WO2008018996A2 - Waveguide assembly imparting acoustic energy to a glass melt - Google Patents

Waveguide assembly imparting acoustic energy to a glass melt Download PDF

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Publication number
WO2008018996A2
WO2008018996A2 PCT/US2007/016827 US2007016827W WO2008018996A2 WO 2008018996 A2 WO2008018996 A2 WO 2008018996A2 US 2007016827 W US2007016827 W US 2007016827W WO 2008018996 A2 WO2008018996 A2 WO 2008018996A2
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WO
WIPO (PCT)
Prior art keywords
waveguide
glass melt
glass
acoustic
vessel
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Application number
PCT/US2007/016827
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French (fr)
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WO2008018996A3 (en
Inventor
Rene Breeuwer
Anne J Faber
William W Johnson
Original Assignee
Corning Incorporated
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Priority to US83569506P priority Critical
Priority to US60/835,695 priority
Application filed by Corning Incorporated filed Critical Corning Incorporated
Publication of WO2008018996A2 publication Critical patent/WO2008018996A2/en
Publication of WO2008018996A3 publication Critical patent/WO2008018996A3/en

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Classifications

    • CCHEMISTRY; METALLURGY
    • C03GLASS; MINERAL OR SLAG WOOL
    • C03BMANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B5/00Melting in furnaces; Furnaces so far as specially adapted for glass manufacture
    • C03B5/16Special features of the melting process; Auxiliary means specially adapted for glass-melting furnaces
    • C03B5/18Stirring devices; Homogenisation
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01FMIXING, e.g. DISSOLVING, EMULSIFYING, DISPERSING
    • B01F11/00Mixers with shaking, oscillating, or vibrating mechanisms
    • B01F11/02Mixing by means of high-frequency, e.g. ultrasonic vibrations, e.g. jets impinging against a vibrating plate
    • B01F11/0266Mixing by means of high-frequency, e.g. ultrasonic vibrations, e.g. jets impinging against a vibrating plate with vibrating the receptacle or part of it

Abstract

A waveguide assembly (10) is provided for imparting ultrasonic energy to a glass melt (12) at an amplitude sufficient to produce acoustic streaming in the melt, thereby mixing the molten glass. The glass melt (12) may, for example, be flowing through a refractory metal vessel (14). In one configuration the waveguide assembly (10) includes a waveguide (18) acoustically coupled to a transducer (16) at one end (22) and the glass melt (12) at the other end (20). The waveguide (18) may be physically coupled to the vessel (14) via a threaded fitting (32, 34) attached to an outside surface of the vessel (14).

Description

WAVEGUIDE ASSEMBLY FOR IMPARTING ACOUSTIC ENERGY TO A GLASS MELT AND METHOD FOR IMPARTING ACOUSTIC ENERGY TO THE GLASS MELT

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

[0001] The present invention relates to mixing molten glass, and more particularly, to a waveguide assembly for imparting sufficient acoustic energy to increase homogeneity within a glass melt.

DESCRIPTION OF RELATED ART

[00021 Manufacturing techniques can now form glass sheets that not only have high optical quality, but can function as substrates for circuitry. One example of such use of glass sheets is in liquid crystal displays (LCDs). When used as substrates in LCDs, the glass must exhibit certain characteristics, wherein these characteristics are dependent upon the glass melt which ultimately forms the glass sheet.

