Cleaning and liquid contact with solids – Processes – Including application of electrical radiant or wave energy...
Reexamination Certificate
2001-01-29
2002-12-31
El-Arini, Zeinab (Department: 1746)
Cleaning and liquid contact with solids
Processes
Including application of electrical radiant or wave energy...
C134S022100, C134S022110, C134S022120, C134S022180, C134S026000, C134S030000
Reexamination Certificate
active
06500269
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a method of cleaning turbine engine components using laser shock peening. The present invention particularly relates to the use of laser shock peening to remove a crust-like debris that buildups on the surface of the internal cooling cavity of an airfoil such as a turbine blade or vane.
A typical gas turbine engine includes a compressor, a combustor, and a turbine. Both the compressor and the turbine include alternating rows of rotating and stationary airfoils in the form of turbine blades or vanes. Air flows axially through the engine, with the compressed gases emerging from the compressor being mixed with fuel in the combustor and burned therein. The hot products of combustion, emerging from the combustor at high pressure, enter the turbine where the hot gases produce thrust to propel the engine and to drive the turbine which in turn drives the compressor.
Gas turbine engines operate in an extremely harsh environment characterized by vibrations and very high temperatures. The airfoils in the turbine are at risk of burning because of the hot gases emerging from the combustor. Various cooling schemes exist to provide adequate cooling to these turbine airfoils. Many of these cooling schemes include intricate internal passages, such as a serpentine passage, that vent cooling air therethrough. The cooling schemes can also include tiny cooling holes formed within the wall structure of the airfoil to allow the cooling air to pass therethrough. See U.S. Pat. No. 5,575,858 (Chen et al), issued Nov. 19, 1996, and in particular FIG. 2, which shows one such airfoil 30 with elaborate internal cooling passages referred to as 38-40.
The air that circulates through the airfoils, particularly during operation on the ground, includes particles of sand, dust, dirt and other contaminants that can be ingested by the engine. The sand, dust, dirt, etc., aided by extremely high temperatures and pressures, can adhere to the surface of the internal cavity of the airfoils and can form a compacted layer or layers of a crust or coating (hereinafter referred to as “crust-like”) of this debris that can reduce the size or block entirely the air holes and the internal passages within the airfoil, thereby reducing the efficiency of the cooling thereof. See U.S. Pat. No. 5,575,858 (Chen et al), issued Nov. 19, 1996. Due to the centrifugal forces at operation in the airfoil during rotation of the compressor and turbine, this crust-like debris especially tends to collect and buildup on the surface of the internal cooling cavities at the tip of the airfoil.
If the accumulation of this crust-like debris on the surface of the internal cooling cavities of the airfoil becomes sufficiently great to block cooling airflow, the metal temperature of the airfoil can greatly increase, leading to premature distress and limiting usability of the airfoil. In particular, external coatings on the airfoil, if heated to a sufficiently high temperature, can oxidize through to the base metal, making the airfoil unserviceable. In addition and if not removed, this crust-like debris can begin to react with the base metal during some high temperature airfoil repair processes, leading to intergranular attack (i.e., corrosion at the grain boundaries of the base metal) on the internal wall of the airfoil. If severe enough, this can produce cracks that go completely through the wall of the airfoil.
To ensure that these internal cavities are passable for the cooling air, the airfoils need to be cleaned periodically during their lifetime to remove this crust-like debris deposited on the surface of these cavities or else be replaced. Since the airfoils are manufactured from relatively expensive materials so as to withstand high temperatures, vibrations and cycling, frequent replacement of all or some of the airfoils can be very costly. Therefore, a method for cleaning these airfoils would be a preferred alternative to replacement. Furthermore, since each engine typically includes hundreds of such airfoils, any reduction in time in cleaning each airfoil could potentially result in tremendous time savings and subsequently lead to significant cost savings.
This crust-like debris can be deposited on either the external or internal surfaces of the airfoil. However, because the buildup of this deposited crust-like debris tends to occur especially in the internal cooling cavities of the airfoil, removal of this debris can be a problem, especially since access to these cavities with conventional cleaning tools or methods is often extremely difficult or even impossible. One prior method for cleaning and removing crust-like debris deposited on the surface of these internal cavities is by exposure to an alkaline or caustic solution, such as a potassium hydroxide solution, under pressure (150-350 psi) and at relatively high temperatures (150-235° C.) for relatively long periods of time (e.g., upwards of 20 hours or more). This is then followed by water blasting under pressure to flush out the softened debris. See U.S. Pat. No. 4,439,241 (Ault et al), issued Mar. 27, 1984. See also U.S. Pat. No. 5,507,306 (Irvine et al), issued Apr. 16, 1996 (manifold clamped to the root of the airfoil components, with heated caustic solution being pumped through the manifold and into the internal cavities of the airfoils); and U.S. Pat. No. 5,575,858 (Chen et al), issued Nov. 19, 1996 (after treating with caustic solution, airfoils are soaked in a chelating agent solution such as the tetrasodium salt of ethylenedarine tetracetic acid (EDTA)). A significant disadvantage in using caustic solutions is the typically long time period required for treatment to ensure that the deposited debris is adequately softened or loosened in the internal cavity of the airfoil. Even after a long period of treatment with the caustic solution, the softening or loosening of the deposited debris can be less than desired, especially when the deposited debris layer is thick or the internal cavity is relatively complicated or intricate in design. Also, the residual caustic solution can remain entrained within the internal cavity, even after high-pressure water flushing, thus potentially causing undesired corrosion of the surface (or any coating thereon) of the internal cavity over time.
Another prior method for cleaning and removing deposited debris from these internal cavities is by immersing the airfoils in water so that the deposited debris becomes saturated therewith, followed by immersion in a cryogenic fluid, such as liquid nitrogen, to cause the residual water in the internal cavities to freeze and cause loosening of the debris, and then pressure flushing with additional water to remove the loosened or dislodged debris. This sequence of water saturation, freezing and high pressure flushing can be repeated to ensure adequate removal of the debris from the internal cavities of the airfoils. See U.S. Pat. No. 5,464,479 (Kenton et al), issued Nov. 7, 1995. A significant disadvantage of this method is that it can potentially subject the airfoils to successive freeze-thaw cycles that can cause cracking and other undesired stresses to be imparted to the airfoil.
Another prior method for cleaning and removing this deposited crust-like debris from these internal cavities involves immersing the airfoils in a tank of cleaning solution, such as a mild alkaline solution, and then immersing an ultrasonic agitator, such as a welding horn, in this tank. The ultrasonic waves that are generated by the welding horn are focused on the portion of the airfoil having the deposited crust-like debris layer, followed by pressure flushing of the airfoil with water to remove the loosened or dislodged debris. See U.S. Pat. No. 5,707,453 (Shurman et al), issued Jan. 13, 1998. See also U.S. Pat. No. 5,938,855 (Bowden), issued Aug. 17, 1999 (ultrasonic agitation of turbine component soaked in a solution of acetic acid.) A disadvantage with this ultrasonic cleaning method is that it is not completely effective in loosening or dislodging the crust-like
Anderson Thomas E.
Colaizzi Tris
Ferrigno Stephen J.
Risbeck James D.
El-Arini Zeinab
General Electric Company
Guttag Eric W.
Haase Guttag & Nesbitt LLC
Ramaswomy V. G.
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