US2158981A - Electrolytic device - Google Patents

Description

I 1939- J. L. COLLINS ET AL 2,158,981

ELECTROLYTIC DEVICE Filed Aug. 5, 1936 INVENTORS JOATEPHLCOLLINS AND BY ROBERT 1% VMV ATTORNEYS Patented May 16, 1939 PATENT OFFICE ELEGI'BOLYTIC DEVICE Joseph L. Collins and Robert Teeple, North Adams, Mass, assignors to Spragne Specialties Application A 5.

Claims.

The present invention relates to the manufacture of electrolytic devices, and more particularly to that of electrolytic condensers having a highly viscous or pasty electrolyte, which condensers 5 are generally referred to as "dry" electrolytic condensers.

Such condensers comprise, as a rule, two electrode foils of which at least one is of film-forming material, for instance of aluminum, zirconium, tantalum, etc., while the other may be of filmforming metal or of non-filming material depending upon the type of condenser. Also depending upon the type of condenser, one or both of the electrodes are provided with a film, which is usually an.electrolytically-formed oxide film.

\ There is also generally provided between the electrode foils a separator, for instance a spacer of gauze, crinoline, Cellophane, paper, or like material, or combinations thereof, also serving as carrier of the viscous electrolyte.

The electrolyte as a rule comprises as ionogen a weal acid, for instance, 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; the electrolyte also comprises an ionizing agent, which may consist of a polyhydric alcohol, for instance, glycerin, ethylene glycol, etc., and also preferably comprises a small but definite amount of water. The electrolyte may also comprise one or more inert substances which may serve to increase its viscosity and/or conductivity.

A novel method of impregnating electrolytic condensers with viscous electrolytes after they have been assembled into a roll or stack (Jointly referred to as sectionsT, has been described in the copending application Ser. No. 754,668, filed November 24, 1934, of Preston Robinson and Joseph L. Collins, according to which the condenser after having been assembled into a section is impregnated in a centripetal field.

Such process has various important advantages compared with prior-art procwses'of applying the electrolyte to'the condenser, it being a quick and efficient process which eliminates various manual operations and waste of the electrolyte, .and also makes it possible to impregnate condenser sections with such types of electrolytes which did not lend themselves to impregnation of sections with prior-art methods.

. In the process of said application the condenser sections are, preferably placed'with their length axis 'in the direction of the centripetal pressure 55 head; thus in case of a centrifuge rotating about Company, North Adams, Hana, a corporation Massachusetts 1938, Serial No. 94,462

a vertical axis, in a radial and substantially horizontal direction.

In said process the impregnation is effected by the centripetal pressure head, i. e., by the pressure difference existing between the outer and 5 inner face of the condenser section, which forces the electrolyte into and through the section from its outer and toward its inner end.

In this process of impregnation, besides such eifect exerted upon the electrolyte by the cenl0 tripetal pressure head, there is also an effect of the centrifugal force in the form of an impact which forces the electrolyte against the inner end face of the section. This latter efiect has therefore the tendency to oppose the centripetal pres- 15 sure head. However, as the pressure exerted by the centripetal pressure head is much greater than that exerted by the centrifugal impact, as long as spacers of good absorbing properties are used, the absorptive force of which overcomes 20 the influence of the centrifugal impact, a satisfactory impregnation of the sections is obtained.

We have found, however, that when spacers of low or limited absorptive properties and/or of relatively low porosity-particularly in the di- 25 rection transverse to the centripetal pressure head-are used in the section, the centrifugal impact may have a very pronounced and deleterious influence, resulting in an unsatisfactory impregnation of the section.

We have found that when spacers of the just stated characteristics are used in such impregnation, the following may take place:

The section shows a satisfactory condition of impregnation to about three-quarters of its length 5 (measured from that end which has been the outer or high-pressure end in the electrolyte), this portion being followed by a very poorly impregnated zone; the inner end of the section is again properly impregnated.

We have found that such a poorly impregnated zone is the result of the centrifugal impact, which opposing the centripetal force causes air or water vapor to be trapped in the above referred to zone, thereby preventing the motion of the electrolyte into this zone.

