Patent Application
20120207608
The invention relates to a turbine blade.
The invention furthermore relates to a method for making a turbine blade.
Turbine blades, and in particular turbine blades of steam turbines, are currently made predominantly of steel. Because of the great weight of steel turbine blades and the resulting high centrifugal forces, the speed of rotation and the maximum blade length of final-stage rotor blades are restricted. As a result of this, the surface area of the outflow of the exhaust casing, and hence the output and efficiency of the turbine, are limited. To increase the output and efficiency of future turbines, more and more thought is being applied to the use of final-stage rotor blades made from fiber-reinforced composite material. Fiber-reinforced composite materials have the advantage of high specific strength at the same time as low weight.
Turbine blades made from fiber-reinforced composite materials are made by compressing and adhering to one another at least two layers of fiber mats of the same or different materials. Suitable fiber mats are, in particular, glass-reinforced fibers or carbon-reinforced fibers. Since fiber-reinforced composite materials only have high strength in the direction of the fibers, the layers of fibers have to be aligned individually to suit the load. Usually, the fiber mats are made from a plurality of fiber mats which have different main directions of the fibers and are laid one on top of the other, to achieve strength in a plurality of directions.
The individual fiber mats are connected to one another by means of a matrix, conventionally a synthetic resin. Here, the proportion of matrix must be sufficiently high for the fiber mats to be fixedly connected to one another. However, too great a proportion of matrix results in a loss of strength in the fiber-reinforced composite material.
Various methods are suitable for making turbine blades of fiber-reinforced composite material, a fundamental distinction being made between open and closed methods. In both methods, fiber intermediates—this term being used to mean fabrics, fiber fabrics or fiber mats—are laid in an impregnation mold and impregnated with the matrix material. During the impregnation, the matrix material is incorporated into the fabric and a composite of matrix material and fiber intermediate is formed. Excess matrix material must be removed during the impregnation and the turbine blade must then cure before it can be taken out of the impregnation mold.
The currently most commonly used open method for making fiber-reinforced composite blades is the hand layup method. In this, the fiber intermediates are laid in the impregnation mold by hand and wetted with the matrix. Then air is removed from the laminate, by pressing against it with the aid of a roller. This is intended to remove from the layers of fiber mat not only air present in the laminate structure but also excess matrix material. The procedure is repeated until the desired layer thickness is achieved. Once all the layers have been applied, the component must cure. Curing is performed through a chemical reaction between the matrix material and a curing agent added to the matrix material. The advantage of the hand layup method is the small tool and low equipment outlay. However, this is offset against a low quality of component (low fiber content) and the high level of manual effort, which requires trained laminators.
Hand layup can also be performed as a closed method. The closed method is performed using a vacuum press. Once the fiber mats have been introduced into the impregnation mold, the mold is covered with a release film, a suction fleece and a vacuum film. A vacuum is generated between the vacuum film and the mold. This has the effect of compressing the composite. Any air still included is removed by suction, and the excess matrix material is absorbed by the suction fleece. This means that a higher quality of component can be achieved than with the open hand layup method.
The prepreg method is a further closed method. In this, fiber mats which are pre-impregnated with matrix material and have thus already been wetted are laid in the impregnation mold. In this case, the resin is no longer liquid but has a solid, slightly tacky consistency. Air is then removed from the composite by means of a vacuum bag and it is then cured, often in an autoclave, under pressure and heat. Because of the operational equipment required (cooling plant, autoclaves) and the demanding process (temperature management), the prepreg method is one of the most expensive manufacturing methods. However, it also enables one of the highest levels of quality of component.
