GB2228217A - A method for connecting turbine wheel discs - Google Patents

Description

1 A METHOD FOR CONNECTING TURBINE WHEEL DISCS The i discs.

nvention relates to a method for connecting turbine wheel In modern turbojet propulsion units,, in the interests of reducing weight, components and sub-assemblies are used which are manufactured from titanium or titanium alloys, in fact particularly for the compressor or fan. For example, where the high-pressure compressor of the gas generator in a propulsion unit is concerned, temperature and other stresses become so great at the final stage or stages of the compressor that they can no longer be accommodated by components. particularly wheel discs, which are made from titanium or titanium alloys; therefore, a relatively early onset of material cracks and the risk of fractures must be expected. In other words, therefore, the admissible creep and temperature stress limit is established at a temperature level of 5000C. for example in the case of a titanium-based alloy; on the other hand, there are far higher outlet or final temperatures at the compressor (70CC and above) which inter alia have to be controlled, with regard to the admissible material creep limit, due to ever pressing need to increase the final compressor pressures in order to reduce fuel consumption. For these reasons, it is necessary for the wheel discs which in practice are stressed comparatively more highly in the case of the compressor, in the region of at least the final compressor stage or stages, to be manufactured from suitable metallic alloys, e.g. from a nickel or nickel-based 2 alloy capable of coping with the correspondingly higher demands made of the materials, in terms of satisfactory creep properties.

In order to be able to exploit to the greatest possible degree the advantage of weight saving which is made possible by using titanium or titanium alloys in the admissible temperature and force loading range, therefore, titanium nd nickel wheel discs have to be connected to each other at a suitable point f or optimum operation. With conventional equivalent material pairings, this is readily possible by conventional welding processes, the rotor discs for example being connected to one another by welded-in intermediate rings. For instance, by way of electron beam welding, the individual wheel discs can be connected to one another in an extremely rational manner to constitute a rotor drum. This rational method of connection cannot however be employed in the case of dissimilar material partners (e.g. intermediate ring of nickel or a nickel alloy, wheel disc or titanium or a titanium alloy). So far, it has not been possible to establish an intimate and durable connection; brittle phases showed themselves in the area of the welded seam; also, the comparatively prolonged welding processes and the heat expansion differences of the two comparatively extremely different types of material which become noticeable during welding obviously stood in the way of a durable connection.

DE-PS 25 10 286 discloses a method of producing a blade-disc connection in which a wheel disc made predominantly from steel 3 is supposed to be welded to a blade made predominantly f rom, titanium via a plate-like composite (titanium/steel) part, the composite part being itself produced by blast welding. This prior art case is not however concerned with a serially optimum possibility of producing a connection between rotor wheel discs to make a rotor drum which can accommodate the extreme temperature and material stress variations and thus widely dissimilar wheel disc materials (titanium or titanium alloy/nickel or nickel alloys) while at the same time ensuring maximum possible utilisation or maintenance of the weight advantage of titanium or titanium alloy in a common turbocomponent, e.g. a compressor.

One object of this invention is to provide a method of the type mentioned at the outset wherein, by selecting and disposing wheel disc pairings (titanium or titanium alloy/nickel or nickel alloys or nickel-based alloy) which are capable of accommodating different operating stresses, an operationally reliable wheel disc connection can be achieved that is readily applicable to series production.

According to the present invention, we propose a method f or connecting together turbine wheel discs particularly though not exclusively, of a compressor rotor, of dissimilar metallic materials such as for example, titanium or a titanium alloy on the one hand and nickel or a nickel or nickel-based alloy on the other, the method comprising forming a doublering member having concentric rings of said dissimilar materials secured together 4 by blast welding and welding each ring to the disc of the same or similar material as the ring.

In the preferred embodiment the double-ring member is formed by cutting a suitable length f rom a double-tube f ormed by blast welding together a first tube of the titanium or titanium alloy and a second tube of the nickel or nickel alloy, arranged concentrically one within the other. After cutting to length the double-ring member is machined as required.

