US3517954A

US3517954A - Electrode section-connecting nipple pre-assembly and process of assembling an electrode joint

Info

Publication number: US3517954A
Application number: US677366A
Authority: US
Inventors: Joseph T Snyder; Charles C Maxfield; Francis H Skinner; James A Whitwell
Original assignee: SGL Carbon Corp
Current assignee: SGL Carbon Corp
Priority date: 1967-10-23
Filing date: 1967-10-23
Publication date: 1970-06-30
Anticipated expiration: 1987-06-30
Also published as: ES359395A1; FR1599803A; SE362186B; DE1804685C3; BR6803337D0; BE722674A; GB1243537A; DE1804685B2; JPS5227374B1; DE1804685A1

Description

June 1970 J. T. SNYDER ETAL 3,517,954

ELECTRODE SECTION-CONNECTING NIPPLE PRE1ASSEMBLY AND PROCESS OF ASSEMBLING AN ELECTRODE JOINT Filed 001;. 23, 1967 United States Patent ELECTRODE SECTION-CONNECTING NIPPLE PRE- ASSEMBLY AND PROCESS OF ASSEMBLING AN ELECTRODE JOINT Joseph T. Snyder, West Nyack, N.Y., Charles C. Maxfield, Chippawa, Ontario, Canada, and Francis H. Skinner and James A. Whitwell, Lockport, N.Y., assignors to Great Lakes Carbon Corporation, New York, N.Y., a corporation of Delaware Filed Oct. 23, 1967, Ser. No. 677,366 Int. Cl. E04g 7/00 U.S. Cl. 287127 7 Claims ABSTRACT OF THE DISCLOSURE An electrode section-connecting nipple pre-assembly is made. The pre-assembly is used in assembling an electrode joint which comprises the pre-assembly and another electrode section. The pre-assembly is made prior to shipment to the user of the joint. It is made in such a manner as to provide a clearance between the non-load bearing flanks of the threads of the connecting nipple and the threads of the socket of the electrode section of the preassembly. Also, prior to shipment of the pre-assembly to the user of the joint, a means is employed to maintain the connecting nipple in a fixed position in the socket of the electrode section of the pre-assembly thereby insuring that the connection of the pre-assembly will not become loose during shipment and thereby also maintaining the aforesaid thread clearance. After the pre-assembly is shipped to the user and is connected to the other electrode section of the final joint assembly, to complete the making of the electrode joint, there is substantially even distribution of clearance between the threads of the nipple and the threads of both electrode sections of the final joint.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to the field of graphite or other carbon electrodes for electric furnaces and like equipment, wherein the electrodes are consumed in use and wherein the electrodes must be continually fed into the furnace or other equipment where they are used. It particularly relates to electrode joints that comprise a double-frusto-conical threaded connecting nipple of electrode material whose two frusto-conically tapering portions are in threaded engagement with respective frustoconical cup-shaped socket recesses in the butt faces of the coaxially aligned electrodes and to the manner in which such a joint is assembled. However, the threaded nipples and their corresponding sockets or bore holes in the electrode sections may also have threaded sides which are parallel to the nipple axis. Such joints serve to add a new electrode to the end of a nearly consumed electrode to permit a continuous furnace operation by replenishing the electrode material in accordance wtih the rate of consumption.

In making such joints, one end of the nipple is screwed into place in a corresponding bore or socket of one of the electrodes to the approximate middle of the nipple and then the other electrode section is threaded to the other end of the nipple until the faces of the electrode sections are in contact. With a tapered nipple, its largest diameter is at its middle and is also at the plane of contact between the electrode sections. The threaded depth of the nipples is generally the same whether measured at the ends of the nipple or at its center and this is true whether the nipple is straight or tapered. It is also usual, with either type of connecting nipple, that in the assembled ice joint each thread will possess a loaded flank, which is nearer the geometric center of the nipple, and a non-load bearing or idle flank which is opposite to the loaded flank. (That is, the idle flank is the flank nearer the ends of the nipple and the loaded flank is the flank nearer the geometric center of the nipple, and this is how these flanks are defined in the present invention.) The loaded flank generally carries most, if not all, of the compressive stress between the nipple and the electrode sections.

