JPH0325262B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of exciting a mold with ultrasonic waves in continuous metal casting.

[Prior Art] In continuous metal casting, a large number of ultrasonic transducers (ultrasonic transducers are abbreviated as transducers in this specification) are arranged in a mold in order to vibrate the inner wall of the mold near the meniscus of molten metal. The technology to provide this is well known, as described in, for example, Japanese Patent Laid-Open No. 62-57742. FIG. 1 is a diagram showing an example of a cross section near the meniscus of a continuous casting mold in which vibrators 1 to 12 are arranged. The inner wall of the mold 13 is vibrated by the vibrations of the vibrators 1 to 12. For example, in order to prevent the inner wall surface of the mold from seizing or states-king between the inner wall surface of the mold and the molten metal 14, the inner wall of the mold must be vibrated in all areas near the meniscus. It is necessary that the wall surface of the machine is always maintained at the desired vibration level. Generally, each of the vibrators 1 to 12 has the same vibration characteristics, but in the conventional method, since the frequencies of the vibrators 1 to 12 were the same,
For example, in Fig. 2, if the ultrasonic waves emitted from transducer A and the ultrasonic waves emitted from transducer B interfere and the phases of both ultrasonic waves are the same, the inner wall of the mold at a distance of AP ₁ = BP ₁ . At _point P, the amplitude doubles and it vibrates violently, but AP ₂ - BP ₂ = λ/2 (where λ = wavelength of the ultrasonic wave)
At point _P2 , the ultrasonic waves from the transducers A and B are interfered with and the amplitude is always extremely small, resulting in seizure, statesking, etc.

[Problems to be Solved by the Invention] Even in a continuous casting mold in which a large number of oscillators with the same vibration characteristics are arranged, the present invention adjusts the interference of ultrasonic waves emitted from each oscillator, and improves the mold quality. The objective is to provide a vibration method that constantly applies desired vibrations to all wall surfaces near the meniscus of the inner wall.

[Means for Solving the Problems] The present invention has the following features: (1) In a continuous casting mold in which a plurality of vibrators having the same vibration characteristics are arranged, the difference in the excitation frequency of each vibrator is maintained within a range of 2 KHz. , and is a method of exciting an ultrasonic vibration mold for continuous casting, which is characterized by changing the excitation frequency of adjacent vibrators and excitation, and (2) changing the excitation frequency of adjacent vibrators. The method of excitation is to change the excitation frequency of each other vibrator placed on one side or both sides of the reference vibrator from the reference vibrator to the vibrator with the maximum excitation frequency (reference vibrator). The method described in (1) above is a method in which the distance is set to gradually decrease as the distance increases.
This is a method of excitation of an ultrasonic mold for continuous casting.

[Operations and Examples] The present invention relates to a mold for continuous casting in which a plurality of vibrators having the same vibration characteristics are arranged. As illustrated in Fig. 1, an ultrasonic vibration mold is equipped with a large number of, for example, electrostrictive vibrators, but it is better for each vibrator to have the same vibration characteristics for better compatibility and to reduce equipment costs. Furthermore, it becomes easy to design the mold vibration pattern by simulation or the like.

In the present invention, each vibrator emits ultrasonic waves with different excitation frequencies. FIG. 3 is a diagram showing an example of frequency-amplitude characteristics of one vibrator. The frequency of each vibrator can be changed using a frequency setting device, but for the frequency f ₀ that gives the maximum amplitude,
When the frequency is set below (f ₀ −1) KHz or above (fo+1) KHz, the amplitude of the ultrasonic wave emitted by the transducer suddenly decreases, as shown in Figure 3.
As a result, the combined amplitude of the ultrasonic waves emitted by each vibrator also decreases significantly. Therefore, it is desirable to keep the amplitude of each vibrator in the range of A ₁ × 70% from the maximum amplitude A ₁ , and the frequency adjustment range to obtain this amplitude is from (fo-1) KHz to ( fo+1)
KHz to 2KHz range. In the present invention, each vibrator is set to have a different frequency between (fo-1) KHz and (fo+1) KHz, so the difference in frequency between the vibrators is within 2 KHz.

In the present invention, adjacent vibrators are vibrated by changing their excitation frequencies. For example, in Figure 2, if the frequency of the ultrasonic waves emitted from transducer A is the same as the frequency of the ultrasonic waves emitted from transducer B, the amplitudes will always be superimposed at point _P1 due to interference, as described above. Double.
Figure 4 A illustrates this state, and the dotted line is
The figure shows the ultrasonic wave emitted from the transducer A at point _P1 , the chain line shows the ultrasonic wave from the transducer B, and the solid line shows the vibration that is a combination of both. Also, at point _P2 , as mentioned above, the vibrations from A and the vibrations from B cancel each other out, resulting in a composite vibration with a constant small amplitude. FIG. 4B illustrates this state.

