Such guide blades are for instance present in turbines and are then normally rotatably arranged by means of pins or spindles extending from opposite ends of each respective guide blade and protruding into adjacent elements connected to a stator part. By means of bearing devices, for example slide bearings, the spindles are rotatably arranged in these elements connected to the stator part.

The supporting elements are normally formed by an outer and an inner stator ring. The rotation of the respective guide blades takes place by a rotation of a respective rotation arm linked to one of the spindles of each guide blade respectively. By rotating the guide blades in a turbine a change of the so called turbine width may thereby be accomplished, defining the amount of a gas or another medium that passes through the turbine at given inlet and outlet pressures thereof.

Turbines are often driven by means of dust-containing gases, permitted to pass through the turbine. A problem usually present thereby is the wear that the material in the turbine is subjected to because of the dust-containing gases getting into contact with it. At rotatable turbine guide blade of the type defined above it has proved itself that the dust in the gases tends to give rise to erosion problems. These erosion problems particularly appear as the material of the supporting elements of the stator erodes in an area where these adjoin the blade of each guide blade respectively with a gap as narrow as possible. When such an erosion has been

permitted to proceed to a certain extent the risk of dust present in the gases penetrating between the spindles of the guide blades and the supporting elements protruded thereby is increased. In that way, dust present in the gases might reach the bearing devices, for example slide bearings, in which the spindles of the guide blades are supported in the supporting elements, thereby giving rise to a premature wear thereof, which in its turn results in costly repairs and shut-offs of the turbine.

SUMMARY OF THE INVENTION The object of the present invention is to provide a device at a guide blade arranged in a rotary machine, which device remedies the erosion problems that tend to be found by supporting elements at end areas of the blade member of the guide blade, particularly during passage of dust-containing gases, thereby remedying the problems resulting because of dust particles that penetrate to the bearing device of the guide blade.

This is obtained by means of a device as initially defined, which is characterized in that it comprises an erosion resistant element arranged in a border area between a blade member of the guide blade and the supporting element.

The gas flows that promote erosion and are normally found in the area between the blade and the supporting element will thereby act upon the erosion resistant element instead of the supporting element, whereby a wear of the latter is counteracted.

According to a preferred embodiment the erosion resistant element is arranged on the guide blade.

Thereby, particularly the advantage of the guide blade and the erosion resistant element being possible to manufacture in one single piece and by the same erosion resistant material if desired is obtained. Alternatively, the erosion resistant element may be arranged on the guide blade subsequently to the manufacture

thereof. However, the element and guide blade together form a smaller, substitutable component in relation to the supporting element which is supposed to be common for a large number of guide blades when it is constituted by a stator ring in a rotary machine of a turbine type.

According to another preferred embodiment of the device according to the invention, the erosion resistant element is fixedly arranged on a spindle projecting from the blade member of the guide blade, and arranged in a corresponding recess in the supporting element.

Thereby, the surface of the erosion resistant element directed towards the blade of the guide blade may be positioned generally in the same plane as the corresponding surface of the supporting element that surrounds the erosion resistant element, that is smooth transition is provided between the erosion resistant element and the supporting element, the surfaces thereof preferably being positioned in alignment. Gas flows generating erosion may thereby be avoided in the area of transition between the erosion resistant element and the surrounding supporting element.

According to another preferred embodiment of the device according to the invention the erosion resistant element is generally annular and at its outer periphery first means are arranged to seal against adjacent portions of the supporting element.

Thereby it is prevented that dust particles present in the gas squeezes through between the erosion resistant element and the supporting element surrounding the latter and in that way find their way to a bearing device at which the spindle of the guide blade is rotatably supported in relation to the supporting element and expose the latter for wear.

According to another preferred embodiment of the device according to the invention the device comprises a supply channel provided for a supply of pressurized medium to a gap between the erosion

resistant element and the supporting element at the opposite side of the first sealing means in relation to the side adjacent to the blade.

Thereby, via the supply channel, a pressure can be generated at said opposite side, said pressure being so high in relation to the pressure of the gases passing the blade that a possibility for dust particles to penetrate up to the bearing device via the gap between the erosion resistant element and the supporting element is further reduced. In combination with the previously defined first sealing means this feature results in a very good obstacle against penetration of dust particles between the supporting element and the spindle as well as between the supporting element and the erosion resistant element.

