JPS6338531A - Method for controlling induction heating of weld zone of seam welded steel pipe - Google Patents

Abstract

PURPOSE:To control heating with high accuracy by predetermining an equation to calculate the temp. at an arbitrary point of a region to be heated, repeating the calculation of the estimated temp. until the estimated temp. of the part to be heated obtd. after the calculation attains a target temp. CONSTITUTION:The physical property value corresponding to the initial temp. of the part to be heated is set to a calculator 4 from a setter 1. The temporally set current value of impressed current is selected by a setter 3 and is inputted to a setter 2. The coefft. corresponding to the temporally set current value is set for the calculator 4. The calculator 4 calculates the estimated temp. of the inside surface and outside surface of a steel pipe P. The calculation is repeated at every specified time. The estimated temp. of the inside surface obtd. after the calculation is outputted to a comparator 6 and the estimated temp. of the outside surface is outputted to a comparator 8. The comparators 6, 8 output the deviation between the estimated and the target temp. to a deviation controller 9. The controller 9 inputs the temporally set current value of the setter 3 as the initial set current value to a current controller 10 if the deviation is in a specified range. The controller corrects the set current value and the estimated temp. is again calculated by the calculator if the deviation is larger than the specified range.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of controlling induction heating for heat treating a welded portion of an electric resistance welded copper pipe.

(Conventional technology) In the manufacturing process of ERW steel pipes, welding is performed locally in order to remove residual stress in the weld, improve the structure of the weld to match that of the base metal, and improve the quality of the weld. Annealing or standardization is performed by heating.

The induction heating method is generally used as a heating method for the welded portion of the ERW steel pipe.
Publication No. 7, Japanese Patent Publication No. 1983-3851, Japanese Patent Application Publication No. 1983-
As disclosed in Japanese Patent No. 116725, a plurality of induction heating coils are installed at intervals in the direction of movement of the steel pipe to locally and continuously heat the welded portion.

In this case, due to the positional relationship between the induction heating coil and the heated steel pipe,
The outer upper surface of the steel pipe to be heated is most easily heated, and therefore the rate of temperature increase is high, whereas the temperature of the inner surface mainly depends on heat transfer from the upper outer surface, so the rate of temperature increase is small.

Further, since the induction heating coils are installed at intervals, the temperature change over time on the outer surface and inner surface of the heated steel pipe at a certain point is as shown in FIG. In the figure, the horizontal axis is time (elapsed time).

The vertical axis is the temperature, P is the steel pipe, Hl, .

By the way, as is well known, the quality of steel material is greatly affected by the temperature during heat treatment. For example, when annealing a welded part of a steel pipe, it is necessary to uniformly heat the welded part to a temperature above the transformation point of approximately 750°C. A#)% If the heating temperature exceeds 1000°C, the crystalline state of the steel will become coarse and the material quality will deteriorate.

Therefore, methods have been proposed for controlling the heating temperature of steel pipe welds within a predetermined temperature range by induction heating, and the temperature control method described in the above-mentioned Japanese Patent Publication No. 60-32687 is one such method. This is one example. In this method, before starting heating, the induction heating coil is initially set using a calculation formula that calculates the voltage applied to the induction heating coil that can maintain the temperature in the thickness direction of the steel pipe at the target value. This method performs feedback control of the upstream induction heating coil and feedforward control of the downstream induction heating coil based on the steel pipe temperature detected at the exit side of the heating coil.

(Problems to be Solved by the Invention) Conventional methods, including the above method, use a relatively simple control model for the initial setting of the induction heating coil before heating starts, and the thickness of the steel pipe and the transfer speed If the conditions such as the gap with the induction heating coil and the final target temperature are the same, the coefficients of the model equation can be used without changing, and the correction control based on the actual temperature after heating starts can also be applied to the induction heating coil. Since only the voltage is corrected and the coefficients of the model equation are not corrected, the control accuracy for the final target temperature is low, and the accuracy of both the initial setting and the corrected setting is low in terms of heating control that includes the temperature inside the steel pipe. It looked inadequate.

(Means for Solving the Problems) In view of the above, the present invention provides high-precision heating for induction heating of welded parts of ERW copper pipes, which heats the entire predetermined region to be heated within a target temperature range. The purpose is to provide a control method.

