Effect of sand dilation on distortions and pattern allowances during steel sand casting

Abstract

Mechanical interactions between the sand mold and casting have a great impact on pattern allowances. In this study, the effect of core expansion on distortions during steel casting is investigated. A hollow steel cylinder is cast using silica and zircon sand cores. The evolution of the cylinder’s inner diameter is measured in situ using LVDTs. During solidification, core expansion is found to distort the inner diameter into a barrel-shaped profile, generating the largest expansion at the mid-height. The experiments are simulated using a sequential thermo-mechanical coupling. In the stress analysis, the steel and sand are modeled using an elasto-visco-plastic constitutive law and the Drucker–Prager Cap model, respectively. The simulations reveal that sand dilation due to shear stresses, as opposed to thermal expansion, accounts for the majority of the increase in the inner diameter. The measured and predicted pattern allowances are found to be in excellent agreement.

Keywords:

• Steel casting
• pattern allowances
• distortions
• stress analysis
• sand dilation

Acknowledgements

This research was sponsored through the Defense Logistics Agency through the American Metal Consortium and the Steel Founders’ Society of America.