Abstract
This paper investigates the properties of green molding sands, and new concepts for evaluating the molding properties are proposed. A new structure parameter called shape factor is introduced to measure the structure of sand compact. A new model to evaluate the flowability of sand compact is developed.Controlling the water content, green strength, and flowability of the molding sand is very important in sand casting process. Although several indices for molding properties have been proposed to measure the state of the green sand, none of them has been universally adopted as a reliable indicator. In this study, experimental results are presented to show how the flowability of silica sand is affected by water content, bentonite and seacoal content. The equation proposed by Shapiro and Kolthoff can well fit the relationship between compacting pressure and 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 compression strength data, with error less than 5%. The model reported here correlates a one-dimensional compaction model with S-M and S-K equation, and derives relative density difference and compression strength difference of the compact. The hardness deviation on the central plane of the compact was taken as the reference to test the estimated strength difference. The trend of the estimated strength difference was consistent with the hardness data. The model can explain the experimental results and directly predicts the uniformity of the compact.The structure parameter shape factor is derived from the hydraulic conductivity. The experimental results showed that the shape factor is very sensitive to the structure variation. The maximum shape factor can be a good index for the best water content.This study also investigated the mulling effects and additive effects. The experiment data showed that the shape factor and the estimated strength difference can clearly reflect the cause of the variation. The researchers as well as the foundrymen can further improve the control of green sand properties.