JP4929984B2 - Continuous casting method - Google Patents

Description

  The present invention relates to a continuous casting method for preventing seizure by increasing the lubricity in a mold and reducing the frictional resistance between the mold and a slab in continuous casting of steel or the like.

  Conventionally, in continuous casting, various techniques have been developed for mold oscillation (vertical vibration) as a technique for reducing the frictional resistance between the mold and the slab by increasing the lubricity in the mold.

For example, Patent Documents 1 and 2 disclose a method using a non-sine vibration waveform in which the rising speed of the mold oscillation is lower than the falling speed.
JP-A 61-20653 JP-A-60-87955

In Patent Document 3, a vibration method for maintaining an appropriate negative strip time set for each steel type is used. In Patent Document 4, a vibration method having a steep waveform in the rising period of mold oscillation is used. In Patent Document 5, mold oscillation is performed. A method is disclosed in which the mold amplitude is increased in accordance with an increase in casting speed while keeping the frequency within a certain range.
JP-A-6-15425 JP-A-8-19845 JP-A-8-187562

  However, since all of the techniques disclosed in Patent Documents 1 to 5 are limited to devise of the mold oscillation method, there is a limit to the effect of reducing the frictional resistance between the mold and the slab. .

Therefore, the applicant has incorporated a mechanism having play into the pinch roll drive system in place of the technology that relies only on oscillation for improving lubricity as in Patent Documents 1 to 5, and reduces the pulling speed when the mold is raised. Patent Document 6 discloses a technique for reducing the frictional resistance in the mold by increasing the drawing speed when the mold is lowered.
Japanese Patent No. 3298586

  Although the technique disclosed by the applicant in Patent Document 6 can reduce the frictional resistance in the mold more effectively than the techniques of Patent Documents 1 to 5 that rely only on oscillation to improve lubricity, There is a demand for extending the durability of machine parts that increase or decrease.

  The problem to be solved by the present invention is that the durability of the technique disclosed by the applicant in Patent Document 6 is further extended.

The continuous casting method of the present invention comprises:
In order to extend the durability in the technology disclosed by the applicant in Patent Document 6,
In continuous casting where the slab is pulled out while oscillating the mold,
By increasing or decreasing the rotational speed of the drive motor that pulls the slab according to the pulling load, the pulling speed Vu when the mold is raised is smaller than the average pulling speed Va during one cycle of oscillation, and when the mold is lowered When controlling the drawing speed Vd to be large,
When the drawing speed Vu or Vd is varied in conjunction with the template oscillation in a period shorter than one cycle of oscillation,
The oscillation waveform of the oscillation is
When the average mold rising speed when the mold displacement is from the lowering limit to the rising limit and averaging the mold rising speed is | Uu |
The relationship between the minimum drawing speed Vu-min of the slab during the mold rising period, the maximum drawing speed Vd-max of the slab during the mold lowering period, and the average drawing speed Va during one oscillation cycle is expressed by the following equation (1): Satisfying the relationship of equation (2)
And,
The relationship between the time difference Δt when the mold lowering speed Ud becomes maximum and the slab reaches the maximum drawing speed Vd-max during the mold lowering period and the oscillation period (1 / f) is as follows ( 3) To satisfy the relationship of the formula,
The most important feature is that the oscillation conditions of the mold are constant and do not change, but are controlled so as to increase or decrease the drawing speed in accordance with the load of the pinch roll.
0.03 | Uu | ≦ Vd-max−Vu-min ≦ 0.5 | Uu | (1)
Va−Vu−min ≦ Vd−max−Va (2)
0.05 × (1 / f) ≦ Δt ≦ 0.40 × (1 / f) (3)
In equations (1) and (2), the speed is positive in the slab drawing direction.

  In the present invention, in order to increase the lubricity in the mold and suppress the occurrence of restraint breakout, the rotational speed of the drive motor that pulls out the slab is used instead of incorporating a mechanism having play in the pinch roll drive system. Since it is performed by controlling, durability can be improved.

