WO2009084817A2

WO2009084817A2 - Ultrasonic wave generating device for controlling solidification structure

Info

Publication number: WO2009084817A2
Application number: PCT/KR2008/006930
Authority: WO
Inventors: Sang-Woo Choi; Goo-Hwa Kim; Jin-Su Bae; Jung-Hwan Kim
Original assignee: Posco
Priority date: 2007-12-27
Filing date: 2008-11-25
Publication date: 2009-07-09
Also published as: CN101909782A; CN101909782B; JP5055435B2; KR101449018B1; KR20090071139A; WO2009084817A3; JP2011507704A

Abstract

There is provided an ultrasonic wave generating device for controlling solidification structure, which is able to prevent some of ultrasonic waves from leaking out by the reflection of the ultrasonic waves on an incidence interface in a transfer process of transferring high-intensity ultrasonic waves generated in an ultrasonic wave transducer to the inside of molten metal. The ultrasonic wave generating device for controlling solidification structure comprises an ultrasonic wave transducer generating ultrasonic waves and applying the generated ultrasonic waves to an inner part of a cast; and a reflective plate enhancing the intensity of ultrasonic waves reflected from a surface of the cast and reflecting the ultrasonic waves back toward the inner part of the cast.

Description

ULTRASONIC WAVE GENERATING DEVICE FOR CONTROLLING SOLIDIFICATION STRUCTURE

Technical Field

[1] The present invention relates to an ultrasonic wave generating device for controlling solidification structure, and more particularly, to a device for preventing some of ultrasonic waves from leaking out by the reflection of the ultrasonic waves on an incidence interface.

[2]

Background Art

[3] Casting is a process that is used to produce primary materials which are parent materials, which are, then, used to make structures widely used in the field of industrial applications, or that is used to melt a parent material and solidify the molten parent material into desired shapes. When molten metal is cooled, the molten metal is solidified into solids with desired dimensional shapes. In this case, the molten metal sets quickly from an outer surface thereof. Although an outer surface of a cast-iron product becomes solidified, an inner part of the cast-iron product having relatively slow heat transfer characteristics is maintained in a liquid phase, and slowly solidified due to its slow heat transfer characteristics. In this case, when the cast-iron product is cooled at a rapid rate, a large amount of grains are produced on the surface of the cast- iron product, thereby forming a fine texture. However, a small amount of grains are slowly produced in the inner part of the cast-iron product, thereby forming a coarse texture.

[4] Materials having such a coarse texture have a low strength, and therefore lots of energy is required in additional processed in order to address desired physical properties to the materials. For example, when a cast slab produced in a continuous casting process has a coarse crystal structure, a structure of the cast slab should be refined in a rolling process by increasing a re -reduction rate at the structure of the cast slab, so that the cast slab can be used to produce a high-grade steel sheet for automobiles. Thanks to the reheating or the high reduction rate, much energy is consumed in such an additional process. As an alternative to the above-mentioned process, there is a new technology to refine grains of molten metal by applying high- intensity ultrasonic waves to the molten metal during solidification. For this purpose, high-intensity ultrasonic waves having the highest energy should be transferred during a casting process to the inside of molten metal whose solidification is in progress, but there are limitations on the energy capacity of high-intensity ultrasonic waves to be generated. Therefore, increasing the transfer efficiency of the generated high-intensity ultrasonic waves is one of important factors for the refinement of grains in a solidification structure.

[5] Conventional ultrasonic wave vibrators are used in an ultrasonic welding machine and an ultrasonic washing machine to directly transfer ultrasonic waves. Meanwhile, since a target of ultrasonic wave transfer is heated to a high temperature of several hundreds degrees centigrade (⁰C) so as to control a solidification structure of molten metal, it is difficult to directly transfer ultrasonic waves to the target. Therefore, it is desirable to generate ultrasonic waves in a cooling fluid and introduce the generated ultrasonic waves to the inside of cast metal whose solidification is in progress. When an ultrasonic wave vibrator is put into the cooling fluid to generate ultrasonic waves and introduce the generated ultrasonic waves to the inside of cast metal whose solidification is in progress, a high proportion of the ultrasonic waves may be reflected and dispersed or leaked out in the cooling fluid due to the high difference in acoustic impedance between the cooling fluid and the casting mold.

[6]

Disclosure of Invention Technical Problem

[7] An aspect of the present invention provides an ultrasonic wave generating device c apable of improving the ultrasonic transfer efficiency, with which ultrasonic waves reflected on the interface between a cooling fluid and a cast are reflected back toward the inside of molten metal, in order to control a solidification structure of cast metal

[8] Another aspect of the present invention provides an ultrasonic wave generating device capable of cooling an ultrasonic wave transducer in a cooling fluid sufficiently to prevent performances of the ultrasonic wave transducer from being deteriorated.

