EP1522729B1 - Progressive cavity pump and stator for such a pump - Google Patents

Abstract

Eccentric spiral pump comprises an inner casing (2) made from wear-resistant elastic material in a cylindrical housing casing (1). An inner surface (3) of the inner casing or the inner casing has a rinsing direction and length on the side facing inward. A screw-like rotor (6, 8) inserted into the inner casing in a first axial position is also provided. An independent claim is also included for an elastomer stator for the eccentric spiral pump. Preferred Features: The inner casing is extended from its front in the radial or axial direction so that the front edge (24) of the rotor rotates eccentrically during the pump operation.

Description

The invention relates to an elongated feed pump as an eccentric screw pump, consisting of a stator and a rotor. The stator may have a cylindrical outer sheath, preferably of metal, and a hollow sheath of a "rigid-elastic" material with a spiral-shaped inner surface and held or receivable by the same. He takes on a corresponding helical or helical rotor. Stator and rotor have the same direction slopes. Also of relevance is the stator itself, with "tight-elastic" lining or elastomeric jacket.

Such pumps are known for various applications, for example as a feed pump for mortar mixtures or other abrasive conveying fluid, see. DE-B 33 04 751 (KTO) with "conical bias" between stator and rotor, becoming stronger to the output MAS. A pump with Elastomerstator is known from DE-A 197 58 086 (Artemis). It corresponds to the preamble of claim 1. In her, a quick installation of the lining should be possible. An axially projecting elastomeric ring is provided for a sealing axial mounting. Likewise, DE-A 198 01 021 (Hunter) is configured.

A metallic, mostly hardened rotor is driven in rotation in operation in one of its pitch or helix opposite sense. In order to keep the rotor in promoting operation relative to the stator in a constant axial position (or position), a corresponding axial holding force must be applied by the input side drive shaft, possibly above the rotor upstream equipment parts, such as clutch, driver, mixing tool or the like .. become. The axial holding force arises as a "Reactio" by the "Actio" caused by the conveyance and forward movement of the conveyed material and the rotation of the rotor in the stator, after the rotor against the pitch of its helix and against the pitch of the helix of the inner lining of the stator (the inner shell) is driven in rotation by the drive means (on the input side).

The forces involved are large, on the one hand by the building up in the pump during operation discharge pressure, on the other hand by the eccentric position of the rotor and in that the rotation in the relative direction of rotation of the rotor opposite to the opposite pitch of the screw flights the rotor against the direction of the Stator loaded axial pushing out.

In order to facilitate the entry of the medium to be pumped ("conveying fluid") into the pump, the jacket (stator) is often widened funnel-shaped on the inlet side.

It has been shown that due to the high load in the elastomer part of the stator considerable signs of wear and disturbances can occur, often after a surprisingly short operating time, for example 2 hours or less.

Also, a flat wear along the screw thread of the rotor can occur, so a general diameter reduction, which reduces the flow rate. This can be counteracted in a longitudinally split housing shell by a retightening (contraction) of axially extending housing segments, with a corresponding reduction in the capacity must be taken into account. Instead, even with one-piece (not split) housing shell and over the pump length remaining permanent winding cross section of the rotor, the clear cross-sectional area of the stator windings from the pump inlet to the pump outlet are steadily reduced, so be provided a certain "conicity", so that the bias between elastomeric Stator jacket and hardened rotor increases towards the outlet. This makes it possible to achieve a reduction in the drive power or an approximately constant delivery rate over longer operating times, cf. to DE-B 33 04 751 . Unlike the "conical" bias works GB-A 1 215 569 (Hertrich), in which a conical jacket achieved by axial displacement of the elastomer inlay, a uniform increase in the bias. An inlet funnel (on the inlet side) is shown in DE-A 44 42 060 (Netzsch) and the basic principle of "monopumps" by René Moineau is shown in DE-A 633 784 .

In practice it turns out that even with perfectly trained and assembled and matched drive system and maintaining the best bias in the jacket by retightening a multi-part housing or by choosing a taper in the stator, a rapid power loss and / or segregation (change in Consistency) of the medium to be conveyed - even with newly replaced stator or rotor - may occur, and can not be remedied by the steps shown. This leads to complaints and complaints on newly re-used rotors or stators, which are qualified as faulty or insufficient, although they meet all specifications and manufacturer were correct. The cause of the sudden reduction in performance or the cyclic change in consistency of the delivery side discharged fluid (in the jargon of users "thick / thin" named) could not be clarified. The manufacturer had supplied proper stators or rotors, the user also has them properly installed in his previously (still) functioning pump device. However, the described error symptoms, in particular an axial groove in the elastomer of the stator which tapers from the suction side to the pressure side of the stator (or widened the other way round), and first of all an improper or poor rubber compound or defective processing of the elastomeric inner part of the stator shell close. Such unexpected errors when using almost new building components (stator or rotor) should be avoided.

