EP3507497A1

EP3507497A1 - Vacuum pump screw rotor

Info

Publication number: EP3507497A1
Application number: EP17749704.7A
Authority: EP
Inventors: Thomas Dreifert; Dirk Schiller; Wolfgang Giebmanns; Roland Müller
Original assignee: Leybold GmbH
Current assignee: Leybold GmbH
Priority date: 2016-08-30
Filing date: 2017-08-08
Publication date: 2019-07-10
Anticipated expiration: 2037-08-08
Also published as: BR112019002011A2; US11293435B2; WO2018041556A1; KR102390690B1; CA3032345A1; CN109642575B; JP2019528400A; KR20190043138A; JP6983872B2; CN109642575A; DE102016216279A1; US20190211822A1; EP3507497B1

Abstract

The invention relates to a vacuum pump screw rotor, comprising at least two helical displacement elements (10, 12) on a rotor shaft. The at least two displacement elements (10, 12) have different slopes, but the slopes of each displacement element are constant. Furthermore, the displacement elements each have a helical recess, each having a contour that remains the same over its entire length. Hereby, a suction-side displacement element (10) has a recess having an asymmetrical contour, and a pressure-side displacement element (12) has a recess having a symmetrical contour.

Description

Vacuum-screw rotor

The invention relates to a vacuum pump screw rotor.

Screw vacuum pumps have two rotor elements in a pump chamber formed by a housing. The rotor elements have a helical contour and are rotated in opposite directions to convey gases. In order to achieve a high internal compression, that is to say a volume ratio between the inlet and the outlet of the pump, it is known that the displacer element of the rotor element, that is to say the helical contour, has a changing incline. On the inlet side or suction side, the slope is large and the volume of the chambers formed per turn also large. The slope decreases in the direction of the outlet, so that the outlet or pressure side, a small pitch and low chamber volume per turn are formed. By providing a variable pitch, low power consumption at low inlet pressures and, at the same time, low thermal loading of the pump can be realized. The provision of changing pitch requires a complex and therefore expensive manufacturing process. In particular, manufacturing such as milling or turning the turns, ie. the screw-line recesses take place in several successive steps. The object of the invention is to provide a vacuum pump screw rotor, which is inexpensive to manufacture with low power consumption and low thermal stress on the pump. It is another object of the invention to provide a corresponding screw vacuum pump and a suitable manufacturing method.

The object is achieved by a vacuum pump screw rotor according to claim 1, a vacuum pump according to claim 12, and a manufacturing method according to claim 17.

The vacuum pump screw rotor according to the invention has at least two helical displacement elements arranged on a rotor shaft. By the displacement elements, the rotor element is formed. According to the invention, the at least two displacement elements have different pitches, wherein the pitch is constant per displacement element. For example, the vacuum pump screw rotor according to the invention has two displacement elements, wherein a first suction-side displacement element has a larger constant pitch and a second pressure-side displacement element has a smaller constant pitch. The inventive provision of several displacement elements, each having a constant slope, the production is considerably simplified.

According to the invention, each displacement element has at least one helical recess which has the same contour over its entire length. The contours are preferably different per displacement element. The single displacement element thus preferably has a constant pitch and a constant contour. This simplifies the production considerably, so that the production costs can be greatly reduced. To further improve the suction power, the contour of the suction-side displacement element, that is to say in particular of the first displacement element in the pumping direction, is asymmetrical. As a result of the asymmetrical design of the contour or of the profile, the flanks can be configured in such a way that the leakage surfaces, the so-called blow holes, in particular, completely disappear or at least have a small cross section. A particularly suitable asymmetric profile is the so-called "Quimby profile". Although such a profile is relatively difficult to manufacture, it has the advantage that there is no continuous blow hole. A short circuit is only given between two adjacent chambers. Since it is an asymmetric profile with different profile flanks, at least two steps are required for the production, since the two flanks must be prepared in different steps due to their asymmetry.

