Modular eccentric screw pump

Abstract

Eccentric screw pump (1) with a rotor (7) forming a conveying screw and a stator (6) forming a screw flight, in which the rotor (7) rotates during conveying operation, wherein the stator (6) consists of multiple stator modules (P1 to Pn) arranged one behind the other along a longitudinal axis (L), each of which in turn consists of a casing tube (12) in which a stator lining (12a) is located, which forms the screw flight, wherein the stator modules (P1 to Pn) are positively connected to one another via their casing tubes (12), characterized in that two immediately successive stator modules (P1 to Pn) are connected to one another via a sleeve (19) which has a sleeve flange (20) projecting radially inwards between the stator modules (P1 to Pn) into the impact area of ​​the stator linings (12a), wherein the sleeve flange (20) beyond the inner diameter of the casing tube (12),protrudes further radially inwards and thus forms a contact surface for the stator lining (12a) of the stator modules (P2 to Pn), and the stator modules (P1 to Pn) are designed such that their stator lining (12a) is pre-tensioned against the sleeve flange (20).

Description

Modular eccentric screw pump The invention relates to an eccentric screw pump with a modularly constructed stator according to the preamble of claim 1. It further relates to a method for manufacturing such an eccentric screw pump according to the preamble of the first dependent claim and a teaching for the corresponding alignment of stator modules during the construction of such an eccentric screw pump. TECHNICAL BACKGROUND Progressive cavity pumps have a wide range of applications. They are a preferred choice, particularly where highly viscous fluids with difficult-to-control consistency and / or solids content need to be pumped. For these reasons, progressive cavity pumps are also used in mineral extraction. High delivery pressure is required in these applications, as well as in other technical uses. It is inherent in the nature of an eccentric screw pump that the rotor and stator must be longer the higher the delivery pressure that the eccentric screw pump is intended to provide. The construction of long metal rotors has long been well mastered. However, the construction of long stators still presents difficulties. The reason for this lies in the stator lining. This consists of a highly elastic material, or alternatively PTFE. It has to form a worm gear, the walls of which the rotor slides along under preload. The stator lining is manufactured by extrusion, injection molding, or a pressing process. For this purpose, a supporting casing tube is used, into which a corresponding mold core is inserted. The mold core forms the future screw thread. The space between the mold core and the casing tube is filled with the material forming the stator lining by extruding, injecting, or pressing the elastomer material into the space. After the injected melt has solidified or vulcanized, the mold core is removed. It is clear that this method of stator manufacturing becomes increasingly prone to errors and more difficult to execute the longer the stator is. The high pressure required to inject the elastomer into the space during the production of longer stators poses a particular challenge. At the same time, it is obvious that the production of stators of different lengths causes a large amount of tooling effort, since a correspondingly long mold core must be kept on hand for each desired length. As a result, the practice has already been adopted of constructing long stators in multiple sections, consisting of several stator modules. The stator modules are manufactured using existing tools. They are then joined together to form a continuous stator of the desired length. The rotor can then rotate within this stator, thereby pressurizing the fluid to be pumped across the entirety of the stator modules arranged in series to the required pressure. DE 10 2005 028 818 B3 describes a stator for a progressive cavity pump and a method for its manufacture. US 2010 316 518 A1 describes a progressive cavity pump and a progressive cavity motor. DE 602 02 873 T2 relates to a method for manufacturing a stator for a progressive cavity pump and the resulting stator. DE 10 2008 021 920 A1 describes a progressive cavity pump. US 3 912 426 A relates to an eccentric cavity fluid converter arrangement. THE UNDERLYING PROBLEM Currently, the production of a long stator from several stator modules proceeds as follows: individual stator modules are cut to length and connected to achieve the required total stator length. Attempts are made to butt-join the exposed end faces of the stator linings at the meeting ends of two consecutively arranged stator modules, or to cold-vulcanize them using a suitable additive. However, this type of connection between two adjacent stator linings is difficult to control in a reproducible manner. Firstly, there are dimensional problems. This is because it is difficult to machine the highly elastic stator lining, which tends to flex elastically during processing, with sufficient precision during cutting to ensure that the adhesive gap or the gap to be bridged by vulcanization is consistently reproducible, i.e., always approximately the same size. Secondly, the bonding or vulcanizing process itself presents a problem. Its quality depends heavily on the skill and conscientiousness of the person performing the work. Furthermore, the associated drying, curing, and reaction times make bonding or vulcanizing time-consuming. As a result, problems repeatedly arise. During pumping, the stator lining is