EP1404973B2 - Method for making a moineau pump stator and resulting stator - Google Patents

Description

The present invention is in the field of gear pumps of the Moineau pump type, also called progressive cavity pumps, and more particularly relates to improvements in the manufacture and structure of the stators of such pumps, these stators comprising a stator cavity. of helicoidal shape and general axial extent within an elongated body.

Given the very complex shape of the stator cavity of this type of pump, the stator is usually made of molded elastomer enclosed in a rigid casing. Such an arrangement is satisfactory in many applications for which the temperature of the product to be moved remains below 140 ° C, maximum acceptable temperature without damage by the elastomer, and for which also the product to be moved is chemically compatible with the elastomer.

• si la température du produit à déplacer est supérieure à 140°C, ce qui est le cas par exemple dans les exploitations pétrolières où l'extraction des produits épais nécessite leur ramollissement préalable par injection de vapeur à des températures de l'ordre de 200 à 250°C,
• si le produit à déplacer n'est pas chimiquement inerte vis à vis de l'élastomère (produits acides ou solvants par exemple),
• dans les installations alimentaires où les pièces au contact du produit doivent être en métal inerte (par exemple acier inoxydable),
• si des produits circulant dans la pompe successivement présentent des températures respectives très différentes (fonctionnements de très basse à très haute température avec la même hydraulique de pompe ; phase de nettoyage en place dans les Installations alimentaires ; sanitation à la vapeur).

On the other hand, stators thus constituted can not be

• if the temperature of the product to be displaced is greater than 140 ° C, which is the case for example in petroleum operations where the extraction of thick products requires their prior softening by steam injection at temperatures of the order of 200 to 250 ° C,
• if the product to be moved is not chemically inert with respect to the elastomer (acidic products or solvents for example),
• in food installations where the parts in contact with the product must be made of inert metal (for example stainless steel),
• if the products circulating in the pump successively have very different respective temperatures (operating from very low to very high temperature with the same pump hydraulics, cleaning phase in place in food plants, steam sanitation).

It has certainly been attempted to manufacture metal stators to overcome the aforementioned drawbacks. However, it was then massive metal stators whose cavity of complex shape was excavated in a metal block with implementation of very complex and slow machining means. These fabrications have proved very expensive so that massive metal stators have never been the subject of extensive industrial implementation and have remained at a stage of quasi-prototypes (in the food industry in particular).

However, only the use of metal stator cavities can overcome the aforementioned drawbacks in various fields of industry, provided however that the cost of such metal cavity stators is not prohibitive.

This is particularly the case for Moineau pumps arranged in accordance with the teachings of the document FR 2 756 018 , pumps which are intended for deep well oil extraction in a high temperature environment requiring that the rotor and the stator, both metallic, be so constituted that an approximately constant positive clearance is maintained between them over a wide range temperatures up to about 300 ° C.

Of course, we already know from the document FR-A-2 794 498 , a structure and a method of manufacturing a Moineau pump stator in which the stator cavity is constituted by a tubular element which may be metallic. However, from the structural point of view, this known stator is of composite type: the metal tubular element defining the stator cavity is secured to an outer casing via an elastic material (such as an elastomer) filling the gap annular between the tubular metal element and the housing; in addition, the tubular element is dimensioned so that, under the action of the elastic filling material, it applies and / or maintains a stress on the rotor of the pump.

A stator thus arranged restricts the range of use of the pump, on the one hand, because of the rotor clamping by the stator (which excludes pumps for abrasive or highly viscous products - such as heavy oils -) and, on the other hand, because of the presence of the filler material such as an elastomer (which excludes pumps intended to operate in high temperature environments - such as deep well oil extraction pumps -).

In addition, the presence of three main constituent parts (tubular element forming a stator cavity, housing, filling material) leads to a relatively high cost.

As regards the method of manufacturing this known stator, it consists in arranging a metal tubular section, with a core inserted inside the latter, in a housing; then to apply a pressure on the outside of the tubular metal section so as to deform to make it fit the shape of the core, said pressure may come from a pressurized fluid introduced into the annular space between the tubular section and the casing ; and finally removing the mandrel and filling the annular space between the tubular element forming a stator cavity and the housing with an elastic material adapted for said tubular member to apply and / or maintain a stress on the rotor.

