JPH04147780A - Method for controlling weld heat input of electro-resistance welded pipe - Google Patents

Abstract

PURPOSE:To prevent the degradation in the control accuracy occurring in welding efficiency and to improve pipe quality by determining the weld heat input in the welding process of an electro-resistance-welded pipe by adding the control output of the previous time and the value obtd. after the change command value of the control output corresponding to a change in welding conditions multiplied by a correction factor. CONSTITUTION:The welding heat input to opposed edges 1a, 2a of an open pipe 2 is outputted by adding the value obtd. after the change command value of the control output for setting the weld heat input determined in accordance with the change in the welding conditions including a pipe forming speed, sheet thickness and welding temp. is multiplied by the correction factor of mathematical expression to the control output value of the previous time in the process of producing the electro-resistance-welded pipe 3 by passing a high-frequency current to the edges 1a, 1a and welding these edges by heating. In the equation, k is the constant determined by the circuit constant of the welding machine and the pipe making size.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an electric resistance welding method that allows the optimal welding heat input to be set in response to changes in welding conditions such as pipe manufacturing speed, plate thickness, and welding temperature. This invention relates to a pipe welding heat input control method.

[Conventional technology]

Straight seam pipe welding methods used to manufacture welded pipes include submerged arc welding, plasma welding, and TI.
There are G-welding methods, high-frequency electric resistance welding methods, and the like, and among these, the high-frequency electric resistance welding method is widely adopted because it is the most efficient process among pipe manufacturing welding processes.

To manufacture ERW pipes by high-frequency ERW welding, a steel band is formed into a cylindrical shape to form an oven pipe in which the joint edge forms a figure 7 shape with the apex at the weld abutment point in plan view. This is done by heating the materials by passing a high-frequency current to reach the welding temperature, and then joining them using a squeeze roll at the abutting point.

In the process of welding such ERW pipes, welding heat input is the most important factor that affects the quality of the ERW weld.For example, if the welding heat input is low, the joint surface will not melt sufficiently, so cold welding will not be possible. Defects occur and the strength of the joint becomes insufficient. Conversely, if it is high, minute oxide defects called penetrators remain on the weld surface.

Therefore, in the past, a welding operator would empirically judge the appearance of the bead after welding, the state of red heat, the state of occurrence of flash, etc., and set the welding heat input.

However, such a method based on the empirical judgment of the operator has the problem that there are large individual differences, it is difficult to set the heat input accurately, and the operator is required to have a high degree of skill.

For this reason, various automatic control systems for welding heat input have recently been attempted. One of these methods is to control the welding heat input by detecting the pipe manufacturing speed, the thickness of the steel strip, and the temperature at or near the welding point (Japanese Patent Laid-Open No. 57-1
No. 65188, JP-A-58-9781, JP-A-54-
No. 137468, JP-A-53-140265).

[Problem to be solved by the invention] However, in this conventional method, welding heat input is controlled in response to changes in pipe manufacturing speed, plate thickness, and welding temperature so as to optimize welding quality. However, the adjustment value of this welding heat input is determined according to a control constant set for each control section or a calculation formula based on a certain law. However, with this method, there is a limit to the improvement of control accuracy, and welding efficiency due to the shape of the joint edge, impeder deterioration, changes in cooling water temperature, etc. It is necessary to consider the ratio of the power

However, because the shape of the welding edge, impeder deterioration, cooling water temperature changes, etc. change from moment to moment, it is extremely difficult to measure all of the factors that affect welding efficiency and reflect them in control. There were other problems.

For this reason, the current welding efficiency is higher than that at the time of setting control constants or calculation formulas (hereinafter referred to as reference time) to determine the adjustment value of welding heat input in response to changes in welding conditions such as pipe manufacturing speed. If the welding efficiency is decreasing, the power actually supplied to the welding part, that is, the heat input adjustment value, will be lower than the input power, that is, the welding heat input adjustment command value, and the welding efficiency will be high. If this is the case, the opposite is true and control accuracy cannot be maintained.

The present invention has been made in view of the above circumstances, and its purpose is to focus on the fact that the oscillation frequency changes due to changes in factors related to welding efficiency, and to correct the welding heat input based on this amount of change. Therefore, it is an object of the present invention to provide a welding human heat control method for electric resistance welded pipes, which enables accurate setting of welding heat input in consideration of welding efficiency.

