JPH07108463B2 - Welding heat input control method for ERW pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is an electric resistance sewing machine capable of setting an optimum welding heat input in response to changes in welding conditions such as pipe manufacturing speed, plate thickness and welding temperature. The present invention relates to a welding heat input control method for a pipe.

[Conventional technology]

There are submerged arc welding method, plug welding method, TIG welding method, high frequency electric resistance welding method, etc. in the straight seam pipe welding method used for manufacturing the electric resistance welding tube. It is widely adopted because it is the most efficient process in the industry.

The production of electric resistance welded pipes by high frequency electric resistance welding is performed by forming the steel strip into a tubular shape and forming the joint edge into a V-shaped open pipe with the welding abutment point as the apex in plan view. Is heated through a high-frequency current to reach the welding temperature and is joined by a squeeze roll at an abutting point.

Thus, in the welding process of ERW pipe, the welding heat input is the most important factor that influences the quality of the ERW welded part. For example, when the welding heat input is low, the joint surface does not melt sufficiently and the welded part If the strength is reduced and cold welding defects are generated, on the contrary, if it is high, minute oxide defects called penetrators remain on the weld surface.

Therefore, in the past, the welding operator set the welding heat input by empirically determining the bead appearance after welding, the red heat state, the flash generation state, and the like. However, such a method based on the empirical judgment of the operator has a large difference among individuals, and it is difficult to accurately set the heat input, and further, there is a problem that 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 tried. As one of the methods, there is a method of setting a welding heat input by detecting a pipe forming speed, a strip steel plate thickness, a temperature at or near a welding point (Japanese Patent Laid-Open No. 57-1568).
80, JP-A-58-9781, JP-A-54-137468, JP-A-SHO
60-106679, JP-A-53-140265).

[Problems to be Solved by the Invention]

By the way, according to such a conventional method, the welding heat input is controlled according to the changes in the pipe making speed, the plate thickness and the welding temperature so that the welding quality becomes the best. The value is determined according to a control constant set for each control classification or a calculation formula based on a certain law. However, with such a method, there is a limit to the improvement of the control accuracy, and the welding efficiency due to the shape of the joint edge, the deterioration of the impeder, the change of the cooling water temperature, etc. It is necessary to take into account the ratio of the generated power.

However, since the shape of the joint edge, the deterioration of the impeder, the change in the cooling water temperature, etc. change from moment to moment, it is extremely difficult to measure and reflect all of the factors related to such welding efficiency. There was a problem such as.

For this reason, the current welding efficiency is lower than the welding efficiency at the time of setting the control constant (hereinafter referred to as a standard, etc.) for determining the increase / decrease value of the welding heat input in response to changes in welding conditions such as pipe manufacturing speed. In such a case, the input power, that is, the electric power supplied to the weld, that is, the input / output value of the input heat is lower than the welding heat input / output command value, and conversely, when the welding efficiency is high. On the contrary, the control accuracy cannot be maintained.

The present invention has been made in view of such circumstances, and an object thereof is to set a control constant or the like, that is, a ratio of a current control output to a control output at a reference time is a current ratio to a welding efficiency at a reference time. It is an object of the present invention to provide a welding heat input control method for an electric resistance welded pipe, which pays attention to representing the ratio of welding efficiencies and uses the ratio to enable accurate setting of welding heat input in consideration of welding efficiency.

[Means for Solving the Problems]

The welding heat input control method for an electric resistance welded pipe according to the present invention is a method for controlling the welding heat input to an edge part of an open pipe by passing a high frequency current through the high temperature current to heat weld to manufacture the electric resistance welded pipe. In the method of controlling heat, the value obtained by multiplying the control output change command value for setting the welding heat input, which is obtained in response to changes in welding conditions including pipe making speed, plate thickness and welding temperature, by the following correction coefficient It is characterized in that it outputs in addition to the immediately preceding control output value.

[Operation] In the present invention, this makes it possible to set the welding heat input in consideration of changes in welding efficiency.

〔Example〕

Hereinafter, the present invention will be specifically described with reference to the drawings illustrating the embodiments.

FIG. 1 is a block diagram showing a control system according to the present invention,
In the figure, 1 is a strip steel, 2 is an open pipe, and 3 is an electric resistance welded pipe. After the strip steel 1 unwound by the uncoiler 11 passes through the looper 12, it is formed into a tubular open pipe 2 by the forming machine 15, and then the work coil 18 sequentially heats its edge portions 1a, 1a, It is pressed by the squeeze roll 19 to form the electric resistance welded pipe 3.