According to another preferred embodiment of the device according to the invention the device comprises second sealing means which are arranged to seal between a spindle of the guide blade and the portions of the supporting element adjacent to this spindle.

If, in spite of this, dust particles would manage to pass the previously defined first sealing means, these second sealing means present a further obstacle that prevents these particles from penetrating to a bearing device provided between the spindle and the supporting element.

According to another preferred embodiment of the device according to the invention the device comprises a draining channel which opens in a gap between the spindle and the supporting element.

The draining channel opens between the second sealing means and a bearing device provided between the spindle and the supporting element.

Thereby, it is possible to drain away possible dust particles that, in spite of the presence of the first and second means and the sealing effect of the supply channel, have managed to pass the previous sealing means and thereby run the risk of reaching the bearing device. Preferably, a pressure is generated in the draining channel,

said pressure being lower than the pressure in the gap between the spindle and the supporting element, resulting in the channel acting as a suction device.

The invention also relates to a rotatable guide blade, characterized in that it is provided with the inventive device at a first of two opposite ends.

According to a preferred embodiment, the guide blade is provided with the inventive device also at the other end.

Further advantages and advantageous features of the invention will be clear from the following description and the other dependant patent claims.

BRIEF DESCRIPTION OF THE DRAWING Hereinafter, a detailed description follows of an embodiment of the invention, referred to by way of example with reference to the attached drawing, in which: Fig 1 is a partially cut sideview showing a guide blade provided with the inventive device at two opposite ends thereof.

DETAILED DESCRIPTION OF AN EMBODIMENT In Fig 1 a guide blade 1 is shown, said guide blade being provided with an embodiment of the device according to the invention at two opposite ends thereof. The guide blade is one of a plurality of guide blades arranged in the rotary machine and connected to the stator.

The rotary machine is a turbine and the guide blades are arranged in rows that are coaxial in relation to the rotational axis of a rotary part arranged in the turbine. By at least one such row rotatable turbine guide blades are arranged, while the turbine guide blades in the rest of the rows may be fixed, that is not rotatably arranged.

Gases flowing through the turbine will pass and be guided by the

guide blades on their way through the turbine. Preferably the turbine is a low pressure turbine by a PFBC-plant.

At its radially outer end the guide blade 1 is provided with an erosion resistant element 2, which is fixedly arranged on the guide blade in the end area of the blade member 3 thereof. The erosion resistant element 2 has the shape of an annular disc and is fixedly arranged on a spindle 4 which extends from the ends of the blade member 3 to a bearing device 5 in which it is rotatably supported.

From the bearing device 5 the spindle 4 extends to a point where it is connected to a rotating arm 6, by means of which the spindle 4, and thereby the guide blade may be rotated.

The erosion resistant element has an extension that generally corresponds to the area at the blade end where the erosion risk is at its largest due to the particular gas flow conditions present there.

The erosion resistant element 2 is further defined as presenting at least one erosion resistant surface, preferably the surface directed towards the blade member 3. The element 2 is positioned in a corresponding recess of a supporting element 7 formed by a stator ring or a part connected to the stator of the rotary machine. At its outer periphery the element 2 is provided with first sealing means 8 which, in the example shown, are comprised by two sealing rings each of which is arranged in recesses at the outer periphery of the element 2 and projects from the latter and bears against the supporting element 7. Each sealing ring respectively comprises for instance two smaller rings arranged close to each other. The small rings as well as the sealing rings constituted thereby may be of a smaller or larger number than two. The first sealing means 8 are arranged to prevent gases passing the blade member 3 from penetrating between the element 2 and the supporting element 7 and in that way finding their way to the bearing device 5.

The spindle 4 extends from the element 2 to the bearing device 5, a gap, though a small one, always remaining between the spindle and the surrounding supporting element 7. Along this gap, dust particles that possibly manage to pass the first sealing means 8 may move on

to the bearing device 5. To prevent this from happening second sealing means 9 are arranged between the spindle 4 and the supporting element 7 between the bearing device 5 and the element 2. The second sealing means 9 comprise three sealing rings in the example shown, said sealing rings being arranged in corresponding recesses in the spindle 4 and projecting from the periphery of the spindle 4 until they bear against the supporting element 7. Also each one of these sealing rings is formed by for instance two smaller rings arranged close adjacent to each other, and also here it is fully possible with more or less of said sealing rings which in their turn may be constituted by more or less of smaller rings.

