US2320495A - Forming circuit - Google Patents

Description

June 1, 1943. WATERMAN 2,320,495

FORMING CIRCUIT Filed Oct. 27. 1939 INVENTOR Herbert Wider/m2 ATTORNEYS Patented June 1,

FORMING CIRCUIT Herbert Waterman, New Bedi'ord, Mass, assignor to Aerovox Corporation, New Bedford, Mass a corporation of New York Application October 27, 1939, Serial No. 301,637

3 Claims.

The present invention relates more especially to the electrolytic formation of insulating film upon a surface of film forming metal and is shown particularly applied to the art of forming electrolytic condensers.

Where it is attempted to apply the forming current to electrolytic condensers in short shocks with intervening long periods of rest for the purpose of minimizing deformation by preventing excessiye rise of temperature, there is a tendency nevertheless to deform during the rest and cooling period, because of the high temperature produced during the formation shocks. Such practice also involves the need for costly supervision and the need for extensive investment in forming equipment, due to the length of time that each condenser section must remain on the rack before it can be removed and replaced.

An object of the invention is to provide a film forming method performed by the use of simple equipment and with minimum power consumption, by which the film is built up under automatic control, without the need for skilled supervision and at substantially the maximum rate compatible with continuous progress :olf formation and without the need for interpolating periods of rest orof cooling to guard against overheating.

According to the invention, the forming potential is applied through,the condenser section, connected in series with a multi-element thermionic tube and a resistance, the latter determining the negative bias of the grid.

In the accompanying drawing in which is shown one of various possible embodiments of the several features of the invention, the figure shows diagrammatically, a circuit for forming electrolytic condensers, illustratively dry condenser sections.

The forming current is derived from a con ventional source of alternating current, which is connected through a step up transformer I to the mains II and I2 between which a difference of potential say of 500 volts is maintained. Be-

tween the mains there is a multi-clement thermionic tube '1 including a plate P, a cathode, de-

sirably in the form of a filament F and a grid sistance R may be linear or non-linear and may have a substantial or a smallpositive or a negative or even a zero temperature coefilcient. The resistance'R in one embodiment is desirably made up of an incandescent filament lamp R. of positive temperature coefficient in series with an ohmic wire resistance Rb. The grid G is connected by a conduit 20 to the same main I! as is the resistance R. Appropriate clips (not shown) serve removably to connect in circuit, a condenser section C to be formed, an electrode i4 being connected to the other main II and the other electrode ii to the plate P.

If desired. the condenser sections could be connected between the said main l2 and the resistance R, instead of in the relation shown in the drawing, or anywhere else in the circuit across the mains H and i2.

Only two thermionic tubes T and associated resistances R are shown, each with a condenser section C connected up to be formed, but it will be understood that in practice a multiplicity of like forming circuits are connected in parallel across the mains.

Desirably the equipment may include a voltmeter V connected to the main I I and having a lead v for selective connection thereof across any section being formed to determine the voltage drop thereacross. Likewise the equipment may include a milliammeter A connected to the main l2 and having a lead a. for selective connection in shunt with the resistance Rb to determine the current flow through any forming circuit, without opening such circuit.

The mode of operation will now be briefly set forth. The condenser sections C either with unformed anodes or with anodes preformed in aqueous 'solution are connected between the plate P of the associated tube and the main ll. Initially the resistance of the condenser section will be relatively low, the electrolyte affording good conduction between its electrodes. The current through the condenser is primarily limited by the effective resistance of the tube. That resistance is determined by the voltage drop across the resistance R, the bias being equal to the voltage drop across such resistance. In the specific embodiment shown the resistance is determined by the current flowing through element Ra. When the current through the circuit decreases, the grid bias (which'is the voltage drop across the resistance R) decreases, thus decreasing the eifective resistance of the tube and increasing the voltage across the condenser section,

As formation of the dielectric film on the anode of the section C progresses, its ohmic resistance increases; with consequent reduction in the current through the series connected parts C, T and R. The difference of potential between the ends of resistance R however decreases more than in proportion to the current decrease since The lamp-R. having a positive temperature resistance co-eflicient, there results a large increase in resistance when the current is high and a corresponding decrease when it is low. Thereby the negative grid bias is accentuated as compared with the effect of that bias when a resistance of constant magnitude is'used.