The invention is based on the object to remedy the situation and to ensure greater service life, to prevent a change in the consistency of the medium to be conveyed and to avoid sudden losses of capacity at almost new replaced components.

This object is achieved according to claim 1 or 10 or 15. With the stator according to the invention (claim 15) itself, the solution is prepared. The associated dependent claims show alternative measures or advantageous additions.

Initially, the described defect alleviated by the invention appeared to be a problem of the elastomer which prematurely worn out at the sealing points (the radially inwardly projecting ribs of the elastomeric helical coil) through an axially extending notch or groove thereby opening or closing a channel for backflow Achieved a poor seal between the helical rotor and the inner surface of the elastomeric lining of the outer shell. The cause was or was not in the elastomer compound or its processing or incorporation, but first had to be identified where the actual cause of this occurring and on a removed stator visible fault symptom was. To this described backflow channel in the interior of the stator, a near the outlet end circumferentially into the stator or its elastomeric lining cut groove joined.

Neither the axially extending, a backflow permitting groove, nor the circumferentially extending notch at the outlet could be symptomatic attributed to the user in the complaint usually described "thick-thin problem", which was expressed by the fact that a pump the conveyor no longer consistently promoted, but alternately promoted sections that had higher and lower water content, so the thickened conveyor with little water content and the strongly segregated water content provided with little coarse-grained material at the outlet under pressure. Apparently a mistake in the area of the mixer or the mortar.

Only an analysis of a wider environment of error symptoms could demonstrate that the error systemology passes through a chain of events that cause the described demixing at the user, but not caused by a manufacturer's malfunctioning pump or replacement parts, or by user incorrectly installed replacement parts but by an axial displacement of the stator and rotor relative to each other. This axial displacement of the rotor in the stator causes a crescent-shaped end present at the front, pressure-side end of the rotor to cut into the elastomer of the stator by the eccentric motion and leave there the described circumferential notch on the entire circumference of the elastomeric stator lining like a sickle. Due to this defect, it is favored during operation, inter alia due to high temperatures of the elastomeric jacket (in the range of 60 ° C to 70 ° C) that an axial piece of the elastomeric stator between the notch and the end (the pressure end) of the stator itself deformed inwardly and (figuratively speaking) radially collapses, whereby the provided on the pressure side passage cross-section is reduced. Due to the reduced passage cross-section forms a higher pressure before the outlet of the pump, which can not escape in the normal way out of the pump on the pressure side, by dispensing the excess relative to the outlet cross-section conveying fluid. This too much conveyed conveyor builds up such a high pressure before the (reduced) outlet of the pump, that a backward flow is created and the sealing line on the inside of the stator is damaged, which leads to the axial groove widening towards the suction side. This was not due to a poor quality of the elastomer as a rigid-elastic inner material or the inner lining of the outer jacket of the stator, but on an operational overpressure situation, due to a cutting forward crescent-shaped end of the helical rotor. Due to the pressure situation described also results in the actually observed only consistency change at the outlet (MAS). The delivery fluid is segregated in the promotion, so it forms chambers with increased water content and chambers with reduced water content, which the user considers and evaluated as a poorly pumping pump that promotes for him initially too much water and then too much coarse material.

The various power transmission points show in the course of permanent use of a pump wear. These cause due to the axial forces described above (towards the drive side, ie contrary to the conveying direction) arise loads on mechanical coupling points, which yield and not be swapped with a rotor change with. Usually they are not made of a hardened material, as the rotor is for its flow rate. A resulting rearward displacement of the axial position of the rotor leads to an intrusion of the crescent-shaped circumferential point of the rotor and the described groove-shaped, circumferential damaged area in the sealing elastomeric jacket. The corresponding solution, on the other hand, seems as simple as it is convincing. The area which is (or would) be damaged by the sickle-shaped edge of the rotor is omitted without altering the actual length of the pump, that is to say without having to shorten the stator with its outer jacket or to make other modifications on site. As a result, the rotor moves with its crescent-shaped edge in a free space. Thus, the edge does not receive a compliant countermeasure where, upon displacement of its axial position, it could damage the stator with its elastomeric interior to trigger the chain of events that the user perceives as a "thick / thin" symptom.

