JPH03254374A - Welding heat input control method for resistance welded tube - Google Patents

Abstract

PURPOSE:To lighten work load of an operator and to reduce weld defects by controlling the output of first heating equipment based on a measured value of a first thermometer and controlling the output of second heating equipment based on measured values of the first thermometer and a second thermometer. CONSTITUTION:The output of the first heating equipment 17 is controlled based on the measured value of the first thermometer 20 provided between the first and second heating equipments 17 and 19. In addition, the output of the second heating equipment 19 is controlled based on the measured value of the second thermometer 22 provided on a welding point or in the vicinity thereof and the measured value of the first thermometer 20. Accordingly, the reduction of weld defects such as a penetrator and the prevention of occurrence of flash can be realized stably and the work load of the operator can be lightened and the variance of control by an individual difference of the operator can be eliminated.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for controlling heat input during welding of an ERW pipe, and particularly to a method for controlling heat input in the process of manufacturing an ERW pipe using two heating devices. It is something.

[Conventional technology]

FIG. 4 is a schematic diagram showing a conventional method of manufacturing an electric resistance welded pipe.
The open pipe 1 is passed through the high-frequency induction heating coil 2a, and the edge portions 1a and 1a on both sides of the open pipe 1 are heated and melted to a temperature where they become molten.
.

When such a high-frequency induction heating coil 2a is energized, the current density at both edge portions 1a, Ia increases due to the proximity effect and skin effect, as shown in FIG. Via both edge portions 1a,
A current is induced that flows through a path along la. At junction point 4, the current density is high and the molten steel flows under the influence of the electromagnetic force, so if the metal has a strong tendency to oxidize, a large amount of oxide is generated.Next, when butt welding, this oxidation There was a problem in that objects were caught between the edge portions 1a and Ia on both sides, resulting in welding defects such as venetrators.

Furthermore, since molten steel scatters due to the flow of molten steel, there is a problem in that intrusion scratches occur on the surface of the open pipe 1 and operational problems occur.

As a method of preventing the generation of penetrators, a method has been used in which the butt welded portion is sealed with an inert gas to prevent oxidation of the molten steel. Furthermore, as a method for preventing the occurrence of flash, a method is used in which the heating temperature is lower than that of the conventional method to reduce the amount of flash generated.

However, in the method for preventing penetrators as described above, it is necessary to install an inert gas sealing device, which poses a problem in that work efficiency is reduced. In addition, in the method of preventing the occurrence of flash, the heating temperature is lower than conventional methods, but this temperature approaches the temperature range where welding defects are likely to occur, making it difficult to perform stable welding. There is.

In order to solve these problems, for example, JP-A-56-168
An apparatus for manufacturing an electric resistance welded pipe using two high-frequency heating devices as disclosed in Japanese Patent No. 981 is used. this is,
The first heating device heats the material to near the melting temperature to provide preheating, and then the second heating device heats the material to a temperature higher than the melting temperature to perform butt welding.

[Problem to be solved by the invention]

In the welding method described above using two heating devices,
1st. The output of the first heating device is controlled by the operator based on empirical judgment based on the red-hot state of the edge between the second heating devices. Similarly, the output of the second heating device is controlled based on empirical judgment.

In such a control method based on the operator's empirical judgment, when the welding speed is changed or the thickness of the open pipe is changed, the first. The output of the second heating device must be controlled instantaneously. Therefore, the operator is required to have high skill level, and it also causes fatigue. Furthermore, there is a drawback that the effects of reducing welding defects such as penetrators and preventing the occurrence of flash cannot be stably achieved.

A method of controlling the output of a heating device by detecting the temperature at or near the welding point has also been proposed (Japanese Patent Laid-Open No. 57-15
6880, JP-A-57-165188.

JP-A-58-9781, etc.). However, since such a control method only controls the output of the second heating device, a satisfactory control result cannot be obtained.

