EP1808576B1 - Turbine shaft for a steam turbine - Google Patents

Description

The invention relates to a shaft for a steam turbine, wherein the shaft has a protective layer applied to at least part of the surface, wherein the protective layer is a lacquer and a method for producing a shaft having a surface and at least one corrugation notch.

Turbine shafts for turbomachinery are among the most thermally and mechanically stressed components. Hydraulic turbines, steam and gas turbines, wind turbines, centrifugal pumps and centrifugal compressors as well as propellers are summarized under the collective term "turbomachinery". All these machines have in common that they serve the purpose of extracting energy from one fluid in order to drive another machine or, conversely, to supply energy to a fluid in order to increase its pressure. In the turbomachine, the energy conversion is indirect and always takes the path over the kinetic energy of the fluid. The example of a steam turbine can be tracked. The flow medium enters the steam turbine and initially flows through a ring of fixed vanes. This increases the speed and thus the kinetic energy of the flow medium at the expense of its pressure or more precisely its potential energy. At the same time created by the shape of the vanes, a velocity component in the circumferential direction of the impeller. In the impeller, the fluid releases its kinetic energy to the rotor by changing the direction and often the amount of velocity as it flows through the channels formed by the blades. The resulting forces drive the impeller. With reduced energy content, the flow medium exits the steam turbine.

Steam turbines can be designed for different pressure ranges of the flow medium. So z. As high-pressure turbine parts, medium-pressure turbine parts and low-pressure turbine parts known. The steam flowing into a high-pressure turbine part can have temperatures of over 600 ° C and a pressure of over 300 bar. The steam flowing into the low-pressure turbine part comparatively has a low temperature of around 40 ° C.

If, during the further expansion of the steam in the low-pressure turbine section, the boundary lines to the wet steam zone are undershot, then initially a supercooled steam is produced whose temperature is below the saturation temperature associated with the vapor pressure. In this unstable state, the vapor is still purely gaseous, because due to the absence of so-called condensation nuclei initially no liquid droplets are formed. At a certain supercooling, however, sets a spontaneous condensation, which runs so fast that one speaks of a condensation impact. The mist droplets that form, the primary droplets, are very small. Even with the further expansion, they hardly grow to diameters above about 0.2 μm due to the progressing condensation.

Due to the streamline curvature in the blading part of the moisture is centrifuged out and collects in the form of a water film or individual strands of water on the hollow sides of the guide and moving blades. From the trailing edge of the water film separates and forms the larger secondary drops with diameters up to about 400 microns. Even larger water particles are not stable in the turbine flow since they are atomized again.

The turbine shafts used in low-pressure turbine parts are subject to a high cyclic vibration load due to continuous bending due to their own weight. The fatigue strength of these turbine shafts is particularly due to the surrounding medium, especially the flow medium steam determined. Here are some areas of the turbine shaft in the so-called wet steam area.

Besides minimizing efficiency, the presence of liquid water has another adverse effect. The metallic materials can be attacked. The so-called drop impact erosion can occur at the leading edges of the blades. In the wake of the vanes, where the steam velocity is flat due to the boundary layer influence, the water droplets are only moderately accelerated. Their relative speed is still high because of the high peripheral speed of the final stage blades. Upon impact with the blade, material removal may occur if the drops have diameters on the order of 50 to 400 μm. Much smaller drops are harmless and larger ones do not occur.

The influence of wet steam, which leads to drop impact erosion at the leading edges of the blades, is also noticeable on the shaft. The wet steam leads to a strong decrease in the fatigue strength of turbine shafts. Estimates have shown that fatigue strength can decrease by a factor of 3 compared to a turbine shaft that experiences air as the ambient medium.

The fatigue reduction of the turbine shaft by wet steam has hitherto been counteracted in that the turbine shaft has been designed to minimize the influence of wet steam. However, by other constructions, the problem of fatigue reduction by wet steam can not be completely excluded. Another known measure is to roughen points on the turbine shaft, which are particularly stressed by the wet steam in terms of corrosion. The Rolieren leads to an increase in the fatigue strength at the critical point, without preventing the access of the medium moisture to the metallic surface. The effect is based on the introduction of residual compressive stresses, which reduce the operating voltages due to interference. However, the Rolieren requires a not inconsiderable expense, which leads to high costs in the production of the turbine shaft.

In the JP 08 128302 A a turbine shaft with a protective film is disclosed.

In the JP 07 279604 A a turbine shaft with an aluminum layer is disclosed.

It would be desirable to find a way to minimize the influence of wet steam on the fatigue strength of turbine shafts.

At this point, the invention begins, whose task is to provide a shaft for a steam turbine, the fatigue strength reduction can be effectively countered by wet steam. Another object of the invention is to provide a method for producing a surface having a surface and at least one wave notch, wherein the fatigue strength reduction is effectively counteracted by wet steam.

