US3717911A

US3717911A - Method of making a nipple-electrode joint

Info

Publication number: US3717911A
Application number: US00113995A
Authority: US
Inventors: I Gazda
Original assignee: SGL Carbon Corp
Current assignee: SGL Carbon Corp
Priority date: 1971-02-09
Filing date: 1971-02-09
Publication date: 1973-02-27
Anticipated expiration: 1990-02-27
Also published as: ES399438A1; FR2124392B1; BR7200698D0; ZA72179B; BE778769A; DE2203226A1; JPS54535B1; CA947052A; FR2124392A1; AU3789772A; IT949660B; DE2203226B2; GB1334627A

Abstract

The invention relates to nipple-electrode assemblies and joints, such as those used in electric arc furnaces, and to a means of distributing thread clearance throughout the assembly and/or joint. These means include the pre-positioning of the nipple in the socket of the electrode section into which the nipple is threaded so as to provide a clearance between the non-load bearing flanks of the threads of said threaded nipple and said threaded electrode socket and the placing within the space between the base of the nipple and the bottom of the socket of the electrode section a hot, non-gaseous fluid, carbonizable material which solidifies upon cooling, thereby preparing a preassembly wherein the nipple is fixed in the electrode section, thereby maintaining the aforedescribed pre-positioning and thread clearance and thereby also providing room for thermal expansion of the threads of the connection. The hot, carbonizable material is introduced into the space between the base of the nipple and the bottom of the socket, while in a hot, fluid condition, through a hole in the nipple after the nipple has been threaded into the electrode socket, after which the carbonizable material solidifies. Upon connection of the projecting end of the nipple into a socket of an electrode section and use in a column of electrodes in an electric arc furnace, the solidified carbonizable material again becomes heated, melts and some of it flows downwardly through the hole into the corresponding space in the socket of the electrode section of the column and then becomes solid and carbonizes due to the heat encountered, thereby locking the nipple in the sockets of both electrode sections joined.

Description

United States Patent 1 Gazda 1 Feb. 27, 1973 METHOD OF MAKING A NIPPLE- ELECTRODE JOINT [7 5,] Inventor: Irvin William Gazda,.lohnson City,

Tenn.

[73] Assignee: Great Lakes Carbon Corporation,

' New York, NY.

[22] Filed: Feb. 9, 1971 2'11 Appl. No.: 113,995

[52] U.S. Cl. ..29/25.14, 13/18, 287/127 E [51] Int. Cl ..H01j 9/00 [58] Field of Search....29/25.l4, 25.13, 25.11, 470.5;

[56] References Cited UNITED STATES PATENTS 3,517,954 6/1970 Snyder et a1 ..287/127 2,510,230 6/1950 Johnson et al ..1 3/18 3,140,967 7/1964 Kaufmann et al. ..l56/91 Primary Examiner-J. Spencer Overholser Assistant ExaminerRichard B. Lazarus Attorney-Wallace F. Neyerlin [57] ABSTRACT The invention relates to nipple-electrode assemblies and joints, such as those used in electric arc furnaces, and to a means of distributing thread clearance throughout the assembly and/or joint. These means include the pre-positioning of the nipple in the socket of the electrode section into which the nipple is threaded so as to provide a clearance between the non-load bearing flanks of the threads of said threaded nipple and said threaded electrode socket and the placing within the space between the base of the nipple and the bottom of the socket of the electrode section a hot, non-gaseous fluid, carbonizable material which solidifies upon cooling, thereby preparing a preassembly wherein the nipple is fixed in the electrode section, thereby maintaining the aforedescribed prepositioning and thread clearance and thereby also providing room for thermal expansion of the threads of the connection. The hot, carbonizable material is introduced into the space between the base of the nipple and the bottom of the socket, while in a hot, fluid condition, through a hole in the nipple after the nipple has been threaded into the electrode socket, after which the carbonizable material solidifies. Upon connection of the projecting end of the nipple into a socket of an electrode section and use in a column of electrodes in an electric arc furnace, the solidified carbonizable material again becomes heated, melts and some of it flows downwardly through the hole into the corresponding space in the socket of the electrode section of the column and then becomes solid and carbonizes due to the heat encountered, thereby locking the nipple in the sockets of both electrode sections joined.

