CENTRIFUGAL PUMP FOR TRANSPORTING SOLID-CONTAINING MEDIA

Description

[0001] The invention relates to a centrifugal pump for conveying solid-containing media with an arrangement for reducing backflow from a first chamber into a second chamber and a closed impeller.

[0002] An example of a solids-containing medium is wastewater, especially municipal and industrial wastewater. This typically includes raw sewage (e.g., dirty water, feces), wastewater (mechanically treated water from clarification tanks), sludge (e.g., activated sludge, fresh sludge, digested sludge, and seed sludge), and rainwater. Industrial wastewater can, under certain circumstances, have a highly corrosive or abrasive effect on the centrifugal pumps used, especially on the components of the centrifugal pump that come into contact with the media.

[0003] Contact with the flowing, solid-containing medium can lead to material loss in the centrifugal pump. This loss is also known as abrasion. Abrasion phenomena can severely impair the functionality of the centrifugal pump. Particularly when additional particles are present in the flow, such as solid particles like sand, this can lead to significant material loss. Wear-resistant materials are then essential to minimize abrasion.

[0004] It is common practice for centrifugal pumps used to pump highly abrasive media to manufacture flow-carrying parts such as the impeller, wear ring, wear plate, etc., from corrosion-resistant non-metallic materials or to coat these parts with a rubber, plastic, or enamel coating. Conventional materials used for this purpose are limited in their strength and corrosion resistance. Furthermore, conventional materials offer only limited wear resistance when in contact with the flowing medium.

[0005] When conveying media containing solids, wear on the impeller caused by the abrasive effect of the dirt particles and a so-called gap widening of an existing gap seal must also be taken into account.

[0006] Gap seals are used in centrifugal pumps to seal spaces with different pressures. The arrangement comprises a non-rotating element and a rotating element. The non-rotating element can be, for example, a wear ring arranged on the casing, or the casing itself or a casing part. The rotating element can be, for example, a race arranged on the impeller, or the impeller itself or a part of the impeller, for example, the impeller cover plate in the case of a closed impeller. Therefore, an increasing loss of efficiency due to abrasive wear can be expected with increasing operating time, especially with dirty water centrifugal pumps with gap seals.

[0007] DE 10 2017 223 602 A1 specifies an impeller for a centrifugal pump with silicon carbide-based fittings. The hardness of the material is intended to protect the centrifugal pump from abrasive wear. To this end, various silicon carbide fittings are placed in a casting tool and then filled with a metallic casting material, forming a closed impeller.

[0008] DE 10 2018 214 650 A1 describes a wear ring-bearing ring pair of a centrifugal pump based on calcium carbonate in the modification aragonite, which is more wear-resistant against abrasive substances due to its high hardness.

[0009] Due to the high brittleness of most abrasion-resistant ceramic materials, the proposed ceramic solutions are generally very expensive and complex to implement for certain component geometries and may lead to operational disruptions (e.g., due to breakage of parts).

[0010] WO 2014 / 201458 A1 describes an electric submersible pump with a diamond coating, wherein the diamond coating at least partially covers at least one component of the electric submersible pump in order to reduce friction, wear or operating temperature of the at least one component.

[0011] US 9 677 560 B1 discloses both a diamond coating and a graphite coating in a centrifugal pump.

[0012] The object of the invention is to provide a centrifugal pump for conveying solids-containing media with a wear-resistant impeller. Furthermore, damage to the impeller ring due to abrasive wear should be effectively reduced. Furthermore, the pump should be able to maintain its efficiency over a long period of time during operation. The centrifugal pump should be characterized by high reliability and a long service life. It should also ensure easy installation. Furthermore, the centrifugal pump should impress with the lowest possible manufacturing costs.

[0013] This object is achieved according to the invention by a centrifugal pump for conveying solid-containing media having the features of claim 1. Preferred variants can be found in the subclaims.

