JP7184109B2 - Seamless steel pipe rolling control method and manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a rolling control method and a manufacturing method for a seamless steel pipe.

As shown in FIG. 3, in a typical plug mill type seamless steel pipe manufacturing process, a seamless steel pipe is produced by heating a billet to a predetermined temperature in a rotary heating furnace (a) and then heating the heated billet in a piercer (b). A hollow shell is formed by piercing and rolling, the hollow shell is stretch-rolled by an elongator (c) and a plug mill (d) to reduce its wall thickness, and the hollow shell is rolled by a reeler (e) to reduce its wall thickness. It is manufactured by making the thickness uniform, reheating the hollow shell in a heating furnace (f), and rolling the reheated hollow shell with a sizer (g). Here, a piercing-rolling mill such as a piercer is used for the piercing-rolling, and a stretching-rolling mill such as a mandrel mill or a plug mill is used for the stretching-rolling. A sizing mill such as a reducer or a sizer is used for sizing rolling.

A sizer used for sizing rolling is a tandem type rolling mill having a plurality of stands arranged in series in the line direction, and the number of stands is generally about 5 to 28. Each stand also has a plurality of grooved rolls. FIG. 4 shows a general two-roll stand type sizer, in which grooved rolls 100 are arranged in series along the conveying direction (line direction) of the seamless steel pipe S. As shown in FIG. Although eight stands are selected for convenience in FIG. 4, an actual sizer can have a larger number of stands. Also, in a two-roll stand type sizer, grooved rolls are arranged with their rotation axes alternately shifted by 90 degrees. That is, the stands in which the rotation axes of the grooved rolls are arranged along the vertical direction and the stands in which the rotation axes of the grooved rolls are arranged along the horizontal direction are alternately arranged. In a three-roll stand type sizer, one stand has three caliber rolls, and each stand is arranged with the rotation axis of the caliber roll shifted by 60 degrees.

In sizing rolling, rolling is performed using such a sizing mill so that the dimensions of the seamless steel pipe are the final finished dimensions. However, due to factors such as wear of grooved rolls and mistakes in setting rolling conditions, the dimensional accuracy and roundness of the outer diameter of seamless steel pipes obtained by sizing-rolling may deteriorate. Against this background, methods have been proposed for improving the outer diameter dimensional accuracy and roundness of seamless steel pipes at the next rolling opportunity. Specifically, in Patent Document 1, when performing sizing rolling on a plurality of hollow shells, based on information such as rolling load and torque when rolling a certain hollow shell, A method for adjusting the pressing position of grooved rolls in subsequent rolling of hollow shells is described. Further, Patent Document 2 describes a method of determining the influence coefficient of the roll groove bottom distance of the last two stands on the delivery side tube outer diameter, and controlling the roll groove bottom distance using this influence coefficient.

Japanese Patent Application Laid-Open No. 2002-102912 JP-A-57-44411

However, as a result of extensive studies, the inventors of the present invention have found that conventional sizing rolling methods such as those described in Patent Documents 1 and 2 have the following problems. .

First, in the conventional sizing method, the outer diameter of the seamless steel pipe is gradually brought closer to the target outer diameter by reduction at each stand of the sizing mill, and the desired outer diameter is obtained by reduction at the final stand. Rolling is performed so that In order to ensure the roundness of the finally obtained seamless steel pipe, the cross-sectional shape of the seamless steel pipe is adjusted by filling the grooved roll with the seamless steel pipe in the final stand. Specifically, as shown in FIG. 5, the grooved rolls 100 used in sizing rolls are used with the facing surfaces of the caliber rolls 100a and 100b separated by a predetermined distance D1 rather than in contact with each other. be. The caliber roll 100 is usually designed so that the caliber shape becomes a perfect circle when the gap between the facing surfaces of the caliber rolls 100a and 100b is a predetermined distance D1. is called the reference gap.

