Sealing ring for turbo machines

Abstract

A sealing ring for a turbo machine to limit and define the radial clearance between the outer edge of a turbine disc and its corresponding stator part is disclosed. The sealing ring is divided into discrete sealing block segments, each comprising a smooth metallic inner strip, an intermediate corrugated metallic strip, and a bundle of flat metal plate layers, with provision for cooling air to be introduced and distributed through each segment.

Description

BACKGROUND OF THE INVENTION

For satisfactory efficiency in the operation of a turbo machine (turbine or compressor), it is vital that the clearance between the tops of the rotor blades and the surrounding stator parts be kept as small as possible. Contact between the rotor blades and the stator, however, might cause considerable damage, and must be avoided. Fluctuating temperatures in the rotor, blades and stator, as well as different rates of heating or cooling induced by changing operating conditions, cause uneven thermal expansion or contraction of the various turbine parts and hence the top clearance gap may vary considerably. In order to avoid the complete disappearance of this clearance gap under the most unfavorable temperature combinations and conditions, the nominal clearance provided must often be chosen so large that the turbine opration is rather inefficient when normal operating conditions prevail.

To improve the above situation, special sealing and screening elements have been provided, the radial position of which is determined by the stator, and the function of which is to screen off the stator from the hot turbine gas and maintain it at a low temperature during turbine operation. In this manner, variations in the temperature in the stator which determines the clearancce are reduced, and the ability to maintain a minimum safe clearance is greatly enhanced.

SUMMARY OF THE INVENTION

The present invention is directed toward a novel improved construction of the aforementioned sealing and screening elements, and provides a sealing device in the form of ring segments, or "blocks", arranged around the stator housing with small peripheral gaps for expansion between segments.

Each sealing block comprises a stack of flat sheet metal layers mounted on a corrugated metal strip, which in turn is supported on a smooth metal strip facing the turbine rotor. Suitable cooling air passages are provided within this assembly to counteract the heat from the turbine gas. The novel construction incorporated into these block segments supplies flexibility and at the same time satisfactory cooling of both the sealing ring and the surrounding stator parts.

Since the successful application of such sealing block segments is strongly dependent on temperature variations between stator and rotor, the use of the block segments of this invention is particularly successful in gas turbines. However, even in steam turbines and turbo compressors, temperature conditions are such that considerable demands are placed on the sealing rings, and hence this invention is of importance for all types of turbo machines.

The present invention will be further described with reference to the accompanying drawings, and defined by the accompanying claims.

DRAWINGS

In the drawings,

FIG. 1 is a sectional view through part of a turbo machine utilizing a sealing ring constructed in accordance with this invention;

FIG. 2 is an enlarged, more detailed view of the sealing ring block and its mounting shown in FIG. 1;

FIG. 3 is a developed view of a sealing ring block seen in axial direction, and with successive layers removed to show the inner construction;

FIG. 4 is a view of the sealing ring block of FIG. 3 as seen in radial direction from the outside; and

FIG. 5 is a view similar to FIG. 3 but showing an alternate embodiment of the sealing ring structure of this invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

In FIG. 1, part of turbine rotor disc 10 is shown with a vane 11 projecting radially therefrom. Guide vane 12 is secured at its head 13 to a flange 14 in stator housing 15. Turbine disc 10 is circumferentially encompassed by the sealing ring 16 of this invention, to ensure that a minimum of gas or steam leaks between rotor disc 10 and stator housing 15, and therefore to maintain a gap 17 between vanes 11 and sealing ring 16 as small as possible consistent with avoiding any contact or catching of vanes 11 by sealing ring 16. To control the variations in gap 17 which might be created by fluctuating temperatures in turbo machine operation, sealing ring 16 is constructed of arcuate stacks of sheet metal plates with provisions for cooling, as will be more fully described hereinafter. Attachment ring 18, secured to head 13 of guide vane 12, maintains sealing ring 16 in position, as shown in fuller detail in FIG. 2.

Attachment ring 18 has flanges 19 and 20 which, in combination with rivets 21, hold together the stacks of sheet metal plates 3, 4 and 5 of sealing ring 16. Each stack of plates forms a block or segment; a plurality of these blocks, arranged circumferentially between flanges 19 and 20 of attachment ring 18 and held in place by rivets 21, together form sealing ring 16 and are spaced from each other with a slight gap to permit peripheral expansion. During operation of the turbo machine, the block segments of sealing ring 16 are cooled by air which is forced inwardly through a cooling channel 22 formed in attachment ring 18 and is then distributed over and through each block.

