US3327929A

US3327929A - Getter vacuum pump

Info

Publication number: US3327929A
Application number: US432439A
Authority: US
Inventors: Robert H Dillenbeck
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1965-01-27
Filing date: 1965-01-27
Publication date: 1967-06-27
Anticipated expiration: 1984-06-27

Description

June 1967 R. H. DILLENBECK 3,327,929

7 GETTER VACUUM PUMP Filed Jan. 27, 1965 INVENTOR: ROBERT H. DILLENBECK,

BY pg/d" ms ATTORNEY.

United States Patent f 3,327,929 GETTER VACUUM PUMP Robert H. Dillenbeck, Altamont, N.Y., assiguor to General Electric Company, a corporation of New York Filed Jan. 27, 1965, Ser. No. 432,439 8 Claims. (Cl. 230-69) ABSTRACT OF THE DISCLOSURE A getter pump characterized by having a condensing wall through which coolant may be passed and defined by a plurality of contiguous tubes.

This invention relates to a getter vacuum pump and more particularly to a vapor vacuum pump of the type wherein the evaporation of suitable getter metal provides a gas gettering metal on a wall surface of the pump.

Vacuum pumps which rely upon the gas adsorbing power of a nascent metal film where the film may be formed continuously by evaporation or even by sputtering are generally referred to as metal evaporation, sublimatation, or getter pumps. The metals to be evaporated are usually chosen from the alkaline earth metals or from the metals of Group IV-A, V-A, and VI-A. For example, titanium is frequently employed as the getter and may be used as a filament winding or as solid blocks or, as known in the art, in a continuously fed Wire. Examples of vacuum pumps utilizing gettering are found in US. Patents 2,925,214 Gurewitsch et al.; 2,858,972 Gurewitsch, and 2,894,679 Herb.

It will be appreciated that the larger getter pumps evaporate large fractions of a gram of titanium each minute, and therefore getter pumps permit ready access to the ultra high vacuum region. However, the overall size of a getter pump is desired to be of a minimum commensurate with sufiicient condensing wall area. Getter pumps are normally operated at high temperatures so that the getter material may be suitably evaporated. Also, because of the high operating temperatures involved, it has been noted that temperature becomes a limiting factor. Many of the parts of the pump including some metals, electrical leads, insulators, et cetera cannot be subjected to temperatures approaching the high evaporating temperatures needed to evaporate such metals as titanium. Furthermore, the collection or condensation of vaporized titanium on the pump wall surfaces subject these surfaces to a high temperature. It has been noted that this wall temperature is so high after continued operation of the pump that the freshly deposited metal film begins to lose its effectiveness as a getter, and because of excessive temperature the pump walls react to release the gas previously trapped therein. A getter pump is desired, therefore, which includes a large condensing Wall area in a minimum space where the wall is effectively cooled to provide optimum condensation without release of adsorbed gases.

Accordingly, it is an object of this invention to provide an improved getter pump.

It is yet another object of this invention to provide improved cooling for a getter pump.

It is another object of this invention to provide increased wall surface for a getter pump without substantially increasing the overall volume.

It is yet another-object of this invention to provide improved cooling and wall characteristics for a getter pump.

It is yet another object of this invention to provide an improved getter pump having a wall surface defined by a helical copper tube coil.

3,327,929 Patented June 27, 1967 Briefly described, this invention in one of its preferred forms includes an integral unit pump having a copper tube coil wound in cylindrical helical fashion so that each turn is contiguously adjacent each preceding turn to define a cylindrical getter pump wall. Within this cylindrical enclosure titanium is evaporated to be collected and condensed upon the inner wall surface. This surface is corrugated or ribbed because of the coil configuration, and provides a markedly increased effective area while at the same time being sufficiently cooled through means of a circulating cooling medium that the wall is maintained at a favorable operating temperature.

This invention will be better understood when taken in connection with the following description and the drawings in which,

FIG. 1 is a side elevational view of one preferred embodiment of this invention, a

FIG. 2 is a bottom view of the embodiment of FIG. 1.

