US3161580A

US3161580A - Graphite joints of highly uniform electrical resistance

Info

Publication number: US3161580A
Application number: US82558A
Authority: US
Inventors: Edward C Thomas
Original assignee: Great Lakes Carbon Corp
Current assignee: SGL Carbon Corp
Priority date: 1961-01-13
Filing date: 1961-01-13
Publication date: 1964-12-15
Anticipated expiration: 1981-12-15
Also published as: CH418427A; DE1515744A1; FR1310932A; GB966619A; ES273591A1

Description

Dec. 15, 1964 E. c. THOMAS 3,151,580

GRAPHITE JOINTS OF HIGHLY UNIFORM ELECTRICAL RESISTANCE Filed Jan. 13, 1961 2 Sheets-Sheet 1 Dec. 15, 1964 E. c. THOMAS 3,161,580

GRAPHI TE JOINTS 0F HIGHLY UNIFORM ELECTRICAL RESISTANCE Filed Jan. 13, 1961 2 Sheets-Sheet 2 FIEA United States Patents 161 see GRAPE toners or runner Urnronrr nrncrnrcar RESldTANtIE Edward C. Thomas, Lewiston, N.Y., assignor to Great Lakes Carbon (Torporatmn, New York, N.Y., a corporation of Delaware Filed Jan. 13, 1961, Ser. No. 82,553 9 Qiaims. (Cl. fil h-288) bers may be low and the variations in same kept at a minimum.

It is well known that graphite anodes have been widely used in electrolytic cells for such processes as decomposing brine solutions to produce chlorine and caustic, etc.

In employing graphite anodes in electrolytic cells such as those of the-mercury cell type, it is customary to support the graphite anodesin a horizontal plane by graphite pins which not only serve to mechanically support the anode in the cell in the proper position but also serve to conduct electrical current from an external power supply to the graphite anode. The anode plates vary in size depending upon the cell design but in general in a mercury cell, the anode assembly usually consists of a rectangilar graphite plate mechanically supported and electrically joined to an outside power source by two graphite pins. More pins are employed if the size of the anode plates used is increased. Several such anode plates are employed in a single electrolytic cell;

In the operation of such electrolytic cells it is very desirable that the joint or connection between the pins and the anode plates not only have sufficient mechanical strength to support the anodes during their useful life but also that the electrical resistance between each of the connecting pins and the anodes be as low and at the same time as uniform as possible, throughout the entire cell. Unduly high resistances, or numerous or wide variations in the electrical resistances of these connections or joints in the cell cause non-uniform deterioration of the anodes. The uneveness of wear and deterioration throughout the cell gives rise to complex operating problems, and requires much more frequent adjustment and subsequent dismantling for repair or reconstruction of the cells than is or would be necessary if'each of the joint resistances were uniformly low and fell within a narrow range of variation in resistance.

Other factors which should and must be considered in making these anodes and mounting them in the cells are the type of sockets employed in same for mounting or receiving the support pins, the machining steps and cost required to make such sockets, the facility with which the support pins may be assembled to the anodes, and the achieving of sufiicient mechanical strength at the joints in order that the pins give adequate support to the anodes suspended in the cells.

The conventional practice of coupling connecting pins to anodes is to thread the ends of the pins and to screw them into threaded sockets in the anode. The types of threaded pins employed are generally three; viz., a pipe thread wherein the outer diameters of the threads are just a little less than the diameter of the main body portion of the pin, a tapered thread wherein the diameter of the threads uniformly diminishes the further the threads extend from the main body portion of the pin, and a shoulder type threaded pin which has a straight thread 3,l6l,5h Patented ec. 15, 1964 ice which is of a substantially smaller diameter than the main body portion of the pin and wherein a shoulder is left on the pin, the face of which shoulder is machined as ilat as possible and perpendicular to the threaded portion of the pin. This type of thread is usually provided with a loose tolerance, and when coupled to a correspondingly threaded socket in an anode plate, graphite to graphite contact is limited to only one side of the thread and to'the aforementioned shoulder on the pin. This particular type of joint depends mainly upon electrical contact at the shoulder for its conductivity. With all of these threaded types of joints and others, the condition of the thread surfaces, both of the pins and of the sockets into which the pins are to be threaded, has been found to be very important. Tool chatter marks or high spots left on the threads result in high and also uneven or non-uniform joint resistances. The joint resistances for these pins also vary considerably depending on the amount of torque employed to tighten them, the optimum amount employed varying for each type of pin. The machining costs attendant upon using threaded pins are, therefore, high and the joint resistances non-uniform.

