Fiber optic interferometric sensor for high temperature mould gap measurement.

Abstract

A temperature sensitive fiber optic Fabry-Perot interferometer based mold gap measurement system that can be employed in foundry and continuous casting facilities for non-ferrous and ferrous production applications. For steel continuous casting, the sensor can also detect crystallite formation in the mold flux layer in the mold gap by detecting reflections from both the flux layer and the steel shell, facilitating direct monitoring of mold lubrication in continuous casting. These interferometers can also be easily multiplexed to measure interface shapes and monitor gap changes at various locations within complex mold designs. The ability to measure strip shape exiting a continuous casting mold during operation provides a new tool to monitor and improve product quality during operation and enhance process safety by detecting conditions that could lead to slab cracking or breakouts.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Patent Application No. 63 / 263,420, filed November 2, 2021, the entire contents of which are incorporated by reference for all purposes. [Background technology]

[0002] Solidification is a fundamental step in all metal manufacturing processes, and most of these processes employ some type of mold to convert the liquid metal into the desired solid shape. The fundamental nature of heat transfer at the mold-metal interface remains largely unknown, especially for complex shaped castings and continuous cast metals. Mathematical models combining solidification, heat conduction, and mechanical stresses have been employed to gain insight into the behavior of gaps that develop at the interface during solidification of static molds. More sophisticated models have also attempted to model and predict the behavior of solidification and heat transfer in continuous casting molds from first principles by including mold flux liquid and crystalline layers in the gap model.

[0003] A fundamental capability lacking in this field is the ability to directly measure the mold gap and temperature profile that develops during the high temperature solidification process. Attempts to measure the mold gap during solidification using linear displacement sensors such as Linear Variable Differential Transformers (LVDTs) have met with limited success. Such displacement sensors are mechanically complex to mount and require temperature compensation. Summary of the Invention

[0004] Aspects of the present disclosure enable accurate mold gap measurement using fiber optic interferometry. The optical interferometer approach provides dynamic measurement of the mold gap at elevated temperatures during casting. The ability to predict and ultimately control local solidification conditions at the mold-metal interface will have a significant overall impact on cast product quality and yield, greatly improving the metals industry's ability to produce new, more difficult to cast alloys and products for both military and industrial markets.

[0005] Sensor technology embodying aspects of the present disclosure can directly impact the quality and yield of ferrous and non-ferrous castings and products (such as sheet, plate, SBQ bar products) produced by continuous casting routes, resulting in a higher quality and lower cost supply chain.

[0006] In one aspect, the temperature sensitive fiber optic Fabry-Perot interferometer based mold gap measurement system can be employed in foundry and continuous casting facilities for both non-ferrous and ferrous production applications. For steel continuous casting, the sensor can also detect crystallite formation in the mold flux layer in the mold gap by detecting reflections from both the flux layer and the steel shell, facilitating direct monitoring of mold lubrication in continuous casting. These interferometers can be easily multiplexed to measure interface shapes and detect gap changes at various locations within complex mold designs. The ability to measure mold shapes exiting a continuous casting mold during a run provides a new tool to monitor and improve product quality during the run and enhances process safety through detection of conditions that lead to slab cracking and breakouts.

[0007] In another aspect, a fiber optic interferometer sensor system for measuring a metal-mold gap includes a ferrule embedded in a wall of the mold, a first end of the ferrule being flush with an inner surface of the mold. An optical fiber has at least an end margin disposed within the ferrule such that an end face of the optical fiber is recessed a predetermined distance from the first end of the ferrule and the inner surface of the mold. The optical fiber is configured to transmit light and receive light reflected from the metal deposited within the mold. The sensor system also includes an interferometer coupled to the optical fiber. The interferometer is configured to measure a distance between the end face of the optical fiber and the metal deposited within the mold as a function of the reflected light from within the mold received by the optical fiber.

[0008] In yet another aspect, a method of measuring a gap between a metal and a mold includes positioning an optical fiber such that an end face of the optical fiber is recessed a predetermined distance from an inner surface of the mold. The optical fiber is configured to transmit light and receive light reflected from the metal deposited in the mold. The method also includes transmitting light through the optical fiber to an interior of the mold with an interferometer system and receiving, with the interferometer system, light reflected from the end face into the optical fiber and light reflected from the metal in the mold into the optical fiber. The method further includes performing, with the interferometer system, a Fabry-Perot interferometer that measures the distance between the end face of the optical fiber and the metal deposited in the mold as a function of the received reflected light.

