JPH11241123A - Apparatus for controlling decarburizing or bluing annealing of steel strip - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute a decarburizing annealing or a bluing annealing without generating abnormality in the quality even in the case of generating the abnormality in a dew point detecting means. SOLUTION: A subtractor 56 obtains a deviation between a dew point target value from a dew point setting circuit 55 and the dew point detected value from the dew point detecting device 14. A control circuit 57 integrates the deviation with time and the integral value is added to the deviation and this result is introduced. An abnormality detecting circuit 58 outputs an abnormality detecting signal when the output signal in the control circuit 57 is out of a pre-fixed range, and the time of the outside of the range is continued for a pre-fixed time or more. A setting circuit 59 sets a steam supplying flow rate from a steam generating source at the time of detecting the abnormality to a pre-fixed value. A change-over circuit 60 changes the output of the setting circuit 59 at the time of detecting the abnormality from the output of the control circuit 57 and gives it to the steam generating source. Singe the control signal is changed at the time of detecting the abnormality, the generation of abnormality in the quality can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for decarburizing or bluing annealing of a steel strip performed in an atmosphere gas having a high dew point. The present invention relates to an annealing control device that can be used. Here, decarburization annealing is annealing for removing carbon in the steel strip, and bluing annealing is annealing for forming a blue oxide film on the steel strip.

[0002]

2. Description of the Related Art Conventionally, decarburizing annealing or bluing annealing is performed by charging a coiled steel strip, for example, a cold-rolled steel strip, into a batch-type annealing furnace with an interval between layers. Thereafter, heat treatment is performed in an atmosphere gas having a high dew point. The dew point of the atmospheric gas is adjusted by mixing water vapor with the atmospheric gas, and the dew point is detected by the dew point detecting means. Water vapor is obtained by, for example, heating water with an electric heater.

FIG. 7 is a time chart for explaining a conventional decarburizing annealing method. Curve 1 in FIG. 7 is a transition curve showing the temporal transition of the heating temperature of the cold-rolled steel strip, curve 2 is a transition curve showing the temporal transition of the dew point of the atmospheric gas, and curve 3 is the supply of steam. It is a transition curve which shows a time transition of an output of an electric heater which is a value corresponding to a flow. The output of the electric heater is expressed as a relative value with the full output being 100%. A straight line 4 in FIG. 7 is a straight line indicating the dew point target value of the atmospheric gas. At time t1, the heating of the cold-rolled steel strip charged in the furnace is started in the atmospheric gas. At time t2, the heating temperature of the cold-rolled steel strip is a predetermined temperature, for example, 7
When the temperature reaches 00 ° C., an atmosphere gas mixed with water vapor is supplied into the furnace. After time t2, the heating temperature of the cold-rolled steel strip is kept constant, and the dew point of the atmospheric gas is controlled to be a predetermined dew point target value, for example, + 50 ° C. by a method described later. During this time, the output of the electric heater fluctuates according to the control signal for dew point control. Although this variation is initially large, it decreases with time, and the output of the electric heater converges to a constant value. At time t5, the holding time of the cold-rolled steel strip reaches a predetermined time, for example, 20 hours, and the cooling of the cold-rolled steel strip is started. Further, the supply of steam to the atmospheric gas is stopped. At time t6, the cooling is completed, and the decarburizing annealing ends.

[0004] The dew point control of the atmospheric gas is performed by obtaining a deviation between a preset dew point target value and a dew point detection value measured by the dew point detection means, and calculating the difference between the deviation and the integral value at a constant rate. The calculation is performed by controlling the flow rate of water vapor mixed with the atmospheric gas, in other words, the power supplied to the electric heater, using the calculation result as a control signal. The control is proportional-integral-derivative control, so-called P
This is called ID control. In order to perform the dew point control accurately, it is necessary to accurately detect the dew point of the atmospheric gas by the dew point detection means. The dew point detecting means is configured to include, for example, a dew point meter, a conduit for introducing atmospheric gas to the dew point meter, a thermostat for keeping the dew point meter warm, and a heat retaining heater for keeping the conduit warm. Further, when the dew point detection value detected by the dew point meter deviates from a predetermined range, an abnormality is notified by an alarm or the like. The dew point meter and the pipeline are kept at a temperature equal to or higher than the dew point, respectively, by a constant temperature bath and a heat retaining heater in order to prevent condensation of water vapor in the atmospheric gas.

