Patent Application
20050265831
The invention relates generally to gas turbine engines, and more particularly, to methods for depositing a coating on a selective area of a turbine component.
At least some known gas turbine engines include rotating components which may contact or “rub” adjacent stationary components during normal engine operation. For example, compressor rotor blades are sized such that a tip of the rotor blade “rubs” an adjacent shroud, thus forming a seal between the compressor rotor blade and the shroud.
To facilitate reducing damage to the compressor rotor blades, at least some known gas turbine engine rotor blades are coated with a wear resistant coating material. Such coatings are generally used to facilitate reducing a rate of wear of the blade caused when the blade contacts a surrounding shroud. Other wear coatings may be deposited along a leading edge of the turbine blade to facilitate decreasing wear caused by contact with environmental particulates, e.g., dirt, sand, that enter the turbine engine during operation. Another type of known wear coating is deposited across components of the turbine engine that are susceptible to wear caused by part-to-part contact during operation. For example, in a high pressure turbine (HPT) and/or a low pressure turbine (LPT) section of a gas turbine engine, wear coatings may be deposited on pre-determined areas of vane sectors that may rub against an adjacent structure, such as a shroud hanger or a pressure balance seal.
At least one known method of depositing a wear coating onto a surface of a gas turbine engine vane sector requires machining a plurality of individual components of the vane sector, depositing a coating material onto an outer surface of the machined components, and then brazing the coated components to produce an inseparable gas turbine vane sector that may be installed in the gas turbine engine. However, applying the wear coating prior to brazing the individual components may require several steps. For example, the components must be masked to prevent the wear coating from being deposited on portions of the component that are not subject to part-to-part wear. Accordingly, coating the separate components prior to assembling the final component, may result in additional fabrication costs, and may thereby increase the overall cost of the component.
In one aspect, a method for assembling a vane sector for a gas turbine engine, the vane sector including an airfoil vane and a platform is provided. The method includes depositing a wear coating material onto a selected area of the platform, positioning the platform adjacent to the airfoil vane, and executing a brazing operation such that the airfoil vane is permanently coupled to the platform portion and such that the wear coating material is bonded across a predefined area of the platform.
In a another aspect, a vane sector for a gas turbine engine is provided. The vane sector includes at least one airfoil vane, at least one platform brazed to the airfoil vane, and a wear coating material deposited onto a selected area of the platform, the wear coating is bonded across a predefined area of the platform when the platform is brazed to the airfoil vane.
In a further aspect, a gas turbine engine including a plurality of vane sectors is provided. Each vane sector includes at least one airfoil vane, at least one platform brazed to the airfoil vane, and a wear coating material deposited onto a selected area of the platform, the wear coating is bonded across a predefined area of the platform when the platform is brazed to the airfoil vane.
During operation, air flows axially through fan assembly 12, in a direction that is substantially parallel to a central axis 34 extending through engine 10, and compressed air is supplied to high pressure compressor 14. The highly compressed air is delivered to combustor 16. Airflow (not shown in
Each airfoil vane 52 includes a first sidewall 60 and a second sidewall 62. First sidewall 60 is concave and defines a pressure side of airfoil vane 52, and second sidewall 62 is convex and defines a suction side of airfoil vane 52. Sidewalls 60 and 62 are joined at a leading edge 64 and at an axially-spaced trailing edge 66 of airfoil vane 52. First and second sidewalls 60 and 62, respectively, extend longitudinally, or radially outwardly, in span from radially inner band 56 to radially outer band 54. An airfoil root 70 is defined as being adjacent to inner band 56, and an airfoil tip 72 is defined as being adjacent to outer band 54.
Referring to
In the exemplary embodiment, wear coating 110 is manufactured with a bonding temperature range that is approximately equivalent to the desired temperature range used to braze the desired engine components together. The bonding temperature is also set such that wear coating 110 densifies and does not flow extensively beyond a planned coating area 118. In use, two powders, i.e. a wear material and a bonding alloy, are selected based on performance and then blended together in a predetermined ratio to achieve a high density bonding to the substrate and to facilitate reducing excessive flow. More specifically, the wear material is an aggregate and the bonding material flows around the aggregate.
