Split pipe for a wet runner pump and method for its manufacture

Description

[0001] The invention relates to a canned tube for a wet rotor pump, consisting of a wound, continuous fiber-reinforced plastic tube, and to a method for manufacturing such a canned tube by winding a strip of continuous fiber-reinforced plastic onto a winding core in two or more layers and then consolidating it, in particular by melting it, to form a dimensionally stable plastic tube.

[0002] Wound split tubes made of fiber-reinforced plastic have long been known in the prior art, for example from European patent application EP 1231048 A2, which teaches how to coat or wrap an extruded, thin-walled plastic tube with a stiffening layer, using a synthetic resin between this layer and the tube.

[0003] A canned tube is used in a wet rotor pump to spatially and hermetically separate the liquid-filled, "wet" rotor chamber, which is typically located inside the canned tube, from the "dry" stator, which typically surrounds the canned tube externally (see German patent application DE 102013004339 A1, paragraph

[0010] ). A wet rotor pump is a centrifugal pump in which the rotor of the electric motor driving the centrifugal pump rotates inside the canned tube, and the rotor chamber is generally open to the pump chamber and thus filled with the pumped fluid. The pumped fluid cools the rotor and the stator and also lubricates the plain bearings supporting the common motor-pump shaft. Wet rotor pumps are frequently used as circulation pumps in heating and cooling systems, but also in drinking water systems and numerous other applications, such as fuel pumps or well pumps.Each individual application already results in numerous requirements that the canned tube must meet due to the nature of the operation. The requirements are correspondingly higher if the wet rotor pump, or rather its canned tube, is to be designed and suitable for all applications simultaneously.

[0004] Patent US 2009 / 026878 A discloses an unwound plastic slotted tube for a wet-rotor submersible pump, which is metallized internally and / or externally to form a hermetically sealed coating. WO 2014 / 063894 A2 describes a diffusion barrier layer for slotted tubes.

[0005] The most important requirement for a canned tube is, on the one hand, to withstand the constant static pressure from the rotor chamber, such as that found in heating or drinking water systems, and on the other hand, to withstand the additional dynamic, intermittent pressure surges that occur, for example, due to suddenly opening or closing valves in the piping system (check valves, electromagnetic valves) to which the wet rotor pump is connected, as these pressure surges are also noticeable in the rotor chamber. For most applications, the internal pressure in the rotor chamber is a maximum of 6 bar nominal pressure. However, in high-pressure applications, an internal pressure of 16 bar nominal pressure is also possible. In drinking water applications, dynamic pressure surges of up to 50 bar can also occur. The fiber-reinforced, wound plastic tube is ideally suited to this task due to its high mechanical strength.However, it lacks other essential qualities.

[0006] The canned tube must be chemically and electrochemically resistant, depending on the pumped medium. Due to abrasive solid particles such as corrosion products or sand swirling around in the rotor chamber, the canned tube must also be wear-resistant. Furthermore, it must prevent the permeation of gases or water vapor from the rotor chamber into the stator chamber. In the case of a drinking water application, the canned tube must also meet the requirements for a drinking water-compliant material. To ensure permanent separation throughout the entire service life of the wet-rotor pump, the aforementioned properties must remain consistently intact. The wound plastic tube only partially meets these requirements. This is because the manufacturing process potentially allows for leaks in the form of holes, capillaries, or interfaces.Furthermore, a thermosetting plastic with an epoxy resin matrix is ​​not resistant to glycols, which are often added to heating water, at higher temperatures.

[0007] In some wet rotor pump designs, the canned tube may also be designed to mechanically support the sliding bearing, i.e., to absorb axial and radial forces. For precise positioning of the sliding bearing within the canned tube, as well as for precise positioning of the canned tube itself within the wet rotor pump, and for sealing purposes, the canned tube may have certain features, such as one or more projections, stops, grooves, chamfers, etc., which cannot be achieved by the wound plastic tube alone.

