EP1656502B1 - Eccentric screw pump equipped with a rotor that is erosion-resistant - Google Patents

Abstract

An eccentric screw pump or an eccentric screw motor has a rotor formed from at least a tubular jacket with at least two layers. The outer layer of the jacket consists of a material that is abrasion-resistant and/or corrosion-resistant.

Description

From the DE 198 52 380 A1 For example, a rotor for an eccentric screw pump or an eccentric screw motor manufactured by cold working is known.

The pump or the motor has a stator with a continuous helical opening in which the rotor rolls in the displacement mode. The stator forms a cylindrical tube which is provided with an elastomeric lining. The elastomeric lining itself constitutes the wall of the through-hole and acts as a seal against the stator.

The stator is composed of a core element and a shell formed around it. The jacket is cold formed starting from a cylindrical tube in the helical shape. This preserves the original cylindrical Tube not only the helical shape as it is required for the rotor, but the tube is thus firmly connected to the core element. In the final state, the thread valleys of the jacket of the stator are firmly and frictionally on the core element. To improve the entrainment effect between the core element and the jacket of the stator, the carrier element may still be provided with longitudinal ribs.

The known rotor is inexpensive to produce in very large quantities. Lengths of up to 6 meters can easily be achieved without the need for a chipping rework of the surface of the stator. The surface of the rotor is very smooth and sufficiently dimensionally stable.

The core element present in the shell prevents the rotor from becoming desorbed when pressurized, which would lead to a pitch error between the stator and rotor and the consequent leakage.

The steel material hitherto used for the known rotor is not strong enough for a number of applications with regard to the abrasion occurring and, for some applications, also not sufficiently resistant to corrosion. In other words, the known rotor is not characterized by a sufficient erosion resistance. Erosion should not only be understood to mean the removal by corrosion, but also the removal by vibratory grinding of the material being conveyed on the surface.

It is also known from the prior art, the To provide stator with a jacket, which also shows a helical shape similar to a helical shape of the through hole. The elastomeric lining, which in turn serves as a sealing material, in these cases has virtually a nearly constant wall thickness. With such a stator, larger pressures can be generated, or larger torques in the case of an eccentric screw motor.

Based on this, it is an object of the invention to provide an eccentric screw pump or an eccentric screw motor, in which the rotor is characterized by a better erosion resistance.

This object is achieved with the eccentric screw motor or the eccentric screw pump with the features of claim 1.

It is another object of the invention to provide a method to produce a rotor exhibiting greater erosion resistance.

The method is characterized by the features of claim 23.

In the eccentric screw pump according to the invention or the eccentric screw motor according to the invention, the rotor is sandwiched. It consists of a radially inner layer and a radially outer layer, wherein the radially outer layer is specially adapted to the higher erosion resistance. It may be more resistant to abrasion or corrosion, or both, than the radially inner layer.

Incidentally, since the more corrosion-resistant materials can be worse form worse with larger wall thickness and / or are much more expensive than the radially inner layer, the radially inner layer can be selected primarily from the viewpoint of strength and cost, so that with a very thin radial outer layer the livelihood is found.

A very homogeneous structure of the rotor can be achieved if the inner tube is a seamless tube. Inhomogeneities, as they would otherwise occur during welding, thereby avoided. Such inhomogeneities could continue as a form error to the outside. However, it is also possible to use a wound tube as the inner tube. At the helical butt joint, the tube is preferably laser welded. The helix should run in opposite directions to the helix of the outer layer.

The inner layer, or the inner tube, consists of an easily deformable steel, which is well suited to dissipate the forces occurring and can be cold formed in a useful manner.

The outer layer may consist of an attached tube. However, such a solution is only suitable for rotors with a short overall length. For rotors with a large overall length, it is advantageous if the outer layer is formed by a wound-up metal strip.

The metal strip is wound on impact in such a way that the individual turns adjoin each other without a gap. A particularly good arrangement is achieved if before the cold forming the helical joint, on which the turns abut each other, is welded. Preferably, the welding is done by means of laser.

Stainless steel V2A, V4A steel or other abrasion-resistant steels may be considered as external material. Since these have a much higher specific gravity than normal steel, the two-layer construction also means a weight saving compared to a rotor made only of stainless steel. This certainly plays a role in rotors with a length of up to 6 meters.

The strength of the rotor can be improved if it has a core element. The rotor may be molded around the core member to provide a good bond with the core member. The core element prevents long rotation of the rotor under load. In addition, with the help of the core element additional torque can be introduced over the length of the rotor. For this purpose, the substantially Rotationsssymentrische and not helically deformed core is better suited.

