JPH0221324B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for elongating and rolling steel pipes, and in particular,
The present invention relates to a method for elongating and rolling a steel pipe, which is suitable for elongating and rolling a hollow tube into which a mandrel bar is inserted using a mandrel mill.

[Prior Art] Generally, the manufacturing process of seamless steel pipes includes a drilling process in which a hole is made in a round bar, a stretching process in which the hollow tube with the hole is stretched to reduce its thickness, and a finishing rolling machine after the stretching process. It consists of three steps: a finish rolling step to reduce the tube to the required outer diameter. That is, as shown in FIG. 1, a raw material round bar 11 is heated to a required temperature in a rotary hearth heating furnace 12, and then punch-rolled by a Mannesmann piercer 13 to form a hollow shell 14.
Since the hollow tube 14 is thick and short, it is stretched to reduce its thickness by a mandrel mill 15 serving as a stretching and rolling mill. The mandrel mill 15 is a rolling mill that performs elongation rolling with a mandrel bar 16 inserted into the hollow tube 14, and usually has 7 to 8 units.
It consists of a base roll stand. Each roll stand is provided with two sets of grooved rolls 17, and the rotational axes of the grooved rolls 17 between adjacent roll stands are offset from each other by 90° in a plane perpendicular to the rolling axis. These hole-shaped rolls 17 are driven independently for each roll stand, and
The lowering position can be adjusted. The hollow raw tube 14 is stretched to double to four times the length by a mandrel mill 15, and becomes a finish rolling mill raw tube 18. The finish rolling mill raw tube 18 is transferred to a reheating furnace 19 as necessary.
After being reheated at , finish rolling is performed at a stretch reducer 20 serving as a finishing mill. As the stretch reducer 20, a three-roll continuous rolling mill is usually used, and 8 to 28 roll stands are successively arranged with their phases shifted by 60 degrees. The rolls constituting this stretch reducer 20 are driven independently for each roll stand, and by appropriately setting the roll rotation speed distribution, tension is applied in the longitudinal direction of the pipe material being rolled to control the wall thickness. . The outer diameter of the tube material is reduced by up to 75% by the stretch reducer 20, and the outer surface of the tube material is defined by the perfect circular hole roll of the last stand of the stretch reducer 20, resulting in relatively excellent external dimensions. A finished tube 21 with high precision can be obtained.

However, if the outer diameter and wall thickness dimensions of the finish rolling mill blank tube 18 are poor, the wall thickness dimensions of the finished tube 21 will be poor. In other words, if the outer diameter and wall thickness of the inlet raw pipe of the stretch reducer 20 are not uniform in the longitudinal direction, the longitudinal wall thickness distribution of the finished outlet pipe will be non-uniform, and the reason for this is: The large diameter portion of the entry side blank pipe has a large amount of actual outside diameter reduction, making that portion of the finished tube 21 thick, and the small diameter portion of the entry side stock tube has a small amount of actual outside diameter reduction, resulting in a finished product. This is because that portion of the tube 21 becomes thin. Therefore, in order to obtain a finished tube 21 with a uniform wall thickness in the longitudinal direction, a finishing mill tube 18 having a uniform outer diameter and wall thickness in the longitudinal direction is manufactured in the mandrel mill 15, which is a pre-process. There is a need to.

By the way, in the mandrel mill 15, the slotted rolls 17 of each stand are rotated more slowly in the upstream stand and faster in the downstream stand in inverse proportion to the cross-sectional area of the tube being rolled. If the volume of material rolled per unit time by each stand is equal,
The cross-sectional shape of the material on the outlet side of each stand is constant. However, the cross-sectional shape of a pipe material exiting a given stand during rolling, which is generally observed during actual rolling, changes in a complex manner from the time when the material tip is bitten to the time when the material bottoms out. , Changes in the lubrication state between the mandrel bar 16 and the hollow tube 14 over time, Changes in the coefficient of friction between the mandrel bar 16 and the hollow tube 14 due to uneven distribution of the amount of lubricant deposited, Stand Possible causes include changes in the tension acting on the material between the stands and changes in the roll neutral point of each stand due to changes in the speed of the mandrel bar 16.

