Centrifugal pump having a device

Abstract

The invention relates to a centrifugal pump having at least one impeller (3, 7, 8) which sits on a drive shaft (14). The drive shaft (14) is supported by a device (18) which comprises at least one media-lubricated plain bearing, wherein the plain bearing comprises an inner arrangement (20) which is connected to the drive shaft (14) for conjoint rotation, and comprises an outer arrangement (21) which is positioned in a stationary manner in the suction housing (4). A gap (24) is formed between the inner arrangement (20) and the outer arrangement (21). The outer arrangement (21) has an element having a cylindrical inner surface (22) which is formed from a bronze material having a hardness of more than 50 HB, and the inner arrangement (20) is formed from a steel material, wherein the inner arrangement (20) has a carbon layer (28).

Description

[0001] 10528A

[0002] Description

[0003] centrifugal pump with a device

[0004] The invention relates to a centrifugal pump with at least one impeller mounted on a drive shaft, wherein the drive shaft is supported by a device comprising at least one media-lubricated sliding bearing, wherein the sliding bearing comprises an inner arrangement which is rotationally fixed to the drive shaft, and an outer arrangement which is stationary in the suction housing, wherein a gap is formed between the inner arrangement and the outer arrangement.

[0005] A centrifugal pump with at least one impeller includes, in particular, multi-stage centrifugal pumps, for example, in a vertical installation. Centrifugal pumps are described as multi-stage when several impellers are arranged one behind the other and the pumping flow passes through them in series.

[0006] Essentially, the delivery head of a single-stage centrifugal pump is determined by the impeller design and the peripheral speed. If the rotational speed cannot be increased further due to external constraints, and, for example, increasing the impeller diameter leads to very low specific rotational speeds and thus uneconomical efficiencies, the delivery head can be increased economically by connecting several stages in series. Changing the number of stages while keeping the dimensions and rotational speeds constant does not change the flow rate of such a multi-stage pump, while the power requirement and the 2 10528A

[0007] The delivery head is proportional to the number of stages. Each stage includes an impeller and a guide vane, which usually contains a recirculation blade.

[0008] Multi-stage, vertical centrifugal pumps in a segmented design are usually mounted on a base plate or designed as a block unit. They typically feature a motor-mounted speed control system and cast radial impellers. Multi-stage centrifugal pumps are used particularly in supra-regional heating water systems, such as district heating networks, where the pump rotor is supported and mounted with a fluid-lubricated radial bearing.

[0009] Plain bearings are frequently used in centrifugal pumps. In this design, a moving component slides within a stationary component. In radial plain bearing designs for centrifugal pumps, the moving component is usually part of the shaft, and the stationary component is a bearing shell in the form of a bushing.

[0010] Multi-section centrifugal pumps are frequently equipped with shaft guide bearings lubricated by the pumped medium, typically in the form of a plain bearing. In these cases, the material selection must be particularly careful, as the specific properties of the lubricating medium often need to be considered. For example, several bearing materials with good tribological properties are available for water as a lubricating medium. These include, for example, metallic alloys, ceramics, elastomers, hard rubber, electrographitized carbon with and without resin impregnation, and hard carbon with resin or antimontane impregnation.

[0011] EP 0752538 A2 discloses a fluid-lubricated plain bearing, particularly in centrifugal pumps, wherein a hard and a soft material serve as sliding partners. The hard partner consists of metal and the soft partner of carbon fiber reinforced carbon.

[0012] If a conveyed medium is contaminated as a bearing lubricant or contains solid impurities such as sand, the use of hard metals or ceramic materials (e.g., silicon carbide) as bearing materials is recommended. Most often, the 3 10528A

[0013] Bearing bushings and shaft protection sleeves made of the same material form a maintenance-free plain bearing.

[0014] EP 0204235 B1 discloses a sliding bearing made of ceramic material for supporting pump shafts, wherein a bearing bushing rotating with the shaft rotates within a bearing made of the same material and the bearing is elastically fixed within a housing and in particular silicon carbide is used as the bearing material.

[0015] Silicon carbide (SiC) is very common for plain bearing sleeves. However, in certain applications, SiC sleeves exhibit an increased susceptibility to vibration-induced fractures.