For this purpose, the method of the present invention heats the welded portion of the ERW steel pipe using an induction heating coil, and the physical property value of the steel pipe to be heated is 1.
A formula for calculating the temperature at any point in the heated region on the exit side of the induction heating coil is determined in advance using the dimensions, induction heating conditions, and temperature of the heated steel pipe on the input side of the induction heating coil,
Prior to heating, temporarily set the set current value to the induction heating coil, calculate the estimated temperature of the pipe outer surface and inner surface of the heated part of the steel pipe on the exit side of the induction heating coil using the temperature calculation formula,
If the deviation between the calculated estimated temperature and the target temperature is within a certain range, the temporary setting current value is set as the initial current value of the induction heating coil, and when the temperature deviation exceeds the certain range, the temporary setting current value is set. Calculating the corrected estimated temperature and calculating the deviation from the target temperature are repeated until the temperature deviation falls within a certain range, and the corrected setting current value at this time is set as the initial current value of the induction heating coil, and this In addition to this, the coefficients in the temperature calculation formula are learningly modified based on the actual measured value of the pipe outer surface temperature of the heated portion of the steel pipe at the induction heating = il exit side after the start of heating. This is a method for controlling induction heating of a welded part.

(effect) First, the control model equation in the present invention will be explained.

As shown in Fig. 3, when an induction heating coil is placed on a steel pipe, the induced current value (b) at the position y in the thickness direction of the heated part of the steel pipe is approximately expressed by the following formula (%) ( 1) The present inventors confirmed through experiments that it can be expressed as:・(1) The engineering in the formula. is the induced current value at the position y-o in the tube thickness direction, that is, on the outer surface of the tube, and this surface induced current value I0 is approximately expressed by the following equation when the set current value of the induction heating coil is I. You can grow it.

■.厘I,・K1・K2・K3・fi...(2) Here, μ is the relative magnetic permeability of steel, σ is the electrical conductivity of steel, and K1 is the set current value. Coefficient determined by (described later) , K2 is a coefficient determined by the shape of the induction heating coil, the efficiency with which the applied current is converted into a magnetic field, the gap between the induction heating coil and the steel pipe, etc.

is a coefficient determined by the thickness of the steel pipe, the outer diameter, and the excitation frequency of the induction heating coil. When the index δ in formula (1) is 4′f: a coefficient determined by the thickness of the steel pipe, the outer diameter, and the excitation frequency of the induction heating coil, it can be approximated by the following formula % formula % (3) The inventors have found that the induced current value at the position y in the tube circumferential direction of the heated part of the steel pipe at the position y in the tube circumferential direction can be approximately expressed by the following equation (XI7). Confirmed by experiment. Here, 5 is a coefficient determined by the outer diameter of the steel pipe.

The induced current value at each point (X, 7) in the heated region of the steel pipe determined from the above equations (1), (2), (3), and (4) (:c, y) and the electrical conductivity σ of the steel Point (x+
The calorific value Q at y) is determined by the following equation.

(x, y) Q(x, a) −”(x, y)/σ ...(5
) Temperature Tx, y, t+ at any point (x, y) after Δ time (for example, 0.1 seconds) from any time (1)
Δ can be determined by the following equation, which is a differential approximation of the well-known two-dimensional heat transfer equation % formula (6), where λ is the thermal conductivity of steel and ρ is the specific heat f:C1 specific gravity.

Cx, a, t Here, X and y indicate the position of the heated part in the pipe circumferential direction and the pipe thickness direction, and the values of X and y when used in equation (7) are ΔX Values (1, 2, 3, . . . m, and 1, 2, 3, . . . ” , n).

Equation (7) is simplified by making the following approximation in order to speed up the calculation. In other words, the specific gravity ρ of the steel does not change much due to the temperature range in which the present invention is applied, so it is kept constant, and the required calculation area in the circumferential direction of the pipe is narrow, about 10 m from the center of the weld, so strictly speaking it should be in the shape of an arc. A friend with a rectangular shape where it should be. Note that in formula (7),
The amount of heat generation Qx, yj is determined from the above equation (5) during induction heating, and is set as QXs)'st-0 since no heat is generated in the section where no induction heating coil is arranged.

In the present invention, the control model equation determined in this way is used to simulate the temperature behavior of a predetermined region of the welded part during induction heating,
Initial settings are made by calculating the set current value of the induction heating coil such that the temperature of the region falls within the target range, and the coefficients of the model equation are corrected according to the actually measured temperature.

(Example) A more detailed explanation will be given below based on examples.

FIG. 1 is a diagram showing the device configuration of a control system in an embodiment of the present invention.

In the figure, 1 indicates the physical properties μ, σ, λ, and C of the steel.

2 for ρ and the coefficient. K3. K4. K5t - Setter to set, 2 is coefficient, setter to set, 3 is setter to set the applied current to induction heating coil H, 4 is (1)
A calculator that estimates the temperature of the heated region of the steel pipe P using equations to (7), a setting device 5 that sets the target inner surface temperature of the steel pipe P, and a device 6 that compares the target inner surface temperature of the steel pipe with the estimated temperature and its deviation. 7 is a setting device that sets the target outer surface temperature of the steel pipe P. 8 is a comparator that compares the target outer surface temperature of the steel pipe with the estimated temperature and outputs the deviation. 9 is the output of the deviation devices 6 and 8. Close or open switch S depending on the setting device 3.
a deviation controller that outputs a signal for correcting the set current value of
0 is a current controller, and 11 is a comparator that compares the actual temperature of the outer surface of the steel pipe measured with a thermometer and the estimated temperature of the outer surface of the steel pipe and outputs the deviation to the setting device 2.

