Turbomolecular vacuum pump with rows of rotor blades and rows of stator blades

Abstract

The invention relates to a turbomolecular vacuum pump comprising rows of rotor blades (3) and rows of stator blades (4) that alternately engage with one another at varying angles of attack (&agr;). The aim of the invention is to improve the properties of such a pump. To this end, at least a part of the blades (1 or 2) of the rows of blades (3 or 4) that are mounted on the pressure side thickens towards the rim facing the pressure side.

Description

[0001] The present invention relates to a turbomolecular vacuum pump comprising rows of rotor blades and rows of stator blades that alternately engage with one another at varying angles of attack.

[0002] The pumping capacity in the pumping chamber of a turbomolecular pump is effected through the interaction between the rotating rotor blades and the stationary stator blades. Commonly the angles of attack of the blades become more shallow from the suction to the pressure side, and the blade increments decrease in said direction.

[0003] The effective pumping capacity Seff of the turbomolecular pump is given through

Seff=Stheo−Sback

[0004] The effective pumping capacity Seff1) is thus equal to the theoretical pumping capacity Stheo reduced by backstreaming which is unavoidable owing to the slots present (gap leakage). Backstreaming increases more and more in the direction of higher pressures. This applies in particular to light gases. With increasing molecular mass the probability for backstreaming of the pumped gases decreases. 1) Translator's note: The German text states “s” here whereas “S” would be appropriate and in line with the remaining text. Therefore a capital S has been assumed for the translation.

[0005] It is the task of the present invention to improve the pumping properties of a turbomolecular vacuum pump of the kind mentioned above.

[0006] This task is solved through the present invention in that at least a part of the blades of the rows of blades that are mounted on the pressure are designed in the area of their rim facing the pressure side such that longer covering sections with respect to the rotor (stator) blades that follow result, so that a higher density against backstreaming is effected. This results in thickening of the blades in the direction of the compression side. Such thickenings needs to be so designed that on the one hand the thickened rims of the blades on the pressure side significantly reduce any backstreaming and on the other hand the pumping cross section is restricted only slightly or to an acceptable extent. This applies to rotor and stator blades.

[0007] Especially effective with respect to the avoidance of any backstreaming are the rims on the pressure side of the thickened blades in such instances where these are located in a plane perpendicular with respect to the rotational axis of the rotor blades. Here the thickenings shall restrict the pumping cross section of the turbomolecular pump by no more than 10% (corresponding to the compression capacity of one stage).

[0008] So that the thickenings will not impair the pumping properties of the turbomolecular pump too much, it is expedient that the thickenings in the cross section through the blades in creases conically in the direction of the pressure side. Preferably the increasing thickening will commence in the direction of the pressure side only on the pressure side half of the width of the blades.

[0009] Further advantages and details of the present invention shall be explained with reference to2) drawing FIGS. 1 to 3. Depicted are in:

[0010] drawing FIG. 1 sections through some blades of a row of rotor and a row of stator blades (depicted by way of a developed view).

[0011] drawing FIGS. 2 and 3 pumping surfaces of a filling stage, said pumping surfaces being designed according to the present invention. 2) Translator's note: The German text states “ . . . anhand von in den . . . ” here whereas “ . . . anhand von den . . . ” would be appropriate. Therefore the latter has been assumed for the translation.

[0012] Depicted in drawing FIG. 1 are sectional views through blades 1, 2 of a row of rotor blades 3 and a row of stator blades 4. The angle of attack &agr; of the blades which are depicted as an example, amounts to approximately 30°. The direction of the rotor's movement, the direction of pumping action and the direction of the backstreaming flow are generally indicated by the arrows 5, 6, 7. From the arrows 8, the existence of pumping channels is apparent, these being formed by the blades 1, 2 as well as the walls of stator and rotor. The rotor axis is designated as 9.

[0013] The pressure side rims of the blades 1 and 2 are thickened on the pressure side (thickenings 10). In that the rim areas 11, 12 are located in a plane perpendicular with respect to the rotor axis 9, there result relatively large surface sections 11, 12 which oppose the backflowing gas molecules (arrow 7).

