Patent Application
20080286108
The present invention generally relates to gas turbine engine components that function in high pressure and elevated temperature environments. More particularly, the present invention relates to methods for coating turbine engine components such as compressor or turbine blades to prevent or minimize wear during rubs with adjacent abradable shrouds.
Turbine engines are used as the primary power source for various kinds of aircraft. The engines are also auxiliary power sources that drive air compressors, hydraulic pumps, and industrial gas turbine (IGT) power generation. Further, the power from turbine engines is used for stationary power supplies such as backup electrical generators for hospitals and the like.
Most turbine engines generally follow the same basic power generation procedure. Compressed air is mixed with fuel and burned, and the expanding hot combustion gases are directed against stationary turbine vanes in the engine. The vanes turn the high velocity gas flow partially sideways to impinge on the turbine blades mounted on a rotatable turbine disk. The force of the impinging gas causes the turbine disk to spin at high speed. Gas turbine engines use the power created by the rotating turbine disk to power a bladed compressor that draws more air into the engine and to energize propellers, electrical generators, or other devices.
Since turbine engines provide power for many primary and secondary functions, it is important to optimize the operating efficiency of compressors and turbines. One way to maximize compressor and turbine efficiency is to minimize high-pressure air leakage between the tips of the blades and the adjacent shroud. In order to accomplish this objective, compressor or turbine blade dimensions are tightly controlled and blade tips can be machined so the installed blades span a diameter that is slightly smaller than the shroud inner diameter. Improvements in compressor or turbine performance are possible when compressor or turbine blade tips can tolerate interference rubs with the adjacent shroud without experiencing significant blade tip wear. Wear of titanium, steel or superalloy blade tips during a rub is undesirable because clearances increase, producing an associated reduction in compressor or turbine performance.
In order to minimize the escape of high pressure air between compressor blade tips and the mating shroud, abrasive blade tip coatings may be applied to machined compressor blades. Further, a porous and abradable ceramic coating may be applied to the shroud as taught by Draskovich in U.S. Pat. No. 5,704,759. The primary function of such coatings is to provide rub-tolerant shroud and blade surfaces that minimize blade damage in the event a compressor blade rubs the surrounding shroud surface. For example, U.S. Pat. No. 5,704,759 discloses a turbine blade body having a tip portion that is coated with an abrasive material. The abrasive material includes a dispersion of discrete particles of cubic boron nitride (CBN) that are formed on the blade tip by an entrapment plating method wherein the CBN particles are entrapped in electroplated nickel with their tips (cutting edges) exposed. However, entrapment plating is difficult to perform on large turbine components such as a compressor impeller. Furthermore, entrapment plating is a somewhat cumbersome process since each turbine blade must be individually coated. Because CBN is very hard and difficult to grind, each of the uncoated blades must be inserted into slots in a hub. Then, the blades are ground at their outer diameters to conform to blue print dimension. Finally, the blades are removed from the hub and individually coated with CBN, and then reinserted into the slots in the hub. The steps of disassembling and reassembling the turbine wheel and its blades are burdensome and inefficient.
Entrapment electroplating of abrasive particles, such as CBN, into a co-deposited NiCoCrAlY matrix has also been applied to turbine blade tips as taught by Wride in U.S. Pat. No. 5,076,897. The hard CBN abrasive particles can cut into porous stabilized zirconia shroud coatings for short periods of up to a few hours until the cubic boron nitride particles are lost due to oxidation.
Accordingly, it is desirable to provide turbine engine components such as compressor and turbine blades that are coated and machined to prevent air leakage between a gas turbine engine shroud and wheel blades. In addition, it is desirable to provide an efficient method for producing such components. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.
According to one embodiment of the invention, a method is provided for coating compressor or turbine blade tips of a bladed disk with abrasive particles. The method includes installing the blades onto a disk, and then cold gas-dynamic spraying the abrasive particles onto the blade tips while the blades are installed in the disk.
According to another embodiment of the invention, a method is provided for coating compressor and turbine blade tips of a bladed wheel with abrasive particles. First, the blade tips are ground to bring the bladed wheel to a predetermined diameter. Then, surfaces of the bladed wheel not requiring coating are masked. After masking the surface not to be coated, the abrasive particles are cold gas-dynamic sprayed onto the blade tips.
The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and
The following detailed description of the invention is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description of the invention.
The present invention includes methods for coating the machined tip of any compressor or turbine blade. The methods are particularly advantageous when the compressor or turbine rotor is fully bladed and machined. The rotor may be an integral bladed disk or a disk with inserted blades. When manufacturing a compressor or turbine wheel that incorporates inserted compressor or turbine blades, the blades are inserted into slots in a disk.