The core element may itself be tubular or solid.

In addition, the gap between the tube or shell of the rotor and the core element can either be left blank or filled with a mass.

In the method according to the invention, a cylindrical tube is first provided. The tube is covered with a metal layer, so that a double-walled structure is obtained. Subsequently, the double-walled structure, which is still cylindrical, helically deformed.

The coating of the cylindrical tube with the outer layer is very simple and can also be done simply because of the simple geometric shape of the tube provided.

Since the outer layer must be applied only with a smaller wall thickness, because the stability of the rotor may be generated in the first place of the inner tube, materials can be used for the outer layer, which would no longer be cold to deform at high wall thickness ,

Advantageously, a seamless tube is used in the method according to the invention.

The seamless tube has expediently a metallically bright surface, so that the connection of the outer layer with the tube by the cold forming is not hindered by oxydrückstände.

The outer metal layer consists in the simplest case of a metal strip which is wound onto the tube. In order to increase the tension, the metal strip can be heated immediately before the contact point before being wound up. The subsequent cooling ensures a shrinkage process that holds the metal strip particularly firmly on the surface of the tube.

The butt joint between adjacent turns is suitably welded to prevent penetration of particles.

The resulting double-walled structure is cold formed. In the forming process, at least at certain points, the outer layer joins the inner tube, similar to the case of leafing. The connection is therefore particularly durable and will not open even with temperature changes.

According to the method according to the invention, a core element may be inserted before forming the coated tube.

Incidentally, developments of the invention are the subject of subclaims. It will also be apparent from the study of the embodiments that a number of modifications are possible.

Fig. 1

eine Exzenterschneckenpumpe in einer perspektivischen Darstellung, teilweise geschnitten

Fig. 2

einen Längsschnitt durch den Stator der erfindungsgemäßen Exzenterschneckepumpe,

Fig. 3

einen Längsschnitt durch den Rotor der erfindungsgemäßen Exzenterschneckepumpe,

Fig. 4

einen Querschnitt durch den Rotor nach Fig. 3, und

Fig. 5

das erfindungsgemäße Verfahren zum Herstellen des Rotors der Exzenterschneckenpumpe beziehungsweise des Exzenterschneckenmotors nach Figur 1 unter Versinnbildlichung der Verfahrensschritte

In the drawing, an embodiment of the object of the invention is shown. Show it:

Fig. 1

an eccentric screw pump in a perspective view, partially cut

Fig. 2

a longitudinal section through the stator of the eccentric screw pump according to the invention,

Fig. 3

a longitudinal section through the rotor of the eccentric screw pump according to the invention,

Fig. 4

a cross section through the rotor of Fig. 3, and

Fig. 5

the inventive method for producing the Rotor of the eccentric screw pump or the eccentric screw motor of Figure 1 under symbolization of the method steps

1 shows a schematic, perspective illustration of an eccentric screw pump 1 according to the invention. The eccentric screw pump 1 includes a pump head 2, a stator 3 in which a rotor 4 illustrated in FIG. 2 rotates, and a connection head 5.

The pump head 2 has a substantially cylindrical housing 6 which is provided at one end with a cover 7, through which a drive shaft 8 is guided outwardly sealed. In the housing 6 opens radially a connection piece 9, which ends at a mounting flange 11. In the interior of the housing 6 is, as usual in eccentric screw pumps, a coupling piece to the drive shaft 8, which is connected to a drive motor, not shown, with the rotor 4 rotatably to couple.

The front end of the housing 6 remote from the cover 7 is provided with a clamping flange 12 whose diameter is greater than the diameter of the substantially cylindrical housing 6. The clamping flange 12 includes a stepped bore 13 which is aligned with the interior of the housing 6. In the stepped bore an unrecognizable investment shoulder is formed, against which the stator 3 is pressed with one end.

The connection head 5 has a cooperating with the clamping flange 12 clamping flange 14, which also includes a stepped bore in which the other end of the stator 3 is inserted. With the stepped bore a wegführende pipe 15 is aligned.

Between the two clamping flanges 12 and 14, the stator 3 is tightened sealed by means of a total of 4 tie rods 16. To accommodate the total of 4 tie rods 16, the two clamping flanges 12 and 14 are provided with four mutually aligned holes 17 which lie on a pitch circle, which is larger than the outer diameter of the housing 6 and the tube 15. Through these holes 17 lead rod-shaped tie rod 16 therethrough. On the side remote from the opposite clamping flange 12 and 14 side 16 nuts 18 are screwed onto the tie rods, with the help of the two clamping flanges 12 and 14 are tightened towards each other.

