Piercing machine, and method for producing seamless metal pipe using the same

A piercing machine that performs piercing-rolling or elongating rolling of a material to produce a hollow shell, the machine comprising:

• a plurality of skewed rolls disposed around a pass line along which the material passes;
• a plug disposed on the pass line between the plurality of skewed rolls;
• a mandrel bar extending rearward of the plug along the pass line from a rear end of the plug;
• an outer surface cooling mechanism disposed around the mandrel bar, at a position that is rearward of the plug;
• and
• a frontward damming mechanism that is disposed around the mandrel bar at a position that is rearward of the plug and is frontward of the outer surface cooling mechanism,
• wherein an outer surface of the hollow shell advances through a cooling zone which has a specific length in an axial direction of the mandrel bar and is located rearward of the plug, as seen from an advancing direction of the hollow shell, the outer surface cooling mechanism ejects a cooling fluid toward an upper part of the outer surface, a lower part of the outer surface, a left part of the outer surface and a right part of the outer surface to cool the hollow shell inside the cooling zone,
• wherein the frontward damming mechanism comprises a mechanism that, when the outer surface cooling mechanism is cooling the hollow shell in the cooling zone, by ejecting the cooling fluid toward the upper part of the outer surface, the lower part of the outer surface, the left part of the outer surface and the right part of the outer surface of the hollow shell, and dam the cooling fluid from flowing to the upper part of the outer surface, the lower part of the outer surface, the left part of the outer surface and the right part of the outer surface of the hollow shell before the hollow shell enters the cooling zone, and
• wherein the outer surface cooling mechanism includes:
• an outer surface cooling upper member disposed above the mandrel bar as seen from an advancing direction of the hollow shell, the outer surface cooling upper member including a plurality of cooling fluid upper-part ejection holes which eject the cooling fluid toward the upper part of the outer surface of the hollow shell in the cooling zone;
• an outer surface cooling lower member disposed below the mandrel bar as seen from the advancing direction of the hollow shell, the outer surface cooling lower member including a plurality of cooling fluid lower-part ejection holes which eject the cooling fluid toward the lower part of the outer surface of the hollow shell in the cooling zone;
• an outer surface cooling left member disposed leftward of the mandrel bar as seen from the advancing direction of the hollow shell, the outer surface cooling left member including a plurality of cooling fluid left-part ejection holes which eject the cooling fluid toward the left part of the outer surface of the hollow shell in the cooling zone;
• and
• an outer surface cooling right member disposed rightward of the mandrel bar as seen from the advancing direction of the hollow shell, the outer surface cooling right member including a plurality of cooling fluid right-part ejection holes which eject the cooling fluid toward the right part of the outer surface of the hollow shell in the cooling zone,
• wherein the frontward damming mechanism includes:
• a frontward damming upper member including a plurality of frontward damming fluid upper-part ejection holes that is disposed above the mandrel bar as seen from the advancing direction of the hollow shell, and that ejects a frontward damming fluid toward the upper part of the outer surface of the hollow shell that is positioned in a vicinity of an entrance side of the cooling zone and dams the cooling fluid from flowing to the upper part of the outer surface of the hollow shell before the hollow shell enters the cooling zone;
• a frontward damming left member including a plurality of frontward damming fluid left-part ejection holes that is disposed leftward of the mandrel bar as seen from the advancing direction of the hollow shell, and that ejects the frontward damming fluid toward the left part of the outer surface of the hollow shell that is positioned in a vicinity of the entrance side of the cooling zone and dams the cooling fluid from flowing to the left part of the outer surface of the hollow shell before the hollow shell enters the cooling zone;
• and
• a frontward damming right member including a plurality of frontward damming fluid right-part ejection holes that is disposed rightward of the mandrel bar as seen from the advancing direction of the hollow shell, and that ejects the frontward damming fluid toward the right part of the outer surface of the hollow shell that is positioned in a vicinity of the entrance side of the cooling zone and dams the cooling fluid from flowing to the right part of the outer surface of the hollow shell before the hollow shell enters the cooling zone,
• wherein the frontward damming upper member ejects the frontward damming fluid diagonally rearward toward the upper part of the outer surface of the hollow shell that is positioned in a vicinity of the entrance side of the cooling zone from the plurality of frontward damming fluid upper-part ejection holes;
• the frontward damming left member ejects the frontward damming fluid diagonally rearward toward the left part of the outer surface of the hollow shell that is positioned in a vicinity of the entrance side of the cooling zone from the plurality of frontward damming fluid left-part ejection holes;
• and
• the frontward damming right member ejects the frontward damming fluid diagonally rearward toward the right part of the outer surface of the hollow shell that is positioned in a vicinity of the entrance side of the cooling zone from the plurality of frontward damming fluid right-part ejection holes.