JPH0216193B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic forge welding temperature control method for controlling the temperature of a tubular skelp before forge welding to a temperature suitable for forge welding in a manufacturing process of forge welded steel pipes.

Conventionally, forge welded steel pipes are produced by forming a band-shaped skelp heated in a heating furnace into a tubular shape using forming rolls, and then heating the edges of the tubular skelp by blowing oxygen from a welding horn, or forming an annular skelp into a ring shape. After heating using a high-frequency induction heating coil, the edge portions were forge-welded using a forge-welding roll. However, the band-shaped skelp described above has a plate thickness variation of about 5%, and the band-shaped skelp leaving the heating furnace also has temperature fluctuations in the heating furnace, so the temperature of the band-shaped skelp is ±
There is a variation of about 40°C, and a temperature difference of about 20°C between the left and right edges.

Furthermore, when heating the edge part of the tubular skelp by induction heating, the temperature of the edge part is 200℃ to 400℃.
℃, but in this case, the temperature during forge welding will further vary due to changes in plate thickness at the edge portion, fluctuations in squelp running speed, etc.

In order to eliminate these drawbacks, methods for keeping the heating furnace extraction temperature constant include measuring the temperature at the time of heating furnace extraction and adjusting the running speed of the skelp, or adjusting the heating temperature using the fuel in the heating furnace. Methods such as doing this were used.

However, with the above method, the response speed of the heating furnace is slow, so it cannot sufficiently follow the sudden temperature change caused by the sudden change in wall thickness before and after the connection between the bottom and top of the band-shaped skelp, and the temperature variation is eliminated. The problem is that it is not. In addition, methods to keep the temperature rise constant during induction heating include adjusting the output of the high-frequency induction heating coil in response to changes in the squelp speed and wall thickness, and measuring the temperature of the forge weld abutment after forge welding. Examples include adjusting the output of a high-frequency induction heating coil. However, even with this method, when measuring the temperature after forge welding, it is difficult to measure the temperature after forge welding because some time has elapsed since the temperature of the tubular skelp edge was completed. The problem is that the temperature of the left and right edges is unknown, and there is no way to control the temperature of the left and right edges, so changes in the wall thickness of the left and right edges and squirting in the heating furnace will directly affect the temperature of the left and right edges. There is a problem in that it is impossible to keep the temperature of the left and right edges constant.

In order to manufacture forge-welded steel pipes with good quality forge-welded joints, it is most important to forge-weld the edges to be forge-welded at a constant temperature (approximately 1350°C) suitable for forge-welding. In these methods, it has been impossible to maintain the temperature of the edge portion to be forge welded constant at the forge welding temperature.

The present invention eliminates the drawbacks of the above-mentioned methods, and is capable of forge welding in the manufacturing process of forge-welded pipes, in which the temperature of the edge portion of the tubular skelp to be forged welded can always be maintained at the forge welding temperature, and the temperature of the left and right edge portions can be maintained at an even temperature. The purpose is to provide an automatic temperature control method.

That is, the present invention forms a band-shaped skelp heated in a heating furnace into a tubular shape with a forming roll, heats the edge portion of the tubular skelp formed into the tubular shape with a heating device, and then forge-welds the edge portion with a forge-welding roll. In the manufacturing process of forge-welded steel pipes to be made into pipes, high-frequency induction heating coils are placed on both edges of the tubular skelp to heat each edge separately. The temperature at both edges of the previous tubular skelp is measured separately, and the position of the high-frequency induction heating coil is adjusted in a direction perpendicular to the tube axis so that the temperature difference between both edges of the tubular skelp is within the target range. , an automatic forge welding temperature control method for forge welded steel pipes, characterized in that the output of the high frequency heating coil is adjusted.

Next, the method of the present invention will be explained in detail with reference to examples shown in the figures.

In FIGS. 1 and 2, a band-shaped skelp 2 heated to a hot working temperature in a heating furnace 1 is formed into a tubular shape by forming rolls 3 and 4, and is then heated between forming rolls 4 and forge welding rolls 5. A high-frequency induction heating coil 6 is disposed on both edge portions 2a, 2a of the tubular squelp 2' shown in FIG. 2 to uniformly heat the end face of the edge portion 2a of the band-shaped squelp 2'.

A squelp thermometer 9 consisting of a scanning radiation thermometer and a forge welding thermometer 7 are provided at the outlet of the heating furnace 1 and on the upstream side of the forge welding roll 5. , and the temperature of the edge portion 2a of the tubular skelp 2' before forge welding, and from the measured temperature values, it is determined that the temperature difference between the two edge portions 2a, 2a of the tubular skelp 2' before forge welding is within 10°C. As shown in FIG. 2, the high-frequency induction heating coil 6 is adjusted horizontally so as to maintain the same range.

