JPH06304636A - Automatic thickness controlling method for butt welded steel tube - Google Patents

Abstract

PURPOSE:To control the thickness of a steel tube with high accuracy by detecting the thickness of a relaying part with a thickness gage whenever a welded part of a skelp passes the thickness gage and measuring a quantity of tracking delay before the thickness of the relaying part is detected by the change of current value of a roll motor at a control rolling stand. CONSTITUTION:The thickness of the skelp 5 in its longitudinal direction is measured continuously by the thickness gage 10 equipped in front of a heating furnace 15, a measured thickness signal is delayed synchronously with a line speed up to the control rolling stand, the control rolling stand is controlled in accordance with a thickness deviation signal being a difference between this delayed thickness signal and a reference thickness signal to control a thickness variation in the longitudinal direction of the tube. Whenever the skelp 5 and the welded part of the skelp pass the thickness gage 10, the relaying part is detected by the thickness gage to measure the quantity of tracking delay before the relaying part is detected. In this way, since each skelp is corrected by the actual result of tracking, the thickness is measured with high accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for preventing variation in wall thickness in the longitudinal direction of a forged steel pipe due to variation in thickness in the longitudinal direction of a skelp, which is a raw material, in a manufacturing process of the forged steel pipe.

[0002]

2. Description of the Related Art A forged steel pipe is manufactured by heating a steel strip called a skelp and thickly forming a rear end portion on the outlet side of a heating furnace.
FIG. 4 shows a manufacturing drawing of a forged steel pipe. The skelp, which is the material, is unwound by the uncoiler 1, corrected by the leveler 2 and cut by the shear 3 between the rear part of the skelp and the front part of the next skelp. The end of the next skelp is welded to form an endless skelp. The skelp 5 is further stored in the loop floor 8 via the pinch roll 6 and the magnet roll 7, and the pinch roll 11 provided on the front surface of the heating furnace 15 which is speed-synchronized with the inlet of the mill stand 38 which is a pipe forming machine is installed. After that, it enters the heating furnace 15.

The heated skelp is mill stand 38
It is formed by the forming roll 17 which is the first stage and is formed into a pipe shape by the forging roll 18 which is the second stage. The pipe-shaped skelp is gradually thinned or thickened by the squeezing rolls (19 to 30) arranged continuously in multiple stages from the third stage onward, external diameter reduction is applied, and the exit side of the mill stand 38. The steel pipe with the desired wall thickness and outer diameter is finished. The outer diameter is determined by the roll caliber of the final stand, and the wall thickness is controlled by changing the roll rotation speed of each stand.

In the above forged tube manufacturing process, the variation of the thickness of the skelp as the raw material in the longitudinal direction directly affects the variation of the thickness of the steel tube as a product in the longitudinal direction.
If it is left unattended, not only the yield will be deteriorated but also a defective product may sometimes be generated. As a method of solving such a problem, the thickness of the skelp has been continuously measured by a thickness meter installed on the entrance side of the heating furnace,
Proposed a method to control the wall thickness of the forged steel pipe by delaying the measured thickness signal from the measurement point to the mill stand synchronously with the line speed and controlling the roll rotation speed of the mill stand according to this thickness signal. Has been done.

An example thereof is the invention disclosed in Japanese Patent Publication No. 54-24394. The invention disclosed here continuously measures the thickness of the skelp on the front side of the heating furnace, and tracks the measured thickness signal to the control rolling stand to control the rolling mill stand according to the difference from the reference thickness of the skelp. A method for controlling and controlling the wall thickness variation in the pipe longitudinal direction due to the wall thickness variation of the skelp is shown.

According to the document, the thickness of the skelp is continuously measured in front of the heating furnace, the measured thickness signal is tracked to the control rolling stand, and the control rolling stand is controlled according to the difference from the reference thickness of the skelp. Is supposed to do. However, when performing highly accurate wall thickness control,
The tracking error at the time of tracking cannot be ignored. That is, since the control is performed according to the difference between the skelp thickness variation and the skelp reference thickness, as the tracking error increases, the deviation from the deviation that should be controlled should be different in order to perform the target thickness control. As a result of controlling such a large amount, there is a problem that it is not possible to control the wall thickness with high accuracy.

As another example, Japanese Patent Laid-Open No. 64-4011.
There is an invention disclosed in Japanese Patent Laid-Open No. According to the document, the thickness variation of the skelp measured in advance is delayed by tracking before being controlled by the controlled rolling stand,
Is supposed to control. Therefore, as the tracking error increases, the amount of deviation different from the deviation that should be controlled in order to perform the target thickness control is controlled, resulting in the problem that the thickness control cannot be performed with high accuracy. It was

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and by accurately correcting the amount to be tracked for each skelp, the high-accuracy of a forged steel pipe can be obtained. To provide a simple automatic wall thickness control method.