Such a method presents or induces several disadvantages which, again, limit the field of use of the pumps equipped with the stators obtained.

A first drawback lies in the fact that the process of deformation, in particular by hydraulic flight, of the initial tubular section is conducted inside the stator housing which thus serves as a pressure chamber. It is then necessary to oversize the housing so that it can mechanically withstand the forming pressures, then after this oversizing becomes useless during operation of the pump.

conversely, if it is desired to avoid excessive oversizing (and then unnecessary) of the housing, it is necessary to limit the forming pressures. This implies that the known process must be limited to the deformation of tubular sections having relatively small wall thicknesses, leading to tubular elements forming a stator cavity which have a relative deformability. This deformability is exploited in the type of pump referred to in the document under consideration since the stator elastically grips the rotor. But in other types of pumps where it is required, between stator and rotor, a game that we want to maintain as constant as possible, such deformability would be a crippling handicap.

It is also, in part, to regulate this deformability of the metal tubular element that it is necessary to provide the addition of an elastic filler material providing a continuous support, over its entire length, of the element. tubular.

Finally, in view of the complex shape of the metal tubular element finally obtained by this process of forming under hydraulic pressure, it must be emphasized that the radial deformation of the initial tubular section is not homogeneous and varies considerably depending on the locations. As a result, the forming of the metal tubular element forming a stator cavity directly and in a single pass from the initially cylindrical tubular section of revolution limits, here again, this process to the treatment of parts having relatively thin wall thicknesses.

The purpose of the invention is therefore to simultaneously remedy the various drawbacks mentioned above and to propose improvements in the manufacture and structure of Moineau pump stators which are of a nature to satisfy the various requirements of the practice, in particular with regard to relates to the stiffness of the stator cavity, the structural simplicity of the stator and the conduct of the manufacturing process.

• une étape préliminaire de formage mécanique au cours de laquelle ledit tube métallique cylindrique de révolution est déformé de manière à préformer une ébauche approchant, intérieurement, la forme et les dimensions de la cavité statorique souhaitée,
• puis une étape de formage définitif au cours de laquelle on soumet ladite ébauche à un processus d'hydroformage, menée à l'intérieur d'une enceinte d'hydroformage, sur une forme de moulage pour obtenir un élément tubulaire métallique rigide formant cavité statorique ayant sa forme et ses dimensions intérieures exactes telles que soit défini, après assemblage du stator avec un rotor, un jeu positif avec le rotor,
• et enfin une étape de montage de l'élément tubulaire métallique formant cavité statorique à l'intérieur d'une enveloppe externe formant carter, avec la so-Ildadsatlon d'au moins les extrémités de l'élément tubulaire métallique à ladite enveloppe.

For these purposes, according to a first of its aspects, the invention proposes an original process for manufacturing a pump-type stator of the Moineau pump type, comprising a stator cavity of axial general extent inside a body. elongated method of manufacturing said stator cavity from a cylindrical metal tube of revolution with a rigid wall, which method according to the invention is characterized in that it comprises the following steps:

• a preliminary step of mechanical forming during which said cylindrical metal tube of revolution is deformed so as to preform a blank approximating, internally, the shape and the dimensions of the desired stator cavity,
• then a final forming step in the course of which said blank is subjected to a hydroforming process, conducted inside a hydroforming enclosure, on a molding form to obtain a rigid metal tubular element forming a stator cavity having its exact shape and internal dimensions as defined, after assembly of the stator with a rotor, a positive clearance with the rotor,
• and finally a step of mounting the metal tubular element forming a stator cavity inside an outer housing envelope, with so-Ildadsatlon at least the ends of the metal tubular element to said envelope.

Thanks to the implementation of the method according to the invention, it is possible to produce a metal tubular element forming a stator cavity which has a wall of relatively large thickness and which, therefore, is perfectly rigid and self-supporting: this element tubular can be secured to the housing that by its ends, resulting in great simplicity of assembly and lower cost and it is ensured the maintenance of clearance between rotor and stator over the entire length of the pump.