Referring now to FIG. 1, there is illustrated an integral getter pump unit which is particularly adapted to be inserted in a vacuum system or within a further kind of vacuum pump such as an ion pump. Accordingly, pump unit 10 comprises a supporting flange or base 11 which supports the various pump component parts in their assembled and operative relationship, and also further serves to support or attach pump unit 10 on or in a defined enclosure. The evaporator portion of this pump comprises in one form a plurality of electrical filaments adapted to conduct electrical current therethrough. These filaments, 12, 13, 14 and 15, each consist of a two-strand twisted helix of .015 tantalum tightly overwound with .005 titanium. In one operative example of this invention the tantalum filament Wire was coiled into a helix of about inch inside diameter with about 5 inch between turns. The number of individual filaments will only be limited by the space characteristics of the pump. These filaments are electrically connected to suitable vacuum electrical lead through means or connectors 16 and 17 which are known in the art. These connectors being combinations of metal and ceramic ferrules and washers provide a metal surface which can be directly brazed to flange 11 yet maintain the lead electrically insulated therefrom. Extended through each of the connectors 16 and 17 is'an electrically conducting

rod

19 and 20 respectively, of a metal such as stainless steel or copper. For each rod there is a

set screw attachment

23 and 24 respectively, to attach and electrically connect one end of the filaments to the rods as shown in FIG. 1.

The other ends of the filaments are electrically connected to and supported by supporting means in the form of a rod 27, of stainless steel for example, which is brazed or welded into a suitable aperture in flange 11 as denoted by 28. At the other end of rod 27 there is provided a suitable transverse metal disk connector 29 also welded or brazed to rod 27. Connector 29 includes a plurality of set

screw arrangements

31, 32, 33 and 34 which electrically and mechanically connect

filaments

12, 13, 14 and 15 therein for electrical connection to the ground side of the electrical circuit. As is known in the art, connection of the required electrical source of power to the

terminals

19 and 20 will provide heating of the

filaments

12, 13, 14 and 15 to a temperature at which the overwound titanium will be evaporated.

Improved means are utilized in order to simultaneously provide an increased wall surface area to collect the evaporated titanium and also to cool the wall. As illustrated in FIG. 1, the collecting wall portion of this pump unit 10 is in the form of a helical coil 35. This helical coil 35 comprises a hollow metal tube of good heat conducting properties wound in the form of a helix so that the individual turns are generally contiguous to provide adequate containment of the evaporated titanium. Coil 35 is utilized as the cooling means for pump unit 10 and is adapted to have a suitable coolant circulated therethrough. Coil 35 is directly supported from flange 11 and has

ends

36 and 37 extending through

suitable connector apertures

38 and 39 in flange 11.

Connectors

38 and 39 each comprise a stainless steel tube 40 and 41 respectively which is suitably brazed or welded into an aperture in flange 11. The connector tubes 40 and 4-1 have an inner diameter Which is sufiicient to pass

coil tube ends

36 and 37 therethrough. Ends 36 and 37 are then suitably brazed to connector tubes 40 and 41 and have threaded coupling means 42 and 43 attached at their extreme ends.

The wound helix wall configuration 35 provides in a limited axial space a maximum amount of Wall area to receive evaporated titanium. The increase in wall area of the coil 35 over a smooth cylinder of the same dimension is about 60%, and wall area plays an important part in the effectiveness of a getter pump. In operation of a getter pump the electrical filaments are energized and titanium is caused to evaporate. The evaporated titanium will condense on the inner surface of the coil 35 as the most appropriate and conducive place. The condensing of a titanium film provides a continuously replenished film of clean titanium which actively adsorbs gases and/or traps molecules of gases in the condensing metal. It is understood that heat must be conducted away from coil 35 quite rapidly not only to reduce its own temperature, but also to maintain a relatively cool wall for elfective titanium vapor condensation. At the same time the wall must be maintained cool to minimize re-evolution of adsorbed gases. Because the coil 35 is also the condensing wall, the heat conducting capacity of this wall coil is greatly improved over the prior methods of winding a coil around about a container and having it brazed thereto. The use of copper as the coil material, in the configuration described, has been found to be a primary advantage in getter pumps. The present invention is a direct improvement also over a double-walled container having cooling passages therein because of the increased amount of surface made available by the corrugations, ridges or ribs of the inner wall surface not only for condensation but also for an overall cooling surface and a relatively flexible surface. The coil material must be chosen from those materials, particularly metals, which display excellent heat conducting and minimum gas release characteristics. It has been found that OFHC copper provides excellent results when utilized in the practice of this invention. Other preferred materials for coil 35 include various copper containing metals, with metals of relatively lower thermal conductivity being less desirable.

