JP2002035817A - Method for controlling metal rolling in seamless steel pipe manufacturing line - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently manufacture a seamless steel pipe whose finishing dimension is secured thanks to the continuously manufacturing line since deflected wall thickness in the circumferential direction is less and the thickness in the end of the pipe is inhibited. SOLUTION: (1) A method for controlling the metal rolling used in the seamless steel pipe manufacturing line connected in series by a boring machine, a drawing roll mill and an outside dia. forming mill and a hot thickness gage to measure a wall thickness dimension after the rolling in the outlet side of the drawing roll mill, and a hot thickness gage to measure a wall thickness dimension after the finishing in the outlet side of the outside dia. forming mill are provided and the method for controlling the metal rolling characterized by the feature that the finishing dimension after the outside forming mill is adjusted to meet the targeted dimension. (2) In the method for controlling the metal rolling described in (1), a hot thickness gage to measure wall thickness dimensions after boring in the outlet side of the boring machine is preferably provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling rolling in the production of a seamless steel pipe, and more particularly, to a method of rolling a seamless steel pipe in a continuous production line, which reduces circumferential wall thickness deviation. Also, the present invention relates to a rolling control method capable of suppressing a thickness deviation in a longitudinal direction, that is, a so-called pipe end thick wall or a pipe end thin wall, and securing a finished dimension.

[0002]

2. Description of the Related Art A so-called Mannesmann tube method has been widely used as a method for hot-working a seamless steel pipe. In this pipe making method, a solid material billet heated to a high temperature is used as a material to be rolled, and the material billet is fed to a drilling machine (a so-called piercer), and a hollow core is formed by piercing the shaft center portion. Get the tube. Next, the obtained hollow shell is fed to a subsequent elongation rolling device such as a mandrel mill and elongation-rolled. After that, it is passed through an outer diameter forming and rolling mill such as a stretch reducer, a sizer, or the like, and then subjected to a refining step of performing shape correction and sizing, thereby producing a seamless pipe as a product.

[0003] In recent years, from the viewpoint of high-efficiency production of seamless steel pipes, these rolling devices have been made continuous and constitute a production line. In particular, in order to cope with the production of small-quantity, high-mix steel pipes from small diameter to large diameter, the management of the dimensional condition after rolling is an important management item in such a production line using Mannesmann pipes. I have.

FIG. 1 is a diagram schematically illustrating a state in which a material billet is pierced and rolled by a piercer. The pair of inclined rolls 1 are arranged opposite to a target with respect to a pass line XX which is a moving axis of the material 2 to be rolled in the rolling direction in the rolling direction. In such a piercer in which the inclined roll 1 is arranged,
The material 2 fed on the pass line XX is bitten by the inclined roll 1 and thereafter moves on the pass line XX while turning, and a hole is made in the shaft center portion by the plug 3. Thus, the hollow shell 2 is formed. During this time, the plug 3 is supported so as to be located between the inclined rolls 1 along the pass line XX.

[0005] In the piercing and rolling having such a configuration, uneven wall thickness occurs in the raw tube after piercing due to heat deviation of the material billet, eccentricity of the plug, bending of the mandrel bar, or misalignment of the piercer. I do. For this reason, when occurrence of thickness deviation is determined after piercing and rolling, measures for improving thickness deviation, such as uniform heating of the material billet, eccentricity adjustment of the piercing plug, or eccentricity adjustment of the piercing machine, are immediately performed.

FIG. 2 is a diagram schematically illustrating a state in which a hollow shell is stretched and rolled by a mandrel mill. A plurality of roll stands having a hole shape composed of a pair of rolling rolls 4 are continuously provided so as to intersect with each other (in the figure, seven roll stands are provided at an intersection angle of 90 °). The mandrel bar 5 is inserted into the hollow shell 2 previously pierced by a piercer, and the roll stands are sequentially subjected to reduction and stretch-rolled. The tube diameter after rolling is determined by the interval geometrically determined by the groove size of the rolling roll and the outer diameter of the mandrel bar.