Despite the relative thickness of the initial tube (for example of the order of 3.5 mm for a diameter of the order of 65 mm), it is possible to obtain a tubular element satisfying all the requirements, despite the individual insufficiencies of the processes used: the preliminary mechanical forming makes it possible to cause significant local radial deformations despite the substantial thickness of the wall to be deformed, but without it being possible to achieve a high precision of shape; on the contrary, the process of hydroforming under very high pressure (for example of the order of 4000 x 10 ⁵ Pa) makes it possible to achieve a precise forming on a core, but provided that the amplitude of the localized radial deformation is relatively small.

The combination of the two processes of mechanical deformation and hydroforming, carried out in two successive stages, makes it possible to collect their individual advantages and to eliminate their drawbacks, and thus to succeed in producing, under economic conditions, a metal cavity stator which can enter into the constitution of Moineau pumps able to operate in difficult conditions.

In one possible embodiment, the preforming step leading to the roughing is carried out, in successive passes, by successive external crushing of the metal tube between jaws facing each other, the metal tube and the jaws being relatively displaced in successive steps, axially and in rotation.

In another embodiment which is preferred, the preforming step leading to the roughing is carried out by relatively moving the metal tube and at least two pressure rollers, said metal tube in particular being able to rotate about its axis while the two rollers, supported on the tube diametrically opposed, are moved parallel to the axis of said tube.

As for the basic terminal step implementing a hydroforming process, it can be performed by compressing the blank on a core disposed inside thereof, which leads to transfer, by direct contact with the outer surface of the core and the inner surface of the blank, the exact shape and the precise dimensions of the core to the stator cavity; or it can be carried out by dilating the blank inside a mold, which implies a good control of the deformation of the metal and a good control of its thickness so that the conformation of the outer face of the mold tubular element in contact with the mold is reflected on its inner face by an exact conformation and a precise dimensioning of the stator cavity.

Once fabricated the metal tubular element forming a stator cavity, the latter is introduced inside a cylindrical tubular envelope, and the ends of the tubular stator cavity are secured to said envelope; then optionally filling the annular space between the stator cavity and the envelope with a rigid filler material to relieve the fasteners in the presence of vibration.

For applications in high pressure pumps that require long stators, at least two stator sections are individually manufactured as described above and are secured end to end, in particular by screwing or welding.

According to a second of its aspects, the invention proposes a pump pump stator of the Moineau pump type, comprising a stator cavity of axial general extent inside an elongate body, characterized in that the stator cavity is defined. by a rigid walled metal tubular element internally having the shape and the dimensions of the stator cavity such that, after assembly of the stator with a rotor, a positive clearance with the rotor and obtained by implementing the method and this tubular element is defined is secured to an outer casing by means of rigid rings forming wedging spacers which are interposed between the ends of said metal tubular element forming a stator cavity and the outer casing.

These rings form flanges for fixing the stator to the adjacent elements upstream and downstream; moreover, in the case of the presence of an outer casing, these rigid rings form wedge spacers interposed between the ends of said metal tubular element forming the stator cavity and the outer casing. The assembly of the rings with the metal tubular element forming a stator cavity and, when this is the case, with the outer casing can be carried out in any appropriate manner, in particular by welding and / or screwing.

Depending on the applications intended for the pump, the annular gap defined between the metal tubular element forming the stator cavity and the casing can be filled with a rigid filling material, for example a thermosetting resin or a cement, capable of reinforcing the vibration resistance of the securing means between the tubular element and the housing.

Thanks to the provisions of the invention, the stator is formed with a stator cavity with a rigid metal wall which is therefore able to meet the specific requirements of various users while the stator cavity is no longer hollowed out in a solid metal body, It is no longer necessary to use, for its manufacture, expensive means and much simpler and less expensive technological solutions can be implemented for this purpose, a particularly effective example will be indicated later.

In the case where it is desired to have a stator of great length (high-pressure pump), it is possible to constitute such a stator by end-to-end joining of at least two stator sections individually constituted as indicated above.

Thanks to all the provisions of the invention, it is possible to have stators of Moineau pumps with a metal stator cavity (for example bronze type UE9 or the like or stainless steel type 316L or the like) that meet the aspirations at least some users, such stators can be manufactured in large series under attractive economic conditions.

