Blade for turbomachine and method for producing a blade, the blade comprising a tip with notches on an abradable coating surface

Abstract

The invention relates to a blade (1) for a continuous flow machine, wherein the blade (1) is formed along a radial direction (3) and has a blade tip (4) and a blade cross-sectional profile with a pressure side (5) and a suction side (6), wherein the blade (1) has a blade tip surface (7) which is opposite a housing inner wall during operation, wherein the blade tip surface (7) has an abradable coating (8), wherein the abradable coating (8) is formed in such a way that a wearing away of the abradable coating (8) takes place during operation, when coming into contact with the housing inner wall, wherein the abradable coating (8) is formed with an abradable coating surface (11), wherein notches (12) are arranged in the abradable coating surface (11).

Description

[0001] The invention relates to a blade for a turbomachine, wherein the blade is formed along a radial direction and has a blade tip and a blade cross-sectional profile with a pressure and a suction side, wherein the blade has a blade tip surface which is opposite a housing inner wall during operation, wherein the blade tip surface has a rubbing layer.

[0002] Furthermore, the invention relates to a method for producing a coating layer.

[0003] In turbomachinery used for processing and handling flowing liquid and / or gaseous media, gaps between moving and stationary components often need to be sealed against the flowing medium. Examples of turbomachinery include steam turbines, gas turbines, compressors, etc.

[0004] In steam turbines, a gap between a rotor and the surrounding casing is sealed to prevent steam from escaping past the blades. The quality of these seals significantly influences the efficiency of these turbomachinery machines.

[0005] In a turbomachine, the principle of swirl change is used to convert the internal energy of a working fluid into the mechanical energy of a rotating component. To prevent the working fluid from leaving the process, the flow-carrying components are generally closed, resulting in an internal flow.

[0006] In order to enable the smooth rotation of a turbomachine component in a flow-guiding geometry, radial gaps between stationary and rotating components are absolutely necessary.

[0007] The radial gaps must be made as small as possible to reduce losses and as large as necessary from an integrity point of view.

[0008] In general, the radial gap between a rotor blade tip of a blade in a turbomachine and the opposite housing is designed in such a way that bridging of the radial gap is avoided in every reasonably assumed operating case.

[0009] In a low-pressure steam turbine, as a type of turbomachine, the problem of droplet impact erosion arises. In these turbomachines, expansions often terminate in a two-phase region of the steam, leading to high erosive stresses on the rotating and adjacent stationary components.

[0010] In turbomachinery, such as steam turbines, freestanding low-pressure blades are primarily used in the low-pressure range. Due to their design, these turbomachinery systems have a comparatively large radial gap between the blade tip and the casing. To prevent excessive losses, it is known to apply abrasive layers to the casing opposite the blade tip. When the blade tip contacts the casing, only the abrasive layer is slightly worn away, resulting in a comparatively small radial gap.

[0011] In principle, radial clearances are minimized primarily through passive design measures, taking into account the fundamentals of mechanics (radial elongation of the blade under the influence of centrifugal force and temperature). Besides minimizing housing ovality and shaft vibrations, for example, cylindrically cut blades are used, which minimize the effects of axial differential expansion.

[0012] On the active side, (hydro-)mechanical devices are used to influence the axial position of the rotor in rotors for conically cut blades.

[0013] Enclosures contain both active, semi-passive and passive solutions for influencing radial play.

[0014] Active solutions include "retractable sealing segments," which only close once flow is established and reduce radial play at rated speed. In bridging situations, spring designs allow the housing geometry to expand circumferentially.

[0015] The semi-passive "spring-loaded sealing segments" function similarly, in which spring constructions allow the housing geometry to expand in the radial direction.

[0016] Passive solutions include scratch-resistant mounting / attaching parts and components, as well as abrasive coatings.

[0017] On the opposite side of the housing, scratch-resistant abrasive coatings are often found.

