US2137834A - Service connecter - Google Patents

Description

Nov. 22, 1938. A. B. DIBNER 2,137,834

SERVICE CONNECTER Filed Jan. 16, 1936 High Tenaile Jim-e (.11,

Low Ele t c'oPPer- 355;? conductwtu v INVENT R.

AbrahamBe/ ard [Jib/7e r Patented Nov. 22, 1938 UNITED STATES SERVICE CONNECTER Abraham Bernard Dibner, lPeekskill, N. Y., as-

signor to Burndy Engineering Company, Inc., a corporation of New York Application January 16, 1936, Serial No. 59,302

Ellaims. My invention relates to improvements in service connecters and more particularly to split bolt service connecters for connecting conductors used in power distribution.

In my former Patent-Re. 20,096, I disclose a split bolt service connecter that is forged, as distinguished from all other previous connecters used in the same field that were made on the screw machine.

Split bolt connecters are threaded, for engagement with a nut and these threads were natural- 1y formed on screw machines and the slotted section removed on milling machines. In order to be able to manufacture split bolt service connecters by the screw machine method, it was necesary that the alloys from which they were fabricated be free cutting.

-Inasmuch as service connecters are used for connecting conductors in power distrlbutien, a metal of the highest degree of conductivity was sought. Pure copper was ideal in this respect and possessed many-other advantages, but one important disadvantage hindered its use, as a screw machine product, namely the tool drag of the 25 metal. Also, to attempt to use pure copper on the screw machine would slow up its operation, because of the formation of troublesome burrs which were expensiveto remove. Slotting the bolt in the milling machine added to the diihcul- 30 ties, and as a result, pure copper was never used :though desired.

' These screw machine difficulties limited the metals that could be used to the so-called free cutting alloys. Copper alloys of this character were the free cutting brasses and the so-called hardware or commercial bronzes, which were in reality brasses containing about 10% of zinc. At no time were split bolt connecters made by the screw machine process manufactured of an alloy 40 containing more than 90% of copper.

In my former Patent Re. 20,096, I'succeeded in manufacturing a split bolt connecter of practically pure copper. I accomplished this by forge ing the split bolt and by rolling or die stamping the threads. I thus succeeded in obtaining results never before accomplished in the field, namely, high conductivity andsubstantial saving in metal formerly lost by milling the slot and cutting down the legs of the bolt from the hexagon head or nut size.

In addition, I succeeded in obtaining a surface to the connecter that increased its strength because the metal was worked. It did not expose the softer metal on the inside as is done by the 55 screw machine process. Thus split bolt con-.

necters now manufactured by the forging process are now made of substantially pure copper.

Pure copper was desired for it was thought that the current flowed through two alternate paths 1) directly from conductor to adjacent conduc- 5 tor within the connecter, and (2) from one conductor to the head of the split bolt, through the legs of the split bolt into the nut, then into the pressure bar and ultimately into the other conductor It was thought that this alternate path 10 should be of the highest degree of conductivity to prevent undue losses in the connection.

I have discovered, however. that this fundamental relationship guiding the art for many years is relatively unimportant. By placing a split bolt connecter of pure copper alongside a split bolt connecter of extremely low conductivity metal and subjecting them to identical tests, namely tightening the nuts to the same wrench torque, I found that over the important range of pressures that the resistance of each connection was substantially identical. Thus I was able to revise entirely the fundamental concepts governing the design of split bolt connecters.

Having established that the conductivity of the connecter metal was unimportant and that pure copper need not be used, and having previously eliminated the necessity of manufacturing split bolt connecters on screw machines, I was able to design a split bolt connecter having qualities 30.

never before possessed in this field.

Accordingly, an important object of my invention is to provide a split bolt connecter in which the strength of thematerial was increased to accommodate the pressure involved without adding to the bulkof the connecter.

Other objects are to provide a connecter that is corrosion resistant, that has a definite yield point, that has a thermal co-efilcient of expansion substantially thatof the conductors them- 40 v selves, and that is more economical to manufacture than connecters previously produced. Other objects of my invention will become apparent from the following description and claims when considered with the accompanying drawing, in which- Fig. 1 is a perspective view of the split bolt connecter nut.

Fig. 2 is a perspective view of the follower or pressure bar.

Fig. 3 is a perspective view of the split bolt.

Fig. 4 is a perspective view of the split bolt connecter illustrating its operation. a

Fig. 5 is a perspective view of the split bolt connecter in reverese position illustrating the lower surface of the pressure bar.