The invention will be better understood on reading the following detailed description of certain embodiments given solely by way of non-limiting examples.

• la figure 1 est une vue simplifiée en coupe longitudinale d'un mode de réalisation possible d'un stator constitué conformément à l'invention ;
• la figure 2 est une vue simplifiée en coupe longitudinale d'un autre mode de réalisation du stator de la figure 1.
• la figure 3 est une vue simplifiée en coupe longitudinale d'un stator long, pour pompe à haute pression, agencé selon l'invention ;
• la figure 4 est une vue agrandie d'une partie du dispositif de la figure 3 ;
• la figure 5 est une vue simplifiée en coupe longitudinale d'encore un autre mode de réalisation d'un stator constitué conformément à l'invention ;
• la figure 6 est une vue en perspective d'un élément tubulaire métallique formant cavité statorique conforme à l'invention ;
• les figures 7A et 7B sont des vues schématiques illustrant respectivement deux modes de mise en oeuvre de l'étape de préformage d'une ébauche tubulaire métallique conformément à l'invention ;
• la figure 8 est une vue schématique illustrant un premier mode de mise en oeuvre de retape d'hydroformage de l'élément tubulaire métallique formant cavité statorique à partir de l'ébauche préformée à l'étape Illustrée aux figures 7A ou 7B ; et
• la figure 9 est une vue schématique Illustrant un second mode de mise en oeuvre de l'étape d'hydroformage de l'élément tubulaire métallique formant cavité statorique à partir de l'ébauche préformée à l'étape Illustrée aux figures 7A ou 7B.

In this description, reference is made to the accompanying drawings in which:

• the figure 1 is a simplified longitudinal sectional view of a possible embodiment of a stator constituted according to the invention;
• the figure 2 is a simplified view in longitudinal section of another embodiment of the stator of the figure 1 .
• the figure 3 is a simplified longitudinal sectional view of a long stator, for high pressure pump, arranged according to the invention;
• the figure 4 is an enlarged view of part of the device of the figure 3 ;
• the figure 5 is a simplified view in longitudinal section of yet another embodiment of a stator constituted according to the invention;
• the figure 6 is a perspective view of a metal tubular element forming a stator cavity according to the invention;
• the Figures 7A and 7B are schematic views respectively illustrating two modes of implementation of the step of preforming a metal tubular blank according to the invention;
• the figure 8 is a schematic view illustrating a first embodiment of hydroforming retape of the metal tubular element forming a stator cavity from the preformed blank to the step illustrated in FIGS. Figures 7A or 7B ; and
• the figure 9 is a schematic view illustrating a second embodiment of the step of hydroforming the metal tubular element forming a stator cavity from the blank preformed in the step illustrated in FIGS. Figures 7A or 7B .

Referring first to the figure 1 , a possible embodiment of stator for Sparrow pump, generally designated by the reference 1, comprises a casing or external rigid casing 2, of elongated shape and generally tubular conformation, inside which is fixed a metallic tubular element 3 with a rigid wall which internally has the shape and dimensions of the desired stator cavity.

An enlarged perspective view of element 3 is given to the figure 6 , which gives a more accurate representation of the Moineau profile, namely a helical gear with an almost elliptical cross section. To the figure 6 the element 3 is illustrated on a length limited to a pitch P of helical winding; D denotes the nominal diameter of the tubular element 3, and E denotes the eccentricity.

The tubular element 3 forming a stator cavity is made of any suitable metal for its mechanical constitution and for the application for which the pump is intended; the choice of material must be such that the metal stator cavity and the metal rotor enclosed therein are made of respective metallic materials which have compatible thermal expansion coefficients so that any dimensional variation of one is accompanied by a substantially identical dimensional variation, in amplitude and direction, of the other in order to maintain an approximately constant positive clearance over a wide temperature range of up to 300 ° C for deep well oil extraction pumps (see below) point the document FR-A-2,756,018 ); likewise, for food applications, the metal material of the stator cavity must be inert with respect to the product; It is the same for example for the pumping of acidic or basic products.

It is possible, for example, to constitute the tubular element 3 forming a bronze stator cavity of the UE9 type or equivalent; or stainless steel type 316L or equivalent.

