US2941829A - Electrode connecting nipple and method - Google Patents

Description

June 21, 1960 G. w. MORELLI 2,941,829

ELECTRODE CONNECTING NIPPLE AND METHOD Filed Aug. 25, 1958 2 Sheets-Sheet 1 I INVENTOR.

, /6 Li) BY AT TORNEYS June 21, 1960 G. w. MORELLI 2,941,829

ELECTRODE CONNECTING NIPPLE AND METHOD Filed Aug. 25, 1958 2 Sheets-Sheet 2 \D N Wrn-n g 3 1 INVENTOR. I Q w Mum;

Q BY AT TOR NEYS United States Patent ELECTRODE CONNECTING NIPPLE NIETHOD Gino W. Morelli, Benzinger Township, Elk County, Pa., assignor to Speer Carbon Company, St. Marys, Pa., a corporation of New York Filed Aug. 25, 1958, Ser. No. 757,075

4 Claims. (Cl. 287-127) This invention relates to connecting members, commonly known as nipples, for joining cylindrical electrodes made of carbon or graphite in end to end relation. Such electrodes are employed, for example, in electric arc furnaces where they may carry several thousand amperes of current. In size they range up to three feet and more in diameter and the larger ones commonly are five or six feet or more in length, and may Weigh as much as several thousand pounds.

In the operation of a furnace the electrode is consumed at the arc end and this requires a gradual feeding of the electrode into the furnace. In order to eliminate shutdown of the furnace for the purpose of replacing an electrode which has been partly consumed with a new one it is customary to provide the ends of the electrodes .with axial screw-threaded sockets, so that a new electrode section may be joined to the outer end of a partly consumed electrode by the use of a screw-threaded nipple.

Such nipples preferably are made of material having substantially similar composition to the electrodes which the nipple connects. As the electrode is gradually consumed at its inner end it will be fed intermittently by electrodes should be smooth planar surfaces and should engage each other closely, which tight face to face relationship should be continuously maintained. During operation of the furnace the electrode will be subjected to severe conditions of temperature and vibration. A mechanical joint between the electrode sections which can be depended 0-11 to remain permanently tight is desirable not only to keep the electrical resistance low, but also to prevent relative movement between the electrodes and the nipple which might result in unscrewing of the electrodes on the nipple, or breakage of the nipple, or the socket walls.

In an effort to insure a permanently tight connection between joined sections of electrode under operating conditions it has been suggested heretofore to apply to the engaging surfaces of the nipple and the socket walls, or to portions thereof, a pitch or other bonding, binding or cementing material which will carbonize under the high temperatures to which the electrode will be subjected in operation. A wide variety of bonding materials has been used, and it has been suggested to apply the bond ing material to the engaging surfaces in various Ways. The ends of the electrode sections usually are machined surfaces and since it is desirable that they be in continuous firm contact with each other it is preferable that the bonding material not penetrate between the opposed end faces of the electrodes. Bonding material here might interfere with the desired close seating of the end faces against each other and increase the electrical resistance of the joint.

, Because of the size and the nature of the materials involved, clearance spaces are provided between the threaded surfaces of the nipple and the sockets in the assembled structure. These thread clearance spaces desirably are occupied in whole or in part by bonding material. The bonding material, a solid at atmospheric temperatures, melts as the temperature of the connected electrode sections rises and flows from reservoirs in the nipple into the thread clearance spaces, where it carbonizes and bonds the opposed thread surfaces together.

It is an object of the present invention to provide an improved nipple for joining electrodes made of carbon or graphite and improved method and apparatus for manufacturing such nipples. Other objects, features and advantages of the invention will become apparent or will be pointed out as the description proceeds.

The nipple of the present invention is in the nature of an improvement over the construction disclosed in the H. W. Abbott Patent No. 2,810,117, October 15, 1957.

A preferred embodiment of the present invention selected for the purpose of illustration and description is shown in the accompanying drawings, in which:

Figure 1 is a view showing the ends of two electrodes connected by a preferred nipple made according to the present invention, the view being partly in elevation, and in vertical section through the electrode joint, with a frag mentary portion of the nipple also being shown in vertical section;

Figures 2 and 3 are fragmentary vertical sections disclosing slightly modified nipple constructions; 1

Figure 4 is a side view, partly in elevation and part1 in vertical section, disclosing a pouring mold fixture for introducing pitch into the grooves of a nipple blank; and

Figure 5 is an end view of the apparatus shown in Figure 4, also partly in vertical section.

