JPH0459065B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an induction heating control method in continuous casting, and in particular, an induction heating furnace is provided in a tundish for continuous casting, and electric power is input to the induction heating furnace so that the temperature of molten metal in the tundish reaches a target temperature. The present invention relates to an improvement in an induction heating control method in continuous casting, which is suitable for use in controlling.

[Conventional technology]

When manufacturing a slab by continuous casting of molten steel, the surface quality of the slab is affected by the temperature of the molten metal in the tundish. Therefore, in order to obtain the desired surface quality of the slab, it is necessary to maintain the steel temperature at a predetermined target value. Therefore, conventionally, an induction heating furnace is provided in the tundish, and the temperature of the molten steel in the tundish is continuously detected to monitor the casting temperature, and the molten steel is transferred to the induction heating furnace so that the molten steel temperature reaches a predetermined target value. The heating amount of the induction heating furnace is adjusted by controlling the input power of the induction heating furnace. Techniques related to induction heating control devices that control the temperature of molten steel in the tundish by adjusting the heating amount of the induction heating furnace include, for example, Japanese Patent Application Laid-Open No.
There is one proposed in Publication No. 20282. That is, in the technique described in this publication, as shown in FIG. An induction heating control device is shown that controls the temperature of the molten steel 12 by controlling the input power to the molten steel 12 according to the input power command ES determined by the temperature of the molten steel 12. In this device, the input power control device 16 controls the amount of power conversion of the power converter 20 in accordance with the input power command ES, thereby controlling the AC power output from the AC power source (for example, 3-phase AC power source) 18. The input power is controlled by converting into a predetermined power or voltage and supplying the power or applying voltage to the induction coil 22 of the induction heating furnace 14. In addition, the reference numeral 8 in the figure is a ladle for charging molten steel 12 into the tundish 10.
The power conversion unit 20 also includes a converter 24 for converting AC power from the AC power supply 16 into DC power, and a converter 24 for converting the converted DC power into AC power of a predetermined voltage, current, and frequency. An inverter 26 and a power factor adjustment capacitor 28 for adjusting the power factor of the output power are provided. Here, in determining the input power command ES, first, the temperature of the molten steel 12 is detected with the continuous type thermometer 30 inserted into the molten steel 12, and then the detected temperature θ _r and the target of the molten steel 12 are determined. The input power calculation unit 32 calculates the input power command ES based on the temperature _θs.
is determined by calculation. This input power calculation section 32 has various calculation sections shown in a block diagram as shown in FIG. 7, and calculations in the calculation sections are performed as follows.
That is, first, the temperature θ _r detected by the continuous thermometer 30
and the target temperature θ _s of the molten steel 12 are compared in the comparator 40 with reference to the power input base value P ₀ and the difference Δθ (=θ _r
−θ _s ). Next, the temperature increase rate calculation section 4
2, the temperature increase rate α (=Δθ/θ _s ) (%) is the ratio of the temperature difference Δθ to the target temperature θ _s
Calculate. Then, the multiplier 44 multiplies the temperature increase rate α by the power input base value P ₀ to calculate the power increase amount α·P ₀ required for temperature control. Next, the adding unit 46 adds the power input base value P ₀ to the power increase amount α·P ₀ to calculate the currently required power input amount ES. During normal operation, the molten steel 1 is controlled by a temperature feedback control thread that controls the input power to the induction heating furnace 14 using the input power command ES determined as described above.
2 temperature is controlled. Note that the signal of the detected temperature θ _r of the continuous thermometer 30 is input to the temperature abnormality detector 34 as well as the input power calculating section 32, and when the detected temperature θ _r is abnormal, the temperature abnormality detector 34 In response to the command, the pattern generator determines the input power command ES based on the input power control mode pattern according to other casting conditions different from the normal time. This pattern generator 36 commands input power.
When ES is determined and the input power command E is input to the input power control device 16, the changeover switch 38 is switched by the command from the temperature abnormality detector 34, and the input power command output from the pattern generator is changed.
ES is now input to the input power control device 16.

