Title:
Insulating and sealing means for evacuated devices
United States Patent 2134578


Abstract:
My invention relates to insulating and sealing means for use in connection with metal receptacles operating under widely varying temperature conditions and containing a vapor or gas under a predetermined pressure, such, for example, as the evacuated metal tanks of mercury arc rectifiers. The...



Inventors:
Remscheid, Emil J.
Application Number:
US5452235A
Publication Date:
10/25/1938
Filing Date:
12/14/1935
Assignee:
GEN ELECTRIC
Primary Class:
Other Classes:
174/50.5, 174/152E, 220/2.3R, 220/378, 313/317
International Classes:
H01J13/26; H01J13/50
View Patent Images:



Description:

My invention relates to insulating and sealing means for use in connection with metal receptacles operating under widely varying temperature conditions and containing a vapor or gas under a predetermined pressure, such, for example, as the evacuated metal tanks of mercury arc rectifiers.

The invention relates particularly to means for insulating and sealing the cathodes, and in certain cases the anodes, of metal tank mercury arc rectifiers and the like, and its object is to provide means for this purpose which are simple, of a high degree of reliability in operation, and of low cost.

In the mercury arc rectifier of the iron tank type, it is usually desirable to insulate the cathode from the metal tank, and for this purpose the mercury is placed in a metal container below the tank and insulated and sealed therefrom. It has been usual practice heretofore to provide, for this insulating and sealing of the cathode container, a large and heavy porcelain ring interposed between metal sealing surfaces of the tank and cathode container respectively. To insure a vacuum-tight seal, hoop-rings of metal, such as aluminum, deformable under heavy pressure, are laid between the upper surface of the large porcelain ring and the tank surface and between the lower surface of the ring and the container surface, and pressure is then applied sufficient to deform and crush the metal hooprings into intimate contact with the porcelain ring surfaces and the metal sealing surfaces.

Difficulties have been encountered, however, in the use of the above-described cathode porcelain ring, such as breakage of the ring under the extremely severe conditions of heavy pressure and varying temperature incident to the operation of high power mercury arc rectifiers. The breakage of the procelain ring necessitates not only a relatively costly replacement but also the shutting down of the rectifier for a protracted period and the complete degassing of the unit in which the porcelain ring breakage occurs.

In accordance with the present invention the above-mentioned and other difficulties are obviated by the provision, in place of the porcelain ring, of a rigid metal member or ring arranged to operate as an insulator by the application to its surface of a coating of insulating material, this material being of such characteristics, however, that the coating not only acts effectively as an insulator but is able to withstand without, cracking, peeling or other damage, the heavy pressure required to deform the metal hoop-rings sufficiently to provide a vacuum-tight seal. Preferably the coating is of the nature of a porcelain enamel or vitreous enamel baked on the rigid metal ring.

In usual mercury arc rectifier apparatus the anodes are sealed from the evacuated receptacle by a suitable sleeve insulator molded between an anode supporting member and a cover member of the receptacle or an extension thereof. In certain cases, however, particularly in those mercury arc rectifier devices of the metal tank type which have only one anode, the anode is preferably directly supported by and electrically connected to a metal cover plate or similar member which is then insulated and sealed from the evacuated tank. It is a feature of the present invention that prior, not entirely satisfactory arrangements for insulating the anode cover plate, such for example, as mercury seals, are dispensed with, and the insulating and sealing of the anode plate is simply and efficiently accomplished by coating the plate with the vitreous material above described, metal hoop-rings which are interposed between the coating and a sealing surface of the metal tank being deformed under heavy pressure to form the seal.

My invention will be better understood from the following description when considered in connection with the accompanying drawings and its scope will be set forth in the appended claim. Referring to the drawings, Fig. 1 is an elevational view, partially in section, of a mercury arc rectifier or the like of the metal tank type, in which a cathode insulating and sealing means in accordance with my invention has been embodied; Fig. 2 is an enlarged sectional view of a portion of a mercury arc rectifier embodying a cathode insulator and seal in accordance with my invention, and Fig. 3 is an elevational view, partially in section, of a single anode mercury arc rectifier in which an anode insulating and sealing means in accordance with my invention has been embodied.

In Fig. 1 the numeral 10 designates a device comprising a metal receptacle or tank I I containing a medium under a predetermined pressure, this device in the present embodiment of the invention being shown for illustrative purposes as a mercury arc rectifier of the multianode, evacuated metal tank, mercury pool type having an opening 12 in the lower portion of the tank, below which opening is mounted a metal member 13 constituting a cathode container. To aid in sealing the opening 12, instead of the usual porcelain ring I provide a rigid ring 14, which may be in form and size substantially the same as the porcelain ring, but which is formed of metal, preferably steel. The ring may be of substantially square cross section as shown in Fig. 1, or may be of other suitable section, for example, the rectangular section shown at 15 in Fig. 2. Hoop rings 16, preferably two, of relatively small cross-section and formed of aluminum or other metal deformable under heavy pressure are laid between the ring 14 or 15 and a metal sealing surface 17 of the receptacle 11, and a similar pair of hoop rings 18 are laid between the rings 14 or 15 and a metal sealing surface 19 of the cathode container 13.

