ES2909699T3 - Stator for an eccentric screw pump - Google Patents

Abstract

Stator (1) for an eccentric helical pump having a rotor (6), where the stator (1) has an elastically flexible coating (3) with an external surface (9), where the coating (3) is wrapped by a rigid casing (2), where an internal surface (4) of the liner (3) configures a two-pitch inclined thread as well as a pump cavity (5) expanded in the axial direction (X) limited to housing the rotor ( 6) of the eccentric helical pump, where the coating (3) of the stator (1) narrows in the axial direction (X) at least in regions, where for this an average wall thickness (W) of the coating (3) , starting from a wall thickness (WE) on the end side, which occurs in the area of a suction side (7) of the stator (1), decreases at least in regions continuously in the axial direction (X) until that a lower average wall thickness (WM) is reached, characterized in that the average wall thickness (W) of the coating (3) starting from the lower average wall thickness (WM) increases again, at least in regions, towards a pressure side (8) of the stator (1) so that towards the pressure side (8) of the stator (1) a widening (10) is configured in the lining (3).

Description

DESCRIPTION

Stator for an eccentric screw pump

The invention relates to a stator for an eccentric screw pump which has a rotor.

The generic type stators have a continuous and helical pump cavity, formed by an elastomer lining in which an eccentrically housed rotor rotates. Due to the eccentric bearing of the rotor between it and the helical casing, chambers are formed during their rotation, which move in a certain way from the suction side of the eccentric helical pump to its pressure side, so that a medium is pressed or transported in the axial direction through the pump or stator.

Stators of this type can be used in eccentric screw pumps in particular for conveying media such as plaster, mortar, oil, etc. In order to improve volumetric capacity with stators of this type, for example, according to EP 0358789 A1, D ^e 19531 318 A1, EP 1522 729 B2 or DE 41 11 166 C 2 , provision is made for the lining to taper from the suction side towards the pressure side. Therefore the elastic flexibility of the lining adapts to the continuously increasing lifting pressure in the axial direction or transport direction. Due to the conical shape of the stator in order to connect to the next component in the eccentric screw pump, a similarly adapted transition piece must be used if the wall thickness of the casing does not change over the entire stator and this also adapts to the conical narrowing.

Furthermore, in the case of such a conical narrowing, the medium increases the forces acting on the lining. If the medium contains, for example, coarse material components, for example pieces of rock, these load the coating more intensively in an already narrowed and less elastically flexible region, so that the coating as a whole wears faster .

The object of the invention is therefore to provide a stator with a higher volumetric capacity that is easy to manufacture, has a high resistance and can be easily integrated into an eccentric screw pump. According to the invention it is provided that an average wall thickness of the stator lining starting from an end-side wall thickness occurring in the region of a preferably cylindrical stator intake side is continuously reduced, i.e. according to a continuous function of arbitrary degree, in the axial direction until a lower average wall thickness is reached, and that the average wall thickness after reaching the lower average wall thickness increases again at least in regions, so that up to one side of stator pressure, a preferably cylindrical enlargement is formed in the lining. By this it is to be understood that the average wall thickness of the coating starting from the lowest average wall thickness increases again directly after reaching or also remains approximately constant after initially reaching over a certain region and only then increases again for configure the flaring on the lining.

This advantageously achieves that in addition to an adaptation of the average wall thickness of the lining in the axial direction to the pump pressures acting in the pump cavity of the stator, a suitable transition can be created on the pressure side. The widening advantageously also allows a connection, for example via a conventional flange, to the next component of the eccentric screw pump. In this connection, for example, an adjustment of the wall thickness can also be carried out as it is carried out predominantly on the suction side so that the same connections, for example flanges, can advantageously be used for both stator sides when the wall thicknesses approximately coincide at the end side on the pressure side and on the suction side.

In addition, the lining towards the pressure side becomes more flexible again, whereby the transported medium, which is normally under high pressure on the pressure side, can be stabilized. The pressure increases at the pressure side flare in concrete only slightly as the lining becomes more flexible again. In contrast, the transported medium in the increasingly hardening region of the coating, due to the continuous reduction of the average wall thickness in a region before widening, experiences a high stress increase which is also desired for the pumping action. in this region. In the region of the expansion, however, no high pressure increase takes place and the medium is thereby stabilized. In the stator according to the invention, therefore, an optimized transfer of the transported medium to the next component of the eccentric screw pump can be realized as a whole.