8 Claims, 8 Drawing Figures PATENTEDFEBZYIQB I sumsnm' FIG. 3a

FIG. 3b

PATENIEUFEBZ? i973 SHEET 0F 4 FIGS METHOD OF MAKING A NIPPLE-ELECTRODE JOINT BACKGROUND OF THE INVENTION 1 Field of the Invention This invention relates to the field of graphite electrodes such as those used in electric arc 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.

In ,order to facilitate this continual feed, the electrode sections are suitably bored and threaded at each 8 end to provide juncture means through a correspondingly shaped and threaded nipple. In this manner, a new electrodeis joined to the one being consumed by inserting a nipple into the bore of either the new or partially consumed electrode section and joining the composite electrode section-nipple assembly to the other electrode section. Such nipples and their corresponding bore holes in the electrode sections may have threaded sides which are parallel to the nipple axis. It is generally more customary and advantageous, however, to taper the nipple so that its largest diameter is at its middle and is also at the plane of contact between the electrode sections. Such a tapered nipple is screwed into place in a correspondingly tapered threaded bore or socket of the electrode section with the small diameter end or nipple base going furthest into the electrodebody'. ln threading the tapered nipples for use in joining electrode sections, the thread depth is generally the same whether measured at the small diameter ends or bases or at the large diameter center. lt is also usual that in the assembled 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 electrode sections to loosen and to become unwound from around the connecting nipples thereby frequently causing high power and/or graphite material losses due to increased electrical resistances at the joints and/or an electrode section becoming completely unthreaded and falling into the metal bath at'the bottom of the furnace.

2. Description of the Prior Art There has been a well recognized need to more evenly distribute the aforedescribed clearance differences in order to reduce or counteract thermal stresses which build up due to lack of expansion room and result in cracking the joint, and various methods have been proposed by those skilled in the art to 'accomplish substantially even distribution of thread clearance. For example, this problem and several Nos. 2,970,854; 2,957,716; 3,088,762; 3,134,616; 3,140,967; 3,517,954; and 3,517,957; and also in German Pat. No. 1,091,253.

The difliculties involved with electrode sections becoming loose and/or unwound from the nipple have also been well recognized and US. Pat. Nos. 2,510,230; 2,735,705; 2,828,162; 2,862,748;- and 3,048,433 offer teachings of typical ways which have been suggested for overcoming this problem.

The present invention also relates to and is concerned with a more even distribution of clearance between the threads of the nipple and the electrode sockets and consequent reduction in thermal stresses between a nipple andthe electrode sections into which it is threaded, and also relates to making the connections between the electrode sections and connecting nipples tighter and less able to become unwound, and

offers a novel and advantageous approach for simultaneously accomplishing each of these conditions or objectives.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a nipple-electrode section assembly or pre-assembly in which there is a more evenly distributed clearance (as compared to conventional commercial practices) between the idle or non-load bearing flanks of the threads of the nipple and the threads of the electrode section socket, so as to provide room for thermal expansion of said threads.

It is another object of this invention to substantially evenly distribute thread'clearance throughout a nippleelectrode section pre-assembly, and also throughout an entire electrode joint assembly comprising two electrode sections having threaded sockets in the ends thereof and a nipple threaded into said sockets, joining the electrode sections together. It is another object of this invention to accomplish the-aforesaid more even distribution of thread clearance in an advantageous and practical manner while simultaneously making the'connections between the electrode sections and connecting nipple tighter and less able-to become unwound and proposed solutions for same are discussed in US. Pat.

in a manner which is also novel as compared to techniques which have been suggested or taught by the prior art for solving these problems. I