The best mode for carrying out the invention according to each claim of the present application will be described below with reference to FIGS.
The present invention was made as an improved invention of Patent Document 6 previously proposed by the applicant, and includes a short-term control function that increases or decreases the drawing speed Vu or Vd of the slab according to the rising and lowering of the mold, At the same time, by providing the drive system of the pinch roll that pulls out the slab with a long-term control function that controls the average value Va of the slab drawing speed to approach the target value, the mechanical device is simplified and durable. Is increased.

  Furthermore, by increasing or decreasing the oscillation frequency f in conjunction with a short-term increase or decrease in the drawing speed V, the absolute value of the mold rising speed Uu is reduced in addition to the drawing speed Vu during the rising period of the oscillation. By the synergistic effect, the relative speed between the mold and the slab is reduced, and the frictional resistance in the mold is lowered.

  In this patent application, “short term” refers to a period of less than one period (1 / f) of oscillation, and “long term” refers to a period of one period (1 / f) or more of oscillation. .

The invention according to claim 1 of the present application is
In continuous casting where the slab is pulled out while oscillating the mold,
By increasing or decreasing the rotational speed of the drive motor that pulls the slab according to the pulling load, the pulling speed Vu when the mold is raised is smaller than the average pulling speed Va during one cycle of oscillation, and when the mold is lowered When controlling the drawing speed Vd to be large,
When the drawing speed Vu or Vd is varied in conjunction with the template oscillation in a period shorter than one cycle of oscillation,
The oscillation waveform of the oscillation is
When the average mold rising speed when the mold displacement is from the lowering limit to the rising limit and averaging the mold rising speed is | Uu |
The relationship between the minimum drawing speed Vu-min of the slab during the mold rising period, the maximum drawing speed Vd-max of the slab during the mold lowering period, and the average drawing speed Va during one oscillation cycle is expressed by the following equation (1): Satisfying the relationship of equation (2)
And,
The relationship between the time difference Δt when the mold lowering speed Ud becomes maximum and the slab reaches the maximum drawing speed Vd-max during the mold lowering period and the oscillation period (1 / f) is as follows ( 3) To satisfy the relationship of the formula,
The continuous casting method is characterized in that the oscillation condition of the mold is constant and is not changed, but is controlled so as to increase or decrease the drawing speed corresponding to the load of the pinch roll.
0.03 | Uu | ≦ Vd-max−Vu-min ≦ 0.5 | Uu | (1)
Va−Vu−min ≦ Vd−max−Va (2)
0.05 × (1 / f) ≦ Δt ≦ 0.40 × (1 / f) (3)
In equations (1) and (2), the speed is positive in the slab drawing direction.

  In the invention according to claim 1 of the present application, the drive motor for pulling out the slab is a motor for driving a pinch roll, and a continuous casting machine is usually equipped with a plurality. This drive motor is normally controlled to keep the extraction speed constant regardless of the load, but in the present invention, it is controlled to increase or decrease the extraction speed according to the load.

Specifically, in the short term, by performing control that allows the drawing speed V to vary in conjunction with the mold oscillation, the pulling speed Vu is decreased during the rising period of the mold due to oscillation. , the downturn is the Ru varied increasing the drawing speed Vd.

That is, the essence of the invention according to claim 1 of the present application is to perform such a short-term control function.
This is to weaken the normal control function of keeping the rotational speed of the motor that drives the pinch roll constant, so that the rotation is slow when the load is large, and the rotation is fast when the load is small. is there.

  Such control is applied according to the pulling load in the short term and in the long term, but in practice, short-term fluctuations in the rotational speed corresponding to the oscillation cycle of the oscillation are clearly seen. In the invention according to item 1, for convenience, it is referred to as a short-term control function.

On the other hand, with only short-term control, the time-averaged drawing speed Va is deviated from the set value due to the load, resulting in inconvenience in operation. Therefore, the invention according to claim 3 of the present application has a function of correcting this deviation. In the long term, a long- term control function for controlling the average drawing speed Va to the target value is provided.

  For example, the actual average drawing speed Va is calculated every 2 seconds for the past 2 seconds (when the oscillation frequency is, for example, 120 cpm, 2 seconds corresponds to 4 oscillation cycles), and the actual value is calculated. The correction value of the drawing speed is corrected so as to correct the deviation of the set value.