When the roll gap of the mandrel mill is changed, uneven wall thickness occurs in the circumferential direction. As described above, the cause of this uneven thickness is that the wall thickness is determined by the interval geometrically determined by the roll roll dimension and the mandrel bar outer diameter as described above. This is because the diameter (dimensions, shape) of the cavity to be formed changes, and accordingly, the space also changes in the circumferential direction. Therefore, when occurrence of uneven wall thickness is detected after rolling, it is necessary to replace the rolling tool and correct or change the roll gap of the mandrel mill.

Further, as will be described later, when the pipe end is significantly thickened in the steel pipe finished by the outer diameter forming and rolling mill, the pipe end hydraulic pressure reduction amount of the mandrel mill is optimized. For example, an operation may be performed in which the roll gap of only the pipe end is operated in the closing direction to reduce the thickness of the pipe end.

FIG. 3 is a diagram schematically illustrating a state in which a hollow steel tube is formed into a finished steel tube by outer diameter forming and rolling with a stretch reducer. Stretch reducers used for finishing rolling of seamless steel pipes are 2 rolls or 3 rolls.
Roll stand 6 consisting of a roll housing is continuously arranged to about 2 to 30 units, and while the outer diameter is sequentially rolled,
By giving a difference in the peripheral speed of the rolling roll between adjacent roll stands, the wall thickness of the hollow shell 2 to be rolled is controlled by applying a tensile force in the longitudinal direction of the pipe during rolling. The sizer also has the same configuration.

[0010] When rolling the tube end of a raw tube with an outer diameter forming machine for a stretch reducer or a sizer, the tensile force applied in the longitudinal direction of the tube is smaller than that of the intermediate portion. If the speed is kept constant, the thickness deviation in the longitudinal direction increases. That is, the thickness of the tube end of the raw tube becomes thicker than the thickness of the intermediate portion, and a tube end thick portion is formed. The portion where the wall thickness is increased only at the end of the pipe is discarded as a defective dimension, which causes a reduction in yield.

Usually, in order to prevent such a decrease in yield due to an increase in the wall thickness of the tube end, a method of controlling the rotation speed of a rolling roll when rolling the tube end of the raw tube is adopted. In order to more effectively control the wall thickness of the pipe end, optimization of the pipe end dynamic control is also performed. Specifically, this is an operation of changing the roll rotation speed only at the pipe end and controlling the pipe end thickness by adjusting the tension with the front and rear rolls.

Conventionally, there is no means for appropriately monitoring the wall thickness fluctuation occurring during the above-described drilling or rolling, and the wall thickness of the pipe is measured in the refining process, which is the final stage of pipe manufacturing, and the uneven wall thickness is measured. In the case where the pipe or the pipe end is thick, a method of controlling the setting conditions of the heating furnace or the rolling mill based on the measurement results has been adopted. In such a method, many uneven thickness defective materials are manufactured until the occurrence of uneven thickness is found, and a realistic effect cannot be expected.

[0013] As described above, when the continuous use of Mannesmann pipe-making equipment is carried out for the purpose of producing seamless steel pipes having a wide range of pipe-making dimensions with high efficiency, a quick response based on the rolling situation is required. It will be requested. For this reason, various methods have been proposed for measuring the occurrence of wall thickness fluctuations during hot rolling of a seamless steel pipe and controlling the wall thickness based on the measurement.

For example, Japanese Patent Publication No. 7-58177 proposes a pipe wall thickness measuring device capable of measuring the thickness deviation of a steel pipe during hot rolling using radiation. As a specific means, the source is so formed as to form an equilateral triangle on an intermediate circle between the outer circumference and the inner circumference of the pipe by three radiations applied to the steel pipe being hot-rolled from the source vessel. A container and a detector are arranged to measure the thickness deviation of the steel pipe.

Japanese Patent Application Laid-Open No. 7-246414 discloses a pipe end wall thickness control method for correcting the roll rotation speed of a stretch reducer using a hot thickness gauge on the stretch reducer exit side. That is, from the wall thickness distribution obtained by measuring the entire length of the pipe with a hot thickness gauge installed immediately after the stretch reducer, the pipe wall thickness increase is quantified, and the roll rotation of each stand is determined from the quantified quantity. A method of correcting the number and correcting the number of stands to be corrected is disclosed.