' There is a further reason which may cause difficulties in impregnation when using the process of said application in case spacers are used, forexample paper spacers, which swell considerably when absorbinga polar liquid of the typeas are the usual electrolytes. v

While in the copending application Ser. No. 740,487, filed August 18, 1934 of Preston Robinson and now United States Patent No. 2,081,068,

issued May 18, 1937, there has been described a method which insures proper impregnation of spacers of this type by imparting to them their full absorptive properties in subjecting them to pre-swelling prior to impregnation, the present invention may in some cases serve as a substitute for such pre-swelling treatment.

Broadly stated, our invention has utility when subjecting condensers to impregnation in a centrifuge, which condensers have spacers of low absorptive properties, or low porosity, or spacers which cannot be pre-swelled, for example starched gauze, or spacers of which the absorptive properties do not increase by pre-swelling, for example, gauze or cotton, and may also be used in some cases as a substitute for pre-swelling, particularly where pre-swelling may have certain drawbacks.

In all such cases the present invention insures the complete and uniform impregnation of the condenser sections in a centrifuge, irrespective of the axial length of the condenser section.

In accordance with the invention, we either eliminate the action of the centrifugal impact and utilize fully and solely the centripetal pressure head, or eliminate the action of the centripetal pressure head and impregnate solely by the action of centrifugal impact. As a rule we prefer to use the centripetal pressure head, and we shall illustrate our invention primarily in connection with such process.

To eliminate the influence of the centrifugal impact when impregnating in a centrifuge, we close the inner end-faces of the sections by baffies or barriersthe main purpose of which is to prevent the electrolyte from being thrown by the centrifugal impact against such end face of the section and being forced into the section.

Such a baiile may be applied to the section in the form of a thin plate properly closing the inner end face of the section, or preferably in the form of a layer of a sealing compound, which seals the inner end of the section. A suitable way to provide such a baiile is to immerse one end of the section (which in the impregnator is to be the inner end of the section) into a molten wax which has a sufficiently high melting point as to remain solid at the impregnating temperature, and which in no way reacts with the electrolyte during impregnation.

The baille in general is preferably of a semipermeable character, to permit escape of air from the section, but to prevent electrolyte from entering into the section under the influence of the centrifugal force.

If impregnation isto be effected solely by the centrifugal impact, the effect of the centripetal pressure head is eliminated by placing the sections in the impregnator with their bafiled ends falling outwardly. This latter method, however, is rarely resorted to, partly-because utilization of the centripetal pressure head usually insures faster impregnation than does the centrifugal impact, and partly because it is difficult to baffle off the high-centripetal pressure without causing collapsing or deformation of the sections when placed in the centrifuge for impregnation.

Depending upon the condenser structure, the container or wrapping used for it, and the arrangement of the terminal leads, one or more terminal leads may pass through the bailled end of the'sections; the baflle thereby, if desired, may also form part of the sealing means in case the section is sealingly provided in a container.

ilin the drawing forming part of the specificat on:

Figure l is a partly sectionized side view of an impregnating installation;

Fig. 2 is a cross-sectional view of a condenser section provided with a bathe, in accordance with the invention.

Referring to Figure 1, the impregnating apparatus, which comprises a rotatable impregnating tank 40, disposed within a cylindrical vat l5, and a motor M for the rotation of the tank 40, is mounted on a base plate In, on which may be also mounted an electrolyte reservoir tank T.

The vat is stationary and carried on the base M by means of three legs H. The vat I5 is provided with a cover 22 hinged at l6 and which can be swung open by means of a handle 25. The cover 22 is provided with a central aperture 24.

Secured to the inner side of the vat I5, by means of supports 30, and surrounding at least the lower half of the tank 40, is provided. a systemof heating coils 3|, connected by means of pipes 32 and 33 leading through the vat l5, to a suitable heatsupply system, preferably to a steam supply (not shown).

The impregnating tank 40 is disposed concentrically within the vat l5, and is provided with a bottom 4|, a cylindrical side wall 42 and a removable cover 45. The cover 45 is provided with a central aperture 46, aligned with the aperture 24 of cover 22. If desired the aperture 46 can be closed by a suitable closure plate (not shown). Around the edge of side wall 42 and nested in a peripheral flange 43 of tank 40, is provided a circular sealing gasket 48. The cover 45 can be tightly secured to the tank by means of closely spaced swing bolts 39 provided on flange 43 and cooperating with lugs 41 of the cover, tightly securing the cover 46 to the tank 40, whereby the compressed gasket48 insures a liquid-tight seal along the periphery of the tank. I

The bottom 4| of tank 40 is preferably formed as a comparatively thick-walled casting, provided with a downward-extending hub 49, through the bore of which passes the vertical driving shaft 50 of the tank 40, the shaft 50 being flxedly connected to the hub 49 and forming therewith a liquid-tight seal. A suitable thrust bearing for the shaft 50 is formed by the bottom face of hub 49 bearing on the bottom of vat I 5 by means of interposed washers 52. At its lower end the shaft 50 is journaled in a. bearing 53 carried by the base plate l0.

