A manufacturing method of a seamless metal pipe includes: preparing a plurality of mandrel bars in which lengths of work portions which come into contact with a hollow shell during elongating are different from one another; selecting a mandrel bar including a work portion having a length corresponding to the number of stands used in thickness reduction, among the plurality of mandrel bars; inserting the mandrel bar selected in the selecting into the hollow shell; and performing the elongating on the hollow shell into which the mandrel bar is inserted. Moreover, in the elongating, outer diameter reduction is performed by one of a preceding-stage stand group and a succeeding-stage stand group and the thickness reduction is performed by the other of the preceding-stage stand group and the succeeding-stage stand group, or the thickness reduction is performed by both of the preceding-stage stand group and the succeeding-stage stand group.

The present invention relates to a plant 10 for rolling a seamless tube. The plant comprises a rotary piercer 20 which is designed to pierce a billet 11 pressed against a plug 22 mounted on a rod so as to obtain a pierced blank 12. The rod is connected to a thrust block 26 designed to oppose the axial thrust which is produced on the rod during piercing. The plant also comprises a longitudinal mill 30 which is designed to roll the pierced blank 12 on a mandrel 32 so as to obtain a semi-finished tube 13. The mandrel is connected to a retaining block 34 designed to impart to the mandrel a predetermined speed during rolling. In the plant according to the invention the thrust block 26 and the retaining block 34 are formed by a single thrust/retaining block 36.

The invention also relates to a method for rolling a seamless tube.

The present invention relates to a plant 10 for rolling a seamless tube. The plant comprises a rotary piercer 20 which is designed to pierce a billet 11 pressed against a plug 22 mounted on a rod so as to obtain a pierced blank 12. The rod is connected to a thrust block 26 designed to oppose the axial thrust which is produced on the rod during piercing. The plant also comprises a longitudinal mill 30 which is designed to roll the pierced blank 12 on a mandrel 32 so as to obtain a semi-finished tube 13. The mandrel is connected to a retaining block 34 designed to impart to the mandrel a predetermined speed during rolling. In the plant according to the invention the thrust block 26 and the retaining block 34 are formed by a single thrust/retaining block 36.

The invention also relates to a method for rolling a seamless tube.

The present invention relates to a compact plant 10 for rolling a seamless tube. The plant comprises a rotary piercer 20 which defines a rolling axis X.sub.PR and is designed to pierce a billet 11 pressed against a plug 22 mounted on a rod so as to obtain a pierced blank 12. The rod is connected to a thrust block 26 designed to oppose the axial thrust during piercing. The plant also comprises a longitudinal mill 30 which defines a rolling axis X.sub.LL and is designed to roll the pierced blank 12 on a mandrel 32 so as to obtain a semi-finished tube 13. The mandrel is connected to a retaining block 34 designed to impart to the mandrel a predetermined speed during rolling. In the plant 10 according to the invention the rolling axes X.sub.PR and X.sub.LL coincide. The invention also relates to a method for rolling a seamless tube.

The present invention relates to a compact plant 10 for rolling a seamless tube. The plant comprises a rotary piercer 20 which defines a rolling axis X.sub.PR and is designed to pierce a billet 11 pressed against a plug 22 mounted on a rod so as to obtain a pierced blank 12. The rod is connected to a thrust block 26 designed to oppose the axial thrust during piercing. The plant also comprises a longitudinal mill 30 which defines a rolling axis X.sub.LL and is designed to roll the pierced blank 12 on a mandrel 32 so as to obtain a semi-finished tube 13. The mandrel is connected to a retaining block 34 designed to impart to the mandrel a predetermined speed during rolling. In the plant 10 according to the invention the rolling axes X.sub.PR and X.sub.LL coincide. The invention also relates to a method for rolling a seamless tube.

The invention relates to a pipe rolling plant 10 comprising a rotary piercer 20, a treatment station 30 and a main rolling mill 40. The rotary piercer and the treatment station are arranged so that the pierced blank 51 leaving them is arranged with the irregular tail 511 facing the main rolling mill 40 and with the regular head 510 facing the mandrel 41. The invention also relates to a rolling mill 40 comprising a plurality of rolling stations 43, each station comprising a plurality of rolling rolls 42, the radial position h of which is adjustable. The rolling mill also comprises a control circuit for calculating and/or measuring the distance d between the axes of rotation r of the rolls and the trailing edge 520 of the pipe 52. The control circuit is also designed to displace the rolling rolls radially towards the outside of the pipe in each rolling station 43.sub.n when the distance d assumes a predetermined value d.sub.0.

The invention relates to a pipe rolling plant 10 comprising a rotary piercer 20, a treatment station 30 and a main rolling mill 40. The rotary piercer and the treatment station are arranged so that the pierced blank 51 leaving them is arranged with the irregular tail 511 facing the main rolling mill 40 and with the regular head 510 facing the mandrel 41. The invention also relates to a rolling mill 40 comprising a plurality of rolling stations 43, each station comprising a plurality of rolling rolls 42, the radial position h of which is adjustable. The rolling mill also comprises a control circuit for calculating and/or measuring the distance d between the axes of rotation r of the rolls and the trailing edge 520 of the pipe 52. The control circuit is also designed to displace the rolling rolls radially towards the outside of the pipe in each rolling station 43.sub.n when the distance d assumes a predetermined value d.sub.0.

A manufacturing method of a seamless metal pipe includes determining whether a preceding-stage stand group is used in outer diameter reduction or in thickness reduction of a hollow shell; and performing elongating on the hollow shell, into which a mandrel bar is inserted, based on the determination. In addition, in the elongating, when the preceding-stage stand group is used in the outer diameter reduction, the hollow shell is rolled in a state where an inner surface of the hollow shell does not come into contact with the mandrel bar in the preceding-stage stand group, and the hollow shell is rolled in a state where the inner surface of the hollow shell comes into contact with the mandrel bar in the succeeding-stage stand group.

A device for handling mandrel rods in a rolling plant for rolling seamless tubes comprises an inserter. The inserter moves a mandrel rod in a rolling direction such that the mandrel rod, starting from an initial state, is pushed into a tube blank situated upstream of the mandrel rod. A retaining device has a fixing unit that is movable along the rolling line and is designed to temporarily hold the mandrel rod at an action point at a rear end of the mandrel rod and to carry out a working stroke. The mandrel rod can be inserted into the rolling mill in the rolling direction and pulled out of the rolling mill counter to the rolling direction by the retaining device. The retaining device is designed such that the starting position of the fixing unit lies between the two ends of the mandrel rod in the initial state.

A device for handling mandrel rods in a rolling plant for rolling seamless tubes comprises an inserter. The inserter moves a mandrel rod in a rolling direction such that the mandrel rod, starting from an initial state, is pushed into a tube blank situated upstream of the mandrel rod. A retaining device has a fixing unit that is movable along the rolling line and is designed to temporarily hold the mandrel rod at an action point at a rear end of the mandrel rod and to carry out a working stroke. The mandrel rod can be inserted into the rolling mill in the rolling direction and pulled out of the rolling mill counter to the rolling direction by the retaining device. The retaining device is designed such that the starting position of the fixing unit lies between the two ends of the mandrel rod in the initial state.