[Problem to be solved by the invention]

By the way, when the throughput flow rate of molten metal in the tundish is changed, the amount of molten metal in the tundish increases or decreases, and after the increase or decrease, a relatively rapid change occurs in the temperature of the molten metal. However, in the conventional induction heating control device,
Since there is a time delay due to the unique temperature measurement time (the time from the start of temperature measurement to the start of temperature control) until the temperature change of the molten metal is detected and the input power is changed, the throughput flow rate is changed as described above. However, there is a problem in that when the input power is changed in response to the change, the input power becomes excessive or insufficient, resulting in large fluctuations in the casting temperature.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned conventional problems, and by controlling the power input to the induction heating furnace based on the temperature of the molten metal in the tundish and the throughput device for the molten metal, only the molten metal temperature can be controlled. To provide an induction heating control method in continuous casting, which can control input power in response to fluctuations in molten metal temperature caused by fluctuations in throughput flow rate, and can accurately control the temperature of molten metal to a target value. The purpose is to

[Means to solve the problem]

The first invention provides an induction heating furnace in a continuous casting tundish, and when controlling the power input to the induction heating furnace so that the temperature of the molten metal in the tundish reaches a target temperature, The above object is achieved by detecting the temperature and controlling the input power based on the difference between the detected temperature of the molten metal and the target temperature and the throughput flow rate of the molten metal in the tundish. In addition, the second invention provides an induction heating furnace in a continuous casting tundish, and when controlling the power input to the induction heating furnace so that the temperature of the molten metal in the tundish reaches a target temperature, the tundish is provided with an induction heating furnace. The temperature of the molten metal in the tundish is determined from the temperature of the molten metal in the ladle for carrying the molten metal into the tundish, and the predetermined conditions for carrying the molten metal into the tundish using the ladle. By controlling the input power based on the difference between the determined temperature and the target temperature and the throughput flow rate of the molten metal in the tending tray,
This also achieves the above objective.

[Effect]

The temperature of the molten metal in the tundish for continuous casting varies depending on the natural drop in temperature of the molten metal itself and the flow rate of the molten metal flowing from the ladle into the tundish. It also varies due to variations in the metal throughput flow rate. Note that this throughput flow rate can be obtained from, for example, the casting speed when pouring the molten metal into the mold, the dimensions of the mold, and the specific gravity of the molten steel. Therefore, in the first invention, the temperature of the molten metal in the tundish is detected, and based on the difference between the detected temperature and the target temperature of the molten metal and the throughput flow rate of the molten metal, the induction heating furnace installed in the tundish is The power input is controlled. Therefore, without waiting for the temperature of the molten metal to fluctuate due to fluctuations in the throughput flow rate,
Since the amount of power input to the induction heating furnace can be controlled in advance by reflecting fluctuations in the throughput flow rate, it is possible to accurately bring the molten metal in the tundish to the target temperature. By the way, molten metal temperature detectors generally require a specific temperature measurement time (time from the start of temperature measurement to the start of temperature control, for example, about 2 minutes) to detect the molten metal temperature. , temperature cannot be detected with good responsiveness, and when the temperature of the molten metal rapidly changes, variations may occur in temperature control. Furthermore, since the temperature detector is generally used in high-temperature molten metal, it is prone to failure, is a consumable item, and is expensive. In addition, in the unlikely event that an accuracy problem occurs in this temperature sensor or the temperature detection signal system connected to this temperature sensor, an accuracy problem will occur in temperature control, and in some cases, the temperature control of molten metal may be interrupted. There are times when it becomes impossible. In order to prevent the above-mentioned malfunctions and problems, the temperature of the molten metal is controlled by controlling the power input to the induction heating furnace installed in the tundish according to a predetermined mode pattern without using a temperature detector. is possible. However, when controlling in this way, the temperature of the molten metal can only be controlled according to a certain mode pattern, so it is impossible to completely prevent the occurrence of a time delay in temperature control, excessive or insufficient input power, etc. cannot be resolved, and in some cases, problems may occur in the temperature of the molten metal. Therefore, in the second invention, the temperature of the molten metal in the tundish is controlled by the temperature of the molten metal in the ladle and the predetermined conditions when carrying the molten metal into the tundish by the ladle, such as the temperature of the molten metal in the tundish. The temperature of the molten metal during pouring is determined by a predetermined calculation based on the temperature loss of the molten metal when the pot is moved onto the tundish, the rate of decrease in the molten metal temperature within the tundish, and the elapsed time during pouring. Then, based on the determined molten metal temperature and the throughput flow rate of the molten metal in the tundish, the molten metal temperature is controlled to the target temperature by controlling the power input to the induction heating furnace. Therefore, in addition to the effects of the first invention, the second invention eliminates the response delay that occurs when the temperature of molten metal is detected by a temperature detector, and further improves the responsiveness of temperature control of molten metal. can be improved.

