EP1715140A1 - Turbine blade with a cover plate and a protective layer on the cover plate - Google Patents

Abstract

The blade has a cover plate (20) formed at a blade leaf (18). A protective layer (28) is applied on a surface of the cover plate by deposit welding, where the surface is turned away from the blade leaf. The cover plate is made of a nickel based alloy or a cobalt based alloy, and the protective layer is formed by an armor alloy of cobalt base. A hard material layer is provided as the protective layer. The blade leaf and the cover plate are manufactured from a single component work piece. An independent claim is also included for a method for manufacturing a steam turbine with multiple turbine blades.

Description

The invention relates to a turbine blade with a cover plate formed on the blade leaf and a steam turbine provided with a number of such turbine blades.

The turbine blades of steam turbines are often provided with a top plate integrally formed on the airfoil. Usually, the turbine blades combined in each case into rows of barrels or guide vanes are arranged on the rotor or on the housing of the steam turbine in such a way that the entirety of the cover plates of a row of blades protruding laterally beyond the airfoil forms a circumferential ring, a so-called cover band. In this case, the cover plates of a blade row associated turbine blades are usually wedged or jammed during installation in such a way that can be dispensed with further fasteners or connecting elements between the individual cover plates. The coupling of the turbine blades in the annular shroud effectively suppresses vibrations or distortions of individual turbine blades occurring as a result of high dynamic stress.

Each of a cover band combined cover plates of a blade row are designed to minimize the secondary flow over the blade tips or the shroud over time caused gap and edge losses. For this purpose, the smallest possible gap width between the shroud and the opposite housing or rotor is sought, especially in full load operation of the steam turbine. On the other hand, scratching during operation should be avoided as much as possible. Especially during transient operations, so z. B. when starting or during load changes, but there is a risk comparatively large, caused by different thermal expansion relative changes in length of the involved components, so that in exceptional cases, however, must be expected to tarnish. In order to keep the extent of potential contact points as small as possible and thus to minimize the frictional forces occurring in the event of contact, come on the shroud or on the opposite housing or rotor mounted, extending in the circumferential direction of metal strips or metal rings, called sealing tapes used. When the rotating and stationary parts approach each other closer than planned, the comparatively thin sealing bands first come into contact with the opposing component, with the surfaces of the two contact partners grinding each other in a usually localized wear region. As a result, sufficient emergency running properties are ensured at least in the case of single or short-term brushing.

However, if such operating conditions occur more frequently, then in the case where the sealing tapes are respectively attached to the shroud opposite turbine component - ie the housing (in the case of a blade shroud) or the rotor (in the case of a Leitschaufeldeckbandes) - the risk of continued, the cover plates or the shroud in its entirety damaging wear. Under certain circumstances, the sealing tape can "eat" deep into the shroud, which after some time can even lead to almost complete removal of the shroud. The stability of the originally annular closed cover plate composite is significantly reduced by wear-induced local interruptions, which favors the occurrence of blade vibrations. In addition, with continued wear or excessive vibration amplitudes macroscopically large fragments or even entire turbine blades can replace, which are then thrown with great force against the turbine blades or housing parts of the subsequent turbine stages. In the extreme case, this can lead to complete destruction of the steam turbine.

The invention is therefore based on the object to provide a turbine blade of the type mentioned above, which is designed with a high efficiency for a particularly reliable and safe operation. Furthermore, a steam turbine equipped with such turbine blades should be specified.

With respect to the turbine blade, the object is achieved according to the invention by applying to the surface of the cover plate facing away from the blade of the turbine blade a protective layer of an alternative material.

The invention is based on the consideration that a steam turbine to achieve a high efficiency for operation with so-called "high steam parameters" should be designed. In particular, a loading of the turbine blades should be done with the highest possible temperature steam. In this case, steam temperatures of over 500 ° C up to about 700 ° C are desired. Accordingly, the turbine blades, but also the flow channel for the steam forming housing components should be made of high temperature resistant material. In view of the comparatively high mechanical loading of the turbine blades, in particular the blades rotating at high speed, the material for producing the respective blade body should meet the highest requirements for mechanical stability and crack resistance at the high operating temperatures designed for this purpose. In order to keep the production costs for the turbine blades as low as possible, the material should also be relatively easy to process at the same time (eg by casting). Furthermore, in order to avoid flow losses, the respective radial gap between the shroud connecting the blade tips of a blade row and the turbine components (ie the turbine housing in the case of a blade shroud or the rotor in the case of a guide shroud cover) should have the smallest possible width. Since it under the influence of the design-provided high operating temperatures as well as on Due to possible deviations in the temperature profile of a symmetrical to the center axis of the steam turbine temperature profile deformation of the rotor and / or the housing and thus deviations of the gap shape can come from a perfect ring shape, should in the design of the steam turbine in the critical regions of the closest approach at least a temporary contact between the shroud and the rotor or housing opposite him not be excluded in principle. Rather, even in the case of brushing to avoid catastrophic turbine damage sufficient emergency running properties should be ensured. Preferably, such squinting should even be allowed repeatedly during regular operation of the turbine, without any significant consequences.