The shaft 50 can be driven by a suitable motor indicated as an electric motor M, the motor M and driving shaft 50 being interconnected by suitable driving means shown as a belt 68, and pulleys 61 and 68.

To obtain a quick stoppage of the rotating tank, braking means are preferably provided, such being indicated by a brake drum 54, mounted on the shaft 50, and a corresponding hand brake 55, one end of which is anchored to one of the supporting legs ll, whereas its other end is controlled by a foot pedal 60, hinged on the leg Ii.

Preferably a timing device (not shown) is connected to the motor and upon pressing of a button starts rotation of the tank and stops such rotation (preferably also applying the brakes), after a preadjusted time interval.

The electrolyte reservoir T, indicated schematically, is preferably a tank of a size adapted to hold sufflcient electrolyte supply for one or two loadings of the tank 40 and is fed at a rate commensurate with the electrolyte consumed in the impregnation. The reservoir T is in practice disposed higher than is the tank 40 so that the electrolyte can be supplied therefrom to tank 40, by gravity.

The electrolyte is preferably preheated in tank T to a temperature slightly above that used during the impregnation. The' temperature and duration of heating the electrolyte in the tank should be such as not to deleteriously affect the electrolyte, but should be sufiicient as to obtain a clear solution also in case of pasty electrolytes.

The electrolyte is supplied from the tank T to the impregnating tank 40 either by means of a flexible metal hose or preferably by means of a pipe system I! which is provided at the exit of the tank T and at the opening 24 of vat i5 with electrodes is to be filmed, and are separated by spacers 4, which may be, in accordance with the invention, spacers which have low absorptive properties and/or low porosity, for example,

dense paper, cellophane, starched gauze, etc. The

- electrode foils are provided with terminal leads foils.

'6 and 1 shown as wires; however, these leads may be formed as integral extensions of the electrode In case the condenser is to be used in rectified current circuits, as a rule only one of the electrodes, namely the anode, is tobe filmed, whereas in alternating circuits both electrodes are filmed, the film formation taking place preferably by the precesses described in the copending applications Ser. No. 548,270 and Ser. No. 741,493 of Preston Robinson now United States Patent No. 2,057,314 and No. 2,057,315 respectively.

The electrode foils are then wound together into a roll, with interposed spacers, made for example, of the previously enumerated absorbent materials. Instead of forming the condenser section as a roll it may be formed as a stack in which case a plurality of aluminum foils with intermediate spacers are assembled into a stack, alternate foils being interconnected to form the two electrodes of opposite polarity.

The assembled sections-which may be held in shape by a rubber band or by twine-are then provided with a baffle 8 at one of their ends, which may be formed of' a layer of suitable sealing compound, for example of .asphalt, which has a flow point substantially higher than is the temperature of the electrolyte during impregnation. The wax layer thereby does not extend to the edges of the electrode foils 2 and l. The layer formsa semi-permeable member through which during impregnation air may be forcedout from the inside by the centripetal pressure head, but which prevents air and/or electrolyte from entering into the section under the action of the centrifugal impact. The condenser sections are then preferably submitted to heating and drying so that when brought into the impregnating tank they are free from moisture and are also preheated to a temperature of between 40 to 70 C.

The condensers are placed in trays or baskets- III, which are also preferably preheated before or after receiving the sections. These trays are of annularv shape and are provided with apertures or are made of meshed wire.

Various forms and arrangements of trays can be used, whereby in case of large-diameter impregnating tanks, the trays are preferably subdivided into segmental portions, all this being more fully described in the above referred to application.

With the pipes l1l8 swung out of the way, the cover 22 of housing I5 is lifted and cover 45 of tank 40 removed.

The individual trays so filled with the condenser sections 28 are then placed into the tank 40, on top of each other, whereby the tank is substantially completely filled by the trays. The cover 45 is then bolted down by means of the swing bolts 39 whereby a tight seal is obtained around the periphery of the tanks due to the compression of the gasket 48. Subsequently the cover 22 or vat I5 is also closed.