The left and right adjustment device 15 adjusts the position in the direction perpendicular to the tube axis, and also adjusts the position of both edges 2 before forge welding.
The output of the high-frequency induction heating coil 6 is adjusted so that the temperature of points a and 2a is 1350±10°C, and the edge part 2a of the tubular skelp 2' during forge welding is automatically maintained at a temperature suitable for forge welding. control.

Next, the control system of the method of the present invention will be explained in detail with reference to the embodiment shown in the drawings. The temperature of the strip-shaped Skelp 2 extracted from the heating furnace 1 is continuously measured in the width direction using a Skelp thermometer 9 that optically scans the strip-shaped Skelp 2 with an instantaneous field of view of about 5 mm width to measure the radiant energy.
The left and right separation circuit 22 separates the temperature pattern from the center of the band-shaped squelp 2 to the left (toward the pipe-making direction) and the temperature pattern from the center to the right of the band-shaped squelp 2. Signals of the highest temperature T _L1 among the temperature patterns to the left from the center of the Skelp 2 and the highest temperature T _R1 among the temperature patterns to the right from the center of the band-shaped Skelp 2 are output.

Usually, a band-shaped skelp 2 heated in a heating furnace 1
is heated by a burner from almost the same plane as the plane of the band-shaped skelp 2, but the edge part of the band-shaped skelp 2 has a larger area receiving heat radiation per unit volume than the center part of the band-shaped skelp 2. ,
The temperature at the edges becomes higher than the temperature at the center,
Therefore, the highest temperature T _L1 in the temperature pattern to the left from the center of the band-shaped Skelp 2 is the left edge temperature, and the highest temperature T L1 in the temperature pattern to the right from the center of the band-shaped Skelp 2 T _R1 is the right edge temperature.

Next, the tubular skelp 2' heated by the high-frequency induction heating coil 6 is optically scanned by a rotating mirror with an instantaneous field of view of approximately 1 mm width x 5 mm length, and a forge welding thermometer 7 that measures the radiant energy is used to detect both edges. The temperature is continuously measured in the width direction in the width including the portions 2a, 2a, and a signal is output, and the thermometer position pulse generator 20 outputs a pulse signal at a fixed position of the rotating mirror.

The temperature signal detected by the forge welding thermometer 7 is processed by the left/right separation circuit 16 and the peak keep circuit 17 in the same way as the temperature signal processing of the Skelp thermometer 9.
The left edge temperature T _L2 of the tubular squelp 2' and the right edge temperature T _R2 of the tubular squelp 2' are output.
Also, the temperature at the edge is higher than the temperature at the center,
Furthermore, since the temperature change at the edge part is the most severe, the temperature signal detected by the forge welding thermometer 7 is output as a differential signal by the differential circuit 18, and the peak position pulse generator 19
outputs left and right edge position signals.
This edge position signal and the output signal from the thermometer position pulse generator 20 are input to the peak position calculation circuit 21 to calculate the time from the thermometer constant position to the edge position. By multiplying the distance from the forge welding thermometer 7 to the tubular skelp 2', the horizontal distance L _L from the thermometer fixed position to the left edge of the tubular skelp 2' can be calculated as follows: A horizontal distance L _R from the position to the right edge of the tubular squelp 2' is calculated and input to the control device 11.

The control device 11 inputs and calculates the signal from the forge welding thermometer 7 and the signal from the Skelp thermometer 9,
Sending a control signal to the thyristor voltage regulator 14,
The thyristor voltage regulator 14 controls the voltage level, the high-frequency oscillator 13 generates a high-frequency current, and the current flowing to the high-frequency induction heating coil 6 through the transformer 12 is controlled, and the left and right positions of the high-frequency induction heating coil 6 are controlled. A control signal is sent to the left-right adjusting device 15 to control the left-right position of the high-frequency induction heating coil 6 that is integrated with the transformer 12.

In order to stabilize the quality of the forge welded joint, it is desirable to keep the temperature constant during forge welding, but the temperature during forge welding cannot be measured due to the presence of forge welding rolls and other equipment.

Therefore, in the method of the present invention, the Skelp thermometer 9
The temperature during forge welding is estimated and calculated based on the signals from the forge welding thermometer 7 and the forge welding temperature, and the temperature is controlled so as to reduce the difference from the target temperature during forge welding. From the measuring position of the forge welding thermometer 7 to the forge welding position, the edge part 2 of the tubular skelp 2'
The temperature of a is determined by thermal radiation, convection and tubular squelp 2'
decreases due to heat conduction to the central part of the body.

