JPS6123559A - Oscillating method of mold for continuous casting of steel - Google Patents

Abstract

PURPOSE:To apply desired compressive force to the solidified shell in a casting drawing speed changes without the need for increasing an oscillation frequency in the stage of drawing a billet at a high speed by specifying an oscillation waveform and the time ratio of a negative strip and determining the oscillation frequency or amplitude by the specific equation according to the drawing speed of the ingot. CONSTITUTION:The casting mold is so vertically oscillated that the oscillation waveform attains the non-sinusoidal waveform having the waveform distortion factor lambda of equation I. Here, tNon-Sin: the displacement when theabove-described non-sinusoidal waveform in one cycle of the oscillation in the above-described casting [Z=SIGMAi1<n>aiSin2pifit, a: the amplitude (mm.), f: the oscillation frequency (cycle/min), t: time (sec)] is max., tsin: the sinusoidal waveform in the above- mentioned one cycle (Z=asin2pift), 0<lambda<1. The mold is so oscillated that the time ratio NSR(t) of the negative strip in one cycle attains <=25%. The oscillation frequency (f) or amplitude (a) of the mold is calculated according to the drawing speed Vc of the ingot by equation II. Here betaNon-Sin: the constant determined by the distortion factor lambda and the ratio NSR(t).

Description

DETAILED DESCRIPTION OF THE INVENTION [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. 8, the molten steel 2 in the ladle 1 is injected into the tundish 4 via the air seal pipe 3. The molten steel 2 injected into the tundish 4 is continuously cast into a mold 6 through a submerged nozzle 5. When the molten steel 2 is poured into the mold 6, the molten steel 2 is cooled and a solidified 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, slabs 7 are continuously produced.

In the continuous steel casting method described above, powder (mold additive) is added into the mold 6 while the mold 6 is vibrated in the vertical direction in order to prevent the solidified shelf 4 from seizing on the inner surface of the mold 6. ing.

The reason why the seizure can be prevented by adding the powder is that the molten powder slag flows between the inner surface of the mold 6 and the solidification shelf 4, and acts as a layer of lubricant.

However, as shown in FIG.
If the inflow of the solidification shelf 1 is reduced for some reason, the seizure occurs and the upper part of the solidification shelf 1 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
A phenomenon in which the molten steel 2 in the unsolidified slab flows out of the slab when it is pulled out of the mold 6 as the slab is pulled out, the so-called phenomenon.
A breakout occurs.

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

Conventionally, the mold 6 is mechanically vibrated vertically so that its vibration waveform is a sine wave, and the amplitude and frequency of the mold 6 are set to the negative strip (in one cycle of vibration of the mold 6, The time ratio NS in which the descending speed is greater than the drawing speed of the slab 7) is expressed by the following formula.
Each was set so that R(t) was maintained within a range of 30 to 40 inches. Within this range, the time ratio NSR (t
), the solidification shelf inside the mold when the mold is lowered,
A compressive force is applied to L, making it difficult for the solidified shelf to break.

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

However, vc: slab drawing speed (f/min), f
: Mold vibration frequency (cycles/m1n), a : Mold amplitude (-a).

In order to increase the slab drawing speed Vc from 1 m/min to about 1.8 m/min in order to increase manufacturing efficiency, it is necessary to maintain the time ratio N5R (t,) within the above range. 6 vibration frequency f or mold 6 amplitude α
It is necessary to increase it in accordance with the slab drawing process Vc. Since it is technically difficult to change the amplitude σ of the mold 6 during casting, the vibration 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 shelf 4 in the mold 6 is more likely to break.

Therefore, it is possible to use powder slag with low viscosity or softening point, but depending on the powder slag, the surface quality of the slab 7 may deteriorate.

Therefore, when drawing the slab 7 at a high speed as described above, there is no need to increase the vibration frequency of the mold 7, and for this purpose, the desired powder slag is allowed to flow between the mold inner surface and the solidification shelf 4. What is desired is a method of vibrating the mold 6 that is capable of applying a desired compressive force to the solidification shelf within the mold 6 even when the slab drawing speed changes.
No such method has been proposed at present.

[Purpose of the invention]

The purpose of this invention is to eliminate the need to increase the vibration frequency of the mold when drawing slabs at high speed, and to apply a desired compressive force to the solidified shell in the mold even when the slab drawing speed changes17. It is an object of the present invention to provide a method for vibrating a mold for continuous casting of steel, which can be used for continuous casting of steel.

It is vibrated upward and downward to form a non-sinusoidal waveform having a shape distortion factor λ, where tNon-8in: the non-sinusoidal waveform in one cycle of the vibration of the casting; 2πf, t, a: amplitude (藺), f , frequency (cycles/m1n), t: time when the displacement of y time (sea) is maximum, t8in: sine waveform in the 1 cycle (z = α5in 2πft, α: amplitude (to), f: frequency (successful in) + t: time (sec)).

