US3071310A

US3071310A - Vacuum pump

Info

Publication number: US3071310A
Application number: US793823A
Authority: US
Inventors: Hayashi Chikara; Kumagai Hiroo
Original assignee: Nihon Shinku Gijutsu KK
Current assignee: Ulvac Inc
Priority date: 1958-03-07
Filing date: 1959-02-17
Publication date: 1963-01-01
Anticipated expiration: 1980-01-01
Also published as: GB851335A; DE1090815B

Description

Jan. 1, 1963 Filed Feb. 17. 1959 CHIKARA HAYASHI ET AL Fig.

VACUUM PUMP 2 Sheets-Sheet 1 H/roo Kama a/ INVEN 0R5 BY flaw/14 M x: M

Jan. 1, 1963 CHIKARA HAYASHI ETAL 3,071,310

VACUUM'PUMP filed Feb. 17, 1959 2 Sheets-Sheet 2 Fig.3

('fifka ra Ha yas/ll' l /l'roo Kama Qa/ INVENTORS ATTORNEY United States Patent 3,671,310 VACUUM PUMP Chikara Hayashi and Hiroo Kumagai, Toyko, Japan, as-

signors to Nihon Shinku Giiutsu, Kabushiki Kaisha (IJapan Vacuum Engineering Co., Ltd), Yokohama City,

apan

Filed Feb. 17, 1959, Ser. No. 793,823 Claims priority, application Japan Mar. 7, 1%8 5 Claims. (Cl. 230-69) This invention relates to a vacuum pump and more particularly, to avacuum pump where metallic barium is used as a getter to produce a high vacuum better than mm. Hg in a large vessel, particularly in a demountable metal system.

Barium has been used as a getter in the production of electronic vacuum tubes. Further, the possibility of making use of barium in vacuum pumps also has been acknowledged by some vacuum engineers and many attempts on this have been made.

The results of these attempts showed that the attainable pumping speeds were less than a few liters per second which were too small to assure a vacuum of the order of 10- mm. Hg or less in a practical system. A far greater pumping speed must be applied to obtain such a high vacuum in a large, demountable system. For this reason, the use barium as a getter in vacuum pumps was abandoned.

In recent years another type of vacuum pump using metallic titanium as a getter has been developed. However, titanium has a relatively high melting point about 1700 C., and it has a tendency to react with all refractory materials and/or heat resisting metals to produce alloys or solid solutions. In order to secure the stable operation of titanium getter ion pumps for prolonged periods, several new designs should be introduced, but the introduction thereof would make the construction of titanium pumps complicated, and make it expensive.

A principal object of this invention is to provide a novel barium getter ion pump and processes for securely evacu-' ating a large vessel to pressures of the order of 10" mm. Hg or below, in other words, producing high vacuums such as 10-" Hg or below, using metallic barium as a getter.

By the present invention, metallic barium, which is easily evaporated at temperatures between 400 C. to 800 C., is used as a getter, and as it is evaporated in a way hereinafter described in detail, the difficulties encountered in titanium getter ion pumps are not only eliminated, but pumping speeds greater than With the titanium pump can be obtained in the practice of this invention, there is provideda distillation chamber wherein raw barium is fed and distilled. The object of this distillation is the purification and degassing of the raw barium. Associated with this chamber there is provided a main pumping chamber for continuously evaporating the distilled barium at a required rate. The distilled liquid barium is introduced into a crucible in the main chamber through a connecting tube. The tube is maintained at a temperature higher than the melting point of barium and thus secures smooth down how of liquid barium from the distillation chamber to the main chamber.

As metallic barium has a melting C. and a nature to be distilled from liquid phase, its refining may be easily accomplished by thedistillation chamber. The distillation chamber is preferably composed of materials such as iron or molybdenum which do not react with barium at a temperature near its melting point.

The barium, refined by degassing and'distillation within the distillation chamber, is flowed down along a heated point: of about 700 I supply pipe of iron or molybdenum and collected within a reservoir vessel made of iron or molybdenum which is located within a main pumping chamber. As the distillation and main pumping chambers are interconnected by means of the supply tube for transporting molten barium, vacuum seal between them may be effected by the molten barium flowing down the supply pipe or the solid barium condensed on the inner periphery of the supply pipe when it is cooled. Thus, the vacuum of the main pumping chamber can be maintained at pressures below 10- mm. Hg, though the vacuum of the distillation chamber is maintained in the order of 10* mm. Hg.

