EP3924628B1 - Load-relieving device - Google Patents

Description

The invention relates to a relief device for compensating for the axial thrust of a turbomachine with a relief element which is non-rotatably connected 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. There are different types of axial thrust compensation.

Essentially three types of balancing devices are known for absorbing the axial thrust: balancing disk, single piston and double piston. All three versions have in common a relief current routed via a gap. The relief flow, which is usually returned to the inlet of the centrifugal pump, represents a leakage loss, which attempts are made to minimize by making the gap widths as small as possible.

The aim is to achieve a controlled position of the rotor for all operating states of the turbomachine in order to ensure trouble-free operation of the turbomachine. When operating the centrifugal pump, contact between moving parts and stationary parts should be avoided as much as possible.

When operating a turbomachine with a balancing disk, the pressure difference that acts between two sides of the balancing element leads to a balancing force that is directed in the opposite direction to the axial thrust. Ideally, the unloading force is just as large as the axial thrust. There is a balance of forces on the runner.

During start-up and shutdown processes, this pressure difference has not yet been built up, so that contact between the relief element and the counter-element occurs without appropriate countermeasures. With the help of spring packs, attempts are made to prevent the radial gap surfaces from starting to tarnish.

In the DE 102 54 041 A1 A multi-stage centrifugal pump is shown. 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.

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

In the DE 1 745 898 U A device for limiting the axial thrust of the pump rotor of a centrifugal machine is described. 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 against a support bearing flange by spring force. Oil lubrication is required for this design. With this design, the overall length of the machine is extended by a corresponding shaft section, where the corresponding housing is sealed against the pumped medium.

The WO 2017/055371 A1 shows an auxiliary turbomachine shaft support system comprising a first assembly configured to axially support the shaft, the first assembly comprising a rotating disk having a portion shaped to be rotationally fixed with the Shaft is connected, and a stator comprising at least one cushion, preferably at least two cushions, and at least one elastic member connected to the cushions and pressing it towards a disk sliding surface.

The US 6,309,174 B1 describes a thrust bearing assembly for a pump having a housing, a shaft with a longitudinal axis and a movable axial position, an inlet opening and an outlet chamber, wherein a pressure within a bearing cavity controls the axial position of the disk and the shaft.

The US 3,664,758 A discloses an axial thrust balancing mechanism for a motor pump, in which two thrust bearings made of a material that allows a certain degree of abrasion are symmetrically arranged and attached to an interior of a pump housing so that they support each end of the motor rotor shaft via two symmetrically arranged thrust washers mounted on the motor rotor shaft between the motor rotor and the thrust bearing with a certain clearance.

The EP 3 121 450 A1 shows a pump for conveying a fluid with varying viscosity, with at least one intermediate channel being provided, which opens into the relief channel between the high-pressure side and the low-pressure side of the rotor, and with a blocking element being provided for influencing the flow through the intermediate channel.

The EP 3 430 270 A1 describes a single or multi-stage centrifugal pump with novel disc-shaped means for balancing the axial forces of the pump. The disk-shaped compensating means are provided with at least one annular groove in at least one of the non-axial counter surfaces of the compensating disk and the counterpart.

The DE 10 2008 040766 A1 discloses a wear protection layer arrangement, in particular for components of a fuel injection system that are exposed to high pressures and temperatures. It is envisaged that at least one second adhesion promoter layer, which is adjacent to the first adhesion promoter layer and has a carbon content, is provided.

The US 2009/060408 A1 shows a bearing or sealing structure with a movable element and a stationary element. In the bearing or sealing structure, at least one of the movable members and the stationary member is made of a material having a thermal expansion coefficient of 8x106/°C or less. The surface of the element made of the material opposite the other element is coated with polycrystalline diamond.

The EP 1 905 863 A2 describes a substrate made of at least one element selected from a group consisting of V, Cr, Fe, Co, Ni, Zr, Nb, Mo, Ta, W, Ir and Pt, a gradient layer containing chromium and carbon and is formed on the substrate, and a hard carbon coating layer formed on the gradient layer, the gradient layer having a component conformation including a gradually decreasing chromium concentration and a gradually increasing carbon concentration from the substrate side to the hard carbon coating layer side, and the hard carbon coating layer contains aluminum.

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 additional lubricant should also be avoided. In addition, the relief device should ensure the lowest possible leakage current and have a long service life. The relief facility should be through a characterized by high reliability. It should also ensure easy installation and be easily accessible for maintenance work. Furthermore, the relief device should be characterized by the lowest possible manufacturing costs.

This object is achieved according to the invention by a device with 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 connected in a rotationally fixed manner to a shaft and the fixed counter-element.

The element can, for example, be designed as a relief disk and the counter element as a counter disk. It is also possible to design the element as a relief piston or as a double piston. The carbon layer effectively prevents damage to the components in the event of contact between the element and counter-element, especially during start-up or shutdown processes.

Carbon layers are layers in which carbon is the predominant component. The carbon layer can be applied, for example, using a PVD (Physical Vapor Deposition), a physical vapor deposition such as by evaporation or sputtering) or a CVD (Chemical Vapor Deposition) process.

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 the element and counter-element. Additionally or alternatively, the counter element, which is designed, for example, as a housing part, can also be coated with the carbon layer.

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

In diamond, each carbon atom forms a tetrahedral arrangement with four neighboring atoms. In 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, four in total, are identified with the designation "sp3". This means that sp3 hybridization is present.