If abrasions occur at the various power transmission points which lead to the rotor being displaced in the stator as a result of the forces occurring in the conveying direction (towards the drive side), then the axial assignment of stator and rotor, which is important for optimum delivery performance, is not more given.

There are various possible embodiments, as the end face of the rotor end is released (claim 6 to claim 9, claim 3). These types of exemptions may be termed "erosion" or retraction or retraction of the elastomeric end region (claim 4). They may be conical, comparable to the entrance side, or chosen in other configurations.

An approximately cylindrical recess of the elastomer material, one of the helical shape of the inner surface following, but greatly widening radially outward shape is also possible, as any other radially outwardly widening design to the back in operation displaced crescent-shaped edge portion of the rotor to a free space grant.

This clearance leads to "no damage" to the sealing elastomeric material, but at the same time ensures that there is some reduction in the effective length of the pump to build up the pressure, with physically the same length. Such a percentage reduction of pressure levels, which may be up to half a stage (claim 3) is compensated according to the invention by an increasing conical bias, as explained above, on the remaining pressure stages. As a result, a power maintenance of the pump and its replacement parts can be ensured, the combinatorial complement (claim 5), but also alone by creating the appropriate design of Elastomerstators (claim 15) is prepared such combinatorial effect, as a replacement or replacement part.

With respect to the rotor or components driving this rotor, axially in front of the pump on the suction side MES (the motor drive, the mixing helix and other couplings) and axially after the pump (a pressure flange or a pump end which serve as spacers), no changes are required respectively. These components can stay the same. Likewise, the installation of the pump remain the same, their axial position can be left unchanged and there must be no operating and handling instructions to eliminate systematically occurring errors. They are already avoided by either delaying or completely preventing their occurrence.

An error in itself located in the drive mechanisms and in front of the actual pump is counteracted by a pressure-side change of the stator shell, which is actually the one neuralgic point at which a maximum of pressure arises and must be guided and held by sealing lines, or up to here should be built. However, this loss of capacity can be compensated by the fact that an increased conical design of the interior contributes to compensate for the remaining pressure levels along the length of the pump, the reduction of power or with a slightly reduced power to continue operating the pump, to avoid a fault symptom that builds up during operation and whose cause research is complex.

The creation of a clearance symbolizes avoiding a damaging contact of the crescent-shaped circumferential end edge (also called peripheral edge) in a rotating movement of the rotor with respect to the elastomeric, ie compliant and softer inner shell of the contrast, much stiffer outer shell of the stator. The clearance symbolizes an axial extent and a radial extent for a reduction of the strength of the elastomeric lining (claim 3, claim 4), or vice versa, a widening of the worm gear in the radial direction on a predetermined axial piece near the exit on the pressure side of the stator.

A damaging wear can also be avoided that the clearance is understood that no pressure contact this crescent-shaped cutting edge arises when a (light) touching contact is allowed and not the optimum of a pure exemption or avoidance of any contact is maintained (claim 10). There will always be a point in time at which the axial drive connection is so severely worn out or shortened axially that a crescent-shaped pressure end of the rotor will touch and rub against the elastomeric casing in a contact with radial pressure, only the time until this occurs can be so far delayed that an acceptable wear of the drive connection has no adverse conveying properties on the screw pump.

On the front side, a circumferential sealing web (claim 16) may also be formed axially projecting and radially far outward on the elastomeric end face, but in its axial extent is substantially less than 2% of the axial length of a stator pitch (a screw stage or a stage on the other hand, he has a completely different task, that of the axial and radial sealing of the connection point of the stator to the further functional parts, without that he would be functionally related to the crescent-shaped end of the rotor or a geometry of the rotor. When installing the stator of the sealing bar is compressed so much until the stiffer outer shell with a metallic pressure-side recording comes into contact (claim 9).

A reduction of the A-measure in the conveying direction in the continuing pressure-loaded section of the screw pump (claim 5) refers to a respective pitch stage in terms of their beginning and their end. The inside width of the inner shell is further reduced substantially uniformly per level. With this increase in the effect of the conicity, ie a stronger rising bias on the pressure-effective portion, with a removal of each bias in the exit-side Zurückversetzungs-, in particular expansion section (the feared engagement of the crescent-shaped cutting effect of Rotor end), a length of at least 2%, preferably between 5% and 10%, can be compensated up to half a step length insofar as the secured against sickle-shaped cutting stator in a pump can perform virtually the same performance, despite a shortened axial Pressure range, after the outer sheath as such is to remain unchanged in its physical total length.