The pressure-side displacement element, in particular the last displacement element in the pumping direction, is provided with a symmetrical contour. The symmetrical contour has the particular advantage that the production is easier. In particular, both flanks can be produced with a symmetrical contour by a rotating end mill or by a rotating side milling cutter in one step. Such symmetrical profiles have only small blowholes, but these are continuous, ie not only provided between two adjacent chambers. The size of the blow hole decreases as the slope decreases. In this respect, such symmetrical profiles can be provided in particular in the pressure-side displacement element, since in a preferred embodiment, this has a smaller pitch than the suction-side displacement element and preferably also as the displacement elements arranged between the suction-side and pressure-side displacement elements. Although the density of such symmetrical profiles is slightly lower, they have the advantage that the production is much easier. In particular, it is possible to use the symmetrical profile in a single step and preferably with a simple end mill or disc milling cutter. This reduces the costs considerably. A particularly suitable symmetrical profile is the so-called "cycloid profile".

The provision of at least two such displacement elements means that the corresponding screw vacuum pump can generate low inlet pressures with low power consumption. The thermal load is low. Arranging at least two displacement elements of constant pitch and constant contour in a vacuum pump according to the invention leads to essentially the same results as in a vacuum pump with a displacement element of varying pitch. At high built volume ratios can be provided per rotor three or four Vedrängungselemente.

In order to reduce the achievable inlet pressure and / or to reduce the power consumption and / or the thermal load, in a particularly preferred embodiment, a pressure-side, that is, in particular in pumping last displacement element on a large number of turns on. Due to a high number of turns, a larger gap between the screw rotor and the housing can be accepted with consistent performance. The gap can in this case have a cold gap width of 0.1 to 0.3 mm. A large number of outlet turns or number of turns in the pressure-side displacement element is inexpensive to produce, since according to the invention this displacement element has a constant pitch and in particular also a symmetrical contour. As a result, a simple and inexpensive production is possible, so that the provision of a larger number of turns is acceptable. Preferably, this pressure-side or last displacement element has more than 8, in particular more than 10 and particularly preferably more than 12 turns. The use of symmetrical profiles in a particularly preferred embodiment has the advantage that both flanks of the profile can be cut simultaneously with a milling cutter. In this case, a supporting of the Milling cutter through the respective opposite edge, so that deformation or bending of the milling cutter during the milling process and thereby caused inaccuracies are avoided.

To further reduce the manufacturing cost, it is particularly preferred to form the displacement elements and the rotor shaft in one piece.

In a further preferred embodiment, the pitch change between adjacent displacement elements is discontinuous or erratic. Optionally, the two displacement elements are arranged in the longitudinal direction at a distance from each other, so that between two displacement elements, a circumferential cylindrical chamber is formed, which serves as a tool outlet. This is particularly advantageous in integrally formed rotors, since the helix producing tool can be brought out in this area in a simple manner. If the displacement elements are manufactured independently of each other and then mounted on a shaft, the provision of a tool outlet, in particular of such a ring-cylindrical region is not required.

In a preferred embodiment of the invention, no tool outlet is provided between two adjacent displacement elements on the pitch change. In the region of the pitch change, both flanks preferably have a defect or recess in order to be able to lead out the tool. Such a defect has no appreciable influence on the compression capacity of the pump, since it is a locally very limited defect or recess.

The vacuum pump screw rotor according to the invention has in particular a plurality of displacement elements. These may each have the same or different diameters. It is preferred here that the Pressure-side displacement element has a smaller diameter than the suction-side displacement element.

In the case of displacement elements which are produced independently of the rotor shaft, they are mounted on the shaft, for example by press fits. In this case, it is preferable to provide elements such as dowel pins for fixing the angular position of the displacement elements to one another.

In particular, in the one-piece design of the screw rotor but also in a multi-piece configuration, it is preferable to produce this made of aluminum or an aluminum alloy. It is particularly preferred to produce the rotor from aluminum or an aluminum alloy, in particular AISi7Mg or AISi 17Cu4Mg. The alloy preferably has a high silicon content of preferably more than 15% in order to reduce the expansion coefficient.