[0014] According to the invention, the closed impeller of a centrifugal pump for conveying solids-containing media is coated with a carbon layer on its surface, particularly the cover plate surface. This greatly increases the hardness of the surface, providing effective protection against abrasive wear caused by the flowing solid particles of the pumped medium.

[0015] The central component of a centrifugal pump is the impeller, which transfers mechanical energy to the fluid as momentum. The impeller shape determines how the flow exits the pump. With regard to the design of the impeller, a distinction is made between closed, semi-open, and open shapes. In a closed impeller, at least one impeller blade is connected to a disc on each side. The front disc, facing the inflow, is called the shroud. The rear disc, which is usually the structural origin of the blade, is called the rear disc. By enclosing a blade with the shroud and rear disc, a closed channel is created, which is aligned by the blade curvature.

[0016] For the wastewater pumping task, closed impellers with a reduced number of blades and a large ball passage are suitable to avoid potential blockages caused by solid particles or clogging in the wastewater. Ideally, closed single-blade impellers and / or closed single-, double-, or triple-channel impellers are used for this purpose. According to the invention, these impellers are coated with a carbon layer, giving them an extremely hard surface, which preferably provides ideal protection against the abrasive and corrosive effects of solid-containing media such as wastewater.

[0017] Advantageously, the shroud of a closed impeller, in particular, has a carbon coating. The shroud is the first to come into contact with the solids-containing medium and is protected against abrasion by the hard carbon coating. In particular, the surfaces of the shroud, which together with a wear ring form a seal to reduce backflow from the discharge chamber to the suction chamber, have a carbon coating. In particular, these are planar-machined radial and / or axial surfaces of the shroud that have a carbon coating.

[0018] Ideally, the inner surface of a closed impeller—that is, the inner walls of a channel formed by the rear disk, the blade flank, and the shroud—also has a carbon coating. This advantageously provides the impeller surfaces, which are directly involved in the momentum transfer from the impeller to the solids-containing medium, with a particularly hard protective layer against abrasion.

[0019] According to the invention, a centrifugal pump for conveying solid-containing media with at least one arrangement for reducing backflow comprises a rotating element that is at least partially coated with carbon. Such an arrangement for reducing backflow is designed according to the invention as a gap seal formed by a split ring and a race.

[0020] This arrangement serves to seal spaces of different pressures and acts as a throttle between them. In this arrangement, a first space is understood as a space with higher pressure and a second space as a space with lower pressure. In a centrifugal pump, the higher-pressure space is the space of the discharge nozzle and the volute casing. The lower-pressure space is the space of the suction area upstream of the impeller.

[0021] According to the invention, at least one race ring is arranged directly on the closed impeller on a radial and optionally additionally on an axial surface of the cover disk, which race ring, together with at least one wear ring, forms a gap seal. According to the invention, this race ring has a carbon coating on at least one radial and optionally additionally on an axial surface. This enormously increases the hardness of a conventional race ring made of a cast material and / or a stainless steel material, which in turn protects, in particular, the surfaces involved in forming the gap seal from the abrasive effects of the solid-containing medium.

[0022] The wear ring of the gap seal, which corresponds to the race, is arranged on the pump housing by means of a press fit and is therefore both stationary and non-rotating. The wear ring is arranged as such directly on the pump housing. According to the invention, the wear ring has a radial

[0023] A carbon coating is applied to a specific surface, namely the wear ring interior, and optionally to an additional axial surface, such as the wear ring face. This significantly increases the hardness of a conventional wear ring made of cast material and / or stainless steel. The wear ring thus receives effective protection against the abrasive effects of solid particles in the pumped medium.

[0024] The carbon coating is particularly advantageous with regard to contact or tarnishing between a race and the corresponding split ring. Due to the carbon coating's particularly smooth surface and its exceptional hardness, the race is insensitive to the rubbing action of a split ring.

