Open Access Thesis
Aluminum castings; Sand, Foundry; Olivine;
The problem addressed in this study is how contaminates in the foundry molding aggregate olivine, affect aluminum castings during the casting process. This research will concentrate on hydrated contaminates, specifically the mineral serpentine. The purpose of this research is to better understand how hydrated minerals contribute to the generation of pinhole porosity defects during the casting process. Understanding how impurities in foundry aggregates affect the casting process would aid in the reduction of scrap caused by core and molding sands, ultimately providing savings to the casting manufacturer.
A foundry grade olivine was compared to a new source of olivine to determine how much pinhole porosity would be produced on a given casting sample based on purity and sourcing of the olivine aggregate. Various testing methods were used for the project: acid demand value, pH, grain fineness number and screen distribution, loss on ignition, differential scanning calorimeter/thermo gravimetric analyzer (DSC/TGA), chemical analysis by x-ray florescence, and the casting trial.
Results indicated there were differences in a given control sample of olivine in the amount of weight loss, screen distribution/GFN, and ADV, as compared to samples tested in which potentially contain hydrated minerals. The predominant relationship to pinhole porosity was results from GFN. The smaller the olivine sand grain became, the greater propensity for pinhole defects.
This increase in fineness levels also corresponded to increases in the LOI and acid consumption of the aggregates. Variation in grain sizing from sample to sample was not designed into the original testing parameters. A clay bond of 8.00% bentonite based on sand was used for all samples. Resulting in the potential for an improper amount of clay bond to compensate for the increased surface area of the finer sand, leading to increased pinhole defects in the castings from potentially un-bonded particles.
Casting results indicated finer grained olivine aggregates had the greatest amount of pinhole porosity. Results were inconclusive in determining if serpentine was generating the pinholing porosity on the aluminum castings. Differences in grain distributions between samples resulted in finer olivine sand having an increased amount of surface area. Reducing the overall clay/sand ratio and introduced the potential for sand grains to break from the mold prematurely and enter the casting during the liquid state, creating a pinhole. The result was aluminum castings that contain sand grain entrapment, causing the majority of the pinhole porosity.
Year of Submission
Master of Science
Department of Technology
Scott Giese, Chair
1 PDF file (xi, 76 pages)
© 2015 Brodie J. Biersner
Biersner, Brodie J., "Preliminary investigation into the cause of pinhole porosity in aluminum metal castings from serpentine impurities in olivine sand" (2015). Dissertations and Theses @ UNI. 206.