[0008] To meet all requirements and applications, it is known to manufacture the slotted tube by combining an outer tube and an inner tube. The outer tube is formed by the wound plastic tube, and the inner tube is a separate, injection-molded component that, after its manufacture, is force-fitted into the outer tube, in particular by pressing, so that an interference fit exists between the two tubes. The inner tube is, for example, made of a glass fiber-reinforced thermoplastic, e.g., PPS (polyphenylene sulfide), with a wall thickness of 0.8 mm and meets the requirements for chemical and electrochemical resistance, dielectric strength, drinking water compliance, diffusion tightness, and abrasion resistance. Furthermore, due to the injection molding process, features can easily be incorporated on the outside and / or inside of the inner tube.Although the inner tube is fiber-reinforced and serves as the actual separation between the rotor and stator chambers, it has only low mechanical tensile strength and therefore cannot withstand the specific pressures encountered in every application. This task is then taken over by the outer tube, which can be considered a local external mechanical reinforcement of the inner tube in a specific area. This is the area between the two axial ends.

[0009] For the outer tube to function as a local mechanical reinforcement for the inner tube, it must fit snugly against the outer surface of the inner tube. To achieve this, tight tolerances of less than 0.1 mm in the outer diameter of the inner tube are required, which are difficult to maintain due to the inherent shape of the tube. Gradual wear of the injection mold, replacement of the mold due to wear, changes to the tube's dimensions or design elements, or even a change in the plastic material used for the inner tube, all necessitate regular revalidation of tolerance compliance. For example, different plastic materials exhibit different shrinkage rates, meaning that even tubes produced on the same injection molding machine and under comparable process conditions can have different tolerances depending on the plastic material used.Regularly revalidating compliance with tolerances is complex and expensive, especially since this has to be done for each motor size or corresponding slotted tube size (diameter, length).

[0010] Furthermore, press fits between two round components are always challenging in practice due to general plastic tolerances and roundness variations. The two tubes must be neither too loosely fitted nor pressed together too tightly.

[0011] It is therefore an object of the present invention to provide a split tube and its manufacturing process that overcomes at least some of the aforementioned disadvantages.

[0012] This problem is solved by a slotted tube having the features of claim 1 and a method having the features of claim 11. Advantageous embodiments are specified in the respective dependent claims and are explained below.

[0013] According to the invention, a canned tube for a wet rotor pump according to claim 1 is provided. A method according to claim 11 is carried out to manufacture the canned tube according to the invention.

[0014] The coating fulfills the functions of the separate inner tube previously used in the prior art, which is absent in the slotted tube according to the invention or is replaced by the coating. Depending on the type of coating, the abrasion resistance can even be improved compared to the pure injection-molded inner tube. The coating is not dimensionally stable itself, but is supported by the plastic tube. In this respect, the plastic tube forms a mechanical support structure for the coating. Thus, the slotted tube according to the invention is a single piece. The joining process of two tubes and the associated disadvantages are therefore eliminated. Tolerance problems that occur in the prior art when injection-molding the inner tube do not arise. Furthermore, the costs for constructing the injection molds for the inner tube are saved. Overall, the production of a slotted tube according to the invention is significantly simpler and more cost-effective.

[0015] Another positive effect of the coating according to the invention is that elastomeric sealing elements can be mounted with less friction loss due to the coating. Furthermore, the coating has the advantage that any defects (e.g., demolding marks) in the interior of the wound tube are covered and sealed by the coating, which further secures the durability and service life of the slotted tube and reduces / mitigates points of attack for chemically abrasive conveyed media.

[0016] In particular, the coating ensures chemical resistance and tightness of the plastic tube, as pores and holes are sealed by the coating. Unlike, for example, impregnation, which, due to the lack of a chemical bond, only provides surface wetting that is not permanent and could be scratched off, the coating according to the invention is chemically bonded to the plastic tube at the molecular level. This chemical bond, i.e., the connection of molecules between the plastic tube and the coating, creates a metallurgical bond. The coating thus forms a diffusion barrier, preventing any medium from diffusing from the rotor chamber into the stator chamber. The tube is therefore hermetically sealed against the medium, and in particular, watertight.

[0017] To manufacture the plastic tube, the continuous fiber-reinforced plastic strip is wound in two, three, or more layers onto a cylindrical core and then consolidated to form a dimensionally stable plastic tube. The plastic tube thus has the shape of a circular cylinder. During winding, a pressure roller can exert force on the core to press the strip onto it. This pressure roller also conveniently acts as a guide roller for the supplied strip, keeping it taut. The fiber orientation is between 90° and 45° to the tube axis and adjusts itself depending on the winding angle.

