A preliminary sand experiment was conducted to verify this equation. A new model was proposed to predict the minimum gas pressure, and a mathematical equation was derived from this model. The aim of this study is to predict the minimum gas pressure needed to prevent sand from collapsing near the kinetic zone. However, this equation was not verified by real casting experiments. In a prior study in this field, Shulyak calculated the minimum gas pressure to prevent the sand from collapsing near the kinetic zone. Successful computer simulations can help to reduce the number of trials and reduce the lead time in the design of new casting products. Hence, further research is imperative to predict sand collapse using a computer before pouring the metal melt. However, limited research has been conducted to simulate sand collapse. Several studies have been conducted to predict and simulate casting failures in lost-foam casting. The gas pressure depends on the cross-section of the sprue and ingate, the height of the pouring basin, the permeability of the sand, the density of the expandable polystyrene pattern, the pouring temperature, and the melting speed. The gas pressure of the kinetic zone can be predicted based on findings from previous studies. Because this gas pressure also prevents sand collapse, it should be maintained at a suitable level. However, if the gas pressure reduces the speed of the molten metal, the pouring duration is long and casting defects, such as a metal fold, can occur. Increasing the instability of the melt tip interface adversely affects product quality. The gas pressure in the kinetic zone has a significant role in preventing the sand collapse in contact with the kinetic zone and in reducing the instability of the interface at the tip of the melt. In lost-foam casting, an expanded polystyrene pattern is vaporized by the heat of the advancing metal melt, forming a gas gap in front of the metal tip. If the residual foam pyrolysis is not completely discharged and the pressure balance in the mold is altered during the pouring operation, the sand may collapse, resulting in casting defects. Many studies have been conducted to identify and solve the causes of casting defects. However, the lost-foam castings are susceptible to the generation of various defect forms. Furthermore, no harmful gas is produced from the core. Moreover, the use of dry sand without coking force and a resin-containing core reduces the manufacturing and waste treatment costs. The lost-foam casting process has several advantages which allow the casting of complex shapes because the molten metal is poured without removing the pattern. Finally, the molten metal is poured, and the melt is replaced with the space occupied by the solid foam pattern, resulting in the desired cast products.
The first step is making the pattern of the desired shape, which molds the expanded polystyrene beads, and the foam pattern is placed in a sand flask, and unbonded sand is poured around the pattern and compacted by vibration. In the last three decades, lost-foam casting process (LFC) has been widely adopted to manufacture complex parts without the need for a core. The results obtained from the preliminary sand experiment and the actual casting experiment validated the equation. In the actual casting experiment, pressure of the kinetic zone in front of the metal tip was directly measured. An actual casting experiment was conducted by melting nodular cast iron to verify this equation. The void ratio of the sand effect on the minimum gas pressure was included in the equation. A new mathematical equation was proposed from the results of the preliminary sand experiment. In this preliminary sand experiment, compressed air was used instead of gas in the kinetic zone. A preliminary sand experiment was conducted to predict the gas pressure and reduce the number of actual casting experiments. Successful computer simulations can help reduce the number of trials and the lead time while designing new casting products. When the minimum gas pressure can be predicted, computer simulation becomes possible. Therefore, the minimum gas pressure for preventing sand collapse is required. The extremely high pressure causes many problems, such as reducing the melt velocity and inclusion of residual decomposition of the pattern in the castings, and very low pressure causes sand collapse. Pressure of the kinetic zone is an essential factor for making defect-free castings in lost-foam casting process.
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