In order to further prevent dust particles from penetrating up to the bearing device 5 a draining channel 10 is provided and opens in the gap between the spindle 4 and the supporting element 7 between the second sealing means 9 and the bearing device 5. In the draining channel 10 a pressure is established which is lower than the pressure in the gap between the spindle and the supporting element, resulting in this channel acting as a suction member and accordingly transporting away and thereby preventing dust particles that possibly have managed to pass the first and second sealing means 8 and 9 respectively from reaching the bearing device 5.

The device also comprises a channel 11 for a supply of a pressurized medium to a gap between the element 2 and the supporting element 7. This supply channel 11 opens at the opposite side of the first sealing means 8 in relation to the blade member 3.

The pressurized medium is preferably air of a certain pressure. The air pressure is suitably of such a dimension in relation to the pressure of the gases passing the blade member 3 of the guide blade that a pressure difference exists between the respective sides of the fist sealing means 8 and the lower of these pressures being found at the side of the sealing means that is adjacent to the blade, resulting in a small air flow being permitted to pass the sealing means in a direction towards the side adjacent to the blade instead of dust-containing gases being permitted to pass in the opposite direction. As an alternative it is of course possible that the channel

11 is arranged in such a way that it opens in the gap present between the spindle 4 and the supporting element 7 somewhere between the first and the second sealing means 8 and 9 or by absence of the second sealing means, between the first sealing means 8 and the bearing device 5.

From the figure it can be seen that the guide blade 1, at its radially inner end, is provided with a device which in principle corresponds to the one described above. On a spindle 4'projecting from the blade member 3 of a guide blade 1 an erosion resistant element 2' is provided. This element 2'has a smaller diameter than the element 2 located at the other end of the blade, this deriving from the fact that different gas flows are present at the two ends of the blade member 3 and that, in this case, a smaller area is critical from an erosion point of view.

Also here first 8'and second 9'sealing means are found, located between the supporting element 7'and the outer periphery of the element 2'and between the supporting element 7'and the outer periphery of the spindle 4'respectively. Furthermore, a draining channel 10'and a supply channel 11'are arranged in the way described above in relation to the first 8'and the second 9'sealing means.

At this radially inner bearing device 5'the guide blade is also radially fixed by means of a locking ring 12. Radial direction is here referred to as the radial direction from a centre axis of the row of guide blades in which the guide blade 1 in consideration is included.

Also the supporting elements 7,7'may comprise an erosion resistant material, for instance as the whole supporting elements 7, 7'are made of an erosion resistant material or as a portion of the supporting elements 7,7'adjacent to each element 2,2' respectively are made of an erosion resistant material. Such a portion may for instance comprise a ring that extends around the element 2,2'and is fixedly arranged in the supporting element 7,7' and adjoining the element 2,2'.

Here, an erosion resistant material is referred to as hard materials, for instance different types of high-alloyed steels, such as white cast iron with approximately 25% Cr and 2% C, or different types of cobalt or nickel based alloys. Also other types of material may come in question, for instance carbides or ceramics. An erosion resistant material may also be obtained by spraying a hard material, for instance, chromium carbide, onto the surface of the element 2,2' and the supporting element 7,7'. The erosion resistant material should also be temperature resistant and stand temperatures above 500°, preferably up to 800°C.

A plurality of variations and modifications of the device according to the invention are of course possible within the scope of the invention and should be easily realised by a man skilled in the art.

The invention should therefore not be looked upon as delimited by the embodiment which here has been described only by way of example and not in a delimiting purpose.

For instance, a plurality of different constructions of the sealing means are possible, and significant possibilities of varying the pressure in the draining channel 10,10'and the supply channels 11, 11'with reference to the pressure of the gas passing the blade member 3 of the guide blades 1 are also given.

Moreover, it is of course possible that the erosion resistance of the erosion resistant element 2 is localise to a certain surface or a certain surface portion of this element, and then preferably a surface or a surface portion in the area where the blade and the element 2, 2'bear on each other or are adjacent to each other and where particularly erosive conditions are found because of the particular flow conditions.