| Core gas defects are among the most aggravating defects because they are difficult to control and may not be found until castings are machined. These defects occur when the pressure in the core is higher than the external pressure acting on the core from the metal-head pressure. The prediction of core and mold gas defects requires a determination of the permeability of the cores and the rate and volume of gas evolved from the cores in contact with molten metal.;Techniques were developed for measuring core permeability and gas evolution. Gas permeability was measured at pressure levels that are seen inside cores during casting. The volume and rate of gas evolution from cores submerged in molten metal was also measured. Use of these techniques was demonstrated on commercial cores that were submerged in molten aluminum and iron.;The effects of common core-making variables and casting temperatures were determined. Permeability depended mainly on compaction level, with increased density associated with reduced permeability. Coatings decreased permeability, while binder, sand type, and additives had no affect. Gas evolution volumes and rates for cores immersed in molten metal were higher in phenolic urethane cold box cores than in epoxy acrylic cores. Higher binder content, additives, coatings, immersion temperatures, core length, and metal contact area all increased evolved gas volumes and rates.;A method for calculating the core pressure in simple geometries was developed and confirmed experimentally. The data generated from the gas evolution measurements were used to build a physical model on binder decomposition and the resultant gas evolution during casting. This model was used to determine the amount of gas evolved from cores at various geometries and temperatures. The model accurately predicted the volume of gas evolved. However, the composition of the gases, the core temperature profile, and more precise interfacial heat transfer and sand thermal conductivity data are also required to match the experimental rate curves. |
