US2374499A - Electric condenser - Google Patents

Description

April 1945- J. c. QUAYLE ET AL ELECTRIC CONDENSER Filed April 10, 1945 W Inventors m M}? M Attorneys Patented Apr. 24, 1945 ELECTRIC CONDENSER Joshua Crcer Quayle, Manley,

Helsby, and

William Cecil Handley, Frodsham, via Warrington, England, assignors to British Insulated Cables Limited, Prescot, England, a British company Application April 10, 1943, Serial No. 482,570

In Great Britain May 22, 1942 5 Claims.

This invention relates to electric condensers of the kind built up of two or more units nested in, or piled on, one another and each comprising a ceramic body having the form of a dish, bowl or cup with electrically conductive coatings on its internal and external surfaces and of such shape that it will nest in a second unit of the same nominal shape and dimensions with a part of its external conductive coating lying in contact with the outer part of the internal conductive coating of the second unit. A body which meets this requirement is a bowl, dish or cup of circular or other smoothly curved cross-sectional form, and of which the internal and external dimensions continuously increase as the rim of the body is approached, the wall thickness of the body when measured in a direction parallel to the axis being a maximum near the rim of the body. Examples of such a body are a portion of a hollow sphere not greater than a hemisphere, a dome of other than spherical form, for instance, parabolic, and a circular cup with a fiat top and outwardly curving or sloping side walls; For the sake of brevity such a body will hereinafter be termed a cupped ceramic body. A part of the internal surface of such a cupped body lying in the region of the rim of the body and bounded by two cylinders, whose axes coincide with that of the body, may be of the same slope as the part of the external surface of the body bounded by the same two cylinders, so that the body will nest in a second body of the same shape and dimensions with a substantial area of its external conductive coating in contact with the outer part of the internal conductive coat- Examples of cupped 1 the other with a part of the external coating of the inner body in direct contact with, or in close proximity to, an outer part of the internal coating of the outer body. At the rim of each body the internal surface curves outwards and the internal conductive coating on the body is continued over a part of the outwardly curving or flared portion and the internal coating of the outer body is seamed to the external coating of the inner or nested body by a fillet of solder contained in a groove formed by the outwardly curved internal surface of the outer body and the adjacent external surface of the inner body. By this construction we avoid a high concentration of electric field between the two coatings of the cupped ceramic body in the vicinity of the edge of the internal coating and provide an adequate electrical and mechanical junction between successive units even in cases where the nesting bodies do not fit together or do not fit together with accuracy.

The ceramic material used is preferably one having a high dielectric constant, for example, rutile and each conductive coating preferably comprises a metallic deposit fired on to the rutile body and backed by plating or spraying silver or copper on to the fired deposit.

In general, the appropriate outward curvature of the internal surface at the rim of the cupped body will be obtained by a rounding off of the internal edge of the rim. Such a rounding off will provide for the necessary stress distribution and give a very accessible groove for the reception of the solder for seaming the contiguous coatings together, except in cases where the wall thickness of the cupped ceramic body is very small, in which cases, the wall of the body may curl over outwardly at its rim.

The edge of the external conductive coating of each cupped ceramic body does not extend to the rim of the cupped body, but is preferably terminated short of the rim by such an amount that the field between the edges of the two coatings runs obliquely through the dielectric, that is, in a direction more or les parallel to the axis of the body. This results in a local increase in dielectric thickness and can be sufficient to prevent an increase in field density in the region of the rim of the cupped body. Preferably the outer part of the external surface of the body curls outwards and backwards from the rim of the body to provide a curved trough surrounding the body and having a mean diameter approximating to that of the rounded off internal edge of the body. The edge of the external conductive coating is continued into the trough and covers a substantial portion of the inner curved wall thereof. This trough also serves to facilitate the soldering together of the adjacent coatings of two successive units of a nest or pile, as will be explained more fully below.

