published_or_final_version / Dentistry / Master / Master of Philosophy

published_or_final_version / Dentistry / Master / Master of Philosophy

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For aluminum alloy casting, degassing is a necessary step for molten metal, which can extract the dissolved hydrogen in the melt. For copper-containing aluminum alloys, a traditional method is that using the mixed gas of inert gas and chlorine as the degassing agent. Because of the toxicity of the gaseous chlorine, the industrial is trying to avoid using it even though this method can contribute to good castings. As a potential solution, the foundry only used argon during degassing, however, the castings with this method were unacceptable since the occurrence of defects. The goal of this project is to develop a new green and clean degassing method for copper- containing alloys without the usage of gaseous chlorine. To achieve this goal, identify those defects and figure out the source of those defects are necessary. Totally four hypotheses of the occurrence of defects were supposed and two of them were discussed in this thesis. They are ineffective hydrogen removal and metal-mold reaction. Experiments were set in WPI and Palmer Foundry to investigate defects from samples with different conditions. This thesis collected and discussed the results from experiments, and made the conclusion that whether these two hypotheses contribute to the occurrence of defects.

Thesis (M.Phil)--University of Hong Kong, 1994. / Includes bibliographical references. Also available in print.

Thesis (M. Phil.)--University of Hong Kong, 1991. / Errata slip inserted. Includes bibliographical references (p. 240-257). Also available in print.

A problem facing the casting industry is inclusions in the finished parts. The inclusions can be sand from the molds, oxides or other impurities in the metal charge. Inclusions lead to costly part repairing or reworking. A study was done to try and find inclusion trapping devices that could be placed in the gating system. The experiments consisted of pouring water and suitable inclusion models into clear, full scale, plastic molds. The fills were video taped for later analysis. The efficiency of the trapping device was determined from the end location of the inclusions. No work was done on other anti-inclusion methods such as ceramic filters, bottom pour ladles, chemical additives, etc. The research showed that a swirl chamber which used centrifugal force to separate inclusions worked quite well if set up correctly. The optimum setup was a vertical swirl chamber with a well. The inlet passage was choked and located below the exit passage. It also worked much better than any setup which tried to use buoyancy for separation. The large volume of the swirl chamber may be objectionable. However, properly shaped inserts, such as an ice-cream cone shape, can be put into the chamber to reduce fill volume while still maintaining good efficiency and fills. The efficiencies of the chambers behave as expected; faster pours are less efficient and bigger chambers (for a constant size mold) are more efficient. The use of outlet chokes may or may not improve separation efficiency, but will improve the filling of the part cavity. / Graduation date: 1993

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Thesis (M. Eng. Sc.)--University of Queensland, 2002. / Includes bibliographical references.

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