The vacuum infusion method is a further closed method for making fiber-reinforced composite blades. In this method, the dry fiber layers are laid in an impregnation mold coated with release agent. A release fabric and a distribution medium are placed over this, and this facilitates even flow of the matrix material. A vacuum sealing tape seals the film to the impregnation mold, and the component is then evacuated with the aid of a vacuum pump. The air pressure presses together the parts that have been laid in the mold and fixes them. The suction applied draws the tempered liquid matrix material into the fiber material. Once the fibers have been completely wetted, the supply of matrix material is stopped and the wetted fiber-reinforced composite material can be cured and removed from the impregnation mold. The advantage of this method is that the fibers are wetted evenly and with almost no air inclusion, and so the components produced are of high quality and there is good reproducibility
The curing times for the individual methods are in each case dependent on the matrix material (resin) that is selected and the curing temperature.
The above-mentioned methods are all good ways to make fiber-reinforced composite blades. However, turbine blades made in such ways have the disadvantage that, because of the material used, they are very susceptible to erosion corrosion. Erosion corrosion occurs at the final stage of turbine blades as a result of water from the flow of steam condensing into droplets and these droplets impacting on the turbine blades at great speed and with high energy. As a result of the high energy of impact of the water droplets, the fiber-reinforced composite material is quickly destroyed.
An object of the present invention is thus to provide a turbine blade, in particular a final-stage blade, for a steam turbine which is made at least in certain regions from fiber-reinforced composite material, which offers a high level of protection against erosion. Furthermore, it is an object of the present invention to specify a method for making a turbine blade of this kind.
The object is achieved by the features of the independent claims.
Advantageous embodiments and further developments, which may be used individually or in combination with one another, form the subject of the subclaims.
The turbine blade according to the invention, in particular a final-stage blade for a steam turbine, wherein the turbine blade is made at least in certain regions from fiber-reinforced composite material, is characterized in that the turbine blade has at least one anti-erosion component. In this case, the anti-erosion component is arranged such that it effectively protects the fiber-reinforced composite material against erosion corrosion. To this end, it is arranged at least at those points on the turbine blade which are under particular load from erosion. By using the anti-erosion component, the turbine blade can be made from fiber-reinforced composite material without there being any reduction in the load from erosion by comparison with turbine blades made from steel. In this arrangement, the weight is significantly reduced because fiber-reinforced composite material is used, as a result of which the centrifugal load is significantly reduced, in particular in the foot region of the turbine blade, which is under very heavy load. Consequently, the blade can be made longer and hence the surface area of the outflow of the exhaust casing can be made larger and the speed of rotation of the turbine increased. This makes the steam turbine more efficient.
An advantageous embodiment of the invention provides for the anti-erosion component to be inserted into the blade contour of the turbine blade. Here, the term “inserted” means that the turbine blade is constructed such that the blade contour is produced by the turbine blade itself and the anti-erosion component. Because the anti-erosion component is inserted into the blade contour of the turbine blade, no change is made to the flow conditions at the turbine blade, as would be the case with an anti-erosion component which was merely attached to the turbine blade. This means that the flow behavior at the turbine blade and thus in the turbine as a whole remains unchanged.
A further advantageous embodiment of the invention provides for the anti-erosion component to be inserted into the blade contour of the turbine blade such that a smooth transition is created between the anti-erosion component and the turbine blade. The smooth transition between the anti-erosion component and the turbine blade avoids edges which could weaken the turbine blade. Moreover, this also avoids edges at the surface of the turbine blade which would result in a displacement of flow.
According to the invention, the inserted anti-erosion component is preferably connected to the turbine blade by laminating and/or gluing and/or securing means, in particular screws, rivets or pins. The anti-erosion components secured in this way ensure a reliable and permanent connection with the turbine blade even at high peripheral speeds and with high centrifugal forces. This is particularly important because anti-erosion components flying off could cause substantial damage to the turbine blade.
A particularly advantageous embodiment of the invention provides for the anti-erosion component to be made from carbide, titanium or ceramic. Carbide, titanium and ceramic are particularly resistant to erosion and are thus particularly well suited as material for the anti-erosion component. As a result of using these materials, the service life of the anti-erosion component can be considerably extended compared with other materials.
