This study focuses on the critical aspect of interfacial heat transfer during the solidification process in metal casting, aiming to optimize these manufacturing processes. Fiber-optic sensors were employed to provide continuous real-time monitoring of mold gaps and temperature profiles during the solidification of A356 aluminum in a permanent mold-casting environment. A specially designed mold system, constructed from unheated, uncoated tool steel, facilitated the seamless integration of these advanced fiber-optic sensors. One key technique used was the Extrinsic Fabry-Perot interferometric (EFPI) sensor, which uniquely utilized molten metal as the second reflection interface for measuring mold gaps. This method yielded impressively accurate results, with a maximum error of just 2μm compared to physical measurements. Additionally, using the Rayleigh backscattering (RBS) technique, a stainless steel-encased fiber provided real-time temperature measurements with an impressive spatial resolution of 0.65mm. The study demonstrates that combining high-resolution temperature profiles with gap evolution measurements significantly enhances our understanding of heat transfer dynamics at the mold-metal interface, proving particularly beneficial for optimizing complex-shaped castings and continuous casting processes. Furthermore, the capability to monitor the shape of the casting in real-time as it exits a continuous casting mold introduces a novel tool for quality control and process safety improvement by early detection of conditions that might lead to slab cracking and breakouts, ultimately enhancing overall process efficiency and reliability.
The continuous casting process for steel production utilizes specially designed oxyfluoride glasses (mold fluxes) to lubricate the mold and control the steel solidification process. The composition of the flux controls important properties, such as viscosity, basicity, and crystallization rate, which in turn influences the quality of the as-cast product. However, these fluxes also interact with the steel during casting, causing chemistry shifts that must be anticipated in the design of the flux.
Today, the in-service chemistry of the flux must be determined by taking flux samples from the mold during casting and then processing the samples off-line to determine chemistry and other physical properties, such as viscosity. Raman spectroscopy provides an alternative method for flux analysis, with the possibility of performing direct on-line analysis during casting. Raman spectroscopy has the unique ability to identify specific molecules through well-resolved vibrational bands that provide fingerprint signatures of the structure of the molecules. Specific peaks in the Raman spectra can be correlated with flux chemistry and viscosity.
The work reported here aims to assess the structure and chemical composition of flux samples at high temperatures using fiber-optic Raman spectroscopy. Results from Raman spectral analyses captured the 1300 °C for a range of flux chemistries are presented. The experimental results demonstrate that the composition-dependent Raman signal shift can be detected at high temperatures and that on-line flux analysis using a high-temperature Raman system shows significant promise.
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