Compressor rotor wheel for turbomachines

(56) Documents cited GB 1497360 (58) Field of search F1C F1T (71) Applicants

Motoren-Und TurbinenUnion Miinchen GmbH, Postfach 50 06 40, 8000 Miinchen 50, Germany, Fed. Rep. of Germany (72) Inventor Wolfgang Weiler (74) Agents

F. J. Cleveland & Company (54) Compressor rotor wheel for turbomachines (57) The rotor wheel comprises a shell 2 with integral blades 1 formed of a heat-resistant metal, e.g. titanium alloy, and rotor disc portions 5 and 6 formed of a high-strength metal, e.g. martensitic steel, each disc portion being connected to the shell by a steel ring (e.g. 13) which is bonded to the shell by explosion welding 14 and to the disc portion by brazing or welding 15. Instead of being brazed or welded directly to the disc portion, the steel may be brazed or welded to a further steel ring which has been bonded to the disc portion by explosion welding.

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GB2 024 959A

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GB 2 024 959 A

SPECIFICATION

Compressor rotor wheel for turbomachines

This Invention relates to compressor rotor wheels for turbomachines, and more particularly to centrifugal compressor rotor wheels, the wheels comprising a blade portion made of a heatresistant metallic material and a rotor disk portion made of a high-strength metallic material, there being a coaxially extending steel connection provided between the blade region and the disk region. Such a rotor wheel is called a compressor rotor wheel of the kind referred to below.

Small gas turbine engines of both the turbojet and the turboshaft configurations are normally fitted with centrifugal or combined axial-radial flow compressors. While such engines may occasionally come recommended for their rather attractive specific fuel consumptions and power weight ratios their acceleration capability at abrupt load changes often leaves room for improvement. This is attributed to the fact that the polar moment of inertia of the rotor, by its very ' conception, is higher than with gas turbine engines having a straight axial-flow compressor where the centrifugal compressor normally carries the largest single share.

Various recommendations made in an attempt to reduce the polar moment of inertia of centrifugal compressor rotor wheels seek their solutions by breaking the monolithic rotor wheel ' down into several assemblies. In one such proposal a rotor blade portion comprising a bladed shell is self-supported and is connected to the disc portion or hub by no means other than flexible and/or inter-locking elements. There are obvious limitations on the use of this construction at elevated speeds and temperatures.

Other solutions have been proposed in which the monolithic rotor wheel is broken down into blades, the shell carrying the blades, and disks absorbing radial forces, where the various constituent parts are optimized for their specific functions and are then brazed together. Owing to the brazing properties of suitable materials, all constituent parts are necessarily made of highstrength, i.e. similar materials. This means, however, that the outer and more moderately stressed zones, which nevertheless comprise the major portion of the moment of inertia of a centrifugal compressor rotor wheel, must equally be made of steel although materials of less density, such as titanium, would fully do the job at these locations.

An object of the present invention is to provide a compressor rotor wheel of the kind referred to which, using dissimilar materials for the blade portion and for the disk portion that cannot be brazed and/or welded together conventionally, will be low in mass and inertia.

According to one aspect of this invention there is provided a compressor rotor wheel of the kind referred to, wherein the steel connection comprises a ring of steel which is connected on one side to the blade portion by explosion welding and on the other side to the rotor disk portion by brazing or welding.

One embodiment of the present Invention comprises a compressor rotor wheel, especially a centrifugal compressor rotor wheel which is low in mass and inertia and which comprises two or more portions, where blades and a shell carrying them are manufactured as an integral part from a suitable heat-resistant alloy of low density, such as a titanium alloy, and where the load-bearing disk-like parts are made of a high-strength material, such as a martensitic steel alloy. In this arrangement the parts are joined together each via one, conceivably segmented, spacer ring of steel explosion welded to the bladed shell and then brazed to the load-bearing disk-like parts or conceivably connected to these parts by fusion or friction welding.

The use of the explosion welding process to join steel and titanium alloys together is being practiced in the construction of chemical apparatus, where it is used to produce perfect surface area connections of relatively thin titanium panels to steel components. Explosion welding has also been referred to In German Patent Specification No. 25 10 286.

The extremely brittle zones known from various experiments exploring the intimate connection of steel to titanium parts by brazing and diffusion, friction or electron beam welding to occur in the joint area are avoided because the explosion welding process is extremely fast.

According to another aspect of this invention there is provided a method of manufacturing a compressor rotor wheel comprising a blade portion made of a heat-resistant metallic material and a rotor disk portion made of a high-strength metallic material, wherein a ring of steel is connected on one side to the blade portion by explosion welding and on the other side to the rotor disk portion by brazing or welding.

Preferably the explosion welded joints are made before the bladed shell is machined, said shell being optionally machined from the solid, cast or manufactured powder metallurgically. Should explosion welding cause inaccuracies these can be eliminated in the course of mechanical machining aimed at preparing the abutting areas between the spacer ring and the load-bearing disk-like parts. These corrections may conceivably be made also when the rotor wheel is finish, machined, when especially the rear wall of the wheel is worked down mechanically or electrochemically in the outer diameter area to a minimum wall thickness imposed by the risk of deformation and/or by manufacturing requirements.

