Sealing Element For A Turbo-machine

Abstract

An arrangement for packing expansion joints on turbo-machines and particularly packing the axially extending gaps provided between adjacent blading of a blade row and circumferentially extending gaps provided between each blade row and an adjacent row of blade segments which serve to provide axial spacing between adjacent rows of blading on the rotor of the machine includes two sets of packing strips inserted respectively in grooves provided along the confronting sides of the blading which establish the axially and circumferentially extending gaps that form intersections with each other. Each packing strip of each set is constituted by two layers which are shifted in a longitudinal direction relative to each other such that one layer of each strip of each set continues across each intersection while an end of the other layer of each strip of one set terminates at an intersection at the side of and is joined to the layer of the other set which continues across that intersection, thus providing a complete sealing not only along the axially and circumferentially extending gaps but also at their intersections.

Description

This invention relates to an improvement for a packing element for expansion joints on turbo-machines of the type which consists of packing strips inserted into grooves of the parts to be sealed from each other, the individual packing strips having cutouts or lobes which are fitted one into the other at least partially at mutually crossing points.

In the case of uncooled multi-stage turbo-machines there is danger, due to the pressure gradient from stage to stage, that the hot operating gases will leave the flow channel through the heat expansion joints between the parts forming the channel walls and will sweep these parts outside the flow channel. This causes, for example, rotor bodies, guide vane supports or housings to be heated up unnecessarily, owing to which they lose in strength and length of life or must be made of expensive, highly heat resistant material.

In the case of cooled turbo-machines there results a considerable loss of cooling gases through the pervious heat expansion joints, as the cooling gas admitted at higher pressure flows into the gas duct. To compensate the lost quantity of cooling gas in gas turbines, removal of a still greater proportion of cooling gas from the circulation is necessary, which in the case of gas turbines would immediately result in a perceptible loss of efficiency.

Unsealed heat expansion joints usually have within the same machine somewhat different sizes, whereby the heating in uncooled machines as well as the cooling effect in cooled machines may turn out to be different. This sometimes brings about warping at stationary or rotating parts, which later leads to damage to the machines.

For the partial elimination of these disadvantages, several different packing modes have been applied, as for example staggered arrangements of the parts or a tongue-and-groove type construction of the parts. It is also known practice in gas turbines of the axial flow type to insert between the rims of rotor and guide vanes packing elements formed of packing strips which are intended to prevent axial and radial passage of the operating medium, for which purpose packing strips are provided which are arranged one after the other in axial packing grooves. Between the individual parts packing strips extending in radial direction are also inserted which cross with the packing strips arranged in the axial direction, the packing strips being provided with tongues and cutouts at the intersections so that the parts interengage.

The disadvantages of these packing constructions are to be seen in that, although a reduction of the leakage is achieved, it is not possible to suppress free passage completely. In particular, on turbo-machine systems with a distribution of heat expansion joints over the rotor and the guide vane support like a grid, residual gaps remain at the intersections and at the butt joints of the packing strips which in accordance with the radial-axial packing of the above described type are not controllable from a sealing point of view. This again leads to the previously mentioned general disadvantages.

The principal object of the present invention is to avoid the above disadvantages and to exclude, almost completely, any leakages between the parts forming the flow channel of a turbo-machine.

The problem is solved according to the invention in that the packing strip is formed with at least two layers, the first of which is shifted relatively to the second layer in the longitudinal direction of the packing strip by at least the amount of the butt joint between the contiguous packing strips, and that the packing strips are fitted together in the circumferential direction and the axial direction, the lobes of the first layer slidingly inserted in the cutouts being covered at the intersections by the relatively offset second layer of the packing strip.

Another form of construction is characterized by an approximately elastically deformable edge zone of the individual layers of the packing strips on the sides toward the bottom of the groove.

A special embodiment of the invention provides that plastically deformable packing inserts are inserted in the groove, on the groove bottom.

