US3615326A

US3615326A - Method of assembling electron discharge devices having sensitive components housed within a glass envelope

Info

Publication number: US3615326A
Application number: US791032A
Authority: US
Inventors: Nathan D Levin
Original assignee: Varian Associates Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1969-01-14
Filing date: 1969-01-14
Publication date: 1971-10-26
Anticipated expiration: 1988-10-26
Also published as: DE2001304A1; NL7000545A; FR2028308A1

Abstract

A method of assembling an electron discharge device having sensitive components housed within a glass envelope. The method comprises the steps of forming a glass envelope, breaking the glass envelope into two separable sections, housing sensitive components within at least one of the two envelope sections, and fusing the two separable sections back together with the sensitive components housed therewithin.

Description

United States Patent Inventor Nathan D. Levin Los Altos Hills, Calif. Appl. No. 791,032 Filed Jan. 14, 1969 Patented Oct. 26, 1971 Assignee Varian Associates Palo Alto, Calif.

METHOD OF ASSEMBLING ELECTRON DISCHARGE DEVICES HAVING SENSITIVE COMPONENTS HOUSED WITHIN A GLASS ENVELOPE 1 Claim, 5 Drawing Figs.

IU.S. Cl 65/56,

65/36 Int. Cl C03b 33/00 Field of Search 65/36, 56,

[56] References Cited UNITED STATES PATENTS 2,169,455 8/1939 Wagner, Sr 65/174 3,246,151 4/1966 Tanaka et al. 250/7 1 .5 3,319,818 5/1967 Hudson 65/56 X Primary Examiner-S. Leon Bashore Assistant Examiner-Saul R. Friedman Attorneys-William J. Nolan and Leon F. Herbert N?! PATENTEDumzs 8,615,326

FIG! Hm INVENTOR.

NATHAN D LEVIN BY METHOD OF ASSEMBLING ELEO'I'RON DISCHARGE DEVICES IIAVING SENSITIVE COMPONENTS li'llO USEllll WITHIN A GLASS ENVELOPE BACKGROUND OF THE INVENTION This invention relates generally to electron discharge devices having sensitive components housed within a glass envelope and particularly to methods of assembling such devices. By the term glass envelope" is meant an envelope consisting substantially, although not necessarily entirely, of glass.

A common procedural step in assembling an electron discharge device having a glass envelope is that of fusing together two glass sections of the envelope by placing the sections in'abutment and heating them by such means as a gas flame. Sensitive electronic components such as electrodes, lead wires, shields, and screens housed within the envelope will, of course, also be heated when the envelope sections are being fused together. As these components may be damaged by such heat it is desirable to minimize their heating by such techniques as placing only the abutting portions of the en velope sections in the flame, which portions are located as far as feasible' from the more heat-sensitive components, and by applying minimal heat for the minimum time required for fusion to occur. This latter technique is dependent upon the degree of intimacy with which the abutting surfaces of the two glass sections mate with each other since additional heating is required to close any gaps therebetween through the flow of molten glass. Though sealers could be used in filling such gaps for fusion to occur they require heat and time far in excess of that which will damage some components.

In addition to the damage which sensitive components of electron discharge devices may suffer from overheating is the damage which chemical byproducts from the heat source itself may cause. Where natural gas is used as a flame fuel, for example, carbon dioxide and water vapor are produced when such is ignited in an oxidizing medium such as air. If airgaps exist between mating glass members of the device envelope, the application of such a flame thereto will cause these vapors to enter the envelope through the gaps before they are fused together. Once the flame is removed and the envelope cooled, these vapors may condense and form contaminants such as carbonic acid and water on the surface of the sensitive components which, depending on the composition thereof, may damage them in a relatively short time. This is particularly true in the case of X-ray image tubes having alkali metal halide scintillators.

The envelopes of most electron discharge devices are generally tubular. When ordering glass tubing it is, of course, possible to specify exacting tolerances for tube wall and outside diameter to ensure that each tube will mate well with each other. Standard catalog tolerance for mill-run glass tubing, however, is typically about lone-twentieth inch for wall thickness and :tthree sixty-fourths inch for outside diameters. The use of such tubing may create the undesirable gaps mentioned above. Nevertheless, the cost of specially run and inspected glass tubing having closer tolerances is so much higher as to be economically prohibitive for mass production.

One solution to this dilemma is to cut each glass tube delivered from the glass manufacturer into an even number of identifiable sections. Each section is formed into an envelope component. Sensitive components are then housed therein. Sections having an edge formed from a single cutting operation are then placed together with such edges in abutment which are then fused together. The two abuttng edges should mate reasonably well since they were formed from the same cut. Nevertheless, the process of forming each section into an envelope component frequently alters their edges, creating mismatches. Furthermore, the damaging of any section will cause its mate to become surplus if efficient production is to be maintained since the runout will not usually match that of a section cut from another tube.

Accordingly, it is the general object of the present invention to provide an improved method of assembling electron discharge devices having sensitive components housed within a glass envelope.