[0003] Typically, the glass used in LCDs is an alkali-free alumino-borosilicate chemical composition. The glass sheet or panel used in the LCD is formed from the controlled cooling of a liquid glass, referred to as a glass melt. However, the glass melt often contains inhomogeneities which can render the resulting glass sheet unsatisfactory for the intended purpose. Examples of such inhomogeneities are gaseous or solid inclusions, and small volumes of deviating density and chemical composition within the glass melt. These latter phenomena are commonly referred to as cord. Uneven distribution of the cord can reduce the usefulness of the resulting glass sheet. For example, in a liquid crystal display device cord can result in visually unappealing anomalies in the display. Specifically, the cord results in local regions having different refractive indices. The local regions of different refractive indices can render the resulting glass unsuitable for a number of precision uses. [0004] Previously, mechanical stirrers have been used to provide direct mechanical stirring of the glass melt. However, the high temperature of the glass melt and aggressive nature of the glass composition can render direct mechanical stirring difficult to implement. The stirring elements must be manufactured from expensive refractory metal components, typically platinum or a platinum-rhodium alloy, to resist the high temperature environment. Additionally, high shear stresses can erode both the stirring element and the glass containing vessel, resulting in the release of undesirable particulate into the molten glass. [0005] Vibrational energy, typically in the form of ultrasonic energy, has been used in a variety of applications. As most commonly experienced, ultrasonic energy is used as a method of agitating a fluid in a cleaning operation, such as ultrasonic cleaning of jewelry. In industrial applications, ultrasonic energy is also frequently employed to degas liquids. That is, to facilitate the removal of gaseous inclusions (bubbles) from a liquid. [0006] In US Patent No. 4,316,734, sonic energy is employed in a glass making process to cause small seeds (bubbles) to coalesce into larger bubbles that buoyantly rise at a faster rate without requiring a change in the viscosity of the glass melt. Consequently, the viscosity of the glass melt can be increased, such as by decreasing the temperature, without unduly affecting the rate at which at least the larger bubbles rise within the melt. The decrease in melt temperature can lead to a meaningful energy savings. [0007] US Patent 4,316,734 is directed to selecting a frequency and energy intensity responsive to the dynamic viscosity of the glass and the acoustic impedance at the interface between the source of the sonic energy and the glass, to provide a mode of operation wherein a substantial percentage of the bubbles in the glass migrate upward. [0008] US Patent No. 2,635,388 is also directed to a method of removing gaseous inclusions from a volume of molten glass. US Patent No. 2,635,388 discloses the use of a heated element that is immersed in the molten glass and ultrasonically vibrated. The heated element causes a localized high temperature, low viscosity region in the melt that, when combined with the agitation provided by the vibrating element, helps to "assemble" the bubbles and facilitate their escape from the glass. Convection currents resulting from the heating cause the whole volume of glass to eventually pass through the localized high temperature region.

[0009] While these and other methods have shown some efficacy in removing bubbles from the glass by the application of sonic energy, they have not been shown to effectively mix molten glass for the purpose of homogenizing the glass (e.g. removing chemical inhomogeneites). Indeed, the method disclosed in US Patent No. 2,635,388 requires insertion of a heated vibratory element into the glass melt. The high temperature, chemically aggressive environment of the glass melt can lead to flow disruption, dissolution of the heated vibratory element over time and possible contamination of the glass melt, depending on the material of the element, or at the least, periodic replacement of the element. Thus, the need remains for a method of mixing glass that can effectively remove cord from the glass melt without the shortcomings encountered by the insertion of additional elements into the melt.

BRIEF SUMMARY OF THE INVENTION

[0010] The present disclosure describes a method by which a waveguide assembly can be used to introduce ultrasound of a given frequency and at a given power level into a glass melt, either as continuous waves or in the form of long (multi-cycle) bursts. To a first approximation, the excitation signal waveforms are sinusoidal, however, due to significant nonlinearities in the melt, the waveforms in the resulting sound field may differ. For the purpose of implementation and theoretical description, multi-cycle bursts maybe treated identically to continuous wave signals. Thus, the sound fields in the excitation apparatus can be treated as essentially monochromatic (single frequency). [0011] The excitation apparatus, converting electrical input energy from a radio frequency power source into acoustical output energy into the melt consists of a daisy- chained series of elements:

1. the transducer proper, consisting in essence of one or more active (piezoelectric) elements, complemented by front and back masses;

2. an optional matching link, a solid object incorporating a discrete or gradual diameter step; 3. a rod waveguide, commonly a constant diameter cylindrical rod.

[0012] To ensure effective transmission throughout this chain, each of these elements is designed to be resonant at the target frequency. In case the losses in a resonant device are negligible, and it is terminated by elements with infinite impedance contrast (infinitely rigid or infinitely soft), its dimensions should be equal to an exact number of half wavelengths. [0013] The wavelength for a given mode shape is equal to the sound speed for the material and wave type in question divided by the frequency. Thus, for a certain frequency, the wavelength differs significantly between the various elements of the chain, being constructed of vastly different materials. Further, the wave type depends to some degree on the cross-section and cross-sectional variation of the elements, affecting the wavelength to a somewhat lesser degree. Finally, as the sound speeds in practical materials are temperature-dependent, so are the wavelengths.

