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.

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.

An apparatus for forging a hollow body from a pre-perforated hollow block includes forging tools that can be driven radially in relation to a forging axis, a clamping head which is displaceable on a guide bed in the direction of the forging axis and includes collet chucks for the hollow block, and a mandrel carriage which is arranged on the side of the clamping head facing away from forging tools, which is displaceable independently of the clamping head along the guide bed, and whose mandrel bar provided with the forging mandrel penetrates the clamping head coaxially to the forging axis. In order to provide advantageous constructional conditions the mandrel carriage includes an axial actuating drive for the mandrel bar and can be coupled in a tension-proof manner to the clamping head.

An apparatus for forging a hollow body from a pre-perforated hollow block includes forging tools that can be driven radially in relation to a forging axis, a clamping head which is displaceable on a guide bed in the direction of the forging axis and includes collet chucks for the hollow block, and a mandrel carriage which is arranged on the side of the clamping head facing away from forging tools, which is displaceable independently of the clamping head along the guide bed, and whose mandrel bar provided with the forging mandrel penetrates the clamping head coaxially to the forging axis. In order to provide advantageous constructional conditions the mandrel carriage includes an axial actuating drive for the mandrel bar and can be coupled in a tension-proof manner to the clamping head.

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.

A device for rolling of pipe blanks has a planetary cross-rolling mill, an advancing bed, a pipe blank feed, a pipe blank advancing unit that pushes the pipe blanks through the planetary cross-rolling mill, proceeding from the advancing bed, the unit having at least one advancing apparatus, and having a mandrel rod and a mandrel rod holder. The pipe blank feed has an axial pipe blank conveying unit that conveys a pipe blank axially into a readiness position, which is provided axially behind the mandrel rod holder. The advancing apparatus is disposed between the planetary cross-rolling mill and the mandrel rod holder, and has a slide.

A device for rolling of pipe blanks has a planetary cross-rolling mill, an advancing bed, a pipe blank feed, a pipe blank advancing unit that pushes the pipe blanks through the planetary cross-rolling mill, proceeding from the advancing bed, the unit having at least one advancing apparatus, and having a mandrel rod and a mandrel rod holder. The pipe blank feed has an axial pipe blank conveying unit that conveys a pipe blank axially into a readiness position, which is provided axially behind the mandrel rod holder. The advancing apparatus is disposed between the planetary cross-rolling mill and the mandrel rod holder, and has a slide.

The invention relates to a method for producing seamless steel tubes in a rolling mill train with one or more consecutively positioned longitudinal or cross-rolling units and an inside tool which is used as mandrel bar or piercing plug during the rolling process. The aim is to provide a method to reduce the eccentricity of the rolling stock considerably. To achieve this, the longitudinal axis of the inside tool is forced by means of an apparatus to a movement in a distance to the longitudinal axis of the rolling stock. Simultaneously the rotation of the tool around its axis is kept, driven by the rolling stock during rolling.

The invention relates to a method for producing seamless steel tubes in a rolling mill train with one or more consecutively positioned longitudinal or cross-rolling units and an inside tool which is used as mandrel bar or piercing plug during the rolling process. The aim is to provide a method to reduce the eccentricity of the rolling stock considerably. To achieve this, the longitudinal axis of the inside tool is forced by means of an apparatus to a movement in a distance to the longitudinal axis of the rolling stock. Simultaneously the rotation of the tool around its axis is kept, driven by the rolling stock during rolling.