Abstract:
An apparatus and method for heat treating the welded area of a repaired gas turbine engine component uses first and second heating elements. The heating elements each include an insulating tube supported by a support rod and wrapped with a conducing wire. One of the heating elements is sized to fit inside a recess in the gas turbine engine component, adjacent to the welded area, while the second heating element is placed outside the recess, but also adjacent to the welded area, thereby heating the welded area from two sides.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    A gas turbine engine typically includes an augmenter, or afterburner, which produces additional thrust from the engine. Thrust augmentation is particularly useful in military aircraft, which often need brief periods of additional thrust during takeoff, climbing, or combat maneuvers. The augmenter typically is disposed in the exhaust section of the gas turbine engine. The gas flow of the augmenter is circumscribed by an augmenter liner and an augmenter case. The augmenter case is disposed outwardly in a radial direction from the augmenter liner, with a cooling space between them. 
         [0002]    Augmenter cases include a cam follower track. During normal use of the gas turbine engine, the cam follower track of the augmenter case becomes worn. The high cost of augmenter cases makes it very desirable to repair the worn area of the cam follower track. Repairing the cam follower track of an augmenter case includes three basic steps: building up the worn area of the cam follower track using a welding process, heat-treating the built-up welded area of the cam follower track to relieve local stress, and machining the welded area of the cam follower track to conform to the desired dimensions. 
         [0003]    The cam follower track of an augmenter case has an elongated shape. This elongated shape makes it difficult to provide heat treatment in a uniform manner to the welded area during the second step of the repair process. 
         [0004]    Therefore, there is a need in the art for an apparatus to provide localized heat treatment of the welded area of a gas turbine engine component that is being repaired, such as the cam follower track of an augmenter case. It is important that the device provide sufficient heat for the stress-relief process, while also minimizing the amount of heat delivered to areas adjacent to the area being repaired. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    The invention is a heating apparatus and method that provides localized heat treatment to the welded area of a repaired gas turbine engine component. The heating apparatus includes two heating elements, the first of which is sized to fit inside a recess in the gas turbine engine component, and the second of which is sized to fit outside the recess, adjacent to the first heating element. The heating apparatus provides heat to the welded area from two sides and minimizes the heat delivered to other parts of the gas turbine engine component. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  shows one embodiment of a heating apparatus including two heating elements. 
           [0007]      FIG. 2  shows a cam follower track with a welded area requiring local stress relief. 
           [0008]      FIG. 3  shows the heating apparatus of  FIG. 1  positioned in and proximate to the cam follower track of  FIG. 2 , with a welded area requiring local stress relief. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0009]      FIG. 1  shows heating assembly  100 , which is used to provide localized heat treatment to the welded area of a cam follower track of an augmenter case that is being repaired. Heating assembly  100  includes heating element  110  and heating element  130 , which are connected together in series (not shown). Heating element  110  of heating assembly  100  is sized to fit inside cam follower track  200  ( FIG. 2 ), while heating element  130  is larger than heating element  110  and is designed to fit outside cam follower track  200 . 
         [0010]    Heating element  110  includes support rod  120 , insulating tube  122  and conducting wire  124 . Support rod  120  must be made of a material that can withstand the heating process without distortion, so that the heating process can be repeated many times. For example, support rod  120  may be made of INCONEL® 625, a nickel-based alloy that has significant strength through a very wide temperature range. Support rod  120  is located inside tube  122  and is used to support tube  122  in proper position. Tube  122  is made of a thermal insulator, typically a ceramic, such as alumina. Tube  122  is surrounded by wire  124 , which is coiled around tube  122  to create a heating element. Wire  124  is made from a metal that has the appropriate resistance to create a heating element. For example, wire  124  may be made of NiCr, which is a well-known material that is available in many different diameters and resistances. Wire  124  is connected to a power supply and control system (not shown). For example, wire  124  may be connected to a 120 volt power supply and a proportional-integral-derivative (PID) controller. 
         [0011]    Heating assembly  100  further includes heating element  130 , which includes support rod  140 , insulating tube  142  and conducting wire  144 . Support rod  140 , like support rod  120 , must be made of a material that can withstand the heating process without distortion, such as INCONEL® 625 nickel-based alloy, so that the heating process can be repeated many times. Support rod  140  is placed inside tube  142  and is used to support tube  142  in place. Tube  142  is made of a thermal insulator, typically a ceramic, such as alumina. Tube  142  is surrounded by wire  144 , which is coiled around tube  142  to create a heating element. Wire  144  is made from a metal, such as NiCr, that has the appropriate resistance to create a heating element. Wire  144 , like wire  124 , is also connected to the power supply and control system (not shown). 
