Radiant tube

Abstract

A radiant tube formed of a heat resistant metal includes at least one bent tube ( 3 A ( 3 C)) which connects straight tubes ( 2 A, 2 B ( 2 C, 2 D)) to each other. Combustion gas from a burner 5 is fed through one of the straight tubes ( 2 A, 2 B ( 2 C, 2 D)). The radiant tube is characterized in that at least as the bent tube 3 A ( 3 C) located closest to the burner 5 , there is employed a cast body having an outer diameter ranging from 150 to 210 mm and a wall thickness ranging from 3 to 8 mm.

1 . A radiant tube formed of a heat resistant metal comprising at least one bent tube which connects a pair of straight tubes to each other to facilitate feeding of a combustion gas from a burner through one of said straight tubes;
 wherein said bent tube located closest to said burner comprises a cast body having an outer diameter ranging from 150 to 210 mm and a wall thickness ranging from 3 to 8 mm.   
     
     
         2 . The radiant tube according to  claim 1 , wherein the bent tube has a smaller wall thickness at its portions near the connections to the straight tubes than the remaining portion thereof. 
     
     
         3 . The radiant tube according to  claim 1 , wherein the radiant tube comprises a plurality of said bent tubes, all of which comprise the cast bodies having the wall thickness ranging from 3 to 8 mm. 
     
     
         4 . The radiant tube according to  claim 1 , wherein the straight tube has a wall thickness of 7 mm or less. 
     
     
         5 . The radiant tube according to  claim 1 , wherein the straight tube has a smaller wall thickness at its portion near the connection to the bent tube than the remaining portion thereof. 
     
     
         6 . (canceled) 
     
     
         7 . The radiant tube according to  claim 2 , wherein the radiant tube comprises a plurality of said bent tubes, all of which comprise the cast bodies having the wall thickness ranging from 3 to 8 mm. 
     
     
         8 . The radiant tube according to any one of  claims 1 - 7 , wherein the straight tube comprises a cast body having a greater wall thickness than that of the bent tube.