FIELD OF THE INVENTION

[0001] The present invention relates to electrode columns for use with electric furnaces, and particularly to electrode slipping systems for such electrode columns.

BACKGROUND OF THE INVENTION

[0002] Electric furnaces are commonly used for melting of metals and for smelting and reduction of ores. In such furnaces, heat is typically supplied to the furnace charge through one or more cylindrical electrodes, each of which is vertically suspended through the furnace roof by an electrode column.

[0003] The electrode column not only supports the electrode, but is also responsible for carrying electrical power to the electrodes, positioning the electrodes based on furnace power requirements, incrementally feeding or "slipping" the electrodes downward into the furnace as they are consumed and, where the electrodes are of the Soderberg type, helping in the baking of the electrodes. It is also desirable to be able to move the electrode incrementally upward, for example to correct for over-slipping or to compensate for rapid bath rise in the furnace.

[0004] In order to perform these functions, a typical electrode column comprises a hoist to control the position of the electrode, an electrode slipping system to incrementally feed the electrode through the electrode column and into the furnace, a paste heater to soften unbaked paste blocks and ensure correct baking of the electrode, a power clamp to deliver electrical power to the electrode, and an electrode seal to prevent excessive release of harmful gases from the opening in the furnace roof through which the electrode extends. [0005] The power clamp typically comprises a number of copper contact pads which are biased against the surface of the electrode to maintain electrical contact with the electrode. This clamping force of the electrode clamp on the electrode through the contact pads is continuously applied, typically only being released for maintenance.

[0006] The electrode slipping system typically comprises a slipping clamp assembly having one or two slipping sleeves which apply a radial clamping force to support the electrode. In prior art slipping clamp assemblies, at least one of the slipping sleeves is provided with means to release the clamping force, thereby permitting the electrode to "slip" downward relative to the electrode column.

[0007] A description of a typical prior art system for incrementally raising and lowering an electrode is the "two-ring" system described at column 1, lines 20 to 34, of U.S. Patent No. 4,481,637 (Evensen) issued on November 6, 1984. According to this system, two holder rings are provided which exert radial forces on the electrode. When feeding the electrode downwardly into the furnace, the pressure of the first of the holder rings is released and the first ring is moved vertically relative to the second holder ring and the electrode, following which the pressure on the first holder ring is reactivated. The pressure on the holder ring is then released and the electrode is fed down by lowering the first holder ring. When the feeding movement is finished, the pressure on the second holder ring is reactivated. Therefore, this two-ring system involves releasing the pressure on at least one of the holder rings during feeding of the electrode.

[0008] Another prior art electrode slipping mechanism is described in U.S. Patent No. 4,243,832 (Parsons et al.) issued on January 6, 1981. The Parsons et al. patent describes and illustrates an electrode slipping system in which two sets of girdle clamps 5,6 are arranged inside a support frame 3, the frame 3 being provided with a lever arm 10 having a double acting ram 11. In order to lower the electrode, the ram 11 is extended with the clamps 6 tightened about the electrode. Extension of ram 11 causes lowering of end 13 of lever arm 10, resulting in the electrode being slipped downwardly against the friction of clamps 5. After the electrode is lowered, the clamps 6 are loosened and moved upwardly to their initial positions. In order to raise the electrode, the clamping forces of the lower clamps 6 are released, and the ram 11 is then extended to lower the clamps 6, after which the clamping force of clamps 6 are reactivated. The clamps 6 are then raised in relation to clamps 5, raising the electrode against the frictional force of clamps 5. Although the clamping forces applied to the electrode by the upper set of clamps 5 are sufficient to support the electrode, the Parsons et al. system nevertheless involves release of the lower clamps 6 during raising and lowering of the electrode.

[0009] Another prior art electrode slipping system is described in U.S. Patent No. 3,898,364 (Hardin) issued on August 5, 1975. The Harden patent discloses a system having a contact clamp 14, a slipping clamp 16 and a torquing clamp 18, each of which can be tightened and released. During operation, the electrode is supported by the contact clamp 14 and is lowered by releasing the clamping pressure on clamps 16 and 18 and moving clamp 14 down relative to 16. Thus, the Hardin patent also discloses a system in which the clamping pressure on the electrode is released.

