US3207423A

US3207423A - Vacuum pump

Info

Publication number: US3207423A
Application number: US211991A
Authority: US
Inventors: Huber Harry; Graulcau Didier
Original assignee: CSF Compagnie Generale de Telegraphie sans Fil SA
Current assignee: Thales SA
Priority date: 1961-09-07
Filing date: 1962-07-24
Publication date: 1965-09-21
Anticipated expiration: 1982-09-21
Also published as: GB951866A; NL282934A; FR1306718A

Description

Sept. 21, 1965 H. HUBER ETAL.

VACUUM PUMP 3 Sheets-Sheet 1 Filed July 24, 1962 INVENTORS H-HUBER, E-DUVAL amt 0 GfimLAE/m BY 7%! ATTORNE Sept. 21, 1965 H. HUBER ETAL 3,207,423

VACUUM PUMP Filed July 24. 1962 s Sheets-Sheet 2 INVENTORSZ H-HUBER; E-DUVAL and 0. Genus/m Sept. 21, 9 H. HUBER ETAL 3,207,423

VACUUM PUMP Filed July 24, 1962 3 Sheets-Sheet 3 1 a a 1 i INVENTORS: H-HUBER, E-DUVAL and D- G am/3a.;

BY W 777. 24

ATTORNE United States Patent 3,207,423 VACUUM PUMP Harry Huber, Eugene Duval, and Didier Grauleau, Paris, France, assignors to CSF--C0rnpagnie Generale do Telegraphic Sans Fill, Paris, France Filed duly 24, 1962, Ser. No. 2119M Claims priority, application France, Sept. 7, 1961, 872,546 3 Claims. (Cl. fill-69) The present invention relates to vacuum pumps operable wit-l1 thermal evaporation of a metal having gettering properties, that is, to devices connected with the enclosures to be evacuated and intended to improve the vacuum by the adsorption effect of the gases on a metal which is evaporated in a continuous manner and the condensation of which is caused in a thin layer along a wall. Titanium is generally chosen as suitable metal for this application by reason of its high chemical activity, particularly insofar as the most common gases are con cerne-d, of the relatively slight vapor pressure of the metallic titanium and of its compounds, and of the stability of most of the titanium compounds in the solid form at ordinary temperature.

The evaporation of the titanium may be assured by any known heating means, for example, by the Joule effect or by electron bombardment; the evaporation of the titanium may be controlled by means which depend on the mode of the heating employed, for example, by varying the heating current in case of heating by Joule effect, or by controlling the intensity of the electron flow emitted by a cathode with a view to bombard the titanium reserve.

The present invention aims at a pump which has a length of life superior to that of the pumps of this type known in the prior art with equality in the pumping speed, or which offers a higher pumping speed with equality in length of life.

Each of these two performance characteristics, namely pumping speed and length of life which are in reciprocal interrelation may obviously be improved by increasing or renewing the titanium reserve, for example, by providing a coil of titanium wire with means for automatically advancing the wire to the extent of the use thereof. However, such a system introduces into the pump movable parts which normally are a source of trouble and also compromise the security of proper operation of the pump. The present invention, therefore, proposes to improve the indicated performances by another a-ppr-oach, which permits avoiding the introduction of movable parts into the pump.

The invention is based on the observation that the end of life of the titanium pump is principally determined .by the separation of the layer of active material condensed on the wall, at the end of a time less than the time of exhaustion of the active material. Consequently, the present invention provides means to increase this time of separation or detachment of the condensed active material in such a manner that it becomes at least equal to the duration of the life of the pump determined by exhaustion of the active material.

A first means in conformity with the present invention consists in giving to the elements of the pump a geometry such that the deposit of active material is as homogeneous as possible over the entire surface of the condensation wall. It is obvious in effect that, all other things remaining the same, the separation of the active material is favored by the non-homogeneity of the deposit and will commence at the place where the same i the thickest.

This geometry according to the present invention is spherical; according to the present invention, the conuse densation wall of the titanium pump will, therefore, have a form materializing at least in part the surface of a sphere of which other portions of the surface are realized, to the extent of need thereof, by auxiliary shields or screens.

With respect to this sphere, there exist two possibilities insofar as the disposition of the titanium reserve is concerned, namely:

(a) Its location at the center of the sphere in which case the reserve has the form of a ball; and

(b) Its location at a point of the surface of the sphere in which case the reserve may be, for example, located in a crucible incorporated within the Walls of the sphere.