In the practice of this invention in one form, a helical coil was wound from copper tubing of inch OD. and 32 feet in length to provide a cylinder having a four inch outside diameter and about a seven inch length. This coil was integrated into the pump unit 10 as illustrated in FIG. 1 and effectively utilized as a getter pump condensing wall. In order to maintain the coil in contiguous form a pair of clamp members 44- and 45 were employed at diametrically opposed positions (FIG. 2) on the coil 35. These clamps, for example 44, include a metal strip 46 attached to the under side of flange 11 by threaded means 47 and extending axially along the outside of coil 35 to the lowermost turn. A pair of metal angle clips 48 and 49 are suitably attached by welding to strip 46 and contain the coil 35 axially therebetween. It is preferred, as illustrated in FIG. 2, to have the coil ends project axially upwardly along the inside of the tube coil 35.

In one operative practice of this invention the getter pump as described Was connected to a system in which the pressure was reduced to about X lO torr. A partial pressure analyzer indicated H to be the total pressure in the system. Water was then circulated through coil 35 for cooling purposes. At the same time about 60 watts of electrical power were dissipated by the filaments. It was found that the total pressure in the system was reduced to 1 10 torr in a short period of time. At this point the coolant through the coils was changed to liquid nitrogen and again about 60 watts of electrical power was dissipated through the filaments. The hydrogen partial pressure was again noted to be reduced by almost two orders of magnitude below the 'test with the watercooled coils. The total pressure of the system was then reduced to about 3 X 1O torr. The result indicates that where the total pressure in the system was about 5 X10 torr with hydrogen being the total pressure, using the pump unit of this invention partial pressure of hydrogen was reduced by three orders of magnitude and the total pressure in the system was reduced to 3X10 torr.

The present invention as previously described may be suitably employed as a complete vacuum pump unit. However, a wider application of these getter pumps is in conjunction with getter ion pumps. Ion pumps have the noted disadvantage of being unable to effectively commence pumping operations at higher pressure ranges. At the same time, evaporator getter pumps have the disadvantage of being unable to eifectively pump certain gases, notably the rare gases and stable hydrocarbons such as methane. Accordingly, the getter pump and the ion pump may be combined within the same housing so that effective pumping may be obtained when both pump units are employed. These pumps may be employed simultaneously, or in series Where the getter pump may be employed to reduce the pressure sufficiently to enable the ion pump to effectively commence pumping. At the same time the evaporation or getter pump may be employed to greatly enhance the speed of the ion pump for those active gases such as oxygen, nitrogen and hydrogen. In other words, the getter pump is not as pressure dependent as the ion pump.

A further advantage of the present invention as described is that the getter pump unit 10 is mounted on one flange to provide an integral unit which may be gainfully employed in many applications as such. The walls of the pump that receive the condensed titanium are so situated that they may be acid cleaned to remove accumulated titanium without injury to the remaining parts of the pump. At the same time the temperature of these walls may be varied from above C. to below liquid nitrogen temperature by passing an appropriate gas or liquid through the coil. In operation of the pump 10, the control arrangement may be such that a choice can be exercised whether or not to use one or more of the filaments depending on what pressure range is desired. In other words, for example, one or more, or all filaments may be employed in a pressure range of 10' torr but when operating in a pressure range of 10- torr only one filament may be so employed. Coil 35, and also

filaments

12, 13, 14 and 15 may each take various individual configurations, i.e., coil 35may be conical, partly spherical, et cetera. The filaments may also take various configurations usually, however, conforming to the shape of the coil.