[00010] As the weight of a typical electrode is substantial, being on the order of about 40 tons, the release of clamping pressure on the electrode during feeding or slipping is undesirable, as the safety factor against dropping the electrode is reduced when one or more clamps is released. Accordingly, there is a need for improved electrode slipping systems in which release of clamping forces on the electrodes is avoided.

SUMMARY OF THE INVENTION

[00011] The present invention overcomes the problems of the prior art described above by providing an electrode slipping system in which the - A -

electrode can be raised or lowered relative to the electrode column without release of the clamping forces on the electrode.

[00012] In the electrode slipping system according to the invention, the electrode column is provided with a slipping clamp assembly comprising at least one movable slipping sleeve which applies a radial clamping force to the electrode. The combined clamping forces of the slipping clamp assembly and the power clamp are sufficient to support the electrode. The magnitudes of the clamping forces applied by the slipping sleeve and by the power clamp are selected such that application of a downwardly directed axial force on the slipping sleeve, in combination with the weight of the electrode, are sufficient to overcome the resistive frictional force of the power clamp, thereby resulting in slippage of the electrode relative to the power clamp without release of the clamping forces. The slipping sleeve can then be raised to its initial position without the release of clamping forces by application of an upwardly directed axial force which is insufficient to overcome the combined weight of the electrode and the resistive frictional force of the power clamp so that the slipping sleeve slides upwardly along the electrode, back to its initial position.

[00013] In particularly preferred embodiments of the present invention, the slipping clamp assembly includes a second slipping sleeve, which may be either stationary or movable relative to the electrode column. Where the second slipping sleeve is movable, the electrode may be raised or "back-slipped" relative to the electrode column by simultaneously applying upwardly directed axial forces on both slipping sleeves, again without releasing the pressure of the slipping sleeves or the power clamp. The slipping sleeves are then moved sequentially downwards relative to the electrode column, so that the slipping sleeves slide downwardly along the electrode back to their initial positions, without the release of clamping force. Downward slipping is accomplished by applying a downwardly directed axial force on one or both sleeves as described in the previous paragraph. [00014] In one aspect, the present invention provides, in combination, a consumable electrode and an electrode column for an electric arc furnace. The electrode is movable downwardly along a longitudinal axis defined by the electrode. The electrode column comprises: (a) a power clamp through which electrical power is delivered to the electrode, the power clamp comprising an annular contact element through which the electrode extends and which is in contact with the electrode, the power clamp exerting a first clamping force on the electrode through said annular contact element; and (b) a slipping clamp assembly comprising at least a first slipping sleeve, the first slipping sleeve having a hollow cylindrical interior through which the electrode extends, the first slipping sleeve exerting a second clamping force on the electrode and being axially movable relative to the electrode and the power clamp. The power clamp and the slipping clamp assembly together support the electrode and the first and second clamping forces are selected such that downward axial movement of the first slipping sleeve, while maintaining the first and second clamping forces, results in downward axial movement of the electrode relative to the power clamp, and such that upward axial movement of only the first slipping sleeve, while maintaining the first and second clamping forces, results in axial movement of the first slipping sleeve relative to the electrode.

[00015] In another aspect, the present invention provides a slipping clamp assembly for holding an axially-extending electrode and for axially raising and lowering the electrode. The slipping clamp assembly comprises: (a) a first slipping sleeve for exerting a first clamping force on the electrode, the first slipping sleeve having a hollow cylindrical interior to receive the electrode; (b) a second slipping sleeve for exerting a second clamping force on the electrode, the second slipping sleeve having a hollow cylindrical interior to receive the electrode, the first and second slipping sleeves being axially spaced apart; and (c) a slipping clamp frame to which both slipping sleeves are connected, both the first and second slipping sleeves being axially movable relative to the frame and independent of one another. [00016] In yet another aspect, the present invention provides a method of axially moving an electrode relative to an electric arc furnace, the electrode being supported by a power clamp and by a slipping clamp assembly. The slipping clamp assembly comprises a first slipping sleeve having a hollow interior through which the electrode extends. The method comprises: (a) applying a first clamping force to the electrode, the first clamping force being applied by the power clamp; (b) applying a second clamping force to the electrode, the second clamping force being applied by the first slipping sleeve; and (c) applying an axially downwardly directed force on the first slipping sleeve while maintaining the first and second clamping forces on the electrode, wherein a combination of the downwardly directed force on the slipping sleeve and a downward force of the electrode are greater than a resistive frictional force of the power clamp, resulting in downward axial displacement of the first slipping sleeve and the electrode relative to the power clamp and the furnace.

