JPS60261655A - Vibrating method of mold for continuous casting of steel - Google Patents

Abstract

PURPOSE:To prevent the generation of breakout and to obtain a billet having an excellent surface characteristic in the stage of oscillating a casting mold and drawing out the billet by controlling oscillation waveform and waveform distortion factor by numerical equations. CONSTITUTION:The billet is drawn at a high speed from the lower part of the casting mold while said mold is oscillated vertically at the non-sinusoidal waveform expressed by equation I in a manner as to satisfy the conditions expressed by equations II and III. In equations I and II, t: time, f: the oscillation frequency (cycle/min) of the non-sinusoidal waveform, a: the amplitude mm. of the non-sinusoidal waveform, lambda: the waveform distortion (0<lambda<1) of the non-sinusoidal waveform, Vc: the casting speed mm./min of the billet. In equation III, tnon-sin: the time when the displacement of the non-sinusoidal waveform in one cycle is max., tsin: the time when the displacement of the sinusoidal waveform (Z= asin2pift) in one cycle is max.

Description

[Detailed Description of the Invention] 2- [Technical Field of the Invention] The present invention relates to a method for vibrating a mold for continuous casting of steel.

[Prior art and its problems]

The continuous steel casting method will be briefly explained with reference to FIG. As shown in FIG. 5, the molten steel 2 in the ladle is injected into the tundish 4 via the air seal pipe 3. The molten steel 2 injected into the tundish 4 is continuously poured into a mold 6 through an immersion nozzle 5.
It will be done. When the molten steel 2 is poured into the mold 6, the molten steel 2 is cooled and a solidification shelf is formed on the inner surface of the mold 6.

The solidified shelf thus formed. is guided by guide rollers 8 and continuously pulled out from the lower part of mold 6 by pinch rolls 9. The unsolidified slab 7 pulled out from the mold 6 is cooled by cooling water from a spray nozzle (not shown), and is finally completely solidified. In this way, the slab 7 is continuously produced.

In the above-mentioned continuous steel casting method, the mold 6 is vibrated downward in order to prevent the solidified shell 7 from burning on the inner surface of the mold 6. additives) are added.

The reason why the addition of the powder can prevent the burning is that the molten powder slag flows between the inner surface of the mold 6 and the solidification shelf and acts as a lubricant.

However, as shown in FIG.
If the inflow of 'icL decreases for some reason, the seizure occurs and the upper part of the solidified shell 'icL breaks off, as shown in FIG. When a part of the solidification shelf 4 is broken in this way, the broken point A moves below the mold 6 as the slab 7 is pulled out.

The thickness of the solidified shell formed at the fracture point A is thinner than the thickness of the solidified shell in other parts, so the thickness of the solidified shell formed at the fracture point A
When the molten steel 2 in the unsolidified slab is pulled out of the mold 6 as the slab is pulled out, a so-called breakout occurs, in which the molten steel 2 in the unsolidified slab flows out of the slab.

Next, a conventional method of vibrating the mold 6 will be explained.

4- Conventionally, the mold 6 has been mechanically vibrated vertically so that its vibration waveform is a sine wave, and the amplitude and frequency of the mold 6 have been controlled by a negative strip (the descending speed of the mold 6 is equal to that of the slab 7). The time ratio NsR(t), expressed by the following formula, was set to be maintained within a range of 30 to 40%. If the time ratio N5R(t,) is maintained within this range, a compressive force is applied to the solidification shelf eL in the mold when the mold is lowered, making it difficult for the solidification shelf to break.

The time ratio N5R(t;) indicates the ratio of the negative strip time in one cycle of the mold 6.

However, Vc: slab drawing speed (ma/m1n), f:
@Frequency of mold vibration (cycles/m1n), a: Amplitude of mold (strike).

On the condition that the time ratio NSR (t,) is maintained within the above range, the slab drawing speed V is increased in order to increase production efficiency.
In order to increase c from 1 m/min to about 1.8 m/m ]-n, the vibration frequency f of the mold 6 and the shaking amplitude α are
It is necessary to increase it in accordance with the slab drawing speed Vc. Since it is technically difficult to change the amplitude a of the mold 6 during casting, the frequency f of the mold 6 is usually increased.

However, if the frequency f of the mold 6 is increased in this way,
Since the amount of powder slag flowing between the inner surface of the mold and the solidified shelf is reduced, the solidified shell 76 in the mold 6 is more likely to break.