[0014] To create an effective excitation chain, all elements should be tuned to the same frequency. As the deviations from the simplifying assumptions may differ per element, this difference may require different adjustments per element. For instance, in the matching link the diameter step is not infinitely steep: it uses a finite filleting radius to limit the resulting stresses in the link during operation. This filleting affects the optimum length somewhat. [0015] The waveguide assembly can be driven at an appropriate resonant frequency, for example, between about 20 kHz and 40 kHz, to impart sufficient acoustic power to the glass melt to enhance mixing within the glass melt. Preferably the acoustic power coupled into the glass melt is greater than about 5 watts (W), preferably at least about 30 watts (W), more preferably at least about 40 W, and most preferably at least about 50 W. In accordance with embodiment of the present invention, sufficient acoustic power can be imparted to the glass mix to incur nonlinear acoustic effects, and in particular, acoustic streaming.

[0016] In one embodiment, a method of mixing a glass melt is disclosed comprising generating an acoustic wave, coupling the acoustic wave to a glass melt through a waveguide, and wherein the acoustic wave imparts sufficient acoustic power to the glass melt to produce acoustic streaming in the glass melt. [0017] By acoustically coupling a waveguide to a glass melt, and producing a standing wave along a longitudinal dimension of the waveguide, sufficient acoustic energy, such as ultrasonic energy, can be imparted to the glass melt to increase homogeneity within the glass melt.

[0018) In another embodiment, an apparatus for imparting acoustic energy to a glass melt in a vessel is disclosed comprising a transducer producing an acoustic wave, a waveguide acoustically coupled to the transducer and the glass melt and wherein the waveguide is configured to create a standing wave in the waveguide at a frequency of the acoustic wave and produce acoustic streaming in the glass melt. [0019] It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed.

[0020] The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings are not necessarily to scale, and sizes of various elements may be distorted for clarity. The drawings illustrate one or more embodiment(s) of the invention, and together with the description serve to explain the principles and operation of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 is a cross sectional view of an apparatus for mixing a molten glass in an exemplary cylindrical vessel according to an embodiment of the present invention. [0022] FIG. 2 is a cross sectional view of another embodiment of an apparatus for mixing glass according to an embodiment of the present invention wherein the waveguide comprises an impedance matching portion.

[0023] FIGS. 3 and 4 are cross sectional views of methods of acoustically coupling the waveguide to the vessel utilizing a threaded socket (FIG. 3) and a threaded stub (FIG. 4) [0024] FIG. 5 is a cross sectional view of another embodiment of an apparatus according to an embodiment of the present invention wherein two waveguides are acoustically coupled to a vessel. [0025] FIG. 6 is a schematic view of an exemplary fusion glass making process utilizing an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0026] Sound is a vibration that travels or propagates through a medium, such as a liquid or gas. The source of this vibration is a repetitive perturbation of the medium. For example, a bell when struck vibrates. The sides of the bell move in relation to the air surrounding it, first creating a high pressure region in the air as a side moves outward, then creating a low pressure region as the side moves inward. The regions of high and low pressure are known as regions of compression and rarefaction, respectively, and they propagate through the medium as a wave by affecting adjacent molecules of the air: a molecule in the air moves back and forth in response to the alternating high and low pressure, and in turn acts on an adjacent molecule, which then acts on a molecule adjacent to it and so on. Thus the regions of high and low pressure propagate through the medium as a wave having a defined amplitude and wavelength. As it propagates, the propagating wave diverges in space and loses energy by absorption. These two effects cause the pressure amplitude to decrease with distance traveled. The propagating wave can also interact with other waves constructively or destructively. For example, the wave may overlap with a reflection of the wave (e.g. from an object's surface) such that the two waves reinforce each other, creating a standing wave. This occurs when the two waves are in phase with each other. Standing waves have defined nodes and antinodes corresponding to areas of minimum pressure and maximum pressure, respectively. Standing waves may be created in a reflecting environment, for example, by adjusting the wavelength (frequency) of the propagating wave to an appropriate number of half wavelengths such that the reflecting waves constructively overlap.

