Method and device for controlling a stretch reducing rolling mill for wall thickness compensation

Abstract

A stretch reducing rolling mill for rolling pipes has a plurality of roll stands arranged in series in a conveying direction of a pipe. A wall thickness measuring device determines a wall thickness progression of the pipe prior to rolling. A control unit controls respective rotational speeds of the roll stands. A pipe position measuring device is arranged in front of the roll stands and continuously measures a current longitudinal coordinate of the pipe. The measured values of the longitudinal coordinate of the pipe are transmitted to the control unit. The control unit controls the rotational speeds of the roll stands based on both the determined wall thickness progression and the transmitted measured values of the current longitudinal coordinate of the pipe, in order to compensate for wall thickness variations of the pipe. A stretch reducing rolling mill is designed to carry out the method.

Claims

1. A method, comprising: providing a stretch reducing rolling mill having a plurality of roll stands (7) arranged one behind the other in a conveying direction of a pipe (6) to be rolled; determining, by a wall thickness measuring device (2-2, 9), a wall thickness progression (4) of the pipe (6) to be rolled prior to rolling; continuously measuring a current longitudinal coordinate (lx) of the pipe (6) by a pipe position measuring device (8) arranged in front of the plurality of roll stands (7) in the conveying direction; transmitting the measured values of the longitudinal coordinate (lx) of the pipe (6) to a control unit (1A, 1B); and controlling, by the control unit (1A, 1B), respective rotational speeds of the plurality of roll stands (7) during the rolling of the pipe based on the determined wall thickness progression (4) and the transmitted measured values of the current longitudinal coordinate (lx) of the pipe, in order to compensate for wall thickness variations of the pipe.

2. The method according to claim 1, wherein the control unit (1A, 1B) controls a rolling of a first section of the pipe based on the measured values of the longitudinal coordinate (lx) of the pipe, while the pipe position measuring device (8) continuously measures the current longitudinal coordinate (lx) of the pipe at a second section of the pipe.

3. The method according to claim 1, wherein the control unit (1B) controls a rolling of a first section of the pipe while the wall thickness measuring device (9) determines a wall thickness progression (4) at a second section of the pipe.

4. The method according to claim 1, wherein the measured values of the longitudinal coordinate (lx) of the pipe measured by the pipe position measuring device (8) are used for determining the wall thickness progression (4) and for transmission to the control unit (1B).

5. The method according to claim 1, wherein the pipe position measuring device (8) measures the longitudinal coordinate (lx) of the pipe only after the wall thickness measuring device (2-2) has determined the wall thickness progression over a total length of the pipe (6) to be rolled.

6. The method according to claim 1, wherein the control unit (1A, 1B) controls rotational speeds of the plurality of roll stands (7) based also on signals from sensors arranged inside the stretch reducing rolling mill and/or behind the stretch reducing rolling mill in the conveying direction of the pipe, in order to compensate for wall thickness variations of the pipe during rolling.

7. A control unit (1A, 1B) for a stretch reducing rolling mill for rolling pipes, the stretch reducing rolling mill having a plurality of roll stands (7) arranged one behind the other in a conveying direction of a pipe (6) to be rolled, wherein the control unit (1A, 1B) is configured to control respective rotational speeds of the plurality of roll stands (7) based on a wall thickness progression (4) of the pipe to be rolled, the wall thickness progression (4) being determined by a wall thickness measuring device (2-2, 9) prior to rolling, wherein the control unit (1A, 1B) is configured to receive measured values of a current longitudinal coordinate (lx) of the pipe (6) measured continuously by a pipe position measuring device (8) arranged in front of the plurality of roll stands (7) in the conveying direction, and wherein the control unit (1A, 1B) is further configured to control the rotational speeds of the plurality of roll stands (7) during the rolling of the pipe also based on the received measured values of the current longitudinal coordinate (lx) of the pipe, in order to compensate for wall thickness variations of the pipe.

8. A stretch reducing rolling mill for rolling pipes, comprising: a plurality of roll stands (7) arranged in series in a conveying direction of a pipe to be rolled; a wall thickness measuring device (2-2, 9) arranged in front of the plurality of roll stands for determining a wall thickness progression (4) of the pipe (6) to be rolled; a control unit (1, 1A, 1B) for controlling respective rotational speeds of the plurality of roll stands (7) during the rolling of the pipe; and a pipe position measuring device (8) arranged in front of the plurality of roll stands (7) in the conveying direction for continuously measuring a current longitudinal coordinate (lx) of the pipe and for transmitting the measured values of the current longitudinal coordinate (lx) of the pipe to the control unit (1A, 1B), wherein the control unit (1A, 1B) is configured to control the rotational speeds of the plurality of roll stands (7) during the rolling of the pipe based on the determined wall thickness progression (4) and the measured values of the current longitudinal coordinate (lx) of the pipe, in order to compensate for wall thickness variations of the pipe.

