Screw pump, screw rotor, method for manufacturing screw rotor, and use of screw pump or screw rotor

Abstract

The screw pump (100) comprises a housing defining a chamber (62) and two screw rotors (10). Each screw rotor (10) comprises a rotor shaft (11) and at least two displacement elements (12, 14) connected to the rotor shaft (11). Each displacement element (12, 14) has at least one helical protrusion (36, 50). One of the displacement elements (12, 14) is a suction side displacement element (12) arranged in a suction side section (64) of the chamber (62). Another of the displacement elements (12, 14) is a pressure side displacement element (14) arranged in a pressure side section (68) of the chamber (62). The suction side displacement element (12) is designed tapered in the conveying direction (22). A gap between the pressure side displacement element (14) and the pressure side section (68) of the chamber at least partially decreases in the conveying direction (22). Further provided are a screw rotor (10), a method for manufacturing the screw rotor (10), and the use of the screw pump (100) or the screw rotor (10).

Description

[Technical Field]

[0001] The present disclosure relates to a screw pump, a screw rotor, a method for manufacturing a screw rotor, and the use of a screw pump or screw rotor. [Background technology]

[0002] Generally, dry-running vacuum pumps, such as screw vacuum pumps, consume high power when operating at low inlet pressures. This can be reduced by the pump's build-in volume ratio, which is the ratio of the swept volume of the suction stage to the swept volume of the discharge stage. The higher the volume ratio, the lower the power consumption.

[0003] Typically, a screw vacuum pump has a suction chamber in a housing, with two screw rotors disposed within the suction chamber. Each screw rotor has at least one displacement element with a helical recess formed by a helical protrusion. The helical protrusion preferably forms multiple turns. Aims at achieving as high an internal volume ratio as possible for screw vacuum pumps, particularly precision screw vacuum pumps. The internal volume ratio is the ratio of the inlet volume to the outlet volume of the vacuum pump. First-generation screw vacuum pumps, such as the Leybold Screwline or the Busch Cobra, have an internal volume ratio of approximately 3 to 4. Current commercially available vacuum pumps, such as the Leybold DRYVAC or Edwards GKS screw vacuum pumps, have a volume ratio of 5 to 7.

[0004] The basic rotor shapes for screw pumps are parallel rotors, also known as cylindrical, and tapered rotors, also known as conical. With parallel rotors, a large volume ratio results in a very small discharge stage, which is difficult to machine. Tapered rotors can be manufactured with a high geometric volume ratio because the discharge stage can be small without machining small, deep grooves. The drawback is that tapered rotors are limited in the number of small discharge stages that can be incorporated. In this case, back leakage through the gaps can cause the discharge stage to have poor compression efficiency, while compression output remains high.

[0005] To achieve low power consumption in a screw pump, two features must be realized: a high volume ratio, i.e., a small number of discharge stages, and a sufficient number of discharge stages to compensate for back leakage. One way to achieve this is with a "hybrid" rotor, which combines a tapered rotor section on the suction side of the pump with a parallel rotor section on the discharge side. Such a rotor type is described, for example, in German Utility Model No. 202017005336.

[0006] Such screw pumps can suffer from thermal problems. For example, during operation, at inlet pressures of, say, 100 to 300 mbar, galling can occur between the rotor and the housing, specifically the stator. Galling is also known as collision. On the other hand, for example, the pumping efficiency of such screw pumps is relatively low. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] German Utility Model No. 202017005336 Summary of the Invention [Problem to be solved by the invention]

[0008] The object of the present disclosure is to provide a screw pump, preferably a screw vacuum pump, a screw rotor, a method for manufacturing a screw rotor, and a use of a screw pump, preferably a screw vacuum pump, with better galling safety, in particular with additionally optimized pumping efficiency. [Means for solving the problem]

[0009] The object of the present disclosure is achieved by a screw pump as defined by claim 1, a screw rotor as defined by claim 18, a method for manufacturing a screw rotor as defined by claim 19, and a use of a screw pump or a screw rotor as defined by claim 21.