[0016] An alternative to ceramic materials for plain bearing sleeves and bushings could be, for example, plain bearing components coated with amorphous carbon. Amorphous carbon is also known as diamond-like carbon and is characterized by its high hardness.

[0017] WO 2023217406 A1 discloses an amorphous, hydrogen-free carbon coating on the surface of a sliding part for use under lubricated conditions and occasionally under dry-running conditions. The coating is disclosed on a ceramic surface, such as silicon carbide (SiC), carbon-containing silicon carbide (SiC-C), silicon-embedded silicon carbide (Si-SiC), and tungsten carbide (WC).

[0018] DE 102020003140 A1 discloses a centrifugal pump with at least one hydrodynamic sliding bearing arrangement. Each sliding bearing arrangement comprises at least one element non-rotatably connected to a shaft and at least one stationary counter-element. At least one element is provided with a carbon layer and at least one counter-element comprises a graphite-containing material.4 10528A

[0019] Especially when using centrifugal pumps in district heating networks, there can be enormous differences or fluctuations in operating parameters between summer and winter operation. These fluctuations can lead to vibrations in the pump's operating mode, meaning that high hardness of the bearing materials alone is insufficient. In particular, the brittleness of the hard bearing materials can prove problematic and lead to crumbling plain bearings.

[0020] The object of the invention is to provide a centrifugal pump with at least one impeller, the drive shaft of which is supported by a device suitable for use with a wide range of operating parameters. The centrifugal pump should also be able to withstand vibrations caused by fluctuations in the operating parameters without damage. The design of the centrifugal pump should facilitate the replacement of spare parts. The centrifugal pump should be simple and cost-effective to manufacture.

[0021] This problem is solved according to the invention by a centrifugal pump with at least one impeller according to the features of claim 1. Preferred embodiments can be found in the dependent claims, the subclaims, the description and the drawings.

[0022] According to the invention, the outer arrangement has an element with a cylindrical inner surface made of a bronze material with a hardness of more than 50 HB.

[0023] Bronze is an alloy consisting of a mixture of two or more metallic elements. The classic composition of bronze consists primarily of copper and tin, with copper being the main component, resulting in bronze being harder than pure copper.

[0024] The bronze material is, for example, an aluminum bronze.5 10528A

[0025] Preferably, the aluminum bronze has a composition of approximately 10 wt.% aluminum and approximately 90 wt.% copper. The aluminum bronze may also contain other alloying elements.

[0026] Aluminum bronze is a bronze alloy that contains aluminum as its main alloying element, in addition to copper and tin. Typically, an aluminum bronze contains approximately 90 wt.% copper, 9-10 wt.% aluminum, and 1-2 wt.% tin.

[0027] Aluminum bronze exhibits excellent corrosion resistance, particularly against seawater and aggressive environments, and also possesses high hardness and advantageous wear resistance. This makes aluminum bronze ideally suited as a material for elements with cylindrical inner surfaces, especially for use in centrifugal pumps for district heating networks.

[0028] The device is designed, for example, as a media-lubricated sliding bearing, wherein the sliding bearing comprises an inner arrangement and an outer arrangement.

[0029] The inner arrangement is preferably designed as a sleeve that is non-rotatably connected to the drive shaft.

[0030] The outer arrangement is stationary in the housing of the centrifugal pump, preferably includes the bushing and a bushing holder, and can be designed, for example, as a one-piece or two-piece assembly.

[0031] A sliding bearing gap is preferably formed between the inner and outer arrangements. Under normal operating conditions, this gap is lubricated by the conveyed medium. Particularly during start-up phases and / or operation with highly fluctuating operating parameters and / or operation under extreme operating parameters, high hardness and wear resistance of the element with a cylindrical inner surface of the outer arrangement, especially the sliding bearing bushing, is advantageous.6 10528A

[0032] Brinell hardness is a method for measuring the hardness of a material by pressing a hard spherical inductor into its surface. A spherical inductor, usually a hard metal ball, is applied to the surface of the material being tested. A specific force is applied to the inductor, causing it to penetrate the material. The load is maintained for a defined time to ensure that the indentation is sufficiently large. The diameter of the indentation is then measured, typically using a microscope.