To admit the electrolyte into the tank 40, the electrolyte supply pipe system I! is brought into a position as to permit its component pipe l8 to project through opening 24 into the vat l5, which also brings pipe l8 into-alignment with the opening 46 of the impregnating tank 40.

Upon opening of the valve IS, the electrolyte 21 is transferred in the desired amount from the reservoir T to the tank 40. The electrolyte is preferably preheated in the reservoir T usually to a temperature of 100l20 C. depending upon the electrolyte used. The determination of the proper amount of electrolyte to be admitted into the tank 40 will appear from the following:

With the condenser sections 28 and the electrolyte 21 provided in the tank, the tank 40 is set into rotation by means of the electric motor M. Rotation of the tank exerts a centripetal force on the electrolyte, which thereby assumes a position sure head of such magnitude is established between the outer and inner end faces of the sections as to radially (corresponding to the axial direction of the sections) force the electrolyte into the sections and thereby cause their thorough impregnation in a comparatively short time. From the above it thus appears that the proper amount of electrolyte to be admitted in the tank 40 is determined by the requirement that all sections placed in the tank be fully submerged in the electrolyte while the tank is in rotation. Instead of admitting the electrolyte before starting the tank to rotate, the electrolyte may be also admitted with the tank already in rotation.

Satisfactory results have been obtained, for instance, with absolute pressure ranging from 50-175 pounds per square inch, and with diiferential pressures between the two end faces of the" condenser ranging from 10-30 pounds per square inch per linear inch. The absolute value of the prevailing centripetal force depends on depends on the axial length of the condenser sections. In this connection it should be noted that the largest, forces are obtained if the condenser sections fall with their length axes in the main direction of the centripetal forces.

The centripetal pressure head falls substantially in the direction of the axis of the condenser, and the baflie 8 provided in accordance with the invention prevents the centrifugal impact from deleteriously influencing the impregnation.

For a tank of given dimensions and a given speed of rotation the duration and temperature of the impregnation depends upon various factors, and primarily upon the viscosity of the electrolyte at the impregnating temperature and the linear lengths of the condensers.

As a rule we prefer to rotate the tank at speeds of about 1200 to 1800 R. P. M., whereby the higher the speed of rotation, the greater the centripetal head obtained. The duration of impregnation may vary between a few seconds to several minutes depending upon the electrolyte; for instance, when impregnating sections 4" long at a temperature of 95 C. with an electrolyte having a viscosity of 3 at this temperature, a timeof impregnation of about five minutes is required as a rule, whereas less viscous electrolytes and shorter sections require correspondingly less time.

In general our invention can be used under the same conditions and with the same type of electrolyte as has been described in the above referred to application.

While we have described our'invention in some specific applications and embodiments, 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:

1. In the manufacture of dry electrolytic devices, the process which comprises, assembling electrodes and spacers into a section, closing one end face of the section, placing said section in a centrifuge with its length axis substantially in a direction perpendicular to the vertical axis of the centrifuge, and impregnating said section with a viscous electrolyte while rotating said centrifuge.

2. In the manufacture of dry electrolytic condensers, the process which comprises, impregnating with a viscous electrolyte a condenser section in a centrifuge under the action of the centripetal force resulting from the rotation of the centrifuge, while providing means to prevent centrifugal action ofthe electrolyte on the section 3. In the manufacture of dry electrolytic condensers, the process which comprises, impregnating a condenser section in a centrifuge with a viscous electrolyte by the action of the centrifugal force resulting from the rotation of said centrifuge, while providing means to prevent centripetal action of the electrolyte on the condenser section.

4. In the manufacture of dry electrolytic condensers, the process which comprises, assembling electrodes and spacers into a condenser section, closing one end face of the section by means of a wax layer, placing said section in a centrifuge with its length axis substantially in the direction of the centripetal pressure head and with sealed end falling inwardly and impregnating said section with a viscous electrolyte while rotating the centrifuge.

5. Inthe manufacture of dry electrolytic condensers, the process which comprises, assembling electrodes and spacers into a condenser section,

sealing one end face of the section by means of a semi-permeable layer, placing said section in a centrifuge with its length axis substantially in the direction of the centripetal pressure head and with the sealed end falling inwardly and impregnating said section with a viscous electrolyte while rotating said centrifuge.

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