[0010] The screw pump of the present disclosure is preferably a screw vacuum pump. More preferably, the screw pump of the present disclosure is a dry-running screw vacuum pump. The screw pump includes a housing defining a chamber. Specifically, the inner wall of the chamber corresponds to the stator of the screw pump. The screw pump further includes two screw rotors. Each screw rotor includes a rotor shaft and at least two displacement elements connected to the rotor shaft. Each displacement element has at least one helical protrusion. Preferably, the helical protrusion includes a plurality of turns. Specifically, the helical protrusions form a helical recess therebetween. One of the displacement elements is a suction-side displacement element disposed in the suction-side section of the chamber. Another of the displacement elements is a pressure-side displacement element disposed in the pressure-side section of the chamber. The suction-side displacement element is designed to be tapered in the conveying direction. A gap between the pressure-side displacement element and the pressure-side section of the chamber decreases in the conveying direction. The gap is a radial gap. This pressure-side section of the chamber is specifically the pressure-side stator element. The gap between the pressure-side displacement element and the pressure-side section of the chamber decreases at least partially, preferably over the entire length between the pressure-side displacement element and the pressure-side section of the chamber. Preferably, the gap between the pressure-side displacement element and the pressure-side section of the chamber decreases at least in the inlet region of the pressure-side displacement element. The inlet region of the pressure-side displacement element is the suction-side region of the pressure-side displacement element and the pressure-side section of the chamber. The outlet region is located at the opposite side of the conveying direction. Preferably, in the outlet region, the gap between the pressure-side displacement element and the pressure-side section of the chamber is constant, specifically the same. It has been found that the inlet region, specifically the inlet section of the pressure-side displacement element and / or the inlet section of the pressure-side section of the chamber, is hot during operation, specifically the hottest in the region of the displacement element or the entire screw pump. In particular, such high temperatures are observed when the inlet pressure is 100-300 mbar. Such high temperatures can lead to thermal expansion of the pressure-side displacement element, specifically the helical protrusion.It has been found that the greatest expansion is at the inlet region of the pressure side displacement element, and therefore the present invention allows for thermal expansion to compensate for the varying clearances, thereby achieving an optimum, preferably constant, clearance during operation.

[0011] The gap between the pressure side displacement element and the pressure side section of the chamber is preferably adjusted so that an essentially uniform gap is formed between the pressure side displacement element and the pressure side section of the chamber during operation, particularly during operation in the inlet pressure range of 100-300 mbar.

[0012] Preferably, the diameter of the pressure side displacement element increases in the transport direction. Preferably, the diameter increases at least partially, preferably over the entire length of the pressure side displacement element, i.e., from the inlet to the outlet of the pressure side displacement element. Preferably, the diameter is the radial diameter of the pressure side displacement element.

[0013] Preferably, the pressure-side displacement element is designed in an inverted cone shape relative to the suction-side displacement element, and preferably, at least partially, preferably over the entire length of the pressure-side displacement element, i.e., from the inlet to the outlet of the pressure-side displacement element.

[0014] Preferably, the gap between the pressure side displacement element and the pressure side section of the chamber decreases at least partially, in particular linearly in the transport direction, over the entire length of the pressure side displacement element, i.e. from the inlet to the outlet of the pressure side displacement element.

[0015] Preferably, the radial gap between the pressure side displacement element and the pressure side section of the chamber, particularly at the inlet, is 100 μm to 500 μm, preferably 130 μm to 450 μm, more preferably 150 μm to 400 μm. Preferably, the radial gap between the pressure side displacement element and the pressure side section of the chamber decreases by 20 μm to 150 μm, particularly over the entire length of the pressure side displacement element, i.e. from the inlet to the outlet of the pressure side displacement element.

[0016] Preferably, the gap between the pressure side displacement element and the pressure side section of the chamber decreases in the transport direction by 10% to 50%, in particular by 15% to 30%, in particular over the entire length of the pressure side displacement element, i.e. from the inlet to the outlet of the pressure side displacement element.

[0017] Preferably, the diameter of at least one helical protrusion of the pressure-side displacement element increases in the transport direction, in other words, the helical protrusion preferably has a conical shape, and the diameter of the helical protrusion is preferably a radial diameter.

[0018] Preferably, the diameter of the at least one helical protrusion of the pressure side displacement element increases in the transport direction by 0.05% to 0.5%, in particular by 0.05% to 0.2%, and this increase is defined in particular over the entire length of the pressure side displacement element, i.e. from the inlet to the outlet of the pressure side displacement element.

[0019] Preferably, the diameter of the at least one helical projection of the suction side displacement element decreases in the transport direction by 3% to 40%, in particular by 5% to 30%, more particularly by 15% to 30%, in particular over the entire length of the suction side displacement element, i.e. from the inlet to the outlet of the suction side displacement element.