Therefore, in the conventional sizing method in which the cross-sectional shape of the seamless steel pipe is made a perfect circle by filling the grooved rolls with seamless steel pipes in the final stand, the gap between the grooved rolls in the final stand is the reference gap. should be controlled as At that time, if the gap is determined, the outer diameter R of the bottom portion of the grooved roll (the distance between the roll bottom portions P1 and P2 of the caliber rolls 100a and 100b shown in FIG. 5) is also determined inevitably. is the outer diameter R of the bottom portion of the grooved roll. For this reason, in the conventional constant diameter rolling method, in order to obtain a desired product outer diameter while ensuring roundness, it is necessary to obtain a product having a desired bottom outer diameter when the gap is arranged so as to be a reference gap. It is necessary to use grooved rolls with an outer diameter. As a result, it is necessary to replace the grooved roll of the final stand each time the outer diameter of the seamless steel pipe to be manufactured changes. Further, when the grooved rolls are worn and the grooved dimensions are changed, the outer diameter dimensional accuracy and roundness are deteriorated, so that the grooved rolls must be re-cut to obtain the desired grooved dimensions. .

In the method described in Patent Document 1, it is necessary to fill the grooved roll of the final stand with the seamless steel pipe in order to ensure the roundness. It is necessary to replace the fluted rolls in the final stand. In addition, since the method described in Patent Document 2 does not consider the wear of the grooved rolls, if the grooved rolls are worn, the outer diameter dimensional accuracy and roundness are corrected to a good state. Can not do it.

The present invention has been made in view of the above problems, and an object of the present invention is to achieve excellent outer diameter dimensional accuracy and trueness even when the grooved rolls are worn without using grooved rolls suitable for individual products. It is an object of the present invention to provide a rolling control method and a manufacturing method for a seamless steel pipe capable of manufacturing a seamless steel pipe having circularity.

A seamless steel pipe rolling control method according to the present invention controls a sizing mill equipped with N (≧2) stands arranged in series in a conveying direction of a seamless steel pipe to reduce the diameter of the seamless steel pipe. A rolling control method for a seamless steel pipe for controlling a rolling process, wherein a target outer peripheral length of a seamless steel pipe to be sizing-rolled and an actually measured outer peripheral length of a seamless steel pipe as a preceding material after the sizing-rolling process are calculated. a second step of controlling the offset amount of the N-1 stand according to the difference value between the target outer peripheral length and the measured outer peripheral length; and a third step of controlling the offset amount of the N-th stand according to the difference value from the measured bottom portion outer diameter of the seamless steel pipe as the material.

The seamless steel pipe rolling control method according to the present invention is characterized in that, in the above invention, the second step includes: In the third step, the difference value between the target outer diameter of the seamless steel pipe to be sizing-rolled and the measured bottom outer diameter of the seamless steel pipe that is the previous material becomes zero. It is characterized by including the step of controlling the amount of offset of the N stand.

A method for manufacturing a seamless steel pipe according to the present invention is characterized by including the step of manufacturing a seamless steel pipe using the rolling control method for a seamless steel pipe according to the present invention.

According to the seamless steel pipe rolling control method and manufacturing method according to the present invention, excellent outer diameter dimensional accuracy and roundness can be achieved even when the grooved rolls are worn without using grooved rolls suitable for individual products. It is possible to manufacture a seamless steel pipe that combines

FIG. 1 is a diagram showing the center of curvature and path center of a caliber roll. FIG. 2 is a flow chart showing the flow of a seamless steel pipe rolling control method according to an embodiment of the present invention. FIG. 3 is a diagram showing the flow of a general plug mill type seamless steel pipe manufacturing process. FIG. 4 is a diagram showing the configuration of a general two-roll stand type sizer. FIG. 5 is a diagram showing the structure of a grooved roll.

As a result of extensive research, the inventors of the present invention calculated the outer peripheral length of the target outer diameter of a seamless steel pipe when performing sizing rolling. At the N-1 stand, rolling is controlled to target the outer diameter of the seamless steel pipe, and at the Nth stand, the outer diameter is controlled to target the outer diameter of the bottom part, thereby improving outer diameter dimensional accuracy and roundness. I learned that I can. Therefore, the caliber rolls 100a and 100b (groove rolls) shown in FIG. By correcting the offset amount D2 of the path center P4, which is the actually measured groove center position with respect to the center of curvature P3, the outer diameter dimensional accuracy and roundness are improved. A rolling control method and a manufacturing method for a seamless steel pipe according to an embodiment of the present invention conceived based on the above findings will be described below.

