MANDREL OF COIL BOX

According to the present invention, a mandrel of a coil box comprises: a cylindrical mandrel main body where a contral shaft is arranged inside, and having a slot into which the leading end of a high temperature bar is inserted; and a guide part arranged inside the mandrel main body from the edge wall in one side of the slot to block cooling and plastic deformation of the leading end of the bar inserted through the slot. According to the present invention, a guide part protruding toward the inside of the mandrel main body from the edge wall in one side of the slot is formed to non-contact the central shaft, when the leading end of the bar is inserted into the slot. Therefore, the cooling and plastic deformation of the leading end of the bar inserted through the slot can be blocked. Furthermore, the inserted length can be reduced. The present invention has an effect for preventing that the surface of a work roll is damaged due to a tail twist generated by the non-uniform temperature of a rolling tail part (corresponding to the leading end of a bar in mandrel coiling) when a steel sheet is rolled; and preventing the poor quality of a material due to damage in the surface of the work roll. In addition, the plastic deformation can not generated and a part contacting an edge wall in the other side of the slot can not be easily bent when the bar is wound in a mandrel by reducing the length of the leading end of the bar inserted through the slot. In other words, the leading end inserted when the bar is wound is not drooping and supporting the guide part by contacting the guide part with the proper force, so the initial inner winding of the bar about the mandrel is smoothly formed. Therefore, the present invention has the advantage of preventing that the operation is interrupted due to defect of forming an initial inner winding.