By means of the stator structure, an improved holding function can also be achieved when the eccentric screw pump is switched off, for example. Backflow of the transported material can occur in the pump cavity when a pressure difference between adjacent chambers in the pump cavity is too high. If a harder lining is selected, reflux appears only in case of higher pressure differences between the chambers. The coating, which hardens in the axial direction, thus with increasing pressure of the conveyed medium, simultaneously also prevents backflow, ie higher pressure differences are possible before the flowback of the conveyed medium.

Preferably, in the case of such a structure, it can also be achieved that, due to the axial course of the average wall thickness of the lining, the stator

- configure in the region of the suction side of the stator a premix zone to homogenize and/or fragment the medium to be transported,

- configure in the region of the pressure side of the stator in the enlargement a stabilization zone to smoothly stabilize and guide the transported medium in the eccentric screw pump, and

- between the premix zone and the stabilization zone configure a high pressure zone with reduced medium reflux to increase the pressure in the pump cavity in the operation of the eccentric screw pump due to the medium wall thickness continuously decreasing in direction axially at least in regions and thus due to the increasing hardness of the coating, the pressure in the high-pressure zone relative to the premix zone and the stabilization zone adapting at least in regions with a pressure gradient higher.

For this reason, the stator is divided into different zones spaced axially apart from one another by the course of the accurately entered average wall thickness, where the transition is preferably defined by the average wall thickness of the lining remaining constant at least in the zone of premix and/or in the stabilization zone. Thus, the transported medium at its inlet to the stator and/or at its outlet from the stator can advantageously be adapted to the modified, tapering shape of the lining in the high-pressure region or to the resulting modified volumetric capacity of the stator. .

Also in parts of the high pressure zone the average wall thickness can be constant. For example, provision can be made for the average wall thickness of the coating to decrease continuously in a first high-pressure region from the high-pressure region in the axial direction to the smallest average wall thickness, where the first high-pressure region joins the premix zone, and in a second high pressure region of the high pressure zone remains approximately constant at the lowest average wall thickness.

The medium therefore advantageously has a zone in which it can be homogenized or fragmented on the suction side or and/or stabilized on the pressure side. Depending on the application and conveyed medium, the respective zone can be precisely adjusted by selecting a corresponding axial expansion or axial width as well as the wall thickness of the lining in the respective zone. The medium can then be "prepared" in the respective zone in the next region in the stator or in the eccentric screw pump. For example the lining in the high pressure zone is stressed less intensely when the flexibility is reduced, since the medium in the premix zone has already been fragmented or homogenized. Therefore, the lining in the high-pressure area wears less intensely. In the stabilization zone the medium is stabilized so that a smoother transition or a smoother exit from the stator can be achieved. For the narrowing of the lining, provision is preferably made for the stator lining to taper in the axial direction, whereby the average wall thickness of the lining decreases from the average wall thickness on the end side in the axial direction by at least by regions, for example in the high pressure zone or in parts of the high pressure zone, in the direction of the pressure side in a linear manner or also following a non-linear function. Therefore, a linear taper is created that will easily occur or a taper according to a non-linear function that is preferably configured by tapering the outer surface of the liner in a linear manner or according to a non-linear function, preferably with an invariable pump diameter in the pump cavity.

Alternatively, provision can also be made for the stator lining to narrow in the axial direction at least in regions as a contour of the outer surface of the lining approaches, starting from the average wall thickness on the end side towards the smaller average wall thickness each again to a contour of the inner surface of the lining made as a two-step inclined thread. The narrowing and thus the adaptation of the average wall thickness to the acting pressure is therefore further intensified in the pump cavity, whereby the narrowing then becomes visible from the outside as well, since preferably the casing also adapts to this two-step form of the outer surface.

In particular, this type of constriction can be provided in the first high-pressure region of the high-pressure zone so that a transition between the preferably cylindrical premixing zone and the second high-pressure region of the high-pressure zone can be set, wherein the shell in the second high pressure region is adapted to the two-pass shape of the outer surface. Thereby a transition from the cylindrical cross section to the helical cross section takes place, whereby in the second high pressure region the average wall thickness remains constant. For this reason, a type of hybrid stator is configured consisting of a cylindrical premix zone and a helical high pressure zone in the second high pressure region. The first region of The high pressure then acts as a transition with the coating which hardens accordingly due to the continuous adaptation of the average wall thickness.

