JPH08246B2 - Tube wall thickness control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a method in which a strip-shaped material is formed into a tube continuously in a cold state,
The present invention relates to a method of obtaining a metal pipe, for example, a steel pipe by rolling a butt portion that extends in the axial direction into a pipe and rolling the pipe.

(Prior Art) Conventionally, in the production of a seamless steel pipe, as disclosed in, for example, U.S. Pat. No. 3,645,121, there are 20 rolling mills called a stretch reducer that form a hole shape with two to three rolls. There is a continuous rolling process consisting of a table.

This is a hollow tube in a high temperature state as a raw tube, to reduce the cross-section of the tube while adjusting the roll rotation speed between the rolling mills and applying tension to the tube, Similarly, it is important to accurately obtain a predetermined wall thickness. Therefore, as so-called elongation length control, the length of the pipe after rolling is detected, and the wall thickness of the pipe is estimated by comparing it with the length of the pipe before rolling so that this value becomes a predetermined value. , The roll speed of each rolling mill is adjusted.

On the other hand, if there is a thickness gauge that can directly detect the thickness in order to grasp the wall thickness of the tube, it may be possible to use this, but in general, there is a problem in accuracy and it has not been put into practical use.

Manufacture of a pipe, which is a target of the present invention, in which a belt-shaped material is continuously roller-formed into a tubular body, and axially extending butting portions are welded into a pipe, and then the cross-section is reduced by a rolling mill row. In the case of the method, the method of estimating the wall thickness by comparing the pipe lengths before and after rolling as described above cannot be adopted.

Because, in the case of the pipe manufacturing method of the present invention, since the length of the material before and after rolling is semi-infinite, it is impossible to measure the length before and after rolling during operation, In addition, it is practically impossible to directly measure the wall thickness of the pipe because the cross-sectional size of the target pipe is small and the wall thickness in the circumferential direction of the pipe changes.

As described above, in the pipe manufacturing method targeted by the present invention, the wall thickness of the pipe in the manufacturing process cannot be accurately estimated, and thus a pipe excellent in wall thickness dimensional accuracy is manufactured. It was extremely difficult to do.

(Problems to be Solved by the Invention) The present invention is to form a pipe having a relatively small size, for example, a pipe diameter of 25 mm or less, into a pipe from a band-shaped material in a cold state, and weld a butt portion extending in an axial direction to the pipe. However, the object of the present invention is to provide a method of manufacturing a tube in which the cross-section is reduced by rolling the tube, which can control the wall thickness with high accuracy.

(Means for Solving the Problem) A feature of the present invention is that a belt-shaped material is formed into a tubular body by roller forming, and a butt portion extending in the pipe axial direction is welded to form a pipe, and continuously. In the method of manufacturing a pipe in which the cross-section is reduced by various rolling, the estimated value or the measured value of the cross-sectional area of the strip, the measured value or the estimated value of the speed of the strip, and the average outer diameter of the target pipe are measured. Calculate the average wall thickness from the value or estimated value and the measured value of the pipe speed at that time, and reduce the cross-section of the pipe with respect to the forming roll speed so that the calculated calculation result becomes the target value of the average wall thickness. The control is performed to change the roll speed of each rolling mill to be performed or the roll speed of each rolling mill with respect to the roll speed of the reference rolling mill among the rolling mills that reduce the cross section of the pipe.

 Hereinafter, the present invention will be described in detail.

INDUSTRIAL APPLICABILITY The present invention is a band-shaped material whose material has a semi-infinite length, is manufactured with high accuracy in both thickness and width, and is cold-worked. It was made paying attention to the fact that it is easy to measure.

 The principle of the present invention will be described below.

 Generally, in continuous rolling, the following relationships are established.

S ₀ · V ₀ = S · V (1) where S ₀ : material cross-sectional area S: product cross-section seat V ₀ : material speed V: product speed relationship of the area and wall thickness, S = π (tD-t 2) ......... (2) where, D: diameter of the tube (outside diameter) t: the cross-sectional area of the thick material of the tube, by the following equation Represented and known.

S ₀ = W ₀ · t ₀ (3) Where, W ₀ : width of the band-shaped material t ₀ : thickness of the band-shaped material Therefore, if V ₀ and V in the equation (1) are measured, S can be known. Assuming the diameter (outer diameter) D of the pipe from the equation (2), t can be calculated as an average value.

In the process targeted by the present invention, the measurement of the velocity V ₀ , V and the measurement of the outer diameter D depend on the contact type measuring roll from the state where the pipe is in the room temperature state, and the non-contact type. It can be performed accurately and easily even by using the formula measuring means.