λ: 0〈λ×1 and negatives expressed by the following formula in one cycle) l) The time ratio N5R(t) of the whelk is 25
% or less, the mold is vibrated in the vertical direction, where vc: slab withdrawal speed (,/n1n), f
: Frequency (cycle/m1n), a : Shaking (fighting)
, According to the slab drawing speed Vc, calculate the vibration frequency f of the mold or the amplitude α of the mold according to the following formula, f°α2βNon-Bid' vc where βNon-81n: the waveform distortion rate λ and the above-mentioned A constant determined by the time ratio N5R(t,), and is thus characterized in that it makes it possible to pull out the slab from the lower part of the mold at a high speed.

[Structure of the invention]

From the above-mentioned viewpoints, the inventors of the present application have discovered that there is no need to increase the vibration frequency of the mold when the slab is pulled out at high speed, and that solidification within the mold does not occur even if the slab drawing speed changes. Various studies were conducted to find a method of vibration of the mold that could apply the desired compressive force to the shell. As a result, instead of making the vibration waveform of the mold a sinusoidal waveform as in the past, the rising speed of the mold can be made slower than the descending speed of the mold, and the rising time of the mold can be made slower than the descending speed of the mold. If the mold is vibrated to create a non-sinusoidal waveform that can be taken for a long time compared to the time, it is not necessary to increase the vibration frequency of the mold when drawing slabs at high speed, and it is possible to reduce the speed of pulling slabs. It was discovered that it is possible to apply a desired compressive force to the solidified shell in the mold even if the

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

First, the non-sinusoidal waveform in this invention will be explained.

As shown in Figure 1, in one cycle of vibration of the mold, the time at which the displacement of the mold reaches its maximum deviates from the sine waveform A by using the waveform expressed by the following formula. Define the distortion factor λ.

However, tNon-8in: the above-mentioned time in the case of a non-sinusoidal waveform (B in Fig. 1), La1n: the above-mentioned time in the case of a sine waveform, λ: λ<10. However, α
: amplitude (U), f: frequency (cycle/m1n), t:
time (sea)), and the non-sinusoidal waveform B is Z
-Σα,,8in2πtit, (where α: amplitude (m
s ), f frequency (cycles/m1n), 1: time (
sec))).

Next, by changing the waveform distortion factor λ of the non-sinusoidal waveform, the relationship between the negative strip time ratio N5R(t) and ΔFdown expressed by the above equation (1) at that time, and the casting under these conditions. The waveform distortion rate λ=0. That is, FIG. 2 shows the results when the mold is vibrated so that the vibration waveform of the mold becomes a sine wave.

The above Δ-Fdown is the load □ 1.2□, 1□ applied to the mold when the mold is lowered. □732. This is the compressive force caused by

As is clear from Fig. 2, when the value of ΔFdown is 130 kg or more, compressive force is always applied to the solidified shell in the mold, so breakout does not occur and the slab surface It can be seen that the results are also good.

Furthermore, it can be seen that when the value of ΔFdown is set to a constant value, the time ratio NSR(t) of the negative strip can be made smaller in the case of a non-sinusoidal waveform than in the case of a sine waveform.

This is because if the mold is vibrated so that its vibration waveform is a non-sinusoidal waveform, the frequency of the mold can be reduced, and as a result, the amount of powder slag flowing in can be increased, and This means that the vibrating mechanical system can also be made smaller. The time ratio NSR (t,
) was found to be 25%.

The range of the waveform distortion factor λ is, as described above, λ〈〈〉, but as is clear from FIG. 3, if λ is set to 02 or more, the breakout occurrence rate becomes smaller.

As mentioned above, when the mold is vibrated so that its vibration waveform is a non-sinusoidal waveform, even if the slab drawing speed changes, the negative strip time ratio NSR (
A method for maintaining 'z) at a predetermined value of 25 inches or less will be described.

When the mold is vibrated so that its vibration waveform becomes a sine waveform m, the product of the mold vibration frequency f and the mold amplitude α in the above equation (1) is expressed by the following equation.

f-α=β81n'"C"' (3) However, β5i
in: Coefficient (-1/2πcos) that is uniquely determined when NSR(t) is a constant value On the other hand, in the case of a non-sinusoidal waveform, almost the same relationship as in the above-mentioned sine waveform holds true.For example, the waveform distortion factor λ
For a non-sinusoidal waveform in which is 032, the relationship between the mold frequency f and slab withdrawal speed Vc when the negative strip time ratio NSR (tJ is 20 inches) was investigated using the mold amplitude α as a parameter. The results are shown in Fig. 4.As is clear from Fig. 4, the mold frequency f and the slab drawing speed ■c have a linear relationship passing through the origin.

Next, assuming the slope of the straight line to be α, the relationship between the slope α and the reciprocal l/a of the amplitude α of the mold was investigated. The results are shown in FIG. As is clear from FIG. 5, since the slope α and the 1/a have a nearly linear relationship, the equation (3) holds true even for non-sinusoidal waveforms, and the coefficient βBin in the equation (3) is It was also found that it depends on the type of vibration waveform of the mold, that is, the waveform distortion rate λ.