In order to achieve a two-step approximation of the outer surface to the inner surface, it is preferably provided that a dimension B of the coating, starting from the average wall thickness on the end side in the axial direction, at least in regions, for example in the region of high pressure or in parts of the high pressure zone, in the direction of the pressure side is continuously reduced and a dimension A of the liner remains constant at the same time. This can simplify the manufacturing process according to this alternative. It is furthermore preferably provided that the average wall thickness of the coating after reaching the lowest average wall thickness and optionally after remaining constant at the lowest average wall thickness (compare second high pressure region), increases abruptly or continuously. to set the flare on the pressure side. A constant increase allows in this respect a smoother transition between the high-pressure zone and the stabilization zone as well as a simpler production. However, an abrupt transition can also be provided in order, for example, to promote stabilization and to keep a further pressure increase of the transported medium within limits.

It is furthermore preferably provided that an internal diameter of the shell corresponds to an external diameter of the cladding, so that the cladding is in contact with the outer surface of the cladding over the entire length of the stator and thus takes the course conical or helical in correspondence with the outer surface, whereby the shell preferably has a constant material thickness. In this case, the casing consists of a material that is harder than the lining, preferably steel. Thus the shell surrounding the liner can be easily adapted to the shape of the narrowing liner, for example by a forming process.

The invention is explained in more detail below by means of exemplary embodiments. The figures show: Figure 1 a stator according to a first embodiment;

FIG. 1a a sectional view of the stator according to FIG. 1;

Fig. 2 a stator in a further embodiment;

figure 2a, 2b sectional views of the stator according to figure 2;

Figure 3 a further embodiment of a stator.

In FIG. 1, a stator 1 is provided which has a tubular casing 2, which is preferably produced from a steel tube, for example by forming. The casing 2 surrounds an elastically flexible coating 3, the internal surface 4 of which has a helical or spiral-shaped contour K4, in which a two-pitch inclined thread is formed.

A pump cavity 5 is formed inside the stator 1, in which a rotor 6 is inserted (FIG. 1a), the rotor 6 being formed as a one-pitch inclined thread and, if appropriate, is in contact under pretension with the elastically flexible lining 3. The eccentrically mounted rotor can rotate in the pump cavity 5 .

The stator 1 has a suction side 7 as well as a pressure side 8, whereby in mounting the stator 1 together with the rotor 6 in an eccentric screw pump (not shown) the medium to be conveyed, for example mud, Mortar or plaster, in chambers from the suction side 7 is transported through the pump cavity 5 in axial direction X to the pressure side 8 when the rotor 6 starts to rotate. In this connection, the pressure in the pump cavity 5 increases continuously towards the pressure side 8 so that a lower pressure acts on the elastically flexible lining 3 on the suction side 7 than on the pressure side 8 .

According to the embodiment in figure 1 the lining 3 on its outer surface 9 has a conical shape, wherein an average wall thickness W of the lining 3 decreases from a position near the suction side 7 of the stator 1 in axial direction X towards the pressure side 8 first of all continuously, ie according to a continuous function. In this case, a contour K9 of the outer side 9 extends from the position close to the suction side 7 in the axial direction X at least in regions linearly downwards, ie according to a linear function. This achieves that the elastic flexibility of the lining 3 on the suction side 7 is higher, for example in the central region of the stator 1 or in the region of the stator 1 with the smallest wall thickness WM. The coating 3 hardens more and more towards the pressure side 8 (approximately linearly).

The conical taper can be adjusted in such a way that an average pump diameter DP does not change over the entire stator 1 so that an adaptation of the rotor 6 is not necessary either. For this, only the surface external 9 tapers in the axial direction X towards the pressure side 8. Basically, however, a continuous adaptation of the average pump diameter DP, in particular a conical narrowing towards the pressure side 8, can also be provided.

