US3156406A - High vacuum pumping method and apparatus - Google Patents

Description

Nov. 10, 1964 Filed March 26, 1962 W. A. LLOYD ETAL HIGH VACUUM PUMPING METHOD AND APPARATUS 2 Sheets-Sheet 1 FIG.3 r

. INVENTORS WILLIAM A. LLOYD PHIROPOULOS BY KIJY TORNEY Nov. 10, 1964 w. A. LLOYD ETAL 3,

HIGH VACUUM PUMPING METHOD AND APPARATUS Filed March 26, 1962 2 Sheets-Sheet 2 I 90 A l 84 A 52 FIG. 7 a; lo g 92 93 A 9| a 92 Kilo 9| E I0 I00 I000 Rs TIME WlLL lm fl g TELOYD RENN ZQPHIROPOULOS BY (ATTORNEY United States Patent 3,156,406 HIGH. VAQUUM PUMPING NETHUD AND APPARATUS Wiiiiam A. Lloyd, Mountain. View, and Renn Zaphiroponlos, Los Altos, Calih, assignors to Varian Associates, Palo Alto, Calif, a corporation of California Filed Mar. 26, 1962, Ser. No. 182,528 8 Claims. ((Jl. 230-69) This application relates to a method and apparatus for obtaining high vacua. More specifically, this invention relates to a high vacuum method and apparatus which includes a cryogenic vacuum'pump.

In many diffusion pump vacuum systems it has been common practice to use cold traps between the main vacuum chamber and the diffusion pump in order to lower the pressure in the vacuum chamber due to condensable vapors or between the diffusion pump and a mechanical forepump in order to protect the mechanical pump from condensable vapors which might be corrosive or harmful tothe pump oil. These traps may exhibit extremely high pumping speeds by becoming sinks for gas molecules whose vapor pressure is above the temperature of the trap surface. For example, a container filled with liquid nitrogen has a theoretical pumping speed for Water vapor of about 95 liters per second per square inch of exposed outer surface.

However, in the above vacuum systems the theoretical pumping speeds of the cold traps is normally greatly reduced because of the conductance limitations between the main vacuum chamber and the traps. It has therefore been proposed to insert cryogenic vacuum pumps (cold surfaces) directly into main vacuum chambers so as to aid preliminary pump-downs in vacuum system applications wherein water vapor forms a large proportion of the gas to be removed. However, this type of vacuum system offers a great many limitations. One great drawback in the use of a. cryogenic pump within the main vacuum chamber has been that once water vapor has been condensed it was necessary to hold it on the pump surface until the entire vacuum operation being undertaken was completed. In most cases this was extremely difficult to do since any sudden rise in system temperature would cause evolution of the condensed water vapor causing a rapid increase in the system pressure.

It is therefore the object of this invention to greatly reduce high vacuum pump-down time of high vacuum systems by utilizing a cryogenic vacuum pump which can be easily and efficiently isolated from the main vacuum. system.

One feature of the present invention is the provision of a novel cryogenic vacuum pump which is adapted for insertion into a vacuum chamber and which includes novel valving apparatus for maintaining the cryogenic pump under vacuum while isolating it from the vacuum. chamber.

Another feature of the present invention is the provision of a cryogenic vacuum pump of the above featured type including apparatus which permits gas evacuation of the area surrounding the cryogenic pump while the valve apparatus is in the isolating position.

Still another feature of the present invention is the provision in a cryogenic vacuum pump of the above featured types of novel insulated liquid filling tubes which allow extremely efiieient cooling of the cryogenic vacuum pump by a cooling liquid.

Another feature of the present invention. is the provision of a cryogenic vacuum pump of the above featured types in a complete high vacuum system whose compact design provides a highly accessible work area within the vacuum system.

Another feature of the present invention is the-provision of a cryogenic vacuum pump adapted for insertion into a vacuum chamber and including valve apparatus which permits complete removal of the cryogenic pump for cleaning thereof while maintaining a vacuum within the vacuum. chamber.

Another feature of the present invention is the provision of a novel manifold mounted cryogenic vacuum pump whichis especially adapted for use with existing bell jar vacuum systems so as to greatly increase the utility thereof.

Another feature. of the present invention is the provision of a cryogenic vacuum pump adapted for insertion into a vacuum chamber and which utilizes a bellows as its cold surface thus providing a simple design with an extremely large exposed surface area and correspondingly large pumping speed.

