JPH0755329B2 - Forged steel pipe automatic wall thickness control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention prevents a variation in wall thickness in the longitudinal direction of a forged steel pipe due to a variation in thickness in the longitudinal direction of a skelp, which is a raw material, in a manufacturing process of the forged steel pipe. It is about technology.

[Conventional technology]

The forged steel pipe is manufactured by heating a steel strip called a skelp, molding it on the outlet side of the heating furnace, and crimping the ends. FIG. 4 shows a manufacturing drawing of a forged steel pipe. The cut plate of the hot rolled coil, which is the material, is unwound by the uncoiler 1, the curl is corrected by the leveler 2, the front and rear of the coil are cut by the shear 3, and then the front end and the rear end of the coil are welded by the flash butt welder 4. And it becomes an endless skelp. The skelp 5 is further stored in the loop floor 8 through 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 50 which is a pipe forming machine is installed. After that, it enters the heating furnace 15. The heated skelp is formed by the forming roll 17 which is the first stage of the mill stand 50, and is formed into a pipe shape by the forging roll 18 which is the second stage. The pipe-shaped skelp is gradually reduced in thickness and reduced in outer diameter by the squeezing rolls (19 to 30) arranged continuously in multiple stages from the third stage onward, and is targeted at the exit side of the mill stand 50. Finished into thick and outer diameter steel pipe. 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 steel pipe manufacturing process, the thickness variation of the skelp as a raw material in the longitudinal direction directly affects the thickness variation of the steel pipe 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 to solve such problems, the thickness of the skelb has been continuously measured by a thickness gauge installed on the inlet side of the heating furnace, and the measured thickness signal is measured from the measurement point to the mill stand at line speed. A method has been proposed in which the wall thickness of a forged steel pipe is controlled by delaying the synchronization and controlling the roll rotation speed of the mill stand according to the thickness signal.

An example thereof is the invention disclosed in JP-A-64-40111.

In the conventional wall thickness control of forged steel pipes, the control unit length (control pitch) in the longitudinal direction of the skelp is equal to or longer than the entire stand length of the control mill, and thus has the drawback of poor control accuracy. There is.

Furthermore, when the control pitch is short and the pipe making speed is high,
In order for the next rotation speed command to enter each mill stand before the motor rotation speed of each mill stand reaches the target rotation speed,
It has a drawback that the control accuracy is not improved.

[Problems to be Solved by the Invention]

The present invention has been made to solve the above problems, and an object of the present invention is to provide an automatic wall thickness control method for forged steel pipes, which controls the roll rotation speed of each stand.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, the present invention, in the forged steel pipe manufacturing process, the thickness deviation in the longitudinal direction of the skelp (hot rolled steel sheet cut plate), which is the material of the forged steel pipe, is measured by an X-ray thickness gauge installed in the front of the heating furnace. The purpose is to continuously measure the thickness deviation signal and perform tracking delay processing to the pipe making line arranged on the rear surface of the heating furnace to prevent the wall thickness variation of the steel pipe after the pipe making caused by the thickness deviation. In the automatic wall thickness control method for forged steel pipes, the deterioration of control accuracy due to the long control pitch and the deterioration of control accuracy due to the response delay of the motor from the motor responsiveness and the standard rotation speed of each stand Determine the control unit length (control pitch) in the longitudinal direction of the skelp to minimize the amount of time, divide the control stands according to the control pitch, and control the roll rotation speed of each stand. It is characterized by.

Specifically, the control unit length is made as short as possible, but the motor rotation speed reaches the target rotation speed before the relevant portion leaves the mill stand. More specifically,
The length of the skelp that advances is the control unit length, which is the time required to reach the target speed determined by the motor characteristics.
The required time is adjusted to be as short as possible while paying attention to the motor speed to reach the target speed stably without overshooting or vibrating the target value. Then, the control stands are classified according to the control unit length. For example, if the control unit length is one stand distance or less, two stands before and after the control unit length are used.
Divide into 3 stands each with a stand.

[Action]

By reducing the control unit length, it is possible to avoid poor control accuracy due to the long control unit length, and this control unit length can be set for the next rotation before the motor speed of the mill stand reaches the target speed. Since the number command is not so short as to enter the mill stand, it is possible to avoid the poor control accuracy due to this short command.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, an X-ray thickness gauge 10 is installed in front of the preheating furnace 12 to continuously measure the thickness of the skelp 5 in the longitudinal direction. The measured thickness signal is sent to the control computer 34 together with the signal of the measurement PLG 31 attached to the pinch roll 11 installed on the rear surface of the X-ray thickness meter, and is generated in the control computer in synchronization with the line speed. Tracking is delayed until the mill stand 50 which is a pipe machine. The skelp 5 is introduced into the mill stand 50 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 parts of the skelp are made to follow the abutting position during forging welding, and is guided to the mill stand 50 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 the squeezing rolls (19 to 30) downstream from the forging roll 18 and subjected to outer diameter reduction, so that the final thickness of the squealing roll 30 is reduced to the desired thickness. The steel pipe 40 having the outer diameter is finished. In the automatic wall thickness control of the present invention, the squeeze roll 20 is used as the pivot stand for each of the stands 20 to 30, and the control computer 34 is used.
It is carried out in. The control flow chart of the present invention will be described below with reference to FIG.

