SYSTEM FOR MEASURING MATERIAL THICKNESSES AT HIGH TEMPERATURES
A sheet-forming apparatus including a crucible for holding a melt of material and a solid sheet of the material disposed within the melt, a crystallizer disposed above the crucible and configured to form the sheet from the melt, and an ultrasonic measurement system disposed adjacent the crystallizer, the ultrasonic measurement system comprising at least one ultrasonic measurement device including a waveguide coupled to an ultrasonic transducer for directing an ultrasonic pulse through the melt.
1 . A sheet-forming apparatus comprising:
a crucible for holding a melt of material and a solid sheet of the material disposed within the melt;
a crystallizer disposed above the crucible and configured to form the sheet from the melt; and
an ultrasonic measurement system disposed adjacent the crystallizer, the ultrasonic measurement system comprising at least one ultrasonic measurement device including a waveguide coupled to an ultrasonic transducer for directing an ultrasonic pulse through the melt.
2 . The sheet-forming apparatus of claim 1 , wherein the waveguide is further configured to direct the ultrasonic pulse through the sheet.
3 . The sheet-forming apparatus of claim 1 , wherein the ultrasonic measurement device comprises a plurality of ultrasonic measurement devices disposed in a laterally-spaced arrangement across a width of the melt.
4 . The sheet-forming apparatus of claim 1 , wherein a tip of the waveguide is disposed within a protective enclosure within the melt.
5 . The sheet-forming apparatus of claim 4 , further comprising a quantity of molten metal disposed intermediate the tip of the waveguide and the protective enclosure for providing a low acoustic impedance coupling therebetween.
6 . The sheet-forming apparatus of claim 4 , further comprising a segmented melt-back heater in communication with the ultrasonic measurement system and configured to melt back portions of the sheet based on a thickness of the sheet measured by the ultrasonic measurement system.
7 .- 15 . (canceled)
16 . The sheet-forming apparatus of claim 1 , wherein the waveguide is further configured to direct the ultrasonic pulse through the sheet, a tip of the waveguide is disposed within a protective enclosure within the melt, a quantity of molten metal is disposed intermediate the tip of the waveguide and the protective enclosure for providing a low acoustic impedance coupling therebetween, and a segmented melt-back heater is communicatively coupled to the ultrasonic measurement system and is configured to melt back portions of the sheet based on a thickness of the sheet measured by the ultrasonic measurement system
17 . A system for measuring a thickness of a sheet of material on a surface of a melt of the material, the system comprising at least one ultrasonic measurement device including a waveguide coupled to an ultrasonic transducer for directing an ultrasonic pulse through the melt and the sheet.
18 . The system of claim 17 , wherein the at least one ultrasonic measurement device comprises a plurality of ultrasonic measurement devices disposed in a laterally-spaced arrangement across a width of the melt.
19 . The system of claim 17 , wherein a tip of the waveguide is disposed within a protective enclosure within the melt and below the sheet.
20 . A method for determining locations of material interfaces in a sheet-forming apparatus comprising:
directing an ultrasonic pulse through a melt of material in the sheet-forming apparatus; and
deriving, from reflections of the ultrasonic pulse at boundaries of the melt, the locations of the material interfaces.
21 . The method of claim 20 , further comprising:
directing the ultrasonic pulse through a sheet of the material disposed in the melt; and
deriving, from reflections of the ultrasonic pulse at boundaries of the sheet, a thickness of the sheet.
22 . The method of claim 21 , further comprising calculating a time of flight for the reflections at the boundaries of the sheet in order to derive the thickness of the sheet.
23 . The method of claim 12 , wherein directing the ultrasonic pulse through the sheet of material comprises directing a plurality of ultrasonic pulses through the sheet of material to ascertain a thickness profile of the sheet across a width of the sheet.
24 . The method of claim 23 , further comprising using the ascertained thickness profile of the sheet to tune a heat profile of a segmented melt-back heater in order to melt back selected portions of the sheet.