US3149716A

US3149716A - Evaporator vacuum pump

Info

Publication number: US3149716A
Application number: US843224A
Authority: US
Inventors: John P Papacosta; Robert W Crews
Original assignee: AB Dick Co
Current assignee: AB Dick Co
Priority date: 1959-09-29
Filing date: 1959-09-29
Publication date: 1964-09-22
Anticipated expiration: 1981-09-22

Description

Sept. 22, 1964 J. P. PAPAC OSTA ETAL EVAPORATOR VACUUM PUMP Filed Sept. 29, 1959 fie. 3.

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United States Patent 3,149,716 EVAPORATOR VACUUM PUMP John P. Papacosta, Los Altos, and Robert W. Crews, Palo Alto, Calif., assignors to A. B. Dick Company Filed Sept. 29, 1959, Ser. No. 843,224 1 Claim. (Cl. 206-.4)

This invention relates to an evaporative, inorganic vapor-type of vacuum pump, and, more particularly, to improvements therein.

Evaporative, inorganic, vapor-type non-magnetic vacuum pumps usually find application in the vacuum-tube art. After a vacuum-tube envelope has been pumped by the usual mechanical or diffusion pump to as low a pressure as is obtainable therewith, the evaporative, inorganic vapor pump is employed. Effectively, this comprises a filament upon which metal has been crimped. The filament is then heated electrically, whereby the metal crimped thereto may adsorb, or absorb, or chemically combine with atoms or molecules of different gases, removing them from the volume to be evacuated. When the metal crimped on the filament is heated to sublimation or evaporation, its vapor is deposited as a film on cooler surrounding surfaces, trapping the gas in and beneath the film.

In the metal crimped on the heating filament, oftentimes because of poor thermal contact with the filament, would not sublimate but would melt and form an amalgam with the filament. When an amalgam is formed, the filament becomes brittle and easily breaks with further heating. Thus, the formation of an amalgam is not desired. Upon heating the filament many times, the crimped metal would fall from the filament because the filament would become deformed as a result of being heated and the crimp was not always effective to hold the metal to the filament. If the filament is not thoroughly cleaned (a. difficult thing to do), then because of the nonuniform contact between the filament and the crimped metal thereon, due to oil or other dirt on the surface of the filament and/or metal, a good heat transfer does not occur between the filament and the metal. Therefore, the metal is not heated to sublimation, but, rather, melts, and then amalgamates with the filament.

An object of this invention is to provide an improved evaporative vacuum pump of the type described wherein amalgamation between the metal attached to the filament and the filament is avoided.

Another object of the present invention is the provision of an arrangement for an evaporative vacuum pump of the type described, wherein a uniform contact is assured between the metal segments mounted on the filament, and the filament.

Yet another object of the present invention is the provision of a novel, useful, and more efficient evaporative type of pump than heretofore obtainable.

These and other objects of the invention are achieved in an arrangement wherein metal segments, such as titanium or zirconium, are spotwelded to a stretched helical tungsten filament which is supported within the region to be evacuated. Because of the use of the spotweld technique for attaching the metal segment to the filament, a uniform contact is assured. Thus, when the filament is heated, the segments effectively go from the metal to the gaseous form without melting, and therefore no amalgamation with the filament occurs. As a result, substantially all the metal attached to the filament is used for pumping.

3,149,715. Patented Sept. 212 1964 The novel features that are considered characteristic of this invention are set forth with particularity in the appended claim. The invention itself, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawing, in which:

FIGURE 1 is a perspective drawing of a tube illustrating the location of the embodiment of the invention therein;

FIGURE 2 is a drawing of a section along the lines 22 of FIGURE 1, showing the embodiment of the invention; and

FIGURE 3 illustrates a detail of the invention.

In FIGURE 1 of the drawing there is shown how the embodiment of the invention may be employed with a tube 10. Two feed-through pins 12, 14 are used to connect heating power to the embodiment of the invention which is an evaporative pump mounted inside the tube.

Referring now to FIGURE 2, which is a section taken along the lines 2-2 of FIGURE 1, there will be seen an embodiment of the invention. This comprises a stretched helical tungsten filament 16, which is supported within a frame. This frame includes the pair of lead-through pins 12, 14, which extend through the tube envelope 16. A nickel bar 18 is welded to one of the lead-through pins 14. A support bar 20 is welded at right angles to the nickel bar 18. The tungsten wire filament is attached to and stretched between the support bar 20 and the leadthrough pin 12. The Weld joint of support bar 20 maintains it in position. In accordance with this invention, metal segments 22 which may either be titanium or zirconium are tack-welded to the tungsten filament. The segments are held against the tungsten filament with a light pressure during welding, and a current is applied sufficient to provide tack welding. FIGURE 3 is a detail showing a metal segment 22 tack welded to the filament 16.

A source of electrical heating energy 24 is connected through a switch 26 to the lead-through pins 14, 12, whereupon the tungsten filament will heat up. It is heated sufficiently to sublimate the metal segments. In view of the uniform and intimate contact assured by the tackwelding technique, rather than the crimping technique used heretofore, there is no amalgamation between the metal segments and the filament.

The operation of the metal, which is called trapping or gettering, may be accomplished at different temperatures as the metal heats up. It may be accomplished either by the metal segments themselves or in the vapor when the metal is heated to evaporation. The metal vapor is deposited as a. film on the cooler surrounding surfaces of the tube envelope, whereby the gas is trapped in and beneath the film. The operation of the pump may be occasional, cyclical, or continuous to achieve the desired amount of evacuation. Such evacuation occurs in the pressure range between 10- and 10* millimeters of mercury. The pump may be operated in conjunction with other devices, such as ion gages or ion pumps, to effect suitable pumping characteristics.

The construction and operation of the pump is simple, convenient, and economical, and no magnetic fields are required to be employed therewith. The envelope with which the pump is used may be of any suitable metal, ceramic or glass. Accordingly, a novel and improved evaporative vacuum pump has been described hereinabove.

References (Iited in the file of this patent UNITED STATES PATENTS Boer May 17, 1932 Flory Feb. 6, 1940 De Boer et al. June 11, 1940 Vandergrift Apr. 1, 1941 Record Mar. 10, 1942 Agule May 31, 1960