US2199519A - Electrolytic device - Google Patents

Description

May 7, 1940- J. L. COLLINS ET AL ELECTROLYTIC DEVICE I Filed July 21, 1937 INVENTORS COLLINS JOSEPH L. & ALEXANDER DURANT J12.

W, cm w A RNFfYS and usually consists of afabric washer impreg- Patented May 7, 1949 ELECTROLYTIC DEVICE Joseph L. Collins and Alexander Durant, In,

ApplicationJuly 21, 1937, Serial No. 154,906.

UNITED STATES PATENT OFFICE 2 Claims. (Cl. 220-44) the electrolyte.

Onthe other hand, the gases liberated during the operation of electrolytic condensers require venting means for their escape. I

Various venting means have been therefore suggested for such condensers, most of which, however, have the common drawback of permittingthe electrolyte to be carried away with the escaping gases. A widely-used venting means which overcomes this difliculty is one in which the, gases escape through a semi-permeable gasket, as described in U. S.'A. Patent #2,005,055 to Robert Sprague-et al.-

Such a semi-permeable gasket is as a rule crimpedly interposed between the. open end of the condenser container and a closure member,

nated with wax or other water-repellent material.

In the usual types of wet electrolytic condensers and under usual operating-conditions, the rate at which gas is liberated in the condenser is less than the rate at which these gasescan pass through the above-described venting means. However, even in some types of wet electrolytic condensers, and particularly in dry electrolytic condensers-which have a lower heat capacity and poorer heat dissipation than wet electrolytic condensers-conditions may arise which cause such a large amount of gas liberation and at such a.- high rate that the usual venting means are unable to handle them.

As a result, pressures of such magnitude may build up in the condenser container as to cause its violent explosion. While such instances are comparatively rare,- they may occur, for example, if a condenser is operated for a prolonged time at a voltage much in excess of its rated voltage. Continued operation at excess voltages not only increases gas liberation at the electrodes due to the electrolytic reaction, but may cause intense evaporation of the electrolyte due to excessive heat development. 'Thisexcessive heat development is due to the cumulative action of,

increased leakage current and power factor which occurs upon prolonged application of excessive voltages, i. e., at higher-than normal voltage the leakage current increases, causing greater'heat development, which in turn increases the power factor of the condenser. The increased power factor further increases heat development, which in turn causes a further increase in the leakage current, and so on, and unless the heat dissipation of the condenser takes care of it, the condenser will be heated up to a point where a violent evaporation of the electrolyte takes place, resulting in the explosion of the condenser container. I

The object of the present invention is to provide' a combination of venting means, a portion of which takes care of the normal venting, and another portion of which becomes effective only when within the condenser a high gas pressure of a predetermined value has built up, which value is selected to be lower than the pressure which would destroythe container.

According to the invention we provide venting means to take care of the normal gas liberation, and emergency venting means to be effected only when the pressure in the condenser container reaches a comparatively high value.

In accordance with the invention, the emergency venting means comprise a weakened portion of the condenser container, which is pierced by a pressure of predetermined value, such value being so selected as to be by a safe margin lower than the pressure which would cause explosion of the container.-

' Preferably we provide the weakened portion of the container in a cover member and in such a manner that piercing of this portion provides for the escaping gases a low-resistant passage of a predetermined cross section.

Such a weakened cover portion can be conveniently obtained and substantially without extra cost with the generally used molded covers made of Bakelite, hard rubber and like materials.

In the preferred embodiment of the invention the normal and the emergency venting means are partly interrelated.

In the drawing forming part of the specification:

Figure 1 is a cross-sectional view ofa ccondenser embodying the venting means of the 'invention;

Fig. 2 is an enlarged cross-sectional view of the cover of the condenser in Fig. 1 taken along the lines 2-2 of Fig. 3;

lfig. 3 is a bottom plan view of the cover of Referring to the drawing, the condenser proper, designated as H, consists of two electrode foils l2 and I3 of which at least one is of film-forming metal, for instance of aluminum, tantalum, zirconium, etc., and is provided with a film, usually formed on the electrode electrolytically and prior to the assembly of the condenser.

Interposed between the electrode foils are spacers ll-H which, together with the foils l2 and II, are wound into a roll. The spacers ll consist of a suitable absorbent material, such as gauze, paper or the like.

The electrolyte I! carried by the spacers, as a rule comprises as ionogen a weak acid of the type of boric acid, phosphoric acid, citric acid, etc., and preferably'also a salt of a weak acid, which, however, does not need to be the salt of the acid used. As ionizing solvent the electrolyte comprises as a rule a polyhydric alcohol, for instance glycerine, ethylene glycol, etc., and also a fixed amount of water. The electrolyte may also comprise one or more inert substances which may serve to increase its viscosity, for instance bentonite, starch, silica gel, etc., and/or a finely divided conducting material, such as magnetite, lead peroxide, graphite, etc. to increase its conductivity as well as its viscosity.

