EP2867532B1 - Screw pump - Google Patents

Description

The invention relates to a screw pump with two screws. Each screw is provided with a first thread and a second thread, the threads each extending from a suction side to a pressure side. The threads are engaged with each other so that the threads are divided into a plurality of working chambers. The volume of the working chambers decreases from the suction side to the pressure side.

Screw pumps of this type can be used to generate a vacuum. The room to be evacuated is connected to the suction side of the pump so that the pump can suck gas out of the room. The gas is compressed in the pump and released on the pressure side at higher pressure. Screw pumps of this type are from the writings EP 1 070 848 A1 . DE 197 48 385 A1 and DE 195 22 559 A1 known.

These screw pumps have a number of advantageous properties and are therefore widely used. However, in comparison with other pumps, the suction power, ie the ability to remove a large volume of gas from a room within a short period of time, is limited. For applications where this is required, Screw pumps are due to their lack of suction so far regularly out of the question. Instead, become other types of pumps used such as Roots pumps.

The invention is based on the object to introduce a screw pump with increased suction power. Based on the above-mentioned prior art, the object is achieved with the features of claim 1. Advantageous embodiments can be found in the subclaims.

According to the invention, the threads each have two threads. The threads are preferably symmetrical to each other in the radial direction. The threads then have a point symmetry such that the threads can be imaged by themselves in a rotation about the screw axis by 180 °.

The invention has recognized that the limited suction power is due, inter alia, to the fact that conventional screw pumps can not be operated at any desired high speed. A limitation of the rotational speed results from the fact that conventional screws have an uneven mass distribution with respect to the screw axis. The uneven mass distribution causes an imbalance that is difficult to control at high speeds. The distribution of masses is uneven because, in the case of the normal (catchy) threads of conventional screw pumps, the thread pitch already ensures asymmetric mass distribution.

With the invention it is proposed to design the thread of the screws zweigängig. This means that each thread has two threads, which are entangled with each other so that they together form a shape according to Art form a double helix. The double-threaded threads are preferably each designed so that there is a symmetrical with respect to the screw axis design. For each outwardly projecting element of the one thread there is therefore a corresponding element of the other thread, which lies in radial direction with respect to the screw axis. Due to the more uniform mass distribution of the double-flighted thread compared to single-start threads, it becomes possible to operate the screw pump at a higher speed, so that the suction power increases.

For operation at high speeds, it is desirable to keep the forces as low as possible not only in the radial direction but also in the longitudinal direction. For this purpose, the pump is preferably designed so that the two threads of a screw work in the opposite direction. The forces exerted by one thread in the longitudinal direction are then compensated by the other thread. Preferably, the threads are aligned so that the suction side in the center of the screw, that is arranged between the two threads. The pressure sides are then formed by the outer ends of the threads, which has the particular advantage that the drive elements and bearings are exposed to the higher outlet pressure. The screw may also be designed so that it also has a symmetrical shape in the longitudinal direction, considering the trapped between the two outer ends of the threaded portion of the screw.

The pump according to the invention comprises a housing in which the two screws are accommodated. In the area of the suction side, the housing is provided with an inlet opening, in the area There is an outlet opening on the pressure side. It has been shown that it is important for a high suction power of the pump to make the inlet opening and the suction side of the pump so that a high volume flow can enter the pump.

The housing according to the invention is designed so that it has a first housing portion and a second housing portion in the region of a thread, wherein in the first housing portion, a suction gap between the housing and the thread, and wherein the housing terminates in the second housing portion with the thread. The fact that the housing terminates with the thread is to be understood so that the leakage gap which necessarily exists between the housing and the thread in the case of dry running pumps is as small as possible (minimum radial distance). The aim today is a value of less than 0.2 mm, preferably about 0.1 mm for the radial minimum distance. Since the two screws of the pump engage each other, the housing in the first housing portion does not close over the entire circumference of the screw with the thread, but only in the peripheral portion in which there is no engagement with the other screw. The second housing section preferably connects to the pressure side of the thread.

In the region of the first housing section, which preferably adjoins the suction side of the thread, the inlet opening of the housing is also regularly arranged. The screw is then surrounded only in the peripheral portion of the housing, which still remains next to the inlet opening and the second screw. If there is a suction gap between the housing and the thread in the first housing section, it is to be understood that in at least one Part of this peripheral portion is a radial distance between the thread and the housing, which is greater than the radial minimum distance. Preferably, the radial distance in the region of the suction gap is at least a factor of 50, preferably a factor of 100, more preferably a factor of 200, greater than the radial minimum distance.

