Drawing rolling method for mandrel mill

Abstract

The present invention provides a drawing rolling method of a mandrel mill capable of preventing overfilling and underfilling by a combination of grooved rolls. When the tube blank Cr content is more than 10%, set the outer diameter of the hollow tube blank so that the ratio (the outer perimeter of the hollow tube blank/the tube blank outer perimeter at the exit side of the finishing mill) is more than 1.1; when the tube blank When the Cr content is less than 10%, the outer diameter of the hollow shell is set so that the ratio is less than 1.1. Set the pass profile of the pass rolls that are respectively arranged on the 1st and 2nd rolling mills, so that the pass circumference determined by the plurality of pass rolls on the 1st rolling stand of the mandrel mill satisfies ( 1) Equation, the girth circumference determined by the plurality of gage rolls installed on the second rolling mill satisfies (2) Equation, and the girth circumference of each of the first rolling mill and the second rolling mill satisfies (3) Equation . After such setting, stretch rolling of the blank pipe is performed using a mandrel mill.

Description

technical field [0001] The present invention relates to a stretch rolling method of a mandrel mill for seamless tubes. Specifically, the present invention relates to a stretch rolling method capable of effectively preventing so-called overfilled or underfilled mandrel mills from being generated in stretch rolling in a mandrel mill. Background technique [0002] In the manufacture of seamless steel pipes by the Mannesmann-mandrel seamless pipe mill, firstly, the round billet or square billet is put into the rotary hearth heating furnace and heated to 1200-1260°C, In the piercing machine, the hollow hollow tube blank is manufactured by piercing and rolling with plugs and rolls. Next, the hollow shell is used as a raw material, and the shell is stretch-rolled by a mandrel mill to reduce the shell to a predetermined thickness. Then, the billet is sizing-rolled to a predetermined outer diameter by a sizing mill to manufacture a seamless steel pipe as a product. [0003] Conven...

AI Technical Summary

Problems solved by technology

When only replacing the groove roll of the mandrel mill for one time, even if the same outer diameter is adjusted for production change, each seamless steel pipe composed of ordinary steel and alloy steel has to be manufactured separately. The replacement time of the grooved roll is doubled

On the other hand, in order not to increase the replacement time of the grooved rolls in the sizing mill, the grooved rolls of the mandrel mill must be replaced every time the production is changed to adjust the outer diameters. No matter how it is done, it will take a long time. Time stops the entire pipe-making process, drastically reducing productivity

[0012] In addition, the invention disclosed in Patent Document 2 also shows the appropriate conditions for specifying a blank pipe made of alloy steel such as 13% Cr steel having a specific size, and has the same problems as the invention disclosed in Patent Document 1.

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