US3646240A

US3646240A - Electrode joint

Info

Publication number: US3646240A
Application number: US67818A
Authority: US
Inventors: John G Lewis
Original assignee: Air Reduction Co Inc
Current assignee: Airco Inc
Priority date: 1970-08-28
Filing date: 1970-08-28
Publication date: 1972-02-29
Anticipated expiration: 1989-02-28

Abstract

A furnace electrode assembly of the type including a pair of electrode sections having tapered threaded sockets and a nipple threaded into each of the sockets to hold the sections in faceto-face contact is characterized by a pair of counterbores at the bottom of the sockets and a portion at the center of the nipple which is devoid of threads.

Description

United States Patent Q 6/1950 Johnsoner Lewis Feb. 29, 1972 [54] ELECTRODE JOINT 3,016,343 1/1962 Krenzke 287/127 E X [72] Inventor: John G- Lewis Ann Arbor Mich. 3,540,764 11/1970 Paus ..13/18 X [73] Assignee: Air Reduction Company, Incorporated, Primary Gilheany New york, y Assistant Examiner-R. N. Envall, Jr. [22] Pl d A 28 1970 Attorney-Edmund W. Bopp and H. Hume Mathews le 1 8- 9 1 21 Appl. No.: 67,818 Y [57] ABSTRACT A furnace electrode assembly of the type including a pair of electrode sections having tapered threaded sockets and a nip- [52] U.S.Cl ..l3/18, 287/127 E ple threaded into each of the sockets to hold the Sections in [51] '3" "Hosb 7/06 face-to-face contact is characterized by a pair of counterbores [58] Field of Search ..13/18; 287/127 E at the bottom f the Sockets and a portion at the center of the nipple which is devoid of threads. [56] References Cited 7 Claims, 2 Drawing Figures UNITED STATES PATENTS Pate nted Feb. 29, 1972 2 Sheets-Sheet 1 FIG.

I N Vli'N'l ()R JOHN G, LEWIS Pa ented Fb.29, 1972 3,646,240.

I 2 She ets-Sheei; 2 I

FIG, 2

. INVENTOR.

' JOHN. GyLEWIS This invention relates generally to electric furnace electrodes, and more specifically relates to an electrode assembly of the type including abutting carbon or graphite electrode sections, which are securely held in face-to-face relationship by a nipple threaded into a socket in each section.

Electrode assemblies of the type indicated in the foregoing paragraph, generally comprising carbon, graphite, or a similar carbonaceous material, are widely utilized in the electric furnaces of the steel making and metal-smelting industries. In the environments to which such assemblies are exposed in these industries, the electrodes and connecting nipple are subjected to great thermal stresses, and to impact loading which occurs, for example, when the electrode assembly is struck by falling scrap or the like. As the electrode assembly is already under considerable mechanical stress, due both to the requirement that is support its own weight and to effects resulting from the torque used to tighten the joint, the added thermal and impact stresses often results in failure of the joint, with cracking or splitting occurring either in the electrode sections, in the nipple, or in both. Such defects will at a minimum result in power being wastefully dissipated at the high-resistance breaks rather than in the metallurgical processes wherein the energy is intended to be dissipated; in other instances complete breakage of the joint may ensue, with resulting collapse of the electrodes into the melt.

In accordance with the foregoing, it is an object of the present invention to provide an electrode joint assembly exhibiting increased ability to withstand thermal and impact loading.

It is a further object of the invention to provide an electrode assembly with increased capabilities for elastic deflection.

It is another object of the invention to provide an electrode assembly, the construction of which prevents the buildup of destructive stress concentrations, such as in thread roots at the base of the electrode socket.

It is a yet further object of the invention to provide a nipple construction for use with electric furnace electrodes, which increases the ability of an electrode assembly utilized therewith to withstand elastic deflection, such as that imposed by impact loading.

It is an additional object of the invention to provide electrode sections for use with a connecting nipple in an electric furnace environment, which sections are possessed of increased elastic deflection properties when in assembly with said nipple, and which moreover include transition for fro transferring the load from the electrode sections to the joint threads and back, without developing the destructive stress concentrations evidenced in conventional structures.

SUMMARY OF THE INVENTION In accordance with the present invention, the foregoing objects, and others as will become apparent in the course of the following description, are achieved by an electrode joint assembly which includes a nipple having a center portion which is unthreaded and of reduced cross section, and a pair of abutting electrode sections which are provided with deep counterbores at the internal terminations thereof, the said electrode sections being preferably provided as well with a BRIEF DESCRIPTION OF DRAWINGS The invention is diagrammatically illustrated, by way of example, in the appended drawings, in which:

FIG. 1 is a vertical cross section through an electrode assembly in accordance with the invention, and illustrates in a generalized fashion the principal features thereof; and,

FIG. 2 is a diagrammatic vertical section of the assembly, and sets forth various parameters significant to the practice of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, a vertical section is shown of an assembly 3 in accordance with the invention. As seen therein, a pair of female electrode sections 4 and 5, typically formed of graphite, carbon, or the like are in face-to-face relationship, with the abutting faces being held in firm contact by the nipple 9, which is threaded into each of the sections 4 and 5 and is formed of material corresponding (essentially identical) to that in the electrode sections. The use of a nipple in the manner set forth to yield an assembly of this general type is conventional, the assembly typically being formed by first inserting the nipple into one threaded socket 6 of a female section and then threading the other section about the nipple until a tight joint is achieved.