[0018] However, these functional coatings fail in droplet-laden flows because, by design, they cannot withstand high mechanical forces, such as those caused by droplet impact erosion.

[0019] So-called honeycomb seal segments, which exhibit anisotropic rubbing properties and can be embedded in the housing wall, promise a solution. However, a problem in practical application is that the resulting hollow structures can fill with solid particles present in the working medium and then lose their positive anisotropic properties.

[0020] Occasionally, on freestanding impeller blades, sealing tip-like structures are also found on the opposite side of the housing, which also serve the purpose of reducing gap losses.

[0021] Turbine blades with rubbing layers are disclosed in documents DE 698 26 096 T2, US 2019 / 309759 A1, US 9 845 685 B2, US 5 434 210 A and US 2020 / 277871 A1.

[0022] The object of the invention is to provide a blade for a turbomachine that can be used in a turbomachine and results in low gap losses during operation.

[0023] This problem is solved by a blade for a turbomachine, wherein the blade is formed along a radial direction and has a blade tip as well as a blade cross-sectional profile with a pressure and a suction side, wherein the blade has a blade tip surface which is opposite a housing inner wall during operation, wherein the blade tip surface has a rubbing layer, wherein the rubbing layer is designed such that during operation, upon contact with the housing inner wall, the rubbing layer is worn away, wherein the rubbing layer (8) has a rubbing layer surface (11) and notches (12) are arranged on the rubbing layer surface (11).

[0024] The invention thus takes the approach of applying a rubbing layer to the blade tip. The rubbing layer is designed such that, in the event of contact with the housing, the rubbing layer is abrasive or abradable, meaning that the radial gap is optimized by material removal from the rubbing layer.

[0025] The individual material particles generated by the abrasive action and remaining in the turbomachine during operation are designed in such a way that they do not cause any damage to the turbomachine. This is achieved by the inventive design of the abrasive layer, which is made possible by the design of the abrasive layer.

[0026] The solution according to the invention is a new approach, since previously the inner wall of the housing was formed with an abrasive layer if required, as residual ovalities of the housing contour can be compensated for at low cost.

[0027] Compared to coating the stationary part, coating the blade offers advantages in the following situation: If variations occur in the radial length of the blades and / or the ovality of the housing, only the layer of the longest blade is abraded in the event of contact. The gaps of the other blades remain unchanged.

[0028] According to the invention, the rubbing layer has a rubbing layer surface, wherein notches are arranged on the rubbing layer surface.

[0029] This measure ensures that the individual pieces of material removed during material abrasion through contact with the inner housing wall do not become too large. The notches essentially act as a predetermined breaking point, leading to the removal of a small amount of material up to a notch that can, in other words, be described as the limit up to which chipping of the coating is possible.

[0030] In other words, the coating layer is segmented perpendicular to the skeletal line of the blade tip profile. This limits any chipping, partial loss, or material loss. The segmentation can be produced either by machining or during the coating process itself.

[0031] Beneficial further training opportunities are listed in the sub-requirements.

[0032] In a first advantageous further development, the rubbing layer is provided with a lubricant.

[0033] The lubricant exhibits abrasive properties. This means that when the lubricating layer comes into contact with an inner housing wall, material is removed from the lubricating layer. However, the material properties of the lubricating layer are such that the individual pieces of material are sufficiently small to minimize the risk of damage from flying debris.

[0034] In a further advantageous embodiment, the lubricant comprises graphite and / or hexagonal boron nitride.

[0035] Graphite and / or hexagonal boron nitride exhibit material properties that are ideal for use as an abrasive layer or as a component of abrasive layers in a turbomachine. The crystal structure and bonding forces in graphite and / or hexagonal boron nitride are such that material erosion of the abrasive layer can occur, with the individual removed material particles being sufficiently small.

[0036] In a further advantageous embodiment, the blade cross-sectional profile can be described with a skeleton line, wherein the rubbing layer is arranged along the skeleton line.

[0037] In a further advantageous embodiment, the blade has a leading edge and a trailing edge, wherein the skid layer is arranged from the leading edge to the trailing edge.

