Screw spindle pump having a stop surface axially adjacent to an end surface of a running spindle

Abstract

A screw spindle pump, including a housing and a drive spindle accommodated therein and at least one running spindle which meshes with the latter and which has in each case two terminal end surfaces. A stop surface is provided axially adjacent to at least one end surface of the running spindle, wherein the running spindle is accommodated displaceably with an axial clearance perpendicular to the stop surfaces.

Claims

1. A screw spindle pump, comprising; at least one running spindle not having a hydraulic axially just balancing; a housing and a drive spindle accommodated therein and the at least one running spindle which meshes with the latter and which has in each case two terminal end surfaces, wherein the drive spindle is hydraulically balanced so that during a pumping operation no or only a negligible axial force acts on the drive spindle, wherein a stop surface is provided axially adjacent to at least one end surface of the terminal end surfaces of the at least one running spindle, wherein the at least one running spindle is accommodated displaceably with an axial clearance perpendicular to the stop surface and is movable against the stop surface.

2. The screw spindle pump according to claim 1, wherein a stop surface is provided axially adjacent to both end surfaces of the at least one running spindle, wherein the at least one running spindle is accommodated with an axial clearance between both stop surfaces.

3. The screw spindle pump according to claim 1, wherein the axial clearance is between 0.3 and 5.0 mm.

4. The screw spindle pump according to claim 1, wherein the stop surface is formed by a coating on the housing, or wherein the stop surface is realized by a stop disk.

5. The screw spindle pump according to claim 4, wherein the coating or the stop disk consists of a ceramic or carbide material or of a hard metal or of a ceramic or carbide material-containing composite material.

6. The screw spindle pump according to claim 4, wherein the coating or the stop disk is composed of a silicon-based material of WC or of Cr.sub.2O.sub.3.

7. The screw spindle pump according to claim 4, wherein the at least one running spindle is accommodated in a running spindle bore which overlaps a drive spindle bore accommodating the drive spindle, wherein the running spindle bores are delimited axially via one or two axial housing shoulders, on which housing shoulder(s) the stop surface is formed or the stop disk is supported.

8. The screw spindle pump according to claim 1, wherein the drive spindle and the at least one running spindle are accommodated in a pump space, which, via a sealing element which seals off between the drive spindle and the housing, is sealed off with respect to a drive side of the drive spindle.

9. The screw spindle pump according to claim 8, wherein an axially pressed surface of the sealing element corresponds substantially to an axially pressed surface of the drive spindle.

10. The screw spindle pump according to claim 8, wherein the sealing element is a mechanical seal.

11. The screw spindle pump according to claim 8, wherein the sealing element is arranged on the drive spindle and seals off with respect to a sealing portion on the housing.

12. The screw spindle pump according to claim 1, wherein the drive spindle is rotatably mounted in the housing only on one side at a portion that extends outside a pump space, which pump space has the drive spindle and the at least one running spindle.

13. The screw spindle pump according to claim 12, wherein the rotatable mounting is realized via a radial bearing.

14. The screw spindle pump according to claim 1, wherein at least one running spindle bore is lined with a slide lining, wherein the at least one running spindle is arranged with a radial clearance with respect to the slide lining.

15. The screw spindle pump according to claim 14, wherein, the slide lining consists of a hydrogenated acrylonitrile butadiene rubber, chlorotrifluoroethylene, an ethylene propylene diene (monomer) rubber, polytetrafluoroethylene, a perfluoroalkoxy polymer, a fluorinated rubber or a perfluorinated rubber.

16. The screw spindle pump according to claim 14, wherein the radial clearance is between 0.01 and 1.0 mm.

17. A method for conveying viscous or pasty foodstuffs, or pharmaceutical, cosmetic or chemical media comprising utilizing the screw spindle pump according to claim 1.

18. The screw spindle pump according to claim 3, wherein the axial clearance is between 1.0 and 3.0 mm.

19. The screw spindle pump according to claim 6, wherein wherein the coating or the stop disk is composed of SiC or Si.sub.3N.sub.4.

20. The screw spindle pump according to claim 16, wherein the radial clearance is between 0.05 and 0.5 mm.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) In the Drawing:

(2) FIG. 1 shows, in a quarter section, a basic illustration of a screw spindle pump according to the invention of a first embodiment, and

(3) FIG. 2 shows, in a quarter section, a basic illustration of a screw spindle pump according to the invention of a second embodiment.