[0014] From drawing FIG. 1, two of the many embodiments for thickening 10 are apparent. At the rotor blades 1 an increase in the thickness d (conical) commences at the bottom half of the blades. It increases in a linear manner in the direction of the pumping action. In the instance of the stator blades 2 the increase in thickness d is not linear; the change in thickness also increases.

[0015] The thickenings are substantially designed on one side since such embodiments may easily be manufactured by milling. The fore-running boundary line of the rotor blades 1 depicted by way of a cross sectional view consists of two straight line sections 1′, 1″, between which there is located the point of change 14. In the instance of the stator blades 2 the rear boundary line with respect to the motion of the rotor is formed by a straight section 2′ and a curve 2″, for example.

[0016] In order to substantially maintain the pumping properties of the pumping channels (arrows 8), the thickenings shall only be implemented in halves of the blades 1, 2 on the pressure side. The angle &bgr; formed by the boundary lines 1″ and 2″ at the point of change 14 with a connecting line 15 which connects the point of change 14 to the bottom end of the in each instance opposing blades, shall preferably be greater than 90°. This measure shall ensure that the pumping cross section, given by the distance a between the blades (line section perpendicular with respect to two adjacent blades) is not restricted by the thickenings 10.

[0017] From WO 99/15793 it is known to provide between a turbomolecular pumping stage and a molecular pumping stage, a filling stage being designed as a centrifugal stage and which comprises of ridges extending substantially radially towards the outside. Filling stages of this kind modified in accordance with the present invention are depicted in drawing FIGS. 2, 3 by way of a top view.

[0018] In the drawing figures, the filling stage is designated as 21, the annular pumping channel of the molecular pump as 22, the ridges modified in accordance with the present invention as 23 and the thus created peripherally open pockets as 24. In the filling stage 21 in accordance with drawing FIG. 2, the wedge shaped ridges 23 extend radially whereas in the filling stage in accordance with drawing FIG. 3 they are inclined backwards with respect to the direction of rotation (arrow 5).

[0019] In that the width of the ridges 23 increases from outside to inside, the width of the peripherally open pockets 24 decreases towards the inside corresponding to the pumped distribution of the gas volumes. Thus both the rim surfaces of the ridges 23 which oppose the backflowing molecules and also the axial sealing surfaces increase.

[0020] The measures detailed all effect an increase in compression and pumping capacity of a turbomolecular pump, be it with or without a filling stage 21 upstream of the molecular pumping stage. This applies in particular to light gases. The surfaces which effect the pumping action in line with the present invention may be produced simply by milling, for example. The measures detailed will be especially effective when being implemented in compression areas with relatively small angles of attack &agr;(&agr;<30°).

Claims

1. Turbomolecular vacuum pump comprising rows of rotor blades (3) and rows of stator blades (4) that alternately engage with one another at varying angles of attack (&agr;), wherein at least a part of the blades (1 or 2) of the rows of blades (3 or 4) that are mounted on the pressure side thickens towards the rim facing the pressure side.

2. Pump according to claim 1, wherein rim areas (11), (12) forming the pressure side rim of the thickened blades (1, 2) in each instance are located in a plane perpendicular with respect to the rotor axis (9).

3. Pump according to claim 1 or 2, wherein the thickenings (10) of the thickened blades in the cross section through the blades (1, 2) are designed conically increasing in the direction of the pressure side.

4. Pump according to claim 3, wherein the thickenings (10) increasing in the direction of the pressure side, commence at the pressure side half of the width of the blades (1, 2).

5. Pump according to claim 3 or 4, wherein the thickenings (10) are provided on both sides or only on one side of the blades (1, 2).

6. Pump according to claim 5, wherein the thickening (10) commences at a point of change (14) and where the angle (&bgr;) formed by the pressure side section (1″, 2″) of the boundary lines (1′, 1,″; 2′, 2″) of the blades (1, 2) with a connecting line (15) which forms the point of change (14) with the bottom rim of the in each instance opposing blade, is greater than 90°.

7. Pump according to one of the above claims, wherein it is equipped with a filling stage (21) implemented by way of a radial stage.

8. Pump according to claim 7, wherein the radial stage comprises ridges (23) extending towards the outside, the width of which decreases towards the outside.