  By controlling the drawing speed, the relative speed between the slab and the mold decreases during the mold rising period when the friction resistance in the mold reaches its peak, so the friction resistance in the mold decreases and the lubricity improves. The

  In the above equation (1), the upper limit value of Vd-max-Vu-min is set to 0.5 Uu. It is difficult to control the difference between Vd-max and Vu-min to be larger than 0.5 Uu. That's why. Moreover, the lower limit value of Vd-max-Vu-min is set to 0.03 Uu because if the difference between Vd-max and Vu-min is smaller than 0.03 Uu, the effect of improving the lubricity by the present invention is sufficient. It is because it is not demonstrated.

  On the other hand, the above equation (2) means that the maximum drawing speed Vd-max of the slab during the mold lowering period is farther from the average drawing speed Va than the minimum drawing speed Vu-min of the slab during the mold rising period. It is that it is a value. This is due to the following reason.

  The phenomenon that the drawing speed V of the slab increases with respect to the average drawing speed Va occurs in the negative strip period in which the lowering speed Ud of the mold exceeds the drawing speed Vd, and the drawing speed V of the slab becomes higher than the average drawing speed Va. Since the decreasing phenomenon occurs in the remaining positive strip period, the negative strip period is shorter than the positive strip period.

  Accordingly, if the drawing speed V of the slab is increased at a time away from the average drawing speed Va as compared with the decreasing period, it is difficult to maintain the average value unless it is pulled away from the average drawing speed Va. This is because it is natural control that the value is farther from the average drawing speed Va than the minimum drawing speed Vu-min in the mold rising period.

  The increase / decrease in the drawing speed in the present invention is caused by the increase / decrease in the in-mold frictional resistance accompanying the mold oscillation. Therefore, in the control, it is natural that there is a slight time delay with respect to the oscillation of the mold, but this time delay Δt is set to the lower limit value (0.05 × (1 / f) of the expression (3). It is difficult for the control according to the present invention to make it less than.

In addition, the presence of this time delay Δt effectively acts to substantially secure a negative strip (a phenomenon in which the mold lowering speed exceeds the drawing speed) in the mold lowering period. This time delay Δt is expressed by the equation (3). If the upper limit (0.40 × (1 / f)) is exceeded, the reduction of the drawing speed Vu in the next mold rising period tends to be delayed, and it becomes difficult to reduce the in-mold frictional resistance targeted by the present invention. Therefore, in the invention according to claim 1 , this time delay Δt is set in the range of the above-described equation (3).

The invention according to claim 2 of the present application is
In the invention according to claim 1 of the present application,
As soon as the instantaneous value of the slab drawing speed V is recognized, the oscillation frequency f defined as a function of the drawing speed V is calculated by the following equation (4), and the calculation is performed in the mold lowering period and the mold rising period. Change to the oscillation frequency f waveform,
Molds increases life of the drawing speed Vu (absolute value) as a template velocity Uu (absolute value) are both to be smaller than the drawing speed Vd of the mold descending period (absolute value) as a template velocity Ud (absolute value), cast Control is performed to change the oscillation frequency f of the mold in accordance with the change of the drawing speed V of the piece .
f = a · | V | ^{b + c} (4)
a, b, and c are coefficients. However, a and b are positive real numbers, and the frequency f is always a positive real number in the drawing speed range applied to the operation.

When the oscillation frequency f is defined as a function of the drawing speed V as in the expression (4) in claim 2 , the frequency f and the drawing speed V are positively correlated. The frequency f increases or decreases according to the increase or decrease of.

When this relationship is synergistic with the control for increasing / decreasing the drawing speed V in accordance with the lowering / raising of the mold as in the first aspect of the present invention, the drawing speed Vu (absolute value) and the mold speed Uu ( A continuous casting method in which both the absolute value) is smaller than the drawing speed Vd (absolute value) and the mold speed Ud (absolute value) in the mold lowering period is realized.

That is, the invention according to claim 2 is further compared to the invention according to claim 1 in which the oscillation condition is constant and does not change, and is controlled so as to increase or decrease only the drawing speed corresponding to the load of the pinch roll. In addition, control is performed to change the oscillation frequency f in accordance with the change in the drawing speed. By such control, the relative speed between the slab and the mold can be more effectively reduced in the mold rising period when the frictional resistance acting between the slab and the mold peaks, and the in-mold frictional resistance further decreases, Lubricity is improved.

