JPH01205862A - Continuous casting method - Google Patents

Abstract

PURPOSE:To prevent the happening to be impossible to draw by discriminating abnormality of equipment or abnormality caused by effect of steel composition based on comparison between theoretical drawing force and the actual drawing force and increasing cooling water rate in the case of the abnormality of the steel composition. CONSTITUTION:An arithmetic unit 11 connected with molten steel surface level meter 31 in a mold 3 and one by one inputting width and thickness of a cast slab CS and current value Id and voltage value Ed of each driving motor 6M for pinch rolls and drawing speed of the cast slab CS, etc., is arranged. The arithmetic unit 11 reads the surface position of the molten steel MS in the mold 3 and the width and thickness sizes of the cast slab CS to find theoretical drawing force and the total actual drawing quantity is operated and compared from data of the driving motor 6M. It is discriminated that the abnormality occurs caused by either the equipment or the effect of steel composition and in the case of the latter, the cooling water rate is increased. By this method, in the case of the abnormality caused by the steel composition, the happening, which the cast slab CS is impossible to draw, is prevented.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a continuous casting method, and particularly relates to a continuous casting method that can suitably avoid a situation in which drawing is not possible especially when the amount of C in molten steel is small and the amount of Si is large. Concerning casting method.

[Conventional technology]

In the continuous casting method, molten metal is continuously injected into a mold, and the molten metal is continuously pulled out toward the bottom of the mold using pinch rolls, etc. to form a continuous slab into a strip, which is then cut into the required dimensions. This is a technique to obtain cast slabs.

By the way, in the continuous casting method, equipment such as the inability to rotate or breakage of the various rolls used to pull out or guide the slab, or damage to the grid installed directly below the mold and connecting between the mold and the roll group, etc. When abnormalities such as bulging of slabs occur, the quality of slabs deteriorates and operations are temporarily halted.

As a method for detecting the above-mentioned abnormality in continuous casting, for example, Japanese Patent Application Laid-open No. 195570/1984 is known. According to this Japanese Patent Application Laid-Open No. 57-195570, when a group of rolls before and after a curved part of a slab drawn from a mold apply compressive force to the slab to correct its shape, The actual current value of the drive motor is measured, and if it exceeds a predetermined value, it is assumed that an abnormality has occurred and the current value supplied to the drive motor of the roll group is reduced, thereby degrading the quality of the slab. The aim is to prevent equipment damage, etc.

However, most of the techniques disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 57-195570 and other conventional techniques related to abnormality detection in continuous casting are continuous casting in a steady state,
In other words, any abnormality was detected during continuous casting under conditions where the slab width was constant and the drawing speed (casting speed) was constant.

By the way, a technology for changing the slab width without interrupting operation during continuous casting, a technique called so-called mold width changing during pouring, has been put into practical use. In such cases, the casting speed is usually changed, and the width of the slab in the area where the width change has been changed changes into a tapered shape, causing a change in the load applied to the pinch rolls, etc. The previously steady state will be disrupted.

Therefore, under conditions where the steady state is artificially disturbed, such as when the mold width is changed, the above-mentioned conventional method will be treated as an abnormality.

Therefore, in order to detect abnormalities in continuous casting not only in a steady state but also when the slab width and pouring speed are changing,
In Publication No. 8, "The total pulling resistance applied to a slab cast by a continuous casting machine is determined as a function of the width, thickness, and drawing speed of the slab from the mold to the final pinch roll. The theoretical pulling force of the slab is taken as the actual pulling force of the slab, and the pulling force of each pinch roll is determined from the power supply voltage and current to each pinch roll drive motor and the slab pulling speed, and the sum is the actual pulling force of the slab. We proposed a continuous casting abnormality detection method characterized by detecting continuous casting abnormalities by comparing the theoretical pulling force and the actual pulling force. (referred to as precedent law).

[Problem to be solved by the invention]

However, in this prior method, the correlation between the theoretical pulling force and the actual pulling force was about 0.75 as a correlation coefficient, which was not high, and therefore there were many false alarms, which was not necessarily satisfactory.

On the other hand, the inventors have discovered that with extremely low carbon materials (C#O), it becomes difficult to pull out even if the pulling force by the pinch rolls is increased, and the pinch rolls eventually slip from the slab, resulting in the inability to pull it out. was often experienced.

