JPS59189040A - Ulttasonic oscillating method of continuous casting mold - Google Patents

Abstract

PURPOSE:To prevent seizure between a material to be cast and a continuous casting mold by applying an ultrasonic oscillation of an adequate amplitude thereon in the direction perpendicular to the contact surface between the material to be cast and the casting mold. CONSTITUTION:An oscillator 7 is disposed in a thin walled part 1' formed to a continuous casting mold 1, and the point C opposite to the center of said oscillator is positioned slightly below the solidification limit at which the solidified shell 2' of a molten metal 4 is formed. The ultrasnoic oscillation forming a continuous amplitude distribution is applied on the metal 4 and the mold 1 in the direction perpendicular to the contact boundary surface between said metal and mold by said oscillator 7 in a way as to oscillate the same at the amplitude A satisfying the following inequality, A>(gh)<1/2>/2<1/2>pif+B, where g: the acceleration of gravity, h; the depth of the solidification limit, f; frequency, B; the bias constant to be empirically determined. The molten metal 4 is thus oscillated at the speed higher than the speed toward the surface of the mold 1 at the solidification limit, by which seizure is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION 0 A method for preventing disease and seizure of the molten material when continuously casting metal in a molten state has been known since ancient times. (Casting) Several meters parallel to direction 3
A so-called mechanical operation method is known in which vibration is caused at a frequency of about 10-20 (l cycles/minute).

On the other hand, recently, JP-A-54-86432 and JP-A-56-1
Methods such as No. 1149, in which a part of the mold is slightly vibrated at high frequency, and do not require a large-scale mechanical mechanism for oscillation, have been invented and have achieved certain effects.

However, sufficient analysis has not been conducted regarding the process conditions when causing slight vibrations, and the vibration conditions are determined by trial and error, and the amplitude distribution and amplitude value are not necessarily optimal. I wanted to.

The present invention realizes an optimal state when a part of the mold is slightly vibrated in a direction perpendicular to the contact interface, based on the behavior analysis results at the contact interface between the cast object and the mold, and has been developed through trial and error. This solution solves all the problems in one fell swoop.

First, the continuous metal casting process will be briefly explained with reference to FIG. After the molten metal 4 is press-fitted into the cooling mold 1 through the immersion nozzle 5, it is heated by the VJ mold 1 to form a solidified shell 2', and is further directly cooled by cooling spray water (not shown). and becomes slab 2. Slab 2
is pulled out in the direction of arrow 3 by a roll gang (not shown).

In addition, molten powder 6 is continuously introduced onto the liquid surface of the molten metal as a moisture 4t between the metal and the mold and as a heat transfer couplant, and this powder is continuously poured downward from the periphery where the mold and metal contact. Casting is carried out while flowing in the form of a film and covering the periphery of the slab. In this case, the molten powder 6 is drawn downward in synchronization with the mechanical on-line movement in the conventional method due to the viscosity between the mold 1 and the metal.

Therefore, the mechanism for preventing seizure between the metal mold and the mold in the conventional method is that even if a minute seizure occurs, it is torn off due to the lubrication by this molten powder and the relative speed between the metal and the mold in the mechanical casting direction. This is due to Koshichi.

On the other hand, the firing prevention mechanism of the metal mold according to the present invention is analyzed as follows, and will be explained below with reference to Figures 42 and 3.

FIG. 2(a) is a schematic enlarged view of the liquid level of the molten metal and the vicinity of the solidification start point when the present invention is applied to the process of FIG. 1. j is the mold and the part that vibrates]'
In order to make it easier to vibrate, the wall is partially made thin, and the vibrator 7 is disposed there.

FIG. 3 is a further abstraction of FIG. 2 (al) in order to explain the behavior of the contact surface between the molten metal and the mold in FIG. 2.

If the minute area ΔS of the vibrating thin-walled portion in FIG. 2 is considered as shown in FIG. 3, the pressure of the molten metal at ΔSK can be treated as an approximately uniform pressure P. The small area ΔS is A- perpendicular to the plane with the plane X as the center (position 0).
Assume that there is a parallel simple harmonic motion between A'. When the frequency of this vibration is f, the motion of ΔS is expressed by equation (1) when the amplitude is A, 4, y'= A sin
2πft (1) where y is the distance i1i between the plane X and ΔS at the time. Here, if the frequency f is sufficiently large, the molten metal can sufficiently follow the movement of ΔS, and a space is created between ΔS and the molten metal in terms of instantaneous IHj. This is a phenomenon called cavitation.

When the molten metal follows ΔS, the speed is
According to L. Bernoulli's theorem, Figure 3 (+))
By considering a flow tube like this, we get K as follows.