subjected to considerable shear forces, especially where high pressure is being pumped. It is therefore not uncommon for even initially flawless adhesive or vulcanization to fail over time. In the worst-case scenario, some of the pumped fluid can gradually penetrate the gap between the casing tube and the stator lining. The fluid then advances there over time, eventually forcing the stator lining radially inwards. This can lead to the stator lining being pressed particularly hard against the rotor in that area, resulting in increased wear. In the worst case, the stator lining can even spontaneously fail due to severe local overload or collapse. An adhesive ensures a seal to the outside, but this can detach and be washed away. THE INVENTIONAL SOLUTION According to the invention, the solution is achieved using an eccentric screw pump according to the first independent claim. A progressive cavity pump is proposed, featuring a rotor forming a screw conveyor and a stator forming a screw thread. During pumping operation, the rotor rotates in such a way that its rotation creates conveying chambers running from the suction side to the discharge side. Depending on the required length, the stator consists of two to a maximum of n stator modules arranged one behind the other along a longitudinal axis of the pump. Each stator module consists of a casing tube. The inner surface of this tube carries a stator lining that forms a worm gear or a portion thereof. The stator modules are positively connected to each other via their casing tubes. The stator lining is preferably permanently bonded to the casing tube. According to the invention, two consecutive stator modules are connected to each other via a special sleeve. This sleeve has a sleeve flange that projects radially inwards between the stator modules into the joint area of ​​the stator linings. The stator modules—especially where they have been cut to length—are designed such that their stator lining rests against the sleeve flange under preload in the direction of the (stator) longitudinal axis L. Typically, the design is chosen to create a preload high enough to prevent pumped fluid from penetrating the area between the sleeve flange and the stator lining against it. This method of mechanically sealing the stator lining in the transition area between two stator modules, which preferably requires no additional adhesive or vulcanizing agent, has the advantage of being quick and reproducible to manufacture. The socket flange provides a precise, rigid sealing surface. The stator lining can be pressed against this surface in such a way that it experiences significant elastic or rubber-like compression. Whether the relevant area of ​​the stator lining was precisely machined during cutting to length is then of minor importance. The only crucial factor is that the relevant area of ​​the stator lining is cut to length in such a way that it is elastically compressed to a minimum degree across its entire contact surface with the socket flange. Any localized occurrence of higher compression is irrelevant.This significantly simplifies the process, as it eliminates the need for precise cutting of the relevant section of the stator lining. The only important factor is that the stator lining is cut to length in such a way that it is elastically compressed to a minimum degree across its entire contact surface with the sleeve flange. Because the stator lining of one preceding stator module never comes into direct contact with the stator lining of the other following module, it is impossible for unfavorable dimensional tolerances to meet and accumulate problematically. The rigid socket flange stabilizes the sealing surface and prevents unwanted warping. The static friction acting on it fixes the stator lining in the radial direction. PREFERRED DESIGN OPTIONS FOR THE INVENTION Ideally, the stator lining at the end of the stator module to be inserted into the socket is designed or prepared such that, before installation in the socket, it protrudes beyond the end face of the casing tube in the direction of the pump's longitudinal axis, preferably by at least 0.75 mm. The end face of the casing tube remains free of the stator lining during installation in the socket. As a rule, the opposite side of a stator module is not trimmed. Therefore, the vulcanized elastomer remains in front of the end face of the casing tube in the insertion direction. For larger stator modules, i.e., those with a considerable diameter, it can be advantageous to machine this other side as well. This involves cutting or turning off the elastomer in front of the end face of the casing tube, so that the stator lining only protrudes axially beyond the casing tube within the area enclosed by the casing tube. This reduces the width of the seal that must be compressed during insertion into the socket. Consequently, the forces required to press the stator module into its correct position within the socket are significantly reduced. The end face of the casing tube remains free of the stator lining in the un-sleeved state. In this way, the stator lining can not only be clamped particularly effectively and tightly against the socket flange. Furthermore, this design takes advantage of the fact that, due to its lateral expansion during clamping, the stator lining tends to penetrate the gap between the end face of the casing tube and the socket flange, becoming wedged in place. This results in a particularly reliable seal and also makes the stator lining in the area of ​​the sealing gap more resistant to the damaging effects of shear forces. Ideally, a design is chosen that ensures