A combination of helical formation and conical expansion of the shell in the exit region provides a lightweight manufacturing technique (claim 8). The screw shell is no longer tapered conically to the pressure-side end, but slightly or more expanded, retains its basic snail shape and in addition receives a conically widening shape. As a result, the conicity in the direction of compression in this section, which is endangered by the crescent-shaped engagement, runs as "counter-conicity", in the sense of an expansion and not a narrowing of the clear space formed by the helical inner surface of the elastomeric inner jacket.

This "widened conicity" can be compared with such a "reducing conicity" or such a clear space, which lies axially further forward, ie opposite to the conveying direction (claim 8), or immediately before the beginning of the counterconceptivity ("widening" conicity) , The expansion extends radially on an axial length such that both directions together achieve a reduction in the wall thickness of the elastomeric inner liner in this axially short piece on the exit side.

Instead of a description of the reduction of the wall thickness of the elastomeric inner lining (elastomeric jacket), it is also possible to speak of a widening of the inner space, based on the worm threads, which constitute the helical or helical inner wall (claim 15).

A cylindrically shaped expansion, retraction or wall thickness reduction (claim 6, claim 16) can pass directly into a circumferentially extending sealing ridge at the front end.

Figur 1

zeigt im Längsschnitt eine Pumpe gemäß einem Beispiel der Erfindung, mit Stator 1,2 und Rotor 6.

Figur 2a, Figur 2b

zeigen im Figurenteil 2a im Längsschnitt einen nicht konischen Stator für eine Exzenterschnecken-Pumpe, im Figurenteil 2b einen Querschnitt durch diesen Stator.

Figur 3a

zeigt einen intakten Kupplungsbereich zwischen einem eintrittsseitigen Ende 8 des Rotors 6 und einem vorgelagerten Mischwerkzeug mit Antrieb, die selbst nicht dargestellt ist.

Figur 3b

zeigt den Kupplungsbereich nach betriebs-bedingtem Verschleiß v an Eingriffsstellen.

Figur 4a, Figur 5a, Figur 6a

zeigen verschiedene Ausführungsformen des Stators gemäß weiteren Beispielen der Erfindung.

Figur 4b, Figur 5b, Figur 6b

zeigen jeweils die entsprechenden Stirnansichten am Austrittsende der Statoren.

A combination of widened screw flight and downstream cylindrical or conical widening without worm gear is possible, as well as the combination of cylindrical and conical widening section with an axial offset from each other (claim 6 and claim 7). The invention will be explained in more detail with reference to schematic drawings of several embodiments. These embodiments illustrate and supplement the invention.

FIG. 1

shows in longitudinal section a pump according to an example of the invention, with stator 1, 2 and rotor 6.

Figure 2a, Figure 2b

in the figure part 2a in longitudinal section a non-conical stator for an eccentric screw pump, in the figure part 2b a cross section through this stator.

FIG. 3a

shows an intact coupling region between an inlet end 8 of the rotor 6 and an upstream mixing tool with drive, which itself is not shown.

FIG. 3b

shows the coupling area after operational wear v at points of intervention.

Figure 4a , Figure 5a, Figure 6a

show various embodiments of the stator according to further examples of the invention.

FIG. 4b, FIG. 5b, FIG. 6b

each show the corresponding end views at the outlet end of the stators.

The eccentric screw pump has in the example, as shown in Figure 1 , an outer cylindrical elongated housing 1 of a predetermined diameter and predetermined length. The housing may be made of steel, for example. In the housing, a hollow cylindrical shell, for example, made of high-wear rubber or the like. Elastomerermaterial firmly attached, the inner surface 3 has a helical contour for the formation of a double-flighted screw channel with double pitch. At the entry-side end face MES, the screw channel is conically widened, as shown at 4, to prevent the entry of an eligible medium to be conveyed to the exit side MAS as a fluid, eg a mixture of water and a Additive to facilitate. The stator can be axially slotted or multi-part, which is not shown separately.

In the inner jacket of the stator 2 is a screw 6, e.g. made of hardened steel. The pitch direction 7 is the same for stator and rotor. The longitudinal axis 11 of the coiled rotor portion is radially offset from the center axis 10 of the screw flights of the stator (the axis of rotation of the rotor) by 2 * e, resulting in the eccentricity 9 (or "e").