A further preferred embodiment of the invention provides for an intermediate layer, in particular an elastic and/or viscoelastic intermediate layer, to be arranged between the anti-erosion component and the turbine blade. Very hard materials bring with them the risk that, because it is very brittle, the material will tend to break up. Using an intennediate layer, in particular an elastic and/or viscoelastic intermediate layer, means that the impact energy of the droplets is absorbed or reduced by the intermediate layer, as a result of which the risk of the hard outer layer of the anti-erosion component breaking up is reduced.
A further advantageous embodiment of the invention provides for the anti-erosion component to have a multi-layer structure. The multi-layer structure may be made of different metal layers, different layers of fiber material or a combination of both. A judicious selection of material for the individual layers may allow different properties of the layers to be combined in advantageous ways. The outermost layer should in this case be as hard as possible, and the underlying layers should to the greatest possible extent absorb the impact energy of the droplets and absorb the structure-borne sound waves which are generated by the impact of the droplets, such that they cannot have an effect on the base material of the turbine blade.
A particularly advantageous embodiment of the invention provides for an anti-erosion component to be arranged at least at the leading edge and/or the trailing edge of the turbine blade. In normal operation of the turbine, the droplets of liquid flowing with the flow of steam impact on the leading edge of the turbine blade and there bring about considerable damage as a result of erosion corrosion. The other regions of the turbine blade are not as subject to erosion. For this reason, at least the leading edge, which is at great risk of erosion, should be constructed to have an anti-erosion component. In some circumstances it is possible to dispense with any other anti-erosion means for the turbine blade. This keeps the weight of the turbine blade as low as possible, minimizing the centrifugal load on the turbine blade. In some circumstances, attaching an anti-erosion component to the trailing edge may also be useful. The trailing edge of the turbine blade is not at risk of erosion in normal operation of the turbine. When the turbine is in ventilation mode, however, it is often the case that water is sprayed into the steam turbine to prevent overheating. The water is conventionally sprayed in against the trailing edge of the turbine blade. This can have the result that in some circumstances the trailing edge of the turbine blade is also subject to erosion. In this case, an anti-erosion component at the trailing edge may reduce the impact of erosion.
A method according to the invention for making a turbine blade using an impregnation mold is characterized by the following method steps:
When the fiber intermediates and the anti-erosion component are laid in the impregnation mold, care must be taken that the anti-erosion component and the fiber intermediates are arranged such that, once the fiber intermediate is impregnated with matrix material, a turbine blade is created into the contour whereof the anti-erosion component can be completely integrated. The term “fiber intermediates” here means, among other things, fabrics, fiber fabrics or fiber mats. As the matrix material, resin is suitable, in particular synthetic resin. The method according to the invention for making the turbine blade has the great advantage that the turbine blade can be constructed with the anti-erosion component integrated, in one method step. There is no need to attach an anti-erosion component subsequently. As a result of integrating the anti-erosion component into the blade contour, the latter is entirely retained, and there is no change in the flow conditions by comparison with conventional turbine blades. There is therefore no need for the turbine to be redesigned from the point of view of fluid mechanics.
A particularly advantageous method for making a turbine blade provides for the anti-erosion component to be laminated into the turbine blade during impregnation. Here, the term “laminated in” means that the anti-erosion component is fixedly connected to the turbine blade by the matrix material. As a result of laminating the anti-erosion component in during impregnation with the matrix material, there is no longer any need to attach or secure the anti-erosion component to the turbine blade subsequently. As a result, the manufacturing work is minimized. By laminating the anti-erosion component in, it is secured to the turbine blade reliably and permanently.
A further advantageous method for making the turbine blade provides, as an additional method step, for the anti-erosion component, after it has been laminated in, to be secured to the turbine blade by additional securing means, in particular screws, rivets or pins. The additional securing has the advantage that even if laminating-in is faulty, the anti-erosion component cannot become detached. It is absolutely imperative to avoid the anti-erosion component becoming detached since this can cause major damage to the turbine blade or to the turbine as a whole.
