US2545411A - Device for regulation of the resistance of an electrolytic cell - Google Patents

Description

March 13, 1951 R J. PERRET-BIT 2,545,411

DEVICE FOR REGULATION 0F' THE RESISTANCE 0F AN ELECTROLYTIC CELL Filed Oct. 29, 1945 2 Sheets-Sheet 1 l! MMX?! s@ QAM a i?? 05ms E wwg W (lq L(3 l m t I g3 www2/7i.'

Ma'rch 13, 1951 R. J. PERRET-BIT 2,545,411

DEVICE FOR REGULATION OF THE RESISTANCE OF' AN ELECTROLYTIC CELL Filed OCt. 29. 1945 2 Sheets-Sheet 2 gaaf-d 47%( Patented Mar. 13, 1951 DEVICE FOR REGULATION OF THE RESIST.- ANCE OF AN ELECTROLY'LIO CELLr Roger Joseph llerret-Bit,n Chambery, France, as-

signer to VCompagnie de Produits Chimiques et Eleotrometallurgiques Alais, Froges et Camargue, Paris, France, a corporation of France Application October 29, 1945 Serial No. 625,387 In France AprilV 7, 194,4

Section 1, Public Law 690, August 8, 1946 Patent expires April 7, 1964 4 Claims.V

The present invention relates to electrolytic cells and more particularly to an electrolytic cell having apparatus for the control thereof.

It is well known that every electrolytic cell comprises electrodes of different polarity, anode and cathode. In certain types of cells, the resistance between the anode and cathode varies during the electrolysis. Furthermore, it is Well known that electrolytio cells for the manufacture of aluminum are provided with carbon anodes that are burned gradually by the free oxygen released at their surface. In cells of this type, the anode is usually movable in a vertical direction to approach or move away from the cathode, which usually forms the bottom of the cell in which the electrolysis takes place. It has been proposed to control the action of the apparatus by keeping the voltage between the electrodes constant. However, in the case of cells where a periodic polarization occurs, this system is defective. In the oase of the electrolysis of aluminum, for instance, the same amount of current may be passed through a plurality of cells and when one of the cells is subjected to anodic polarization, the voltage -across its terminals is increased and the current passing through other cells located in the same circuit is decreased. The voltage on these cells decreases also and, yet, withdrawing the anodes will not overcome the difficulty and keep the voltage at the desired control value.

One object, therefore, of this invention is to provide an apparatus wherein means is provided for adjustingr the interelectrode distance of an electrolytic cell so as to always obtain a desired bath resistance.

Other objects of the applicants invention will appear from the following description of specific embodiments thereof.

The preferred embodiments of the present invention, as hereinafter described with reference to the drawings, are given by Way of example only. In the drawings:

Figure 1 is a diagrammatic view of an arrangement according to the present invention for measuring the resistance of the bath of an electrolytic cell, and, eventually, controlling this resistance.

Figure 2 is a diagrammatic view of another arrangement according to the present invention for indicating the voltage that should exist across the terminals of the electrolytc cell if the resistance of the bath were adjusted to the desired value, the indication being independent of the current flowing through the cell at the time of the measurement.

Figure 3 is a diagrammatic showing of a device according to the present invention for signalling at any time the difference, if any, between the actual value of the resistance of the bath and the desired value of this resistance, with a view to enabling adjustment of the resistance in question.

Figure 4 is a diagrammatic view of another embodiment ofy the instant invention.

In the arrangement illustrated in Figure 1, the applicant makes use of a balanced relay having crossed actuating coils I and 3 mounted on a common pivot 35, the principle of which is well known in the art. On one of thev coils l of this apparatus, there is impressed by means such as leads 3| and 32 a voltage proportional to the amount of current ilowing through the electrolytic cell l0, said cell having electrodes 25 ,and 26 with power leads 21 and 28 attached thereto, by means such as shunt 2 or other equivalent means, for instance, a direct current transformer of a known type. The other coil 3 has impressed thereon by means such as leads 33 and 34 a potential difference proportional to the voltage across the terminals of the electrolytic cell reduced by an amount to be described later, and supplied by a battery 4 and a potentiometer 5 associated therewith. Variable resistances or rheostats 6 and 1 are provided for adjusting the proportionality factors of the device. The device further includes connections 8 and 9 contacted by an actuated member 36 operative by the crossed coils to act either on a signalling means or an automatic inter-electrode resistance adjusting means, such as the motor-driven electrode-adjusting means generally designated 24.

