US2196401A - Baffle for ignitrons - Google Patents

Description

Patented Apr. 9, 1940 UNITED STATES BAFFLE F Joseph Slepian,

Pakala, Forest Hills,

Pittsburgh, and

R IGNITRONS William E. Pa., assignors to Westinghouse Electric & Manufacturing Company,

East Pittsburgh, Pa. sylvania a corporation of Penn- Application February 26, 1938, Serial No. 192,774

2 Claims.

Our invention relates to a vapor-electric converter and particularly to means for controlling or preventing arcbacks in make-alive type converters.

In make-alive type converters, it is customary to use a single anode-and cathode separated by a relatively small distance and to reinitiate a cathode spot at the beginning of each conducting half cycle. Heretofore there has been noted a random tendency to arcback, that is, to form an go riod. While the causes of these random arcbacks are unknown, it is believed that at least some of the faults are the result of bombardment of the anode by particles or drops thrown off by the cathode, or possibly by momentary failure of the condensing surfaces to condense the vapor produced during the preceding conducting half cycle.

In the construction according to our invention, we prevent this possible bombardment of the anode as well'as preclude a rush of vapor to the anode space by providing shields substantially protecting the anode surface from that portion of the cathode surface which wasactive during the conducting half cycle.

This is accomplished according to our invention by providing a substantially cylindrical shield surrounding the sides of the anode and a substantially flat shield interposed between the end of the anode and the active portion of the 40 cathode surface, space being left between the side shield and the end shield, so that the arc stream may freely flow between the anode and the cathode. In order to prevent the are spot from wandering from underneath the end shield, we prefer to use a bailie of suitable material for retaining the cathode spot on that portion of the cathode area which is shielded by the end baflle.

As the presence of non-condensed or non-condensable gas may in part be responsible for the fault in the valve, we prefer to arrange the parts according to our invention so that the flow of vapor from the cathode to the condensing sur- 55 face sweeps past the shield opening and acts as a molecular pump to maintain the spaceinside the shield in a high state of evacuation.

It is accordingly an object of our invention to provide a vapor-electric device of the make-alive type having shields for preventing bombardment of the anode during the non-conducting periods.

It is a further object of our invention to provide a shield structure for a make-alive type rectifier.

It is a further object of our invention to provide means for retaining the cathode spot in a predetermined portion of the cathode area.

It is also an object of our invention to provide a shield arrangement which maintains the anode area free from deleterious gases.

Other objects andadvantages of our invention will be apparent from the following detailed descriptions taken in conjunction with the drawing in which a Figure 1 is a vertical sectional elevation of a make-alive valve according to our invention; and

Fig. 2 is a fragmentary elevational view of the end ofthe shield assembly,

In the illustrated embodiment of the invention, the vapor-electric device comprises a suitable envelope l, preferably of metal, having suitable cooling elements, preferably in the form of coppercoils 2, applied to the exterior thereof for maintaining the walls of the envelope l at a temperature sufliciently low to condense the vapor given off by the vaporizable reconstructing cathode 3, which occupies all or at least a major portion of the bottom of the envelope I. Cooperating with this vaporizable cathode 3 is a suitable anode 4, preferably constructed of graphite, although any suitable material may be utilized and supported in vacuum-tight relation to the envelope I by means of a suitable insulator herein shown as a porcelain bushing 5. A make-alive electrode 6, that'is, an electrode composed of high resistant or substantially non-conducting material capable of generating a cathode spot upon the passage of current therethrough to the cathode, is mounted in permanent contact with the cathode 3. While this make-alive electrode 6 may be mounted in any suitable manner, we prefer to mount the same on a rod or lead-in l, which is conducted through the side of the envelope I by a suitable vacuum-tight insulating bushing 8. The make-alive electrode 6 is so adjusted that in normal operation of the converter the make-alive electrode 6, or at least a portion thereof, will be in permanent contact with the cathode material.

In order to protect the anode 4 from the par- Placed between the active anode face and the cathode 3 is a suitable shield II, which may be supported in any desired manner, but preferably is hung by brackets I2 to the aforementioned lateral shield II]. The face shield I I may be of any desired configuration, but for reasons presently to appear we prefer to make it substantially dish-shaped with the concave side facing the active portion of the cathode surface.

While normally the cathode spot during any conducting half cycle will not wander a material distance from the make-alive electrode 6, it is desirable to provide a suitable baffle, preferably in the form of an insulating ring I l, of quartz, porcelain or other refractory insulating material, and to anchor or otherwise maintain this insulating baffle in a position so that no portion of the active surface of the cathode material 3 will be exposed to the active face of the anode 4. Instead of rigidly anchoring the insulating baflle I4, a suitable retaining ring I 5 may be connected to the baflle I4, the retaining ring I5 being of such size that the active cathode spot may not be shifted out from under the end bafile or face shield II of the anode.

The shields ill and II provide an enclosure immediately surrounding the anode with an opening for the passage of the arc stream. The cathode spot is formed under the end shield and the vapor flows in general from the vicinity of the cathode spot to the cooled walls, which pro vide the necessary condensing area. The vapor thus passes or sweeps across the arc opening and acts in a manner similar to a molecular vapor pump, and, in fact, by proper designing of the end shield I I and the spacing between the shields IO and II, becomes a very efficient vapor pump to eliminate all traces of gas from the anode enclosure, particularly in view of the fact that the anode space will normally operate at an elevated temperature, the vacuum in the enclosure will be maintained to a high degree of perfection.

While our invention is applicable to either sealed off or pumped type valves, in the event a pumped valve is utilized, we prefer to provide a suitable deflector I6 to prevent any material entering the valve through the pump connection I! from striking either the anode 3 or its associated shield structure I9--I I.

While we have shown and described a specific embodiment of our invention, it will be apparent to those skilled in the art that many changes and modifications may be made therein without departing from the true spirit of our invention or the scope of the appended claims.

We claim as our invention:

1. An electric valve comprising an evacuated envelope, a mercury pool cathode in said envelope, an anode cooperating with said cathode, a control electrode of high resistance material in contact with said cathode during normal operation of the Valve, means for cooling the wall of said envelope, a shield interposed between said envelope and the sides of said anode, said shield being closely spaced from said anode, a second shield interposed between the anode and cathode, said first and second shields being spaced from each other.

2. An electric valve comprising an evacuated:

envelope, a mercury pool cathode in said envelope, an anode cooperating with said cathode, a control electrode of high resistance material in contact with said cathode during normal operation of the valve, means for cooling the wall of said envelope, a shield interposed between said envelope and the sides of said anode, said shield being closely spaced from said anode, a second shield interposed between the anode and cathode, said first and second shields being spaced.

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