The flowability of bentonite bonded green molding sand

This paper investigates the properties of green molding sands, and a new model to evaluate the flowability of sand compact is developed. Controlling the flowability of the molding sand is extremely important in the sand casting process. Although several flowability indices have been proposed to measure this property, none of them has been universally adopted as a reliable indicator of the flowability. In this study, experimental results are presented to show how the flowability of silica sand is affected by water content, bentonite and sea-coal content. The equation proposed by Shapiro and Kolthoff can well fit the relationship between the compacting pressure and the relative density. The coefficients of S–K equation were substituted into the strength equation proposed by Sheppard and McShane. The S–M equation matches the green compaction strength data, with an error less than 5%. The model reported here correlates a one-dimensional compaction model with the S–M and S–K equations, and derives the relative density difference and the compression strength difference of the compact. The experimental results showed that the green strength reached the maximum at the ratio of moisture-to-bentonite of around 0.33. The hardness deviation on the central plane of the compact was taken as the reference to test the estimated strength difference. The results indicated that the flowability increased as the water content decreased. The model can explain the experimental results and directly predicts the uniformity of the compact. The estimated relative density difference ΔDr can be a new index of the flowability. For lowest ΔDr, the best water content occurs at around w%=3.0.