The invention, in a preferred embodiment, comprises the makingof an improved nipple-electrode section pre-assembly, such as described, by:

a. Providing a hole starting at a point in an end face of one-half of the nipple and terminating at a point in the surface of the other half of the nipple;

b. pre-positioning the nipple nipple and the in of the electrode section by threading an end thereof possessing a hole in its end face into the internally threaded socket so as to provide s space between the base of the nipple and the bottom of the electrode section socket and a clearance between the non-load bearing flanks of the threads of said threaded nipple and the opposing faces of the threads of the electrode socket, said non-load bearing flanks of the threads being those nearer to the ends than to the'geornetric center of the nipple; I

c..introducing a hot, non-gaseous fluid, carbonizable material through the exposed end of the hole of the nipple in sufficient quantity so that immediately upon in- -between the base of the nipple and the bottom of the socket of the electrode section without undergoing any subsequentexpansion; and

d. permitting said hot fluid material to become substantially solid by cooling it to ambient temperature, thereby fixing the nipple in the electrode section and thereby also maintaining the thermal expansion of the threads of the connection.

Preferably the pre-positioning of the nipple in step b is effected by utilizing a temporary positioning means, such as is described hereinafter, which temporarypositioning means is removed after the hot fluid material has been cooled and become substantially solid, as in step d.

The invention embraces not only the process of making the connection or pre-assembly but also the nippleelectrode-section pre-assembly itself, and the electrode joint assembly made by coupling a second electrodesection to the improved nipple-electrode section preassembly, and also the process of making said joint as-' sembly.

Other objects, and coincident advantages, and a complete understanding of the invention will be apparent to those skilled in the art after a study of the drawings, and a reading of the specification and claims.

BRIEF DESCRIPTION OF THE DRAWINGS It has been found that the foregoing objects are achievable by making a nipple-electrode section preassembly such as illustrated in vertical cross-section in FIG. 1 and by using such a pre-assembly as a part of each joint assembly used in the electrode column.

FIG. 2 illustrates auxiliary equipment,viz. a centering jig, which may be used as a temporary positioning means in carrying out the processes of or in making the pre-assemblies of the present invention.

FIG. 3 illustrates in FIGS. 3a, 3b, 3c and 3d embodiments of four alternate hole orientations or arrangements in the nipple that may be employed in the present invention besides the use simply of a central hole as illustrated in FIGS. 1 and 2. The nipple must always possess at least one hole extending in an axial or generally lengthwise direction (c.f. FlGll), but, as is apparent from FIG. 3d, one or more additional holes may also sometimes be employed in conjunction therewith. (This is discussed in more detail hereinafter). The axial or generally lengthwise hole must always start at a point in an end face of one-half of the nipple and terminate at a point in the surface at the other half of the nipple. Preferably the lengthwise hole will extend from one end face of the nipple to the other end face, as illustrated in FIGS. 1, 3a, 3b and 3d. Less preferably it may also terminate at a point in the surface of the other half of the nipple which is not in the opposite end face of the nipple.

FIG. 30 illustratesv this possible embodiment of the invention.

FIGS. 4 and 5 illustrate the final assembled joints described in the present invention, (employing the preassembly illustrated in FIGS. 1 and 2), FIG. 4 illustrating the condition of the joint when first assembled and FIG. 5 illustrating the condition of the joint thereafter after there has been melting and downward flowing of some of the carbonizable material from the space between the base of the nipple and the bottom of the socket of the electrode section of the pre-assembly.