For example, when the frequency of transducer A is increased, the relative phase of the ultrasonic waves from A and B changes moment by moment, so the vibrations do not always overlap at point _P1 . Figures 4(c) and 4(d) show this state. or
Similarly, at the _P2 point, the vibrations are not always canceled out, and a combined vibration with the same amplitude as the _P1 point is obtained. Above we have explained an example in which there are two oscillators, but for example, when m oscillators with the same frequency are arranged as shown in Figure 5A, the combined amplitude is calculated by the following formula.
It is indicated by A ₀ .

Ao＝ΣAncos {ω(t −|ln−x|／ν)e ^-an( | ^ln−x | ⁾ ...(1) An: Amplitude coefficient due to difference in position when each vibrator has the same power, ω: 2πf( However, f: excitation frequency Hz),
t: Vibration elapsed time (sec), ln: Distance between the No. 1 transducer and each transducer, x: Vibration position with the No. 1 transducer position as the origin, ν: Sound wave propagation speed of the mold, an: Amplitude of each transducer The reduction coefficient when propagating to other parts.

This composite amplitude is expressed as shown in FIG. 5B with respect to the position χ of the mold, indicating that a region where the composite amplitude is always low is generated in some parts.

However, in this case as well, by changing the frequencies of the adjacent vibrators, the amplitude distribution at each position on the inner surface of the mold can be flattened, as shown in FIG.

In the present invention, the maximum frequency difference between the vibrators is 2 KHz as described above, but the minimum is 0.01 KHz, and below this, the effect is small.

In addition, in the present invention, when excitation is performed by changing the excitation frequency of adjacent vibrators, the vibrator (reference vibrator) with the maximum excitation frequency is placed on one side or both sides of the reference vibrator. If the excitation frequency of each of the other oscillators is set to gradually decrease as it moves away from the reference oscillator, the amplitude distribution of the beat wave will progress directionally with elapsed time, so there will be no periodicity at any position on the mold. Therefore, it is possible to provide a uniform and preferable amplitude distribution.

FIG. 6 is a diagram showing a model of the frequency of each vibrator. For example, FIG. 6A shows an example in which the frequencies of each of the vibrators 3, 4, 5, and 6 in FIG. 1 are randomly changed and set. Figure 6(b) is an example in which the oscillator 3 is used as the reference oscillator, and the excitation frequencies of the 4th, 5th, and 6th oscillators are set to become smaller as they move away from the reference oscillator 3. This is an example in which the vibrator 4 is used as a reference vibrator and the excitation frequency of the earth vibrator is similarly set to decrease sequentially. Figure E shows a similar example in which the vibrator 6 is used as a reference vibrator. In Figure 6 A, since the amplitude distribution of the beat wave does not proceed in one direction,
The effect is smaller than in the case of B, C, D, and E, which progress in a direction.

[Effects of the Invention] Since the present invention is a method of using a large number of vibrators with the same characteristics, vibration control is easy and equipment costs can be reduced. According to the present invention, there is always no part of the ultrasonic vibrating mold where the vibration is small, and the vibration of each part of the ultrasonic vibrating mold is made uniform and the amplitude is increased. Therefore, seizure of the molten metal and the inner wall of the mold is eliminated, breakout accidents can be prevented, and the quality of the slab surface is improved, making scratch removal and surface maintenance easier or unnecessary.
Yield and efficiency are greatly improved.

[Brief explanation of the drawing]

Figure 1 is a diagram showing an example of a cross section of a vibrating mold for continuous casting in which a large number of vibrators are arranged, and Figure 2 is a diagram showing the interference of ultrasonic waves emitted from two vibrators on the inner wall surface of the mold. Figure 3 is a diagram showing the relationship between frequency and amplitude of individual oscillators, Figure 4 is a diagram showing an example of the combined vibration in Figure 2, and Figure 5 is a diagram showing the relationship between the frequency and amplitude of each vibrator. FIG. 6 is a diagram showing the amplitude, and is a diagram showing an example of a model of the set frequency of each vibrator in a mold in which a large number of vibrators are arranged.

Claims (1)

[Scope of Claims] 1. In a continuous casting mold in which a plurality of vibrators with the same vibration characteristics are arranged, the excitation frequency of adjacent vibrators is set within a range of 2 KHz or less between the excitation frequencies of each vibrator. A method of exciting an ultrasonic vibration mold for continuous casting, which is characterized by changing the vibration. 2 The method of excitation by changing the excitation frequency of adjacent vibrators is to apply vibrations to the vibrator (reference vibrator) with the maximum excitation frequency, and to vibrate other vibrators placed on one or both sides of the reference vibrator. 2. A method for exciting an ultrasonic vibration mold for continuous casting according to claim 1, wherein the vibration frequency of the vibrator is set to gradually decrease as the distance from the reference vibrator increases.