[Means to solve the problem]

The welding heat input control method for an ERW pipe according to the present invention includes a method for controlling welding heat input to the opposite end edges of an open pipe in the process of passing a high frequency current through the opposite end edges of an open pipe and heat welding to manufacture an ERW pipe. In the heat control method, the value obtained by multiplying the control output change command value for welding heat input setting, which is determined in response to changes in welding conditions including pipe manufacturing speed, plate thickness, and welding temperature, by the following correction coefficient. It is characterized in that it is output in addition to the immediately previous control output value.

Oscillation frequency when the current oscillation frequency is referenced. However, k: A constant determined by the circuit constant of the welding machine and the pipe manufacturing size [effect] In the present invention, this changes the welding efficiency. It becomes possible to set the welding heat input taking into account the

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on drawings showing embodiments thereof.

FIG. 1 is a block diagram showing a control system according to the present invention,
In the figure, 1 indicates a steel band, 2 an open pipe, and 3 an electric resistance welded pipe. Obi a restored by uncoiler 11
41 is louver 12! After passing through the tube, it is formed into a tubular open pipe 2 by a forming machine 15, and then its edge portions 1a and 1a are successively heated by a work coil 18, and then pressed together by a squeeze roll 19 to form an electric resistance welded pipe 3.

A plate thickness gauge 13 for measuring the plate thickness of the steel strip 1 is disposed upstream of the forming machine 15. The plate thickness gauge 13 is configured to measure the plate thickness based on the interval between the rolls that contact the steel strip 1 vertically, and the detected plate thickness value is transmitted to the plate thickness signal converter 1.
4, the analog plate thickness signal t.

and output to the computer 26. In addition, the plate thickness total 13
Alternatively, a non-contact thickness gauge using radiation, ultrasound, etc. may be used.

The work coil 18 receives voltage supply from the heating power source 21 . The voltage supplied from the heating power source 21 to the work coil 18 is controlled by a control voltage signal (2) output from the computer 26.

In the heating power source 21, a voltage value or current value is detected by a probe placed in its oscillation circuit, and the detected voltage value or current value is converted into a frequency signal f by a frequency signal converter 29, and then sent to a computer 26. Output. The frequency signal converter 29 calculates the frequency by performing frequency analysis or high-speed data sampling (at least 107 data/second or more) to determine the time of one cycle of the waveform.

A thermometer 22 is placed at or near the welding point. As the thermometer 22, a two-color thermometer or an optical thermometer such as a radiation thermometer is used. When using this optical thermometer, it is common to use an image fiber to prevent high frequency noise and the like. The temperature value detected by the thermometer 22 is converted into an analog temperature signal T by a temperature signal conversion device 23 and output to a computer 26 .

A speed meter 24 for measuring the tube manufacturing speed of the electric resistance welded tube 3 is provided downstream of the squeeze roll 19. The speed meter 24 is configured to detect the speed by measuring the rotational speed of the roll in contact with it using a pulse generator, and the detected speed value is converted into an analog speed signal V by the speed signal converter 25. , is output to the computer 26. In addition,
The tube manufacturing speed may be detected by measuring the number of rotations of the forming rolls.

The calculator 26 includes pipe manufacturing information (the outer diameter of the electric resistance welded pipe 3 to be manufactured,
(wall thickness, material, etc.) are inputted via the pipe manufacturing information input device 27, and the target temperature T0 is inputted via the target temperature input device 28, respectively. The calculator 26 receives the pipe manufacturing information, the target temperature, the plate thickness signal from the plate thickness signal converter 14, and the temperature signal from the temperature signal converter 23.

Based on the speed signal from the speed signal converter 25 and the frequency signal from the frequency signal converter 29, a control output (control voltage) for the heating power source 21 is calculated in the procedure described below, and this is applied to the heating power source 21. Output.

In the method of the present invention, control output (control voltage) ■.

is the following (as shown in Equation 11), the previous control output (control voltage) V;-+ and the control voltage change command value ΔV7.ΔV corresponding to large changes in welding temperature, plate thickness, and pipe manufacturing speed.

The sum of Δ■9 multiplied by the correction coefficient α is added and the following (
1) Obtain according to the formula. This makes it possible to set the control output (control voltage) in consideration of changes in welding efficiency.

