US2921108A - Furnace electrode holding means - Google Patents

Description

Jan. l2, 1960 w. MEFFERT FURNACE ELECTRODE HOLDING MEANS Filed May 1, 195e Mite 772e/fsr BY i f@ ,@/Mu/ ./ttorney United States Patent O 2,921,108 FURNACE ELECTRODE HOLDING lVIEANS Walter Melfert, Duisburg-Buchholz, Germany, assiguor to Demag-Elektrometallurgie G.m.b.H., Duisburg, Germany, a corporation of Germany Application May 1, 1958, Serial No. 732,376

Claims priority, application Germany'May 11, 1957 7 Claims. (Cl. 13-16) This invention relates to electric arc furnaces and more particularly to means for holding arc furnace electrodes during operation.

Electrodes. composed of amorphous carbon or graphite are widely utilized in electric arc melting and reduction furnaces. These electrodes generally comprise cylinders 1 to 2 meters long which are assembled to the desired length by means of mating threaded portions on the ends thereof. Because the diametrical tolerances of these electrodes may be as great as i2%, irregularities result in the electrode. surface at the joints between adjacent electrode sections. Such electrodes are weakest from a structural standpoint at the point at which the two electrode sections are joined, due to the threaded portions and because of the irregularities on the surface.

Electrode clamping or holding means according to the prior art included rigid pressure plates or jaws which were forced directly against the surface of the electrode by some pressure producing means. Due to their rigidity,

. these prior art clamping devices were incapable of applying a uniform pressure on an irregular electrode surface. This non-uniformly applied pressure produced bending moments at the electrodes weakest structural point, tending to damage or break them.

It is an object ofthe invention to provide means for clamping an arc furnace electrode which will not damage the, electrode at its joints or at other irregular regions on its surface. It is a further object of the invention to provide an inflatable clamping means for an arc furnace electrode wherein the electrode weight is supported by tensile stresses in the inflatable means. Other objects `of, the invention will be apparent-from the detailed description of the invention taken in connection with the accompanying drawings in which: f Fig. 1v is an elevational view, partly in section, of a pertinent part of an electric furnace including an electrode and clamping means according to the invention;v

',Fig. 2 lshows a cross section of a portion of one embodiment f the arc furnace electrode clamping means according to the invention; and Y Fig. 3 shows a cross section of a portion of another embodiment of the arc furnace electrode clamp means according to the invention.

The objects of the invention `are accomplished by means offa preferably metallic annular supporting member surrounding the arc furnace electrode and radially spaced therefrom, and inatable means of a pliable material, such as rubber, `disposed on the inner surface of said annular .support means and in contact with the electrode surface, whereby the electrode will be clamped upon -inflation of said means. Because of the pliability of the Vinflatable member, it exerts a uniform force on the electrode surface regardless of irregularities thereon.

By locating the upper anchoring point of the inatable means on ythe annular supporting member a predeter- Lmined radial and longitudinal-distance from the uppermost contact point of said inflatable means on said electrode, the weight of the electrode can be supported by tensile stresses in the inflatable means.

Fig. 1 shows an arc furnace electrode 4 having cylindric al sections 5, 6, 7 and 8 which are joined end to end by suitable mating threaded portions 9. Because of dimensional variations in the individual electrode sections, irregularities 10 occur at the junction between the electrode members. The electrode is energized by bus bar 12 through contact jaws 13 to melt furnace charge 11 in a manner well known in the art. Holding means 14 exert suitable pressure on contact jaws 13 so that theyare held in good electrical contact with the electrode 4, but which jaw pressure does not prevent the electrode 4 from sliding between the contact jaws 12 without binding as the electrode is raised and lowered in response to variations in electrode voltage and current in a manner well known in the art.

The electrode support means 16, constituting the invention, includes a rigid cylindrical rim member 18 and a pliable diaphragm that is generally designated by the numeral 20 and is hermetically sealed to the rim member by upper and lower diaphragm clamping means 22 and 24 respectively, whereby the rim 18 and diaphragm 2t) provide an annular pressure chamber 26 around the electrode 4. Diaphragm 20 may be of any suitable material, such as rubber, which is inatable, has high tensile strength and a high coefficient of friction with respect to carbon. It is understood that the diaphragm may be reinforced by means of nylon or wire mesh, to increase its tensile strength. A suitable conduit 28 leading to a fluid pressure source that is not shown is connected to an opening 30 in rim member 18 for pressurizing and exhausting the interior of chamber 2.6. When pressurized, diaphragm 20 applies sufficient force to the surface of electrode 4 to support its weight. When diaphragm 20 is deflated, electrode 4 passes freely therethrough.

Rim member 18 is rigidly connected to any suitable electrode regulating device such as a hydraulic ram 32 which is controlled by a servomechanism symbolized at 33 and which in turn responds to Voltage and current signals derived from the arc current by means that are not shown but are well known in the art.