[0005] The component of the atmosphere gas before the steam mixing in the decarburization annealing is, for example, 75% H ₂ -N ₂ (hereinafter referred to as AX gas), and the dew point of the atmosphere gas mixed with the steam is, for example, + 50 ° C. is there. As described above, the atmosphere gas in the decarburization annealing has a high dew point and thus is decarburizable, and has a high hydrogen concentration and is reducible. Therefore, carbon in the cold-rolled steel strip reacts with steam at an appropriate heating temperature, for example, 700 ° C., and is decarbonized as C0 gas, and no oxide film is formed on the surface of the cold-rolled steel strip.

[0006] The bluing annealing is heat-treated by the same method as the decarburizing annealing, and the dew point is controlled by the same method. The component of the atmosphere gas before the water vapor mixing in the brewing annealing is, for example, 12% H ₂ -N ₂ (hereinafter referred to as HN gas), and the dew point of the atmosphere gas mixed with the water vapor is, for example, + 40 ° C. As described above, the atmosphere gas in the bluing annealing is an oxidizing atmosphere gas because of its high dew point and low hydrogen concentration, and the surface of the cold rolled steel strip has a blue color at an appropriate heating temperature, for example, 450 ° C. Is formed. Further, since carbon in the cold-rolled steel strip is prevented from being diffused by the oxide film, the carbon is not decarburized even at a high dew point. Hereinafter, the atmosphere gas mixed with water vapor may be referred to as a high dew point atmosphere gas.

[0007]

As described above, the dew point control of the high dew point atmosphere gas in the decarburization or bluing annealing is performed by the PID control, so that the detected dew point value matches the dew point target value. Is precisely controlled. However, when an abnormality occurs in the dew point detecting means during the heat treatment, for example, an abnormality such as condensation of water vapor in the atmospheric gas due to a failure in the constant temperature bath, condensation in the piping due to a failure in the heat retaining heater, and a failure in the dew point meter itself occurs. In some cases, accurate dew point measurement may be difficult.
Of these, when dew condensation occurs in the pipe, the pipe line is closed, so that the detected value of the dew point hardly fluctuates from the detected value at that time, and is thereafter maintained at a substantially constant value.
In this case, since the dew point detection value is apparently within the specified range, no alarm is issued. Therefore, it is difficult to recognize the occurrence of the abnormality, and the heat treatment is continued without recognizing the abnormality as it is.

Further, since the dew point detection value shows a substantially constant value, the deviation between the dew point target value and the dew point detection value also becomes substantially constant. Therefore, as shown by the curve 2 in FIG. 7, for example, when an abnormality occurs in the dew point detection means at time t3 and the dew point detection value at that time is larger than the dew point target value indicated by the straight line 4, the gas is mixed with the atmospheric gas. The control signal for decreasing the steam flow rate, that is, the output of the electric heater is the time t.
It is sent continuously after 3. Further, when the deviation is constant in the PID control, since the integral value increases linearly with time, the control signal increases with time. Therefore, as shown in FIG. 7, after time t3, the output of the electric heater represented by the curve 3 rapidly decreases, and finally becomes zero at time t4. As a result, the dew point becomes very low, and quality abnormalities such as insufficient decarburization or poor bluing occur.

An object of the present invention is to solve the above-mentioned problems and to provide a steel strip decarburizing or bluing annealing control apparatus capable of performing heat treatment without causing quality abnormality even if an abnormality occurs in the dew point detecting means. To provide.

[0010]

According to the present invention, a steel strip is heat-treated by supplying an atmosphere gas and water vapor into a heat treatment furnace, and a dew point of a mixed gas of the water vapor and the atmosphere gas reaches a predetermined dew point target value. Control device for steel strip decarburization or bluing annealing that controls the flow rate of steam supply in such a manner that a steam flow source that variably generates steam and supplies it to the heat treatment furnace and a dew point detection that detects the dew point of the atmospheric gas Means, a dew point setting means for setting the dew point target value of the atmospheric gas, a subtraction means for obtaining an output deviation of the dew point setting means and the dew point detection means, an output of the subtraction means is integrated with respect to time, and the integrated value is subtracted. Control means for deriving the result in addition to the output, and responding to the output of the control means, wherein the time during which the output of the control means deviates from a predetermined range and is out of the range is continued for a predetermined time or more. When the abnormality is detected, abnormality detecting means for outputting a signal indicating that an abnormality is detected, setting means for setting a predetermined steam supply flow rate of the steam generation source, and output of the setting means controlled in response to the output of the abnormality detecting means And a switching means for switching from the output of the means to give to the steam generating source.