The spacers it are impregnated with the electrolyte l5 either prior to or after the assembly into a roll. The condenser II is surrounded by a cylindrical metallic container Ill, from which it is suitably insulated by air spaces or insulating spacers.

The annular cover It, inserted in the open end. of container Ill and abutting against an annular indentation thereof, ispreferably a molding of a suitable insulating material, as hard rubber, Bakelite, or the like. At its top the cover It is provided with a peripheral recess 21, the fiat surface of said recessed portion being provided with a narrow annular ridge 35.

Close to the periphery of the top face 53 of its not recessed portion, the cover is provided with a small cylindrical cavity 3| extending downwardly to the level of surface 54 and having thin side and top walls 33 and 34 respectively, these forming the weakened portions of the cover.

Beneath and concentrically with the cavity 3| there is provided in the cover I! a cylindrical cavity 30 of larger diameter, the cavity 30 extending to the bottom face 58 of cover ll.

As appears from Figs. 2 and 3, in the top face 54 of the recessed portion of the cover a crescentshaped opening or fissure 32 is formed.

The cover is also provided with two terminal posts i1 and i8, which are preferably molded into the cover and to which are connected the electrodes i2 and I3 by connecting strips II and 23 respectively.

Outside electrical connection of the electrodes I can be made by means of nuts 2i and 22 secured to the threaded ends of the posts l1 and I8.

Preferably the cover It is provided with projecting flat-faced bosses i|5'l cooperating with the nuts 2| and 22.

A semi-permeable washer-shaped gasket 23 of impregnated fabric or a washer of soft rubber, to which water-repellent material has been added,

is disposed in recess 21 and is pressed against the cover it by the crimped end 60 of the containc It. The ridge 3! insures the proper location (I cover it.

As will be noted from Figs. 2 and 3, in the portion 6|, which covers the crescent fissure 32, the gasket 28 is directly exposed to the pressure existing within the container; this portion of the gasket serving as the venting means through which the gases escape during the normal operation of the condenser. In case'the gasket is of semi-permeable material the gases pass through it without necessarily lifting the exposed gasket portion 6|. However, if the gaskets are nonporous, for example made of soft rubber, the exposed gasket portion 5| is lifted by the pressure of the gases and permits their escape through the opening so created. However, if because of unusual conditions, for example the prolonged application of a voltage much in excess of the rated voltage of the condenser, the gas liberation assumes such proportions as to tend to build up in the container Iii a pressure which would blow up the container, before such critical pressure is built up, i. e. at a pre-selected lower value, the cover will be pierced at its weakened portion. Such piercing of the cover, i. e. the forcible ejection of the wall portions 33 and 34, offers a passage of the cross section of cavity 3| for the escape of the gases, which is sufficiently large to permit the venting of the gases even under such unusual conditions.

It should be noted that the large amount of heat generated in the condenser incidental to the prolonged application of an excessive voltage, further weakens the wall portions 33 and 34 and thus facilitates their ejection.

The relative and actual dimensions of the venting means depend on a number of factors, such as the amount of gases required to be handled by the normal venting means, the pressure at which the piercing of the cover is to take place, overall dimensions and material of the cover, etc.

For example, in the case of a hard rubber cover I Thickness of thinnest portion of wall 33: 1/

Distance of common axis of cavities 30 and 3| 1 from edge of cover: 95

Maximum width of crescent fissure 32: ,5 The above dimensions are given as an illustration only, as wide variations may take place in same in view of the various factors involved.

While we have described our invention in connection with specific embodiments and in specific examples, we do not wish to be limited thereto,

but desire the appended claims to be construed as broadly as permissible in view of the prior art.

What we claim is:

l. Venting means for electrolytic condensers having a container closed by a cover, said means comprising a vent gasket and a recessed portion in the cover to receive same, said cover being provided with two concentric cavities, one on top of the other, the upper cavity being of very small diameter and the lower cavity of somewhat larger diameter, the upper cavity being partly surrounded by a thin wall portion and the lower cavity having a fissure under said gasket, said venting means being adapted to vent the gases developed in the normal operation of the condenser through the bottom cavity and the gasket 7" portion overlying the fissure, and to vent gases at pressures considerably in excess of the normal pressures by the rupture of said thin wall portions to thereby liberate the gas through said bottom cavity and through the opening provided by the removal of said wall portions.

2. In an electrolytic device, a container and a cover for said container, means to permit the escape of gases developed in said device, said 10 means comprising a low-pressure vent and a highpressure vent in cooperative relationship with each other, said high-pressure vent comprising a weakened portion of said cover adapted to be detached from the rest of said cover, said lowpressure vent comprising a fissure at said weakened portion of the cover and an overlying semipermeable gasket secured over said fissure by said container.

JOSEPH L. COLLINS.

ALEXANDER DURANT, JR.

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