[0033] This diameter is then used to calculate the Brinell hardness (HB). The Brinell hardness is represented by the ratio of the applied load to the surface area of ​​the indentation.

[0034] In one embodiment of the invention, the cylindrical inner surface is made of a bronze material with a hardness greater than 150 HB, preferably with a hardness greater than 250 HB, and particularly with a hardness greater than 350 HB. This results in a bushing that is highly wear-resistant, especially for extreme and vibration-generating operating parameters of the centrifugal pump.

[0035] For example, the outer arrangement features at least one integrated lubricating element made of graphite. High wear resistance alone is often insufficient for plain bearings. In particular, a bushing with a large number of evenly distributed lubricating elements achieves emergency running properties through integrated emergency lubrication.

[0036] In one variant, the element with a cylindrical inner surface has many cylindrical graphite pins that are integrated into the body of the bushing.

[0037] The advantage of graphite in plain bearings lies in its ability to act as a dry lubricant. The use of graphite pins in plain bearings offers the benefits of uniform lubrication, low friction, and reduced wear, without the need for external lubrication. 7 10528A

[0038] The integrated lubricating elements ensure the emergency running capability of the device before the media lubrication can take effect and / or if the media lubrication cannot be permanently and completely ensured, for example due to cavitation in the centrifugal pump.

[0039] In one variant of the invention, the outer arrangement comprises a further element for fixing sealing elements.

[0040] The further element is preferably designed as a bushing holder. Two sealing elements, preferably in the form of O-rings, hold the bushing holder in position.

[0041] In one embodiment of the invention, the bushing holder of the outer arrangement has a bulge which is held in position by two O-rings. Advantageously, the O-rings also act as vibration dampers, which can be beneficial during the vibration-prone operation of the centrifugal pump.

[0042] For example, the other element is designed as a bushing holder made of chrome steel and is therefore particularly robust and wear-resistant.

[0043] In an alternative embodiment of the invention, the outer arrangement is formed in one piece. For example, the bushing holder and the bushing are formed in one piece and made of a bronze material.

[0044] In one embodiment of the invention, the inner arrangement is made of a steel material.

[0045] For example, the internal structure is made of chromium steel and is therefore particularly robust and wear-resistant. 8 10528A

[0046] In an advantageous embodiment of the invention, the inner arrangement is made of a martensitic steel, for example 1.4021 or 1.4057.

[0047] In another variant of the invention, the inner arrangement is made of a precipitation-hardened steel, for example 1.4022.

[0048] In an alternative version of the invention, the inner arrangement is made of a heat-treated steel, for example a 1.7225.

[0049] In a preferred embodiment of the invention, the inner arrangement comprises a carbon layer. A thin carbon layer is characterized in particular by its extreme hardness.

[0050] For example, the carbon layer is formed from a ta-C and / or an aC:H.

[0051] Carbon layers are defined as layers in which carbon is the predominant component. The carbon layer can be applied using, for example, PVD (Physical Vapor Deposition – such as by evaporation or sputtering), CVD (Chemical Vapor Deposition), PECVD (Plasma Enhanced Chemical Vapor Deposition) processes, or a combination of these processes.

[0052] The properties of the carbon layer are influenced, among other things, by the state of its atomic bonding. The atomic bonds belonging to the graphite crystal lattice (a total of three) are designated as "sp2". This represents sp2 hybridization.

[0053] In a diamond layer, each carbon atom forms a tetrahedral arrangement with four neighboring atoms. In this spatial arrangement, all atomic distances are equally small. Therefore, very strong bonding forces act between the atoms in all spatial directions. This results in the high strength and 9 10528A

[0054] The extreme hardness of diamond. The atomic bonds belonging to the crystal lattice of diamonds, a total of four, are designated with the abbreviation "sp3". Thus, sp3 hybridization is present.

[0055] In a particularly advantageous embodiment 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.

[0056] The carbon layer is preferably formed as a hydrogen-containing amorphous carbon layer, which is designated as aC:H according to the VDI 2840 guideline.

