EP3924628A1

EP3924628A1 - Load-relieving device

Info

Publication number: EP3924628A1
Application number: EP20704818.2A
Authority: EP
Inventors: Markus PITTROFF
Original assignee: KSB SE and Co KGaA
Current assignee: KSB SE and Co KGaA
Priority date: 2019-02-15
Filing date: 2020-02-07
Publication date: 2021-12-22
Anticipated expiration: 2040-02-07
Also published as: CN113396287A; EP3924628B1; WO2020165046A1; DE102019001120A1; EP3924628C0

Abstract

The invention relates to a load-relieving device for compensating the axial thrust of a turbomachine. The load-relieving device has an element (4), which is connected to a shaft (2) for conjoint rotation. Together with a stationary counter-element (5), at least one gap (8, 7, 8) is formed. At least in some regions between the element (4) and the counter-element (5), a carbon layer (10) is arranged.

Description

description

Relief device

The invention relates to a relief device for compensating the axial thrust of a turbomachine with a relief element which is connected in a rotationally fixed manner to a shaft and forms a gap together with a counter-element fixed to the housing.

The axial thrust is the resultant of all axial forces acting on the rotor of a turbomachine. A distinction is made between different types of axial thrust compensation.

There are essentially three types of relief devices known for absorbing the axial thrust: relief disc, single piston and double piston. Common to all three versions is a relief current routed through a column. The relief flow, which is mostly returned to the inlet of the centrifugal pump, represents a leakage loss, which one tries to minimize with the smallest possible gap widths.

The aim is to achieve a position of the rotor that is controlled for all operating states of the turbo machine in order to ensure trouble-free operation of the turbo machine. When the centrifugal pump is in operation, moving moving parts should be avoided as much as possible. When a turbo machine with a relief disk is in operation, the pressure difference that acts between two sides of the relief element leads to a relief force that is directed against the axial thrust. In the ideal case, the relief force is just as great as the axial thrust. There is an equilibrium of forces on the runner.

This pressure difference has not yet built up during start-up and shutdown processes, so that contact between the relief element and the counter-element occurs without appropriate countermeasures. An attempt is made to prevent the radial gap surfaces from tarnishing with the aid of spring assemblies.

DE 102 54 041 A1 shows a multistage centrifugal pump. The double piston of a relief device is attached to a shaft. The double piston is surrounded by a housing part with which it forms radial gaps. There is an axial gap between the radial gaps. The axial gap has a variable width s.

DE 199 27 135 A1 describes a relief device for multistage centrifugal pumps in which a cardanic ring is used. The cardanic ring is dimensioned so that it is elastically deformed by the residual thrust. The cardanic ring is arranged in a separate sealed space.

DE 1 745 898 U describes a device for limiting the axial thrust of the pump rotor of a centrifugal machine. A contact of the relief element on the counter element is prevented by the fact that a freely movable axial bearing and an outer bearing ring rest in a limiting manner on a support bearing flange by spring force. Oil lubrication is required for this construction. With this construction, the overall length of the machine is extended by a corresponding shaft section where the corresponding housing is sealed against the pumped medium. The object of the invention is to provide a relief device for compensating for the axial thrust of a turbomachine, in which permanent damage to the components is effectively prevented. The measure should not lead to an additional length of the turbomachine. A separate housing and the use of an additional lubricant should also be avoided. In addition, the relief device should ensure the lowest possible leakage flow and have a long service life. The relief device should be characterized by a high level of reliability. It should also ensure simple assembly and be easily accessible for maintenance work. Furthermore, the relief device should be distinguished by the lowest possible manufacturing costs.

According to the invention, this object is achieved by a device having the features of claim 1. Preferred variants can be found in the subclaims, the description and the figures.

In the relief device according to the invention, a carbon layer is arranged at least in some areas between the element, which is non-rotatably connected to a while and the stationary counter-element. The element can for example be designed as a relief disk and the counter-element as a counter-disk. A design of the element as a relief piston or as a double piston is also possible. The carbon layer effectively prevents damage to the components in the fold of a rubbing against element and counter-element, in particular when starting or stopping.

The carbon layers are understood to mean layers in which carbon is the predominant component. The carbon layer can be applied, for example, with a PVD (physical vapor deposition), a physical vapor deposition, for example by evaporation or sputtering) or a CVD (chemical vapor deposition) method. The layer is preferably applied to the element designed as a relief disk, relief piston or double piston, in particular on possible contact surfaces of element and counter-element. Additionally or alternatively, the counter element, which is designed as a housing part, for example, can also be coated with the carbon layer.