[0020] Preferably, the inclination of the pressure-side displacement element, particularly the conical shape, is smaller than the inclination of the suction-side displacement element, particularly the conical shape. Preferably, the inclination of the suction-side displacement element is 2 to 8°. Preferably, the inclination of the pressure-side displacement element is 0.01° to 1°, particularly 0.05° to 1°, more particularly 0.05° to 0.5°.

[0021] Instead of the diameter of the one or more helical projections of the pressure side displacement element increasing, the one or more helical projections of the pressure side displacement element can also have a constant diameter, i.e. a cylindrical shape.

[0022] Preferably, the inner diameter of the pressure-side section of the chamber decreases in the conveying direction. This pressure-side section of the chamber corresponds to the stator of the pressure-side displacement element. The reduction in the inner diameter of the pressure-side section of the chamber can be at least partially, preferably end-to-end, in a linear or curved manner.

[0023] Preferably, the internal volume ratio of the screw pump is at least 4, in particular at least 7.

[0024] Preferably, the diameter of the inner element of the suction-side displacement element increases at least partially, in particular from end to end, in the conveying direction. Preferably, the inner element increases conically. This inner element is preferably part of the rotor shaft.

[0025] Preferably, the diameter of the inner element of the pressure side displacement element is essentially constant, in other words, the inner element of the pressure side displacement element has the same diameter from end to end, and this inner element is preferably part of the rotor shaft.

[0026] Preferably, each displacement element has at least one helical recess, which is preferably formed by the helical protrusion, in particular between the turns of the helical protrusion.

[0027] Preferably, the volume of the spiral recess of the suction-side displacement element is larger than the volume of the spiral recess of the pressure-side displacement element.

[0028] Preferably, the displacement elements have substantially the same diameter at their opposing end faces.

[0029] Preferably, the diameter of the pressure side displacement element, in particular the average diameter or maximum diameter, is 5 to 35%, in particular 10 to 25%, smaller than the inlet diameter of the suction side displacement element.

[0030] Preferably, the suction side displacement element has a volume ratio of at least 4, in particular at least 7.

[0031] Preferably, the pressure side displacement element has a volume ratio of 1 to 3, in particular 1 to 1.5, more particularly 1.0001 to 1.1.

[0032] Preferably, the diameter of the pressure side displacement element is between 70 mm and 200 mm.

[0033] Preferably, the diameter of the suction side displacement element is between 80 mm and 300 mm in the region of the pump inlet.

[0034] Preferably, the diameter of the suction side displacement element is between 65 mm and 180 mm in the transition region to the pressure side displacement element, the transition region corresponding to the outlet region of the suction side displacement element.

[0035] Preferably, the diameter of the pressure side displacement element is between 65 and 180 mm in the region of the outlet of the pump and / or the outlet of the pressure side displacement element.

[0036] Preferably, the number of turns of the helical protrusion of the pressure side displacement element is at least 3, particularly at least 5, more particularly at least 8. Preferably, the number of gaps between turns of the pressure side displacement element is at least 2, particularly at least 4, more particularly at least 7.

[0037] Preferably, the number of turns of the helical protrusion of the suction side displacement element is between 3 and 6. Specifically, the number of gaps between turns of the suction side displacement element is between 2 and 5.

[0038] Preferably, a further displacement element is provided which is arranged upstream of the suction-side displacement element in the flow direction, this further displacement element preferably having a substantially cylindrical shape.

[0039] The present disclosure further discloses a screw rotor for a screw pump. Preferably, the screw rotor of the present disclosure is a screw rotor for a screw vacuum pump, more preferably a screw rotor for a dry-running screw vacuum pump. The screw rotor includes a rotor shaft and at least two displacement elements coupled to the rotor shaft. Each displacement element has at least one helical protrusion. Preferably, the helical protrusion includes a plurality of turns. One of the displacement elements is a suction-side displacement element. Another of the displacement elements is a pressure-side displacement element. The suction-side displacement element is designed to be tapered in the conveying direction. The diameter of the pressure-side displacement element increases in the conveying direction. The suction-side displacement element is preferably arranged in a suction-side section of a chamber of the screw pump. The pressure-side displacement element is preferably arranged in a pressure-side section of a chamber of the screw pump.

[0040] Preferably, the screw rotor for the screw pump comprises one or more features as defined for the screw pump above in this disclosure.

[0041] Preferably, the screw rotor for the screw pump is a screw rotor for a screw pump as defined above.