[0057] The carbon layer can additionally contain metallic and / or non-metallic doping. Generally, metal-containing aC:H carbon layers are designated aC:H:Me. The metal Me can be, for example, tungsten, titanium, silicon, or tantalum. With tungsten as the dopant, the designation is aC:H:W. An aC:H coating containing a non-metal (doping, for example, with oxygen), designated aC:H:X, where X represents a non-metal, is also applicable. The non-metal X can be, for example, oxygen, nitrogen, fluorine, or boron. The designation Me for metallic doping and X for non-metallic doping is also applicable to other variants of carbon layers. A doped ta-C layer is designated ta-C:Me or ta-C:X depending on the dopant, and a doped aC layer is designated aC:Me or aC:X depending on the dopant.

[0058] In one variant of the invention, the carbon layer is an amorphous carbon layer, in particular a tetrahedral hydrogen-free amorphous carbon layer, also known as a ta-C layer, characterized by a high proportion of sp 3 is characterized by hybridized carbon.

[0059] The carbon coating exhibits a very low coefficient of friction combined with very good chemical resistance. The coating hardness is 10 10528A

[0060] comes very close to the hardness of diamonds, with the hardness in the aC:H formulation being more than 10 GPa, and / or less than 30 GPa, preferably 20 - 25 GPa.

[0061] For example, the hardness of the carbon layer in the ta-C version is more than 40 GPa, and / or less than 75 GPa.

[0062] Doped carbon layers of the form aC:H:X and aC:H:Me typically exhibit lower hardness compared to aC:H. This hardness is generally greater than 8 GPa and / or less than 20 GPa. Due to the lower hardness, faster run-in of the layer system is usually observed.

[0063] In one embodiment of the invention, the carbon layer is applied as a coating to the outer surface of the inner arrangement in the form of a sleeve. The thickness of the layer is advantageously more than 0.5 pm, preferably more than 1.5 pm, and particularly more than 2 pm. Furthermore, it is advantageous if the carbon layer is less than 10 pm, preferably less than 5 pm, and particularly less than 3 pm.

[0064] Surface roughness plays a crucial role in tribological systems, as it directly influences friction and wear mechanisms. Due to its thinness, a PVD coating does not smooth the surface. Depending on the PVD coating process, this can negatively affect roughness parameters for tribological applications. Ideally, the surface should be as smooth as possible before coating. This smoothness should also be selected based on the desired layer thickness and residual stresses within the coating. Post-treatment of the PVD coating to reduce roughness parameters is possible.

[0065] Depending on the component load, roughness values ​​of R on the finished product with PVD coating are z (average roughness depth) preferably less than 2 pm and R P k (Reduced Peak Height) preferably less than 1 pm. For highly stressed components, roughness values ​​of R are required. z(average roughness depth) preferably less than 1 pm,11 10528A

[0066] especially smaller than 0.7 pm, and R P k (Reduced Peak Height) preferably less than 0.2 pm.

[0067] Especially when the centrifugal pump is operated under fluctuating and / or extreme operating conditions, the carbon layer of the inner assembly is subjected to enormous stress. Surprisingly, it has proven advantageous to place a CrN layer between the carbon layer and the chromium steel of the inner assembly.

[0068] Chromium nitride coatings are often applied to metallic surfaces to increase their lifespan and performance. A chromium nitride layer can be thin to allow precise control over material properties and is typically produced by PVD, CVD, or PECVD processes. The chromium nitride coating demonstrably improves the material's hardness, corrosion resistance, and wear resistance.

[0069] In one variant of the invention, the thickness of the CrN layer is less than 3 pm, preferably less than 1.5 pm, and can, for example, prevent flaking of the aC:H layer under extreme operating conditions of the centrifugal pump, since the coating serves as a hardness gradient to the softer base material.

[0070] In one embodiment of the invention, a CrC layer or a WC:C layer is arranged between the carbon layer and the chromium steel of the inner arrangement. In this embodiment of the invention, the CrN layer is replaced by the CrC layer or the WC:C layer, achieving similarly advantageous effects.

[0071] For example, the plain bearing is located in the suction area of ​​the centrifugal pump. It supports and mounts the pump rotor with its multiple impellers on the side of the centrifugal pump facing away from the motor.12 10528A

[0072] For example, the invention comprises a medium-lubricated plain bearing with a tribological pairing of a carbon layer on a chromium steel sleeve against a bushing made of a copper-based material, in particular bronze. The carbon coating reduces the coefficient of friction of the bearing pairing and leads to higher durability of the coated sleeve.