An advantageous form of construction is characterized according to the invention by the length of the packing strips, which in the axial direction and in the circumferential direction corresponds approximately to the length of the parts to be sealed from each other, minus one strip width.

The advantages of the invention reside, on the one hand, in that a separate securing of the packing strips against shifting becomes unnecessary, since the packing strips are mutually anchored by the intersecting layers of the packing strips, and on the other hand, in that even the radial gaps or passageways at the intersections are sealed almost completely.

In the special form of construction with lobes and cutouts at the individual layers of the packing strips, it has been found to be advantageous that the layers have a reinforcement of the cross-section area at the intersection where the greatest radial loads and expansion forces engage.

The cooling effect is improved in cooled turbo-machines, the heat damming effect being influenced much more favorably at the intermediate sections or segments provided for this purpose, because the transfer of heat occurs now only be conduction, and not by radiation acting directly on the housing or rotor.

Another advantage of the invention is to be seen in that the packing strips are mutually strutted during every operational state by the narrow slideways of the lobes and cutouts, whereby the wear tendency is reduced.

Further it is advantageous to dimension the individual layers of the packing strips so that the edge zones of the layers are pressed one against the other during temperature rise, whereby there is formed at the packing strips an uninterrupted band of a blocking zone, which precludes the issuance of a cooling medium, for example, helium.

A major advance is achieved by the opening up of a new field of application, since such turbo-machines packed according to the invention can, for example, be installed in the direct circuit of a gas-cooled atomic reactor. Also for the transport or poisonous or corrosion-favoring substances an advantage becomes attainable, since on the one hand a loss of the cooling gas or an admixture thereof into the operating gas is practically avoided, and on the other hand the need for corrosion-proof material is considerably reduced since the parts made of corrosion-resistant material are limited to the parts coming into direct contact with the aggressive operating gas.

The invention will now be described in detail and is illustrated in the accompanying drawings with reference to a preferred mode of construction, all parts not necessary for an understanding of the invention having been omitted for greater clarity. In the drawings:

FIG. 1 is an axial section through a turbo-rotor according to prior art;

FIG. 2 is a radial section along line A--A in FIG. 1;

FIG. 3 is a top view in direction B according to FIG. 1;

FIG. 4 is a detail of the packing constructed according to the present invention;

FIG. 5 is a section along line D-D in FIG. 4;

FIG. 6 is an oblique elevation of an intersection packed according to the invention;

FIG. 7 shows a further example of construction according to the invention, in the cold state; and

FIG. 8 shows the construction according to FIG. 7 at the operating temperature of the turbo-machine.

In FIG. 1 there is marked by the reference symbol 1 the rotor of a turbo-machine, where in annular grooves 2 the blades 3 are inserted and anchored by means of their T-shaped feet 4. Between the individual blade rows 5 and 5', intermediate sections 7 are inserted in annular grooves 6; between the blade feet 4 and the intermediate sections 7 there is thus formed a gap 8, which in uncooled machines permits penetration of the operating medium into the interstice 10. Thereby the rotor 1 is heated directly by the operating medium, which is undesirable because of the disadvantages mentioned in the introduction.

In cooled machines there is supplied through the interstice 10 a medium which carries the heat away from the rotor 1 and from the blade feet 4 and intermediate sections 7. If packing arrangements are not provided, cooling gas must be supplied in large quantities and at a higher pressure than that at the point in the flow channel 11 corresponding to the respective gap 8, to suppress the unhindered entrance of hot or operating gas into the interstice 10.

To keep these gases away from the rotor 1, it has been proposed to arrange grooves 12 at the cheeks of the intermediate sections 7 and of the blade feet 4 and to insert packing strips 9 therein. At first glance it would appear that it is thus possible to seal the interstice 10 from the flow channel 11 and to improve conditions. However, it was found that with such arrangements great leakage gaps still occur, which it is not possible to provide for by the known elements, and which lead to the initially mentioned disadvantages.