With such an arrangement, the Iangle of deiiection of the coils and their actuated member for contacting the connections 8 and 9, that is, 0, is such that tangent Q-fa-t a,

a1 being the valuer of the. ampere-turns of coll 3. and a2 being the value of the ampere-turns of coil l. Now,

U being the voltage across the cell, I the current flowing therethrough, and u the constant voltage supplied by the battery 4.

tangent Thus it can be seen that the device permits the obtaining, at any time, of the value of the interelectrode resistance R. It further permits, through connections 8 and 9, of yadjusting this resistance to a desired relationship to the current supply.

When several electrolytic cells are connected in series, the adjustment of the inter-electrode distance between the electrodes in any given cell may be based upon the indications supplied by a voltmeter II, shown in Figure 2, connected by leads 33 and 34 in shunt across the terminals of each cell lil having electrodes 25 and 2'5 with power leads 2i' and 2% attached thereto. However, this voltmeter gives reliable indications for use in adjusting the inter-electrode spacing and resistance only so long as the current is of a nominal value for which the cell has been set. If the cell undergoes an anode effect and the current is, thus, modied considerably, the above-described voltmeter method cannot be used.

With the arrangement shown in Figure 2, a measuring device I2 indicates at any time, irrespective of the current owing through the cells, the value of the voltage that should exist across the particular cell under consideration, so that the resistance of that cell can be adjusted accordingly. The measuring device may be a voltmeter connected to the terminals of a potentiometer I3, which. in turn, is in series with similar potentiometers corresponding to other cells, respectively. The current flowing through these potentiometers originates in a device I4 which may be a direct-current transformer or a shunt connected to the line feeding the cells and is brought to said potentiometers through leads 3l and 32. With this arrangement, the voltage on the volt meter I2 is proportional to the current flowing through the cell. However, the scale on the voltmeter is so arranged that the pointer shows a voltage proportional to the current but increased by a constant voltage equal to the internal electromotive force of the cell, since this latter force makes itself felt on the terminals of the cell and must be taken into consideration.

Potentiometer I 3 is adjusted in such manner that, when the value of the current is the nominal value, the voltmeter I2 exactly indicates the desired value of the voltage to be impressed on the cell, this adjustment being different for the various cells. It then becomes necessaiy only to adjust the inter-electrode distance to the point where the readings of the voltmeter II and I2 of a given cell coincide and the inter-electrode resistance has then been adjusted to the desired amount.

This results from the following derivation:

The deilection 01 of the voltmeter I2 is:

but, due to the peculiar graduation of this voltmeter, the reading 02 is as follows:

and, if u is chosen sol as to be equal to e, the internal electromotive force of the cell,

If the potentiometer I3 has been adjusted so that, when the current through the cell is equal to the nominal value, the reading on the voltmeter I2, that is 02, is equal to the voltage existing across said cell when the inter-electrode resistance has the desired value, Ro, then:

In other words, as long as this adjustment of the potentiometer I3 is maintained, K1=Ro and, whatever the current intensity I through the cell, the value 02 read on the voltmeter I2 will be the voltage that should exist across the cell when the inter-electrode resistance is adjusted to Re, the desired value.

