SCREW PUMP

Abstract

A screw pump, including a housing with a running bore having at least two intersecting bores, each of which receives a spindle, wherein the spindles have worm screw profiles which intermesh in portions and in operation bend in a defined bending direction under a hydraulic bending pressure, wherein each bore is configured as a slot with a longer first axis of symmetry and a shorter second axis of symmetry standing orthogonally thereto, wherein the longer first axis of symmetry runs in the bending direction.

Claims

1. A screw pump, comprising a housing with a running bore having at least two intersecting bores, each of which receives a spindle, wherein the spindles have worm screw profiles which intermesh in portions and in operation bend in a defined bending direction under a hydraulic bending pressure, wherein each bore is configured as a slot with a longer first axis of symmetry and a shorter second axis of symmetry standing orthogonally thereto, wherein the longer first axis of symmetry runs in the bending direction.

2. The screw pump according to claim 1, wherein in unloaded state, the spindles are arranged offset from the center of the first axis of symmetry.

3. The screw pump according to claim 2, wherein the spindles are positioned such that, for a defined pressure difference between a suction side and a pressure side of the pump or within a defined differential pressure range, the width of a gap between the worm screw profiles and the bore inner wall in the direction of the first axis of symmetry is greater than the width of the gap in the direction of the second axis of symmetry.

4. The screw pump according to claim 1, wherein each bore is formed from two separate intersecting single bores, the bore axes of which are offset from one another in the bending direction, or as a milled bore, or as a bore ground from a cylindrical bore.

5. The screw pump according to claim 1, wherein the two single bores extend over the entire length of the housing.

6. The screw pump according to claim 1, wherein each bore consists of two bore portions adjoining one another axially, wherein the central axes of the bore portions are angled relative to one another.

7. The screw pump according to claim 1, wherein each spindle has two axially adjacent worm screw profiles with equal and opposite pitch, provided in the region of the longitudinal center of the respective spindles.

8. The screw pump according to claim 1, wherein it is a fluid pump or a multiphase pump.

9. A housing for a screw pump according to claim 1, with a running bore having at least two intersecting bores, each of which receives a spindle, wherein the spindles have worm screw profiles which intermesh in portions and in operation of the screw pump bend in a defined bending direction under a hydraulic bending pressure, wherein each bore is configured as a slot with a longer first axis of symmetry and a shorter second axis of symmetry standing orthogonally thereto, wherein the longer first axis of symmetry runs in the bending direction.

10. The housing according to claim 9, wherein each bore is formed from two separate intersecting single bores, the bore axes of which are offset from one another in the bending direction, or as a milled bore, or as a bore ground from a cylindrical bore.

11. The housing according to claim 9, wherein the two single bores extend over the entire length of the housing.

12. The housing according to claim 9, wherein each bore consists of two bore portions adjoining one another axially, wherein the central axes of the bore portions are angled relative to one another.

13. A method for producing a housing for a screw pump according to claim 1, comprising a running bore formed from at least two intersecting bores, wherein to form each bore, either at least two separate intersecting single bores, the bore axes of which are offset from one another, are bored in a housing body, or each bore is milled with the two different axes of symmetry, or each bore is formed by grinding a cylindrical bore with the two different axes of symmetry.

14. The method according to claim 13, wherein the two single bores extend over the entire length of the housing body.

15. The method according to claim 13, wherein each bore consists of two bore portions adjoining one another axially, wherein the central axes of the bore portions are angled relative to one another, wherein to form the bore portions, two separate single bores are bored on the two mutually opposite sides of the housing body.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0023] In the drawing:

[0024] FIG. 1 a perspective view of a screw pump according to the invention in partially cut-open state,

[0025] FIG. 2 the cut-open inner housing with two spindles of the screw pump from FIG. 1,

[0026] FIG. 3 an end view of a housing from FIG. 2 showing the running bore,

[0027] FIG. 4 a general illustration of the formation of the two bores forming the running bore, each of which consists of two intersecting single bores,

[0028] FIG. 5 a general illustration of a slot-like bore and spindle arranged off-axis thereto in unloaded state,

[0029] FIG. 6 the arrangement from FIG. 5 with loaded spindle,

[0030] FIG. 7 a general illustration of a centric bore with spindle arranged off-axis according to the prior art,

[0031] FIG. 8 the arrangement from FIG. 7 with loaded spindle, and

[0032] FIG. 9 a general illustration of a screw pump or housing with two bore portions arranged at an angle to one another.