DETAILED DESCRIPTION OF THE INVENTION

(4) FIG. 1 shows, in a partial section, a screw spindle pump 1 according to the invention comprising a housing 2, which here, by way of example, consists of four housing parts 2a, 2b, 2c and 2d. The housing is therefore of modular construction. A pump space 3 with an axial access 4 and with a radial access 5 is formed in the housing interior. The conveying direction of the screw spindle pump 1 is reversible, that is to say, according to conveying direction, the access 4 can be the suction connector and the access 5 can be the pressure connector, or vice versa. Even though a radial access 5 and an axial access 4 are shown here, the access configuration may also be different, for example with two radial accesses, which may also be offset about the housing longitudinal axis.

(5) Beside the pressure space 3, the housing 2 also has a bearing space 6, in which, as will be described below, the mounting of a drive spindle is realized.

(6) The screw spindle pump 1 furthermore comprises a spindle set, comprising a centrally arranged drive spindle 7 with a drive spindle profile 8 and two running spindles 9, arranged laterally adjacently and so as to be offset from one another by 180°, with respective running spindle profiles 10, wherein the drive spindle profile 8 meshes with the running spindle profiles 10. The example shows two running spindles 9, it being alternatively also possible for only one running spindle 9 or for three running spindles 9 to be provided.

(7) The drive spindle 7 or the drive spindle profile 8 is accommodated in a corresponding drive spindle bore (not shown in more detail here) in the housing 2 or in the housing part 2b, while the two running spindles 9 are accommodated in corresponding running spindle bores 11 in the housing 2 or in the housing part 2b. The two running spindle bores 11 overlap the drive spindle bore 9 in a known manner, wherein the bores form a substantial part of the pump space 3.

(8) In the region of the two running spindle bores 11, the two housing parts 2a and 2c have corresponding housing shoulders 12, which serve as support surfaces for in each case one stop disk 13, which stop disks are axially spaced apart from one another and accommodate between them in each case one running spindle 9. Each stop disk 13 forms a stop surface for the end surface of the axially adjacent running spindle 9 or has such a stop surface. They are planar on both sides, thus bearing in a planar manner against the corresponding housing shoulders 12 as well as being surface-parallel to the corresponding planar end surfaces of the running spindles 9. Each running spindle 9 is accommodated between the two stop disks 13 with a small axial clearance, between 0.3 and 5.0 mm, in particular between 1.0 and 3.0 mm, according to the structural size of the screw spindle pump, and can thus be slightly displaced axially. The maximum axial clearance is set via the thickness of the stop disks 13 used, so that it can be minimized and the dead space there can be minimized.

(9) The stop disks 13 are for example disks composed of a ceramic material or composed of a ceramic material-containing composite material, preferably composed of a technical ceramic. Preferably, use is made of a silicon-based material, in particular SiC or Si.sub.3N.sub.4. Alternatively, each stop disk 13 may also be composed of a carbide material, for example WC. The use of stop disks 13 composed of hard metal is also conceivable. Extremely low-wear stop disks 13 are thus involved, wherein the respective running spindle 9, which is manufactured from a corresponding, for example kolsterized or cold-nitrided high-grade steel, is correspondingly wear-resistant too. Both the spindles and the housing are manufactured from a stainless high-grade steel, which is suitable in particular for use in the food industry, the medical industry, the pharmaceutical industry and the chemical industry.

(10) The drive spindle 7 is, as the partially sectional figure shows, guided out of the pump space 3 into the bearing space 6, where it is mounted via a radial bearing 14, a rolling bearing preferably in the form of a single- or multiple-row ball bearing or of a roller- or barrel-type bearing, in the housing 2. In this way, the rotational mounting of the drive spindle 7 is thus realized in a single bearing plane. A single such bearing plane is sufficient since, as will be discussed below, the drive spindle 7 is hydraulically balanced axially, the drive spindle 7 being acted on during pump operation as a consequence therefore by no or only a negligible axial force, and also however by no or only a negligible radial force as a result of the symmetrical arrangement of the two running spindles 7 on both sides, which for their part are hydraulically supported or mounted via a lubricating film, specifically both axially and radially, which will be discussed below.