As an alternative to using. threaded pins, the art has partly turned to employing a different type of joint between graphite connecting pins and anodes, namely interference or pressed joints. FIGURE 2 illustrates this type of joint as well as the improvement of this invention, which will be discussed in more detail hereinafter. These joints depend upon the fact that graphite is somewhat elastic or springy or pressure-compliant in nature and may be forced or compressed into sockets whose internal diam eters are slightly less than the external diameters of the portions of the pins forced into same. This difference in diameter, which may be termed interference should not be too great for if this occurs, the engaging portion of the pin or the socket of the anode begins to fail in its springiness. For example, for a 4 inch diameter pin, assembly forces of approximately 700 pounds and 2400 pounds are typical for interferences of 4 thousandths and 16 thousandths respectively. The force necessary to open or pull apart the joints is approximately equal to the closing force for interferences up to 12 thousandths. At 16 thousandths interference, however, the force required to open the joint is from about 25% to about 50% less than the closingforce due to incipient flaws which had been induced in thesocket wall by excessive tensile strain or by other causes.

This type of joint, however, also has .somedisadvantages. Machining tolerances for the external diameter of the engaging portion of the pin and for the internal diameter of the sockets are narrow because of the requirement of obtaining an interference falling within a fairly narrow range, such as above-described. And even within this range the electrical resistances of the joints vary considerably depending upon the interference. In other words, the joint resistance for an interference of four thousandths is appreciably higher than the joint resistance for an interference of twelve thousandths. This type of joint, therefore, although in many ways an improvement over threaded joints in that the machining costs, joint resistances andvariations in same are reduced somewhat, still possesses these same disadvantages, but on a reduced basis.

It is an object, therefore, of this invention to produce graphite to metal or graphite to graphite couplings or joints wherein a high degree of uniformity of electrical resistance between the members coupled or among a series of such coupled members is obtained.

It is an additional object of this invention to accomplish the foregoing while maintaining low joint resistance.

It is an additional object of this invention to accom- 3 plish the foregoing while employing pressed-fit joints or couplings.

It is another object of this invention to accomplish the foregoing by modifying the coupling pins, and particularly the engaging portions thereof, which are employed in making such pressed-fit joints.

It is another object of this invention to accomplish the foregoing by means of a liquid-tight joint or coupling, between the graphite connecting pin and electrical conducting member to which it is coupled, when liquidtightness of the joint is of advantage or importance when the electrical system of which the joint is a part, is in operation.

Most specifically, it is an object of this invention to provide means for mechanically supporting and coupling anodes in electrolytic cells to an external power supply wherein the resistances of the joints between the coupling members and the anodes are low and of minimized variation in values and wherein the cost of machining the sockets of the anode, the facility with which the support pins may be assembled to the anodes, and the mechanical strengths of the joints all combine to make an optimum system for minimizing construction and operational costs and maximizing electrolytic cell life without the necessity of frequent repair and adjustment.

It is a finding of this invention that the foregoing objects may be achieved by utilizing connecting pins in which there are means for making the socket engaging portions of said pins more pressure compliant, when coupled into sockets of the anodes or other type graphite or metal members to which they are connected, than they would be if no such means were employed.

