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Investment Shell Cracking

Investment casting is growing in North America and is seen as a means for steel casting to penetrate high value added markets and high production markets such as automotive. The purpose of this project is to investigate and reduce the occurrence of investment shell cracking defects in investment casting. Shell cracking may occur during dewaxing or pouring. The dewaxing problem is one of superposition of stresses due to constraint of free strain of the wax by the shell. The wax will have a higher thermal expansion coefficient than the refractory shell. Robustness of the shell in dewaxing and thermal shock resistance during pouring may depend on strength and/or on plane strain critical stress intensity of more exactly critical crack extension force. It is our concept that the appropriate bench scale control tests coupled with manufacturing evaluations will reveal methods to control the process for lower scrap rates. The scope of work includes developing bench scale tests for ceramic shells and wax (polymer) pattern materials and designing a standard test casting. Then we would apply those tests to production materials collected four to size times from participating foundries with concurrent evaluation of defect occurrence from selected worst example case history castings and standardized test casting. The bench test results would then be correlated with the manufacturing results. After that, researchers will examine process parameters which can be used to achieve the desired trend or range for the bench test parameters and run confirmation tests to determine that the desired results are achieved in manufacturing.
Tri-State University
Malcolm Blair
Steel Founders' Society of America
780 McArdle Drive
Unit G
Crystal Lake, IL  60014

phone: (815) 455-8240
fax: (815) 455-8241

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