DETAILED DESCRIPTION OF THE DRAWINGS AND OF THE PREFERRED EMBODIMENTS As illustrated in FIG. 1, the nipple l, which as previously stated is preferably tapered, was threaded into a correspondingly tapered and threaded socket of electrode section 2. The nipple was provided with a central, axial or longitudinal hole 8 which extended lengthwise from one end face 6 of the nipple to the other end face 9. The nipple had a major diameter of 10 74 inches, the diameter of the longitudinal hole was 1 is inch and the diameter of the electrode section 2 was 20 inches. The nipple also had a one-third pitch, i.e. three threads per inch, and a taper of l to 6, i.e. its radius decreased by 1 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 hand-tight", i.e. until the threads of both the nipple and electrode socket section were completely engaged. The nipple was then pre-positioned in the electrode section socket by being backed-off a slight amount such as an eighth tum (i.e. 45) so as to provide a clearance between the idle flanks of the threads of said threaded nipple and said threaded electrode socket. A centering jig temporary positioning means was employed during the pre-positioning of the nipple. (More is stated resuch fluid, carbonizable materials and their nature or composition hereinafter). An excess of the hot, fluid, carbonizable material was employed (and this is typical) and this extended partially up the lengthwise or longitudinal hole such as to level 10, which is typically at least midway up the hole 8 and more preferably to a level such as will substantially fill the hole 8 as well as the space 5. As the material cooled to ambient temperature it solidified and substantially or completely filled any void area in the space 5 and also served to fix the nipple in the desired position in the electrode socket. The solidification of the material also maintained the aforediscussed pre-positioning and thread clearance of the nipple, thereby also providing room for thermal expansion of the threads of the connection. The pre-positioning of the nipple also caused the upper faces or load-bearing flanks l1 (viz. the flanks nearer the geometric center of the nipple) to contact the mating faces of the threads of the socket and also caused or created a slight gap or clearance 12 at the idle or nonload bearing flanks or sides 13 of the thread, viz. the

flanks nearer the end 6 of the nipple. (It is clear from, the foregoing discussion, of course, that the pre-as- Drilling the hole 8 off-center may also be resorted to and typical ways that this might be done are illustrate in FIG. 3, embodiments 3a, 3b and 3c. In FIG. 3a the axis of the hole is parallel with the axis of the nipple. In FIG. 3b the hole extends lengthwise from one end face of the nipple to the other end face but the hole is at an angle 7 to the nipple axis. In FIG. 3c the hole starts at a point in an end face of one-half of the nipple and terminates at a point in the surface of the other half of the nipple (as do also the holes of FIGS. 1, 3a and 3b) but does not fully extend to the other end face of the nipple. In other words it exits on the threaded lateral surface of the nipple. This is not as desirable as exiting from a position on r the end face of the nipple but it does define an operable position for introducing the hot fluid material into the 'hole and is within the scope of the present invention.

Also, in this embodiment, the point of exit of the hole on the threaded lateral surface is preferably nearer the end than the center of the nipple but is also typically a distance of at least about one-sixth the length of the nipple from the end.

FIG. 3d illustrates the use of two lateral or generally

transverse holes

8a and 8b which intersect or connect at an angle with the lengthwise hole 8. These holes are typically of smaller diameter than the lengthwise hole 8. FIGS. 3a, 3b, 3c and 3d also show the typical position of the carbonizable material within the clearance space 5 and the holes 8 (and 8a and 8b) of the pre-assembly before the exposed nipple end of the pre-assembly is connected to another electrode section.

, The invention is intended'to cover pre-positioning of the nipple so as to cause a clearance between the idle flanks of the nipple and the threads of the socket of the electrode section no matter how the pre-positioning of the nipple is effected so long as the other steps of the invention are practiced. However, it is preferred that an auxiliary device or temporary positioning means such as a centering jig" be used in order to provide optimum pre-positioning of the nipple.

(The backing-off of 45 of the nipple in the embodiment just described in satisfactory for a nipple having a pitch and taper as set forth. In a more general sense, the number of degrees"backed-ofi'" 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 l to 6, the number of degrees backed off will typically be a value from about 45 to about 90; for standard nipples having a one-fourth pitch (four 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 135).

In the embodiment'of FIG. 2, such a centering jig is illustrated, and is employed in order to pre-position the nipple in the electrode socket and in order to provide a clearance at the idle flank .of the threads of the nipple and the internal threads of the electrode section into which the nipple is threaded.

The centering jig consists of an internally threaded plate 18 which is threaded onto one end of the nipple 1. Casters .19 are coupled through holes in the centering plate to la inch diameter bore air cylinders 17. Three casters and three .air cylinders are typically 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) provides air under pressure to air cylinders 17. The arrangement is such that the casters 19 push in one direction against the face of the electrode section while the threaded plate 18 pulls the nipple 1 in the opposite direction, thus applying an axial pressure or force upon the nipple and pre-positioning the nipple in the socket of the electrode section, and thus providing a. clearance between the non-load bearing or idle flanks 13 of the threads of the nipple and the threads of the electrode section. (Axial or lengthwise and transverse or clockwise directions are shown in FIG. 1).