In this type of joint, the half that is assembled first usually contains little or no clearance at the idle flank while maximum clearance occurs at the idle flank of the second half assembled.

Such electrode joints are generally mechanically weaker than the full-bodied portions of the electrodes. The joints are therefore particularly susceptible to breaking and are also subjected to additional stresses by thermal tensions occurring during heating and/or cooling and shrinking of the electrodes. The high current loading of modern electro-furnaces causes additional stresses by overheating in the nipple portion at the junction places between the nipple and the electrode sockets. All such thermal stresses are particularly critical with electrodes of large diameters, and in electric furnaces operating at very high voltages as are used for reducing the meltingin period and increasing the furnace capacity.

Description of the prior art The art has Well recognized the aforedescribed inherent mechanical weaknesses of electrode joints and the stresses and thermal tensions to which they are subjected and has taken or suggested several steps or procedures for minimizing same. As a part of the joint problem, the art has also recognized the adverse consequences of improper or asymmetrical screwing-in of the connecting nipple into the sockets of the electrode sections joined by same, and has suggested various expedients for minimizing or overcoming this problem. U.S. Pats. 2,957,716; 2,970,854; 3,088,762; 3,134,616 and 3,140,967 and German Pats. 1,091,253 and 1,100,838 are all, for example, very pertinent to the problem of equal flank spacing or evenly distributed thread clearance in electrode joints and to ways of providing same.

However, these patents and any other prior art references presently known have all approached or attacked the problem of providing even distribution of thread clearance from the point of view of trying to completely solve the problem at the place or site at which the joint is actually used and none have considered or suggested the possibility that a good part of the problem might be solved or overcome if part of the making of the final joint were carried out or accomplished elsewhere than at the users site, such as at the site of the manufacturer of the electrode sections and the nipple. The present invention is addressed to and based upon the taking of this latter approach to the solving of electrode joint problems and especially the problem of even distribution of thread clearance in electrode joints.

SUMMARY OF THE INVENTION An electrode section-connecting nipple pre-assembly is made. The pre-assembly is used in assembling an electrode joint which comprises the pre-assembly and another electrode section. The pre-assembly is made prior to shipment to the user of the joint. It is made in such a manner as to provide a clearance between the idle or non-load bearing flanks of the threads of the connecting nipple and the threads of the electrode section of the preassembly through the use of a temporary positioning means which is also used to coaxially position the nipple in the electrode section. Also, prior to shipment of the pre-assembly to the user of the joint, a means distinct from the temporary positioning means is employed to maintain the connecting nipple in a fixed position in the socket of the electrode section of the pre-assembly, after removal of the temporary positioning means thereby insuring that the connection of the pro-assembly will not become loose during shipment and thereby also maintaining the aforesaid thread clearance. After the preassembly is shipped to the user and is connected to the other electrode section of. the final joint assembly, to complete the making of the electrode joint, there is substantially even distribution of clearance between the threads of the nipple and the threads of both electrode sections of the final joint.

Following are some of the features or benefits and advantages which can be attained by proceeding in accordance with the present invention and by making or employing a nipple-electrode section pre-assembly in a manner such as just described:

(1) The connecting nipple can be centered or floated in one of the electrode sections in the plant of the manufacturen That is, it can be made in such a manner as to provide a clearance between the non-load bearing flanks of the threads of the connecting nipple and the threads of the socket of the electrode section of the pre-assembly. The nipple remains in this assembled form in the electrode section with the aforedescribed thread clearance and the pre-assembly is shipped to the customer. The possibility of the condition of the assembled form being changed or of the nipple becoming loose in transit or when the pre-assembly is connected to the electrode train of the furnace is eliminated by using a paste or cement or a locking substance or some other means as part of the pre-assembly to maintain the nipple in the fixed floating, centered position in the socket of the electrode with the aforedescribed thread clearance. A primary advantage of proceeding in this manner is that the assembling of an improved electrode joint is made more reproducible as compared to prior art techniques because a vital part of its total assembly is carried out under closely controlled conditions rather than by those at the plant of the user of the joint who may not appreciate the problems involved in centering the nipple and the disadvantages which can result if the nipple is not properly centered.