The invention is further based on the consideration that the quality of such emergency running properties is determined by the friction behavior between the respective contact surfaces. In addition to the properties of a possibly existing at the interfaces liquid film of condensed vapor particles is directly the respective surface material of the two friction partners in the frictional properties, not only the lowest possible friction coefficient is sought, but also the nature of the friction occurring in the friction should be considered ,

The so-called "adhesion wear" caused by the formation of a local interface adhesive bond and subsequent tearing of the solid-state compound was recognized as being particularly harmful, which is connected to material break-out and material transfer to the friction partner which contacts the break-out point. In other words, microparticles removed from one of the friction partners collect on the surface of the other friction partner and can form larger lumps there, which in turn increase the wear effect. Due to its wedge effect, the accumulated material exerts blows on the rotor shaft.

It is precisely this self-reinforcing mechanism of adhesive wear, in which, under certain circumstances, comparatively large fragments detach from the wear point, should be avoided for permanently reliable operation of the steam turbine with occasional brushing actions taken into account. However, it is possible that those materials whose use for reasons of strength or for reasons of processability are preferred for the production of the turbine blades and the cover plates formed on them, may be in relation to the surface opposite the shroud (as a rule the surface of a metallic sealing strip) unfavorable friction behavior. By applying a protective layer of an alternative material on the surface of the respective cover plate or the shroud therefore additional degrees of freedom for selectively influencing the friction pairing are provided. Namely, this outer layer need not perform a supporting function, but instead may be specifically aimed at providing particularly favorable friction and wear properties in relation to the respective friction partner, in particular while avoiding adhesive wear. In view of the achievable advantages is a slightly increased production costs quite acceptable.

In order to avoid possible breakage points, the blade body of the turbine blade comprising the airfoil blade and the cover plate, which is particularly heavily loaded, is advantageously made of a one-component workpiece. As heat-resistant material for the cover plate or the entire blade body, for example, steel, in particular steel with 10% to 13% chromium content, could be used. As a particularly heat and corrosion resistant material which is suitable for steam temperatures of up to 700 ° C, however, is preferably used as a base material for the blade body, a nickel-based alloy or a cobalt-based alloy.

Advantageously, the protective layer applied to the surface of the respective cover plate is formed by a so-called cobalt-based armor alloy. The composition of the alloy is specifically oriented to a high heat resistance and wear resistance and the provision of an advantageous friction behavior in interaction with the respective (potential) friction partner, ie in particular a metallic sealing strip opposite the respective shroud. It is regarded as advantageous in this case if the two contact surfaces in the case of brushing with the removal of relatively small metallic dust particles abrade each other, without resulting in the material transfer or the outbreak of larger portions. The microscopically fine grinding dust is simply entrained with the steam flowing through the turbine and transported away from the flow channel.

In the specific case, the composition of the protective layer forming armor alloy must be matched to the material of the opposing sealing bands. In the context of comparative experiments, it has generally proved advantageous to use, in addition to cobalt (chemical symbol: Co), also proportions of nickel (Ni), iron (Fe), chromium (Cr), manganese (Mn), carbon (C) , Silicon (Si) and tungsten (W). The following composition is particularly advantageous (in percent by weight): Ni Fe C Cr Mn Si W Max. 3 Max. 3 1.1-1.2 28 1.0-1.1 1.0-1.1 4.5

Such armor alloys are also known under the registered trademark of the Deloro Stellite Company "Stellite". Particularly preferred in the context of the new concept is the use of the material class "Stellite No. 6".

Preferably, the hard alloy used for arming the shroud is applied to the shroud surface by a cladding process applied and thus materially connected to the base material. In this case, the coating material by applying weld beads in one or more layers with z. B. a gas, arc or inert gas welding applied to the workpiece surface. Also, the so-called plasma powder build-up welding or laser beam buildup welding can be used. The applied surfacing alloys are added as wire, rod, powder or paste depending on the chosen method. Due to their generally smooth and flat surface, the cover plates or shrouds of turbine blades can be coated particularly well in this way.

