JPS58196109A - Method for elongation rolling of steel pipe - Google Patents

Abstract

PURPOSE:To make the distribution of the wall thickness in the longitudinal direction of a finished pipe rolled by the next stretch reducer uniform, by uniformly controlling the outer diameter and the wall thickness of a hollow blank pipe in its longitudinal direction, in elongating the hollow blank pipe into a blank pipe for a finish mill by a mandrel mill. CONSTITUTION:A round blank bar 11 is heated by a heating furnace 12 and is processed into a hollow blank pipe 14 by a Mannesmann piercer 13, and the pipe 14 is elongated into a blank pipe 18 for a finish mill by plural pairs of grooved rolls 17 after inserting a mandrel bar 16 into the pipe 14 by a mandrel mill 15. After the blank pipe 18 is heated again by a heating furnace 19, the pipe 18 is fed to a stretch reducer 20 to be processed into a finished pipe 21. In this case, the bulge width measured at the stand of the mill 15 are analyzed, and the signals of a hydraulic servocontrolling device basing on the analyzed results are inputted to a hydraulic pressure generating device, then the roll chocks of the roll 17 for elongation are driven by a hydraulic cylinder device to control the rolling reduction of the rolls 17, thereby the wall thickness in the direction of the blank pipe 18 is made uniform to perform the finishing process by the stretch reducer 20.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for elongating and rolling steel pipes, and more particularly to a method for elongating and rolling steel pipes suitable for elongating and rolling a hollow shell tube into which a mandrel bar is inserted using a mandrel mill.

In general, the manufacturing process for seamless steel pipes consists of a drilling process in which holes are made in the raw material round bar, a stretching process in which the perforated hollow shell tube is stretched to reduce its thickness, and a finish rolling process in which the finished abrasive tube is rolled as required. It consists of three steps: finish rolling to reduce the diameter to the outer diameter. That is, as shown in FIG. 1, the raw material round bar 11 is heated in a rotary furnace 12 to a required temperature at t, and then piezoelectrically punched by a Mannesmann viasser 13 to form a hollow shell 14.

Since this hollow tube 14 has a thick wall and a biased part, it is stretched with a thinning by a mandrel mill 15 serving as a stretching and rolling mill. The mandrel mill 15 is a rolling mill that elongates and rolls a hollow tube 14 with a mandrel bar 16 inserted therein, and is usually composed of 7 to 10 roll stands. Each roll stand is equipped with two sets of grooved rolls 11, and the grooved rolls 17 are arranged between adjacent roll stands.
The rotation axes of the two are arranged so as to be shifted 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 their rolling positions 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. Finish rolling mill The raw pipe 18 is reheated in a reheating furnace 19 if necessary, and then finished rolled in a stretch reducer 20 serving as a finishing mill.

For the stretch reducer 20, a 30-hole continuous rolling mill is usually used, and 8 to 28 roll stands are successively arranged with a phase difference of 60° from each other. The rolls that make up this stretch reducer 2° are driven independently for each roll stand, and by appropriately setting the distribution of roll rotation speeds, tension is applied in the longitudinal direction of the tube being rolled to control the wall thickness. . The stretch reducer 2o reduces the outer diameter of the tube material by a maximum of 75,116 mm, and the outer surface of the tube material is shaped by the perfect circular hole roll of the last stand of the stretch reducer 20, resulting in a relatively hard finished tube 21 with external dimensional accuracy. can get.

However, if the precision of the outer diameter and wall thickness of the finish rolling mill blank tube 18 is poor, the precision of the wall thickness of the finished tube 21 becomes long. In other words, if the outer diameter and wall thickness of the inlet raw tube of the stretch reducer 20 are not uniform in the longitudinal direction, the longitudinal wall thickness distribution of the finished outlet tube will be uneven. The large diameter portion of the raw 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 material tube has a small amount of actual outside diameter reduction, resulting in the finished tube 21. This is because that part becomes thin. Therefore, in order to obtain the finished tube 21 with a uniform wall thickness in the longitudinal direction, it is necessary to manufacture the finished rolled mill tube 1B with a uniform outer diameter and wall thickness in the longitudinal direction in the mandrel mill 15, which is one of the processes. There is.