The suction gap has the effect that the sucked gas can not only enter the working chambers in the radial direction, but can also move through the suction gap from one working chamber into the next working chamber. By providing the gas with an additional path into the working chamber, the working chamber can fill faster, which has a positive effect on the suction power.

The larger the suction gap, the more gas can enter this way in the working chambers. Preferably, the suction gap extends adjacent to the input opening in the circumferential direction over at least 10%, preferably at least 20%, more preferably at least 30% of the peripheral portion with which the housing surrounds the screw in the second housing section. In the region in which there is no longer any overlap between the suction gap and the inlet opening, the suction gap can extend over a correspondingly larger peripheral portion of, for example, at least 50%.

In the longitudinal direction, the suction gap preferably extends over at least 20%, more preferably over at least 30%, more preferably over at least 40% of the length of the thread. Accordingly, the second housing portion is significantly shorter than the length of the thread and extends For example, not more than 80%, preferably not more than 70%, more preferably not more than 60% of the length of the thread. In contrast to conventional pumps thus serves a comparatively long portion of the thread for filling the working chambers, while the portion in which the compression takes place, in which thus completes the housing with the thread, is relatively short. The extent of the suction gap in the longitudinal direction may substantially correspond to the screw portion occupied by the first 360 ° turn of the thread. The thread therefore has a large pitch in the inlet area. Preferably, the first 360 ° turn, viewed from the suction side, assumes at least 20%, preferably at least 30%, more preferably at least 40%, of the length of the thread. Overall, each thread of the double-threaded thread preferably comprises at least three, more preferably at least four full 360 ° windings.

Between the first housing portion and the second housing portion and thus at the transition from the suction gap to the region in which the housing terminates with the thread, a transition edge may be formed. Once the thread terminates with the transition edge, the working chamber is closed and the actual compression begins. If the transition edge were aligned parallel to the thread through which the termination occurs, the chamber would be closed abruptly. This would be good for the efficiency of the pump, but also increases the noise level. Preferably, the transition edge is therefore oriented to include an angle with the circumferential direction corresponding to the thread pitch, the angle being smaller than the thread pitch.

In order to be able to suck in large volumes, it is also advantageous if the housing is provided with a large inlet opening. For example, the entrance opening may be greater than 60%, preferably 80%, more preferably 100% of the cross-sectional area of the screw. The cross-sectional area of the screw indicates the contour defined by the screw. Based on this contour, which is regularly cylindrical, the radial distances between the thread and the housing can be determined.

In order to further improve the filling of the working chambers, a distance between the inner ends of the two threads of a screw can be provided. As a result, additional space is gained through which the gas can also enter the working chambers in the longitudinal direction.

The printed pages are regularly formed by the outer end of the threads, which means that the printed pages are spaced apart. Preferably, a conduit is provided which extends from the pressure side to an outlet opening of the pump. In an advantageous embodiment, the line is a bore which is formed between the two screws of the pump in the pump housing, wherein the bore is further preferably at least partially disposed within a resting on both screws tangential surface.

The pump can be designed so that the two screws can be released together with the drive as a unit from the pump housing. This offers the possibility to install the pump firmly in a larger system, wherein in particular the inlet opening and the outlet opening of the pump housing can be firmly connected to corresponding piping of the plant. When maintenance or repair becomes necessary, the connections between the pump housing and the system remain and only the screw and drive unit is released from the pump housing and replaced with another unit. This avoids long downtime during maintenance and repair.

Preferably, for this purpose, the screws are each provided at their end remote from the drive with a bearing which is slidably received in a bearing receptacle of the pump housing. When the unit of screws and drive is pulled out of the pump housing, the bearing is released from the bearing mount and is removed with it out of the pump housing.

The pump according to the invention is preferably dimensioned so that it reaches an intake capacity of more than 5000 m ³ / h and thereby can compress the gas from 1 mbar to 100 mbar. For this purpose, the diameter of the screws is preferably greater than 20 cm. The pump can be designed for operation at a speed of more than 10,000 rpm.

By combining a high suction power with a large compression, the screw pump according to the invention opens up applications that were previously inaccessible to the screw pumps. In order to generate a vacuum with a low pressure at a simultaneously large volume flow, a pump arrangement of two pumps connected in series is usually used, wherein the first Pump is commonly referred to as a booster pump and the subsequent pump as a backing pump. The series connection of two pumps is therefore expedient because, according to the gas law (pressure * volume = constant, assuming constant temperature), the backing pump can be designed for a much smaller volume flow than the booster pump.

