Load reduction device

Abstract

The invention relates to a load relief device for compensating the axial thrust of a turbomachine. The load relief device comprises an element (4) connected to a shaft (2) for co-rotation. Together with a fixed counterpart element (5), at least one gap (8, 7, 8) is formed. At least in some areas between the element (4) and the counterpart element (5), a carbon layer (10) is arranged.

Description

Technical Field

[0001] The present invention relates to a load-reducing device for compensating for the axial thrust of a turbomachinery, the load-reducing device having a load-reducing element that is rotatably connected to the shaft and forms a gap with an opposing element fixed to the housing. Background Technology

[0002] Axial thrust is the result of all axial forces acting on the impeller of a turbomachinery. Distinctions are made between various types of axial thrust compensation.

[0003] There are essentially three known types of unloading devices for absorbing axial thrust: unloading discs, single-piston devices, and double-piston devices. All three designs share the characteristic of guiding relief flow through the gap. The majority of the relief flow returning to the centrifugal pump inlet is leakage loss, which is attempted to be minimized through the minimum gap width.

[0004] The goal is to achieve a rotor state that is controlled for all operating states of the turbomachinery, thereby ensuring uninterrupted operation. In the operation of a centrifugal pump, friction between moving parts and stationary parts should be avoided, if possible.

[0005] In the operation of turbomachinery with a load shearing disc, the pressure difference acting between the two sides of the load shearing element results in a load shearing force opposite to the axial thrust. Ideally, the load shearing force is exactly the same as the axial thrust. A force balance exists on the rotor.

[0006] During start-up and shutdown operations, the pressure differential has not yet been established, resulting in contact between the unloading element and the opposing element without appropriate countermeasures. An attempt is made to prevent the radial clearance surfaces from abutting each other by means of a spring assembly.

[0007] DE10254041A1 discloses a multistage centrifugal pump. A double-piston unloading device is fixed to a shaft. The double pistons are surrounded by a housing section, forming a radial clearance between the double pistons and the housing section. An axial clearance exists between the radial clearance. The axial clearance has a variable width s.

[0008] DE19927135A1 describes a load shedding device for a multistage centrifugal pump, in which a universal joint is used. The universal joint is sized such that it can elastically deform under residual thrust. The universal joint is housed in a separate sealing space.

[0009] DE1745898U describes a device for limiting the axial thrust of a centrifuge pump rotor. The unloading element is prevented from traveling upwards against the opposing element by means of a freely moving axial bearing and an outer bearing ring abutting and limiting the support bearing flange via spring force. This configuration requires oil lubrication. In this configuration, the structural length of the machine extends through a corresponding section of the shaft in which the housing in question is sealed relative to the conveyed medium. Summary of the Invention

[0010] The object of this invention is to provide a load-reducing device for compensating for the axial thrust of turbomachinery, wherein permanent damage to components is effectively prevented. This measure does not result in any additional structural length to the turbomachinery. It is also desirable to avoid the use of a dedicated housing and any additional lubricant. Furthermore, the load-reducing device ensures minimal leakage flow and has a long service life. The load-reducing device is characterized by high reliability. Additionally, it ensures simple assembly and easy access for maintenance operations. Moreover, the load-reducing device is characterized by minimal manufacturing costs.

[0011] According to the invention, this objective is achieved by a device having the features of claim 1, and preferred variations can be found in the dependent claims, the specification and the drawings.

[0012] In the load-reducing device of the present invention, the carbon layer is at least disposed in the region between the element rotatably connected to the shaft and the fixed opposing element.

[0013] The component can take the form of, for example, a load-reducing disc, and the opposing component can take the form of a counter disc. The component can also be designed as a load-reducing piston or a double piston. The carbon layer effectively prevents damage to the components in the event of friction between the component and the opposing component, especially during start-up or shutdown operations.

[0014] A carbon layer is understood to be a layer in which carbon is the main component. Carbon layers can be applied, for example, by PVD (physical vapor deposition), physical vapor deposition (e.g., by evaporation or sputtering), or CVD (chemical vapor deposition) methods.

[0015] This layer is preferably applied to elements designed as unloading discs, unloading pistons, or dual pistons, particularly to the possible contact surfaces between the element and the opposing element. Additionally or alternatively, the opposing element, designed as part of the housing, may also be coated, for example, with a carbon layer.

[0016] Amorphous carbon layers are preferred, especially tetrahedral hydrogen-free amorphous carbon layers, also known as ta-C layers. The atomic bonds belonging to the graphite lattice (a total of 3 in each case) are referred to as "sp2". This is the case of sp2 hybridization.

[0017] In diamond, each carbon atom forms a tetrahedral arrangement with four neighboring atoms. In this spatial arrangement, all atomic spacings are equally small. Therefore, very strong binding forces act between the atoms and in all spatial directions. This results in diamond's high strength and extremely high hardness. The atomic bonds belonging to the diamond lattice, in each case a total of four, are referred to as "sp3". Thus, this is the case of sp3 hybridization.

[0018] In a particularly advantageous variant of the invention, the carbon layer is composed of a mixture of sp3-hybridized carbon 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 the carbon network.