Referring to the drawings, Figure 1 shows the upper end of an electrode 11 and the lower end of an electrode 12 joined by the screw-threaded nipple 13. The electrodes may be either carbon or graphite and may sometimes be described herein simply as being made of carbonaceous material. The electrodes 11 and 12 are provided at their ends with axially disposed screw-threaded sockets for receiving and engaging the externally threaded nipple 13. In the illustrative embodiment the sockets are frustoconical and the nipple tapers down from its longitudinal midpoint toward each end to match the sockets. It will be understood that this invention is applicable to cylindrical nipples as well as to tapered nipples. Cylindrical nipples are more commonly used for joining amorphous carbon electrodes, while tapered nipples usually are used for graphite electrodes. The size of the nipple desirably will be proportioned to the electrode size to provide maximum mechanical strength as a Whole, in accordance with conventional practice.

Figure 1 shows an electrode joint as it might appear before being subjected to heat suflicient to cause the fusible thermosetting bonding material contained in the nipple reservoirs to melt and flow from the reservoirs into the thread clearance spaces 14, Where it will be carbonized by the heat. Located between the longitudinal center of the nipple and each end face thereof is a circumferem tial reservoir 19 for holding bonding material. These reservoirs are formed, preferably before the nipple is threaded, by cutting circumferential grooves in the nipple blank. This may be done on a lathe.

The bonding material 20 is introduced into the circurnferential grooves before the nipple threads are cut. This bonding material may be a pitch derived from petroleum, coal tar, or natural asphalts, or a combination of two or more of such pitches. The bonding material desirably liquifies at a temperature somewhere between at its ends about 6%.". cut with their centers about 3" from the ends of the nipple.

190" Q and 200 (1., begins to carbonize at about 400 C., and becomes completely carbonized at about 600 C.

The pitches ordinarily used for this purpose are more or le s brit l "Ii t e c rcum r n i grooves in the nipple blank are filled with piteh entirely to the outer eu faee of, the hlank there is danger that the pitch may .ehip or break out during the ensuing threading operation, the pi gh increases the wear on the thread cutting I99? While h s di is llt ma minimize-d y adding asphalt or other plasticising material to the pitch, or by reducing the speed of the thread cutting operation, the rred arnangement should permit a .free selection of the bonding material, and the threading of the nipple at speeds limited only by the nature of the material-formns the n p le l k Applicant has discovered that this desired result can be accomplished by modifying the known practise in filling pitch int o the circumferential grooves of the nipple blank. According to the present invention, after the piteh is introduced into the groove the outer circumferential surface of the ring of pitch lies entirely below the root of the subsequently formed threads. In other words, the thread cutting tool need not engage the bonding mat r al at al Moreover, this result may be attained without materially increasing the depth of the circumferential groove, whieh would reduce the diameter of the nipple at that point and might impair its strength. ln the nipple of the present invention the reservoir space is provided by undercutting one or both sides of the groove below the root of the threads which are formed on the nipple.

As may be seen clearly in Figure l, which discloses the shape of the grooves in transverse section, these circumferential grooves have substantially parallel planar side walls 15 which are undercut at 16. The region of shown in Figure 3 the undercut is rectangular in section.

Reference numbers used on Figures 2 and 3 are the same as used for corresponding parts on Figure 1, except that prime ('1) and double prime marks have been added. It will be understood that the precise shape of the undercut may be varied. These undercut grooves may be formed in various ways. For example, they may be formed on a lathe by using a suitably sha ed turning tool which is run into the blank to the desired slot depth and then moved to right and left to give the desired width of slot undercut.

The dimensions of the grooves are selected to provide reservoir space for holding the amount of bonding 'material required to fill the desired proportion of the thread clearance spaces. In calculating this capacity of the reservoirs it is necesary, of course, to keep in mind that in accordance with the present invention the outer circumferential surface of the ring of bonding material in the circumferential groove lies entirely below the root of the threads on the nipple surface.

Merely by way of example, and without limitation on the invention, dimensions for one particular nipple for joining 14" electrodes will be given. The nipple was 12" long. The diameter at its center was about 8 /2", and Circumferential grooves were The threat of these grooves was /2 wide and the underlltr f the shape shown in Figure l of the drawings, had a maximum width of The depth of the undercut was and this was spaced below the top of the threaded surface, at the center line of the groove, making ring to hold the latter firmly and accurately in position in the outer mold ring.

the total distance from the top of the thread to the bottom of the groove only Obviously the dimensions of the nipple and the number and dimensions of the grooves may be varied from these figures.