Starting from the smaller wall thickness WM of the lining 3, the stator 1 has a widening 10 towards the pressure side 8, through which the average wall thickness W increases to a wall thickness WE on the end side. The end-side wall thickness WE on the suction side 7 preferably corresponds to the end-side wall thickness WE on the pressure side 8 . Therefore the elastic flexibility or the hardness of the coating 3 on the front sides of the stator 1 is approximately identical. According to the sectional view in Fig. 1 a, a dimension A A and a dimension B B can be indicated for the stator 1, each indicating a thickness of the lining 3 in a Z Z direction or in a Y Y direction. coating 3 in axial direction X according to this embodiment it is provided that both dimension A A and dimension B B continuously decrease in axial direction X from the corresponding position. As a result, the average wall thickness W is continuously reduced to the minimum wall thickness WM. Since the casing 2 is in surface contact with the liner 3, preferably it is bonded or vulcanized, its internal diameter D is also continuously reduced. An external diameter E of the liner 3 thus corresponds to the internal diameter D of the casing. two.

By conical narrowing of the lining 3 starting from the suction side 7 and the subsequent widening 10 on the pressure side 8, the stator 1 is subdivided into three zones V, H, S or regions:

In a premixing zone V beginning on the suction side 7 of the stator 1, a relatively low pressure acts in the pump cavity 5 . At the same time, due to the comparatively high average wall thickness W in the premix zone V, a high elastic flexibility or low hardness of the coating 3 is given. This premix zone V is therefore suitable for fragmenting or precompressing a medium. coarse-grained, fed through the suction side 7, for example mortar, plaster or clay which may possibly still contain coarse material components, for example rock pieces, and to mix it evenly resulting in a homogeneous medium.

Due to the high elastic flexibility in this premix zone V the liner 3 can absorb the forces acting during the fragmentation of these coarse material components without the liner 3 being significantly damaged in this respect beyond normal wear. This is favored since in the premix zone V also low pressures act in the pump cavity 5 and these increase only very slightly. This can ensure optimal mixing.

The average wall thickness W lies in the constant premix zone V for the wall thickness WE on the end side. From a certain position in the axial direction X the premix zone Z becomes a high-pressure zone H, where this is initiated by a reduction in the average wall thickness W of the liner 3. By reducing the thickness W of medium wall, the elastic flexibility of the liner 3 is reduced. At the same time the pressure inside the pump 5 increases in the axial direction X, so that the conveyed medium also acts with greater force on the liner 3. However, since In the premixing zone V, a fragmentation and homogenization of the conveyed medium has already taken place, the lining 3 in the high-pressure zone H is subjected to less stress since the material components of the medium have rather smaller particle sizes.

At the same time, due to the elastic flexibility of the lining 3 being smaller or decreasing in the axial direction X in the high-pressure region H, a higher volumetric capacity can be achieved, since the material of the lining 3 offers an increasingly higher resistance with respect to a reflux through the sealing line between the rotor 6 and the lining 3 of the stator 1 for the medium to be conveyed. Due to the decreasing average wall thickness W or the increasing hardness of the coating 3, the pressure increases more strongly in the high-pressure zone H than in the premix zone V. Also in the high-pressure zone H, for example, due to the higher pressure in the pump cavity 5 as well as the decreasing elastic flexibility of the lining 3, a fragmentation of coarse material components still present can take place. Actually these appear only isolated and have decreased very significantly down to the minimum wall thickness WM so that damage to the lining 3 beyond normal wear can be largely avoided.

Due to the conical structure of the high-pressure zone H, the backflow behavior of the stator 1 can be improved. Backflow of the conveyed medium can occur when a pressure difference between adjacent chambers in the pump cavity 5 is too high. If a harder lining 3 is selected, back flow only appears in case of higher pressure differences between the chambers. The coating 3, which hardens in the axial direction X, thus with increasing pressure of the transported medium in the pump cavity 5, also prevents backflow at the same time, i.e. higher pressure differences are possible before the transported medium refluxes.

Starting from the minimum wall thickness WM in the stator 1 in the axial direction X, a stabilization zone S is attached which is located in the region of the pressure side 8 or the expansion 10. In the stabilization zone S the average wall thickness W of the coating 3 increases again and then runs constant so that the elastic flexibility of the coating 3 increases again or the hardness of the coating 3 decreases again. For this reason, as also in the premixing zone V, a slight build-up of pressure in the pump cavity 5 takes place on the outlet side.

In the transition region to the next component of the eccentric screw pump, that is to say on the pressure side 8 of the stator 1, little wear therefore occurs and the transported medium stabilizes before the transition to the next component.