To insulate the cathode container 13 from the receptacle 1 the rigid metal rings, 14 or 15, are provided with a coating 20 (clearly indicated in Fig. 2) of insulating material, which in the present embodiment of the invention is a porcelain enamel or vitreous enamel preferably having substantially the composition: 8.6% feldspar, 30.4% borax, 31% silica, 3.7% sodium nitrate, 4% soda ash, 22.3% calcium carbonate, 1% cobalt oxide, and 1% nickel oxide. Preferably the ring is given two coats of the enamel, the first coat being baked on at a furnace temperature of approximately 830° C. the second coat then being applied, and baked on at the above temperature. After the second coat the insulating surface is given a high potential test, for example, of 3000 volts.

If desirable a third and possibly a fourth coating of the enamel may be given the ring, all coatings being kept relatively light to insure a smooth surface.

33 When the insulation coated metal rings 14 or 15 and the hoop-rings 16 and 18 are in position in the apparatus 10, the cathode container 13 is drawn upwardly toward the receptacle II by suitable means such as bolts 21, causing a heavy pres, sure to be exerted upon the hoop-rings between the enamel surfaces 20 and the metal sealing surfaces 17 and 19, thereby deforming and crushing the hoop-rings to form a vacuum-tight seal.

The hoop-rings, being of relatively small cross, section, present to the enamel coating a relatively small area of contact per unit length.

Nevertheless, I have found that the relatively thin enamel coating withstands, without crushing, the heavy pressure concentrated along the small area Sand required to deform and flatten the hooprings.

I have found that in operation of the mercury arc rectifier apparatus illustrated in Figs. 1 and 2, the insulating and sealing means, comprising the 65 enamel coated rigid steel rings, 14 or 15, and the aluminum hoop-rings 16, 18 held under heavy pressure between the enamel coating 20 and the metal surfaces 17 and 19, maintains a high vacuum in the tank 11 and at the same time withstands the severe expansion and contraction effects due to the relatively large temperature variations incident to the operation of the rectifier.

The cathode insulating and sealing means illustrated in Fig. 1 therefore retains all the advantages of the prior means which included the porcelain ring. Further, however, since the rings 14 or 15 are of steel instead of the fragile porcelain, breakage of the ring, and the attendant abovedescribed expense, is entirely prevented, and the life of the cathode insulating and sealing portion of the apparatus is practically unlimited. In Fig. 3, the numeral 22 indicates a mercury arc rectifier or like device comprising a metal receptacle or tank 23 and having only one anode 24, which is supported by the tank cover plate 25.

Preferably the anode is directly connected to the plate 25 as by screwing the anode to a metal stud 26 which may be welded to the plate. To insulate from the metal tank 23 the anode 24, thus electrically connected to cover plate 25, the plate 25 is provided at least on its under surface 27 with an enamel coating 28 as described in connection with Figs. 1 and 2. To seal the anode, attached to cover plate 25, hoop-rings 29, similar to hoop-rings 16, 18, are interposed between the enamel coating 28 and the metal sealing surface 30 of the tank 23, and heavy pressure is applied to cover plate 25, as by bolts 31, to deform and crush the hoop-rings 29 into intimate contact with the coating 28 and the surface 30.

The operation of the anode insulating and sealing means illustrated in Fig. 3 will be readily understood by reference to the description of operation of the cathode insulating and sealing means of Figs. 1 and 2.

My inverition has been described herein in par- 33 ticular embodiments for purposes of illustration.

It is to be understood, however, that the invention is susceptible of various changes and modifications and that by the appended claim I intend to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is: In an arc discharge apparatus comprising an evacuated metal receptacle and an electrode, means to insulate and to seal said electrode from said receptacle including a metal member, a sealing ring of metal deformable only under relatively heavy pressure, a thin coating of vitreous enamel on said metal member including approximately 8.6% feldspar, 30.4% borax, 31% silica, 3.7% sodium nitrate, 4% soda ash, 22.3% calcium carbonate, 1% cobalt oxide, and 1% nickel oxide, said sealing ring being interposed between said coating and a metal sealing surface of said appa- 5s ratus, and means to press said ring between said coating and said sealing surface to deform substantially said ring, thereby to form a vacuumtight seal between said metal member and said sealing surface. EMIL J. REMSCHEID.