In contrast to conceivable alternative coating methods, such. As vapor deposition, surface hardening, nitriding or boron-forming surface coatings in the micron range, the protective layer thus produced has a significant thickness of preferably about 1 mm or more. Thus, a comparatively long life of the protective layer is ensured, which in principle survives the complete removal of the opposite sealing tape, without the base material of the cover plates is damaged.

In a preferred alternative embodiment, a hard material layer is provided as a protective layer on the surface of the cover plate facing away from the airfoil. As hard materials, materials which are natural for the person skilled in the art and which do not have to be subjected to heat after-treatment for hardening are referred to as natural-hard materials. The use of such hard materials has the advantage that the wear of a protective layer produced therefrom is comparatively low even after prolonged use, and that in the case of a contact instead the comparatively softer sealing strip on the cover plate opposite housing or rotor of the steam turbine is processed , So only from time to time the sealing tape must be renewed.

Hard materials with covalent, ionic or metallic bonding are known. A prominent representative of covalently bonded hard materials and the hardest naturally occurring mineral is diamond. Among the hard materials with ionic bond, for example, alumina or chromium oxide, but also counted ceramics.

The coating provided for protecting the respective cover plate or cover band is preferably made of a metallic hard material. With regard to their friction behavior and due to their mechanical and thermal stability, the carbides and nitrides formed by the elements of the transition metals are preferred. As a particularly preferred hard material chromium carbide or titanium nitride or boron nitride is provided.

The plasma coatings, flame spraying or PVD (Physical Vapor Deposition) generated by preferably also on an industrial scale hard coatings are characterized by a good adhesion to the metallic substrate of the cover plate and high purity and thus by particularly well-defined and unadulterated surface properties. The thickness of such hard material thin layers is usually in the micron range.

The protective layer could each be applied individually to the cover plates of the turbine blades before they are mounted on the rotor or on the housing of the steam turbine. When applying a hard material thin film (such as by a PVD process or by plasma spraying or the like), but especially in an armor by build-up welding ("Stellitieren"), it is particularly advantageous that formed from the cover plates of the already assembled turbine blades and on Circular turned cover band to undergo a total of coating. The necessary to apply the protective layer manufacturing steps (which may include a pre- and post-treatment) are so each on a a plurality of cover plates comprehensive section of the shroud applied. In the mounted state, only comparatively few long weld beads are to be drawn over the circumference of the shroud, as opposed to hundreds of short weld beads in the individual blades for surfacing. The method now provided is faster and safer in process engineering terms and provides better quality due to the lower number of settling and settling points. It is also particularly suitable for repairing or upgrading a worn or uncoated old shroud.

Advantageously, an abrasive layer is applied to the hard material layer. In mutual contact, the metallic sealing tape can first in this abrasive, d. H. incorporate soft layer before it comes into contact with the underlying hard material layer. The sealing tape is not damaged on contact with the abrasive layer, but retains its original dimensions and sealing effect. In other words, since the surface contour of the abrasive layer adapts to the overlying or sliding sealing tape (the abrasive layer "gives as needed"), the radial clearance between the rotating and stationary parts of the steam turbine can be kept deliberately small, resulting in a high efficiency contributes.

The indicated turbine blade is preferably part of a steam turbine. But it could also be used in a gas turbine. In each case, a number of such turbine blades are combined to form a row of blades, wherein the cover plates of the turbine blades associated with a blade row are each shaped and arranged in relation to one another in such a way that they form a circumferential covering strip coated with a protective layer of an alternative material. In the case of a blade row, the coated surface of the associated blade shroud is advantageously opposite a number of circumferentially disposed on the inside of the turbine housing Sealing tapes provided. In the case of a guide blade row, such sealing strips are advantageously arranged opposite the coated surface of the guide blade cover strip on the outside of the turbine shaft.

Preferably, such a sealing band comprises a number of ring-shaped bent or formed strips, which are made of a high heat-resistant, cold-workable steel, in particular of a martensitic or austenitic steel or a nickel-based material. The following table lists some suitable examples with their chemical names, their trade names (if any) and their international material numbers: Chemical name Material number trade name X20CrMo13KG 1.4120 X22CrMoV12-1KG 1.4923 X6CrNiMoTi17-12-2 1.4571 X6NiCrTiMoVB25-15-12 1.4980 A286 NiCr23Co12Mo 2.4663 Inconel 617 NiCr20Ti 2.4951 Nimonic 75

Instead of in a corresponding receiving guts caulked (ie solidified with Stemm material in their seat) or directly inserted ("rolled") sealing tapes also on the shroud opposite turbine component (rotor or housing or a sub-segment thereof) molded or turned-sealing ribs provided be. If necessary, the sealing bands or sealing ribs can also be designed to run in a spiral around the circumference.

