Abstract
Vacuum arc remelting (VAR) is used widely throughout the specialty metals industry to produce superalloy and titanium alloy cast ingots. Optimum VAR casting requires that the electrode melting rate be controlled at all times during the process. This is especially difficult when process conditions are such that the temperature distribution in the electrode has not achieved, or has been driven away from, steady state. This condition is encountered during the beginning and closing stages of the VAR process, and also during some process disturbances such as when the melt zone passes through a transverse crack. To address these transient melting situations, a new method of VAR melt rate control has been developed that incorporates an accurate, low-order melting model to continually estimate the temperature distribution in the electrode. This method of model-based control was tested at Carpenter Technology Corporation. In the first test, two 0.43-m-diameter alloy 718 electrodes were melted into 0.51-m-diameter ingots. Aggressive start-up and hot-top procedures were used to test the dynamic capabilities of the control technique. Additionally, a transverse cut was placed in each electrode with an abrasive saw to mimic an electrode crack. Accurate melt rate control was demonstrated throughout each melt. The second test used an electrode size and grade proprietary to the host company. Because it was not stress relieved after the primary casting process, the electrode was known to possess multiple cracks that make accurate melt rate control impossible using standard VAR controller technology. This electrode was also successfully melted with good melt rate control using the model-based controller.
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Drip shorts are momentary arc interruptions due to metal drips bridging the electrode gap and contacting the ingot pool surface. See F.J. Zanner: Metall. Trans. B, 1979, vol. 10B, pp. 133–42 for a detailed description of drip-short signatures.
M.C. Flemings: Solidification Processing, McGraw-Hill, New York, NY, 1974, p. 245.
T. Suzuki, T. Shibata, K. Morita, T. Taketsuru, D.G. Evans, and W. Yang: Proc. 2001 Intl. Symp. on Liquid Metal Processing and Casting, A. Mitchell and J. Van Den Avyle, eds., American Vacuum Society, Santa Fe, NM, 2001, pp. 325–37.
L.A. Bertram, J.A. Brooks, D.G. Evans, A.D. Patel, J.A. Van Den Avyle, and D.D. Wegman: Proc. 1999 Intl. Symp. on Liquid Metal Processing and Casting, A. Mitchell, L. Ridgway, and M. Baldwin, eds., American Vacuum Society, Santa Fe, NM, 1999, pp. 156–67.
L.A. Bertram, R.L. Williamson, D.K. Melgaard, J.J. Beaman, and D.G. Evans: Patent No. 6,115,404, Sept. 5, 2000.
J.J. Beaman, R.L. Williamson, and D.K. Melgaard: Proc. 2001 Intl. Symp. on Liquid Metal Processing and Casting, A. Mitchell and J. Van Den Avyle, eds., American Vacuum Society, Santa Fe, NM, 2001, pp. 161–74.
L.A. Bertram and F.J. Zanner: Modeling and Control of Casting and Welding Processes, S. Kou and R. Mehrabian, eds., TMS, Warrendale, PA, 1986, p. 95.
See B. Jüttner and V.F. Puchkarev: in Handbook of Vacuum Arc Science and Technology, R.L. Boxman, D.M. Sanders, and P.J. Martin, eds., Noyes Publications, Park Ridge, NJ, 1995, p. 119.
F.J. Zanner and L.A. Bertram: Proc. 8th Conf. Vacuum Metallurgy, A. Mitchell, ed., TMS, Warrendale, PA, pp. 512–52.
P.N. Quested, K.C. Mills, R.F. Brooks, A.P. Day, R. Taylor, and H. Szelagowski: Proc. 1997 Intl. Symp. on Liquid Metal Processing and Casting, A. Mitchell and P. Aubertin, eds., American Vacuum Society, Santa Fe, NM, 1997, pp. 1–17.
F.J. Zanner: Metall. Trans. B, 1981, vol. 12B, pp. 721–28.
R.L. Williamson, F.J. Zanner, and S.M. Grose: Metall. Mater. Trans. B, 1997, vol. 28B, pp. 841–53.
C.L. Hysinger, J.J. Beaman, R.L. Williamson, and D.K. Melgaard: Proc. 1999 Intl. Symp. on Liquid Metal Processing and Casting, A. Mitchell, L. Ridgway, and M. Baldwin, eds., American Vacuum Society, Santa Fe, NM, 1999, pp. 145–55.
See any text on control theory and application, e.g., B. Friedland, Control System Design: An Introduction to State-Space Methods, McGraw-Hill, Inc., New York, NY, 1986. P.N. Quested, K.C. Mills, R.F. Brooks, A.P. Day, R. Taylor, and H. Szelagowski: Proc. 1997 Intl. Symp. on Liquid Metal Processing and Casting, A. Mitchell and P. Aubertin, eds., American Vacuum Society, Santa Fe, NM, 1997, pp. 1–17.
F.J. Zanner, R.L. Williamson, R.P. Harrison, H.D. Flanders, R.D. Thompson, and W.C. Szeto: in Superalloy 718–Metallurgy and Applications, E.A. Loria,ed., TMS, Warrendale, PA, 1989, pp. 17–32.
These codes were developed by the late Lee A. Bertram. Sandia National Laboratories, Livermore, CA. Both start-up and hot-top procedures were developed by the following team: Lee Bertram; David Evans, Special Metals Corporation (New Hartford, NY); Ashish Patel, Carpenter Technology Corporation (Reading, PA); and Rodney Williamson, Sandia National Laboratories (Albuquerque, NM).
This test was originally suggested by Charles Adasczik, now with Carpenter Technology Corporation.
F.J. Zanner, R.L. Williamson, and R. Harrison: Proc. 9th Vacuum Metallurgy Conf., A. Mitchell, ed., TMS, Warrendale, PA, 1988, pp. 55–74.
L.A. Bertram, C.B. Adasczik, D.G. Evans, R.S. Minisandram, P.A. Sackinger, D.D. Wegman, and R.L. Williamson: Proc. 1997 Intl. Symp. on Liquid Metal Processing and Casting, A. Mitchell and P. Aubertin, eds., American Vacuum Society, Santa Fe, NM, 1997, pp. 110–32.
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Williamson, R.L., Melgaard, D.K., Shelmidine, G.J. et al. Model-based melt rate control during vacuum arc remelting of alloy 718. Metall Mater Trans B 35, 101–113 (2004). https://doi.org/10.1007/s11663-004-0100-y
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DOI: https://doi.org/10.1007/s11663-004-0100-y