Due to the greatly increased suction power compared to conventional screw pumps, it is possible to use the screw pump according to the invention as a booster pump. The invention accordingly relates to a pump arrangement comprising a booster pump and a fore pump in which the booster pump is a screw pump according to the invention. A pump arrangement in which a screw pump is used as a booster pump, has independent inventive content, even without the threads of the screws are formed zweigängig.

In comparison with Roots pumps, which are usually used as a booster pump, the screw pump according to the invention provides a considerably higher compression. Considering a stationary operating state of the pump arrangement, in which the booster pump can suck in substantially the maximum possible volume flow and the pressure is kept constant at a low value of, for example, less than 1 mbar, classical single-stage Roots pumps only provide a compression by a factor of 10. The volume flow through the subsequent backing pump is therefore according to the gas law only by a factor of 10 smaller than the volume flow through the booster pump.

The screw pump according to the invention provides in the stationary operating state, in which substantially the maximum possible volume is sucked in and the pressure is kept constant below 1 mbar, a compression by at least a factor of 50 or even a factor of 100. This results in completely new possibilities in the design of the pump assembly. Thus, in the steady-state operating state described, the volume flow through the backing pump can be smaller by at least a factor of 50, preferably at least 100, than the volume flow through the booster pump. The volume flow at the inlet of the booster pump in the stationary operating state is preferably greater than 1000 m ³ / h, more preferably greater than 5000 m ³ / h.

The use of the screw pump according to the invention as a booster pump also opens the possibility to use a liquid ring vacuum pump as a fore pump. Liquid ring vacuum pumps are not suitable for pressures below the vapor pressure of the working fluid. In general, therefore, these pumps can not be used for pressures below 30 mbar. The screw pump according to the invention comes to an outlet pressure of more than 30 mbar, even if the inlet pressure is below 1 mbar. The invention thus makes it possible to use a liquid ring vacuum pump as the fore pump.

Also described is a screw for such a screw pump. The screw comprises two threads each extending from a suction side to a pressure side. The threads each have two threads, with the threads preferably in the radial direction are symmetrical to each other. The screw can be developed with further features which are described with reference to the pump according to the invention.

Fig. 1:

eine perspektivische, teilweise weggebrochene Darstellung einer erfindungsgemäßen Schraubenpumpe;

Fig. 2:

einen Ausschnitt der Pumpe aus Fig. 1 in vergrößerter Darstellung;

Fig. 3:

die Ansicht aus Fig. 2 in einem anderen Zustand der Pumpe;

Fig. 4:

eine schematische Querschnittsansicht einer erfindungsgemäßen Schraubenpumpe entlang der Achse einer Schraube;

Fig. 5A/B:

Schnitte entlang den Linien A-A und B-B in Fig. 4;

Fig. 6:

die Ansicht aus Fig. 4 in einem anderen Zustand der Schraubenpumpe; und

Fig. 7:

ein Blockdiagramm einer erfindungsgemäßen Anordnung.

The invention will now be described by way of example with reference to the accompanying drawings with reference to an advantageous embodiment. Show it:

Fig. 1:

a perspective, partially broken away view of a screw pump according to the invention;

Fig. 2:

a section of the pump Fig. 1 in an enlarged view;

3:

the view Fig. 2 in another state of the pump;

4:

a schematic cross-sectional view of a screw pump according to the invention along the axis of a screw;

Fig. 5A / B:

Cuts along the lines AA and BB in Fig. 4 ;

Fig. 6:

the view Fig. 4 in another state of the screw pump; and

Fig. 7:

a block diagram of an inventive arrangement.

A pump according to the invention in Fig. 1 includes two screws 14 received in a pump housing 15. One of the screws 14 is visible due to the pump housing 15 is not fully shown over the entire length, while the other screw 14 is substantially hidden by the pump housing 15. The two screws 14 are in engagement with each other, which means that the thread projections of a screw 14 in the recess between two threaded projections of the other screw 14 engage.

The pump comprises a control and drive unit 16 in which an electronically controlled drive motor 17 is arranged for each of the screws 14. The electronic control of the drive motors 17 is set up so that the two screws 14 run completely synchronously with each other without the thread projections of the screws 14 touching each other. As additional security against damage to the screws 14, the two screws 14 are each equipped with a gear 18. The gears 18 are engaged with each other and cause a forced coupling of the two screws 14 in the event that the electronic synchronization of the screws 14 fails.

