Ceramic fabrication development of large static components has been an integral part of the U.S. Government sponsored gas turbine development programs. Carborundum has produced sintered alpha silicon carbide transition ducts which have been successfully tested in Garrett’s AGT 101 engine having a turbine inlet temperature of 2500°F. Injection molding as opposed to isopressing/green machining was chosen for the development project because of its near net shape capability and high volume potential.
Mold design is important to minimize internal flaws and provide uniform green density. Injection molding control variables also influence external surface quality as determined by knit lines and blisters. Statistically designed three level experiments were instrumental in isolating the control variables which influence part quality and to determine their optimum values. Flow modeling was used to verify field trials and optimize specific molding variables to minimize pressure, shear rate and shear stress gradients within the part as well as suggest gating options.
Destructive and nondestructive evaluation was then used to evaluate the quality of ducts at various processing steps. Dual energy tomography and X-ray fluorescence are being developed as techniques for measuring the density and composition of molded parts.