DETAILED DESCRIPTION OF THE INVENTION

[0033] FIG. 1 shows, in a partially cut-open perspective view, a double-flow screw pump 1 according to the invention comprising an external housing 2 with an inner housing 3 formed as an insert, in which two spindles 4, 5 (see FIG. 2) are arranged which serve to draw in, convey and deliver a fluid or a fluid-gas mixture. For this, on the housing side, an inlet is provided as depicted by arrow P1, via which the fluid is drawn in. The fluid is delivered under pressure via an outlet (not shown in detail) arranged at 90° in the example shown, as depicted by the arrow P2.

[0034] The two spindles 4, 5 each have two worm screw profiles 6, 7 and 8, 9 respectively, wherein the worm screw profile pairs 6, 7 and 8, 9 have mutually opposing pitches. This means that the screw pump 1 is a double-flow screw pump. In the known fashion, the worm screw profiles 6 and 8 intermesh, as do the worm screw profiles 7 and 9.

[0035] The two screw spindles 4, 5 are supported and rotationally mounted at their ends via a corresponding bearing means 10, 11 or 12, 13, wherein the bearing means 10-13 are usually plain bearings.

[0036] The two spindles 4, 5 are received in a running bore 14 which has the form of a “horizontal figure-of-eight” and is shown as a general depiction in FIG. 3. FIG. 3 shows an end view of the housing 3 looking onto the running bore 14, which extends axially straight through the housing 3.

[0037] The running bore 14 consists of two separate bores 15, 16 which intersect, forming two central shoulders 17. A spindle 4, 5 is received in each bore 15, 16 and rotates therein, wherein one spindle is the drive spindle coupled to a drive motor while the other spindle is the running spindle. In the example shown, as an example, spindle 5 is the drive spindle while spindle 4 is the trailing running spindle. The spindles 4, 5 are received in the running bore 14 or in the bores 15, 16, spaced from the adjacent bore inner wall so that they can rotate without contact. Accordingly, a gap is formed surrounding the two spindles 4, 5, which also has the form of a horizontal figure-of-eight.

[0038] According to the invention, each of the bores 15, 16 is configured as a slot, i.e. each bore 15, 16 is not a circular bore but has a longer and a shorter axis of symmetry. Naturally, the two bores 15, 16 intersect, but a defined, specific slot geometry is assigned to each bore.

[0039] FIG. 4 shows a general illustration of this. The two bores 15, 16 are shown. Each bore 15, 16 consists of two intersecting single bores 18, 19 in the case of the bore 15, and 20, 21 in the case of the bore 16. The two single bore pairs 18, 19 and 20, 21 have respective bore or central axes Z1 and Z2, which are here spaced apart from one another in a bending direction R. This bending direction R is the direction in which the respective spindle 4, 5 bends under the hydraulic bending pressure which is present in the housing 3 and results from the pressure difference between the suction side and the pressure side. This bend is admittedly minimal but still present, and results from the spindles 4, 5 being effectively supported at the ends via the bearing means 10-13. This defined bend deformation in the bending direction R now leads to the worm screw profiles 6, 7, 8, 9 slightly changing their position relative to the bore inner wall, compared with the unloaded state, so that—as will be described below—the width of the corresponding gap surrounding the respective spindle 4, 5 or the respective worm screw profile 6-9 varies.

[0040] In FIG. 4, purely for reasons of clarity, the respective single bores 18, 19 or 20, 21 are shown considerably spaced apart from one another by distance a between their central axes Z1. In fact, the distance a amounts for example to just 0.1-0.3 mm, i.e. is minimal but measurable.