During melting of charge 11, the lower electrode member 5 is gradually consumed. After a predetermined portion of electrode section 5 has been expended, it is necessary to attach another electrode section to the uppermost electrode section 8 in order to maintain suitable electrode length. After this has been accomplished, clamping means 16 is moved to a new position on electrode 4 which is determined by the new electrode length. If this new position is at the junction between two electrode members, as shown in Fig. 1, diaphragm 20 will conform to any irregularity 10 in the electrode surface. It can be seen, therefore, that the force exerted by diaphragm 20 will be evenly distributed over its bearing surface on electrode 4. If, on the other hand, in place of clamping member 18 there were substituted a plurality of rigid plates for surrounding and gripping the electrode, as in the prior art, the force transmitted by said rigid plates on the left side of electrode 4 would be applied entirely on electrode section 8 while the entire force exerted by said plates on the right side of electrode 4 would be on electrode section 7. This would result in a couple around the junction of the two electrode sections tending to cause fracture at the threaded portion 9. d

Referring now to Fig. 2 which shows the electrode clamping means in greater detail, the diaphragm 20 has a cylindrical sidewall 36 which surrounds and bears on electrode 4. Sidewall 36 is continuous with a curved 3 upper wall 38 that extends generally laterally of the electrode 4 and it is also continuous with a lower Wall 40 that has a curved portion 41 connected to the lower edge of sidewall 36 and a second straight portion 42 that is tangent to said curved portion 41 and that extends laterally of electrode 4. Enlargedportions. 4-4 and 46 are formedr at the outer edge of each of the upper and lower Walls 38 and 40. Each of said enlarged portions 44 and 46 is provided with an annular inwardly extending tongue and groove 48 and 50 respectively. Eachof the enlarged portions 44 and 46 also has a lip portion 56 and 58 respectively, each of which extends toward each other in a direction generally parallel to the sidewall. An annular hollow portion 60 and 62 is provided in each of the enlarged portions 44 and 46, respectively, to allow each of said enlarged portions to be deformed during the clamping of the diaphragm 20 in the clamp members 22 and 24. The surface of the sidewall 36 may be roughened with irregularities 64 to increase the lfriction between the two surfaces.

An annular outwardly extending flange 66 is attached by welding, for example, to @the upper end of rim 18. The llange 66 has a plurality of circularly located tapped holes 68. The upper diaphragm clamping means 22 includes a lirst disc shaped portion 70 which overlays flange 66 and the upper surface of enlarged portion 44 of diaphragm 20 and it also has an enlarged annular inside margin 72. Enlarged margin 72 has a radially outwardly extending tongue and groove 74 on its lower side which mates with tongue and groove k48 of the upper enlarged portion 44 of diaphragm 20 to provide a hermetic seal for chamber 26 and also to anchor the edge of the upper wall 38 of diaphragm 20. Upper clamping means 22 is secured to flange 66 by a plurality of bolts 84 which pass through a plurality of circumferentially spaced holes 82 in said support means and are threaded into tapped holes 68. Enlarged portion 78 of lower clamping means 24 also has a rearwardly extending annular tongue and groove 79 which cooperates with tongue and groove 50 of lower enlarged portion 46 of diaphragm 20 to effect a hermetic seal and anchor the lower Wall 40 in the manner described with respect to the upper clamping means 22. The lower support member 24 is secured to the rim member 18 in any suitable manner, such as by welding at 80. A cylindrical bracing member 86 having a plurality of openings 92 to allow circulation of fluid is disposed within chamber 26 and has enlarged upper and lower ends 88 and 90, respectively, which bear against edges of the upper and lower Walls 38 and 40 of diaphragm 20 to facilitate holding the grooves in place. Bracing'member 86 also holds lip portions 56 and 58 in the edges of diaphragm 20 against the rim portion 18 to help provide the hermetic seal for chamber 26.

The inner edge 94 of the enlarged portion 78 of lower clamping means 24, which provides support for the planar portion 42 of the lower Wall 40 of diaphragm 20, can be no closer to the electrode surface than the maximum allowable deviations d in the electrode surfaces. This allows a gap 95 to exist between electrode 4 and support means 24. The frictional force between electrode 4 and sideiwall 36 of diaphragm 20 tends to drag the diaphragm into gap 95 thereby subjecting it to a shear stress at edge 94. Because the diaphragm is much stronger in tension than it is in shear, it is preferable that the weight of the electrode 4 be transmitted to the diaphragm as a tensile stress.

It has been found that if the difference between radii of curvatures R and r of the upper and lower walls 38 and 40 respectively is such that the diiference between the vertical components of the pressure forces acting on the unsupported portions of said walls is equal to a major portion of the electrode weight, the electrode 4 will be substantilaly supported by the pressure medium and the vtensile strength ofthe upper wall 38. The remainder of the load is absorbed by the upper clamping means 22.