According to the present invention, the control means integrates the deviation between the dew point target value and the dew point detection value with respect to time, and adds the integrated value to the deviation to derive the result. The abnormality detection means is
When the output of the control means deviates from a predetermined range for a predetermined time or more, an abnormality detection signal is output. The switching means switches the output of the setting means from the output of the control means when the abnormality detection signal is issued, and supplies the output to the steam generation source. With this, when an abnormality is detected, the output of the setting unit is switched to the steam generation source and applied instead of the output of the control unit, so that it is possible to avoid the occurrence of a problem caused by the abnormality as in the related art. . That is, in the related art, when the dew point detecting means is abnormal, for example, a pipe clogging due to dew condensation occurs and the deviation is kept constant, the output of the control means increases with time because the integral value increases with time. Although the output of the water vapor generation source continuously increases or decreases with the lapse of time, the switching can avoid such a problem in the present invention. Therefore, the output of the water vapor generation source does not become excessively large or small.

Further, the water vapor generation source of the present invention responds to a control signal from a switching means and expresses the signal in response to a control signal from a water tank for storing water, an electric heater for heating and evaporating water in the water tank. Power driving means for supplying electric power to the electric heater in accordance with the steam supply flow rate to drive the electric heater.

According to the present invention, since the water vapor source is configured to evaporate water by an electric heater,
Steam can be reliably generated with a simple configuration.

Further, the abnormality detecting means of the present invention includes a first setting circuit for setting a first threshold value of an output of the control means, and a second setting circuit for setting a second threshold value of an output of the control means. A comparison circuit responsive to the output of the control means for transmitting a signal indicating that the output of the control means is out of the range when the output of the control means is out of the range of the first threshold value and the second threshold value;
Timer means for responding to the output of the comparing circuit, measuring an elapsed time from when the output of the control means goes out of the range, and transmitting an abnormality detection signal when the elapsed time is equal to or longer than a predetermined time. Features.

According to the present invention, the abnormality detecting means compares the output of the control means with the first and second predetermined threshold values by the comparison circuit, and determines the first and second threshold values determined by the output of the control means. When the value is out of the range, the timer measures the duration outside the range, and when the duration exceeds a predetermined time, an abnormality detection signal is generated. Even if the output of the means fluctuates, there is no risk of erroneous determination.

Further, the setting means of the present invention includes a third setting circuit for setting a steam supply flow rate for decarburizing annealing to a predetermined value, and a fourth setting circuit for setting a steam supply flow rate for bluing annealing to a predetermined value. And switch setting means for switching the outputs of the third and fourth setting circuits and providing the output to the switching means.

According to the present invention, the setting means can switch and set the steam supply flow rate for decarburization annealing and the steam supply flow rate for bluing annealing. In addition, it is possible to easily set the steam supply flow rate.

[0018]

FIG. 1 is a block diagram showing an electrical configuration of an annealing control device according to a first embodiment of the present invention. The annealing control device 7 is a device for controlling the dew point of the high dew point atmosphere gas in decarburizing annealing or bluing annealing, and is provided in, for example, a heat treatment facility 8 as shown in FIG. As shown in FIG. 2, the heat treatment equipment 8 includes a batch type heat treatment furnace 9, an atmosphere gas generation source 10, a water vapor generation source 11, a mixer 13, and a dew point detection device 14 serving as dew point detection means. Is done.

The batch type heat treatment furnace 9 includes a base 17 on which the steel strip 16 is placed, an inner cover 18 covering the steel strip 16 and the base 17, an outer cover 19 covering the inner cover 18, and a base fan provided on the base. 20 and a gas burner 21 provided on the outer cover 19. Steel strip 1
Reference numeral 6 denotes, for example, a cold rolled steel strip of ordinary steel, which is wound in a coil shape with an interval between layers. Atmospheric gas source 10
Is a first atmospheric gas generating source 23 for generating the AX gas.
And a second atmosphere gas source 24 for generating the HN gas.
Consisting of Both the AX gas and the HN gas are low dew point gases, and are supplied to the mixer 13 via the first pipe 35. The first pipe 35 is provided with a first valve 36, a second valve 37, and a third valve 38. Each of the valves 36, 37, and 38 opens and closes the first pipe 35, and supplies AX gas or HN gas. Is selectively supplied to the mixer 13.

As shown in FIG. 3, the water vapor generating source 11 includes a water tank 26 for storing water, an electric heater 27 for heating and evaporating water in the water tank 26, and a power driving device 28 as power driving means. It is comprised including. The power driving device 28 includes, for example, a servomotor and a slip transformer. The servomotor responds to a control signal from line 61, as described below, to drive a slip transformer to transform the voltage of the AC power supply. Thereby, electric power corresponding to the steam supply flow rate indicated by the control signal is supplied to the electric heater 27.
The water tank 26 is provided with a water supply pipe 33 and a drain pipe 34 to keep the amount of water in the water tank 26 constant. The electric heater 27 is provided with a power meter 39 for detecting the output power of the electric heater 27.

