US2730297A - High-vacuum molecular pump - Google Patents

Description

Jan. 10,1956

Filed March 23 1951 A. C. VAN DORSTEN ET AL' HIGH-VACUUM MOLECULAR PUMP 1 N V EN TOR. Amer/mus @zemsus L zNDOIeSTE/V By ADRIAIVU/S MJIWIOEFF United States Patent 2,730,297 HIGH-VACUUM MOLECULAR PUMP Adrianus Cornelis van Dorsteu and Adrianus Verhoell,

Eindhoven, Netherlands, assignors to Hartford National Bank and Trust Company, Hartford, Conn., as trustee The invention relates to high-vacuum molecular pumps. High-vacuum molecular pumps may be used for various purposes, for example, for maintaining a vacuum in electron-microscopes or electronic valves. The pumps hitherto known are generally constructed either as difiusion pumps, for example mercury or nickel diffusion pumps, or as pumps in which the high-vacuum is obtained by relative rotation of two bodies. The high-vacuum pump according to the invention is of the latter type. A known form of this latter type is the Holweck high-vacuum molecular pump which comprises a rotor and a stator, one of these parts closely surrounding the other, the surrounding surface being conical, and one of these parts being provided at the area of the surrounding surface with a helical groove, which is open towards the said surface and the diameter of which increases towards the suction side.

An object of the present invention is to provide a high vacuum molecular pump having a rotor and a stator, one of which surrounds the other, the inner part being frustoconical in shape and the outer part being provided with a continuous pump groove in which the bottom thereof is invariably at the same distance from the axis of rotation of the pump.

This construction enables the groove to be provided accurately and in a simple manner.

In the high-vacuum molecular pumps hitherto known, the spacing between the bottom of the groove and the axis of rotation increased or decreased. This variation rendered manufacture of the pump comparatively difiicult.

The rotor and/or the stator may be provided with one or more cylindrical wall elements being surrounded on either side by one or more of the first mentioned parts and being provided at the area of the surrounding surfaces located on either side of said cylindrical wall element with a continuous pump groove open towards said surfaces. The pump capacity may thereby be doubled or, for example, quadrupled, without any increase in length of the high-vacuum molecular pump, while at the same time the diameter of this pump is not increased excessively.

In order that the invention may be more clearly understood and readily carried into effect, it will now be described more fully with reference to the accompanying drawing, in which:

Fig. 1 is a diagrammatic view of one embodiment of a high-vacuum molecular pump according to the invention being provided with a helical pump groove and Fig. 2 shows an alternative form of a pump groove,

Figs. 3 and 4 show alternate embodiments of the molecular pump according to the present invention.

Fig. 1 shows a high-vacuum molecular pump having a suction side and a pressure side and provided with a rotor 1, comprising a chamber 2, open at one end. Both the inner and the outer surfaces of the cylindrical wall of the rotor 1, are frusto-conical. The pump comprises two stators 3 and 4, These stators are provided with 2,730,297 Patented Jan. 10, 1956 helical grooves 5 and 6, respectively, which can be provided in the stators in a simple manner, since the bottom of each groove is equally spaced apart from the axis I-I of the rotor. The grooves exhibit a cross-sectional area which increases towards the top of the pump. The medium to be discharged is supplied to the grooves along the axis of the rotor through a channel 7 and the evacuated medium is discharged through a channel 8. The charnher 2 in the rotor 1 serves as a preliminary vacuum-space and communicates through ports 9 with the channel 8. The rotor is provided with shaft 10 which at the top and at the bottom is journalled in ball bearings 11, and 12 respectively. The ball bearing 12 bears on a sleeve 13, which is adapted to move in an axial direction I-I and which is urged against the rotor by a spring 14. At the top of the rotor the ball bearing 11 is held with the use of a bolt 15. Secured to the bottom of the rotor 1 is the armature 16 of an electric motor, which armature is surrounded by a stator 17.