Thus, it is possible to produce the compressor and/or turbine rotors on the wheel disc side with an eye to a still acceptably good creep limit from titanium or a titanium alloy and where the creep limit of the titanium (or titanium alloy) is exceeded, to use one or a plurality of wheel discs of nickel or a nickel alloy.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which:

Fig. 1 shows in cross-section the connection between a wheel disc consisting of a titanium alloy and belonging to the penultimate compressor stage to a wheel disc consisting of a nickel alloy and belonging to the final stage of the compressor; Fig. 2 shows some of the steps in the process of manufacture, with reference to an upper half, shown as a longitudinal section, of a double tube where the component parts ?i 1 are connected to each other by blast welding and with doublering members which can be separated therefrom; and Fig. 3 shows, extending in an axial direction, a profile section through a double-ring member obtained by the separation according to Fig. 2 and machined to the desired dimensions to constitute an intermediate rotor ring, the double-ring member being provided with an external sealing comb (labyrinthine seal).

Fig. 1 illustrates the connection which has to be made between a wheel disc 1 of the penultimate compressor stage and which is made from a titanium alloy and a wheel disc 2 of the final compressor stage and produced from a nickel alloy. On the wheel discs 1 and 2 are blades 3 and 4. Blades 6 belonging to the final compressor stage are mounted on the outside of the compressor housing 5. Fig. 2 shows a double-ring member 7 which in this case is finished to constitute an intermediate ring, and which is composed of two annular components 8, 9.

For series production and having regard to the high operational reliability of the connection between the dissimilar wheel disc partners, the initial "double-tube production,' is particularly advantageous; from the outset, it permits of dimensional tenability (wall thicknesses) to what will subsequently be the installation and connection requirements; furthermore, it permits of a surface-wise favourable and homogeneous welding of long components (blast welding or explosive welding) involving the two tubular cylinders; therefore, it is possible to accept 6 the premise that the composite or double-ring members which are separated f rom the double tube will be absolutely rigidly and structural intimately connected. After appropriate finishing, a composite part is available which can on the titanium side be bonded to the associated like or similar-material wheel disc and on the nickel side bonded to the associated like or similarmaterial wheel disc by the application of conventional welding processes (diffusion, fusion or friction welding) without any difficulty.

In the course of the machining to shape, but possibly also when cutting to length the relevant composite parts or double-ring members, a local over-dimensioning may be taken into account in order to compensate for any localised shrinkage of material or fluctuations in form resulting from the subsequent welding-in process.

Other features of the invention are set forth in the appendant claims.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which; To produce such a double-ring member a double tube 10 is formed by inserting one tube 11 co-axially within another tube 12.

These tubes are joined to each other by blast welding along the line S; one tube 11 is made from titanium or a titanium alloy while the other tube 12 is made from nickel or a nickel alloy or 7 possibly a nickel-based alloy.

Once this double tube 10 has been produced, double-ring members 7 or 13 and 14 which are structurally intimately rigidly and reliably securely joined to each other by the blast welding process are cut from the double tube 10 to the required overall length (course dimension) along the lines L,, L2 and L3.

In the next stage, the double-ring member 7 according to Fig. 3 can be machined to the required intended dimensions, preferably by a cutting process. In keeping with the disposition and demands requirements according to Fig. 1, the machining process according to Fig. 3 is preceded by a spatially offset localised construction of the lateral ends with end faces El, E2 of one and of the other annular components 8, 9.

The machining according to Fig. 3 furthermore includes the construction of a labyrinthine- like sealing comb K on the one annular component 8 which is shown here.

Following machining, the relevant double-ring member 7 (Fig. 3) is welded along the laterally outer end faces El and E2 to confronting and laterally projecting wall portions 131, 141 (Fig 1) on the week discs 2, 1, e.g. by fusion or friction welding or by some other current welding process such as for example electron beam welding; in other words, the one or here upper component 8 which consists for example of a nickel alloy is welded along El to the same or similar partner (wheel disc 2 of 8 nickel alloy) while the other or here lower component 9 which consists for example of a titanium alloy is welded along E2 to the same or equivalent partner (wheel disc 1 which consists of a titanium alloy).