[0042] The present disclosure further discloses a method for manufacturing a screw rotor for a screw pump. Preferably, the method is for a screw vacuum pump, more preferably for a dry-running screw vacuum pump. The method includes the step of preparing a screw rotor. The prepared screw rotor includes a rotor shaft and at least two displacement elements connected to the rotor shaft. Each displacement element has at least one helical recess. Preferably, the helical protrusion includes a plurality of turns. One of the displacement elements is a suction-side displacement element. Another of the displacement elements is a pressure-side displacement element. The pressure-side displacement element is designed to be substantially cylindrical. Another step of the method includes machining the pressure-side displacement element to achieve an increasing diameter in the transport direction of the pressure-side displacement element.

[0043] Preferably, the machining is performed to achieve a pressure side displacement element having one or more features as defined above for the pressure side displacement element of the screw pump of the present disclosure.

[0044] Preferably, the machining is carried out by turning and / or milling and / or grinding.

[0045] The present disclosure further discloses a method for manufacturing a screw pump. Preferably, the method is a method for manufacturing a screw vacuum pump, more preferably a dry-running screw vacuum pump. The method includes the steps of the above-defined method for manufacturing a screw rotor for a screw pump. Another preferred step of the method is to place at least one, preferably two, screw rotors manufactured by the steps of the above-defined method for manufacturing a screw rotor for a screw pump into a pump housing.

[0046] The present disclosure further discloses the use of a screw pump as defined above for generating a vacuum, or the use of a screw rotor as defined above, in particular two of the screw rotors as defined above, in a screw pump, preferably a screw vacuum pump (100), more preferably a dry-running screw vacuum pump (100), for generating a vacuum.

[0047] The present disclosure will now be described in more detail with reference to preferred embodiments and the accompanying drawings. [Brief explanation of the drawings]

[0048] [Figure 1] 1 is a schematic side view of a prior art screw rotor. [Figure 2] 1 is a schematic cutaway side view of a portion of a prior art screw vacuum pump; [Figure 3] 1 is a schematic side view of one embodiment of a screw rotor according to the present disclosure; FIG. [Figure 4] 1 is a schematic cutaway side view of a portion of one embodiment of a screw vacuum pump according to the present disclosure; FIG. [Figure 5a] 4 is a schematic detailed side view of an embodiment based on detail section V of FIG. 3. [Figure 5b] 4 is a schematic detailed side view of an embodiment based on detail section V of FIG. 3. [Figure 6] FIG. 10 is a schematic cutaway side view of a portion of another embodiment of a screw vacuum pump according to the present disclosure. [Figure 7] 1 is a graph showing the radial clearance of a prior art screw vacuum pump. [Figure 8] 1 is a graph illustrating the radial clearance of one embodiment of a screw vacuum pump according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0049] Similar or identical components or elements are identified in the figures with the same reference numerals or variations thereof (eg, 51 and 51a-51e).

[0050] The screw rotor 10 shown in FIG. 1 preferably corresponds to the screw rotor of German Utility Model No. 202017005336. The screw rotor 10 comprises a rotor shaft 11 supporting two displacement elements 12, 14. Two cylindrical ends 16, 18 of the rotor shaft serve to receive bearings for supporting the screw rotor in the pump housing. The rotor shaft can also be supported in an overhanging manner, i.e., on one side.

[0051] The displacement element 12 on the right side of FIG. 1 is conical and tapers in a transport direction 22 from a pump inlet 20, which is located on the right side of FIG. 1 but not shown, to a pump outlet 24, which is located on the left side of FIG. 1 but not shown.

[0052] The helical recess 26 of the conical suction-side displacement element 12 is designed to reduce its volume. This is achieved, on the one hand, by the conical outer shape of the displacement element 12. The conical outer shape of the displacement element 12 is achieved by the diameter of the helical protrusion 36 of the displacement element decreasing (see also FIG. 3). On the other hand, the volume reduction is achieved by the inner part 28 of the displacement element 12 expanding in the conveying direction (see also FIG. 3). Thus, the individual chamber volumes formed by the two intermeshing screw rotors decrease in volume in the conveying direction 22.

[0053] In the illustrated embodiment with only two displacement elements 12, 14, the end face 30 of the displacement element 12 facing the pump outlet 24 or facing the pressure side of the pump abuts the end face 32 of the pressure-side displacement element 14. The end face 32 faces the pump inlet or the suction side of the vacuum pump. The diameters of the two displacement elements 12, 14 are preferably substantially the same around the end faces 30, 32.