9. The stretch reducing rolling mill according to claim 8, wherein a conveying path of the pipe (6) to be rolled from the pipe position measuring device (8) to a first roll stand (7-1) of the plurality of roll stands (7) of the stretch reducing rolling mill in the conveying direction is shorter than a total length of the pipe (6) to be rolled.

10. The stretch reducing rolling mill according to claim 8, wherein a conveying path of the pipe (6) to be rolled from the pipe position measuring device (8) to a first roll stand (7-1) of the plurality of roll stands (7) of the stretch reducing rolling mill in the conveying direction is shorter than a half of a total length of the pipe (6) to be rolled.

11. The stretch reducing rolling mill according to claim 8, wherein a conveying path of the pipe (6) to be rolled from the pipe position measuring device (8) to a first roll stand (7-1) of the plurality of roll stands (7) of the stretch reducing rolling mill in the conveying direction is shorter than a quarter of a total length of the pipe (6) to be rolled.

12. The stretch reducing rolling mill according to claim 8, wherein a conveying path of the pipe (6) to be rolled from the wall thickness measuring device (9) to a first roll stand (7-1) of the plurality of roll stands (7) of the stretch reducing rolling mill in the conveying direction is shorter than a total length of the pipe (6) to be rolled.

13. The stretch reducing rolling mill according to claim 8, wherein a conveying path of the pipe (6) to be rolled from the wall thickness measuring device (9) to a first roll stand (7-1) of the plurality of roll stands (7) of the stretch reducing rolling mill in the conveying direction is shorter than a half of a total length of the pipe (6) to be rolled.

14. The stretch reducing rolling mill according to claim 8, wherein a conveying path of the pipe (6) to be rolled from the wall thickness measuring device (9) to a first roll stand (7-1) of the plurality of roll stands (7) of the stretch reducing rolling mill in the conveying direction is shorter than a quarter of a total length of the pipe (6) to be rolled.

15. The stretch reducing rolling mill according to claim 8, wherein the pipe position measuring device (8) and the wall thickness measuring device (9) are configured for simultaneous measurement of the pipe (6) to be rolled and are configured as an integrated device (10).

16. The stretch reducing rolling mill according to claim 8, wherein a conveying path of the pipe to be rolled between the wall thickness measuring device (2-2) and the pipe position measuring device (8) is longer than a total length of the pipe (6) to be rolled.

17. The stretch reducing rolling mill according to claim 8, wherein the stretch reducing rolling mill is coupled to or provided with sensors arranged inside the stretch reducing rolling mill and/or behind the stretch reducing rolling mill in the conveying direction of the pipe, and wherein the control unit (1A, 1B) is configured to control the rotational speeds of the plurality of roll stands (7) also based on signals from the sensors, in order to compensate for wall thickness variations of the pipe during rolling.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) To illustrate the proposed method and the proposed stretch reducing rolling mill, exemplary embodiments of the present invention will now be presented with reference to the following figures.

(2) FIG. 1 schematically illustrates a stretch reducing rolling mill with a wall thickness measuring device and a proximity sensor in front of the roll stands, which represents a starting point for the exemplary embodiments shown in FIG. 2 and FIG. 3.

(3) FIG. 2 schematically illustrates a stretch reducing rolling mill of an exemplary embodiment with a wall thickness measuring device and a separate pipe position measuring device in front of the roll stands.

(4) FIG. 3 schematically illustrates a stretch reducing rolling mill of an exemplary embodiment with an integrated wall thickness measuring device and pipe position measuring device in front of the roll stands.

(5) In the figures, identical or similar components are designated with the same reference signs across figures.

DETAILED DESCRIPTION

(6) For better clarification of the exemplary embodiments, a stretch reducing rolling mill with a wall thickness measuring device and a proximity sensor in front of the roll stands is first presented with reference to FIG. 1. This represents the starting point for the exemplary embodiments illustrated in FIG. 2 and FIG. 3.