Conventionally, in order to make it possible to roll tubes with a uniform outer diameter and wall thickness in the longitudinal direction, mandrel mills have forcibly changed the rotational speed of each roll of the mandrel mill during rolling. A shape control technology has been proposed that adjusts the applied tension and makes it possible to cancel out uneven outer diameter and wall thickness distribution.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional shape control technology for mandrel mills, the roll rotational speed distribution for the next rolled material is determined based on the rolling results of the previously rolled material in rolling in the same lot. Although such feedback control between pieces is possible, intra-piece dynamic control such as controlling the longitudinal outer diameter distribution of the same tube material during rolling cannot be performed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for elongating steel pipes in which the outer diameter of the same pipe material in the longitudinal direction is adjusted during rolling in a mandrel mill, and the outer diameter of the pipe material on the exit side of the mandrel mill can be controlled with high precision. do.

[Means for Solving the Problems] The present invention relates to a method for elongation rolling of steel pipes in which a hollow shell into which a mandrel bar is inserted is elongated by a mandrel mill having n individually driven roll stands arranged in series. In the method, the acceleration/deceleration rate (ΔNj) of the roll rotational speed Nj at the j-th stand with respect to the reference rotational speed Noj = {(Nj) - (Noj)}/(Noj) is the standard for the pipe material bulge width Bj at the exit side of the j-th stand The influence coefficient Aj on the rate of change (ΔBj) with respect to the bulge width Boj = {(Bj) − (Boj)} / (Boj) ... is calculated and stored in advance as (Aj) = (ΔNj) / (ΔBj) ... , Measure the pipe material bulge width Bi at the outlet side of the i-th stand upstream from the j-th stand, and calculate the rate of change of the measured value Bi with respect to the reference bulge width Boi (ΔBi) = {(Bi) - (Boi)}/(Boi )..., and based on the influence coefficient Aj of the j-th stand, calculate the adjusted acceleration/deceleration rate (ΔNj')=(Aj)・(ΔBi)..., and at the same time, at least the roll rotation speed Nj in the j-th stand is At the adjusted acceleration/deceleration rate ΔNj', the roll rotational speed from the i+1st stand onward is adjusted so that the roll rotational speed Nj' is calculated as (Nj') = (ΔNj')・(Noj) + (Noj)... , Measure the pipe material bulge width Bj' at the outlet side of the j-th stand of the part where the pipe material bulge width Bi was measured at the outlet side of the i-th stand, and calculate the actual rate of change (ΔBj) of the measured value Bj' with respect to the reference bulge width Boj. ′)={(Bj′)−(Boj)}/(Boj)… The above-mentioned influence coefficient Aj is modified to make it zero.

[Function] In controlling the outer diameter of the material to be rolled in mandrel mill rolling, it is important to know not only the cross-sectional area of the material to be rolled at the exit side of each stand, but also the outer circumference length of the material to be rolled. This is because tubes having the same cross-sectional area may have different outer circumferential lengths. If the outer circumference of the tube material exceeds a certain value, the material to be rolled will bite out of the roll gap, causing rolling defects on the outer diameter of the tube material, so it is important to control the outer circumference length of the material to be rolled during rolling. becomes.

On the other hand, in mandrel mill rolling, it is geometrically clear that there is a certain proportional relationship between the outer circumferential length of the tube material and the bulge width. Therefore, it is practical and meaningful to control the bulge width as an alternative to controlling the outer circumferential length of the tube. In other words, since the present invention employs the bulge width as a representative shape of the pipe material to control the outer diameter of the pipe material, it is possible to realize highly accurate control of the outer diameter of the pipe material, and it is extremely practical. be.

That is, in the present invention, the influence coefficient of the acceleration/deceleration rate of the roll rotation speed, which is a control factor, on the bulge width, which is the shape of the tube material on the exit side, is constantly verified and corrected, and the outer diameter irregularity that occurs in the initial stage of rolling is Uniformity is detected in the upstream stand, and the detection result is fed forward to the downstream stand. Ununiformity in outer diameter that occurs upstream until the end of rolling is detected in the upstream stand, and the detection result is fed forward to the downstream stand. By eid forwarding and correcting in the downstream the non-uniformity of the outer diameter that has occurred upstream until the end of rolling, it becomes possible to correct the outer diameter of the same tube material in the longitudinal direction during rolling. This makes it possible to correct the outer diameter of the same tube material in the longitudinal direction during rolling, and to control the outer diameter of the tube material on the exit side of the mandrel mill with high precision.