a gap remains between the end face of the casing tube of the respective stator module and the socket flange. This means that the insertion depth into the socket is not determined by the end face of the casing tube. This facilitates the precise alignment of the stator modules within the socket connecting them. As a result, the stator's helical thread can continue with exceptional accuracy across the joint between two stator modules. Preferably, the outer tube of a stator module has a shoulder at its end facing the socket for insertion into the socket. With a suitable socket design, this allows even long, modular stators to be provided with a completely smooth outer surface – without radial protrusions formed by the sockets, which could cause snagging. This is highly advantageous, for example, for pumps to be installed in boreholes, but also in the food industry due to improved cleanability. Ideally, the aforementioned shoulder has a shoulder that aligns with the end face of the sleeve. This means that both stator modules are inserted into the sleeve until the sleeve face contacts the shoulder. At this point, the longitudinal alignment of the stator modules is correct. Simultaneously, this ensures that the stator lining is tensioned against the sleeve flange with precisely the correct preload. Without any special intervention from the installer, this prevents excessive tension from building up, which could potentially lead to crushing of the stator lining and impair its function. Advantageously, the stator lining of a stator module has an enlarged inner diameter at its end facing the sleeve, such that the stator lining does not come into contact with the rotor in the immediate vicinity of the sealing point. This prevents the lateral expansion to which the stator lining is subjected in the vicinity of the sealing point from having a negative effect. It is important to ensure that the stator lining does not come into contact with the rotor anywhere under the influence of the lateral expansion imposed upon it, resulting in increased pressure. Preferably, the stator lining has a tapered section at its end facing the socket, forming a usually conical recess. This ensures that the stator lining has the necessary elasticity along its longitudinal axis at its end face. Ideally, the stator lining terminates in a cylindrical sealing section or a cylindrical annular extension, unless a design such as that shown in Fig. 10 has been chosen, which then results in a non-cylindrical sealing section, as shown in Fig. 10a. The dimensioning of the sealing section in the radial direction is often chosen so that the internal pressure present during pumping exerts a self-reinforcing effect on the cylindrical sealing section: Under the influence of the internal pressure in the radial direction from inside to outside, a certain transverse expansion occurs, which in turn causes the cylindrical sealing section to press even more firmly against the socket flange in the direction of the longitudinal axis L. For this purpose, the sealing section has a wall thickness in the radial direction preferably no more than 9 mm, better no more than 6.5 mm. The sealing section preferably extends more than 2.5 mm and ideally more than 4 mm in the direction of the pump's longitudinal axis. ANOTHER ASPECT OF THE INVENTION Another aspect of the invention is to provide a method by which long stators can be manufactured from stator modules in a particularly simple and safe manner. ANOTHER INVENTIONAL SOLUTION As part of a further solution according to the invention, a method for manufacturing a stator of a progressive cavity pump of the type according to the invention is proposed, which utilizes the separate production of stator modules, preferably manufactured as identical parts. Each stator module consists of a casing tube with a stator lining that is typically, or preferably, permanently attached to it. At least a portion of the finished stator tubes is subsequently cut to length. In a subsequent step, these stator modules are connected to one another by means of sockets. Two stator modules to be connected are inserted into a common socket to such a depth that their stator linings are elastically clamped (usually against the socket), thus creating a seal between the socket and the stator lining. PREFERRED FURTHER DESIGN OPTIONS OF THE INVENTION Ideally, the end face of the casing tube of a stator module to be joined is machined or turned down in such a way that the stator lining previously located in the machined section of the casing tube projects freely beyond the end face of the remaining casing tube in the direction of the pump's longitudinal axis. This makes it particularly easy to ensure that the stator lining is elastically clamped against the socket when the stator module is inserted. For this purpose, the inventive method uses a sleeve having a sleeve flange that extends radially inwards to the free end faces of the stator linings. This causes the stator linings to be clamped against the sleeve flange as they are inserted into the sleeve. Before connecting the stator parts to the sleeve, the stator lining of the stator module in question is machined or turned by cutting into its worm gear in such a way that its clear inner diameter increases, preferably continuously or in a continuous conical shape. Further design options, advantages and modes of operation will become apparent from the following description of the exemplary embodiments based on the figures. LIST OF FIGURES Fig. 1 shows the basic structure of a progressive cavity pump, here still without the modular stator structure according to the