Each screw 14 is provided with two threads 19 so that the pump has a total of four threads 19. The threads 19 each extend from a suction side 20 in the center of the screw 14 to a pressure side 21 at the outer ends of the screw 14. The two threads of a screw 14 are oriented in opposite directions, so that they work from the suction side 20 to the pressure side 21 out ,

Each of the threads 19 comprises a first thread 22 and a second thread 23. The threads 19 are thus double-threaded in the sense that the threads 22, 23 are interlocked with each other so that together they form a double helical shape. The two threads 22, 23 are shaped so that the threads 19 are symmetrical in the radial direction. Looking at the screw 14 from the pressure side of the first thread 19 to the pressure side of second thread 19, so the screw 14 also has a longitudinal symmetry.

The threads 19 are designed so that in the region of the suction side 20, a larger volume between two adjacent thread projections is included as in the region of the pressure side 21. The volume of the working chambers, which corresponds to the trapped between the thread projections volume, thus reduced from the suction side to Pressure side, so that gas contained in the working chamber is compressed on the way from the suction side to the pressure side.

The housing 15 of the pump is provided with an inlet opening 24 which is arranged to provide access to the suction sides 20 of all four threads 19. In order to allow a large volume flow into the pump, the inlet opening 24 has a large cross-section. In the exemplary embodiment, the cross-sectional area of the inlet opening 24 is greater than the circular contour spanned by a screw 14.

In order to further improve the volume flow into the working chambers, a suction gap 25 is formed on the housing 15 of the pump, which adjoins the inlet opening 24 and follows the contour of the screw 14 in the circumferential direction. In the longitudinal direction of the suction gap 25 extends approximately over half the length of the thread 19 between the suction side 20 and the pressure side 21. In the circumferential direction, the dimension of the suction gap 25 varies with the inlet opening, the farther the inlet opening 24 extends at the relevant site to the side , the shorter is the extent of the suction gap 25 in the circumferential direction at this point. At the widest point of the inlet opening 24 extends the Suction gap 25 over a circumferential angle of about 45 °. In the region in which the inlet opening 24 no longer covers the suction gap 25, the suction gap 24 extends over a circumferential angle of approximately 120 °. The dimension of the suction gap 25 in the radial direction corresponds to the distance between the pump housing 15 and the contour of the screw 14 in this area. This distance is on the order of about 10 mm.

Due to the suction gap, the gas is not limited to entering the working chambers in the radial direction, but the gas can also move through a thread projection into the working chamber through the suction gap. The volume flow into the working chamber is thereby further increased.

Another contribution to increasing the volume flow into the working chamber is achieved in that there is a gap between the suction side 20 of the first thread 19 of a screw 14 and the suction side 20 of the second thread 19 of the screw 14. As a result, 14 space remains in the center of the screw, through which the gas can also enter in the radial direction in the working chamber.

The area in which the suction gap 25 extends (= first housing portion 26), serves to fill the working chambers. In the adjoining second housing section 27, the distance between the housing and the contour of the screw 14 is as small as is technically possible (radial minimum distance). In the second housing section, the compression takes place and leakage flow from one working chamber into the next working chamber is undesirable.

At the transition from the first housing section 26 to the second housing section 27, a transition edge 28 is formed. The transition edge 28 extends in the circumferential direction over the entire suction gap 25 and defines the transition from the suction gap 25 to the second housing portion 27, in which there is the minimum radial distance between the housing 15 and the screw 14.

The compression begins as soon as the working chamber has merged into the second housing section, as soon as the thread projection which delimits the working chamber towards the suction side has concluded with the transition edge 28. The transition edge 28 is arranged so that the termination between the thread projection and the transition edge 28 takes place at a time when the working chamber still has its maximum volume.

Viewed in the circumferential direction, the transition edge 28 includes an angle with the transverse direction, which is smaller than the pitch of the thread projection, which terminates with the transition edge 28. This ensures that the conclusion between the thread projection and the transition edge 28 is not abrupt, but extends over a short period of time. This reduces the operating noise of the pump.

The actual volume compression takes place in a short section of the thread immediately after completion of the working chamber. The subsequent further turns of the thread serve to seal and cause a thermodynamic compression.

On the pressure side 21 of the thread 19, the gas is discharged from the working chamber. Through a bore 29 in the pump housing 15, the compressed gas is brought together from the outer pressure sides 21 to a central outlet opening. The outlet opening, which is not visible in the figures, is disposed opposite the inlet opening 24. The bore 29 is like the FIGS. 2, 3 and 5 show integrated into the pump housing 15 and extends between the two screws 14, wherein the line 29 is partially disposed within a resting on both screws 14 tangential surface 35.

According to Fig. 6 the pump according to the invention is constructed so that the control and drive unit 16 together with the screws 14 forms a structural unit, which can be pulled out of the housing 15 as such. If maintenance or repair is required, the assembly can be replaced without having to dislodge the pump housing 15 from the plant environment.