[0038] In an advantageous embodiment, the skeleton line has a length D and the rubbing layer is arranged only in a region in front of the downstream edge, where: d = (0.4 to 0.9) x D, where d is the length of the rubbing layer along the skeleton line up to the downstream edge.

[0039] This advantageous further development thus proposes not to provide the entire blade surface with the coating, but essentially only the area in front of the trailing edge.

[0040] Advantageously, the notches are essentially perpendicular to the skeletal line.

[0041] Likewise, the notches are advantageously formed at equidistant intervals from each other.

[0042] In an advantageous further development, the wiping layer is continuous from the pressure side to the suction side.

[0043] In an advantageous further development, the rubbing layer is designed such that a rubbing action occurring during operation with an inner housing wall leads to the removal of the rubbing layer, thereby creating a contact surface through removal, the contact surface becoming wider by further abrasion in the radial direction towards the blade root.

[0044] This measure enables an initial process in which the smear layer essentially rubs itself into place. This means that with each subsequent contact between the smear layer and the inner wall of the housing, the contact area between the smear layer and the inner wall of the housing becomes increasingly larger.

[0045] Advantageously, the rubbing layer is formed on the blade tip surface in such a way that, viewed in cross-section, the rubbing layer represents a tip at an obtuse angle.

[0046] In other words, the rubbing layer is like a blunt point pointed towards the inner wall of the housing. When the rubbing layer comes into contact with the inner wall, the point is worn away first. With increasing contact, the contact area becomes progressively wider.

[0047] In a particularly advantageous embodiment, the smear layer has a slot which is arranged such that the removal of the smear layer results in a measurable length L of the slot and the height of the layer can be determined via the length L.

[0048] This slot thus provides an indicator that makes it easy to determine how far the coating layer has been worn away, or how thick the coating layer is.

[0049] The slit can be made across the entire width of the coating layer or across part of the width of the coating layer.

[0050] In an advantageous further development, several slots per shovel are arranged in the scouring layer.

[0051] The slot is machined from the edge on the blade surface of the suction or pressure side to the tip. If the tip is worn away during operation, a slot length in the plane can be measured when looking down at the rubbing layer. This length can then be used to calculate the thickness of the rubbing layer using geometric properties and trigonometric considerations.

[0052] The slots can take over the function of notches and also serve as a predetermined breaking point. Thus, the fragment sizes can be limited by the slots.

[0053] The problem directed towards the method is solved by a method for producing a rubbing layer on a blade surface, wherein the rubbing layer is applied to the blade tip by means of a thermal spray coating process, such as APS or HVOF, wherein the rubbing layer is provided with a lubricant, such as graphite and / or hexagonal boron nitride, wherein the rubbing layer (8) is formed with a rubbing layer surface (11), wherein notches (12) are arranged on the rubbing layer surface (11).

[0054] Advantageously, a polymer is added to the rubbing layer to create a porous structure of the rubbing layer.

[0055] In a particularly advantageous embodiment, a first heat treatment is carried out before the coating layer is applied to the blade, in which the blade is hardened, wherein after the first heat treatment the coating layer is applied, wherein after the application of the coating layer a second heat treatment is carried out at a temperature in which the blade is stress-relieved, wherein the temperature is selected such that the polymer in the sprayed coating layer melts and thereby creates a porous structure of the coating layer.

[0056] This advantageous process ensures that the polymer melts during the second heat treatment and is removed from the coating layer, thus giving the coating layer a porous structure in a simple and cost-effective manner.

[0057] In an advantageous further development, notches are applied to the coating layer, arranged along the skeleton line, whereby the notches are produced during or after the coating process using a machining process, such as milling.

[0058] The invention is explained in more detail below with reference to specific embodiments and drawings.

[0059] The properties, features and advantages of this invention described above, as well as the manner in which they are achieved, will become clearer and more easily understood in connection with the following description of the exemplary embodiments, which are explained in more detail in conjunction with the drawings.

