US2693547A - Ignitor - Google Patents

Description

G. LEWlN IGNI'I'OR Nov. 2, 1954 Filed May 28, 1952 NTOR BY; 2 2 ATTORNE United States Patent .n I a.

IGNITOR Gerhard Lewin, Maplewood, N. 1., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application May 28, 1952, Serial No. 290,589

6 Claims. (Cl. 313-355) This invention relates to ignitor and particularly to ignitors for use in mercury-pool ignitrons.

In general there are two types of ignitors known, of which one is coreless and the other provided with. a core which extends well below the mercury surface. The ignitor dips into the mercury pool, and where the pool level changes, as by vaporization of part of the mercury during use, or by tilting of the ignitron, the resistance lengthwise of the coreless ignitor is a variable. The purpose of the ignitor being provided with a core is to avoid this variation of longitudinal resistance under the differing conditons of use and attendant waste of energy above the mercury surface. A disadvantage of such an ignitor with a core is that the current density is uniform over the whole immersed portion of the ignitor rather than being concentrated at the mercury surface or meniscus. Much current is therefore wasted and high currents are required to instigate the arc.

According to the present invention, a principal feature is to have the conductive advantage of a core in an ignitor and at the same time obtain a concentration of current at the mercury surface.

More specifically, the invention contemplates an ignitor with a core having a relationship such that at any level, within the operating range, of mercury around the core, the conductivity to the core will be greatest at the level of the mercury surface.

Other objects of the invention will appear to persons skilled in the art to which it appertains, both by direct recitation thereof and by implication from the context as the description proceeds.

Referring to the accompanying drawing in which like numerals of reference indicate similar parts throughout the several views:

Figure l is a vertical sectional view of an ignitron showing my improved ignitor in elevation therein;

Figure 2 is a longitudinal sectional view of my ignitor in the form disclosed in Fig. 1; and

Figures 3 and 4 are similar longitudinal sectional views of modified forms of ignitors embodying the invention.

Giving attention initially to the general ignitron construction of Figure 1, arbitrarily selected for illustrative purposes, there is provided a cylindrical casing of steel or other sturdy material having a bottom 12 integral therewith and a header 13 sealed at the upper rim of said casing to provide a closed envelope adapted to be evacuated.

The header provides appropriate lead-in seals 14, 15 for electrode leads 16, 17 respectively for an anode 18 and ignitor 19 within the casing. The lead-in seals each include a glass or other insulating sleeve 20 by which the leads are kept electrically distinct from each other and from the casing. The anode 18 is located toward the top of the casing, well above the bottom wall 12, whereas the ignitor 19 is located below the anode and is directed toward and terminates at its bottom in the vicinity of, but above, the bottom wall A pool of mercury or other reconstructing cathode material 21 is provided in the bottom of the container and is of sufficient normal depth for the ignitor to always be partially immersed therein. The mercury level, however, is not always at the same elevation on the ignitor due to various causes and in the past this variation of level has had its serious effects with resistive ignitors in change of firing characteristics of the ignitron and frequently caused arcing and skipping of firing to the detriment of supplementary apparatus. Attempt has been heretofore made in the art to overcome this deficiency of resistive ignitors,

ice

by providing a conductive core, but this did not prove successful due to the spreading out of the current path from the mercury pool to the ignitor core.

In its broadest aspect, the present invention provides .a conductive core 22 for the .ignitor, .said'core being coaxially disposed and having a surface within the resistive body 23 and said surface and the outer surface of.

said body having a tapered relationship such that the radial distance between the surface increases at successive cross sections taken nearer to the lower end of thecore than at the normal level of the pool. This progressive increase of radial thickness .of the resistive body to the core may be variously accomplished, and in Figures 1 and 2 is obtained by tapering the lower end of the core, as at 24, from the normal diameter of the core at about the cathode surface level, to a point at a distance from the bottom of the ignitor body and well below the normal cathode surface level. The corresponding or opposite outer wall of the ignitor body may be cylindrical as shown in Figs. 1 and 2, thus increasing the current path radially of the body to the core at successive levels downwardly. As current prefers the shortest path, it now will be clear that at any location of the mercury level, within its usual range of variation, the shortest current path will be from the mercury surface or meniscus to the core. Thus, the current density is greatest at the surface of the mercury at whatever level the mercury may happen to be at the moment.

