ANODE CLAMP

Abstract: A removable anode clamp for use during bake-out of the cathode of an aluminum reduction cell comprises a spring-­ loaded roller (18) forcing the anode rod (12) against the anode bus (11), but at the same time permitting vertical movement relative to the anode rod (12), the spring-loaded roller (18) being carried by a yoke (17) which is attached to the anode bus (11).

Description: ANODE CLAMP Background of the Invention This invention pertains to anode clamps used in an aluminum reduction cell, and particularly to such clamps useful during bake-out of the cathode of the cell. Aluminum is commonly produced by the electrolytic reduction of aluminum oxide to aluminum metal in an electrolytic cell comprising a carbonaceous cathode which forms a dish for holding the molten aluminum produced, together with an overlying layer of electrolyte or bath in which the aluminum oxide to be reduced is dissolved. An electric current is introduced into the cell by means of anodes suspended in and contacting the electrolytic bath. These anodes are mechanically and electrically connected by means of vertical anode rods embedded in the anodes and attached to anode bus bars suspended over the reduction cell. Unidirectional electric current is introduced to the cell through the anode bus, anode rods, and anodes, passing through the electrolytic bath, thereby reducing the aluminum oxide to aluminum metal, and leaves the cell by passing through the pad of molten aluminum and the underlying cathode, from which it is removed by collector bars and thence carried to the anode bus of the adjacent cell. Because the anodes are consumed in the electrolytic reduction process, and because molten aluminum builds up within the cell and is removed from time to time, it is necessary to vertically adjust the position of the anodes so as to maintain a roughly constant distance between the anode face and the layer of molten aluminum. Accordingly, the clamps by which the anode rods are attached to the anode bus must permit vertical adjustment from time to time. Such anode clamps are well known and exemplary showings are given in U.S. 3,575,840, U.S. 3,888,757, and U.S. 4,025,414. While such prior art anode clamps are adequate for use during operation of the cell, they are far from satisfactory for use during the so-called cathode "bake-out" period. After a reduction cell has been newly constructed or rebuilt after a campaign of use, it is necessary, prior to operation of the cell, to preheat or bake the cathode, that is to say, the carbonaceous material at the bottom of the cell which forms a container for the molten aluminum and overlying molten electrolyte. While there are various methods of conducting such bake-out, one common method is to do it by passing electric current through the cell. In this method, a bed of sized carbon resistor material is evenly spread over the carbon blocks making up the cathode, and the anodes with attached anode rods are lowered onto the bed. Partial or full line amperage is then fed through the cell and the resistance heat generated bakes the cathode ramming paste placed between and around the cathode blocks and heats up the cathode body prior to introduction of the electrolytic bath. Because of thermal expansion of both the anode and cathode blocks, it is necessary to readjust the anode rod clamps frequently during this bake-out process, for example every hour or so. Accordingly, this method of bake-out is highly labor intensive, and consequently expensive, when it is realized that a normal bake-out can tzke from 20 to 36 hours or more. Frequently, there is not enough manpower to perform the required anode clamp adjustments as often as desirable. Failure to adjust the anode clamps leads to uneven anode current distribution, with consequent localized hot spots in the cathode. These can cause cracks within the cathode blocks and the anode blocks and assemblies can also be damaged. Also, some areas of the cathode will not heat up adequately. All these problems can cause subsequent operational difficulties and reduce the overall life of the cell. At least two methods have been proposed to overcome these problems of bake-out. One is to leave the anode clamps loose. However, since typical anode clamps are not designed to allow slippage between the anode rods and the anode bus, loosening them enough to allow such slippage leads to nonuniform current flow. Also, such looseness tends to lead to electric arcing between the anode rod and and anode bus, causing pitting of the surfaces of both. Another solution is to use temporary flexible straps to connect the anode rods and anode bus during the bake-out period, while leaving the clamps loose. However, such straps are heavy and difficult to connect; in some instances, it is necessary to use a crane to place and remove them. Also, such flexible strap equipment is expensive and easily damaged if not handled properly. Finally, such straps can be difficult to remove in the extremely hot environment over an aluminum reduction cell. The present invention is directed to a simplified and more satisfactory solution to the problem of an anode clamp for use during bake-out of an aluminum reduction cell. Summary of the Invention It has now been found, according to this invention, that a satisfactory anode clamp for use during bake-out is one comprising (1) a yoke adapted to be attached to the anode bus of an aluminum reduction cell, (2) contact means carried by the yoke and adapted to engage an anode rod in the aluminum cell in such a manner as to permit relative motion along the longitudinal axis of the anode rod between the contact means and the anode rod, and (3) resilient means carried by the yoke to urge the contact means into contact with the anode rod. Brief Description of Drawings Figure 1 is a perspective view of a clamp according to this invention; Figure 2 is a sectional view along the line 2--2 of Figure 3, with certain parts omitted for purposes of clarity; Figure 3 is a plan view, partially in section, of an anode clamp according to the present invention in place; and Figure 4 is a front elevation view of the clamp. Detailed Description One embodiment of the invention, the scope of which is defined in the claims, is shown in the drawings and hereafter described. In the drawings, 11 indicates the anode bus and 12 the anode rod to be clamped thereto. Brackets 13a and 13b are bolted to anode bus 11 and carry the removable anode clamp, generally indicated by 14, which is retained in place by bearing against studs 16a and 16b, on brackets 13. Brackets 13 and studs 16 are part of the regular, permanent anode clamp, the details of which are not shown for purposes of clarity in illustrating the removable anode clamp of the present invention. It will be understood by those skilled in the art that studs 16 are rotated to engage arms (not shown) that are part of the permanent clamp for anode rod 12. It will also be understood that details bf the structure of the clamp of the present invention may be modified so that it will fit mechanically on other forms of regular or permanent anode clamps or on the brackets carrying such clamps. The clamp of this invention comprises a generally U-shaped yoke 17, the ends 20b and 20c of which rest on brackets 13, and the central portion of which carries rollers 18 which bear against anode rod 12. (In the specific embodiment shown in the drawings, bracket 13b is lower than bracket 13a. Accordingly, one arm of yoke 17 is off-set from the other. To prevent twisting of the clamp when it is engaged, one arm of yoke 17 is made of two pieces a lower piece 20b which rests on bracket 13b and an upper piece 20a located in the same plane as the opposite arm 20c of yoke 17. It will be understood that this arrangement is peculiar to use of the clamp of the present invention with the particular configuration shown, and is not an essential feature of the invention.) As shown more clearly in Figure 2, rollers 18 are urged against anode rod 12 by spring 19 within a housing carried on yoke 17. In addition, handle 21 turns threaded rod 22 so as to increase or decrease the force exerted by spring 19 on rollers 18. While the spring used may be any suitable type of spring, the type of spring known as a spring washer or Bellville spring has been used successfully, and is illustrated schematically in Figure 2. The clamp of the present invention may be made of any suitable material, usually nonmagnetic, for example stainless steel. However, parts, for example the rollers, may be made of other suitable materials such as high temperature plastic. It will be appreciated that the clamp of the present invention is set in position during the bake-out operation, after which it can be removed and the conventional clamp, as mentioned above, engaged while the cell is being operated to produce aluminum. It will also be understood that either spring 19 alone or screw 22 alone can be used to exert pressure on roller 18, although a combination of the two can be used. The advantages of the clamp of the present invention over prior art clamps is that the anode rod can move vertically in response to expansion of the anode and/or cathode during bake-out, while at the same time intimate contact is maintained between the anode rod and the anode bus. Also, the clamps of the present invention are simply and easily installed and removed, particularly because of their relatively light weight compared with, for example, flexible straps. Finally, the clamps of the present invention are relatively inexpensive to manufacture, easy to maintain, and durable. It will be understood that the spring and roller pieces shown can be replaced by equivalent structures. For example, instead of a spring, one could use an hydraulic or pneumatic force exerting cell. Similarly, instead of the rollers, one could use a curved leaf spring to maintain the anode rod in contact with the anode bus while at the same time permitting relative vertical movement between the two.