The present invention has been made in view of the above circumstances, and reduces the workload of the operator when manufacturing electric resistance welded pipes using two heating devices, as well as reduces welding defects and the occurrence of flash. It is an object of the present invention to provide a welding heat input control method for electric resistance welded pipes that can stably achieve prevention.

[Means to solve the problem]

In the welding heat input control method for electric resistance welded pipes according to the present invention, opposing edge portions of an oven pipe are sequentially heated and melted using a first heating device and a second heating device, and then subjected to a squeeze roll using a squeeze roll. In the process of manufacturing an electric resistance welded pipe by joint welding, the first heating device and controlling the output of the second heating device based on the detection result of a second thermometer placed at or near the welding point and the detection result of the first thermometer. shall be.

[Effect]

In the welding heat input control method for electric resistance welded pipes of the present invention, a first thermometer is disposed between a first heating device and a second heating device, and a second thermometer is disposed at or near the welding point. Place a thermometer. Then, the output of the first heating device is controlled so that a predetermined preheating temperature is obtained based on the detection results of the first thermometer, and the predetermined welding temperature is controlled based on the detection results of the first thermometer and the second thermometer. The output of the second heating device is controlled so that the temperature is obtained.

〔Example〕

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

FIG. 1 is a schematic diagram showing the implementation state of the manufacturing process of an electric resistance welded pipe using the control method of the present invention, in which 3 indicates a squeeze roll and 1 indicates an open pipe. Uncoiler 11
After passing through a looper 12, the steel strip 10 unwound by the above is formed into a tubular shape by a forming machine 15 to become an oven pipe 1. A plate thickness gauge 13 for measuring the plate thickness of the steel strip 10 is disposed on the upstream side of the working path of the forming machine 15. The plate thickness gauge 13 is configured to measure the plate thickness by measuring the interval between rolls that contact the steel strip 10 vertically, and the detected measurement value is converted into an analog plate thickness by the plate thickness signal converter 14. It is converted into a signal t8, and the plate thickness signal t is output to the calculator 26. Note that as the plate thickness gauge 13, a non-contact type plate thickness gauge using radiation, ultrasonic waves, or the like may be used.

The open pipe 1 is heated at its edge portion 1a by a first heating work coil 16 and a second heating work coil 18.
, la are sequentially heated and then pressed together by a squeeze roll 3 to form a pipe 30. Here, the first heating work coil 16 heats the edge portions 1a, la to the preheating temperature, and the second heating work coil 18 heats the edge portions 1a, la.
Heat la to welding temperature. First heating work coil 16. The second heating work coils 18 are connected to the respective first heating power sources 17 . It receives voltage supply from a second heating power source 19. The voltage supplied from each of these heating power sources 17819 to the work coils 16.18 is controlled by the control voltage signal V i (11+ V i (Z)) output from the computer 26. 16
and the first heating power source 17 constitute a first heating device, and the second heating work coil 18 and the second heating power source 1 constitute a first heating device.
9 constitutes a second heating device.

Between the work coil 16 and the work coil 18, a first
A thermometer 20 is arranged. Further, a second thermometer 22 is arranged at or near the welding point. Optical thermometers such as a two-color thermometer or a radiation thermometer can be used as these thermometers 20 and 22.

Furthermore, when using these optical thermometers, an image fiber may be used to prevent high frequency noise and the like. The measured value detected by each thermometer 20.22 is converted into an analog temperature signal T by a temperature signal converter 21.23.

)l T□2. The temperature signal T i (1
) + T i (Z) are output to the computer 26, respectively.

On the downstream side of the work path of the squeeze roll 3, a speed meter 24 for measuring the pipe manufacturing speed of the pipe 30 is provided. The speed meter 24 is configured to detect the speed by measuring the number of rotations of the rolls in contact using a pulse generator, and the detected measurement value is converted into an analog speed signal V by the speed signal converter 25. The speed signal V is outputted to the computer 26. Note that the tube manufacturing speed may be detected by measuring the number of revolutions of the forming rolls.