(11) Furthermore, provision is made of a single sealing element 15, this preferably being a radial mechanical seal which is arranged on the drive spindle 7 and seals off with respect to a corresponding sealing seat in the housing 2. Via this one spindle seal or sealing plane, the entire pump room 3 is sealed off with respect to this side, that is to say with respect to the drive side. This means that the fluid or medium can flow only from the access 4 to the access 5, or vice versa, there being excluded a passage toward the bearing side or drive side (the actual pump drive being connected to the corresponding end-side running-spindle connecting piece 16).

(12) As described, the drive spindle 7 is hydraulically balanced axially, so that no or only a completely negligible axial force acts on the drive spindle 7. This is achieved in that, with respect to the drive spindle profile 8, the sealing element 15 is designed in a corresponding manner. The design is such that that surface of the sealing element 15 which is subjected to pressure by the medium, that is to say effectively the surface facing in the direction of the pump space 3, is substantially equal in size to the axially pressed surface of the working spindle profile 8. The axially pressed surface of the working spindle profile 8, as seen in the spindle longitudinal direction, is made up, in a known manner resulting from the meshing engagement of the working spindle profile 8 into the running spindle profiles 10, of multiple, partly sickle-shaped surface portions of the working spindle profile 7, which surface portions combine additively to form a total surface. Said total surface is then almost or, ideally, completely equal in size to that annular surface of the sealing element 15 which faces toward the pump space and is pressed axially. Any difference in surface area should be at most 10%, preferably at most 5%. The pressures acting on the respective surfaces are each directed oppositely with respect to one another, and so, since both surfaces are subjected to the same pressure, an ideally complete pressure balance is the result and accordingly the drive spindle 7 is effectively free of pressure or hydraulically balanced, so that, ideally, no or only a negligible axial force acts thereon.

(13) As a result, it is however consequently also the case that there is no mechanical transmission of force to the two running spindles from the drive spindle 7, since this is positionally fixed axially during operation. Only a working pressure-induced, small axial displacement of the running spindles 9 occurs, which leads to a small axial movement of the running spindles 9 in the running spindle bores 11 and to the corresponding end surface of the respective running spindle 9 running up against the respective stop disk 13. The two surfaces running against one another are preferably slidingly mounted hydrostatically via a thin lubricating film of the medium to be conveyed, so that, in this region, no wear occurs.

(14) For further minimization of the dead space and for improvement of the efficiency, resulting from a minimization of the medium backflow via existing gaps, the respective running spindle bore 11 is furthermore provided with a slide lining 16, this preferably being a slide lining 16 composed of a plastic such as HNBR, EPDM, PTFE, CTFE, PFA, FKM or FFKM. The thickness of the slide lining 16 is selected in such a way that only a minimal radial clearance between the respective running spindle 9, that is to say the outer lateral surface thereof, and the slide lining 16 is obtained, wherein said radial clearance should lie between 0.01 and 1.0 mm, in particular between 0.05 and 0.5 mm. This means that, here too, there is only a minimum clearance, thus allowing minimization of any backflow, which is associated with an improvement of the efficiency. Here, too, there is effectively established a corresponding medium lubricating film, via which the running spindles 9 are effectively mounted slidingly with respect to the slide lining 16, with the result that, here too, no abrasion occurs.

(15) During operation, the drive spindle 7 is driven via the drive in a known manner, said drive spindle rotating. Via the profile engagement, there necessarily occurs rotation also of the running spindles 9 and the corresponding conveyance of the medium from the access 4 to the access 5, or vice versa, that is to say from the suction connector to the pressure connector, according to the direction of rotation of the drive spindle 7. During the run-up, the two running spindles 9 are, as described, axially displaced minimally by way of the build-up of the working pressure and resulting from the minimum axial clearance within the profile engagement, and in each case run against one of the stop disks 13, where they are preferably mounted slidingly via the formed lubricating film from the medium to be conveyed. Owing to the minimum gaps, an extremely small backflow occurs, which leads to an improvement of the efficiency.

(16) The exemplary embodiment of the screw spindle pump 1 as per FIG. 2 corresponds to that from FIG. 1 in terms of basic construction. Here, too, there is provided a modular housing 2 comprising by way of example three housing parts 2a, 2b, 2c and 2d. A pump space 3 with an axial access 4 and with a radial access 5 is formed in the housing interior. Here, too, the conveying direction of the screw spindle pump 1 is reversible. Beside the pressure space 3, the housing 2 also has a bearing space 6, in which, as will be described below, the mounting of a drive spindle is realized.