In particular, when the edge of a tubular skelp is rapidly heated by high-frequency induction heating, the depth of heat penetration is shallow and the temperature change due to heat conduction is rapid. The amount of temperature drop from the thermometer measurement position to the forge welding position changes. The amount of temperature decrease ΔT from the measurement position of the forge welding thermometer 7 to the forge welding position is approximately expressed by the following formula.

ΔT _L = (T _2L − T _1L − C) × α ΔT _R = (T _2R − T _1R − C) × α ...(1) T _2L , T _2R : Tubular squelp at the measurement position of forge welding thermometer 7 2' edge part 2a temperature (°C) T _1L , T _1R : Temperature (°C) of the edge part 2a of the tubular squelp 2 at the measurement position of the squelp thermometer 9 (°C) C: Constant (°C) 0 to 30°C α: Coefficient α is a coefficient determined by the thickness of the skelp, the speed of the skelp, the distance from the measurement position of the forge welding thermometer 7 to the forge welding position, the heat penetration depth, etc., and is used in the range of 0 to 1.

The temperature of the squelp edge at the forge welding position (T ₃ ) is expressed as T _3L = T _2L −ΔT _L T _3R = T _2R −ΔT _R (2), so the lower temperature of T _3L and T _3R is T. ₃ , the temperature is compared with the target temperature _T30 , and the deviation output is input to the thyristor voltage regulator 14. or,
The temperature of both edges of the tubular skelp 2' at the forge welding position,
_The deviation ΔT ₃ between T _3L and T _3R is expressed as ΔT ₃ = T _3L − _{T 3R (} 3).
The output is input to the left/right adjustment device 15 of the high frequency induction heating coil 6. The amount of heat input Q by the high-frequency induction heating coil 6 and the amount of increase T _UP in the temperature of the edge portion of the tubular skelp 2' at the forge welding position are approximately proportional to each other. Therefore, the thyristor voltage regulator 14 is controlled so as to adjust the amount of heat input to the high frequency induction heating coil 6 in proportion to the output difference between T ₃ and T ₃₀ .

Next, when the high-frequency induction heating coil 6 is shifted to the left, the left edge begins to be heated by the right coils 6 to 2, so the amount of temperature increase at the left edge is equal to that at the right edge. Become bigger. Also, when the high-frequency induction heating coil 6 is shifted to the right, the right edge begins to be heated by the left coils 6 to 1, so the amount of temperature increase at the right edge is greater than that at the left edge. Become.

Therefore, when ΔT ₃ >0, the high-frequency induction heating coil 6 is moved to the right, and when ΔT ₃ <0, the high-frequency induction heating coil 6 is moved to the left. A signal of ΔT ₃ is input to 15 to perform position adjustment.

Next, the control device 11 will be explained in detail.

FIG. 3 is a block diagram showing the configuration of the control device 11 shown in FIG. 1. From the forge welding thermometer 7 to the input terminal 43 of the left edge temperature T _L2 of the tubular squelp 2', the right edge temperature T _R2 of the tubular squelp 2'.
The signal from the forge welding thermometer 7 is input to the input terminal 43' of the forge welding thermometer 7, and the input terminal 24 of the horizontal distance L _R from the fixed position of the forge welding thermometer to the right edge of the tubular squelp 2'. The signal from the squelp thermometer 9 is input to the input terminal 44 for the right edge temperature T _L1 and the input terminal 44' for the right edge temperature T _R1 of the band-shaped squelp 2. A comparator 25 compares the input current signal from the input terminal 43 and the input current signal from the input terminal 44, and outputs the difference signal to the comparator 27. The comparator 27 compares the output signal of the comparator 25 with the output signal of the constant generator 26, outputs the difference signal to the coefficient unit 28, multiplies the coefficient by the coefficient unit 28, and outputs the result. Find _ΔTL of .

A comparator 29 compares the output signal from the input terminal 43 and the output signal from the coefficient multiplier 28, outputs the difference signal, and calculates the equation (2). This output signal is the estimated value of the forge welding temperature of the left edge,
The signal is input to the comparator 31. Comparator 31 and comparator 2
The output signal from the forge welding temperature target setting device 30 is compared with the signal from the forge welding temperature target setting device 30, and the difference signal is outputted to the calculator 32. The same control as described above is also performed when outputting a difference signal between the estimated value of the forge welding temperature of the right edge portion and the target value of the forge welding temperature.