Referring to the drawing, reference numeral i0 designates a conventional nut, II the follower or pressure bar, I2 the split bolt which is forged into the position illustrated so that the two legs 53 are arranged in parallel position, the space between the two legs wide enough to permit the pressure bar H to slide freely within the same. The pressure bar Ii is of prismatic construction and is provided with two shoulders I extending longitudinally of the contact face and is provided with a frictioned surface I5 for securely gripping the conductor. The nut I0 is positioned around the pressure bar I l as illustrated in Fig. 4, the lower surface of which rests on the shoulders M. The upper portion of the pressure bar is sliced at It as indicated by the dotted lines in Fig. 2, forcing a section of the metal ll against the upper surface of the nut securely and permanently positioning the said pressure bar within the aperture of the nut, with the pressure bar rotatable freely therein. In assembling the nut and pressure bar with the split bolt, the pressure bar is inserted within the two legs of the bolt and the nut rotated, permitting the pressure bar to travel in a path determined by the flat parallel sides iii of the inner surface of the legs iiwhile the nut is being rotated. In Fig. 4, two sections of cable I! are shown in position'within the space formed by the two projecting legs, and the nut I0 is thereafter rotated until the proper degree of pressure is applied to the cables, the flat surfaces 2! on the two sides of the head of the split bolt I! being useful for holding the bolt in position while tightening the nut. slippage with regard to the U-bolt is avoided by the frictioned surface of the split bolt II at 20 as indicated in Fig. 3.

A service connecter similar to the one above described is illustrated in my Patent No. 1,873,- 559 issued August 23, 1932..

As previously explained, I found that the problem of conductivity was relatively unimportant, and I established that the resistance of the connection depended not upon the conductivity of the split bolt, but almost solely upon the total pressure with which the conductors are forced together. This additional and fundamental relationship has never before been recognized.

In addition, it was previously assumed that in a service connecter, the contact at the pressure bar and at the head of the bolt were important. I have discovered that the resistance of the connection depends not upon the area of contact at the pressure bar and at the head of the split bolt, but upon the pressure that is exerted between the conductors themselves by the service connecter, and that as the pressure increases, the resistance on the direct path between the conductors is cut down to a very low value. low is this direct contact resistance between conductors and so comparatively high is the resistance of the alternate path of current flow through the connecter itself as to render unnecessary the manufacture of the connecter of pure copper; i. e. high conductivity.

Having established that high pressures were necessary, it became important that the alloy of which the split bolt service connecter was to be manufactured should have as much strength as possible irrespective of its conductivity.

In order to obtain high .pressure between conductors, it is, of course, necessary that the alloy of which a split bolt service connecter is contween threads and on the face of the nut.

structed, be sumciently strong to apply that pressure. It is a well known fact that in tightening any sort of bolt, including split bolts, about of the wrench torque exerted by the lineman in tightening these bolts, is wasted in friction be- It is. therefore, evident that in order to obtain high pressures on the conductors, it is necessary that the connecter withstand much greater wrench torque than would be necessary if there were no friction between the moving parts. Thus again, it is established that for efilcient operation, the service connecter must be made of an alloy of extremely high strength. Specifically, this becomes evident when it is recalled that the line- 'men who ordinarily install these service. connecters have only a limited number of tools which they carry to the top of the pole, in the field. In general, they carry only one wrench. Therefore, they must tighten large service connecters and small service connecters with just a single wrench, which is generally a fairly big one in order to make sure that the largest size of service connecter is tightened sufllclently. This means that a small size of service connecter may often be over-stressed because of the great number of inch-pounds that can be exerted on the connecter with a large wrench. In order to prevent such over-stressing, I repeat that it is, of course, necessary that the alloy of which the service connecter is made be of, extremely high strength, and should, for most purposes, have a tensile strength in excess of 45,000 pounds per square inch. There is still another consideration which must be taken into account and that is the factor of reusability. Although the service connecter may be stressed to a point which does not cause its failure, it may be so twisted that when the joint is disconnected, the connecter will be useless for further service. This is a distinct economic disadvantage. Many joints are taken apart every year and are salvaged for further use. If this advantage is eliminated, there is no economic reason for using a split bolt service connecter rather than one of the older methods. For this reason, a connecter which is made of a high strength alloy having a high and definite yield point, and which can be reused many times is of definite utility.

