EP4170132A1 - Blade for turbomachine and method for producing a blade, the blade comprising a tip with an abradable coating - Google Patents

Abstract

The invention relates to a blade (1) for a turbomachine, the blade (1) being formed along a radial direction (3) and having 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, during operation, is opposite an inner wall of the housing, the blade tip surface (7) having an abradable layer (8), the abradable layer (8) being formed such that, during operation, upon contact with the inside wall of the housing, the abradable layer (8) is removed.

Description

The invention relates to a blade for a turbomachine, the blade being formed along a radial direction and having a blade tip and a blade cross-sectional profile with a pressure side and a suction side, the blade having a blade tip surface which is opposite an inner wall of the housing during operation, the blade tip surface having a has abradable layer.

Furthermore, the invention relates to a method for producing an abradable layer.

In turbomachines for treating and processing flowing, liquid and/or gaseous media, gaps between moving and stationary components often have to be sealed against the flowing medium. Examples of a turbomachine are steam turbines, gas turbines, compressors, etc.

In steam turbines, a gap between a rotor and a housing surrounding it is sealed in order to block the steam from passing blade rings. The quality of these seals has a significant impact on the efficiency of these turbomachines.

In a turbomachine, the principle of the change in swirl is used to convert the internal energy of a working fluid into the mechanical energy of a rotating component. So that the working fluid cannot leave the process, the flow-guiding components are usually closed, resulting in an internal flow.

In order to allow a fluid machine component to rotate smoothly in a flow-guiding geometry, radial gaps between stationary and rotating components are absolutely necessary.

The radial gaps must be as small as possible to reduce losses and as large as necessary from the point of view of integrity.

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 operating case that can be reasonably assumed.

In a low-pressure steam turbine as an embodiment of a turbomachine, there is also the problem of droplet impact erosion. The expansions in these turbomachines often end in a two-phase area of the water vapor, which leads to high erosion loads on the rotating and the adjacent stationary components.

In turbomachines, such. B. in steam turbines, free-standing low-pressure blades are used primarily in the low-pressure range. Due to the design, such turbomachines have a comparatively large radial gap between the blade tip and the housing. So that the losses do not become too great, it is known to arrange abrasive layers on the housing opposite the blade tip. When the blade tip touches the housing, only the abrasive layer is slightly removed, which creates a comparatively small radial gap.

In principle, the radial clearances are minimized primarily by passive design measures, taking into account the fundamentals of mechanics (radial elongation of the blade under the influence of centrifugal force and temperature). In addition to minimizing housing ovalization and shaft vibrations, cylindrical blades are used, for example, which minimize the effects of differential axial expansion.

On the active side, (hydro)mechanical devices for influencing the axial position of the rotor are used on rotors for conically cut blades.

Active, semi-passive and passive solutions for controlling radial play can be found in housings.

The active solutions include the "Retractable Sealing Segments", which only close once the flow has developed and reduce the radial play at nominal speed. In the case of bridging, spring constructions allow the housing geometry to expand in the circumferential direction.

The semi-passive "resilient sealing segments" work in a similar way, in which spring constructions allow the housing geometry to expand in the radial direction.

Passive solutions include built-in/add-on parts and components that are tolerant of rubbing, as well as abrasive coatings.

On the opposite side of the housing you will often find rubbing-tolerant abrasive coatings.

However, these functional coatings fail in droplet-loaded flows because they do not withstand high mechanical forces, such as e.g. B. caused by drop impact erosion, can endure.

So-called honeycomb seal segments, which have anisotropic rubbing properties and can be embedded in the housing wall, promise a remedy. The problem here in practical use is that the resulting hollow structures can fill with solid particles that are present in the working medium and then lose their positive anisotropic properties.

Occasionally, free-standing rotating blades are also found on the opposite side of the casing with constructions similar to a sealing tip, which also have the task of reducing gap losses.

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

This object is achieved by a blade for a turbomachine, the blade being formed along a radial direction and having a blade tip and a blade cross-sectional profile with a pressure side and a suction side, the blade having a blade tip surface which is opposite an inner wall of the housing during operation, the The blade tip surface has an abradable layer, the abradable layer being formed in such a way that the abradable layer is removed during operation when it comes into contact with the inner wall of the casing.

