WO2008018997A2

WO2008018997A2 - Method and apparatus for characterizing a glass melt by ultrasonic illumination

Info

Publication number: WO2008018997A2
Application number: PCT/US2007/016836
Authority: WO
Inventors: Rene Breeuwer; Anne J Faber; William W Johnson
Original assignee: Corning Incorporated
Priority date: 2006-08-04
Filing date: 2007-07-26
Publication date: 2008-02-14
Also published as: WO2008018997A3; KR101500920B1; JP2009545757A; TW200825031A; CN101500955A; CN101500955B; TWI359119B; KR20140130477A; KR20090048616A

Abstract

A system is provided for characterizing a molten glass, wherein a waveguide (20a) is acoustically coupled to an exterior surface (34) of a vessel (10) retaining a quantity of glass melt. An acoustic wave is imparted into the glass melt (15) by a first transducer (24a) through a first waveguide (20a) wherein portions of the wave are reflected within the glass melt and received through a second waveguide (20b) and a resulting signal is produced by a second transducer (24b) and analyzed to characterize the glass melt.

Description

METHOD AND APPARATUS FOR CHARACTERIZING A GLASS MELT BY ULTRASONIC ILLUMINATION

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

[0001] The present invention relates to characterizing a fluid, and more particularly, to characterizing a glass melt by illuminating the glass melt with ultrasound.

DESCRIPTION OF RELATED ART

[0002] High quality glass is formed by the controlled cooling of a glass melt. However, the glass melt can include inhomogeneities such as solid and gaseous inclusions and small volumes of deviating density and chemical composition commonly referred to as cord. Specifically, the formation of 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.

[0003] Typically, characteristics of a glass melt are determined by sampling the glass during various stages of processing, or by installing in-line sensors, such as thermocouples. In high temperature, industrial glass making processes, the molten glass is typically contained by and/or flowed through enclosed conduits insulated about the entire outer perimeter of the conduit, making sampling all but impossible. [0004] On the other hand, few in-line sensors have the capability of sustained operation at the high temperature used in the processing of glass. While thermocouples have been used to measure temperature within the glass melt of some processes, the use of the thermocouples is undesirable, as the thermocouples deteriorate at an unacceptable rate. Further, the insertion of a sensor within the glass melt can foul the sensor, create a flow disruption, or create an unacceptable heat loss to the system, thereby reducing product quality. BRIEF SUMMARY OF THE INVENTION

[0005] The present system noninvasively characterizes a glass melt, wherein corrective procedures or modifications to glass melt processing parameters can be applied in response to the sensed characteristic so as to produce a resulting glass having nominal characteristics. That is, the present system provides an increased knowledge of glass melt characteristics, which knowledge allows processing parameters to be correspondingly adjusted, thereby enhancing the quality of the resulting product. [0006] More particularly, the system can provide a method of characterizing a glass melt by coupling an acoustic wave into the glass melt through an exterior surface of a vessel, the vessel retaining a volume of the glass melt, and the acoustic wave reflecting from inhomogeneities within the glass melt, detecting the reflected acoustic wave, and determining or detecting the presence of inhomogeneities (including both gaseous and solid) in the glass melt corresponding to the detected reflected acoustic wave. [0007] In a further configuration, the system for characterizing a glass melt includes a vessel for containing the glass melt, a first acoustic waveguide coupled to an exterior surface of the vessel for acoustically coupling an acoustic wave from a first transducer to the glass melt, a second acoustic waveguide coupled to an exterior surface of the refractory metal vessel for acoustically coupling a reflected acoustic wave from the glass melt to a second transducer, the reflected acoustic wave coinciding with an inhomogeneity in the glass melt and wherein neither the first nor second waveguides directly contact the glass melt.

[0008] 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.

[0009] 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 maybe 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 SEVERAL VIEWS OF THE DRAWINGS [0010] FIG. 1 is a cross-sectional schematic view of an apparatus for sensing and/or characterizing a glass melt in accordance with an embodiment of the present system. [0011] FIG. 2 is a cross sectional closeup view of coupling between a waveguide and the wall of a vessel for containing a glass melt for the apparatus of FIG. 1. [0012] FIG. 3 is a cross sectional closeup view of another method of coupling a waveguide and the wall of a vessel for containing a glass melt for the apparatus of FIG. 1.