invention. Fig. 2 shows the basic structure of a single stator module for such a progressive cavity pump. Figs. 3, 3a, 4, and 5 show the structure of a longer stator for such a progressive cavity pump using individual stator modules, in exploded view. Fig. 6 shows an enlarged section of an end of a stator module prepared according to the invention and cut to the required length. Fig. 7 shows a further enlarged section from Fig. 6. Fig. 8 shows two stator modules of the type according to the invention in an assembled state. Fig. 9 shows an extreme magnification of a joint using a sleeve according to the invention. Fig. 10 shows an alternative second embodiment of the invention.Figure 10a shows how the sealing section is designed in the embodiment according to Figure 10. Figure 11 shows the pot-shaped base body of a jig for aligning the stator modules to be joined in a perspective view from an oblique front view. Figure 12 shows a side view of Figure 11. Figure 13 shows the complete jig for aligning the stator modules to be joined in a perspective view from an oblique front view. Figure 14 shows the jig according to Figure 13 in its intended application, placed on a stator module in a position where a positioning guide line can be drawn along the edge of the ruler. PREFERRED EXAMPLES OVERVIEW Fig. 1 shows the eccentric screw pump 1, which forms the basis of the invention, as a whole. The main components of such an eccentric screw pump 1 are the suction housing 2 and the pump section 3 which is in flow communication with it. The inlet 4 for the medium to be pumped is provided on the suction housing 2. The pumped medium is discharged via outlet 5 located at the end of pump section 3. The preferred design is a block construction, even though this is not mandatory under patent law. The pump motor 9 is then flanged to the suction housing 2. The pump motor 9 drives the rotor 7, which will be described in more detail below, via the usually cardan-type drive train 10. The pump section 3 is formed by the stator 6 with the rotor 7 rotating inside it. The rotor 7 is formed by a worm gear, which can be classified as a round-threaded screw. Compared to a normal screw, the rotor 7 has a larger pitch, a greater thread depth, and a smaller core diameter. The stator 6 is designed to complement the rotor 7. It forms a worm gear, but with twice the pitch length and an additional thread. This arrangement creates a series of conveying chambers 8 between the stationary stator 6 and the rotor 7, which rotates eccentrically within it. The conveying chambers 8 move continuously and without changing their shape from their inlet side, formed by the trumpet 18 at the suction housing 2, to their outlet side, i.e., to the outlet 5. This pressurizes and conveys the medium contained in the conveying chambers 8. The speed of rotation of the rotor 7 can be used to control the movement speed of the conveying chambers 8 towards the outlet side and thus the theoretical pump delivery rate. The maximum possible differential pressure of the progressive cavity pump 1 can be determined by the number of stages, i.e., the number of stator windings. For the design of a stator 6, a maximum stage pressure of 6 bar per stage is typically used as a specific value. Therefore, it is immediately obvious that the stator 6 must be correspondingly long if the progressive cavity pump 1 is to handle, for example, a differential pressure of 240 bar. Additionally, the tightness of the current contact line between rotor and stator affects the suction capability and the achievable delivery pressure of the pump. In the example of the pump shown in Fig. 1, the stator is constructed in one piece, whereas the invention differs from this with its modular design. STATOR STRUCTURE Fig. 2 provides a more detailed overview of how the stator 6 of the progressive cavity pump 1 described in Fig. 1 is constructed, in which its rotor 7 rotates. The stator consists of a casing tube 12, ideally a single piece, but possibly also in multiple parts, which in the latter case is provided with separation joints parallel to the tube's longitudinal axis. The elastic stator lining 12a is bonded or vulcanized into the casing tube 12. The elastic stator lining is typically bonded to the casing tube via an adhesion promoter. It ideally consists of an elastomer. The stator 6 is provided in its inlet area with a mostly conical extension, the so-called trumpet 18. The casing pipe 12 typically has a shoulder 13 on each of its end faces on the outer casing. The start and end flanges, designated by reference numerals 14 and 15 in Fig. 1, are placed onto the respective shoulder 13. The start and end flanges 14 and 15 are then typically clamped against each other in the direction of the pump's longitudinal axis L using a number of threaded rods or expansion bolts 30. The stator lining 12a is usually designed so that it covers the end faces of the casing tube 12 and thereby forms a sealing collar in the form of a flat gasket 16, against which the initial or final flange 14, 15 is pressed in a sealing manner in the direction of the pump longitudinal axis L. FIRST EXECUTION EXAMPLE - WITH MULTI-PART STATOR According to the invention, the stator 6 – unlike that shown in Figs. 1 and 2 – is not made of a single piece. Instead, it has a modular structure, as illustrated, for example, in Figs. 3, 3a to 5. In the embodiment shown in Figures 3, 3a to 5, the stator 6 consists of n stator modules P1 to Pn, which are generally identical. Each module consists of a casing tube 12 with the stator lining 12a inserted within it. In the present embodiment, the stator lining 12a