EP0178766B1

EP0178766B1 - Anode clamp

Info

Publication number: EP0178766B1
Application number: EP85306131A
Authority: EP
Inventors: Warne R. Hale; Rodney D. Zabreznik; Peter A. Yong
Original assignee: Kaiser Aluminum and Chemical Corp
Current assignee: Kaiser Aluminum and Chemical Corp
Priority date: 1984-10-18
Filing date: 1985-08-29
Publication date: 1988-11-02
Also published as: NO853983L; EP0178766A1; CA1263948C; NO170292C; DE3566001D1; CA1263948A; AU4850485A; NO170292B

Description

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. Specifically, U.S. 4,025,414 discloses an anode clamp which is designed to prevent downward movement of the anode by effecting a binding between the anode clamp and the anode rod in contact therewith.
After a reduction cell has been newly constructed or rebuilt after a compaign 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 take 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 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

The invention provides an anode clamp for use in continuously urging an anode rod against an anode bus so as to maintain intimate electrical contact of the anode rod with the anode bus in an aluminium reduction cell during the bake-out of the cathode bottom portion of the cell, the clamp comprising a yoke arranged adjacent to the anode rod, portions of the yoke serving as a carrier for an anode rod contacting means which is provided with a curved anode rod contacting surface, and being characterised by resilient biasing means carried by the yoke and urging the anode rod contacting means and the anode rod contacting surface thereof against a portion of the anode rod, the contacting surface being movable along the anode rod substantially parallel to the longitudinal axis of the anode rod whilst being urged into intimate contact with the rod by the resilient biasing means, whereby the anode rod is urged against the anode bus regardless of movement of the anode rod relative to the anode rod contacting means or the anode bus.

Brief description of drawings

An embodiment of the invention will now be described by way of example with reference to the drawings, in which:

Figure 1 is a perspective view of an anode clamp;
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 the clamp in place; and
Figure 4 is a front elevational view of the clamp.

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 16a, 16b 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 16a, 16b 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 of the structure of the clamp of the present invention may be modified so that it will fit mechanically on otherforms 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 resting 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 18 on rollers 18. While the spring used may be any suitbale 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 the spring 19 alone can be used to exert pressure on roller 18, although a combination of the spring and the screw 22 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 pneumaticforce 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

1. An anode clamp for use in continuously urging an anode rod against an anode bus so as to maintain intimate electrical contact of the anode rod with the anode bus in an aluminium reduction cell during the bake-out of the cathode bottom portion of the cell, the clamp comprising a yoke (17) arranged adjacent to the anode rod (12), portions of the yoke (17) serving as a carrier for an anode rod contacting means (18) which is provided with a curved anode rod contacting surface, and being characterised by resilient biasing means (19) carried by the yoke (17) and urging the anode rod contacting means (18) and the anode rod contacting surface thereof against a portion of the anode rod (12), the contacting surface being movable along the anode rod substantially parallel to the longitudinal axis of the anode rod whilst being urged into intimate contact with the rod (12) by the resilient biasing means, whereby the anode rod (12) is urged against the anode bus (11) regardless of movement of the anode rod (12) relative to the anode rod contacting means (18) or the anode bus (11).

2. An anode clamp according to claim 1, wherein the rod-contacting means comprises a roller (18), the axis of rotation of which is transverse to the longitudinal axis of the anode rod (12).

3. An anode clamp according to claim 1 or 2, wherein the resilient biasing means comprises at least one spring (19).

4. An anode clamp according to claim 3, wherein the spirng comprises at least one spring washer (19).

5. An anode clamp according to claim 3 or 4, wherein means (21, 22) are provided for adjusting the force exerted by the spring (19).

6. An anode clamp according to claim 5, wherein means are provided for tensioning the spring of the biasing means (19).

7. An anode clamp according to claim 6, wherein the tensioning means comprises a screw means (22).

8. An anode clamp according to any previous claim, wherein the yoke (17) is affixed to the anode bus (11).