A further advantageous method for making the turbine blade provides for the anti-erosion component to be provided, before impregnation, with a release agent and, after impregnation, to be secured to the turbine blade by gluing and/or additional securing means, in particular screws, rivets or pins. The subsequent attachment of the anti-erosion component has the advantage that it can still be trimmed by machining before the final securing, or positioning of the anti-erosion component on the turbine blade can easily be corrected.
A second method according to the invention for making a turbine blade using an impregnation mold is characterized in that the impregnation mold is constructed such that, after impregnation, a recess which is constructed to complement the anti-erosion component is present at the points on the turbine blade at which an anti-erosion component is to be attached, and in that the method has the following method steps:
Here, too, the subsequent attachment of the anti-erosion component has the advantage that it can still be trimmed by machining before the final securing, or positioning of the anti-erosion component on the turbine blade can easily be corrected.
Exemplary embodiments and further advantages of the invention will be explained below with reference to the drawing. The following are shown schematically:
Throughout the figures, like components or those having like functions are provided with like reference numerals.
Because turbine blades made from fiber-reinforced composite material are highly susceptible to erosion corrosion, the turbine blade 1 has an anti-erosion component 2 at the leading edge 6. The leading edge 6 is at most risk of erosion because it is essentially here that the water droplets impact.
In the exemplary embodiment, the anti-erosion component 2 is only attached in the upper half of the leading edge 6. Erosion has the greatest effect in this region of the leading edge 6, since it is here that the highest peripheral speeds occur when the turbine is in operation. The anti-erosion component 2 is inserted into the blade contour of the turbine blade 1 such that a smooth transition with no edges is created between the anti-erosion component 2 and the turbine blade 1.
In this arrangement, the anti-erosion component can be laminated in directly when the turbine blade is made or indeed can be connected to the turbine blade later by gluing or additional securing means, in particular screws, rivets or pins. Once laminated in, the anti-erosion component 2 can additionally be secured using securing elements to ensure that the anti-erosion component 2 is reliably secured to the turbine blade 1. If during operation of the turbine the anti-erosion component were to become detached, for example because of faulty lamination, it could cause substantial damage to the turbine blades 1 and it is therefore imperative that it be avoided.
Preferably, the anti-erosion component 2 should be made from carbide, titanium or ceramic. The high level of hardness of these materials ensures a high resistance to erosion and hence a long service life of the anti-erosion component 2. Because the anti-erosion component 2 is manufactured such that it is inserted seamlessly into the blade contour of the turbine blade 1, there is no need for subsequent machining of the anti-erosion component 2. This brings considerable advantages, since it is extremely difficult for the hard materials to be machined subsequently, and this entails substantial manufacturing work.
The turbine blade 1 additionally has a second anti-erosion component 2 at the trailing edge 7 of the turbine blade 1. In normal operation, the trailing edge 7 is not at risk of erosion since there is no impact of droplets here. The anti-erosion component 2 at the trailing edge 7 of the turbine blade 1 is provided for ventilation mode. In the ventilation mode of the steam turbine, to prevent overheating water is sprayed onto the turbine blade 1 from behind. During this, in unfavorable conditions it may happen that water droplets impact on the trailing edge 7 of the turbine blade 1. These then result in increased erosion effects at the trailing edge 7. For this reason, an anti-erosion component 2 is provided at the trailing edge 7 of the turbine blade 1.
By providing the anti-erosion components 2 in the regions of the turbine blade 1 which are at risk of erosion, the turbine blade made from fiber-reinforced composite material may also be used in the wet steam region of a steam turbine. This has not hitherto been possible. By using turbine blades made from fiber-reinforced composite material, the weight of the turbine blade may be significantly reduced. Reducing the weight of the turbine blade has the result that the centrifugal load on the turbine blade, particularly in the sensitive region of the blade foot, may be reduced or, with the same tensile load, the blade may be made longer and hence the outflow cross-section of the exhaust casing may be made larger. An increase in the cross-section of the exhaust casing and an increase in the speed of rotation of the turbine result in greater efficiency of the steam turbine.