Pipe manufacturing information (outer diameter, wall thickness, material, etc. of the pipe 30 to be manufactured) is input to the computer 26 via the pipe manufacturing information input device 27 . Further, a target temperature (target preheating temperature T0°2.target welding temperature T., 2)) is input to the calculator 26 via a target temperature input device 28. Based on 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 converters 21 and 23, and the speed signal from the speed signal converter 25, the computer 26 calculates the following: In the procedure described later, a control output (control voltage) at the heating power source 17.19 is calculated and outputted to the heating power source 17.19.

Next, the content of calculations performed by the computer 26 will be explained.

FIG. 2 is a flowchart showing the contents of this calculation. In the following operation description, calculation procedures will be described for each case (when there is no change in the plate thickness and welding speed), (when the welding speed changes), and (when the plate thickness changes).

The contents of each character in FIG. 2 are as follows.

(Left below) ■ = Welding speed signal Vi-1' Previous welding speed signal d
v: welding speed dead zone t,: plate thickness signal ji-1: previous plate thickness signal dt: plate thickness dead zone T,. , :Temperature signal Ti(2)' of the first thermometer 20'Temperature signal T0° of the second thermometer 22, :Target preheating temperature To(21:Target welding temperature V=u+'To the first heating power source 17 control voltage signal Vi
-1+I Me 1 + Previous control voltage signal V to the I de power source 17, +z+' Control voltage signal ■i to the second heating power source 19
-1+21: Previous control voltage signal KP(1) to second heating power source 19: Preheating temperature proportional constant [first heating power source 17
] Kl (11' preheating temperature differential constant [first heating power supply 17
]K11+11' preheating temperature integral constant [first heating power supply 1
73KF (21: Welding temperature proportional constant [Second heating power source 1
9] K1 (z+: welding temperature differential constant [second heating power source 1
9] Kotz: Welding temperature integral constant [Second heating power source 1
9] Kvu>'Speed fluctuation compensation constant [first heating power source 17
]K□2. : Speed fluctuation compensation constant [second heating power source 19]
Kto, : plate thickness variation compensation constant [first heating power supply 17] K
t, 2. : Plate thickness variation compensation constant [second heating power supply 19] (
When there is no change in plate thickness and welding speed> First, the welding speed signal V is taken into the computer 26 from the speed signal converter 25 (step Sl), and the difference ΔV between Vi and the previous value v, -1 is calculated. is calculated (step S2). Since Δ■ is not larger than the welding speed dead zone dv (Step S3:
No), proceed to Pro Tsuku ■.

The plate thickness signal t, is taken into the computer 26 from the plate thickness signal converter 14 (step S4), t, and the previous value t, -.
The difference Δt from 1 is calculated (Ste knob S5). Δt
.

is not larger than the plate thickness dead zone dt (step S6
: No), proceed to block ■.

In block ■, the temperature signal T of the first thermometer 20,...
.

is taken in from the temperature signal converter 21 (Ste knob S7), and the target preheating temperature Ton+ is taken in from the target temperature human power device 2nd (Ste knob S8), and the difference ΔT between the two is taken in.
,. , is calculated (step S9). The calculator 26 has preheating temperature control constants Kp(1), K+(B, KO
(+1 is input (step SIO, Sll, 5
12). Each of these preheating temperature control constants KF+1)l K
11l, K11<11 is calculated in advance or determined empirically, and is divided into sections according to the outer diameter, plate thickness, material, and welding temperature of the pipe. These control constants, the difference Δ
T=m Difference from the previous time ΔTi-1+If Difference from the time before the previous time ΔTi-2
(11), the modified control voltage ΔV, (1) at the first heating power source 17 is calculated as shown in the following equation (1) (step 513).