FIG. 2 shows a radial section through the turbo-rotor 1 along line A--A in FIG. 1, similar parts having been marked by corresponding reference symbols. It can be seen that for the packing according to the known proposal also packing strips 9' have been provided, which are inserted in the axial direction at the circumference between the blade feet 4 and the intermediate sections not shown. For this, corresponding grooves 12' have been provided, which now extend in the axial direction instead of in circumferential direction like the grooves 12 (see FIG. 1).

If the rotor is viewed in direction B and its surface developed, there results the representation as shown in FIG. 3. The section along line C--C in FIG. 1 shows the viewer a lattice-work or grid formed by the packing strips 9 and 9'. From this it is visible that there are still passageways 15 between the butt joints 13 of the packing strips 9 and 9' and also at the intersections 14.

FIG. 4 shows a detail of a radial section through a rotor 1 on a larger scale, a packing strip 16 of the form according to the invention being inserted in the groove 12 along the circumference. The blade feet 4 are separated by the gap 8, which is blocked in radial direction by the first layer 17 of the packing strip 16. The second layer 18 thereof is displaced in the example shown by approximately one blade division in the circumferential direction. The length of the individual packing strips 16 is equal to double the division of the blade row less the strip width and double the width of gap 8. In combining blade groups into segments, the segment length is analogously taken as division. The packing strip length in the axial direction is determined in the same manner as above, except that instead of the division measured at the blade row the distance between the blade rows 5 and 5' is considered. When arranging intermediate sections 7, it is necessary to consider the dimension of the length of the packing strip by replacement of double the division by the axial length sum resulting from blade feet 4 and intermediate section 7.

Between the layers 17 and 18 of the packing strip 16 staggered in circumferential direction, the individual layers 19 and 20 of the packing strips 16' are inserted in axial direction, and this so that between the butt joints of the individual layers of the packing strips 16 a corresponding layer of the packing strip 16' is inserted crosswise.

FIG. 5 shows a transverse section of the packing strip 16 along line D--D of FIG. 4, forces which in the operating state act on the layers 17 and 18 being indicated by the arrows. By suitable design of the groove 12 or respectively of the groove bottom 21 in the blade foot 4 or respectively the intermediate section 7 it can be achieved that the layers 17 and 18 of the packing strips are pressed firmly against one another at the mutual contact areas of the edge zones 22 as soon as the edges of the packing strips get into the zone of the groove base radius. The packing strips 16 and 16' are provided at the edge zones 22, but not at the mutual contact areas of the layers 17 and 18, with a slightly rounded 45.degree. bevel. It is thereby achieved that material displaced by plastic deformation finds sufficient space to give way and that besides the gripping forces act on the edge zone 22 in an evenly distributed manner.

For better comprehension of the subject matter of the invention, there is shown in FIG. 6 a parallel perspective representation of an intersection 14. The packing strips 16 and 16' again are composed of the individual layers 17, 18 and 19, 20, which are arranged in a staggered manner relative to each other. To achieve a perfect packing, it is necessary to pack, or to avoid, also the butt joints 23 which are necessary because of the heat expansion of the material when starting a turbo-machine.

The mere staggering of the individual layers 17 to 20 of the packing strips does not, however, achieve perfect tightness between flow channel 11 and interstice 10, which in the present FIG. 6 must be conceived above or respectively below the intersection 14. The gap or joint 8 is defined by the blade feet 4 and intermediate sections 7, the thin solid lines 24 and the broken lines 25 indicating the contours of the expansion joint 8.

At the front sides of the individual layers 17 to 20 of the packing strips 16 and 16' cutouts 26 are provided, the visible representation being limited to the upper layer 17 of the packing strip 16 and to the upper layer 19 of the packing strip 16'.

At the longitudinal sides of the packing strips 16 and 16' with the layers 18 and 19 there are arranged lobes 27 corresponding to the cutouts 26. These cutouts 26 and lobes 27 are arranged in like manner with respect to all packing strip layers 17 to 20, so that expediently they can be simply exchanged for one another. This can be the case also when the axial lengths of the rotor blades are different than those of the intermediate sections 7.

