US3239134A - Residual gas removing means for vacuum pumps - Google Patents

Description

March 8, 1966 G. N. STEELE 3,239,134

RESIDUAL GAS REMOVING MEANS FOR VACUUM PUMPS Filed April 14, 1964 2 Sheets-Sheet 1 Gordon IV. Steele INVENTOR.

BY cu W 29m G. N. STEELE March 8, 1966 RESIDUAL GAS REMOVING MEANS FOR VACUUM PUMPS 2 Sheets-Sheet 2 Filed April 14, 1964 INVENTOR.

28 Gordon N. Steele United States Patent C 3,239,134 RESIDUAL GAS REMOVING MEANS FOR VACUUM PUMPS Gordon N. Steele, Santa Barbara, Calif., assignor to Sigmatron, Inc., a corporation of California Filed Apr. 14, 1964, Ser. No. 359,717 11 Claims. (Cl. 230-69) This invention relates to improvements in the production of high vacuums and more particularly to the attainment of a higher order of vacuum which is beyond the capability of vapor-actuated pumping systems or diffusion pumps by use of a novel auxiliary pump device involving the vaporization of titanium and/or other reactive metals, such booster pumps being referred to as getter pumps.

In connection with the requirements of modern technology, in recent .years, high vacuum pumping systems such as the diffusion type of pumps with which the present invention is concerned, have required the use of booster pumps to increase the vacuum produced by removal ofresidual gases from the evacuated chamber to which the diffusion pumping systems are connected. Various modified diffusion pumping systems have been devised wherein low pressure residual gases are removed from the evacuated chamber by dynamic pumping means involving the compression of the low pressure gases and discharge thereof to atmosphere or without any discharge from the hermetically sealed evacuated chamber utilizing an ion pumping system wherein the low pressure gas is consumed within the working chamber. The use of a getter pump as the auxiliary pumping device for achieving the high vacuum, has however been found to be a more satisfactory method for removal of the residual low pressure gases in view of its high gas handling capability and because of the arrangement of the present invention, less expensive and relatively easy to operate as compared to getter pump arrangements heretofore proposed.

The removal of residual gases without discharge thereof from the hermetically sealed working chamber is achieved by getter pump arrangements, based upon the chemical reactivity of titanium films or other reactive metals toward all gases except the noble gases such as helium, neon, argon, etc. These noble gases are removed from the evacuated working chamber however, by the diffusion pumping system with which the getter pump is associated. In this regard, the getter pump is restricted operation-wise to one end of a vacuum pressure range attainable by the diffusion pumping system alone.

It is therefore a primary object of the present invention to provide an auxiliary booster pump device for removal of residual gases from a hermetically sealed ,vacuum chamber by vaporization of a gettering material such as titanium or other reactive metals in a more efiicient and less expensive manner than was heretofore possible.

An additional object of the present invention in accordance with the foregoing object, is to provide a getter pump device having a reactive film bearing surface directly exposed to the working vacuum chamber so as to provide better access of the residual gases thereto and to a larger surface unimpeded by baflles or other restrictions as compared to getter pump arrangements wherein the reactive films have been remotely located from the vacuum working chamber.

A still further object of the present invention is to provide an auxiliary getter pump unit, one or more of which may be mounted at the suction inlet end of a working vacuum chamber without any modification of the plumbing in the diffusion pumping system in order to achieve any required pumping speed or capacity. In

view of the aforementioned operational capabilities of "ice the accessory or booster pump devices of the present invention and its versatility insofar as installation is concerned, the getter pump device of the present invention is particularly suited for ultra-high vacuum requirements ofenergy particle accelerators, vacuum evaporators, environmental test chambers and other such equipment.

These together with other objects and advantages which will become subsequently apparent reside in the .details ofconstruction and operation as more fully hereinafter described and claimed, reference being had to theaccompanying, drawings forming a part hereof, wherein like.

numerals refer to like parts throughout, and in which:

FIGURE Us a perspective view showing a single auxiliary getter pump device of the present invention in one installational arrangement.

FIGURE 2 is a. partial sectional view taken substantially through a plane indicated by section line 22 in FIGURE 1.

FIGURE 3 is a sectional view taken substantially through a plane indicated by section line 33 in FIG- URE 2.

FIGURE 4 is an enlarged partial sectional view through the getter. pump unit.

FIGURE 5 is a front elevational view of a stack arrangement of a plurality of getter pump units.

Referring now to the drawings in detail, and initially to FIGURE 1, it will be observed that the getter pump unit generally referred to by reference numeral 10, is installed on the base plate 12 to which the working vacuum chamber 14 is usually secured and hermetically sealed on the inlet end of the conduit 16 which forms part of the. high vacuum pumping system with respect to which the getter pump unit 10.of the present invention is an accessory vacuum booster. The high vacuum pumpingsystems with which the present invention is concerned, are well-known and conventional, being referred to .as diffusion. pumps which operate on the principle that a liquid having relatively heavy molecules when vaporized by raising the temperature thereof, may be accelerated by flow through suitable nozzles in adirection away from the region to be evacuated thereby colliding against molecules ahead of the nozzles forcing them toward a mechanical fore pump to thereby reduce the pressure within the evacuated region. The vapors within the diffusion pump are thereafter recondensed and recirculated through a continuous operating cycle. Pumping systems of this type can achieve pressures less than 10- Torr, which is low enough to permit functioning of the getter pump 10 by bringing the chamber 14 to an operating pressure range within which vaporization of the reactivemetal may occur. Once functioning, the getter pump unit of the present invention is capable of reducing the pressure within the vacuum chamber to approximately 5 10- Torr. This ultra high vacuum pressure is achieved whenv the collection rate of gases from all sources withinthe chamber and back migration from the diffusion pump, equals the speed of the getter pump.