[0018] According to the invention, the first plastic is a thermoplastic polymer, for example PPS (polyphenylene sulfide), which possesses good chemical resistance. Consolidation is then achieved by melting, i.e., heating to a temperature above the melting point of the first plastic. This can be done, for example, using a laser, an infrared emitter, or hot gas, which is suitably directed at the gap between the pressure roller and the winding core. The continuous fibers are almost completely enclosed or embedded within the polymer matrix by the melting process, with adjacent layers being welded or fused together to form a dimensionally stable composite. A unidirectionally fiber-reinforced thermoplastic semi-finished product, also known as tape, can be used to manufacture fiber-reinforced composite components (FRP). This gives the tube particularly high strength.

[0019] According to another, unclaimed embodiment, the first plastic can be a thermoset with an epoxy matrix. The corresponding chemical crosslinking process can also be thermally activated to consolidate the matrix.

[0020] Furthermore, it is advantageous if the continuous fibers are carbon fibers. These result in particularly high strength of the plastic tube, which is subsequently also referred to as CFRP (carbon fiber reinforced plastic) tube. Additionally, the carbon fibers enable the initial plastic to be melted using a laser.

[0021] Various techniques are suitable for applying the coating. The same applies to the material of the second polymer, whereby the application process depends on the second polymer, or vice versa, since the different polymers require different processing methods, or a specific method may not be suitable for processing every polymer.

[0022] For example, the coating can preferably be produced by deposition from the liquid phase. This can be done using a low-temperature process (<400°C). For this, the coating can be created by immersing the plastic pipe in a bath of the second polymer (so-called dip-coating). This results in a complete and coherent coating of the plastic pipe, both inside and out. Alternatively, the coating can be applied by spraying. In this case, the plastic pipe and a nozzle located inside the plastic pipe can be moved relative to each other while the second polymer is ejected from the nozzle. Another alternative is to produce the coating by deposition from the gas phase. This can be achieved by low-temperature vapor deposition of a reactive, polymer-based layer bound in a carrier gas within a reactor.Here, the plastic pipe is completely and materially bonded coated inside and out.

[0023] According to the invention, the coating is a chemically inert, polymer-based material. It can, for example, consist of a fluoropolymer, in particular PTFE (polytetrafluoroethylene), PVDF (polyvinylidene fluoride), PFA (perfluoroalkoxy polymer), FKM (fluorocarbon rubber), or PFPE (perfluoropolyether). A PTFE coating, for example, has the advantage of being certified for drinking water, so that the wet rotor pump can be used for pumping drinking water. Furthermore, PTFE has the advantage of being chemically inert, having non-stick properties and very low friction, and is also temperature-resistant. From a process engineering perspective, it has the advantage of being relatively easy to apply, as this can be done using a low-temperature process.

[0024] As an alternative to a fluoropolymer, the coating can consist of an aromatic compound or aromatic polymer. PPS or a polyaryletherketone (PAEK) are particularly preferred. PPS has the advantage of being mechanically stable and therefore exhibiting low wear, which is beneficial with regard to potential particles in the rotor chamber. At the same time, PPS has good sealing properties. It also offers the advantage of optimal chemical bonding to the plastic tube, provided the tube is also made of PPS. PEEK (polyetheretherketone) is a preferred example of a polyaryletherketone. Other alternatives for an aromatic polymer coating include LCP (liquid crystalline polymers), HPPA (polyphthalamides), PAI (polyamide-imide), or PSU (polysulfones).

[0025] According to a further advantageous development, the coating can contain ceramic particles. It thus forms a polymer-ceramic coating. This enhances the mechanical properties of the coating.

[0026] To achieve a chemical bond between the plastic pipe and the coating, the inner surface of the plastic pipe is chemically or chemico-physically pretreated before the coating is applied, so that near-surface molecular bonds of the first polymer or the fiber coating (e.g., silane) are broken and activated (chemically reactive). According to the invention, this is done in a low-pressure plasma, preferably in a low-pressure plasma process in which the plastic surface of the pipe is etched and activated by ion bombardment. Alternatively, as not claimed, the surface pretreatment can be carried out by immersion in or spraying of a chemico-physically active fluid that etches the surface of the plastic pipe.