The refined barium introduced into the reservoir vesset is heated by suitable means to appropriate temperatures at which vaporization of barium can be efiected. The vaporized barium is eiiused through one and/or more slits formed in the wall of reservoir vessel into. the main pumping chamber and deposited on the inside of the walls of the main pumping chamber to form fresh barium films successively thereon. These barium films catch oxygen, hydrogen, nitrogen, and other gases impinged thereupon, so that a sort of vacuum pumping action is generated there.

The rate of evaporation of barium in order to get desired pumping speed in the range of pressures of 10 10 mm. Hg shall be enough to supply sufficient quantities of barium in the main chamber. The quantities of barium will, in turn, depend on the dimensions or size of the main pumping chamber. The rate of evaporation of barium is fairly large between 400 C. and 700 C., and it may be in fact easily sublimed. The pumping action effected by a barium film will disappear when it has caught a certain amount of oxygen, hydrogen and nitrogen, so that it is necessary to continue a formation of the barium film condensed on the inner surface of the wall of the main chamber in order to maintain continuous pumping action. To this end there is needed to provide some means for supplying a refined barium such as prepared within a certain distillation chamber or a prerefined barium continuously into a crucible placed within a main pumping chamber, and means for continuously evaporating the barium in the crucible to form barium films on the inner surface of the main pumping chamber; 7 In this type of arrangement, theoretically attainable orders of vacuum will be limited by the amount of gases accompanied by the barium flowing from the distillation chamber or furnace to the main chamber, assuming there is no leakage in the main chamber and/ or no source of gases in the main chamber. Therefore, the attainable orders of vacuum will determined by the purity of the distilled barium or the effectiveness of distillation processes. In accordance with this principle, distillation and refining of barium shall be most carefully considered in this invention.

In practice, as a certain amount of gas will be evolved from structural members and gaskets used at junctions in a pumping system, ultimate vacuum will be obtained by the balance between the rates of gas evolution abovementioned and the rate of pumping speed.

In one embodiment of the invention wherein rubber gaskets were used at junctions, the attained vacuum was of an order of l0 mm. Hg. From this result, ifthe heat resisting metal gaskets are used in place of rubber gaskets, the attainable vacuum will be much improved, and a vacuum of 10' mm. Hg wiil be possibly expected, since the gas evolution from metal gasket is less than that of rubber gaskets.

Generally speaking, pumping speed largcly'varies with the sort of gases and also depend upon thequantity of barium evaporated per unit time and the efiective area of condensed barium film.

Therefore, it will be seen" that the present pumping mechanism essentially differs from that of pumps such as a diffusion vacuum pump.

If we express the pumping speed of this barium pump by the volume of a specified gas pumped out per unit time and measured at the inlet pressure, as similar to in the case of a diffusion vacuum pump, though such a definition being ambiguous in this case, it is possible to obtain a pumping speed nearly close to the ideal pumping speed which is expected for perfect vacuum.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:

FIG. 1 is a diagrammatic view, in section, of one embodiment of the invention.

FIG. 2 is a diagrammatic sectional view of a conventional gate valve used in the embodiment of FIG. 1.

FIG. 3 is again a diagrammatic view of another embodiment of the invention.

FIG. 4 is a diagrammatic sectional view taken on a center line of FIG. 3.

Referring now to FIG. 1, there is shown one embodiment of the invention where 1 indicates a main pumping chamber having mounted therein cylindrical casing. Within the cylindrical casing there is provided an evaporation furnace 3 for receiving and evaporating the refined barium which has been subjected to a treatment of degassing and distillation. One end 5 of the main chamber 1 is connected to a manifold (not shown) and other end 6 is connected to fore pump assembly indicated at 30. A distillation chamber indicated generally at 7 is provided with an upright portion 8 extended from a portion of the casing 3 and a separate tower 9 for the degassing and distillation of barium. Within the tower 9 there is provided a distillation furnace 11 including a distillation crucible 10. The distillation chamber 7 is in communication with a barium loading assembly 40 and an auxiliary pump 50. The main chamber 1 and the distillation chamber 7 are connected by a supply pipe 13.

In the practice of the invention metallic barium is first placed within a distillation crucible 14) mounted in the distillation chamber 7, and the two chambers, the distillation chamber and the main chamber, are roughly evacuated by means of fore pumps 30 and 50 such as a conventional oil diffusion pump and oil rotary pump.