The invention thus takes the path of applying an abradable layer to the blade tip. The abradable layer is designed in such a way that if the abradable layer comes into contact with the housing, the abradable layer is abrasive or abradable, i.e. the radial gap is optimized by removing material from the abradable layer.

The individual pieces of material that are created by the abrasive effect and remain in the turbomachine during operation are designed in such a way that they do not cause any damage in the turbomachine. In addition, the individual pieces of material are comparatively small, which is achieved by the design of the abradable layer according to the invention.

The solution according to the invention is a new approach, since previously the inner wall of the housing was designed with an abrasive layer if required because residual ovality in the housing contour can be compensated for at low cost.

Compared to coating the stationary part, coating the blade has advantages in the following situation: If there are variances 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 rubbing. The gaps of the remaining blades remain unchanged.

Advantageous developments are specified in the dependent claims.

In a first advantageous development, the abradable layer is provided with a lubricant.

The lubricant has abrasive properties. This means that when the abradable layer comes into contact with an inner wall of the housing, material is removed from the abradable layer, with the material properties of the abradable layer being such that the individual pieces of material are small enough to minimize the risk of damage from a piece of material that has been removed flying around.

In a further advantageous development, the lubricant includes graphite and/or hexagonal boron nitride.

Graphite and/or hexagonal boron nitride in particular have 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 removal of the abradable layer can occur, with the individual removed pieces of material being sufficiently small.

In a further advantageous development, the blade cross-section profile can be described with a skeleton line, wherein the abradable layer is positioned along the mean line.

In a further advantageous development, the blade has a leading edge and a trailing edge, the abradable layer being arranged from the leading edge to the trailing edge.

In an advantageous development, the skeleton line has a length D and the abradable layer is only arranged in an area in front of the trailing edge, where: d=(0.4 to 0.9)×D, where d is the length of the abradable layer along the skeleton line up to the trailing edge.

With this advantageous development, it is therefore proposed not to provide the entire surface of the airfoil with the abradable layer, but basically only the area in front of the trailing edge.

In a particularly advantageous development, the abradable layer has an abradable layer surface, with notches being arranged on the abradable layer surface.

This measure ensures that the individual pieces of material removed do not become too large when material is removed through contact with the inner wall of the housing. Basically, the notches act like a predetermined breaking point and lead to the removal of a piece of material up to a notch, which can thus be referred to in other words as a limit up to which the abradable layer can flake off.

In other words, the abradable layer is segmented normal to the mean line of the blade tip profile. This limits any chipping, partial loss or abrasion. The segmentation can be produced either by machining or during the coating process itself.

Advantageously, the notches are formed substantially perpendicular to the mean line.

Likewise, the notches are advantageously formed at equidistant distances from one another.

In an advantageous development, the abradable layer is designed to be continuous from the pressure side to the suction side.

In an advantageous development, the abradable layer is formed in such a way that rubbing against an inner wall of the housing during operation leads to the abrasion of the abradable layer, with the result that a contact surface is created by abrasion, the contact surface becoming wider towards the blade root as a result of further output in the radial direction.

With this measure, an initial process is made possible in which the abradable layer rubs in as it were. This means that a contact surface between the abradable layer and the inner wall of the housing increases with further contacts between the abradable layer and the inner wall of the housing.

For this purpose, the abradable layer is advantageously formed on the blade tip surface in such a way that the abradable layer represents a tip at an obtuse angle when viewed in cross section.

In other words, the abradable layer is aimed at the inner wall of the housing like a blunt point. If the abradable layer rubs against the inner wall of the housing, the tip is removed first. With increasing contact, the contact surface becomes wider and wider.

In a particularly advantageous development, the abradable layer has a slot which is arranged in such a way that the abradable layer can be removed to a measurable length L of the slot leads and over the length L a height of the layer can be determined.

This slit thus provides an indicator that can be used to easily find out how far the abradable layer has been removed or how thick the abradable layer is.

The slit can be introduced both over the entire width of the abradable layer and over part of the width of the abradable layer.

In an advantageous further development, several slots per blade are arranged in the abradable layer.