The stator 3 is, as shown in FIG. 2 shows a tubular jacket 19 with a constant wall thickness, which surrounds an interior space 20. The jacket 19 is made of steel, a steel alloy, light metal or a light metal alloy. It is shaped so that its inner wall 21 gets the outer shape of a multi-start screw. Its outer side 22 has a correspondingly similar shape with a diameter corresponding to the wall thickness of the shell 19 is greater than the diameter of the interior of the shell 19th

The jacket 19 terminates at its ends with end faces 23 and 24 which extend at right angles to its longitudinal axis 25. The longitudinal axis 25 is the axis of the interior 20.

In the simplest case, the interior 20 has the shape a double-threaded screw. Thus, also the cross section, which is surrounded by the outer surface 22, each seen at right angles to the longitudinal axis 25, the shape of an oval, similar to a racetrack. In order to adapt this particular geometry to the stepped bore 13, sit on the jacket 19 on each front end of a completion or Reduzierring 26. Alternatively, the ends can also be formed into cylindrical tubes. The end ring 26 includes a through hole 27, which coincides with the course of the outer surface 22 over the length of the end ring 26. In other words, the end ring 26 acts in the broadest sense as a nut, which is screwed onto the thread, which is defined by the jacket 19. The length of the thread corresponds to the thickness of the end ring 26.

Radially outwardly, the end ring 26 is bounded by a cylindrical surface 28 which merges in the axial direction into a plane surface 29 facing away from the shell 19.

On the inner side 21 of the jacket 19 is provided over its entire length with a continuous liner 32. The liner 32 is made of an elastically resilient, preferably elastomeric material, such as natural rubber or synthetic material, and has approximately the same wall thickness at each location.

As can be seen in FIG. 3, the rotor 4 is composed of a core element 33, a rotor shell 34 and a coupling head 35.

The core element 33 is in the illustrated embodiment, a thick-walled steel tube with an at least originally cylindrical outer peripheral surface 36 and a continuous cylindrical interior 37.

The core element 33 is straight and therefore tubular in shape, because the interior does not provide any appreciable contribution to the strength in question, but only adds weight. But it can also be massive.

At its right in Fig. 3 end of the core member 33 is provided with a threaded pin 38. At the opposite end, the core member 33 includes a threaded bore 39.

The jacket 34 of the rotor 4 is also a tube with an inner wall 40 and an outer surface 41. The outer surface 41 forms a thread that continues over the entire axial length of the jacket 34. It begins at 42 and ends at 43. The number of turns of the thread formed by the outer surface 41 is one less than the number of turns of the through-hole 20 in the stator. 3

As the cross section in Fig. 4 reveals, the rotor 4 in the embodiment shown has a four-start thread, i. along the mantle 34 extend helically a total of four strips. Since the passage opening 20 is correspondingly five continuous, forms the five-start thread in the through hole 20 a total of five helically extending strips of elastomeric material.

In Figure 4, the cross section through the rotor 4 is shown. The rotor shell 34 has two layers and consists of an inner layer 44 and an outer layer located thereon Layer 45. The inner layer 44 consists of an originally cylindrical steel tube with good ductility and a strength suitable for the application.

The outer layer 45, however, consists of an erosion-resistant material, that is, a material that is little worn or abraded by the medium to be pumped and / or that is chemically attacked by the medium to be pumped little. A suitable material is for example stainless steel such as a V2A or a V4A. The wall thickness of the inner layer 44 is between 1 mm and 5 mm, while the wall thickness of the outer layer 45 can be between 1 mm and also 5 mm. The production of this rotor 4 is explained below with reference to FIG 5.

The shell 34 is, as already mentioned, tubular, which is why the inner surface 40 of the outer surface 41 follows at a constant distance.

As a result of the helical deformation of the shell 34 whose outer surface 41 seen alternately forms thread crests 46 and thread valleys 47. Due to the Mehrgängigkeit the thread valleys 47 and the crest 46 appear not only in the longitudinal direction, but, as the cross section of FIG each sectional plane seen in the circumferential direction.

The dimensions of the cylindrical straight tube, from which the jacket 34 is cold worked, are selected such that after the final deformation to the helical shape of the shell 34 with its inner peripheral surface 40 in the region of the thread valleys 47 (relative to the outer contour), the outer peripheral surface 36th of the core element 33 at least touched.

