Term of Award

Fall 2021

Degree Name

Master of Science, Mechanical Engineering

Document Type and Release Option

Thesis (open access)

Copyright Statement / License for Reuse

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

Department

Department of Mechanical Engineering

Committee Chair

Mingzhi Xu

Committee Member 1

Jingjing Qing

Committee Member 2

Shaowen Xu

Abstract

Fused silica is widely used for investment casting shell molds. Fused silica shells are discarded after being used for casting one time. This is due to the transformation of fused silica to beta cristobalite above 1652℉ (900℃). To reduce cost and waste of investment casting foundries, this study is exploring a method to inhibit transformation of fused silica and reclaim it from high temperature investment casting shells. This research has employed firing to minimalize fused silica transformation to cristobalite. The phase transformation is minimalized due to sintering and coarsening of the particles during firing. Coarsening reduces surface area to volume ratio of the particles. This reduces the available energy to activate phase transformation. In this study, the strength of shells after various firing conditions was measured to understand how strength is affected when particles are coarsened to prevent phase transformation. It was concluded that densification, over sintering, phase transformation, and particle growth have competing effects on shell strength. Particularly, it was found that over sintering can compromise shell strength in as few as 3 hours at higher temperatures. Consequently, more layers may need to be added to increase strength of shells that will be fired for long periods of time. This will increase processing time. Coarsening of particles did not inhibit phase transformation. This is thought to be due to the amount of sodium in the shell building material, which encourages phase transformation. The author suggests future researchers to utilize a colloidal binder system that has lower sodium content (<0.22wt%).

Research Data and Supplementary Material

No

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