Stretch-reducing mill having improved diameter tolerance and wall thickness tolerance

Abstract

A stretch-reducing mill (1) for producing seamless pipes (R), which comprises a plurality of roll stands (10), which are arranged one after the other in a conveying direction (F) of the pipes (R) and each have three rolls (11) arranged at an angular distance of 120°, wherein the roll stands (10) are divided into at least two groups (A, B) each having at least two roll stands (10); the rolls (11) of adjacent roll stands (10) within a group (A, B) are inclined relative to each other by an intra-group angle αI; and the rolls (11) of the roll stands (10) of adjacent groups (A, B) are inclined relative to each other by a group angle αG that is less than the intra-group angle αI.

Description

TECHNICAL FIELD[0001]The invention relates to a stretch-reducing mill for the production of seamless tubes, which has a plurality of roll stands arranged one behind the other in a conveying direction of the tubes, each with three rolls arranged at an angular distance of 120°.BACKGROUND OF THE INVENTION[0002]In the manufacture of seamless tubes, stretch-reducing and / or sizing mills are used which have several rolling stands arranged one behind the other in the conveying direction of the tube. The roll stands usually have three rolls which are arranged symmetrically about the pipe at an angular distance of 120°.[0003]It is known to arrange adjacent roll stands offset by 60° relative to one another, so that sections of the tube to be rolled are rolled alternately in the caliber base and from the caliber jump of the rolls. Thus, WO 2017 / 068533 A1 describes a rolling mill with a first section, which has several roll stands and is set up for rolling via a mandrel introduced into the tube,...

AI Technical Summary

Benefits of technology

This invention improves the quality of rolling for seamless tubes by creating a more complete and even wall thickness. This is achieved through a group of rolls that are inclined at an angle, which allows for a better match of the inner and outer polygons of the tube. The angle is small to prevent damage to the rolling stock. The rolls within the groups are shaped to prevent material from getting into the gap between them. The neutral roll stands are part of the same groups as the active roll stands, which helps to maintain a consistent temperature and prevents damage to the pipe. This patent text provides a technical solution for improving the rolling quality of seamless tubes.

Problems solved by technology

Especially in the case of thick-walled pipes in connection with large diameter reductions, the inside of the pipe is unevenly formed in the stretch-reducing mill due to the uneven speed distribution between the caliber base and the caliber jump of the rolls.

When the rolling mill functions as an extraction mill, additional complications result from temperature differences from the preceding stretching unit, which also cause different forming conditions between the caliber base and the caliber jump.

A four-roller design as an alternative is mostly out of the question due to the limited installation space for the roller bearings and the associated low capacity to absorb the forming forces.

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