut l4 may consist of any type of threaded member having an internally threaded bore Hi, the threads of which are complementary to the threads I! on the shank N3 of the bolt I3.

Various types of nuts may be employed, such as square, hexagonal, etc., but I prefer to employ a hexagonal nut which may be of such size with relation to the spring |5 that the corners [9 of the nut effect some locking section with respect to the portion 25 of the two easy bends 2| in the spring l5.

In other words, the size of the nut may be such that when it is engaging the spring l5, and one of the corners 9 passes the portion 25 of the spring, the corner must press the spring inwardly and ride up slightly over the portion 20. Thus the spring acts as a nut look.

In other embodiments the invention, however, the nut l4 may be smaller, its corners having no engagement with the portions 20 of the spring IE, but its flat upper surface 22 engaging the flat lower surface 23 on the legs of the spring.

The present split-bolt I3 is preferably made by a series of blanking, coining and bending operations out of a strip of sheet metal.

The bolt I3 is preferably provided with an elongated head 24 which is best shown in Fig. 6. This head is elongated for the purpose of providing it with an increased area of contact in the partially cylindrical groove 25. Thus the head 24 is more than twice as long as it is wide, and the groove 25 extends longitudinally of the head on its lower side.

The head 24 is preferably provided with a plurality of flat sides, such as, for example, 26-32. However, it is not necessary that these surfaces all be plane, and it is sulficient if the two opposed surfaces 21, 3| be plane and parallel so that they may be gripped by a wrench.

In other embodiments of the invention the head may take various shapes, provided it is relatively narrow and elongated for the purposes set forth.

The head 24 supports the shank l8, which consists of a pair of legs 34, 35 separated by a parallel-sided groove 36. The groove 35 terminates at its upper end adjacent the head 24 in the partially cylindrical end surface 25 which extends up into the head 24 and is preferably substan tially cylindrical throughout so as to engage a straight cylindrical wire or substantially cylindrical cable.

The size of the partially cylindrical groove or the radius of this curved surface is preferably a few thousandths less than the radius of the wire on which it is to be used so that as the wire or cable is resiliently forced into the groove at the cylindrical surface 25 the wire can fit itself to the groove by extruding some slight portion of the material necessary for this action in the wire, thus providing a maximum area of contact between the wire l0 and the groove 25. 7

It should be noted that the groove 36 has its sides preferably only substantially parallel, as some manufacturing methods require a small amount of draft such as, for example, on the order of five degrees per side longitudinally with respect to the axis of the bolt.

The shank l8 of the bolt is substantially cylindrical and is provided with threads I! and preferably with a grooved cylindrical portion 31 which aids in locating the nut on the bolt and in starting the nut on the threads.

The sides 38, 39 of the groove 25 are preferably substantially plane and parallel, but the groove is also preferably slightly widened, as indicated at 45, adjacent each lateral opening of the groove. This may also be accomplished by making the groove sides 38, 33 slightly convex.

The threads H on the legs 34, 35 of shank [8 are, of course, substantially helical, being interrupted only by the fact that a portion of the material is cut away at the slot 35.

The clamping spring l5 may be made of various types of metal, preferably spring steel or spring bronze, and if the former, they are preferably cadmium or copper plated. This spring is preferably made of sheet metal, so that it may be formed out of a strip by various stamping and bending operations at a minimum expense.

The amount of resiliency of the spring is preferably such that it may be compressed even to a solid condition without passing its elastic limit.

The shape of the spring may vary, depending upon various embodiments of the invention, but it is preferably of substantially the shape shown in Figs. 3 and 4. It has a pair of legs 4|, 42 which are parallel to each other and located to pass through the bore of the nut l4 when the spring is in the bolt.

The legs 4|, 42 may be flat, but are preferably partially cylindrical, the external cylindrical surface 43 conforming substantially to the inside of the nut so that there are no sharp corners on the spring engaging and damaging the threads of the nut.