[0025] Carbon coatings are layers in which carbon is the predominant component. The carbon coating can be applied using, for example, a PVD (Physical Vapor Deposition) process, a physical vapor deposition process (e.g., by evaporation or sputtering), or a CVD (Chemical Vapor Deposition) process.

[0026] According to the invention, this is a tetrahedral, hydrogen-free amorphous carbon layer, also referred to as a ta-C layer. The atomic bonds associated with the graphite crystal lattice (three in total) are designated "sp2," indicating sp2 hybridization.

[0027] In a diamond layer, each carbon atom forms a tetrahedral arrangement with four neighboring atoms. In this spatial arrangement, all atomic distances are equally short. Therefore, very strong bonding forces act between the atoms in all spatial directions. This results in the high strength and extreme hardness of diamond. The atomic bonds belonging to the crystal lattice of diamonds, four in total, are designated "sp3." This represents sp3 hybridization.

[0028] In a particularly advantageous variant of the invention, the carbon layer consists of a mixture of sp3- and sp2-hybridized carbon. This layer is characterized by an amorphous structure. Foreign atoms such as hydrogen, silicon, tungsten, or fluorine can also be incorporated into this carbon network.

[0029] The inventive arrangement of a carbon layer on a closed impeller and an element for preventing backflow, such as a race, leads to a considerable reduction in abrasive wear.

[0030] By applying a carbon coating to a closed impeller, particularly to the radial and / or axial surfaces of the cover plate, which are used to form a sealing gap, an extremely smooth surface with non-stick properties is created without the need for complex mechanical post-processing of the impeller. Furthermore, several impellers can be placed in a coating reactor, preferably designed as a vacuum chamber, where the ta-C coating is applied under moderate thermal stress. Thus, the centrifugal pump with a closed impeller according to the invention is characterized by relatively low manufacturing costs.

[0031] In a particularly advantageous variant of the invention, the carbon layer is applied as a coating to an impeller and / or a race. The thickness of the layer is advantageously more than 0.5 µm, preferably more than 1.0 µm, in particular more than 1.5 µm. Furthermore, it proves advantageous if the carbon layer is less than 18 µm, preferably less than 16 µm, in particular less than 14 µm.

[0032] Ideally, the carbon coating has an extremely smooth axial surface with non-stick properties, in which the mean roughness value R a of the carbon layer is less than 0.7 µm, preferably less than 0.5 µm, in particular less than 0.3 µm.

[0033] The ta-C coating exhibits a very low coefficient of friction while simultaneously offering very good chemical resistance. The hardness of the coating is very close to that of diamond, with the hardness preferably being more than 20 GPa, preferably more than 30 GPa, in particular more than 40 GPa, and less than 120 GPa, preferably less than 110 GPa, in particular less than 100 GPa.

[0034] With an average strength of 40 to 75 GPa, ta-C coatings are harder than aC:H coatings. Furthermore, ta-C does not contain hydrogen. Therefore, it can be assumed that ta-C is more resistant to water (at temperatures above 80 °C) than aC:H. In contact with other—particularly polar—liquids containing hydrogen-bonded molecules, ta-C may also be more resistant than aC:H.

[0035] Preferably, the carbon layer is not applied directly to the impeller and / or race, but rather a bonding layer is applied first. This layer is preferably made of a material that both adheres well to steel and prevents carbon diffusion, e.g., by forming stable carbides. Thin layers of chromium, titanium, or silicon are suitable bonding layers that meet these requirements. Chromium and tungsten carbide have proven particularly effective as bonding agents.

[0036] In an advantageous variant of the invention, the coating has an adhesion promoter layer, which preferably contains a chromium material. The adhesion promoter layer preferably consists of more than 30 wt.%, preferably more than 60 wt.%, in particular more than 90 wt.% chromium.

[0037] The ta-C coating according to the invention is a simple, quickly implemented, and cost-effective coating for closed impellers and / or races in centrifugal pumps. In addition to very high hardness, the coating according to the invention also exhibits excellent sliding properties and good chemical resistance.