The turbine blade 1 which is described is made entirely from fiber-reinforced composite material. However, a construction in which only a partial region is made from fiber-reinforced composite material is also conceivable. Thus, for example, the turbine blade could be made from fiber-reinforced composite material and the blade foot could be made from steel or titanium.
The methods according to the invention for making a turbine blade having an anti-erosion component will be explained in more detail below.
The manufacture of a turbine blade having one or more anti-erosion components 2 takes place using an impregnation mold. In this case, the impregnation mold provides the foam of the turbine blade to be made.
To make the turbine blade, in a first manufacturing step the fiber intermediates are laid in the impregnation mold together with the anti-erosion component 2. Here, care must be taken that positioning of the anti-erosion component 2 is correct. For this purpose, the anti-erosion component 2 may be fixed to the impregnation mold. Once the fiber intermediates and the anti-erosion component 2 have been laid in the impregnation mold, the impregnation procedure is performed. During this, the resin is introduced into the fiber intermediates. This introduction may be carried out using an open or a closed method. The various methods have already been explained in detail in the introduction to the description, so more detail will not be given here. Once the fiber intermediates have been impregnated with the resin, the turbine blade 1 has to cure. Here, the cure time is dependent on the matrix material selected and on the ambient temperature. Once the matrix material has cured, the turbine blade 1 can be removed from the impregnation mold. The anti-erosion component 2 can be connected to the turbine blade 1 in various ways. On the one hand, the anti-erosion component 2 can be laminated directly to the turbine blade 1. In this case, the connection between the anti-erosion component 2 and the turbine blade 1 is made by means of the matrix material. Additional securing by means of securing means 3, in particular screws, rivets or pins, may be performed subsequently. Another method for making the turbine blade 1 provides for the anti-erosion component 2 to be provided with a release agent before the impregnation. As a result of this, during the impregnation procedure the anti-erosion component 2 is not connected to the turbine blade 1. The anti-erosion component 2 is secured to the turbine blade in a further method step, by gluing and/or additional securing means 3 such as screws, rivets or pins.
A further method for making a turbine blade 1 having an anti-erosion component 2 provides for an impregnation mold to be used which has a recess at the point at which the anti-erosion component 2 is later to be attached. Once the turbine blade 1 has cured, the anti-erosion component 2 can be incorporated by gluing and/or additional securing means 3 such as screws, rivets or pins.
Attaching the anti-erosion component 2 subsequently has the advantage that if fitting is imprecise this can be corrected before the actual securing. Machining the anti-erosion component 2 before it is secured to the turbine blade 1 is easier to accomplish, in particular with the hard materials which are preferably used, such as carbide, titanium or ceramic, which can substantially only be machined by grinding.
The methods presented above for making the turbine blade 1 having an anti-erosion component 2 all have the distinguishing feature that it is possible in a very simple manner to construct a turbine blade 1 in which an anti-erosion component 2 can be integrated such that the blade contour does not differ from the blade contour of conventional turbine blades 1. There is no need to attach an anti-erosion component or additionally to provide a coating as an anti-erosion measure. If they become too worn, the anti-erosion components 2 can simply be removed and replaced by new anti-erosion components 2. By using anti-erosion components 2 which are not susceptible to erosion, for the first time it becomes possible to use turbine blades made from fiber-reinforced composite materials in the wet steam area.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2009 047 798.5 | Sep 2009 | DE | national |
This application is the U.S. National Stage of International Application No. PCT/EP2010/063871, filed Sep. 21, 2010 and claims the benefit thereof. The International Application claims the benefits of German application No. 10 2009 047 798.5 DE filed Sep. 30, 2009. All of the applications are incorporated by reference herein in their entirety.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2010/063871 | 9/21/2010 | WO | 00 | 4/27/2012 |