[0060] Identical components or components with the same function are marked with the same reference numerals.

[0061] Exemplary embodiments of the invention are described below with reference to the drawings. These drawings are not intended to be drawn to scale; rather, where helpful for explanation, they are presented in a schematic and / or slightly distorted form. For further details regarding the teachings directly apparent from the drawings, reference is made to the relevant prior art.

[0062] It shows: Figure 1 is a perspective view of a turbine blade according to the invention. Figure 2 is an enlarged view of a detail of the turbine blade according to the invention. Figure 3 is a top view of a blade surface of the blade according to the invention. Figure 4 is a top view of a blade surface of the blade according to the invention. Figure 5 is a schematic representation of the blade tip of the blade according to the invention. Figure 6 is a schematic representation of a detail of the blade according to the invention.

[0063] In the Figure 1 A perspective view of a blade 1 is shown. The blade 1 has a blade root 2 suitable for mounting in a rotor (not shown). The blade root 2 has a so-called fir tree shape. Other embodiments of the blade root 2 are known, such as plug-in and saddle roots, Laval roots, hook roots, or T-root designs. Such blades 1 can be used in turbomachinery, such as steam turbines, gas turbines, or compressors. The blade 1 is formed along a radial direction 3 and has a blade tip 4 and a blade profile with a pressure side 5 and a suction side 6.

[0064] The blade 1 has 3 differently shaped blade cross-sectional profiles along the radial direction.

[0065] The Figure 2Figure 1 shows an enlarged view of the blade tip 4 of the blade 1. The blade tip 4 has a blade tip surface 7 which, during operation, faces an inner wall of the housing (not shown).

[0066] The blade tip surface 7 is inclined at an angle to the radial direction 3, whereby the blade tip surfaces 7 are essentially parallel to the inner wall of the housing.

[0067] A rubbing layer 8 is arranged on the blade tip surface 7. The rubbing layer 8 is applied to the blade tip surface 7 primarily to further improve gap losses. The rubbing layer 8 is designed as an abrasive wear layer, minimizing the risk of damage upon contact with the inner housing. The rubbing layer 8 is thus designed such that, during operation, contact with the inner housing wall results in the removal of the rubbing layer 8.

[0068] To enable the removal of the rubbing layer 8, the rubbing layer 8 is made of a lubricant. This lubricant comprises graphite and / or hexagonal boron nitride.

[0069] To improve the abrasive properties of the rubbing layer 8 and to enable its removal, the rubbing layer 8 is designed to be porous. This means that the rubbing layer 8 contains a relatively large number of small cavities.

[0070] The cavities that create porosity in the coating layer 8 are produced as described below.

[0071] In a first step, a process for producing the coating layer 8 on a blade surface 7 is carried out. The coating layer 8 is applied to the blade tip surface 7 using a thermal spray coating process, such as APS or HVOF, and is provided with a lubricant, such as graphite and / or hexagonal boron nitride.

[0072] Furthermore, a polymer is added to the rubbing layer 8 to create the porous structure of the rubbing layer 8.

[0073] In a next step, before the application of the coating layer 8, a first heat treatment is carried out, in which the blade 1 is hardened.

[0074] After the first heat treatment, the coating layer 8 is applied, followed by a second heat treatment at a temperature at which the blade 1 is stress-relieved. The temperature is selected such that the polymer in the sprayed coating layer 8 melts. This creates small cavities in the coating layer 8, ultimately resulting in a porous structure.

[0075] The blade 1 can be made of steel, titanium or composite materials.

[0076] The Figure 4 shows a view of the blade tip 4 towards the leading edge 9.

[0077] The cross-sectional profile of the blade 1 can be described by a skeleton line, which is common practice in turbomachinery design. The rubbing layer 8 is arranged along the skeleton line. In a first embodiment, the rubbing layer 8 therefore covers the entire blade tip surface 7.