[0041] This offset of the single bores 18, 19 in the bending direction R now leads to the resulting bore 15, 16 having a slot-like geometry, i.e. no longer having a circular bore form or inner wall form but a slightly elongated bore form. Each single bore 15, 16 therefore has a longer first axis of symmetry S1 which extends in the bending direction R, and a second shorter axis of symmetry S2 orthogonally thereto. The axes of symmetry S1, S2 for the bore 15 are shown, while the geometry of the bore 16 is identical. The length difference between the axes of symmetry S1 and S2 finally corresponds to the distance a between the two central axes Z1, Z2, i.e. is also approximately 0.1-0.3 mm.

[0042] As described, FIG. 4 is a purely general illustration with respective single bores 18, 19 or 20, 21 which are spaced exaggeratedly far apart from one another. As a result, in FIG. 4, a shoulder exists on the right-hand side of the bore 15 and on the left-hand side of the bore 16. This is however only marginally pronounced for the given minimal axial offset a, i.e. has a height of a few microns, and accordingly does not hinder the spindle movement or bend and also has no influence on the pump operation.

[0043] The function of this slot-like design of the bores 15, 16 in comparison with a purely centric bore (previously usual in the prior art) becomes clear when FIGS. 5 and 6 are compared with FIGS. 7 and 8. FIG. 5 in the form of a general illustration shows a slot-like bore 15 which is here shown closed for reasons of description and illustration (the following description presenting the fundamental principle naturally applies equally to the second slot-like bore 16, which supplements the bore 15 to form the running bore 14 of figure-of-eight shape). Furthermore, as a general illustration, the spindle 4 and the outer periphery of the worm screw profile 6 are shown. As FIG. 5 shows, between the inner wall 22 of the slot-like bore 15 and the outer periphery 23 of the worm screw profile 6, a peripheral gap 24 is formed which is annular in the example shown and in which the fluid to be conveyed collects during operation (in the running bore, the gap to be assigned to the respective bore 15, 16 has only a ring-segment shape, wherein the two ring segments supplement one another into the figure-of-eight form). Furthermore, the longer first axis of symmetry S1 and the shorter second axis of symmetry S2 are shown. The drawing also shows the diameter D of the spindle 4 and its longitudinal or central axis ZS. This is evidently spaced from the longitudinal center or central axis Z of the bore 15 by a distance b, against the bending direction R. This means that, as shown in FIG. 5, it is offset slightly upward from the middle of the bore 15. Distance b finally corresponds to distance a by which the two single bores 18, 19 forming the bore 15 are offset.

[0044] If now, in operation, a hydraulic bending pressure acts on the spindle 4 in the direction of the bending direction R, this bends slightly. FIG. 6 shows this operating situation, wherein here the region of maximum spindle bend is shown. Evidently, the central axis ZS of the spindle 4 and the central axis Z of the bore 15 coincide in this example. The spindle 4 thus bends slightly down in the bore 15. This means that the width B1 of the here annular gap or space 24, viewed in the direction of the first longer axis of symmetry S1 and hence in the bending direction R, is almost the same as in the unloaded state. Viewed in the direction of the second shorter axis of symmetry S2, however, the width B2 of the gap 24 is significantly narrower. The gap width changes accordingly around the periphery, or constricts from the upper and lower axis points on the first axis of symmetry S1 to the lateral axis points on the second axis of symmetry S2, which is also the case in the running bore. This results from the fact that the two single bores 18, 19 each have a bore diameter d1, d2 which is slightly smaller than the diameter which a purely centric bore would have. Such a centric bore 25, as would be provided in the prior art, is shown in dotted lines in FIG. 6. Evidently, the diameter of such a centric bore would correspond to the length of the longer first axis of symmetry S1. Viewed in the direction of the shorter second axis of symmetry S2, the comparison in FIG. 6 clearly shows that the width B2 of the gap 24 is significantly smaller compared with the situation of the centric bore 25. As a result, as FIG. 6 furthermore clearly shows, the total cross-sectional area of the gap 24 is significantly smaller in the embodiment of a slot-like bore 15 compared with the cross-sectional area in the case of a centric bore 25, which in turn leads to the possibility of a significant reduction in leakage volume, and accordingly an improvement in the delivery volume and also the efficiency of the screw pump.

