The objective of this thesis investigation was to design an experiment to investigate superheat effect on gate velocities pressurized and unpressurized gating system each having two gates, and to analyze statistically any interrelationship between these variables in CO₂ molds. A discussion on metal flow through different parts of a gating system, with a minimum of turbulence and gas aspiration, and a discussion of hydrodynamic principles relating to gating systems were given. The realization of these conditions is desirable because it results in improved casting, fewer rejects, and greater economy in a casting production. This was followed by a discussion on metal flow variables. Principle and use of instrumentation used in the experiment was discussed. Split-split-plot type of statistical design was used. Statistical analysis of results were made. The author concluded that, the type of gating system (pressurized or unpressurized) and individual gate location have significant effect, whereas superheat (100-300°F.) has no significant effect on gate velocities of aluminum - 12 percent silicon in CO₂ molds. Also, all the there variables are independent of each other. / Master of Science

Production of casting in sand molds is the basic original method employed by the foundry industry. Other methods are the results of the technological advances, but none has resulted in the extreme flexibility of the sand casting process. The control of the sand properties is important in order to produce casting of good quality. This paper presents a limited analysis of the properties of the green molding sand and the fluidity of Aluminum•Silicon alloys in the green sand molds. The fluidity is the casting property of an alloy or metal, in a qualitative measure to completely fill the mold before it solidifies and is normally expressed as inches of flow in a small channel. The properties of the green molding sand with change in the composition of sand viz., clay and moisture contents. The standard AFS procedure is suggested in testing the physical properties of the green molding sand. In fluidity test a standard method of molding, melting and pouring is suggested to control certain variables. The statistical analysis of results indicates that there is no appreciable difference in the fluidity values 1. For different metal composition (Aluminum 12% silicon and Aluminum 6% silicon) 2. In green sand molds of vary composition of clay and moisture (clay 5%, 7% and 10%, moisture 5% and 7%) / Master of Science

"Aluminum-Silicon and Aluminum-Copper alloys are important non-ferrous casting alloys. Different methods have been applied to improve their casting characteristics, their microstructure and consequently, their mechanical properties. Application of mechanical vibrations to the mold during solidification of the alloy is one of these methods. In this study, the effect of controlled mechanical vibrations on the dendrite coherency point, the hot tearing tendency, and the microstructure of B206, B390, and binary Al-7%Si alloys was evaluated. The dendrite coherency point was determined using the two-thermocouple method. The hot tearing tendency was evaluated using the crack susceptibility criterion (CSCb) and by means of measurements using a specially designed ring mold. Microstructure characterization was performed using optical and scanning electron microscopy coupled with image analysis. It was found that mechanical vibrations refine the microstructure of the alloys; and, in the case of B390 alloy, it resulted in significant improvement in the distribution of the primary silicon particles. In the case of B206 and Al-7%Si alloys, where aluminum is the primary phase, mechanical vibrations caused the dendrite coherency point to shift towards lower temperature, i.e., towards higher fraction solid. This shift, together with the refinement of the grain structure, manifested itself in significant reduction in the incidence of hot tearing in B206 castings. "

Thesis. 1976. M.S. cn--Massachusetts Institute of Technology. Dept. of Mechanical Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by John R. Potter. / M.S.cn

Mathematical models of heat flow and elastic stress generation based on the finite-element method have been developed and utilized to analyze the Epic-3 Monofrax-S casting process (Monofrax-S is primarily composed of 47-57% A1₂O₃, 34-41% ZrO₂ and 10-15% SiO₂). The results of the mathematical analysis, in conjunction with information obtained from a comprehensive industrial study, has led to the development of mechanisms for the formation of the various crack types found in this casting process. Thermal stresses have been predicted to be generated early in the solidification process in association with rapid cooling of the refractory surface as it contacts the initially cool mould and again later in the solidification process in conjunction with the tetragonal-to-monoclinic phase transformation which occurs in the zirconia component of Monofrax-S. The mathematical analysis has also helped to identify indirectly a potential mechanism for the generation of mechanical stresses. Based on an understanding of the generation of tensile stresses, recommendations have been made for modifications to the moulding and casting procedures in order to reduce the propensity for the formation of cracks. The modifications have included changes to the mould construction and geometry to reduce the generation of mechanical stresses and changes to the moulding materials to impact on the flow of heat at key times during solidification and cooling. With the recommendations in place, the casting process has been re-examined with the mathematical models to verify the impact of the modifications. The predictions show that the modifications have acted to reduce tensile stresses associated with the formation of Type-A and -B cracks. Preliminary industrial trials with the modified mould have yielded blocks free of these defects. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate