US3477381A

US3477381A - Turbo-molecular pump

Info

Publication number: US3477381A
Application number: US693793A
Authority: US
Inventors: Willi Becker
Original assignee: PFEIFFER VAKUUMTECHNIK
Current assignee: ARTHUR PFEIFFER HOCHVAKUUMTECHNIK GMBH; PFEIFFER VAKUUMTECHNIK
Priority date: 1966-12-30
Filing date: 1967-12-27
Publication date: 1969-11-11
Anticipated expiration: 1986-11-11
Also published as: DE1503704B2; CH482119A; DE1503704C3; GB1155700A; FR1582018A; DE1503704A1

Description

Nov. 11, 1969 w. BECKER wunawmmcumn PUMP Filed Dec. 27, 1967 n Inventor 6r- WL. 5, 9 ,M

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United States Patent Int. Cl. F0141 /02, 5/22; F0411 3/00 US. Cl. 103-84 4 Claims ABSTRACT OF THE DISCLOSURE A stator or rotor disc for a turbo-molecular pump consists of a two-part securing ring between the two parts of which are clamped their radially extending blades which are twisted to overlap each other and at the free ends have tip portions substantially parallel to the axis of rotation and welded one to the other.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to turbo-molecular pumps, that is to say to low'pressure vacuum pumps. The term molecular pump is understood to mean vacuum pumps which operate in a molecular flow range, i.e. in a flow range in which the free length of trajectory of the molecules in the evacuated space is so great that they can fly from one wall to the other wall of the space Without impeding each other. If a space of this kind is delimited by two walls possessing a high relative speed with respect to each other, e.g. by a fixed and by a rotating wall, a kinetic impulse in the direction of motion of the movable wall is imparted to the molecules appearing at the moving wall. The pumping action of the molecular pump is based on this impulse.

A particularly effective form of the molecular pumps are turbo-molecular pumps which are built up from separate discs or plates, rotating and stationary discs following each other with small spacing in the axial direction of the pump. The movable discs are referred to as rotor discs, the stationary ones as stator discs. Both discs are so shaped that they form blades at the periphery, that is to say in such form that passages are produced between adjacent blades, which respectively subtend acute and obtuse angles with the direction of motion of the rotating discs, i.e. the passages or ducts of one co-ordinated pair of discs consisting of a rotor disc and a stator disc have a mirror-image position relative to their plane of separation.

Description of the prior art Discs of the above kind are either produced from massive discs, the passages referred to being milled out of the discs, or from an annular metal sheet or plate which is subdivided at the periphery by radial cuts along the radial length of the blades, and from which the separate blades are twisted through the desired angle to the plane of the sheet or plate during the same operation. A disadvantage of the massive discs first mentioned is that the number of slits is limited for reasons of strength. A disadvantage of the second kind of disc is the defective stability of the blades during incursions of air into the pump. In order to obtain an adequate stability at all in this case, it is necessary to leave the blades plane at the outer periphery of the discs, i.e. to leave a closed ring at the periphery of the blades, which interconnects the separate blades. This ring reduces the blade area at the point at which it is most efiective. A further essential disadvantage of the second kind of blades is that the blades ice are not optically opaque. In point of fact, it is of quite essential importance in turbo-molecular pumps, that the edge of a bladesituated at the front in the direction of displacement, should overlap the edge of the preceding 5 blade situated at the rear in the same direction, at least so far that a ray of light directed parallel to the axis of rotation cannot traverse the ring of blades. Only in this manner is an undersirable rebound of the molecules against the direction of delivery prevented, i.e. is the possible performance of the pump exploited fully. If the blades are bent from solid sheet or plate however, as specified, the desirable opaqueness is not attainable.

It is an object of the invention to provide discs, that is to say both rotor and stator discs, which combine the advantages of both known disc structures without possessing their disadvantages.

SUMMARY According to the invention there is provided a rotary or stationary disc for a turbo-molecular pump comprising a ring and separate blades each formed from sheet or plate material and fastened to the ring to subtend as appropriate an acute or an obtuse angle with the plane of rotation of the disc. The length of the blades considered in the peripheral direction of the disc is so chosen to this end, that the leading edge portion of each blade overlaps the trailing edge of the blade preceding it in the direction of rotation, to the extent that the ring of blades is impenetrable to a ray of light parallel to the axis of rotation.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a radial section through a rotor and stator disc and the corresponding securing rings according to the invention, 1