The nipple 9 shown in FIG. 1, unlike conventional nipple constructions of the prior art, is not shaped so as to essentially conform to the internal cavity defined by sockets 6, but rather includes a center portion 11 which is not only devoid of threads, but which is moreover at the center thereof reduced in cross section as compared to the end portion of the nipple. As a result, nipple 9 is actually in threaded contact with sections 4 and 5 only at the ends thereof beyond the portion 11.

The electrode sections 4, 5 in addition to having the usual threaded sockets 6 therein, include at the terminations of sockets 6, contiguous,

voluminous counterbores

7 and 8,

which smoothly merge with the threaded sockets 6. The sections 4 and 5 also may include shallow relief grooves 2 in their abutting faces.

The specific characteristics of the assembly 3 construction shown in broad outline in FIG. 1, are best seen in the diagrammatic depiction of FIG. 2. With respect firstly, to the nipple 9, it is seen therein that the nipple 9 is of length M, and differs from conventional constructions in having a center unthreaded portion 11 of length L. This portion 11 is of a reduced cross section, the minimum diameter D being not greater than the minor diameter of the first adjacent thread and preferably being less than the minor diameter C of the small end threads of sections 4, 5. (Typically C-D='k inch for nipples for 20 or 24 inch electrodes.) This portion 11 not only renders the nipple better able to absorb impact loads elastically, but as portion 11 will stretch farther under a given preload, it will tend too to keep the joint tight within reasonable limits of mismatch of the coefficient of thermal expansion of the electrode and nipple. The length L in a typical 20 or 24 inch diameter (.I graphite electrode joint may be in the range of 2 to 9 inches; while the upper end of this range permits a higher degree of flexure in the joint under dynamic loa;ing, account must also be taken of stresses induced by shear deflection of the remaining threads of nipple and socket under dynamic loading. The shear deflection referred to occurs much as though thin coaxial cylinders of graphite slide over each other like the sections of a telescope. In consideration of this factor, it is preferably for L to be at the lower end of the range cited (preferably about 10 to 15 percent of the diameter of the electrode joint), the reduced tensile deflection resulting from a shorter value of L being more than offset by the increased number of threads which can simultaneously carry load because of the flexibility in shear just mentioned.

The reduced portion 11 of nipple 9 is typically formed to be equivalent to a standard nipple from which the center threads have been machined to yield a straight section of length N and diameter D, an arc OP (which is a surface of revolution) being formed to smoothly connect the thus reduced section with the remaining threads at the end of the nipple. This smooth arc OP serves to transfer the load from electrode proper to the joint threads without destructively concentrating stress.

The

counterbores

7 and 8 of FIG. 1 and 2 are produced by removing material below thethreaded socket 6 of electrode sections 4 and 5 to a diameter A, not less than minor diameter C of the small end nipple threads; preferably A is somewhat greater than B, the major diameter of the large end threads in a typical case A is about 1 inch larger than B for or 24 inch electrodes. The largest practical fillet radius, e.g., radius of 6 inches, is used to join minor diameter of threads and the bore diameter and to terminate the bore in a rounded bottom.

The

counterbores

7 and 8 provide a portion of electrode which is less stifi than the electrode proper and thereby serve as transition zones between the electrode and the joint. As was mentioned in connection with are OP, the surface of revolution represented by arc EFG serves to transfer the load from electrode proper to joint threads and back again without destructive concentration of stress. It should be noted, however, that arcs EF, EG, and OP, all may be made parabolic.

The shallow relief grooves 2, described in connection with FIG. 1, are seen in FIG. 2 to extend out from the large end of sockets 6 to a diameter specified as I. I will typically exceed dimension B by from 2 to 4 inches in the case of the typical 20 or 24 inch electrode. i.e., (l-B) will representatively be of the order of 9 to 20 percent the value of dimension J. Grooves 2 will representatively be less than 0.100 inch in depth.

Grooves 2 aid the socket threads to deflect more nearly as a unit, and also tend to force the compressive reactions on the electrode section faces to occur farther away from the CD. of the socket threads. This salutary effect is enhanced and compounded by the construction referred to, wherein dimension D is made less than C, and A is made greater than B.

While the present invention has been particularly described in terms of specific embodiments thereof, it will be apparent that numerous variations may be made without departing from the invention. Accordingly, the present invention is to be broadly construed, and limited only by the scope and spirit of the claims appended hereto.

