JPH0234714B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling welding heat input in an electric resistance welded tube manufacturing mill during the start-up period of the mill and during the steady operation period of the mill.

Electric current-carrying electric resistance welded pipes are produced by sequentially bending a strip of raw material into an O-shaped cross section using forming rolls so that the edges on both sides face each other, and passing this through an induction coil, or by bending the strip with the edges on both sides facing each other. It is manufactured by sliding a contact chip onto the contact tip, passing a high frequency current through the edge portions on both sides, heating and melting these portions with gel heat, and passing them between squeeze rolls for butt welding.

By the way, in the manufacturing method of electric resistance welded pipes as described above, the welding conditions, especially the appropriateness of the heat input amount, are extremely important requirements that affect the welding quality.
For example, if the amount of heat input is insufficient, the edges on both sides will not be welded together, a so-called cold defect will occur, and if the amount of heat input is too much, the edges on both sides will melt and fall off, a so-called burn-through phenomenon, which will deteriorate the quality of the pipe. This will result in lowering the value. For this reason, in the past, skilled workers monitored the flame color of the part to be welded, the appearance of the weld bead, etc., and set and adjusted various conditions empirically. could not be done. For this reason, in recent years, attempts have been made to automatically control the amount of heat input. One such method is to detect the thickness and transfer speed of the strip, which is the material for the ERW tube, during stable operation of the ERW tube manufacturing mill, that is, the welding speed of the tube, and to store these detected values as reference values. A method has been proposed in which the thickness and transfer speed of the strip detected during operation are compared with the respective reference values, and the current flowing through the strip is controlled according to the deviation of the detected value from the reference value. (Japanese Patent Application Laid-open No. 52-69842). However, this method focuses on the strip thickness and transfer speed as factors that cause excess or deficiency in the amount of heat input. There are various factors such as the material, the outer diameter of the ERW pipe to be manufactured, the material, the amount of upset, and the welding temperature, and even though there is a very close relationship between the amount of upset and welding heat input, these factors are often ignored. However, since the welding zone temperature is detected by a radiation thermometer installed downstream of the welding point, it has the disadvantage that it cannot be sufficiently effective. Since this process was not controlled, the quality of the welded parts of the pipes produced during this period was poor, resulting in defective products and poor pipe manufacturing yields.

The present invention has been made to eliminate the drawbacks of the prior art, and its purpose is to:
There is a period of stable operation of the tube manufacturing equipment (manufacturing mill) in which the strip transfer speed, which is an important factor influencing welding heat input, in other words, the rate of change in the tube welding speed is small and almost constant, and the rate of change is large until then. Heat input control is performed based on different relational expressions for each start-up period, and the amount of upset is also used for control, making it possible to significantly improve the quality of ERW pipes and the pipe manufacturing yield. The present invention provides a method for controlling welding heat input of electric resistance welded pipes.

The heat input control method for welding an electric resistance welded pipe according to the present invention is to apply electric current to butt weld while heating and melting both edge portions of an open pipe, which is formed by bending into a cylindrical shape so that both edge portions of a metal band face each other. In the manufacturing process of welded pipes, the thickness of the metal strip, the temperature of the part to be welded, the amount of upset, and the welding speed are detected, and the rate of change in the welding speed is used as a reference value for determining the start-up period and stable operation period of the pipe manufacturing equipment. A first heat input control amount related to the rate of change of the welding speed, assuming that the period exceeding the period is a rising period;
The second heat input control amount of the feedback based on the detected values of the wall thickness, the temperature of the welded part, and the welding speed is used for heat input control, and the period in which the rate of change of the welding speed is below the reference value is a stable operation period. The second
A heat input control amount, a third heat input control amount of a feed forward based on the detected value of the wall thickness, and a fourth heat input control amount based on the detected value of the upset amount are used for heat input control. Features.