[0027] According to a further alternative according to the invention, pretreatment is achieved by first applying an adhesion promoter (primer) to the inside of the plastic pipe, with which it forms a chemical bond. In this case, the adhesion promoter forms a primer onto which the coating is then applied, with which the adhesion promoter also forms a chemical bond. Thus, in this embodiment, the chemical bond between the coating and the plastic pipe does not occur directly, but indirectly via the adhesion promoter, which forms a chemical bond with both the plastic pipe and the coating. In addition to promoting adhesion, the primer serves to reduce intrinsic stresses between the layer systems, which in turn improves the adhesion strength under dynamic (mechanical) and chemical stress.The adhesion promoter can preferably be applied using a low-pressure plasma process. Alternatively, the adhesion promoter can be applied from the liquid phase by spraying.

[0028] It is advantageous if the coating does not exceed a maximum thickness, for example, 300 µm, as cracks could form if the coating is too thick. The coating thickness also depends on the coating material. For example, the coating thickness can be greater when using PTFE than with a PPS coating.

[0029] The plastic pipe, for example, has a thickness or wall thickness between 0.25 mm and 1.5 mm. This wall thickness can be achieved with just two or three layers of the tape.

[0030] The outer diameter of the plastic pipe can be between 30mm and 80mm, depending on the motor size of the wet rotor pump.

[0031] In one design variant, the plastic pipe can have a diameter widening at one axial end, which serves as an assembly aid for a sealing ring so that it can seal in a form-fitting manner.

[0032] Furthermore, in one version, the plastic pipe can have an additional coating on its outer surface. The material of this additional coating can be different from the inner coating. However, it can also be identical to the inner coating, for example, if the inner coating is created by immersing the plastic pipe in a polymer bath.

[0033] In one design variant, the slotted tube can be closed at one axial end by a base, thus forming a slotted pot. The base can be produced directly during winding, for example, by also winding the strip over the axial end of the winding core. Alternatively, the base can be produced separately and welded to one end of the plastic tube in a subsequent manufacturing step.

[0034] Preferably, the plastic tube is manufactured in meter lengths, with the split tube forming a cut-off section of the plastic tube or being manufactured from such a cut-off section. Thus, during winding, a longer tube is produced than required, which is then cut into individual sections. This results in a substantially uniform wall thickness of the plastic tube along its entire axial length, since the winding process cuts off the thicker sections at the ends of the plastic tube, which are created by folding the tape. The sections are then further processed into split tubes according to the invention by applying the coating according to the invention to the inside. Due to the comparatively short sections, handling during coating and any necessary pretreatment is simple.

[0035] However, it is also possible to first coat the inside of the plastic pipe, which is manufactured in meter lengths, and then cut it into individual sections. This method is particularly advantageous if the coating is applied by immersing the plastic pipe in a bath of the second polymer, because in this case the coating is applied along the entire axial length. However, because the individual sections are cut, the end faces are not coated, which would not be the case if the sections were individually dip-coated.

[0036] Further features, advantages and properties of the slotted tube according to the invention and its manufacturing process are explained below with reference to exemplary embodiments and the accompanying figures.

[0037] It should be noted that, within the context of this description, the terms "exhibit," "comprise," or "include" in no way preclude the presence of other characteristics. Furthermore, the use of the indefinite article for an object does not preclude its plural form.

[0038] The reference symbols retain their meaning from one figure to the next. Identical reference symbols denote identical or at least functionally equivalent elements. They show: Fig. 1: A slotted tube according to the invention in axial cross-section. Fig. 1a: An enlargement of the cutout X at the axial end of the slotted tube with a first embodiment. Fig. 1b: An enlargement of the cutout X at the axial end of the slotted tube with a second embodiment. Fig. 1c: An enlargement of the cutout X at the axial end of the slotted tube with a third embodiment. Fig. 1d: An enlargement of the cutout X at the axial end of the slotted tube with a fourth embodiment. Fig. 2: An enlargement of a section of the layer transition between the wound plastic tube and the coating.