Turning now to
The turbine blade 150 includes an airfoil 152. The airfoil 152 includes a concave curvature face and a convex face. In operation, hot gases impinge on the airfoil 152 concave face and thereby provide the driving force for the turbine engine. The airfoil 152 includes a leading edge 162 and a trailing edge 164 that firstly and lastly encounter an air stream passing around airfoil 152. The blade 150 also includes a tip 160. In some applications the tip may include raised features commonly known as squealers.
The turbine blade 150 is mounted on a turbine disk 146 that is part of a wheel 20 depicted in
As previously discussed, the turbine blade 150 depicted in
According to an exemplary embodiment, the abrasive particles are cubic boron nitride (CBN). The CBN preferably has an average particle diameter ranging between 25 and 100 microns. Other abrasive materials may also be suitably applied by a cold gas-dynamic spraying process. Some exemplary abrasive materials include diamond, silicon carbide (SiC), yttrium aluminum garnet (YAG), and cubic zirconia. Diamond and CBN are harder than SiC, YAG and cubic zirconia. However, these and other suitable abrasive materials may be selected based on their high temperature oxidation resistance properties. The abrasive coating composition also may vary depending on the type of blades that are being coated and the intended operational conditions for the blades.
As previously discussed, a single layer of abrasive particles 14 are imbedded into compressor and turbine blade tips using a cold gas-dynamic spraying process which accelerates the particles to supersonic velocities. Turning now to
The cold gas dynamic spray process is referred to as a “cold spray” process because the particles are applied at a temperature that is well below their melting point. The kinetic energy of the particles on impact with the target surface, rather than particle temperature, causes the substrate to plastically deform and bond the particles with the target surface.
A variety of different systems and implementations can be used to perform the cold gas-dynamic spraying process. For example, U.S. Pat. No. 5,302,414, entitled “Gas-Dynamic Spraying Method for Applying a Coating” describes an apparatus designed to accelerate materials and to mix particles of the materials with a process gas to provide the particles with a density of mass flow between 0.05 and 17 g/s·cm2. Supersonic velocity is imparted to the gas flow, with the jet formed at high density and low temperature using a predetermined profile. The resulting gas and powder mixture is introduced into the supersonic jet to impart sufficient acceleration to ensure a particle velocity ranging between 300 and 1200 m/s.
According to the present invention, the cold gas-dynamic spray system 100 applies abrasive particles onto a compressor or a turbine blade tip. Although the process is referred to as “cold spraying,” some warming of the gas and/or particles may be advantageous in order to provide the abrasive particles with sufficient energy to embed into a turbine blade tip. The system typically uses gas pressures of between 5 and 20 atm, and at a temperature ranging between about 300 and 1000° F. Furthermore, the abrasive particles may be warmed to a temperature of up to about 500° F. However, any warming of the particles and/or the propellant gas is tailored to maintain the particle temperatures well below their melting points. As non limiting examples, the gases can comprise air, nitrogen, helium and mixtures thereof. Again, this system is but one example of the type of system that can be adapted to cold spray powder materials to the target surface. The system 100 is typically operable in an ambient external environment.
A unique advantage provided by cold gas-dynamic spraying abrasive particles is the ability to deposit the abrasives onto the tips of blades that are installed on a disk. As previously discussed, many conventional methods of coating compressor and turbine blades with abrasives are somewhat cumbersome processes since the methods require that each turbine blade be individually coated. Because CBN and other suitable abrasives are very hard and difficult to grind, each of the uncoated blades are inserted into slots in a disk using conventional methods, and the blades are then ground at their outer diameters to conform to the bladed disk's blue print dimension. The blades are thereafter removed from the disk and individually coated with the abrasive material, and then reinserted into the slots in the disk. The steps of disassembling and reassembling the turbine wheel and its blades are burdensome and inefficient. Returning now to
According to the embodiment depicted in
Turning now to
With the blades installed on the hub, the blade tips are ground to predetermined or blueprint dimensions as step 62. During operation of a gas turbine engine, the turbine wheel blades are surrounded by a shroud. Engine power and operational efficiency are optimized by forming the compressor or turbine wheel to have a diameter that minimizes the blade tip to shroud clearance, which prevents wasteful high pressure air leakage between the blades and the shroud.
As step 64, a protective mask is applied to protect surfaces of the bladed disk where the deposition of abrasive particles is not permitted. The protective mask may include strips of rubber or sheet metal with airfoil shaped slots to expose the tips of the blades.
As step 66, the tips of the installed compressor or turbine blades are coated with abrasive particles by a cold gas-dynamic spraying process. According to the exemplary embodiment depicted in
As necessary or useful, an optional heat treatment may be performed as step 68 after cold gas-dynamic spraying the abrasive particles onto the turbine blade tips and before installing the compressor or turbine wheel into an engine. A heat treatment may improve metallurgical bonding between the abrasive particles and the turbine blade material.
While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It is understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.