(2) Because of conditions at the site of where the joint is used, it is very difiicult to make a good joint in which the nipple is properly centered at such site. Usually the customer or user of the electrode sections and connecting nipples makes a non-floating pre-assembly at the plant so as to have it ready in case of breakage or major butt losses, etc., in the electrode train of the furnace, such often occurring daily in some steel furnace plants. The said non-floating pre-assembly does not provide the optimum positioning of the nipple as described herein and it may also be on the floor for any length of time, even a day or longer during which time it is typically unprotected. Dust or partices can collect on or in the threads of the pre-assembly, and the threads or faces of same can also be bumped or damaged, etc., because of the exposed conditions of the pre-assembly. Foreign objects on the threads of the joint, or damaged threads, are, of course, very detrimental to the making of optimum joints and/ or to optimum joint performance. In the case of the present invention, a floating pre-assembly has already been made for the customer and the end protectors, which are referred to hereinafter, can be left on until the last minute because they can be removed very quickly. In other Words, there is no longer any concern on the part of the customer of the time required to take nipples and electrode sections out of separate boxes or crates and to make a pre-assembly as there is under the usual former practices. Under former practices, this time element is also, of course, of great concern because it can cause furnace down-time and consequent production losses and this is the reason why the customer typically made one or more pre-assemblies in order to try to avoid or minimize such furnace down-time.

(3) Pre-assembly at the plant of the manufacturer or prior to shipment to the user more readily permits the selection of the proper class or type of nipple to correpond with the electrode. The relative values of the coefficients of thermal expansion (CTEs) of the nipple and of the electrode sections connected by the nipple are very important for proper or optimum joint design and performance, but knowledge of these values is much more within the province of the manufacturer or supplier than it is to the user, who may be entirely unaware of these factors at the time he makes the joint connections. The foregoing considerations apply also, but to a lesser degree, to such relative properties of the nipple and electrode sections as strength and resistivity, which should also be intelligibly matched with a proper consideration of their values in order to insure the making of optimum joints. The possibility, therefore, of the customer or the user of the joint using nipples which do not match well with the electrodes, or vice versa, is eliminated or reduced;

(4) The customer or user of the joint is provided with a labor-saving inasmuch as half of his customary assembling operation is eliminated and he is not required to assemble a free nipple into one of the electrodes. Rather, the customer joins one nipple, electrode-section pre-assembly to another such pro-assembly (which may already be on the furnace) or to another electrode section, such as to the last electrode section of the electrode train of the furnace. The cost-saving to the customer varies, therefore, depending on whether the customer made assemblies on the floor or on the furnace. Regardless of which method he uses, the employment of pre-assembly of the present invention provides a labor-savings.

An obvious danger of shipping an electrode-nipple preassembly is the possibility of damage while in transit. This is overcome in the present invention by protecting the entire exposed machined threaded portion and end or face of the nipple (and typically also, the electrode section face as Well) with a suitable covering, such as molded polyurethane foamed resin. The opposite socketed end of the electrode section of the pre-assembly, which is internally threaded, is also typically covered such as with a standard type end protector, viz cardboard taped to the face.

BRIEF DESCRIPTION OF THE DRAWING It has been found that the foregoing advantages or benefits are achievable by making a nipple-electrode section pre-assembly as illustrated in vertical cross-section in the attached drawing and by using such a pro-assembly as part of each joint assembly used in the electrode train. The drawing also illustrates auxiliary equipment or temporary positioning means, viz a centering jig, which may be used in carrying out the process or in making the preassembly of the present invention.