tapers in the inlet area, forming a trumpet-shaped channel 18 that precedes the subsequent worm gear. The end face of the first stator module P1, facing the trumpet, generally remains unchanged. The same generally applies to the end face of the last stator module Pn, facing away from the trumpet 18. Otherwise, the stator modules P1 to Pn undergo post-processing so that they look as follows: On the trumpet-side end face of the stator modules P1 to Pn, the shoulder 13 is typically turned further. The machining or turning is carried out in such a way that the shoulder 13 becomes shoulder 13*. The shoulder 13 or 13a is thus designed so that – viewed along the longitudinal axis L – it projects further towards the center of the respective stator module. The quantitative length of the shoulder 13*, labeled DL in Fig. 3, depends on the individual circumstances. The technical advantages of this and the corresponding qualitative considerations will be explained in more detail later. Where no shoulder 13 is yet provided because the start and end flanges are attached in another way (not shown in the figure), the shoulder 13* is turned from a solid block. The stator modules P1 to Pn are subsequently connected using sleeves 19, as shown in Fig. 3a. Each of the sleeves 19 according to the invention has a sleeve flange 20 projecting radially inwards from the actual sleeve body, against which the respective end face of the respective stator module P1 to Pn bears. Fig. 8 shows how the connection of two immediately consecutive stator modules P1, P2, etc., using such a sleeve 19 looks. The stator modules P1 to P(n-1) according to Fig. 3, Fig. 4 are preferably cut to length on the end face facing away from their trumpet 18 such that: • the required number of turns is obtained and thus the total required length; • and that the stator winding of the preceding stator module is geometrically correctly continued by the stator winding of the immediately following stator module as soon as two stator modules are permanently connected to each other by means of a sleeve 19, taking into account the axial extension of the sleeve flange 20, which is inserted during the sleeve process and will be described in more detail below. Subsequently, the stator modules P1 to P(n-1) are also provided on their end face facing away from the trumpet 18 with a step 13* of the type described above. Figures 6 and 7 show the end face of a stator module P(nx) with 1 ≤ X < n, prepared for coupling and facing away from the respective trumpet 18, according to Figures 3 and 4. Based on this, further essential technical details of the preferred solution according to the invention can now be identified. As can be seen, the said end face of the casing tube 12 of the stator module P(nx) has been cut to length or turned down such that the stator lining 12a projects beyond the end face of the casing tube 12 by the amount Delta-L in the direction along the longitudinal axis L, cf. Fig. 7 . As can be seen further, the stator lining 12a (on the side facing away from the trumpet 18) has been turned from the center outwards so that it has an inclined, usually conical tapered section 21, see also Fig. 7. This generally means that the worm gear has been cut or partially machined to form the tapered section. The helix angle SW is roughly in the range of 30° to 50°, see Fig. 6. Ideally, it is 45°. The tapered section 21 preferably terminates at the end face in a cylindrical-ring-shaped sealing section 22, see Fig. 7. The latter has a (completely or substantially) radially constant wall thickness. Ideally, its wall thickness in the radial direction is less than 1 / 3, preferably less than 1 / 4, of the smallest radial wall thickness of the stator lining 12a in its regular, “undisturbed” area. Fig. 9 illustrates what the joining point looks like when the end face of a stator module P(nx) designed according to Fig. 6 and Fig. 7 with 1 ≤ X < n has been inserted into a sleeve 19 from one side and is thereby connected to the trumpet-side end face of the subsequent stator module inserted into the sleeve 19 from the other side. Here it can be clearly seen again how the socket 19 forms a radially inwardly projecting socket flange 20. The socket flange 20 typically projects (more than just insignificantly) beyond the inner diameter of the casing pipe 12, extending even further radially inward. The socket flange 20 forms a contact surface on one side (right side in Fig. 9) for the stator lining 12a of the pump section module P2 to Pn, which inherently overlaps the end face of the casing pipe 12 in the manner of a flat gasket 16. This flat gasket 16 is clamped between the socket flange 20 and the end face of the casing pipe 12 facing it. It thus seals, generally hermetically. In practice, it is often a decisive advantage if this flat gasket 16 is firmly clamped between the socket flange 20 and the end face of the casing pipe 12 facing it, because the stator lining 12a of the stator module P2 to Pn is subjected to shear forces during pump operation, which tend to move it out of the socket 19 in the direction of SR (thrust direction), i.e., to the right in the case of Fig. 9.Because the flat gasket 16, which is integrally formed by the stator lining 12a, is firmly clamped on this side, it is now prevented in any case that a gap or microgap may open up at some point - whereupon fluid may possibly creep into the area between the inner surface of the casing tube 12 and the outer surface of the stator lining 6 under the influence of the internal pressure. The socket flange 20 forms a contact surface for the stator lining 12a on its other side, the