Pumps

30 and 50, an oil diffusion pump and an oil rotary pump, respectively, are arranged in series, and a plurality of conventional valves well known in vacuum engineering are provided at 31, 32, 51 and 52. Both pumping chamber 1 and distillation chamber are subjected to rough evacuation by the oil rotary pump and then to a fine evacuation by the oil diffusion pump. By these operations of the pumps, the main pumping chamber 1 is evacuated to a pressure below mm. Hg, and the distillation chamber 7 to a pressure below 10 mm. Hg. The detailed explanation of these evacuation or pumping actions is omitted here, since the same is well known'to those skilled in the art of vacuum engineering.

When a predetermined vacuum is established in each of the two chambers, the distillation crucible 10 is heated by a heating means 14 surrounding it. The metallic barium contained in the distillation crucible 10 is then subjected to a degassing treatment.

The degassing treatment is gradually performed while keeping a valve 15 slightly open, and watching the vacuum in the chamber so that a coarse vacuum may not contaminate the barium. When the degassing of barium has been completed, the heating means 14 is more energized to evaporate the barium in the crucible 10. The evaporated barium, in turn, is condensed upon the inside wall surface 12 of the distillation furnace 11. During the distillation, the valve 15, of course, is lowered to its closed position to prevent loss of barium. Following the condensation of barium, a-heating means 16 is energized to heat the inside wall 12 of the distillation furnace 11.

When the barium condensed on the wall 12 is sutficiently heated, it is changed into a liquid state and flows down along the wall 12 into a supply pipe 13. At this time, a heating means 17 surrounding the supply pipe 13 is energized to heat the supply pipe 13, so that the distilled liquid barium will easily be introduced through the supply pipe 13 into a reservoir, or crucible 4 located within an evaporation furnace 3. The above-mentioned barium feeding or storing operation is not needed every time the pumping operation is actuated, since the pumping action will be continued until the barium stored within the reservoir 4 is used up.

When the barium within the distillation crucible 10 is used up, a certain amount of fresh metallic barium in grains is supplied into the distillation crucible 10 through a feeding pipe 42 and a gate valve 40, without breaking the vacuum of the distillation chamber 7. A gate valve 40 serves as a loading means of metallic barium.

The gate valve 40 used in this invention is of a conventional type Well known to those skilled in the art. The principle of the gate valve will be briefly explained. Referring to FIG. 2, the gate valve 40 is composed of the principal members such as a cylinder 41 and a slide valve 43. The cylinder 41 includes an extension 44 having a cup 45 and an outlet 46. The slide valve 43 includes two spaced disks 47 and 47 and a rod member 48 connecting the two disks 47 and 47 In a normal operation of the main chamber 1, the disks 47 and 47 are situated at the place as shown in full line. On the other hand, when a supply of additional metallic barium into the distillation crucible 10 is needed, the slide valve 43 is shifted rightwards, as shown in imaginary line in FIG. 2, and a cap 45 is removed therefrom to load the granular or flake of metallic bariums through the gate valve 41. In this position, the right section of the cylinder with respect to the disk 47 is exposed to atmospheric air while the left section is maintained at the original vacuum since the disk 47 securely shut down the communication between these two sections. After the loading operation was completed, the cap is securely jointed on its original place, and then the right section is evacuated through a pipe line 49 to a desired pressure. The charged barium will fall down through the outlet 46 into a feed pipe 42 as the slide valve is moved to its original position, and finally collected within the distillation crucible 10 and distilled in the same manner as above-mentioned.

Molten barium accumulated within the reservoir 4 is heated by a heating means 18 surrounding it to suitable temperatures, such as 400 C.700 C., at which molten barium passes into the gaseous state. The gaseous barium is ejected through a slit 19 perforating the side walls of the reservoir 4 and evaporating furnace 3 into the main pumping chamber 1, and deposited to form a bari-- um film 20 on the wall of the main pumping chamber 1.. The coated metallic barium can adsorb or absorb gases such as oxygen, hydrogen, nitrogen and argon. This. absorption by the metallic barium film generates the pumping action of the main pumping chamber 1 while the inert gases such as argon and helium are not ab sorbed by barium unless they are ionized by suitable means. To this end a filament member of tungsten 21 is provided ahead of the jet orifice or slit 19 and energized by suitable means to emit thermo-electrons. On the other hand, a grid 22 is provided at a place adjacent the inner surface of the main pumping chamber 1 and maintained at high voltages on the order of 1000 v. to accelerate the thermoelectron emitted from the filament means 21. By this means, rare gases such as argon are ionized, and absorbed by the coated barium film. Since the presence of a small quantity of argon in air greatly reduces the pumping speed with regard to air, it is desirable to continuously evacuate the main pumping cham ber 1 by means of the oil diffusion pump 33.