SUMMARY OF THE INVENTION Therefore, the main object of the present invention is to provide a method that can accurately determine the cause of the impossibility of extraction, and also that can prevent the impossibility of extraction.

[Means to solve the problem]

The above problem was solved by the theoretical pulling force determined as a function of the cross-sectional size of the slab and the pulling speed between the mold and the endmost pinch roll, and the load and pulling speed of each pinch roll's drive motor. The actual pulling force, which is the sum of the roll pulling forces, is compared, and when these deviations are large, an abnormality is determined. Based on the magnitude of these deviations and the level of the actual pulling force, it is determined whether the equipment is abnormal or the steel composition is abnormal. Based on the effect, it is judged whether it is abnormal or not, and if it is considered to be an abnormality based on the influence of the steel composition and will lead to the impossibility of extraction, the problem will be solved by increasing the amount of cooling water.

[For production]

When the C content in the molten steel is low and the Si content is high, the actually measured drawing force becomes large, leading to poor drawing. Also in this case, the difference between the theoretical pulling force and the actual pulling force becomes large.

As a result, when abnormalities in continuous casting are judged based only on the preceding method, the difference between the theoretical pulling force and the actual pulling force is large;
Even if it is determined to be abnormal, it cannot be determined whether the above-mentioned difference is large due to equipment abnormality or whether it is due to the aforementioned molten steel composition.

However, according to the present invention, by determining the amount of deviation between the theoretical pulling force and the actual pulling force and the level of the actual pulling force, it is possible to distinguish between an equipment abnormality and an abnormality based on the influence of the steel composition. Moreover, the influence of the steel composition, especially when the C content is low and the St content is large, tends to lead to the inability to pull out. can be avoided.

[Specific structure of the invention]

The present invention will be explained in more detail below.

As is well known, during continuous casting, molten steel MS melted in a tI4 furnace (not shown) is transported to the continuous casting equipment using a ladle 1 and is temporarily stored in a tandy dish 2. The nozzle 21 of the tundish 2 is opened into the mold 3, and the molten steel MS is injected into the mold 3 so that the surface level within the mold 3 is constant. The molten steel MS injected into the mold 3 is cooled by the mold 3, and a solidified shell SS is formed around it. A grid 4 is provided directly below the mold 3, and a large number of guide rolls 5 R, 5 are provided on a roller apron 5 below the grid 4.
After the molten steel MS is guided by R, . Ru.

Now, in FIG. 1, the pull-out resistance Fw of the slab CS from the mold 3 to the endmost pinch roll 6RE of the pinch roll group 6 is given by the following equation (11).

Fw =fs+ +fg +fR+fs +fr
-(1) However, f-: Pulling resistance inside the mold fg Pulling resistance inside the mold fR: Pulling out (friction) resistance of the slab/roll fs: Straightening pulling resistance of the slab CS fr: Roll rolling resistance due to straightening reaction force As stated in the publication related to the previous method, each drawing resistance is a function of the cross-sectional size of the slab and the casting speed.
Therefore, the theoretical drawing force F- can also be determined as a function of the cross-sectional size of the slab and the casting speed.

Next, the actual pulling force, that is, the actual pulling force will be explained. FIG. 5 is a block diagram showing the configuration of the drive circuit of the pinch roll 6R, and is an AC type 2I! The rectifier 52a of the converter 52 converts the alternating current from the converter 51 into direct current, and the commutator 52b converts the alternating current again into alternating current to supply power to the motor 6M, thereby controlling the rotation of the remoter 6M. The output of the motor 6M is sent to the pinch roll 6 via the reducer 59.
This is the configuration given to R, but the rectifier section 52a and commutation section 52b
DC side current [
d as a direct current and side voltage Ed by the voltage detector 54B.
, the drawing speed Vc is determined by the pulse generator 57 and frequency/voltage (F/V) converter 58 provided on the output shaft 6S of the motor 6M, and the motor is determined by the strain gauge 60 attached to the output shaft 59S of the reducer 59. 6M torque TR
It is designed to detect.

The output P of the drive motor 6M of each pinch roll 6R is as follows (
2) Given by Eq.

P=TR・ω =Ed・Id (2) However, TR: Torque Ed: DC side voltage Id: DC side current ω: Angular speed From (2) 2 above, torque TR is as follows (3) It is expressed by the formula.