[0054] 1, the pressure-side displacement element 14 has a cylindrical shape and a helical protrusion 36 that forms a helical recess 34.

[0055] In the illustrated embodiment, the recesses 34 form eight turns in the pressure side displacement element 14 .

[0056] FIG. 2 is a schematic cutaway side view of a portion of a screw vacuum pump 100 including the screw rotor 10 of FIG.

[0057] Only one screw rotor 10 of the screw vacuum pump 100 and a cross section of a wall 60 of the housing of the vacuum pump 100 are shown. The housing defines a chamber 62 therein.

[0058] The illustrated right section of wall 60 corresponds to suction side section 64 of chamber 62 and forms a stator for suction side displacement element 12, while the illustrated left section of wall 60 corresponds to pressure side section 68 of chamber 62 and forms a stator for pressure side displacement element 14.

[0059] The gap between the suction-side displacement element 12 and the suction-side section 64 of the chamber 62 is the distance A between the outer surface 38 of the helical protrusion 36 of the suction-side displacement element 12 and the inner surface 66 of the suction-side section 64 of the chamber 62. R Preferably, the distance A R is constant, i.e., the distance A R has the same value for the entire suction-side displacement element 12.

[0060] The gap between the pressure-side displacement element 14 and the pressure-side section 68 of the chamber 62 is constant. Therefore, the distance between the outer surface 52a of the turn 51a of the right helical protrusion 50 of the pressure-side displacement element 14 and the inner surface 70 of the suction-side section 68 of the chamber 62 is TIFF0007825698000001.tif6150 is the distance between the outer surface 52e of the turn 51e of the left helical protrusion 50 of the pressure-side displacement element 14 and the inner surface 70 of the suction-side section 68 of the chamber 62. It is the same as TIFF0007825698000002.tif6150. Preferably, the distance A R and TIFF0007825698000003.tif6150 and TIFF0007825698000004.tif6150 is the same.

[0061] In a screw pump with a screw rotor 10 as shown in Figures 1-2, when operating at low inlet pressures, compression occurs primarily in the pressure-side displacement element 14, resulting in low power consumption for the screw pump. However, when operating in the range of, for example, 100-300 mbar, compression occurs in the tapered suction-side displacement element 12, and the gas reaches atmospheric pressure before entering the pressure-side displacement element 14. The pressure-side displacement element 14 does not contribute to compression; it only transports the gas and functions as a rotating cooling fin, i.e., cooling the gas and the rotor. When operating at low inlet pressures, power consumption is low and rotor temperatures are also low. During operation, for example, at inlet pressures of 100-300 mbar, compression power is high and compression occurs in the tapered suction-side displacement element 12. This results in a high power density in this region, resulting in high rotor temperatures.

[0062] A key issue with the gap is the temperature profile of the pump 100. When operating at low inlet pressures, the high volume ratio results in low power consumption and low rotor temperatures. This results in a relatively small radial gap heat loss. However, at inlet pressures of, for example, 100-300 mbar, the compression power is high and the compression takes place in the tapered suction-side displacement element 12. This results in a high power density in this region, which in turn leads to higher rotor temperatures and a larger radial gap heat loss, particularly in the transition region between the displacement element 12 and the pressure-side displacement element 14.

[0063] The effect of changing the radial clearance due to thermal effects on the vacuum pump 100 of FIGS. 1-2 is shown in FIG.

[0064] The bottom graph of FIG. 7 shows the radial clearance over the length of the screw rotor 10.

[0065] Curve C shows the gap in the cold state. In the cold state, the gap is constant. Preferably, the gap is: TIFF0007825698000005.tif6150= TIFF0007825698000006.tif6150=A R Corresponds to.

[0066] Curve W shows the gap in the warm state, preferably at an inlet pressure of 100-300 mbar, in particular 200 mbar. In the warm state, the gap decreases along the length of the screw rotor 10 in the transport direction, thereby reaching the minimum gap in region Q. A gap bulge can be seen in this region Q. This gap reduction poses a risk of causing galling.

[0067] The radial clearance has been found to be the most critical clearance for pump performance. It needs to be as small as possible, but still allow the pump to operate safely under all conditions, including the 100-300 mbar region where the rotor reaches its maximum temperature. Therefore, the radial clearance needs to be designed for this operating region.

[0068] FIG. 3 illustrates one embodiment of a screw rotor 10 according to the present disclosure.

[0069] This embodiment is based on the screw rotor 10 of FIG.

