Process for manufacturing a seamless tube

Abstract

A high quality hollow material pipe is produced surely by controlling the number of times of rotary forging and shear deformation in an unsteady region during biting, preventing occurrence of flaw on the inner surface resulting from rotary forging effect and / or shear deformation at the top of the hollow material pipe, preventing uneven thickness from worsening at the top of the hollow material pipe, preventing mis-roll such as poor biting or releasing, and preventing the outside diameter at the bottom of the hollow material pipe from increasing. Using a pair of inclination rolls, a pair of disc rolls and a plug, the ratio (Dg / d) between thediameter (Dg) at the gorge portion of the inclination roll and the outside diameter (d) of a billet, the ratio (Dd / d) between the diameter (Dd) at the bottom of groove of the disc roll and (d), the ratio (Dd / Dg) between (Dg) and (Dd), the entrance face angle (theta1) of the inclination roll, and the square root of product (NsDf)<0.5> of the number of revolutions (Ns) of the billet in the biting unsteady region and the outside diameter reduction in thickness (Df) of that billet are made to satisfy a predetermined relational expression, and punching rolling is performed while the billet is rotary-moved to obtain a hollow material pipe and produce a seamless pipe finally.

Description

technical field [0001] The invention relates to a method for manufacturing seamless steel pipes. Specifically, the present invention relates to a method of manufacturing a seamless steel pipe through a process of piercing and rolling a billet using a piercer (inclined rolling mill) to manufacture a hollow shell. Background technique [0002] Generally, seamless steel pipes are produced by a Mannesmann plug mill method or a Mannesmann mandrel mill method. When producing seamless steel pipes by the above method, first, a round bar-shaped solid billet (in this specification, simply referred to as "slab") is inserted into a heating furnace and heated to a predetermined temperature. Next, the steel billet is taken out from the heating furnace, and the steel billet is pierced and rolled by a piercer to form a hollow billet. Then, mainly for the purpose of reducing the wall thickness of the hollow shell, the hollow shell is elongated and rolled using a plug mill, a mandrel mill, ...

AI Technical Summary

Problems solved by technology

[0009] As mentioned above, in the invention disclosed in Patent Document 1 or Patent Document 2, in addition to the internal properties of the billet and the thermal deformation ability, the rotational speed of the billet when the disc roll is used as the pipe guide of the piercer, the external Diameter reduction rate, etc., lead to inner surface defects and uneven thickness in the front part of the manufactured hollow tube blank, and the outer diameter of the rear part of the hollow tube blank increases, making it impossible to manufacture a full-length high-quality tube from the front part to the rear part. Hollow tube blank

[0010] In addition, in the past, although the front part of the hollow tube was cut off or repaired, the hollow tube had no inner surface defects and uneven thickness throughout the entire length, but this would definitely increase the manufacturing cost.

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