FIGS. 3 and 4 clearly illustrate the construction of block segments which form sealing ring 16. For simplicity and clarity, FIG. 3 is shown as a developed straight view, but in reality each block segment is arcuately curved so that it forms one sector of ring 16. The main body of each sealing block comprises a bundle of parallel flat sheet metal plates oriented perpendicularly to the turbine shaft, the outermost layer on each side of the bundle being a series of substantially rectangular cover plates 5. Between the two cover layers 5, alternate layers of differing plates 3 and 4 (to be described below) are sandwiched to complete the bundle or stack. The radially innermost end of each sealing block of ring 16, adjacent to rotor 10, is faced with a smooth metal strip 1, on which a sinuously corrugated metal strip 2 is superposed. Strips 1 and 2 are attached to each other along their lines of contact by such conventional means as, for example, point welding. Plates 3 and 4 are shaped at their inner edges to follow generally the curvature of corrugated strip 2.

It can be observed in FIG. 3, where successive layers of plates have been removed from left to right to show the interior plates of a sealing block segment, that outer cover plates 5 are substantially rectangular and extend the entire height of the block. Behind the cover layer 5 is a layer of plates 3, each shaped with a peak extending into and secured to one of the radially inward depressions of corrugated strip 2, preferably by point welding. Except for these secured peaks, the inner edges of plates 3 are spaced from corrugated strip 2, providing cooling gaps 6 therebetween.

Analogously, the next successive layer of plates 4 are shaped to contact and be secured in the same manner to the radially outward peaks of corrugated strip 2, while the remaining inner edge surfaces of plates 4 are spaced from strip 2, thus also forming cooling gaps 6. The interruption of cooling gaps 6 by welded contact points forces cooling air on its way along corrugated strip 2 to cross over constantly between the metal layers 3 and 4, ensuring efficient cooling of strip 2 and the inner portions of plates 3 and 4. The cooling air emerges from cooling gap 6 into space 7 between adjacent sealing blocks.

As previously described, the cooling air is introduced into sealing ring 16 through channel 22 in attachment ring 18. Plates 4 are made shorter in height than plates 3, between which air distribution channels 8 are thereby formed. At either end of each sealing block and in each plate 4 layer, plates 4a, similar to plates 4 but of a height equal to plates 3, serve as end boundaries to channels 8, while the radially outward limit of these channels 8 is defined by attachment ring 18.

In addition, plates 3 are omitted from their layers in the area of air introduction channel 22, so that a transverse connection between distribution channels 8 is created, as well as openings 9 down through the sealing block for direct communication with cooling gaps 6 along corrugated strip 2.

During operation of the turbo machine, it is evident that smooth metal strip 1 comes into direct contact with the hot gas or steam in vanes 11 and 12 so that strip 1, which receives substantially no cooling, assumes the ambient temperature and correspondingly expands. This causes corrugated strip 2 to be straightened out somewhat and plates 3 and 4 are slightly separated from each other so that cooling air from distribution channels 8 can penetrate between the plates along the entire sealing block providing uniform and efficient cooling, the cooling process becoming more effective the more strip 1 is expanded by increasing temperature. Spaces 7 between adjacent sealing blocks permit this expansion freely, like the rail gaps in a railway track. Flanges 19 and 20 of attachment ring 18 may be interrupted as shown in FIG. 4 so that they overlap spaces 7.

It should be noted that in FIG. 4, for clarity, the boundary lines between different layers of sheet metal, as well as between metal sheets and spaces, have been drawn in heavy lines, while the boundaries between similar sheets are designated by lighter lines.

As may be seen in FIG. 2, a groove 23 in attachment ring 18 may be provided in order to assist in the distribution of air from channel 22 to the sealing block segment.

It has been noted above that, although shown straight in FIG. 3, each sealing block segment is in reality arcuate, constituting a sector of sealing ring 16. For this purpose, plates 3 and 4 may be shaped with non-parallel converging side edges so that they automatically form a ring sector when the plates for each layer are fitted together. Alternatively, it is possible to make all the plates with parallel edges so that narrow wedge-shaped spaces formed between the plates in any layer will permit cooling air to pass from distribution channels 8 toward cooling gaps 6. The latter arrangement makes it possible to use the same plates for sealing rings of different diameters.