Therefore, in a non-sinusoidal waveform, if the product of the mold frequency f and the mold amplitude α is expressed in the same form as in equation (3),
It becomes as follows.

f・α=βNon-8in'vc" (4) However, βNon-8in: a coefficient determined by the waveform distortion rate λ and the negative strip time ratio N5R (1).

Next, the coefficient βNon-8in is determined from various wave distortion rates λ and the negative strip time ratio N5R(t,).
was determined, and the relationship between the coefficient βNon-51n and the waveform distortion rate λ was investigated using the time ratio N5R(t) as a parameter.

The results are shown in FIG.

In this way, the negative strip time ratio NS
The waveform distortion rate λ and the coefficient β with R(t) as a parameter
Once the relationship with Non-8in is determined, from FIG.
seek. In this way, the coefficient βNon-8in
Once obtained, the coefficient βNon− is added to the equation (4) above.
8in% The mold vibration frequency f or mold amplitude α is calculated by substituting the mold vibration frequency f or mold amplitude α and the slab withdrawal speed vc at that time. Like this KL
,-C41;i. □58. Eh, yo. □ )a
Based on this, if the mold is vibrated, even if the slab withdrawal speed Vc changes, the negative strip time ratio NSR (
t) can be maintained at a predetermined value of 25% or less. Note that normally, the vibration frequency f of the mold is calculated by substituting the amplitude α of the mold before the slab drawing speed changes into the above equation (4).

The time when casting was performed while vibrating the mold under the conditions of waveform distortion rate λ-027, negative strip time ratio NSR (t, ) = 15 cm, and amplitude α = 30 cm, the mold vibration frequency f, and the casting time. An example of changing the single pull-out speed vc is shown in the seventh
As shown in the figure.

〔Effect of the invention〕

As explained above, according to the present invention, even if the slab drawing speed changes, a desired compressive force can always be applied to the solidified shell in the mold, and when the compressive force is kept constant. , the negative strip time ratio N5B(t
, ) can be made smaller than in the case of a sinusoidal waveform, so the vibration frequency of the mold can be made small. Therefore, powder slag can be sufficiently flowed between the solidified shell and the mold, so even when the slab is pulled out from the mold at high speed, breakout does not occur, and the slab with excellent surface quality can be obtained. Can be cast.

[Brief explanation of drawings]

FIG. 1 is a graph showing vibration waveforms of molds according to the present invention and the conventional method, and FIG. 2 is a graph showing N5R(t) and ΔFdo.
FIG. 3 is a graph showing the relationship between λ'' and breakout occurrence rate. FIG. 4 is a graph showing the relationship between VC and f with a as a parameter.
The figure is a graph showing the relationship between 1/α and α, and Figure 6 is a graph showing the relationship between 1/α and α.
λ and βNon-8in with 5R(t) as a parameter
FIG. 7 is a graph showing the relationship between time and Vc and f. FIG. 8 is a sectional view showing an outline of the continuous casting method. FIG. 9 is a graph showing the cause of breakout. FIG. In the drawing, l... Ladle 2... Molten steel 3... Air seal pie 4... Tundip 7 Up 5... Immersion nozzle 6... Mold 7... Slab 7°. ...Coagulation soil 8...Guide roller 9...Vinch roll 10...Powder slag

Claims (1)

[Claims] The mold has a vibration waveform having a waveform distortion factor λ expressed by the following formula.
It is vibrated in the vertical direction so as to have a non-sinusoidal waveform with λ=(t_N_o_n_−_S_i_n−t_S_i_
n)/t_S_i_nHowever, t_N_o_n_-_S_
i_n: the non-sinusoidal waveform in one cycle of vibration of the casting (Z=Σ^n_i_=_1a_iSin2πf
_it, a: amplitude (mm) f: frequency (cycle/min), t: time (sec)) maximum displacement, t_S_i_n: sine waveform in the above one cycle (Z=aSin2π ft, a: amplitude (mm), f: vibration frequency (cycles/min), t: time (sec)), λ: 0<λ<1, and the time ratio NSR (t ) is 25% or less, the mold is vibrated in the vertical direction, and NSR(t)={1-(1/π)cos^-^1(-(
V_c)/(2πfa))}×100(%) However, V_
c: Slab drawing speed (mm/min), f: Vibration frequency (cycles/min), a: Amplitude (mm), According to the slab drawing speed V_c, the vibration frequency f of the mold according to the following formula. Or calculate the amplitude a of the mold, f・a=β_N_o_n_−_S_i_n·V_c, where β_N_o_n_−_S_i_n: a constant determined by the waveform distortion rate λ and the time ratio NSR(t). A method for vibrating a mold for continuous casting of steel, characterized in that it is possible to withdraw from the lower part of the mold at high speed.