Claims: CLAIMS: 1. An anode clamp, for use in an aluminum reduction cell during bake-out of the cathode, characterized by comprising a yoke (17) for attachment to the anode bus (11) of an aluminum reduction cell, contact means (18) carried by the yoke (17) and arranged to engage an anode rod (12) in the aluminum reduction cell in such a manner as to permit relative motion along the longitudinal axis of the anode rod (12) between the contact means (18) and the anode rod (12) and resilient means (19) carried by the yoke (17) and arranged to urge the contact means (is) into contact with the anode rod (12). 2. An anode clamp according to claim 1, wherein the contact means comprise at least one roller (18) with its axis of rotation at right-angles to the longitudinal axis of the anode rod (12). 3. An anode clamp according to claim 1 or 2, wherein the resilient means comprise at least one spring (19). 4. An anode clamp according to claim 3, wherein the spring (19) is a spring washer. 5. An anode clamp according to claim 3 or 4, wherein means are provided for adjusting the force exerted by the spring (19). 6. An anode clamp according to any preceding claim, wherein means are provided for adjusting the force exerted by the contact means (18) upon the anode rod (12). 7. An anode clamp according to claim 6, wherein the yoke (17) carries a screw (22) adjustable by means of a handle (21) for urging the roller (18) into contact with the anode rod (12).

Inventors: HALE, WARNE R., YONG, PETER A., ZABREZNIK, RODNEY D.
Applicants: KAISER ALUMINUM & CHEMICAL CORPORATION
Application year: 1985
Main classification: C25C3
IPC codes: C25C3