The effect of the invention according to the claim 2 will be described with reference to FIGS. 1 and 2, the vertical axis indicates the slab drawing direction as positive.
FIG. 1 shows that the rotational speed of the drive motor for pulling the slab is increased or decreased according to the pulling load, so that the pulling speed Vu when the mold is raised or the pulling speed when the mold is lowered is shorter than one cycle of oscillation. When the speed Vd is varied in conjunction with the oscillation of the mold and is controlled so as to match the average drawing speed Va during one oscillation period with the target value in a period longer than one oscillation period, in the example that satisfies the conditions of claim 2, in order to facilitate understanding of the change in the oscillation frequency of the waveform of the mold (a diagram), because the extremely drawing speed V (c view) of the slab is varied and wherein It does not satisfy (1) and (2) in item 1 . Further, for simplification, the expression (3) of claim 1 is not satisfied.

As a comparison with FIG. 1, FIG. 2 shows an example in which the conditions are the same except that the result of the short period fluctuation of the drawing speed V is not reflected in the waveform of the oscillation frequency of the mold.
In addition, when casting is actually performed under such conditions, the change in the oscillation frequency waveform further affects the fluctuation of the drawing speed, which further affects the oscillation frequency waveform. However, in order to simplify the explanation, the fluctuations in the drawing speed are compared as the same.

  1 and FIG. 2, the oscillation stroke is 5 mm, the frequency (average value in FIG. 1) is 2.0 cps, and the average drawing speed Va of the slab is 13.33 mm / sec. The determined negative strip rate (NSR) is 50%. Under this condition, the coefficients a, b, and c in the above equation (4) are 0.15, 1.0, and 0, respectively.

In FIG. 1, as a result of the change in the oscillation frequency based on the above equation (4) corresponding to the microscopic change in the drawing speed, the drawing speed Vu and the mold speed Uu (absolute value) during the mold rising period ) are both appeared features defined in claim 2 that is smaller than the mold downturn drawing speed Vd and the mold velocity Ud (absolute value).

  On the other hand, in FIG. 2, an oscillation frequency corresponding to the average value (0.8 m / min) of the drawing speed is given, and the oscillation vibration is a simple sine waveform.

As in the invention according to claim 2 , in order to change the oscillation frequency (waveform) in accordance with the increase / decrease of the drawing speed accompanying the lowering or raising of the mold, at least 1 of the oscillation period (1 / f) is required. It is necessary to recognize the drawing speed at a pitch of / 4 or less, more preferably 1/10 or less, and immediately reflect it in the mold vibration control through the calculation according to the equation (4).

The invention according to claim 4 of the present application is
In the invention according to any one of claims 1 to 3 of the present application,
A mold having a round cross section or a rectangular cross section having a value obtained by dividing the average mold width by the average mold thickness is 1.0 to 4.0 is used.

  The method of changing the drawing speed and the oscillation vibration waveform according to the present invention is performed in accordance with the fluctuation of the pinch roll drawing load. Therefore, it is a condition for the invention to exert its function that the in-mold frictional resistance is reflected in the pinch roll drawing load.

  If the mold has a round cross section or a rectangular cross section of 1.0 to 4.0 when the average mold width is divided by the average mold thickness, bulging between rolls of the slab is relatively small. Is easily reflected in the pinch roll pulling load.

However, if the slab shape with a rectangular ratio that is obtained by dividing the average mold width by the average mold thickness exceeds 4.0, the bulging between rolls increases, so the slab is restrained in the roller apron, and the friction in the mold It becomes difficult for resistance to be reflected in the pinch roll pulling load.
Therefore, when the casting mold specified in claim 4 is used, the inventions according to claims 1 to 3 easily exhibit their functions.

Furthermore, from the viewpoint of suppressing bulging between rolls, it is preferable that the casting speed is 1.2 m / min or less, or the secondary cooling specific water amount is 0.5 liter / kg-steel or more.
Further, as the type of the continuous casting machine, a vertical type or a curved type in which the slab behavior in the mold is easily transmitted to the pinch roll is more suitable for the present invention than the vertical bending type.