FIG. 2 is a flow chart showing the flow of a seamless steel pipe rolling control method according to an embodiment of the present invention. As shown in FIG. 2, in the rolling control method for a seamless steel pipe according to an embodiment of the present invention, first, a control device such as a computer controls a target outer peripheral length C of a seamless steel pipe to be sizing-rolled and a previous material. A measured outer circumference D of a certain seamless steel pipe after sizing is calculated (step S1). Specifically, by inputting the target outer diameter ODaim of the seamless steel pipe to be sizing-rolled into the following formula (1), the control device determines the target outer diameter C of the seamless steel pipe to be sizing-rolled. calculate. In addition, the control device calculates the average outer diameter of the seamless steel pipe measured by the outer diameter measuring device installed on the delivery side of the sizing mill when rolling the seamless steel pipe, which is the previous material, according to the following formula (2). By inputting the diameter (measured average outer diameter) ODactual, the measured outer circumference D of the seamless steel pipe, which is the previous material, is calculated. In this embodiment, the average outer diameter ODactual of the seamless steel pipe is the average value of the outer diameters measured at nine points in the circumferential direction of the seamless steel pipe.

Next, the control device corrects the difference between the target outer peripheral length C of the seamless steel pipe to be sizing calculated in the process of step S1 and the measured outer peripheral length D of the seamless steel pipe as the previous material (step S2). ). Specifically, the control device controls the difference value (C- D) is calculated. Then, the control device controls the offset amount T of the N-1th stand according to the difference value (CD) when rolling the seamless steel pipe to be sizing-rolled. For example, when rolling a seamless steel pipe to be sizing-rolled, the control device uses the following formula (3) to set the offset amount of the N-1th stand so that the difference value (CD) becomes zero. Control T. In equation (3), R represents the radius of curvature of the grooved roll, and S represents the offset amount of the N-1 stand when rolling the seamless steel pipe as the previous material.

Next, the control device corrects the difference between the target outer diameter ODaim of the seamless steel pipe to be sizing-rolled and the measured bottom outer diameter ODbottom of the seamless steel pipe as the preceding material (step S3). Specifically, the control device calculates the difference value between the target outer diameter ODaim of the seamless steel pipe to be sizing-rolled and the measured bottom outer diameter ODbottom of the seamless steel pipe as the preceding material. Then, when rolling a seamless steel pipe to be sizing-rolled, the control device controls the offset amount V of the Nth stand according to the difference value between the target outer diameter ODaim and the measured bottom portion outer diameter ODbottom. For example, when rolling a seamless steel pipe to be sizing-rolled, the control device uses the following formula (4) so that the difference between the target outer diameter ODaim and the measured bottom outer diameter ODbottom becomes zero. to control the offset amount V of the Nth stand. In equation (4), U represents the offset amount of the Nth stand when the seamless steel pipe, which is the previous material, is rolled. As a result, seamless steel pipes can be produced that have both excellent outer diameter dimensional accuracy and roundness even when the grooved rolls are worn, without using grooved rolls that match individual products.

The rolling control method and manufacturing method for a seamless steel pipe, which is an embodiment of the present invention, can be used to manufacture a seamless steel pipe of any size without particular limitation. However, the stiffness of the tube is correlated with the ratio of the wall thickness t to the outer diameter OD of the tube (t/OD). If the value of t/OD×100 is 1.9% or more, the rigidity is improved, and as a result, it is possible to prevent the inner and outer surfaces of the pipe from being damaged due to buckling during sizing rolling. Therefore, from the viewpoint of preventing scratches, the value of t/OD×100 is preferably 1.9% or more, more preferably 2.1% or more, and 2.5% or more. It is even more preferable to have On the other hand, if the value of t/OD×100 is 25% or less, it is possible to prevent sizing failure caused by excessive rigidity, and as a result, it is possible to control the outer circumference of the tube more reliably. Therefore, the value of t/OD×100 is preferably 25% or less, more preferably 24% or less, and even more preferably 21% or less. In the present invention, the target outer diameter of the pipe may be used as OD for obtaining t/OD.

