Method and device for producing seamless steel pipes having low eccentricity

Abstract

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.

Claims

1. A method of producing seamless steel tubes in a rolling mill train with one or more consecutively positioned longitudinal or cross-rolling units and a tool, which is used inside the rolling stock (1) during rolling, implemented as a mandrel bar or as a plug bar (4) with a piercing plug (3) arranged on a front tip of the bar (4), comprising piercing the rolling stock (1) with the piercing plug (3), rotating (7) the piercing plug (3) around its longitudinal axis (10) by rotating (5) the rolling stock (1) around its longitudinal axis of rotation (9), offsetting a longitudinal axis of rotation (10) of the piercing plug (3) a distance (11) from the longitudinal axis of rotation (9) of the rolling stock (1), keeping the rotational motion (7) of the piercing plug (3) around its longitudinal axis (10) in the direction of the rotation (5) of the rolling stock (1), and revolving the longitudinal axis of rotation (10) of the piercing plop (3) about the longitudinal axis (9) of the rolling stock (1).

2. A method according to claim 1, wherein the rotational motion of the piercing plug (3) generated by the rolling stock (1) generates the rotational movement of the axis (10) of the piercing plug (3) in an opposite direction to the rotation of the piercing plug (3).

3. A method according to claim 2, wherein the rotational motion of the piercing plug (3) and revolving of the axis (10) of the piercing plug (3) about the longitudinal axis (9) of the rolling stock (1) are in opposite clockwise or counterclockwise directions from one another.

4. A method according to claim 1 wherein the longitudinal axis (10) of the piercing plug (3) is forced to rotate with a higher frequency compared to the rotation of the rolling stock (1).

5. A method in accordance with claim 1, wherein the piercing plug (3) revolves around the axis (17) of the bar (4) upon rotation of the piercing plug (3) about its axis (10).

6. A method according to claim 1, additionally comprising passing the rolling stock (1) between a pair of rolls (2) as the rolling stock (1) is pierced by the piercing plug (3).

7. Apparatus for generating movement (11) of a longitudinal axis of rotation (10) of a piercing plug (3) a distance from a longitudinal axis of rotation (9) of rolling stock (1) pierced by the piercing plug (3), comprising a mandrel bar or plug bar (4) with the piercing plug (3) arranged on a front tip of the bar (4), such that rotational motion of the piercing plug (3) around its longitudinal axis (10) is kept in the direction of the rotation of the rolling stock (1), wherein the piercing plug (3) is arranged on the bar (4) with the respective axes of rotation (17, 10) offset from one another, the piercing plug (3) revolves around the axis (17) of the bar (4) upon rotation of the piercing plug (3) about its axis of rotation (10), and the axis of rotation 10 of the piercing plug (3) revolves about the axis (9) of rotation of the rolling stock (1).

8. A method according to claim 1, comprising arranging the piercing plug (3) on the front tip of the bar (4), arranging the axis (10) of the piercing plug (3) offset from the axis (17) of the bar (4), and driving and rotating the rolling stock (1) between two rotating rolls (2) by the rotating (7) piercing plug (3).

9. An apparatus according to claim 7, wherein the piercing plug (3) is arranged on the bar (4) to rotate in an opposite direction from rotation of the axis (10) of the piercing plug (3).

10. An apparatus according to claim 7, wherein the piercing plug (3) comprises a shaft (14) and additionally comprising gliding surfaces (16) through which the piercing plug shaft (14) is supported on the bar (4), the position of the longitudinal axis (10) of the piercing plug (3) is influenced without changing the rotational motion of the piercing plug (3).

11. An apparatus according to claim 7, wherein the piercing plug (3) comprises a shaft (14), the bar (4) comprises an adapter in turn comprising a hollow gear wheel (15) in which the shaft (14) is positioned such that rotational motion (7) of the piercing plug (3) generates rotation (11) of the axis (10) of the piercing plug (3) in an opposite direction.

Description

EXPLANATION TO THE FIGURES

(1) FIG. 1: Representation of the piercing process in a cross-rolling mill with help of a longitudinal section of the assembly of rolling stock and tools.

(2) FIG. 2: Representation of the piercing process in a cross-rolling mill with help of a cross section of the assembly of rolling stock and tools. (The representation is without showing the sidewise guides as they are irrelevant in the described context.) In FIG. 2a a centric piercing process is shown and in FIG. 2b an eccentric piercing process.

(3) FIG. 3: Representation of a cross section of the rolling stock with eccentricity of the wall thickness. The value of eccentricity is determined with (t.sub.maxt.sub.min)/(t.sub.max+t.sub.min)100%.

(4) FIG. 4: Representation of the distribution of the wall thickness of the rolling stock versus longitudinal coordinate and circumferential coordinate of the rolling stock.

(5) FIG. 5: Representation of a device for generating an eccentric rotational movement of the plug axis with which the rotation of the plug is in the direction and with the speed of the rotation of the rolling stock.

(6) FIG. 6: Representation of the generation of a rotational movement of the piercing plug axis which is opposite to the rotational motion of the piercing plug, with help of a gear wheel rolling inside a hollow gear wheel.

LIST OF REFERENCE NUMERALS

(7) 1 Rolling stock

(8) 1a Direction of rolling

(9) 2 Working roll

(10) 3 Piercing plug

(11) 4 Plug bar

(12) 5 Rotational motion of the rolling stock

(13) 6 Rotational motion of the rolls

(14) 7 Rotational motion of the piercing plug

(15) 8 Rotational motion of the plug bar

(16) 9 Longitudinal axis of the rolling stock

(17) 10 Longitudinal axis of the piercing plug

(18) 11 Rotational motion of the plug axis

(19) 12 Line of equal wall thickness

(20) 13 Angle between a line of equal wall thickness and the longitudinal axis of the rolling stock

(21) 14 Shaft of the plug with annual gear

(22) 15 Hollow gear wheel

(23) 16 Gliding surface

(24) 17 Longitudinal axis of the plug bar