Hereinafter, experimental results performed to verify the present invention will be described.
A first embodiment of the present invention is shown in FIG. Also in this FIG. 3, the vertical axis | shaft makes positive the drawing direction of slab.

FIG. 3 shows that in a vertical continuous casting machine having a mold width of 800 mm and a mold thickness of 100 mm, [C] = 0.05 mass%, [Si] = 0.02 mass%, [Mn] = 0.2 mass%. , [Sol.Al] = 0.04 mass% low carbon plain steel with a mold oscillation stroke of 4.2 mm, a frequency of 3.82 cps, and an average drawing speed of 27.9 mm / sec. When casting, the example of transition of mold displacement, mold speed, and drawing speed when the invention according to claim 3 that is dependent on claim 1 of the present application is applied is shown. Note that the average drawing speed (27.9 mm / sec) is a target value and at the same time an actual value.

(Contrast with claims 1 and 3 )
In the embodiment shown in FIG. 3, the drawing speed is increased or decreased in conjunction with the drawing load (mainly mold lowering / raising) in the short term as defined in claim 1 of the present application. As defined in claim 3, casting is performed at an average drawing speed that matches the target value in the long term.

Pull vent rate to the average increase rate -32.1Mm / sec the mold, the difference between the maximum value and the minimum value of the drawing speed is an average 2.8 mm / sec. This is in a range satisfying the expression (1) of claim 1 .

  Since the maximum value or minimum value of the drawing speed varies for each oscillation period as shown in FIG. 3C, it is defined as an average value of an arbitrary section including at least two periods. The value of 2.8 mm / sec is the difference between the average values of the three points marked with ● and three points marked with ○ in FIG.

As shown in FIG. 3 (c), the drawing speed is relatively sharp when the mold is lowered, and has a maximum value and a minimum value, drawing a comparatively gentle curve when the mold is raised. This indicates that the difference between the average value and the maximum value is larger than the difference between the average value and the minimum value, that is, the expression (2) of claim 1 is satisfied.

  Specifically, the average of the three maximum values indicated by ● in FIG. 3C is 29.4 mm / second, the average of the three minimum values indicated by ○ is 26.6 mm / second, The difference from the average value (27.9 mm / sec) is 1.5 for the local maximum and 1.3 for the local minimum. The maximum value here refers to the maximum value for each cycle, and the minimum value refers to the minimum value for each cycle.

Pull vent rate maximum value takes time (FIG. 3 (c) ● mark in) the mold lowering speed shown in FIG. 3 (b) is a delay of about 0.04 to 0.05 seconds than the time of maximum Yes. This is a delay corresponding to about 15% to 20% of the oscillation period (about 0.26 seconds), and satisfies the expression (3) of claim 1 .

(Contrast with claim 2 )
In the continuous casting under the conditions shown in FIG. 3, the coefficients of the equation (4) that define the relationship between the oscillation frequency f (cps) and the drawing speed V (mm / second) are a = 0.609 and b = 0.5 and c = 0.60, and this point satisfies the provisions of claim 2 .

However, since the calculation of the oscillation frequency f by the equation (4) is performed with respect to the average drawing speed during a period of one or more cycles of the oscillation, the short-term fluctuation of the drawing speed becomes the oscillation frequency f. Was not reflected. Therefore, the average speed (absolute value) of the mold speed shown in FIG. 3 (b) is equal to 32.1 mm / second both at the time of descent and at the time of ascent, and Claim 2 is not satisfied.

(Contrast with claim 4 )
The casting conditions in FIG. 3 have a rectangular ratio of 800 mm for the mold width and 100 mm for the mold thickness (a value obtained by dividing the average mold width by the average mold thickness is 8.0), and claim 4 is not satisfied.

(Comparison with conventional technology)
The average friction force in the mold at the time of casting under the conditions of FIG. 3 was calculated from the measured value of the oscillation hydraulic pressure. As a result, the conventional method that does not use the drawing speed control according to the present invention, that is, casting under the condition that the short-term fluctuation of the drawing speed is small (Vd-max-Vu-min <0.03 Uu) (other conditions are the same). Compared with the case, the average friction force in the mold was reduced by 13%.

