Centrifugally-cast tube and related method and apparatus for making same

Abstract

An improved centrifugally-cast tube is provided, along with a related method and apparatus of making the tube. The tube includes a plurality of grooves and bosses that are mechanically machined into an interior surface of the tube, such as by a broaching process. The profile of grooves and bosses may be defined by a plurality of intersecting concave and convex radii. The tube is resistant to creep, carburization and metal dusting. The tube also has an enhanced heat transfer rate, and a desirable surface roughness. A method of making the tube is also provided. The method essentially consists of mechanically deforming the interior surface of the tube by passing a series of cutting inserts on support rings having incrementally-differing dimensions over the interior surface. An apparatus is also provided which includes a telescoping shaft upon which is mounted at least one cutting tool that has a plurality of cutting inserts and is adapted to form a plurality of grooves and bosses in the interior surface of the tube. The grooves and bosses may be straight or spiraled.

1 . A centrifugally-cast tube comprising: 
 a tubular body made from a creep-resistant alloy,    the body having an exterior surface and an interior surface,    the interior surface including a plurality of bosses and a plurality of grooves, and    the plurality of bosses and grooves being mechanically machined into the interior surface.    
     
     
         2 . The tube of  claim 1 , wherein the plurality of bosses and grooves are defined by a plurality of intersecting concave and convex radii.  
     
     
         3 . The tube of  claim 1 , wherein the plurality of bosses and grooves are formed by a broaching process.  
     
     
         4 . The tube of  claim 1 , wherein the interior surface is resistant to carburization and metal dusting.  
     
     
         5 . The tube of  claim 1 , wherein the surface roughness and dimensional accuracy of the interior surface is superior to that of a centrifugally-cast tube wherein the plurality of bosses and grooves are formed by a electrochemical machining process.  
     
     
         6 . The tube of  claim 1 , wherein the plurality of bosses and grooves form a profile that is at least 5% longer than a circumference of a smallest circle that encompasses the entire resulting profile.  
     
     
         7 . The tube of  claim 1 , wherein the interior surface has a surface roughness of less than 125 RMS (CLA).  
     
     
         8 . A method of improving a centrifugally-cast tube comprising: 
 passing a first cutting tool having a plurality of first cutting inserts through a bore of the tube so as to mechanically remove a first quantity of material from the bore and to commence the formation of a plurality of grooves and bosses;    passing a second cutting tool having at plurality of second cutting inserts through the bore so as to mechanically remove a second quantity of material from the bore and to continue the formation of the plurality of grooves and bosses, the plurality of second cutting inserts having dimensions different than corresponding dimensions of the plurality of first cutting inserts; and    continuing to pass additional cutting tools having a plurality of additional cutting inserts through the bore so as to continue to mechanically remove additional quantities of material from the bore until a desired profile of grooves and bosses is achieved, each set of additional cutting tools having dimensions different than corresponding dimensions of the cutting inserts employed in the immediately preceding pass.    
     
     
         9 . The method of  claim 8 , wherein the dimensions of each subsequent set of cutting tools are larger than the corresponding dimensions of the cutting tools employed in the immediately preceding pass.  
     
     
         10 . The method of  claim 9 , wherein the dimensions incrementally increase at a rate of between 0.05 mm and 0.1 mm per pass.  
     
     
         11 . A method of improving a centrifugally-cast tube comprising: 
 forming a plurality of grooves and bosses in an interior surface of the tube by mechanically deforming the interior surface.    
     
     
         12 . The method of  claim 11 , wherein the plurality of grooves and bosses are gradually formed by passing a series of cutting tools having incrementally-differing dimensions over the interior surface.  
     
     
         13 . An apparatus for improving a centrifugally-cast tube comprising: 
 a first and a second guide adapted to hold the tube;    a telescoping shaft adapted to pass longitudinally through a bore of the tube; and    at least one cutting tool attached to the shaft and including a plurality of cutting inserts, the cutting tool being adapted to mechanically form a profile of grooves and bosses within the bore of the tube.    
     
     
         14 . The apparatus of  claim 13 , wherein the cutting inserts are indexable.  
     
     
         15 . The apparatus of  claim 13 , wherein the cutting inserts are provided with concave cutting surfaces.  
     
     
         16 . The apparatus of  claim 13 , wherein the cutting inserts are provided with convex cutting surfaces.  
     
     
         17 . The apparatus of  claim 13 , wherein the at least one cutting tool includes a plurality of cutting tools attached to the shaft, and further including at least one spacer collar disposed about the shaft and adapted to maintain the cutting tools in spaced relationship.  
     
     
         18 . The apparatus of  claim 13 , further including means for lubricating the apparatus.  
     
     
         19 . The apparatus of  claim 13 , further including means for attaching the at least one cutting tool to the shaft.  
     
     
         20 . The apparatus of  claim 13 , further including means for attaching the at least one cutting tool to the shaft.  
     
     
         21 . The apparatus of  claim 13 , further including at least one centering guide.