[0038] The invention also enables the coating of impeller geometries with specific dimensions. Furthermore, impeller geometries can be realized that were previously difficult to achieve with ceramic materials due to manufacturing constraints. In particular, most metallic materials are characterized by higher ductility compared to ceramic materials.

[0039] The advantage of the increased hardness provided by the ta-C coating is that small and large solid particles, which are often present in solids-containing media, now have a significantly reduced abrasive effect on the impeller and / or the seal race. Due to the flow, these solid particles normally act like an abrasive. Impellers and seal races coated with ta-C have an extremely hard protective layer against abrasion, which significantly increases their service life when pumping solids-containing media.

[0040] PECVD / PACVD processes are preferably used for coating. Plasma excitation of the gas phase occurs through the coupling of pulsed DC voltage, medium-frequency (kHz range), or high-frequency (MHz range) power. The coupling of pulsed DC voltage has also proven effective for maximizing process variability with different workpiece geometries and loading densities.

[0041] PVD processes are ideally used for coating. These processes are particularly simple and involve low process temperatures. This technology results in coatings that can also incorporate foreign atoms, if required. The process is preferably conducted in such a way that structural and dimensional changes in the materials to be coated (metallic, gray cast iron, etc.) are excluded.

[0042] Compared to a CVD diamond coating, the ta-C coating has the advantage that the coating temperature for CVD diamond coatings is 600 to 1000 °C, while for amorphous carbon coatings such as ta-C, it is significantly below 500 °C. This is of particular technical relevance for coating metallic materials. The production of PVD diamond coatings is not possible.

[0043] Further features and advantages of the invention will become apparent from the description of embodiments based on the drawings and from the drawings themselves. Fig. 1Sectional view of a centrifugal pump for conveying solids-containing media with a closed single-vane impeller, Fig. 2Sectional view of a closed three-channel impeller, Fig. 3Perspective view of a closed multi-channel impeller, Fig. 4Enlarged section in the area of ​​the suction mouth, Fig. 5Detailed section of a rotating element.

[0044] Fig. 1 shows a sectional view of a centrifugal pump for conveying solids-containing media with an arrangement for reducing backflow 13 from a first chamber into a second chamber. The arrangement 13 comprises a stationary, non-rotating element 2, which in this exemplary embodiment interacts with the closed single-blade impeller 4. The element 2 is designed as a split ring. The solids-containing medium flows into the pump via the suction inlet 1, is imparted with kinetic energy by the closed single-blade impeller 4, which is connected to the shaft 9 in a rotationally fixed manner by the fastening 12, and leaves the pump housing 10 via the pressure port 5. The shaft 9 is rotatably mounted by the ball bearings 8. The bearing carrier cover 7 closes the pump chamber in the direction of the drive. According to the invention, the closed single-blade impeller 4 is coated with a carbon layer, preferably with an amorphous carbon layer, in particular with ta-C.In particular, the cover plate 3 and the inner wall surfaces 11 of the closed single-blade impeller 4 have a layer of ta-C. This provides particularly ideal protection against abrasive wear and also against the closed single-blade impeller 4 colliding with the non-rotating element 2.

[0045] Fig. 2 shows a sectional view of a closed three-channel impeller. The impeller 4 consists of a support disk 11, from which the blades (not shown) protrude. A cover disk 3 closes the space between the blades and the support disk 11 in such a way that closed channels are formed. Furthermore, the cover disk 3 of the impeller 4 has an axial surface in the form of an impeller end face 23 and a radial surface 24, both of which are machined to be particularly planar. According to the invention, the impeller end face 23 and the radial surface 24 are coated with a layer of carbon, in particular with ta-C. The impeller end face 23 and / or the radial surface 24 form a so-called gap seal with a stationary and non-rotating wear ring (not shown) arranged in the pump housing.Due to the ta-C coating, the gap seal forming surfaces of the impeller 4 are particularly protected against abrasive wear caused by the conveyance of a solids-containing medium and the associated loss of efficiency.