This insures that, in spite of the tensile stresses in the diaphragm 20, the transition points between the sidewall 36 and the upper and lower walls 38 and 40 respectively will be smooth curves without sharp points of discontinuity. This difference in the radii Ycan be expressed as follows:

1L DvrP Where W is the weight Aof the electrode, D is the diameter of the electrode and P is the internal pressure Awithin the chamber 26.

The other dimensions of the diaphragm 20 can be determined from the expressions:

T. l DTP R*(120 om.) (me lig/(Cmap +2 mi R=13 cm.

W h- PrrD It can thus be seen that the dimensions of the diaphragm 20 necessary to insure that it will assume the desired shape can be determined from the weight of electrode 4 andthe working pressure inside chamber 26.

While diaphragm 20 is shown-as a unitary member it ispunderstood that it may comprise a plurality of individual diaphragms disposed on the inner surface of rim 20 in circumferentially spaced apart relation. l

yFig. 3'shows an alternate means of anchoring the diaphragm 20' illustrated with respect to the upper clamping means 22 and includes a pair of matching annular semi-circular grooves and 101 in flange 66 and annular member 70' respectively. The enlarged portion 44 of diaphragm 20 has a circular cross section which fits between grooves 100 and 101. A suitable reinforcing ring 103 may also be provided in enlarged portion 44.

I claim: y

l. In combination with an 4electrode for an electric arc furnace, means for supporting said electrode comprising a hermetically sealed continuous chamber surrounding said electrode and being in contact with the surface thereof, the side of said chamber adjacent said electrode being of a pliable material, means associated with said chamber for introducing fluid under pressure therein, whereby said pliable side will exertv a force on said electrode suicient to support the weight thereof.

2. In combination with an electrode for an electric aro furnace, means for supporting said electrode comprising a hermetically sealed toroidal chamber sur.- rounding said electrode and being in contact with the surface thereof, the side of said toroidal chamber adjacent said electrode being of a pliable material, means -pressure therein to force said pliable diaphragm means against :the surface of said electrode so that the force exerted by said diaphragm means on said electrode will be sufcient to support the weight thereof.

4. In combination with an electrode for an electric arc furnace, means for supporting said electrode com.

prising a hermetically sealed continuous chamber surrounding said electrode, the side of said chamber adjacent said electrode being of a pliable material, the other side of said chamber being substantially rigid, a portion of said pliable side bearing on said electrode, means associated with said chamber for introducing uid under pressure therein whereby said pliable side will exert a force on said electrode suicient to support the weight thereof, the junction between the upper edge of said pliable side and said rigid side being disposed a predetermined radial and longitudinal distance above the uppermost point of that portion of said pliable wall which bears on said electrode, whereby the Weight of said electrode will be transmitted as a tensile stress in that portion of said pliable side between said uppermost point and'said junction.

5. In combination with an electrode for an electric arc furnace, a device for supporting said electrode cornprising an annular diaphragm having a sidewall sur- .rounding said electrode and bearing thereon, said diaphragm also having upper and lower walls extending generally outward of, said electrode, said upper wall having an arcuate cross-section, annular rim means disposed radially of said sidewall and having means for securing the edges of said upper and lower walls, said diaphragm and rim providing a hermetically sealed charnber, means associated with said chamber for lling said chamber with fluid under pressure whereby said diaphragm will exert a force on said electrode suficient t0 support lthe weight thereof, said means for securing the edge of said upper wall being a predetermined radial and longitudinal distance from the upper edge of said side wall whereby the weight of said electrode will be transmitted as a tensile stress in said upper wall.

6. In combination with an electrode for an electric arc furnace, a device for supporting said electrode comprising an annular diaphragm having a sidewall surrounding said electrode and in contact therewith, said diaphragm also having upper and lower arcuate walls extending generally outward of said electrode, annular rim means for said diaphragm disposed radially from said sidewall and having means for securing the edges of said upper and lower walls, said diaphragm and rim means providing a hermetically sealed chamber, means communicating with said chamber for filling saidchamber with a fluid under pressure, said rim means also having annular support means extending radially inward and terminating in an inner edge a predetermined distance from said electrode for supporting a portion of said lower wall, the radial distance between said upper wall clamping means and the inner edge of the lower wall supporting means being proportional to the ratio of the weight of said electrode to the product of the electrode diameter times the unit pressure within said chamber.

7. Means for supporting an electrode of an electric arc furnace, including rim means surrounding at least i a portion of said electrode and being radially spaced therefrom, pliable diaphragm means disposed on said rim means adjacent said electrode and being in contact therewith, the edges of said diaphragm means being secured to said rim means in a hermetically sealed relation, forming chamber means therewith, said rim means including means for introducing fluid under pressure into said chamber means so that said diaphragm means will be forced against the surface of said electrode with suflicient force to support the weight thereof.

References Cited in the le of this patent UNITED STATES PATENTS 2,758,145 Bjerkas Aug. 7, 1956 FOREIGN PATENTS 386,631 Germany Dec. 14, 1923

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