In the above control system, first, the heated part (welded part) of the steel pipe P
Physical property values μ, σ corresponding to the initial temperature.

λIC1ρ and coefficients K, jK4. is set from the setter 1 to the calculator 4. Here, as the initial temperature, the average value of the actual temperatures of the steel pipe welded portion on the inlet side of the induction heating coil H is used. The coefficient 2 is determined by the shape, efficiency, and gap between the induction heating coil H and the steel pipe, and the coefficient 4 is determined by the thickness, outer diameter, and excitation frequency of the induction heating coil P, and K is It is determined by the outer diameter of the steel pipe P. On the other hand, at this time, the setting device 3 selects a provisional current value for the applied current to the induction heating coil H from a table stored in advance according to the thickness classification of the steel pipe P and inputs it into the setting device 2. (the switch S is in an open state), the setter 2 sets a coefficient corresponding to the tentatively set first flow value to the arithmetic unit 4.

Using equations (1) to (7), the computing unit 4 calculates Δ from the time when a certain virtual point in the length direction of the steel pipe P reaches the heating area by the induction heating coil. Calculate the estimated temperature. Then, the physical property values μ, σ, and λ corresponding to the estimated temperature after a time of this Δ.

Using C, the estimated temperatures of the inner and outer surfaces of the steel pipe after Δ has elapsed are calculated again using equations (1) to (7).

When this calculation is repeated every time Δ, the length of the induction heating coil H in the longitudinal direction of the steel pipe is t-L, the speed of the steel pipe is V, and the number of repetitions of the calculation is N.

T! - The value of t determined by t becomes t≧N×Δt, and the calculated temperature is the estimated temperature of the inner or outer surface of the steel pipe on the exit side of the induction heating coil H.

The calculator 4 calculates in this way and outputs the estimated inner surface temperature of the steel pipe P to the comparator 6, and outputs the estimated outer surface temperature of the steel pipe P to the comparator 8.

The comparators 6 and 8 output the deviation between this estimated temperature and the target temperature to the deviation controller 9.

The deviation controller 9 switches the switch 8 if the output of the comparator 8 is zero or negative and the output of the comparator 6 is within a predetermined range.
'lff is changed from open to closed, and the temporary setting current value of the setting device 3 is inputted to the current controller 10 as the initial setting current value.

When the output of the comparator 6 is positive, that is, the estimated internal temperature is higher than the target internal temperature, a predetermined value is subtracted from the temporary setting current value of the setting device 3 to obtain a corrected setting current value, or the comparator 8
When the output of υ is larger (or smaller) than a predetermined range, subtract (or increase) a predetermined 9 constant value from the temporary setting ta value of the setting device 3 to obtain the corrected setting current value, and make this correction. The estimated temperature of the inner and outer surfaces of the steel pipe on the exit side of the induction heating coil is again calculated by the calculator 4 using t- as a coefficient corresponding to the set current value.

After repeating the calculation of the estimated temperature on the output side of the induction heating coil and the comparison with the target temperature until the temperature deviation between the two falls within a certain range, switch s6 is closed to initialize the corrected setting current value of the setting device 3. The current value is input to the current controller 10 as a set current value.

In this way, the initial current value for the induction heating coil H is set, and heating of the steel pipe P is started. While the steel pipe P is being heated, the temperature of the outer surface of the steel pipe on the outlet side of the induction heating coil H is measured using a thermometer, the measured temperature and the estimated outer surface temperature are compared by a comparator 11, and the temperature deviation is output to the setting device 2. do.

The setting device 2 adjusts the temperature according to the sign and magnitude of this temperature deviation.
Modify the coefficient corresponding to the set current value using t-learning,
For the steel pipe to be heated next time, this modified coefficient is
The estimated temperature is calculated using the following. The above is a control method for the first-stage induction heating coil when heating is performed with one induction heating coil or when heating is performed with a plurality of induction heating coils.

Next, a method of controlling the second and subsequent stages of induction heating coils when heating is performed using a plurality of induction heating coils will be described with reference to the embodiment shown in FIG.