32 is an arithmetic unit that compares the output signal of the comparator 31 and the output signal of the comparator 31', outputs the smaller signal to the converter 33, and outputs the difference signal to the converter 37. The converter 33 is a converter that converts a current signal into a voltage signal and outputs it to the gate 45. The gate 45 is closed when the output of the high-frequency induction heating coil 6 is manually adjusted, and is opened when the output is automatically adjusted. 35 is a heater, gate 45
The output signal from the thyristor voltage regulator 14 and the output signal 34 from the thyristor voltage regulator 14 are added and input to the thyristor voltage regulator 14 . Converter 37 is a converter that converts a current signal of ΔT ₃ into a voltage signal and inputs it to gate 40 . 38 is a position movement range setting device for the high-frequency induction heating coil 6, which is a horizontal distance L ₁₀ from the forge welding thermometer position to the left edge of the tubular skelp 2', and from the thermometer position to the right side of the tubular skelp 2'. This is to set the horizontal distance L _R0 to the edge. If the fixed position of the forge welding thermometer is chosen so that the left edge of the tubular skelp 2' is always to the right of the fixed position of the forge welding thermometer, then L _L > L _L0 and L _R < L _R0 . and if it is outside this range, the high frequency induction heating coil 6
However, there is a risk that the high-frequency induction heating coil 6 may come into contact with the edge of the tubular skelp 2' and be damaged.
Automatic control of left and right adjustment is stopped.

A comparator 39 compares the input signal from the input terminal 24 and the input signal from the position movement range setter 38, and outputs L _L -L _L0 and L _L0 -L _R to the gate 40.
The gate 40 is open only when L _L -L _L0 >0 and L _R0 -L _R >0, and is closed when the above conditions are not met, and the signal from the converter 37 is sent to the gate 46 .
The gate 46 is closed when the horizontal adjustment of the high-frequency induction heating coil 6 is performed manually, and is opened when the horizontal adjustment is performed automatically. 42 is an adder, gate 46
The output signal from the high-frequency induction heating coil 6 and the output signal 41 from the left-right adjustment device 15 of the high-frequency induction heating coil 6 are added and input to the left-right adjustment device 15 of the high-frequency induction heating coil 6 to perform position adjustment.

Since the present invention is an automatic forge welding temperature control method in the manufacturing process of forge welded steel pipes as described above, the peak temperature at the left edge portion and the peak temperature at the right edge portion immediately before forge welding are measured, and the peak temperature at the right edge portion is measured. It is possible to reduce the deviation temperature and control the edge temperature to a constant value, so the edge temperature immediately before forge welding can be kept constant, and the forge welding temperature can be controlled to an appropriate value, resulting in good quality forge welded joints. It is possible to manufacture products with high quality, and the effect in terms of quality control is extremely large.

In addition, in the method of the present invention, the forge welding temperature is estimated and calculated from the edge temperature of the strip-like skelp measured with a skelp thermometer and the edge temperature of the tubular skelp measured with a forge welding thermometer. Even if the forge welding temperature is determined by adding a certain constant to the edge temperature of the tubular skelp measured in the forge welding temperature, the difference from the true forge welding temperature will be somewhat large, but this method can be easily substituted. It is.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the method of the present invention, FIG. 2 is a sectional view taken along line AA in FIG. 1, and FIG. 3 is a block diagram of a control device according to the method of the present invention. 1...Heating furnace, 2...Striped skelp, 2a...
Edge portion, 3, 4... Forming roll, 5... Forge welding roll, 6... High frequency induction heating coil, 7... Forge welding thermometer, 9... Skelp thermometer, 15... Left and right adjustment device.

Claims (1)

[Claims] 1. Forge welding, in which a band-shaped skelp heated in a heating furnace is formed into a tube shape with a forming roll, the edge portion of the tubular skelp formed into the tube shape is heated with a heating device, and then the edge portion is forge welded with a forge welding roll to form a tube. In the steel pipe manufacturing process, high frequency induction heating coils are placed on both edges of the tubular skelp,
Each edge is heated separately, and the temperature of both edges of the tubular skelp before forge welding is measured separately using a thermometer installed on the upstream side of the forge welding roll, and the temperature difference between both edges of the tubular skelp is within the target range. So that
An automatic forge welding temperature control method for a forge welded steel pipe, characterized in that the position of the high frequency induction heating coil is adjusted in a direction perpendicular to the tube axis, and the output of the high frequency heating coil is adjusted.