9522973 Chun Real-time monitoring of the solidification front in metal casting operations will greatly enhance manufacturing productivity. In the casting of aluminum alloys for example, the shape, location, and velocity of the solidification front affect casting speed, ingot integrity, and macrosegregation. Ingot recovery loss due to cracking now amounts to as much as 10% for both aerospace and common alloys. At present, information on the solidification front is obtained either experimentally or numerically. Experimental methods include installation of a thermocouple-tree in the solidification zone, measurement of the secondary dendrite arm spacing of cast ingots, or by "doping" the liquid metal with grain refiners. While these techniques provide valuable information on the solidification front, they cannot be used for on-line, closed-loop control of the process. Efforts have also focused on the three-dimensional numerical ingot casting models to simulate, for example, mold filling and start-up and steady-state conditions. Although much progress has been made, there is no direct method of verifying these numerical models. In the current research, using high energy (5-10 MeV) gamma rays generated by a compact, linear electron accelerator (LINAC), the differences in gamma ray transmissivity due to differences in the density of the solid and liquid metals will be measured. Because the attenuation coefficients of the liquid and solid metals are about the same but their densities are different (typically 4-12 percent), it is possible to estimate the liquid (or solid) fraction of metal in a solidifying ingot. Moreover, by scanning the gamma ray beam across the solidifying ingot appropriately, a three-dimensional image of the solidification front can be obtained using the reconstruction techniques of computerized tomography. The direct result of the proposed work would be an enabling technology for the on-line monitoring of solidification front and the closed-loop control of casting oper ations. Expected research outcomes are: (i) design and fabrication of a sensor system, (ii) identification of characteristic signals that reveal such undesirable process conditions as ingot cracking and breakout, and (iii) characterization of the extent and morphology of the mushy zone at the solidification front. In primary metals processing, ingots are cast and rolled or slabs are continuously cast. The final property of the product is strongly influenced by what goes on at the molten metal and frozen solid interface. This is a dynamic state and there are no known non-invasive monitoring techniques that can lead to feedback control interface. If this innovative idea works, the casting industry could benefit by cutting waste and rework, which could translate into driving down the manufacturing cost while concurrently improving the quality.
