Dissertations and Theses @ UNI

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Open Access Thesis

Abstract

This investigation was conducted in response to a commercial steel foundry approaching the University of Northern Iowa for assistance with a recurring defect they experienced on a production casting. The defect was described as a mass of metal that penetrated and consumed the interstices of their chromite molds and cores, and it was determined to consist of fayalite. After an extensive literature review, it was concluded that the foundry experienced the double-skin defect, a niche quality issue that most commonly occurs in heavy-section steel casting with chromite molding materials

After it was determined that the double-skin defect was occurring, a methodology based on prior research was developed to understand the causation. Casting emissions data for the ester-cured phenolic resin system utilized by the commercial facility was collected to further understand the impact of mold atmosphere on double-skin penetration defects. High-temperature aggregate testing was also conducted to study the performance properties and characteristics of chromite sand with various levels of quartz contamination when exposed to temperatures seen in heavy-section steel casting.

The measured casting emissions data collected from the aforementioned estercured phenolic resin system matched data from prior research quite well, and exhibited a trend that coincided with an extrapolated version of the fayalite stability region. Utilizing the data collected, an algorithm was developed to predict the formation of double-skin penetration by means of the chemical penetration mechanism. Similarly, the results of the high-temperature aggregate testing provided the basis of the second proposed model, which was developed to predict the same defect by the mechanical penetration mechanism.

Both models showed some level of agreement with the production casting, but it was determined that mechanical penetration was the principle mechanism for double-skin formation, as its associated algorithm predicted the defect more accurately than the version based on the chemical mechanism. The proposed models in their current state, however, could be used by commercial foundries within process simulation software packages to help make educated process and material decisions, and they are described in detail herein.

Year of Submission

2019

Degree Name

Master of Science

Department

Department of Technology

First Advisor

Dr. Scott Giese, Chair, Thesis Committee

Date Original

2019

Object Description

1 PDF (XI, 55 Pages)

Language

en

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