[0070] In contrast to the screw rotor 10 of Figure 1, the screw rotor 10 of Figure 3 shows a pressure-side displacement element 14 with a helical protrusion 50 of an inverted cone shape compared to the suction-side displacement element 12. In particular, the diameter of the pressure-side displacement element 14 increases in the conveying direction 22. As shown, the diameter of the suction-side displacement element 12 in the inlet region TIFF0007825698000007.tif6150 shows the diameter of the suction-side displacement element 12 in the outlet region. Smaller than TIFF0007825698000008.tif6150. Diameter of spiral protrusion 50 TIFF0007825698000009.tif6150 is determined in the winding 51a, while the diameter of the helical protrusion 50 TIFF0007825698000010.tif6150 is determined in volume 51e.

[0071] Preferably, the diameter of the helical projection 50 of the pressure side displacement element 14 increases in the transport direction by 0.05%-0.5%, specifically by 0.05%-0.2%, specifically over the entire length of the pressure side displacement element 14, i.e., from the inlet to the outlet of the pressure side displacement element 14.

[0072] With reference to FIG. 1, the inner diameter D of the pressure-side displacement element 14 corresponds to the outer diameter of the inner element 54 of the pressure-side displacement element 14 or the diameter of the spiral recess 34. RP is preferably constant for the pressure side displacement element 14. Therefore, the diameter D RP has the same value over the entire length of the pressure-side displacement element 14 in the transport direction 22 .

[0073] 3, the inner and outer diameters of the suction-side displacement element 12 are the same as those in FIG. 1. The diameter in the inlet region of the suction-side displacement element 12 is smaller than the diameter in the outlet region of the suction-side displacement element 12. Exemplarily, the diameter in the first region on the right side of the helical protrusion 36 is TIFF0007825698000011.tif7150 is shown, which shows the diameter of the second region on the left side of the spiral protrusion 36. The outer diameter of the inner element 42 of the suction-side displacement element 12 or the inner diameter of the suction-side displacement element 12, which corresponds to the diameter of the spiral recess 26, preferably increases in the conveying direction 22. Exemplarily, the diameter in the first region to the right of the spiral recess 26 TIFF0007825698000013.tif7150 is shown, which shows the diameter of the second region on the left side of the spiral recess 26. Smaller than TIFF0007825698000014.tif7150.

[0074] 3 shows an embodiment of a screw vacuum pump 100 according to the present disclosure. The screw rotor 10 of the embodiment corresponds to the screw rotor 10 of FIG.

[0075] The right side of FIG. 3, ie the section of the suction side displacement element 12, corresponds to the embodiment of FIG.

[0076] On the left side, i.e., in the section of the pressure side displacement element 14, the diameter of the helical protrusion 50 of the pressure side displacement element 14 increases, so that the gap between the pressure side displacement element 14 and the pressure side section 68 of the chamber 62 decreases in the transport direction 22. This is because the distance between the helical protrusion 50 in the right region of the pressure side displacement element 14 and the pressure side section 68 of the chamber 62 TIFF0007825698000015.tif6150, which is the distance between the spiral protrusion 50 in the left region of the pressure-side displacement element 14 and the pressure-side section 68 of the chamber 62 Larger than TIFF0007825698000016.tif6150.

[0077] Preferably, the gap between the pressure side displacement element 14 and the pressure side section 68 of the chamber 62 decreases by 10% to 50%, particularly by 15% to 30%, in the transport direction 22. This decrease specifically defines a decrease over the entire length of the pressure side displacement element 14, i.e., from the inlet to the outlet of the pressure side displacement element 14.

[0078] FIG. 5a is a detailed side view of section V of FIG.

[0079] As indicated by the inclined reference line 58, the helical projection 50 of the pressure side displacement element 14 increases in diameter in the transport direction, where a linear increase is implemented as shown.

[0080] Left-hand diameter of 51d TIFF0007825698000017.tif7150 is the right diameter of the left-handed 51d Larger than TIFF0007825698000018.tif7150. Left-handed 51d minimum diameter TIFF0007825698000019.tif7150 is the maximum diameter of the central winding 51c Larger than TIFF0007825698000020.tif7150.

[0081] The diameter is measured between the outer surfaces 51d, 51c, 51b of the helical projection 50, whereby the opposite outer surface of the helical projection 50 is not shown in Figure 5a.

[0082] FIG. 5b shows an alternative embodiment of the pressure side displacement element 14 according to FIG. 5a.