Another feature of the present invention is the provision of a cryogenic vacuum pump adapted for insertion into a vacuum chamber and which includes structure for supporting a gas sorbent material thereby facilitating the pumping of noncondensable gases.

Another feature of the present invention is the method of producing extremely clean high vacua in a very short period of time with the strategic use of sorbent vacuum pumps, cryogenic vacuum pumps and electrical sputter ion pumps.

These and other features of the present invention will become more apparent upon a perusal of the. following specification taken in conjunction with the accompanying drawings wherein FIG. 1 is a plan view of a vacuum system embodiment of the present invention showing the position of sorbent vacuum pumps, electrical sputter-ion pump, cryogenic vacuum pump and vacuum bell jar,

FIG. 2 is a cross section view of the vacuum system of FIG. 1 taken along line 2--2 in the direction of the arrows,

FIG. 3 is an enlarged cross section of a preferred cryogenie vacuum pump shown in the vacuum system of FIG. 2 as indicated by the line 3-3,

FIG. 4 is an operating diagram showing pressure vs. pump-down time characteristics for the vacuum system of FIGS. 1- and 2,

FIG. 5 is a cross section view of another cryogenic vacuum pump embodiment of the present invention.

FIG. 6 is a cross section view of another cryogenic vacuum pump embodiment of the present invention,

FIG. 7 is a cross section. view of another embodiment of the cryogenic. vacuum pump shown in FIG. 3, and

FIG. 8 is a perspective view of still another cryogenic vacuum pump embodiment of the present invention.

Refering now to FIGS. 1 and 2, the vacuum system 11 has a hollow manifold 12 which is rectangular in both its plan andside views. In the center of the manifold top 13 is a circular opening 14 which is covered by a removable elongated vacuum bell jar 15. A pair of high vacuum valves 16 are attached over apertures in a side wall of the manifold 12' so as to provide gas communication therewith. A sorption vacuum pump 17 is connected to each of the high vacuum valves 16.. Mounted on one side of the bell j-ar 1-5 is a valve assembly 11% supported by a flange: plate 19' which covers a second circular opening 21 in the manifold cover 13. A screw driving assembly 22 including a bellows vacuum seal 23- extends through the plate 19 and is attached to valve plate 24-. Rotational movement ofv the hand wheel 25 produces a vertical motion of the valve plate 24 along the guide rods 26 so as to either seal or open an aparture 27 formed by the valve seat 28 in the bottom of the manifold 12. Attached on the underside of manifold 12 over the valve seat aperture 27' is the throat 29 of an electrical sputter-ion pump o 31. The cryogenic vacuum pump 32 is accommodated by another circular opening 33 in the manifold cover 13 adjacent the bell jar and opposite the valve assembly 18.

It will be noted that the system arrangement of FIGS. 1 and 2 provides an easily accessible, incumbrance free work area which includes the bell jar 15 and the manifold area directly below the bell jar 15.

As shown more clearly in FIG. 3, the cryogenic pump opening 33 is covered by a circular mounting flange 34 which is bolted to the manifold cover plate 13 and a vacuum seal provided therebetween by the O-ring 35. The circular mounting flange has a central aperture 36 formed by a recessed shoulder portion 37 which supports an annular washer 33. An annular bellows plate 41 and associated O-ring 42 are attached in a vacuum tight manner to the underside of the recessed shoulder 37 by a plurality of bolts 43 which extend through the annular washer 33. The high vacuum tight bellows 44 is attached, for example, by brazing at its upper end to the bellows plate 41 and at its lower end to a mounting nut The mounting nut 45 is attached by, for example, brazing to the inner bottom of a cup-shaped valve plate 46. he flanged rim 47 of the cup-shaped valve plate 46 includes an O-ring 48 adapted to make a vacuum seal with the underside of circular mounting flange 34 so as to form an auxiliary vacuum compartment 49. The cup-shaped valve plate 46 is held in alignment by a plurality of guide rods 51 which screw into the underside of circular mounting flange 34 and pass through apertures in the flanged rim t7.

Mounted within the auxiliary vacuum compartment is a hollow metallic donut structure 52 whose top surface has a plurality of apertures 53 which communicate with attached inner tubes 54. The inner tubes 54 extend through apertures 55 in the circular mounting flange 34 and terminate in outwardly flared portions 56. These outwardly flared portions 56 are attached by, for example, brazing to the inwardly flared portions 57 of outer tubes 8 which enclose and are spaced from the inner tubes 54. The outer tubes 58 are attached vacuum tightly to the surfaces of apertures 55 thereby supporting the donut structure 52. The inner tubes 54 provide inlets for filling the hollow donut structure 52 with a liquid coolant. Also, the double spaced apart tubing structure provides a long heat conduction path including the lengths of both inner tubes 54 and outer tubes 55 between the donut structure 52 and the circular cover plate 34. This design greatly reduces the loss of cooling liquid by evaporation from the outer vacuum wall surface.

