Product Description
PaperID: 2004
EventID: 1021
Author: George Salomon, Ronald Doles, Francois Batllo, Nalco Water
Abstract:
Cristobalite is a polymorph form of silica converted from quartz or fused silica and stable only at temperature above 1470C. Because of the energy intensive reconstructive nature of the transition from cristobalite to quartz or tridymite upon cooling, Cristobalite remains in a metastable form at low temperature in silica base investment casting shells. Furthermore as the temperature decreases, cristobalite undergoes a crystalline phase transition from its cubic form beta to a tetragonal form alpha around 220C. This phase transformation is accompanied by a volume contraction of about 5% creating strains, defects and cracks in the shell. While some casting applications benefit from weaker fired shells with easier shell removal or knock-out, others rely on the mechanical integrity of the fired shell for dimensional and throughput consistency.
In this work, the factors impacting cristobalite formation in investment casting shells were investigated by determining the impact of material composition, chemical and physical properties as well as heat cycle on the crystalline structure and strength of the material.
Paper Pages: 10
Paper Year: 2016
Paper Index: 4:107
Paper Source: 83