[0083] As also implemented in Figure 5a, the right turn 51b and the central turn 51c of the helical projection 50 have a diameter that increases in the transport direction. In particular, the surfaces 52b, 52c of the turns 51b, 51c therefore have a conical shape.

[0084] However, the left-hand turn 51d of the helical protrusion 50 has a cylindrical shape and therefore a constant diameter. In this embodiment, only a portion of the helical protrusion 50 has an increasing diameter. In other words, the diameter of the helical protrusion 50 increases partially over the length of the pressure-side displacement element 14.

[0085] 6 shows another embodiment of a screw vacuum pump 100 according to the present disclosure. The screw rotor 10 of this embodiment corresponds to the screw rotor 10 of FIG.

[0086] The wall 60 of the housing of the screw vacuum pump 100 is based on the embodiment of Figure 2. However, in contrast to Figure 2, the pressure side section 68 of the chamber 62 has an inner diameter that decreases in the transport direction 22.

[0087] The gap between the pressure-side displacement element 14 and the pressure-side section 68 of the chamber 62 again decreases in the transport direction 22. The distance between the right-hand helical projection 50 and the pressure-side section 68 TIFF0007825698000021.tif6150 is the distance between the left spiral protrusion 50 and the pressure side section 68 Larger than TIFF0007825698000022.tif6150.

[0088] In the illustrated embodiment, a constant pitch is implemented for the change in diameter of the helical projection 36 and / or the helical projection 50. However, it is also possible to have a varying pitch, for example an increasing or decreasing pitch in the transport direction 22.

[0089] The embodiment shows only one screw rotor 10. The screw pump of the present disclosure preferably has a second screw rotor, preferably identical in terms of clearance to the screw rotor 10 defined herein.

[0090] The screw rotor 10 of the embodiment is a screw rotor 10 for a screw vacuum pump, preferably for a dry-running screw vacuum pump. However, the screw rotor 10 of the present disclosure, specifically the screw rotor 10 as shown in the figure, can also be a screw rotor 10 for a general screw pump. The screw pump 100 of the embodiment is a screw vacuum pump 100, preferably a dry-running screw vacuum pump 100. However, the screw pump 100 of the present disclosure, specifically the screw pump 100 as shown in the figure, can also be a general screw pump.

[0091] FIG. 8 illustrates the effect of reducing the gap between the pressure side displacement element 14 and the pressure side section 68 of the chamber 62 in accordance with the present invention.

[0092] The bottom graph of FIG. 8 shows the radial clearance over the length of the screw rotor 10 of FIG.

[0093] Curve C' shows the gap in the cold state.

[0094] The curve W' shows the gap in the warm state, preferably at an inlet pressure of 100-300 mbar, in particular 200 mbar. In the warm state, the gap decreases with respect to the length of the screw rotor 10 in the transport direction.

[0095] In contrast to the significant clearance reduction (area Q) in prior art vacuum pumps (see FIG. 7), the screw rotor 10 and / or screw vacuum pump 100 according to the present invention exhibits an essentially constant change in the clearance, specifically in the area Q'.

[0096] The risk of "galling" can therefore be reduced. On the other hand, the invention allows the radial clearance to be optimized, in particular minimized, in order to achieve optimum pump efficiency. [Explanation of symbols]

[0097] 10 screw rotor 11 rotor shaft 12. Suction side displacement element 14 Pressure side displacement element 22 Transfer direction 36 Spiral protrusion 50 Spiral protrusion 62 Chamber 64 Suction Side Section 68 Pressure Side Section 100 screw pump

Claims

1. A screw pump (100), a housing defining a chamber (62); Two screw rotors (10); Each of the screw rotors (10) comprises: rotor shaft (11) at least two displacement elements (12, 14) coupled to the rotor shaft (11), each of the displacement elements (12, 14) having at least one helical protrusion (36, 50); Equipped with one of the displacement elements (12, 14) is a suction-side displacement element (12) disposed in a suction-side section (64) of the chamber (62); Another one of the displacement elements (12, 14) is a pressure-side displacement element (14) disposed in a pressure-side section (68) of the chamber (62); the suction-side displacement element (12) is designed tapered in the transport direction (22), a gap between the pressure-side displacement element (14) and the pressure-side section (68) of the chamber at least partially decreases in the transport direction (22); A screw pump (100) in which a gap between the pressure-side displacement element (14) and the pressure-side section (68) of the chamber (62) is adjusted so that a uniform gap is formed between the pressure-side displacement element (14) and the pressure-side section (68) of the chamber (62) during operation.