V, −V, 10 α (ΔV, +Δ■, +Δ■v)...
(11 However, (1): Control voltage Vi-1' to the heating power source 21 Previous control voltage i to the heating power source 21... (2) To: Constant determined by the circuit constant of the welding machine and the pipe manufacturing size f, : Current oscillation frequency α=k fo : Oscillation frequency at reference time ΔV t = K t ・ΔT=Kt (T; T
=-+)...(3) ΔV1=Kt ・Δt=Kt
(tHt=-+)...(4) ΔVv=Kv ・ΔV
-Ky (vi ” i-+)...(5) KT
:Temperature fluctuation compensation constant Kt :Plate thickness fluctuation compensation constant Kv :Speed fluctuation compensation constant T, :Thermometer temperature signal T=-+ :Previous thermometer temperature signal t, :Plate thickness signal ji-1'previous Plate thickness signal ■: Welding speed signal Vi-1' Previous welding speed signal By the way, in the conventional method, the control output ■ is shown below (6)
As shown in the formula, the previous control output V, , welding temperature, plate thickness,
The value was determined by adding the control output change command value corresponding to each change in pipe manufacturing speed.

V, =■, -, +ΔVT+Δ■, +Δ■9 ... (6
) Next, the relationship between the control output and the oscillation frequency will be explained.

FIG. 2 is a graph showing the relationship between control output and oscillation frequency.

When welding efficiency is poor, in order to obtain a welded product of good quality, the control output should be the control output at the standard ■. Must be greater than ■1.

At this time, the oscillation frequency increases from f6 at the reference time to fl because the impedance of the circuit changes in response to the change in welding efficiency.

Also, if welding efficiency is good, use the control output as the reference control output■. A welded product of good quality can be obtained by making the value smaller than (2). At this time, the oscillation frequency is
It decreases from fo at the reference time to f2.

FIG. 3 is a graph showing the relationship between the current and reference oscillation frequency ratio f, /fo and the current and reference control output ratio V, /V0 when a good welded product is obtained.

It can be seen from FIG. 3 that vi /Vo is proportional to f and /f0.

The slope k of the straight line is a constant indicating the influence of a change in the oscillation frequency on a change in the control output, and is determined by the circuit constants of the welding machine and the pipe size. Further, V and /V0 shown here indicate the magnification of the control output that should be increased or decreased in response to changes in welding efficiency, and are equal to α in equation (, 11).

Therefore, the oscillation frequency f0 at the reference time and k determined by experiment are stored in advance in the calculator 26 for each tube manufacturing size, and the formula (1
), it is possible to implement highly accurate welding heat input control that also takes welding efficiency into consideration.

Next, a comparative test between the method of the present invention and the conventional method will be explained.

Using a steel strip with a carbon content of 0.07% by weight, the target dimension is diameter 3.
In the process of manufacturing an electric resistance welded pipe with a length of 4 m and a wall thickness of 3.9 m, pipe manufacturing was performed by the method of the present invention and the conventional method, respectively, while changing the pipe manufacturing speed. The results are shown in Table 1.

(Left below) As is clear from Table 1, when the method of the present invention is used, the temperature variation is significantly reduced compared to when the conventional method is used, and the number of defects is also significantly reduced. I understand.

〔effect〕

As described above, in the method of the present invention, when there is a difference in welding efficiency with respect to the reference value, it is possible to reliably prevent deterioration of control accuracy due to the difference in welding efficiency, and to significantly improve pipe quality. The invention has excellent effects.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the implementation state of the method of the present invention, and FIG.
The figure is a graph showing the relationship between control output and oscillation frequency.
The figure is a graph showing the relationship between the ratio of oscillation frequencies at the current and reference times and the ratio of control outputs at the current and reference times when a good welded product is obtained. 1... Steel band 2... Open pipe 3... ERW pipe 13... Plate thickness meter 14... Plate thickness signal converter 1
5... Molding machine 18... Work coil 21... Heating power source 22... Thermometer 24... Speed meter 26...
-Calculator 25...Speed signal conversion device 27...Pipe manufacturing information input device 28...Target temperature input device 29...
Frequency signal conversion device patent Applicant Sumitomo Metal Industries Co., Ltd. Agent Patent attorney Noboru Kono Figure

Claims (1)

[Claims] 1. In the process of manufacturing an ERW pipe by passing a high frequency current oscillated by an oscillator through opposite end edges of an open pipe and heat welding, the welding heat input to the end edges is reduced. In the control method, the value obtained by multiplying the control output change command value for welding heat input setting, which is determined in response to changes in welding conditions including pipe manufacturing speed, plate thickness, and welding temperature, by the following correction coefficient is calculated as the value of the previous value. A method for controlling welding heat input of an electric resistance welded pipe, characterized by outputting an output in addition to a control output value. Current oscillation frequency correction coefficient = k Oscillation frequency at reference time, where k: Constant determined by welding machine circuit constant and pipe manufacturing size