[00017] In yet another aspect, the present invention provides a method of axially moving an electrode relative to an electric arc furnace, the electrode being supported by a power clamp and by a slipping clamp assembly. The slipping clamp assembly comprises a first slipping sleeve having a hollow interior through which the electrode extends, and a second slipping sleeve having a hollow interior through which the electrode extends. The method comprises: (a) applying a first clamping force to the electrode, the first clamping force being applied by the power clamp; (b) applying a second clamping force to the electrode, the second clamping force being applied by the first slipping sleeve; (c) applying a third clamping force to the electrode, the third clamping force being applied by the second slipping sleeve; and (d) applying an axially upwardly directed force on each of the first slipping sleeve and the second slipping sleeve while maintaining the first, second and third clamping forces on the electrode, wherein a combination of the upwardly directed forces on the slipping sleeve is greater than a downward force of the electrode and a resistive frictional force of the power clamp, resulting in upward axial displacement of the slipping sleeves and the electrode relative to the power clamp and the furnace. BRIEF DESCRIPTION OF THE DRAWINGS

[00018] The invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[00019] Figures 1a to 1c illustrate a preferred electrode slipping system according to the present invention including one slipping sleeve, and the method by which the electrode is fed downwardly using this system;

[00020] Figures 2a to 2d illustrate an electrode slipping system according to an embodiment of the present invention including two slipping sleeves, in which both slipping sleeves are movable, and a preferred method by which an electrode is fed downwardly using this system;

[00021] Figures 3a to 3d illustrate a method by which the electrode slipping system of Figure 2 is used for upward, back slipping of the electrode;

[00022] Figure 4 is a side elevation view of a preferred slipping system according to the present invention, comprising two movable slipping sleeves;

[00023] Figure 5 is a front elevation of a preferred electrode slipping system according to the invention having two movable slipping sleeves; and

[00024] Figure 6 is a top plan view, partly in cross section, of the electrode slipping system of Figure 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[00025] Figures 1 to 3 are schematic illustrations showing the operation of preferred electrode slipping systems according to the present invention. [00026] Figures 1a to 1c schematically illustrate a consumable electrode 10 for an electric arc furnace (not shown) being supported by an electrode column 12, of which only the power clamp 14 and slipping sleeve 16 are shown. The remaining components of the electrode column 12 are not shown since they are not necessary for an understanding of the invention as described with reference to Figures 1a to 1c. It will be appreciated that the electrode column may also be provided with the other components mentioned above, and that the slipping sleeve comprises part of a slipping clamp assembly which also includes other components as more fully described below.

[00027] As mentioned above, the electrode 10 is suspended vertically and defines a longitudinal axis L shown in Figure 1a.

[00028] Figures 1a to 1c illustrate the steps involved in incrementally feeding the electrode 10 downwardly along the longitudinal axis into the furnace. The power clamp 14 comprises an annular contact element through which the electrode extends and which is in contact with the electrode 10. The power clamp 14 exerts a first radial clamping force on the electrode 10 through the annular contact element.

[00029] The slipping sleeve 16 has a hollow cylindrical interior through which the electrode 10 extends. The first slipping sleeve 16 exerts a second radial clamping force on the electrode 10 and is movable in the axial direction relative to the electrode 10 and the power clamp 14.

[00030] In order to displace the electrode 10 downwardly along the longitudinal axis L, an axially directed downward force is applied on slipping sleeve 16 in the direction of arrow A, while maintaining the clamping forces of power clamp 14 and slipping sleeve 16.

[00031] It will be appreciated that the weight of electrode 10 constitutes a downward force which is directed parallel to the longitudinal axis L and is represented in Figure 1a by arrow W. The forces A and W shown in Figure 1a are countered by a resistive frictional force of the power clamp 14, represented by arrow R in Figure 1a. The magnitudes of the clamping forces produced by power clamp 14 and sleeve 16 are selected such that downward axial movement of the slipping sleeve 16, without release of the clamping forces, results in downward axial movement of the electrode 10 relative to power clamp 14. In other words, the combined magnitude of the forces represented by arrows A and W is greater than the resistive force R, and therefore the electrode 10 is caused to slip downwardly through the power clamp 14 to the position shown in Figure 1b, thus feeding the electrode 10 by an amount X into the furnace.