On the inlet side MES, the rotor 6 is extended beyond the beginning of the stator at 8 to form in the axis 10 a screw head 17 (Fig. 3a), via which the rotor can be driven in a direction of inclination of stator and rotor opposite sense. The outlet opening 5 of the stator of the pump is specially designed on the outlet side MAS. Further details below.

A taper k is represented by a black, increasing edge region of the helical screw in Figure 1, which is operated with an increasing contact pressure from the input side 4 to the output side 5 to account for the increasing delivery pressure and the sealing lines to delineate the delivery chambers better in elastomeric stator jacket 2 form. Such delivery chambers are illustrated in the upper portion of Figure 1 between the screw channel (formed by the Innenwandformung 3 of the elastomeric liner 2) and the outer wall of the elongated coil 6. Also above, the sealing lines of the chambers are represented in cross section by the short black overlap strips which, even during operation, do not overlap, but by yielding the elastomeric material create a pressure sealing effect to the stator as well as the continuous zone k.

The axial direction is denoted by z, also as a conveying direction, wherein the two axes 10, 11 are offset eccentrically and can be seen with the offset 9.

In addition to be worked by cylinder coordinates with z for axial direction and r for the radial direction.

Mention should be made of the length of a slope or a step, which is denoted by L1 in Figure 2a , visible on a double-flighted helix of the stator, wherein the associated inner wall 3 forms a clear interior I, in which no rotor is used in this figure.

For optimum delivery performance and the lowest possible wear, precise adjustment and adjustment of the pump parts is required. This includes that an axial position z1 of the rotor relative to the stator during pump operation is maintained as accurately as possible. With regard to the very high forces acting axially against the conveying direction z on the rotor, this requires a very high counter-holding force, which must be applied to the rotor via the drive side, which promotes wear on the parts transmitting the driving force. The consequences are illustrated by comparing FIGS . 3a and 3b . On the left is an intact coupling between the screw head 17 and the driver 16,18 of an upstream mixing tool 15 (only partially shown) shown. On the right the same coupling is shown in worn condition. The consequence of the wear is that the rotor has changed its position z1 relative to the stator by the offset 19, whereby it has migrated into the stator counter to the conveying direction. The measure .DELTA.z corresponds to the offset 19 and the widening of the provided with a recording worm head 17 in the coupling 18 on the driver 16 of the mixing tool 15, wherein in particular the locations indicated in Figure 3b with v wear of an axial removal of the non-hardened driver tool relative to the Hardened steel of the rotor subject.

Figures 2 show the stator in a normal training. The inlet end 4 is flared, while the worm gear is unchanged as far as in the direction perpendicular to the axis 10 extending plane 22, in which the outlet-side opening 5 'of the shell 2 is located. If, in this casing, a rotor such as the rotor 6 according to FIG. 1 is in its working position z1 and driven in rotation, it performs a considerable flexing work on the elastomer casing 2 surrounding it. At this, a crescent-shaped edge 24 is correspondingly involved in the output-side end face 25 of the rotor 6, since in the shell of Figure 2a, the worm threads continue unchanged to the mantle end face in the plane 22. The crescent-shaped end edge 24 works thereby, when the offset .DELTA.z becomes larger, in the material of the shell, and causes a corresponding notch or even a cut. These can have a radial depth of up to 3 mm and more. The jacket elastomer becomes hot, up to 60 ° to 70 ° Celsius and bulges, folds a little way inwards, and reduces the outlet cross-section of the opening 5 for the conveyed medium (conveying fluid).

It has been found that this changes the consistency of the pumped mixture cyclically, caused by an increased pressure on the pressure side and damage to the stator by an axially forming groove, which coiled circumferentially extending sealing lines breaks through. After a short time, the pump can become unusable.

As shown in FIGS. 1 and 4 to 6 , the occurrence of such damage can be effectively avoided. The outlet opening 5 of the shell 2 is widened compared to an assumed regular screw surface course and thus precludes a pressure-exerted touch the crescent-shaped end edge 24 of the rotor with the jacket 2 during operation, preferably even if the rotor due to wear of parts in the drive path (s 3) changes its predetermined regular axial position z1 relative to the stator counter to the conveying direction (by offset 19 or Δz in FIG. This creates a state as it is pictorially represented as clearance or exemption G. The crescent-shaped edge 24 shown in section as a sharp, less than 180 ° having cutting edge, does not touch the elastomeric sheath 2, but a distance is provided.

