Piercing and rolling plug, method of regenerating such piercing and rolling plug, and equipment line for regenerating such piercing and rolling plug

An equipment line for regenerating a piercing and rolling plug for recycled use on a piercing and rolling mill to be employed in seamless steel pipe production, the equipment line comprising:

• a mandrel delivery and receipt apparatus for delivering a mandrel with the plug being mounted thereon and recovering the mandrel after use in piercing and rolling;
• a plug exchange apparatus for receiving the mandrel after use in piercing and rolling from the mandrel delivery and receipt apparatus and delivering the mandrel to the mandrel delivery and receipt apparatus after replacement of the regenerated plug for the as-used plug in piercing and rolling;
• a shot blasting apparatus for receiving the as-used plug in piercing and rolling from the plug exchange apparatus and subjecting the surface of the as-used plug in piercing and rolling to shot blasting;
• and
• an electric arc spraying apparatus for receiving the plug treated in the shot blasting apparatus;
• regenerating the plug by electric arc spraying by use of an iron wire in such a manner that the spray nozzle is gradually distanced from the surface to be sprayed, thereby forming a film which is composed of oxides and Fe, and comprises higher levels of oxides on a surface layer side than on the base metal side;
• and delivering the thus-regenerated plug to the plug exchange apparatus,
• wherein, being arranged in above order and in these apparatuses so arranged, the as-used plugs in piercing and rolling are successively replaced each with the regenerated plug to be mounted on the mandrel and fed to the piercing and rolling mill, which is performed in a repeated manner.