US2894776A - Electrode joint - Google Patents

Description

y 1959 H. v. JOHNSON 2,894,776

ELECTRODE JOINT Filed Aug. 12, 1954 United States Patent fliice 2,894,776 Patented July 14, 1959 ELECTRODE JOINT Harry V. Johnson, Niagara Falls, N .Y., assignor to Union Carbide Corporation, a corporation of New York Application August 12, 1954, Serial No. 449,374 6 Claims. (Cl. 287-127) This invention relates to an electrode joint, especially one of the sort used for large furnace electrodes, and has for an object to reduce the danger of breakage in a threaded nipple joining two electrode sections.

This application constitutes a continuation-in-part of application, Serial No. 300,243, filed July 22, 1952, now abandoned.

A precise analysis of the stresses in such a joint has not been possible because of the high temperature within a furnace when any rupture may occur. Vibration, thermal and mechanical shock, and other causes have been considered in striving to diagnose the cause of any rupture in the nipple. My diagnosis has pointed to the conclusion that flexure is an important factor. The closest known prior art construction is that of Patent No. 2,510,230 dated June 6, 1950 for Electrode Joint, of which I was one of the joint inventors. This was perhaps too stiff at the nipple. In that construction, pitch on being heated, melted and filled the clearance spaces between nipple threads. On further heating the pitch carbonized, acting as a binder to hold the nipple and electrode sections against becoming loosened or unscrewed.

According to the present invention, the hazard of possible nipple failure has been reduced, not by strengthening the nipple, but by shielding it and causing more of the flexural impact stresses to be transmitted directly between electrode sections and without passing through the nipple. More specifically, the end faces of the electrode sections are bonded by pitch filling the pores and crevices in the end faces while these end faces are in good mechanical and electrical contact. Also the clearance spaces between the threads of the nipple and electrode sections are left free, uncemented, and unfilled by pitch. In this way very slight tilting or sliding of the contacting threads of the nipple and electrode may occur as impact flexure is transmitted between the electrode sections. If the face bond should break on the tension side under flexural impact, the localized nipple stresses are not excessive.

In the accompanying drawing:

Fig. 1 is an elevation view partly in section of an electrode joint embodying this invention. Fig. 2 is an enlarged detail of a modification of Fig. 1. Fig. 3 is a view similar to Fig. 1 showing in partial section another embodiment of the invention. Fig. 4 is a detail showing the clearance spaces between threads of the electrode joint of Fig. 1 whichare not filled with pitch.

The invention is an electrode joint comprising a pair of electrodes each having a conventional cavity for reception of a customary nipple, and, additionally, at least one of such electrodes having a recess on an end face into which is placed a carbonizable material, such as pitch, which upon heating becomes liquid and then changes to a carbon residue, acting as a binder.

Referring to the drawing, Fig. 1 illustrates an electrode joint embodying the invention comprising an upper electrode section 10, a lower electrode section 11, and

a threaded nipple 13, all constructed of carbonaceous electrode material. The upper section 10 is provided with a threaded socket 14 to receive the upper end of the nipple 13, and the lower section 11 has a similar threaded socket 15 to receive the lower end of the nipple 13. In the lower end face 16 of the upper section iii is an annular recess or reservoir 17 filled with pitch. As the electrodes become heated during use, this pitch melts and flows into the natural crevices and pores adjacent to the recess 17, and upon further heating carbonizes to form a strong, electrically conductive bond between the abutting end faces of the electrode sections.

In the embodiment of the invention illustrated in Figs. 2 and 3, Figure 2 representing a modification of Figure 1 and showing an annular recess 29 in a lower electrode section instead of a recess in the upper section, an electrode joint comprises an upper electrode section 20, a lower electrode section 22, each having conventional sockets 24, 26, respectively, for reception of a usual nipple 27. In the upper end face 28 of the lower section 22 is an annular recess 29 and in the lower end face 30 of the upper section 20 is an annular recess 31 out of register with the recess 29. Both of the recesses 29, 30, are filled with carbonizable material. In this joint there are thus provided two bonds between abutting end faces of the electrodes. Although gravity may not be expected to cause pitch to flow out of the reservoir shown in the upper end face of a lower electrode section, nevertheless on heating, expansion and foaming will cause considerable pitch to overflow from the recess 29.

Electrode joints embodying the invention are strong after heating and resist loosening during service. Tests have shown that the joint is not loosened by the application of twice the torque applied in assembling the sections. In addition to greater strength, the joint of the invention has better electrical properties than unbonded joints in that its electrical resistance is lower.

The carbonizable material that is most generally satisfactory for use in the invention is coal tar pitch having a melting point of about C. to 175 C. In tests conducted in a production run on steel melting furnaces using 20 inch diameter graphite electrodes, joints of the type illustrated in Fig. l were utilized. The recess in the end face of the upper electnode section was /2 inch wide and M3 inch deep. When filled this recess takes about 0.85 pound of pitch. It was filled with a coal tar pitch having a melting point of C. The end face area rendered unavailable for bonding by the mouth of the recess is not more than about 6% to 15% of the entire area of the end face. This pitch recess should be about 1% inches from the nipple and about 2%. inches from the outer edge of the end face. Over the test period the joint of the invention was satisfactory, no loosening occurred, and no joint was broken. The pitch recess is placed nearer the nipple than to the electrode periphery in order that the recess will not become exposed by oxidation of the periphery until the joint reaches or approaches the arc.

