JPH0819845A - Mold vibration method in continuous casting - Google Patents

Abstract

(57) [Summary] [Objective] By improving the vibration method of the mold in continuous casting, stable operation and good quality slab are obtained. [Structure] In continuous casting using a vertically vibrating mold, the vibration waveform applied to the mold has a steep waveform portion with a rising speed of 40 mm / s or more in the rising period.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to continuous casting of steel, and proposes a method of vibrating a mold which enables stable operation and obtains a slab of good quality. In continuous casting, mold lubricant (hereinafter simply referred to as powder) used from the viewpoint of stabilizing the operation, especially breakout, is amply supplied between the inner wall of the mold and the solidification shell, that is, powder above a certain value is consumed. It is important to say that technical development for this purpose is ongoing.

[0002]

2. Description of the Related Art Heretofore, as means for increasing powder consumption, a) optimization of powder physical properties. For example, decrease in viscosity η and freezing point temperature T _m . b) Optimization of mold vibration conditions. For example, "CAMP-ISIJ, Vol 5 (1992), p1221.
.About.1224 ", increase of positive strip time t _p (time range in which the descending speed of the mold is relatively slow with respect to the casting speed) and increase of the amplitude S. Etc. are known.

However, the conventional measures for increasing powder consumption have the following problems, and it is very difficult to select the optimum value.

Problems of Low Viscosity of Powder When the viscosity η becomes low, the probability that the powder on the molten metal surface will be entrained by the flow of molten steel becomes high, and as a result, internal defects including the surface and subepidermal skin occur due to the powder. Therefore, there is a limit to lowering the viscosity.

Lowering Freezing Point Temperature of Powder Reducing the freezing point temperature T _m reduces the thickness of the solid-phase powder film between the mold and the solidification shell, and reduces the heat transfer resistance. Therefore, the heat removal amount of the mold increases, and the risk of occurrence of slab surface cracks (longitudinal cracks, corner lateral cracks, etc.) increases.

Problems of Positive Strip Time and Increase in Amplitude under Mold Vibration Conditions Increasing the positive strip time T _p and amplitude S deepens the oscillation mark depth and causes surface defects (lateral cracks, powdery and inclusion defects). Etc.).

[0007]

SUMMARY OF THE INVENTION The present invention is intended to solve the above-mentioned problems advantageously, and an object thereof is to propose a preferable mold vibration method in continuous casting.

[0008]

According to the present invention, as a result of the inventors' detailed study of the relationship between the vibration condition of the mold and the powder consumption in continuous casting of steel, the powder is consumed in the rising period of the mold. That is, it was achieved by obtaining new knowledge that the consumption amount increases with an increase in the rising speed of the template.

That is, the gist of the present invention is as follows. In continuous casting in which a slab is drawn downward using a mold that oscillates in the vertical direction, the vibration waveform applied to the mold has a steep waveform portion with a rising speed of 40 mm / s or more during the rising period. It is a mold vibration method. Further, the rising portion of the vibration waveform applied to the mold has a steep stepped waveform portion. In addition, the reference vibration waveform applied to the mold in the section is a sine wave.

[0010]

The operation of the present invention will be described below. The present invention
When performing continuous casting by vibrating the mold vertically,
The essence is to rapidly increase the rising speed at any time point (one time point or more per cycle) within the rising period of the vibration waveform of the mold, thereby increasing the powder consumption amount. This allows for more stable continuous casting operations.

Further, an example of the vibration waveform of the basic mold of the present invention will be described with reference to FIGS. 1 (a) and 1 (b). FIG. 1 (a) is a graph showing the relationship between the displacement of a mold and time which are suitable for the present invention, and FIG. 2 (b) is a graph showing the relationship between the displacement speed of the mold and time. These Figure 1
In (a) and (b), the displacement waveform of the mold is a sine wave and the displacement speed of the mold is rapidly increased at points A and B, which are rising, and the displacement waveform is stepped at points A and B. It becomes a waveform part.

Next, the reason why the powder consumption increases by applying such vibration to the mold will be described.

Conventionally, it is considered that the molten powder flows from the meniscus portion between the mold and the solidification shell so as to be dragged by the mold during the downward movement of the mold, and flows backward from the mold-solidification shell to the meniscus portion during the rising phase. It was thought that the powder consumption amount would be the amount obtained by subtracting the reverse flow rate to the meniscus portion during the rising period from the inflow amount between the mold and the solidified shell during the mold lowering period.