It is preferably an amorphous carbon layer, in particular a tetrahedral, hydrogen-free amorphous carbon layer, which is also referred to as a ta-C layer. The atomic bonds belonging to the crystal lattice of graphite (total of 3 each) are identified with the designation “sp2”. This is an sp2 hybridization.

In diamond, each carbon atom forms a tetrahedral arrangement with four neighboring atoms. With this spatial arrangement, all atomic distances are equally small. There are therefore very high binding forces between the atoms in all spatial directions. This results in the high strength and extreme hardness of the diamond. The atomic bonds belonging to the crystal lattice of diamond, a total of four each, are identified with the designation "sp3". There is thus an sp3 hybridization.

In a particularly favorable 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 built into this carbon network.

The arrangement according to the invention of a carbon layer leads to a considerable reduction in the removal of components rubbing against one another. The carbon layer increases the sliding ability to such an extent that damage to the element and the counter-element is effectively prevented even if it is touched. The invention makes it possible to realize very small spar dimensions. This minimizes the leakage flow and thus increases the efficiency of the centrifugal pump. There is no need for complex maintenance work. This lowers the operating costs. By arranging a carbon layer between the element and the counter-element, an extremely smooth axial surface with non-stick properties is created without the need for complex mechanical reworking of the components. The relief device according to the invention is thus characterized by relatively low manufacturing costs.

In a particularly favorable variant of the invention, the carbon layer is applied as a coating to the element and / or the counter-element. The thickness of the layer is advantageously more than 0.3 mm, preferably more than 0.6 mm, in particular more than 0.9 mm. Furthermore, it proves to be advantageous if the thickness of the layer is less than 30 mm, preferably less than 25 mm, in particular less than 20 mm.

In a variant of the invention, the element or counter-element is covered by means of a simple masking device in order to leave only the desired coating area free. Several elements or counter-elements can also be introduced into the coating reactor, which is preferably designed as a vacuum chamber, at the same time, with the ta-C coating being applied under moderate thermal stress. The element or counter-element is ready for use immediately after the coating process without any rework. The ta-C coating has a very low coefficient of friction and, at the same time, very good chemical resistance. The hardness of the coating comes very close to the hardness of diamond, the hardness preferably being more than 20 GPa, preferably more than 30 GPa, in particular more than 40 GPa, but less than 120 GPa, preferably less than 110 GPa, in particular less than 100 GPa . The carbon layer is preferably not applied directly to the element or counter-element, but rather an adhesion promoter layer is provided first. This is preferably made of a material that both adheres well to steel and prevents carbon diffusion, e.g. B. through the formation of stable carbides. Thin layers of chromium, titanium or silicon are preferably used as adhesion promoting layers that meet these requirements. In particular, chromium and tungsten carbide have proven useful as adhesion promoters.

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

It proves to be advantageous if the thickness of the adhesion promoter layer is more than 0.03 mm, preferably more than 0.06 mm, in particular more than 0.09 mm and / or less than 0.21 mm, preferably less than 0, 18 mm, in particular less than 0.15 mm.

The ta-C coating according to the invention is a simple, quick and economical process. In addition to being very hard, the coating according to the invention also has excellent sliding properties and good chemical resistance.

In addition, the invention also enables thin-walled elements or counter-elements with smaller dimensions to be coated, which would be very difficult to achieve with conventional coatings.

The advantage of the higher hardness due to the ta-C coating is due, on the one hand, to the fact that small solid particles, which are often contained in the media, collect in the area between the element and the counter-element. As they move, these solid particles act like an abrasive and work their way into the surface of the Elements a. As a result, grooves can occur on the surface of conventional elements, which lead to wear on both parts and leakage.

Ideally, PVD processes are used for coating. These processes are relatively simple and have a low process temperature. This technology leads to layers in which foreign atoms can also be incorporated as required. The deposition temperatures are typically well below 500 ° C. The process is preferably carried out in such a way that changes in structure and dimensions of the materials to be coated (metallic, high and low-alloy stainless steels, etc.) are excluded.

Alternatively, PECVD / PACVD processes can be 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. For reasons of maximized process variability with different workpiece geometries and load densities, the coupling of pulsed DC voltage.

According to the invention, normal standard series parts such as relief disc, relief piston, relief double piston or housing parts can be coated with ta-C on the possible contact surfaces with the method. This results in an enormously improved wear and sliding behavior.