One end of a hollow elbow tube 59 is attached to the surface of another aperture 61 in circular mounting flange 34 to provide gas communication into the auxiliary vacuum compartment 49. The other end of hollow elbow tube 59 is attached to a vacuum flange 62 adapted for connection to another pumping mechanism (not shown) whose utility will be explained below.

Mounted on the annular washer 33 is a pair of annular ball bearing assemblies 65 which straddle an externally extending circular shoulder 64- of a hollow internally threaded nut shaft 63. Secured to the circular mounting flange 34 by bolts 66 is a domed cover 66 which encloses the ballbearing assemblies 65 and which has a central aperture through which the nut shaft 63 passes. A screw shaft 67 passes entirely through the nut shaft 63 and has external threads which engage the internal threads of nut shaft 63 and of mounting nut 45. Supported by the domed cover 66 is a hand wheel 68 which is secured to nut shaft 63 by a set screw 69.

The nut shaft 63 and the hand wheel 68 are prevented from movement in the vertical direction by the domed cover 66 and recessed mounting flange shoulder 37 while the cup-shaped valve plate 46 and attached mounting nut 45 are prevented from rotational movement by the guide rods 51. Thus, rotational movement of the hand wheel 68 will produce a vertical movement of screw shaft 67 and a corresponding vertical movement of cup-shaped valve plate 46. In this way the valve plate 4-6 can be lowered on the guide rods 51 to expose the donut structure 52 as shown in FIG. 2.

In the operation of this vacuum system the main vacuum chamber 71 including the area within the bell jar 15 and the manifold 12 is first evacuated to about 50 mm. Hg by an oil free vacuum pump such as, for example, a water jet exhauster vacuum pump (not shown) with the valve plate 24 and the cup-shaped valve cover 46 in the closed positions and the sorption pumps 17 valved off. The water jet forepump is then valved off and the liquid nitrogen cooled sorption pumps 17 sequentially utilized to further reduce the pressure Within the main vacuum chamber 71 to about 10* millimeters of mercury. At this time, both E the sorption pumps 17 are valved off and both the valve plates 24 and 46 are opened to provide gas access between the main vacuum chamber 71 and both the sputter-ion pump 31 and the donut structure 52. Condensablc vapors within the main vacuum chamber 71 are then condensed at an extremely rapid rate upon the outer surface of the donut structure 52 which has been previously filled through tubes 54 with a cooling fluid such as, for example, liquid nitrogen. This pumping action in addition to that provided by the sputter-ion pump 31 will quickly reduce th system pressure to a desired value. In other applications where the gases condensed on the cold donut structure 52 have a high vapor pressure (for example, 16- mm. Hg) at liquid nitrogen temperature the valve cover 46 can again be closed at about this pressure to isolate the donut structure 52 from the main vacuum chamber 71 thus preventing re-evolution of these condensed vapors. With cup-shaped valve cover 46 closed the auxiliary vacuum chamber 49 will maintain the vapors in condensed form upon the outer surface of the cold donut structure 52. The vacuum cover 50 can then be removed from the flange 62 and another vacuum pump (not shown) connected thereto to remove the gases formed by the evolution of the condensed vapors after elimination of the cooling fluid from the donut structure 52. In this way, the cryogenic cold surface 52 can be cleaned of .condensables and again utilized for further pumping action by re-chilling of the donut 52 and opening of cup-shaped valve cover 46.

These particular sequencies of operation are particularly effective because of the characteristics of the vacuum pumps utilized. For example, when the pressure within the main vacuum chamber 71 is in the region of about 10- millimeters of mercury and below, a large percentage of the gas load is created by evolution of gas from the inner walls of the system. This evolved ga contains a high percentage of water vapor and the liquid nitrogen cooled cryogenic pump 32 exhibits its extremely high pumping speed primarily for water vapor. Thus the cryogenie pump 32 is particularly effective during this period of the pump-down operation.