By the way, in the mandrel mill 15, the slotted rolls 17 of each stand are rotated in inverse proportion to the cross-sectional area of the tube being rolled, with the upstream stand being rotated slower and the downstream stand being rotated farther. If the volume of material rolled in each stand per unit time is equal, the cross-sectional shape of the material at the exit side of each stand will be 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 tip of the material is bitten to the time when the end of the material is removed. is the coefficient of friction between the mandrel bar 16 and the hollow shell 14 due to the temporal change of fI4ff#stateff between the mandrel bar 16 and the hollow shell 14, and the non-uniform distribution of the amount of adhesion of the hollow material. Changes in the force acting on the material between the stands, changes in the roll neutral point of each stand due to changes in the speed of the mandrel bar 16, etc. can be considered.

Conventionally, in order to be able to roll a tube material with a uniform outer diameter and wall thickness in the longitudinal direction using a mandrel mill, for example,
A shape control technology has been proposed in which the rotational speed of each roll of a mandrel mill is forcibly changed during rolling to adjust the tension acting on the material between the stands, thereby making it possible to cancel out uneven outer diameter and wall thickness distribution. .

However, the shape control technology using the above roll rotation speed control method in a mandrel mill has a limit based on the limit of the rotation speed control technology of the main electric motor that drives the rolls.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for elongating and rolling steel pipes that allows the outer diameter and wall thickness of a pipe material on the exit side of a mandrel mill to be controlled with high precision without controlling the roll rotation speed.

In order to achieve the above object, the present invention provides 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 partial dynamic roll stands arranged in series. In the case where the rate of change (Bi) of the pipe material bulge width (B1) of the first stand with respect to the reference bulge width (Bes) K is used as a parameter, the first
The adjustment rate of the roll reduction amount with respect to the reference amount in at least one reduction control stand in the stand or the final stand is the change rate (Δ Measure the pipe material bulge width (B,) on the exit side of the first stand, and calculate the actual rate of change (jni) of the measured value (Bi) with respect to the reference bulge width (Bob). Based on the above-mentioned influence coefficient, the i conversion rate (
) is set to zero, and at the same time as measuring the bulge width (Bi ), the roll reduction amount of the roll reduction control stand is adjusted by the adjustment rate, and the Bulge width (B+
Measure the pipe material bulge width (Bρ) at the exit side of the steel j stand of a certain part of ), and calculate the reference bulge width (
The influence coefficient is modified in order to make the actual rate of change (jB', ) with respect to Bj) zero.

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 ■-W@ in Fig. 3,
Figure #15 is a sectional view taken along line V-V in Figure 3 (7).

First, the basic concept of the present invention will be explained.

In other words, in groove rolling, as is well known, when applying forward or backward tension in the longitudinal direction of the rolled material, the material contracts in the width direction and expands in the longitudinal direction; When spinning or applying backward compressive force, the material tends to expand in the width direction and contract in the longitudinal direction. This tendency is exactly the same in the rolling of tube materials. Here, according to the findings of the present inventors, the expansion and contraction of the rolled material in the width direction corresponds well to the increase and decrease in the bulge width, which is the outer diameter of the tube material in the direction perpendicular to the roll rolling direction. Therefore, the reference bulge l1ll of the bulge width (Bi) measured in @1 stand of the mandrel mill! (B,i)
When the rate of change ( )Bθ is positive, in order to apply tension in the longitudinal direction of the pipe material in that part, the roll reduction position of at least one reduction control stand selected in the first stand to the final stand is adjusted to By closing the tube at the same time as the measurement of the bulge width and reducing the flow rate of material from the upstream side per unit time, it becomes possible to roll the outer diameter of the tube material at that portion to the reference bulge width as a target value. On the other hand, if the rate of change (Bi) of the bulge width (B, ) measured at the ili stand with respect to the reference bulge width (Bob) is negative, in order to apply compressive force in the longitudinal direction of the pipe material in that part,
The roll reduction position of at least one reduction control stand selected in the first stand to the final stand is opened at the same time as the measurement of the bulge width, and the flow rate of material from the upstream side per unit time is increased. It becomes possible to roll the outside diameter of the pipe material to the target value.Hereinafter, embodiments of the present invention will be described in detail. As shown in FIG. 2, a hollow tube 1 into which a mandrel par 16 is inserted
4 is sequentially rolled down by the rolls 17 provided in each stand of the mandrel mill 15, as shown in FIG. They are supported by a roll chock 31 and can be moved independently by a main electric motor, and their lowered positions can be adjusted independently by a hydraulic cylinder device 32. The hydraulic cylinder device 32 is operated by hydraulic pressure generated in a hydraulic pressure generating device 33, and its lowered position can be adjusted by a hydraulic control servo valve 34. Note that the hydraulic control servo valve 34 can be controlled by a hydraulic servo control device 35.