Iclaim:

1. In a furnace electrode assembly of the type including a pair of electrode sections having tapered threaded sockets therein and a nipple threaded into each of said sockets and holding said sections in firm face-to-face contact, the improvement comprising:

a. a pair of counterbores at the bottom of said sockets, of

diameter at least as great as the small end diameter of said socket;

b. said nipple including a portion at the center thereof which is devoid of threads and includes a cross section of diameter less than the minor diameter of the first adjacent thread thereto; and

c. shallow recessed relief grooves being formed in the abutting faces of said electrode sections, said grooves being concentric with said nipple and sockets and extending outward from said socket.

2. Apparatus in accordance with claim 1 wherein the diameter of said counterbore is grater than the large end diameter of said sockets.

3. Apparatus in accordance with claim 2 wherein said counterbores are smoothly jointed to said small ends of said sockets by surfaces of revolution.

4. Apparatus in accordance with claim 1 wherein said nipple portion devoid of threads includes a center length of uniform diameter less than the minor diameter of the small end of said sockets, said center length being smoothly joined to threads present at the alternate ends of said nipple by surfaces of revolu,ion.

5. In a furnace electrode assembly of the type including a pair of electrode sec,ions having tapered threaded sockets therein and a nipple threaded into each of said sockets and holding said sections in firm face-to-face contact, the im-t provement wherein:

said nipple includes a portion at the center thereof which is devoid of threads and includes a center length of uniform diameter less than the minor diameter of the small end of said sockets, said center length being smoothly oined to threads present at the alternate ends of sard nrpp e by surfaces of revolution.

6. In a furnace electrode assembly of the type including a pair of electrode sections having tapered threaded sockets therein and a nipple threaded into each of said sockets and holding said sections in firm face-to-face contact, the improvement comprising: a pair of counterbores at the bottom of said sockets, the diameter of said counterbore being greater than the large end diameter of said sockets.

7. Apparatus in accordance with claim 6, wherein said counterbores are smoothly joined to said small ends of said sockets by s$rfaces of revolu,ion.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIDN Patent No. ,646,240 Dated February 29, 1972 Inventor(s) John G; Lewis It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as show below:

Column l, line &9, after "transition" insert the word zones a line &9, delete "fro Column 2-, line 56, "loa ing should read loading line 62, "preferably" should read preferable Column 3, line 17, "Ed" should read FG Column line 12, "grater" should read greater line 15, "jointed" should read joined line 22, "revolu,ion" should read revolution line 24, "sec,ions" should read sections line &3, ".s$.rfaces" should read surfaces line #3, revolu,ion" should read revolution Signed and sealed this 11th day of July 1972.

( SEAL) Attest:

EDWAR D I LFLETC HER, Jll R0 BERT GOTTSCHALK .Attestinp; Officer Commissioner of Patents F ORM PO-1050 (10-69) USCOMM-DC 60376-P69 u.s. GOVERNMENT PRINTING OFFICE I969 0-366-334 UNlTED STATES PATENT OFFICE I CERTIFECATE OF QORREfi'llQN Patent No. 3,646,240 Dated February 29, 1972 Inventor(s) John G. Lewis It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 2-9, after "transition" insert the word zones line 49, delete "fro'.

Column 2, line 56, "loa;ing" should read loading line 62, "preferably" should read preferable Column 3, line 17, "Ed" should read FG Column line 12, "grater" should read greater line 15, "jointed" should read joined line 22, "revolu,ion" should read revolution line 24, "sec,ions" should read sections line 43, "s$rfaces" should read surfaces line 43, revo1u,ion" should read revolution Signed and sealed this 11th day of Jul; 1972.

(SEAL) Attest:

EDWARD I LFLETCHER T ROBERT GOTTSCHALK Attestinp; Officer Commissioner of Patents FORM PO-1050 (10-69) USCOMM'DC 50376-1 69 U.S GOVERNMENT PRINTING OFFICE: I969 O-366-335

Claims

1. In a furnace electrode assembly of the type including a pair of electrode sections having tapered threaded sockets therein and a nipple threaded into each of said sockets and holding said sections in firm face-to-face contact, the improvement comprising: a. a pair of counterbores at the bottom of said sockets, of diameter at least as great as the small end diameter of said socket; b. said nipple including a portion at the center thereof which is devoid of threads and includes a cross section of diameter less than the minor diameter of the first adjacent thread thereto; and c. shAllow recessed relief grooves being formed in the abutting faces of said electrode sections, said grooves being concentric with said nipple and sockets and extending outward from said socket.

4. Apparatus in accordance with claim 1 wherein said nipple portion devoid of threads includes a center length of uniform diameter less than the minor diameter of the small end of said sockets, said center length being smoothly joined to threads present at the alternate ends of said nipple by surfaces of revolution.

5. In a furnace electrode assembly of the type including a pair of electrode sections having tapered threaded sockets therein and a nipple threaded into each of said sockets and holding said sections in firm face-to-face contact, the improvement wherein: said nipple includes a portion at the center thereof which is devoid of threads and includes a center length of uniform diameter less than the minor diameter of the small end of said sockets, said center length being smoothly joined to threads present at the alternate ends of said nipple by surfaces of revolution.

7. Apparatus in accordance with claim 6, wherein said counterbores are smoothly joined to said small ends of said sockets by surfaces of revolution.