Further, Japanese Patent Application Laid-Open No. Hei 8-71616 discloses a hot wall thickness gauge installed between a mandrel mill and an extractor for a retract type mandrel mill in which an extractor for extracting a pipe from a mandrel bar is arranged. A rolling control method has been proposed that improves the accuracy of the set gap of the grooved roll of the final stand based on the measured thickness measurement result of the final stand.

[0017]

As described above, when manufacturing a seamless steel pipe in an actual operation, an appropriate thickness suppression measure must be taken immediately on the basis of the cause of the thickness unevenness, in accordance with the judgment of the occurrence of the thickness unevenness. Must. In addition, thick pipe ends generated by stretch reducers and the like must also be treated at the same time as measures for suppressing uneven wall thickness. Therefore, as in the conventional method for controlling the thickness, simply measuring the deviation in thickness at a specific rolling mill or controlling the wall thickness at the pipe end can take measures to suppress the thickness defect required as a production line. Absent. For this reason, the occurrence of defective materials due to a certain amount of uneven wall thickness and thick pipe ends has been unavoidable.

The present invention has been made in view of the problems of the conventional seamless steel pipe production line, and has two or more hot thermometers arranged on the production line to provide meat for each rolling mill. By grasping the causes of thickness fluctuations, and immediately changing and correcting the rolling setting conditions, there is little uneven wall thickness in the circumferential direction over the entire length of the pipe, and at the same time, the occurrence of thick pipe ends is suppressed, and the target finish size is further reduced. It is an object of the present invention to provide a rolling control method capable of manufacturing a seamless steel pipe that can be secured.

[0019]

In order to solve the above-mentioned problems, the present inventor has studied various occurrences of wall thickness abnormalities that occur in each rolling mill, and found that the abnormalities in the finish after the outer diameter forming and rolling were completed. The effects on dimensions were analyzed. As a result, to grasp the thickness abnormality caused by each rolling device, and to detect the thickness abnormality, so that it can be immediately applied to the rolling of the next material,
It was found that if the rolling setting conditions could be changed and modified, it would be effective for efficient production of seamless steel pipes.

The present invention has been completed based on the above findings, and has as its gist a rolling control method used in a seamless steel pipe production line of the following (1) and (2). (1) A rolling control method used in a production line of a seamless steel pipe in which at least a punching machine, a stretching rolling mill and an outer diameter forming rolling mill are continuous, and a thickness dimension after rolling on an output side of the stretching rolling mill. And a hot thickness gauge for measuring the finished thickness dimension on the outlet side of the outer diameter forming and rolling mill, and the thickness variation from the measured thickness distribution. The rolling control method is characterized by specifying the factors (1) and (2) and adjusting the finished dimensions after the outer diameter forming and rolling mill so as to match the target dimensions. (2) In the rolling control method of the above (1), further, a hot thickness gauge for measuring a thickness dimension after drilling is arranged on the exit side of the drilling machine, and a deviation from the measured thickness distribution is provided. Judging meat occurrence,
It is desirable to adjust the finished dimensions after the outer diameter forming and rolling mill so as to match the target dimensions. Thereby, the occurrence state of the wall thickness abnormality can be grasped individually for the drilling machine, the stretching rolling mill, or the outer diameter forming rolling mill, and the finish dimension of the steel pipe can be accurately matched with the target dimension. .

The hot thickness gauge used in the present invention does not require any special specifications, and may be any conventional thickness measuring instrument.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The rolling control method of the present invention is intended for a continuous seamless steel pipe production line, and a hot thickness gauge is arranged on the output side of a piercer or a mandrel mill which is a drawing rolling mill. In addition, by arranging a hot thickness gauge on the exit side of the outer diameter forming and rolling mill comprising a stretch laser or a sizer, it is possible to actually measure the rolling thickness on the exit side of the apparatus to be arranged. This allows not only to determine the cause of the wall thickness abnormality, but also to grasp the difference from the target wall thickness at the exit, and to adjust the rolling schedule, for example, piercer tool change, roll gap of the mandrel mill in order to match the finished dimensions. The change, and further, the change in the rotation speed setting of the stretch reducer can be performed, and the change can be immediately applied to the rolling of the next material.