'In both cases, the density of deposit along the internal wall of the sphere by the active material evaporated by the reserve is constant according to Lamberts law.

A second means to increase the duration of separation consists in increasing the roughness or unevenness of the internal walls of the sphere, for example, by providing them with grooves.

Accordingly, it is an object of the present invention to provide a vacuum pump of the type described herein above which avoids the shortcomings and drawbacks encountered in the prior art by simple means.

It is another object of the present invention to provide a vacuum pump of the type described hereinabove which has a greater length of life than the prior art pumps known heretofore with the same pumping speed or a higher rate of pumping speed with the sam life length.

Still a further object of the present invention resides in the provision of a vacuum pump which correlates the supply of gettering material to be coextensive with the life expectancy of the other parts without the need of movable parts within the pump.

A further significant object of the present invention resides in the provision of a vacuum pump operable by thermally evaporating a gettering metal in which the period of time is effectively increased before the layer of the active material condense-d along the walls of the pump begins to separate therefrom.

These and other objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, several embodiments in accordance with the present invention, and wherein FIGURE 1 is a longitudinal cross sectional view through a first embodiment of a vacuum pump in accordance with the present invention;

FIGURE 2 is a longitudinal cross sectional view through a second embodiment of a vacuum pump in accordance with the present invention;

FIGURE 3 is a longitudinal cross sectional view through a third embodiment of a vacum pump in accordance with the present invention, and

FIGURE 4 is a partial view of a portion of the internal surface of the Walls of any one of the pumps of FIG- URES l to 3.

Referring now to the drawing wherein like reference numerals are used throughout the various views to designate like parts, and more particularly to FIGURE 1, the pump illustrated therein is in communication with the evacuated enclosure or vessel (not shown) through an orifice 1. The pump is thereby fixed to the walls of this enclosure with the aid of a metallic joint 2. The pump is contained within a housing constituted by a vat-like receptacle, for example, made of stainless steel, and forming the condensation walls cooled by a liquid circulating within the coil 4. According to the present invention, at least one portion of the wall of the receptacle 3 has, as indicated at 5, a spherical configuration flowing through the tubulure 8. The shield 7 is dimensioned and disposed in such a manner as to leave a pas-. sage or flow channel between the inside of the sphere and. the orifice 1 and that, at the same time, the projections coming from the center of the sphere outside of the solid angle occupied by the shield 7, fall always on the walls of the receptacle 3. Also, according to the present invention, the reserve of the active material as-'. sumes the. shape of a titanium ball 9; realized, for example, by fusion within vacuum in the course of a preliminary operation, this ball 9 being supported by a metallic rod 10, for example, made of molybdenum and leaving across an insulating passage 11 through a me-. tallic joint 12 incorporated within the. walls of the receptacle 3. In order to. realize, for example, a heating by electron bombardment, the rod 10 is carried at an anode potential by a suitable external source (not shown). For the same purpose, there is provided a filament 13 supported by two rods .14 leaving across the insulating passages 15 through the same metallic joint 12, these rods 14 being connected to a heater source (not shown) and being carried at the cathode potentialof the source ofvoltage supply for the rod v10. The receptacle 3 is carried at a still more negative potential than the cathode potential by any suitable means.

If the electron current of the, filament 13 is sufiiciently intensetto ionizetheresid-ual molecules of gas within the enclosure of the pump, then the'device will function as a pump having a dual effect of ionization and getter as is known in the art; 'Otherwise, an auxiliary filament 16 may be provided, supported by the same rods 14 and intended to emit a current owing to which the ionization will be complete.

The modified embodiment of the pump of FIGURE 2, in which the same reference numerals have been used as in FIGURE 1 to designate analogous elements, differs from the embodiment of FIGURE 1 by the fact that the source of the active material is no longer' placed at the center of the sphere 6 but instead at a point of the surface thereof, particularly at a lower .point,the orifice 1 being oriented toward the top as inthe embodiment of FIGURE 1. The titanium is no longer a molten ball but fills a crucible 17 placed at the level of the spherical walls within an appendage 18 connected to the receptacle 3. The bombardment filament 13 is placed in the vicinity of the walls of the crucible 17, :and a thermal shield 19 is disposed between the filament 13 and the outside. The auxiliary ionization filament 16 has been placed toward the center of the sphere but could also be suppressed if the necessity thereof does not become noticeable.

