SCREW ROTOR

Abstract

A screw rotor for screw vacuum pumps, comprising a rotor shaft which bears at least two displacement elements. The displacement element is conical in the conveying direction and the adjoining conveying element has a cylindrical design.

Claims

1. Screw rotor for screw vacuum pumps, comprising a rotor shaft, at least two displacement elements connected with the rotor shaft, each having at least one helical recess, wherein a suction-side displacement element is designed tapering in the conveying direction, wherein a pressure-side displacement element is designed substantially cylindrically.

2. Screw rotor of claim 1, wherein the suction-side displacement element is designed to constantly decrease in the conveying direction.

3. Screw rotor of claim 1, wherein the interior volume ratio is greater than 8.

4. Screw rotor of claim 1, wherein the displacement element have substantially the same diameter at the end faces directed towards each other.

5. Screw rotor of claim 1, wherein the diameter of the substantially cylindrical displacement element is smaller by 5-35% than the suction-side diameter of the conical displacement element.

6. Screw rotor of claim 1, wherein the tapering displacement element has a volume ratio greater than 4.

7. Screw rotor of claim 1, wherein the at least cylindrical displacement element has a volume ratio of 1 to 3.

8. Screw rotor of claim 1, wherein the diameter of the tapering displacement element is 80 to 300 mm in the region of the pump inlet.

9. Screw rotor of claim 1, wherein the diameter of the tapering displacement element is 65 to 180 mm in the transition region to the cylindrical displacement element.

10. Screw rotor of claim 1, wherein the diameter of the substantially cylindrical displacement element is 65 to 180 mm in the region of the outlet.

11. Screw rotor of claim 1, wherein the number of windings of the cylindrical displacement element is greater than 6.

12. Screw rotor of claim 1, wherein the number of windings of the tapering displacement element is 3 to 6.

13. Screw rotor of claim 1, wherein a further displacement element is provided that is arranged upstream of the tapering displacement element in the flow direction, the further displacement element being preferably substantially cylindrical in shape.

14. Screw vacuum pump with a housing defining a suction chamber and two screw rotors of claim 1 arranged in the suction chamber.

15. Screw rotor of claim 5, wherein the diameter of the substantially cylindrical displacement element is smaller by 10-25% than the suction-side diameter of the conical displacement element.

16. Screw rotor of claim 6, wherein the tapering displacement element has a volume ratio greater than 8.

17. Screw rotor of claim 11, wherein the number of windings of the cylindrical displacement element is greater than 10.

18. Screw rotor of claim 17, wherein the number of windings of the cylindrical displacement element is greater than 2.

19. Screw rotor of claim 3, wherein the interior volume ratio is greater than 10.

20. Screw rotor of claim 19, wherein the interior volume ratio is greater than 12.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The FIGURE is a schematic side view of an embodiment of a screw rotor according to the disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0033] The screw rotor illustrated comprises a rotor shaft 10 supporting two displacement elements 12, 14. The two cylindrical ends 16, 18 of the rotor shaft serve to receive bearings for supporting the screw rotor in a pump housing. It is also possible to support the rotor shaft in an overhung manner, i.e. on one side.

[0034] The displacement element 12 on the right in the FIGURE is conical and tapers in the conveying direction 22 from a pump inlet 20 which is arranged on the right in the FIGURE but not illustrated therein, towards a pump outlet 24 which is arranged on the left in the FIGURE but not illustrated therein. A helical recess 26 of the conical displacement element 12 is designed such that the volume decreases. This is achieved on the one hand due to the conical outer shape of the displacement element 12 and on the other hand due to the inner portion 28 of the displacement element 12 widening in the conveying direction. Individual chamber volumes formed by the two meshing screw rotors thus reduce their respective volume in the conveying direction 22.

[0035] In the embodiment illustrated in which only two displacement elements 12, 14 are provided, an end face 30 of the displacement element 12 which is directed towards the pump outlet 24 or towards the pressure side of the pump, abuts on an end face 32 of the cylindrical displacement element 14. The end face 32 is directed towards the pump inlet or in the direction of the suction side of the vacuum pump. The diameters of the two displacement elements 12, 14 are substantially the same in the region of the end faces 30, 32.

[0036] The cylindrical displacement element 14 has a helical recess 34 as well.

[0037] In the embodiment illustrated the same has a constant pitch, wherein a decrease in pitch is also possible in the conveying direction 22 for further compression. Due to the recess 34 8 windings are formed in the embodiment illustrated.