As illustrated at figure 1 or at figure 6 , the tubular element 3 is relatively thick walled, that is to say that the thickness of its wall is a few percent (for example 6%) of its nominal diameter: the essential is that the thickness of this wall must be sufficient to impart excellent rigidity to the tubular element 3.

The tubular element 3 is secured to the outer casing in any appropriate manner suitable for obtaining a rigid assembly and indeformable axis. In the embodiment shown in figure 1 , wedging rings 4 are interposed between the respective ends of the tubular element 3 and the housing and mechanically fixed thereto, in particular by screwing or preferably by welding. Such a welded joint is shown on the enlarged partial view of the figure 4 , on which is schematized in 5 the weld bead of the ring 4 on the front end of the tubular element 3 and 6 the weld bead of the ring 4 with the end of the housing 2 in which it is partially engaged.

If the tubular element 3 thus arranged does not have sufficient longitudinal rigidity, it is necessary to provide one or more intermediate support by setting intermediate ring (s) lntermediaire (s).

It may be advantageous, in certain applications for using the pumps equipped with a stator according to the invention, to take advantage of the presence of the free gap between casing and tubular element to circulate a fluid for purposes specific. In particular, it is possible to circulate a hot fluid (water vapor, hot water, for example) to heat - and thus fluidify - a thick product / pasty moved by the rotor to facilitate this movement (case of a thick oil pumped in a deep well, for example). It is therefore necessary to fit the casing with holes, axially spaced, inlet 25 a and outlet 25 b for this fluid, as shown in figure 1 in dashes.

It may also be necessary to reinforce the vibration resistance of the fasteners and for this purpose, the solution illustrated in FIG. figure 2 which consists in filling the annular gap 7 between the tubular element 3 and the casing 2 with a rigid filling material 8 (for example a thermosetting resin, a cement, a cement ceramic, etc.): this results elimination, or at least attenuation, of the vibrations of this element 3.

To form long stators (the discharge pressure of a Moineau pump is all the higher as the number of progressive cavities is high, and therefore the pump is long), it is possible to assemble mechanically end to end several stator sections individually constituted as indicated above. To the figure 3 , by way of example, a long stator formed by the end-to-end joining of two stators 1 such as the one of FIG. figure 1 . The mechanical assembly of the two stators 1 can be carried out in any appropriate way, in particular by screwing or preferably by welding. On the enlarged view of the assembly area of the two stators 1 given to the figure 4 the weld bead of the two end-to-end stators has been designated by 9: for this purpose, the end faces of the abutting rings 4 are chamfered and the weld bead 9 is deposited in the annular groove. thus constituted.

The provisions which have just been exposed with regard to Figures 2 and 3 can advantageously be combined to form long stators, for example such as those used in petroleum extraction pumps (which may, for example, have lengths of the order of 9 meters).

For short stators, the tubular metal element 3 forming the stator cavity may, on its own, have sufficient rigidity and the presence of a housing 2 becomes superfluous. As illustrated in figure 5 , the stator 1 then consists only of the tubular element 3.

In this case, to facilitate the assembly of said tubular element 3 to adjacent upstream and downstream elements, it is desirable to provide the presence of the aforementioned rings 4, secured (welded or screwed in particular) to the ends of the tubular element 3 and to outside thereof, said rings then constituting assembly flanges.

The metallic tubular element 3 can be manufactured by any appropriate means. However, its complex general shape as well as the dimensional accuracy and the quality of the surface state required for its internal face which is, strictly speaking, the stator surface make the usual means too expensive and / or difficult to implement. too long to allow industrial mass production.

It is to overcome this difficulty that the invention advocates an original process that will now be exposed.

It starts from a tubular cylindrical metal section of revolution, made of the desired metal, rigid wall (for example, whose wall thickness can be up to about 6% of the outer diameter of the tube).

A preliminary preforming step is first carried out during which the initial metal tube is mechanically deformed so as to preform a tubular blank having, internally, approximately the shape and dimensions of the desired stator cavity. The formal and dimensional approximation may, for example, be of the order of 5%.