As has been previously explained, present service connecters that are forged are made of pure copper. Pure copper is of course not strong but this was provided for by increasing its size, thereby adding to its strength. Pure copper connecters were therefore oversized and proportionately more costly. Pure copper has the further disadvantage in that it has no definite yield point. It will creep or stretch at even atmospheric temperatures. By creep" is meant a very gradual elongation of the metal when it is subject to pressure. Such elongation is essentially undesirable in a service connecter which may remain installed for a period of 20 to 25 years. the pressure between the wires is relieved and the resistance of the. joint increases. This may progress until such a point is reached that the resistance is sogreat that radio interference will result. In some veryfew cases, the resistance may increase to such a point that the joint may burn out and fail entirely. Radio interference has become an extremely difficult problem and one with which the utilities are experiencing much difliculty. A loose joint will spark and sputter causing considerable static in the neighborhood. This creates many complaints andit is often nec- As the metal creeps,

essary that a utility company send out a crew of men to examine all the joints in the neighborhood untilthe improper connection is found.

It will therefore be evident that the service connecter be made of a metal having a high and 'definiteyield point which. should, I have found,

be in excess of 20,000 pounds per square inch.

Thus, we have so far established the necessity of metal having an extremely. high strength and one possessing a high and definite yield point. This, of course, immediately eliminates the possibility of using pure copper although as has been explained, attempts have been made to use pure copper by increasing the'bulk of the connecter. This is not only expensive, but still does not eliminate the creep of the metal.

Alloys having a high tensile strength and high conductivity are of course known but are either so expensive as to be relegated to what are commonly termed laboratory alloys or offer little resistance to corrosion and cracking, or are too hard for so-called commercial forgings.

Again, alloying copper to increase its strength ,by as little as 1% of another metal, will reduce its conductivity by as much as50%. The alloys contemplated in my invention have in excess of 93% copper and a conductivity running as low as 4%. A split bolt. service connecter installed out of doors is subject to wide variations of temperature. Not only does the atmospheric temperature change daily and with the seasons, but variations in the electrical load cause different temperature rises. It is, therefore, important that the thermal co-efficient of expansion of the alloy from which the connecter is made be substantially identical with the thermal co-eflicient of expansion of the conductor wires. This'is normally accomplished by using an alloy containing a high percentage of copper. The lower the copper percentage, the greater variation there is in the thermal co-efflcient of expansion and the more chance there is of the connecter loosening by not contracting or expanding in the same proportion as the wire does. The alloy, of which the service connecter is made should, therefore, contain a high percentage of copper, and I have found that its thermal co-efiicient of expansion should not vary by more than 10% with the thermal co-eiflcient of expansion of pure copper.

One of the most important factors concerning the nature of the material from which connecters are made is its resistance to corrosion. The great bulk of service connecters are installed outdoors and are subject to atmospheric corrosion. Such corrosion may be more or less severe depending dustrial fumes, saline vapors, etc., are present.

However, all ordinary atmospheres are sufficiently corrosive .to cause considerable damageto many alloys, and it is only in very dry or desert climates that atmospheric corrosion can bemore or less neglected. Ordinary atmospheric corrosion results in a progressive attack on the surface of the alloy exposed to the air, and in certain severely corrosive atmospheres, may penetrate so deeply after a considerable number of years, that failure of the part in service may take place. Such action is accentuated by galvanic or electrolytic corrosion. Electrolytic corrosion is caused by the potential difference between dissiniilar metals in the presence of an electrolyte. Such an electrolyte may often be just the moisture in the air, or such moisture contaminated by sulphuric fumes often found in industrial atmospheres. Thus, if an iron connecter be used to clamp copper wires,

the potential difference would be such that in a very short time the iron would corrode and the connecter would fail. It is for this reason that service connecters used to clamp copper wires must be made of copper alloys. These alloys must be such that the potential difference between them a'nd pure copper is negligible so thatno galvanic corrosion results. An alloy containing over 93% of copper satisfies this requirement.

Unfortunately, although most copper alloys, even those containing a considerable proportion of alloying elements, are not subject to electrolytic corrosion when in contact with copper itself, many copper alloys are subject to an extremely serious type of deterioration which may be designated as season-cracking. Season-cracking results from a combination of, unrelieved internal stresses in the alloy with atmospheric corrosion.

The corrosion attacks the metal, and weakens it along the grain boundaries. When the grain boundaries have been sufliciently weakened, the internal stresses will crack the metal. Alloys of copper containing zinc are especially subject to this form of failure. Various methods have been used to relieve the internal stresses in cold worked rod. The most successful of these methods is the use of a relief anneal which is supposed to relieve the internal stresses without annealing the rod sufiiciently to cause it to lose much of the desirable properties of high strength and greater hardress which are a result of the cold working processes. For this reason, any rod of which screw machine service connecters must be made, cannot be cold worked so that the full potential strength of the material can be attained. In addition, because of season-cracking, certain aloys such as those containing more than 15% of zinc, are no longer used widely for service connecters. At one time, the yellow brasses were in almost universal use as split bolt service connecters, but because of the many failures which resulted from the use of this material, yellow brass is now used only in certain localities where the dry climate and uncontaminated air causes the atmospheric corrosion to be negligible.