The slot is machined from the edge on the blade surface of the suction or pressure side to the tip. When the tip is removed during operation, a slit length in the plane can be measured in the top view of the abradable layer, with which the thickness of the abradable layer can be calculated via geometric properties and trigonometric considerations.

The slits can take over the function of the notches and also serve as predetermined breaking points. Thus, fragment sizes can be limited by the slits.

The object directed towards the method is achieved by a method for producing a rubbing layer on a blade surface, the rubbing layer being applied to the blade tip by means of a thermal spray coating process, such as APS or HVOF, the rubbing layer being coated with a lubricant such as graphite and / or hexagonal boron nitride is provided.

Advantageously, a polymer is added to the abradable layer to create a porous structure of the abradable layer.

In a particularly advantageous development, before the abradable layer is applied to the blade, a first heat treatment is carried out, in which the blade is hardened, the abradable layer being applied after the first heat treatment, with a second heat treatment being carried out at one temperature after the abradable layer has been applied wherein the blade is stress relieved at a temperature such that the polymer in the sprayed abradable layer melts, thereby creating a porous structure in the abradable layer.

What is achieved with this advantageous method is that the polymer melts during the second heat treatment and is removed from the abradable layer, as a result of which the abradable layer is given a porous structure in a simple and cost-effective variant.

In an advantageous development, notches are applied to the abradable layer, which are arranged along the skeleton line, the notches being produced during the coating process or after the coating process using a machining process such as milling.

The invention is explained in more detail below using specific exemplary embodiments with reference to drawings.

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

Identical components or components with the same function are identified with the same reference symbols. Exemplary embodiments of the invention are described below with reference to the drawings. These are not intended to represent the exemplary embodiments to scale, rather the drawing, where useful for explanation, is in schematic and/or slightly distorted form. With regard to additions to the teachings that can be seen directly in the drawing, reference is made to the relevant state of the art.

Figur 1

eine perspektivische Darstellung einer erfindungsgemäßen Turbinenschaufel,

Figur 2

eine vergrößerte Darstellung eines Details der erfindungsgemäßen Turbinenschaufel,

Figur 3

eine Draufsicht auf eine Schaufeloberfläche der erfindungsgemäßen Schaufel

Figur 4

eine Draufsicht auf eine Schaufeloberfläche der erfindungsgemäßen Schaufel

Figur 5

eine schematische Darstellung der Schaufelspitze der erfindungsgemäßen Schaufel

Figur 6

eine schematische Darstellung eines Details der erfindungsgemäßen Schaufel

Show in it:

figure 1

a perspective view of a turbine blade according to the invention,

figure 2

an enlarged view of a detail of the turbine blade according to the invention,

figure 3

a plan view of a blade surface of the blade according to the invention

figure 4

a plan view of a blade surface of the blade according to the invention

figure 5

a schematic representation of the blade tip of the blade according to the invention

figure 6

a schematic representation of a detail of the blade according to the invention

In the figure 1 a blade 1 can be seen in a perspective view. The blade 1 has a blade root 2 which is suitable for fastening in a rotor (not shown). The blade root 2 here has a so-called fir tree root shape. There are other embodiments known for the blade root 2, such as. B. plug-in and rider feet, Laval foot, hooked foot or T-foot designs. Such blades 1 can in turbomachines such. B. steam turbines, gas turbines or compressors are used. The blade 1 is 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 .

The blade 1 has blade cross-sectional profiles of different design along the radial direction 3 .

The figure 2 shows the blade tip 4 of the blade 1 in an enlarged representation. The blade tip 4 has a blade tip surface 7 which, during operation, is opposite an inner wall of the housing (not shown).

The blade tip surface 7 is inclined at an angle with respect to the radial direction 3, the blade tip surface 7 thereby being formed essentially parallel to the housing inner wall.

An abradable layer 8 is arranged on the blade tip surface 7 . The abradable layer 8 is applied to the blade tip surface 7 essentially to further improve the gap losses. In this case, the abradable layer 8 is designed as an abrasive wearing layer, in which the risk of damage is minimized in the event of contact with the inner housing. The abradable layer 8 is thus designed in such a way that, during operation, the abradable layer 8 is eroded when it comes into contact with the inner wall of the housing.

