The invention relates to gas turbine engines. More particularly, the invention relates to gas turbine engines having turbine blades with outer diameter (OD) shrouds.
Typical gas turbine engines include interspersed stages of rotating airfoils (blades) and non-rotating airfoils (vanes) in each of the compressor and turbine sections. Many different blade and vane configurations exist. Among blades, many typical configurations include an airfoil extending from an airfoil inboard end at a platform to a free tip. A mounting root (e.g., a convoluted so-called “fir tree”) depends from the platform for attaching the blade to a separate disk. In such configurations, the tips of the mounted blades may rotate in close facing proximity to an associated circumferential blade outer air seal (BOAS) assembly carried by the engine case.
In some configurations, the airfoils carry mid-span and/or OD shrouds. The term “shroud” is often used interchangeably to denote the individual segment carried by an individual blade and the resulting full circumferential structure provided by the combination of segments of the stage of blades as attached to their associated disk.
A particular example of a blade stage having an OD shroud is the HPT first stage (T1) of the Pratt & Whitney (division of United Technologies Corporation, East Hartford, Connecticut) JT8D long-used, for example, in Boeing 727, 737, and DC-9/MD80 aircraft. Damage has been observed to the outboard surfaces of the OD shrouds.
A variety of restoration techniques have been proposed for turbine engine components. These include welded prostheses, and various build-up repairs including brazing, welding, and depositions. U.S. Patent Application Publication 20050178750A1 discloses laser cladding remanufacturing of sulphidation-attacked turbine engine parts, with specific reference to platforms. U.S. Patent Application Publication 20040086635A1 discloses laser cladding remanufacturing of a damaged gas turbine engine stationary (non-rotating) shroud.
One aspect of the invention involves a method for restoring a turbine engine blade. Material is removed from a wear/damage site on an OD shroud of the blade. Additional material is laser cladded to the site and then machined to restore the shroud.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
Like reference numbers and designations in the various drawings indicate like elements.
The blade may be made as a superalloy casting (e.g., of a nickel-base superalloy such as MAR-M-200+Hf originally developed by Lockheed Martin or PWA1447 of Pratt & Whitney), optionally coated (e.g., with a thermal barrier coating such as PWA70/73 dual coating, PWA 270/273 dual coating, or PWA 36095 platinum aluminide, all of Pratt & Whitney). The exemplary blade 20 has an airfoil 22 extending radially outward from an inboard end 24 at an outboard surface 26 of a platform 28. The radial direction is defined relative to an engine centerline when the airfoil is mounted to a disk (not shown). The blade includes a fir tree attachment root 30 depending from an inboard surface (underside) 32 of the platform 28. The blade includes an OD shroud 34 at the outboard end 36 of the airfoil. The shroud underside 38 and platform outboard surface 26 locally define respective outboard and inboard extremes of the engine core flowpath.
The airfoil includes a leading edge 40, a trailing edge 42. The airfoil has a generally concave pressure side 44 and a generally convex suction side 46 extending between the leading edge 40 and the trailing edge 42.
For reference,
Due to factors not fully understood, the wear in the region 110 may be particularly significant. There may be a relationship to the relative thinness of the shroud in this region as further influenced by dynamic factors.
Although not required,
After any further cleaning, restoration material may be built up atop the machined facets.
Exemplary laser cladding techniques and apparatus are disclosed in U.S. Patent Application Publication 20050178750A1, the disclosure of which is incorporated by reference herein as if set forth at length. Exemplary cladding material has a composition that is preferably essentially the same as the base material of the blade at the facets.
After buildup, the buildups may be machined to restore the original local contour. The machining may involve a slight machining along non-built-up areas (e.g., intact portions of the surfaces 64 and 74 for continuous circularity). After machining, the blade may be locally or generally recoated.
Relative to tungsten inert gas (TIG) welding laser cladding is believed to generate a substantially smaller heat affected zone in the area being repaired. As a result, there is a reduction in post-weld stress and the structural integrity of the part is not compromised. There is also reduced or eliminated chances of distortion of the part which may be encountered with TIG welding. Laser cladding also offers a fast cycle time and high repeatability.
One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, the nature of particular damage may influence the appropriate repair. The choice of any particular known or yet-developed laser cladding apparatus may also influence details. Accordingly, other embodiments are within the scope of the following claims.