[0046] Fig. 3 shows a perspective view of a closed multi-channel impeller 4. Starting from the support disk 11, the blades 25 protrude in the direction of the media inflow. The cover disk 3 closes the space with the blades 25 and the support disk 11, so that at least one partially closed channel 26 is formed. According to the invention, the inner wall surfaces of the channel 26 have a ta-C coating that protects the impeller 4 made of conventional cast material and / or stainless steel material against the abrasive effect of the flowing solid particles. In this way, standard impellers can be manufactured cost-effectively from known material and, by coating them with a carbon layer up to 18 µm thick, can be made suitable for highly abrasive applications. According to the invention, the impeller end face 23 and the radial surface 24 are also coated with a layer of carbon, in particular with ta-C.These gap seal-forming surfaces of the cover plate 3, which form a gap with a split ring (not shown) to reduce backflow from the pressure side to the suction side of the centrifugal pump, are thus particularly protected against abrasive wear and the associated loss of efficiency of the centrifugal pump.

[0047] Fig. 4 shows an enlarged detail in the area of ​​the suction mouth 1 according to the invention. The centrifugal pump has an arrangement for reducing backflow 13 in the form of a gap seal. This comprises a rotating component 14, which is designed as a bearing ring, and a non-rotating component 2, which is designed as a split ring. The rotating component 14 is arranged on a radial outer side of the cover plate 3 of the impeller 4. The rotating component 14 thus rotates with the impeller 4. The non-rotating component 2 is arranged on the pump housing 10 and has a radial inner side of the ring as a guide, which interacts with the radial outer side of the rotating component 14 and forms the gap seal. The rotating component 14 and the element 2 are coated with ta-C according to the invention. This achieves particularly ideal protection against abrasive wear.

[0048] When executed as shown in Fig. 4 In addition to an arrangement for reducing backflow 13, a further arrangement 20 is provided, which comprises a rotating element 22 and a non-rotating element 21. The rotating element 22 is designed as a ring, which is also referred to as an angular race, and which is arranged on the axial end face of the cover plate 3. For this purpose, the rotating element 22 has a projection 19 extending in the axial direction, which engages in a groove 15 in the cover plate 3. The non-rotating element 21 is designed as an axially displaceable ring, which is guided by a surface 16 of the pump housing 10 against radial displacement. A force generating element 17 exerts a force on the non-rotating element 21 and presses the non-rotating element 21 against the rotating element 22. The force generating element 17 is designed as a spring. In the exemplary embodiment, a corrugated spring is used.In an alternative variant of the invention, the use of a group or sinusoidal spring is conceivable. The non-rotating element 21 is sealed to the housing part 10 by a sealing element 18. The sealing element 18 is preferably an O-ring.

[0049] The rotating element 22 and the non-rotating element 21 are made of a stainless steel material, which is coated with ta-C according to the invention. The two axially facing end faces of the rotating element 22 and the non-rotating element 21 are pressed together by the force-generating element 17. This creates a minimal gap. Friction is minimized by the ta-C coating. A lubricating film of pumped medium forms in the gap between the contacting surfaces of the rotating element 22 and the non-rotating element 21. The arrangement 20, together with the device 13, prevents backflow from a pressure chamber 5 of the pump into a suction chamber 1 of the centrifugal pump.

[0050] Fig. 5shows a detailed section of a rotating element 14, 22 in the form of a race, which is coated with a carbon layer, in particular with ta-C, on an axial surface 27 and on a radial surface 28. By coating at least one race end face and at least one race outer face with ta-C, races can be made from a conventional cast material and / or a stainless steel material and can be given wear-resistant properties by means of the ta-C coating. The thickness of the ta-C layer is more than 0.5 µm, preferably more than 1.0 µm, in particular more than 1.5 µm and / or less than 18 µm, preferably less than 16 µm, in particular less than 14 µm.The hardness of the ta-C coating is preferably more than 20 GPa, preferably more than 30 GPa, in particular more than 40 GPa and less than 120 GPa, preferably less than 110 GPa, in particular less than 100 GPa and thus protects the ordinary race from the abrasive action of the solid particles of the pumped medium.

