GB2052317A

GB2052317A - Improvements in rotors for turbo- molecular pumps

Info

Publication number: GB2052317A
Application number: GB8013318A
Authority: GB
Original assignee: Leybold Heraeus GmbH
Current assignee: Balzers und Leybold Deutschland Holding AG
Priority date: 1979-06-11
Filing date: 1980-04-23
Publication date: 1981-01-28
Also published as: JPS56593A; CH646229A5; JPS649475B2; GB2052317B; FR2458351B1; FR2458351A1; DE2923632A1

Abstract

A method of producing a blade ring 1 for the rotor of a turbo-molecular pump; before making the radial slots 9 to form the blades 10, the disc is so machined that it has a thickness which decreases radially outwards in a continuous or stepwise manner, Figures 1 or 2. <IMAGE>

Description

SPECIFICATION Improvements in rotors for turbo-molecular pumps The invention relates to a method of producing a blade ring for the rotor of a turbo-molecular pumps, wherein a disc is first provided in its edge zone with radial slots and the remaining portions are turned about their radial middle axes so that said portions form the required blades. In addition, the invention is concerned with a rotor equipped with blade rings of this type.

The production of blade rings in the abovementioned manner is known, for example, from "Vakuumtechnik", Vol. 23, No. 4, pp 109 et seq. On the one hand, the blades should be as thin as possible so that they can be easily rotated and so that their end faces are as small as possible. Related to the surface of the blades, these end faces have an "angle of pitch" at right angles thereto, i.e. all molecules which strike this end face acquire an impulse opposed to the required delivery direction caused by the blade surface itself. This unrequired influence of the end surfaces increases with the thickness of the blades.

On the other hand, blades produced in the abovementioned manner should not be too thin, lest they do not have adequate strength at the high rotational speeds that are used. Furthermore blades formed by slotting and subsequent twisting have a width and therefore a mass which increase in the radially outward direction, and this imposes additional requirements as regards strength. Finally, the discs used for producing the blade rings should not be too thin, since, for example when they are being machined on one side, they may be caused to vibrate and this has an adverse effect as regards reliable machining.

In the case of all of the known turbo-molecular pumps, the rotors of which have blade rings produced by the initially stated method, a compromise is made between these contradictory requirements as regards blade thickness, which compromise limits the properties of the turbo-molecular pump in a decisive manner.

In a further category of turbo-molecular pumps, the blade rings are produced simply by forming inclined slots in the edge zones of rotor discs (see for example Swiss Patent Specification 532,199).

Although such a method of manufacture avoids end surfaces having a false "angle of pitch" on the blades, it is considerably more expensive than the method of manufacture of the initially stated kind to which the present invention relates.

The object of the present invention is that of so improving the known method of producing a blade ring for the rotor of a turbo-molecular pump wherein a disc is first provided, in its edge zone, with radial slots, and the remaining portions are turned about their radial middle axes to form the required blades, that the turbo-molecular pumps, the rotors of which have blade rihgs produced by this method, exhibit considerably better properties than previously.

According to the invention, this object is achieved by a method of producing a blade ring for the rotor of a trubo-molecular pump, which comprises machining a disc so that it has a thickness which decreases radially outwards in a continuous or stepwise manner, forming radial slots in the edge zone of the machined disc by sawing, and turning the remaining portions about their radial middle axes so that said portions form the required blades.

A rotor having blade rings produced in this way can be operated at considerably higher speeds, i.e. at considerably higher peripheral speeds, since because of the radially outward decreasing thickness of the blades their mass also decreases in the ouward direction. Aturbo-molecular pump equipped with such a rotor therefore acquires a considerably better suction capacity and a higher compression, particularly for light gases such as H2. Precisely in the outer zones in which the peripheral speed is particularly high, the thickness of the blade and therefore the troublesome end surface are small, and this is likewise of advantage as regards the pump properties. In the hub zone the blade ring is preferably thicker than in the edge zone by a factor of 5 to 15.

For a disc diameter of approximately 18 cm, it has proved advantageous to use a thickness which diminishes from approximately 5 mm to approximately 0.5 mm.