left side in Fig. 9. This surface previously projected beyond the end face of the casing tube 12 by the amount Delta-L in the direction along the longitudinal axis L. During the socketing process, the elastic material of the stator lining 12a is typically compressed first by the portion of the socket flange 20 that lies radially within the inner surface of the casing tube 12. This compression alone can, in many cases, result in a hermetic seal. Due to the aforementioned compression, this portion of the stator lining 12a, which protrudes by the amount Delta-L, usually also experiences transverse expansion. This preferentially results in at least a portion of the stator lining 12a, which previously protruded by the amount Delta-L, penetrating the gap between the socket flange 20 and the end face of the casing tube 12 opposite the trumpet and becoming wedged there. Thus, the stator lining 12a is also particularly securely fixed between the socket flange 20 and the end face of the casing tube 12 on this side. This is relevant in a number of practical cases, even though this is usually the less critical side from the perspective of the risk of gapping. This is because the stator lining of the stator module P1 to P(n-1) on this side tends to be subjected to shear forces during pump operation, which are more likely to drive it into the socket 19. As can be clearly seen in Fig. 9, (viewed here from right to left) the end face of the trumpet 18, the inner circumferential surface of the socket flange 20, and the inner circumferential surface of the sealing section 22 merge seamlessly or smoothly into one another. Steps or recesses where pumped fluid or its components could accumulate and later complicate the cleaning of the progressive cavity pump 1 are eliminated. This significantly simplifies, for example, batch changes or periodic cleaning in the food industry. It is also clearly visible in Fig. 9 that not only the sleeve flange 20, but above all the stator lining 12a immediately surrounding it, does not come into contact with the rotor, but maintains a distance from it, even under the influence of the transverse strain to which the stator lining 12a is subjected as a result of its tension against the sleeve flange 20. This is because the immediate contact zone between the stator lining 12a and the sleeve flange 20 is located either at the end face of the trumpet 18, which is not combed by the rotor by design, or because it is located at the end face of the tapered section 21, for which the same applies. This prevents undesirably high friction between the stator lining 12a and the rotor 7, which is destructive, from occurring as a result of lateral expansion in the area of ​​the immediate contact zone between the stator lining 12a and the sleeve flange 20. This also results in a simple but effective dimensioning rule for the tapered section 21. Its extension in the direction parallel to the longitudinal axis L must be so large that the stator lining 12a only comes into contact with the rotor 7 outside its area influenced by the transverse strain. In the design, the following further important aspect has preferably been taken into account and accordingly implemented constructively in the design of the sleeves 19 and / or the paragraphs 13*: The insertion depth into the sleeve 19 is not limited by the fact that the outermost, free end face of the respective casing tube 12 abuts against the sleeve flange 20 or that the pressure in the stator lining 12a clamped between the free end face of the casing tube 12 and the sleeve flange 20 becomes so high locally that the insertion process comes to a more or less defined end. Instead, the insertion depth is determined by the fact that the free end face of the socket sleeve 23 (see Fig. 3a) abuts the end face of the shoulder 13* of the outer pipe 12. The fact that the free end face of the socket sleeve 23 is welded to the outer pipe 12 and the end face of the shoulder 13* after the socketing process does not change the position thus predetermined. This is because the welding is done at specific points and progresses gradually in the circumferential direction. Therefore, the welding process does not alter the position already determined. Initially, the area not yet being welded maintains this position. Later, the welded and cooled area takes over this function. As announced, the length DL of the shoulder 13* must be discussed again in connection with the welding process. Reference is again made to Fig. 9. The length DL is chosen such that the shoulder of the shoulder 13* is shifted so far inwards towards the center of the stator module that the heat generated during welding, which flows partially inwards through the casing 12 into the stator lining 12a, never reaches the end face of the stator lining 12a. Should a local separation of the stator lining 12a from the casing 12 occur in the area of ​​the heat-affected zone WZ (see Fig. 9, lower left, dotted line), which is not normally intended, due to heat, this separation will be located far enough away from the end face of the stator lining or from the sealing point between the socket flange 20 and the stator lining 12a.As a result, despite the local detachment, no fluid can penetrate between the outside of the stator lining 12a and the inside of the jacket tube 12. SECOND EXAMPLE Fig. 10 shows a second embodiment of the invention, with a differently designed stator 6. This is a version in which the casing tube 12 is preferably made of aluminum. The inner surface of the casing tube 12 adopts the helical topography of the stator lining 12a. As a result, the stator lining 12a can be