2. 2. The screw pump (100) of claim 1, wherein the diameter of the pressure-side displacement element (14) increases in the conveying direction (22).

3. 2. The screw pump (100) according to claim 1, wherein the pressure-side displacement element (14) is designed in an inverted cone shape relative to the suction-side displacement element (12).

4. 2. The screw pump (100) of claim 1, wherein a gap between the pressure-side displacement element (14) and the pressure-side section (68) of the chamber (62) decreases at least partially linearly in the transport direction (22).

5. 2. The screw pump (100) of claim 1, wherein a gap between the pressure-side displacement element (14) and the pressure-side section (68) of the chamber (62) decreases by 10% to 50% in the transport direction (22).

6. 2. The screw pump (100) of claim 1, wherein a diameter of the at least one helical protrusion of the pressure-side displacement element (14) increases in the conveying direction (22).

7. 7. The screw pump (100) of claim 6, wherein the diameter of the at least one helical protrusion of the pressure-side displacement element (14) increases in the conveying direction (22) by 0.05% to 0.5%.

8. The screw pump (100) of claim 1, wherein an inner diameter of the pressure side section (68) of the chamber (62) decreases in the conveying direction (22).

9. The screw pump (100) of claim 1, wherein the screw pump (100) has an internal volume ratio of at least 4.

10. The screw pump (100) of claim 1, wherein the suction side displacement element (12) has a volume ratio of at least 4.

11. The screw pump (100) of claim 1, wherein the pressure side displacement element (14) has a volume ratio of 1 to 3.

12. 2. The screw pump (100) of claim 1, wherein the diameter of the inner element (42) of the suction-side displacement element (12) increases in the conveying direction (22).

13. 2. The screw pump (100) of claim 1, wherein the diameter of the inner element (54) of the pressure side displacement element (14) is substantially constant.

14. The screw pump (100) of claim 1, wherein each of the displacement elements (12, 14) has at least one helical recess (26, 34).

15. 15. The screw pump (100) according to claim 14, wherein the volume of the spiral recess of the suction side displacement element (12) is greater than the volume of the spiral recess of the pressure side displacement element (14).

16. 2. The screw pump (100) according to claim 1, further comprising a displacement element arranged upstream of the suction-side displacement element (12) in the conveying direction (22), the displacement element having a substantially cylindrical shape.

17. A screw rotor (10) for a screw pump (100), comprising: a rotor shaft (11); at least two displacement elements (12, 14) coupled to the rotor shaft (11), each of the displacement elements (12, 14) having at least one helical protrusion (36, 50); Equipped with One of the displacement elements (12, 14) is a suction-side displacement element (12), Another one of the displacement elements (12, 14) is a pressure side displacement element (14), the suction-side displacement element (12) is designed tapered in the conveying direction (22), the diameter of the pressure-side displacement element (14) increasing in the conveying direction (22); The pressure-side displacement element (14) is a screw rotor (10) for a screw pump (100), wherein a gap between the pressure-side displacement element (14) and a pressure-side section (68) of a chamber (62) of the screw pump (100) is adjusted so that a uniform gap is formed between the pressure-side displacement element (14) and the pressure-side section (68) of the chamber (62) during operation.

18. A method for manufacturing a screw rotor (10) for a screw pump (100), comprising the steps of: providing a screw rotor (10), the screw rotor (10) having a rotor shaft (11) and at least two displacement elements (12, 14) connected to the rotor shaft (11), each of the displacement elements (12, 14) having at least one helical recess (26, 34), one of the displacement elements (12, 14) being a suction-side displacement element (12) that is tapered in the conveying direction (22), and another of the displacement elements (12, 14) being a pressure-side displacement element (14) that is substantially cylindrical in design; machining the pressure side displacement element (14) to have an increasing diameter in said transport direction (22); adjusting the pressure side displacement element (14) so ​​that a gap between the pressure side displacement element (14) and a pressure side section (68) of a chamber (62) of the screw pump (100) is formed between the pressure side displacement element (14) and the pressure side section (68) of the chamber (62) during operation.

19. 19. The method of claim 18, wherein the machining step is performed by turning and / or milling and / or grinding.

20. Use of a screw pump (100) according to any one of claims 1 to 16 for generating a vacuum or use of a screw rotor (10) according to claim 17 in a screw pump (100) for generating a vacuum.

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