[0027] Ordinary standing waves can be quite powerful. However, extremely intense sounds can result in a nonlinear response in the medium through which they propagate. Such nonlinear responses can include shock waves, acoustic saturation (the medium is unable to absorb additional sonic energy) and acoustic streaming, or a process by which a net flow of the medium through which the sound wave is propagating results. That is, the vibrating molecule described above does not merely "move in place" about a mean position without an overall net change in position. During acoustic streaming the mean position of the molecule actually changes.

[0028] Acoustic streaming has been used to manipulate the behavior of liquids, such as, for example, moving relatively low temperature liquids, moving bubbles and ejecting liquids as droplets. Acoustic streaming has also been applied to localized mixing of very small liquid volumes (i.e. microfluidic mixing). A far more difficult task is to incur acoustic streaming in a high viscosity, high temperature bulk liquid, such as a molten glass in a high volume glass manufacturing operation to effectively, and economically, mix or homogenize the glass.

[0029] The term "glass melt" encompasses any of a variety of glass compositions that are above their respective softening point. Typically, glass melts are on the order of 12000C to 17000C. The term "glass" includes material with a random, liquid-like (noncrystalline) molecular structure. The manufacturing process of glass requires that raw materials be heated to a temperature sufficient to produce a completely fused melt, that, when cooled, becomes rigid without crystallizing. The glass, and hence glass melt, can be any of a variety of compositions including, but not limited to soda lime glass, lead glass, borosilicate glass, aluminosilicate glass, 96% silica glass, fused silica glass and alumino- borosilicate silicate. The term "acoustic wave" is meant to encompass mechanical vibrations transmitted through a medium. In one configuration, the acoustic wave is within the ultrasonic range, with the target frequency typically between approximately 20 kHz to approximately 40 kHz.

[0030] The present invention encompasses a waveguide assembly 10, shown in FIG. 1, for imparting acoustic energy via an acoustic wave into a glass melt 12 contained in a vessel 14 and thereby mixing the glass melt.

[0031] Vessel 14 can be any of a variety of configurations. In one configuration, vessel 14 defines a flow path for molten glass selected in conjunction with waveguide assembly 10 to allow mixing within a given percentage of the cross-sectional area of the flow path. Thus, the vessel can receive a flow of molten glass from an upstream position and allow the glass melt to flow to a downstream position. For example, vessel 14 can be a pipe through which molten glass is flowed. In one configuration, vessel 14 includes an open top permitting the waveguide assembly to access and contact the glass melt. It is also contemplated that the vessel can include a port or aperture below the level of the glass melt through which a portion of the waveguide assembly is disposed so as to couple the waveguide assembly and the glass melt. In yet another construction, the waveguide assembly can be acoustically coupled to the vessel on an exterior surface of the vessel that avoids previously described shortcomings of prior art mixing methods. By acoustically coupled what is meant is that a first element is coupled to a second element in such a way that sound waves can propagate from the first element to the second element, preferably, but not necessarily, with minimal loss of amplitude.

[0032] Vessel 14 is preferably constructed of a refractory metal, such as platinum or a platinum-rhodium alloy, and including, for example, an alloy of 80% platinum -20% Rhodium. Vessel 14 preferably includes an inlet opening and an outlet opening such that molten glass may flow through the vessel, such as in a continuous or semi-continuous glass making operation. However, it should be noted that methods of the current invention may be performed on molten glass that is not flowing.

10033] Waveguide assembly 10 is constructed to efficiently convert radio frequency (rf) power into acoustic power, and comprises a transducer 16 for accomplishing the conversion, and a waveguide 18 to transmit the resulting acoustic power to glass melt 12. To enhance efficiency of the power transmission, waveguide assembly 10 is constructed to match acoustic impedances within the assembly and resonate at the target frequency. Thus, given the assumption that losses in a resonant assembly are negligible, and the waveguide assembly is terminated by components with an infinite impedance contrast (infinitely rigid or infinitely soft), the longitudinal dimension of the waveguide assembly should be equal to an exact number of half wavelengths.

[0034] In one embodiment, a first end 20 of waveguide 18 is acoustically coupled to glass melt 12 through vessel 14 and second end 22 of waveguide 18 is coupled to transducer 16. Waveguide 18 (and waveguide assembly 10) has a first hot end 20, generally at a temperature in excess of 12000C, and more typically between about 12000C to 1,7000C, and a relatively cool second end 22 preferably at an ambient temperature or at least a temperature conducive to operation of the transducer. Conventional ultrasonic transducers will typically only tolerate temperatures up to approximately 5O0C. At higher temperatures, the transducers will eventually suffer permanent damage due to internal debonding caused by thermal expansion or to depolarization. In one configuration, the temperature of transducer 16 is maintained at less than 1000C, and in a further configuration less than 500C.