[00032] To complete the process of lowering electrode 10, the slipping sleeve 16 must be returned to its initial position. Thus, an upwardly directed axial force represented by arrow B in Figure 1b is applied to the slipping sleeve 16. This force B is opposed by the weight W of the electrode 10, and is also resisted by the frictional force of power clamp 14 on electrode 10, represented by arrow R' in Figure 1b. The magnitudes of the clamping forces are selected such that the upward axial movement of only slipping sleeve 16, while maintaining the clamping forces of power clamp 14 and slipping sleeve 16, results in upward axial movement of the slipping sleeve 16 relative to electrode 10. In other words, the magnitude of force B is insufficient to overcome the combined effect of forces W and R', and therefore the slipping sleeve 16 slides upwardly on the electrode 10. It is emphasized that the upward displacement of slipping sleeve 16 is accomplished without release of the clamping forces of power clamp 14 or slipping sleeve 16, and that there is substantially no slippage of the electrode relative to the power clamp 14. The final position of slipping sleeve 16 is illustrated in Figure 1c. The electrode 10 can be further fed into the furnace by repeating the steps shown in Figures 1a to 1c. It will be appreciated that the sequence of steps involved in lowering the electrode 10 can be varied from the sequence described above with reference to Figures 1a to 1c. For example, the slipping sleeve 16 may be moved upwardly away from its initial position before it is lowered. In other words, the order of the steps shown in Figures 1a and 1b can be reversed.

[00033] Figures 2a to 2d and 3a to 3d schematically illustrate a second preferred embodiment of the present invention comprising an electrode column 28 in combination with electrode 10 for an electric arc furnace (not shown). The electrode column 28 in the second preferred embodiment comprises a power clamp 30 exerting a first clamping force on electrode 10, a first slipping sleeve 32 exerting a second clamping force on electrode 10 and a second slipping sleeve 34 exerting a third clamping force on electrode 10. Slipping sleeves 32 and 34 have a hollow cylindrical interior through which electrode 10 extends. Both the first and second slipping sleeves 32,34 are movable relative to the stationary components of electrode column 28, including power clamp 30. Preferably, the first and second slipping sleeves 32,34 are independently movable relative to one another.

[00034] Downward feeding of electrode 10 is accomplished by simultaneously exerting downward, axially directed forces Ai and A2 on slipping sleeves 32 and 34 while maintaining the first, second and third clamping forces on electrode 10. The magnitudes of the first, second and third clamping forces are selected such that the combined magnitude of forces Ai, A2 and the weight W of electrode 10 are greater than the frictional resistive force Ri exerted on electrode 10 by power clamp 30. Accordingly, the application of downward forces Ai and A2 results in downward axial movement of the electrode 10 relative to the stationary components of electrode column 28, including power clamp 30. Therefore, the electrode 10 is caused to slip downwardly through the power clamp 30, to the position shown in Figure 2b, thus feeding the electrode 10 by an amount "x" into the furnace. Figure 2b illustrates the position of electrode 10 and the configuration of electrode column 28 after this operation.

[00035] Preferably, the slipping sleeves 32 and 34 are returned to their initial positions one at a time, as illustrated in Figures 2b to 2d. As shown in Figure 2b, the first slipping sleeve 32 is moved upwardly to its initial position by application of an upwardly directed force B1. The magnitude of force B1 is less than the combined magnitudes of resistive frictional force R1' of power clamp 30, R2' of second slipping sleeve 34 and the weight W of electrode 10. Accordingly, movement of only the first slipping sleeve 32 upwardly, while maintaining the first, second and third clamping forces, results in upward axial movement of the first slipping sleeve 32 relative to the electrode 10 and to the remainder of electrode column 28.