The generated steam is supplied to the mixer 13 via the second pipe 41. The second pipe 41 is provided with a steam valve 43, and the steam valve 43 is connected to the second pipe 4.
1 is opened and closed to supply / stop the steam to the mixer 13. As described above, the steam generation source 11 is
Is configured to evaporate water, so that steam can be reliably generated with a simple configuration. When the steam valve 43 is open, the mixer 13 mixes the low dew point atmosphere gas from the atmosphere gas generation source 10 with the steam from the steam generation source 11 to generate a high dew point atmosphere gas as a mixed gas. On the other hand, when the steam valve 43 is closed, the mixer 13 passes the atmospheric gas from the atmospheric gas generation source 10 as it is.
The atmosphere gas from the mixer 13 is supplied to the internal space 45 of the inner cover 18 via the third conduit 44. When the low dew point atmosphere gas and the high dew point atmosphere gas are collectively referred to, they are simply referred to as atmosphere gas.

As shown in FIG. 4, the dew point detector 14 includes a dew point meter 47, a thermostat 48, and a fourth conduit 49. The dew point meter 47 is, for example, a detector that adsorbs moisture in the atmospheric gas to the sensor element and measures the impedance change at that time to detect the dew point. Constant temperature bath 48
Is a container having a storage space 50 surrounded by warm water,
The dew point meter 47 is stored in the storage space 50. Constant temperature bath 48
Is provided with a water supply pipe 51 and a steam blowing pipe 53, and the temperature of the hot water is adjusted by the amount of steam to be blown. The temperature of the storage space 50 is maintained at a temperature equal to or higher than a predetermined dew point target value by adjusting the hot water temperature.

The fourth pipe 49 branches off from the third pipe 44 and guides the atmospheric gas from the third pipe 44 to the storage space 50 of the thermostatic chamber 48. Since the diameter of the fourth pipe 49 is configured to be smaller than the diameter of the third pipe 44, the amount of atmospheric gas that can be diffused can be reduced. 4th pipeline 49
Is kept at a temperature equal to or higher than a predetermined dew point target value. The atmosphere gas is introduced into the storage space 50 of the constant temperature bath 48 via the fourth conduit 49, and the dew point is measured by the dew point meter 47. Since the fourth conduit 49 and the storage space 50 are kept warm as described above, dew condensation of water vapor in the atmospheric gas is prevented. The atmospheric gas supplied from the third conduit 44 to the internal space 45 in the inner cover 18 is blown by the base fan 20 and circulates in the internal space 45 through the gap between the layers of the steel strip 16. The gas burner 21 heats the inner cover 18, the inner cover 18 heats the atmosphere gas, and the atmosphere gas heats the steel strip 16. In addition, steel strip 16
Is measured by a thermocouple (not shown).

As shown in FIG. 1, the annealing control device 7 includes the dew point detecting device 14, a dew point setting circuit 55 as dew point setting means, a subtractor 56 as subtraction means, and a control circuit 57 as control means. An abnormality detection circuit 58 serving as abnormality detection means
And a setting circuit 59 serving as setting means, and a switching circuit 60 serving as switching means. Dew point detector 14
Is configured as described above, detects the dew point of the atmospheric gas, and sends it to the subtractor 56. The dew point setting circuit 55 is a circuit realized by, for example, a potentiostat, and sets the dew point target value of the high dew point atmosphere gas and sets
Send to 6. The dew point target value is +5 for decarburization annealing.
0 ° C. and + 40 ° C. for bluing annealing. The subtractor 56 calculates the deviation between the dew point target value and the dew point detection value, and sends the obtained deviation signal to the control circuit 57.

The control circuit 57 is realized by, for example, a differentiation / integration circuit and has a transfer function having a proportional element, an integral element, and a differential element. The transfer function is a function defined by the ratio between the output signal and the input signal of the circuit. The transfer function G1 of the proportional element is expressed by equation (1) when the proportional gain is K, and the transfer function G2 of the integral element is expressed by equation (2) when s is a differential operator and C is a constant. The transfer function G3 of the differential element is expressed by equation (3), where L is a constant. Here, 1 / s represents an integral operator.