ΔV= +11 = KP(.(ΔT8..−ΔTi−
1+11)+Kzn'ΔT,,,+Knu+ (ΔT=<++ 2ΔTi-1(1)+Δ
Ti-2N)]...(1) Next, proceed to block (2). In block (2), the temperature signal Ti(2) of the second thermometer 22 is taken in from the temperature signal conversion device 23 (step 514), and the target welding temperature To<2+ is taken in from the target temperature input device 28 (step 515). , the difference ΔT=+Z) between the two is calculated (step 316). Temperature signal T of second thermometer 22
□2. and the temperature signal T of the first thermometer 20 divided by the temperature signal T=tz (step 517). α; (= (T=+.-T=+u)
/T:+z+) represents the ratio of the temperature to be raised by the second heating device to the temperature required in the weld zone. The calculator 26 has a welding temperature control constant K F in advance.
(21+K I (Z) + K D (2) is input (steps 518, 519, 520).

For each of these welding temperature control constants □2) I K+tz++
KD (□, is pre-calculated or determined empirically and is the outer diameter of the pipe.

Classified by plate thickness, material, and welding temperature. These control constants, α, 1 difference ΔTi (21 + previous difference ΔTi = -
+. ), based on the difference ΔT, -1□, from the previous time, the following (2
) As shown in FIG. 2, a changed control voltage ΔVif21 in the second heating power source 19 is calculated (step 521).

ΔVi(21=αi(KP(2)(ΔTi(21
-ΔTi-1+21)+Kl(Z)'ΔT (2)+KD(□, (ΔT1□, -2ΔT4-Bz++ΔT=-
ztz+) )...(2) Here, the equation (2) above does not take into account the temperature drop at the edge between the first heating device and the second heating device due to thermal diffusion, but At the welding speed, this temperature drop is minute and can be almost ignored. If this temperature drop causes problems with temperature control, introduce a heat conduction calculation formula in (2) 2 above, or segment the pipe by outer diameter, plate thickness, material, target preheating temperature, and welding speed. The welding temperature control constants obtained may be input into the calculator 26 in advance.

Changed control voltage ΔVif obtained in blocks ■ and ■. .

ΔVi(2+) is the previous control voltage signal Vi−1(1)
+ V i-1 + Z), the current control voltage signal ■
Calculate i +11 + V i (□, Step 5
22), output to each heating power source 17.19 (step 5
23).

(When the welding speed changes) In step S3 of block ■, the difference ΔV becomes larger than the welding speed dead zone dv (step S3: YE
S), proceed to block ■. The speed fluctuation compensation constant KVC11 for the first heating power source 17, which is classified according to the outer diameter, plate thickness, material, and welding speed, has been entered into the computer 26 in advance (step 524), and the compensation constant is set to □1°. Difference ΔVi
Accordingly, the changed control voltage ΔV at the first heating power source 17, as shown in equation (3) below. , is calculated (step 5
25).

ΔV i (++ = K v <.・Δ■1
...(3) Next, proceed to block ■. Outer diameter, plate thickness,
A speed fluctuation compensation constant KV (21) for the second heating power source 19 segmented by material welding speed is inputted in advance to the calculator 26 (step 526), and a compensation constant KV (
2), the difference Δ■, and the previous ratio α, -1, the following (4) is obtained.
The modified control voltage ΔV = <t at the second heating power source 19 is calculated as shown in the equation (step 527).

ΔVi121=αi−1'Kv(21'Δv,
−(4) Changed control voltage Δ■ calculated as above
,. ,.

ΔVi (Z) is the previous control voltage signal Vi-1<11+
In addition to Vi-1(Z), the current control voltage signal V i (11+V i (21) is calculated (step 522) and output to each heating power source 17.19 (step 523).

(When the plate thickness changes) In step S6 of block ■, the difference Δt becomes larger than the plate thickness dead zone d1 (step S6: YES)
, proceed to block ■. The plate thickness variation compensation constant K t (11) for the first heating power source 17, which is classified according to the outer diameter, plate thickness, material, and welding speed, is manually entered in the calculator 26 in advance (step 528), and the compensation constant Kt Using (1) and the difference Δt, the variable voltage Δ■, . . . in the I-th heating power source 17 is calculated as shown in the following equation (5) (step 529).

ΔV,. ) = K t (1)・Δt1 ・・
・(5) Next, proceed to block ■. Outer diameter, plate thickness, material.