DETAILED DESCRIPTION OF THE DRAWING AND THE PREFERRED EMBODIMENTS In the embodiment illustrated in the drawing, a centering jig is employed in order to apply an independent axial or longitudinal pressure or force upon the nipple and in order to provide a clearance at the idle flanks of the threads of the nipple and the opposing internal threads of the electrode section into which the nipple is threaded.

Nipple 1, which as previously stated is preferably tapered, was pre-heated to C. and was then threaded into a correspondingly threaded socket of electrode section 2. The nipple had a one-third pitch, i.e. three threads per inch, and a taper of 1 to 6, i.e. its radius decreased by one inch for every 6 inches of length of the nipple away from the maximum diameter. The nipple was threaded into the socket until its major diameter, indicated generally at 3, coincided approximately with the plane of the face 4 of the electrode section and until it was handtight, i.e. until the threads of both the nipple and electrode socket section were completely engaged. In the illustrated embodiment, the nipple was provided with a lengthwise (longitudinal) hole 8 between its ends 6 and 9. Also in this embodiment, the nipple had a major diameter of the diameter of the longitudinal hole was 1%" and the diameter of the electrode section was The aforementioned centering jig consists of an internally threaded plate 18 (2 inches thick) which was threaded onto the free end of the nipple. Casters 19, were coupled through holes in the centering plate to 1 /2" diameter bore air cylinders 17, and contacted the face 4 of the electrode section 2. Three casters and three air cylinders were used, the casters being so spaced as to form an equilateral triangle against the face 4 of the electrode section 2. A source of air (not shown) provided air under pressure (200 psi. each) to the air cylinders. The arrangement was such that the casters 19 pushed in one direction against the face 4 of the electrode section while the threaded plate 18 pulled the nipple 1 in the opposite direction, thus applying an axial pressure or force upon the nipple. While this axial force was still being applied, the nipple was backed off a slight amount (e.g. 45) thus providing a clearance 12 between the idle flanks 13 of the threads of the nipple and the opposing flanks of the threads of the socket of the electrode section 2 and thus prepositioning the nipple in the socket of the electrode section. This axial pressure also caused the load-bearing flanks 11 of the threads of the nipple (viz the flanks nearer the geometric center of the nipple) to remain in direct and close contact with the mating threads of the electrode socket. A two-component polyurethane foaming material was then mixed for about 20 seconds and a measured amount of same was injected through the lengthwise or longitudinal hole 8 and into the cavity or space 5 between the base 6 of the nipple and the base or bottom 7 of the electrode section socket. A sufiicient amount of the foaming material was employed so as to substantially fill the space 5 and extend well up into the longitudinal bore 8 after foaming and becoming rigid. The nipple-electrode section assembly was in a horizontal position when this was done and the electrode was then rolled 180 in order to assist the foaming material in substantially filling this space, after foaming. The-assembly was maintained in a fixed position for approximately 10 minutes, to allow the foaming material to expand, set and become rigid, after which the pressure was released and the jig removed. The specific (floating) positionof the nipple in the electrode section socket, previously provided by the centering jig, was maintained by the setting and expansion of the foaming material.

When such a nipple-electrode section pre-assembly as just described is added to a second electrode section of an electric furnace electrode column or train, the nipple in the resulting 3-membered joint (viz two electrode sections with the nipple half-threaded into each) will be so located that there will be a substantially even distribution of clearance between the idle flanks of the threads of both halves of the nipple in the electrode section sockets of the final joint assembly, rather than the common and objectionable condition typically encountered in the prior art of no clearance at the idle flank of the threads of the nipple-half first assembled and maximum clearance at the idle flank of the threads of the second nipple-half assembled. Stated in another way, the assembling of an improved electrode joint is made more reproducible as compared to prior art techniques wherein the entire assembly operation is carried out at the plant of the user.

