Page 275 - Manufacturing Engineering and Technology - Kalpakjian, Serope : Schmid, Steven R.

254 Chapter 10 Fundamentals of Metal Casting

of grains and dendrites influence properties of the solidified casting. Solidification
time is a function of the volume and surface area of a casting (Chvorinov’s rule).
The grain structure of castings can be controlled by various means to obtain de-
sired properties. Because metals contract during solidification and cooling, cavi-
ties can form in the casting. Porosity caused by gases evolved during solidification
can be a significant problem, particularly because of its adverse effect on the me-
chanical properties of castings. Various defects also can develop in castings from
lack of control of material and process variables.
Although most metals shrink during solidification, gray cast iron and some alu-
minum alloys actually expand. Dimensional changes and cracking (hot tearing)
are difficulties that can arise during solidification and cooling. Seven basic cate-
gories of casting defects have been identified.
Melting practices have a direct effect on the quality of castings, as do foundry op-
erations, such as pattern and mold making, pouring of the melt, removal of cast
parts from molds, cleaning, heat treatment, and inspection.

KEY TERMS

Aspiration Fluidity Microsegregation Riser
Bernoulli’s theorem Freezing range Mold Runner
Casting Gate Mushy zone Segregation
Chills Gating system Normal segregation Shrinkage
Columnar dendrite Heterogeneous nucleation Porosity Skin
Columnar grain Homogeneous nucleation Pouring basin Solidification
Cored dendrite Inoculant Reynolds number Sprue
Dendrite Macrosegregation Rheocasting Turbulence

BIBLIOGRAPHY

Alexiades, V, Mathematical Modeling of Melting and Kurz, W, and Fisher, D.]., Fundamentals of Solidification,
Freezing Processes, Hemisphere, 1993. Trans Tech Pub., 1994.
Ammen, C.W, Metalcasting, McGraw-Hill, 1999. Liebermann, H.H. (ed.), Rapidly Solidified Alloys, Marcel
Analysis of Casting Defects, American Foundrymen’s Society, Dekker, 1993.
1974. Reikher, A., and Barkhudarov, M., Casting: An Analytical
ASM Handbook, Vol. 15: Casting, ASM International, 2008. Approach, Springer, 2008.
Campbell, ]., Castings, Butterworth-Heinemann, 2nd ed., Steel Castings Handbook, 6th ed., Steel Founders’ Society of
2003. America, 1995.
Campbell, J., Castings Practice: The Ten Rules of Casting, Stefanescu, D.M., Science and Engineering of Casting
Butterworth-Heinemann, 2004. Solidification, Springer, 2002.
Cantor, B., O’Reilly, K., Solidification and Casting, Taylor & Yu, K.-O. (ed.), Modeling for Casting 86 Solidification
Francis, 2002. Processing, CRC Press, 2001.
“Casting,” in Tool and Manufacturing Engineers Handbook,
Volume ll: Forming, Society of Manufacturing
Engineers, 1984.

REVIEW QUESTIONS

l0.|. Explain Why casting is an important manufacturing |0.3. What are dendrites? Why are they called so?
process. I0.4. Describe the difference between short and long freez-
l0.2. What are the differences between the solidification of ing ranges.
pure metals and metal alloys? |0.5. What is superheat? Is it important?