Claims

1. Centrifugal pump for conveying solids-containing media, having at least one arrangement for reducing a backflow (13, 20) from a first space into a second space, and having a closed impeller (4) which comprises a rear shroud (11) away from which at least one blade (25) projects, said at least one blade being covered by a cover shroud (3) in such a way that at least one at least partially closed channel (26) is formed, wherein the surface of the impeller (4) at least partially has a layer of carbon, wherein the closed impeller (4) interacts with a non-rotating counterpart element (2, 21) which is arranged directly on the pump casing (10), wherein the counterpart element (2, 21) at least partially has a layer of carbon, wherein the centrifugal pump has an arrangement for reducing a backflow (13) in the form of a gap seal, wherein the gap seal comprises a rotating component (14), which is in the form of a running ring, and a non-rotating component (2), which is in the form of a split ring, wherein the rotating component (14) is arranged on a radial outer side of the cover shroud (3) of the impeller (4), wherein the rotating component (14) rotates with the impeller (4), wherein the non-rotating component (2) is arranged on the pump casing (10) and has a radial ring inner side as a guide, which interacts with the radial ring outer side of the rotating component (14) and forms the gap seal, characterized in that the rotating component (14) and the non-rotating component (2) are coated with a tetrahedral hydrogen-free amorphous carbon layer or ta-C, wherein, in addition to the arrangement for reducing a backflow (13), a further arrangement (20) comprising a rotating element (22) and a non-rotating element (21) is provided, wherein the rotating element (22) is in the form of a ring and is arranged on the axial end face of the cover shroud (3), wherein the rotating element (22) has an axially extending projection (19) which engages into a groove (15) in the cover shroud (3), wherein the non-rotating element (21) is in the form of an axially displaceable ring which is guided by a surface (16) of the pump casing (10) against radial displacement, wherein a force-generating element (17) exerts a force on the non-rotating element (21) and presses the non-rotating element (21) against the rotating element (22), wherein the force-generating element (17) is in the form of a spring, wherein the non-rotating element (21) is sealed off from the casing part (10) by a seal element (18), wherein the seal element (18) is preferably an O-ring, wherein the rotating element (22) and the non-rotating element (21) are formed from a high-grade-steel material coated with ta-C, wherein the two axially mutually facing end faces of the rotating element (22) and the non-rotating element (21) are pressed onto one another by the force-generating element (17).

2. Centrifugal pump according to Claim 1, characterized in that the cover shroud (3) of the closed impeller (4) has a layer of carbon on a radial surface (24).

3. Centrifugal pump according to Claim 1 or 2, characterized in that the cover shroud (3) of the closed impeller (4) has a layer of carbon on an axial surface (23).

4. Centrifugal pump according to one of Claims 1 to 3, characterized in that the inner walls of completely enclosed spaces of the impeller (4) at least partially have a layer of carbon.

5. Centrifugal pump according to one of Claims 1 to 4, characterized in that the closed impeller (4) is made of a metallic material, preferably a cast material or a rust-resistant steel material.

6. Centrifugal pump according to one of Claims 1 to 5, characterized in that the thickness of the carbon layer is greater than 0.5 µm, preferably greater than 1.0 µm, in particular greater than 1.5 µm, and / or less than 18 µm, preferably less than 16 µm, in particular less than 14 µm.

7. Centrifugal pump according to one of Claims 1 to 6, characterized in that the surface hardness of the surface of the counterpart element (2) coated with a carbon layer is greater than 20 GPa, preferably greater than 30 GPa, in particular greater than 40 GPa, and / or less than 120 GPa, preferably less than 110 GPa, in particular less than 100 GPa.