[0078] The blade 1 further has a leading edge 9 and a trailing edge 10, wherein the rubbing layer 8 is arranged from the leading edge 9 to the trailing edge 10 in the first embodiment.

[0079] In another alternative embodiment, the length of the skeleton line is D, wherein the rubbing layer 8 is arranged only in a region in front of the downstream edge 10, where: d = (0.4 to 0.9) x D, where d is the length of the rubbing layer 8 along the skeleton line up to the downstream edge 10.

[0080] Therefore, in this alternative embodiment, it is not necessary to form the entire blade 1 with the rubbing layer 8, but only an area in front of the trailing edge 10.

[0081] The rubbing layer 8 has a rubbing layer surface 11, wherein notches 12 are arranged on the rubbing layer surface 11.

[0082] The notches 12 are positioned on the surface of the stripping layer 11 such that, during operation, a breakage of the stripping layer 8 only results in the breakage of a segment 13 located between two notches 12. The notches 12 can therefore be considered as predetermined breaking points, at which a breakage of the stripping layer 8 is intended in the event of operating conditions that cause the stripping layer 8 to be subjected to material-abrasive conditions.

[0083] The notches 12 are essentially perpendicular to the skeleton line, which reduces manufacturing effort. Furthermore, the notches 12 are arranged at equidistant intervals along the skeleton line.

[0084] The notches 12 are produced during or after the coating process using a machining process, such as milling.

[0085] When producing the rubbing layer 8 on the blade tip surface 7, the rubbing layer 8 is formed continuously from the pressure side 5 to the suction side 6.

[0086] The rubbing layer 8 is designed such that a rubbing with a housing inner wall occurring during operation leads to a removal of the rubbing layer 8, whereby a contact surface (not shown) is created by removal, the contact surface becoming wider by further abrasion in radial direction 3 towards the blade root 2.

[0087] For this purpose, the rubbing layer 8 is formed on the blade tip surface 7 in such a way that the rubbing layer 8, viewed in cross-section, represents a tip 14 at an obtuse angle.

[0088] To determine the condition of the rubbing layer 8, the rubbing layer 8 is provided with an abrasion indicator 15. For this purpose, the rubbing layer 8 has a slot 16 which is arranged such that wear of the rubbing layer 8 leads to a measurable length L of the slot and the height of the rubbing layer 8 can be determined from this length L.

[0089] For this purpose, the slot 16 is inserted from the edge on the printing side 5 to the tip 14, which is in the Figure 3 is depicted. In the Figure 2 A side view of the abrasion indicator 15 can be seen.

[0090] During operation, the coating layer 8 can be removed, so that the contact surface, which is located in the Figure 2The line 17, represented by a line 17, becomes increasingly wider. This line 17 is essentially parallel to the blade tip surface 7.

[0091] In this state, a measurable slot 16 of length L is visible. By determining L, the height H of the rubbing layer 8 can be calculated using simple trigonometric geometry. Therefore, it is possible to deduce the state of the rubbing layer 8 simply by observing the length L of the slot 16.

[0092] In the Figures 5 and 6 The abrasion indicator 15 is shown in more detail schematically, wherein the Figure 6 a sectional view of the Figure 5 along line 17.

[0093] The curved blade tips 4 are preferably used in low-pressure final stage blades in low-pressure steam turbines. The circumferential speed of the blade tip 4 can be greater than Mach 1. This allows for use in the aerodynamic range of subsonic, transonic, and supersonic flows.

[0094] The above characteristics of a blade 1 can be varied within a row of blades in a turbomachine.

[0095] The blade 1 is used in a wet steam flow.

[0096] Furthermore, the above characteristics can be varied from blade row to blade row and from turbine flux to turbine flux depending on the machine design and operational requirements.

[0097] The invention can be combined with a non-contact blade vibration measuring system, since the distance of the blade tip 4 from the measuring sensor can be minimized by the rubbing layer 8.