         [0012]    In repairing a damaged cam follower track in the augmenter case of a gas turbine engine, the first step is to build up the worn area of the cam follower track using any suitable welding process. Next, heating assembly  100  is used to provide local stress relief of the newly-welded area of the cam follower track. While heat treating the welded area of the repaired cam follower track, enough heat must be placed uniformly along the welded area to complete the stress relief cycle. 
         [0013]    At the same time, it is desirable to minimize the heating of adjacent areas, such as nearby assembly rivets, which might be damaged by the high heat needed for stress relief. A gas turbine engine, including the augmenter case, is built with parts that have very close tolerances and must have specific dimensions in order to fit together with the other parts of the gas turbine engine. Heating of the augmenter case during repair of the cam follower track may alter those dimensions. Areas adjacent to the cam follower track, especially nearby assembly rivets, may be damaged if they are heated to the high temperature needed for local stress relief of the repaired area of the cam follower track. Assembly rivets, for example, must be kept below about 600° F. (315° C.). 
         [0014]    It is also desirable to prevent surface contamination of the titanium augmenter case. The augmenter case is made of titanium, which is very sensitive to surface contamination. Temperature is the primary factor driving surface contamination of titanium, so heat treating increases the danger that the titanium surface of the augmenter case will become contaminated. Surface contamination of titanium begins around about 600° F. (315° C.), while heat treating of the welded area typically requires temperatures around about 1100° F. (595° C.). 
         [0015]    Finally, a sharp temperature gradient between the welded area of the cam follower track that is being heated and the areas adjacent to it is not desirable. A sharp temperature gradient may introduce unwanted stress in the material of the augmenter case. 
         [0016]    As shown in  FIG. 2 , the welded area  220  is along an edge  210  of cam follower track  200 . As shown in  FIG. 3 , after the damaged area of the cam follower track has been built up during the welding step, heating element  110  is positioned inside cam follower track  200 , adjacent to welded area  220 . Heating element  130  is positioned outside of cam follower track  200 , along the other side of welded area  220 . In some applications, thermocouples may be attached along welded area  220  to monitor temperatures and control the heating process. 
         [0017]    After heating element  110  and heating element  130  are properly positioned with respect to welded area  220 , heating element  110  and heating element  130  are turned on for an appropriate amount of time to provide heat treatment to welded area  220 . The two heating elements on either side of the welded area ensure thorough and uniform heating the welded area. 
         [0018]    To reduce oxidation and contamination of the titanium augmenter case, the augmenter case may be sectioned off and sealed inside a polycarbonate tent, which is then filled with an inert gas, such as argon. Fans or focused air-cooling can be used to cool the exterior areas of the augmenter case that are not being heat-treated. 
         [0019]    The area to be heat-treated is sealed inside the tent, and the inert gas is continuously pumped into the tent to eliminate, or at least minimize, the oxygen in the tent. Power is then applied to the heating elements until an appropriate temperature is obtained. In embodiments, the stress relief process calls for heating the augmenter case to a temperature of about 1100° F. (595° C.) and holding the augmenter case at that temperature for approximately 90 minutes in an inert gas atmosphere. Upon completion of the heating process, the heating elements are removed and the augmenter case is cooled to room temperature. The process can then be repeated on other cam follower tracks in the same case until all necessary repairs are completed. 
         [0020]    The invention is a heating apparatus and method that provides localized heat treatment to the welded area of a repaired gas turbine engine component, such as the cam follower track of an augmenter case. The heating apparatus includes two heating elements, the first of which is sized to fit inside a recess in the engine component, such as the cam follower track, and the second of which is sized to fit outside the recess, adjacent to the first heating element. The heating apparatus provides heat to the welded area from two sides and, by focusing heat application on the welded area, the apparatus minimizes the heat delivered to other parts of the engine component. 
         [0021]    Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For example, the heating apparatus could be used to locally heat treat any weld-repaired area on an engine case or engine hardware. Due to the round shape of the heating elements, this design is particularly advantageous for use in heat treating either inside or outside corners, or on edges where two surfaces meet.