[Example] The present invention will be explained in more detail below.

Fig. 2 is a control system diagram showing a mandrel mill to which the present invention is applied, Fig. 3 is a model diagram showing the rolling state by the mandrel mill, Fig. 4 is a sectional view taken along the - line in Fig. 3, and Fig. 5 The figure is a sectional view taken along the - line in FIG. 3.

As shown in FIG. 2, the hollow tube 14 into which the mandrel bar 16 has been inserted is sequentially rolled down by rolls 17 provided on each stand of the mandrel mill 15, as shown in FIG. This becomes the finish rolling mill blank tube 18. Here, in each stand, the rolls 17 are supported by a roll chock (not shown) and can be driven independently by a main motor 31. The rotational speed of each main motor 31 can be controlled by a main motor control device 32. On the other hand, a bulge width sensor 34 is installed on the exit side of the i-th stand 33i of the mandrel mill 15.
is arranged, and a bulge width sensor 35 is arranged on the exit side of the j-th stand 33j downstream from the i-th stand. The detection signals of each bulge width sensor 34, 35 are analyzed in a bulge width measuring device 36, and the bulge width shown in FIG. 4 and FIG. 5, respectively.
Bi and Bj can be measured. Generally, for the rolled material rolled by the rolls 17,
The part that contacts the bottom of the roll caliber is called the groove bottom, and the part that does not come into contact with the roll caliber is called the flange part. The bulge width is the distance between both flanges. Therefore, the bulge width is the outer diameter of the pipe material in the direction perpendicular to the roll rolling direction, and the measurement of the bulge width is the width of the rolled material in the roll axis direction. In addition, in FIG. 2, the bulge width sensor 35 installed on the exit side of the stand 33j is described as measuring the width of the rolled material in the direction perpendicular to the roll axis; Since the figure is a system diagram, it is intended to only show that the sensor 35 is installed on the exit side of the stand 33j.
Also measures the width of the rolled material in the roll axis direction. According to the findings of the present inventors, it has been recognized that the expansion and contraction of the rolled material in the width direction corresponds well to the increase and decrease in the bulge width. Each of the above bulge width measurement values is transmitted to the main processing unit 37.

As mentioned above, it is well accepted that the bulge width corresponds well to the change in the outer circumferential length of the pipe material (expansion/contraction in the width direction of the rolled material). By measuring the bulge width, the expansion and contraction of the outer circumference can be evaluated. This means that the direction of the roll axis on the stand immediately before measuring the bulge width is not limited. Therefore, in FIG. 2, the roll axes of the stands 33i and 33j immediately before measuring the bulge width are shifted by 90 degrees from each other, but it is not possible to make the roll axes directions different in this way. It is not an essential component of the present invention.

That is, the main processing unit 37 calculates the roll rotation speed Nj at the j-th stand as shown in FIG.
Acceleration/deceleration rate (ΔNj) with respect to the reference rotational speed Noj = {(Nj) − (Noj)}/(Noj) ... is the rate of change of the pipe material bulge width Bj on the exit side of the j-th stand with respect to the reference bulge width Boj (ΔBj) = { (Bj)−(Boj)}/(Boj)... is calculated and stored in advance as (Aj)=(ΔNj)/(ΔBj).... Therefore, the main processing unit 37 measures the pipe material bulge width Bi on the exit side of the i-th stand upstream from the j-th stand, and uses the measured value.
The rate of change of Bi with respect to the standard bulge width Boi (ΔBi) = {(Bi) - (Boi)}/(Boi)... is calculated, and based on the influence coefficient Aj of the j-th stand, the adjusted acceleration/deceleration rate (ΔNj') = Calculate (Aj)・(ΔBi)... At the same time, the main processing unit 37 calculates the roll rotation speed Nj at least at the j-th stand at the adjusted acceleration/deceleration rate ΔNj′ calculated as (Nj′)=(ΔNj′)·(Noj)+(Noj)… The main motors 31 from the (i+1)th stand onwards are drive-controlled via the main motor control device 32 so that the rotational speed of each roll is adjusted so that the rotational speed of each roll becomes Nj'.