After the grooves have been cut in the nipple blank and pitch rings formed therein to the desired depth the blank may be threaded inbonventional manner and the pitch rings will not be disturbed. If the pitch shrinks as it cools and loosens slightly in its groove it will be held, nevertheless, by the undercut. Even if the pitch ring should be fractured in subsequent handling of the conipleted nipple the undercut would hold much or all of the pitch in the groove.

The pitch may be filled into the circumferential grooves of the nipple blank accurately to the desired depth by use of the special pouring mold fixture shown in Figures 4 and 5. This fixture is designed so that simply by interchanging the inside mold rings and adjusting these rings relative to each other to the proper spacing it can be used for filling pitch into several sizes of nipple blanks.

Secured on the upper face of a base 21 are two similar track members 22 arranged in spaced parallel relation. The overhanging inner edges of these track members define with the base 21 a channel in which two similar blocks 23 may be slidably adjusted toward and away from each other.

Mounted in upright position on each of the blocks 23 is the lower half of a split circular mold ring 24, to which is pivotally connected at 25 the complementary top half 26 of the mold ring. Opposite the pivotal connection 25 the lower and upper halves of the mold ring are provided, respectively, with the matching members 27, 28 which engage each other and insure alignment of the two halves of the mold ring when they are turned together.

upper half of the mold ring may be provided with a handle 29 for convenience in turning it about the pivot 25.

As shown, the lower and upper halves 24, 26 of the mold ring are provided on their inner surfaces with circumferential grooves 34, 36 for receiving in keyed engagement the halves 35, 37 of a split inside mold'ring. A series of split inside mold rings have similar outside dimensions and different inside dimensions may be used interchangeably in the pouring mold fixture, adapting it for use with a range of sizes of nipple blanks. The inner side of the inside mold ring conforms to the shape and size of the nipple blank with which it is to be used .andis provided with a centrally disposed circumferential nib which enters the groove in the nipple blank and limits the depth of pitch which can be received in the groove. This. is shown in the left hand side of Figure 4, where 40 is the nipple blank. Each half of the outer mold ring may be provided as shown at 33 with one or more drilled holes to receive screws for engaging matching-tapped holes in the halves of the split inside mold At the top, the outer and inner mold rings are provided with aligned openings forming a pouring spout 38 to receive molten pitch, and to either side thereof with other aligned openings 39 to serve as vent holes.

The invention herein described may be variously modified and embodied within the scope of the subjoined Claims.

I claim:

1. A nipple for joining two carbonaceous electrodes which have axially disposed threaded sockets in the ends thereof, the nipple comprising a carbonaceous body threaded from end to end to engage the sockets for drawing the electrodes into snug end to end relation when they l are screwed together onto the nipple, with thread clearance spaces between the threaded surfaces of the sockets and the nipple in the assembled structure, the said carbonaceous body having between the longitudinal center thereof and each of its end faces a circumferential groove, and in each said groove a ring of fusible thermo-setting bonding material which will melt, flow into the thread clearance spaces, and carbonize under the expected temperatures to which the joined electrodes will be subjected, to bond the electrodes firmly to the nipple, the outer circumferential surface of the ring of bonding material lying entirely below the root of the threads on the nipple.

2. A nipple for joining two carbonaceous electrodes which have axially disposed threaded sockets in the ends thereof, the nipple comprising a carbonaceous body threaded from end to end to engage the sockets for drawing the electrodes into snug end to end relation when they are screwed together onto the nipple, with thread clearance spaces between the threaded surfaces of the sockets and the nipple in the assembled structure, the said carbonaceous body having between the longitudinal center thereof and each of its end faces a circumferential groove the side walls of which are undercut below the root of the threads on the nipple, and a ring of fusible thermosetting bonding material in each said groove filling the undercut portion of the groove.

3. A nipple according to claim 2, in which the outer circumferential surface of the ring of bonding material lies outside the undercut portion of the groove and entirely below the threaded surface of the nipple.

4. In the manufacture of a nipple for joining two carbonaceous electrodes which have axially disposed threaded sockets in the ends thereof, the method which comprises forming between the longitudinal center and each of the end faces of a carbonaceous nipple blank a circumferential groove having radially disposed substantially planar side walls, undercutting the side walls of said grooves spaced radially inwardly below the surface of the blank, temporarily blocking the outer circumferential regions of said grooves outside of the undercut portions,

forming in the undercut portion of each said groove a ring of fusible thermosetting bonding material, and forming an external thread from end to end of the blank with the threaded surface located radially entirely outside of the rings of bonding material.

References Cited in the file of this patent UNITED STATES PATENTS 2,255,184 Osenberg Sept. 9, 1941 2,421,105 Warren May 27, 1947 2,810,117 Abbott Oct. 15, 1957

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