In the embodiment shown in Figure 3, the applicant makes use of a differential balanced relay of a known type having two actuating coils I and 3 which are movable in the air gap of a permanent magnet. Coil I is subjected by means such as leads 3l, 32 to a voltage proportional to the current flowing through the electrolytic cell it having electrodes 25 and 26 with power leads 2l and 28 attached thereto, obtained by means such as shunt 2, or the like. The other coil 3 is subjected by means such as leads 33, 34 toI a voltage proportional to the difference between the voltage across the cell III and a voltage of the value of the internal electromotive force of the cell. In the example, the latter voltage is supplied by a battery 4 associated with a potentiometer 5. Rheostats and 'I are provided for adjusting the proportionalities of the device. Two opposed springs, not shown, are provided to act upon the actuated member 3B of the relay so as to exert no force thereon when it is in a median position. On the other hand, they resist slightly the torque exerted by the fields of the coils I and 3. The actuated member will, of course, contact either connections 8 or 9 to set the adjusting means 24 in motion when the difference between the electromagnetic fields of the coils I and 3 gets high enough. Accordngly,

where e is the driving torque exerted on the actuated member, a1 is the ampere-turns of coil I and a2 is the ampere-turns of the coil 3. Generally speaking, when e is equal to zero, both ci' the connections are open.

Now, a1=K1(U-u) and if the constant value u is chosen equal to the value of e, the electromotive force of the cell,

But the voltage across the electrolytic cell, that is, U is equal to RI -l-e, R being the inter-electrode resistance, I the current flowing through the cell, and e the internal electromagnetic force of the cell. Therefore:

the connection 9 will be closed, Athe adjusting means 24 being vactuated correspondingly to adjust the inter-electrode spacing and resistance. Furthermore, it can be seen that this action is independent of the current flowing through `the cell.

In the embodiment illustrated in Figure 4, the applicant makes use of a differential balanced relay of the known type having two actuating coils movable in the air gap of a permanent magnet. One of these coils, that is, 20 has by means such as leads 3| and 32 a voltage proportional to the current flowing through the cell I0, which is provided with electrodes 25 and 26 having power leads 2'I and 28 attached thereto, increased by a voltage equal to the internal electromotive force of the cell and brought about by means of a battery I9 associated with a potentiometer I8. The iirst-mentioned voltage above is brought about by means such as a shunt multiplier I6, a simple shunt, a direct current transformer, or any similar device giving a voltage proportional to the current flowing through the cell. As illustrated, this embodiment contemplates the use of a plurality of cells operating in the same circuit and the potentiometers I1 for the coils 20 make use of the same shunt multiplier I6.

The other coil I5 of the relay is subjected by means such as leads 33 and 34 to a voltage proportional to the voltage across the terminals of the cell. ITwo springs, not shown, are mounted to act in opposition on the actuated member of the relay, so that said member remains ordinarily in a neutral position between connections 2| and 22 which lead to the adjusting means generally designated 24. The actuated member moves under the inuence of the opposed electromagnetic fields of the coils 20 and I5 and contacts the connection 2I or the connection 22, depending on which inuence is greater, to actuate the adjusting means 24 in a corresponding manner. Now.

Where ai is the ampere-turns of the coil 29, I is the current flowing through the cells and u is the voltage across the potentiometer I8 brought about by the battery I9.

Also,

where a2 is the ampere-turns of the coil I5 and U is the voltage across the cell.

Consequently,

e being the difference between the ampere-turns of coil 20 and those of coil I5. Since,

where R is the inter-electrode ,resistance of .the .cell ,and e is 'the internal electromotve force thereof,

If the potentiometer is adjusted so that K11L=Kse then e=K1K2IK3RI Now, if we adjust the potentiometer I'I so lthat R0, the desired inter-electrode Vresistance is equal to the ratio .of KiKa to K3, or

then the value of E for the particular cell whose potentiometer has been so adjusted lwill be as follows:

So that when the actual inter-electrode resistance R. is equal to the desired value Ro, the actuated member of the relay will be in a neutral position. If, however, the Value of R goes above or below the desired value R0, the actuated member will contact the proper connection 2I or 22, and the adjusting means 24 will be set in motion to adjust the inter-electrode space and the resistance R to the proper value.