FIGURE 3 differs from the embodiment of FIGURE '-1 by 'the fact that the orifice 1 is'oriented toward the bottom, the crucible 17 being disposed as in the preceding embodiment of FIGURE 2 at the bottom of the sphere 6. The rod supports a foot portion having several branches 20 from which is suspended the crucible 17. The joint 12 with the passages 11 and ispl-aced toward the top of the spherical wall 5. As in the pre- In all cases, the internal spherical surfaces may be provided with grooves or ridges to increase the adherence 4 of the deposit of the active material, these grooves being indicated in FIGURE 4 and designated therein by reference numeral 21 which shows a view of a portion of the internal surface 5 that may belong to any one of the pumps of FIGURES 1 to 3.. 1

The coil 4 may be brazed 'to the receptacle 3 and cooled by water or eventually by freon from a refrigerating installation.

The

passages

11 and 15 may be realized by a seal of pure alumina and titanium. The joints 2 and 12 may be of the type having a gold, copper or aluminum ring, as is known in the art. 1 g

The operation of the pumps described hereinabove does not require anydetailed explanation thereofsince it is generally known in the art. Nevertheless, the improved performances thereof are significantly noteworthy ince they may attain, by means of a suitable dimensioning the following figures:

Minimum pumping speed: 10,000 liters per second. Vacuum limit: less than 10 torr,

Length of :life with',permanent pumping at pressures lower than 10" torr, at least 2,000 hours.

While we have shown and described several embodi rnents in accordance with the present invention, it is; understood that the same is not limited thereto, but is susceptible of many changes and modifications within the spirit and scope thereof as known to a person skilled in the art.. For example,any control means known to a person skilled in the art may be associated with the heating system for the active metal in order to increase the temper ature to the extent that the evaporating surface decreases by use in such a manner as to conserve a constant evapora tion speed of the metal and, therefore, a constant pump ing speed. The heating system by bombardment may itself be replaced by any other equivalent system without departing from the spirit of the present invention.

Thus, it is clear that the present invention is susceptible of many changes and modifications within the spirit and scope thereof, and we therefore do not wish to be limited to the details shown and described herein, but intend to cover all'such changes andmodifications as are encompassed by the scope of the appended claims. I

We claim:

1. A high vacuum pump having an orifice for communication with the enclosure to be evacuated and including means for thermally evaporating a metal having gettering properties and means for condensing said metal on a wall, said wall having a shape materializing at least in part a sphericalsurface, and at least one additional shield having a part spherical surface substantially completing the sphere defined by said wall surface, said shield being separated from said wall by an interval forming passage between the inside of said sphere and said orifice.

2. A pump as defined in claim 1, wherein said passage is bounded by wall portions extending from said spherical wall, said wall portions being shaped and positioned so that the projections of said gettering metal coming from the inside of said sphere outside of thesolid angle occupied by said shield fall on said walls.

3. Apump as defined in claim 1, further comprising a plurality of grooves of the internal surface of said sphere. I References Cited by the Examiner UNITED STATES PATENTS 2,920,002 1/ 60 Auwarter 204-298 X l 3,056,740 10/62 Holland et al 230*69 X 7 FOREIGN PATENTS 1,095,455 12/60 Germany.

LAURENCE V. EFNER, Primary Examiner,

Claims

1. A HIGH VACUUM PUMP HAVING AN ORIFICE FOR COMMUNICATION WITH THE ENCLOSURE TO BE EVACUATED AND INCLUDING MEANS FOR THERMALLY EVAPORATING A METAL HAVING GETTERING PROPERTIES AND MEANS FOR CONDENSING SAID METAL ON A WALL, SAID WALL HAVING MATERIALIZING AT LEAST IN PART A SPHERICAL SURFACE, AND AT LEAST ONE ADDITIONAL SHIELD HAVING A PART SPHERICAL SURFACE SUBSTANTIALLY COMPLETING THE SPHERE DEFINED BY SAID WALL SURFACE, SAID SHIELD BEING SEPARATED FROM SAID WALL BY AN INTERVAL FORMING PASSAGE BETWEN THE INSIDE OF SAID SPHERE AND SAID ORIFICE.