In the following, the content of the control for suppressing the uneven wall thickness occurring in the circumferential direction of the steel pipe to be rolled and the control for suppressing the thick wall portion at the pipe end which causes the thickness deviation in the longitudinal direction of the pipe will be described separately. I do. 1. About wall thickness deviation suppression in the circumferential direction Wall thickness deviation occurring during hot rolling of seamless steel pipes is wall deviation due to deviation of the mill core generated by piercer, counter-wall thickness deviation due to improper tool generated in mandrel mill, and It can be broadly divided into uneven thickness caused by a roll stand generated by a stretch reducer or a sizer. These can be distinguished by measuring the wall thickness distribution because the factors of occurrence are different.

For example, since the thickness deviation due to the piercer is due to the eccentricity, the entire circumference (development angle: 360
°) occurs at one point. The uneven thickness generated by the mandrel mill occurs at two or four locations. Further, uneven thickness generated in the stretch reducer or the like occurs at three places or six places.

The measures for suppressing uneven thickness having different causes are also different. For uneven thickness generated by the piercer, adjustment of the mill core and change of the rolling tool are performed. On the other hand, for opposing uneven wall thickness generated by the mandrel mill, changing the mandrel mill roll gap or changing the rolling tool is effective, and further suppressing uneven thickness generated by the stretch reducer or sizer. The rolling setting of the stretch reducer or the sizer is changed.

Next, securing the finished dimensions after the outer diameter forming and rolling will be described. Thickness deformation models for analysis simulations using the finite element method were created, and analysis and examination were performed on the actual production line. From the results of these studies, it is necessary to obtain a predetermined finish size at the outlet of the mandrel mill (or the piercer outlet if necessary) in order to secure the target finishing dimensions at the outlet of the outer diameter rolling mill of the stretch reducer or sizer. Needs to be added. The thickness deviation is based on the mandrel mill dimensions, sizer dimensions, raw material,
It is determined by the heating temperature and the like.

For example, a billet size of 225φ, a steel grade carbon steel is heated at 1230 ° C., and then pierced and elongation-rolled to make the output size of the mandrel mill an outer diameter of 276φ × wall thickness of 15t, and the size output size of the sizer is 197φ × When finish rolling with a thickness of 16 tons, add a maximum thickness deviation of 0.4 mm in the circumferential direction on the exit side of the mandrel mill to suppress thickness deviation on the exit side of the sizer and secure the target dimensions. Can be.

FIGS. 4 and 5 show the mandrel mill outlet side,
And the thickness measurement value on the mandrel mill exit side and its thickness target, and the thickness measurement value on the sizer exit side, which were measured by placing a hot thickness gauge on the exit side of the sizer which is the final outer diameter rolling mill And the wall thickness target. The abscissa in the figure is indicated by the development angle in order to observe the thickness distribution over the entire circumference. In each case, the rolling schedule is such that the above-mentioned billet size of 225φ is made into a mandrel mill with an outside diameter of 276φ × wall thickness of 15t, and the size of the sizer is 197φ with an outside diameter of 197φ × wall thickness of 16t.

In the rolling shown in FIG. 4, the thickness target value on the exit side of the mandrel mill is 0.4 mm deviation (15.2 m from the target 15 mm).
m-14.8 mm) should be added, but as shown in the measured wall thickness, the thickness deviation is 0.6 mm (15.3 mm-14.7 mm). For this reason, the target thickness of 16 mm on the exit side of the sizer
On the other hand, it can be seen that an uneven thickness of about 0.2 mm (16.1 mm-15.9 mm) remains.

On the other hand, in the rolling shown in FIG. 5, a thickness deviation of 0.4 mm should be provided on the exit side of the mandrel mill, while a thickness deviation of 0.2 mm (15.1 mm -14.9m
m), a thickness deviation (16.1mm-15.9mm) of about 0.2mm from the target thickness remains on the exit side of the sizer.