[0035] Transducer 16 functions to convert rf power to vibrational motion. The transducer can be any of a variety of commercially available transducers such as a Langevin or a Tonpilz-type ultrasonic transducer. The transducer is driven by a signal generator 24 and a high-frequency power amplifier 26, as is well known in the art. Signal generator 24 is in turn controlled by controller 28, such as a computer-based controller. [0036] The excitation signal voltage and frequency input to the transducer may be controlled by controller 28 to maintain transducer 16 at an optimum working point for efficient ultrasonic generation. That is, waveguide assembly 10 is driven at a resonant frequency. Langevin-type transducers in particular are known for having a narrow resonance frequency bandwidth, and a resonance characteristic that is dependent upon the medium. Since the waveguide assembly, and especially the waveguide, may be exposed to a range of temperatures, the resonant frequency may be temperature dependent. [0037] To match acoustic impedances between transducer 16 and waveguide 18, waveguide 18 may comprise a matching link portion 30. In one configuration, shown in FIG. 2, matching link 30 is designed to have a length of approximately one half the wavelength of the target frequency within the matching link. Thus, a length of a compatible material, such as steel, is selected to be approximately one half the wavelength of the target signal within the steel. Although steel can be employed for matching link 30, other materials of acceptable acoustic properties and loss can be used, wherein for each such material, the optimum dimensions of the matching link are selected to match the acoustic impedance of the transducer to the acoustic input impedance of the waveguide. [0038] Matching link 30 is configured to minimize signal reflections at the interface between the transducer and the matching link and similarly the interface between the matching link and the remainder of the waveguide. Thus, the amount of reflected power at each interface is minimized and the total power delivered to glass melt 12 is maximized. 10039] As described, transducer 16 is acoustically coupled to waveguide 18 at waveguide end 22. The remaining end 20 of waveguide 18 is immersed in the glass melt or, more preferably, acoustically coupled to an exterior surface of vessel 14 so that the acoustic power is transferred to the glass melt through vessel 14.

[0040] Shown in FIGS. 3 —4 are several methods of acoustically coupling waveguide 16 to vessel 14 in accordance with embodiments of the present invention. FIG. 3 illustrates an internally threaded socket (fitting) 32 attached to an exterior surface of vessel 14. Accordingly, end 20 of waveguide 18 comprises an external thread so that waveguide 18 can be threaded into socket 32. Alternatively, in a preferred embodiment depicted in FIG. 4, waveguide 18 comprises an internally threaded recess at end 20 sized to cooperate with a threaded stud (fitting) 34 attached to an external surface of vessel 14. Stud 34 is preferably welded to vessel 14. Preferably, end surface 23 of stud 34 is perpendicular to the longitudinal axis of the stud 18 (stud 34 has a flat end face), and contacts the internal recess of stud 34 across the entire end surface so that acoustic power is not coupled through the thread contact only.

{0041] Waveguide 18 is selected to resonate (support a standing wave) at the target frequency. Thus, waveguide 18 preferably has a length equal to an integer half wavelength of the target frequency in the waveguide. In some embodiments, waveguide 18 can be partially immersed within glass melt 12, wherein the un-immersed length of the waveguide may act as a thermal buffer between transducer 16 and glass melt 12. In un-immersed embodiments, the entire length of waveguide 18 may act as a thermal buffer [0042] Waveguide 18 is desirably comprised of a material sufficient to resist the high temperatures experienced in a glass making operation, which can in some cases exceed 16000C. This is true whether waveguide 18 is in contact with the molten glass, or merely in contact with vessel 14. Satisfactory materials have been found to include dense alumina, ceramic or refractory metal alloys which maintain a high elastic modulus at high temperatures such as alumina, zirconia and Pt-Rh alloys.

[0043] Although waveguide 18 is a generally cylindrical or simple stepped horn, it is understood that waveguide 18 can have a bell shape, block shape, or a spool shape (slotted or unslotted). Waveguide 18 can be a solid rod or a tube or a hollow cylinder having a diameter on the order of the solid rod.