On the upstream side of the forming machine 15, a plate thickness meter for measuring the plate thickness of the strip steel 1
13 are provided. The plate thickness meter 13 is configured to measure the plate thickness based on the distance between the rolls that come into contact with the strip steel 1 vertically, and the detected plate thickness value is an analog plate thickness measured by the plate thickness signal converter 14. The signal t _i is converted and output to the computer 26.
As the plate thickness gauge 13, a non-contact type plate thickness gauge using radiation, ultrasonic waves, or the like may be used.

The work coil 18 is supplied with voltage from the heating power source 21. The voltage supplied from the heating power source 21 to the work coil 18 is controlled by the control voltage signal V _i output from the computer 26. A thermometer 22 is arranged at or near the welding point. As the thermometer 22, an optical thermometer such as a two-color thermometer or a radiation thermometer is used. When using this optical thermometer, it is common to use an image fiber in order to prevent high frequency noise and the like. The temperature value detected by the thermometer 22 is converted into an analog temperature signal T _i by the temperature signal conversion device 23 and output to the computer 26.

On the downstream side of the squeeze roll 19, a speedometer 24 for measuring the pipe making speed of the electric resistance welded pipe 3 is provided. The speedometer 24 is configured to detect the speed by measuring the rotation speed of the contacting roll using a pulse generator, and the detected speed value is converted into an analog speed signal v _i by the speed signal converter 25. , Is output to the computer 26. In addition, the number of rotations of the forming roll may be measured to detect the pipe manufacturing speed.

The pipe manufacturing information (outer diameter, wall thickness, material, etc. of the electric resistance welded pipe 3 to be manufactured) is supplied to the computer 26 via the pipe manufacturing information input device 27, and the target temperature T ₀ is _supplied to the target temperature input device 28. Input respectively. The computer 26 uses the pipe manufacturing information, the target temperature, the plate thickness signal from the plate thickness signal converter 14, the temperature signal from the temperature signal converter 23, and the speed signal from the speed signal converter 25 to perform the procedure described later. At, the control output (control voltage) to the heating power source 21 is calculated, and this is output to the heating power source 21.

In the method of the present invention, the control output (control voltage) V _i is the previous control output (control voltage) V _i-1 as shown in the following equation (1).
And the value obtained by multiplying the sum of the control voltage change command values ΔV _PID , ΔV _t , and ΔV _v corresponding to changes in welding temperature, strip steel temperature, and pipe making speed by the correction coefficient α Ask according to. This makes it possible to set the control output (control voltage) in consideration of the change in welding efficiency.

V _i = V _i-1 + α (ΔV _PID + ΔV _t + ΔV _v ) (1) where V _i : Control voltage to heating power supply 21 V _i-1 : Previous control voltage to heating power supply 21 V _A : Current control voltage to the heating power supply V _I : Control voltage to the heating power supply when the constant is set ΔV _PID = K _P (ΔT _i −ΔT _i-1 ) + K _I · ΔT _i + K _D (ΔT _i -2
ΔT _i-1 + ΔT _i-2 ) (2) ΔV _t = K _t · Δt (t _i −t _i-1 )… (3) ΔV _v = K _v · Δv = K _v (v _i −v _{i- 1} ) (4) K _P : welding temperature proportional constant T _i : thermometer temperature signal T _i-1 : previous thermometer temperature signal K _I : welding temperature integration constant K _D : welding temperature differential constant t _i : Plate thickness signal t _i-1 : Previous plate thickness signal K _t : Plate thickness fluctuation compensation constant K _v : Speed fluctuation compensation constant v _i : Welding speed signal v _i-1 : Previous welding speed signal In equation (1) As the previous control voltage V _i-1 , the control voltage immediately before may be used as it is, or an average value of a plurality of control voltages including the control voltage immediately before and over a predetermined time period before this may be used. Further, as the control voltage to the heating power source (control voltage at the time of reference) when setting the constant that gives the correction coefficient α, the control voltage at the time of setting the calculation formula for obtaining the welding conditions may be used.

By the way, in the conventional method, the control output V _i is added to the previous control output V _i-1 by the control output change command values corresponding to the changes of the heating temperature, the plate thickness and the pipe making speed, as shown in the following equation (5). It was decided as a value.

