Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
1998-07-10
2001-01-23
Speer, Timothy M. (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S142000, C428S161000, C428S163000, C428S167000, C428S469000, C428S472000, C427S318000, C427S327000, C427S330000
Reexamination Certificate
active
06177174
ABSTRACT:
PRIORITY CLAIM
This application is based on and claims the priority under 35 U.S.C. §119 of German Patent Application 197 30 008.1, filed on Jul. 12, 1997. The entire disclosure of German Patent Application 197 30 008.1 is incorporated herein by reference.
FIELD OF THE INVENTION
The invention relates to an anti-wear or armor coating provided on the surface of a metal engine component, which is to make grazing contact with and be abrasively bedded into a bedding-in coating or lining on a second component of the engine. The armor coating comprises a ceramic layer having alternating peaks and depressions therebetween for receiving and carrying away abrasion material. This armor coating is especially for the rotor or stator of a jet turbine engine. The invention further relates to a method of providing such an armor coating on a metal engine component.
BACKGROUND INFORMATION
Armor coatings and/or abradable bedding-in linings are provided on engine components such as on the tips of sealing fins of labyrinth seals or the tips of rotor blades, in order to hinder the abrasive wear of the coated components during grazing contact between the armored component and the other component provided with a bedding-in coating. Since the efficiency of a compressor or a turbine is largely dependent on the gap width between the rotating component and the stationary component, this efficiency is reduced with increasing abrasive wear, for example of the blade tips, as a result of grazing contact processes.
Generally, the armor coating abrades or cuts itself into an opposing bedding-in coating of a second component during operation of the engine. Such bedding-in coatings generally consist of a layer of an abradable, corrosion resistant and erosion resistant material. However, if the strength and hardness of the bedding-in coating is increased in order to increase the erosion and temperature resistance thereof, then the abrasive wear of the engine components will also be increased, so that it is necessary to provide an armor coating thereon. By providing such an armor coating, it is achieved that a minimized gap width will be formed between the armor coating and the bedding-in coating as a result of the grazing contact therebetween.
Known armor coatings comprise a ceramic layer that is thermally sprayed onto the surface of the respective engine component. In order to provide, on the armor coating, a profiled surface having edges or peaks that are adapted to cut into the opposing bedding-in coating, as well as free spaces or depressions between respective peaks for receiving and carrying away the abraded material, the known thermal spray process is carried out using a perforated mask consisting of a wire mesh arranged over the component surface. Then the coating material is sprayed through the wire mesh mask, whereby the spray is selectively blocked in a pattern determined by the mask so as to form peaks and depressions in the spray coating applied to the engine component. The size and geometry of the respective peaks or edges is determined and may be varied by the position and type of wire mesh that is used as the mask, as well as the spraying stream angle and the like.
In practice, this known process has been found to suffer several disadvantages. First, it has been found that the wire mesh completely covers the component surface or completely blocks the spray application at certain locations and thereby causes the formation of defects, gaps or voids in the coating layer. This also causes undesirable variations in the coating layer thickness, and makes it impossible to achieve a uniform surface profiling over the entire circumference of the component. Furthermore, the known process requires a complicated preparation of the component surface as well as handling of the wire mesh, and involves difficulties in maintaining the required spraying stream angle and limiting that angle to the range specified by the known process.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the invention to provide an armor coating of the above described general type, which comprises a coating layer and surface profiling that are as uniform as possible over the entire workpiece surface to be coated. It is a further object of the invention to provide a method of providing such an armor coating on an engine component in a manner that is production-technically simple, cost economical, and reliable. The invention further aims to overcome or avoid the disadvantage of the prior art, and to achieve additional advantages, as apparent from the present description.
The above objects have been achieved by an armor coating on a metal engine component according to the invention, wherein the armor coating comprises a ceramic layer that is applied onto a surface of the engine component, and that has a profiled surface including peaks and free spaces or depressions between the peaks for carrying away abraded material when the armor coating makes grazing contact with a bedding-in coating of another engine component. Further according to the invention, the profiled surface of the armor coating is formed by providing a corresponding profiled surface on the engine component itself, and particularly by plastically deforming the surface of the engine component, before applying the armor coating thereon.
Thus, the engine component itself has a profiled surface including peaks and valleys or depressions, which have been formed by cold working deformation, whereby the material of the engine component is compressed and hardened. Namely, in order to form such a profiled surface, material is not machined or otherwise removed from the engine component. Instead, the surface of the component is formed and compressed by cold forming processes in order to produce the peaks and depressions therebetween. To achieve this, an appropriate tool is pressed into the surface of the engine component before it is coated with the ceramic armor coating material. The depressions may be in the form of valleys, grooves, notches, pits, troughs, indentations or the like.
Thereafter, the armor coating is applied onto the profiled surface of the engine component, whereby the armor coating itself advantageously has a uniformly profiled and coated surface, without requiring the complicated use of a wire mesh or other screening mask for covering portions of the component surface. Furthermore, the present method avoids the formation of the defects that typically arise to a great extent when using such a wire mesh mask. A further advantage is that the armor coating may have deeper grooves or other depressions than can be achieved by prior art methods. In this context, the profiled surface of the armor coating can be embodied exactly as needed to provide an optimum abrasive wear with consideration of the relative motion between the engine component having the armor coating thereon and the second engine component that may have a bedding-in coating thereon.
In a preferred embodiment of the invention, a knurling operation is carried out for profiling the surface, i.e. deforming the surface by cold working to achieve the desired profile. This knurling operation is carried out by pressing a knurling tool into the surface of the engine component that is to be armor coated. In this context, standardized knurling forms with numerous different diameters, profile angles and pitches, may be used, such as knurling tools with flutes parallel to the axis of the tool, right or left spiraling flutes or knurlings, combined left and right spiral knurlings or cross knurlings with raised or depressed peaks, for example. In the event special component configurations are to be profiled, then special knurling tools can be produced for carrying out the profiling.
It may be suitable for particular applications, if the peaks and depressions forming the profiled surface extend substantially parallel to a rotational axis of the component. Throughout this specification, it should be understood that the term “rotational axis” of the armor-coated engine component refers to an axis about which t
Fasse W. F.
Fasse W. G.
MTU Motoren - und Turbinen-Union Muenchen GmbH
Speer Timothy M.
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