[0009] Other objects and features of the present disclosure will be in part apparent and in part pointed out hereinafter. [Brief description of the drawings]

[0010] [Figure 1] 1 illustrates a Fabry-Perot interferometer sensor according to an embodiment; [Diagram 2] 2 is an example of the sensor of FIG. 1 used to detect gaps in a mold according to an embodiment. [Diagram 3] FIG. 3 is an enlarged view of the mold according to the embodiment of FIG. 2. [Figure 4] FIG. 13 is an enlarged view of a mold according to an alternative embodiment.

[0011] Corresponding reference numbers indicate corresponding parts throughout the drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Aspects of the present disclosure relate to the deployment of a fiber optic interferometer-based mold gap measurement system that can be employed in foundry and continuous casting facilities for both non-ferrous and ferrous manufacturing applications. With reference to FIG. 1, an embodiment of a sensor 100 includes at least one optical fiber 102 powered by a swept laser 104. Light exits the optical fiber 102 at a sensor head 106. A detector 110 detects the light reflected back through the optical fiber 102 and processes it in a processor or computer 112. In the illustrated embodiment, an optical circulator 114 prevents the reflected light from returning to the laser 104. If the sensor 100 includes multiple optical fibers 102, an optical switch 118 can be used to switch between the optical fibers carrying the optical signals. In this manner, the sensor 100 forms an external Fabry-Perot interferometer (FPI).

[0013] 2 is a cross-sectional view of an example of a mold 202 containing metal 204. As shown, a solidified shell 206 of metal 204 develops during the solidification process. As shown, mold 202 has a wall 210 in which optical fiber 102 of FPI sensor 100 is embedded. Wall 210 includes an opening shaped and sized to receive ferrule 212 (i.e., sensor head 106). In an embodiment, ferrule 212 includes a retainer 214 for securing ferrule 212 in place within wall 210. Ferrule 212 has an orifice shaped and sized to receive optical fiber 102. Ferrule has a distal end 212a flush with inner surface 216 of wall 210 and a proximal end 212b through which optical fiber 102 extends and is connected to laser 104 and detector 110. In an embodiment, distal end 212a is configured to have a larger diameter than proximal end 212b. Additionally, the distal end 212a of the ferrule 212 has an interior surface configured to face the interior of the mold 202. The ferrule 212 is embedded in an opening in the wall 210 such that the interior surface of the ferrule 212 at the distal end 212a is flush with the interior surface 216 of the wall 210. According to aspects of the present disclosure, the optical fiber based sensor 100 uses the principles of Fabry-Perot interferometry to directly measure the gap between the mold 202 and the metal 204.

[0014] FIG. 3 is a close-up view of the interface between the optical fiber 102 and the shell 206. As shown in FIG. 3, the end face 302 of the optical fiber 102, when inserted into the ferrule 212, does not lie flush with the distal end 212a of the ferrule 212 and the inner surface of the wall 210. Instead, the optical fiber 102 is set back or recessed a predetermined distance from the inner surface of the wall 210 when the ferrule 212 is installed. By setting back the optical fiber 102, a gap 304 formed between the end face 302 and the metal 204 (or the shell 206 of the metal 204) can be measured. The size of the orifice through the ferrule 212 is configured such that when poured into the mold 202, the surface tension of the molten metal 204 will prevent the molten metal from penetrating the orifice or otherwise filling the recess. In this manner, the gap 304 between the optical fiber 102 and the inner surface 216 of the wall 210 is maintained throughout the casting process, and light emitted by the optical fiber 102 is incident on and reflected from the metal 204, allowing measurement of the gap 304. Because the distance the fiber 102 is recessed from the end face of the distal end 212a is known, the gap between the shell 206 and the inner surface 216 of the wall 210 can be determined.

[0015] In the illustrated embodiment, the orifice has a diameter of 2r, where r is defined by the following formula (1): Defined by TIFF2024542055000002.tif17138.

[0016] where γ is the surface tension, θ is the contact angle, ρ is the density, g is the acceleration of gravity, and h is the height of the liquid metal 204 above the orifice.