[0013] FIG. 4 is a plot of travel time for an acoustic signal as a function of temperature for an acoustic path in an experimental set up.

[0014] FIG. 5 is a diagrammatic view of an exemplary glass making system utilizing the sensing/characterizing apparatus of FIG. 1.

[0015] FIG. 6 is a plot showing the sensing transducer output voltage as a function of sample (record) over time.

DETAILED DESCRIPTION OF THE INVENTION

[0016] Sound is a vibration that travels or propagates through a medium, such as a liquid or air. 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 speed and wavelength. [0017] hi accordance with the present invention, a method of characterizing a molten glass is disclosed employing a basic pulse-echo technique: electrical pulses are created by a high frequency pulse generator and converted into acoustic (sound) waves by a suitable transducer, for example a piezoelectric transducer acoustically coupled to the glass melt by a first waveguide. The ultrasonic waves propagate through the waveguide and are transmitted into the glass melt through a vessel containing the melt. In the melt, the sound waves are attenuated and scattered by inhomogeneities, if present, and reflected from boundaries. The reflected waves can be detected by a second transducer acoustically coupled to the glass melt through a second waveguide, wherein the acoustic waves can be converted back to an electric signal. The signal is amplified and can be processed by a suitable data acquisition system. For example, the signal can be processed, for example, by a computer that can measure such parameters as transit time, amplitude and frequency of the acoustic wave. These parameters convey information about the physical and geometrical properties of the molten glass medium, e.g. the ultrasonic attenuation, the presence of inhomogenities (bubbles), flows in the melt, the temperature of the melt and so forth.

[0018] The term "glass" includes material with a random, liquid-like (non-crystalline) molecular structure. The manufacturing process of glass requires that raw materials be heated to a temperature sufficient to produce a relatively low viscosity melt, which, when cooled, becomes rigid without crystallizing. The glass melt can be any of a variety of compositions including soda lime glass, lead glass, borosilicate glass, aluminosilicate glass, 96% silica glass, fused silica glass and alumino-borosilicate glass. The term "glass melt" or "molten glass" 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 "acoustic wave" is meant to encompass the mechanical vibrations transmitted through the medium. In one configuration, the acoustic wave is within the ultrasonic range, that is between approximately 100 kHz and 300 kHz.

[0019J In accordance with an embodiment of the present invention, an exemplary apparatus 8 for characterizing a glass melt is shown in FIG. 1 and comprises vessel 10, a pair of acoustic waveguide assemblies 12, 14 and controller 16. Vessel 10 may be surrounded by a thermally insulating refractory jacket 18.

[0020] Vessel 10 can be any of a variety of configurations which retain a volume of the glass melt. Vessel 10 can be self-contained, with either an open or closed top, and retaining a volume of the glass melt. In one configuration, vessel 10 defines a flow path selected in conjunction with the waveguide assemblies 12, 14 to allow sensing within a given percentage of the cross-sectional area of the flow path. Thus, vessel 10 can hold or can receive glass melt flow from an upstream position and allow the glass melt to flow to a downstream position. Vessel 10 can be a tube for example, through which a glass melt flows, and FIG. 1 then illustrates a cross sectional view of the tube. [0021] Vessel 10 should be comprised of a material that can withstand the intended operating temperatures for glass melts, typically on the order of approximately 800⁰C to approximately 1700⁰C. The vessel preferably comprises a metal selected from the platinum group metals, including platinum, rhodium, iridium, ruthenium, palladium, osmium or alloys thereof. However, other high temperature materials may also be used. For example, molybdenum may serve as an effective vessel material by itself or in combination with other materials.