One solution for implementing this preforming step consists in hammering the initial tube, as illustrated in FIG. Figure 7A by exerting a diametrical pressure (arrows 11) on the tube 12 taken between two jaws 10 integral with a press. The jaws 10 are shaped and mutually arranged (for example offset angularly relative to one another) so as to indent the tube to form the valleys or "valleys" of the helical windings. The jaws 10 providing localized deformations, It is necessary to proceed in successive passes along the tube which is moved, not by step, simultaneously axially (arrow 13) and in rotation (arrow 14) to follow the profile of the Moineau propeller .

Another solution, currently preferred, is to deform the tube between at least two rotary rollers, as shown in FIG. Figure 7B . As in the previous solution, the tube 12 is rotated about its axis (arrow 14). Simultaneously, several rollers 21 (in practice two rollers 21 diametrically opposed) are pressed towards each other so as to locally crush the tube between them: at the same time as the tube turns on itself, the two rollers 21 turn around their respective axes 22 (arrows 23) and a relative axial displacement is generated between the tube 12 and the set of rollers 21. In the example illustrated in FIG. Figure 7B , the rotating tube is not moved axially, while it is the set of rotating rollers 21 which is moved (arrows 24) parallel to the axis of the tube.

Once the blank has been prepared, the final step of final shaping of the blank 12 is carried out in order to obtain the tubular element 3 forming a stator cavity. According to the invention, this final shaping is carried out by a hydroforming process, that is to say that one of the faces (inner or outer) of the blank 12 is subjected to a hydraulic pressure, which, considering the rigidity of the metal wall, must be high and which is exerted uniformly at each point of the surface, so that the wall of the blank, in spite of its rigidity, is pressed on a reference footprint that she marries closely and of which she keeps the exact shape and dimensions.

According to a first mode of implementation illustrated in figure 8 , the blank 12 is threaded onto a core 15 having, externally, the exact desired conformation for the stator cavity. The blank / core assembly is placed in a closed chamber 16 (hydroforming chamber) which is filled with a liquid 17. By putting this liquid under pressure, the blank 12 (arrows 18) is crushed on the core 15 The metallic tubular element 3 is thus formed, the inner face of which is exactly shaped according to the external shape of the core 15 (hydroforming by compression on an inner core).

According to a second embodiment illustrated at figure 9 the blank 12 is introduced into a mold 19 having a cavity 20 shaped to the exact shape to be given to the tubular element 3 to form a stator cavity. The ends of the blank 12 are sealed and the internal volume of the blank is filled with liquid 17. By putting this liquid under pressure, is crushed (arrows 18) the blank 12 against the wall of the mold cavity 20 The tubular element 3 is thus formed (hydroforming by expansion against an external mold).

It will be noted that in the process of hydroforming by compression on an inner core, it is the inner face of the tubular element 3 (that is to say, strictly speaking the face defining the stator cavity itself). who is in contact with the nucleus and who marries directly and closely the form of the latter. On the other hand, in the process of hydroforming by dilation against the wall of a molding cavity, it is the outer face of the tubular element 3 which is brought into direct and close contact with the molding wall, whose shape it conforms to: the internal face of the tubular element 3 faithfully reproduces this form only if the thickness of the wall of the element 3 is perfectly controlled, especially perfectly uniform.

• dimensions intérieures de l'élément tubulaire métallique fini : $$\mathrm{D}=42,3\mathrm{mm}$$
  
  $$\mathrm{D}+4\mathrm{E}=72,8\mathrm{mm}$$
  
• périmètre de la fibre moyenne de l'élément : 204,8 mm
• rétreint lors de la déformation par hydroformage : environ 5 %
• diamètre de la fibre moyenne du tube initial : 68,44 mm
• diamètre intérieur du tube initial ayant une épaisseur de 3,5 mm : 65 mm.

The hydroforming process may, for example, be carried out under the following conditions:

• internal dimensions of the finished metal tubular element: $$\mathrm{D}=42,3\mathrm{mm}$$
  
  $$\mathrm{D}+4\mathrm{E}=72,8\mathrm{mm}$$
  
• perimeter of the average fiber of the element: 204.8 mm
• shrinkage during deformation by hydroforming: about 5%
• diameter of the average fiber of the initial tube: 68.44 mm
• inner diameter of the initial tube having a thickness of 3.5 mm: 65 mm.