[0039] Fig. 1 Figure 1 shows a canned tube 1 for a wet rotor pump in axial cross-section. The canned tube 1 consists of a two-layer wound, carbon fiber reinforced thermoplastic tube 2, hereinafter referred to as CFRP tube 2, which has an internal permeation-reducing, in particular diffusion-tight, polymer coating 3. An enlargement of a section X from Fig. 1 at the axial end of the slotted tube 1 is in Fig. 1a depicted.

[0040] Fig. 2 Figure 1 also shows an enlarged view of a section of the layer transition between the CFRP tube 2 and the coating 3. The CFRP tube 2 consists of a first polymer 7, here PPS, in which the carbon fibers 6 are embedded as continuous fibers. The CFRP tube 2 is thus formed by a fiber-reinforced composite material, with the first polymer being the so-called matrix. Only two layers 2a, 2b of a continuously wound strip 8 are shown as an example, although there can actually be three, four, or more layers. The strip 8 was wound onto a smooth core, so that the inner surface 2a' of the plastic tube 2 is also smooth. A smooth core has the advantage that the plastic tube 2 can be easily slid off it. The coating 3 is applied to this inner surface 2a', of which... Fig. 2 Only a section is shown.

[0041] Coating 3, shown here as a purely exemplary application, consists of PTFE, which is particularly abrasion-resistant and suitable for drinking water, and also increases the chemical resistance of the PPS-made CFRP tube 2. Coating 3 seals the CFRP tube 2, which, due to the manufacturing process, may have defects, capillaries, or exposed fiber areas, especially those poorly wetted with the matrix. In general, fluoropolymers like PTFE offer even better sealing (permeation barrier) and improved liquid repellency. Their surface tension, abrasion resistance, and permeation rates are also superior. Furthermore, fluoropolymers have the advantage of good dry friction properties, which improves the assembly of elastomeric seals. A PTFE coating, for example, results in lower frictional forces during assembly.

[0042] Alternatively, the coating can be made of PPS, which has the advantage of being much more compatible with the PPS matrix of the CFRP matrix material (also e.g. PPS), with PPS also already having good properties regarding chemical resistance and being suitable for pump applications.

[0043] A chemical bond 9 exists at the molecular level between the CFRP tube 2 and the coating 3, resulting in a material-bonded composite of the first and second polymers 7, 3 and / or the carbon fibers 6 and the second polymer 3. This ensures diffusion tightness and abrasion resistance.

[0044] In an embodiment not shown, an adhesion promoter (primer) could also participate in the material composite and have a material bond to both the first polymer 7 and / or the carbon fibers 6, as well as to the second polymer 3.

[0045] To achieve chemical bond 9, the inner surface 2a' of the CFRP tube 2 is pretreated so that near-surface chemical bonds of the first polymer or of any carbon fiber coating present to improve matrix adhesion (which may be silane, for example) are broken at the molecular level and thus become reactive. This is achieved by applying a corresponding energy input, which can be thermal (i.e., by heating), chemical (e.g., by etching), or chemophysical (e.g., by plasma). Etching can be carried out by the adhesion promoter.

[0046] In plasma pretreatment, the CFRP tube 2 is immersed in a gas that is subsequently ionized by the application of energy. This causes electrons to leave the gas's atomic shells, forming positively charged ions. The CFRP tube 2 acts as the anode. The electrons are therefore accelerated towards the CFRP tube 2, creating holes in the material. More precisely, this bombardment breaks the bonds of the first polymer 7 and / or the carbon fiber coating by knocking out bonding electrons. This leaves behind open, chemically reactive bonds in the CFRP tube 2. To ensure that the pretreatment only occurs on the inner surface 2a' of the CFRP tube 2, and not on the outside, the generation of the ionized gas can be configured to take place exclusively within the interior enclosed by the CFRP tube.By immediately coating the inside 2a' of the CFRP tube 2, molecules of the second polymer 3 attach to the open bonds and thus form a new material composite between CFRP tube 2 and coating 3.

