JPH0246311B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a welding heat input control method for an electric resistance welded pipe, and more specifically, a method for controlling the welding heat input of an electric resistance welded pipe, in particular, measuring the temperature distribution in the circumferential direction in the vicinity of the electric resistance welding part and controlling the welding heat input in accordance with the supplied power. This invention relates to a welding heat input control method for electric resistance welded pipes, which controls welding heat input by determining special parameters that have a positive correlation.

[Prior art] ERW pipes are made by continuously bending steel strips in the width direction to form a tubular shape, and then applying high-frequency power to the abutting portions to perform resistance heating or induction heating. It is manufactured by welding parts under heat and pressure.

When manufacturing such electric resistance welded pipes, welding heat input is a factor that affects the quality of the steel pipe product, particularly the quality of the welded part.

Conventionally, welding heat input for this type of ERW pipe was managed by an operator visually determining the heat input condition and manually setting the welding voltage, but this method However, the workability is poor and the degree of dependence on the skill level of the individual operator is large, resulting in variations in quality.
Delays in welding control due to fluctuations in heating conditions can cause quality deterioration and weld defects, making it difficult to obtain stable quality in the manufacture of ERW pipes that require high strength and toughness. It was hot.

For this reason, in recent years, along with recent advances in temperature measurement technology, measurement values based on temperature measurements near the electric resistance welded pipe using radiation thermometers, two-color thermometers, etc., or calculated values such as the average value of the measurement values, Welding heat input is managed by determining the deviation from the set temperature and controlling the deviation to zero. In this control method, a method has also been proposed that takes into account the welding speed and the thickness of the welded part (Japanese Patent Laid-Open No. 140265/1983).

[Problems to be Solved by the Invention] However, as shown in FIG. When the wall thickness is constant), it becomes impossible to judge the level of the welding heat input, and there is a problem that accurate control cannot be performed.

The applicant has confirmed that the phenomenon in which the measured temperature saturates or decreases on the high heat input side is due to the influence of latent heat of fusion and the influence of oxides formed on the surface near the welding point V. In both cases, it has been confirmed that the phenomenon is caused regardless of whether a radiation thermometer or a two-color thermometer is used, that is, regardless of the measurement method.

Regardless of the cause, the present invention was invented in view of the above situation, and by measuring the temperature distribution in the circumferential direction near the electric resistance welding part and calculating the result, it is possible to adjust the power supply to By finding special control parameters that have a positive correlation and performing feedback control to reduce the deviation from the set value of these parameters to zero, ERW pipes of high quality and stable quality can be obtained. The object of the present invention is to provide a method for controlling heat input during welding of pipes.

[Means for Solving the Problems] That is, the method according to the present invention for achieving the above object is to
When measuring the temperature distribution (T(x)) of
Let the peak temperature be T _nax , and let the minimum and maximum values of the X coordinate at which the distribution temperature is equal to or higher than a predetermined reference temperature T _p be a and b (T _p = T (a) = T (b)), respectively. Furthermore, the temperature at which T ₁ = 0.5 × (T _nax − T _p ) + T _p
When the minimum and maximum values of the X coordinate that are greater than or equal to T ₁ are defined as c and d, respectively (T ₁ = T(c) = T(d)), S _s
=∫ ^b _a T(x)dx, S _I =T _nax ×(ba-a), W=b-
Parameters represented by a, H=d−c, respectively
This method calculates S _s , S _I , W, or H, and performs feedback control of welding heat input so that one of these parameters becomes an appropriate setting value for each control parameter.

[Operation] First, the theoretical basis on which the present invention was made will be explained.

FIGS. 2A and 2B are explanatory diagrams of a method of manufacturing an electric resistance welded pipe by high-frequency welding. In Figure A, power supply contacts 2 are attached to both edges of the strip 1 formed continuously.
When the high-frequency current 3 is installed and a high-frequency current is applied, the high-frequency current 3 flows along the V-shaped end face, thereby the heating energy is concentrated on the edge surface, and the heated part is pressurized by the squeeze roll 4 and forged, thereby forming a steel pipe. are produced continuously. Figure B shows the case of the induction welding method, in which steel pipes are similarly manufactured continuously by passing a high frequency current through the working coil 2-1.

In order to quantitatively grasp the heat input state at the seam convergence point 5, a temperature distribution detector 7 equipped with an optical system 6 is placed above the seam convergence point.

Figure 3 A, B, and C are temperature distribution detectors 7, respectively.
This is an example of the temperature distribution (T(x)) in the circumferential direction (X-axis direction) obtained by. Figure A shows a case where the welding machine voltage is low, that is, a low heat input state, Figure B shows a case where normal welding is performed, and Figure C shows a case where the welding machine voltage is high, that is, a high heat input state.

In addition, the welding conditions in Fig. 3 are for a pipe outer diameter of 114.3
mmφ, wall thickness 6.35mmt, mill speed 23m/min, work coil distance 110mm, and squeeze amount 0.5mm.