FIG. 2 is a view of several rotor blades with their securing ring,

FIG. 3 is a section along the line III-III of FIG. 1, and

FIG. 4 is a view of a blade according to the invention before its deformation.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, the driving spindle 1 of a turbo-molecular pump is rotatable with a securing ring for the blades of a rotor disc. The securing ring consists of first and second two

parts

2 and 3 and the rotor blades 4 are held between the two parts. Each blade 4 is produced from a plane sheet or plate illustrated in FIG. 4. This sheet or plate has a main portion 6 of circle segment shape, a root portion 7 stepped down in width relative thereto, and a tip portion 5 joined to it at an obtuse angle. The sheet or plate is deformed along the broken lines marked A to F. The tip portion 5 is bent over at right angles about the line F, and the main portion 6 is twisted about the line B according to the blade angle illustrated in FIG. 3. The angle marked alpha in FIG. 4 is so determined that on twisting of the main portion 6 relative to the root portion 7, the lateral edges 8 of the tip portion are laid parallel to the rotor plane of the blades as shown in FIG. 1.

The root portion 7 is bent over at right angles about the lines A to D so that, as shown in FIG. 1, a U-shaped profile is formed. The first ring part 2 has a U-shaped recess 9, and the second ring part 3 has a T-shaped crosssection whereof the limb 10 fits into the recess 9. In the recess 9 are also situated the U-foldled parts of the root portion 7 of each blade, so that the blades are held in the ring portion 2 by the ring part 3. When the blades are so positioned the leading edge portion of each blade overlaps the trailing edge of the blade preceding it in the direction very thin in the radial direction is thus produced, which provides the blades 4 with stability in the axial direction and protects them against twisting or buckling during air incursions.

The blades marked 13 of a stator disc are held in a securing ring which consists of first and second parts 14 and 15. In this case, the ring part 15 has an angular, for example a V, shape and and is secured in position by a swaged or beaded flange 16. In this case, the root portions of the blades are bent over only twice. The blades are widest at the point of transition from the root portion to the main portion, but are otherwise constructed in the same manner as the rotor blades. The tip portions of the blades 13 are shown at 17, in FIGS. 1 and 3.

Blades according to the invention result in optimum exploitation of space and thus in high suction capacity of the pump for small dimensions. Because of the narrow root portions, the blades can be positioned with such spacing along the periphery that their edges overlap each other. A satisfactory pressure ratio is thus obtained for each stage formed by a rotor and stator disc,

Discs according to the invention will advantageously be arranged at the low-pressure vacuum side of the turbomolecular pump, milled discs can be employed as hitherto close to the rough-vacuum side. Although these have a lower suction capacity, this is no longer of such importance in the rough-vacuum stage, because the gases to be pumped 011' have already been powerfully precompressed by the low-pressure vacuum stages. The combination has the advantage that the rather costly disc according to the invention are employed only where it is sensible to do so, whereas the simple disc fulfil the same purpose at the rough-vacuum side where a high suction capacity is not as necessary.

I claim:

1. A disc for a rotary turbo-molecular pump comprising a two part securing ring having opposed outer surfaces, individually formed blades secured between the two part ring, each blade being formed from a sheet metal strip including a middle part, a foot part by means of which the blade is secured to the ring, and a head part bent essentially at a right angle relative to the middle part which before it is bent, it forms an obtuse angle with the middle part, the middle part being turned as to the foot part so that the side edges of the head part are essentially parallel to the ring outer surfaces, the head parts of adjacent blades overlap relative to each other, and secured by spot welding to each other, the distance of the blades in the direction of the circumference being so calculated that the front directed edges of each blade in the same direction of rotation are spaced at least as to overlap that the ring of blades will direct impervious parallel light rays.

2. A disc according to claim 1, wherein the root portion of a blade is folded at right angles to the fiat sheet approximately to U shape.

3. A disc according to claim 1, wherein a second part of the securing ring consists of a ring of T-shaped crosssection and the first part includes a U-shaped recess into which a limb of the T-shaped ring is insertible to secure the blade roots therebetween.

4. A disc according to claim 3, wherein a first part includes a projecting flange and wherein the flange extends over against the second part after insertion of said limb in the U-shaped recess.

References Cited UNITED STATES PATENTS 764,230 7/ 1904 Edwards 25377 941,411 11/1909 Gilson 25377 1,072,233 9/1913 Imle. 1,347,327 7/ 1920 Dickinson. 2,357,279 8/ 1944 Rendelstein 230-113 2,405,190 8/ 1946 Darling. 3,168,977 2/1965 Garnier et al 230118 3,189,264 6/1965 Becker 103-84 FOREIGN PATENTS 1,121,516 5/1956 France.

20,818 1906 Great Britain. 258,870 1/ 1928 Italy.

6,955 6/ 1896 Sweden.

HENRY F. RADUAZO, Primary Examiner US. Cl. X.R. 103-89; 25377