[0009]

In order to achieve the above object, the present invention provides a skelp (steel strip of hot rolled steel sheet) which is a material of a forged steel pipe by a thickness gauge installed in the front of a heating furnace in a forged steel pipe manufacturing process. ), The thickness in the longitudinal direction is continuously measured, and the thickness signal measured by the thickness gauge is delayed synchronously with the line speed up to a control rolling stand arranged in a continuous multi-stage on the rear surface of the heating furnace. Based on the thickness deviation signal, which is the difference between the thickness signal and the preset reference thickness signal, the control rolling stand is controlled, and the wall thickness due to the skelp thickness fluctuation among the wall thickness fluctuations in the longitudinal direction of the pipe is controlled. In the method of controlling the fluctuation, the relay part, which is a skelp and a welded part of the skelp, detects the relay part with a thickness gauge every time the thickness gauge is passed, and the motor current value of the roll of the control rolling stand. Due to changes in , Measuring the tracking delay amount until the relay portion is detected, and correcting the tracking amount from the thickness gauge to the control rolling stand so that the tracking calculation of the skelp thickness deviation signal after that is accurately performed. According to the principle of constant mass flow, the automatic wall thickness control method of a forged steel pipe is characterized by suppressing the wall thickness variation in the longitudinal direction of the pipe by controlling the rotation speed of each stand.

[0010]

In the present invention, the amount of tracking should be performed for each skelp even if the tracking error becomes large when the delay in controlling the skelp wall thickness variation measured in advance before the control by the control stand is controlled. However, the thickness of the steel pipe can be controlled with high accuracy because it is accurately corrected according to the track record.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, an X-ray thickness meter 10 is installed in front of the preheating furnace 12 and continuously measures the thickness of the skelp 5 in the longitudinal direction. The measured thickness signal together with the signal of the PLG 31 (pulse generator) for length measurement attached to the pinch roll 11 installed on the rear surface of the X-ray thickness meter,
It is sent to the control computer 34, and within the control computer, tracking delay is performed in synchronization with the line speed up to the mill stand 38 which is a pipe making machine. The skelp 5 is introduced into the mill stand 38 via the preheating furnace 12, the return drum 13, the turnaround 14, and the heating furnace 15. The skelp is controlled by the preform roll 16 arranged on the rear surface of the heating furnace so that both edge portions of the skelp are made to follow the abutting position at the time of forge welding, and is guided to the mill stand 38 to form the first stage forming roll 17 And formed into a pipe shape by the forging roll 18. The pipe-shaped skelp is gradually reduced in thickness by an squeezing roll (19 to 30) downstream from the forging roll 18 and subjected to outer diameter reduction, so that the squelch has a desired wall thickness on the exit side of the squeezing roll 30 in the final stage. Outer diameter steel pipe 37
Is finished. The automatic wall thickness control of the present invention is executed by the control computer 34 for each of the stands 20 to 30 with the squeezing roll 20 as the pivot stand.

A control flow chart of the present invention will be described below with reference to FIG. The relay portion, which is a welded portion of the skelp and the skelp, has a large variation in wall thickness as compared with the portion other than the relay portion of the skelp and is usually several percent or more thick. Therefore, the relay portion is easily detected by the thickness gauge, and further, when the relay portion passes through the control rolling stand, a large current fluctuation appears from the motor for the control rolling stand. It can be easily determined. Therefore, a pulse generator (PLG) is used up to the relay detection in the third, fourth, or fifth controlled rolling rolls in which a relatively large current fluctuation appears compared to the relay detection by the thickness gauge. Pulse number a
Is counted, and the skelp advance amount d'per pulse is calculated by the following equation (1). d '= l / a (1) where l is the skelp from the thickness gauge to the third, fourth or fifth controlled rolling roll The distance is converted to length.

Next, in the skelp advance amount d'per pulse, when a peculiar value happens to be detected, n times (usually 5
Every time the relay unit passes the amount of skelp advance per pulse of (about times), the moving average is calculated by the following equation (2). d = (previous correction value d ′ + second previous correction value d ′ + ... + n previous correction value d ′) / n (2) Next, the skelp per pulse obtained by the equation (2). Based on the amount of advance (tracking correction value) and the count amount of PLG, tracking calculation is performed as the distance moved from the thickness meter as in the following equation. Tracking distance from thickness gauge = count of d x PLG (3)

Next, a control method using the above tracking correction will be described with reference to FIG. First, a target stretch pattern as shown in FIG. 2 is calculated for each roll in advance in the upper process computer 35 shown in FIG. Pipemaking is performed by setting the initial number. Next, as described above, when the variation in thickness in the longitudinal direction of the skelp is delayed by the X-ray thickness gauge 10 and the PLG 31 for length measurement, the thickness reduction at each stand is reduced by the predetermined thickness reduction rate at each stand. The control computer 34 calculates the meat amount Δti.

Further, in synchronization with the timing in which the variation in thickness of the skelp in the longitudinal direction is delayed by tracking, the control computer 34 controls the pipe speed in each throttle roll downstream of the pivot stand to follow the variation in thickness. Determined by the formula. ΔVi = h (Δti) (4) Here, the function h is determined for each size and type by the constant mass flow.

Next, the pitch diagram PDi (Δt) corresponding to the skelp thickness variation Δt is calculated in the control computer 34 by the following equation. PDi (Δt) = PDi ₀ × I (Δt) (5) Here, PDi ₀ is the pitch diagram at each control stand when there is no skelp thickness variation, and the function I is the skelp. It is a function showing the relationship between the thickness variation and the rate of change of the pitch diamond, and the function I is determined in advance as follows.

