Mandrel bar null for seamless steel tubes production

摘要

PROBLEM TO BE SOLVED: To enable the change of an only rolling part, to re-machine the only rolling part when a flaw occurred on the rolling part, and to enable the reduction of a re-machining cost and the supply quantity of a stock to a limit by dividing the mandrel bar main body into the rolling part coming into contact with a shell and a holding part which does not come into contact with the shell, and combining them with threads. ;SOLUTION: The mandrel bar is divided into the rolling part 3 coming into contact with the shell and the holding part 2 which does not come into contact with the shell, and the divided parts are connected by connecting threads 19, The threads 19 have tapers in a range of 1/16 to 1/6 in the ratio of a diameter in the longitudinal direction to a distance in the longitudinal direction. the workability of connecting by the threads can be improved by a mechanism that the fitting of the threads is started after the tip of a male thread has been inserted into the inside of a female thread to some extent. Consequently, making the rolling part ultrasmall is realized, and minimizing length required for the re-machining at the time of the wear of the rolling part and the occurrence of the flaw, becomes possible.;COPYRIGHT: (C)1998,JPO