On the other hand, the fifth stand (31, i) of mandrel mill 18
A bulge width sensor 36 is arranged on the exit side of the first stand (31D), and a bulge width sensor 37 is arranged on the exit side of the first stand (31D) downstream of the second stand.Each bulge width sensor 36
, 37 are analyzed in the bulge ring measuring device 38, and the bulge widths Bi and #I shown in FIG.
The bulge width Bl shown in FIG. 5 can be measured. Each of the above bulge width measurement values is transmitted to the main processing unit 39.

As shown in FIG. 6, the main processing unit 39 calculates the width (Bo
), the adjustment rate for the standard reduction amount of the roll reduction 1 in at least one reduction control stand in the first stand or the final stand is the pipe material on the outlet side of the J stand. Bulge width (town)
The influence coefficient on the rate of change (ΔBj) with respect to the standard bulge width (Bo3) is stored in advance. Therefore, the main processing unit 39 calculates the change in the first stand output based on the actual rate of change (ΔB1) of the bulge width (Bi) measured at the first stand output side with respect to the reference bulge width (Boi) and the above-mentioned influence coefficient. Standard bulge width (Bo 3) of pipe material bulge width (town)
The adjustment rate of the roll reduction amount in the reduction control stand is calculated so that the rate of change (ΔBj) to zero is zero, the calculation result is transmitted to the hydraulic servo control device 35, and the bulge width (
Simultaneously with the measurement of Bi), the hydraulic cylinder device 32 of the reduction control stand is driven via the hydraulic control servo valve 34, and the amount of reduction of the roll 17 is adjusted by the above-mentioned adjustment rate.

Here, the amount of adjustment of the rolling position in the rolling control stand is set within a range in which the exit side cross-sectional area ratio of each stand is approximately equal to the exit side cross-sectional area ratio of each stand at the standard rolling position.

The main processing unit 39 also calculates the actual value of the bulge width (machi) on the exit side of the J-th stand of the portion where the bulge width (Bi) was measured on the exit side of the i-th stand in the 11r arrangement with respect to the reference bulge width (B...). The rate of change (ΔB1) is calculated and the actual rate of change (ΔB1) is calculated.
In order to make B1) zero, the influence coefficients stored in advance are tested and corrected.

Next, concrete implementation results of the present invention will be explained. That is, FIG. 7 is an explanatory diagram showing the roll groove bottom thickness distribution in a mandrel mill having seven roll stands. In this mandrel mill, the raw tube wall thickness is 1
On the 5th, the finished pipe wall thickness was 7 mm, and the thickness of the bottom next to the roll in the standard reduction distribution from the 1st stand to @7 stand was 12 m +, 11 mm, and 11 mm, respectively, as shown by the solid lines.
9 m.