[0019] The carbon layer arrangement of the present invention results in a significant reduction in wear on components that rub against each other. The carbon layer increases lubricity to such an extent that damage to the components and opposing components can be effectively prevented even under conditions of friction.

[0020] This invention enables the achievement of very small clearance dimensions. This minimizes leakage flow and thus increases the efficiency of the centrifugal pump. Complex maintenance is not required. This reduces operating costs.

[0021] Arranging a carbon layer between the component and the opposing component creates a very smooth axial surface with anti-adhesion properties, without requiring any complex remapping of the parts. Therefore, the unloading device of the present invention is characterized by relatively low production costs.

[0022] In a particularly advantageous variant of the invention, a carbon layer is applied as a coating to the element and / or the opposite element. The thickness of the layer is advantageously greater than 0.3 μm, preferably greater than 0.6 μm, and especially greater than 0.9 μm. It has also been found advantageous when the layer thickness is less than 30 μm, preferably less than 25 μm, and especially less than 20 μm.

[0023] In a variation of the invention, the element or opposite element is covered by a simple shielding device so that only the desired coating area is exposed. Alternatively, multiple elements or opposite elements can be introduced simultaneously into the coating reactor, preferably designed as a vacuum chamber, to apply the ta-C coating under moderate thermal stress.

[0024] The component or its counterpart is ready for use immediately after the coating operation without any additional work. The ta-C coating has a very low coefficient of friction and excellent chemical stability. The hardness of the coating is very close to that of diamond, preferably greater than 20 GPa, preferably greater than 30 GPa, especially greater than 40 GPa, but less than 120 GPa, preferably less than 110 GPa, and especially less than 100 GPa.

[0025] Preferably, the carbon layer is not applied directly to the element or the opposite element, but rather a tackifier layer is provided first. This is preferably composed of a material that has both good adhesion to steel and prevents carbon diffusion, for example, by forming stable carbides. The tackifier layer used, which meets these requirements, preferably comprises a thin layer of chromium, titanium, or silicon. Chromium carbide and tungsten carbide have been found to be particularly suitable as tackifiers.

[0026] In an advantageous variant of the invention, the coating has an adhesion promoter layer that preferably comprises a chromium material. This adhesion promoter layer is preferably composed of chromium in an amount greater than 30% by weight, preferably greater than 60% by weight, and especially greater than 90% by weight.

[0027] It has been found that it is advantageous when the thickness of the tackifier layer is greater than 0.03 μm, preferably greater than 0.06 μm, especially greater than 0.09 μm, and / or less than 0.21 μm, preferably less than 0.18 μm, especially less than 0.15 μm.

[0028] The ta-C coating of this invention is a simple, rapid, and economically feasible method. In addition to very high hardness, the coating of this invention also exhibits excellent sliding properties and good chemical stability.

[0029] Furthermore, the present invention can also achieve coating of thin-walled elements or relative elements with relatively small dimensions, which is difficult to achieve only when using conventional coating.

[0030] One reason why the higher hardness produced by the ta-C coating is advantageous is that small solid particles, typically present in the medium, accumulate in the area between the component and the opposing component. Due to this movement, these solid particles act like abrasives and thus penetrate into the surface of the component. As a result, grooves appear on the surface of the conventional component, leading to wear and leakage between the two parts.

[0031] Ideally, PVD methods are used for coating. These methods are relatively simple and have low process temperatures. This allows for the introduction of foreign atoms into the layers if desired. Deposition temperatures are typically well below 500°C. The process is preferably implemented in a way that excludes microstructural and dimensional variations of the material to be coated (metals, high-alloy and low-alloy stainless steels, etc.).

[0032] Alternatively, PECVD / PACVD methods can be used for coating. Here, plasma excitation of the gas phase is achieved by introducing a pulsed DC voltage or medium-frequency (kHz range) or high-frequency (MHz range) power. The input of a pulsed DC voltage has also been found useful due to the maximum process variability with different workpiece geometries and loading densities.

[0033] According to the present invention, this process allows for the coating of common, standard, mass-produced components, such as unloading discs, unloading pistons, unloading double pistons, or housing components, with ta-C on possible contact surfaces. This achieves a significant improvement in wear and sliding characteristics. Attached Figure Description

[0034] Other advantages and features of the invention will be apparent from the description of the introduced embodiments with reference to the accompanying drawings and from the drawings themselves.

[0035] The attached diagram shows:

[0036] Figure 1 It shows the details of the cross-section of a multistage centrifugal pump.

[0037] Figure 2 This is a schematic diagram of the load reduction device. Detailed Implementation

[0038] Figure 1 A centrifugal pump with a housing 1 and a shaft 2 supporting multiple impellers 3 is shown. The accompanying drawing shows only two of the impellers 3 by way of example only. On the shaft 2 is an element 4, a load shearing device implemented as a double piston in the working example. Element 4 is surrounded by an opposing element 5, which in the working example is formed by a portion of the housing. Element 4 and the opposing element 5 form two radial clearances 6 and 7. Between the radial clearances 6 and 7 is an axial clearance 8. The axial clearance 8 has a variable width s. A hydrodynamic axial bearing 9 is provided at the pressure-side end of the centrifugal pump.