The employment of such means for increasing pressure compliance in the engaging portions of the pins used in making pressed fit joints or connections reduces the variations occuring in the electrical resistances of such joints and also permits much easier assemblage of such joints by allowing looser production tolerances compared to the use of pressed fit pins having no means therein for increasing the mechanical pressure complying characteristics of the pins. In other words, the employment of such means in such pins not only achieves an additional degree of freedom when the pins are pressed into theanode sockets, permitting diametrical compression of the engaging portion of the pin in response to the compressive force imparted by the close fitting socket, but also reduces the undesired variations in the electrical resistance of such joints, thereby obviating the aforedescribed disadvantages brought about by such variations. The advantageous mechanical compliance brought aboutby the use of such means serves to reduce variation in tightness in the pin to socket assembly, thereby normalizing an otherwise pressure dependent, interference dependent joint resistance.

The invention and its various features will become clearer after consideration of the attached drawings wherein:

FIGURE 1 is a top view of a pin coupled to an electrical conducting member such as an anode plate;

FIGURE 2 is a vertical sectional view of the pinelectrical conducting member of FIGURE 1 and is taken through the line 22 of said figure;

FIGURE 3 is an end view of the bottom of the pin of FIGURE 2;

FIGURE 4 is a vertical sectional View of another pinelectrical conducting member type of joint embraced within the present invention;

FIGURE 5 is an end View of the joint of FIGURE 4, taken along the line 55 of said figure;

FIGURES 6 and 8 are bottom end views of connecting pins showing other modifications of the invention;

FIGURES 7 and 9 are fragmentary vertical sectional views of the pins of FIGURES 6 and 8 and taken along the lines 7-7 and 99 respectively of said figures; and

FIGURE 10 is a vertical sectional view of a modifica- 4 tion of the pin-electrical conducting member type of joint shown in FIGURE 4.

All of the joints of this invention are characterized by the employment of graphite connecting pins which are press-fitted by means of unthreaded engaging portions into nonthreaded sockets in the electrical conducting mem bers to which the pins are coupled.

With reference to the figures, the pins may generally be described as comprised of a main body portion 1, adapted (such as by means of a threaded well 8) for coupling to an external power supply, and an engaging portion 2 which is adapted to be press-fitted, or forcefitted, or frictionally engaged in non-threaded sockets of the members It) to which the pins are coupled. The engaging portion of the pin is of a general cylindrical shape and in a preferred form is flared into and integral with the main body portion of the pin, and chamfered at the peripheral edge of its face. It should be appreciated that the main body portion, though most conveniently circular in cross section, may also be square, octagonal, etc, if desired, and that although its cross-sectional area will generally be greater than the cross-sectional area of the engaging portion, this is not essential to the practices of this invention, the dimensions of the engaging portion of the pin in relation to the socket into which it is inserted being the important consideration.

Each of the pins also possess means within the engaging portion of the pin for making the engaging portion 2 more pressure compliant, as it is forced into the socket, than it would be if the means were absent. The means within the engaging portion for accomplishing this may be an annular kerf 3, typically from about to about ,5, inch wide, which is substantially concentric with the circumference of the engaging portion, as is the case with the pin shown in FIGURES 2 and 3. Alternatively, it may be a cylindrical hole 4 having a fiat base, or a modified type of cylindrical hole 4a having a sloping base the centers of which holes are on the approximate axis of the pin, as with the pins of FIGURES 4 and 10 respectively. Or the means may comprise three straight noncontiguous or non-joining kerfs 5 of substantially equal length, none of which extend as far as the pins periphery, and which kerfs, if extended to intersect with each other would approximately form an equilateral triangle, the middle of each of the kerfs being substantially equidistant from the periphery of the engaging portion of the pin, as with the pin of FIGURES 6 and 7.

The means may also be shown in FIGURES 8 and 9 wherein three straight kerfs 6 of substantially equal length, none of which extends as far as the periphery are also employed but which kerfs intersect with each other to approximately form a triangle. As with the kerfs of FIGURE 6, the middle of each of these kerfs is substantially equidistant from the periphery of the engaging portion of the pin.