【Example】

Embodiments of the present invention will be described in detail below with reference to the drawings. First, a first example will be explained. As shown in FIG. 1, this first embodiment is an induction heating method for heating molten steel 12, which is carried into a tundish 10A with a ladle 8, to a target temperature by heating it in an induction heating furnace 14. A control device for detecting the temperature θ _r of the molten steel 12 in the tundish 10,
For example, a consumable continuous thermometer 30 and a detected temperature θ _r
and the target temperature _θs , and calculate the casting speed _Vr of the molten steel 12, the dimensions ( _{mold size} ) _{Ms of} the mold into which the molten steel 12 is poured, and the molten steel 12. From the specific gravity ω, the throughput flow rate W (ton/
The microcomputer 48 is provided with a microcomputer 48 for calculating the input power (minute), and an input power calculating section 50 for calculating the input power command ES from the difference Δθ and the throughput flow rate W calculated by the microcomputer 48. The microcomputer 48 and input power calculation section 50 include a second calculation section that performs each calculation.
As shown in the block diagram of Fig.
A fourth multiplication section 52, 54, 58, 60, a subtraction section 56 for subtraction, and a constant section 61 are provided. Each of these arithmetic units 52 to 60 and constant unit 61 can be configured by either an arithmetic circuit or arithmetic program software. In addition, regarding the other configurations, those having the same configuration as the conventional induction heating control device shown in FIG. 6 are given the same numbers, and the explanation thereof will be omitted. The operation of the first embodiment will be explained below. The induction heating control device according to the first embodiment includes:
In advance, the microcomputer 4 calculates the casting speed V _r , mold size M _s , specific gravity ω of molten steel, and specific heat ρ of molten steel.
8, and is input to and stored in the input power calculating section 50. The temperature of the molten steel 12 in the tundish 10 varies depending on the natural drop in the temperature of the molten steel 12 and the flow rate of the molten steel 12 from the ladle 8 to the tundish 10, and the throughput flow rate W of the molten steel 12 in the tundish 10. It also varies depending on. Therefore, in order to deal with such temperature fluctuations,
In the induction heating control device, first, the temperature θ _r of the molten steel 12 is actually measured by the continuous thermometer 30, and the fluctuation in the throughput flow rate W is measured by the casting speed V _r and the (mold size) M for pouring the molten steel 12. _s and the specific gravity ω of the molten steel 12, the microcomputer 4
8 is determined by calculation. Then, the microcomputer 48 calculates the difference Δθ between the actual measured value (detected value) θ _r of the molten steel 12 and the target temperature θ _s of the molten steel 12, and calculates the calculated difference Δθ together with the determined throughput flow rate W. is transmitted to the input power calculation section 50. The input calculation unit 50 calculates the input power command ES from the difference Δθ between the transmitted temperatures θ _r and θ _s and the flow rate W of the fluid. The calculations in the microcomputer 48 and input power calculation section 50 are executed according to the calculation block diagram in FIG. That is, as shown in the figure, the throughput flow rate W is calculated by first multiplying the casting speed V _r by the first multiplier 52.
and mold size M _s , and a second multiplier 54 multiplies the calculation result of the first multiplier 52 by the molten steel specific gravity (ω) to calculate the throughput flow rate W. Further, the difference Δθ between the target temperature θ _s and the molten steel temperature θ _r in the tundish is calculated by the subtraction unit 56 . These calculated scraped flow rate W and temperature difference Δθ are multiplied by the third multiplier 58, and a constant for temperature conversion outputted from the constant part 61, for example, molten steel specific heat ρ, is applied to the fourth multiplication result. The multiplication unit 60 calculates the power input amount ES. The input power calculation unit 50 inputs the input power command ES calculated as described above to the input power control device 18. The input power control device 18
controls the power converter 20 in accordance with the input power command ES, and adjusts the power input to the induction heating furnace 14 to maintain the temperature θ _r of the molten steel 12 at the target temperature θ _s . to control feedback. As described above, in this induction heating control device, not only can the power input to the induction heating furnace 14 be controlled in accordance with fluctuations in the molten steel temperature _θr , but also induction heating can be performed in response to fluctuations in the soup flow rate W. The amount of power input to the furnace 14 can be controlled. Therefore, it is possible to control the input power amount and thus the molten steel temperature θ _r in advance without waiting for temperature fluctuations of the molten steel 12 to occur due to fluctuations in the throughput flow rate W. Next, a second example will be described. In this second embodiment, the molten metal 12 is transferred to the tundish 10 using a ladle 8 instead of actually measuring the molten steel temperature θ _r using a continuous type thermometer 30 in the first embodiment. This is an induction heating control device that determines the temperature θ _r of the molten metal 12 in the tendish 10 from predetermined conditions at the time of delivery. This induction heating control device includes the above-mentioned conditions, measurements, the temperature (ladle temperature) θ _A of the molten steel 12A in the ladle 8 after scouring or degassing, and the temperature while the ladle 8 is being transported onto the tundish 10. temperature loss θ _B and