A rotor for a turbo-molecular pump generally has a plurality of superposed blade rings, the blade of which often has lengths which differ in stages and/or different angles of pitch, the arrangement being such that the angle of pitch and/or length of blade diminish from the high-vacuum side to the forevacuum side. A rotor having blade rings produced in accordance with the invention can therefore be so produced, for example, that first independent discs can be produced with the rquired blae rings, and these rings then are fitted together in the rquired sequence. However, it is particularly advantageous to make such a rotor from a solid workpiece.For this purpose a cylindrical block, made of aluminium for example, is first provided with recesses disposed at right angles to its longitudinal axis, this being done in such a way that the blade rings can be produced from the remaining annular ribs or discs. This step of forming the recesses e.g. by turning, can be carried out simultaneously in such a way that the remaining portions have a thickness which decreases radially outwards. Thereafter, the blades are formed by sawing and twisting as described.Some embodiments of the invention will now be described by way of example, reference being made to the accompanying drawings in which: Figure 1 is a cross-sectional view of one form of blade ring provided by the invention; Figure 2 is a cross-sectional view of another form of blade ring provided by the invention; Figure 3 is a partial axial elevational view of the blade ring of Figure 2, and Figure 4 is an axial cross-section of a one-piece rotor comprising a plurality of blade rings, at an intermediate stage in its production in accordance with the present invention.

Figure 1 illustrates a blade ring 1, the thickness of which continually diminishes in the edge zone 2. The thickness of the hub 3 with the axial bore 4 is so selected that when a plurality of such rings are superposed and secured to each other, a rotorfora turbo-molecularvacuum pump is formed.

Figure 2 shows a blade ring the thickness of which does not diminish continuously in the radially outward direction, but does so in three steps 5,6 and 7.

Figure 3 shows, in axial view, part of a ring 1 formed in the manner of Figure 2. Figure 3 also shows a number of radial slots 9, which can be formed, for example, by sawing. The portions 10, remaining between the slots 9, are turned about their radial middle axes and thus formed the required blades. Depending upon the position of the blade ring in relation to the high-vacuum side of the pump, blades of different lengths, angle of pitch or width may be required. The length and width of the blades can be determined by the length or depth and the spacing of the slots 9. Different angles of pitch are obtained by differing degrees of twist. Finally, it may be required, particularly on the high-vacuum side, for the blades to be spaced from each other by as great a distance as possible. This can be achieved by wider saw blades for forming the slots 9.

Figure 4 shows a still unfinished rotor 11 in accordance with the invention and made from a solid workpiece. Forthis purpose a cylindrical aluminium block having radial recesses 12 was provided.

The spacing between the recesses and their depth was such that from the remaining material blade rings 13 can be produced in the manner of the invention. For this purpose, the radially outwardly diminishing thickness is imparted to the parts 13 either directly during the forming of the recesses 12 by turning, or subsequently by a separate machining operation using turning tools. In the illustrated example, a stepwise diminishing thickness of the parts is against selected. There then follows the sawing and twisting of the outer zones of the parts 13 in the manner described in connection with Figures 2 and 3, so that a one-piece rotor 11 is formed.

A rotor for a turbo-molecular vacuum pump, produced in accordance with the invention, can be operated at speeds up to 40% greater than in the case of a rotor in accordance with the prior art, i.e.

having blades of constant thickness. If, for example, an aluminium rotor is designed in accordance with the teachings of the prior art to turn at 42,000 r.p.m then if produced in accordance with the invention it is possible to operate it at approximately 59,000 r.p.m. This results in considerable increases in the compression valves and an improved suction capacity, particularly as regards light gases.

Claims

1. A method of producing a blade ring for the rotor of a turbo-molecular pump, which comprises machining a disc so that it has athickness which decreases radially outwards in a continuous or stepwise manner, forming radial slots in the edge zone of the machined disc by sawing, and turning the remaining portions about their radial middle axes so that said portions form the required blades.

2. a method of producing a rotorforaturbo- molecular pump, which comprises producing a plurality of blade rings individually by the method of Claim 1, and subsequently joining them together to form a rotor

3. A method of producing a rotor for a turbomolecular pump, the rotor having a plurality of blade rings made by the method of Claim 1, wherein the rotor is turned, at least partially, from a solid workpiece.

4. Arotorforaturbo-molecularvacuumpump when produced by the method of Claim 2 or Claim 3, wherein the blades forming the blade rings have a thickness which decreases radially outwards in a continuous orstepwise manner.

5. A rotor according to Claim 4, wherein in the hub zone the blades have a thickness which is greaterthan that in the edge zone by a factor of 5 to 15.

6. A rotor according to Claim 4 or Claim 5, which comprises a one-piece rotor.

7. A rotor according to any one of Claims 4 to 6, wherein the blades of different blade rings are differeent as regards spacing, width, length and angle of pitch.

8. A method of producing a blade ring for the rotor of a turbo-molecular pump, according to Claim 1 and substantially as hereinbefore described.

9. A blade ring our a rotor for a turbo-molecular pump substantially as herein before described with reference to the accompanying drawings.