.free end of the nipple. The centering jig device was then tumed on" by pressurizing the air cylinders 17 to 200 psi each. (Casters 19 were in contact with the face 4 of the electrode section 2). By doing this an axial force was exerted upon the nipple in a direction away from the electrode section. While this axial force was still being applied, the nipple was backed off 45 thus providing a clearance 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 pre-positioning the nipple in the socket of the electrode section. This axial pressure also caused the loadbearing flanks ll. of ,thethreads of the nipple (viz. the flanks nearerthe geometric center of the nipple) to remain in direct and close contact with the mating threads of the electrode socket. Coal tar pitch, having a melting point of C, was heated to 200C and a measured amount of this hot molten fluid was injected through the 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 sufficient amount of the pitch was employed so as to, immediately upon introduction without undergoing any subsequent expansion, substantially fill the space 5 and extend well up into the longitudinal bore 8, such as to a height as illustrated in FIG. 1. The nipple-electrode section pre-assembly was maintained in a fixed position until the molten pitch material had cooled to substantially ambient temperature, thereby causing the pitch to become substantially solid, after which the pressure was released and the jig removed. (A typical cooling time is from 5 to 10 minutes). The pitch solidified at a temperature substantially the same as its melting point. The specific (floating) position of the nipple in the electrode section socket, previously provided by the centering jig, was maintained by the solidification of the pitch which also tightly fixed the nipple in the electrode section socket. The pre-assembly was thus in the desired condition for subsequent employment in an electrode joint by coupling the pre-assembly to a second electrode section.

An obvious danger of shipping an electrode-nipple pre-assembly is the possibility of damage while in transit. This can be 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 asuitable covering, such as molded polyurethane foamed resin. The opposite socketed end of the electrode section of the pre-assembly, which is internally threaded may also be typically covered, such as with a standard type end protector, viz. cardboard taped to the face. These coverings are, of course, removed before the pre-assembly is added to the other electrode section of the joint. I

The pre-assembly is coupled to a second electrode section as illustrated schematically in FIG. 4. This is accomplished by threading the projecting end of the nipple into the socket of the second electrode section until the end faces. of the two sections joined by the nipple are in planar contact. It will be noted that in the illustrated condition the joint has just been made and the pre-assembly of the electrode section 2 and nipple 1 are at the top of the joint and the second electrode second 20 to which the pre-assembly is joined is at the bottom of the joint. This relative position of the electrode sections is essential to the success of the joints made according to the present invention. The second electrode section to which the pre-assembly is connected is the upper electrode in the column of electrodes foran electric arc furnace prior to this threading step, after which, of course, the electrode section of the pre-assembly becomes the upper electrode in the column. The making of the joint and the relative positions of the electrode sections applies both to on furnace and off furnace assembling techniques. The material in clearance space and hole 8 in this FIG. 4 is still in its solidified condition and has not yet melted.

When the thus assembled joint is then heated up, as it is when it is used in an electrode column of a steel furnace, the joint first reaches a temperature which is sufficiently high so as to melt the pitch and thus cause a downward flowing of a portion thereof from clearance space 5 through hole 8 toward a corresponding clearance space 5a between the other end of the nipple l and the bottom of the socket in electrode section 20. (In the embodiment of FIG. 30 the pitch would still flow toward the lower clearance space, even though the exit end of the hole terminates at the surface threads of the nipple rather than at the other end face of the nipple). When the pitch thus melts in this embodiment most of it flows into clearance space 5a but some of it also stays in clearance space 5, particularly at the peripheral portions thereof. When the joint is then further heated the pitch in both clearance spaces becomes solid and carbonized, thereby locking the nipple in each of the sockets of the joined electrode sections.

There are several materials which may be used in the present invention to fill the space 5 between the base of the nipple and the base of the electrode section socket in order to float the nipple in the socket of the elecand in order to be functionable later in the locking sections to the nipple when the pre-assembly is incorporated in an electrode joint and the joint is heated in operation. Pitches and tars are particularly suitable.