That is, as shown in FIG. 7, when the bulge width Bi at the i-th stand is smaller than the reference bulge width Boi, the main processing unit 37 operates so that a compressive force is applied relatively to that part of the pipe material. Above bulge width
Simultaneously with the measurement of Bi, at least the roll rotational speed Nj in the j-th stand achieves a change based on the calculated adjusted acceleration/deceleration rate ΔNj′,
The roll rotational speed after the i+1th stand is reduced from the reference rotational speed as the later stages of the stand progress. Conversely, if the bulge width Bi measured at the i-th stand is larger than the standard bulge width Boj, at least one The i+th
The roll rotational speed after the first stand is increased from the reference rotational speed for later stands.

Note that the adjustment of the roll rotational speed after the i+1th stand is substantially such that the roll rotational speed Nj at the jth stand achieves a change based on the adjusted acceleration/deceleration rate ΔNj′ calculated above, and the bulge width Bi Any device that applies compressive force or tensile force relatively to the measurement part is sufficient; therefore,
If the traction motor control system has good responsiveness, at the same time as measuring the bulge width Bi, pattern P ₁ is shown in Figure 8.
As _shown in _FIG .
The roll rotational speed Ni ₊₂ after the i+2nd stand may be changed by the adjusted acceleration/deceleration rate ΔNj'.

Here, if the influence coefficient of the acceleration/deceleration rate of the roll rotation speed in each stand mentioned above on the change in bulge width is not accurately grasped, the effect of modifying the outer diameter of the pipe material may be insufficient or may be excessive. There is a possibility that too many corrections may result in defective products.

Therefore, the main processing unit 37 in the present invention
Measures the pipe material bulge width Bj' at the outlet side of the j-th stand of the part where the pipe material bulge width Bi is measured at the outlet side of the i-th stand, and calculates the actual change rate ( In order to make ΔBj′)={(Bj′)−(Boj)}/(Boj)... zero, the influence coefficient Aj is constantly tested and can be modified.

Next, concrete implementation results of the present invention will be explained. The specific results of this implementation are that a full float mandrel mill using a mandrel bar with a diameter of 127 mm was used to produce an inlet pipe with an outer diameter of 175 mm, a wall thickness of 18.5 mm, and a length of 5300 mm. length 16000
The number of roll stands was 8, the roll diameter of each stand was 560 mm, the distance between stand axes was 1120 mm, and the bulge width sensor was installed on the fourth stand. They were placed on the exit side and on the exit side of the 7th stand. Here, the time T seconds from when an arbitrary part of the pipe material reaches the i-th stand to when it reaches the j-th stand can be regarded as a constant value in practice, and the speed of the pipe material at the exit side of the i-th stand can be If vmm/sec and the distance between the roll axes is lmm, it can be calculated using the following equation (1).

T= _j-1 〓 ⁱ⁼ⁱ (l/vi) seconds...(1) In this specific implementation result, the above time T is
It will be 0.91 seconds.

According to this specific implementation result, the variation in the bulge width on the exit side of the fourth stand is as shown in FIG. Since it is 0.91 seconds before the bulge width measured part in the fourth stand reaches the seventh stand, during that time, the roll rotation speed in each of the fifth to eighth stands is changed to the seventh stand.
By controlling based on the acceleration/deceleration rate shown in the figure, it is possible to obtain the target outer diameter of the tube material on the exit side of the final stand. As a representative example, the results of measuring the bulge width on the exit side of the seventh stand are shown in FIG. In the case where the control according to the present invention was not performed, as shown by the broken line, the bulge width fluctuation on the exit side of the 7th stand shows a similar tendency to the bulge width on the exit side of the 4th stand, but the control according to the present invention was not performed. In the case shown by the solid line, it is recognized that the longitudinal distribution of the bulge width observed at the exit side of the fourth stand is almost completely corrected at the exit side of the seventh stand. That is, in the present invention, the influence coefficient of the acceleration/deceleration rate of the roll rotation speed, which is a control factor, on the bulge width, which is the shape of the tube material on the exit side, is constantly verified and corrected, and the outer diameter irregularity that occurs in the initial stage of rolling is Uniformity is detected in the upstream stand, and the detection result is fed forward to the downstream stand. Ununiformity in outer diameter that occurs upstream until the end of rolling is detected in the upstream stand, and the detection result is fed forward to the downstream stand. By eid forwarding and correcting in the downstream the non-uniformity of the outer diameter that has occurred upstream until the end of rolling, it becomes possible to correct the outer diameter of the same tube material in the longitudinal direction during rolling.