With correspondingly greater deformation, it is also possible to additionally slightly deform the outer peripheral surface 36 of the core element 33, as a result of which the outer circumferential surface 36 acquires flat grooves 48 which follow the contour of the thread valleys 47. If the deformation is continued in this way, arises between the shell 34 and the core member 33 not only a frictional, but also a positive connection in the area of the interior of the shell 34 bulging thread valleys 47 with the core member 33. In addition, due to the Deformation even cold welding between the jacket 34 and the core member 33 made at the contact points.

Since the semifinished product, as mentioned, from which the jacket 34 is made, a cylindrical tube whose diameter is larger than the outer diameter of the core member 33, between the core member 33 and the shell 34 helically extending gaps 49. The number of these helical spaces 49 is equal to the number of thread crests 46, which can be seen in the cross section of the rotor 4 in the circumferential direction. Depending on the application, these spaces 49 can either remain empty or filled with a mass. This mass can e.g. Resin or filled with light metal powder resin.

The production method of the rotor 4 consisting of the layers 44 and 45 is illustrated in a very schematic manner in FIGS. 5 to 7.

It is first a blank drawn, seamless steel tube 51 provided with a suitable wall thickness and a suitable length of several meters. The steel tube 51 is wound on the outside with a metal strip 52, which later forms the outer layer 45. The metal band 52 is a band of a corresponding stainless steel or other steel. As can be seen from FIG. 6, the band 42 is wound on the outside of the steel tube 51 as a catchy screw. In this case, it forms adjacent turns 53, which are separated by a respective helically extending butt joint 54. The winding of the metal strip 52 is done so that the butt joint 54 is closed as possible.

The butt joint 54 is welded during winding or in a separate step by means of a laser beam 55 and filler material to achieve a smooth, homogeneous cylindrical surface. Other welding methods are also possible. It can be welded through to connect the band 52 in the region of the butt joint 54 with the support tube 51 cohesively.

Immediately before the metal strip 52 impinges on the tube 51, it is heated, for example by means of a gas flame 56 or inductively. This ensures that the metal strip 52 generates a considerable tension in the circumferential direction after winding on the tube 51 and the cooling.

After the band 52 is wound over the entire length of the tube 51 and the butt joint 54 is also welded over the entire length, the core element 33 is inserted according to FIG. Subsequently, the structure by cold deformation, for example, rolls by means of a variety of rollers, of which only one is indicated at 57, brought in the desired helical shape.

During rolling, the metal strip 52 connects very intimately with the outer surface of the underlying steel tube 51st

The metal strip 52 forms, after the step of Figure 6 is completed, on the metal steel tube 51, a second, outer tube which sits firmly and under tension in the circumferential direction frictionally on the outer peripheral surface of the tube 51. The two tubes, namely the tube formed by winding and the seamless, inner steel tube are so firmly connected to each other after winding that they are no longer separated.

The subsequent rolling process according to FIG. 7 ensures an even more intimate bond, which at least to a certain extent resembles the plating of a metal layer.

By rolling, which in itself leads to a stretching of a piece of metal, surprisingly, the outer, made by winding pipe does not separate from the underlying tube 51. Rather, both are formed together in the desired helical shape, at the same time also the intimate connection with the core element 33 is produced.

Instead of just one metal band, several metal bands can be wound up as a multi-start screw. Furthermore, the winding process can be repeated to create several layers one above the other.

The invention has been explained with reference to an eccentric screw pump. However, it will be readily apparent to those skilled in the art that the invention is by no means limited to progressing cavity pumps. Rather, according to the inventive method according to the figures 5 to 7 and rotors for eccentric screw motors or Mudmotoren are produced. As a result, in each case a displacement machine is obtained, which contains a very resistant rotor.

Claims (32)