The backing-off of 45 of the nipple in the embodiment just described is satisfactory for a nipple having a pitch and taper as set forth. In a more general sense, the

number of degrees backed-off will depend on the pitch and taper of the nipple because the clearance between the threads is a function of these two variables. For standard nipples having a one-third pitch and a taper of 1 to 6, the number of degrees backed off will typically be a value from about 45 to about for standard nipples having a one-fourth pitch (4 threads per inch) and a taper of 1 to 6, the number of degrees backed off will typically be a value from about 60 to about There are several materials which expand upon solidification and which may be used in the space 5 between the base of the nipple and the base of the electrode section socket in the present invention in order to help float the nipple in the socket of the electrode section and in order to maintain the nipple in a fixed position in the electrode socket. Such materials include foaming resins which expand and become rigid upon foaming. Most of these are made by mixing the foamable material with a catalyst and/ or foaming agent just before introducing or injecting the mixture into the aforesaid space. Such foamable resin materials which become rigid upon setting include polyurethane, polystyrene and polyvinyl chloride resin formulations well known to those skilled in the art of making rigid plastic foams.

Several molten metal alloys also have the property of expansion upon solidification and may be used in the space 5 in the present invention in order to maintain the desired clearance between the threads and in order to maintain the nipple in a fixed position in the electrode socket. (As the metal solidifies and expands, the nipple 1 is kept or locked in the desired position in the socket of the electrode.) The following compositions, wherein the numbers are approximate percentages by weight, and having the properties set forth opposite same, are typical or preferred alloys which may be used:

Properties Melting temperature or range Electrical resistivity of alloy in ohm-inches 0. 82X 10 5 O. 49X 10- Alloy copper (e) 15 antimony, 82 lead, 3 tin 275 Because of the fact that all of the foregoing alloys exhibit a cumulative growth during and after solidification (as a result of expansion either upon being cooled from their molten state to their solid state, and/or because of linear growth after solidification), a very tight connection is made between the nipple and the electrode section. The connection so made is also very strong mechanically and has a very low electrical resistance.when any of these alloys is used in making the pre-assemblies or joints as described herein.

The present invention is intended to include any nippleelectrode section pre-assembly made prior to shipment to the user wherein the pre-assembly is made in such a manner that a temporary positioning means is employed to provide a clearance between the idle or nonload bearing flanks of the threads of the connecting nipple and the threads of the socket of the electrode section of the preassembly, and wherein, prior to shipment of the pre-assembly to the user, a means distinct from the temporary position means is employed to fixedly maintain the connecting nipple in the position in the socket of the electrode section of the pre-assembly initially provided by the temporaty position means, thereby also maintaining the aforesaid thread clearance after the temporary position means has been removed. Although the foregoing described techniques (referred to in connection with the drawing) for accomplishing these conditions are preferred, it should be appreciated that there are several other ways also of carrying out the invention. For example, the pre-assembly does not have to be made using a nipple containing a lengthwise hole and an expandable material injected or introduced through said hole. Rather, the nipple may be solid but floated in the electrode section socket by using a centering jig to hold it temporarily in place as described and it may then be fixed permanently in place in several ways such as by providing or drilling one or more transverse holes in the electrode section socket wall and injecting a cement or paste or binder in said holes and heating said materials until they set so as to lock the nipple in place. (Preferably such hole or holes would lead to the space between the base of the nipple and the bottom of the electrode socket, but it or they may also lead to the threaded area between the nipple and the socket.) Or locking pins may be inserted or driven through such radial holes so as to exert a mechanical locking action (rather than a cementing action) against the nipple, so as to maintain the nipple in a fixed position in the electrode socket of the pre-assembly, with the idle flanks of the threads of the nipple floating in the electrode socket. Or a lengthwise hole may be used in the nipple, together with a centering jig to hold the nipple temporarily in place, and a filling substance may then be injected through the hole to fill the space between the base of the nipple and the bottom of the electrode socket. The filling substance need not be expandable, just so long as enough of it is in jected into the space while the axial force is still being applied by the centering jig, so that when the centering jig is removed, the idle flanks of the threads of the nipple are prevented from falling or moving and thus contacting the mating flanks of the threads of the socket.