[0022] Waveguide assemblies 12, 14 are acoustically coupled to vessel 10 to define an acoustic path extending from first waveguide assembly 12 through a portion of the vessel wall into the glass melt 15 retained within the vessel, and from the melt through an opposed portion of the vessel wall and into the remaining waveguide assembly 14. [0023] FIG. 1 discloses the pair of acoustically coupled waveguide assemblies 12, 14 as co-linear and diametrically opposed across the vessel, thereby providing a straight acoustic path between the waveguide assemblies. This arrangement is particularly suited to detecting inhomogeneities having significant dimensions with respect to the acoustic wavelength, such as larger glass bubbles, such as on the order of millimeters in diameter, crossing the acoustic path. Such a passage can cause an amplitude reduction of the ultrasonic signal detected by the receiving transducer. In an alternative arrangement, suited to the detection of small inhomogeneities, such as small bubbles in the sub-millimeter scale, the waveguides may be arranged in a V-shape. [0024] In a further configuration, it is contemplated that a plurality of waveguide assembly pairs 12, 14 can be acoustically coupled to the vessel. The waveguide pairs are preferably collinear and diametrically opposed with respect to the vessel, but may be oriented in a plurality of V-shapes if needed, depending on the application. [0025] As waveguide assemblies 12, 14 are essentially identical, the following description will be directed to waveguide assembly 12, with the understanding that the description of individual components, unless otherwise stated, pertains equally to waveguide assembly 14. Components of waveguide assemblies 12 and 14 are differentiated in the drawings by the suffixes "a" and "b", respectively, appended to the individual components. Waveguide assembly 12 includes waveguide 20a comprising core rod 21a and cladding tube 22 a, and transducer 24a, wherein one end of waveguide 20a is acoustically coupled to the transducer and the other end of waveguide 20a is acoustically coupled to vessel 10. Preferably, waveguide 20a is physically coupled or affixed to vessel 10 as well as acoustically coupled, hi some embodiments, waveguide 20a is also physically coupled to transducer 24a. Methods of physically coupling waveguide 20a can include soldering/welding, threaded fittings, or any other methods as may be practical.

[0026] As transducer 24a cannot reliably function at the elevated temperatures associated with the glass melt and the refractory vessel, waveguide 20a is acoustically coupled between transducer 24a and refractory vessel 10 to space the transducer from the vessel. This spacing produces a temperature gradient along a length of waveguide 20a which allows the transducer to operate at a lower temperature than the refractory vessel and the glass melt. [0027] Transducer 24a is a suitable transducer for producing an ultrasonic signal. For example, transducer 24a may be a Langevin or Tonpilz-type transducer. Transducer 24a converts the electrical signal generated by signal generator 23 and amplified by amplifier 25 into an acoustic signal or wave. Signal generator 23 and amplifier 25 can be operably coupled to transducer 24a through control lines 29, 31 in a conventional manner. Controller 16 is operably connected to signal generator 23 through control lines 27. Controller 16 may be, for example, a dedicated processor or computer. [0028] The acoustic coupling of transducer 24a to waveguide 20a for conveying an acoustic signal or wave to the glass melt can include biasing waveguide 20a against transducer 24a. The biasing can be accomplished by a loading of the waveguide (or the transducer) or a separate biasing member such as a spring. However, a more solid coupling, such as soldering/welding or threaded fittings, can enhance signal transmission from the transducer to the waveguide.

[0029] Waveguide 20a is an elongate member capable of transmitting ultrasonic signals. Although waveguide 20a can have any of a variety of configurations, such as stepped or tapered horns or folded configurations, an elongate member has been found to perform as a suitable waveguide. Because waveguide 20a will at one end be coupled to vessel 10, waveguide 20a should be capable of resisting the high temperatures experienced by the vessel while at the same time performing as an effective waveguide. Thus, waveguide 20a is preferably comprised of a refractory metal core rod 21a such as platinum or a platinum alloy such as a platinum rhodium alloy. In one configuration, the outer diameter of core rod 21a is about 3 mm. Waveguide 20a preferably also comprises cladding tube 22a. Cladding tube 22a is preferably a ceramic material, such as mullite (3 AI2O₃2SiO₂), and providing a higher velocity path for the acoustic wave than the core rod. Cladding tube 22a preferably extends along substantially the entire length of core rod 21a. The outer diameter of core rod 21a should be selected to fit snugly within a bore of cladding tube 22a. In selected configurations, an acoustic coupling agent may be disposed between core rod 21a and cladding tube 22a to ensure adequate acoustic coupling between the core rod and the cladding. Alternatively, waveguide cladding 22a may be formed around core rod 21a.

[0030] To maintain a suitable operating temperature for transducer 24a, cladding tube 22a may be shortened so that an approximately 8-10 mm length of core rod 21a at the end adjacent transducer 24a is exposed. A cooling airflow may be passed over the exposed portion of core rod 21a through passage 30a to maintain the temperature at the interface of the transducer and the waveguide below approximately 50°C. [0031] Referring to FIG. 1, outer tube 32a can be disposed concentrically about each waveguide. Outer tube 32a should be spaced apart from waveguide 20a so that an annulus is formed between waveguide 20a and outer tube 32a. The annulus, may, for example, contain air.