Fig. 4 shows the inevitable clearance spaces 32 which exist at the threads of the nipple. If there were no clearance spaces at each end of the nipple it would be impossible, without great expense, to have the bottom of the socket in each electrode section contiguous the nipple as well as having the end faces of each electrode section in contact. Due to the end faces of each electrode section around the nipple being of larger area than the base of the nipple socket in each section, it is preferable to have the end faces in good mechanical and electrical contact for the sake of improved conductivity. In the present invention the nipple may slide slightly or tilt slightly in the socket of each section as fiexure occurs in the electrode joint. In the present case these clearance spaces around all nipple threads are vacant and the threads are uncemented in order that the aforementioned sliding or slight tipping may occur unimpeded. This means that less localized flexural stresses in the joint occur in the nipple than was the ease in the aforementioned construction of Patent No. 2,510,230 where the presence of the pitch binder filling clearance spaces adjacent the nipple threads made the joint much stiffer, causing substantially all the flexural stresses to be transmitted through the nipple locally. In that prior patent construction there was little or no bonding between the end faces and any bonding that did exist was incidental and unintentional. In the present case on the other hand bonding between the contiguous end faces of the electrode sections does exist and any small amount of pitch that may exude from the pores and crevices in an end face into the nipple thread clearance space is no more than enough to fill only about 5 percent of the thread clearance volume adjacent the interfaces and so small as to be immaterial and not impede the slight sliding or tilting movements referred to. In other words any slight amount of pitch which may get into the nipple thread clearance space in the present invention is not enough to cause an objectionable amount of fiexural stress to be transmitted through the nipple. When the end faces of the electrode sections are bonded, flexural stresses are transmitted directly between such sections without having any substantial amount of those stresses having to pass through the nipple. In the present invention it will be noted there are no longitudinal or transverse passageways formed in the nipple to facilitate the flow and spread of pitch. In fact a much smaller quantity of pitch is used in the present invention than in the former patent construction.

Instead of having a wire gauze or other means to prevent the pitch in granular form from falling out of its recess or reservoir, it has been found that the pitch may be cast or molded into the recess and when so molded is not in danger of falling out under the influence of gravity at temperatures Well below its melting point. A reason for the construction of Fig. 3 is not so much to provide a better bond resulting from two reservoirs being used than is obtainable from one reservoir as shown in Fig. 1, but rather the construction of Fig. 3 is more nearly fool proof in operation, that is the electrode sections when being united by the nipple may sometimes inadvertently become connected wrong side up. It is to constitute a safeguard against this accidentally happening that the construction of Fig. 3 is primarily intended to be safer and avoid the possibility of electrode sections being connected without any pitch bond between them.

What is claimed is:

1. In a connecting joint between sections of an electric furnace electrode comprising electrode sections, a nipple threaded into a socket in each section holding abutting faces of said sections in contact, the improvement comprising at least one electrode section being provided on its face with a reservoir containing a predetermined amount of liquefiable pitch, positioned substantially concentrically with the electrode circumference,

said pitch being adapted upon heating to liquefy and flow from said reservoir, inwardly and outwardly through pores and crevices in the contiguous end faces of said joint, and upon continued heating to carbonize and to bond such end faces and to maintain them in abutting engagement while leaving clearance spaces between said nipple threads and said socket largely unfilled by said pitch.

2. An electrode joint according to claim 1 in which melted pitch will flow by gravity from its recess.

3. In a process of connecting electric furnace electrode sections comprising threading a nipple into each section, uniting said sections with their end faces abutting one another while having clearance spaces adjacent the nipple threads, heating a pitch binder in just sufficient amounts to fill the area of abutting faces, in a reservoir in at least one such section, melting and flowing said pitch from its reservoir, and carbonizing said pitch on further heating the same to bond the surfaces contiguous to said carbonized pitch hinder, the combination therewith of the improvement for connecting said sections to reduce fiexural stresses in said connected sections from having to pass through said nipple, said improvement including locating said pitch reservoir contiguous an end face of at least one of said sections, and of a size such that only a minor portion of the area of said end face in one section outside said nipple is taken up by said reservoir, melting the pitch in said reservoir, causing it to flow radially outwardly and radially inwardly from said reservoir in crevices and pores in the abutting end faces of said sections.

4. An electric furnace electrode joint comprising a nipple threaded into sections of said electrode, at least one section of said electrode being provided with a recess into which a cementitious thermal setting binder is molded in suificient amount to just fill the abutting face area of the electrode sections, said binder being of a type adapted to be melted on heating and capable of flowing by gravity out of said recess into pores and crevices in contacting surfaces and adapted on further heating to thermally set and bond said contacting surfaces.

5. An electrode joint according to claim 4 in which said binder is an electrically conductive pitch having a melting temperature between about C. and C.

6. An electric furnace electrode section containing a threaded axial socket for reception of a nipple, an end face of said section around the nipple socket containing a generally circular recess, a predetermined amount of a thermally setting binder in said recess, and said recess being closer to the nipple socket than to a periphery of the section, said binder being adapted to melt on becoming heated and to flow out of said recess into any pores and crevices in the end face.

References Cited in the file of this patent UNITED STATES PATENTS 1,008,002 Allen Nov. 7, 1911 1,743,888 Hamister Jan. 14, 1930 2,093,390 Wyckofi Sept. 14, 1937 2,147,254 Hinderliter Feb. 14, 1939 2,510,230 Johnson et al. June 6, 1950 FOREIGN PATENTS 351,151 Great Britain June 25, 1931 new

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