A further axial backward displacement by more than Δz according to FIG. 3b would lead to an axially further displaced axial position of the rotor 2 in connection with a potentially pending (loading) contact, despite a widened configuration of the outlet opening 5. A pure contact itself is not harmful yet, only one which leads with additional pressure load to a cutting action in the elastomer, which would then cause the axially further to the pressure side portion of the elastomer jacket to unwanted displacements radially inward. But even this radial inward displacement can be done a bit far at the outwardly in thickness greatly reduced elastomeric sheath 2, if the exit-side end face of the rotor and the cutting edge close to it should exert pressure on the elastomeric sheath, but it is still radially set back and opens a larger cross section at the outlet MAS.

It can be seen from FIG. 1 that the area of the reduction of the jacket wall thickness 2 near the end face at the exit MAS is not a large axial distance, but a substantial radial widening of the exit opening 5. For comparison of the lengths, reference may be made to a step L1 according to FIG are taken, several of which are provided along the entire length L of the stator by the elastomeric inner lining.

In order to define a conicity k according to FIG. 1, a change in the clear dimension of the interior can be indicated by specifying the percentage reduction, corresponding to a percentage reinforcement or thickening of the elastomer jacket 2 become. This indication can also extend to the fact that the A-measure and the C-measure according to FIG. 2b are specified as changing in the course of the z-direction. The two dimensions A and C define the largest and smallest dimension of the interior, corresponding to the largest and the smallest distance of the inner surface of the elastomeric lining 2 in the section of Figure 2a.

The shape of the widening 5 of the end MAS of the stator can be different.

In FIG. 5 , the widening 5a is conically shaped approximately in accordance with the widening at the entry end 4. The plan view of the flared end is shown in FIG. 5b.

A similar plan view results in the embodiment according to FIG. 6 , in which the widening 5b has a stepped design. This corresponds to a substantially cylindrical retraction of the elastomer wall 2 '.

The embodiment according to FIG. 4 corresponds with the widening 5c substantially to the shape shown in FIG. 1, with an additional screw portion in the z5 section. FIG. 4b shows the corresponding plan view.

In spite of the apparently identical views, FIG. 5b shows a bevel at the widening or widening 5a, FIG. 6b a cylindrical recess 5b, or a plan view at an end-face, radially directed surface and FIG. 4b a combination of a conical widening connected to a helical leakage 5c at conicity other than that which led to the widening portion of length z5 (in the previously stored area and the preceding stages). Such a helical formation connected to a conical or cylindrical configuration can also be described as a conical shape is maintained, with inverted conicity, so one that relaxes a compressive load, or does not arise and is directed outwards to a thinner wall thickness 2 'of the elastomeric jacket 2, or but significantly and more so conically widened that gap distances between a crescent-shaped edge 24 of Figure 1 and the inner surface of the expansion 5 can be seen even with a built-rotor.

All embodiments have in addition a frontally arranged circumferential web-shaped seal 21, for sealing attachment to further intermediate sections (recording) in the transition section to the delivery hose on the Pressure side. This circumferential ridge 21 is disposed radially far outward on the elastomeric inner jacket, near the rigid housing or outer jacket 1. It extends in the axial direction by far less than 2% of a step length L1, and has no influence on the protection of the inner wall of the elastomer liner 2 against damage caused by the rotor. When installed, this bridge is almost completely compressed.

To illustrate the axial extension and the radial widening, a group of reference symbols is shown in FIG. 6a , such that the residual wall thickness 2 'which arises after introduction of a cylindrical recess 5b or a cylindrical expansion 5b preferably matches a radial thickness of the circumferential web just explained 21. The axial extent z5 of the retraction or widening, generally to be described as "clearance G" of Figure 1, shall be related to the length L1 of a step (a thread). The size of the radial expansion r5 corresponds to a shape along the axial distance z5 on which the expansion r5 takes place. It does not have to be constant, but, as can be seen from FIGS. 5a and 4a , can vary circumferentially and also assume different values in the longitudinal direction z.

In the axial direction z5, the widening or widening for the release of the jacket from the end edge of the rotor should be at least 2%, preferably above 3%, or 5% to 10% of a stage L1 of the stator worm 3. For a better understanding, such a stage is shown in FIG. At a step length of e.g. 110 mm, the lower limit of the extension is about 2 mm to 4 mm, but may also be 5 mm to 11 mm and more, up to a half step.