The advantages achieved by the invention are, in particular, that the degrees of freedom obtained by applying a protective layer to the respective cover plate are selectively exploited with regard to choice of material and surface structuring for an advantageous effect on the frictional behavior against a possibly occurring with the cover plate in contact sealing tape. The radial games between the rotating and the fixed part of the steam turbine can be made smaller, since there are relatively favorable emergency running properties in contact. As a result, better efficiencies can be realized than by sufficiently large radial clearances or a generous safety distance contact is avoided under all circumstances. The relevant for the stability of the annular shroud structure shroud base material is protected by the applied protective or separating layer against friction and / or corrosion-related wear. If the protective layer has sufficient hardness, abrasion phenomena can largely be relocated on one side to the sealing strip, which can be renewed from time to time in a comparatively simple manner.

FIG 1

eine schematische Darstellung einer Dampfturbine im Längsschnitt (Ausschnitt),

FIG 2

einen Querschnitt durch eine Dampfturbine gemäß FIG 1 mit einer Mehrzahl von zu einer Schaufelreihe zusammengefassten Turbinenschaufeln, wobei die Deckplatten der einzelnen Turbinenschaufeln zu einem umlaufenden Deckband zusammengeführt sind,

FIG 3

eine Detaildarstellung einer mit einer Deckplatte versehenen Turbinenschaufel in einer Dampfturbine nach FIG 1, wobei auf die Deckplatte eine Schutzschicht aus einem Alternativmaterial aufgebracht ist,

FIG 4

eine Turbinenschaufel mit einer eine Schutzschicht aufweisenden Deckplatte in einer alternativen Ausführungsform, und

FIG 5

eine Turbinenschaufel mit einer eine Schutzschicht aufweisenden Deckplatte in einer weiteren alternativen Ausführungsform.

Various embodiments of the invention will be explained in more detail with reference to a drawing. Show:

FIG. 1

a schematic representation of a steam turbine in longitudinal section (detail),

FIG. 2

1 with a plurality of turbine blades combined into a row of blades, the cover plates of the individual turbine blades being brought together to form a circumferential shroud,

FIG. 3

1 a detailed view of a turbine blade provided with a cover plate in a steam turbine according to FIG. 1, wherein a protective layer of an alternative material is applied to the cover plate,

FIG. 4

a turbine blade with a protective layer having a cover plate in an alternative embodiment, and

FIG. 5

a turbine blade with a protective layer having a cover plate in a further alternative embodiment.

Identical parts are provided with the same reference numerals in all figures.

FIG. 1 shows a steam turbine 2 with a number of rotatable blades 6 connected to the turbine shaft 4. The rotor blades 6 are each arranged in a ring-shaped manner on the turbine shaft 4 and thus form a number of rotor blade rows. Furthermore, the steam turbine 2 comprises a number of fixed vanes 8, which are also fixed in a ring shape with the formation of rows of vanes on a turbine housing 10 of the steam turbine 2. The limited by the turbine shaft 4 and the turbine housing 10 flow channel 12 of the steam turbine 2 is traversed in a direction parallel to the central axis 14 main flow direction of a vaporous working medium M, the input side heated to a temperature of about 540 ° C and under a high pressure of z , B. 250 bar standing steam relaxes work while driving by impulse transmission to the blades 6, the turbine shaft 4 drives. The guide vanes 8, on the other hand, serve to guide the flow of the working medium M between in each case two rows of rotor blades or rotor blade rings viewed in the flow direction of the working medium M. A successive pair of a ring of vanes 8 or a row of vanes and a ring of blades 6 or a blade row is also referred to as a turbine stage.