[00036] Similarly, Figure 2c illustrates the return of second slipping sleeve 34 to its initial position by application of axially upwardly directed force B2 on only the second slipping sleeve. As shown in Figure 2c, the magnitude of upward force B2 is less than the combined magnitude of resistive frictional forces R-i1 and R2' of power clamp 30 and first slipping sleeve 32, and the weight W of electrode 10. Accordingly, upward movement of only the second slipping sleeve 34, while maintaining the first, second and third clamping forces, results in axial movement of the second slipping sleeve 34 relative to the electrode 10. After return of slipping sleeves 32,34 to their initial positions, the electrode 10 and electrode column 28 have the configurations shown in Figure 2d.

[00037] It will be appreciated that the sequence of steps involved in slipping the electrode 10 downwardly can be varied from the sequence described above with reference to Figures 2a to 2d. For example, the slipping sleeves 32, 34 may be moved upwardly away from their initial positions before they are lowered together. In other words, the steps shown in Figures 2b and 2c may be performed before the step shown in Figure 2a. Furthermore, the order of the steps shown in Figures 2b and 2c can be reversed.

[00038] One advantage of using the electrode column 28 of the second preferred embodiment is that it can also accomplish "back slipping", or upward feeding, of electrode 10. This may be required to correct for inadvertent, excessive downward slipping, or to compensate for a rapidly increasing level of molten material in the furnace. Back slipping is now explained with reference to Figures 3a to 3d.

[00039] Electrode 10 is fed upwardly by simultaneous application of upward, axially directed forces B1 and B2 on the first and second slipping sleeves 32,34. The magnitudes of the clamping forces are selected such that the combined magnitude of upward forces Bi and B2 is greater than the weight W of electrode 10 combined with the resistive frictional force R1 of power clamp 30. Accordingly, application of upward forces B-i and B2 results in upward axial movement of the electrode 10 relative to the stationary components of electrode column 28, including power clamp 30. Therefore, the electrode 10 is caused to slip upwards through the power clamp 30 to the position shown in Figure 3b, thus withdrawing the electrode 10 by an amount "X" from the furnace.

[00040] The return of the slipping sleeves 32,34 to their initial positions is illustrated in Figures 3b and 3c. In Figure 3b, an axial, downwardly directed force A1 is applied only to the second slipping sleeve 34. The magnitudes of the forces are selected such that the combination of downward force A1 and the electrode weight W is less than the combined resistive forces R-i1 and R2' of the power clamp 30 and first slipping sleeve 32. Accordingly, the second slipping sleeve 34 moves downwardly relative to electrode 10 and the stationary components of the electrode column 28, to the position shown in Figure 3c. Similarly, the first slipping sleeve 32 is moved downwardly as shown in Figure 3c by application of downward axial force A2 which, in combination with electrode weight W, is insufficient to overcome resistive forces R1' and R3' of the power clamp 30 and the second slipping sleeve 34, respectively. Accordingly, the first slipping sleeve 32 moves downwardly relative to electrode 10 and relative to the stationary components of electrode column 28 to the position shown in Figure 3d.

[00041] It will be appreciated that the sequence of steps involved in back slipping the electrode 10 can be varied from the sequence described above with reference to Figures 3a to 3d. For example, the slipping sleeves 32, 34 may be moved downwardly away from their initial positions before they are raised together. In other words, the steps shown in Figures 3b and 3c may be performed before the step shown in Figure 3a. Furthermore, the order of the steps shown in Figures 3b and 3c can be reversed.

[00042] It will also be apparent from the above discussion of Figures 2a to 2d and 3a to 3d that the fundamental principle involved in slipping and back slipping of electrode 10 is that moving either of the slipping sleeves 32, 34 by itself causes it to slide over the electrode 10 without causing the electrode 10 to move. However, moving both sleeves 32, 34 simultaneously in the same direction causes movement of the electrode 10 in the same direction.

[00043] Figures 4 to 6 illustrate a preferred electrode slipping system according to the present invention, comprising a slipping clamp assembly 40 for holding an electrode 10 and for raising and lowering the electrode along a longitudinal axis L (Fig. 4) defined by the electrode 10.