designed with a reduced wall thickness in the radial direction. As can be clearly seen in Fig. 10, this means that it is no longer possible to simply cut the stator modules P1 to P(n-1) to length on their side facing away from the trumpet and then connect them to the trumpet 18 of the next stator module P2 to Pn. Instead, in this embodiment, both end faces of the stator modules P2 to P(n-1) must actually be cut to length so that the desired conditions are achieved and the respective end faces of the casing tubes 12 meeting in a socket 19 have (completely or substantially) the same local internal geometries at their outermost edges, cf. Fig. 10. In some cases it will even be necessary to trim the sleeve flanges 20, i.e. to machine or turn them in the area of ​​their inner circumference so that the sleeve flanges 20 do not (not at all or only insignificantly) protrude radially inwards beyond the adjacent stator lining 12a. However, this is the only relevant difference compared to the first embodiment, so what has been said above also applies analogously to this second embodiment. THEORY ON THE ALIGNMENT OF STATOR MODULES RELATIVE TO EACH OTHER As mentioned above, it is extremely important to correctly align the stator modules P1 to Pn relative to each other before fixing the sleeves 19, specifically so that the linings 12a of the stator modules P1 to Pn form a continuous worm gear against whose inner surface the continuous rotor 7 bears with uniform pressure. If one of the stator modules P1 to Pn is not correctly aligned, its stator lining will come into contact with the continuous rotor 7 with a significantly higher pressure than the stator linings of the other stator modules (P1 to Pn). The consequence is not only a loss of efficiency but also premature wear. In order to position the stator sections easily and quickly during assembly, the teaching 24 according to the invention, shown in Fig. 11, Fig. 12, Fig. 13 to Fig. 14, is preferably used. The gauge body 25 is formed by a pot whose inner diameter is designed such that this pot can be pushed by hand (completely or at least substantially) radially free of play onto the outer circumferential surface of the casing tubes of those stator modules for whose alignment the gauge is intended. As can be seen in Fig. 13, the gauge body 25 is equipped with a worm gear 26. This is complementary to the worm gear formed by the stator lining 12a of the intended stator modules P1 to Pn. The worm gear 26 can be inserted into the worm gear of the respective stator module P1 to Pn, thereby forcing a rotational movement. The gauge body 25 is thus held (completely or at least substantially) without play in the circumferential direction relative to the outer tube 12. The gauge body 25 has at least one, preferably several, windows 27. Each window 27 is designed to visually indicate whether the gauge body 25 has been fully pushed onto the casing tube 12 of the respective stator module P1 to Pn, which generally means being pushed on until the stator lining abuts the cup base 25a. For this purpose, it is particularly advantageous if the window 27 intersects both the cup casing 25b and the cup base 25a of the gauge body 25. The pot casing 25b is equipped with at least one, preferably several, marking aids 28. These marking aids 28 are designed as flags. These flags project beyond the pot casing 25b in the direction of the stator's longitudinal axis L. They extend into a surface of the casing tube 12, which, when connected, is not covered by the socket casing 23 but preferably abuts directly against the end face of the socket 19. Each flag has only one straight edge 29 running parallel to the longitudinal axis L, which serves to guide a scriber or a pin. With the aid of this scriber or pin, a corresponding reference mark is applied to the casing tube 12 of the stator module P1 to Pn to be marked. The worm core 26 is adjusted on the pot base 25b taking into account the fact that the sheath tubes 12 of two stator modules P(nx-1) and P(nx) with (0 ≤ X < n), which are to be attached to one another by means of a sleeve 19, are separated from each other by a predetermined amount in the direction of the longitudinal axis L by the sleeve 19. The adjustment is such that the stator modules P(nx-1) and P(nx) are correctly aligned with each other when they have been inserted into the sleeve 19 in such a way that the reference marks attached to them by means of the teaching according to the invention are aligned with each other in a direction parallel to the longitudinal axis L. The doctrine also takes into account the distance of the tension. REFERENCE MARK LIST 1 Eccentric screw pump 2 Suction housing 3 Pump section 4 Inlet 5 Outlet 6 Stator 7 Rotor 8 Pumping chamber 9 Pump motor 10 Power train 11 Pressure housing 12 Jacket tube 12a Stator lining 13 Shoulder 13* Enlarged shoulder 14 Starting flange 15 End flange 16 Flat gasket formed by the stator lining 12a on the end face 17 Not assigned 18 Trumpet 19 Socket 20 Radially inward projecting socket flange 21 Tapered section 22 Sealing section 23 Socket shell 24 Positioning gauge 25 Gauge body, id R.like a pot 25a Pot bottom 25b Pot shell 26 Worm core 27 Window 28 Marking aid 29 Ruler edge 30 Expansion screw P1 First stator module P(n-1) Penultimate stator module Pn Last stator module before the outlet 5 Delta-L Amount by which the stator lining 12a projects beyond the shell tube 12 in the direction of the longitudinal axis L on a cut end face of a stator module L Longitudinal axis of the stator and rotor DL ​​Length of the shoulder 13* SW Helix angle WZ Heat-affected zone SR Shear direction (see Fig. 9 ).