FIG. 2 shows a detail of a cross section through the steam turbine 2 that is perpendicular to the central axis 14 and on which a number of turbine blades 16 -in this case a number of rotor blades 6 -can be seen. The annularly mounted on the turbine shaft 4 blades 6 have at their head-side, ie radially outward End in each case an integrally formed on the profiled airfoil 18 and laterally projecting cover plate 20. The cover plates 20 each two adjacent blades 6 touch each other. The cover plates 20 are in fact clamped against one another during assembly of the rotor blades 6 on the turbine shaft 4 such that a closed annular composite, a so-called shroud 22, is formed. As a result, twisting of the individual airfoils 18 or vibrations of the blade tips are effectively suppressed. In aerodynamic terms, while a concern of adjacent cover plates over their entire axial extent (in the direction of the turbine axis) is desirable, but not always to realize for structural reasons. A "line contact" during operation, in which the band is thus closed only at one point in the axial direction of extent (as shown in FIG. 2), is quite sufficient in practice.

The radial gap 24 between the circular outer circumference of the shroud 22 and the opposite inside of the turbine housing 10 on the one hand kept as small as possible in order to minimize the gap losses (by the secondary flow of the working medium M on the blade tips or on the shroud 22 away). On the other hand, the radial gap 24 is dimensioned so broad that certain fluctuations in the radii or deviations from the circular shape, which usually occur during operation of the steam turbine 2, or which are caused by mechanical influences, do not lead to a rubbing on of the rotating shroud 22.

In addition to the rotor blades 6, the guide vanes 8 of the steam turbine 2 can also have cover plates 20 integrally formed on the respective airfoil 18, which in their entirety form a cover strip 20 assigned to the respective guide blade row, in this case a guide blade cover strip which is analogous (but not closer here) ) is separated from the turbine shaft 4 by a radial gap 24.

The efficiency of the steam turbine 2 is optimized by the specification of a particularly small radial clearance, which, however, also increases the probability of grazing. In order nevertheless to be able to ensure high operational reliability, the turbine blades 16 of the steam turbine 2 are specifically designed to provide favorable emergency running properties. This will be explained with reference to the rotor blade 6 shown by way of example in FIG. 3 in a detailed representation. All relevant considerations can also be easily transferred to the guide vanes 8 of the steam turbine 2.

The turbine blade 16 schematically illustrated in FIG. 3, which is embodied as a rotor blade 6, has a cover plate 20 formed on the blade 18, the blade body comprising the blade 18 and the cover plate 20 being made of a single-component workpiece to achieve high mechanical stability and temperature resistance made of a nickel-based alloy. The cover plate is provided on its side facing away from the blade 18, ie the turbine housing 10 of the steam turbine 2 side facing with a plasma spray applied by means of protective layer 28 made of chromium carbide. Opposite the protective layer 28 and spaced therefrom by a radial gap 24, a sealing band 30 composed of a plurality of ring segments is arranged circumferentially on the inside of the turbine housing 10. If, as a result of thermal expansion processes within the steam turbine 2, the sealing strip 30 temporarily comes into contact with one of the cover plates 20 or with the cover strip 22 formed by the entirety of the cover plates 20 of a row of blades, then the base material of the respective cover plate 20 protected by the protective layer 28 from wear. Due to the comparatively high hardness of the protective layer 28 formed from a hard material (here in the exemplary embodiment of chromium carbide), the sealing strip 30 is processed in a targeted and reliable manner in the first place when touching each other, so that it does not penetrate into the actual cover plate 20 or the shroud surface can penetrate.

The turbine blade 16 from FIG. 4, which may be designed as a rotor blade 6 or as a guide blade 8, has a similar construction to the turbine blade known from FIG. 3, although an additional abrasive layer 32 has been applied to the protective layer 28. The radial gap 24 between the double-coated shroud 22 and the sealing strip 30 opposite it is designed so small that adjusts the configuration shown in FIG 4 during operation of the steam turbine 2, in which the sealing strip 30 already in the abrasive layer 32nd but generally does not contact the underlying hard material protective layer 28. As a result, on the one hand, a particularly good sealing of the flow channel 12 is achieved, on the other hand, due to the favorably chosen properties of the abrasive layer 32, no appreciable friction losses occur. The protective layer 28 made of a hard material still protects the shroud 22 in the event of larger fluctuations in the gap distance and thereby ensures acceptable emergency running properties.

In the guide vane 8 shown in FIG. 5, the cover plate 20 or the cover strip 22 formed by all the cover plates 20 of the guide vane row has a gradation adapted to a grading of the opposite turbine shaft 4, so that a labyrinthine angled sub-channel 34 of the flow channel 12 is formed therebetween. The sub-channel 34 is sealed by the circumferentially arranged on the turbine shaft 4 sealing strips 30, wherein in each case during the operation of the steam turbine 2 in its width fluctuating radial gap 24 remains. In order to provide particularly favorable emergency running properties in the case of an on-stripe, the cover plate 20 or cover band 22 made of a highly heat-resistant material is made of an alternative material, as in the previous examples, with a protective layer 28 matched to the sealing strip material with regard to its friction and wear properties overdrawn. The protective layer 28 could again be made of a hard material. In the present case, however, it is a layer of stellite applied to each of the steps constituting the steps by build-up welding, originally approximately 1.0 mm thick, but slightly reduced by post-processing.