A second embodiment of the present invention is shown in FIG. Also in FIG. 4, the vertical axis is positive in the drawing direction of the slab.
FIG. 4 shows a vertical continuous casting machine having a mold width of 800 mm and a mold thickness of 200 mm, [C] = 0.05 mass%, [Si] = 0.02 mass%, [Mn] = 0.2 mass%. , [Sol.Al] = 0.04 mass% low carbon plain steel, mold oscillation stroke is 4.2mm, frequency is 2.33cps (at the average drawing speed), and the average drawing speed of the slab is When casting at 17.0 mm / sec, it shows an example of transition of mold displacement, mold speed, and drawing speed when the inventions according to claims 1 to 4 of the present application are applied. The average drawing speed (17.0 mm / sec) is a target value and at the same time an actual value.

(Contrast with claims 1 and 3 )
In the embodiment shown in FIG. 4, the drawing speed is increased or decreased in conjunction with the drawing load (mainly mold lowering / raising) in the short term as defined in claim 1 of the present application. As defined in claim 3, casting is performed at an average drawing speed that matches the target value in the long term. In FIG. 4, it seems that the drawing speed gradually decreases while increasing or decreasing, but in the longer term, the average drawing speed was as the target value.

With respect to the drawing speed shown in FIG. 4 (c), the average difference between the maximum value and the minimum value of the drawing speed was 2.5 mm / sec, while the average ascent speed of the mold was −19.5 mm / sec. This is in a range satisfying the expression (1) of claim 1 .

  Since the maximum value or minimum value of the drawing speed varies for each oscillation period as shown in FIG. 4C, it is defined as an average value of an arbitrary section including at least two periods. The value of 2.5 mm / second is the difference between the average values of the three marks ● and ◯ in FIG.

As shown in FIG. 4 (c), the drawing speed is relatively sharp when the mold is lowered, and has a maximum value and a minimum value, respectively, by drawing a relatively gentle curve when the mold is raised. This indicates that the difference between the average value and the maximum value is larger than the difference between the average value and the minimum value, that is, the expression (2) of claim 1 is satisfied.

  Specifically, in FIG. 4C, the average of the three maximum values indicated by ● is 19.0 mm / second, the average of the three minimum values indicated by ○ is 16.5 mm / second, The difference from the average value (17.0 mm / sec) is 2.0 for the maximum value and 0.5 for the minimum value. The maximum value here refers to the maximum value for each cycle, and the minimum value refers to the minimum value for each cycle.

Pull vent rate maximum value takes time (FIG. 4 (c) ● mark in) the mold lowering speed shown in FIG. 4 (b) is a delay of about 0.06 to 0.12 seconds than the time of maximum Yes. This is a delay corresponding to about 14% to 28% of the oscillation period (about 0.43 seconds), and satisfies the expression (3) of claim 1 .

(Contrast with claim 2 )
In the continuous casting under the conditions shown in FIG. 4, the coefficients of the equation (4) that define the relationship between the oscillation frequency f (cps) and the drawing speed V (mm / sec) are a = 0.137, b = 1.0 and c = 0, which satisfies the provisions of claim 2 .

Then, using this equation (4), the oscillation frequency f that changes in accordance with the short-term fluctuation of the drawing speed was calculated and reflected in the mold vibration control. As a result, molds average speed during descent (absolute value) is 20.0 mm / sec, mold average speed (absolute value) and 19.1 mm / sec ascent, withdrawal speed during descent is large, the second aspect Satisfies.

(Contrast with claim 4 )
The casting conditions in FIG. 4 satisfy the fourth aspect, in which the mold width is 800 mm, the mold thickness is 200 mm, and the value obtained by dividing the mold average width by the mold average thickness is 4.0.

(Comparison with conventional technology)
The maximum frictional force in the mold when cast under the conditions shown in FIG. 4 was calculated from the measured value of the oscillation hydraulic pressure. As a result, the conventional method which does not use the drawing speed and mold vibration control according to the present invention, that is, the short-term fluctuation of the drawing speed is small (Vd-max-Vu-min <0.03Uu) and the short-term drawing speed fluctuation is reduced. The maximum frictional force in the mold was reduced by 8% compared to the case of casting under conditions not reflected in mold vibration control (however, other conditions were the same).