Further advantages and features of the invention emerge from the description of exemplary embodiments with reference to drawings and from the drawings themselves.

It shows

1 shows a detail of a multistage centrifugal pump shown in section,

2 shows a schematic representation of a relief device. 1 shows a centrifugal pump with a housing 1 and a shaft 2 that carries several impellers 3. In the drawing, only two of the running wheels 3 are shown by way of example. On the shaft 2 there is also an element 4 of a relief device, which in the exemplary embodiment is designed as a double piston. The element 4 is surrounded by a counter-element 5, which in the exemplary embodiment is formed by a housing part. Element 4 forms two radial gaps 6 and 7 with the counter element 5. Between the radial gaps 6 and 7 there is an axial gap 8. The axial gap 8 has a variable width s. A hydrodynamic axial bearing 9 is arranged at the pressure-side end of the centrifugal pump.

The relief device is designed in such a way that, if possible, there is a residual thrust in all operating states of the centrifugal pump, which acts in the direction of the suction side. Starting from a maximum width s of the axial gap 8 in the idle state of the centrifugal pump, for example, elastic deformation, preferably a cardanic ring, closes the gap 8 under operating conditions to a predetermined minimum width at which the surfaces of the double piston 4 bounding the gap 8 come into contact and the housing part 5 is avoided if possible. According to the embodiment shown in Figure 1, the axial gap 8 has a self-regulating function. According to the invention, a carbon layer 10, which is shown in FIG. 2, is arranged at least in some areas between the element 4 and the counter-element 5.

FIG. 2 shows an enlarged schematic representation of a relief device designed as a double piston with an element 4, which is non-rotatably connected to a shaft 2 and, together with a stationary counter-element 4, forms two radial gaps 6 and 7 and an axial gap 8. The axial gap 8 has a variable width s. A carbon layer 10 is arranged between the element 4 and the counter-element 5 at least in some areas. The element 4 is coated with the carbon layer. It is an amorphous carbon layer 10, which is introduced into the relief device as a ta-C coating of the element 4. The thickness of the coating is preferably in the range between 1 and 20 mm, where the coating has a chromium-containing 0.1 mm thick adhesion promoter layer between the element 11 and the carbon layer 14,

Claims

Claims relief device

1. Relief device to compensate for the axial thrust of a turbomachine with an element (4) which is non-rotatably connected to a shaft (2) and together with a stationary counter element (5) forms at least one gap (6, 7, 8), characterized in that, that between the element (4) and the counter-element (5) a carbon layer (10) is arranged at least in some areas.

2. Relief device according to claim 1, characterized in that it is an amorphous carbon layer (10),

3. Relief device according to claim 2, characterized in that it is a tetrahedral, hydrogen-free amorphous carbon layer (10).

4. Relief device according to one of claims 1 to 3, characterized in that the carbon layer (10) is applied as a coating on the element (4) and / or the counter-element (5).

5. Relief device according to claim 4, characterized in that the coating has an adhesion promoter layer.

6. Relief device according to claim 5, characterized in that the adhesion promoter layer consists of more than 30 wt .-%, preferably more than 60 wt .-%, in particular more than 90 wt .-% of chromium.

7. Relief device according to claim 5 or 6, characterized in that the thickness of the adhesion promoter layer is more than 0.03 mm, preferably more than 0.06 mm, in particular more than 0.09 mm and / or less than 0.21 mm, is preferably less than 0.18 mm, in particular less than 0.15 mm.

8. Relief device according to one of claims 1 to 7, characterized in that the surface hardness of the element (4) and / or the counter-element (5) with the carbon layer (10) is more than 20 GRa, preferably more than 30 GPa, in particular more than 40 GPa and / or less than 120 GPa, preferably less than 110 GPa, in particular less than 100 GPa.

9. Relief device according to one of claims 1 to 8, characterized in that the thickness of the carbon layer (10) is more than 0.3 mm, preferably more than 0.6 mm, in particular more than 0.9 mm and / or less than 30 mm, preferably less than 25 mm, in particular less than 20 mm.

10. Relief device according to one of claims 1 to 9, characterized in that the element (4) is designed as a relief disk.

11. Relief device according to one of Claims 1 to 10, characterized in that the element (4) is designed as a relief piston

12. Relief device according to one of claims 1 to 1 1, characterized in that the element (4) relief double piston is formed.

13. Relief device according to one of claims 1 to 12, characterized in that the counter element (5) is designed as a housing part.