[0026]

(Equation 1)

The transfer function G of the control circuit 57 is expressed by (1)
Since it is the sum of Expression (3), it is expressed by Expression (4). When the output signal of the control circuit 57 is xo and the deviation signal, which is the input signal thereof, is xi, the equation (5) is established from the definition of the transfer function G.

[0028]

(Equation 2)

The control circuit 57 integrates and differentiates the deviation signal xi, which is the output of the subtractor 56, with respect to time as shown in the equation (5), and adds the integral value and the differential value to the deviation signal xi at a constant rate. , Is derived as an output signal xo. The output signal xo of the control circuit 57 is
0 and sent to the abnormality detection circuit 58. The output signal xo of the control circuit 57 sent to the switching circuit 60 is given as a control signal to the servomotor of the power drive device 28 of the steam generation source 11 via the line 61. As a result, the electric power corresponding to the steam supply flow rate indicated by the control signal is supplied to the electric heater 27 as described above, so that the dew point of the atmospheric gas is accurately controlled so as to reach the dew point target value. As described above, since the control circuit 57 is configured not only to pay attention to the current value of the deviation signal but also to pay attention to the time change of the deviation signal, the control circuit 57 performs highly accurate dew point control. Can be. Such control is performed by the PID as described above.
Called control.

However, in the PID control, when an abnormality occurs in the dew point detecting device 14, there is a problem that the output of the electric heater 27 of the steam generation source 11 continuously increases or decreases as time elapses as described above. That is, for example, when the fourth conduit 49 of the dew point detection device 14 is blocked due to condensation of water vapor due to poor heat retention, the dew point detection value does not fluctuate, so that the deviation signal may be maintained at a constant value. In such a case,
Although the differential value becomes zero, the integral value increases or decreases with the lapse of time, so that the output of the control circuit 57 continuously increases or decreases with the lapse of time, and the above-described problem occurs. The annealing control device 7 of the present embodiment is configured so as to effectively prevent such a problem from occurring as described later.

The abnormality detection circuit 58 includes a first setting circuit 63
, A second setting circuit 64, a comparison circuit 65, and a timer 66
It is comprised including. The first and second setting circuits 63,
Reference numeral 64 denotes a circuit realized by, for example, a potentiostat, which sets a first threshold value and a second threshold value of the output signal of the control circuit 57 to predetermined values. The first and second thresholds are set to values outside the range of variation of the output signal of the control circuit 57, and are set to the same set values for both decarburizing annealing and bluing annealing. You.

The comparison circuit 65 is a circuit realized by, for example, two operational amplifiers. When the output signal of the control circuit 57 exceeds the first threshold value in response to the output of the control circuit 57, When the voltage falls below the threshold, a signal indicating that the output signal of the control circuit is out of the range of the first and second thresholds is transmitted. The output signal of the comparison circuit 65 is sent to the timer 66 via the OR circuit 67. Timer 66 is, for example, a transistor timer, and responds to an output signal of comparison circuit 65 to output the first
Then, the elapsed time after the value falls outside the range of the second threshold value is measured. When the elapsed time exceeds a predetermined time, an abnormality detection signal is transmitted and sent to the switching circuit 60 and the alarm device 68. The alarm device 68 is, for example, a buzzer, and notifies an operator that an abnormality has occurred in the dew point detection device 14 in response to an output of the abnormality detection circuit 58.

As described above, when an abnormality occurs in the dew point detecting device 14, the output signal of the control circuit 57 continuously increases or decreases with the passage of time. By comparing the first and second threshold values, an abnormality of the dew point detection device 14 can be detected. Further, the abnormality detection circuit 58 is provided when the output signal of the control circuit 57 is out of the predetermined range of the first and second threshold values and the duration outside the range is longer than the predetermined time. 14 is determined to be abnormal, the control circuit 5
Even if there is a temporary change in the output signal of No. 7 due to disturbance, there is no possibility of erroneous determination.

The setting circuit 59 includes, for example, the third setting circuit 6
9, a fourth setting circuit 70, and a manual changeover switch 71 as a changeover setting means. Setting circuit 59
Is a circuit realized by a potentiostat, for example, and sets the flow rate of steam supplied from the steam source 11 at the time of the abnormality detection, that is, the power supplied to the electric heater 27 to a predetermined value. The output of the setting circuit 59 is sent to the switching circuit 60. The third setting circuit 69 is a circuit for setting a set value for decarburizing annealing, and is connected to the switching circuit 60 by the manual changeover switch 71 at the time of decarburizing annealing. The fourth setting circuit 70 is a circuit for setting a set value for bluing annealing, and is connected to the switching circuit 60 by a manual changeover switch 71 during bluing annealing.