Claims

1. Blade (1) for a continuous flow machine, wherein the blade (1) is formed along a radial direction (3) and has a blade tip (4) and a blade cross-sectional profile with a pressure side (5) and a suction side (6), wherein the blade (1) has a blade tip surface (7) which is opposite a housing inner wall during operation, wherein the blade tip surface (7) has an abradable coating (8), wherein the abradable coating (8) is formed in such a way that the abradable coating (8) is worn away during operation when coming into contact with the housing inner wall, wherein the abradable coating (8) has an abradable coating surface (11), characterized in that notches (12) are arranged on the abradable coating surface (11).

2. Blade (1) according to Claim 1, wherein the abradable coating (8) is provided with a lubricant.

3. Blade (1) according to Claim 2, wherein the lubricant comprises graphite and / or hexagonal boron nitride.

4. Blade (1) according to one of the preceding claims, wherein the blade cross-sectional profile can be described with a median line, wherein the abradable coating (8) is arranged along the median line.

5. Blade (1) according to one of the preceding claims, wherein the blade (1) has a leading edge (9) and a trailing edge (10), wherein the abradable coating (8) is arranged from the leading edge (9) as far as the trailing edge (10).

6. Blade (1) according to one of Claims 1 to 4, wherein the length of the median line is D and the abradable coating (8) is arranged only in a region upstream of the trailing edge (10), wherein: d = (0.4 to 0.9) x D, where d is the length of the abradable coating (8) along the median line as far as the trailing edge (10).

7. Blade (1) according to one of the preceding claims, wherein the notches (12) are formed substantially perpendicularly to the median line.

8. Blade (1) according to one of the preceding claims, wherein the distances of the notches (12) from one another are equidistant.

9. Blade (1) according to one of the preceding claims, wherein the abradable coating (8) is formed continuously from the pressure side (5) as far as the suction side (6).

10. Blade (1) according to one of the preceding claims, wherein the abradable coating (8) is formed in such a way that abrasion occurring during operation by a housing inner wall leads to the abradable coating (8) being worn away, wherein, as a result, a contact surface produced by abrasion is produced, wherein the contact surface becomes wider in the radial direction (3) toward the blade root (2) as a result of further abrasion.

11. Blade (1) according to one of the preceding claims, wherein the abradable coating (8) is formed on the blade tip surface (7) in such a way that the abradable coating (8), viewed in cross section, represents a tip (14) at an obtuse angle.

12. Blade (1) according to one of the preceding claims, wherein the abradable coating (8) has a slot (16), which is arranged in such a way that wear of the abradable coating (8) leads to a measurable length L of the slot (16), and a height of the abradable coating (8) can be determined via the length L.

13. Method for producing an abradable coating (8) on a blade tip surface (7) of a blade of a flow machine, wherein the abradable coating (8) is applied to the blade tip surface (7) by means of a thermal spray coating process, such as APS or HVOF, wherein the abradable coating (8) is provided with a lubricant, such as graphite and / or hexagonal boron nitride, wherein the abradable coating (8) is formed with an abradable coating surface (11), characterized in that notches (12) are arranged on the abradable coating surface (11).

14. Method according to Claim 13, wherein a polymer is added to the abradable coating (8) to produce a porous structure of the abradable coating (8).

15. Method according to Claim 13 or 14, wherein, before the application of the abradable coating (8) of a first thermal treatment, the blade (1) is carried out, in which the blade (1) is hardened, wherein, after the first thermal treatment, the abradable coating (8) is applied, wherein, following the application of the abradable coating (8), a second thermal treatment is carried out at a temperature at which the blade (1) is low-stress-annealed, wherein the temperature is chosen in such a way that the polymer in the abradable coating (8) sprayed on melts and as a result gives rise to a porous structure of the abradable coating (8).

16. Method according to one of Claims 13 to 15, wherein notches (12) which are arranged along the median line are applied to the abradable coating (8), wherein the notches (12) are produced during the coating process or after the coating process by a material-removing method, such as milling.

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