At the lower end of each leg 4|, 42 there is a laterally turned retaining portion 44, 45, which is located adjacent the end of the shank |8 when the spring is clamped on a pair of conductors H),

The width of the stock of which the spring I5 is made may vary, but it is preferably of a width slightly narrower than the width of the slot or groove 35 in the bolt l3 so that the spring has a freely sliding engagement in the slot of the bolt.

At the upper end of each leg 4|, 42 the spring is bent outwardly and laterally at 46, preferably at substantially right angles, so that the radial portions 47, 48 of the spring have their lower fiat surfaces 23 located to engage the upper fiat surface 22 of the nut.

At a point radially outwardly of the nut |4, indicated by the numeral 49, each leg of the spring is bent outwardly, in Fig. '3, forming an integral, partially cylindrical, easy bend 50. These easy bend portions 50 are integrally joined to the upper elongated clamping portion 5| of the spring which engages the lower side of the wire I This clamping portion 5| is also formed with a V-shaped or partially cylindrical groove 25 which is preferably a few thousandths, such as one or two or three thousandths, smaller in radius than the radius of the wire II which it is intended to engage.

The method of assembly of the parts is as follows:

The spring I5 may-have its legs 4|, 42 bent together far enough so that the retaining flanges 44, 45 clear the inner threaded portions of the nut and then the legs 4|, 42 may be inserted into the nut. Then the clamping portion 5| of the spring is inserted into the slot 36 of the nut, and the nut is threaded on the shank N3 of the bolt l3, the nut rotating as the spring l5 merely slides longitudinally into the slot 36.

The operation of my split-bo1t connector is as follows:

This connector is adapted to be applied to line conductors when energized by means of the improved tool which is shown in my copending application, Serial No. 639,438, filed January 5, 1946, entitled Tools for Applying Connectors to Energized Transmission Lines and the Like and which has since matured into U. S. Patent No. 2,505,186, granted April 25, 1950. It can, of course, also be applied to deenergized conductors by means of the usual wrenches and other tools.

When the connector is to be applied to the line the head of the bolt I3 is clamped in the connector tool, the tap wire ll is held by 'a pair of clamping members in proper position to be inserted inside the slot,.and the nut 14 is held by a wrench member of the tool below and spaced from the bolt so that the bolt can first be placed on the line. Then the wrench is driven upward with respect to the bolt until the nut brings the spring into engagement with the tap Wire which is forced up into the slot until the nut is in position to engage the threads of the bolt.

Rotation of the tool then causes the nut to be threaded on the shank E8, the clamping spring l5 resiliently engaging the lower wire II, which is forced into the groove 52, and which forces the upper wire If! into the groove '38.

It will be recalled that these wires are slightly larger by a few thousandths than the groove into which they are to be forced, and this causes the groove surfaces to have an increased contact engagement with each wire.

The flow of the material of the conductors quickly fits the conductors snugly in the grooves so that the bearing area equals substantially onefourth of the conductor surface and extends over a considerable length due to the elongated nature of the groove in the spring and elongated groove in the head.

Instead of two lines of contact, as would be the case with a V-shaped groove, this connector has two cylindrical areas of contact, these areas being also elongated.

As the spring I5 is compressed the bending takes place at the easy bends 59, and the spring may be compressed without injury until the radial legs 41, 48 engage the lower surface of the clamping portion 5 I.

As the nut rotates on the shank I8, engaging the threads I1, the spring 15 slides in the slot 36. The flexibility and resiliency of the sprin is such that a relatively low unit pressure is applied to the conductors, and the tendency of the relatively soft conductor material to flow out from under the clamping surfaces of the connector is substantially reduced.

In an event, sufiicient tension may be placed upon the spring so that any tendency of the extrusion effect on the conductors to loosen the conductors is taken up by following movement of the spring.

The spring also acts frictionally to prevent the loosening of the nut by vibration, and in some embodiments of the invention may actually act as a nutlock, the corner of the nut being unable to pass'the portion 26 of the spring without extraordinary rotative force applied to the nut.

While the unit pressure in pounds per square inch applied to the conductors is low enough to substantially eliminate flow of the conductors out from under the clamping surfaces, it is still sufficient to provide an adequate pressure for sound electrical contact.