In other words, when the molten metal with pressure P and density ρ is suddenly released in a vacuum, the initial velocity is 2 P = 22 ~ ρ■... (2) Here, from the molten metal liquid level to ΔS Let h be the vertical depth of
Substituting 4) into equation (3) (V=JQg lower than /C...(5) Therefore, the molten metal is (
5) If the speed is above 2, it will not be possible to follow the vibration of ΔS, and seizure will not occur between the mold and the mold, or even if it occurs, it will be immediately shaken off.

Differentiating equation (1) to find the velocity of motion V' of ΔS, y'
2A-2πfcO52πft , -(6)(6
) maximum value V'+11aX is when CO32πft = 1 ■'maX=A・2πf −...(7
) As mentioned above, seizure will not occur with the opposing mold where the following speed of the molten metal is smaller than the moving speed of ΔS.

That is, v(v'maX, ,...
(8) By substituting equations (5) and (7) into equation (8), π2 h (2-A2f2 ・(9) By moving the amplitude A to the left side and rearranging, the following equation is obtained.

A > v”ii d/1/Tπf+B...(
10) Satisfying this (jω2) is the condition that the sintering f size with the molten metal in the mold will not occur.Here, as shown in Fig. 2 (
In the case of a 2+1 vibration device, f is constant, so it is practical to vary the amplitude A according to the depth hK. Based on this idea, we calculate the distribution of υ and swing rl from the liquid level M (h - 0) to the position of ΔS (h = s ) (Fig. 2fb) from equation (9). It becomes a parabola 8 like this. However, it is better to make the parabola 8 have an amplitude slightly larger than the limit by 5 degrees, so a slight bias B (sometimes positive and sometimes negative) can be set by experiment. It is best to add it to the parabola 8. The solidification start point in Fig. 2 (1) is the position on the slab, and the solidification start position limit in Fig. 2 (C1) is the depth h above the mold. C is the vibration point.

The optimal amplitude is given by the above, but in order to practically give a parabolic amplitude, as shown in Fig. 4 (al) (・τ
, vertical direction 7~L 7-2... are arranged in an array, and the amplitude of each is adjusted, as shown in Fig. 4+b). Envelope 8-2 is the second
One method is to obtain the optimum amplitude curve shown at 8 in the figure ())).

In addition to this, there is also a small oscillator in the width direction of the mold.
It is also extremely effective to arrange them in a box shape so that the IJ force direction has a uniform amplitude.

Furthermore, a method for economically providing an approximate optimum amplitude will be described below.

As shown in Fig. 2 (a), there is one vibrator in the vertical direction, and it is arranged so that the position C corresponding to the center of the vibrator is slightly below the solidification limit of the molten metal, and vibrates. If the dimensions of the portion 1' are set exactly at the wavelength of the heartbeat and are larger than twice the distance between the upper limit of the melting total flexion liquid level required for operation and the lower limit of the solidification position, as shown in Fig. 2 (b ) is close to X in Figure 2 (C
) can be realized.

Furthermore, as is clear from the equation (as is clear from the force), if either the amplitude or the frequency is given, the other will naturally be determined from the vibration speed of the mold.If the casting speed is very slow, the solidification limit depth h
is very small, so theoretically the frequency is extremely low,
The amplitude is also very small and may be sufficient. Therefore, it is convenient to first determine the frequency from the casting speed and heat removal conditions, and then determine the dimensions of the vibrating part shown in FIG. 1j' (this determines the vibration rlj distribution).

Furthermore, since the frequency must be changed somewhat due to changes in Young's modulus as the mold is heated by the object to be cast, it is convenient to make it variable within an appropriate range.

Further, according to this method, the solidified shell is caused by the static pressure of the melt to
Since the maximum speed of vibration of the casting bar (() is higher than the speed at which it tries to come into close contact with the J-shape, it is effective to reduce frictional resistance even in the case of operating conditions where solids↑S1≦ are in contact with each other. It is extremely effective.

As described above, according to the method of the present invention, an optimum vibration state can be achieved reliably and economically, and it is possible to prevent the casting object and the mold from collapsing.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of the continuous casting process, Fig. 2 is a schematic diagram of the case where the present invention is applied to the process of Fig.
Figure +i+ is a theoretical amplitude distribution diagram of the method of the present invention, Figure 2 fc) is an approximately optimal amplitude distribution diagram of the present invention, Figure 3 (
aL (bl is a schematic diagram of the behavior of the j-shaped object to be cast, the fourth
Figure ta+, (b) is a schematic diagram of the device of the present invention and an amplitude distribution diagram in that case. 1. Mold 2 Solidification shelf... vibrator Figure 3 (0) Figure 4 (0)

Claims (1)

[Claims] In a continuous casting mold that applies ultrasonic vibration in a direction perpendicular to the contact area between the casting object and the mold, a continuous amplitude distribution is created so that vibration [1) A satisfies the following formula. A method of ultrasonic vibration of a continuous casting mold, characterized by a forming grate. A>In7-1'iπf+B However, g: Acceleration of gravity h: Solidification limit depth f: Frequency B: Bias constant