Furthermore, by increasing the average wall thickness W by the wall thickness WE on the end side in the region of the widening 10, a connection can be provided, for example via a flange, to the next component of the eccentric screw pump. On the suction side 7 and the pressure side 8 of the stator 1, advantageously identical or standardized flanges or connections can be used with the same wall thickness WE on the end side. Due to the external shape of the stator 1, it can be unequivocally determined in which orientation the stator 1 is to be mounted on the eccentric screw pump.

According to a further embodiment of the stator 1 which is shown in FIG. 2, the reduction of the average wall thickness W in the axial direction X is achieved by a continuous adaptation of the outer surface 9 of the lining 3 to the helical inner surface 4 of the lining. 3. The outer surface 9 accordingly forms from a certain axial position also a two-pitch inclined thread. Since the casing 2 is in surface contact with the outer surface 9 of the liner 3 or adhered or vulcanized to it, the casing 2 from a certain axial position also follows the shape of the inclined two-pitch thread of the surface. internal 4.

For this reason, too, the stator 1 is subdivided in the axial direction X into a premixing zone V, a high-pressure zone H and a stabilization zone S, whereby an average wall thickness W is initially formed in the premixing zone V. approximately constant which corresponds to the average wall thickness WE on the end side. Thereby a high elastic flexibility of the lining 3 is achieved over a certain region, whereby the medium delivered via the suction side 7 can be fragmented or mixed or homogenized without in this respect damaging the lining 3 significantly more. beyond normal wear.

Starting from a certain axial position the average wall thickness W of the lining 3 decreases continuously (dotted line in figure 2), where this, as already mentioned, is achieved because the outer surface 9 of the lining 3 adapts continuously to the inclined two-pitch thread formed by the inner surface 4. This also causes a continuous narrowing of the lining 3 in the axial direction starting from the suction side 7 in the direction of the pressure side 8. In contrast to the embodiment in FIG. 1, however, the reduction in the average wall thickness W or the increase in hardness takes place along a different, steeper course, which further enhances the pumping effect, since a high pressure rise.

Also in the embodiment according to FIG. 2, by continuous narrowing of the lining in the axial direction X, a high-pressure zone H is formed, in which the elastic flexibility of the lining 3 decreases continuously with pressure in the pump cavity 5 at the same time. increasing time. Therefore, at the beginning of the high-pressure zone H, if it is still necessary, a fragmentation of coarse material components can take place, where due to the even lower pressure in the pump cavity 5 a coating damage 3. In the further axial course the conveyed medium is further homogenized so that in the region of minimum wall thickness a low-wear conveyance can be achieved at the same time with maximum volumetric capacity.

Starting from the smaller wall thickness WM, the average wall thickness W increases again in the embodiment according to FIG. 2 in the region of the widening 10 and then remains constant, so that a stabilization zone S is formed in this case as well. In this, the pressure in the pump cavity 5, due to the reduced flexibility, increases only slightly, so that a low-wear and smooth transition can be provided with a stabilized medium to the next component in the eccentric screw pump. Also in this case the end-side wall thickness WE on pressure side 8 corresponds to the end-side wall thickness WE on suction side 7 to create an identical connection on both end faces of stator 1.

According to the sectional views in figure 2a and 2b which are associated with the embodiment in figure 2 it can be distinguished that the dimension AA and the dimension BB for configuring the continuous narrowing of the lining 3 are adapted in the axial direction X in a different way . Figure 2a shows the section through the stator 1 in the premix zone V, where the dimension AA or the dimension BB in this axial position essentially coincide with the dimensions A, B in figure 1a of the first embodiment. In FIG. 2b, the section through the stator 1 is shown in the high-pressure zone H, ie after narrowing. AA dimension does not vary versus the state in premix zone V (see Figure 2a). Only the BB dimension has been reduced compared to the state in the premix zone V. The continuous narrowing of the lining 3 in the axial direction is thus achieved only by adapting the dimension B B.

The semi-axes HA1, HA2 of the casing 2 or of the cladding 3 also behave in a corresponding manner. A first semi-axis HA1 oriented in the Z direction remains constant in the axial direction X, while a second semi-axis HA2 oriented in the Y direction is continuously tapered. . Since shell 2 is in surface contact with shell 3, the half axes HA1, HA2 of shell 2 (internal surface) and shell 3 (external surface) correspond.