In other words, the main novel aspects of the present invention do not reside in the particular means which are employed to maintain the nipple fixed in the electrode socket, with a clearance between the non-load bearing flanks of the threads of the nipple and the threads of the socket, but rather reside in the broader concepts of providing a pre-assembly, of preparing this pre-assembly in a prescribed manner so as to have the aforedescribed thread clearance prior to shipping it to the user of same, and in insuring, prior to shipment of the pre-assembly to the user, that the user receives same in the same ideal condition that it was when-it was shipped (no matter what particular means are employed to maintain the nipple in this condition). By so following or carrying out these concepts, the aforediscussed several advantages of the present invention over the prior art practices are thus realizable when the pre-assembly is then shipped to its user and is then added to another internally threaded electrode section to complete the making of the electrode joint.

It is to be understood that the invention is not limited to the specific details which have been offered merely for illustrative purposes and that modifications may be made Within the scope of the appended claims without departing from the spirit of the invention.

I claim:

1. A process of producing a ready for shipment electrode section-nipple pre-assembly, for use in an electrode joint comprised of said pre-assembly and a second electrode section, said nipple being threaded and said sections possessing correspondingly threaded internal sockets extending inwardly from their end faces, which comprises:

(a) threading one end of a threaded nipple into the internally threaded socket of an electrode section in such a manner as to coaxially position the nipple in said electrode section socket by a temporary posi- 8 tioning means and also in such a manner that the temporary positioning means provides a clearance between the non-load bearing flanks of the threads of said nipple and of said threaded electrode socket, the other end of said threaded nipple projecting outwardly from said socket;

(b) employing a means distinct from the temporary positioning means to fixedly maintain the nipple in the position in the electrode socket provided by step (a) with the coaxial positioning and the thread clearance preserved; and

(c) removing said temporary positioning means from said nipple fixedly pre-positioned in the electrode section;

said pre-assembly being adapted to be added to a second electrode section to complete the making of the electrode joint by threading the projecting end of the nipple into said second electrode section thereby also providing substantially even distribution of clearance between the threads of said nipple and the threads of the sockets of the electrode sections in the making of the final joint assembly.

2. A ready for shipment electrode section-nipple preassembly made according to the process of claim 1.

3. A ready for shipment electrode section-nipple preassembly made according to the process of claim 1 wherein the projecting threaded portion and the face of the nipple on one end of the pre-assembly are protected with a covering before the pre-assembly is shipped to its place of use.

4. A pre-assembly made according to the process of claim 1 wherein the threaded socket of the electrode section and the nipple threaded into said socket are correspondingly tapered.

5. In the process of assembling an electrode joint comprising two electrode sections containing internally threaded sockets which extend inwardly from end faces of said sections and a threaded nipple connecting said sections by being threaded into said sockets, the improvement wherein the joint is made utilizing the preassembly of claim 1.

6. A process of assembling an electrode joint according to the process of claim 5 wherein the projecting threaded portion and the face of the nipple on one end of the pre-assembly are protected with a covering before the pre-assembly is shipped to its place of use and wherein the covering is removed before the preassembly is added to the other electrode section of the joint.

7. A process of assembling an electrode joint according to the process of claim 5 wherein the threaded sockets of the electrode sections are tapered and wherein the nipple threaded into said sockets are tapered and wherein the nipple threaded into said sockets is correspondingly tapered.

References Cited UNITED STATES PATENTS 3,140,967 7/1964 Kaufmann et al. 287-127 X 2,873,765 2/ 1959 Gregory 138-96 2,957,716 10/1960 Kaufmann et al.

2,989,087 6/ 1961 Higgins 138-96 3,088,762 5/1963 Kaufmann et al.

3,134,616 5/ 1964 Kaufmann.

DAVID J. WILLIAMOWSKY, Primary Examiner W. L. SHEDD, Assistant Examiner US. Cl. X.R.