[00044] The slipping clamp assembly 40 comprises a first, or lower, slipping sleeve 42 for exerting a first radial clamping force on electrode 10. The first slipping sleeve 42 is cylindrical and has a hollow cylindrical interior 44 through which electrode 10 extends. The slipping clamp assembly 40 also comprises a second, or upper, slipping sleeve 46 for exerting a second radial clamping force on electrode 10. The second slipping sleeve 46 is also cylindrical and has a hollow cylindrical interior 48 through which electrode 10 extends. The slipping sleeves 42, 46 preferably have a height to width ratio of approximately 1:1. This helps to limit pinching forces against the electrode at the tops and bottoms of the sleeves 42, 46.

[00045] The slipping clamp assembly 40 further comprises a slipping clamp frame 50, having an upper surface 52 to which the second slipping sleeve 46 is connected and a lower surface 54 to which the first slipping sleeve 42 is connected. As shown in Figure 4, the slipping sleeves 42 and 46 are axially spaced relative to one another and are located below and above the slipping clamp frame 50, respectively. Although not shown in the drawings, the slipping clamp frame 50, the slipping clamp assembly 40 and the other components of the electrode column are preferably supported and positioned by one or more support members. For example, the slipping clamp frame 50 and other components of the electrode column may be suspended by hydraulic cylinders or wire ropes (not shown) from one or more overhead girders (not shown) or the like.

[00046] The first and second slipping sleeves 42,46 of assembly 40 are independently movable relative to one another, and to the slipping clamp frame 50, along the longitudinal axis L. Thus, the slipping clamp assembly 40 is analogous to the assembly described above with reference to Figures 2a to 2d and 3a to 3d, which incorporates individually movable slipping sleeves 32 and 34, and is able to feed the electrode 10 upwardly and downwardly along axis L. The operation of slipping clamp assembly 40 will be further described below.

[00047] As mentioned above, the slipping sleeves 42 and 46 are movably connected to the slipping clamp frame 50. Each slipping sleeve 42,46 is preferably connected to frame 50 by at least one force-generating device by which the sleeves 42, 46 can be moved along the longitudinal axis. In the preferred embodiment, each force-generating device comprises a fluid- pressurized mechanism 56 through which each slipping sleeve 42, 46 is connected to the frame 50. The fluid-pressurized mechanism 56 may preferably be actuated by hydraulics or pneumatics. In the preferred embodiment described below, the fluid-pressurized mechanism 56 is hydraulically actuated, and comprises a hydraulic cylinder 58.

[00048] ' The hydraulic or pneumatic cylinder 58 can be extended and retracted along the longitudinal axis and is rotatably connected to a cylinder clevis at each of its opposite ends. As shown in Figure 4, one end of each cylinder 58 is attached to the frame 50 through a first cylinder clevis 60. The other end of each hydraulic cylinder 58 is attached by a second cylinder clevis 62 to a lever arm 64.

[00049] Each lever arm 64 is generally transverse to the longitudinal axis, having a first end 66 through which it is secured to hydraulic cylinder 58 by cylinder clevis 62, and having a second end 68 through which it is rotatably attached to the upper or lower surface 52,54 of frame 50 by an arm clevis 70. As shown in Figure 6, the lever arms 64 are substantially tangential to the cylindrical slipping sleeves 42, 46, with a central portion 72 of each lever arm 64 being rotatably connected to a slipping sleeve 42 or 46 by a rotatable connection 74. As shown in Figure 4, the rotatable connection 74 may comprise a pin 75 projecting from each side of the slipping sleeve 42 or 46, the pin 75 engaging an oversized hole 77 in a central portion 72 of one of the lever arms 64 to allow limited horizontal movement of the sleeves 42, 46. Thus, the ends 66 and 68 of each lever arm 64 are rotatably connected to cylinder clevis 62 and arm clevis 70, and the central portion 72 of each lever arm 64 is rotatably connected to a slipping sleeve 42 or 46. It will be appreciated that other types of combined connections which are rotatable and translatable horizontally are known to persons skilled in the art and may be used instead of the pin 75 and oversized hole 77 arrangement shown in Figure 4.

[00050] It will be seen from the front view of Figure 5 and the plan view of Figure 6 that each slipping sleeve 42,46 is provided with a pair of lever arms 64. The paired lever arms 64 of each slipping sleeve 42, 46 are substantially parallel to one another, extending along opposite sides of the slipping sleeve 42, 46. As shown in the plan view of Figure 6, the first ends 66 of each pair of lever arms are secured to opposite ends of a lever cross member 76, with each cross member having a central portion 78 between its ends through which it is connected to the frame 50 by fluid-pressurized mechanism 56.