  The present invention is not limited to the above example, and it goes without saying that the embodiment may be appropriately changed within the scope of the technical idea described in each claim.

  For example, in the above embodiment, the oscillation waveform is a sinusoidal waveform, but the oscillation waveform targeted by the present application is not limited to a sinusoidal waveform as long as the prescribed conditions of the claims are satisfied, and a non-sinusoidal waveform. But it ’s okay.

  In addition, although general PID (Proportional Integral Derivative) control is used as the correction in the present invention, it is not limited to this control method.

  The present invention can be applied not only to low carbon steel slabs as shown in the examples but also to continuous casting of medium carbon steel slabs and high carbon steel slabs.

It is a figure explaining (4) Formula of the invention which concerns on Claim 2 of this invention, (a) is a figure which showed transition of mold displacement, (b) is a figure which showed transition of mold speed, (c) is It is the figure which showed transition of the drawing speed of slab. It is a figure similar to FIG. 1 when the track record of the short period fluctuation of the drawing speed is not reflected in the oscillation waveform. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure explaining 1st Example of this invention, (a) is a figure which showed transition of mold displacement, (b) is a figure which showed transition of mold speed, (c) is drawing speed of slab drawing. It is the figure which showed transition. It is the same figure as FIG. 3 explaining the 2nd Example of this invention.

Claims (4)

In continuous casting where the slab is pulled out while oscillating the mold,
By increasing or decreasing the rotational speed of the drive motor that pulls the slab according to the pulling load, the pulling speed Vu when the mold is raised is smaller than the average pulling speed Va during one cycle of oscillation, and when the mold is lowered When controlling the drawing speed Vd to be large,
When the drawing speed Vu or Vd is varied in conjunction with the template oscillation in a period shorter than one cycle of oscillation,
The oscillation waveform of the oscillation is
When the average mold rising speed when the mold displacement is from the lowering limit to the rising limit and averaging the mold rising speed is | Uu |
The relationship between the minimum drawing speed Vu-min of the slab during the mold rising period, the maximum drawing speed Vd-max of the slab during the mold lowering period, and the average drawing speed Va during one oscillation cycle is expressed by the following equation (1): Satisfying the relationship of equation (2)
And,
The relationship between the time difference Δt when the mold lowering speed Ud becomes maximum and the slab reaches the maximum drawing speed Vd-max during the mold lowering period and the oscillation period (1 / f) is as follows ( 3) To satisfy the relationship of the formula,
A continuous casting method, wherein the oscillation condition of the mold is constant and does not change, and is controlled so as to increase or decrease the drawing speed corresponding to the load of the pinch roll.
0.03 | Uu | ≦ Vd-max−Vu-min ≦ 0.5 | Uu | (1)
Va−Vu−min ≦ Vd−max−Va (2)
0.05 × (1 / f) ≦ Δt ≦ 0.40 × (1 / f) (3)
In equations (1) and (2), the speed is positive in the slab drawing direction. As soon as the instantaneous value of the slab drawing speed V is recognized, the oscillation frequency f defined as a function of the drawing speed V is calculated by the following equation (4), and the calculation is performed in the mold lowering period and the mold rising period. Change to the oscillation frequency f waveform,
The casting speed Vu (absolute value) and the mold speed Uu (absolute value) in the mold rising period are both smaller than the drawing speed Vd (absolute value) and the mold speed Ud (absolute value) in the mold lowering period. 2. The continuous casting method according to claim 1, wherein control is performed to change the oscillation frequency f of the mold in accordance with the change of the drawing speed V of the piece .
f = a · | V | ^{b + c} (4)
a, b, and c are coefficients. However, a and b are positive real numbers, and the frequency f is always a positive real number in the drawing speed range applied to the operation. 3. The continuous casting method according to claim 1 , wherein, in a period longer than one period of oscillation, control is performed so that an average drawing speed Va during one period of oscillation matches a target value . 4. The continuous casting according to any one of claims 1 to 3, wherein a round cross section or a rectangular cross section mold having a value obtained by dividing a mold average width by a mold average thickness is 1.0 to 4.0 is used. Way .

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