FIG. 4 illustrates the dramatic effect achieved by the use of the cryogenic pump 32 in the pump-down sequence described above. Curve A represents a pump-down curve of the vacuum system 11 in the sequence described above with pressure within the system 7i plotted on the vertical log scale and pump-down time on the horizontal log scale wherein zero time begins with the system at atmospheric pressure. Curve B is a similar pump-down curve for the vacuum system 11 in the sequence described above except that the cryogenic vacuum pump 32 is not utilized. As illustrated by curve A, the use of the cryogenic pump 32 produced a pressure below 10- millimeters of mercury in approximately 40 minutes. Curve B shows that the same vacuum system operated without the cryogenic vacuum pump 32 achieved a pressure of only slightly below 10" millimeters of mercury in the same period of time.

In the particular vacuum system test, the main vacuum chamber 71 comprised a volume of about 4 cubic feet and the cryogenic vacuum pump donut 52 exhibited an exposed outer surface area of about 100 square inches. A sputterion pump having a rated pumping speed of 400 liters per second and sorption pumps of the type described in US. patent application No. 91,837 were used.

FIG. 5 shows another cryogenic vacuum pump embodiment wherein elements which are the same as those shown in FIG. 3 are given identical reference numerals. The primary differences from the embodiment of FIG. 3 are that the valve control mechanism 72 passes through the bottom of manifold 12 rather than through the manifold cover plate 13 and the guide rods 73 are embedded in manifold cover 13 rather than in circular mounting flange 34. This embodiment otters the advantage that the cupshaped valve cover 46 can be vacuum sealed against the manifold cover 13 to isolate the donut structure 52 from the main vacuum system 71 after which the entire cryogenic pump structure 74, including donut structure 52, inlet tubes 54, circular mounting flange 34 and elbow tube 59 can be removed from manifold cover 13 without letting the main vacuum system 7 1 up to atmospheric pressure. Thus, for example, an operator could remove an exceptionally contaminated donut structure 52 for chemical cleaning While maintaining the main vacuum system 71 under high vacuum.

FIG. 6 shows another embodiment of a cryogenic vacuum pump for mounting in a vacuum system such as that shown in FIGS. 1 and 2. Mounted on the manifold cover 13 is a hollow cylindrical casing 80 having a top end wall 81 which supports an inner bellows 82 and a spaced apart outer bellows 83 The concentric bellows 82 and 83 are sealed at their upper ends to the inside of the topend wall 81 and at their lower ends by a circular bellows plate 84 which supports a valve plate 85. A plurality of guide rods 99 are embedded into the underside of manifold cover 13 and provide guidance for vertical movement of the valve plate 85. A plurality of tubes 86 extend through the top end wall 8 1 into the chamber 87 formed between inner bellows 82. and outer bellows 83 and a flanged tube d8 extends through cylindrical casing 8d to provide gas communication thereinto. A driving mechanism 89, similar to that shown in FIG. 3, extends through top end wall 8 1 and inner bellows S2 and is attached to bellows plate 84-. By utilization of the driving means 89 the bellows 82 and 83 can be placed in their extended position as shown in FIG. 6 or can be withdrawn into the cylindrical casing till while the attached valve plate 85 forms a vacuum seal on the underside of manifold cover 13.

The operation of this embodiment is the same as that described with the embodiment of FIG. 3 except that in this case the outer surface of outer bellows 83 serves as the cryogenic vacuum pump cold wall after the chamber 87 has been filled with a liquid coolant through the filling tubes 36. The advantage of this embodiment is the increased pumping speed obtainable by the extremely large surf-ace cold area exhibited by the corrugated bellows surface.

A disadvantage of this embodiment as opposed to the embodiments of FIGS. 3 and 5 is that the entire liquid coolant container (the bellows 82 and 83) must be raised or lowered by the driving mechanism 89 rather than merely the valve plates as is the case in the embodiments of 3 and 5. This somewhat complicates the mechanical structural problems because of the increased mass it is neces- I sary to move. Also, in the embodiments of FIGS. 3 and 5 the containers for the liquid coolant (donut structure 52'.) are completely stationary and thereby require no moving liquid seals to allow filling thereof.

FIG. 7 illustrates another embodiment of the donut structure 52 of FIG. 3. A plurality of compartments 91 are formed by brackets 92 which extend about and are attached, for example, by brazing, to the outer circumferential surface 93 of the donut structure 52. The compartments 91 are filled with a highly gas sorbent material 94;

such as, for example, activated charcoal or molecular sieve. In operation the sorbent material 94 having been cooled by the cold surfaces of donut structure 52 and brackets 92 will soi'b many gases which are non-condensible on the cold metallic surfaces of donut structure 52. In this way a much larger variety of gases may be pumped by the cryogenic vacuum pump 32.