[0032] One end of outer tube 32a is bonded to exterior surface 34 of vessel 10. Bonding of outer tube 32a to the vessel wall enhances the definition of areas on the vessel wall for radiating and receiving acoustic energy (i.e. acoustic waves). As vessel 10 is typically surrounded by refractory insulating material 18, outer tube 32a functions to keep the insulating material away from the vicinity of the contact point between the waveguide and the vessel, and also provides space for cooling of the waveguide. Outer tube 32a may, for example, comprise a ceramic such as Al₂O₃. The bonding or physical coupling of outer tube 32a to vessel 10 may, for example, utilize a refractory adhesive. [0033] In some embodiments, waveguide 20a may be coupled to vessel 10 by first soldering/welding a threaded fitting such as receptacle 35 to vessel 10, as illustrated in FIG. 2. Complementary threads are formed at an end of waveguide 20 (e.g. at an end of core rod 21), and the waveguide coupled to the vessel by threading the waveguide into the receptacle. As shown in FIG. 2, receptacle 35 is in the form of a collar with internal threading, while waveguide 20a includes external threads at an end thereof for physically coupling to receptacle 35 and hence vessel 10. Preferably, receptacle 35 comprises platinum or a platinum-alloy. Alternatively, as depicted in FIG. 3, coupling between waveguide 20a and vessel 10 may be accomplished by attaching a threaded stub 40 to vessel 10 (e.g. by soldering or welding), and forming a complementarily threaded recess into waveguide 20a (i.e. core rod 21a), whereupon waveguide 20a may be threaded onto stub 40, thereby coupling waveguide 20a to vessel 10 through stub 40. In a simpler approach, core rod 21a may be soldered/welded directly to vessel 10. [0034] It has been found beneficial when coupling waveguide 20a to fitting 35 or stub 40, to ensure a good planar contact between the physical coupling means. That is, the end face of core rod 21a should preferably be transverse to the longitudinal axis of the waveguide, and make complete contact with the base of the internal threaded bore in fitting 35 such that the interfacial contact area 36 between the end of the rod and the fitting, and not the threads thereof, are relied upon for substantial acoustic coupling. This principal is true also for the interfacial contact area 38 between the end of core rod 21a and stub 40, if used.

[0035] In operation, acoustic signals (acoustic waves) are produced by transducer 24a and acoustically coupled into waveguide 20a. The acoustic signals propagate through waveguide 20a to vessel 10 and are subsequently introduced into glass melt 15 by the vessel. The propagating acoustic wave is reflected by inhomogeneities in the molten glass. The reflected acoustic wave propagates through the vessel wall and is received by second waveguide assembly 14 comprising core rod 21b and cladding 21b. The acoustic signal travels through waveguide 20b to receiving transducer 24b where a corresponding electrical signal is created by the transducer and directed to preamplifier 33 through line 37 and amplifier 26 through line 39 before reaching controller 16 via line 40. The electrical signal may then sampled and recorded. A digital oscilloscope may also be used to digitize the received signal, wherein each digitized sample comprises a "record".

[0036] The frequency of the acoustic wave produced by transducer 24 is selected to detect the presence of small bubbles, cording or other imperfections of interest. However, it is understood the signal frequency must be sufficiently low so that losses along the acoustic path are acceptable. Preferably, the frequency of the acoustic wave i between about 100 kHz and 300 kHz.

[0037] The measured travel time of an acoustic wave in the glass melt corresponds to a temperature of the glass melt. It has been determined that within a certain temperature range, the correlation between travel time and temperature is substantially linear. Thus, the travel time of acoustic pulses between the waveguide assemblies can be determined and used to calculate the temperature of the melt. That is, travel time for a range of temperatures can be determined. The resulting correlation can then be used to ascertain the temperature of the melt based on a measured travel time. For example, FIG. 4 depicts travel time on the vertical axis as a function of temperature for an experimental arrangement where the path through the glass melt between the transmitting portion of the vessel and the receiving portion of the vessel was only 55 mm. The figure shows a substantially linear correlation between temperature and time from about 1400⁰C to about 1550⁰C. The change in direction of the plot between about 1550⁰C and 1575°C is thought to be due to softening of the platinum vessel at these high temperatures. It is believed that by addressing this issue, such as with alternative materials, the temperature range could be extended to perhaps about 1600⁰C, and with a longer path it would be possible to achieve an accuracy within a couple of degrees.