Therefore, it is possible to lower the viscosity or softening point of the powder slag, but depending on the powder slag, the slab
surface quality deteriorates.

Therefore, when the slab 7 is pulled out at a high speed as described above, there is no need to increase the vibration frequency of the mold 7, and the desired powder slag can flow between the mold inner surface and the solidification shelf 4. Although a method of vibrating the mold 6 is desired that can apply a desired compressive force to the solidification shelf within the mold 66-, such a method has not been proposed at present.

[Purpose of the invention]

The purpose of this invention is to provide a mold vibration method that does not require increasing the vibration frequency of the mold when a slab is pulled out at high speed, and that can apply a desired compressive force to the solidified shell within the mold. It is about providing.

[Summary of the invention]

This invention provides a mold vibration method for continuous casting of steel, in which the mold is vibrated continuously in the vertical direction with a non-sinusoidal waveform represented by z=,Σ1Zpsin2πf,t...4A) so as to satisfy the following conditions. -・-1〉0...(B) ■-λ Vc; However, in the above formulas (A) and (B), t: time, f: frequency 7 of the non-sinusoidal waveform. - (cycle/m]n), a: amplitude of the non-sinusoidal waveform (-, m), λ: waveform distortion of the non-sinusoidal waveform (0×λ〈]), Vo: slab drawing speed (,,, /mjn), the waveform distortion λ is expressed by the following formula, where, in formula (C), tNon−sl. : Time at which the displacement of the non-sinusoidal waveform in 1 cycle reaches its maximum point, 'bsin : Sine waveform in 1 cycle (Z =
The time when the displacement of a sj, n2rft ) reaches its maximum is thus characterized in that it is possible to pull out the iron piece from the lower part of the mold at a high speed in kB.

[Structure of the invention]

As stated above, the inventors of the present application 'f! , from the perspective of slab
8- We have conducted various research in order to find a mold vibration method that does not require increasing the vibration frequency of the mold and can apply the desired compressive force to the solidified shell within the mold when drawing the mold at high speed. Ta. As a result, instead of making the vibration waveform of the mold a sinusoidal waveform as in the past, it was found that it is better to use a non-sinusoidal waveform that slows down the mold's rising speed and increases its descending speed.

This invention was made based on the above-mentioned knowledge. The present invention will be explained in detail below.

First, as shown in Figure 1, we calculate the waveform distortion expressed by the following formula as a value representing how much the time when the mold takes its maximum displacement within one cycle of vibration deviates from the sine waveform A. Define the rate λ.

However, jNon-sin: non-sinusoidal waveform (B in Figure 1)
The above time in the case of tsin: the above =91 time in case of a sine waveform, λ: 0〈λ×1゜The above sine waveform A is Z = asin2πft (however, a: amplitude (fin, [), f: Frequency (cycle/m1n
), t: time (sec)), and the non-sinusoidal waveform B is expressed as 2-Σα4 sin 2πr41 (however,
a amplitude (,,), f: L=1 frequency (cycle/n11n), t: time (sec)
).

When the mold is vibrated vertically so that the vibration waveform becomes a non-sinusoidal waveform, the average rising speed of the mold is Vup s n
If the average descending speed of the mold is 'i'down, then the following equation holds approximately.

(1+λ) Vup −(]−λ) “down '・
(3) As shown in Figure 1, if the frequency and amplitude of sinusoidal waveform A and non-sinusoidal waveform B are the same, the maximum displacement will be at the same position for both, so lO- Vup X jean -si. =a=44)V s 1
nX tB ln −α --(5) holds, and Vup X tNon-sin = Vsin X j
sjn'·(6).

Therefore, from equations (1) and (6), Vup×(1+λ) −V , n=−('i') holds, and from equations (3) and (7), the non-sine waveform distortion factor λ When the mold is vibrated in a waveform, the average rising speed up and average falling speed Vdown of the mold are:
The respective formulas are as follows.

However, f: frequency of vibration of the mold (cycle: /m1n), a:
Mold amplitude (+I+3).

The speed ratio of the negative strip when the mold is vibrated so as to have a non-vibration waveform, that is, when the mold is lowered, the average lowering speed of the mold Vdown is the slab withdrawal speed V
The ratio NsR between the speed faster than c and the slab drawing speed can be expressed as follows.

