GB2084262A

GB2084262A - Improvements in rotary machines

Info

Publication number: GB2084262A
Application number: GB8125641A
Authority: GB
Original assignee: Rockwell International Corp
Current assignee: Boeing North American Inc
Priority date: 1980-09-19
Filing date: 1981-08-21
Publication date: 1982-04-07
Also published as: FR2490721B1; DE3125469A1; DE3125469C2; JPH0357282B2; FR2490721A1; GB2084262B; JPS5783606A; SE450588B; SE8104135L

Abstract

A turbine rotor 16 has metal blades 24 protected thermally by ceramic sheaths 22 retained to surround the respective blades 24 by respective metal caps 26 attached to the tops of the blades. The outer edge of each sheath 22 abuts against the respective cap 26 so that when the rotor 16 rotates, the sheaths 22 are subject to compressive centrifugal force F1, tensile centrifugal force being taken by the metal blades 24. <IMAGE>

Description

SPECIFICATION Improvements in rotary machines This invention relates to rotary machines, for example turbomachinery and particularly ,,turbomachinery such as pumps and turbines for high-temperature operation.

In order to improve performance and fuel economy, it has been proposed to operate turbines at elevated turbine inlet temperatures.

Inlet temperatures above 24000F are theoretically desirable. However, such temperatures are well above the operating capabilities of even the most advanced high-strength metals without requiring complex and costly cooling methods. High temperature ceramics have the highest potential for fulfilling the goals of accommodating high inlet temperatures without complex cooling requirements. Unfortunately, ceramics are brittle in nature. Moreover, fabrication costs for ceramic turbine components have been high, since the prior art method of producing high-strength, dimensionally-accurate shapes has required hot pressing and grinding. Accordingly, years of research and many millions of dollars have been expended to define and minimize tensile stresses in ceramics and to develop improved methods of fabricating ceramic turbine components.Ceramic components have also been proposed to avoid abrasion and erosion by substances such as coal slurries. Ceramic rotors and blades have been produced and tested; however, they are subjected to tensile stresses in a centrifugal force field, and thus highly subject to failure.

In an embodiment of the present invention, thermally insulating shields or sleeves formed of ceramic materials are provided while metals are employed to provide strength against tensile centrifugal forces, the ceramic shields being secured to the thereby thermally-protected metal structures in a manner such that the ceramic shields are subjected only to compressive centrifugal forces. The thermally-insulating shields or sleeves formed of ceramic materials which are subjected only to compressive loads surround metal elements which provide resistance against centrifugal and tensile forces.

Injection molding techniques have been developed which permit ceramic components to be fabricated inexpensively in large quantities with extremely high uniformity and with outstanding characteristics of strength, density and surface finish, even in complex shapes. Turbine components of a preferred embodiment of the .invention can accommodate inlet temperatures above about 24000 F.

The invention is defined in claim 1 The invention will now be described in more detail, solely by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a diagrammatic representation of prior art ceramic turbomachinery components.

Fig. 2 is an isotopic view of a portion of a turbine wheel having shielded blades embodying the present invention.

Fig. 3 is a transverse section through a portion of the turbine wheel of Fig. 2.

Fig. 4 is a horizontal section through one of the blades of the turbine of Fig. 2.

Fig. 5 is a horizontal section through an alternative form of the turbine blade of Fig. 2.

Fig. 6 is an exploded view of a turbine blade of another embodiment of the invention.

In order to meet the high-temperature and erosion requirements of modern turbomachinery, the prior art has proposed providing ceramic components, such as the turbine wheel indicated generally at 2 in Fig. 1. The ceramic turbine wheel 2 of the prior art typically comprises a plurality of blades 4 which could be formed integrally with the turbine hub 6, as indicated at 8, or could be formed as removable inserts, having foot portions 10 which mated with suitable slots 1 2 provided in the hub 6. However, it will be apparent that when the wheel 2 is rotated, centrifugal force places the blades 4 in tension, as indicated by arrow 14.

Since ceramics are brittle and are especially susceptible to tensile failure, these prior art ceramic turbomachinery components have not been satisfactory.

Figs. 2 to 4 show a turbine wheel, indicated generally at 16, formed in accordance with the present invention, having a metal hub 1 8 carrying a plurality of composite blades, indicated generally at 20. Each of the blades 20 is formed with a ceramic shield 22, having an appropriate aerodynamic external configuration, as best seen in Fig. 4, encircling a metal core 24 which is attached to the hub 18, as seen in Fig. 3. The shield 22 is secured to the core 24 by a metal cap member 26. The core 24 may be formed integrally with the hub 18, as seen at 28 in Figs. 2 and 3, or may be secured to the hub 18 by suitable means, such as the footing 30 of Fig. 2. Similarly, the cap member 26 may be formed integral with the core 24, as seen at 32 in Fig. 2, or may be secured to the core 24 by a suitable retaining means, such as a bond 34.With this structure, when wheel 1 6 is rotated the ceramic shields 22 will be forced against the cap member 26 under force F, and the tensile loads will be carried by the metal cores 24 and cap members 26. Thus, the ceramic shields 22 will be subjected only to compressive loads, which ceramics have been shown to bear very well.