In order to allow abrasion of the abradable layer 8, the abradable layer 8 is made of a lubricant. The lubricant includes graphite and/or hexagonal boron nitride.

In order to improve the abrasive properties of the abradable layer 8 and to enable abrasion of the abradable layer 8, the abradable layer 8 is made porous. This means that a comparatively large number of small cavities are formed in the abradable layer 8 .

The cavities that create porosity in the abradable layer 8 are made as described below.

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

Furthermore, a polymer is added to the abradable layer 8 to produce the porous structure of the abradable layer 8 .

In a next step, before the abradable layer 8 is applied, a first heat treatment is carried out, during which the blade 1 is hardened.

After the first heat treatment, the abradable layer 8 is applied, and after the abradable layer 8 has been applied, a second heat treatment is carried out at a temperature at which the blade 1 is stress-relieved. The temperature is selected in such a way that the polymer in the abradable layer 8 sprayed on melts. This creates small cavities in the abradable layer 8 which ultimately lead to a porous structure of the abradable layer 8 .

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

The figure 4 shows a view of the blade tip 4 in the direction of the leading edge 9.

The blade cross-sectional profile of the blade 1 can be described with a skeleton line, which is common practice in the construction of turbomachines. The abradable layer 8 is thereby along the arranged skeleton line. In a first embodiment, the abradable layer 8 therefore covers the entire blade tip surface 7.

The blade 1 also has a leading edge 9 and a trailing edge 10, the abradable layer 8 being arranged from the leading edge 9 to the trailing edge 10 in the first embodiment.

In a further alternative embodiment, the length of the mean line is D, with the abrading layer 8 being arranged only in a region in front of the trailing edge 10, where: d=(0.4 to 0.9)×D, where d is the length of the abrading layer 8 along the mean line to the trailing edge 10.

Thus, in this alternative embodiment, the entire blade 1 does not have to be formed with the abradable layer 8, but only an area in front of the trailing edge 10.

The abradable 8 has an abradable surface 11, with the abradable surface 11 having notches 12 thereon.

In this case, the notches 12 are applied to the abradable layer surface 11 in such a way that, during operation, a bursting away of the abradable layer 8 only results in a segment 13 arranged between two notches 12 bursting away. The notches 12 can thus be regarded as predetermined breaking points at the locations of which the abradable layer 8 is intended to break in the event that operating conditions occur which result in the abradable layer 8 being subjected to material-removing conditions.

In this case, the notches 12 are formed substantially perpendicularly to the skeleton line, which reduces the manufacturing effort. Furthermore, the notches 12 are arranged at equidistant intervals along the mean line.

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

When the abradable layer 8 is produced on the blade tip surface 7 , the abradable layer 8 is formed continuously from the pressure side 5 to the suction side 6 .

The abradable layer 8 is formed in such a way that rubbing against an inner wall of the housing during operation leads to the abrasion of the abradable layer 8, with the result that a contact surface (not shown) is created by abrasion, the contact surface being further driven in the radial direction 3 towards the blade root 2 becomes wider.

For this purpose, the abradable layer 8 is formed on the blade tip surface 7 in such a way that the abradable layer 8, seen in cross section, represents a tip 14 at an obtuse angle.

In order to be able to determine the condition of the abradable layer 8 , the abradable layer 8 is provided with an abrasion indicator 15 . For this purpose, the abradable layer 8 has a slit 16 which is arranged in such a way that a removal of the abradable layer 8 leads to a measurable length L of the slit and via the length L a height of the abradable layer 8 can be determined.

For this purpose, the slot 16 is introduced from the edge on the pressure side 5 to the tip 14, which is shown in FIG figure 3 is shown. In the figure 2 A side view of the abrasion indicator 15 can be seen.

In operation, the abradable layer 8 can be removed, so that the contact surface in the figure 2 is shown with a line 17, is getting wider. This dash is 17 arranged essentially parallel to the blade tip surface 7 .

In this condition, a measurable slit 16 of length L is visible. By determining L, a height H of the abradable layer 8 can thus be determined by simple trigonometric geometry considerations. It is therefore possible, so to speak, to deduce the state of the abradable layer 8 merely by looking at the length L of the slot 16 .