[9] Still another aspect of the present invention provides an ultrasonic wave generating device capable of reflecting some of ultrasonic waves, which are generated in an ultrasonic wave transducer and reflected on the interface without entering cast metal, on a parabolic reflective plate in a direction vertical to the interface.

[10] Yet another aspect of the present invention provides an ultrasonic wave generating device capable of adjusting a path so that the path, which spans from a point on the interface on which ultrasonic waves are reflected to a point where ultrasonic waves are reflected back to the interface via a reflection point inside a parabolic reflective plate, can be an integer multiple of one wavelength or one wavelength length.

[H]

Technical Solution

[12] According to an aspect of the present invention, there is provided an ultrasonic wave generating device for controlling a solidification structure including an ultrasonic wave transducer generating ultrasonic waves and applying the generated ultrasonic waves to an inner part of a cast; and a reflective plate enhancing the intensity of ultrasonic waves reflected from a surface of the cast and reflecting the ultrasonic waves back toward the inner part of the cast.

[13] In this case, the ultrasonic wave generating device may further include a cooling fluid flowing while surrounding the ultrasonic wave transducer and maintaining the ultrasonic wave transducer below a predetermined temperature.

[14] Also, the ultrasonic wave transducer may include a transducer horn amplifying generated ultrasonic waves, wherein the sum of a distance from a front end of the transducer horn to the reflective plate and a distance from the reflective plate to the cast is an integer multiple of the half wavelength of ultrasonic wave.

[15] Furthermore, the reflective plate may be in a parabolic shape.

Advantageous Effects

[16] As described above, the ultrasonic wave generating device according to one exemplary embodiment of the present invention may be useful to prevent generated ultrasonic waves from being dispersed or leaked out since high-intensity ultrasonic waves are used to control a solidification structure.

[17] Also, the ultrasonic wave generating device according to one exemplary embodiment of the present invention may be useful to gain the high economic benefits since the solidification structure is effectively refined by employing high-intensity ultrasonic waves to improve the transfer efficiency of ultrasonic waves.

[18]

Brief Description of Drawings

[19] FIG. 1 is a block diagram illustrating an ultrasonic wave generating device for controlling a solidification structure according to one exemplary embodiment of the present invention.

[20] FIG. 2 is a partial exploded view illustrating a peripheral portion of an ultrasonic wave transducer as shown in FIG. 1.

[21]

[22] <Brief description of major parts in drawings>

[23] 100: molten metal 200 : cast

[24] 300: housing 310: inlet

[25] 320: outlet 400: ultrasonic wave transducer

[26] 410: ultrasonic wave vibrator 420: transducer horn

[27] 500: reflective plate 600: cooling fluid

[28] 700: reflected ultrasonic waves [29]

Best Mode for Carrying out the Invention

[30] Hereinafter, exemplary embodiments of the present invention will be described in detail referring to the accompanying drawings. However, the description proposed herein is just a preferable example for the purpose of illustrations only, not intended to limit the scope of the invention, so it should be understood that other equivalents and modifications could be made thereto without departing from the scope of the invention. In the accompanying drawings, it is considered that parts having the same configuration and functions have substantially the same reference numerals.

[31] FIG. 1 is a block diagram illustrating an ultrasonic wave generating device for controlling a solidification structure according to one exemplary embodiment of the present invention. Referring to FIG. 1, a cast 200 becomes filled with a molten metal 100 during solidification, and an ultrasonic wave transducer 400 for generating ultrasonic waves and applying the generated ultrasonic waves to an inner part of the cast 200 is arranged outside the cast 200.

[32] Referring to a configuration of the ultrasonic wave transducer 400, the ultrasonic wave transducer 400 includes an ultrasonic wave vibrator 410 and a transducer horn 420. The ultrasonic wave vibrator 410 generates ultrasonic waves in constant wavelength intervals, and the transducer horn 420 is coupled to a lower surface of the ultrasonic wave vibrator 410 to amplify the ultrasonic waves generated in the ultrasonic wave vibrator 410.

[33] Since ultrasonic waves are hardly transferred through the air, high-powered ultrasonic waves are transferred to a surface of the cast 200 by the medium of liquid. Then, since high-tempearture heat is transferred from the molten metal 100 in the cast 200 to the ultrasonic wave transducer 400, the liquid is used to cool the ultrasonic wave transducer 400, thus to protect the ultrasonic wave transducer 400 from the high- tempearture heat, and maintain performances of the ultrasonic wave transducer 400.