Each block segment of sealing ring 18 is formed by providing the sheet layer 3, 4 and 5 with holes to accept rivets 21, and its shape when mounted is determined by the curvature of flanges 19 and 20 of attachment ring 18.

In the embodiment of the inventive sealing ring 16 of FIGS. 1-4, and as clearly shown in FIG. 3, the radial height of each block segment is defined by the height of plates 3. Since plates 3, attachment ring 18 and stator housing 15 are all cooled to a certain known temperature, only the temperature expansion of rotor 10 need be considered when determining the size of gap 17 between vanes 11 and sealing ring 16.

FIG. 5 illustrates an alternate embodiment of a sealing block segment, in which plates 4' correspond to plates 4 but have full height. In this construction, when the sealing block segment stretches peripherally due to the expansion of strip 1, it shrinks radially, since, as corrugated strip 2 is stretched and straightened, high plate layers 4' are pulled down between low plate layers 3'. By suitable dimensioning of the corrugations in strip 2 in relation to the coefficient of expansion of strip 1, this feature can be exploited to predetermine the width of gap 17 between stator sealing 16 and rotor vane 11, and thus to maintain gap 17 at a constant minimum value with varying temperature and load in the turbo machine.

For compressors and gas turbines, the cooling of the block segments of sealing ring 16 is preferably accomplished by providing compressed air to channel 22, whereas for steam turbines, cool steam of suitable pressure may be employed.

Claims

I claim:

1. Sealing ring for a turbo machine for limiting and defining the radial clearance between the outer edges of the vanes of a turbine rotor disc and the corresponding stator housing, the sealing ring being composed of a plurality of sealing block segments which are mounted circumferentially on the stator housing, spaced from each other by peripheral gaps, cooled by air flowing through them, and which comprise:

a smooth arcuate metallic strip on the inner surface of each sealing block segment facing the turbine rotor disc;

a sinusoidally corrugated metallic strip mounted on the radially outward side of said smooth metallic strip so that its inner corrugations are secured to said smooth metallic strip along the lines of contact between said two strips; and

a stack of parallel flat metallic sheets mounted on the radially outward side of said corrugated metallic strip, the faces of said metallic sheets being oriented transversely to the corrugations of said corrugated metallic strip and perpendicular to the turbine shaft, said metallic sheets being divided into sectors having a width corresponding to the pitch of the corrugations of said corrugated strip, the inner edge contour of said sheet sectors being so adapted to the shape of said corrugated strip that a channel for cooling air is formed between said corrugated strip and sectors of said sheet stack.

2. Sealing ring according to claim 1, further comprising:

a pair of sheet layers for each sealing block segment each divided into sectors, positioned as a cover layer on either side of said sheet stack and extending radially outwardly from said smooth metallic strip to the outer periphery of the sealing block, thereby sealing the block and said cooling channel on both sides.

3. Sealing ring according to claim 1, wherein said sheet sectors in each layer of said sheet stack are displaced half the pitch of the corrugations of said corrugated strip with respect to the sectors of the adjacent sheet layer.

4. Sealing ring according to claim 3, wherein the radially inwardly directed point of each said sector in every second sheet layer of said sheet stack is attached to the bottom of the corresponding corrugation in said corrugated strip, while the alternate sheet layers of said sheet stack are attached at each of their said sectors to the radially outward top of the corresponding corrugation in said corrugated strip.

5. Sealing ring according to claim 1, wherein in every second sheet layer of said sheet stack the radial height of said sectors is less than the radial height of said sectors in the alternate sheet layers, so that distribution channels for cooling air are formed between the sheet layers in the outward portion of each sealing block segment, all said sectors at the ends of each block segment having full radial height to close said air distribution channels at their ends.

6. Sealing rings according to claim 1, wherein cooling air is supplied to each sealing block segment through an air introduction channel in the stator, and wherein said sectors of the layers of said sheet stack in an axial zone adjacent to said air introduction channel are formed with reduced radial height, to distribute cooling air over each sealing block.

7. Sealing ring according to claim 1, wherein cooling air is supplied to each sealing block segment through said air introduction channel in the stator and, in order to provide for passage of cooling air to said channel between said corrugated strip and said sheet stack, a suitable selected number of said sectors of the layers of said sheet stack are omitted.