[00051] Having now described the components of slipping clamp assembly 40, the following is a description of how actuation of fluid-pressurized mechanisms 56 will result in axial movement of slipping sleeves 42,46. For example, longitudinal extension of the hydraulic cylinder 58 associated with lower slipping sleeve 42 results in downward displacement of the first ends 66 of lever arms 64, together with cross member 76 and the slipping sleeve 42. The second ends 66 of lever arms 64 are pivoted about the arm clevises 70, with the central portions 72 of lever arms 64 being displaced downwardly with some rotation about connections 70 and 74. Due to the rotation of the central portion 72 of lever arm about pivot 70, connection 74 moves relative to oversized hole 77. Retraction of hydraulic cylinder 58 will similarly result in upward displacement of slipping sleeve 42 back to its initial position shown in Figures 4 and 5.

[00052] The upper slipping sleeve 46 is displaced upwardly from its initial position by extending the hydraulic cylinder 58 to which it is connected. Extension of cylinder 58 results in upward displacement of the first ends 66 of lever arms 64, together with cross member 76 and the attached slipping sleeve 46. The second ends 68 of lever arms 64 are pivoted about arm clevises 70 and the central portion 72 is rotated about connection 74 and 70 as described above. Retraction of hydraulic cylinder 58 results in downward displacement of slipping sleeve 46 back to its initial position shown in Figures 4 and 5.

[00053] The slipping sleeves 42,46 are of relatively simple construction, each comprising a substantially cylindrical shell 79. Each of the shells 79 has two attachment flanges 80,82 which are substantially parallel to one another and which are biased toward one another by slipping clamp springs 88 acting on spacer rods 90 so that the slipping sleeves 42,46 exert a radially inwardly directed clamping force on electrode 10. As shown in Figure 5, the flanges 80,82 are biased by a single spring 88 or a plurality of axially spaced springs 88 located at one end of a spacer rod 90. It will be appreciated that the flanges 80, 82 can instead be biased by slipping clamp springs arranged in pairs, with the springs 88 of each pair being positioned at the ends of spring rods 90 to either side of the flanges 80 and 82. It is to be noted that the slipping sleeves 42,46 preferably have no means of releasing the clamping pressure on electrode 10, since release of clamping pressure is neither required or desired in the present invention. It will be appreciated that biasing together of flanges 80,82 is not necessarily accomplished by spring pressure, and that other means of biasing the flanges 80,82 may instead be used. For example, the biasing force may be generated by hydraulic or pneumatic devices provided on the shell 79.

[00054] New sections of casing are continually added to Soderberg electrodes, and therefore normal fabrication tolerances must be expected. Problems with reliable electrode operation can occur because variations in shape of the electrode affect how well it can be held. Variations such as diameter, roundness, straightness and quality must all be accommodated passively. Accommodation of these tolerances is provided in the present invention by carefully selecting tension of springs 88, providing slipping sleeves 42, 46 with horizontal freedom of movement, maintaining a height to width ratio of about 1:1, and by providing the sleeves 42, 46 with form compliance around their perimeter and form stiffness vertically.

[00055] Perimeter form compliance is an important feature because it accommodates variations in electrode casing diameter, roundness and overall quality of fabrication. It enables the slipping sleeves 42, 46 to adapt their shape to that of the electrode 10. Furthermore, this feature permits an evenly distributed radial compression on the electrode 10. However, in combination with the perimeter form compliance, the sleeves 42, 46 must also be stiff in the vertical direction as this is the primary direction of friction loads.

[00056] In addition to the benefits mentioned above, the electrode slipping system according to the invention can help to reduce maintenance costs by minimizing furnace downtime during maintenance or replacement of the individual slipping sleeves. Specifically, in the system comprising two slipping sleeves 42, 46 and the power clamp 30, any one of these three clamps may be released without requiring further electrode-securing measures. This reduces the amount of labour required for maintenance and allows for a rapid return to service.

[00057] Although the invention has been described in connection with certain preferred embodiments, it is not intended to be limited thereto. Rather, the invention is intended to include all embodiments which may fall within the scope of the following claims.