In all cases the means employed for making the engaging portion more pressure compliant extends longitudinally from the bottom face of said portion toward the main body portion. Because it is the engaging portion only which takes part in the pressure fitting of the pin into the socket, it may be unnecessary to extend the kerfs into the main body portion.

The greater the surface area of contact between the periphery of the engaging portion of the pin and the walls of the socket, the lower is the resistance of the joint.' Thus the use of pins which are 5 inches in diameter results in less joint resistance than the use of pins 3 inches in diameter. It follows from this that for any given size pin, it is preferred that none of the kerfs, or means employed, to make the engaging portion of the pin more pressure compliant, cleave the periphery of the engaging portion of the pin, for such cleavage reduces the contact area between the pins and the socket, thus tending to increase the joint resistance.

Such cleavege also, if it extends above the height of the socket, permits electrolyte to get between the pin and anode when the'jointsare used in electrolytic cells. This is undesirable because the effects of even the mild and inchoate electrolytic action which would take place in the cavitacious confines of the joined members would tend to erode the graphite structure much as it does at the bottom of the plate. Degeneracy of the graphite structure would ultimately lead to a looser-higher resistance joint.

And finally such cleavage tends to reduce the frictional engagement between the engaging portion of the pin and the socket walls thus lowering'or reducing the amount of force required to open or pull apart the joints.

On the other hand, it may be possible to employ a kerf, either alone or in conjunction with the pressure compliant increasing means already described, which cleaves the periphery at no more than one place. This might sometimes be resorted to in order to gain an additional degree of pressure complying or an alternative manner for obtaining same, if it can be done without too greatly adversely affecting the foregoing discussed properties sought for the joint. It is considered that any peripheral cleavage more than this would detract more from the other qualities sought or required for the joint than it would bring or add to same in the way of increased pressure complying.

Therefore, no peripheral cleavage is preferred but a maximum of one region of peripheral cleavage may some times be resorted to when practicing the invention. The nature of the mechanical properties of a particular type of graphite may also sometimes demand it. If pins having such cleavage are employed in electrolytic cells, the kerf should extend no further from the bottom face of the pin than to within about 80-90% of the depth of penetration of the engaging portion of the pin into the anode socket, so that the liquid tightness of the joint is not impaired. In other words, it should extend longitudinally from the face of the engaging portion toward, but short of, the main body portion. This depth of penetration limitation is not required if the pin is employed where liquid-tightness is not required, or where the pin has no peripheral cleavage.

With these qualifications, if a kerf is employed which cleaves the periphery, it may typically be a radial slot extending out to the periphery from the annular kerf of FIGURE 2. Or it might comprise a single Archimedean curving kerf, one end of which extends out as far as the peripheral contact surface.

The precise dimensions and locations of the kerfs or other means employed to make the engaging portions of the pins more pressure compliant are not critical and may be varied widely within the spirit of the invention. Thus the diameter of the annulus 3 and its dimension are capable of wide variation. So also are the diameters of the

holes

4 and 4a, or the distances of the

kerfs

5 and 6 from the periphery of the pin. The only important factors limiting these variations are that the increased pressure compliance desired should be obtained, thereby equalizing the contact forces of the engaging portion of the pin in the socket, and that the mechanical stability of the pin in the socket should not be impaired. By this latter point is meant that the kerfs or other means employed should not be so placed that the pins will snap or break when inserted into the sockets or when in prolonged use therein, and that the withdrawal forces of the pins from the sockets should not be so reduced that the pins will become disengaged from the bodies to which they are coupled. The desired results of this invention are easily obtained despite these minor considerations which should be heeded and which will be obvious to one skilled in the art.

