Piercing apparatus, plug used for piercing apparatus, and method for producing seamless steel pipe
View Patent ↗There is provided a piercing apparatus in which the occurrence of an inner surface flaw in a hollow shell is suppressed. A piercing apparatus ( 10 ) according to an embodiment of the present invention is the piercing apparatus ( 10 ) which pierces a billet ( 18 ). The piercing apparatus ( 10 ) has a plug ( 14 ). The plug ( 14 ) has a through hole ( 30 ). The through hole ( 30 ) extends along the central axis, and allows the central portion of the billet ( 18 ) being pierced to pass therethrough.
1. A piercing apparatus for piercing a billet, comprising:
a plug having a through hole which extends along a central axis of the plug and through which a central portion of the billet being pierced is allowed to pass, and
a mandrel connected to a rear end of the plug, the mandrel having a connection hole extending on a central axis of the mandrel and connectable to the through hole, a size of the connection hole being equal to or larger than a size of the through hole at a position where the connection hole connects to the through hole.
2. The piercing apparatus according to claim 1 , wherein the plug comprises:
a shell part having an outside diameter which increases from a front end of the plug toward the rear end thereof; and
a nose part which is provided at a front end of the shell part, and protrudes to an axial direction of the plug, and
the through hole has an opening in a center of a front end of the nose part.
3. The piercing apparatus according to claim 2 , wherein
the nose part has an outside diameter which increases from the front end of the plug toward the rear end thereof; and
a taper angle of a fore end portion of the shell part is larger than a taper angle of a rear end portion of the nose part.
4. The piercing apparatus according to claim 3 , wherein a front end surface of the nose part is flat.
5. The piercing apparatus according to claim 3 , wherein a peripheral edge of the front end surface of the nose part is rounded.
6. The piercing apparatus according to claim 1 , wherein a transverse cross-sectional shape of the through hole increases from a front end of the plug toward the rear end thereof.
7. The piercing apparatus according to claim 1 , wherein the piercing apparatus further comprises a plurality of rolls arranged around an axial direction of the plug.
8. The piercing apparatus according to claim 7 , wherein the piercing apparatus is of an inclined rolling type in which each of the plurality of rolls is an inclined roll.
9. The piercing apparatus according to claim 7 , wherein
the piercing apparatus is of a press roll type, and wherein the piercing apparatus further comprises a pusher rod for pushing the billet into the plug, and each of the plurality of rolls is a grooved roll.
10. The piercing apparatus according to claim 1 , wherein
the piercing apparatus is a piercing press type, and wherein the piercing apparatus further comprises a container for accommodating the billet, and the plug press-pierces the billet in an axial direction of the billet.
11. A method for producing a seamless steel pipe, comprising the steps of:
preparing a piercing apparatus comprising a plug having a through hole extending along a central axis of the plug and a mandrel connected to a rear end of the plug, the mandrel having a connection hole extending on a central axis of the mandrel and connectable to the through hole, a size of the connection hole being equal to or larger than a size of the through hole at a position where the connection hole connects to the through hole; and
piercing a billet by using the piercing apparatus while a central portion of the billet is allowed to pass through the through hole in the plug.