It has a second microcomputer 62 for calculating the molten steel temperature θ _r in the tundish 10 from the rate of decrease δ of the molten steel temperature in the tundish 10 and the elapsed time t of the molten steel 12 in the tundish 10. . The second microcomputer 62 also calculates the difference Δθ between the calculated molten steel temperature θ _r and the target temperature θ _s and inputs it to the input power calculating section 50 . As shown in the block diagram of FIG.
In addition to the calculation unit included in the microcomputer 48 of the embodiment, a second subtraction unit 64 and a fifth multiplication unit 6
6. An adding section 68 is provided. Each of these arithmetic units can be configured as either an arithmetic circuit or arithmetic program software. It should be noted that the configuration of the induction heating control device according to the second embodiment other than the above is the same as that of the first embodiment, so similar parts are given the same numbers and explanations thereof will be omitted. The operation of the second embodiment will be explained below. The induction heating control device according to the second embodiment includes:
The pouring speed V _r , mold size M _s , specific gravity ω of molten steel, and specific heat ρ of molten steel are input in advance to the second microcomputer 62 and input power calculating section 50 and stored therein. In order to grasp the temperature θ _r of the molten steel in the tendess 10 during pouring, the temperature θ _A of the molten steel 12A in the ladle 8 after scouring or degassing (ladle temperature), and the temperature θ Temperature loss θ _B , rate of decrease in melting temperature δ in tundish 10, and tundish 10
The elapsed time t of the molten steel 12 within the molten steel 12 is input into the second microcomputer 62. In this second microcomputer 62 and the power calculation unit 50, input power is calculated by each calculation unit shown in FIG. That is, as shown in the figure, the throughput flow rate W is calculated by the first and second multipliers 52 and 54 from the casting speed V _t , mold size M _s and molten steel specific gravity ω. In addition, the molten steel temperature in the tundish 10 θ _r is the molten steel temperature in the ladle 8 (ladle temperature).
A second subtractor 64 subtracts θ _A and the temperature loss θ _B in the ladle 8 to obtain the molten steel temperature θ _r . The molten steel temperature θ _r calculated in this way is
In the following, the calculated molten steel temperature is referred to as θ _ra . Then, the calculated molten steel temperature θ _ra and the target temperature θ _s are subtracted by the first subtractor 56 to obtain a temperature difference Δθ ₁ (=
Find θ _ra −θ _s ). Next, in order to add the temperature drop in the tundish dish to this temperature difference Δθ ₁ , the rate of temperature drop in the tandice dish δ is multiplied by the elapsed time t in the fifth multiplication unit 2 66 to obtain the temperature drop in the tandice dish θ _t
Calculate. This calculated temperature drop θ _t is added to the determined temperature difference Δθ ₁ in an adding section 68 to correct it, and the corrected temperature difference Δθ ₂ (=Δθ ₁ +θ _t ) is calculated. Then, the calculated temperature difference Δθ ₂ is multiplied by the throughput flow rate W in the third multiplier 58, and the result is multiplied by the molten steel specific heat ρ in the fourth multiplier 60 to obtain the input power command ES. As described above, in this second embodiment, the _tundish internal temperature θ _r is determined by calculation according to the block diagram in FIG. has been decided. By the way, in the first embodiment, since the temperature inside the tundish is actually measured by the continuous type thermometer 30, from the start of temperature detection to the start of control of the induction heating furnace 14, due to the temperature measurement time, 2 to
It took 3 minutes and the response was poor. On the other hand, in this second embodiment, the input power ES is determined by calculating and grasping the temperature θ _r of the molten steel in the tundish 10.
The responsiveness of the input power control of the induction heating furnace 14 to a change in the molten steel temperature θ _r was about 0.5 seconds. Therefore,
In this second embodiment, the controllability of the molten steel temperature is significantly improved compared to the first embodiment. Next, a control example will be described in which the power input to the induction heating furnace 14 of the tundish 10 is controlled using the induction heating control device according to the present invention and the conventional induction heating control device as shown in FIG. 6 above. In this case, as shown in Fig. 5A, the casting speed V _r is varied over time by predicting mold breakout, etc., and the casting width is also changed as shown in Fig. 5B. It's on. Therefore,
The throughput flow rate W from the tundish 10 also fluctuates as shown in FIG. Under these circumstances, in the conventional induction heating agent control device, as shown in Figure D, the amount of electricity is not controlled by following the throughput flow rate W without delay, so it is difficult to change the timing of changing the amount of input electricity. (change timing) was delayed, and the molten steel temperature in the tundish was not constant and was causing large fluctuations. Moreover, due to this fluctuation, there is a great risk that the mold will break out at a location where the temperature is too high, as shown in FIG. On the other hand, when the input power amount is controlled by the device of the present invention, as shown in Figure E, the input power value is controlled to follow the throughput flow rate W with good responsiveness, so the molten steel in the tundish The temperature remains almost constant with almost no fluctuations. Therefore, it can be seen that the molten metal in the tundish can be controlled to a constant temperature to form a continuous structure regardless of the change in the throughput flow rate W according to the present invention. Further, even during non-regular casting, continuous casting can be continued because there is no temperature rise and there is no fear of mold breakout. In the above embodiments, molten metal is exemplified as the molten metal whose temperature is controlled in the tundish, but the molten metal according to the present invention is not limited to this, and the present invention can also be used when casting other molten metals. The invention can be put into practice.