While I have disclosed in the above description what I deem to be practical and elicient embodiments of my invention, it should be understood that I do not wish to be limited thereby. Changes may be made in the arrangement, disposition, and form of the parts without departing from the principle of the present invention as brought out in the accompanying claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. An electrolytic apparatus comprising a cell for holding an electrolyte, two electrodes in said cell, adjusting means for moving one of said electrodes toward and away from the other electrode, power leads provided on said electrodes for connection with a direct-current source, a balanced relay comprising two opposed actuating coils and an actuated member, said actuated member moving between a connection for causing the adjusting means to move said one electrode toward the other electrode and a connection for causing said adjusting means to move said one electrode away from said other electrode, means connected across said power leads for impressing on one of said coils a voltage proportional to the inter-electrode resistance, and means connected to one of said power leads for impressing on the other of said coils a voltage proportional to the current flowing between the electrodes.

2. An electrolytic apparatus as recited in claim l, wherein: the means for impressing on one of said coils a voltage proportional to the interelectrode resistance includes a potentiometer in series with the coil and a battery shunted across said potentiometer.

3. An electrolytic apparatus comprising a plurality of units connected in series each having a cell for holding an electrolyte, two electrodes in said cell, adjusting means for moving one of said electrodes toward and away from the other electrode, power leads provided on said electrodes for connection with a direct-current source, a balanced relay with each unit having two opposed actuating coils and an actuated member, said actuated member moving between a connection for causing the adjusting means to move said one electrode toward the other electrode and a connection for causing said adjusting means to move said one electrode away from said other electrode, means connected across said power leads for impressing on one of said coils a voltage proportional to the inter-electrode resistance, and means connected to one of said power leads for impressing on the other of said coils a Voltage proportional to the current flowing between the electrodes, said means for impressing a voltage proportional to the current flowing between the electrodes being common to like coils in all of the units.

4. An electrolytic apparatus as recited in claim 3, wherein: said means for impressing on the other of said coils a voltage proportional to the current owing between the electrodes acts through a potentiometer having a battery shunted thereacross.

ROGER JOSEPH PERRET-BIT.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,396,919 Brace Nov. 15, 1921 1,449,861 King Mar. 27, 1923 1,547,984 Weber July 28, 1925 1,587,106 Edelman June 1, 19267 1,604,584 Keeler Oct. 26, 19261 2,150,015 Witham Mar. 7, 1939\` 2,296,867 Osborne Sept. 29, 1942` 2,343,885 Coleman Mar. 14, 1944'1 2,401,722 Clapp June 11, 1946-;

FOREIGN PATENTS Number Country Date 333,727 Great Britain Aug. 21, 193()j

Claims (1)

1. AN ELECTROLYTIC APPARATUS COMPRISING A CELL FOR HOLDING AN ELECTROLYTE, TWO ELECTRODES IN SAID CELL, ADJUSTING MEANS FOR MOVING ONE OF SAID ELECTRODES TOWARD AND AWAY FROM THE OTHER ELECTRODE, POWER LEADS PROVIDED ON SAID ELECTRODES FOR CONNECTION WITH A DIRECT-CURRENT SOURCE, A BALANCED RELAY COMPRISING TWO OPPOSED ACTUATING COILS AND AN ACTUATED MEMBER, SAID ACTUATED MEMBER MOVING BETWEEN A CONNECTION FOR CAUSING THE ADJUSTING MEANS TO MOVE SAID ONE ELECTRODE TOWARD THE OTHER ELECTRODE AND A CONNECTION FOR CAUSING SAID ADJUSTING MEANS TO MOVE SAID ONE ELECTRODE AWAY FROM SAID OTHER ELECTRODE,MEANS CONNECTED ACROSS SAID POWER LEADS FOR IMPRESSING ON ONE OF SAID COILS A VOLTAGE PROPORTIONAL TO THE INTER-ELECTRODE RESISTANCE, AND MEANS CONNECTED TO ONE OF SAID POWER LEADS FOR IMPRESSING ON THE OTHER OF SAID

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