The occurring reduction of the pump-effective length of the stator is compensated by a corresponding increase in the bias voltage k between the rotor and stator. The conicity can be seen in the sectional view through inclined connecting lines 21 in FIGS. 5a, 6a . They correspond to the illustrated conicity k, which ensures an increased bias to the pressure side. The change in taper takes place in an advantageous manner by continuous change of the A-measure. The percentage reduction of this level per level should be at least 0.4%.

For a better understanding, some definitions used are explained below. Thus, the number of stages of the stator is equal to the stator length divided by the pitch of its flights. The conicity of the stator screw results from the difference the C and A measures MES entry and exit MAS, where the reduction is evenly distributed over the number of slopes (steps). The mean of the A measure per step is the A measure at the entrance of the step less the A measure at the exit of the step. In this sense, here the percentage reduction of the A measure per step is understood to mean the A measure difference per step multiplied by 100 and divided by the A measure at the input of the step.

As can be seen from FIG. 1 as well as from FIGS. 5a and 6a, the A dimension is reduced in the conveying direction, ie in the direction of the stator output MAS.

A segregation, ie a consistency change of the pumped medium, as well as early wear of the pump parts can be avoided in a very simple manner and with the possibility to compensate for a reduction in the purchase of pump power.

Claims (18)

1. Eccentric screw pump having an inner casing (2) made from wear-resistant and resilient material in a single-part or multi-part cylindrical housing casing (1); wherein an inner surface (3) of the casing (2) or the inner casing (2) is designed spirally with predetermined pitch direction and pitch length on its side (3) pointing inwards; having a helical or spiral rotor (6, 8) inserted with pretension in the casing in a first axial position (z1) and with radial eccentricity (9) and mounted (15, 16) on the drive side in this position and having the same pitch direction (7) as the stator (2); characterised in that an outlet opening (5) of the stator (2) is expanded starting from its end-face end on a piece of the axial conveying length radially outwards on its entire periphery so that an end-face edge (24), which rotates in pump operation, of the rotor end (23) placed close to the outlet opening - preferably for wear-related axial displacement (19; Δz) of the rotor - can be rotated in contact-free or released (G) manner with respect to the inner surface (3) of the stator.
2. Eccentric screw pump according to claim 1, having a stator made from a single-part cylindrical housing (1) and the inner casing (2) made from elastomer material arranged to be fixed therein, the inner surface (3) of which is designed to be running helically or spirally about the longitudinal axis (10; z), and having the helical, elongated rotor (6), which with its central axis (11) opposite the longitudinal axis (10) of the stator, is arranged in the stator to be radially offset by a predetermined amount (9, e) in a given axial position (z) opposite the stator, which has the same pitch direction as the inner casing and can be driven in rotating manner - opposite to the pitch direction of the inner surface (3) of the inner casing - and is mounted in the given axial position (z) starting from a drive side (8); wherein

   - the inner casing (2) is hollowed out or widened from its outlet-side end-face (22) both in radial and in axial direction by such an amount that an outlet-side end-face edge (24) of the rotor (6) rotates circulating eccentrically during pump operation - not stressing the inner surface (3) of the casing (2);

   - to compensate a power loss, a decrease of the greatest internal width (A dimension) of the screw channels formed by the inner surface (3) and distributed over the remaining length of the stator, is provided in the stator (2) as greater conicity.
3. Eccentric screw pump according to claim 1 or 2, characterised in that free flow (G) of the outlet-side peripheral edge (24) of the rotor (6) produced by radial and axial setting-back of an outlet-side end-face surface (22) of the stator casing (2), exists axially counter to the conveying direction on a longitudinal section (z5), which is at least 2% of an axial length of a stator pitch (screw stage L1), in particular is above 3%, between 5% and 10%, or up to half a stage.
4. Eccentric screw pump according to claim 3, characterised in that the setting-back, in particular as hollowing-out or expansion, has dimensions so that the free flow (G) is retained even for wear-related axial displacement (19, Δz) of the rotor (6).
5. Eccentric screw pump according to one of the previous claims, wherein to compensate the power loss occurring due to the setting-back of a section (z5) of the outlet-side end-face surface (22) of the stator (2) and the thus related shortening of its at least one spiral which is effective conveying

   (i) a reduction of the internal width of the screw channel is provided as A-dimension reduction in conveying direction for each pitch stage (L1) of the stator casing (2) of at least 0.4%; or