【Effect of the invention】

As explained above, according to the present invention, since the power input to the induction heating furnace is controlled based on the molten steel temperature and the throughput flow rate, it is possible to control the molten metal temperature in the tundish to a desired target value with good responsiveness. I can do it. Therefore, when performing continuous casting by changing the throughput flow rate during non-regular casting, it is possible to continuously perform casting without stopping the casting and maintaining the molten metal temperature appropriately, which improves the quality of the cast product. An excellent effect can be obtained in that a continuous structure can be continuously formed while ensuring the following.

[Brief explanation of the drawing]

FIG. 1 is a block diagram including a partial sectional view showing the configuration of an induction heating control device according to a first embodiment of the present invention, and FIG. 2 is a microcomputer that calculates the amount of power input in the first embodiment. FIG. 3 is a block diagram showing the calculation unit of the second
FIG. 4 is a block diagram including a partial cross-sectional view showing the configuration of the induction heating control device of the embodiment; FIG. FIG. 5 shows the conventional induction heating control device and the present invention.
A diagram showing a comparison of changes in input electric power and molten steel temperature with respect to changes in pouring speed, pouring width, and throughput flow rate. Fig. 6 is a block diagram including a partial cross-sectional view showing the configuration of a conventional induction heating control device. , 7th
The figure is a block diagram showing each calculating section that calculates the amount of power input in the conventional induction heating apparatus. 8...Ladle, 10...Tandaitsuyu, 12...
... Molten steel, 14 ... Induction heating furnace, 16 ... AC power supply, 18 ... Power input control device, 20 ... Power conversion unit, 22 ... Induction coil, 24 ... Converter, 26 ... Inverter, 28 ... Power factor adjustment capacitor, 30... Continuous thermometer, 48, 62...
...First and second microcomputers, 50...
Input power calculation unit, 52, 54, 58, 60, 66
...first, second, third, fourth, and fifth multipliers, 5
6, 64...first and second subtraction sections, 61...constant section, 66...addition section.

Claims (1)

[Claims] 1. An induction heating furnace is provided in a continuous casting tundish, and when controlling the power input to the induction heating furnace so that the temperature of the molten metal in the tundish reaches a target temperature, Induction in continuous casting, characterized in that the temperature of the metal is detected, and the input power is controlled based on the difference between the detected temperature of the molten metal and a target temperature, and the throughput flow rate of the molten metal in the tundish. Heating control method. 2. An induction heating furnace is installed in a continuous casting tundish, and when controlling the power input to the induction heating furnace so that the temperature of the molten metal in the tundish reaches a target temperature, molten metal is introduced into the tundish. Determine the temperature of the molten metal in the tundish from the temperature of the molten metal in the ladle and predetermined conditions when carrying the molten metal into the tundish using the ladle, A method for controlling induction heating in continuous casting, characterized in that the input power is controlled based on a difference in target temperature and a throughput flow rate of molten metal in the tending dish.