The changeover circuit 60 includes an automatic changeover switch 73
, A fixed terminal 74a, and individual terminals 74b and 74c, and switches the connection between the circuits in response to the output of the abnormality detection circuit 58. That is, during normal operation, the switching circuit 60 brings the automatic switching switch 73 connected to the fixed terminal 74a into contact with the individual terminal 74b, and the control circuit 5
7 and the steam generation source 11 are connected. On the other hand, when an abnormality is detected, the automatic changeover switch 73 is brought into contact with the individual terminal 74b, and the connection is switched to connect the setting circuit 59 to the water vapor generation source 11. As a result, when an abnormality is detected, the electric power corresponding to the steam supply flow rate indicated by the output signal of the setting circuit 59 is supplied to the electric heater 27, so that the above-described problem does not occur and the occurrence of a quality abnormality such as insufficient decarburization is prevented. Can be prevented.

FIG. 5 is a time chart for explaining the decarburizing annealing method according to the present invention, and FIG. 6 is a flow chart for explaining the operation of the annealing control device shown in FIG. A curve 75 in FIG. 5 is a transition curve showing a temporal transition of the heating temperature of the steel strip 16, a curve 76 is a transition curve showing a temporal transition of the dew point of the atmospheric gas, and a curve 77 is a curve of the control circuit 57. The electric heater 27 having a value corresponding to the output signal
5 is a transition curve showing the transition of the output of FIG. The output of the electric heater 27 (hereinafter referred to as a heater output) is represented by a relative value with the output full power being 100%. The straight line 78 in FIG. 5 is a target value of the dew point of the atmospheric gas, for example, +50.
Is a reference line representing ° C., a straight line 79 is a limit line representing an upper limit value of the heater output, and a straight line 80 is a limit value representing a lower limit value of the heater output. The upper and lower limit values of the heater output are set in advance to values corresponding to the first and second threshold values of the output signal of the control circuit 57. Steel strip 1 for decarburization annealing
Reference numeral 6 denotes a cold-rolled steel strip of ordinary steel, the carbon content of which is, for example, 0.05%. The dimensions of the steel strip 16 are, for example, a thickness of 1.0 mm and a width of 914 mm, and its weight is 15 tons.

Prior to the start of decarburizing annealing, the steel strip 16 is placed on a base 17 with its axis oriented vertically and covered by an inner cover 18. Internal space 45 of inner cover 18
Is supplied with a low dew point AX gas, and air is purged. The low dew point AX gas is continuously supplied even after the completion of the purge. Further, the inner cover 18 is covered with an outer cover 19, and preparation for decarburization annealing is completed. Referring to FIG. 5A, at time t11, gas burner 21 is ignited, and heating of steel strip 16 is started in the low dew point AX gas. Time t
At 12, the heating temperature of the steel strip 16 reaches a predetermined temperature, for example, 700 ° C., and the steam valve 43 is opened.
Thereby, the steam is sent to the mixer 13 and mixed with the low dew point AX gas, so that the high dew point AX gas is generated. The generated high dew point AX gas is supplied to the internal space 45 of the inner cover 18.

Referring to FIG. 6, in step a1, the dew point of the high dew point AX gas is detected by the dew point detecting device 14. In step a2, the difference between the dew point target value and the dew point detection value is obtained by the subtractor 56. In step a3, the output signal xo of the control circuit 57 is calculated by the above equation (5), and the power supplied to the electric heater 27 is PID-controlled based on the calculated signal. Thus, after time t12, the dew point is controlled within a small fluctuation range centered at + 50 ° C. Further, the heater output represented by the curve 77 fluctuates according to the output signal xo of the control circuit 57. Although this fluctuation is large at the beginning, it becomes smaller with time, and the heater output converges to a constant value. Further, the heating temperature of the steel strip 16 is maintained at 700 ° C.

At time t13, the dew point detection value does not fluctuate, and is kept constant, for example, at + 52 ° C. This is a phenomenon that occurs when the fourth conduit 49 of the dew point detector 14 is clogged as described above. As a result, the output signal xo of the control circuit 57 increases as time elapses as described above, so that the heater output continuously decreases as time elapses after time t13. Step a4
Then, it is determined whether the output signal xo of the control circuit 57 is within the range of the first and second thresholds. The first threshold value of the output signal xo is a threshold value corresponding to the upper limit value of the heater output, and is, for example, 90% of the full output of the electric heater 27 (expressed as 90% of the heater output). The second threshold value of the output signal xo is a threshold value corresponding to the lower limit value of the heater output, and is, for example, 40% of the heater output. If this determination is affirmative, it is determined that the output signal xo is within the range, and the process returns to step a1 again. The processing from step a1 to step a4 is repeated until the determination in step a4 becomes negative. If the determination in step a4 is negative, it is determined that the output signal xo is out of the range at time t14,
Proceed to step a5.

