Manufacturing method for strut shield collar of gas turbine exhaust diffuser

Abstract

A method for casting a collar ( 44, 46 ) for a heat shield ( 36 ) of a strut ( 32 ) in a gas turbine exhaust section ( 20 ). A casting geometry ( 60, 70 ) is defined with extra wall thickness ( 56, 68 ) in an area of wall curvature ( 53, 54 ), which provides a flow path beyond a final geometry of the collar to facilitate a flow of molten metal in the mold ( 63, 64 ). The extra thickness is removed after casting, leaving the collar in its final geometry, which may have uniform wall thickness (T, T2). The extra thickness in the casting geometry may be provided by increased radius (R3) in the wall curvature and/or by casting feed portals ( 66, 68 ) that span the wall curvature between a tubular portion ( 50 ) and a flange ( 52 ) of the collar.

The invention claimed is: 
     
         1 . A method for manufacturing a collar for a gas turbine exhaust diffuser strut shield, the method comprising:
 casting the collar of metal in a mold that provides a flow path defining a casting geometry of the collar in excess of a final geometry of the collar, wherein the flow path facilitates a flow of the metal through a casting restriction region into the final geometry; and then   removing excess metal beyond the final geometry to conform the collar to the final geometry.   
     
     
         2 . The method of  claim 1 , wherein:
 the metal is a superalloy;   the flow path in excess of the final geometry enables the flow of the superalloy into the mold without pressure or vacuum assistance; and   the casting is performed by gravity feed without pressure or vacuum assistance.   
     
     
         3 . The method of  claim 1 , wherein:
 the final geometry of the collar comprises a tubular portion with a flared flange on one end thereof and a smoothly curved transition there between;   the flange is disposed at an oblique angle relative to the tubular portion, and the transition varies from an area of lesser curvature angle on a first side of the tubular portion to an area of greater curvature angle on a second side thereof; and   the flow path in excess of the final geometry comprises space in the mold for an extra wall thickness in the collar along the area of greater curvature angle, and the removing step removes the extra wall thickness.   
     
     
         4 . The method of  claim 3 , wherein the extra wall thickness is provided by increasing a radius of curvature of an exterior surface of the curved transition in the casting geometry over the final geometry. 
     
     
         5 . The method of  claim 3 , further comprising providing the tubular portion and the welding flange with a uniform wall thickness in the final geometry. 
     
     
         6 . The method of  claim 3 , wherein the curvature angle is less than 85 degrees on the first side of the tubular portion and greater than 100 degrees on the second side thereof. 
     
     
         7 . The method of  claim 3 , further comprising casting the collar in a superalloy material that cannot flow around the area of greater curvature angle in the final geometry by gravity, but can flow around the area of greater curvature angle in the casting geometry via the flow path in excess of the final geometry by gravity. 
     
     
         8 . The method of  claim 1 , wherein:
 the final geometry of the collar comprises a tubular portion with a flared flange on one end thereof and a smoothly curved transition there between;   the flange is disposed at an oblique angle relative to the tubular portion, and the transition varies from an area of lesser curvature angle on a first side of the tubular portion to an area of greater curvature angle on a second side thereof; and   further comprising providing the flow path in excess of the final geometry by providing a plurality of mold feed portals, at least some of which span between the tubular portion and the flange across the transition area of greater curvature angle.   
     
     
         9 . The method of  claim 8 , further comprising providing the tubular portion and the welding flange with a uniform wall thickness in the final geometry. 
     
     
         10 . The method of  claim 1 , further comprising providing the final geometry with a uniform maximum thickness dimension around a curved transition area between a tubular portion and an oblique flared flange on an end of the tubular portion. 
     
     
         11 . A product formed by the method of  claim 1 . 
     
     
         12 . A product formed by the method of  claim 3 . 
     
     
         13 . A product formed by the method of  claim 8 . 
     
     
         14 . A method for manufacturing a collar for a gas turbine exhaust diffuser strut shield, the method comprising:
 casting the collar in a casting geometry with extra wall thickness beyond that of a final geometry of the collar in a curved transition area between a tubular portion and an oblique flared flange on an end of the tubular portion, wherein the extra wall thickness facilitates a flow of a molten metal into the final geometry; and   removing the extra wall thickness beyond the final geometry, leaving the final geometry with a uniform maximum thickness dimension around the curved transition area.   
     
     
         15 . The method of  claim 14 , further comprising:
 providing the final geometry with the transition area varying from a curvature angle of less than 85 degrees on a first side of the collar to a curvature angle of greater than 100 degrees on a second side of the collar;   the extra wall thickness is provided in the transition area on at least the second side of the collar;   and the removing step leaves the final geometry with the uniform maximum thickness dimension in the transition area around both the first and second sides of the collar.   
     
     
         16 . A product formed by the process of  claim 15 . 
     
     
         17 . The method of  claim 15 , further comprising providing the extra wall thickness in the casting geometry by a plurality of casting feed portals that span across the transition area between the tubular portion and the flange on an inner surface of the casting geometry. 
     
     
         18 . A product formed by the process of  claim 17 . 
     
     
         19 . The method of  claim 14 , further comprising providing the transition area in the final geometry with a curvature of compound radius having a relatively shorter radius adjacent the tubular portion and a relatively longer radius adjacent the flange. 
     
     
         20 . The method of  claim 14 , further comprising checking for the final geometry during the removing step with a manual template comprising an edge with a curvature of the transition area of the final geometry.