From the results shown in FIGS. 4 and 5, the rolling schedule of the mandrel mill (including the piercer schedule, if necessary) is changed so that the wall thickness target and the measured wall thickness at the outlet side of the mandrel mill match. By setting
It can be seen that the target finish dimensions can be ensured on the exit side of the sizer in the rolling of the subsequent material.

In the above-described example, the thickness deviation caused by the mandrel mill is shown. However, in the actual operation, the thickness deviation caused by the piercer, the thickness deviation caused by the stretch reducer or the sizer, and the like are added. Therefore, a hot thickness gauge is installed on the outlet side of all rolling mills installed on the production line, and the occurrence of uneven thickness is determined for each rolling device. Based on the result, the unevenness of the finished dimension is reduced. It is desirable to change the schedule for each rolling mill so as to match the target dimensions as much as possible.

As described above, the uneven wall thickness generated in the rolled steel pipe has periodicity. Therefore, by performing the Fourier transform on the measured thickness on the exit side of the rolling mill, it becomes easy to predict the cause of the occurrence of uneven thickness from the periodicity of the thickness distribution. Therefore, in the present invention, it is effective to combine Fourier analysis when determining occurrence of uneven thickness of the piercer and the mandrel mill with one hot thickness gauge.

2. Reducing Pipe End Thickness As mentioned above, to correct the pipe end thickening generated in the outer diameter forming and rolling mill, optimize the mandrel mill pipe end hydraulic pressure reduction amount, and also use the stretch reducer or the sizer rotation speed pipe end. Optimization of the dynamic control is performed.

In order to secure the finished dimensions, a thickness deformation model for an analysis simulation using the finite element method was created in the same manner as in the case of the above-mentioned uneven thickness suppression, and the analysis and examination were performed on a production line of an actual machine. According to the study results, in order to secure the target dimensions on the exit side of the stretch reducer or the sizer, it is necessary to reduce the wall thickness of the pipe end by a predetermined amount on the exit side of the mandrel mill. The thickness of the thin pipe end is determined by the dimensions of the mandrel mill, the size of the sizer, the material, the heating temperature and the like.

For example, after heating a billet size of 225 φ and ordinary steel at 1230 ° C., piercing and elongating and rolling, the output size of the mandrel mill is set to an external diameter of 276 φ × thickness 9.5 t, and the output size of the sizer is set to an external diameter. In the case of finish rolling at 219 φ × thickness 10 ton, the thickness of the pipe end at the exit side of the sizer can be suppressed by setting the thickness of the pipe end at the exit side of the mandrel mill to about 1.5 mm.

FIGS. 6 and 7 show the mandrel mill outlet side,
And the thickness measurement value of the mandrel mill exit side and its thickness target, which was measured by placing a hot thickness gauge on the exit side of the sizer which is the final outer diameter molding machine, and the thickness measurement value on the exit side of the sizer It is a figure which shows a thickness target. In both figures, the thickness distribution over the entire length from the tip of the material to be rolled after the mandrel mill and the sizer is shown by the length ratio (%) of the material to be rolled.
The rolling schedule shown in FIGS. 6 and 7 is based on the above-mentioned billet size 276φ being the outside diameter of the mandrel mill and having the outer diameter of 276φ × thickness 9.5t and the outer diameter of the sizer being the outer diameter.
197φ x 10 tons in thickness.

In the rolling shown in FIG. 6, the thickness should be reduced to 1.5 mm (8.0 mm) with respect to the target thickness of 9.5 mm at the exit side of the mandrel mill. (9.0m
m). For this reason, the pipe end thick part is about 1 mm thick (11.0 mm) with respect to the target thickness on the sizer exit side. In this case, measures such as changing the setting of the mandrel mill or inspecting the cylinder of the mandrel mill are performed so as to increase the thin-walled pipe end on the mandrel mill outlet side.