In step a5, it is determined whether or not the duration of the output signal xo outside the range is equal to or longer than a predetermined reference time, for example, 0.2 hr. If this determination is negative, it is determined that the change is temporary, and the process returns to step a1 again. Step a1 to step a5
Is repeated until the determination in step a5 becomes affirmative. If the determination in step a5 is affirmative, it is determined that an abnormality has occurred at time t15, and the process proceeds to step a6. In step a6, FIG.
As shown in (2), an abnormality detection signal is issued and a buzzer sounds.

In step a7, the control signal for the electric drive 27 of the electric heater 27 is switched in response to the abnormality detection signal. That is, instead of the output signal xo from the control circuit 57, the output signal from the third setting circuit 69 is provided as a control signal to the power driving device 28 of the electric heater 27. Thus, after time t15, the heater output increases, and when the output of the third setting circuit 69 reaches, for example, 70% of the heater output, the heater output is maintained at that value. Time t1
In No. 6, the holding time of the steel strip at the heating temperature reaches a predetermined time, for example, 20 hours, and the decarburization reaction ends.
Therefore, the steam valve 43 is closed, and the supply of steam is stopped. At time t17, the heating treatment of the steel strip ends, and cooling is started. Thereby, the annealing control device 7
Is completed. At time t18, the cooling is completed, and the decarburizing annealing ends.

As described above, the annealing control device 7 detects the occurrence of the abnormality of the dew point detecting device 14 by the abnormality detecting circuit 58,
When an abnormality is detected, the control circuit 57 controls the dew point of the atmospheric gas.
Is switched from the PID control to the fixed control based on the setting output of the third setting circuit 69, so that the residence time when the heater output is less than the lower limit can be shortened. Therefore, the occurrence of quality abnormalities such as insufficient decarburization can be reliably prevented.

As described above, although the present embodiment mainly describes decarburization annealing, bluing annealing can be similarly performed. That is, the bluing annealing may be performed under the following conditions. Heating temperature: 450 ° C, atmosphere gas: HN gas,
Dew point target value of atmospheric gas: + 40 ° C., setting output of fourth setting circuit 70 upon detection of abnormality: heater output 65%. Other conditions are the same as in the case of decarburizing annealing.

As a second embodiment of the present invention, the input signal to the abnormality detection circuit may be as follows. That is, in the first embodiment, although the output signal xo of the control circuit 57 is input to the abnormality detection circuit 58, the output signal xo of the control circuit 57 is provided in the electric heater 27 instead of the output signal xo of the control circuit 57. The output signal of the power meter 39 may be configured to be input. In this case, the output signal of the power meter 39 is compared with the first and second threshold values, that is, the upper and lower limits of the heater output, and the power meter 39
Is out of the range of the upper and lower limits, and when the time out of the range continues for a predetermined time or more, an abnormality detection signal is output. Thus, the abnormality detection circuit of the present embodiment can reliably detect the occurrence of an abnormality of the dew point detection device 14, similarly to the abnormality detection circuit 58 of the first embodiment. Other configurations of the present embodiment are the same as those of the first embodiment.
The description is omitted because it is the same as that of the embodiment.

As a third embodiment of the present invention, the steam generation source may be configured as follows. That is, the steam generation source according to the present embodiment includes a boiler provided with a burner, a flow control valve, and an opening adjustment unit. Other configurations of the present embodiment are the same as those of the first embodiment or the second embodiment. The flow control valve is provided in a pipe for guiding fuel to the burner, and controls the flow rate of fuel, for example, butane gas supplied to the burner. The opening degree adjusting means is, for example, a servomotor, and adjusts the opening degree of the flow control valve so as to supply the fuel flow rate represented by the control signal from the switching circuit 60 in response to the control signal. Since the control signal indicates a fuel flow rate corresponding to a required steam supply flow rate, the steam supply flow rate can be controlled by this.

[0046]

As described above, according to the first aspect of the present invention, when an abnormality is detected, the output of the setting means is supplied to the steam supply source instead of the output of the control means. The output does not become too large or too small. As a result, it is possible to prevent occurrence of quality abnormalities such as insufficient decarburization or poor bluing when the output of the steam generation source is too small. Further, it is possible to prevent the life of the steam generation source from being shortened when the output of the steam generation source is excessive.