[0044] In one configuration, a cooling stream 36 is directed over a portion of waveguide 18 (or matching link 30 if employed) to assist in providing an appropriate operating temperature for transducer 16. The cooling stream can be air at ambient (e.g. room) temperature at a readily obtainable flow rate. However, it is understood cooling stream 36 can be a cooled flow. It is further understood that the shorter the waveguide, the greater the required cooling may be, and may include a chilled cooling stream at higher flow rates. An ambient air cooling stream has been found adequate with a waveguide of a wavelength length. Typically, the cooling stream is directed over the waveguide (or matching link) adjacent the transducer. It is advantageous for the cooling stream to be at a steady state, thereby allowing waveguide 18 to reach an equilibrium status. [0045] Because waveguide 18 comprises a hot end and a cold end, a thermal gradient exists along the longitudinal dimension of waveguide 18 that alters the velocity of the sound wave propagating through waveguide 18. The frequency of the acoustic wave generated by transducer 16 may be adjusted as necessary to maintain resonance within waveguide assembly 10 in order to impart sufficient acoustic power to glass melt 12. Also associated with temperature differences are changes in ultrasonic losses and in the acoustic properties of the melt. Thus, even though the waveguide is kept in resonance by frequency adjustment, the electrical input impedance of the transducer at resonance may vary. The temperature gradient along waveguide assembly 10 between the glass melt 12 and the room temperature transducer 16 results mainly in a variation of the speed of the acoustic wave along the longitudinal dimension of the waveguide assembly, and secondarily in thermal expansion and, thus, a change in density. The two effects together may result in a corresponding variation in acoustic impedance, defined as the acoustic pressure divided by the resulting volume velocity, along the length of the waveguide assembly. Consequently, the temperature induced variation in acoustic impedance along the longitudinal dimension of the waveguide assembly should be taken into account when selecting components for. apparatus 10, for example, the waveguide material, length and cross section. [0046] The optimal length of waveguide 18 is dependent, inter alia, on the choice of material for the waveguide and the temperature of the waveguide during operation. A waveguide length of approximately one wavelength for the target acoustic wave frequency has been found to be a satisfactory length of waveguide 18 for some embodiments, as this length allows a sufficient temperature gradient along the length of the waveguide to allow transducer 16 to operate at less than 1000C and permits waveguide assembly 10 to be tuned, via the signal frequency, to operate at a resonant frequency.

[0047] As waveguide 18 is acoustically coupled to glass melt 12, the waveguide delivers acoustic power in the form of ultrasonic vibrations to the glass melt through vessel 14. Upon introduction of sufficient power to the glass melt, movement of the glass melt that promotes mixing sufficient to increase the homogeneity of the glass melt can be induced. That is, cording can be reduced and uniformly distributed throughout the glass melt. In some embodiments, the acoustic power coupled into the glass melt may also produce cavitation with the melt, whoch can lead to high local flow velocities in the melt. Cavitation can also aid in fining of the glass (gaseous inclusion removal) by creating vacuum bubble sites where dissolved gases can coalesce and rise to the surface of the glass melt.

[0048] In certain embodiments, more than one waveguide may be employed to enhance mixing of the molten glass. Shown in FIG. 5 is an embodiment wherein two waveguides are physically coupled to vessel 14. Preferably, the longitudinal axes of the two waveguides are orthogonal. It should be understood that more than two waveguides may be employed. Referring to FIG. 6, there is shown a schematic view of an exemplary glass manufacturing system 42 in accordance with an embodiment of the present invention that uses a fusion process to make glass sheets. The fusion process is described, for example, in U.S. Patent No. 3,338,696 (Dockerty). The exemplary fusion glass manufacturing system 42 includes a melting furnace 44 (melter 44) in which raw feed materials are introduced as shown by arrow 46 and then melted to form molten glass 12. The glass manufacturing system 42 further includes components that are typically made from platinum or platinum- containing metals such as platinum-rhodium, platinum-indium and combinations thereof, but which may also comprise such refractory metals as molybdenum, palladium, rhenium, tantalum, titanium, tungsten, or alloys thereof. The platinum-containing components may include fining vessel 50 (e.g. finer tube 50), a melter to finer connecting tube 52, a mixing vessel 54 (e.g. stir chamber 54), a finer to stir chamber connecting tube 56, a delivery vessel 58 (e.g. bowl 58), a stir chamber to bowl connecting tube 60, and a downcomer 62. Molten glass is supplied to inlet 64 that is coupled to forming vessel 66 (e.g. fusion pipe 66). Molten glass supplied to forming vessel 66 through inlet 64 overflows forming vessel 66, and dividing into two separate glass flows that flow down converging external surfaces of forming vessel 66. The two separate glass flows recombine at the line where the converging forming surfaces meet to form a single glass sheet 68. Typically, forming vessel 66 is made from a ceramic or glass-ceramic refractory material. [0049J Because the outside surfaces of the separate glass flows descending the converging forming surfaces of forming vessel 66 do not contact the forming surfaces, the combined glass sheet, having pristine outer surfaces, is well suited for the manufacture of liquid crystal displays.