Claims

Eccentric screw pump (1) with a rotor (7) forming a conveying screw and a stator (6) forming a screw flight, in which the rotor (7) rotates during conveying operation, wherein the stator (6) consists of multiple stator modules (P1 to Pn) arranged one behind the other along a longitudinal axis (L), each of which in turn consists of a casing tube (12) in which a stator lining (12a) is located, which forms the screw flight, wherein the stator modules (P1 to Pn) are positively connected to one another via their casing tubes (12), characterized in that two immediately successive stator modules (P1 to Pn) are connected to one another via a sleeve (19) which has a sleeve flange (20) projecting radially inwards between the stator modules (P1 to Pn) into the impact area of ​​the stator linings (12a), wherein the sleeve flange (20) beyond the inner diameter of the casing tube (12),protrudes further radially inwards and thus forms a contact surface for the stator lining (12a) of the stator modules (P2 to Pn), and the stator modules (P1 to Pn) are designed such that their stator lining (12a) is pre-tensioned against the sleeve flange (20). Eccentric screw pump (1) according to claim 1 , characterized in that the respective stator lining (12a) at the end of the stator module (P1 to Pn) to be inserted into the socket is designed such that, before installation in the socket, it projects beyond the end face of the casing tube (12) in the direction of the pump longitudinal axis (L), preferably by at least 0.75 mm, ideally in a range between 0.5 mm and 1.5 mm. Eccentric screw pump (1) according to claim 1 or 2, characterized in that a gap exists between the end face of the casing tube (12) of the respective stator module (P1 to Pn) and the socket flange (20). Eccentric screw pump (1) according to claim 3, characterized in that the said gap is at least partially filled by the stator lining (12a). Eccentric screw pump (1) according to one of the preceding claims, characterized in that the jacket tube (12) of a stator module (P1 to Pn) has at its end facing the socket (19) a - preferably enlarged - shoulder (13*) for insertion into the socket (19). Eccentric screw pump (1) according to claim 5, characterized in that the - preferably enlarged - shoulder (13*) has a shoulder for contact with the end face of the sleeve shell (23). Eccentric screw pump (1) according to one of the preceding claims, characterized in that the stator lining (12a) of a stator module (P1 to Pn) has a reduced inner diameter at its end facing the sleeve (19). Eccentric screw pump (1) according to claim 7, characterized in that the stator lining (12a) has a tapered section (21) at its end facing the socket (19), which forms a preferably conical recess. Eccentric screw pump (1) according to claim 8, characterized in that the stator lining (12a) forms a conical recess with a helix angle SW in the range of 30° to 50° and which ideally terminates in a preferably cylindrical sealing section (22). Eccentric screw pump (1) according to claim 8, characterized in that the sealing section (22) has a wall thickness of no more than 9 mm, preferably no more than 6.5 mm in the radial direction and that the sealing section (22) preferably has an extension of more than 2.5 mm and ideally more than 4 mm in the direction of the pump longitudinal axis (L). Method for manufacturing a stator (6) of an eccentric screw pump (1) according to claim 1, in separate manufacturing of preferably identical stator modules (P1 to Pn) to be connected to each other by sleeves (19) in a subsequent step, each consisting of a jacket tube (12) with a stator lining (12a) firmly connected thereto, characterized in that two stator modules (P1 to Pn) to be connected to each other are inserted so deeply into a common sleeve (19) that their stator linings (12a) are elastically tensioned. Method according to claim 11, characterized in that the end face of the casing tube (12) of a stator module (P1 to Pn) to be inserted into the sleeve is turned down such that the stator lining (12a) previously located in the turned-down part of the casing tube (12) projects freely beyond the end face of the casing tube (12) in the direction of the pump longitudinal axis (L). Method according to claim 11 or 12, characterized in that a sleeve (19) is used which has a sleeve flange (20) which extends radially inwards to in front of the free end faces of the stator linings (12a), so that the stator linings (12a) are clamped by their contact with the sleeve flange (20) when being inserted into the sleeve (19). Method according to one of claims 11 to 13, characterized in that the stator lining (12a) of the stator module (P1 to Pn) to be inserted into the sleeve is machined or turned down before installation in the sleeve in such a way that its clear inner diameter increases, preferably continuously or in a continuously conical manner.

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