[0017] With further reference to Figures 1-3, the working principle of a fiber optic Fabry-Perot Interferometer (FPI) sensor 100 is illustrated. An optical fiber 102 is employed to directly measure the gap 304 that occurs during the solidification process between the mold 202 and the metal 204 using the principles of Fabry-Perot interferometry. Fabry-Perot interferometry is used to measure the distance between two parallel reflective surfaces. The advantages of this sensor technology are that it is insensitive to temperature changes in the gap 304, is simple to install, and is not subject to electromagnetic interference.

[0018] The optical fiber end face 302 and the reflector (i.e., metal 204) form an external Fabry-Perot interferometer with a cavity length (i.e., gap 304) of L. The interference signal (I) is given by the following equation (2): Given as TIFF2024542055000003.tif15136.

[0019] where I1 and I2 are the intensities of light reflected from the end face 302 of the optical fiber 102 and the reflector, respectively, φ is the initial phase difference of the interferometric sensor 100, n is the refractive index of air (approximately 1), and L is the length of the air cavity (i.e., the gap 304). The space between two consecutive minima in the spectrum is defined as the free spectral range (FSR) and is given by the following equation (3): It can be expressed as TIFF2024542055000004.tif18132.

[0020] Here, λ is the wavelength of the propagating light. In other words, the cavity length can be demodulated by calculating the FSR of the interference spectrum. The change in cavity length ΔL is given by the following equation (4): It can be found at TIFF2024542055000005.tif14137.

[0021] FSR1 and FSR2 are the FSR values ​​before and after the displacement.

[0022] In use, the optical fiber 102 is inserted into the ferrule 212, which is inserted into the wall 210 of the mold 202. Initially, a reflective surface may be butted against the inner surface of the wall 210 on the optical fiber 102. The laser 104 emits light through the optical fiber 102, which is set back in the ferrule 212. The light is reflected off the reflective surface and back through the optical fiber 102 to the detector 110. The computer 112 processes the reflected light and calculates the distance between the end face 302 of the optical fiber 102 and the reflective surface. This distance is the baseline calibration distance between the optical fiber 102 and the inner surface of the wall 210. As the molten metal 204 is poured into the mold 202, a solidified shell 206 begins to form against the inner surface of the wall 210 of the mold 202. The solidified shell 206 is formed due to the temperature difference between the mold 202 and the molten metal 204, thus forming an initial layer of solidified metal 204. During pouring, the laser 104 shines light through the optical fiber 102, and the solidified shell 206 acts as a reflector for the fiber optic FPI sensor 100. The light is reflected off the solidified shell 206 and transmitted back through the optical fiber 102 to the detector 110. The computer 112 processes the reflected light and calculates the distance between the optical fiber 102 and the solidified shell 206. When the solidified shell 206 is first formed, the measured distance between the optical fiber 102 and the solidified shell 206 is equal to the calibrated distance because there is no shrinkage of the metal 204. However, as the metal 204 continues to solidify, the metal begins to shrink and a gap 304 increases, including the portion formed between the inner surface 216 of the mold 202 and the solidified shell 206. Once this gap 304 forms, the light emitted from the optical fiber 102 is used to measure a distance that is greater than the calibrated distance. Using the fiber optic FPI sensor 100, the difference in distance between the optical fiber 102 and the metal 204 is measured over the span of the molding process.

[0023] Referring to FIG. 4, an alternative embodiment of the present disclosure is shown. In this embodiment, the fiber optic FPI sensor 100 is implemented in a continuous casting mold 202. The optical fiber 102 is embedded in the mold 202, and a flux film 402 separates the optical fiber from the metal 204. The flux material is configured so that the metal 204 flows through the mold 202. As mentioned above, Fabry-Perot interferometry is used to measure the distance between two parallel reflective surfaces. In the case of continuous casting of steel, the sensor 100 can detect crystallite formation in the mold flux layer in the mold gap 304 by detecting reflections from both the flux film 402 and the shell 206 to facilitate direct mold lubrication monitoring for continuous casting. Also, these interferometers can be easily multiplexed to perform interface shape measurements or gap variation monitoring at various locations within a complex mold design. The ability to measure the shape of the cast strip exiting the continuous casting mold during operation provides a tool to monitor and improve product quality during operation and enhances process safety by detecting conditions that lead to slab cracking and breakouts. The fiber optic FPI 100 detects crystallite formation in the flux film 402 within the gap 304 by detecting reflections from both the flux film 402 (shown as R1) and the metal shell 206 (shown as R2), facilitating direct monitoring of mold lubrication for continuous casting. Additionally, the fiber optic FPI 100 is configured to measure the thickness of the flux film 402 since light can penetrate the flux film.