Preferably the load-bearing disk-like portions are made of a high-strength titanium alloy. Where the disk portions are joined to the bladed shell via two, conceivably segmented, spacer rings of a steel alloy, the rings are first joined by explosion welding to the respective adjacent component and then brazed or conceivably welded together.

The purpose of the steel spacer rings between

GB 2 024 959 A the two major assemblies made of dissimilar titanium alloys is to avoid brittle areas which would be inevitable when the parts are welded together. When they are brazed together, the difficulties resulting from the propensity of 70 titanium for oxidation are eliminated, and the problems posed by the dissimilar heat treatments used in the aging of the finished assembly composed of dissimilar titanium alloys are alleviated by suitable selection of the braze alloy 75 and the brazing temperature.

Two forms of centrifugal compressor rotor wheel in which this invention is embodied are described now by way of example with reference to the accompanying drawings, in which:— 80

FIG. 1 is a half section of one form of centrifugal compressor rotor wheel sectioned in a plane which contains the axis of the wheel; and

FIG. 2 is a view similar to Figure 1 of another form of centrifugal compressor wheel. 85

FIG. 1 shows a centrifugal compressor rotor comprising a shell 2 carrying centrifugal compressor rotor blades 1 and being formed as an integral part from a suitable, heat-resistant alloy of low density, such as a titanium alloy. Together 90 with the centrifugal compressor rotor blades 1, this shell 2 is made as a casting, is machined from the solid or is manufactured powder metallurgically.

At two axially and radially spaced-apart 95 locations 3 and 4, the shell 2 is connected to rotor disk portions 5 and 6 via steel connections. Each portion 5 and 6 exhibits axially projecting annular portions 8 and 9,10 and 11 which extend coaxially to the rotor centerline 7. The two rotor 100 disk portions 5 and 6 are welded together at a location 12 lying between the two annular portions 8 and 11.

A steel spacer ring 13 is initially joined to the shell 2 by an explosion welding process to form an 105 explosion weld 14.

Following removal of any inaccuracies possibly caused by the explosion welding process and perhaps after finishing the shell 2 carring the centrifugal rotor blades 1, the shell 2 is welded or brazed to the rotor disk portions 5 and 6, respectively. The brazed or welded joint between 110 the spacer ring 13 and the respective associated rotor disk portion 5 is indicated by the numeral 15.

The connection of the shell 2 to the rotor disk portion 6 at the location 4 is made in the same manner and sequence used at the location 3 as 115 just described.

The rotor disk portions 5 and 6 are made of a high-strength steel alloy. The relatively thin-walled, shell 2 is provided with additional stiffening ribs 16 which are optional. 120

Parts of the rotor shown in Figure 2 that are similar to like parts of the rotor shown in Figure 1 are identified in this specification by the references that were used in their description with reference to FIG. 1. However, two steel spacer 125 rings are provided for the connection at each of axially and radially spaced locations 17 and 18.

The first step taken in the manufacture of the blade-to-disk connection at the location 18 is an explosion weld operation, where a spacer ring 19 is first joined to the shell 2 by explosion welding to ^;form an explosion weld 21 while on the other side another spacer ring 20 is first joined by explosion welding to the respective rotor disk portion 5, to * form another explosion weld 22. The rings at the location 17 are similarly joined to the shell 2 and the rotor disk portion 6 by explosion welding.

The shell 2 is brazed or welded to the rotor disk portions 5 and 6, respectively, by brazing or welding the two rings of the connection together, only after the shell 2 is finish machined and inaccuracies possibly caused by the explosion welding process have been eliminated. The respective braze or weld joint between the two ,.

spacer rings 19 and 20 is indicated in FIG. 2 by the numeral 23.

The preferred form of rotor wheel illustrated in {

FIG. 2 is suited for a blade-to-disk connection · where the major components of the rotor, which would here be the shell with its centrifugal compressor rotor blades 1 on the one hand and the rotor disk portions 5 and 6 on the other, are made of dissimilar titanium alloys, namely, from a suitable temperature-resistant alloy for the shell 2 and the blades 1 on the one hand and from a highstrength titanium alloy for the load-bearing rotor disk portions 5 and 6, respectively, on the other.

The spacer rings 13, 19 and 20 of the wheel shown in FIG. 1 or FIG. 2 may optionally be composed of various ring segments.

As will further become apparent from the drawings the spacer rings 13 or 19 and 20 are arranged at a relatively steep or obtuse angle with the rotor centerline 7 to provide relatively large welding or brazing faces for relatively high strength of the respective blade-to-disk connection.

The invention is applicable to the rotor wheel of a gas turbine engine having combined axial-radial flow compressors as well as to turbochargers.