According to the second aspect of the present invention, since the water vapor generation source is configured to evaporate water by the electric heater, it is possible to generate water vapor reliably with a simple configuration.

According to the third aspect of the present invention, the abnormality determination of the dew point detecting means is performed when the output of the control means is out of the range between the predetermined first and second threshold values and outside the range. Since the determination is performed when the time is equal to or longer than a predetermined time, there is no risk of erroneous determination even if there is a temporary output fluctuation of the control means due to disturbance.

According to the present invention, the setting means can switch and set the steam supply flow rate for decarburizing annealing and the steam supply flow rate for bluing annealing. The steam supply flow rate can be set quickly and easily even for annealing.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an electrical configuration of an annealing control device according to a first embodiment of the present invention.

FIG. 2 is a system diagram showing a simplified configuration of heat treatment equipment to which the annealing control device shown in FIG. 1 can be suitably applied.

FIG. 3 is a system diagram showing a simplified configuration of a steam generation source shown in FIG. 1;

FIG. 4 is a simplified system diagram showing the configuration of the dew point detecting device shown in FIG. 1;

FIG. 5 is a time chart for explaining a decarburizing annealing method according to the present invention.

6 is a flowchart for explaining the operation of the annealing control device shown in FIG.

FIG. 7 is a time chart for explaining a conventional decarburizing annealing method.

[Explanation of symbols]

 7 Annealing control device 9 Batch type heat treatment furnace 10 Atmospheric gas generating source 11 Steam generating source 13 Mixer 14 Dew point detecting device 27 Electric heater 43 Steam valve 47 Dew point meter 48 Constant temperature bath 55 Dew point setting circuit 56 Subtractor 57 Control circuit 58 Abnormality detection Circuit 59 Setting circuit 60 Switching circuit 63 First setting circuit 64 Second setting circuit 65 Comparison circuit 66 Timer 68 Alarm 69 Third setting circuit 70 Fourth setting circuit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C21D 11/00 C21D 11/00 C23C 8/14 C23C 8/14

Claims (4)

[Claims] 1. An atmosphere gas and steam are supplied into a heat treatment furnace to heat treat a steel strip, and a steam supply flow rate is controlled so that a dew point of a mixed gas of the steam and the atmosphere gas becomes a predetermined dew point target value. In a control device for decarburizing or bluing annealing of a steel strip, a steam generation source for generating steam at a variable flow rate and supplying the steam to a heat treatment furnace, a dew point detecting means for detecting a dew point of an atmosphere gas, and the dew point of the atmosphere gas A dew point setting means for setting a target value; a subtraction means for obtaining an output deviation of the dew point setting means and the dew point detection means; an output of the subtraction means integrated with respect to time; an integrated value is added to an output of the subtraction means; In response to the output of the control means and the output of the control means, an abnormality is detected when the output of the control means is out of the predetermined range and is out of the range for a predetermined time or more. Abnormality detecting means for outputting a signal indicating that the abnormality has occurred, setting means for setting a predetermined steam supply flow rate of the steam generating source, and responding to the output of the abnormality detecting means, switching the output of the setting means from the output of the control means. Control means for decarburizing a steel strip or bluing annealing, comprising: switching means for applying to a steam generation source. 2. The water vapor generating source includes: a water tank for storing water; an electric heater for heating and evaporating water in the water tank; and a water vapor supply indicated by the signal in response to a control signal from a switching unit. 2. The control apparatus for decarburizing or bluing annealing of a steel strip according to claim 1, further comprising: power driving means for supplying electric power to the electric heater in accordance with the flow rate to drive the electric heater. A first setting circuit for setting a first threshold value of an output of the control means; a second setting circuit for setting a second threshold value of an output of the control means; A comparison circuit responsive to the output of the means for transmitting a signal indicating that the output of the control means is out of the range when the output of the control means is out of the range of the first threshold value and the second threshold value; A timer means for measuring an elapsed time since the output of the control means is out of the range, and transmitting an abnormality detection signal when the elapsed time is equal to or longer than a predetermined time. Item 3. The control device for decarburization or bluing annealing of a steel strip according to item 1 or 2. 4. A setting circuit, comprising: a third setting circuit for setting a steam supply flow rate for decarburizing annealing to a predetermined value; a fourth setting circuit for setting a steam supply flow rate for bluing annealing to a predetermined value; 4. The control apparatus for decarburization or brewing annealing according to claim 1, further comprising: switch setting means for switching the output of the third and fourth setting circuits and applying the output to the switching means.