Referring to Figs. 7 to 17, these figures illustrate the condition of the split-bolt during the successivesteps which are taken in the method of its manufacture.

The present split-bolt is preferably made of sheet metal, and the first step in its manufacture consists in making the blank 60, which is shown in Figs. 7 to 9., which may be stamped out of a strip or sheet of metal by means of suitable dies. The sheet metal of which the blank is made is preferably of the same vertical dimension as the thickness which is shown in Fig. 9.

The blank consists of a flat piece of sheet metal having a pair of parallel, straight sides 28, 29, which later form the ends of the elongated grooved body of the bolt. The laterally projecting, substantially rectangular end portions 34 and 35 of the blank 50 are intended to be used to form the legs 35, -35 of the split-bolt, and they are provided with the reduced end portions 31, which form the smaller cylindrical end portions of the shank of the bolt.

The straight edges 16 of these laterall projecting portions 34 and 35 are the parts of the blank which will later be threaded.

The tapered parts of the narrow portions 3d, 35, which are located adjacent the rectangular portion '60 of the blank, are provided in order to assure a full thread at the headof the shank l8. Due to the drawin action imposed on the metal, it has been found that straight sides parallel to each other all the way to the head of the bolt do not allow enough stock for full threads at the head side of the thread coining die.

As the portions 3 3 and 35 are intended to be formed into the legs of the s lit-bolt, they are relatively narrow, and their length corresponds substantially to the threaded length of the bolt shank.

As the central, substantially rectangular portion of the blank '60 is intended to form the elongated head, with its groove and downwardl extending portions on both sides of the groove, this body portionis relatively wide. The distance between the edges 2-3 and 29 corresponds to the length of the elongated head, which has an eX- tended contact area with the conductor wire on which it is secured.

The next step in the making of the split-bolt preferably consists in the coining of a head, and this is done by a stamping operation, with suitable dies, which changes the blank of Figs. 7 to 9 to the shape of Figs. 10 :to 12.

According to this operation, those portions of the body indicated by the numerals -54 and which project upward and downward from the legs 34, 35 in Fig. 7, are compressed until the metal flows laterally, making these portions thinner and wider, as indicated at El and in This leaves the central portion of the body between the legs 34, 35, and indicated by the nu meral 63, of the Same thickness as the legs 34, 35, and reduces the thickness 0f the portions iii, 52 to that required for forming a pair of laterally projecting hoods, indicated at 61, 62, on Fig. l, and greatly increases the length of the elongated head, while utilizing the same amount of metal as is present in Fig. 7.

In some embodiments of the invention the operation which is later described with respect to Figs. 15 to 17, that is, the coining of the threads, may be combined with the second operation just described, that is, the coining of the head, as shown in Figs. 1 0 to 12.

In other embodiments of the invention the coining of the threads may be performed later.

The next operation to be performed on the split-bolt connector is preferably illustrated in Figs. 13 and 14, and, according to this operation, the metal body in the condition of Fig. is bent into shape of Figs. 13 and 14. This is done by means of suitable dies, which are adapted to bend the metal member 66 into substantially U-shape, as shown in Fig. 13, simultaneously forming an elongated transverse cylindrical groove 25 which is preferably a few thousandths less in radius than the wire which it is intended to engage.

The inner surfaces 38, 39 of the legs 34 and 35 provide a clearance on each side of the two wires,

. and may be substantially parallel.

The next step in the formation of the split-bolt connector comprises the coining of the threads on the metal member of Figs. 13 and 14 to place it in the condition of Figs. 15 to 17.

The term coining, as employed in the present specification and claims, is intended to denote the pressing of the metal, by means of suitable dies, to the very close tolerances, such as the operations which are involved in the making of metal coins.

The operation of the formation of the threads not only changes the outer surfaces of the legs 34 and 35 from the rectangular, fiat surfaces at the opposite sides of Fig. 14 to cylindrical surfaces shown in Fig. 16, but impresses upon the cylindrical surfaces the helical threads ll, which are complementary to those of the nut M.