However, as a result of various experiments conducted by the inventors, the following new finding, which is completely different from the above, was obtained.

That is, the powder adheres to the inner wall of the mold. Then, the solid phase powder thus adhered becomes thicker toward the lower part of the mold. On the other hand, the solidification shell of the molten metal supplied to the mold becomes thicker as it goes downward, and the amount of shrinkage increases as it goes down due to thermal shrinkage. Therefore, the passage of the liquid phase powder film between the mold and the solidification shell (hereinafter simply referred to as the passage) is not parallel to the vibration direction of the mold but is inclined.

Therefore, in the mold descending period, the passage width becomes wider and the liquid-phase powder film becomes thicker to generate a negative pressure, and the negative pressure causes the powder in the meniscus portion to flow into the passage so that the powder is sucked into the passage, and at the lower end of the mold. In, the powder does not flow out, but rather sucks the liquid-phase powder adhering to the surface of the solidified shell into the passage.

In the rising stage of the mold, on the contrary, the passage width becomes narrower and the liquid phase powder film becomes thinner, so that the internal pressure P rises and the liquid phase powder in the passage is pushed out, so that the meniscus portion above the mold is pushed out. It was found that the water flows back to the outside from the lower end of the mold while flowing back to the outside.

Here, the above-mentioned conventional idea and the mechanism of the inflow and outflow of the liquid phase powder between the mold and the solidification shell at the time of vibration of the mold according to the knowledge of the present invention are explained.
This will be described in more detail. In FIG. 2, 1 is a mold, 2 is a molten metal, 3 is a solidification shell, 4 is a liquid phase powder, 5
Is a solid phase powder fixed to the mold 1.

In this figure, the conventional idea is that as the mold 1 descends, the liquid phase powder 4 moves between the mold 1 and the solidification shell 3 as shown in arrows a and b in the meniscus portion as the mold 1 descends. From the lower end of the mold 1 to the outside, and as the mold 1 rises during the ascending phase of the mold 1, the liquid phase powder 4 flows from between the mold 1 and the solidification shell 3 as shown by arrows c and d. At the lower end of the mold 1, it flows from the outside into the space between the mold 1 and the solidification shell 3 while flowing back to the part.

On the other hand, according to the findings of the present invention, since the interval D (passage width) between the solid phase powder 5 and the solidification shell 3 is widened during the descending period of the mold 1, the liquid phase powder 4 is contained in this passage. As indicated by arrows e and f, it flows in from the meniscus portion and the lower end of the mold 1, and during the rising period of the mold 1, the interval D, that is, the width of the passage is narrowed and the pressure P of the liquid phase powder 4 in the passage is decreased.
Therefore, the liquid powder in the passage 4 flows back to the meniscus portion as shown by arrows g and h, and flows out from the lower end of the mold 1 to the outside.

Therefore, in the present invention based on the above-mentioned findings, the inflow amount of the liquid phase powder from the outside at the lower end of the mold in the mold lowering period is subtracted from the outflow amount of the liquid phase powder from the lower end of the mold in the rising period of the mold to the outside. The amount of powder becomes almost powder consumption, and the increase of this powder consumption increases the pressure P of the liquid powder in the passage in the mold rising period to increase the outflow amount of the liquid powder from the lower end of the mold. Can be achieved by increasing the rate of rise of the.

In order to increase the powder consumption in this case, the mold ascending speed should be 40 mm / s during the mold ascending period.
It is effective to give the abrupt change as described above, and it is preferable to give the abrupt velocity change so that the rising portion of the vibration waveform of the mold has a steep stepped waveform portion. In addition, the vibration waveform of the mold at that time may be a sine wave that is commonly used.

[0023]

EXAMPLE A continuous casting machine having a mold equipped with an electro-hydraulic actuator driven short lever type mold vibration wave control type oscillation device was used to obtain a cross-sectional size of 110.
mm × 400 mm low carbon steel (JIS G 3141, SPCC) slab is cast, and at the time of casting, a vibration waveform conforming to the present invention and a conventional vibration waveform (sine wave) are applied to the mold to cause vibration. The powder consumption (usage per unit slab area ---- Kg / m ² ) was measured.