(17) Here, too, the screw spindle pump 1 comprises a spindle set, having a central drive spindle 7 with a drive spindle profile 8 and two laterally adjacent running spindles 9, arranged so as to be offset from one another by 180°, with respective running spindle profiles 10, wherein the drive spindle profile 8 meshes with the running spindle profiles 10. The example shows two running spindles 9, it being alternatively also possible for only one running spindle 9 or for three running spindles 9 to be provided.

(18) The drive spindle 7 is accommodated in a corresponding drive spindle bore in the housing 2, while the two running spindles 9 are accommodated in corresponding running spindle bores 11 in the housing 2. The two running spindle bores 11 overlap the drive spindle bore 9 in a known manner, wherein the bores again form a substantial part of the pump space 3.

(19) In the region of the two running spindle bores 11, the two housing parts 2a and 2c have corresponding housing shoulders 12. The housing shoulders 12 are axially spaced apart from one another are. In each case one running spindle 9 is accommodated between them. Each housing shoulder 12 is provided with a coating 17 which forms a stop surface for the end surface of the axially adjacent running spindle 9. The coating 17 is composed for example of Si.sub.3N.sub.4, SiC, WC or Cr.sub.2O.sub.3 and is applied directly to the respective housing shoulder 12. The end surfaces of the running spindles 9 are planar, thus bearing in a planar manner with respect to or against the corresponding coatings 17 of the housing shoulders 12. Each running spindle 9 is accommodated between the two housing shoulders 12 or the low-wear coatings 17 with a small axial clearance, between 0.3 and 5.0 mm, in particular between 1.0 and 3.0 mm, according to the structural size of the screw spindle pump, and can thus be slightly displaced axially. Here, too, the running spindles 9, during operation, run against the stop surfaces, or coatings 17, and ideally are supported or slidingly mounted there via a hydraulic lubricating film. The coatings at any rate exhibit, like the running spindles themselves, extremely low wear, and so permanent operation is ensured.

(20) Thus, here, the stop surfaces are realized directly on the housing itself by means of the coatings 17. The arrangement of the separate stop disks, as in the exemplary embodiment according to FIG. 1, is not necessary here. The same advantages as those described for the exemplary embodiment according to FIG. 1 are still achieved.

(21) Otherwise, the construction of the screw spindle pump 1 shown in FIG. 2 corresponds to the example from FIG. 1, that is to say that, here too, a radial bearing 15 for mounting the drive spindle 7 is provided and at least the running spindle bores 11 are also lined with a slide lining 16. Reference is therefore made to the statements with regard to the pump from FIG. 1, these applying equally to the pump according to FIG. 2.

(22) For the case in which the screw spindle pump 1 is not reversible, only one stop disk 13, or coating 17, forming the stop surface is provided for each running spindle bore 11, specifically at the suction-side end of the respective running spindle bore, because the running spindle 9 moves by a minimal amount toward the suction side during operation.

(23) It can be seen that the screw spindle pump according to the invention has a simple design, since it manages without a device for hydraulic thrust balancing of the running spindles 7, said device being disadvantageous in the case of conveyance of foodstuffs or other hygienically sensitive media. It is rather the case that the configuration of the screw spindle pump allows it to be able to be cleaned in the assembled state, since, apart from the pump space, there are no other volumes in which the medium to be conveyed can be contained. This makes possible simple flushing of the screw spindle pump in the installed state, that is to say “cleaning in place”. The integration of the stop disks 13 allows the permissible axial clearance of the running spindles 9 to be minimized, wherein, as stated, direct disk run-up is realized, so that there is no disadvantageous dead space in this pump space region.

(24) Through the use of three spindles, specifically the drive spindle 7 and the two running spindles 9, a relatively pressure-stiff conveyance characteristic curve is made possible since the screw spindle pump 1 has a very dense profile. This allows applications with greater dosing accuracy. The dense profile also results in better suction behavior, resulting in an improvement of the efficiency. Furthermore, the screw spindle pump 1 or the spindle set is also hydraulically synchronized, that is to say is set automatically during operation, with there being no mechanical transmission of force between the drive spindle 7 and the running spindles 9.

(25) 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.