As is clear from these figures, the peak temperature of high heat input welding (Figure 3c) is higher than that of normal welding (Figure 3B).
are almost the same, but the width of the distribution has become wider. This corresponds to the fact that, as shown in FIG. 1, the measured peak temperature tends to saturate or decrease on the high heat input side. Furthermore, at low heat input (FIG. 3A), the peak temperature is low and the width of the distribution is narrow. For example, the following parameters can be extracted from such temperature distribution characteristics. (4th
(see figure).

(a) T _nax ; maximum temperature (peak temperature) in the obtained temperature distribution T(x).

(b) W = b - a; The minimum and maximum values of the X coordinate at which the obtained temperature distribution T (x) is equal to or higher than the predetermined reference temperature T _p are respectively a and b (T _p = T (a) = T(b))
When , the temperature distribution width is defined as ba.
The obtained temperature distribution T(x) is a predetermined reference temperature T _p
It can also be said to be the maximum temperature distribution width when the temperature is above.

(c) S _s =∫ ^b _a T(x)dx; Integral value corresponding to welding heat input within the temperature distribution width defined by W above.

(d) S _I =T _nax ×W; Approximate value of S _s above. This corresponds to finding S _s simply and approximately.

(e) H=d−c; T ₁ = 0.5×(T _nax −T _p )+T _p The minimum _and maximum values _of the T(c)=T(d))
When , the temperature distribution width is defined as d−c. Since it is a kind of half-width, its characteristics as a control parameter are qualitatively the same as those of W.

Note that the reference temperature T _p is determined in consideration of at least the following two conditions. That is, the reference temperature T _p (°C) must be equal to or lower than the peak temperature during welding at which cold welding defects occur.

It should be made as large as possible due to the resolution of the temperature distribution detector and the calculation time and capacity constraints of the calculator.

Of the parameters (a) to (e) above, the present invention provides
Although it is not possible to quantitatively understand the welding heat input state using T _nax , it is possible to accurately and quantitatively understand the parameters W, S _s , and S _I , which have a positive correlation with welding heat input, according to H. This is due to the knowledge gained.

In other words, the parameters just extracted from the temperature distribution
The relationships between T _nax , W, S _s , S _I and H and welding machine voltage _EP are shown in FIGS. 5A to 5D, respectively. In the same figure, T _p =
The temperature was set at 1200 (℃).

As shown in Figure A, the relationship between T _nax and E _P is
It can be seen that, similar to the measurement results using conventional radiation thermometers, two-color thermometers, etc., there is a tendency to saturate on the high heat input side. On the other hand, as shown in the remaining figures B to D, the parameters S _s , S _I , W, and H all depend on the welding machine voltage E _P
It can be seen that there is a significant positive correlation with Therefore, by using the parameters S _s , S _I , W, or H instead of T _nax , the heat input state can be understood quantitatively.

Therefore, set values S _sp , S _Ip , W _p , and H _p are set for each parameter S _s , S _I , W, and H, and the welding heat input is controlled so that the set values match the actual values. This allows welding with a desired welding heat input. Of course, it is sufficient to use any one of the above parameters as a control parameter.

Note that, as can be seen from the relationship between S _s and S _I and the relationship between W and H, parameters that have a positive correlation with welding heat input are not limited to S _s , S _I , W, and H. In other words, for example, it has a proportional relationship with S _s and W.
If we specify other parameters S _n (=m・S _s ) and W (=n・W), welding machine voltage E _P and S _s or W
A similar relationship exists between welding machine voltage E _P and S _n or
It is clear that this also holds true qualitatively with W _o regardless of the values of the proportionality coefficients m and n. The present invention is due to the discovery of a special parameter that has a positive correlation with welding heat input,
As a technical concept, the existence of other parameters such as S _n and W _o as described above is not excluded.

[Embodiments of the Invention] Next, embodiments of the method according to the present invention will be described with reference to the drawings.

FIG. 6 is a block diagram illustrating an apparatus for carrying out a method according to an embodiment of the present invention, and FIG. 7 is a block diagram illustrating a part of FIG. 6 in more detail.

The optical system 6 and the temperature distribution detector 7 are installed above the seam convergence point 5. The optical system 6 is composed of a lens, a filter, etc., and in order to prevent the lens and filter from being damaged or clouded, air
The structure is equipped with a purge and water cooling jacket. Further, for this optical system 6, a light guide fiber such as a glass fiber may be used.

The temperature distribution detector 7 includes a temperature distribution sensor 71, a driver 72 for reading out each element of the temperature distribution sensor 71, and a video signal amplifier 73. The luminance distribution in the circumferential direction of the seam portion is imaged on the temperature distribution sensor 71 via the optical system 71. As this sensor, for example, a photodiode array (linear array, CCD, etc.) is used. The output is then supplied to a video signal amplifier 73.

The temperature distribution detector control section 8 includes a start pulse oscillator 81, an A/D converter 82, and a brightness distribution storage circuit 8.
4. Temperature distribution memory circuit 85 and sequence circuit 8
It consists of 6.