[0024] In another embodiment, the sensor 100 preferably includes multiple optical fibers 102 arranged in a one or two dimensional array distributed on the inner surface 216 of the mold 202. A swept laser 104 powers each of the optical fibers 102 and a detector 110 detects the light reflected through each for processing by a computer 112. In this embodiment, the fiber optic FPI sensor 100 is implemented in an array to provide mold exit and temperature profile measurements.

[0025] In yet another embodiment, the optical fiber 102 can emit light with tunable polarization to measure reflectivity as a function of polarization and determine if the surface is isotropic.

[0026] Experimental data demonstrates the application of the Fabry-Perot interferometer sensor 100 to measure the gap 304 using permanent mold casting with A356 aluminum. The experiment shows that the solidified metal surface (i.e., solidified shell 206) acts as a reflector during the solidification process, allowing tracking of the mold gap 304 that occurs as the casting shrinks and pulls away from the mold 202. This technique further enables gap and profile monitoring in the continuous casting of slabs and billets. For example, common off-corner defects that can form in slabs and billets can be detected using the techniques disclosed herein, avoiding costly breakout events and quality losses. Also disclosed herein is a Rayleigh scattering-based fiber optic interrogation technique that measures the temperature profile along the fiber passing through the gap 304 with sub-millimeter resolution and millisecond sampling rates. In combination with the interferometer sensor 100, the measurement system provides new insight into mold-metal gap behavior for many types of casting and continuous casting processes.

[0027] This sensor 100, coupled with other recent advances in fiber optic sensor systems, provides improved knowledge of the heat transfer behavior at the mold-metal interface, enabling foundry and continuous caster manufacturers in the ferrous and non-ferrous production sectors to significantly improve the quality and yield of their cast products. The sensor 100 further provides the necessary tools to assist in the development of new advanced high strength alloy systems that often pose manufacturing challenges to existing metal manufacturers, thereby enabling new developments for military and commercial applications. Finally, the application of the sensor 100 for real-time monitoring of the casting process provides direct feedback on the state of the casting process, enabling real-time control of the casting process.

[0028] When introducing elements of aspects of the invention or embodiments thereof, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements.

[0029] Not all of the depicted components shown or described may be required. Additionally, some implementations and embodiments may include additional components. Variations in the arrangement and type of components may be made without departing from the spirit or scope of the claims defined herein. Additional, different, or fewer components may be provided, and components may be combined. Alternatively, or in addition, a component may be implemented by multiple components.

[0030] The foregoing description describes aspects of the invention by way of example and not by way of limitation. This specification describes several embodiments, adaptations, variations, alternatives and applications of aspects of the invention, including what is currently contemplated to be the best mode of carrying out aspects of the invention, enabling one skilled in the art to make and use the aspects of the invention. Moreover, it is to be understood that aspects of the invention are not limited in application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. Aspects of the invention are capable of other embodiments and of being practiced or carried out in various ways. It will also be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

[0031] It will be apparent that modifications and variations are possible without departing from the scope of the invention as defined in the appended claims. Because various changes may be made in the structure and methods described above without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense.

[0032] In view of the above, it will be seen that the several advantages of the aspects of the invention are achieved and other advantageous results attained.

[0033] The Abstract and Overview are provided to allow the reader to quickly grasp the nature of the technical disclosure. They are submitted with the understanding that they will not be used to interpret or limit the scope or meaning of the claims. The Overview is provided to introduce in a simplified form some of the concepts that are further described in the Detailed Description. The Overview is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the claimed subject matter.

Claims

1. 1. A fiber optic interferometer sensor system for measuring a metal-mold gap, comprising: a ferrule embedded in a wall of the mold, the ferrule having a first end flush with the interior surface of the mold; an optical fiber having at least an end margin disposed within the ferrule such that an end face of the optical fiber is recessed a predetermined distance from the first end of the ferrule and from an inner surface of the mold, the optical fiber being configured to transmit light, the optical fiber being further configured to receive light reflected from metal deposited within the mold; and 1. A fiber optic interferometer sensor system including: an interferometer coupled to an optical fiber, the interferometer configured to measure a distance between an end face of the optical fiber and metal deposited within the mold as a function of reflected light received by the optical fiber from within the mold.

2. 10. The fiber optic interferometer sensor system of claim 1, wherein the interferometer utilizes Fabry-Perot interferometry.