This also results in the two-pitch helical outer contour K9 of the stator 1, which is visible from the outside due to the simultaneous adaptation of the casing 2 to the outer surface 9 of the cladding 3. By means of this design the subdivision of the stator 1 into different zones V, H, S can also be supported since by adapting the helical wall thickness in the axial direction the elastic flexibility can be optimally adapted to the pressure ratios in the cavity 5 of bomb.

According to FIG. 3, compared to the embodiment of FIG. 2, it is provided that the width VB of the premix zone V in the axial direction X is increased compared to the previous embodiments. Thus, depending on the field of use of the stator 1, for example, the expansion through which a low-wear homogenization or mixing of the conveyed medium is to take place can be precisely determined. Thus, the dimension of coarse material particles in the high-pressure zone H can be reduced and thus precisely influence the wear on the liner 3. Also the width S ^b of the stabilizing zone S can be adjusted accordingly to give a sufficiently large region in the middle for stabilization and thus to optimize the transition, for example depending on the field of application. Correspondingly, a width HB of the high-pressure region H can also be selected to fix the region in which the volumetric capacity is to be increased by a corresponding adaptation of the pressure gradient. This can be done in adaptation in mutual coordination with the course of the average wall thickness W in order to achieve a corresponding pressure increase along the transport direction.

The widths VN, HB, SB can also be variably set in correspondence in the first exemplary embodiment according to FIG. 1.

In FIG. 3, it is further provided that the high-pressure region H is subdivided into two high-pressure regions H1, H2. In a first high-pressure region H 1 of the high-pressure zone H, the average wall thickness W first continuously decreases in the axial direction X until the smallest average wall thickness WM is reached. In the second high pressure region H2 of the high pressure zone H the average wall thickness W remains approximately constant at the lower average wall thickness WM. Then the average wall thickness W of the lining 3 increases again starting from the smaller average wall thickness WM towards the pressure side 8 of the stator 1 so that on the pressure side 8 the widening 10 is formed in the lining 3.

With this structure, a type of "hybrid stator" is provided which is formed of a cylindrical stator in the premix zone V and a two-pass helical stator in the second high-pressure region H2 of the high-pressure zone H. The average wall thicknesses W within the two hybrid components (cylindrical stator in the premix zone V and two-pass helical stator in the second high-pressure region H2) are different in this respect but constant in each case. The transition between the two hybrid components is ensured by the continuous adaptation of the average wall thickness W in the first high-pressure region H1, whereby at the same time an adaptation of the coating hardness is also achieved as achieved in the first variants embodiment in FIG. 1 and FIG. 2. In the stabilization zone S, the widening 10 is formed by continuous adaptation of the average wall thickness W.

reference list

1 stator

2 wrap

3 lining

4 inner surface of lining 3

5 pump cavity

6 rotor

7 suction side

8 pressure side

9 outer surface of lining 3

10 widening

to dimension A

B dimension B

D inner diameter of casing 1

E outside diameter of liner 3

DP mean pump diameter

H high pressure zone

H1 first high pressure region of H high pressure zone H2 second high pressure region of H high pressure zone HB width of H high pressure zone

HA1 first half axis

HA2 second half axis

K4 contour of inner surface 4 of cladding 3 K9 contour of outer surface 9 of cladding 3

S stabilization zone

SB width of the stabilization zone

V premix zone

VB width of premix zone V

W average wall thickness

WE wall thickness on the end side

WM minor wall thickness

X axial direction

Y,Z direction Y,Z

Claims (15)

