Doctoral Dissertations

Date of Award

12-2004

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Civil Engineering

Major Professor

Dayakar Penumadu

Committee Members

Roberto S. Benson, Eric C. Drumm, Baoshan Huang

Abstract

Because of its unique advantages on energy savings and casting complex shaper, Lost Foam Casting (LFC) has been widely used as a replacement to the conventional techniques (sand and investment castings). In order to continuously improve the quality of the Lost Foam Casting process for reducing scrap rate and increasing energy savings, the US Department of Energy through its National Industrial Competitiveness through Energy, Environment, and Economics (NICEEE) program sponsored the present study to develop new characterization techniques for enhancing the understanding of the fundamental properties of the refractory materials used in The Lost Foam Casting process. In this study, new techniques are proposed to characterize the refractory materials’ properties such as particle size, particle shape, rheological behavior, transport properties, microstructure, thickness, as well as packing properties. The rheological properties of the refractory coating slurries are characterized by a series of laboratory experiments using a rotational rheometer including the creep and recovery test, the thixotropic loop test, and oscillatory tests. A number of commercial particle sizing instruments based on different theoretical backgrounds are investigated for evaluating a suitable technique for reliable characterization of slurries used in this research. A quantitative approach to characterize particle shape is also investigated for particles in the refractory coating slurry. This study also proposes a new apparatus to evaluate the transport properties and microstructure of the refractory coatings. The proposed interpretation method of measured gas flow data considers the “slippage” and inertia effects that occur in measuring gas permeability of porous materials. The microstructure information obtained from the proposed technique is found to be well correlated with the transport properties of the porous coating materials. A procedure using a three-dimensional computational fluid dynamics code (FLOW3D) is developed to simulate experimental gas flow data for solving complex boundary value problems. This paper also presents a novel coating thickness measurement system for the dry refractory LFC coatings. By comparing a number of commercially available refractory coatings, it is found that the coating thickness on the expandable polystyrene foam patterns is not uniform and depends on the coating type, topography of the foam surface, and coating properties such as surface tension, thixotropic loop area, mean particle size diameter, and viscosity. In this study, the effects of dilution and dispersion on the coating properties such as transport properties and microstructures are also investigated. Results show that the dilution and dispersion have opposing influences on the pore size and transport properties. The pore characterization technique developed in this study is used to determine the effects of drying (oven versus air dry) on the pore size and transport properties. In addition, this study also includes another part of the permeability system, the un-bonded granular materials used in the Lost Foam Casting process. Three types of particle sizing techniques (sieve analysis, Laser Light Scattering and Imaging Analysis) are used to characterize the particle size and shape information of two types of un-bonded granular materials (sand and mullite). A three-dimensional (3-D) computer program is developed to simulate the packing behavior of granular materials at a loose state using a “drop and roll” method. This study provides a systematic characterization of the LFC refractory coating slurries, dried refractory coating, and the granular media. This study also demonstrates the application of proposed characterization techniques for coating quality control using statistical process control charts. In addition, numerical models are also developed to predict the coating performance such as its coating thickness and transport properties. The results from this study are likely to have a significant impact on improving the Lost Foam Casting process. The characterization tools developed in this study are being currently used in a large Lost Foam Casting foundry for improving the process at production scale.

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