Although I have described my invention with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

I claim:

1. In combination, a graphite pin electrically coupling an external power supply to an electrical conducting member having-a non-threaded socket receiving an en gaging portion of said pin under compression, said pin being characterizedby having a main body portion coupled to saidengaging portion and to an external power supply, said engaging'portion being interiorly cut away to make it more pressure compliant than said engaging portion would be if the interior cutting were absent, said cutaway portion extending longitudinally from the face of the engaging portion in the direction of the main body portion and terminating within said graphite pin.

2. An electrical combination according to claim 1 wherein the non-threaded socket of the electrical conducting member is cylindrical in shape and wherein the engaging portion of the pin is of a general cylindrical shape flared into and integral with the main body portion of the pin, and chamfered at the peripheral edge of its face.

3. An electrical combination according to claim 1 wherein the interior cutting which makes the engaging portion more pressure compliant comprises an annular kerf substantially concentric with the circumference of the engaging portion.

4. An electrical combination according to claim 1 wherein the interior cutting which makes the engaging portion more pressure compliant comprises three straight non-contiguous keris of substantially equal length, none of which extend as far as the periphery of said engaging portion, and which if extended to intersect with each other would approximately form an equilateral triangle, the middle of each of these kerfs being substantially equidistant from the periphery of said engaging portion.

5. An electrical combination according to claim 1 wherein the interior cutting which makes the engaging portion more pressure compliant comprises three straight kerfs of substantially equal length, none of which extend as far as the periphery of said engaging portion, and which kerts intersect with each other to approximately form a triangle, the middle of each of these kerfs being substantially equidistant from the periphery of said engaging portion.

6. An electrical combination according to claim 1 wherein the interior cutting which makes the engaging portion more pressure compliant comprises a hole of a generally cylindrical shape, the center of which hole is on the approximate axis of said pin.

7. An electrical system for use in an electrolytic cell comprising in combination a graphite anode having a non-threaded socket adapted to receive an engaging portion of a graphite coupling pin under compression, and a graphite coupling pin frictionally engaged in said socket, said pin being characterized by having a main body portion coupled to said engaging portion and to an external power supply, said engaging portion being interiorly cut away to make it more pressure compliant than said engaging portion would be if the interior cutting were absent, said cut away portion extending longitudinally from the face of the engaging portion in the direction of the main body portion and terminating within said graphite pin, and said engaging portion also having a peripheral cleavage extending inwardly to said cutaway portion, said peripheral cleavage being completely surrounded by and lying entirely within said socket.

8. An electrical system for use in an electrolytic cel comprising in combination a graphite anode having 2 non-threaded socket adapted to receive an engaging por tion of a graphite coupling pin under compression, ant a graphite coupling pin frictionally engaged in said socket said pin being characterized by having a main body portion coupled to said engaging portion and to an ex ternal power supply, said engaging portion being in teriorly cut away to make it more pressure compliant than said engaging portion would be if the interior cutting were absent, said cut away portion extending longitudinally from the face of the engaging portion in the direction of the main body portion and terminating within said graphite pin.

9. An electrical system according to claim 7 wherein the non-threaded socket of the graphite anode is cylindrical in shape and wherein the engaging portion of the pin is of a general cylindrical shape flared into and integral with the main body portion of the pin, and chamfered at the peripheral edge of its face.

References Cited in the file of this patent UNITED STATES PATENTS

Claims

1. IN COMBINATION, A GRAPHITE PIN ELECTRICALLY COUPLING AN EXTERNAL POWER SUPPLY TO AN ELECTRICAL CONDUCTING MEMBER HAVING A NON-THREADED SOCKET RECEIVING AN ENGAGING PORTION OF SAID PIN UNDER COMPRESSION, SAID PIN BEING CHARACTERIZED BY HAVING A MAIN BODY PORTION COUPLED TO SAID ENGAGING PORTION AND TO AN EXTERNAL POWER SUPPLY, SAID ENGAGING PORTION BEING INTERIORLY CUT AWAY TO MAKE IT MORE PRESSURE COMPLIANT THAN SAID ENGAGING PORTION