On the other hand, in the rolling shown in FIG. 7, despite the fact that the tube end thinning amount was 1.5 mm on the exit side of the mandrel mill and the target was attained, a tube end thickness of about 1 mm was generated on the exit side of the sizer. I have. In this case, the amount of change in the number of revolutions at the pipe end is not as intended, or the timing of the change in the number of revolutions is shifted, so the setting change of the sizer number of revolutions should be performed. Take measures such as checking the sizer motor.

In the rolling control method of the present invention, by combining the above-described techniques for suppressing uneven wall thickness in the circumferential direction and reducing the wall thickness at the pipe end, a uniform wall thickness distribution is provided over the entire length of the pipe, and It is possible to manufacture a seamless steel pipe having small uneven wall thickness.

In other words, at least two or more hot rolls are desirably provided on the output side of a rolling mill provided on a production line in which at least a punching machine, a stretching rolling mill and an outer diameter forming and rolling mill are continuous. A thickness gauge is arranged to determine the cause of uneven wall thickness and the occurrence of thick pipe end, and change the rolling setting so that these factors can be eliminated. As a result, there is little unevenness in wall thickness during the rolling of the next material, and at the same time the occurrence of thick pipe ends is suppressed, and a seamless steel pipe with a secured finish dimension can be manufactured, reducing the dimensional inspection defect rate and improving the yield. Can be done.

[0042]

According to the rolling control method used in the seamless steel pipe production line of the present invention, when rolling a seamless steel pipe in a continuous production facility, there is little uneven wall thickness in the circumferential direction, and The thickness deviation in the direction, that is, the thickness of the pipe end is suppressed, and the seamless steel pipe having the finished dimensions secured can be manufactured. As a result, the dimensional inspection failure rate can be reduced, and the yield can be improved.
This enables efficient multi-product small-lot production of seamless steel pipes.

[Brief description of the drawings]

FIG. 1 is a diagram schematically illustrating a state in which a material billet is pierced and rolled by a piercer.

FIG. 2 is a diagram schematically illustrating a state in which a hollow shell is stretched and rolled by a mandrel mill.

FIG. 3 is a diagram schematically illustrating a state in which a hollow steel tube is subjected to outer diameter forming and rolling with a stretch reducer to produce a finished steel tube.

FIG. 4 is a diagram showing the relationship between the measured wall thickness on the mandrel mill exit side and the target thickness thereof and the relationship between the measured wall thickness on the exit side of the sizer and the target thickness by the development angle of the pipe circumference.

FIG. 5 shows the relationship between the measured wall thickness on the mandrel mill exit side and the target thickness, and the relationship between the measured wall thickness on the sizer exit side and the target wall thickness, as in FIG. FIG.

FIG. 6 is a diagram showing the relationship between the measured thickness on the mandrel mill exit side and the target thickness thereof and the relationship between the measured thickness on the exit side of the sizer and the target thickness by the length ratio of the material to be rolled.

FIG. 7 shows the relationship between the measured value of the thickness on the mandrel mill exit side and the target thickness and the relationship between the measured thickness value on the exit side of the sizer and the target thickness in the same manner as in FIG. FIG.

[Explanation of symbols]

 1: inclined roll, 2: material billet, hollow shell 3: plug, 4: rolling roll 5, mandrel bar 6, roll stand

Claims (2)

[Claims] 1. A rolling control method used in a seamless steel pipe production line in which at least a punching machine, a stretching rolling machine, and an outer diameter forming rolling machine are continuous, wherein a rolled meat is provided on an output side of the stretching rolling machine. A hot thickness gauge for measuring a thickness dimension, and a hot thickness gauge for measuring a finished thickness dimension on an outlet side of the outer diameter forming and rolling mill, and a thickness is measured from a measured thickness distribution. A rolling control method characterized in that a factor of thickness variation is specified and a finished dimension after an outer diameter forming and rolling mill is adjusted to match a target dimension. 2. A hot thickness gauge for measuring a thickness dimension after drilling is arranged on the exit side of the drilling machine, and the occurrence of uneven thickness is determined based on the measured thickness distribution. 2. The rolling control method according to claim 1, wherein the finishing dimension after the diameter forming and rolling mill is adjusted to match the target dimension.