Each of the heating means 14, 16', 17 and 18 has a thermal shield assembly similar to the shield means 23 asshown in the heating means 16. These shields are useful to minimize the heat loss due to radiation. A set of electrodes 24 are mounted on the side wall of the tower 9 near its top and serves as electrical terminals to feed power to the heating means in the distillation chamber- 7 and to measure the temperatures of the interior of main pumping chamber '1. Similarly, anelectrode 25 ismounted on the wall of the main pumping chamber 1 and used in the same way as the electrode 24. At least one or more vacuum gauges 26 mounted on the shell 2 are used in measuring the vacuum of. the main chamber 1. To secure the vacuum of the main pumping chamber a plurality of packings and gaskets such as indicated at 27 is provided in all junctions of the structural members. These packings and gaskets are of special organics or preferably of suitable metals.

FIGS. 3 and 4 show another embodiment of the invention wherein a main chamber and an evaporating system are the same as those illustrated in FIG. 1, but a mode of charging a main pumping chamber with the refined barium to be evaporated and to be coated on the wall of the main chamber differs from that of FIG. 1.

In this embodiment, metallic barium having a high degree of purity, which is prepared at a place outside of this pumping means by subjecting it to vacuum distillation, is fed into the main pumping chamber by suitable means, as described hereinafter in detail, and then treated in the same manner as illustrated and described in FIG. 1 to establish a pumping action Within the main pumping chamber 1.

Referring to FIGS. 3 and 4, metallic barium having a high degree of purity is held in an iron reservoir 4 located within an evaporating furnace 3 which furnace is movable inwards or outwards of the main pumping chamber 1. The iron reservoir 4 is tightly sealed with some metal having a melting point lower than barium and is isolated from ambient atmosphere. The evaporating furnace 3 is fixed on one end of a drawbar means 101 and may be moved to ride on or leave a base box 102 through forward and backward movements of the drawbar means 101. The drawbar means 101 includes an electrically insulated handle 122, and slides within a preparation chamber 105, keeping air-tightness of the chambers 1 and 5. At both ends of the drawbar 101, there are provided

electrodes

103, 103, and at both ends of its rod there are provided

electrodes

104, 104. These electrodes serve as electric current source for heating means to heat the evaporating furnace 3. The preparation chamber 105 includes a valve means of gate type having a valve 107 which acts to shut off the communication between the main chamber 1 and the preparation chamber 105, so that the preparation chamber may be exposed to atmospheric air without breaking the vacuum of the main pumping chamber 1.

The preparation chamber has at its one side an exhaust port 108 connecting to auxiliary pump (not shown) and a set of valves 109, and at other side a charging port 110. On one end of the preparation chamber, a vacuum seal means 111, an electric insulator and a vacuum seal are provided. The vacuum seal means 111 serves as a support for the evaporating furnace 3.

By this arrangement, the drawbar means 101 carrying the evaporating furnace 3 is safely moved forward and rearward with respect to the gate valve means 106 during the operation of the evaporation furnace, without breaking the vacuum of the preparation chamber 105. The vacuum sealing means 111 provides at its one end a position indicator means 112 indicating the positions at which the evaporation furnace 3 lies on the base box 102 or in the predetermined place within the preparation chamber 105.

When barium in the evaporating furnace 3 has been used up, the evaporating furnace 3 is drawn back into chamber for refining the preparation. chamber by" handlingv the drawrod means 101, and then a gate valve 106 (schematically rep? resented) is closed to seal the main chamber 1 from the. preparation chamber 105, while. a loading. port is opened, and the evaporation furnace 3- is replaced with a new evaporation furnace. After a fresh evaporation furnace has been mounted in place on the drawrod means 101, the loading port 110 is closed, and then the preparation: chamber 105 is. evacuated to a requiredpressure.

and finally the valves: 1 09, 109 mounted at the section leading to an exhaustport 108are closed,- while the gate valve 106 is opened, and the evaporation furnace 3 is moved toward the base box- 102 through the advance ofthe drawrod-means 101,. and finally fixed on thebase box 102. Thus, the pumping action of the" main pumping chamber 1 is continuedagain until: the barium in the evaporation furnace is exhausted.

Further, a continuous pumping action will be accomplished by arranging another unit comprising a prepara tion chamber and a drawrod means similar to the above in symmetry with respect to the main chamber 1.

It will be noted that FIGS. 3 and 4 lack fore pump means and a filament member and a grid means such as illustrated in FIG. 1, but it is merely for a convenience of a drawing, so that it will be preferable to be mounted therein.