[0050] In accordance with embodiments of the present invention, apparatus 10 may be advantageously employed within the platinum-containing portions of glass manufacturing system 42. For example, one or more apparatus 10 may be acoustically coupled to the fϊner-to-stirrer connecting tube 56 or stir chamber 54 in order to mix (homogenize) the molten glass. In a conventional stir chamber, a stirrer 70 is rotated in the molten glass to homogenize the glass. Apparatus 10 may be employed to supplement stirrer 70 by simultaneously applying ultrasonic energy to the glass melt while the stirrer is rotating, or apparatus 10 may be used in place of stirrer 70. Example 1

[0051] Alumino borosilicate glass cullet was remelted at a temperature in a platinum- rhodium crucible (vessel) disposed in a furnace and wherein the furnace varied in temperature between 13500C and 15350C. A waveguide comprised an alumina portion and a steel impedance matching portion was used to acoustically couple a Tonpilz-type ultrasonic transducer operating between approximately 20 kHz and 25 kHz to the glass melt by immersing a length of the alumina portion in the glass melt. The alumina portion had a diameter of 22 mm and a length of approximately 43.2 cm. A significant resonance condition was attained at an operating frequency of between 21.1 kHz and 21.4 kHz, as indicated by the transducer electrical impedance minimum (the frequency was tuned over the foregoing range to maintain resonance due to temperature dependence of the waveguide). The maximum input power of 44 W was attained at a furnace temperature of 13500C. Cobalt oxide was added to the glass melt in an amount of about 200 ppm to provide visual confirmation of acoustic streaming. The glass was cooled and removed from the crucible. Visual examination of the cooled glass showed acoustic streaming-induced mixing of the cobalt oxide "dye" and the glass.

Example 2

[0052] An alumino borosilicate glass was melted at a temperature between 13500C and 14000C in a platinum-rhodium crucible (vessel) disposed in a furnace and subsequently maintained at a temperature of 14500C. A waveguide comprised an alumina portion and a steel impedance matching portion was used to acoustically couple a Tonpilz-type ultrasonic transducer operating between approximately 20 kHz and 25 kHz to the glass melt. The alumina portion had a diameter of 22 mm and a length of approximately 43.2 cm. The alumina portion of the waveguide was physically coupled to the crucible via a threaded stud welded to an exterior surface of the crucible and an internally threaded recess in the alumina portion of the waveguide. The impedance matching portion was coupled to the transducer via an adhesive reinforced threaded. A significant resonance condition was attained at an operating frequency of between 22.5 kHz and 23 kHz, as indicated by a transducer electrical impedance minimum (the frequency was tuned over the foregoing range to maintain resonance due to temperature dependence of the waveguide). The power input to the glass melt was between 40 W and 50 W.