The present invention will be specifically explained below based on drawings showing its implementation state. FIG. 1 is a block diagram showing a tube mill and its control system used to implement the welding heat input control method for electric resistance welded pipes according to the present invention (hereinafter referred to as the method of the present invention), and in the figure, SQ is a squeeze roll, an IC indicates an induction coil, and OP indicates an open pipe.
The open pipe OP is made by cutting the strip SP fed out from the uncoiler UC to the same width using a trimmer TM, and passing it through a group of forming rolls FR to form a cross section C.
Due to its shape, the edge parts E and E on both sides are bent into an O-shaped cross section facing each other, and the edge parts E and E are passed through an induction coil IC to heat the edge parts E and E, and the squeeze roll is heated.
It is transferred toward the SQ side in the direction of the white arrow, and the edge parts E and E on both sides are heated and melted. At the same time, it reaches between the squeeze rolls SQ and side pressure is applied, and the edge parts E and E on both sides are butt-welded. It is designed to be manufactured into a pipe P. In such a pipe manufacturing process, the thickness meter 1 measures the thickness d of the strip SP, the upset amount measuring device 2 measures the amount of upset U during tube manufacturing, and the speed meter 3 measures the amount of the tube P. , in other words, the transport speed v of the strip SP is
The welding part temperature pattern measuring device 4 is adapted to measure the warm distribution on the edge end face of the open pipe OP immediately before the welding point.
The thickness meter 1 measures the thickness of the strip SP in the longitudinal direction by detecting a roll gap between rolls 5a and 5b which are brought into rolling contact with the front and back surfaces of the strip SP. The speed meter 3 is composed of a pulse generator etc. connected to a roll 4a which is in rolling contact with the pipe P, and the transfer speed of the pipe P is determined from the number of pulses emitted according to the rotation speed of the roll 4a, in other words. It is designed to detect welding speed. It goes without saying that the thickness gauge 1 is not limited to the one having the configuration shown in the drawings, and a known thickness gauge such as an ultrasonic thickness gauge can be used.

The upset amount measuring device 2 is a gap meter facing the upper outer peripheral surface of the final stage fin pass roll FR ₁ .
G ₁ is equipped with a gap meter G ₂ (only one is shown) facing the outer peripheral surface on the opposite side to the opposite side of the squeeze roll SQ, and the gap meter G ₁ is connected to the gap meter G ₁ . The separation dimension d ₁ between the and Finpass roll FR ₁ , and the gap gauge G ₂ from the gap gauge G ₂ .
and the distance between each squeeze roll SQ circumferential surface d ₂ , d ₃
is read in, and the upset amount U is detected according to the following equation (1).

U=2(G _F −G _S )+2R _F (θ _F −α/2) −2R _S・θ _S …(1) However, G _F = d ₁゜−d ₁ +G _F゜ G _S = (d ₂゜−d ₂ ) + (d ₃゜−d ₃ )＋G _S゜ G _F : Roll gap of fin pass roll G _S : Roll gap of squeeze roll R _F : Caliber diameter of fin pass roll R _S : Caliber diameter θ of squeeze roll _F : Angle between the arc of the cross section of the balance of the fin pass roll and its center θ _S : Angle of the arc of the cross section of the squeeze roll's balance with the center d ₁゜, d ₂゜, d ₃゜, G _F゜, G _S゜ are both initial setting values. The temperature pattern measuring device 4 at the edge portions E and E of the open pipe OP has already been applied for by the present applicant (Japanese Patent Laid-Open No. 77924/1983). However, its outline is shown in FIG. 2. FIG. 2 is a block diagram of the temperature pattern measuring device 4, in which numeral 41 indicates an image guide and numeral 42 indicates a lens. The object side terminal of the image guide 42 is the edge part E in the open pipe OP,
The other terminals are placed so as to be able to capture E and its vicinity within the field of view, and the other terminals are placed facing the lens 42, through which the image guide 41
The field of view of the part facing the terminal is captured by the image pickup tubes 43a, 43.
The images are taken at points b and 43c. The image captured by Image Guide 41 is Half Mira 4
4a, the light enters the image pickup tube 43a through the optical filter 44b whose transmitted wavelength component has a peak wavelength of λ ₁ , and some of the light reflected by the optical filter 44b has a reflected wavelength component whose peak wavelength is λ ₂ (λ ₁ <λ ₂ ) and enters the image pickup tube 43b through the optical filter 44c,
Further, the light reflected by the half mirror 44a is made to enter a color image pickup tube 43c. The image pickup tube 43c is for capturing the shape of the welded part of the open pipe OP, and a vidicon or the like is used, whereas the image pickup tubes 43a and 43b capture information for performing two-color temperature calculations as described below. A photoelectric conversion element capable of random scanning, such as an image disector, is used. A common X polarized light signal (horizontal direction) and Y polarized light signal (vertical direction) are inputted to the image pickup tubes 43a and 43b through a calculation position setter 45 and a scan control circuit 46, and are emitted from each image pickup tube 43a and 43b, respectively. The video signals VD ₁ and VD ₂ thus obtained are taken into a signal processing circuit 47 and subjected to two-color temperature calculation, and then inputted to a video signal control circuit 48 as a temperature pattern signal. In the video signal control circuit 48, the video signal from the image pickup tube 43c and the temperature pattern signal are combined and displayed on the monitor 49 as an image composite temperature pattern signal, for example, in the image display section shown in FIG. The image of the part captured by the image guide 41,
In the image display section indicated by , a temperature pattern in the horizontal direction (tube axis direction) is displayed, and in the image display section indicated by , a temperature pattern in the vertical direction (tube circumferential direction) is displayed. As a result, both edge portions E of the open pipe OP immediately before welding,
The temperature of E can be understood as the temperature distribution in the moving direction of the open pipe OP and the temperature distribution in the pipe circumferential direction.