Whereas Figure 1 shows the difierential of radial distances obtained by tapering the core, the same effect may be obtained by us of a cylindrical core and tapering the outer surface of the ignitor body outwardly toward its lower end as shown with core 22a and ignitor body 23a in Figure 3.

A more pronounced progressive differential of radial current path may be obtained, if desired, by opposite tapering of the core and ignitor body, and this reversely tapered combination is shown in Figure 4 using the tapered core 22 first described and the tapered body 23a last described.

The ignitor body may be of any usual or appropriate material or mixture, of which boron, boron carbide, and boron nitride may be given as examples. The body is integrated at its upper end with a suitable head 25 of graphite or other material to which the lead-in rod 17 may be secured. The head 25 is conductive and makes good delectrical contact with both said core and said lead in ro In any of the constructions shown, the tapering to obtain the increase of radial current path, begins at least no lower than the maximum level of the mercury surface and continues downward at least as far as minimum level to which the mercury may sink in use. Furthermore, the distance of the bottom of the core from the bottom of the ignitor body is at least as great as the radial distance of the bottom of the core to the side surface of the ignitor body so that, within the operating range of mercury levels, the shortest path for the current is always from the mercury surface radially to the core.

I claim:

1. An ignitor comprising a resistive body portion having a peripheral outer surface, and a more conductive core in said body portion said core having a peripheral surface, said body portion throughout its length that surrounds said core being in contact with said peripheral surface of said core, and said surfaces being separated one from the other at progressively greater distances toward the bottom end of the ignitor, and said core having its bottom end spaced from the bottom of said body portion substantially the same distance as the radial spacing of the bottom of the peripheral surface of the core from the peripheral outer surface of said body portion.

2. An ignitor comprising a resistive body portion having a cylindrical outer surface, and a more conductive core in said body portion, said core having a tapered section within said cylindrical body portion and thereby providing a progressively increasing radial distance through the body portion of the core at different transverse planes through said core from top to bottom of the said tapered section thereof.

3. An ignitor comprising a resistive body portion having a tapered outer section increasing in diameter toward the 'lowerend thereof, and a more conductive core longitudinally and centrally disposed in said body portion, said body portion providing a progressively increasing radial distance from the outer surface thereof to the core at different transverse planes through the core and tapered section :of the body portion.

4. An ignitor comprising a resistive body portion having a tapered outer section increasing in diameter toward the lower end thereof, and a cylindrical core of uniform diameter longitudinally and centrally disposed .in said body portion, said body portion providing a progressively increasing radial distance from the outer surface thereof to the cylindrical core at difierent planes through the core and tapered section of the body portion.

5. An ignitor comprising a resistive body portion having a tapered outer section, and a more conductive core having a section reversely tapered with respect to and within the tapered body portion section and thereby providing a progressively increasing radial distance from the outer surface of the tapered section of the body portion to the tapered section of said core at difierent transverse planes through said tapered sections.

6. An ignitor comprising a resistive body portion having a tapered outer section increasing in diameter progressively to the lower end thereof, and a more conductive core having a tapered section decreasing in diameter progressively to the lower end thereof, said tapered section of the core being coaxially disposed within the tapered section of the body portion thereby providing in- (creasing radial distances from the outer surface of the tapered section of the body portion to the tapered section of said core at different transverse planes through said tapered sections.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,358,615 Arnott Sept. 19, 1944 FOREIGN PATENTS Number Country Date 573,550 Great Britain Nov. 26, 1945

Images