INNER-SURFACE CONTROL TOOL, PLUG, MANDREL, HOT-ROLLING MILL, PUNCHING PRESS, AND DRAW BENCH

摘要

This inner-surface control tool is provided with a mandrel, a plug that is removably joined to said mandrel, and a joining member that magnetically joins the plug and the mandrel to each other. Either the plug or the mandrel has a column-shaped part that extends in the direction of the axis thereof, and the other has a connection hole, extending in the direction of the axis thereof, into which the column-shaped part is inserted. The abovementioned joining member is a permanent magnet attached to the column-shaped part and/or the connection hole.