GB2302711A

GB2302711A - A turbine disc with blade seal plates

Info

Publication number: GB2302711A
Application number: GB9512965A
Authority: GB
Inventors: Neil Milner Evans
Original assignee: BMW Rolls Royce GmbH
Current assignee: Rolls Royce Deutschland Ltd and Co KG
Priority date: 1995-06-26
Filing date: 1995-06-26
Publication date: 1997-01-29
Also published as: WO1997001695A1; GB9512965D0

Abstract

The blades 2 of a turbine disc 1 are held in the axial direction using seal plates 4, which at the same time seal the blade root section 3 against leakage losses. The seal plates 4 are cast in such a manner that they have a directionally solidified crystal structure in the circumferential direction (7)(figure 2). In this way the stress loading of the individual components is reduced and deformation of the seal plates 4 reduced in the circumferential direction (7), whereby the size of the gaps between the seal plates (4) is kept small over the operating lifetime of the turbine.

Description

A TURBINE DISC WITH BLADE SEAL PLATES The invention relates to a turbine disc with a large number of inset blades, whose root sections are held and sealed by means of several inset seal plates inserted between the disc and blade root flanges in the direction of the circumference. DE 41 10 214A1 gives an example of the previously proposed state of the technology.

The seal plates mentioned above are set particularly into slots in the blade root flanges and into the turbine disc and act, since they are pressed by the fluid-pressure conditions within the turbine against the slot walls, especially as the sealing of the blade root sections. Any fluid leakage flow over the blade root sections on the turbine blades should thereby be avoided. However a small leakage flow can still arise and especially through the gaps between the individual seal plates. It is therefore attempted to make these gaps as small as possible, on the other hand however account must be taken of their heat expansion behaviour in the dimensioning of the individual components. Further the seal plates can deform to a small extent due to the load or stress conditions present, so that for this reason an unwanted increase of the gap size between individual seal plates can arise.

For example it has been established, that the overall gap size between the seal plates increases with increasing turbine operating time, and that this is under the influence of pressure loading in the peripheral direction.

This pressure loading in the peripheral direction is disadvantageous apart from this insofar as the resultant loads or stresses are introduced into the blade root flanges and via these to the blade root sections. In this way, but also directly, these loads or stresses reach into the disc and lead generally thereby to an increased loading of these components, particularly due to the increased radial loads or stresses.

It is therefore an aim of the present invention to provide improvements to the seal plates, by which on the one hand better sealing, and on the other hand lower stress loading, result.

To address this task it is foreseen that the seal plates are cast in such a manner that they exhibit a directionally soldified crystal structure in the circumferential direction.

The casting technique for directionally solidified casting is known in turbine blades. An example is described in DE-OS 29 01 724. If then this known casting technique is applied to the seal plates in the manner described, then this results in a reduced modulus of elasticity (Young's Modulus), due to the crystal grains being oriented in the circumferential direction. Because of this lower peripheral loads or stresses are set up in the annularly adjacent seal plates, which again generate the radial loads or stresses explained above in the blade root flanges, the blade root sections and the turbine disc itself only to a reduced extent. The reduced peripheral load or stress again results in lower plastic deformation of the seal plates, so that an improved sealing is thus set up, since the increase in the gaps between the seal plates now occurs to a lesser extent.

The attached Figures, described below show an example of a segment of a turbine disc with seal plates according to the present invention and an advantageous further development of the present invention.

In Figure 1 a turbine disc 1 is shown in section. In this turbine disc 1, distributed around the circumference, several blades 2 are assembled, as is known. As is usual the root section 3 of the blade 2 shown exhibits a fir tree profile. In the axial direction of the turbine disc 1 the blades are held using several seal plates 4, which are assembled similarly in a circumferential direction between the turbine disc 1 and the blade root flanges 5 and thus form an essentially closed ring.

Figure 2 shows the elevation X from Figure 1 of an individual seal plate 4. On both edges 6a, 6b of each seal plate lie the neighbouring seal plates 4, which are not shown1 so that, however, a narrow gap appears between neighbouring seal plates, which was explained fully in the introductory description and via which a leakage air flow can penetrate the necessary fluid in the turbine.

As explained, the seal plates are cast in such a manner that they exhibit a directionally solidified crystal structure, i.e. in the direction of the arrow 7. As already explained the sealing effect is noticeably increased thereby, and the stress loading on the individual components noticeably reduced. An increased lifetime for these components results. Further in the slots 8a, 8b in the turbine disc 1 and in the blade root flange 5, in which the seal plates 4 are inserted, protective strips 9 can be provided to prevent friction wear. These protective strips 9 are preferably provided between the rear side of each seal plate 4 and the corresponding slot wall, since the chief pressure conditions arise on this side of every seal plate 4. These protective strips 9 can be renewed at a drive unit overhaul, however these as well as other details can be formed deviating completely from the example of embodiment shown, without abandoning the scope of the claim.

Claims

CLAIMS:

1. A turbine disc with a multiplicity of inset blades (2), whose root sections (3) are held and sealed by means of several inset seal plates (4) inserted between the disc (1) and blade flanges (5) in the direction (7) of the circumference, characterised in that the seal plates (4) are cast in such a manner that they exhibit a directionally solidified crystal structure in the circumferential direction (7).

2. A turbine disc according to claim 1, characterised in that the seal plates (4) are inserted into the turbine disc with protective strips (9) interposed to prevent friction wear in the slots (8a, 8b) in the turbine disc (1) and/or in the blade root flanges (5).

3. A turbine disc substantially as described herein with reference to the attached drawing.