It will be understood that the hot gas which drives the turbine wheel 1 6 conventionally passes through inlet and outlet conduits (not shown) so that the hot gas contacts the blade 20 in the region indicated at 36 in Fig. 3. Thus, the ceramic shields 22 provide thermal insulation for the cores 24.

If desired, shoulders 38 may be provided on the shields 22 to also provide thermal protection for the cap members 26. This also permits provision of a space 40 which accommodates radial thermal expansion of the shields 22. Moreover, if necessary or desirable, cooling conduits 42 may be provided in the hub 18 to deliver coolant fluid between the ceramic shields 22 and the metal cores 24. As seen in Figs. 3 and 4, the ceramic shields may be formed with suitable recesses 44 to permit the coolant fluid to flow in the space 44 between the shield 22 and the core 24 and exiting through passages 46 formed between the cap 26 and shield 22. Alternatively, as seen in Fig. 5, coolant recesses 48 similar to recesses 44 of Fig. 4, may be formed in the exterior surface of the cores 24.In addition, since stator members are not subjected to centrifugal force and, hence, are less critical than the rotating members, the cap members of the stators (not shown) may be formed of ceramic and may be formed integral with the shields.

Fig. 6 is an exploded view of an alternative form of the turbine blade of Fig. 2 having a metal blade core 50 formed integral with a turbine wheel 52. However, it should be understood that the core 50 could be formed separate and could be secured to the wheel 52 by any suitable attaching means. A ceramic shield 54 is provided having the exterior surface 56 shaped to provide a desired aerodynamic configuration and formed with a central opening 58 which is shaped to slide easily over the blade core 50 providing a space therebetween.A blade sheet 60 formed of corrugated metal is interposed between the core 50 and shield 54 (in the space indicated at 44 in Fig. 3) to form a compliant layer which accommodates differential thermal expansion of the core 50 and shield 54, damps or cushions aerodynamic loads between the shield 54 and core 50, and also defines a plurality of channels for coolant fluid which may be introduced between the core 50 and shield 54 by suitable inlet and drain conduits in the wheel 52, as indicated in dotted lines at 62 and 64. A blade cap 66 serves to close the outer end of opening 58.

The cap 66 may have its underside formed with a plurality of ridges, as seen at 68, to permit coolant fluid to flow across the outer end of the core 50. Finally, suitable bonding material (not shown) serves to secure the blade cap 66 and shield 54 to the core 50, the ridges 68 being bonded to the end of the core 50 and permitting fluid flow between these ridges across the end of the core 50.

Claims

1. A rotary machine comprising a rotor having a rotatable hub and a plurality of blades projecting from the periphery of the hub; each of the said blades comprising a metal core secured for rotation with the hub; and a ceramic shield encircling the said core and positioned to protect the core from deleterious effects of fluid passing through the machine, the shield being retained in such a manner as to be subjected only to compressive centrifugal forces when the rotor rotates.

2. A rotary machine according to claim 1, wherein metal cap means engages the said shield in a manner such as to place the shield in compression during rotation of said rotor, the cap means serving to retain the shield in a position about the core.

3. A rotary machine according to claim 1, wherein the exterior surface of the said shield is of aerodynamic configuration.

4. A rotary machine according to claim 1, wherein the said shield is formed to provide a space between the shield and the said core, and means are provided in the hub for delivering coolant fluid to the said space.

5. A rotary machine according to claim 1, wherein a plurality of stator vanes are mounted in proximity with the rotor blades, each stator vane comprising a metal core, and a ceramic shield encircling the vane core to protect the said vane core from deleterious effects of fluid passing through the machine.

6. A rotary machine according to claim 4, wherein compliant means are positioned in the said space to resiliently support the said shield.

7. A rotary machine according to claim 6, wherein the compliant means is a corrugated sheet.

8. A rotary machine according to claim 7, wherein the corrugations of the said sheet extend substantially radially with respect to the said hub and serve to define a plurality of channels for fluid passing through the said space.

9. A rotary machine according to claim 1, wherein a plurality of recesses is provided, each recess encircling a respective one of the said cores and formed to receive the foot of the respective shield to restrain the shield against lateral forces and substantially to prevent coolant fluid flow from escaping at the foot of the respective shield.

9. A rotary machine according to claim 1, and substantially as described hereinbefore with reference to Figs. 2, 3 and 4 or Figs. 5 or 6 of the accompanying drawings.

New claims or amendments to claims filed on 18th December 1981.

Superseded claims 1.

New or amended claims: Original claim 9 renumbered as claim

10.

1. A rotary machine comprising a rotor having a rotatable hub and a plurality of blades projecting from the periphery of the hub; each of the said blades comprising a metal core secured for rotation with the hub; and a ceramic shield encircling the said core and positioned to protect the core from deleterious effects of fluid passing through the machine, the shield being formed with no substantial laterally projecting portions and being retained in such a manner as to be subjected only to compressive centrifugal forces when the rotor rotates.