First, for each roll, based on the size and steel type to be piped from now on, the upper process computer 35 shown in FIG.
Calculation is performed in the inside, and thereby, the number of rotations of each roll is initialized to perform pipe making.

Next, the control pitch is determined from the motor responsiveness and the standard rotation speed of each stand so as to minimize the total deterioration of the control accuracy due to the long control pitch and the control accuracy due to the motor response delay. To do. If the pipe making conditions do not change significantly, this control pitch will be a constant value. Next, the control stands are divided according to the control pitch. Since the pipe extends in the longitudinal direction during pipe making, the length of the pipe may become longer toward the stand at the rear stage.

Next, the X-ray thickness meter 10 and the PLG31 for length measurement shown in FIG. 1 track the thickness variation in the longitudinal direction of the skelp, calculate the average of the thicknesses for each control pitch, and delay the synchronization. Then, a roll rotation speed command is issued to each stand so that the wall thickness of the steel pipe after pipe making becomes a desired thickness, and the pipe is made accurately.

It should be noted that FIG. 2 shows the case where the control pitch becomes the minimum.
When the distance between the stands and the 21 stands is 1 (m) and the elongation is f, the control pitch P (m) is Pl / f.

At this time, the motor rotation speed command for the nth control part is 21 when the nth first tip enters the 20 stand.
It is fed to the stand and kept feeding until the first tip of the (n + 1) th control part enters the 20th stand.

At this time, the motor speed command for the n-1th control part is given to the 22 stand when the n-1th first tip enters the 21 stand, and the first tip of the nth control part is 21st. You can keep giving until you enter the stand.

In the same manner, the rotation speed command is given one after another and the pipe is manufactured.

As shown in Fig. 2, when the control pitch is not less than one stand distance but not more than one stand distance and not more than two stand distance, it is divided into 20 and 21 and 22, 22 and 23 and 24, ... When the distance between two stands is more than the distance between three stands and less than the distance between three stands, it is divided into each stand such as 20 and 21 and 22 and 23, 23 and 24. For example, in the above, when the n-th tip enters the 20 stand, the rotation speed commands N ₂₁ + ΔN ₂₁ (n) and N ₂₂ + ΔN ₂₂ (n) are set to 21,22.
Give the stand until the n + 1th tip enters the 20th stand. Here, N is the motor reference rotation speed for making the skelp reference thickness the desired thickness, ΔN is the motor correction rotation number for correcting the thickness deviating from the skelp reference thickness, and the subscripts ₂₁ and ₂₂ are stands. The number (n) indicates a correction amount for the control portion n. Others follow this.

〔The invention's effect〕

From the motor responsiveness and the standard rotation speed of each stand, the control pitch is determined so that the total deterioration of the control accuracy deterioration due to the long control pitch and the control accuracy deterioration due to the motor response delay is minimized. Since the control stand is divided according to the control pitch and the roll rotation speed of each stand is controlled, the control accuracy of the conventional skelp control pitch is higher than that of the control method in which all stand lengths of the control mill are more than the control accuracy. Is improved.

[Brief description of drawings]

FIG. 1 is an explanatory view showing the system configuration of the present invention, FIG. 2 is a representative example showing the timing of a rotation speed command given to each stand, FIG. 3 is a control flow chart, and FIG. 4 is a mill stand for forged steel pipes. Illustration showing the production line up to this point 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: Turn around 15: Heating furnace, 16: Preform roll 17: Forming roll, 18: Forging roll 19 to 30: Drawing roll 18-a to 30-a: Roll Drive motor 31: PLG for length measurement, 32: Rotation detector 33: Roll drive main board, 34: Control computer 35: Process computer, 36: Operation panel 40: Steel pipe, 50: Mill stand

Claims (1)

[Claims] 1. In a forged steel pipe manufacturing process, a thickness deviation in the longitudinal direction of a skelp (hot rolled steel sheet cut plate), which is a material of the forged steel pipe, is continuously measured by an X-ray thickness gauge installed on the front surface of a heating furnace. Tracking delay processing of the thickness deviation signal to the pipe making line located on the rear surface of the heating furnace, and from the response of the motor and the standard rotation speed of each stand, the control accuracy due to the long control unit length in the longitudinal direction of the skelp , The control unit length in the longitudinal direction of the skelp is determined so that the total deterioration amount due to the control response deterioration of the motor and the total deterioration amount are minimized, and the control stand according to the control unit length in the longitudinal direction of the skelp. A method for automatically controlling the wall thickness of a forged steel pipe, characterized in that the roll rotation speed of each stand is controlled.