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 incorporated into this carbon network.

The arrangement of a carbon layer according to the invention leads to a significant reduction in the removal of components that rub 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 rubs against it.

The invention enables very small gap dimensions to be achieved. This minimizes the leakage flow and thus increases the efficiency of the centrifugal pump. Complex maintenance work is no longer necessary. This reduces 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 post-processing of the components. The relief device according to the invention is therefore characterized by relatively low manufacturing costs.

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

In a variant of the invention, the element or counter-element is covered using a simple masking device in order to leave only the desired coating area free. Several elements or counter-elements can also be introduced simultaneously into the coating reactor, which is preferably designed as a vacuum chamber, with the ta-C coating being applied under moderate thermal load.

The element or counter-element is ready for use immediately after the coating process without any further work. 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 is very close to the hardness of diamond, with 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 .

Preferably, the carbon layer is not applied directly to the element or counter-element, but rather an adhesion promoter layer is first provided. This preferably consists 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. Chromium and tungsten carbide have proven particularly useful as adhesion promoters.

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% 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 µm, preferably more than 0.06 µm, in particular more than 0.09 µm and/or less than 0.21 µm, preferably less than 0. 18 µm, in particular less than 0.15 µm.

The ta-C coating according to the invention is a simple, quick and economical process. In addition to very high hardness, 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, on the one hand, that small solid particles, which are often contained in the media, accumulate 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 element. This means that grooves can appear on the surface of conventional elements, which lead to wear of 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, if required. The deposition temperatures are typically well below 500 °C. The process is conducted preferably in such a way that structural and dimensional changes in 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, medium-frequency (KHz range) or high-frequency (MHz range) power. In order to maximize process variability with different workpiece geometries and load densities, the coupling of pulsed direct voltage has also proven successful.

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

Further advantages and features of the invention result from the description of exemplary examples based on drawings and from the drawings themselves.

This shows

• Fig. 1 a section of a multi-stage centrifugal pump shown in section,
• Fig. 2 a schematic representation of a relief device.

Fig. 1 shows a centrifugal pump with a housing 1 and a shaft 2, which carries several impellers 3. In the drawing, only two of the wheels 3 are shown as examples. 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. There is an axial gap 8 between the radial gaps 6 and 7. The axial gap 8 has a variable width s. A hydrodynamic axial bearing 9 is arranged at the pressure 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 resting state of the centrifugal pump, the gap 8 is closed under operating conditions to a predetermined minimum width, for example by an elastic deformation, preferably of a gimbal ring, at which contact is made between the surfaces of the double piston 4 delimiting the gap 8 and the housing part 5 is avoided if possible. According to the in Figure 1 In the embodiment shown, the axial gap 8 has a self-regulating function. Between the element 4 and the counter-element 5, a carbon layer 10 is arranged at least in areas Figure 2 will be shown.

Figure 2 shows an enlarged schematic representation of a relief device designed as a double piston with an element 4, which is connected in a rotationally fixed manner to a shaft 2 and, together with a fixed counter-element 5*, 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 at least in areas between the element 4 and the counter element 5. 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 μm, the coating having a chromium-containing 0.1 μm thick adhesion promoter layer between the element 11 and the carbon layer 14.

Claims (10)

1. Load relief device for compensating for the axial thrust of a jet engine, having an element (4) which is rotationally conjoint with a shaft (2) and forms at least one gap (6, 7, 8) together with a fixed opposing element (5), wherein a carbon layer (10) is disposed at least in regions between the element (4) and the opposing element (5), characterized in that it is a tetrahedral hydrogen-free amorphous carbon layer (10) and the carbon layer (10) has been applied as a coating to the element (4) and the opposing element (5).
2. Load relief device according to Claim 1, characterized in that the coating has an adhesion promoter layer.
3. Load relief device according to Claim 2, characterized in that the adhesion promoter layer consists of chromium to an extent of more than 30% by weight, preferably more than 60% by weight, especially more than 90% by weight.
4. Load relief device according to Claim 2 or 3, characterized in that the thickness of the adhesion promoter layer is more than 0.03 pm, preferably more than 0.06 µm, especially more than 0.09 pm, and/or is less than 0.21 pm, preferably less than 0.18 pm, especially less than 0.15 µm.
5. Load relief device according to any of Claims 1 to 4, characterized in that the surface hardness of the element (4) and/or the opposing element (5) having the carbon layer (10) is more than 20 GPa, preferably more than 30 GPa, especially more than 40 GPa, and/or is less than 120 GPa, preferably less than 110 GPa, especially less than 100 GPa.
6. Load relief device according to any of Claims 1 to 5, characterized in that the thickness of the carbon layer (10) is more than 0.3 pm, preferably more than 0.6 pm, especially more than 0.9 pm, and/or is less than 30 pm, preferably less than 25 pm, especially less than 20 µm.
7. Load relief device according to any of Claims 1 to 6, characterized in that the element (4) takes the form of a load relief disk.
8. Load relief device according to any of Claims 1 to 6, characterized in that the element (4) takes the form of a load relief piston.
9. Load relief device according to any of Claims 1 to 6, characterized in that the element (4) takes the form of a double load relief piston.
10. Load relief device according to any of Claims 1 to 9, characterized in that the opposing element (5) takes the form of part of the housing.

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