[0038] To detect the presence of bubbles, the digitized data is examined from a storage device, or real time on an oscilloscope, for transit or travel time as a function of pulse time and the magnitude (voltage) of the received signal.

[0039] The present configuration thus allows for determination of acoustic signal travel time through the glass melt for the purpose of determining a temperature of the melt, as well as bubble detection in the glass melt. Advantageously, the apparatus and method of the present invention may be used in a glass manufacturing system, such as a manufacturing system for forming glass sheets.

[0040] Referring to FIG. 5, 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 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 48. The glass manufacturing system 42 further includes components that are typically made from platinum or platinum-containing metals such as platinum-rhodium, platinum-iridium 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), melter to finer connecting tube 52, mixing vessel 54 (e.g. stir chamber 54), finer to stir chamber connecting tube 56, delivery vessel 58 (e.g. bowl 58), stir chamber to bowl connecting tube 60, and 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, dividing into two separate glass flows that flow down converging external surfaces of forming vessel 66. The two separate molten 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.

[0041] 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.

[0042] In accordance with an embodiment of the present invention, apparatus 8 may be advantageously employed within the platinum-containing portions of glass manufacturing system 42. For example, one or more apparatus 8 may be coupled to any one or more of the following components: melter to finer tube 52, finer 50, finer-to- stirrer connecting tube 56 or stir chamber 54 in order to detect the presence of inhomogeneities in the molten glass. If inhomogeneities are detected, remedial action may be taken as is known in the art for reducing such inhomogeneities. For example, bubbles may be reduced by varying an atmosphere external to the finer (e.g. by increasing the amount of hydrogen contained in the atmosphere. Cord may be mitigated by increasing the stirring speed in the stirring chamber. Of course the method and apparatus of the present invention is not limited to use in a fusion glass making system as described herein, but may be employed in any glass forming operation that uses metallic vessels to process the molten glass.

Example 1

[0043] Several waveguides, each comprising approximately 3 mm diameter platinum- rhodium core rods were dry-inserted into mullite cladding tubes having an outer diameter of approximately 9.5 mm. The core rods were soldered to the external surface of a platinum-rhodium, generally cylindrical crucible having a diameter of approximately 55 mm in a co-linear relationship such that a longitudinal axis of each waveguide coincided. The mullite cladding tubes were shortened on each platinum alloy rod so that the exposed ends of the rods could be passed perpendicularly through holes in stainless steel tubes. A commercially available 1 MHz 0.25 inch ultrasonic transducer was lightly pressed against each platinum rod of each waveguide (e.g. a transmitting transducer and a receiving transducer), with an ultrasonic couplant disposed between the transducers and the rods. The stainless steel tubes carried a cooling airflow that maintained a temperature at the interface of the waveguides and transducers at approximately 50⁰C.

[0044] Second, Al₂O₃ outer tubes were arranged concentrically about each waveguide and affixed to the crucible to define the radiating and reception areas of the crucible. The resulting assembly was inserted into a tubular oven with provision for the waveguides to extend through and beyond the oven.

[0045] An alumino borosilicate glass was premelted in a separate vessel to ensure the removal of preexisting bubbles in the glass. The glass was then transferred to the crucible. In one configuration, the transmitting transducer was driven by a Metrotek MP 217 pulser, operated at maximum pulse width, damping resistance and amplitude. Received signals detected by the receiving transducer through the second waveguide were routed through a Bruel & Kaer 2637 preamplifier with a 0.1 — 1.4 MHz filter in combination with a Bruel & Kaer 2638 conditioning amplifier set to 0.05 - 2 MHz bandwidth and 20 dB amplification. The signals were digitized with 8 bit resolution by a LeCroy 9450 digital oscilloscope for a total of 2,500 samples recorded at a 10 MHz sample rate, starting after an 80 μs trigger delay.