   (ii) an internal width of the inner casing per stage (L1) is reduced by more than essentially 0.4%, wherein the internal width is reduced essentially continuously from the inlet opening (4) to the outlet opening (5).
6. Eccentric screw pump according to claim 1 or claim 2, wherein the expansion has (5b) an essentially cylindrical shape section.
7. Eccentric screw pump according to claim 1 or claim 2 or claim 6, wherein the expansion (5) of the pressure-side opening has an essentially conical shape section (5a), in particular also with essentially conical widening as run-in cone (4) on the inlet side (MES) of the stator or the pump.
8. Eccentric screw pump according to claim 1 or claim 2 or claim 7, wherein on a piece (z5) of the axial length close to the outlet side (MAS), the spiral inner surface (3) is widened (5c) radially outwards and axially forwards towards the pressure side, in particular counter to an essentially continuously running reduction of the radial dimension of the inner surface (3) before the said axial piece (z5), starting close to the inlet side of the stator or the pump.
9. Eccentric screw pump according to claim 1 or 2, wherein a pressure-side end-face end of the stator supports an annular elastomer bar (21), for sealing when installing the stator, with respect to pressure-side mounting.
10. Process for operating an eccentric screw pump having a casing (2) made from elastomer material which can be introduced into an essentially cylindrical housing (1) or arranged there, the inner surface (3) of which is designed spirally, to mount a helical rotor (6) which can be inserted with pretension in the elastomer casing in a predetermined axial position and with predetermined radial eccentricity (9) and supported on the drive side in this position; characterised in that an outlet opening (5; 5a, b, 5c) of the stator (2) is expanded starting from its end-face end and counter to an axial conveying direction or is radially widened, so that in pump operation, a peripherally rotating end-face edge (24) on the rotor end (23) of the rotor (6) - preferably for axial displacement (19; Δz) of the rotor, opposite the stator - rotates in contact-free manner or without considerable pressure contact with the inner surface (3) of the elastomer casing (2).
11. Process according to claim 10, wherein the cylindrical housing is single-parted as a peripherally continuous casing, or provided with at least one axial slot, or is multi-parted provided with several axial slots.
12. Process according to claim 10, wherein the widening or expansion (5a, 5b; 5) is essentially cylindrical, conical or spiral on the pressure-side end-face end of the stator, or has a combination of such sections.
13. Process according to claim 10, wherein the stator has an in particular conically designed expansion (4) on its end face-side inlet side.
14. Process according to claim 10, wherein the length (z5) of the expansion (5) extending back axially is greater than 2%, preferably 5% and less than 50%, of the axial length (L1) of a stage of the spiral of the stator, than a stator pitch.
15. Elastomer stator, suitable for a eccentric screw pump according to claim 1, having an essentially stiff outer casing and an inner casing (2) made from elastomer material which is more flexible with respect to the outer casing arranged therein, the inner surface (3) of which is designed to be running helically or spirally about a longitudinal axis (10), to mount a helical or spiral, eccentric rotor (6), which can be introduced into the stator casing in a predetermined axial position (z1) with respect to the latter, and is mounted (18, 16, 17) in its axial position starting from a drive side, wherein the elastomer inner casing (2) is designed to be reduced back from its outlet-side end face (z5)

    (i) in axial direction

    (ii) with respect to a spiral inner surface (3) axially further forwards (to the inlet side MES) in radial direction (r5) in order to provide free flow (G) during pump operation about an outlet-side end-face edge (24) of the rotor (6), and wherein the spiral inner surface (3) decreases essentially continuously from the end face-side inlet side in its inner dimension as far as the wall thickness of the elastomer casing (2) designed (r5, z5) to be reduced.
16. Elastomer stator according to claim 15, wherein a peripheral bar (21) made from elastomer material is formed on the outlet side (MAS), which projects axially, in particular between it (21) and the start of the first radial expansion (r5, 5b) extending a piece (z5) axially, exists an essentially cylindrical reduction of the wall thickness of the elastomer casing (2).
17. Elastomer stator according to claim 16, wherein a residual wall thickness (2') of the elastomer inner casing has in the region of the radial expansion (5b) essentially the same radial thickness as the peripheral bar (21) projecting on the outlet side (MAS).
18. Elastomer stator according to claim 15, wherein the inner dimension of the spiral inner surface (3) decreases by at least 0.4% per stage as far as the radial expansion (5, 5a, 5b, 5c).

Images