| 摘要 |
PROBLEM TO BE SOLVED: To provide an internally grooved heating tube produced by electric stitching system in which the ridge part of a roll in a grooving mill is protected from chipping. SOLUTION: Under developed state, inner surface of a heating tube 1 is sectioned into a plurality of regions R1, R2,..., Rn of specified width continuous in the length direction. A large number of fins 10 having a specified torsional angleθwith respect to the tube axis are formed in the odd regions R1 when viewed from one side and a large number of fins 11 having a specified torsional angle -q with respect to the tube axis are formed in the even regions R2. The height h or the base part width w of the fins 10, 11 increases gradually toward the boundary part 12 of odd and even regions R1, R2 and the maximum value of the height h or the base part width w is in the range of 1.04-1.3 of the minimum value.
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