One example carried out by the barium getter ion pump of the type shown in FIG. 1 will be noted here.

(1) The main pumping chamber having a diameter of 14 inches was evacuated to the pressures below l0-' mm. Hg, where synthetic rubber gaskets were used in the junctions of the pumping system.

(2) The pumping speed obtained under a vacuum 10 mm. Hg was over 4000 l./sec. relative to oxygen.

As is apparent from the above data, the barium getter ion pump in accordance with the present invention is advantageous in that it is possible to obtain higher vacua than that presently obtainable by diffusion pumps, without the disadvantage of the backstreaming of oil to the high pressure side and/ or deposition of the backstreaming oil on the walls of pumping system, which difliculties are inherent in diffusion pumps. In the diffusion pump, it is necessary to provide trap means to prevent a backstreaming of oil, but such a provision of trap means will make the construction of pumping system complicated and impose tedious maintenance problems. The barium getter ion pump of the present invention is able to eliminate these disadvantages and will excellently serve as an evacuating pump for nuclear experiment equipments, and particularly for particle accelerators or thermonuclear reactors. It is believed that in the near future, the pump of this invention will become indispensable in nuclear reaction equipment and will provide an epoch-making improvement in the fields of vacuum engineering, the manufacture of vacuum bulbs, the refining of metals, and the coating of metals on substrates.

Since certain changes may be made in the above apparatus and process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description, or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A pump comprising a housing having an evacuation chamber and a vaporization chamber formed therein, said evacuation chamber having a wall upon which vaporized gettering substance is coated by condensation, means associated with said housing for connecting said evacuation chamber to a vessel to be evacuated, said vaporization chamber being in communication with the evacuation chamber and having means therein for directing a vaporized getter to said evacuation chamber, means for the removal of gas from the evacuation chamber, said means including means in said vaporization by distillation and degassing an unrefined getter therein, and means in said vaporization chamber for vaporizing said getter after the same has been refined.

2. A pump in accordance with claim 1 wherein the gettering substance which is refined and vaporized is barium.

3. A pump comprising a housing having an evacuation chamber and a vaporization chamber formed therein, said evacuation chamber having a Wall upon which a vaporized getter is coated by condensation, means associated with said housing for connecting said evacuation chamber to a vessel to be evacuated, said vaporization chamber being in communication with the evacuation chamber and having means therein for directing a vaporized getter to said evacuation chamber, means for the removal of gas from the evacuation chamber, said means including means in said vaporization chamber for refining by distillation and degassing an unrefined geter therein, means in said vaporization chamber for vaporizing said getter after the same has been refined, said gas removal means also including mechanical pumping means for initiating the evacuation of the evacuation and vaporization chambers, and a valve controlled inlet formed in said housing for the introduction ,of raw getter into the vaporization chamber without loss of vacuum.

4. A pump in accordance with claim 3 wherein the gettering substance which is refined and vaporized is barium.

5. A pump in accordance with claim 3 wherein means are included in said evacuation chamber for ionizing relatively inert gases present therein and for accelerating the movement of the ions thus produced so that the same can be absorbed by the condensed barium.

References Cited in the file of this patent UNITED STATES PATENTS 2,850,225 Herb Sept. 2, 1958

Claims

1. A PUMP COMPRISING A HOUSING HAVING AN EVACUATION CHAMBER AND A VAPORIZATION CHAMBER FORMED THEREIN, SAID EVACUATION CHAMBER HAVING A WALL UPON WHICH VAPORIZED GETTERING SUBSTANCE IS COATED BY CONDENSATION, MEANS ASSOCIATED WITH SAID HOUSING FOR CONNECTING SAID EVACUATION CHAMBER TO A VESSEL TO BE EVACUATED, SAID VAPORIZATION CHAMBER BEING IN COMMUNICATION WITH THE EVACUATION CHAMBER AND HAVING MEANS THEREIN FOR DIRECTING A VAPORIZED GETTER TO SAID EVACUATION CHAMBER, MEANS FOR THE REMOVAL OF GAS FROM THE EVACUATION CHAMBER, SAID MEANS INCLUDING MEANS IN SAID VAPORIZATION CHAMBER FOR REFINING BY DISTILLATION AND DEGASSING AN UNREFINED GETTER THEREIN, AND MEANS IN SAID VAPORIZATION CHAMBER FOR VAPORIZING SAID GETTER AFTER THE SAME HAS BEEN REFINED.