In any case the material to be used must be one which is a solid at ambient temperatures (and preferably also up to a temperature of at least about 50C), must be one which will readily melt or flow as a non-gaseous fluid when heated (preferably at relatively low temperatures such as between about C and about C), (so that it can be readily utilized in preparing the preassembly and also later in preparing the electrode joint), must be one which will resolidify when cooled to ambient temperatures (and preferably by the time it reaches a temperature of about 80C, must be one which is carbonizable (i.e. one that leaves a substantial amount of carbon residue upon heating so that it can perform its locking function in the preparation of the electrode joint when the joint is heated to a temperature hot enough to re-melt the material and then to carbonize it), and must be one which does not undergo significant expansion, such as of a foaming" type, when changing from the liquid to the solid state (so that its volume does not change substantially in going back from the solid to the liquid state when the electrode joint is heated in operation).

The preferred materials contain substantial amounts of pitch, such as all pitch, or pitch-carbon flour combinations, or pitch-mixed with minor amounts of carbon aggregate and plasticizer, for example, a mixture comprised of at least about 50 parts pitch and up to about 50 parts carbon aggregate, preferably flour", the term flour" typically designating a material having a particle sizing such that all of it would pass through a 20 mesh Tyler screen, a maximum of I percent would be retained on a 35 mesh screen, and 50 to 55 percent of it would pass through a 200 mesh screen. The pitch may be either coal tar pitch or petroleum pitch. Carbon aggegate" is intended to include such materials as finely ground graphite particles (preferred) finely ground calcined or raw petroleum coke particles, finely ground coal particles and mixtures, the carbon aggregate preferably also all being 10 Tyler mesh.

The material may also include a minor percentage of plasticizer, such as up to about 5 percent by weight of the carbonizable material or pitch, in order to produce a less brittle pre-assembly. Typical materials that might be used as plasticizers or plasticizing agents include stearic acid, kerosene, tars and pitches of lower melting point, etc.

When an electrode section-nipple pre-assembly as described herein is added to a second electrode section of an electric arc furnace column or train, the, nipple in the resulting three-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 inthe prior art of no clearance at the idle flank of the threads of the nipple-half assembled first and maximum clearance at the idle flank of the threads of the second nipple-half assembled. Consequently, there is a reduction in the terminal stresses between the nipple and the electrode sections into which it is threaded with the result that there is a reduction in the degree of splitting and breakage of the joint in furnace operation.

The net efiect, therefore, of centering or balancing the nipple in the joint, is that there are fewer mechanical breakdowns or failures in the operation of the furnace. There are also other advantages inherent in making the nipple-electrode section pro-assemblies and joints in accordance with the present invention. For example, the incidence of thread stripping from the sockets of the threaded electrode sections is virtually precluded because of the more uniform thread loading attending the centering of the nipple. Also, the same material that is used in the preparation of the pre-assembly acts to lock the joint in a tight position upon its use in the furnace thus further acting to prevent unwinding of the electrode joint and thus carrying out two distinct functions which in prior art practices were only capable -of being performed by two separate and distinct solutions for the two problems of: (a) nipple balancing; and (b) nipple fixing in the sockets of the electrode sections.

As has been indicated in connection with FIG. 3d, the possible use of one or more holes in the nipple, in addition to the lengthwise hole illustrated in the drawings, is also within the scope of the invention. Such hole or holes may, for example, be within the nipple in one or both ends thereof and connect at an angle or intersect the hole which extends lengthwise in the nipple; or such hole or holes may take the form of a slot or slots at the surface of the nipple and extend in the lengthwise direction of the nipple from point(s) short of the major diameter and extending to one end of the nipple so as to connect with or communicate with the clearance space between the base of the nipple and the bottom of the electrode section socket. Such additional hole or holes or slot(s) may sometimes be desirably resorted to in order to increase the strength of the connection between the nipple and the electrode section(s) to which it is joined, particularly in cases where the requirement to disengage the nipple from either or both of the electrode sections to which it has been joined is not likely to occur.