In some embodiments of the invention some preliminary coining of the rectangular sections may be performed for the purpose of partially pro-forming a portion of the thread side. This pre-forming of the rectangular sections on the thread side will increase the life of the thread coining die, and can be done at the same time the top is coined.

The two legs 34, 35 of the split-bolt may be provided with an initially outward spreading tension so that the threads ll resiliently engage the internal threads of the nut l4 and tend to impose a frictional resistance to the movement of the nut, which acts after the manner of a lock nut.

My method of making the split-bolt connectors may be briefly summarized as follows:

A blank is first preferably stamped out of sheet metal; but, in some embodiments of the invention, the blank may be cast, and this is of particular advantage, as cast metal blanks may have the exact characteristics with respect to stamping, extruding, etc. which are desired, but which it is difficult to attain in a sheet metal which has been already subjected to rolling operations, etc.

The metal blank having been stamped or cast, it may then be subjected to coining or forming operations for forming a head, but, if cast, this head may be formed simultaneously during the casting operation.

The blank is then bent in substantially U- shape, and formed with a wire engaging groove at its yoke, which is slightly smaller in diameter than the wire which it is intended to engage, and, thereafter, the legs of the U-shaped blank are subjected to a coining operation for the formation of the helical threads, adapted to engage a clamping nut.

The present method has the advantage that the split-bolts may be made very rapidly, at a very low cost, and this method is particularly adapted for volume production. All of the advantages inherent in the split-bolt connector of my prior application may be maintained, plus the feature of high strength material, either in copper alloy or aluminum alloy.

The present bolt may be provided, according to this method, with the lowered sides of the end hoods so that they cover and further protect both the line conductor and jumper conductor, and there is a marked saving in the use of metal over any of the methods of the prior art.

I desire it to be understood that the steps of forming the blank, coining the head, bending the blank and coining the threads, may sometimes be combined, or the sequence of these steps may be changed, thus increasing the rate of production.

It will thus be observed that I have invented an improved split-bolt connector and an improved method of manufacture of the connector with particular reference to the split-bolt, by means of which these connectors may be made in mass production, at a very low cost. The reduction in the cost of manufacture permits the sale of these connectors at a price which is in the range of a vast number of users.

In another embodiment of the invention wire stock may be employed for making blanks by upsetting the wire at its mid section and then flattening the mid section to obtain the blank which is necessary to form the split-bolt of the connector. By using wire another operation is added, that is, the upsetting; but this reduces the scrap losses that are incurred in blanking the members out of strip.

While I have illustrated a preferred embodiment of my invention, many modifications may be made without departing from the spirit of the invention, and I do not wish to be limited to the precise details of construction set forth, but desire to avail myself of all changes within the scope of the appended claim.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States, is:

The method of making electrical connectors of the split bolt type for maximum contact engagement with an electrical conductor of predetermined size, which comprises stamping a metal blank of uniform thickness out of sheet metal, said blank having a substantially rectangular central body provided with a pair of oppositely extending narrow legs to be threaded, and each leg having a further short extension of smaller size to be unthreaded, forming a head on said blank by compressing those portions of the rectangular body which project laterally with respect to the elongated legs, the said compressing forming a pair of opposite and parallel fiat shoulders on said body and thinning by compressing the laterally projecting compressed portions to form laterally widened hoods on said head for elongated engagement with said conductor, while maintaining the central portions and legs of uniform thickness, bending the members so formed into substantially U-shape with parallel fiat legs of substantially uniform thickness, and having a smaller partially cylindrical formation on the inside of the yoke of said U-shaped member, which is a few thousandths of an inch smaller in diameter than said conductor which it is intended to receive, and simultaneously performing the compressing of the external surfaces of said legs 'into partially round shape, and the coining upon said external surfaces matching helical threads adapted to threadedly receive a standard nut, the narrower end portions of said legs being formed into short cylindrical guiding portions of reduced diameter.

DAVID C. HUBBARD.

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

UNITED STATES PATENTS Number Name Date Seward July 19, 1864 Snook Jan. 23, 1877 Number Hubbard May 31, 1949

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