tions and related it to air gap formation. More recently, investigators have made an effort to inject higher con- ductivity helium gas into the air gap to improve interfa- cial heat transfer between the casting and the mold.3, 5 & 6 Given all of this, there are still further research opportu- nities in determining a relationship between air gaps, ef- fective contact pressure and times and resulting effective heat transfer coefficients as well as further opportunities in developing a means to implement these for productiv- ity gains in a manufacturing plant.
In this work, the novel concept of movable water cooled chills has been put to the test. The study involves:
• Design of experiments to evaluate the thermal and microstructural characteristics of castings produced under different cooling scenarios using chills,
• Computer simulations to determine the interfacial heat transfer coefficients (HTC) using different chill scenarios, and
• Microstructure analysis of the cast specimens. Table 1. Experimental Conditions
Figure 1. (a) 3D model of mold-chill assembly; (b) Location of thermocouples. (a)
(b)
Figure 2. Electronic circuit (voltage cut off switch) used to signal and record air gap formation. 66 International Journal of Metalcasting/Spring 11
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