V'c...(10) Therefore, from equations (9) and (10), ■−λ　Vc holds true.

The inventors of the present invention conducted castings by varying the NSR, that is, by varying the vibration conditions of the mold, and measured the electrical discharge of the mold. As a result, it was found that when NSR becomes positive, that is, when it becomes , compressive force acts on the solidified shell in the mold.

For example, in FIG. 2(A), according to the method of the present invention, the frequency f
= 1.20 cpm, amplitude a-±3 Wa, velocity ratio of negative strip λ-o, 5. Slab drawing speed vc”1B, OOyg/ml, n, and negative strip speed ratio NSR=0.6
Figure (B) shows the results of mold weight variation when casting under the conditions of (A), except that λ was set to 0 and NSR was set to -0, 2. This shows the results of mold weight variations when casting with .

As is clear from FIGS. 2(A) and 2(B), according to the method (A) of the present invention, unlike the conventional method (B), it is possible to apply a desired compressive force to the solidified shell in the mold. Recognize .

Further, in equation (12), f is 52 (cycles/min) when the right side is 0.2, a is 10 boars, λ is 0.2, and VC is 1800 yB/min. on the other hand,
When λ is 0, that is, a sine waveform, and other conditions are the same, f is 43 (cycles/m1n). From this, according to the method of the present invention, under the same conditions, the mold is =1
3- The frequency f of the mold can be lowered compared to the case where the mold is vibrated in a sinusoidal waveform.

Next, the relationship between the NSR and the frequency of breakout occurrence was investigated when casting and producing by the method of the present invention and the conventional method. The results are shown in FIG.

As is clear from FIG. 3, when casting is performed while the mold is vibrated according to the method of the present invention, the frequency of occurrence of breakouts is significantly reduced compared to the conventional method. It can also be seen that as the value of λ increases, the frequency of breakout occurrence decreases.

Furthermore, the relationship between the negative strip time TN, the oscillation mark depth (see FIG. 1), and the depth of the oscillation mark was investigated when casting by the method of the present invention and the conventional method. The results are shown in FIG.

As is clear from FIG. 4, according to the method of the present invention, the depth of the oscillation mark can be made shallower than in the conventional method. That is, according to the present invention, a slab with excellent surface properties can be manufactured.

〔Effect of the invention〕

=14- According to the present invention, it is possible to produce a slab that is less likely to break out even when the slab is drawn at high speed and has excellent surface properties.

[Brief explanation of the drawing]

FIG. 1 is a graph showing vibration waveforms of molds according to the method of the present invention and the conventional method. FIG.
B) Figure is a graph showing the variation in weight of the mold when the mold is vibrated by the conventional method. Figure 3 is a graph showing the relationship between NR8 and breakout frequency. Figure 4 is the graph showing the relationship between NR8 and breakout frequency. Figure 4 is the negative strip time. FIG. 5 is a cross-sectional view schematically showing the continuous casting method, and FIG. 6 is a cross-sectional view showing the broken state of the solidified shell. In the drawings, ]... Ladle 2... Molten steel λ 5 Pa air seal pie 4... Tundish dip 5... Immersion nozzle 6... Mold 7... Slab 74... Solidification Shell 8...Guide roller 9/Pinch roll] 0...
Powder slag applicant Nippon Kukkan Co., Ltd. agent Natsuo Shioya (and 2 others) Figure 2 (A) Cloud 5R (B) Akira 4 Figure

Claims (1)

[Claims] In a method of vibrating a mold during continuous casting of steel, the @
The mold is vibrated continuously in the vertical direction with a non-sinusoidal waveform expressed by z=,ΣaLsin2πfzt-(A)n=1, so as to satisfy the following conditions, 4fcL] ” -1)O...( B) 1-λ Vc However, in the above formulas (A) and (B): t: time, f: frequency (cycles/min) of the non-sinusoidal waveform, -1'-a: amplitude of the non-sinusoidal waveform (-, m), λ: Waveform distortion of the non-sinusoidal waveform (0<λ<]), c: Slab drawing speed (to/mi'n), the waveform distortion λ is expressed by the following formula, sin However, in the above equation (C), jean-sjn', ] the time at which the displacement of the non-sinusoidal waveform in a cycle is maximum, jsin: the sine waveform in one cycle (Z =
A method for vibrating a mold for continuous casting of steel, characterized in that the time when the displacement of as1n2πft) is maximum.