FIG. 8 illustrates a cryogenic pump vacuum system adaptor 1011 for greatly increasing the capabilities of existing bell jar vacuum systems. A cryogenic pump 101 of the type shown in FIG. 3 is mounted in the top end wall 102 of a manifold :103 in the same manner as described in conjunction with FIG. 3. Adjacent the cryogenic pump 1111 in the manifold top end wall 102 is an aperture 104 which is aligned with another aperture 1% of substantially the same size in the bottom end wall 106 of the manifold 10.3. A plurality of strengthening rods 167 arepositioned between top end wall 162 and bottom end wall 106 in the region between the cryogenic pump 101 and the apertures 1&4 and M5.

In the use of the system adaptor the bell jar of an existing vacuum system (not shown) would be removed and replaced in a vacuum tight manner by the manifold 163 with the bottom end wall aperture aligned with the opening formerly covered by the bell jar. The removed bell jar would then be remounted in a vacuum tight manner over the top end wall of aperture 1114, thus adding the interior of manifold 103, which includes cryogenic pump 1M to the existing vacuum system.

Thus the vacuum system adaptor 11%) allows an existing vacuum system to be easily converted to a system having a cryogenic vacuum pump positioned within the main vacuum chamber. Without conductance limitations the cryo genic pump may then function to greatly increase the system performance as described above,

Many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof. For example only, in the operation of the vacuum system shown in FIGS. 1 and 2 the sorp tion vacuum pump 17 could be utilized to reduce the main chamber pressure directly from atmospheric thereby dispensing with the necessity for an additional forepump. It is therefore 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 high vacuum system apparatus comprising a main vacuum chamber, a cryogenic vacuum pump positioned Within said main vacuum chamber, and movable means positioned within said main vacuum chamber for isolating said cryogenic vacuum pump within said main vacuum chamber.

2. The apparatus according to claim 1 including an electrical sputter-ion vacuum pump connected for gas communication with said main vacuum chamber, and valve means positioned within said main vacuum chamber for valving said electrical sputter-ion pump off from said main vacuum chamber.

3. The apparatus according to claim 1 wherein said main vacuum chamber comprises a manifold having apertured walls, said cryogenic vacuum pump being mounted on one of said Walls and extending within said manifold through one of said apertures.

4. The apparatus according to claim 3 wherein said movable means is mounted on a wall of said manifold opposite to the wall on which said cryogenic vacuum pump is mounted.

5. The apparatus according to claim 1 wherein said cryogenic vacuum pump includes a container portion adapted to be filled with a cooling fluid, and wherein said container portion is formed by a pair of bellows.

6. The apparatus according to claim 1 wherein said cryogenic pump includes a container portion adapted to be filled with a cooling fluid, means forming additional.

compartments adjacent the outer surface of said container portion, and wherein the additional compartments formed by said means contain a gas absorbent material.

7. The apparatus according to claim 3 wherein said manifold forming said main vacuum chamber is adapted for mounting onto a bell jar high vacuum system.

8. A high vacuum system apparatus comprising a main vacuum chamber, a cryogenic vacuum pump positioned within said main vacuum chamber, movable means positioned within said main vacuum chamber for isolating said cryogenic vacuum pump Within said main vacuum chamber, said movable means having an open and closed position, said movable means forming an auxiliary vacuum chamber within said main vacuum chamber about said cryogenic vacuum pump when in closed position, and tubulation means connected to said auxiliary vacuum chamber for providing gas communication to said auxiliary vacuum chamber.

References Cited in the file of this patent UNITED STATES PATENTS 2,197,079 Penning Apr. 16, 1940 2,897,036 Gale et al. July 28, 1959 2,985,356 Beecher May 23, 1961 3,009,629 Garin et al Nov. 21, 1961 3,027,651 Nerge Apr. 3, 1962 3,056,740 Holland et a1. Oct. 2, 1962 FOREIGN PATENTS 376,565 France June 17, 1907

Claims (1)

1. A HIGH VACUUM SYSTEM APPARATUS COMPRISING A MAIN VACUUM CHAMBER, A CRYOGENIC VACUUM PUMP POSITIONED WITHIN SAID MAIN VACUUM CHAMBER, AND MOVABLE MEANS POSITIONED WITHIN SAID MAIN VACUUM CHAMBER FOR ISOLATING SAID CRYOGENIC VACUUM PUMP WITHIN SAID MAIN VACUUM CHAMBER.

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