[0073] The substrate of the coated sliding component is, for example, a stainless steel, such as a 13% chromium steel, an austenitic-ferritic duplex steel or a nickel-based alloy.

[0074] For example, the hardness of the aC:H coating is 25 GPa, which corresponds to approximately 2500 HV.

[0075] By replacing the otherwise standard SiC or graphite bushings with a bushing made of a bronze alloy, the bushing and bushing holder can, for example, be manufactured as a single piece. This reduces the number of parts and the assembly effort. Furthermore, the bronze bushing is vibration-damping, significantly less brittle, and therefore less susceptible to breakage.

[0076] Further features and advantages of the invention will become apparent from the description of exemplary embodiments with reference to the drawings and from the drawings themselves.

[0077] This shows:

[0078] Fig. 1 shows a sectional view of an exemplary centrifugal pump,

[0079] Fig. 2 shows a detailed sectional view of the device,

[0080] Fig. 3 shows a sectional view of the element with a cylindrical inner surface.

[0081] Fig. 1 shows a sectional view of an exemplary centrifugal pump. The multi-stage centrifugal pump has a radial flow inlet 1 and a radial 13 10528A

[0082] Flow outlet 2 is provided. The hydraulics of the centrifugal pump have a bearing and are connected to the motor (not shown) via a shaft coupling.

[0083] The pumped medium enters the centrifugal pump via the suction casing 3 and is accelerated outwards by the suction impeller 4. In the flow contour of the stage casing 5, the kinetic energy of the pumped medium is converted into pressure energy, and the pumped medium is guided via the guide vane 6 to the next impeller 7. This process is repeated through all stages until the last impeller 8, and is then directed via the discharge casing 9 to the discharge flange 10, through which it exits the centrifugal pump.

[0084] The backflow of the pumped medium from the stage housing 5 into the suction area of ​​the preceding impeller 4, 7 is prevented by a throttle gap 11. A relief piston 12 may be located on the rear side of the last impeller 8, via which axial thrust compensation is achieved by hydraulic forces. The hydraulic system is limited on the rear side of the last impeller 8 and the relief piston 12 by a sealing housing 13, through which the drive shaft 14 passes. The shaft passage 15 through the sealing housing 13 is sealed against the environment by a dynamic shaft seal 16.

[0085] The drive shaft 14 is supported by rolling bearings 17 and a device 18 in the form of a plain bearing, which are received by a bearing housing 19 and the suction housing, respectively. The bearing housing 19 is connected to the suction housing 3.

[0086] Figure 2 shows a detailed sectional view of the device 18. The device 18 is designed as a media-lubricated sliding bearing, the sliding bearing comprising an inner arrangement 20 and an outer arrangement 21.

[0087] The inner assembly 20 is designed as a sleeve made of 13% chromium steel, in the illustrated embodiment 1.4021, and is rotationally fixed to the drive shaft 14. The outer assembly 21 is stationary in the suction housing 314 10528A

[0088] The centrifugal pump is positioned and comprises an element with a cylindrical inner surface 22 in the form of a bushing, as well as a further element 23 in the form of a bushing holder, in the two-part version. The gap 24 of the sliding bearing is formed between the inner arrangement 20 and the outer arrangement 21.

[0089] The bushing holder of the outer arrangement 21 has a bulge 25 which is held in position by two sealing elements in the form of O-rings 26.

[0090] O-rings 26 also act as vibration dampers.

[0091] The bushing of the outer arrangement 21 has a hardness of 320 HB and is made of aluminium bronze.

[0092] The chromium steel sleeve of the inner arrangement 20 has a CrN layer 27 with a thickness of 0.5 to 1.5 µm. A carbon layer 28 in the form of an aC:H coating is applied to the CrN layer 27. The thickness of the aC:H coating is 2.5 µm and the hardness of the aC:H coating is 25 GPa. The average roughness depth R z The coated chrome steel sleeve has a thickness of less than 2 pm.