Yo. Stator (1) for an eccentric screw pump having a rotor (6), where the stator (1) has an elastically flexible lining (3) with an external surface (9), where the lining (3) is surrounded by a rigid wrapper (2), where an internal surface (4) of the lining (3) configures a two-pitch inclined thread as well as a cavity (5) of the pump expanded in the axial direction (X) limited for the housing of the rotor (6) of the eccentric screw pump , wherein the lining (3) of the stator (1) tapers in the axial direction (X) at least in regions, where for this an average wall thickness (W) of the lining (3), starting from a thickness (WE) The wall thickness on the end side, which occurs in the area of a suction side (7) of the stator (1), decreases at least in regions continuously in the axial direction (X) until a smaller thickness is reached (WM ) medium wall, characterized by what the average wall thickness (W) of the cladding (3) starting from the smallest average wall thickness (WM) increases again, at least in regions, towards a pressure side (8) of the stator (1) so that towards the pressure side (8) of the stator (1), a widening (10) is formed in the lining (3). Stator (1) according to claim 1, characterized in that due to the axial course of the average wall thickness (W) of the lining (3) - in the region of the suction side (7) of the stator (1) a premix zone (V) is configured to homogenize and/or fragment the medium to be transported, - in the region of the pressure side (8) of the stator (1) in the enlargement (10) a stabilization zone (S) is formed in order to stabilize and smoothly guide the conveyed medium in the eccentric screw pump, and - between the premix zone (V) and the stabilization zone (S) a high pressure zone (H) is configured to increase the pressure in the pump cavity (5) during the operation of the eccentric screw pump due to the thickness (W) of medium wall that decreases continuously in axial direction (X) at least by regions. Stator (1) according to claim 2, characterized in that the average wall thickness (W) of the coating (3) does not vary in the premix zone (V) and/or in the stabilization zone (S). Stator (1) according to claim 2 or 3, characterized in that the average wall thickness (W) of the lining (3) continuously decreases in a first high pressure zone (H1) of the high pressure zone (H). in the axial direction (X) and in a second high-pressure zone (H2) of the high-pressure zone (H) remains approximately constant at the smallest mean wall thickness (WM), where the first high-pressure zone (H1) pressure joins the premix zone (V). Stator (1) according to one of the preceding claims, characterized in that the lining (3) of the stator (1) tapers conically in the axial direction (X), the average wall thickness (W) of the lining (3 ) decreases for this from the mean wall thickness (WE) on the end side in the axial direction (X) in the direction of the pressure side (8) linearly or according to a non-linear function. 6. Stator (1) according to claim 5, characterized in that the external surface (9) of the coating (3) narrows linearly or also following a non-linear function to achieve the decrease in the linear average wall thickness (W) or that follows a non-linear function starting from the mean wall thickness (WE) on the end side. Stator (1) according to one of Claims 1 to 4, characterized in that the lining (3) of the stator (1) tapers in the axial direction (X) as a contour (K9) of the outer surface (9) approaches. of the lining (3) starting from the mean wall thickness (WE) on the end side towards the smaller mean wall thickness (WM) increasingly to a contour (K4) of the inner surface (4) of the lining (3 ) made as a two-step inclined thread. Stator (1) according to claim 7, characterized in that a dimension B (B) of the cladding (3) starting from the average wall thickness (WE) on the end side in the axial direction (X) is continuously reduced by the direction of the pressure side (8) and a dimension A (A) of the liner (3) remains constant at the same time. 9. Stator (1) according to claim 7 or 8, characterized in that a first semi-axis (HA1) of the casing (2) remains constant in the axial direction (X), and a second semi-axis (HA2) of the casing (2) perpendicular to the first semi-axis (HA1) is continuously reduced in the axial direction (X). Stator (1) according to one of claims 7 to 9, characterized in that the contour (K9) of the outer surface (9) of the lining (3) in the region where the average wall thickness (W) is corresponds to the wall thickness (WE) on the end side, is approximately round, and in the region where the average wall thickness (W) corresponds to the smallest average wall thickness (WM) runs parallel to the contour (K4) of the internal surface (4) of the lining (3) realized as a two-step inclined thread. Stator (1) according to one of the preceding claims, characterized in that the average wall thickness (W) at the widening (10) on the pressure side (8) corresponds to the wall thickness (WE) at the side of the ends on the suction side (7). Stator (1) according to one of the preceding claims, characterized in that the average wall thickness (W) of the lining (3) after reaching the lowest average wall thickness (WM) increases abruptly or continuously to form the widening ( 10) on the pressure side. Stator (1) according to one of the preceding claims, characterized in that an average pump diameter (DP) of the pump cavity (5) also narrows in the axial direction (X) towards the pressure side (8) to the less by regions, preferably it does not vary linearly, or in the axial direction (X) throughout the stator (1). Stator (1) according to one of the preceding claims, characterized in that an internal diameter (D) of the casing (2) corresponds to an external diameter (E) of the lining (3) so that the casing (1) all over the stator (1) is in contact with the outer surface (9) of the lining (3), where the casing (2) is adapted by deformation to a contour (K9) of the outer surface (9). Stator (1) according to one of the preceding claims, characterized in that the casing (1) has a constant material thickness in the axial direction (X).