It is understood by those skilled in the art that the embodiments illustrated with reference to the figures can be modified in many ways, without abandoning the concept essential for the invention. For example, a gradation could also be provided in the case of a blade cover strip, or the grading could have a contour that deviates from FIG. Finally, a plurality of sealing rings or sealing strips 30 spaced apart in the axial direction of the steam turbine 2 could also be combined to form a group of sealing strips 30 which lie opposite the respective shroud 22 and thus realize a multiple sealing.

Claims (23)

Turbine blade (16) having a cover plate (20) integrally formed on the blade (18), in particular for use in a steam turbine (2), wherein a protective layer (28) of a surface facing away from the blade (18) of the cover plate (20) Alternative material is applied. A turbine blade (16) according to claim 1, wherein the blade body comprising the airfoil (18) and the cover plate (20) is made of a one-component workpiece. A turbine blade (16) according to claim 1 or 2, wherein the cover plate (20) is made of a nickel-base alloy or a cobalt-base alloy. A turbine blade (16) according to any one of claims 1 to 3, wherein the protective layer (28) is formed by a cobalt-based armor alloy. The turbine blade (16) of claim 4 wherein the armor alloy is at most 3% nickel, at most 3% iron, about 1.1% to 1.2% carbon, about 28% chromium, about 1.0% to 1.1% manganese , about 1.0% to 1.1% silicon and 4.5% tungsten. A turbine blade (16) as claimed in claim 5, wherein the protective layer (28) is applied to the cover plate (20) by build-up welding. A turbine blade (16) according to any one of claims 4 to 6, wherein the respective steel sheet (36) has a thickness of about one millimeter or more. Turbine blade (16) according to one of claims 4 to 7, wherein the respective steel sheet (36), in particular by welding, is firmly bonded to the cover plate (20). Turbine blade (16) according to one of claims 1 to 3, in which a hard material layer is provided as the protective layer (28). Turbine blade (16) according to claim 9, wherein the hard material layer is made of a metallic hard material. Turbine blade (16) according to claim 10, in which as hard material chromium carbide or titanium nitride or boron nitride is provided. Turbine blade (16) according to one of claims 9 to 11, wherein the hard material layer by plasma spraying or by a PVD method on the cover plate (20) is applied. Turbine blade (16) according to one of claims 9 to 12, wherein an abrasive layer (32) is applied to the hard material layer. Steam turbine (2) with a number of turbine blades (16) combined in each case into rows of blades according to one of claims 1 to 13. Steam turbine (2) according to Claim 14, in which the cover plates (20) of the turbine blades (16) associated with one row of blades are each shaped and arranged in relation to one another such that they form a circumferential cover band (22). A steam turbine (2) according to claim 15, wherein said blade row is a blade row. Steam turbine (2) according to claim 16, wherein the coated surface of the shroud (22) opposite a number of circumferentially on the inside of the turbine housing (10) arranged sealing strips (22) and / or sealing ribs is provided. A steam turbine (2) according to claim 17, wherein said blade row is a vane row. Steam turbine (2) according to claim 18, wherein the coated surface of the shroud (22) opposite a number of circumferentially on the turbine shaft (4) arranged sealing strips (22) and / or sealing ribs is provided. A steam turbine (2) according to claim 17 or 19, wherein a sealing band (22) comprises a number of metal strips bent in the shape of a ring segment. A method of manufacturing a steam turbine having a number of turbine blades (16) combined to form rows of blades according to any one of claims 1 to 13, wherein the cover plates (20) of the turbine blades (16) associated with a row of blades are each shaped and arranged in relation to each other in that they form a circumferential shroud (22), the protective layer (28) being applied to the shroud (22) only after the assembly of the turbine blades (16) on the turbine shaft (4) or on the turbine casing (10). A method according to claim 21, wherein the protective layer (28) is applied in each case in a number of manufacturing steps to one of a plurality of cover plates (20) formed, contiguous portion of the shroud (22), wherein processed in each manufacturing step each of the entire section or is treated. A method according to claim 22, wherein a cobalt-based armor alloy is applied by build-up welding.

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