8 vm, 7 m, 7 m, 7 m. The bulge width sensor is installed on the exit side of the M3 stand and the exit side of the 5th stand, and 1 is used as the reduction control stand.
The first stand and the second stand were selected, and a control circuit similar to that shown in Figure w42 was used. According to this implementation result, the bulge width turbidity constant value during rolling measured at the exit side of the third stand was as shown in FIG. The bulge width measured at the exit side of the 5th stand when the roll-down control of the 1st stand and @2 stand was implemented and when the roll-down control was not performed are shown by the solid line and the broken line in Figure 9, respectively. It is. That is, according to the implementation of the present invention, it is recognized that the outer diameter of the exit side of the mandrel mill can be controlled with high accuracy.

In the above-mentioned specific example, the roll reduction position adjustment amount of the #1 stand and the #I2 stand is 11 at the maximum, respectively, as shown by the broken line in FIG. Since the standard cross-sectional area of the second stand is larger than that of the second stand, the rolling down position V@adjustment amount in the second stand is set to be larger than the rolling down position adjustment amount in the second stand. . In addition, in the above specific implementation results, the data sampling 5fjIL of the bulge width measuring device 38 is 33+++s+ seconds, and the frequency of commands from the hydraulic control servo device 35 to the hydraulic control servo valve 34 is 66-seconds, which is different from the conventional example. It has been recognized that the shape of the pipe material can be controlled at a relatively faster response speed than the shape control technology based on the roll rotation speed control method.As described above, the method for elongating steel pipe according to the present invention According to this, it becomes possible to control the outer diameter of the tube material on the exit side of the mandrel mill with high precision. The present invention is widely applicable to full-float mandrel mills, semi-float (restrain-type) mandrel mills, fixed mandrel mills, multi-stand pipe mills, and the like.

[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 a sectional view taken along the line W-W in FIG. 3, FIG. 5 is a sectional view taken along the line ■-v in FIG. 8 is a diagram showing a typical roll reduction distribution in a mandrel mill to which the present invention is applied, FIG. 8 is a scale diagram showing the bulge width on the exit side of the third stand in an embodiment of the present invention, and FIG. 9 is a diagram showing a typical roll reduction distribution in a mandrel mill to which the present invention is applied. FIG. 7 is a diagram showing the bulge width on the exit side of the fifth stand in the example. 14...Hollow tube, 15...Mandrel mill, 16
... Mandrel bar 117 ... Roll, 32 ... Hydraulic cylinder device, 35 ... Hydraulic servo control device, 36.37 - Bulge width sensor - 38 ... Bulge width measuring device, 39 - Main processing unit, Bi
, Bj - Bulge width measurement value, Bo only a Boj... Reference bulge width, ΔBi, ΔBj - rate of change. Fig. 3 Fig. 4 Fig. 51 Fig. 6 Fig. 7 Time from V material tip biting (tightening) Fig. 9 Time from pipe material nine biting (killing)

Claims (1)

[Claims] (1) In a steel pipe elongation rolling method in which a hollow pipe into which a mandrel bar is inserted is elongated by a mandrel mill in which each movable roll stand of ys group is successively arranged, the width of the pipe material bulge on the exit side of the 111 stand is (Town) When the rate of change (jBi) with respect to the standard bulge width (80 pieces) is used as a parameter, the standard reduction amount of the roll reduction amount in at least one reduction control stand in the first stand or the final stand. The adjustment rate for llj is the reference bulge width (B-ρ
Memorize the influence coefficient on the rate of change (Bj), measure the pipe material bulge @ (Bl) on the exit side of the final stand, and calculate the change of the cough constant value (Bi) with respect to the standard bulge width (B@1). Based on the change [jBl) and the influence coefficient, the first
Standard bulge width (B) of pipe material bulge width (town) of stand
Calculate the adjustment rate of the roll reduction amount in the pre-pressure distribution lowering control stand so that the rate of change (jBl) with respect to OJ) is zero, and at the same time as measuring the bulge width (Bi), adjust the roll reduction amount of the rolling reduction control stand as described above. At the same time, the pipe material bulge width (Bj) at the exit side of the first stand of the measurement part of the bulge width (Bρ) is measured, and the actual change (Bj) with respect to the standard bulge width (BOJ) of the determined value (Town) is measured.
A method for elongating and rolling a steel pipe, comprising modifying the influence coefficient so as to make "j) zero.