[0039] The unloading device is designed to result in as much residual thrust as possible in the suction direction under all operating conditions of the centrifugal pump. Starting from the maximum width s of the axial clearance 8 in the stationary state of the centrifugal pump, for example, through elastic deformation, preferably elastic deformation of the universal joint, the clearance 8 is closed under operating conditions until a defined minimum width is reached, at which point, if possible, contact between the surfaces of the double pistons 4 and the surfaces of the portion of the housing 5 defining the clearance 8 is avoided. Figure 1 The design shown features a self-adjusting axial clearance 8. According to the invention, the carbon layer 10 is at least disposed in the region between element 4 and the opposing element 5, which... Figure 2 As shown in the image.

[0040] Figure 2An enlarged schematic diagram of a load-reducing device designed as a dual-piston assembly is shown. This device has an element 4 rotatably connected to a shaft 2 and forming two radial gaps 6 and 7 and an axial gap 8 together with a fixed opposing element 4. The axial gap 8 has a variable width s. A carbon layer 10 is disposed at least in the region between element 4 and the opposing element 5. Element 4 is coated with a carbon layer. This is an amorphous carbon layer 10 introduced into the load-reducing device in the form of a ta-C coating of element 4. The coating thickness is preferably in the range of 1 to 20 μm, wherein a 0.1 μm thick chromium-containing adhesion promoter layer is present between element 11 and carbon layer 14.

Claims

1. A load relief device for compensating the axial thrust of a turbomachine, comprising an element (4) which is rotationally coupled to a shaft (2) and which forms at least one gap (6, 7, 8) with a fixed counter element (5), It is characterized in that The carbon layer (10) is arranged at least in the region between the element (4) and the opposing element (5), wherein the carbon layer (10) has been applied as a coating to the element (4) and / or the counter element (5), Wherein, the carbon layer (10) is a tetrahedral hydrogen-free amorphous carbon layer.

2. The load reduction device according to claim 1, characterized in that: The coating has an adhesion promoter layer.

3. The load reduction device according to claim 2, characterized in that: The adhesion promoter layer consists of chromium to an extent of more than 30% by weight.

4. The load reduction device according to claim 2 or 3, characterized in that: The thickness of the adhesion promoter layer is greater than 0.03 μm.

5. The load reduction device according to any one of claims 1 to 3, characterized in that: The surface hardness of the element (4) and / or the opposing element (5) having the carbon layer (10) is greater than 20 GPa.

6. The load reduction device according to any one of claims 1 to 3, characterized in that: The thickness of the carbon layer (10) is greater than 0.3 μm.

7. The load reduction device according to any one of claims 1 to 3, characterized in that: The element (4) takes the form of a load relief disc.

8. The load reduction device according to any one of claims 1 to 3, characterized in that: The element (4) takes the form of a load-relieving piston.

9. The load reduction device according to any one of claims 1 to 3, characterized in that: The element (4) takes the form of a double load-reducing piston.

10. The load reduction device according to any one of claims 1 to 3, characterized in that: The counter element (5) is in the form of a housing segment.

11. The load reduction device according to claim 3, characterized in that: The adhesion promoter layer consists of chromium to an extent of more than 60% by weight.

12. The load reduction device according to claim 11, characterized in that: The adhesion promoter layer consists of chromium to an extent of more than 90% by weight.

13. The load reduction device according to claim 4, characterized in that: The thickness of the adhesion promoter layer is greater than 0.06 μm.

14. The load reduction device according to claim 13, characterized in that: The thickness of the adhesion promoter layer is greater than 0.09 μm.

15. The load reduction device according to claim 4, characterized in that: The thickness of the adhesion promoter layer is less than 0.21 μm.

16. The load reduction device according to claim 15, characterized in that: The thickness of the adhesion promoter layer is less than 0.18 μm.

17. The load reduction device according to claim 16, characterized in that: The thickness of the adhesion promoter layer is less than 0.15 μm.

18. The load reduction device according to claim 5, characterized in that: The surface hardness is greater than 30 GPa.

19. The load reduction device according to claim 18, characterized in that: The surface hardness is greater than 40 GPa.

20. The load reduction device according to claim 5, characterized in that: The surface hardness is less than 120 GPa.

21. The load reduction device according to claim 20, characterized in that: The surface hardness is less than 110 GPa.

22. The load reduction device according to claim 21, characterized in that: The surface hardness is less than 100 GPa.

23. The load reduction device according to claim 6, characterized in that: The thickness of the carbon layer (10) is greater than 0.6 μm.

24. The load reduction device according to claim 23, characterized in that: The thickness of the carbon layer (10) is greater than 0.9 μm.

25. The load reduction device according to claim 6, characterized in that: The thickness of the carbon layer (10) is less than 30 μm.

26. The load reduction device according to claim 25, characterized in that: The thickness of the carbon layer (10) is less than 25 μm.

27. The load reduction device according to claim 26, characterized in that: The thickness of the carbon layer (10) is less than 20 μm.

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