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Metal Casting Technologies : June 2007
METAL Casting Technologies June 2007 37 casting thickness is less than 8mm, we can choose filling rate of 40--50mm/s. When casting thickness is over 10mm, we can choose filling rate of 30--40mm/s. It is worth pointing out that, if we choose a higher filling rate, more attention has to be paid to gas penetration of the mold. 4. APPLICATION OF CGCE This kind of CGCE, designed in our laboratory, has been used in several foundry factories in China to produce important large-size aluminum alloy castings, Fig.7 is the real pressure-tracing curves when a large-size aluminum alloy casting (up to 2.5 ton) was a filled mold. From the figure, we can see that the pressure-tracing control precision is less-than 0.3KPa. In the casting, we get σb of 320MPa, and δ of 5% (A357, T6). Fig. 8(a) and Fig. 8(b) show microstructure at the same position of a A357 casting, which is shaped under gravity and counter- gravity conditions respectively. For counter-gravity casting, since the casting is formed under pressure, primary and secondary dendrites are broken, and are distributed evenly which is favorable for improving σb and δ of the castings. 5. SUMMARY Advanced counter-gravity casting equipment has been developed for the production of large-size thin-walled aluminum alloy castings with high-quality requirements in resin sand mold. The maximum weight of castings can be up to 2.5 tons. The whole filling process is controlled by self-designed software with PID algorithm improved by fuzzy control thoughts. Combining the software with the assembled valve system, we can obtain satisfied pressure-tracing behavior. By using the gating system different from that of gravity casting, the inherent features of counter-gravity casting can be fully utilized. The castings produced by this method have satisfactory microstructure and mechanical properties. ● References  T. Q. Ren, H.F. Lin and W. J. Cao. Liquid surface pressure control system in differential pressure diecast. China Casting Machine, (1988)(1):p. 32  G. R. Kamat. Low Pressure Counter Gravity Casting of Aluminium Alloys, Transactions of the Indian Institute of Metals (India), Vol.45 (1992)(3), p. 177  G. D. Chandley, Counter Gravity Casting of Aluminum in Investment and Sand Molds. American Foundrymen's Society, Inc., (1986), p. 209  M. E. Li, G. C. Yang, Infuence of filling patterns on solidification process of thin wall plate castings produced by low pressure casting. Foundry (China), Vol. 49 (2000)(7), p. 418  X. F. Yao, T. J. Chen. Development and trend of pressure control systems applied on molten metal in low pressure die casting. China Casting Equipment and Technology, (1998)(4), p. 13  Q. W. Duan, X. Q. Dong and H. J. Liu, et al. Study and application of liquid surface pressure control system in CLP-5 low pressure diecast. Casting, (1995) (11), p. 13