The aluminum used in a further preferred embodiment of the invention has a low expansion coefficient. It is preferred if the material has an expansion coefficient of less than 18 * 10 ^-6 / K. In a further preferred embodiment, the surface of the displacement elements is coated, wherein in particular a coating against wear and / or corrosion is provided. In this case, it is preferable to provide an anodic coating or another suitable coating depending on the field of application.

Furthermore, the invention relates to a screw vacuum pump. This has two intermeshing vacuum pump screw rotors as described above. The two screw rotors are arranged in a pump chamber formed by a pump chamber. Usually, one of the two screw rotors is connected to a drive device such as an electric motor. The two screw rotors can be connected via gears, which are arranged in particular on the rotor shafts be. As a result, there is also a synchronization of the counter-rotating screw rotors. In a particularly preferred embodiment, it is possible, in particular due to the inventive design of the screw rotors, to achieve an internal compression of the screw vacuum pump of at least two, in particular at least four. Such a high internal compression is possible in particular due to the design of the two rotors with at least two compression elements each having a constant pitch and in particular a constant contour with a further high number of turns of the pressure-side displacement element. This is possible in particular, although large gaps are permitted in the region of the pressure-side displacement element. The large gaps in particular have the advantage that the thermal load is distributed more uniformly on the pressure-side displacement element. In particular, the thermal expansion of the corresponding displacement element and thus the risk of contact of the displacement element is avoided on the inside of the housing. Another related aspect is that the screw rotors have a lower coefficient of expansion than the housing. In particular, the expansion coefficient of the housing is at least 5%, and more preferably at least 10% greater than that of the screw rotors.

It is preferred here that the housing is made of an aluminum alloy with a lower silicon content than the silicon content in the material of the screw rotors. This ensures a higher thermal expansion of the housing relative to the screw rotors. This ensures in particular that during operation, ie. with increasing thermal load, the gap may indeed be lower, but always a sufficient gap between the outside of the displacement elements and the inside of the pump chamber remains.

Furthermore, the invention relates to a method for producing a screw rotor as described above. The production takes place here in particular such that the displacement elements and the rotor shaft are integrally formed. In a first step, a base body for the screw rotor is provided. The helical recesses for producing the displacement element are produced by means of a form milling cutter such as a milling cutter or disc milling cutter. This is done per displacement element in a separate step, since the slope and in particular the contour of the helical recesses are different per displacement element.

In the case of displacement elements with a symmetrical contour, it is preferred that the recess be made with a single tool, in particular in a single operation. Furthermore, it is preferred that the tool images the outer contour of the recess, so that the production can preferably take place on both flanks in one work step. In the asymmetric part, the flanks must be machined by two different tools.

It is preferred that a tool outlet is produced, in particular in one-piece screw rotors, prior to the production of the helical recesses. Such a ring-cylindrical recess can be made by milling or turning.

In a particularly preferred embodiment, no such tool outlet is provided. Instead, a recess is provided in an edge of an adjacent displacement element. This creates the defect or recess when taking out the milling cutter.

The basic body used is in particular cylindrical, so that from a single body, the rotor shaft can be produced with it optionally subsequent shaft journals and in particular also the displacement elements. It is also possible to use a base body which is designed as a semi-finished and already recesses and / or has journal. The preparation of the body can be done for example by casting.

The invention will be explained in more detail with reference to a preferred embodiment with reference to the accompanying drawings.

Show it :

1 is a schematic plan view of a first preferred embodiment of a vacuum pump screw rotor,

FIG. 2 is a schematic plan view of a second preferred embodiment of a vacuum pump screw rotor. FIG.

3 is a schematic sectional view of displacement elements with asymmetrical profile,

Fig. 4 is a schematic sectional view of displacement elements with symmetrical profile and

5 is a schematic sectional view of a screw

Vacuum pump.