An additional advantage of the present invention is that if for any reason it is desired to unthread one of the electrode sections from the nipple (after carbonization) this may readily or controllably be accomplished with certain of the embodiments by using untorquing pressures of the same order or at levels slightly higher than the joint assembly torque level. This is not possible with many joints of the priorart without causing mechanical damage or destruction of one or more of the joined members.

1. 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 correspondingly threaded nipple connecting said sections by, being threaded into said sockets, the steps comprising:

. pre-positioning the nipple in the socket of one of the electrode sections by threading an end thereof possessing a hole in its end face into the internally threaded socket so as to provide a space between the base of the nipple and the bottom of the electrode section socket and a clearance between the non-load bearing flanks of the threads of said threaded nipple and the opposing faces of the threads of the electrode socket, said non-load bearing flanks of the threads being those nearer to the ends than to the geometric center of the nipple, the other end of said threaded nipple projecting outwardly from said socket;

. introducing a hot, non-gaseous fluid, carbonizable material through the exposed end of the hole in the projecting end of the nipple in sufficient quantity so that immediately upon introduction it at least substantially fills the space between the base of the nipple and the bottom of the socket of the electrode section without undergoing any subsequent expansion;

d. permitting said hot fluid material to become substantially solid by cooling it to ambient temperature, thereby fixing the nipple in the electrode section to provide an electrode section-nipple pre-assembly and thereby also maintaining the pre-positioning and thread clearance of (b) and providing room for thermal expansion of the threads of the connection;

. threading the projecting end of the nipple into the socket of the second electrode section until the end faces of the two sections joined by the nipple are in planar contact, said second electrode section being the upper electrode in the column of electrodes for anelectric arc furnace priorto this threading step; and

f. heating the electrode joint so that a portion of the substantially solid carbonizable material first becomes fluid and flows downwardly from the 1 space wherein it had been introduced and solidified, through the hole in the nipple toward the space between the opposite end of the nipple and the bottom of the socket of the second electrode section, after which the carbonizable material becomes solid and carbonized, thereby locking the nipple in-each of the sockets of the joined electrode sections.

2. A process according to claim 1 wherein the hole extends lengthwise-from one end face of the nipple to the other end face.

3. A process according to claim 1 wherein the hot, fluid, carbonizable material includes a substantial amount of pitch.

4. A process according to claim 3 wherein the hot, fluid, carbonizable material consists of pitch mixed with minor amounts of plasticizer and carbon aggregate.

5. A process according to claim 1 wherein the amount of hot, fluid, carbonizable material employed and introduced through the exposed end of the hole of the nipple in step c is sufiicient, before cooling, to substantially fill the hole in the nipple as well as the space 8. A process of assembling an electrode joint according to the process of claim 3 wherein after step d 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 pre-assembly is added to the other electrode section of the joint by the carrying out of steps e andf of claim 1.

Claims

2. A process according to claim 1 wherein the hole extends lengthwise from one end face of the nipple to the other end face.
3. A process according to claim 1 wherein the hot, fluid, carbonizable material includes a substantial amount of pitch.
4. A process according to claim 3 wherein the hot, fluid, carbonizable material consists of pitch mixed with minor amounts of plasticizer and carbon aggregate.
5. A process according to claim 1 wherein the amount of hot, fluid, carbonizable material employed and introduced through the exposed end of the hole of the nipple in step c is sufficient, before cooling, to substantially fill the hole in the nipple as well as the space between the base of the nipple and the bottom of the socket of the electrode section.
6. A process accordinG to claim 3 wherein in step b the nipple is hand-tightened as far as it will go into the electrode socket and is then back off a slight amount in the procedure of providing the thread clearance of said step.
7. A process according to claim 3 wherein a centering jig is employed to assist in providing the prepositioning of the nipple and the thread clearance of step b.
8. A process of assembling an electrode joint according to the process of claim 3 wherein after step d 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 pre-assembly is added to the other electrode section of the joint by the carrying out of steps e and f of claim 1.