In the Figures 5 and 6 the abrasion indicator 15 is shown in more detail in a schematic manner, the figure 6 a sectional view of the figure 5 along line 17 shows.

The curved blade tips 4 are preferably used in low-pressure final stage blades in low-pressure steam turbines. In this case, the peripheral speed of the blade tip 4 can be at values greater than Mach 1. This enables use in the aerodynamic range of subsonic, transonic and supersonic flows.

The above features of a blade 1 can be varied within a row of blades in a turbomachine.

The blade 1 is used in a wet steam flow.

In addition, the above features can be varied from blade row to blade row and from turbine duct to turbine duct depending on engine design and operational requirements.

The invention can be combined with a non-contact blade vibration measurement system since the distance between the blade tip 4 and the sensor can be minimized by the abradable layer 8 .

Claims (17)

Blade (1) for a turbomachine, 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 (5) and a suction side (6), the blade (1) having a blade tip surface (7) which, during operation, faces an inner wall of the housing, wherein the blade tip surface (7) has an abradable layer (8), characterized in that the abradable layer (8) is designed in such a way that during operation the abradable layer (8) is removed when it comes into contact with the inner wall of the housing. Blade (1) according to claim 1,
wherein the abradable layer (8) is provided with a lubricant. Blade (1) according to claim 2,
wherein the lubricant comprises graphite and/or hexagonal boron nitride. Blade (1) according to one of the preceding claims, wherein the blade cross-sectional profile can be described with a mean line, the abradable layer (8) being arranged along the mean line. Blade (1) according to one of the preceding claims, wherein the blade (1) has a leading edge (9) and a trailing edge (10), the abradable layer (8) being arranged from the leading edge (9) to the trailing edge (10). Blade (1) according to one of Claims 1 to 4,
wherein the length of the mean line is D and the abradable layer (8) is arranged only in a region in front of the trailing edge (10), where the following applies: d = (0.4 to 0.9) x D, where d is the length of the abradable layer ( 8) along the mean line to the trailing edge (10). A blade (1) according to any one of the preceding claims wherein the abradable (8) has an abradable surface (11) with notches (12) disposed on the abradable surface (11). Blade (1) according to claim 7,
the notches (12) being formed substantially perpendicular to the mean line. Blade (1) according to claim 7,
the distances between the notches (12) being equidistant from one another. Blade (1) according to one of the preceding claims, in which the abradable layer (8) is continuous from the pressure side (5) to the suction side (6). Blade (1) according to one of the preceding claims, wherein the abradable layer (8) is formed in such a way that rubbing against an inner wall of the housing during operation causes the abradable layer (8) to be eroded, with a contact surface resulting from abrasion being produced, the Contact surface becomes wider by further output in the radial direction (3) towards the blade root (2). A blade (1) according to any one of the preceding claims, wherein the shroud (8) is formed on the blade tip surface (7) such that the shroud (8) presents a tip (14) at an obtuse angle when viewed in cross-section. Blade (1) according to any one of the preceding claims, wherein the abradable layer (8) has a slot (16) which is arranged such that erosion of the abradable layer (8) results in a measurable length L of the slot (16) and over which the length L is a height of the abradable layer (8) can be determined. Method for producing a abradable layer (8) on a blade tip surface (7),
the abradable layer (8) being applied to the blade tip surface (7) by a thermal spray coating process such as APS or HVOF, the abradable layer (8) being provided with a lubricant such as graphite and/or hexagonal boron nitride. Method according to claim 14,
wherein a polymer is added to the abradable layer (8) to create a porous structure of the abradable layer (8). Method according to claim 14 or 15,
wherein the blade (1) is subjected to a first heat treatment prior to the application of the abradable layer (8), during which the blade (1) is hardened, the abradable layer (8) being applied after the first heat treatment, wherein after the application of the abradable layer ( 8) a second heat treatment is carried out at a temperature at which the blade (1) is stress-relieved, the temperature being chosen such that the polymer in the sprayed abradable layer (8) melts and thereby causes a porous structure of the abradable layer (8). . Method according to one of claims 14 to 16,
wherein on the abradable layer (8) notches (12) are applied, which are arranged along the mean line, the notches (12) during the coating process or after the coating process with a cutting process such as milling.

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