Id TR=Ed ・□ ・・・・・・(3) ω As shown in Figure 7 of the above publication, torque TR and withdrawal speed Vc
It is understood that there is a very strong correlation between the product of Fn and the motor current 1d, and between the product of the pulling force Fn and the pulling speed Vc and the motor current, that is, there is a relationship of TR-VcOCId Fn -VcOCId. be done. Therefore, the pulling force F
n is expressed as the following formula (4).

Id Fn = K ・ □ vc 9.8 vc: Pulling speed ηlI: Motor efficiency ηi: Reducer efficiency ηS: Rectifier efficiency Note that 1d in the above formula (4) is calculated as (measured current) - (no-load current) shall be.

As a result, (the theoretical pulling force Fw determined by equation 11 and the total sum ΣFn (hereinafter referred to as actual total pulling force) of the actual pulling force Fn of each pinch roll 6R determined by equation (4) match (measurement errors, etc.) Of course, it is necessary to take this into consideration and set the allowable range), so that normal continuity can be maintained even when the drawing speed (casting speed) Vc and slab width W are changing due to changes in mold width, etc. It can be assumed that casting is taking place.

Note that the above explanation assumes that the P/R drive motor is a three-phase AC motor V V V F (Variable Voltage
PWM (Pulse Width Mo) control
(duration), when a DC motor is used, there is a relationship between torque and armature current, so the actual pulling force can be easily determined.

Therefore, an arithmetic device 11 shown in FIG. 1 is prepared. As described in the above-mentioned publication, this calculation device 11 includes various calculation formulas, basic data, theoretical pulling force Fw and actual total pulling force ΣFn.
The allowable value α and the like are input and set by the setting device 12, and the calculation results etc. are displayed on the display device 13.

The calculation device 11 includes a hot water level gauge 31 provided in the mold 3.
The detected scene position, the inner dimension of grid 4, i.e. slab C8
Width W and thickness T1 of the current value 1d and voltage value Ed of the drive motor 6M of each pinch roll 6R, the moving speed of the slab CS detected by the speed meter 14 provided at an appropriate position, that is, the drawing speed (casting speed) Vc, etc. are input sequentially.

Next, the actual processing of the method of the present invention will be explained according to the flowchart of FIG. 6 showing the contents of the calculation processing by the calculation device 11.

The arithmetic device 11 reads the current value Id and voltage value Ed of each drive motor 6M of each pinch roll 6R, and also reads the pulling speed Vc from the speedometer 14,
For each, the actual pulling force Fn is calculated using the above equation (4). Then, the actual total pulling force ΣFn is obtained by summing the pulling forces Fn of each drive motor 6M, and the display 13
to be displayed.

Next, the computing device 11 calculates the temperature of the I in the mold 3 from the hot water level gauge 31.
The inner dimensions of the aMS melt level position are read from the grid 4, i.e., the width W and thickness T of the slab CS, each drawing resistance is calculated, and based on this result, the theoretical drawing force is calculated using the above formula (1). F
s1 is calculated and displayed on the display 13.

When the actual total pulling force ΣFn and the theoretical pulling force Fw are determined in this way, the arithmetic unit 11 compares the absolute value of the difference between the two with a predetermined tolerance value α, and if 1ΣFn−Fnl>α, then some A predetermined alarm is issued to indicate that an abnormality has occurred.

In this way, the theoretical pulling force of the slab is determined according to the momentary changes in the casting width of the slab, the drawing speed, etc., and it is determined based on this and the current, voltage, etc. of the drive motor of the pinch roll used for pulling the slab. By comparing the actual drawing force applied to the slab, abnormalities in continuous casting can be detected not only in a steady state but also in cases where the drawing speed is not constant, such as when changing the mold width.

However, after proposing the prior method for the correlation between F- and ΣFn as described above, the inventors continued to operate many times on actual machines, and as a result, the correlation coefficient between them was approximately 0.75. , it was not necessarily high.

Therefore, in calculating the theoretical pulling force, the present inventors calculated the drawing speed, slab cross-sectional dimension, degree of superheating of molten steel, amount of spray water,
One type of powder, molten steel composition (C, S.

Considering Si) etc. as a variable factor, we created various calculation formulas that took this into account, and examined their validity. When we corrected them based on the amount of carbon in molten steel, we found that the correlation coefficient was 0, as shown in Figure 2. It improved to .85.

Next, the relationship between the amount of carbon and the measured pulling force was investigated with the drawing speed and slab dimensions constant, and the results shown in FIG. 3 were obtained. It can be seen that for medium carbon material, the drawing resistance of 50 to 60 tons becomes 70 to 80 tons when the carbon content is around zero.