Reference numeral 6 is an arithmetic and control unit, and from the thickness gauge 1, the plate thickness data in the longitudinal direction of the strip SP is transmitted.
The upset amount measuring device 2 provides data regarding the amount of upset during pipe manufacturing, and the speed meter 3 provides data regarding the amount of upset during pipe manufacturing.
data on the transfer speed, that is, the welding speed, and the temperature pattern in the longitudinal direction immediately before the welding point including both edge portions E, E or the specific position of the short side edge portions E, E immediately before welding from the temperature pattern measuring device 4. The temperature is read, and the calculations shown below are performed separately for 1 when the tube mill starts up and 2 when the tube mill is in stable operation, and a command is given to the voltage application device 7 to adjust the voltage applied to the induction coil IC. It is designed to emit a signal.

(1) Heat input control during the startup period of the tube mill The arithmetic and control unit 6 controls the thickness d of the strip SP,
The transfer speed (welding speed) v, the upset amount U, and the temperature T of the edge portions E, E at a specific position immediately before the butt welding point between the edge portions E, E on both sides are read, and these and the preset pipe to be manufactured are read. Based on the outer diameter D of P, etc., the applied voltage V, in other words, the amount of heat input, is calculated based on the empirically determined equation (2) below.

V=K・f(v, d, D, T, U) ...(2) In addition, in the above equation (2), the plate thickness d is at a different position from the temperature measurement position just before the welding point, so tracking is not necessary. Then, calculate and input the temperature measurement position.

The outer diameter D and constant K of the pipe P are prepared in advance in a table, and are selected and adopted as appropriate each time the pipe manufacturing conditions are changed.

A command signal is issued from the arithmetic control device 6 to the voltage application control device 7 in order to realize the amount of heat input calculated based on equation (2), but the reading of each data as described above is repeated at a predetermined timing, and the strip When a change occurs in the transfer speed v, plate thickness d, etc., the heat input control amount is calculated accordingly, and the voltage application control device 7 is sent from the calculation control device 6 each time.
A command signal is issued to modify the applied voltage.

The above control is sequentially repeated and continued during the start-up period of the tube mill, in other words, during the period when the rate of change per hour of the transfer speed of the strip SP is equal to or higher than the reference value a and dv/dt > a. After the tube mill reaches a stable operating state, it switches to heat input control during the stable operating period (2), which will be described later.

The specific control procedure during the start-up period of the tube mill will be explained according to the flowchart shown in FIG. First, the speed meter 3 reads the transfer speeds v ₁ , v ₂ ...v _i-1 , v _i ... of the pipe P at predetermined timing (step), and each read transfer speed
The difference Δv _i (v _i −v _i-1 ) between v i _-1 and v _i is calculated (step), and the transfer speed Δv _i (corresponding to dv/dt, that is, the rate of change in welding speed) is determined in advance. Determine whether it is larger than a certain value a (step) and NO
In the case of Δv _i a, the process moves to the routine for the stable operation period of the tube mill, which will be described later.
In the case of YES, that is, when Δv _i >a, the pipe outer diameter D determined based on the pipe manufacturing schedule, the wall thickness d _i of the strip SP input from the thickness gauge 1, and the upset amount measuring device 2 are input. The proportional constant Kv selected based on the upset amount U _i is read from the constant table, and the heat input control amount ΔV _i corresponding to the change in transfer speed is calculated based on the following equation (3) (step).

ΔV _i = Kv・Δv _i ...(3) Next, this heat input control amount ΔV _i , the heat input amount V _i-1 calculated and set in the previous cycle, the outside diameter D of pipe manufacturing, and the transfer speed described later The heat input amount V _i to be newly set from v i and the heat input control amount _ΔVfb determined by the proportionality constant Kfb selected based on the plate thickness d _i is as follows.
Calculation is performed based on equation (4) (step), and a command signal is issued to the voltage application control device 7 to realize this heat input amount V _i (step). Δv _i >a
During this time, the process returns to step 1 and the above-described process is repeated in sequence.

V _i =ΔV _i +V _i-1 +ΔVfb (4) Here, ΔV _i corresponds to the above-mentioned first heat input control amount, and ΔVfb corresponds to the second heat input control amount.

(2) Heat input control during the stable operation period of a tube mill As mentioned above, when the rate of change Δv _i of the transfer speed or welding speed in a step becomes less than the reference value a, that is, when it becomes Δv _i a, Assuming that the tube mill has entered a stable operating state, heat input control is performed according to the following routine. From the temperature pattern measurement device 4, temperatures T ₁ , T 2 , T ₂ ,
...T _{i -1} , T _i ... are read (step), and the edge portions on both sides immediately before welding are determined based on the detected values and the thickness d, material M, and outside diameter D of the strip SP in the pipe manufacturing schedule. E,E
The difference ΔT _i (=T _i - T ₀ ) from the target temperature T ₀ of Transfer speed v _i detected by d _i and speedometer 3
Based on _the proportionality constant K _I and other proportionality constants K _D selected based on the feedback data of Calculate based on formula (5) (step).