In Fig. 2, 12 calculates the temperature change from when the steel pipe P exits the previous induction heating coil until it reaches the next induction heating coil, and calculates the temperature of the steel pipe at the entrance side of the next induction heating coil. This is a calculation unit that calculates . This calculation uses the above-mentioned equation (7), where Tx, a1. Substitute the final output of the calculator 4 of the induction heating coil control system in the previous stage (the estimated temperature of the inside and outside of the steel pipe P when the switch 8 is closed) into
Calculate the temperature for each time with Δ as Q, A, and tto (zero) in the same equation, and after the travel time required for the steel pipe P from the exit side of the induction heating coil in the previous stage to the entrance side of the induction heating coil in the next stage has elapsed. The estimated temperature of the inner and outer surfaces of the steel pipe P is calculated and input as the initial temperature to the arithmetic unit 4 of the primary stage control system.

Another point that differs from the calculations in the first stage control system in the calculations in the second and subsequent stage control systems is as follows.

At the same time, the coefficients of the first-stage control system based on the actual measured temperature on the outside surface of the first-stage steel pipe were corrected in a feedback manner, and the coefficients of the second-stage control system were also corrected in a Tweed 7-Oward manner. The correction for this is to calculate the estimated temperature using t-. Other than the above two points, the calculation and setting methods for the control system at each stage are the same.

In this way, the current value applied to the induction heating coil at each stage is set optimally, and the temperature of the steel pipe on the exit side of the induction heating coil is
The entire area to be heated is controlled within the target range.

(Effects of the Invention) As described above, the method of the present invention is used as a control model for induction heating of a welded portion of ERW steel pipes, and for setting the initial current value of the induction heating = coil before the start of heating. A formula for calculating the temperature at an arbitrary point in the region is determined in advance, and the temperature calculation is continued until the estimated temperature of the outside and inside of the tube of the heated section calculated using this temperature calculation formula falls within a certain range with respect to the target temperature. Since the initial current value is determined by repeating the calculation of the estimated temperature, the initial current value can be optimally set. Furthermore, since the coefficients in the temperature calculation formula are modified based on the actual temperature measured during heating, the initial current value for the primary heating material and the initial current value for the downstream induction heating coil can be set more optimally. be able to. It has an excellent effect.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the device configuration of a control system in an embodiment of the present invention, and FIG. 2 is a diagram showing the device configuration of a control system in an embodiment in which the present invention is applied to induction heating coils arranged in multiple stages. FIG. 3 is a diagram showing temporal temperature changes on the outer and inner surfaces of the steel pipe during heating. 1.2, 3, 5, 7... Setting device, 4.12... Arithmetic unit, 6, 8.11... Comparator,
9... Deviation controller, 10... Current controller, S
...Switch, P...Steel pipe, ■...Induction heating coil, D...'& seismic intensity meter Figure 1, Figure 2

Claims (1)

[Scope of Claims] 1. When heating the welded portion of an ERW steel pipe using an induction heating coil, each value of the physical property values, dimensions, induction heating conditions, and temperature of the steel pipe to be heated on the inlet side of the induction heating coil is determined. A formula for calculating the temperature at an arbitrary point in the heated area on the exit side of the induction heating coil is determined in advance, and prior to heating, a set current value to the induction heating coil is temporarily set, and the induction temperature is calculated using the temperature calculation formula. The estimated temperatures of the outer and inner surfaces of the heated section of the steel pipe on the exit side of the heating coil are calculated, and if the deviation between the calculated estimated temperature and the target temperature is within a certain range, the provisional current value is set as the initial current of the induction heating coil. When the temperature deviation exceeds a certain range, the temporary setting current value is corrected and the calculation of the estimated temperature and the deviation from the target temperature are repeated until the temperature deviation falls within the certain range. 1. A method for controlling induction heating of a welded part of an ERW steel pipe, the method comprising: setting a corrected current value at the time as an initial current value of an induction heating coil. 2. When heating the welded part of an ERW steel pipe with an induction heating coil, the physical properties of the steel pipe to be heated, dimensions, induction heating conditions, and temperature values of the steel pipe to be heated on the input side of the induction heating coil are used to determine the output of the induction heating coil. A formula for calculating the temperature at an arbitrary point in the heated area on the side is determined in advance, and a set current value for the induction heating coil is temporarily set prior to heating, and the steel pipe at the exit side of the induction heating coil is Calculate the estimated temperature of the tube outer surface and inner surface of the heated part, and if the deviation between the calculated estimated temperature and the target temperature is within a certain range, set the provisional current value as the initial current value of the induction heating coil, and When the temperature deviation exceeds a certain range, the provisional setting current value is corrected, and the calculation of the estimated temperature and the deviation from the target temperature are repeated until the temperature deviation falls within the certain range, and the corrected setting current value at this time is calculated. Set as the initial current value of the induction heating coil,
Guidance of an ERW steel pipe welded part, characterized in that the coefficients in the temperature calculation formula are learnedly modified based on the measured value of the pipe outer surface temperature of the heated part of the steel pipe on the exit side of the induction heating coil after heating has started. Heating control method.