Referring now to FIGURES 2 and 3 in particular, it willbe observed that the ,unit 10 is interconnected between the inlet end of the conduit 16 and the open end of the chamber 14 by means of an enclosure 18 having an annular wall portion 20 interconnecting awsealing flange portion 22 and a mounting flange portion, 24 forming an axial passage. Theannular wall portion 20 has an internal vapor condensing surface 26 radially spaced from the axial passage but directly exposed to the space within the vacuum chamber 14 mounted in sealed relation on the mounting flange 24. An O-ring seal 28 is therefore seated within an annular recess 30 formed in the sealing flange 22 so as to seal the mounting of the annular member 18 onthe base plate 12 to which the conduit 16 is connected.

Also, mounted exteriorly on the wall portion 20 are parallel spaced cooling coils 32 through which a coolant such as water is circulated in order to remove heat and maintain the internal vapor condensing surface 26 at the proper temperature for condensing the film of reactive metal thereon. Accordingly, the cooling coils may be connected to a suitable coolant circulating system. It Will also be apparent, that other facilities could be provided for maintaining the proper temperature for thevapor condensing surface such as some air cooling system.

The annular vapor condensing surface 26 forms a relatively large and directly exposed surface on which a reactive film is deposited by condensation, the material originating from a vapor source generally referred to by reference numeral 34. As more clearly seen in FIG- URES 3 and 4, the vapor source 34 has an annular configuration peripherally bordering the axial passage within the enclosure 18 and parallel spaced from the vapor condensing surface 26 so as to avoid impeding the fluid communication between the vacuum chamber 14 and the conduit 16. Evaporation of the source of reactive material is produced electrically by a heating filament in the form of an annular core 36 electrically connected by the leads 38 to a pair of electrodes 40 adapted to be connected to a low voltage source from which current is supplied to the filament core 36. The leads and electrodes are mounted in the wall portion 20 by insulators 42 which prevent deposition of vapor on the electrodes. The filament core 36 is made of an electrically conductive refractory material such as molybdenum, tungsten, titanium-tungsten or other suitable metallic wire constituting a refractory matrix which does not form a low melting eutectic with the reactive material carried by the filament core. The reactive material 44 is spirally wrapped about the filament core so that there is substantially no change in the resistance of the filament as the reactive material is evaporated by the heat generated when current flows through the heater filament. Accordingly, a substanialiy constant and regulated rate of evaporation may be maintained in order to achieve the optimum pumping speed for the getter pump unit. The reactive material is preferably made of titanium wire although it will be appreciated that other forms of reactive metals may be used such as zirconium, berylium, aluminum, chromium and magnesium. When the titanium metal is vaporized, it may be deposited in a film-like form on the vapor condensing surface 26 so that it may react with the residual gases as aforementioned which include all gases except the noble gases removed by the diffusion pump system.

The vapor source 34 also includes an annular shield member 46 which is arcuate in cross section and made of a thermally non-conductive material. For example, the shield member may be comprised of many thin radiation bafile laminations as a result of which the internal concave surface 48 of the shield member is encouraged to operate hot so that a film of titanium vapor may deposit thereon and vapor prevented from entering the vacuum space within the chamber 14. Accordingly, titanium vapor will migrate only toward the condensing surface 26 from an annular outlet opening 49 formed by the shield.

From the foregoing description, the construction and operation and utility of the getter pump device will be apparent. It will therefore be appreciated, that the configuration of the getter pump device provides a relatively large source of reactive metal vapor directly exposed by an annular vapor condensing surface to the vacuum chamber without impeding operation of the diffusion pump system with which the invention is associated. Operational efiiciency is further achieved by the hot wall vapor shield 34 while the evaporation rate may be controlled through the current source in view of the substantially constant resistance of the heater filament as aforementioned. Also, the mounting and removal of the pump device is facilitated for replacement of the vapor til source and cleaning of the condensing surface 26 on which the reactive film is formed and by means of which the residual gases are immobilized forming titanium compounds thereon. In view of the installational arrangement, a plurality of getter pump units may be stacked or ganged as illustrated in FIGURE 5 in accordance with varying pumping speeds and requirements of the vacuum system with which the invention is associated. The modular application of the getter pump units, their operational efiiciency and relatively inexpensive cost. of manufacture and operation, will therefore be of considerable value in connection with the rehabilitation of presently available and conventional diffusion pumping systems for vacuum pressure requirements greater than the capabilities of such systems.