The hydroforming process is carried out using, as a liquid medium, water brought to a pressure of the order of 4 × 10 ⁸ Pa for a duration of about 10 minutes.

Once the tubular element 3 has been completed, the assembly of the stator is completed by joining this element 3 to the casing 2, for example by means of rings 4, in particular welded, and optionally with filling of the gap 7 between the element 3 and the casing 2, according to the indications given above in relation to the Figures 1 to 4 .

The manufacturing method of the element 3 according to the invention is capable of being used industrially and allows industrial mass production of the metal tubular element 3 forming a stator cavity. The provisions of the invention therefore make it possible to envisage serial production and acceptable costs of Moineau pumps equipped with metal cavity stator adapted to meet the needs in at least some areas of the industry, and in particular the pumps in which positive play must be maintained between stator and rotor.

Claims (10)

1. A method for manufacturing a stator (1) of a Moineau-type gear pump, this stator comprising a stator cavity running generally axially inside an elongate body, the method consisting in manufacturing said stator cavity from a rigid-walled metal tube that is cylindrical of revolution, the method being characterized in that it comprises the following steps:

   - a preliminary mechanical-forming step during which said metal tube that is cylindrical of revolution is deformed so as to preform a rough form (12) that internally approximates to the shape and dimensions of the desired stator cavity,

   - then a definitive-forming step during which said rough form (12) is subjected to a hydroforming process, performed inside a hydroforming chamber, on a molding form (15, 19) to obtain a tubular metal element (3) forming a stator cavity with its exact shape and interior dimensions such that, once the stator has been assembled with a rotor, a positive clearance with the rotor is defined,

   - and finally a step of mounting the tubular metal element (3) that forms the stator cavity inside an outer casing forming a housing (2), with at least the ends of the tubular metal element (3) being joined to said casing (2).
2. The method as claimed in claim 1, characterized in that the preforming step leading to the rough form (12) is performed by successive external crushings (11) of the metal tube between opposing jaws (10), the metal tube and the jaws being moved relative to one another in successive steps, axially (13) and in terms of rotation (14).
3. The method as claimed in claim 1, characterized in that the preforming step leading to the rough form (12) is performed by moving relative to each other the metal tube and at least two press rollers arranged symmetrically in contact with it.
4. The method as claimed in claim 3, characterized in that the metal tube is rotated about its axis and the rollers are moved parallel to the axis of the tube, at the same time being pressed forcibly against the tube.
5. The method as claimed in any one of claims 1 to 4, characterized in that the hydroforming process is performed by compressing the rough form (12) onto a core (15) arranged inside it.
6. The method as claimed in any one of claims 1 to 4, characterized in that the hydroforming process is performed by expanding the rough form (12) placed inside a mold (19).
7. The method as claimed in any one of claims 1 to 6, characterized in that the annular space (7) between the tubular metal element (3) and the outer casing (2) is filled with a filler material (8).
8. A method for manufacturing a very long stator, characterized in that at least two stator portions (1) are manufactured individually as claimed in any one of claims 1 to 7 and in that they are joined together (9) end to end.
9. A stator (1) of a Moineau-type gear pump, comprising a stator cavity running generally axially inside an elongate body, characterized in that the stator cavity is defined by a rigid-walled tubular metal element (3) internally having the shape and dimensions of the stator cavity such that, when the stator is assembled with a rotor, a positive clearance is defined with the rotor, and which is obtained by implementing the method as claimed in any one of claims 1 to 8, in that this tubular element (3) is joined to an outer housing (2) using rigid rings (4) forming wedging spacer pieces which are inserted between the ends of said tubular metal element (3) forming the stator cavity and the outer housing (2), and in that the annular gap (7) defined between the tubular metal element (3) forming the stator cavity and the housing (2) is filled with a filler material (8) able to enhance the resistance to vibration of the means that join the tubular element and the housing together.
10. The stator as claimed in claim 9, characterized in that the housing is provided with an inlet orifice (25a) and an outlet orifice (25b) which are axially distant from one another, for admitting and circulating fluid in the gap between the housing (2) and the tubular metal element (3).

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