[0045] FIGS. 7 and 8 show, for comparison, the arrangement of the spindle 4 in a centric bore 25, i.e. a bore with constant diameter which corresponds to the length of the first axis of symmetry S1. Here too, the central axis ZS of the spindle 4 is off-axis relative to the central axis Z of the circular centric bore 25, i.e. here too there is an axial offset against the bending direction R.

[0046] If now the spindle 4 is loaded in operation, it bends slightly, as shown in FIG. 8. Evidently, the spindle 4 then lies quasi-centrally in the centric bore 25. There is an annular peripheral gap 24 which has approximately the same width B1 over the entire periphery, i.e. the gap width which is present only at the upper and lower axis points in the embodiment according to the invention. Evidently, the cross-sectional area of the annular gap 24 shown in FIG. 8 is significantly larger than the area of the gap 24 according to FIG. 6.

[0047] The reduction in gap area according to the invention, or the reduction in the distance of the bore inner wall from the spindle viewed in the plane of the shorter second axis of symmetry S2, results from the slot-like design and the fact that this offers the possibility of creating the respective bore from two single bores, the respective individual diameters d1, d2 of which are each smaller than the diameter d of a cylindrical bore which would be suitable for receiving the spindle bend in the same fashion. This means that d1, d2<d.

[0048] Although it is described above that the respective bore 15, 16 is formed from two single bores 18, 19 or 20, 21 which are made next to one another and intersect, in principle it is also possible to form the respective bore 15, 16 by means of a milling cutter, which firstly produces a bore and secondly however can also be moved slightly in the bending direction in order to create the slot geometry. This too has a diameter which is smaller than the diameter of the drill which would form a centric bore as is usual in the prior art.

[0049] In the exemplary embodiment of the figures described above, each bore 15, 16 extends linearly through the housing 3. Alternatively, however, it is also possible to form the respective bore 15, 16 from two mutually adjoining bore portions, the central axes of which are angled slightly relative to one another in order, via this relatively angled design of the bore portions, to receive the form of the generated spindle bend. A general illustration of such an arrangement is shown in FIG. 9. This shows the example of the housing 3 and the bore 15. The latter consists of two bore portions 15a, 15b, wherein each bore portion in turn consists of two separate intersecting single bores 18a, 19a and 18b, 19b, which intersect as described above with respect to the first alternative of the invention. This means that here too, the single bores 18a, 19a or 18b, 19b are offset minimally by distance a in the bending direction. Evidently, the bore portions 15a, 15b are not aligned with one another but stand at an angle α≠180° to one another, i.e. are tilted or offset quasi-centrally in the bending direction R.

[0050] FIG. 9 furthermore shows diagrammatically the course of the central axis ZS of the spindle 4 which, because of the spindle bend, is necessarily also slightly bent. The angled position of the bore portions 15a, 15b approximately follows this course of the bending line or curved axis path, so that finally the resulting quasi-angled or kinked bore 15 is better adapted to the spindle geometry resulting from hydraulic loading.

[0051] Here too, naturally the bend and the angled position are shown significantly exaggerated for illustration purposes. In fact, the angle α amounts to only a few minutes.

[0052] Although the exemplary embodiments described, in particular in FIGS. 1-4, show a double-flow screw pump with two spindles, the invention is naturally not restricted thereto. Rather, it may also be a single-flow screw pump, wherein only one worm screw profile is provided on each spindle. In addition, more than two spindles may be provided, i.e. a central working spindle and two parallel running spindles may be provided. In principle, the slot-like design of the respective spindle bore according to the invention may be used wherever a spindle bend is created in operation because of the given hydraulic pressure conditions and must be compensated.

[0053] While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.