FIG. 4 shows the amount of actual thinning when the acceleration / deceleration command corresponding to the target thinning allowance is output to the control motor from the relationship of constant mass flow with the pitch diagram PDi being constant. It should be noted that the negative thickness reduction is actually a thickness increase. If the pitch diamond is constant even if the amount of wall thinning changes, the pipe forming phenomenon becomes as shown by the broken line A shown in FIG. However, in the actual pipe making phenomenon, the pitch diamond also changes due to the change in the rotation speed of the control roll due to the change in the amount of wall thinning. It becomes like the solid line B shown in FIG. Therefore, the solid line B is the function f (Δt) of the thickness reduction amount Δt.
Then, the equation (5) for calculating the pitch diagram according to the skelp plate thickness variation is given by the following equation. PDi (Δt) = PDi ₀ × I (Δt) = PDi ₀ × f (Δt) / Δt (6) Equation (5) is determined in advance as described above.

Next, a roll rotation speed acceleration / deceleration command downstream of the pivot stand is calculated in the control computer 34 by the following equation. ΔNi = ΔVi / (π × PDi (Δt)) (7) Next, the rotational speed of the succeeding stand at the stand downstream from the i-th stand is calculated for each stand, and the above formula ( 5)
The control computer 34 is added to the number of revolutions calculated in
To give a speed command to each stand roll drive main slab 33 to control the speed of each stand roll rotation driving motor, the rotation speed is controlled, and a steel pipe having a target wall thickness and outer diameter is produced accurately.

FIG. 5 shows the results when the present invention was not carried out, and FIG. 6 shows the results when the present invention was carried out. In FIG. 5, since the tracking deviation occurs, the control accuracy is deteriorated because the portion to be originally controlled arrives at the control rolling stand with a delay, whereas in FIG. 6, accurate tracking is performed. Therefore, the pipe is manufactured with extremely high control accuracy.

[0020]

As described above, according to the present invention, even if the tracking error becomes large when the delay in controlling the thickness variation of the skelp measured in advance before the control by the control stand is controlled, the skelp becomes large. Since the amount to be tracked for each time is accurately corrected based on the track record, it is possible to control the thickness of the steel pipe with high accuracy.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a system configuration of the present invention,

FIG. 2 is a graph showing a target stretch coefficient for each stand of a typical size and a target roll rotation number for each stand,

FIG. 3 is a control flow diagram according to the present invention,

FIG. 4 is a diagram showing the relationship between the target thickness reduction amount and the actual thickness reduction amount of a forged steel pipe when the pitch diamond of a typical size is fixed and the mass flow is controlled to be constant.

FIG. 5 is a view showing a pipe forming result when the present invention is not carried out;

FIG. 6 is a diagram showing a pipe forming result when the present invention is carried out;

FIG. 7 is a diagram showing the results of manufacturing a forged steel pipe when the present invention is not carried out;

FIG. 8 is a view showing the production results of a forged steel pipe when the present invention is carried out,

FIG. 9 is a view showing a production line of a forged steel pipe up to a mill stand.

[Explanation of symbols]

 1 Uncoiler 2 Leveler 3 Shear 4 Flash butt welder 5 Skelp 6 Pinch roll 7 Magnet roll 8 Loop floor 10 X-ray thickness gauge 11 Pinch roll 12 Preheating furnace 13 Return drum 14 Turnaround 15 Heating furnace 16 Preform roll 17 Forming roll 18 Forging Roll 19-30 Squeezing roll 18-a-30-a Roll drive motor 31 Length measuring PLG 32 Rotation detector 33 Roll drive main board 34 Control computer 35 Process computer 36 Operation panel 37 Steel pipe 38 Mill stand

Claims (1)

[Claims] 1. In the forged steel pipe manufacturing process, the thickness in the longitudinal direction of the skelp (steel strip of hot-rolled steel sheet), which is the material of the forged steel pipe, is continuously measured by a thickness gauge installed in front of the heating furnace, The thickness signal measured by the thickness meter is delayed synchronously with the line speed up to the control rolling stand continuously arranged in multiple stages on the rear surface of the heating furnace, and the thickness is the difference between the delayed thickness signal and the preset reference thickness signal. In the method of controlling the control rolling stand based on the deviation signal to control the wall thickness fluctuation caused by the thickness fluctuation of the skelp among the wall thickness fluctuations in the longitudinal direction of the pipe, a skelp and a skelp weld. Each time the relay section passes through the thickness gauge, the relay section is detected by the thickness gauge, and the tracking delay amount until the relay section is detected by the change in the motor current value of the roll of the control rolling stand. Total The tracking amount from the thickness gauge to the control rolling stand is corrected so that tracking calculation of the thickness deviation signal of the skelp thereafter is accurately performed, and the rotation speed of each stand is determined according to the principle of constant mass flow. An automatic wall thickness control method for a forged steel pipe, characterized in that the wall thickness variation in the longitudinal direction of the pipe is controlled by controlling.