[0046] In a first part of the experiment, with a clear acoustic path in the glass melt, the time domain response for about 250 records was recorded and averaged. A thin ceramic tube having an outside diameter of about 10 mm and an inside diameter of 6 mm was inserted into the melt within the crucible through the ceiling of the furnace. Compressed nitrogen was slowly blown into the glass melt through the tube to generate bubbles near the bottom of the crucible that rose to the surface of the melt. A bubble flask in the compressed nitrogen line allowed an approximate indication of the instant each bubble was generated. The temperature of the furnace was about 1570°C. [0047] Without the bubble tube, the ultrasonic path was clear and the time domain response as indicated by the oscilloscope was quite stable. The bubble tube was subsequently introduced into the melt and at about record 250 the first bubbles were generated at a fairly constant rate of about 1 bubble per every 1 — 2 seconds. During the experiments, an oscilloscope screen was used to display time response fluctuations. These fluctuations occurred at the rate of bubble generation.

[0048] As in the preceding example, the records were filtered through a 200 kHz fourth order Butterworth filter, their envelope computed and the average envelope over the initial unperturbed period (in this case the first 150 records) was subtracted. Between records 250 and 550, 13 bubble passages were observed in the response plot. [0049] FIG. 6 illustrates a simple output showing the sensing transducer output voltage as a function of sample (record) over time for the preceding experiment. The presence of detected bubbles can be clearly seen as a series of thirteen voltage spikes starting at about record (sample) 250, corresponding to the thirteen released bubbles. Oddly, a voltage reduction was anticipated for the bubble indication. It is thought that the voltage increase is a result of imperfect alignment of the transmit and receive transducer assemblies or a focusing effect by the bubbles.

[0050] While the invention has been described in conjunction with specific exemplary embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, the present invention is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims.

Claims

What is claimed is:

1. A method of characterizing a glass melt in a vessel (10) comprising: coupling an acoustic wave into the glass melt through an exterior surface (34) of the vessel (10); detecting a reflected acoustic wave in the glass melt; and determining the presence of inhomogeneities in the glass melt corresponding with the detected reflected acoustic wave.

2. The method according to claim 1 , further comprising flowing the glass melt through the vessel.

3. The method according to claim 1 , wherein determining the presence of inhomogeneities in the glass melt corresponds to at least one of measuring a transit time, an amplitude and a frequency of the reflected acoustic wave.

4. The method according to claim 1, wherein the inhomogeneities are gaseous.

5. The method according to claim 1 , wherein the inhomogeneities are solid.

6. The method according to claim 1 , wherein the coupling an acoustic wave comprises coupling a first ultrasonic transducer (24a) to a surface (34) of the vessel (10) through a first waveguide (20a).

7. The method according to claim 6, wherein the transducer (24a) is a piezoelectric transducer.

8. The method according to claim 6, wherein the reflected acoustic wave is acoustically coupled to a second ultrasonic transducer (24b) through a second waveguide (20b) coupled to the exterior surface (34) of the vessel (10).

9. The method according to claim 1, wherein the vessel (10) is comprised of platinum.

10. The method according to claim 8, wherein each of the first and second waveguides (20a, b) comprises an elongate metallic core rod (2 la,b) and a non-metallic cladding (22a,b).

11. The method according to claim 8 wherein the first and second waveguides (20a,b) each comprise a core (21a,b) and a cladding (22a,b).

12. The method according to claim 1 wherein the determining the presence of inhomogeneities further comprises determining a temperature of the glass melt.

13. An apparatus for characterizing a glass melt comprising: a vessel (10) for containing the glass melt (15); a first waveguide (20a) coupled to an exterior surface (34) of the vessel (10) for acoustically coupling an acoustic wave from a first transducer (24a) to the glass melt (15); and a second waveguide (24b) coupled to the exterior surface (34) of the vessel (10) for acoustically coupling a reflected acoustic wave from the glass melt (15) to a second transducer (24b), the reflected acoustic wave coinciding with an inhomogeneity in the glass melt.

14. The apparatus according to claim 13, wherein the vessel (10) comprises platinum.

15. The apparatus according to claim 13, further comprising first and second tubes (32a,b) physically coupled to the vessel concentric with the first and second waveguides (20a,b) for defining acoustic radiating and receiving areas, respectively, of the vessel.

16. The apparatus according to claim 13, wherein the first and second waveguides (20a,b) are aligned along a common longitudinal axis.

17. The apparatus according to claim 16, wherein each of the first and second waveguides comprises a metallic core sleeved with a non-metallic cladding.

18. The apparatus according to claim 17, wherein the first and second waveguides (20a,b) are aligned along a diameter of vessel (10).

19. A glass making system (42) comprising the apparatus of claim 13.