ΔVfb=K _p (ΔT _i −ΔT _i-1 )+K _I ΔT _i +K _D (ΔT _i −2ΔT _i-1 +ΔT _i-2 ) ……(5) The calculation to obtain ΔVfb up to this step is Δv _i > This shall also apply to case a.

Next, the heat input control amount ΔVfb is based on the feedback data such as the plate thickness d _i of the strip SP and the pipe transfer speed v _i , and the third heat input control amount ΔVff is based on the feedback data of the strip SP. ,
Based on the fourth heat input control amount ΔVu corresponding to the change in the amount of upset U _i detected by the amount of upset measuring device 2, the edge portions on both sides E, which are the parts to be welded, are
The total heat input control amount ΔV _i required to make E match the target temperature T ₀ is calculated according to the following equation (6) (step).

ΔV _i = ΔVfb + ΔVff + ΔVu ...(6) Then, based on this total heat input control amount ΔV _i and the heat input amount V _i-1 set in the previous cycle, the heat input amount V _i to be newly set is as follows (7) The calculation is performed according to the formula (step), and a command signal is issued to the voltage application control device 7 to realize the calculation (step).

V _i =ΔV _i +V _i-1 (7) During Δv _i a, the process returns to step 1 and repeats the process from step to sequentially.

In addition, the heat input control amount ΔVff corresponding to the change in the thickness of the strip SP and the heat input control amount ΔV _U corresponding to the change in the upset amount U, which are the feed forward data used in the above steps, are processed as follows. is required. That is, the heat input control amount ΔVff is determined by first reading data regarding the plate thicknesses d ₁ , d ₂ . . . d _i-1 , d _i . Select the corresponding proportionality constant Kff. On the other hand, the difference Δd _i between the read plate thicknesses d _i-1 and d _i
(=d _i −d _i-1 ), and then, based on this plate thickness change amount Δd _i and the proportionality constant Kff, the heat input control amount ΔVff corresponding to the plate thickness change is calculated according to the following equation (8). Obtained by calculation.

ΔVff=Kff・Δd _i ...(8) The same applies to the heat input control amount ΔVu, and the upset amounts U ₁ , U ₂ , ...U _i-1 , U _i ..., and based on this, select the corresponding proportionality constant Ku from the constant table. On the other hand, the difference _{ΔU i (} U _{i −}
U _i-1 ), and then, based on this upset change amount ΔU _i and proportionality constant K _U , calculate the heat input control amount ΔV _U corresponding to the change in the upset amount according to equation (9) below. It is obtained by

ΔV _U =K _U・ΔU _i ...(9) As described above, in the present invention, different heat input control amounts are used during the start-up period and the stable operation period of the pipe manufacturing equipment, so that the amount of heat input that was conventionally controlled is different. Welding heat input control is performed even during the start-up period, which improves the welding quality and yield during this period.In addition, heat input control is performed using the upset amount during the stable operation period, which improves control accuracy during this period. The effect is that the welding quality is improved by improving the welding quality.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the implementation state of the method of the present invention,
Fig. 2 is a schematic diagram of a temperature pattern measuring device for a welded part used in the method of the present invention, Fig. 3 is an explanatory diagram showing the display mode on the monitor of the temperature measuring device, and Fig. 4 is a flow chart showing the control process. . 1... Thickness gauge, 2... Upset amount measuring device, 3...
Speedometer, 4...Temperature pattern measuring device, 5...Arithmetic control section, 7...Voltage application control device, SP...Strip,
SQ...squeeze roll, IC...induction coil.

Claims (1)

[Scope of Claims] 1. In the process of manufacturing an electric resistance welded pipe in which both edge portions of an open pipe are formed by bending into a cylindrical shape so that the edge portions on both sides of a metal band face each other are butt-welded while being heated and melted, The thickness of the metal strip, the temperature of the part to be welded, the amount of upset, and the welding speed are detected, and the period during which the rate of change in welding speed exceeds the reference value for distinguishing between the startup period and the stable operation period of pipe manufacturing equipment is considered to be the startup period. If there is, a first heat input control amount related to the rate of change of the welding speed and a second heat input control amount of feedback based on the detected values of the wall thickness, the temperature of the welded part and the welding speed are used for heat input control, The period in which the rate of change of the welding speed is less than or equal to the reference value is considered to be a stable operation period, and the second heat input control amount and the third heat input control amount of the feed forward based on the detected value of the wall thickness are calculated. , and a fourth heat input control amount based on the detected value of the upset amount for heat input control.