The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention as claimed. I

What is claimed as new is as follows:

1. In combination with a vacuum producing system connected to a chamber to be evacuated, a getter pump for removing residual gases from said chamber comprising, an annular vapor condensing surface establishing a fluid tight connection between the vacuum system'and the evacuated chamber, a heating filament mounted in radially spaced relation to the vapor condensing'surface, a source of reactive material carried on the heating filament for vaporization, shield means mounted in close spaced relation to the heating filament for directing flow of vaporized reactive material toward the vapor condensing surface, and cooling means disposed in heat conductive relation to the condensing surface to condense a film of said vaporized reactive material on the condensing surface for immobilizing the residual gases by reaction with the film of reactive material.

2. The combination of claim 1 wherein said shield means comprises, a cross-sectionally arcuate member operatively mounted relative to the evacuated chamber to prevent escape of said vaporized reactive material into the evacuated chamber, said member having an internal thermally non-conductive surface on which a vapor fil is formed and maintained in heated condition.

3. The combination of claim 2 wherein said heating filament :is made of a refractory matrix core for the source of reactive material forming a high melting eutectic therewith.

4. The combination of claim 3 wherein said source of reactive material comprises, titanium wire spirally wound about the heating filament to substantially minimize any change in resistance of the heating filament with vaporization of the source.

5. The combination of claim 1 wherein said heating filament is made of a refractory matrix core for the source of reactive material forming a high melting eutectic therewith.

6. The combination of claim 5 wherein said source of reactive material comprises, titanium wire spirally wound about the heating filament to substantially minimize any change in resistance of the heating filament with vaporization of the source.

7. The combination of claim 1 wherein said source of reactive material comprises, titanium wire spirally wound about the heating filament to substantially minimize any change in resistance of the heating filament with vaporization of the source, electrode means extending through said vapor condensing surface and connected to the heating filament for supply of current thereto, and a source of voltage connected to said electrode means through which the evaporation rate of the source of reactive material is regulated.

8. In combination with a difiusion pump capable of establishing a vaporizing pressure for a gettering material, a getter pump device comprising, an annular condensing wall, a heater filament mounted in parallel spaced relation to said condensing wall, electrical means connected to said heater filament for supply of current thereto, a reactive metal wire spirally wound on said heater filament for evaporation in response to heat generated by the flow of current in the filament, and a thermally non-conductive shield partially enclosing said filament and reactive metal Wire forming an annular outlet for flow of vaporized reactive metal toward the condensing wall.

9. In combination with a diffusion pump capable of establishing a vaporizing pressure for a gettering material within a working chamber, a getter pump device comprising, an enclosure connected to the pump device having a condensing surface forming an unobstructed passage into said working chamber, a heater filament mounted in spaced relation to said condensing surface peripherally bordering said passage and carrying said gettering material thereon, and thermally non-conductive shield means blocking exposure of the filament to said passage to confine vaporization of the gettering material to a region adjacent the condensing surface without blocking exposure thereof to residual gases in the working chamber.

10. In combination with a vacuum producing system and a chamber enclosing a working space, a getter pump for removing residual gases from said working space comprising an enclosure connecting said chamber to the system and having a vapor condensing surface, a heating filament mounted in spaced relation to said condensing surface within said enclosure, a source of reactive material carried on the heating filament for vaporization, shield means mounted in close spaced relation to the filament for preventing vapors of said reactive material emitted from the source from entering the working space, said shield means being heated by the filament to prevent condensation of the vapors thereon and being operatively positioned within the enclosure to avoid blocking fluid communication between the system and the chamber, and cooling means 'operatively mounted on said condensing surface to condense a film of said vaporized reactive material for reaction with residual gases in the working space.

11. In combination with a vacuum producing system and a chamber enclosing a working space, a getter pump for removing residual gases from said Working space comprising an enclosure connecting said chamber to the system and forming an axial passage into said working space, a condensing wall mounted by said enclosure in radially spaced relation to the axial passage, a heating filament mounted within the enclosure in a position peripherally bordering said axial passage, a source of reactive material carried on the heating filament for vaporization, shield means mounted in close spaced relation to the filament blocking exposure thereof to the axial passage, and cooling means mounted on said condensing wall to condense a film of said vaporized reactive material for reaction with residual gases in the working space.

MARK NEWMAN, Primary Examiner.

WARREN E. COLEMAN, Examiner.

Claims (1)

1. IN COMBINATION WITH A VACUUM PRODUCING SYSTEM CONNECTED TO A CHAMBER TO BE EVACUATED, A GETTER PUMP FOR REMOVING RESIDUAL GASES FROM SAID CHAMBER COMPRISING, AN ANNULAR VAPOR CONDENSING SURFACE ESTABLISHING A FLUID TIGHT CONNECTION BETWEEN THE VACUUM SYSTEM AND THE EVACUATED CHAMBER, A HEATING FILAMENT MOUNTED IN RADIALLY SPACED RELATION TO THE VAPOR CONDENSING SURFACE, A SOURCE OF REACTIVE MATERIAL CARRIED ON THE HEATING FILAMENT FOR VAPORIZATION, SHIELD MEANS MOUNTED IN CLOSE

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