Wear coating 110 can be applied to the engine component, using the braze-tape process described herein, on any orientation surface of the engine component. More specifically, wear coating 110 can be applied to either rub surface 112 or rub surface 113 even when the rub surfaces are up-side down, i.e. 360 degrees from horizontal, or to a rub surface positioned on a bottom surface of a component, e.g. a bottom surface of platform 56. Wear coating 110 has a length 120, a width 122, and a thickness 124 that are variably selected to ensure that wear coating 110 does not extend beyond planned coating area 118 when wear coating 110 is bonded during the brazing operation.
In operation, wear coating 110 is applied to at least one of rub surface 112 and rub surface 113. In one exemplary embodiment, wear coating 110 is applied to rub surfaces 112, 113 using a preform such as a sintered braze tape for example. In another embodiment, wear coating 110 is applied to rub surfaces 112, 113 using a salt and pepper method. More specifically, the powder is sprayed over a surface and then the adhesive is sprayed over the surface. This technique continues until the desired coating thickness has been applied to rub surfaces 112 or rub surface 113. Suitable adhesives completely volatilize during the brazing step and can include for example, but are not limited to including, a polyethylene oxide and an acrylic material. Adhesive 126 may be applied to rub surfaces 112 or 113 utilizing one of various techniques such as, but not limited to, coating wear coating 110 using a liquid adhesive, or applying a mat or film of double-sided adhesive tape to wear coating 110.
After wear coating 110 is applied to rub surface 112 or 113, a brazing operation is performed to facilitate permanently airfoil vane 52 is permanently coupled to at least one of platform 54 or 56, and such that wear coating material 110 is bonded across a predefined area 118 of the platform substantially simultaneously with the brazing operation. More specifically, wear coating 110 can be applied to rub surfaces 112 or 113, and airfoil vane 52 can be permanently coupled to either platform 54 or 56 during a single brazing operation. The brazing operation is performed using at least one of a vacuum furnace or a protective atmosphere, such as but not limited to, argon and nitrogen for example.
During the brazing operation, wear coating 110 is fused to wear surface 112 or 113 without any substantial attendant melting of the substrate. The brazing temperature is largely dependent upon the type of braze alloy used, but is typically in a range of approximately 950° Celsius (C) to approximately 1260° C.
In one embodiment, brazing is carried out in a furnace including a controlled environment, such as a vacuum or an inert atmosphere. Brazing in a controlled environment advantageously facilitates preventing oxidation of the braze alloy and underlying materials, including the substrate, during heating, and facilitates a more precise control of part temperature and temperature uniformity. Following heating, wear coating 110 is fused to either platform 54 or 56, and the braze alloy is permitted to cool, such that a metallurgical bond is formed against the underlying material thus retaining wear coating 110 against rub surface 112 or 113. In another exemplary embodiment, wear coating 110 is pre-sintered to remove a wear coating binder and increase a density of wear coating 110. Wear coating 110 is then affixed to rub surface 112 or 113 using resistance welding for example.
The methods described herein facilitate applying a wear-coating to rub surfaces of a component during a standard braze fabrication cycle regardless of the angle of the component surface with respect to horizontal. The wear coating can be applied without excessive flow, such that the wear coating remains in the design area while retaining dimensional tolerances allowed for the coating. The methods described herein also facilitate eliminating the requirement for a separate wear resistant coating application step prior to brazing the turbine components.
The above-described methods and systems for applying a wear coating on a selective area of a turbine engine component is cost-effective and highly reliable for facilitating coating a portion of a component where a coating is desired and for facilitating preventing the coating from contacting a portion of the component where a coating is not desired. As a result, the methods and apparatus described herein facilitate fabrication and maintenance of components in a cost-effective and reliable manner.
Exemplary embodiments of combinations of gas turbine engine components and wear coatings are described above in detail. The combinations are not limited to the specific embodiments described herein, but rather, components of each combination may be utilized independently and separately from other components described herein. Each combination component can also be used in combination with other system components.
While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