A variation of season-cracking which is of especial concern in the design and selection of materials for service connecters, is stress-corrosion-cracking. result of the combination of corrosion and internal stresses; stress-corrosion-cracking is the result of corrosion and externally applied stresses. One feature of my invention consists in heat treating the material in the juncture of the two legs, before bending, which I have found eliminates internal stresses considerably and hence reduces season-cracking.

Externally applied stresses are always present in an installed service connecter. Inasmuch as the efficiency of a connecter results largely. from the pressure it exerts on the wire it clamps, it is extremely desirable that these stresses be high, However, the greater the externally applied Ordinary season-cracking is astresses, the more subject the material is to stress-corrosion-cracklng. Thus, many alloys which would normally be immune to seasoncracking, may fail as a result of atmospheric corrosion combined with high externally applied stresses. Alloys with as little at 10% of zinc have been known to fall within two years, when season-cracking. It is not immune to stress-corrosion-cracking. The greater the percentage oi copper in the alloy, and the smaller the percentage of zinc, the less subject is the alloy to stress-corrosion-cracking'. For this reason, it is extremely desirable to manufacture service connecters of an alloy containing more than 93% oi copper, and with no zinc at all in its composition. The use of such alloys is made possible by the forging process.

Summarizing the various features of my invention, I have found that using an alloy of copper containing more than 93% copper, possessing high tensile strength and a definite yield point, and sacrificing conductivity in order to obtain these last two essential qualities, that I can manufacture a forged split bolt connecter with a tensile strength ranging as high as 110,000 pounds per square inch. Thus I obtain a split bolt connecter which has a high factor of reusability and will not creep as compared to the present types, enabling me to apply a contact pressure of an extremely high order, thus insuring a connection with a very low resistance and a high degree of efllciency. In addition, I obtain a relatively corrosive free metal eliminating to a great extent season-cracking and stress-corrosion-cracking, with a thermal co-eflicient of expansion due to its high copper content closely approximating that of the copper wire itself, thus preventing loosening'of joints, etc.

The service connecter herein described is made by the metal forging process which broadly includes, in my definition, such methods as hot and cold forging, stamping, coining, die pressing, and anyprocess which involves the flow of metal under pressure. 7

I have thus described my invention, but I desire it understood that it is not confined to the particular form shown and described, the same being merely illustrative, and that the invention may be carried out in other ways without departing from the spirit of my invention, and,'therefore, I claim broadly the right to employ all equivalent instrumentalities coming within the scope of the appended claims, and by means of which, objects of my invention are attained and new results accomplished, as it is obvious that the particular embodiments herein. shown and described are only some of the many that can be employed to attain these objects and accomplish these results.

Having described my invention, what I claim and desire to secure by Letters Patent, is as follows:

1. An electrical connecter of the split bolt type having a forged split bolt made of a copper alloy with an electrical conductivity substantially less than that of pure copper, a tensile strength of over 45,000 pounds per square inch, and having a yield point in excess of 20,000 pounds per square inch.

2. An electrical connecter of the split bolt type having a forged split bolt made of a copper alloy with an electrical conductivity substantially less than that of pure copper, a tensile strength of over 45,000 pounds per square inch and having a a thermal co-eflicient of expansion which does not vary by more than 10% from that of pure copper.

3. An electrical connecter of the split bolt type having a forged split bolt made of a copper alloy having a tensile strength of over 45,000 pounds per square inch and having an electrical conductivity of from 4 to 45% of that of pure copper.

4. An electrical connecter of the split bolt type having a forged split bolt made of a copper alloy having a thermal co-eii'icient of expansion which does not vary by more than 10% from that of pure copper, and having an electrical conductivity of from 4 to 45% of that of pure copper.

5. An electrical connecter of the split bolt type having a forged split bolt made of a copper alloy containing more than 93% copper, having a yield point in excess of 20,000 pounds per square inch, a tensile strength of over 45,000 pounds per square inch, a thermal co-efl5lcient of expansion which does not vary by more than 10% from that of pure copper and an electrical conductivity of from 4% to 45% of pure copper.

ABRAHAM BERNARD DIBN'ER.

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