The blades 6 shown in Fig. 1 are assembled to form a conductive 0 grid with an inner ring 15 which carries a run-on lining cooperating with the labyrinthine seal K (Fig. 3); the result is a rotor/stator seal.

Particularly with regard to the cutting shaping of the outer ring component 8 (Fig. 3) as a rotating part of a labyrinthine seal (sealing comb K), even at the production stage of the double tube 10 (Fig. 2), the wall thickness Wl of the individual tube 12 was advantageously chosen to be greater than that of the other individual tube 11.

To carry out the blast welding connection according to Fig. 2, it is possible to use for the inner tube 11, for example, a titanium alloy, also referred to in technical jargon as a socalled "wrought titanium alloy". The chemical composition (proportions as a percentage of the mass) of this alloy might be as follows: A-1=6; Mo=2; Sn=2; Zr=4 possibly with traces of C; Fe; N2; 02 and Si, the balance being titanium=85. The relevant wheel disc 1 can be produced from this or from a similar equivalent titanium alloy.

For the outer tube 12 it is possible to use a highly heat- 9 resistant nickel alloy which is suitable for a cutting type of shaping or machining process. The chemical composition of this alloy may be substantially as follows: Ni=50; M=3; Nb+Ta=5; Ti=l; Al=0.5; Co=0.5; Cr=18 along with traces of inter alia C; Si; Mn; P; S and Ag, the balance being Fe=20%. The relevant wheel disc 2 (Fig. 1) can be produced from this or from a very similar or equivalent nickel alloy.

Claims (9)

CLAIMS:

1. A method for connecting together a wheel disc of a turbine, particularly of a compressor rotor. of titanium or a titanium alloy and a wheel disc of a nickel alloy, wherein a first tube of titanium or a titanium alloy and a second tube of nickel or a nickel or nickel based alloy concentric therewith are joined together by blast welding to form a double tube from a portion of which a double-ring member is formed, and wherein the titanium part of the double-ring member is welded to the titanium or titanium alloy wheel disc and the nickel part of the doublering member is welded to the nickel or nickel alloy wheel disc.

2. A method according to claim l., wherein welding of the double-ring member to the associated like or similar material wheel disc partner is carried out by fusion or friction welding.

3. A method according to claim 1 or 2, wherein the doublering member is machined particularly by a cutting process, to desired dimensions prior to being welded to the wheel disc.

4. A method according to any preceding claim wherein intermediate rotor rings are produced from the appropriate double-ring members.

5. A method according to any preceding claim wherein a portion of a double-ring member forms the rotating part of a rotor/stator 4 seal.

6. A method according to any preceding claim wherein the double tube (10) is produced from two tubes (11, 12) of different wall thickness, the portions (8) of a double-ring member (7) which are provided with a sealing member contour being produced from the tube (12) which has the relatively greater wall thickness (W1).

7. A method according to any preceding claim wherein the double-ring member is so machined that there are spatially staggered surface portions of one and of the other portion (8,9) which can be matched and welded to superficially flush and cooperating rotor portions (131, 141) of one or other of the wheel discs (2, 1) of like or equivalent material.

8. A method for connecting together turbine wheel discs of dissimilar materials, the method comprising forming a doublering member having concentric rings of said dissimilar materials secured together by blast welding, and welding each ring to the disc of the same or similar material as the ring.

9. A method for connecting together turbine wheel discs substantially as hereinbefore described with reference to the accompanying drawings.

1 Published 1990 at The Patent Office. State House. 6671 High Holborn. London WC1R4TP.Purther copies maybe obtained from The PatentOfficeSales Branch, St Mary Cray. Orpington, Kent BR5 3RD Printed by Multiplex techniques ltd. St Mary Cray, Kent, Con 1'87