At the end of the screw 14 facing away from the control and drive unit 16, a bearing 31 is arranged which sits firmly on the shaft and is slidably received in a bearing receptacle 34 of the pump housing 15. When the assembly is pulled out of the housing 15, the bearing 31 is released from the bearing receptacle 34 and is also removed from the housing 15.

An application example of a screw pump according to the invention is in Fig. 7 shown where a pump assembly of a booster pump 30 and a backing pump 33 is connected to a space to be evacuated 32. The booster pump 30 is a screw pump according to the invention, the fore pump 33 is a liquid ring vacuum pump. The pump arrangement is dimensioned so that from the space 32, a volume flow of 4000 m ³ / h can be sucked to keep the pressure in the space 32 at 0.5 mbar constant.

For this purpose, the booster pump 30, whose screws 14 have a diameter of about 25 cm, operated at a speed of about 15,000 rpm. At the output of the booster pump 30 and thus at the input of the fore pump 33 is a pressure of about 50 mbar. According to the gas law, this means for the backing pump 33 a volume flow of 400 m ³ / h. The backing pump 33 compresses this volume flow to atmospheric pressure and releases it to the environment.

Claims (13)

1. Screw pump having two screws (14), in which screw pump each screw (14) has a first thread (19) and a second thread (19), in which screw pump the threads (19) extend in each case from a suction side (20) to a delivery side (21), and in which screw pump the threads (19) are in engagement with one another, with the result that the threads (19) are divided into a plurality of working chambers, the volume of which decreases from the suction side (20) to the delivery side (21), wherein the threads (19) have two thread turns, wherein a housing (15) is provided, in which the screws (14) are received, and in that the housing (15) is designed in such a way that it has a first housing section (26) and a second housing section (27) in the region of a thread (19), there being a suction gap (25) between the housing (15) and the thread (19) in the first housing section (26), and there being a minimum radial spacing between the housing (15) and the thread (19) in the second housing section (27).
2. Screw pump according to Claim 1, wherein the screws (14) have a design which is symmetrical in the longitudinal direction if in each case that section of the screw (14) is viewed which is enclosed between the two outer ends of the threads (19).
3. Screw pump according to Claim 1 or 2, wherein the radial spacing between the housing (15) and the thread (19) in the region of the suction gap (15) is greater than the radial minimum spacing by at least the factor 50, preferably the factor 100, further preferably the factor 200.
4. Screw pump according to one of Claims 1 to 3, wherein the extent of the suction gap (15) in the circumferential direction corresponds to at least 10%, preferably at least 20%, further preferably at least 30% of the circumferential section, in which the housing (15) surrounds the screw (14) in the first housing section (26).
5. Screw pump according to one of Claims 1 to 4, wherein the extent of the suction gap (25) in the longitudinal direction corresponds to at least 20%, preferably at least 30%, further preferably at least 40% of the length of the thread (19).
6. Screw pump according to one of Claims 1 to 5, wherein a transition edge (28) is formed between the first housing section (26) and the second housing section (27).
7. Screw pump according to one of Claims 1 to 6, wherein the housing (15) is provided with an inlet opening (24), and in that the inlet opening (24) is greater than 60%, preferably 80%, further preferably 100% of the cross-sectional area of the thread (19).
8. Screw pump according to one of Claims 1 to 7, wherein the inner ends of the two threads (19) of a screw (14) are spaced apart from one another.
9. Screw pump according to one of Claims 1 to 8, wherein a line (29) is provided which extends from a delivery side (21) which is arranged on the outside to an outlet opening, the line (29) extending between the two screws (14) and being arranged at least partially within a tangential face (35) which rests on both screws (14).
10. Screw pump according to one of Claims 1 to 9, wherein it has a unit comprising the two screws (14) and the drive (16), and in that the unit is connected releasably to the pump housing (15).
11. Pump arrangement comprising a booster pump (30) and a following forepump (33), wherein the booster pump (30) is configured according to one of Claims 1 to 10.
12. Pump arrangement according to Claim 11, wherein, in a steady-state operating state, in which the booster pump (30) sucks in substantially the maximum possible volumetric flow and the pressure at the inlet of the booster pump (30) is kept constant at a value of less than 1 mbar, the volumetric flow through the forepump (33) is smaller than the volumetric flow through the booster pump (30) by at least the factor 50, preferably at least the factor 100.
13. Pump arrangement according to Claim 11 or 12, wherein the forepump (33) is a liquid ring vacuum pump.

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