Doctoral Dissertations
Abstract
"The effect of a variety of processing parameters was investigated to provide a better understanding of the mechanism by which foam patterns are decomposed and their decomposition products are transported through the refractory coating in the lost foam casting process. These tests have led to a refinement of current physical models for mold filling and provide additional insight into the formation of casting defects in the process.
In Paper 1, castings were poured over a wide range of temperatures using different coating permeabilities. Higher pouring temperature led to faster fill velocity when using a high permeability coating, although the effect was smaller if a low permeability coating was used. Thermal analysis indicated that the metal-foam interface gap was narrow when filling a high permeability coating pattern, while the gap was much wider in a low permeability coating pattern. Models based on thermal analysis were proposed to explain the effects of pouring temperature and coating permeability on mold filling. The metal fill velocity is determined by the foam recession rate when coating permeability is high; relaxation of interface gap pressure controls the metal fill rate when the coating permeability is low.
In Paper 2, simulation tests describe the physical changes that occur when BPS and PMMA foams are decomposed. The flow-through tests showed that high coating permeability and high metal temperature speed the rate of transport of decomposition products through the coating. The heating simulation tests provided details for how EPS and PMMA foams decompose and interact with the coating in different ways. In particular, the tests showed that a portion of the refractory coating was exposed to air and gases in the gap between the liquid metal and the decomposing BPS foam, which allowed gases to be transported through the coating. Only a brief period of time, however, is available before the coating is wetted and completely covered by liquid polymer.
In Paper 3, the coating permeability, foam density, and foam density gradients were found to influence the metal velocity and the shape of the metal front during mold filling by both aluminum and cast iron. A relatively flat metal front profile was characteristic of high coating permeability; elongated convex profiles were features associated with low permeability coating. Casting surface imperfections were mainly a function of metal-foam interface structures and polymer pyrolization characteristics. Low permeability coating aluminum castings have the best chance to produce a perfect surface quality. High permeability coating iron castings can be free from surface defects provided an overflow mechanism is attached to the top far end of the casting"--Abstract, p. iv
Advisor(s)
Askeland, Donald R.
Ramsay, Christopher W.
Committee Member(s)
Watson, John L.
O'Keefe, T. J. (Thomas J.)
Tsai, Hai-Lung
Department(s)
Materials Science and Engineering
Degree Name
Ph. D. in Metallurgical Engineering
Publisher
University of Missouri--Rolla
Publication Date
Summer 1995
Journal article titles appearing in thesis/dissertation
- A study on mold filling control mechanicsms in the expendable pattern casting (EPC) process
- A study of the foam-metal-coating interaction in the lost foam casting process
- Effect of foam density and bead fusion of metal fill in the lost foam casting process
Pagination
xviii, 157 pages
Note about bibliography
Includes bibliographical references.
Rights
© 1995 Xiaojun Liu, All rights reserved.
Document Type
Dissertation - Restricted Access
File Type
text
Language
English
Thesis Number
T 6992
Print OCLC #
45425237
Recommended Citation
Liu, Xiaojun, "The mechanisms of mold filling and casting defect formation in the lost foam casting process" (1995). Doctoral Dissertations. 1325.
https://scholarsmine.mst.edu/doctoral_dissertations/1325
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