In the above, the casting speed Vc was 0.8 m / mi
n, mold frequency f is 2.5 Hz, total amplitude So is 2, 4
And 3 mm of 8 mm. The vibration waveform applied to the mold conforming to the present invention is shown in FIGS. 3 (a) and 3 (b).
Based on this, it will be described below. 3 (a) and 3 (b),
FIG. 3 (a) is an explanatory view of a mold vibration waveform of the adaptation example of the present invention used in the embodiment, and FIG. Explanatory drawing, FIG.3 (b) is explanatory drawing of the vibration waveform which has one step-shaped waveform part of a steep slope in the rising period per 1 cycle of a sine wave. The reference waveform is not limited to the sine wave.

That is, one of the vibration waveforms according to the present invention which is applied to the mold is the waveform shown in FIG.
S is 0.25 So, steep climb speed is 20, 30, 40, 60,
80, 100 mm / s, and the other one is the waveform shown in FIG. 3 (b), where the total amplitude So is 2 mm and the step amplitude ΔS is
0.25 So, the rising speed of the steep slope was 50 mm / s. Here, the method of changing the rising speed was performed by changing the rising time.

The results of these measurements are shown in FIGS. FIG. 4 is a graph showing the relationship between the rising speed of the steep part of the waveform and the powder consumption amount.
It is clear that the consumption increases sharply at 40 mm / sec or more.
FIG. 5 is a graph showing the relationship between the total amplitude (So) of the mold and the powder consumption. The conformity example in the figure is the data of the steep ascent rate of 40 to 100 mm / sec.

As is apparent from FIG. 5, when the ascending speed of the steep slope is set to 40 mm / sec or more, the vibration waveform of the mold is sine wave as compared with the conventional example, and the powder consumption of the conforming example of the present invention is smaller than that of the conventional example. You can see that it is increasing. The same effect was obtained when the vibration waveform of the mold was not a sine wave.

[0028]

INDUSTRIAL APPLICABILITY According to the present invention, in continuous casting using a vertically vibrating mold, the vibration waveform applied to the mold is
In the ascending period, the ascending speed has a steep corrugated portion of 40 mm / s or more. According to the present invention, the powder consumption amount for performing good continuous casting is increased as in the conventional case. As a means, there is no need to increase the amplitude when oscillating the mold, the positive strip time, the decrease of the powder viscosity and the solidification temperature, etc., so it is caused by the slab surface defect due to the increase of the oscillation mark depth and the powder entrainment. Slabs with excellent quality can be stably cast without causing problems such as subcutaneous and internal defects of slabs, surface cracks of slabs, and the like.

[Brief description of drawings]

FIG. 1 (a) is a graph showing the relationship between the displacement of a mold suitable for the present invention and time. (B) is a graph showing the relationship between the displacement speed and time of the mold suitable for the present invention.

FIG. 2 is an explanatory view showing a conventional idea and a mechanism of inflow and outflow of liquid phase powder between a mold and a solidification shell during vibration of the mold according to the knowledge of the present invention.

FIG. 3 is an explanatory diagram of a mold vibration waveform of a conforming example of the present invention used in an embodiment. (A) is an explanatory view of a vibration waveform having two steep stepped waveform portions in a rising period per cycle of a sine wave. (B) is sine wave 1
It is explanatory drawing of the vibration waveform which has one step-shaped waveform part of a steep slope in the rising period per cycle.

FIG. 4 is a graph showing a relationship between a rising speed of a steep portion of a waveform and a powder consumption amount.

FIG. 5 is a graph showing the relationship between the total amplitude (So) of the mold and the powder consumption.

[Explanation of symbols]

 1 Mold 2 Molten Metal 3 Solidifying Shell 4 Liquid Phase Powder 5 Solid Phase Powder

Claims (3)

[Claims] 1. In continuous casting in which a slab is drawn downward using a vertically oscillating mold, the vibration waveform applied to the mold has a rising speed during the rising period.
A mold vibration method having a steep corrugated portion of 40 mm / s or more. 2. A continuous casting mold in which a vertically oscillating mold is used to draw a slab downward, and a steep step-like corrugated portion is provided in a rising portion of a vibration waveform applied to the mold. Vibration method. 3. The method for vibrating a mold in continuous casting according to claim 2, wherein the reference vibration waveform applied to the mold is a sine wave.