Of course, when cutting the inner and outer beads by welding,
Since the cross-sectional area is reduced by this amount, this must be taken into consideration in the above equation. Further, as the value of the outer diameter D of the pipe, the set value of the roll gap in the rolling mill can be used.

FIG. 1 shows a procedure for carrying out the pipe wall thickness control method of the present invention.

Further, as a simple method, if the relationship between the pipe speed V or V / V ₀ and the wall thickness t is experimentally obtained in advance, the relationship between the roll speeds of the rolling mills can be directly used by directly utilizing these relationships. Change it,
Control can be performed so as to obtain a target pipe wall thickness. The procedure at that time is shown in FIG. The principle of this procedure is exactly the same as that of the procedure shown in FIG. 1. When the measurement and detection errors are zero, the principle is the same as that of the procedure of FIG. Contains various errors, the method shown in FIG. 2 is more accurate.

To change the roll speed of each rolling mill in order to change the pipe speed, the rolling speed of the reference rolling mill in each forming roll and rolling mill train is set to N ₁₀ , N ₂₀ , ... N _{n, 0.} For example, (N ₁₀ ′ −N ₂₀ ′) / N ₁₀ ′> (N ₁₀ −N ₂₀ ) / N ₁₀ , ……, (N _n-1,0 ′ −N _{n, 0} ′) / N _{n-1 , 0} ＞ (N
By setting N ₁₀ ′, N ₂₀ ′, ... N _{n, 0} ′ so that _n−1 −N ₂₀ ) / N _n−1 , a speed difference is generated in the pipes between the stands (rolling mills). Squeezing, which causes tension in the tube, changes the stretch and changes the tube speed. This amount can be given experimentally and analytically.

(Example) With a facility including an uncoiler, a roller forming machine, a welding machine, a rolling machine, a pinch roller, and a winding machine, a tube having a diameter (outer diameter) of 25 mm and a wall thickness of 2 mm is obtained by roller forming from a strip coil. Continuously, 8 rolling mills have a diameter of 12.5
The cross section was reduced to mm.

Belt speed V ₀ before roller forming, tube speed V after rolling
Was detected with a measuring roll. For the thickness and width of the strip-shaped material and the pipe diameter after rolling, when using typical values measured in advance, a predetermined wall thickness of 2.8 mm is obtained when V / V ₀ = 1.83.

Initially, V / V ₀ = 1.61 was obtained when rolling was performed at a standard rotation speed in a roller forming machine and 8 rolling mills. Therefore, when the number of rotations of the eight rolling mills was gradually changed so that tension was generated in the pipes (the speed difference increased toward the latter stage stand), V / V ₀ = 1.83. When the tube at this time was cut later and the wall thickness was measured, it was 2.8 mm as targeted.

(Effects of the Invention) Since the present invention is configured and operated as described above, the pipe-shaped member is formed into a tubular body by roller forming, and the abutting portion extending in the pipe axial direction is welded to form the pipe. In the pipe manufacturing method in which the cross-section is continuously reduced by continuous rolling, the wall thickness of the pipe can be controlled with high accuracy, so that a metal pipe with excellent cross-sectional dimension accuracy can be obtained. Further, in the above-described method for manufacturing a pipe, when the thickness of the material changes, the material changes during rolling, the material is collapsed, twisted, or the like, and the stretching is changed.

[Brief description of drawings]

FIG. 1 is a diagram showing the procedure for carrying out the present invention, and FIG. 2 is a diagram in which the relationship between the pipe speed V or V / V ₀ and the wall thickness t is obtained in advance and each rolling is performed using this relationship. It is a figure which shows the procedure in other embodiment of this invention which performs the control which changes the roll speed of a machine.

Claims (1)

[Claims] 1. A method for producing a pipe, comprising forming a strip-shaped material into a tubular body by roller forming, welding a butt portion extending in the pipe axial direction to form a pipe, and continuously reducing the cross-section by rolling. The estimated value or the measured value of the cross-sectional area of the strip, the measured value or the estimated value of the speed of the strip, the measured value or the estimated value of the average outer diameter of the target pipe, and the speed of the pipe at that time The average wall thickness is calculated from the measured value, and the roll speed of each rolling mill that reduces the cross-section of the pipe with respect to the forming roll speed or the cross-section of the pipe is calculated so that the calculated calculation result becomes the target value of the average wall thickness. A method for controlling the wall thickness of a pipe, which is characterized in that control is performed to change the roll speed of each rolling mill with respect to the roll speed of a rolling mill serving as a reference among rolling mills that perform reduction.