(7) FIG. 1 schematically shows the pipe measuring process (see phase A) and the pipe rolling process (see phase B). In a phase A, which is clearly before the pipe to be rolled enters the roll stands, the pipe 6 to be rolled is guided in its longitudinal direction through the wall thickness measuring device 2-2, which radiometrically measures a current wall thickness s of the pipe 6 during the pipe movement and transmits it to an evaluation unit 3. Together with the measurement of the current wall thickness s, a measurement of the current longitudinal coordinate lx of the pipe 6 is performed in a pipe position measuring device 2-1 during the passage of the pipe 6 through the wall thickness measuring device 2-2. The measurement of the current longitudinal coordinate lx can be carried out optically, for example, as illustrated in FIG. 1. The evaluation unit 3 assigns the measured current wall thicknesses s and the measured current longitudinal positions lx of the pipe 6 to be rolled, at which the wall thickness measurements are carried out, to one another and thus determines a wall thickness progression 4 of the pipe 6 to be rolled. From the measured current longitudinal coordinates of the front and rear pipe ends, the evaluation unit 3 also determines the total pipe length lges of the pipe 6 to be rolled.

(8) The determined wall thickness progression 4 and the determined total pipe length lges are transmitted by the evaluation unit to a control unit 1 for the stretch reducing rolling mill. The measurement of the current longitudinal coordinate lx of the pipe 6 explained with respect to FIG. 1 serves exclusively to determine the wall thickness progression 4, and the measured values of the current longitudinal coordinate lx are not transmitted separately to the control unit 1. The control unit 1 is designed to control the respective rotational speeds of the roll stands 7 or their work rolls, as the case may be, on the basis of the wall thickness curve 4 determined and transmitted by the evaluation unit 3. After the determination of the wall thickness progression 4, the pipe 6 to be rolled is fed to a reheating furnace (not illustrated) and then, marked in FIG. 1 as phase B for the same pipe 6, to the roll stands 7 of the stretch reducing rolling mill. To record the arrival of the pipe 6 to be rolled at the stretch reducing rolling mill, a proximity sensor 5 designed as a photocell is arranged at a distance a in front of the roll stands 7 of the stretch reducing rolling mill. The proximity sensor 5 records the arrival of the pipe tip of the pipe 6 to be rolled and reports the detection point in time t0 to the control unit 1, whereupon the control unit 1 continuously measures the time t from this point in time t0. The distance a between the proximity sensor 5 and the first roll stand 7-1 is known to the control unit 1. The approach speed v of the pipe 6 to the first roll stand 7-1 is also known to the control unit 1. The approach speed v can be a predetermined value or can be derived during operation, for example, from the rotational speeds of the roller table motors.

(9) For controlling the rotational speeds of the roll stands 7 during the passage of the pipe through the roll stands 7, the control unit 1 requires current position information as to which location or longitudinal position, as the case may be, of the pipe to be rolled currently reaches the first roll stand 7-1. With this current position information, the control unit 1 determines from the previously determined wall thickness progression 4 of the pipe 6 to be rolled whether the location of the pipe that currently enters the first roll stand 7-1 has a wall thickness s that deviates from the nominal wall thickness, which makes it necessary to change the rotational speeds of the roll stands. The control unit 1 determines the required rotational speed changes by means of an algorithm known per se, wherein the extent of the rotational speed changes depends on the size of the wall thickness deviation. The control unit determines the current position or longitudinal coordinate lx, as the case may be, of the pipe entering the first roll stand 7-1 as:
lx=lges+a−v.Math.(t−t0)

(10) This calculation rule provides position values for lx in the limits of 0≤lx≤lges.

(11) With the control of the rotational speeds of the roll stands 7 illustrated in FIG. 1 for the purpose of compensating for variations in the wall thickness of the pipe to be rolled, the longitudinal coordinate lx currently entering the first roll stand 7-1 is determined indirectly, specifically by measuring the time t since the point in time t0 determined by the proximity sensor 5 and by using the approach speed v of the pipe 6.

(12) FIG. 2 illustrates an exemplary embodiment of a proposed stretch reducing rolling mill, which results from a modification of the structure illustrated in FIG. 1. In the exemplary embodiment illustrated in FIG. 2, the wall thickness progression 4 is determined as already explained with reference to FIG. 1, such that no further explanation is required. However, instead of the proximity sensor 5 illustrated in FIG. 1 for detecting the pipe tip, in the exemplary embodiment illustrated in FIG. 2, a pipe position measuring device 8 is provided, which continuously and with high temporal resolution measures the current longitudinal coordinate lx of the pipe 6 or the pipe length lx1, as the case may be, which has already passed the pipe position measuring device 8. The pipe position measuring device 8 is arranged at a distance a in front of the first roll stand 7-1 of the stretch reducing rolling mill and continuously measures the current longitudinal coordinate lx of the pipe. The measured values of the pipe position measuring device 8 are continuously transmitted to the control unit 1A. The control unit 1A determines the current position or longitudinal coordinate, as the case may be, of the pipe 6 entering the first roll stand 7-1 as:
lx=lges−lx1+a

(13) This immediate determination of the longitudinal position of the pipe 6 currently entering the first roll stand 7-1 offers the advantage of a higher accuracy of the determination of the position of the pipe than with the structure illustrated in FIG. 1. Since the position of the pipe entering the first roll stand 7-1 in accordance with the exemplary embodiment of FIG. 2 can be determined very precisely, the control unit 1A can determine the current wall thickness s of the pipe at this position very precisely from the determined wall thickness progression 4, and can therefore also control the rotational speeds of the roll stands 7 very precisely on the basis of the determined current wall thickness.