While this invention has been described with reference to particular and exemplary embodiments thereof, it is to be understood that numerous changes can be made by those skilled in the art without actually departing from the invention as disclosed, and it is intended that the appended claims include all such equivalent variations as come within the true spirit and scope of the foregoing disclosure.

What is claimed and desired to be secured by Letters Patent of the United States is:

1. A getter pump unit comprising in combination,

(a) heating means to evaporate a getter metal,

(b) vapor condensing wall means in surrounding relationship to said heating means, said wall being composed of a plurality of rows of tubes,

(c) said wall having its inner surface facing said heating means defining a plurality of parallel hollow ridge-like projections,

((1) said ridge-like projections defining a wall portion of a coolant passage,

(e) and said projections being of a metal having very high heat conducting characteristics and substantially free from adsorbed gases.

2. A getter pump unit comprising in combination,

(a) heating means to evaporate a getter metal,

( b) vapor condensing wall means in surrounding relationship to said heating means, said wall comprising a helical coil wound from a tube,

(c) said wall having its inner surface facing said heating means defining a plurality of parallel convolutes,

(d) said convolutes defining a portion of a coolant passage,

(6) said convolutes being of a metal having very high heat conducting characteristics and substantially free from absorbed gases.

3. The invention as recited in claim 2 wherein said wall is a helical coil formed from a copper surfaced tube with the individual turns in contiguous relationship.

4. The invention as recited in claim 2 wherein said wall is a helical coil of a substantial member of contiguous small diameter coils, said coils being of gas free copper tubing.

5. The invention as recited in claim 4 wherein said getter metal is titanium.

6. An integral getter pump unit comprising in combination,

(a) a flange support member,

(b) an electrical heater element supported from one side of said flange,

(c) a getter metal in contact with said electrical heater element,

(d) 'means passing through said flange adapted to connect said heater element to a source of electrical power,

(e) a cylindrical wall in surrounding and concentric relationship to said heater element,

(f) said wall being in the form of a contiguous helical coil of copper containing tubing adapted to circulate a coolant therethrough,

ter metal is titanium and said coil is gas free copper.

8. An integral getter pump unit comprising in combination,

(a) a vacuum sealing flange unit having vacuum sealing means incorporated therewith,

(b) a plurality of vacuum feed through electrical connectors attached centrally to one side of sad flange,

(c) a plurality of electrical filaments extending from the other side of said flange and connected at one end to said electrical connectors,

(d) means connecting the other end of said filaments to a common point,

(e) titanium metal overlying said filaments and adapted to be evaporated by electrical heating of said filaments,

(f) a cylindrical wall extending from said flange in concentric and surrounding relationship to said filaments,

(g) said wall being formed of a contiguous helical coil of gas free copper tubing,

(h) means to fluid connect said tubing through said flange to a pair of connectors to permit a flow of coolant through said coil so that titanium metal vapor is condensed directly on the surface of said coils,

(i) said fluid connection means including means to support said coil from said flange,

(j) said coil being so wound that the farthest end of said coil is inturned to have the fluid passage extend axially along the inner wall of said cylinder.

References Cited UNITED STATES PATENTS 2,913,167 11/1959 Herb 23069 ROBERT M. WALKER, Primary Examiner.

LAURENCE V. EFNER, Examiner.

Claims

1. A GETTER PUMP UNIT COMPRISING IN COMBINATION, (A) HEATING MEANS TO EVAPORATE A GETTER MEAL, (B) VAPOR CONDENSING WALL MEANS IN SURROUNDING RELATIONSHIP TO SAID HEATING MEANS, SAID WALL BEING COMPOSED OF A PLURALITY OF ROWS TO TUBES, (C) SAID WALL HAVING ITS INNER SURFACE FACING SAID HEATING MEANS DEFINING A PLURALITY OF PARALLEL HOLLOW RIDGE-LIKE PROJECTIONS, (D) SAID RIDGE-LIKE PROJECTIONS DEFINING A WALL PORTION OF A COOLANT PASSAGE, (E) AND SAID PROJECTIONS BEING OF A METAL HAVING VERY HIGH HEAT CONDUCTING CHARACTERISTICS AND SUBSTANTIALLY FREE FROM ADSORBED GASES.