More specifically, it is an object of the present invention to provide an improved method of sealing together two glass sections of an electron discharge device envelope without damaging sensitive components housed within the glass envelope sections.

Yet more particularly it is an object of the present invention to provide a method of fusing together two glass sections of an electron discharge device envelope without overheating or poisoning sensitive components of the device housed within the envelope sections.

SUMMARY OF THE INVENTION Briefly described, the present invention is a methodof assembling an electron discharge device having sensitive components housed within a glass envelope. The method comprises the steps of forming a glass envelope, breaking the glass envelope into two separate sections, housing sensitive components within at least one of the two envelope sections, and fusing the two separate sections back together with the sensitive components housed therewithin.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a schematic diagram of the internal components of an X-ray image tube,

FIG. 2 is an external, diagrammatic profile view in elevation of a glass envelope for the tube shown in FIG. ll,

FIGS. 3 and 4 are two external, diagrammatic profile views in elevation of two poorly mating envelope sections placed together for assembly, and

FIG. 5 is an external, diagrammatic end view in elevation of two poorly mating envelope sections placed together for assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now in more detail to the drawings, there is illustrated in FIG. 1 an X-ray image tube comprising an evacuated glass envelope ll. Not shown in the figure for clarity are several plugged cavities in the glass envelope through which electrically conducting feedthrough pass, an exhaust pump appendage, and a small exhaust tubulation.

The face portion of the tube inclludes an input screen 2 which comprises a scintillator located adjacent the envelope and a photocathode overlaying the scintillator. The scintillator comprises a thin layer of an X-ray sensitive phosphor, the functional utility of which may be damaged if heated excessively or exposed to certain chemical byproducts of inflamed, common heating fuels. The photocathode comprises a layer of alkali antimonide.

With reference also to FIG. 2, it can be seen that such image tubes were heretofore typically formed and assembled by forming two separate cup-

shaped envelope sections

6 and 7 from two glass tubes of like diameter. Anode 4, viewing screen 5, and a portion of electrode 3 were then formed within envelope section 6. The balance of electrode 3 and the scintillator were formed within section 7. The two envelope sections were then placed in abutment and fused together by means of a gas flame to form seam 3. Several electrically conductive feedthroughs 9 are symbolically shown extending through the envelope sections.

Frequently the mutually abutting surface of

sections

6 and 7 do not well mate as exaggeratedly illustrated in FIGS. 3, 4 and 5. In FIG. 3, for instance, the lower edge of section 6 is tilted toward that of section 7. As a result of this mismatch a gap exists between the upper portions of these two sections. In FIG. 4 the runout is irregular at the lip of each cup-shaped envelope section, likewise creating gaps therebetween when placed in abutment for sealing. In FIG. 5 a mismatch is shown between the roundness of the two envelope sections, creating gaps therebetween. Obviously, each of these illustrated cases will require extensive heating for the relatively large gaps to be closed through fusion of the glass. During such heat treatment byproducts from the flame employed may enter the envelope sections through the gaps and contaminate the sensitive electronic components housed therein.

The method of the present invention serves to prevent formation of the aforementioned gaps between glass envelope sections and to reduce the size of any which nevertheless do occur. This, of course, will substantially alleviate the enumerated problem caused by extensive flame heating and chemical contamination.

in one embodiment of the invention a mill-run glass tube is shaped into an X-ray image tube envelope. The periphery of the tubular envelope is then scratched by rotating the tube against a sharp cutting edge to form a parting line. The glass tube is next rotated with the circular scratch or parting line passing through a gas flame. This action soon causes the envelope to undergo thermal shock due to the presence of differential expansion gradients adjacent the scratch. This results in the envelope cracking into two sections along the circular scratch.

. Internal, electronic components, including an alkali metal halide scintillator, are next housed within the two sections. The two envelope sections are then placed back together in abutment to reform the envelope. if desired, common points at the abutment may be identified by marking each section. This enables the assembler to place the two sections back together in their exact former, relative positions after the sensitive components have been enhoused. This permits a nearly perfect rematch to be made. The tubular envelope is then rotated with the abutting portions of the two envelope sections passing through a flame again fueled by gas, causing the two envelope sections to fuse together. Following this, the envelope is evacuated, a layer of photocathodic material is vacuum-deposited over the alkali metal halide scintillator and the envelope is completely sealed.

It should be understood that the just-described embodiment is merely illustrative of principles of the invention. Obviously many modifications may be made therein without departing from the spirit and scope of the invention as set forth in the following claims.

What is claimed is:

l. A method of assembling an electron discharge device having sensitive components housed within a glass envelope, comprising the steps of forming a glass envelope; separating said glass envelope into at least two sections by scratching the exterior surface of said envelope to form a parting line extending about a periphery of said envelope, and heating said envelope in the regions adjacent said parting line to create thermal stresses causing fracture of the envelope along the parting line; housing said sensitive components within at least one of said two sections; placing said sections in abutment along said parting line in the same relative orientation as before said fracture; and heating the abutting portions of said sections to the extent necessary to cause fusion of the glass in the regions adjacent said parting line whereby said sections are joined together in a vacuumtight fashion.