Furthermore, as the amount of carbon approaches zero, the variation in pulling resistance increases, reaching values of 60 to 160 tons.
It was also found that if the pulling force exceeds 150 tons, there is a possibility that it will not be possible to pull it out.

When this drawing resistance with zero carbon content (#O) was analyzed, it was found that it changes depending on the Si content.

FIG. 4 shows the relationship between the amount of silicon and the pulling force. The amount of Si and the pulling force form a mountain shape as shown in the figure.

Therefore, when casting molten steel with a Si content of 0.6% and 1.0%, for example, if it is cooled with twice the amount of normal cooling water, the drawing resistance will decrease from 150 tons to about 100 tons, and there is a possibility that drawing will not be possible. Almost gone. There was also no abnormality in slab quality. Therefore, as shown in FIG. 4, when the drawing limit capacity is 150 tons, if this is exceeded or there is a risk of exceeding it, the inability to draw can be avoided by increasing the amount of cooling water compared to the normal case.

Therefore, in order to avoid non-removal,
It has been found that the amount of cooling water can be controlled via the cooling water amount control device 14 according to the amount of C and the amount of Si in the molten steel within a range that does not affect the quality of the slab. This is thought to be because if the water flow rate is large, the shell thickness increases and bulging becomes difficult.

Therefore, as shown in FIG. 1, by calculating the theoretical pulling force from the drawing speed, slab size, molten steel composition, etc. in the arithmetic unit 11, and comparing it with the actual drawing force calculated from the motor current, By determining the amount of deviation of At the same time, it is possible to control the amount of cooling water and prevent it from becoming impossible to pull out. Additionally, in the event of equipment malfunction, an alarm is issued to prompt the operator to stop casting and repair the defective equipment.

Specifically, whether the abnormality is due to equipment abnormality, for example, abnormality in pinch roll alignment, or whether the abnormality is due to the influence of C and Si components can be determined by distinguishing as shown in FIG. That is, there is no influence of the amount of C and Si,
When the roll alignment is also normal, it is assumed that the theoretical drawing resistance is 1001-ton, as shown in line A. If the actual pulling resistance is around 100 tons, it is considered normal. On the other hand, when the actual pulling resistance is 150 tons, as shown in line B, the deviation from the theoretical pulling force is large, so it is considered to be some kind of abnormality, and the actual pulling force is not very high (not 50 tons). It is determined that the deviation by tons is due to roll alignment abnormality.Furthermore, as shown in line C, the actual pulling resistance is 1
When the weight is 70 tons, the above deviation is so large that it is thought that the influence of C and Si is also occurring, and when calculating the theoretical pulling force taking into account the influence, it is 160 tons.
t, their deviations are small and therefore the roll alignment is normal and C and Si
If the actual pulling force is 220 tons, then of course some abnormality has occurred, and if the theoretical pulling resistance including the effects of C and Si is 180 tons, The deviation from this theoretical drawing resistance is as large as 401-tons, and therefore, C and Si
It is assumed that the roll alignment abnormality is also added to the influence of the above.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to identify whether an equipment abnormality is caused by molten steel components, and in the case where the abnormality is caused by molten steel components, it is possible to prevent the failure of extraction.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of continuous casting equipment for carrying out the method of the present invention, and Figures 2 to 4 show the measured pulling force (actual pulling force).
FIG. 5 is a circuit diagram of an example of an actual pulling force measuring device, FIG. 6 is a flowchart illustrating the method of the present invention, and FIG. 7 is a diagram showing the actual pulling force. FIG. 3 is an exemplary diagram of pull-out resistance. 3...Mold, 6M...Pinch roll drive motor, 6R...Pinch roll, 11...Arithmetic unit, 14
...Cooling water flow control device, CS...Slab. Figure 1 Figure 2 Box 1 & 61 Slope Figure 3 Cf Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] (1) The theoretical pulling force calculated as a function of the cross-sectional size of the slab and the pulling speed between the mold and the last pinch roll, and each pinch roll calculated from the drive motor load and pulling speed of each pinch roll. The actual pulling force, which is the sum of the pulling forces of A continuous casting method characterized in that the amount of cooling water is increased when it is determined that the abnormality is based on the influence of the steel composition and that it is considered to be impossible to pull out.