[0093] Under normal operating conditions, the gap 24 of the sliding bearing is lubricated by the pumped medium. Particularly during start-up phases and / or operation with highly fluctuating operating parameters and / or operation under extreme operating parameters, the high hardness and thus the wear resistance of the sliding bearing bushing, in combination with the smooth hardness of the sliding bearing sleeve and the emergency lubricating graphite pins in the bushing, ensures trouble-free and long-lasting operation of the centrifugal pump.

[0094] Fig. 3 shows a sectional view of the element with cylindrical inner surface 22. The bushing of the outer arrangement 21 is made of aluminum bronze and has a hardness of 330 HB.

[0095] The element with cylindrical inner surface 22 of the bushing of the outer arrangement 21 also has a plurality of integrated lubricating elements 29 in the design as 15 10528A

[0096] Cylindrical graphite pins are integrated into the body of the bushing. The graphite in the bushing acts as a dry lubricant, especially under extreme and fluctuating operating conditions of the centrifugal pump. 16 10528A

[0097] Reference symbol list

[0098] 1 Radial flow inlet 16 Shaft seal

[0099] 2 Radial flow outlet 17 Rolling bearings

[0100] 3 Suction housings 18 Device

[0101] 4 suction impeller 19 bearing housing

[0102] 5-stage housing 20 Internal arrangement

[0103] 6 Guide wheel 21 Outer arrangement

[0104] 7 Impeller 22 Element with cylindrical inner surface

[0105] 8 Last wheel 23 Further element

[0106] 9 pressure housings 24 gaps

[0107] 10 Pressure flange 25 Curvature

[0108] 11 Throttle gap 26 O-rings

[0109] 12 relief pistons, 27 CrN layer

[0110] 13 Sealing housing 28 Carbon layer

[0111] 14 Drive shaft 29 Integrated lubrication elements 15 Shaft feedthrough

Claims

17 10528A Patent claims centrifugal pump with a device 1. Centrifugal pump with at least one impeller (3, 7, 8) mounted on a drive shaft (14), wherein the drive shaft (14) is supported by a device (18) comprising at least one media-lubricated sliding bearing, the sliding bearing comprising an inner arrangement (20) which is rotationally fixed to the drive shaft (14), and an outer arrangement (21) which is stationary in the suction housing (4), wherein a gap (24) is formed between the inner arrangement (20) and the outer arrangement (21), characterized by that the outer arrangement (21) has an element with a cylindrical inner surface (22) formed from a bronze material with a hardness of more than 50 HB, and the inner arrangement (20) is formed from a steel material, wherein the inner arrangement (20) has a carbon layer (28).

2. Centrifugal pump according to claim 1, characterized in that the element with cylindrical inner surface (22) is made of a bronze material with a hardness of more than 150 HB, preferably with a hardness of more than 250 HB, in particular with a hardness of more than 350 HB.

3. Centrifugal pump according to claim 1 or 2, characterized in that the outer arrangement (21) has at least one integrated lubricating element (29) made of graphite.18 10528A 4. Centrifugal pump according to one of claims 1 to 3, characterized in that the outer arrangement (21) comprises a further element (23) for fixing sealing elements.

5. Centrifugal pump according to claim 4, characterized in that the further element (23) is made of chromium steel.

6. Centrifugal pump according to one of claims 1 to 4, characterized in that the outer arrangement (21) is formed in one piece.

7. Centrifugal pump according to one of claims 1 to 6, characterized in that the inner arrangement (20) is made of chromium steel.

8. Centrifugal pump according to one of claims 1 to 7, characterized in that the carbon layer (28) is formed from a ta-C and / or an aC:H and / or an aC and / or a ta-C:Me and / or an aC:Me and / or an aC:H:Me and / or a ta-C:X and / or an aC:X and / or an aC:H:X layer, wherein Me comprises at least one of the elements tungsten, titanium, silicon or tantalum, and wherein X comprises at least one of the elements oxygen, nitrogen, fluorine or boron.

9. Centrifugal pump according to one of claims 1 to 8, characterized in that a CrN layer (27) is arranged between the carbon layer (28) and the steel material of the inner arrangement (20).

10. Centrifugal pump according to one of claims 1 to 9, characterized in that the device (18) is arranged in the suction area of ​​the centrifugal pump.

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