1. Eccentric screw pump or eccentric screw motor (1),
   with a stator (3), which contains a through stator bore (20) having a screw-shaped structure,
   with a screw-shaped rotor (4), which is adapted to the stator bore (20) and has a pipe (34) deformed in a screw shape,
   characterised in that the pipe (34) is made up of an inner layer (44) and at least one outer layer (45), which are jointly formed into a screw-shaped structure, wherein the outer layer (45) is made of a material, which differs from the material of the inner layer (44), and
   with a coupling head (35), which is connected to the rotor (4) to be fixed against rotation.
2. Eccentric screw pump or eccentric screw motor according to claim 1, characterised in that the material of the outer layer (45) is more abrasion-resistant and/or more corrosion-resistant than the material of the inner layer (44).
3. Eccentric screw pump or eccentric screw motor according to claim 1, characterised in that the inner layer (44) consists of a seamless pipe (51).
4. Eccentric screw pump or eccentric screw motor according to claim 1, characterised in that the inner layer (44) is made of a steel.
5. Eccentric screw pump or eccentric screw motor according to claim 1, characterised in that the outer layer (45) consists of at least one metal band (52).
6. Eccentric screw pump or eccentric screw motor according to claim 5, characterised in that the at least one metal band (52) of the outer layer (45) is wound onto the inner layer (44) in a screw shape.
7. Eccentric screw pump or eccentric screw motor according to claim 6, characterised in that the abutting points (54) between adjacent windings (53) of the at least one wound metal band (52) are welded.
8. Eccentric screw pump or eccentric screw motor according to claim 7, characterised in that the abutting points (54) are laser welded.
9. Eccentric screw pump or eccentric screw motor according to claim 1, characterised in that the material of the outer layer (45) is formed by a corrosion-resistant and/or highly abrasion-resistant steel.
10. Eccentric screw pump or eccentric screw motor according to claim 9, characterised in that the steel is selected from the materials V2A, V4A.
11. Eccentric screw pump or eccentric screw motor according to claim 1, characterised in that the rotor (4) contains a core element (33), which is connected to the pipe (34) by frictional and/or positive engagement.
12. Eccentric screw pump or eccentric screw motor according to claim 11, characterised in that the pipe (34) is positively connected to the core element (33) in the region of the thread grooves (47) by merely pressing in the core element (33) in the region of the thread grooves (47) of the pipe (34) to form at least one shallow groove (48) running in a screw shape.
13. Eccentric screw pump or eccentric screw motor according to claim 11, characterised in that at least one interstice (49) running in a screw shape is contained between the core element (33) and the pipe (34).
14. Eccentric screw pump or eccentric screw motor according to claim 11, characterised in that the core element (33) is tubular.
15. Eccentric screw pump or eccentric screw motor according to claim 11, characterised in that the core element (33) is solid.
16. Eccentric screw pump or eccentric screw motor according to claim 13, characterised in that the at least one interstice (49) running in a screw shape is filled with a compound.
17. Eccentric screw pump or eccentric screw motor according to claim 13, characterised in that the at least one interstice (49) running in a screw shape is empty.
18. Eccentric screw pump or eccentric screw motor according to claim 1, characterised in that the stator (3) has a wall (32), which is formed by an elastomeric compound.
19. Eccentric screw pump or eccentric screw motor according to claim 1, characterised in that the stator (3) is formed from a shell (19) with an elastomeric lining (32).
20. Eccentric screw pump or eccentric screw motor according to claim 19, characterised in that the elastomeric compound has a substantially constant wall thickness over a large portion of the extent of the stator (3).
21. Eccentric screw pump or eccentric screw motor according to claim 1, characterised in that the shell (19) has a screw-shaped structure, which is similar to the stator bore (20).
22. Eccentric screw pump or eccentric screw motor according to claim 1, characterised in that the shell (19) has a cylindrical structure and the lining (32) has a cylindrical outer peripheral face.
23. Process for the production of a rotor of an eccentric screw pump or an eccentric screw motor with a stator (3) containing a through stator bore (20), which has a screw-shaped structure, wherein the process includes the following steps:

    a cylindrical pipe (51) is provided,

    the pipe (51) is encased with a metal layer (52) such that a double-walled structure (51, 52) is formed,

    the double-walled structure (51, 52) is shaped into the screw-shaped structure of the rotor (4).
24. Process according to claim 23, characterised in that the cylindrical pipe (51) is a seamless pipe.
25. Process according to claim 24, characterised in that the cylindrical pipe (51) has a metal bright-finished outer peripheral face.
26. Process according to claim 23, characterised in that the metal layer is formed from at least one metal band (52).
27. Process according to claim 26, characterised in that the metal band (52) is wound onto the inner pipe (51) such that the windings (53) abut against one another substantially without any gap.
28. Process according to claim 23, characterised in that the abutting point (54) between adjacent windings (53) is welded.
29. Process according to claim 23, characterised in that the metal band (52) is continuously heated before being wound onto the pipe (51).
30. Process according to claim 23, characterised in that the double-walled structure (51, 52) is cold-formed.
31. Process according to claim 30, characterised in that a core element (33) is inserted into the double-walled structure (51, 52) before the cold-forming.
32. Process according to claim 31, characterised in that the core element (33) has longitudinal ribs.

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