In the first preferred embodiment of the vacuum pump screw rotor, the rotor has two displacement elements 10, 12. A first suction-side extension element 10 has a large pitch of approximately 50-150 mm / revolution. The slope is constant over the entire extension element 10. The contour of the helical recess is constant. The second pressure-side displacement element 12 again has a constant pitch over its length and a constant contour of the recess. The pitch of the pressure-side displacement element 12 is preferably in the range of 10 - 30 mm / revolution. be- - Lo rule the two displacement elements is a ring-cylindrical recess 14 is provided. This serves to realize a tool outlet due to the one-piece design of the screw rotor shown in FIG.

Furthermore, the integrally formed screw rotor has two bearing seats 16 and a shaft end 18. With the shaft end 18, for example, a gear is connected to the drive.

In the second preferred embodiment shown in Fig. 2, the two displacement elements 10, 12 are made separately and then fixed on a rotor shaft 20, for example by pressing. Although this production is somewhat more expensive, but the cylindrical distance 14 between two adjacent displacement elements 10, 12 as a tool outlet is not required. The bearing seats 16 and the shaft ends 18 may be an integral part of the displacement elements. Alternatively, a continuous shaft 20 can also be made of another material that differs from the displacement elements 10, 12.

3 shows a schematic sectional view of an asymmetrical profile (eg a Quimby profile). The illustrated asymmetrical profile is a so-called "Quimby profile". The sectional view shows two screw rotors that mesh with each other and whose longitudinal direction is perpendicular to the plane of the drawing. The opposite rotation of the rotors is indicated by the two arrows 15. Relative to a plane 17 running perpendicular to the longitudinal axis of the displacement elements, the profiles of the flanks 19 and 21 per rotor are configured differently. The opposing edges 19, 21 must therefore be made independently. However, therefore, although somewhat more complex and difficult production has the advantage that no continuous blow hole is present, but only between two adjacent chambers is a short circuit. Such an asymmetric profile is preferably provided in the suction-side displacement element 10.

The schematic sectional view in Fig. 4 again shows a cross section of two displacement elements or two screw rotors, which in turn rotate in opposite directions (arrows 15). Relative to the axis of symmetry 17, the flanks 23 are designed to be symmetrical per displacement element. In the illustrated in Fig. 4 preferred embodiment of a symmetrically designed contour is a cycloid profile.

A symmetrical profile, as shown in FIG. 4, is preferably provided in the pressure-side displacement elements 12.

The further embodiment shown in FIG. 5 again is a one-piece design. To lead out the tool, such as a milling cutter, a recess or defect is provided in the flank of the displacement element 12.

Furthermore, it is possible that more than two displacement elements are provided. These may possibly also have different head diameters and corresponding foot diameters. In this case, it is preferred that a displacement element with a larger head diameter at the inlet, i. is arranged on the suction side in order to realize a greater pumping speed in this area and / or to increase the built-in volume ratio. Furthermore, combinations of the embodiments described above are possible. For example, one or more displacement elements may be made integral with the shaft or an additional displacement element independent of the shaft and then mounted on the shaft.

A schematic sectional view of a vacuum pump (FIG. 5) shows in a housing 22 two vacuum pump screw rotors 26 arranged in a pump chamber 24. The two rotors are mounted in the housing via bearings 28. outsourced. With two shaft ends 18 each gear wheels 32 are connected. These mesh with each other, so that a synchronization of the two waves is guaranteed. One of the two gears 32 is connected to a drive device such as an electric motor.

As can be seen from FIG. 5, the suction of the gas takes place in the region of the suction-side displacement elements 10, as shown by an arrow 34. The expulsion of the gas takes place in accordance with as shown by an arrow 36 at the end of the second, pressure-side displacement element 12th

Claims

claims

A vacuum pump screw rotor having at least two helical displacement elements (10, 12) arranged on a rotor shaft, wherein the at least two displacement elements (10, 12) have different but constant pitches per displacement element and the displacement elements (10, 12) each screw at least one - Line-shaped recess having in each case over its entire length constant contour, characterized in that a suction-side displacement element (10) has an asymmetrical contour, and that a pressure-side displacement element (12) has a symmetrical contour.