The start pulse from the start pulse generator 81 activates the driver 72 of the temperature distribution detector 7, and the linear array 71 is scanned by this driver. The video signal obtained by this scanning is amplified by a video signal amplifier 73, passes through an A/D converter 82, a brightness distribution storage circuit 83, and is converted into a temperature signal by a temperature conversion circuit 84. and,
It is stored in the temperature distribution storage circuit 85. The temperature distributions stored at this time are, for example, in FIGS. 3A, B,
The content is as shown in C. The sequence circuit 86 is a circuit that adjusts the timing of start pulse generation and the timing of reading, reading, or calculating the memory circuits 83 and 85.

The calculation unit 9 reads out the temperature distribution stored in the temperature distribution storage circuit 85 and performs calculation for determining the above-mentioned control parameter, for example, the half width H.
The calculation in this calculation unit 9 is not the upper value H,
The control parameter may be any one of S _s , S _I , and W.

The control parameters calculated by the calculation unit 9 are as follows:
It is supplied to the heat input control calculation unit 10 at a frequency of Hz.
This calculation unit 10 smoothes the input numerical value according to the fluctuation situation in the steady state, and smoothes the input value to a set value H _p
(or S _sp , S _Ip , W _p ) and calculate a corrected value of the welding machine voltage corresponding to the welding heat input according to the deviation thereof. This correction value signal is supplied to the high frequency oscillator power supply section 11, which causes the welding machine voltage 12
is feedback-controlled so that the welding heat input is at an appropriate value.

FIG. 8 is a block diagram of an apparatus for carrying out a method according to another embodiment of the present invention.

In the figure, the thickness of the steel plate 1 before welding is detected by a plate thickness detector 20, and the speed detector 21 detects the transport speed of the steel plate. These plate thickness and speed signals are then supplied to a set temperature calculator 22, where the set temperature is determined. In the present invention, the set value H _p (or S _sp , S _Ip , W _p ) of the control parameter is further determined based on this set temperature, and this set value is supplied to the heat input control calculation section 10 . That is, in correspondence with the above embodiments (FIGS. 6 and 7), it can be said that the set values of the control parameters are changed in response to changes in welding conditions. Therefore, the operations of the temperature distribution detector 7, the temperature distribution detector control section 8, the calculation section 9, the heat input control section 10, and the high frequency oscillator circuit power supply section 11 in the figure are the same as in the above-described embodiment.

In the above embodiments, the parameters for welding heat input are determined based on the temperature distribution near the welding area, and simple feedback control is performed. Needless to say, the present invention can also be applied to control systems that perform forward control.

[Effects of the Invention] As is clear from the above description, the method according to the present invention measures the temperature distribution in the circumferential direction near the electric resistance welding part, determines the control parameters that have a positive correlation with the supplied power, and controls the control parameters. Since the welding heat input is controlled by parameters, it is possible to accurately control the welding heat input, and as a result, a high-quality and stable ERW part can be obtained, making it possible to manufacture high-quality ERW pipes. ing.

[Brief explanation of drawings]

Figure 1 is a characteristic diagram of the measured temperature of the ERW part, Figure 2 A and B are explanatory diagrams of the manufacturing method of ERW pipes by high frequency welding, and Figure 3 A, B, and C are temperature distributions in the circumferential direction, respectively. FIG. 4 is an explanatory diagram for determining the control parameters according to the present invention, FIG. 5 A, B, C, and D are characteristic diagrams of the control parameters, respectively, and FIG. A block explanatory diagram of an apparatus for carrying out such a method, FIG.
FIG. 8 is a block explanatory diagram showing a part of the block explanatory diagram in more detail, and FIG. 8 is a block explanatory diagram of an apparatus for carrying out a method according to another embodiment of the present invention. 1...Strip, 2...Power contact, 2-1
...Working coil, 3...High frequency current, 4...
...Squeeze roll, 5... Seam convergence point, 6...
Optical system, 7...Temperature distribution detector, 8...Temperature distribution detector control unit, 9...Calculation unit, 10...Heat input control calculation unit, 11...High frequency oscillator power supply unit, 12...
welder voltage.

Claims (1)

[Claims] 1. Circumferential direction (X-axis direction) near the welding point of the ERW pipe
In the temperature distribution (T(x)), the peak temperature is T _nax , and the distribution temperature is a predetermined reference temperature T _p
The minimum and maximum values of the above X coordinates are respectively a and b (T _p = T(a) = T(b)), and furthermore, T ₁ = 0.5
The minimum and maximum values of the X coordinate at which the temperature T ₁ or higher is x (T _nax - T _p ) + T _p are c and d (T ₁ = T
(c)=T(d)), S _s =∫ ^b _a T(x)dx, S _I =T _nax ×(ba-a), W=
An electric resistance welded pipe characterized in that welding heat input is controlled so that any one of parameters S _s , S _I , W, and H expressed by b-a and H=d-c becomes a set value. Welding heat input control method.