〔Example〕
In this example, a billet was pierced and rolled by a piercer to form a hollow shell, and then the hollow shell was stretch-rolled by an elongator and a plug mill and rolled by a reeler. After that, the hollow shell was rolled by a sizer to produce a seamless steel pipe. For the sizing rolling, a 2-roll stand type sizing mill was used in which each stand had two grooved rolls. Table 1 below shows the outer diameter and wall thickness of the hollow shell subjected to sizing-rolling (that is, the hollow shell after stretching and rolling) and the sizing-rolling conditions. Table 1 also shows the target outer diameter ODaim and thickness after sizing rolling. The rolling temperature (the temperature at the outer surface of the hollow shell to be subjected to sizing rolling) was uniformly set at 900° C. in order to prevent the motor of the sizing mill from tripping. In addition, the rolling conditions were corrected based on the outer diameter dimensional accuracy and roundness of the first rolled seamless steel pipe, and the outer diameter dimensional accuracy and roundness of the next rolled seamless steel pipe were evaluated. The outer diameter dimensional accuracy and circularity of the obtained seamless steel pipes were evaluated by the following procedures.

First, the maximum outer diameter ODmax (mm) and the minimum outer diameter ODmin (mm) of the finally obtained seamless steel pipe are measured on the delivery side of the sizing mill, and are defined by the following formula (5). An average outer diameter ODave was determined. Then, using the obtained average outer diameter ODave (mm) and the target outer diameter ODaim (mm), the outer diameter dimensional accuracy was determined by the following formula (6). In addition, the roundness was obtained by the following formula (7).

The evaluation results of outer diameter dimensional accuracy and circularity are also shown in Table 1 below. As can be seen from the results shown in Table 1, in the inventive examples satisfying the conditions of the present invention, the rolling conditions could be modified so as to obtain seamless steel pipes having both excellent outer diameter dimensional accuracy and roundness. Further, in the examples of the present invention, improvement in outer diameter dimensional accuracy and circularity of the next material is described, and similar effects were obtained for subsequent materials.

Although the embodiments to which the invention made by the present inventors is applied have been described above, the present invention is not limited by the descriptions and drawings forming a part of the disclosure of the present invention according to the present embodiments. That is, other embodiments, examples, operation techniques, etc. made by those skilled in the art based on this embodiment are all included in the scope of the present invention.

100 grooved roll 100a, 100b caliber roll

Claims (3)

A seamless steel pipe rolling control method for controlling a sizing rolling process of a seamless steel pipe by controlling a sizing mill equipped with N (≧2) stands arranged in series in the conveying direction of the seamless steel pipe. There is
a first step of calculating a target outer peripheral length of a seamless steel pipe to be sizing-rolled and a measured outer peripheral length of a seamless steel pipe as a preceding material after the sizing process;
a second step of controlling the offset amount of the N-1th stand according to the difference value between the target perimeter length and the measured perimeter length;
a third step of controlling the offset amount of the Nth stand according to the difference value between the target outer diameter of the seamless steel pipe to be sizing-rolled and the measured bottom portion outer diameter of the seamless steel pipe as the preceding material;
A rolling control method for a seamless steel pipe, comprising: The second step includes controlling the offset amount of the N-1th stand so that the difference value between the target outer circumference and the measured outer circumference becomes zero,
In the third step, the offset amount of the Nth stand is controlled so that the difference value between the target outer diameter of the seamless steel pipe to be sizing-rolled and the measured bottom outer diameter of the seamless steel pipe as the preceding material becomes zero. The rolling control method for a seamless steel pipe according to claim 1, comprising the step of: A method for producing a seamless steel pipe, comprising the step of producing a seamless steel pipe using the rolling control method for a seamless steel pipe according to claim 1 or 2.

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