The condition that increase in field density is to be prevented by increasing the distance through the dielectric in the neighbourhood of the edge of the unit, may be used to define a limit of the slope of the outer part of the unit. If We consider the case of a unit limited by surfaces swept out by lines rotated about the axis of the unit, these lines being curves in the neighbourhood of the axis and straight in the outer parts and separated by a distance which is approximately constant when measured normal to the surfaces, a limit to the inclination of these outer straight lined parts to a line parallel with.

the axis is set by the requirement that the sine of the angle of inclination should not be greater than the ratio of the normal thickness of the dielectric to the increased thickness required at the outer edges.

The invention will be further described with the aid of the accompanying drawing wherein Figure 1 is an elevation, partly in section, of a condenser built up, in accordance with the invention, of two units of the same size and shape, and

Figure 2 is an elevation, partly in section, of a condenser built up of two similar units which are of the same general form as those shown in Figure 1 but are not perfectly circular.

Each of the two units consists of a rutile cupped body I of substantially uniform thickness. The general form of the inner surface of the body is that produced by the rotation about an axis of a line comprising an arc of a circle subtending an angle of about 60, with one end lying on the axis and its outer end continued in a tangential straight line making an angle of 30 to the axis. The wall of the body being of contsant thickness save near its edge or rim 2, the outer surface is of the same form and parallel with the inner surface save in the region of the rim 2, to which reference will be made later. The width of the part of the internal surface of each ceramic body that is tangential to the spherical portion is of the order of four times the normal wall thickness to provide for a substantial area of contact between the inner surface of the upper and the outer surface of the lower body. This ensures that when the two bodies are fitted together, their axes will be coincident and their rims lie parallel to one another. The whole of the inside surface of the body is provided with a conductive coating 4 which is continued over a part of the rounded off internal edge of the rim 2. The outside surface of the body is also provided with, a conductive coating 5 which does not, however, extend to the edge of the rim. As will be seen,

.,the outer part of the inside coating of the outer member lies in contact over a considerable area with the outer part of the outside coating of the inner member, thus connecting the two condenser units in series. I

The two units are maintained in piled or nested formation by applying, where the curved surface of the lower edge of the inner coating i on one unit leaves the surface of the outer coating 5 of the nested unit, a circumferentially extending fillet 6 of solder which seams solders the coatings together and connects the units mechanically. Where a condenser is built up of more than two units, this will be done between each pair of units so that all the units are mechanically jointed together and, at the same time, the units are connected electrically in series.

The soldering operation is facilitated and other important electrical advantages obtained by arranging that the radially outer part 3 of the exunits of the pile.

, shape from the nominal.

ternal surface of each body curls outwards and backwards from the rim 2 of the body to form a circumferential channel 7 into which the coat-. ing 5 on the outside wall of the member extends. The position of this channel 1 is such that the rounded internal edge 2 of the rim of the superposed member dips into the channel. The outer conductive coating 5 preferably covers the greater part of the inside surface of the channel, thereby, in effect, providing the coating with a curled edge and avoiding high concentration of the electric field in the region of the edge of the outer coating. With the same object in view, the surface of the fillet 6 of solder uniting the adjacent conductive coatings 4 and 5 is continued to the edge of both coatings and is rounded so as to form a smooth continuation of edge of the inner coating 4. By this means, the outer parts of both electrodes of each unit are in the form of smoothly curved surfaces and, owing to the fact that they are spaced apart by a thickness of dielectric material which is substantially greater than the normal thickness of the dielectric between the remaining portions of the electrodes (since between the curved edges it is measured in a direction substantially parallel to the axis of the unit, the stress can be made substantially the same here as in the main part of the dielectric.