The plate thickness variation compensation constant 2> for the second heating power source 19 classified by welding speed is input into the calculator 26 in advance (step 530), and the compensation constant 2. and the difference Δt
, and the previous ratio α, -1, as shown in equation (6) below,
Changed control voltage ΔVi (2) in the second heating power supply 9
is calculated (step 531).

Δ■□, 2〉=αi−1・K t (ゎ・Δ1.・
...(6) Changed control voltage Δ calculated as above
■i+11+ΔViH) is the previous control voltage signal Vi-
1+1)+Vi-1(.

In addition to this, is this system? 1llii pressure signal V,. ++
Vi+Z) is calculated (step 522) and output to each heating power source 17.19 (step 523).

A description will be given of changes in preheating temperature, welding temperature, and plate thickness when an electric resistance welded tube is manufactured using the control method according to the present invention and the conventional control method (controlling the temperature visually). FIG. 3 shows this result. Both the present invention example and the conventional example,
The pipe size has an outer diameter of 50.8 m, a plate thickness of 5.011 mm, and the materials are C: 0.16%, Mn: 0.50%,
It is a carbon steel containing 0.13% Si, the target preheating temperature is 780°C, the target welding temperature is 1500°C, and the welding speed is a constant 60m/min.

In the conventional example, both the preheating temperature and the welding temperature decrease as the plate thickness suddenly increases in the center of the chart. This is because the welding operator cannot simultaneously and quickly control the outputs of the first and second heating devices in response to changes in plate thickness. Further, even in the first half and the second half of the chart, where there is little change in plate thickness, the preheating temperature and welding temperature both have fluctuations of about ±20° C. with respect to the target values, and are unstable. Therefore, the number of welding defects was also found to be as high as 0.35/m.

On the other hand, in the example of the present invention, even if the plate thickness changes rapidly in the center of the chart, there is almost no change in the preheating temperature and welding temperature, and rapid control is realized. Further, in the first half and the second half of the chart where the plate thickness changes are small, the fluctuation range of the preheating temperature and welding temperature with respect to each target value is about ±10° C., and is extremely stable.

Therefore, the number of welding defects is also 0.05/m, which is significantly reduced compared to the conventional example.

Furthermore, the control method of the present invention was carried out by changing the welding speed, and the preheating temperature and welding temperature were measured. Although detailed temperature changes in the preheating temperature and the welding temperature in this case are omitted from illustration, even in this case, there was almost no change in both temperatures due to changes in the welding speed, and the number of welding defects was small.

〔Effect of the invention〕

As detailed above, in the control method of the present invention, the output of the first heating device is controlled based on the measured value of the first thermometer provided between the first and second heating devices, and Since the output of the second heating device is controlled based on the measured value of the second thermometer and the measured value of the first thermometer installed nearby, it is possible to reduce welding defects such as penetrators and prevent the occurrence of flash. It can be achieved stably and reduce the workload of the operator.
The present invention has excellent effects such as being able to eliminate variations in control due to individual differences among workers.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the implementation state of the manufacturing process of an electric resistance welded pipe using the control method of the present invention, FIG. 2 is a flow chart showing the control process of the present invention, and FIG. 3 is a diagram showing the example of the present invention and the conventional example. Figures 4 and 5 are diagrams showing the control results in the conventional electric resistance welded tube manufacturing method. 16. First heating work coil 17. First heating power source 18. ...Second heating work coil 19.
...Second heating power source 20...First thermometer 22.
...Second thermometer 26...Calculator 30...Pipe

Claims (1)

[Claims] 1. Opposing both side edge portions of the open pipe are
In the process of manufacturing an electric resistance welded pipe by sequentially heating and melting it in a heating device and a second heating device, and butt welding it with a squeeze roll, the first heating device and the second heating device The output of the first heating device is controlled based on the detection result of a first thermometer placed between the welding point and the first temperature. A welding heat input control method for an electric resistance welded pipe, characterized in that the output of the second heating device is controlled based on the detection result of the electric resistance welded pipe.