(14) An essential difference between the stretch reducing rolling mills illustrated in FIG. 1 and FIG. 2 with upstream measuring devices is that, with the exemplary embodiment illustrated in FIG. 2, the measured values of the current longitudinal position of the pipe to be rolled are continuously transmitted to the control unit 1A, and the control unit 1A controls the rotational speeds of the roll stands also on the basis of these measured values, in order to compensate for wall thickness variations of the pipe to be rolled.

(15) The exemplary embodiment in accordance with FIG. 2 also provides a particularly great ability to compensate for wall thickness variations of the pipe to be rolled, if the pipe position measuring device 8 measures the current longitudinal coordinate of a rear section of the pipe, while the control device 1A simultaneously controls the rotational speeds of the roll stands 7 during the rolling of a front section of the pipe. In such a case, the conveying path of the pipe from the pipe position measuring device 8 to the first roll stand 7-1 of the stretch reducing rolling mill is shorter than the total length lges of the pipe 6 to be rolled.

(16) The exemplary embodiment illustrated in FIG. 2 is preferably used if a stretch reducing rolling mill with an already existing wall thickness measuring device, which measures the pipe to be rolled well before it enters the roll stands, is to be improved with regard to the precision of the compensation of wall thickness variations.

(17) FIG. 3 illustrates an additional exemplary embodiment of a proposed stretch reducing rolling mill, with which, unlike the exemplary embodiment of FIG. 2, a wall thickness measuring device 9 is arranged close to the first roll stand 7-1 of the stretch reducing rolling mill. The conveying path of the pipe to be rolled from the wall thickness measuring device 9 to the first roll stand 7-1 is shorter than the total length lges of the pipe 6 to be rolled. Preferably, the pipe is simultaneously in the wall thickness measuring device 9 and the roll stands 7 of the stretch reducing rolling mill for a major part of the rolling time. The pipe position measuring device 8 is preferably designed together with the wall thickness measuring device 9 as an integrated device 10, such that the pipe position measuring device 8 and the wall thickness measuring device 10 measure the pipe 6 simultaneously.

(18) As illustrated in FIG. 3, the measured values of the pipe position measuring device 8 are duplicated and simultaneously fed to the evaluation unit 3 for determining the wall thickness progression 4 and to the control unit 1B for controlling the rotational speeds of the roll stands. While the pipe position measuring device 8 continuously measures the longitudinal coordinate lx and continuously transmits a corresponding data stream to the control unit 1B, the evaluation unit 3 continuously transmits a data stream to the control unit 1B, which represents the determined wall thickness progression 4 of the already measured pipe section. As already explained with reference to FIG. 2, the control unit 1B, taking into account the known distance a of the integrated device 10 of the pipe position measuring device and the wall thickness measuring device from the first roll stand 7-1, determines from the measured length coordinate of the pipe currently transmitted by the pipe position measuring device which pipe position or pipe coordinate, as the case may be, is currently entering the first roll stand, and which pipe section has already entered the roll stands 7. At the same time, the control unit 1B determines the current wall thickness at the pipe position currently entering the first roll stand 7-1 from the data stream of the wall thickness progression 4 and calculates any necessary rotational speed corrections on the basis of this data, so that the wall thickness variations of the pipe to be rolled are corrected during rolling.

(19) The exemplary embodiment illustrated in FIG. 3 offers a particularly high precision with regard to the compensation of wall thickness variations of the pipe to be rolled, since the current wall thickness and the current longitudinal coordinate of the pipe are measured at a small distance from the first roll stand, while at the same time a front section of the pipe is rolled.

LIST OF REFERENCE SIGNS

(20) 1, 1A, 1B Control unit 2-1 Pipe position measuring device 2-2 Wall thickness measuring device 3 Evaluation unit 4 Determined wall thickness 5 Proximity sensor 6 Pipe 7 Roll stands 7-1 First roll stand 8 Pipe position measuring device 9 Wall thickness measuring device 10 Integrated measuring device a Distance between proximity sensor or pipe position measuring device, as the case may be, and first roll stand lges Total length of the pipe lx Longitudinal coordinate lx1 Pipe length already measured by pipe position measuring device s Wall thickness of the pipe t0 Point in time of pipe tip detection t Current time v Approach speed of the pipe