Since strong gripping forces must be expected because of the heat expansion during the starting or stopping of the turbo-machine, the cutouts 26 in the individual layers of the packing strips 16 and 16' are provided with large curvatures, the radii of which preferably correspond to half the width of the cutout 26, so as to avoid as much as possible an additional notch effect at the individual layers 17 to 20 of the packing strips 16 and 16'. The lobes 27 are likewise rounded, their form being adapted to that of the cutouts 26 and the width of the lobes being chosen so that the lobes 27 are guided for lateral sliding in the cutouts 26. The width of the lobes 27 must, however, be greater in every state than the maximum width of the expansion joints 8 between parts to be packed. The length of the lobes 27 is at least as great as the butt joints 23, so that a close guiding of the lobes 27 in the cutouts 26 during every operating state is ensured.

The arrows indicate the possible path of the cooling gas or operating medium which remains open by the minimum gaps necessary for the adaptation of the gripping forces during operation. It can be seen that now any radial and axial passage of the medium is blocked in all directions.

By the almost perfect sealing of the flow channel, it is possible to admix the cooling gas at a suitable point under control, whereby the losses of efficiency resulting from the removal of cooling air are approximately compensated by the removal of cooling air. At sufficient cooling output, on the other hand, an increase of the total efficiency of the installation can be achieved by the reduction of the quantity of cooling gas.

FIG. 7 shows another embodiment of the invention, as used, for example, in gas turbine rotor packings. For packing strips 16, made of highly heat resistant materials, it is proposed to insert in groove 12 an insert 30 which simply absorbs the gripping forces by deformation and yet insures sealing.

FIG. 8 shows the same construction as FIG. 7, the difference being that the packing strips 16 and the gap 8 have been changed by the temperature rise in the materials and the insert 30 is deformed in order to improve the tightness. This is achieved because the gas no longer flows along the longitudinal gap in the bottom of the groove to the next butt joint 23 between the packing strips 16, since the packing strips 16 form a tight strip offering gapless packing at the edge zones 22 clamped in the groove bottom.

The subject matter of the invention is, of course, not limited to what is represented in the drawings. Thus, instead of the lobes and cutouts, there may be used a fitting together of the front sides of the individual layers of the packing strips in corresponding cutouts on the longitudinal side of the packing strip layers, the individual layers having toward the front areas offsets insertable one into the other.

Claims

I claim:

1. In an arrangement for packing expansion joints on turbo-machines and more particularly packing the axially extending gaps provided between adjacent blading of a blade row and circumferentially extending gaps provided between each blade row and an adjacent row of blade segments which serve to provide axial spacing between adjacent rows of blading on the rotor of the machine, the combination comprising a first set of packing strips inserted in grooves provided along those confronting sides of the blading which establish the axially extending gaps, a second set of packing strips inserted in grooves provided along those confronting sides of the blading which establish the circumferentially extending gaps that intersect said axially extending gaps, each of said packing strips of each set being constituted by two layers which are shifted in a longitudinal direction relative to each other such that one layer of each strip of each set continues across each intersection of said axial and circumferentially extending gaps while an end of the other layer of each strip of one set terminates at an intersection at the side of the layer of the other set which continues across said intersection, and means for interconnecting the strips of said first and second sets in the axial and circumferential directions at said intersections by interconnecting the ends of the layers of the strips of one set at their junctions with the sides of the layers of the strips of the other set.

2. A packing arrangement for turbo-machines as defined in claim 1 wherein said means for interconnecting the layers of the strips of said first and second sets in axial and circumferential directions are constituted by inter-engaging lobes and cutouts provided on the layers.

3. A packing arrangement for turbo-machines as defined in claim 1 wherein the layers of each said packing strip includes elastically deformable edge zones facing the bottom of the groove in which it is inserted.

4. A packing arrangement for turbo-machines as defined in claim 1 and which further includes plastically deformable inserts located at the bottom of each groove.