[34] Since characteristics of piezoelectric materials are generally maintained only within a temperature of up to 300⁰C, the piezoelectric materials should be cooled to prevent the piezoelectric characteristics from being deteriorated. Also, since an increase in temperature of the ultrasonic wave transducer 400 causes electrical impedance to be changed and causes outputs of ultrasonic waves to be reduced, the ultrasonic wave transducer 400 should be maintained below a certain temperature in order to maintain the optimum outputs of ultrasonic waves. For this purpose, a cooling fluid 600, which flows while surrounding the ultrasonic wave transducer 400 arranged outside the cast 200, should show its functions to the full extent. Also, the cooling fluid 600, which is cooled to a low temperature, flows through an inlet 310 of a housing 300 to cool the ultrasonic wave transducer 400, and then should be discharged through an outlet 320 of the housing 300.

[35] A cavitation phenomenon is caused in high-intensity ultrasonic sound fields to form bubbles. Then, the bubbles existing on a transfer path of ultrasonic waves interrupts the transfer of the ultrasonic waves, thus to reduce a transfer rate of the ultrasonic waves to the inner part of the cast 200. In order to prevent side effects, such as the generation of bubbles, caused by the cavitation phenomenon, it is necessary to remove the bubbles by allowing the cooling fluid 600 to flow. In general, bubbles and suspended solids existing in the high-intensity ultrasonic sound fields gathers in a node point by means of the standing wave effects of ultrasonic waves, and forms a finding force in respect to a transfer direction of the ultrasonic waves. Therefore, since the binding force is weaker toward the flank in the transfer direction of the ultrasonic waves, bubbles around the ultrasonic wave transducer 400 are discharged through the outlet 320 by allowing the cooling fluid 600 flowing through the inlet 310 to flow along the flank in the transfer direction of the ultrasonic waves.

[36] FIG. 2 is a partial exploded view illustrating a peripheral portion of an ultrasonic wave transducer as shown in FIG. 1. Referring to FIG. 2, a parabolic reflective plate 500 is arranged around the transducer horn 420, and the reflective plate 500 enhances the intensity of ultrasonic waves reflected from a surface of the cast 200 and reflects the ultrasonic waves back toward the inner part of the cast 200. The reflective plate 500 faces a front end 420a of the transducer horn 420 and the cast 200. Here, the sum of a distance from the front end 420a of the transducer horn 420 to the reflective plate 500 and a distance from the reflective plate 500 to the cast 200 is an integer multiple of the half wavelength of ultrasonic wave.

[37] The ultrasonic waves generated in the ultrasonic wave transducer 400 are discharged from the front end 420a of the transducer horn 420, and then transferred to a surface of the cast 200 via the cooling fluid 600. Due to the difference in acoustic impedance between the cooling fluid 600 and the cast 200, some of the ultrasonic waves are not transferred to the inner part of the cast 200, but reflected back toward the cooling fluid 600. Then, some of the generated ultrasonic waves are dispersed and leaked out in the cooling fluid 600.

[38] In accordance with the present invention, however, the intensity of the ultrasonic waves transferred to the inner part of the cast 200 is improved since the parabolic reflective plate 500 installed around the transducer horn 420 reflects the ultrasonic waves reflected on the surface of the cast 200 back toward the cast 200. In order to enhance the re-reflection efficiency of ultrasonic waves toward the inner part of the cast 200, the reflective plate 500 has a parabolic structure in which the angle of reflection of the ultrasonic waves is vertical to the surface of the cast 200 when the ultrasonic waves reflected from the front end 420a of the transducer horn 420 are reflected back toward the inner part of the reflective plate 500. Also, a length of the path, which spans from the front end 420a of the ultrasonic wave transducer 400 to the interface of the cast 200 to which ultrasonic waves are transferred after they are reflected on the reflective plate 500, becomes an integer multiple of wavelength length. In this case, the outputs of the ultrasonic waves are enhanced due to the constructive interference of the ultrasonic waves.

[39] The exemplary embodiments of the present invention have been described in detail with reference to the accompanying drawings. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the scope of the invention will become apparent to those skilled in the art from this detailed description.

Claims

[1] An ultrasonic wave generating device for controlling a solidification structure, comprising: an ultrasonic wave transducer generating ultrasonic waves and applying the generated ultrasonic waves to an inner part of a cast; and a reflective plate enhancing the intensity of ultrasonic waves reflected from a surface of the cast and reflecting the ultrasonic waves back toward the inner part of the cast.

[2] The ultrasonic wave generating device of claim 1, further comprising a cooling fluid flowing while surrounding the ultrasonic wave transducer and maintaining the ultrasonic wave transducer below a predetermined temperature.

[3] The ultrasonic wave generating device of claim 1, wherein the ultrasonic wave transducer comprises a transducer horn amplifying generated ultrasonic waves, wherein the sum of a distance from a front end of the transducer horn to the reflective plate and a distance from the reflective plate to the cast is an integer multiple of the half wavelength of ultrasonic wave.

[4] The ultrasonic wave generating device of claim 1, wherein the reflective plate is in a parabolic shape.