V _i = V _i-1 + ΔV _PID + ΔV _t + ΔV _v (5) FIG. 2 is a graph showing the difference between the method of the present invention and the conventional method in the relationship between the pipe-making speed and the control voltage. The pipe making speed and the control voltage are plotted on the vertical axis. In the graph, a curve a represents the case of the method of the present invention, a curve b represents the case of the conventional method, and a curve c represents the above-mentioned control constants K _P , K _I , K _D , K _v , and K _t . The relationship between each pipe manufacturing speed and the control voltage is shown.

As shown by the curve c, in the state of the standard pipe-making speed v ₍₁₎ , the above-mentioned control constant K _P is determined based on the welding conditions at that time.
Etc. Or set the calculation formula and determine the optimum control voltage V _{I (1)} according to the formulas (2), (3) and (4), and when the pipe making speed changes to v ₍₂₎ , follow the formula (4). It is assumed that the control output (control voltage) increases by ΔV _v according to the change in the pipe making speed, and the control voltage becomes V _{I (2)} .

The control contents of the conventional method and the method of the present invention will be described when the welding efficiency at the time of setting the control constant K _{P and the} like, that is, when the welding efficiency decreases due to various condition changes.

First the conventional process control voltage of the control constant setting time to the control at the pipe producing speed v ₍₁₎ is started by V _{I (1),} actually due to poor welding efficiency control voltage V _{A (1} It is assumed that the control is started in the state of ₎ . Now the pipe making speed is v ₍₁₎ to v ₍₂₎
If it moves to, the computer determines the control voltage change command value Δ at the reference time corresponding to the speed change v ₍₂₎ −v ₍₁₎ according to the equation _(2).
The value obtained by adding V _v (= K _v (v ₍₂₎ −v ₍₁₎ )) to the previous output value V _i−1 is output as the control voltage.

However, since V _i-1 is V _{A (1)} instead of V _{I (1)} , the control voltage V _{A (2 ′)} immediately after the speed change becomes V _{A (1)} + ΔV _v , and the welding efficiency is poor. Insufficient heat input of V _{A (2)} −V _{A (2 ′)} with respect to the control voltage V _{A (2)} required to obtain good welding quality.

On the other hand, in the method of the present invention, the control voltage immediately after the speed change becomes V _{A (1)} + αΔV _v according to the equation ₍₁₎ , the ratio of the welding efficiency before the speed change is utilized, and the ideal control voltage V _A value close to _{A (2)} is obtained. On the contrary, when the welding efficiency is higher than that at the reference time, the ideal control voltage can be similarly obtained.

Note that the above example is the case where the control is started from the steady state, but if the last α at the time of the previous welding is stored,
The control according to the curve a can be performed from the beginning even in the section from v ₍₀₎ to v ₍₁₎ at the start of pipe manufacturing.

Therefore, the manual operation is performed only at the start of the first pipe production, but at the time of subsequent pipe production start, highly accurate control based on the previous data becomes possible.

Further, although the above description shows the superiority of the present invention with respect to the change in speed, even when there is a change in the plate thickness and welding temperature, the same correction of the welding efficiency is performed by the formula (1), and the optimum welding efficiency is obtained. A control voltage is obtained.

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

Using steel strip with carbon content of 0.15% by weight, the target dimension is 65 mm,
In the process of manufacturing an electric resistance welded pipe having a wall thickness of 4.0 mm, the pipe manufacturing speed was changed and the pipes were manufactured by the method of the present invention and the conventional method, respectively. The results are shown in Table 1.

As is apparent from Table 1, it is understood that when the method of the present invention is used, the temperature variation is significantly reduced and the number of defects is also significantly reduced as compared with the case where the conventional method is used.

〔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 description of drawings]

FIG. 1 is a block diagram showing an implementation state of the method of the present invention, and FIG.
The figure is a graph showing the control contents of the method of the present invention and the conventional method. 1 ... Strip steel, 2 ... Open pipe, 3 ... ERW pipe 13 ... Plate thickness gauge, 14 ... Plate thickness signal converter, 15 ... Forming machine, 18 ... Work coil, 21 ... Heating power supply , 22 …… thermometer 24 …… speedometer, 26 …… calculator, 25 …… speed signal converter 27 …… pipe manufacturing information input device

Claims (1)

[Claims] 1. A method for controlling welding heat input to an edge portion of an open pipe, wherein a high frequency current is passed through the edge portion to oppose each other, and heat welding is performed to manufacture an electric resistance welded tube. , Outputs the control output change command value for welding heat input setting, which is obtained in response to changes in welding conditions including plate thickness and welding temperature, multiplied by the following correction coefficient, in addition to the immediately preceding control output value. A welding heat input control method for an electric resistance welded pipe characterized by the above.