3. 3. The fiber optic interferometer sensor system of claim 1, wherein the ferrule includes a retainer at its distal end for retaining the ferrule within the walls of the mold.

4. 10. The fiber optic interferometer sensor system of claim 1, wherein the optical fiber transmits polarized light.

5. 5. The fiber optic interferometer sensor system of claim 4, wherein the interferometer is configured to measure the reflectivity of the metal in the mold as a function of polarization.

6. 6. The optical fiber interferometer sensor system of claim 4 or 5, wherein the interferometer is configured to use polarized light to detect whether the surface of the metal in the mold is isotropic.

7. a flux film is applied to an interior surface of the mold, the flux film configured to allow metal to flow within the mold; 10. The fiber optic interferometer sensor system of claim 1, wherein the interferometer is configured to measure the thickness of the flux film as a function of the reflected light from within the mold received by the optical fiber.

8. 10. The fiber optic interferometer sensor system of claim 1, wherein the interferometer is further configured to measure a temperature profile of the metal within the mold using Rayleigh scattering.

9. the ferrule includes an orifice in which the optical fiber is disposed; 10. The fiber optic interferometer sensor system of claim 1, wherein the orifice is sized small enough so that surface tension prevents metal in the mold from entering the orifice.

10. 10. The fiber optic interferometer sensor system of claim 1, wherein the interferometer is insensitive to temperature changes that affect the predetermined distance between the end face of the optical fiber, the first end of the ferrule, and the inner surface of the mold.

11. 10. The fiber optic interferometer sensor system of claim 1, wherein the interferometer is configured to be multiplexed to take measurements at multiple locations on the interior surface of the mold.

12. 1. A method for measuring a metal-mold gap of a mold having metal deposited therein, comprising: positioning an optical fiber such that an end face of the optical fiber is recessed a predetermined distance from an inner surface of the mold, the optical fiber being configured to transmit light, the optical fiber being further configured to receive light reflected from metal deposited within the mold; transmitting light through an optical fiber into the interior of the mold with an interferometer system; receiving, with an interferometer system, light reflected within the optical fiber from the end face of the optical fiber; receiving light reflected from the metal in the mold into an optical fiber with an interferometer system; and performing Fabry-Perot interferometry with an interferometer system to measure the distance between the end face of the optical fiber and the metal deposited in the mold as a function of the received reflected light.

13. further comprising embedding the ferrule in a wall of the mold; the ferrule has a first end flush with the inner surface of the mold; 13. The method of claim 12, wherein the optical fiber has at least an end margin disposed within the ferrule such that the end face of the optical fiber is recessed a predetermined distance from the first end of the ferrule and the inner surface of the mold.

14. 14. The method of claim 12 or 13, wherein transmitting light through an optical fiber comprises transmitting polarized light.

15. 15. The method of claim 14, further comprising measuring the reflectivity of the metal in the mold as a function of polarization with an interferometer system.

16. 15. The method of claim 14, further comprising detecting whether the surface of the metal in the mold is isotropic using polarized light with an interferometer system.

17. 13. The method of claim 12, wherein a flux film is applied to an interior surface of the mold, and further comprising performing Fabry-Perot interferometry with an interferometer system to measure the thickness of the flux film as a function of the received reflected light.

18. The method of claim 12 , further comprising performing Rayleigh scattering interferometry to measure a temperature profile along the optical fiber with an interferometer system.

19. positioning the array of optical fibers so that end faces of the optical fibers in the array are recessed a predetermined distance from an inner surface of the mold; transmitting light through each optical fiber into the interior of the mold with an interferometer system; receiving, with an interferometer system, light reflected within each optical fiber from an end face of each optical fiber; receiving light reflected from the metal in the mold into an optical fiber with an interferometer system; performing Fabry-Perot interferometry with an interferometer system to measure the distance between the end face of the optical fiber and the metal deposited in the mold as a function of the received reflected light; and The method of claim 12, further comprising multiplexing the measured distances to generate a profile of the gap between the metal and the mold.

20. transmitting light into the interior of the mold through an optical fiber to a reflective surface positioned flush with the interior surface of the mold; receiving light reflected from the reflective surface into the optical fiber; determining the distance from the end face of the optical fiber to the reflecting surface as a function of the received reflected light; and The method of claim 12, further comprising calibrating the predetermined distance based on the determined distance from the end face of the optical fiber to the reflective surface.

Images