The task directed towards the shaft is achieved according to claim 1 by applying a protective layer to at least part of the surface, wherein the protective layer is a lacquer which is a high-temperature lacquer and is suitable for temperatures up to more than 600 ° C.

The invention is based on the idea that the influence of the wet steam can essentially be counteracted by an effective protective layer. The places that are particularly burdened by the wet steam, ie the fatigue strength is greatly reduced by wet steam due to stress corrosion cracking, are applied to at least part of the surface with a protective layer. The protective layer has the effect that the small droplets of wet steam roll off the paint surface without significantly damaging it. In any case, the stress applied surface of the turbine shaft material is not affected by the presence of the wet steam, since it is precisely the surface due to the high voltage there has a significant impact on the fatigue strength of the entire turbine shaft. As a result, a reduction in the fatigue strength due to the corrosive attack of droplets from the wet steam is effectively countered.

It is advantageous to attach the paint in the shaft axis direction in an axial section over the entire circumference. Since the turbine shaft is usually operated at high speeds, 50 Hz or 60 Hz, the droplets from the wet steam exert an influence on the entire circumference of the shaft surface. Therefore, it is advantageous if the shaft is provided with this paint over the entire circumference.

The invention is also based on the aspect that it does not appear necessary to provide the entire turbine shaft surface with the protective layer for cost reasons. Rather, the idea is based on treating the lacquer according to the invention with the lacquer only at the most heavily stressed areas where the fatigue strength would be reduced by wet steam.

Advantageously, the protective layer is applied to a wave notch. It has been shown that especially a shaft which has corrugations is loaded precisely at these points by wet steam as a result of stress corrosion cracking (SpRK). In particular, the fatigue strength at the wave notches is reduced by wet steam.

The wave notch is in this case arranged between a first region of the shaft with a first radius and a second region of the shaft with a second radius. The first radius is different from the second radius. The wave notch also has a notch radius.

Under a paint in the context of this invention, a paint or a paint-like material is to be understood, which is used for targeted coating of individual local areas and its high protective effect, such. B. the adhesion, the density and / or chemical resistance obtained by a subsequent heat treatment. The heat treatment is carried out in such a way that the base material is not affected in its strength. The lacquer or lacquer-like material can be used up to temperatures of over 600 ° C and remains sufficiently elastic after firing on the turbine shaft. This makes it advantageous if a high-temperature varnish is used as the varnish and this is suitable at temperatures of more than 600.degree.

The object directed to the method is achieved according to claim 5 by a method for producing a surface having a surface and at least one corrugation notch, wherein on the corrugation notch, a paint is applied and then carried out a heat treatment.

The advantages of the method correspond to the advantages mentioned in the device. Therefore, reference is made at this point to the comments on the wave.

In particular, it is advantageous if the heat treatment comprises the following steps: heating to 430 ° C - 450 ° C, holding time 0.1h to 3h and cooling at 20 ° C - 80 ° C / h to 300 ° C.

The inventors have recognized that the layer can be applied particularly effectively with the abovementioned temperature values and times. In particular, the protective effect, such as. As the adhesion, density or chemical resistance is particularly high.

Embodiments of the invention are described below with reference to the drawings. In this case, provided with the same reference numerals components have the same operation.

Figur 1

eine Schnittdarstellung durch einen Teil einer Niederdruckteilturbine;

Figur 2

eine Seitenansicht einer Turbinenwelle;

Figur 3

eine Seitenansicht eines Teiles einer Welle mit Wellenkerbe.

Showing:

FIG. 1

a sectional view through a part of a low pressure turbine part;

FIG. 2

a side view of a turbine shaft;

FIG. 3

a side view of a part of a wave with wave notch.

In the FIG. 1 a low-pressure turbine section 1 is shown in a sectional view. The low-pressure turbine part 1 has a turbine shaft 3 which is symmetrical about an axis of rotation 2. The turbine shaft 3 has various radii that become larger toward the center 4 of the turbine shaft. On the turbine shaft 3 so-called wheel discs 5 are applied. For clarity, only two wheel discs 5 are provided with the reference numeral 5. The wheel discs 5 are usually arranged by shrinking onto the turbine shaft 3. On the wheel discs 5, the blades 6 are attached. Especially in the low-pressure part of a steam turbine, the rotor blades 6 are long and can be values of more than 1.20 m. Also rotationally symmetrical about the axis of rotation 2, the inner housing 7 is formed. The inner housing 7 carries the guide vanes 8. For clarity, only two guide vanes 8 are provided with the reference numeral 8. Low-pressure steam flows into the low-pressure turbine section 1 through inflow channels, not shown, and flows in the flow channel 9 in the direction 10 and 11. The temperature and the pressure of the steam are thereby it can not be ruled out that it will "wet" the vapor and form droplets.