[0053] It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Claims

WHAT IS CLAIMED IS:
1. A method of mixing a glass melt comprising generating an acoustic wave and coupling the acoustic wave into a glass melt (12) through a waveguide (18), characterized in that the acoustic wave imparts sufficient acoustic power to the glass melt to produce acoustic streaming in the glass melt.
2. The method according to claim 1 wherein the acoustic power coupled into the glass melt is at least about 5 W.
3. The method according to claim 1 wherein the acoustic power coupled into the glass melt is at least about 50 W.
4. The method according to claim 1 wherein a frequency of the acoustic wave is between about 20 kHz and 40 kHz.
5. The method according to claim 1 wherein the glass is contained by a refractory metal vessel (14).
6. The method according to claim 4 wherein the waveguide is physically coupled to a threaded fitting (32, 34) on a surface of the vessel.
7. The method of claim 1 wherein the acoustic wave produces cavitation in the glass melt.
8. The method according to claim 1 wherein the step of coupling the acoustic wave to the glass melt comprises contacting the glass melt with the waveguide.
9. The method according to claim 1 further comprising forming the glass melt into a glass sheet (68).
10. The method according to claim 5 wherein the glass melt is flowed through the vessel (14).
11. The method according to claim 1 wherein the acoustic wave is a standing wave.
12. An apparatus for imparting acoustic energy to a glass melt in a vessel (14) comprising a transducer (16) producing an acoustic wave and a waveguide (18) acoustically coupled to the transducer and the glass melt, characterized in that the waveguide (18) is configured to create a standing wave in the waveguide at a frequency of the acoustic wave and produce acoustic streaming in the glass melt (12).
13. The apparatus according to claim 12 wherein the waveguide (18) is physically coupled to the vessel (14).
14. The apparatus according to claim 12 wherein a portion of the waveguide (18) adjacent to the transducer (16) has a temperature less than. 1000C.
15. The apparatus according to claim 12 wherein a frequency of the acoustic wave is between 20 kHz and 40 kHz.
16. The apparatus according to claim 12 wherein the waveguide (18) comprises an impedance matching link (30) coupled to the transducer (16).
17. The apparatus according to claim 12 further comprising a plurality of waveguides (18) acoustically coupled to the glass melt (12).
PCT/US2007/016827 2006-08-04 2007-07-26 Waveguide assembly imparting acoustic energy to a glass melt WO2008018996A2 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
US83569506P true 2006-08-04 2006-08-04
US60/835,695 2006-08-04

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
CN 200780029050 CN101500953B (en) 2006-08-04 2007-07-26 Waveguide assembly for imparting acoustic energy to a glass melt
JP2009523768A JP2009545512A (en) 2006-08-04 2007-07-26 Methods for imparting acoustic energy to the waveguide assembly and the glass melt for imparting acoustic energy to the glass melt
KR1020147026502A KR101546640B1 (en) 2006-08-04 2007-07-26 Waveguide Assembly for Imparting Acoustic Energy to a Glass Melt and Method for Imparting Acoustic Energy to the Glass Melt

Publications (2)

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JP2010163292A (en) * 2009-01-13 2010-07-29 Ihi Corp Glass melting furnace
WO2012118722A3 (en) * 2011-02-28 2012-11-08 Corning Incorporated Ultrasonic transducer assembly for applying ultrasonic acoustic energy to a glass melt
US8490433B2 (en) 2011-02-28 2013-07-23 Corning Incorporated Method for applying ultrasonic acoustic energy to a glass melt
US9061928B2 (en) 2011-02-28 2015-06-23 Corning Incorporated Ultrasonic transducer assembly for applying ultrasonic acoustic energy to a glass melt

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JP6268669B2 (en) * 2013-10-24 2018-01-31 株式会社Ihi Settling control and sedimentation control method of the foreign matter in the liquid

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US4549896A (en) * 1984-08-27 1985-10-29 Owens-Corning Fiberglas Corporation Apparatus and method for removing gaseous inclusions from molten material
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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2010163292A (en) * 2009-01-13 2010-07-29 Ihi Corp Glass melting furnace
WO2012118722A3 (en) * 2011-02-28 2012-11-08 Corning Incorporated Ultrasonic transducer assembly for applying ultrasonic acoustic energy to a glass melt
US8490433B2 (en) 2011-02-28 2013-07-23 Corning Incorporated Method for applying ultrasonic acoustic energy to a glass melt
US9061928B2 (en) 2011-02-28 2015-06-23 Corning Incorporated Ultrasonic transducer assembly for applying ultrasonic acoustic energy to a glass melt

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CN101500953A (en) 2009-08-05
CN101500953B (en) 2012-10-17
TWI359118B (en) 2012-03-01
KR20090048617A (en) 2009-05-14
KR101546640B1 (en) 2015-08-21
JP2009545512A (en) 2009-12-24
TW200827313A (en) 2008-07-01
KR20140130500A (en) 2014-11-10
WO2008018996A3 (en) 2008-09-12

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