As described above, according to the steel pipe elongation rolling method according to the present invention, the outer diameter of the same pipe material in the longitudinal direction is corrected during rolling in the mandrel mill, and the outer diameter of the pipe material on the exit side of the mandrel mill is controlled with high precision. It becomes possible to do so. The present invention applies to full-float type mandrel mills, semi-float type (restrain type)
Widely applicable to mandrel mills, fixed mandrel mills, multi-stand pipe mills, etc.

[Brief explanation of drawings]

Fig. 1 is a process diagram showing a general steel pipe manufacturing process, Fig. 2 is a control system diagram showing a mandrel mill to which the present invention is applied, Fig. 3 is a model diagram showing the rolling state in the mandrel mill, and Fig. 4 is − in Figure 3.
5 is a sectional view taken along the - line in FIG. 3, FIG. 6 is a diagram showing the influence coefficient in the embodiment of the present invention, and FIG. 7 is a diagram showing the acceleration of the roll rotation speed in the present invention. A diagram showing a deceleration state, FIG. 8 is a diagram showing an acceleration/deceleration state different from that in FIG. 7, FIG. 9 is a diagram showing the bulge width on the exit side of the fourth stand in an embodiment of the present invention, and FIG. 10 FIG. 7 is a diagram showing the bulge width on the exit side of the seventh stand in the embodiment of the present invention. 14...Hollow tube, 15...Mandrel mill, 16
...Mandrel bar, 17...Roll, 31...Main motor, 32...Main motor control device, 34, 35...Bulge width sensor, 36...Bulge width measuring device, 37...Main processing unit, Bi, Bj...Bulge width measurement value, Boi, Boj
...Reference bulge width, ΔBi, ΔBj... Rate of change.

Claims (1)

[Scope of Claims] 1. In a method for elongating and rolling a steel pipe, in which a hollow pipe into which a mandrel bar is inserted is elongated by a mandrel mill having n individually driven roll stands arranged in series, the j-th stand Acceleration/deceleration rate (ΔNj) of roll rotational speed Nj with respect to reference rotational speed Noj = {(Nj) − (Noj)}/(Noj) ... is the rate of change of the pipe material bulge width Bj at the exit side of the j-th stand with respect to the reference bulge width Boj (ΔBj) = {(Bj) − (Boj)} / (Boj) ... Calculate and store the influence coefficient Aj in advance as (Aj) = (ΔNj) / (ΔBj) ... upstream from the j-th stand. Measure the pipe material bulge width Bi on the exit side of the i-th stand on the side, and calculate the rate of change of the measured value Bi with respect to the standard bulge width Boi (ΔBi) = {(Bi) - (Boi)}/(Boi)... Based on the influence coefficient Aj of the j-th stand, the adjusted acceleration/deceleration rate (ΔNj')=(Aj)・(ΔBi)... is calculated, and at the same time, the roll rotation speed Nj in at least the j-th stand is at the above-mentioned adjusted acceleration/deceleration rate ΔNj'. (Nj')=(ΔNj')・(Noj)+(Noj)... The roll rotational speed from the i+1st stand onwards is adjusted so that the roll rotational speed Nj' is calculated as (Nj')=(ΔNj')・(Noj)+(Noj)... Measure the pipe material bulge width Bj' at the exit side of the j-th stand of the part where the pipe material bulge width Bi was measured on the side, and calculate the actual rate of change of the measured value Bj' with respect to the reference bulge width Boj (ΔBj') = {(Bj ′)−(Boj)}/(Boj)... A method for elongating and rolling a steel pipe, characterized in that the influence coefficient Aj is corrected to zero.