The rotation of the rotor results in that the molecules of the medium contained in the high-vacuum space at the top of the molecular pump are conveyed into the grooves 5 and 6 so that at the top of the pump a highvacuum is produced in the channel 7. The spacing between the cylindrical wall of the rotor 1 and the stators 3 and 4 can be adjusted at will with the use of the bolt 15. If the pressure of the high-vacuum side increases suddenly, the rotor is loaded in an axial direction. Since the rotor is capable of moving slightly in the axial direction I-I, it will then move, so that the spring 14 is slightly compressed. Owing to this shift the spacing between the rotor and the stators increases, so that a pressure exchange between the high-vacuum side and the low-vacuurn side can take place. Thus the rotor will be moved back into its initial position by reason of the stress of the spring 14, so that the pump is immediately capable of reproducing in the high-vacuum space the wanted pressure under atmospheric pressure. In the high-vacuum molecular pump shown in Figure l, the rotor comprises a cylindrical wall and on either side of the cylindrical wall of the rotor there is a stator having a pump groove and the pump has double the capacity of a known highvacuum molecular pump of the same size.

It will be obvious that the rotor may comprise two or more wall elements instead of one in order to provide a greater number of grooves, for example three, four, or more with the same size of pumps. The capacity of the pump is thus tripled, quadrupled or multiplied by a factor greater than four without the necessity of altering the size of the pump substantially.

The continuous pump groove is built up from a plurality of channels 21 arranged at right-angles to the axis II-II of the rotor. By means of inclined channels 22 the channels 21 are connected to form a continuous pump groove.

In Figs. 1 and 2, the pump grooves are provided in the stator, but, as an alternative, they may he provided in the rotor. For example, Fig. 3 shows a rotor 23 provided with two rotor parts while the stator part 24 is mounted within the rotor parts. Stator part 24 is provided with a pump groove 25 at both its inner and outer sides, thus causing the suction side of the pump to be present at the top of the pump. In Fig. 4 the rotor 26 is provided with two parts and the stator 27 with three parts. Stator 27 has four pump grooves 28. In the construction shown in Fig. 4 the suction side of the pump is also at the top of the pump.

What we claim is:

l. A high-vacuum molecular pump being provided with a suction side and a part 'frus'to-conical in shape and an outer part being provided 'with a surface juxtaposed "to "said innerpart, a "c'o'ntinuous pump groove in said outer part which extends from said suction side to the pressure side of said pump and 'opens'out adjacent to said inner part, the cross-sectional area of saidlgroove being constructed and arranged to increase progressively toward the suction side of said pump, and allpoints on the bottom of said groove being at the same radial distance from the axis of rotation of said pump.

2. A' high vacuum molecular pump as claimed in claim 1 wherein said rotorrpart and stator part are provided with at least one cylindrical wall element.

3. Ahigh-vacuum molecular pumpbeing provided with a suction side and a pressure sideand comprising two stator parts, a rotor part mounted within said stator parts, said rotor partbeingjprovidedwith surfaces which make said rotor part frust'o-conical'in shape and an outer -part being provided with a surface juxtaposed to said inner part, continuous groove means in said stator parts extending from said suction sidetothe pressure side of said pump and opening out adjacent to 'said surfaces of said rotor part, the cross-sectional area of said groove means being constructed and arranged to increase progressively toward the suction side of said pump, and all points on the bottom ofsaid groove means being at the same radial distance from the axis of rotation of saidpump.

4. A high vacuum molecular pump being provided with a suction side and a pressure side and comprising a rotor having at least two spaced parts and a stator mounted within said parts of said rotor, at least two continuous pump "grooves in the "area between said 'spaced'parts, the cross-sectional area of each of said grooves being constructed and arranged to increase progressively toward the suction side of said pump, and all points on the bottom of each of said grooves being at the same radial distance from the axis ofrotation of said pump.

5. A highvacuummolecular pump being provided with a suctionsideand a pressure side and comprising a rotor having at least two'spaced parts and a stator having at least three spaced parts, said rotor parts being mounted in the spacesformed by said stator parts, at least four continuous pump grooves in the area between said stator spaced parts, the cross-sectional area of each of said grooves being constructed and arranged to increase progressively toward he suction side of said pump, and all points on the bottom of each of said grooves being at the same radial distance from the axis of rotation of said pump.

References Citediin' the tile of this patent UNITED STATES PATENTS 1,492,846 "Holweck' May '6, 1924 1,810,083 Norinder June 16, 1931 FOREIGN PATENTS 242,084 Great Britain Nov. 5, 1925 605,902 Germany Nov. 20, 1934 887,499 France .a Aug. 16, 1943

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