Thus, when the forming current would otherwise be too high, the resultant high negative grid bias depresses it and when it would otherwise be low, the resultant low negative grid bias raises it. Therefore an effective and automatic control is brought about; which on the one hand precludes over-heating and deformation of the film, and on the other hand accelerates the otherwise retarded rate of film formation, particularly at more advanced stages of formation where a faster rate is permissible than would occur, were the forming current from a constant voltage source passed through merely an inert resistance in series with the condenser section. The operation proceeds automatically and without intermis sion, progressively and without partial deformation at any stage. There is great economy of electric power, and no loss due to over-heatin or burning out of sections. The complete formation of a condenser section of 500 volts is thus safely accomplished in less than two hours and for some units in as little as fifteen minutes according to the present method, where from six to twelve hoursor more are required in commercial practices heretofore in common use. The capital investment for forming equipment for a given output is reduced in like ratio. The completion of the formation of each section can readily be verified by measuring with voltmeter V the voltage across. the same, and with milliammeter A, the leakage current through the section.

While tubes or resistances of a wide variety of construction could be employed to advantage in carrying out the method set forth, it is adequate for present purposes to use a three-element vacuum tube of Type 45, the filament current of which is 1.5 amperes applied at a voltage of 2.5, the applied voltage of which tube is 275 and its current 36 milliamperes and the grid bias of which is minus 56 volts. The lamp Ra. may desirably be of 10 to 15 watts and the resistance Rb in series therewith of about 12 ohms.

Since the multi-elernent thermionic tube it self serves as a rectifier, raw alternating current may be utilized for the formation, as previously set forth. It is of course also possible to use direct current where available, for forming condensers according" to the method and with the circuit set forth.

The forming method set forth is useful not only for ageing condensers with preformed anode foil, but also for the entire formation of foil in condenser units that have not been preformed. while most useful for forming wound sections of dry electrolytic condensers, it is also applicable to the formationpf the anodes of wet electrolytic condensers.

Wherever in the claims the term mains is used without specific reference to alternating current and without distinguishing positive from negative, the claim is intended to be generic to direct and alternating current operation. In the former case it will be understood of course that the plate of the thermionic tube would be so disposed in the circuit that positive potential is applied to the plate.

The invention is not limited in application to the formation of condensers or like electrolytic cells but maybe utilized in other electrolytic forming operations. In all applications the metal to be formed is. of the film forming type, and it is in contact with an appropriate electrolyte during the formation. 7

As many changes could be made in the above method and system and many apparently widely different embodiments of this invention could be made without departing from the scope of the claims, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

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

1. Means for forming electrolytic condensers, comprising a condenser section having electrodes and intervening electrolyte, a multielement thermionic tube and a resistance unit connected in series with the electrodes.of the condenser section, said tube having its grid connected with the negative end of the resistance unit, thereby to apply to said grid, a bias controlled by the decreasing leakage current through the progressively forming condenser.

2. An installation for forming electrolytic condensers comprising a pair of mains, a condenser section to be formed having one electrode connected to one main, a multi-element thermionic tube having the plate thereof connected to the remaining electrode of. the condenser section to be formed, a resistance unit connected in series with the thermionic tube to the other main ofthe circuit, said resistance including an element with a substantial temperature resistance co-efiicient, said tube having a grid connected to the negative end of the resistance unit for application of a bias to such grid, controlled by the leakage current through the progressively forming condenser.

3. The installation defined by claim 2 in which the resistance unit includes a filament lamp and an ohmic resistance connected in series therewith.

. HERBERT WATERMAN.

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