2. Vacuum pump screw rotor according to claim 1, characterized in that at least two rotor elements are provided with respective helical displacement elements, wherein the displacement elements have different, but per displacement element constant slopes.

3. Vacuum pump screw rotor according to claim 1 or 2, characterized in that the pressure-side displacement element (10) has more than 8, in particular more than 10 and particularly preferably more than 12 turns.

4. Vacuum pump screw rotor according to one of claims 1 to 3, characterized in that a pressure-side displacement element is formed catchy.

5. Vacuum pump screw rotor according to one of claims 1 to 4, characterized in that the rotor shaft and the displacement elements (10, 12) are integrally formed.

6. Vacuum pump screw rotor according to one of claims 1 to 5, characterized in that the at least one pitch change between adjacent displacement elements (10, 12) is discontinuous (erratic).

7. Vacuum pump screw rotor according to one of claims 1 to 6, characterized in that the profile of the suction-side displacement element (10) is at least biasiochfrei formed on one of the flanks.

8. Vacuum pump screw rotor according to one of claims 1 to 7, characterized in that between two displacement elements (10, 12) is provided on the pitch change a tool outlet.

9. Vacuum pump screw rotor according to one of claims 1 to 8, characterized in that between two displacement elements (10, 12) on the pitch change a defect in at least one of the flanks of the displacement element (10, 12) is provided.

10. Vacuum pump screw rotor according to one of claims 1 to 9, characterized in that the entire vacuum pump screw rotor made of aluminum or an aluminum alloy, in particular AISil7Cu4Mg is made.

11. Vacuum pump screw rotor according to one of claims 1 to 10, characterized in that the aluminum has a lower coefficient of expansion, in particular less than 18 * 10 ^{~ 6} 1 / K and in particular a high silicon content of at least 15% is provided.

12. Screw vacuum pump, with two intermeshing screw rotors according to one of claims 1 to 11, a surrounding the screw rotors housing (22), and connected to one of the two screw rotors drive direction.

13. Screw vacuum pump according to claim 12, characterized in that the internal compression of the screw vacuum pump is at least 2, in particular at least 4.

14. Screw vacuum pump according to claim 12 or 13, characterized in that the screw rotors have a lower coefficient of expansion than the housing (22), wherein the expansion coefficient of the housing (22) in particular at least 5% and more preferably at least 10% greater than that of the screw rotors ,

15. Screw vacuum pump according to one of claims 12 to 14, characterized in that the housing (22) is made of aluminum or an aluminum alloy.

16 screw vacuum pump according to one of claims 12 to 15, characterized in that a gap between the pressure-side displacement elements and the housing having a height of 0.05 mm to 0.5 mm, preferably 0.1 mm to 0.3 mm ,

17. A method for producing a screw rotor according to one of claims 1 to 11, comprising the steps of:

Providing a basic body of the screw rotor, producing a helical recess of a first displacement element by means of a form milling cutter or a grinding wheel, and

Producing a further helical recess of a further displacement element by means of another form milling cutter or grinding wheel.

18. The method according to claim 17, characterized in that the production of displacement elements with symmetrical profile is carried out with a single tool, in particular in a single operation.

19. The method according to claim 17 or 18, characterized in that between adjacent displacement elements before the preparation of the helical recesses a particular cylindrical annular recess is produced as a tool outlet.

20. The method according to any one of claims 17 to 19, characterized in that between two adjacent displacement elements for leading out the tool in at least one flank, a recess is formed.

21. The method according to any one of claims 17 to 20, characterized in that each displacement element for producing the helical - I l ^¬ gen recess a the outer contour of the helical Ausneh tion mapping tool is used.

Method according to one of claims 17 to 21, characterized in that the base body is cylindrical.

23. The method according to any one of claims 17 to 22, characterized in that the base body is formed as a semi-finished with already partially preformed recess and / or journals.