The shaft 3 is rotated by the energy conversion. The low-pressure steam subsequently flows out of the outflow region 12 out of the steam turbine. The low-pressure steam is in this case deflected in a diffuser housing 13 and led to a condenser, where the steam condenses to water.

In the FIG. 2 the shaft 3 of a low pressure turbine part 1 is shown. The low-pressure shaft 3 has different diameters in its longitudinal direction. In this case, the turbine shaft 3 may be formed mirror-symmetrically to the mirror axis 14. However, the turbine shaft does not necessarily have to be mirror-symmetrical to the mirror axis 14. The different diameters d0, d1, d2, d3, d4 and d5 are different from each other. The diameters d0 to d5 to the left of the mirror axis 14 are generally the same size as the diameters d5 to d0 on the right side of the mirror axis. However, this is not absolutely necessary, in particular, the diameters may be slightly different.

As a result, the turbine shaft 3 has a surface which, as it were, runs discontinuously.

Between a first region 16 of the shaft 3 with a radius d4 and a second region 17 of the shaft with a second radius d5 is a discontinuous transition, wherein between these two areas 16, 17 a wave notch 18 is formed. In the FIG. 2 is the wave notch with a circle 19 for the sake of clarity better indicated.

The regions 16 and 17 with the radii d4 and d5 are given by way of example only. Of course, wave scores occur wherever two different areas with two different radii are. Further examples would be the transition from the area with the diameter d1 to the area with the diameter d2 or the transition of the area with the diameter d3 to the area with the diameter d4. Nevertheless, in the FIG. 2 To make it clear at which points the turbine shaft is heavily loaded, in particular by the influence of the wet steam, the wave notches are indicated by circles 19.

The shaft 3 can be used for a turbomachine, in particular for a low-pressure turbine part 1. At least on a part of the surface 15, a protective layer 20 is applied.

The protective layer may be a paint or a material having elastic properties, such. B. rubber.

When viewed in the shaft axis direction 21, the protective layer is mounted in an axial section, for example between 17 and 18, over the entire circumference of the shaft.

The wave notch has a notch radius 23 and thus provides a steady transition from the radius d4, for example, to the radius d5. The course of the wave notch 18 need not necessarily correspond to a circle segment, but rather the term notch radius 23 should be understood to mean that the first area 16 and the second area 17, which have different radii d4 and d5 respectively, do not change into each other in a discontinuous manner, ie. H. The wave radius d4 changes in the region 22 from the radius d4 to a different radius from d5.

By lacquer is to be understood a lacquer or lacquer-like material, which can be used for the targeted coating of individual local areas and its high protective effect, eg. As adhesion, density, chemical resistance obtained by a subsequent heat treatment. The heat treatment is carried out in such a way that the basic active substance in its strength is not affected. The paint is protective up to over 600 ° and remains sufficiently elastic after firing.

• Erwärmen auf430°C - 450°C, Haltezeit 0,1h bis 3h und Abkühlen mit 20°C - 80°C/h auf 300°C.

In a method for producing a surface and at least one wave notch having shaft 3, the heat treatment comprises the following steps:

• Heat to 430 ° C - 450 ° C, hold for 0.1h to 3h and cool at 20 ° C - 80 ° C / h to 300 ° C.

Claims (6)

1. Shaft (3) for a steam turbine,
   wherein the shaft (3) has a protective layer (20) applied to at least part of the surface (15),
   wherein the protective layer (20) is a coating,
   characterized in that
   the coating (20) is a high-temperature coating and is suitable for temperatures up to and above 600°C.
2. Shaft (3) according to Claim 1,
   wherein the protective layer (20) is applied over the entire circumference as seen in the shaft axial direction (21) in an axial section (16, 17, 22).
3. Shaft (3) according to either of the preceding claims,
   wherein the shaft (3) has a shaft fillet (18) onto which the protective layer (20) is applied.
4. Shaft (3) according to Claim 3,
   wherein the shaft fillet (18) is arranged between a first region (16) of the shaft (3) having a first radius (d4) and a second region (17) of the shaft (3) having a second radius (d5),
   wherein the first radius (d4) and the second radius (d5) are different, wherein the shaft fillet (18) has a fillet radius (23).
5. Method for producing a shaft (3), according to one of Claims 1 to 4, having a surface (15) and at least one shaft fillet (18),
   characterized in that
   a coating (20) is applied to the shaft fillet (18), which is followed by a heat treatment.
6. Method according to Claim 5,
   wherein the heat treatment comprises the following steps:

   heating to 430°C - 450°C, holding time 0.1h to 3h and cooling at 20°C/h - 80°C/h to 300°C.

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