[0047] Fig. 1b und 1c Figures 2 and 3 show a second and third embodiment in which the slotted tube 1 also has a coating 4a, 4b on its outside. This outer coating 4a is shown in the second embodiment according to Fig. 1b with regard to material and thickness identical to the inner coating 3. It may, for example, have been produced together with the inner coating 3 by immersion in a polymer bath and thus be due to process engineering, without the outer coating 4a fulfilling a special purpose or being desired.

[0048] In the third version variant according to Fig. 1c In contrast, the outer coating 4b differs from the inner coating 3 and / or is thinner than in the second variant. The outer coating 4b may have been selected according to a specific desired functional purpose, such as minimizing friction, and applied using a specific application method.

[0049] Fig. 1c Figure 1 shows a further development of the third embodiment, in which the slotted tube 1 has a diameter expansion 5 at its axial end. This expansion forms a chamfer for the assembly of elastomeric seals, e.g., sealing rings (O-rings). Without the chamfer, placing and inserting a round seal would be more difficult, and there would be a risk of damage or twisting of the O-ring seal during installation.

[0050] It should be noted that the foregoing description is given merely as an example for illustrative purposes and in no way limits the scope of protection of the invention. Features of the invention that are indicated as "may", "exemplary", "preferred", "optional", "ideal", "advantageous", "if applicable" or "suitable" are to be considered purely optional and likewise do not limit the scope of protection, which is exclusively defined by the claims.

Claims

1. Split tube (1) for a wet rotor pump, consisting of a dimensionally stable plastic tube (2) made by winding a tape (8) of endless-fibre reinforced thermoplastic plastic material (7), wherein the plastic tube (2) has an inner permeation-reducing polymer-based coating (3) made of a fluoropolymer or aromatic polymer and there is a chemical bond (9) between the plastic tube (2) and the coating (3).

2. Split tube (1) according to claim 1, characterised in that the coating (3) is made of PTFE.

3. Split tube (1) according to claim 1, characterised in that the coating (3) is made of PPS or PEEK.

4. Split tube (1) according to one of the preceding claims, characterised in that the coating (3) contains ceramic particles.

5. Split tube (1) according to one of the preceding claims, characterised in that the coating (3) has a thickness of no more than 300µm.

6. Split tube (1) according to one of the preceding claims, characterised in that the plastic tube (2) has a thickness of 0.25 mm to 1.5 mm.

7. Split tube (1) according to one of the preceding claims, characterised in that the plastic tube (2) has an enlargement of the diameter (5) of at one axial end.

8. Split tube (1) according to one of the preceding claims, characterised in that the plastic tube (2) has an additional outer coating (4) that, in particular, is identical to the inner coating (3).

9. Split tube (1) according to one of the preceding claims, characterised in that the plastic tube (2) is made of PPS, PPA, PA or PC.

10. Split tube (1) according to one of the preceding claims, characterised in that the endless fibres are carbon fibres.

11. Method for the production of a split tube (1) for a wet rotor pump according to one of the claims 1 through 10, in which a tape (8) of a first endless-fibre reinforced thermoplastic plastic material (7) is wound on a winding core in two or more layers and subsequently consolidated, in particular fused, to form a dimensionally stable plastic tube (2), wherein the inside of the plastic tube (2) is coated with a permeation-reducing polymer-based coating (3) made of a fluoropolymer or an aromatic polymer so that a chemical bond (9) is formed between the plastic tube (2) and the coating (3), wherein the inside of the plastic tube (2) being chemically or chemically-physically pre-treated in a low-pressure plasma in order to break apart molecular bonds close to the surface of the first synthetic material (7) or of a coating of the endless fibres (6) before applying the coating (3), and / or with the chemical bond (9) being realised using a bonding agent that forms a chemical bond (9) with the plastic tube (2) on the one hand and a chemical bond (9) with the coating (3) on the other hand.

12. Method according to claim 11, characterised in that the coating (3) is produced using spray application.

13. Method according to claim 11 or 12, characterised in that the coating (3) is produced by precipitation in a low-temperature process.

14. Method according to claim 11, characterised in that the coating (3) is produced by dipping the plastic tube (2) in a bath (dip coating).

15. Method according to one of the claims 11 through 14, characterised in that the plastic tube (2) is produced as bulk stock and the split tube (1) is a cut section of the plastic tube (2) or is made from a cut section.