Sufiiciently close approach to uniformity of dimensions and form for close fitting of the units in the way shown in Figure 1 cannot readily be obtained in a large number of cupped members of th same nominal size and form of ceramic material; accordingly, in order to obtain sets of units which fit closely together, it becomes necessary to resort to careful selection from a large number of manufactured units and to the ultimate rejection of a substantial proportion which cannot be made to fit closely together. The provision of the circumferential channel I and the use of a fillet 6 of solder to joint the outer parts of adjacent conductive coatings renders it unnecessary to obtain a close fit between successive This permits of units being used which differ slightly in dimensions and Figure 21 of the draw- 5 in shows a condenser built up of two units one (or both) of which is not truly circular, so that the upper is supported by the lower at, perhaps, two or three places only around the circumference thereof, none of which lies in the plane in which the section is taken. If desired, the cupped bodies may be so shaped and dimensioned that the rim of one body rests in the bottom of the trough 7 round the outside of the next lower member without the coatings on the adjacent surfaces of the two bodies being in direct contact, so that the only connection between the inside coating 6 of one body and the outside coatin 5 of the body nesting therein is by way of the circumferential fillet 6 of solder.

The cupped body of the lower unit of the con-. denser shown in Figure 2 is closed by a metal disc 8 with a beaded edge 9 which is soldered to the edge of the conductive coating 4 on the inside of the body. In the centre of this plate is an internally screwed socket member H constituting, at the same time, a connector terminal and an attachment for a support member. The cupped body of the upper unit carries a terminal ring 12 soldered to the central part of the outer conductive coating thereon. This ring is provided with three equidistant tapped holes for connecting purposes.

What we claim as our invention is:

1. An electric condenser comprising at least two cupped ceramic bodies nested one within the other, conductive coatings on the internal and external surfaces of each body, -said internal coating continuing over a part of an outwardly curving portion of the internal surface at the rim of the body, and means for seaming the internal coating of one body to the external coating of the body nested therein, said means comprising a circumferentially extending fillet of solder contained in a groove formed by the outwardly curved internal surface of the one body and the adjacent external surface of the nested body.

2. An electric condenser comprising at least two cupped ceramic bodies nested one within the other, conductive coatings on the internal and external surfaces of each body, said internal coating continuing over a part of an outwardly curving portion of the internal surface at the rim of the body, and said external coating terminating short of the rim of the body whereby the electric field between the edges of the two coatings passes obliquely through the dielectric in a direction substantially parallel to the axis of the body, and means comprising a circumferentially extending fillet of solder contained in a groove formed by the outwardly curved internal surface of the one body and the adjacent external surface of the nested body, seaming the edge of the internal conductive coating on the one body to the edge of the external conductive coating on the nested body.

3. An electric condenser as specified in claim 2, wherein the ceramic bodies are similar in form and a part of the internal surface of each body lying in the region of the rim of the body sine of the angle of which is not greater than the ratio of the normal thickness of the dielectric to the increased thickness of dielectric required between the edges of the coatings.

4. An electric condenser comprising at least two cupped ceramic bodies, each having a rim of which the internal edge is rounded ofif, a conductive coating on the internal surface of the body which continues over a part of the said rounded off edge, an external surface of which the radially outer part curls outwards and backwards from the rim of the body to form an an nular trough, and a conductive coating on the external surface of the body which extends into the annular trough, said bodies being nested one within the other with the rounded edge of one body entering the annular trough of the body nested therein, and means for eircumferentially seaming the edge of the internal coatin of one body to the coating on the surface of the trough of the body nested therein, said means comprising solder contained in said trough.

5. An electric condenser comprising two or more nested cupped ceramic bodies having con.- ductive coatings on their internal and external surfaces and having the external coating of each nesting body seamed to the edge of the contiguous internal coating of the next body by a fillet of solder contained in a circumferential groove formed by a part of the external surface of the nesting body and the rounded internal edge of the body in which it nests, wherein the exposed interior of the body at one end of the condenser is closed by a metal disc which is soldered along its entire edge to the edge of the conductive coating on the internal surface of that body and carries one terminal of the condenser, and the body at the other end of the condenser carries a metal terminal ring soldered to the central part of the external conductive coating thereon.

JOSHUA CREER QUAYLE. WILLIAM CECIL HANDLEY.

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