ers made three assump- tions: both Southern and Western Bentonite clays absorb the dye; increasing the amount of clay lowers the dye concentration in solution; and the dye is absorbed by the different types of clays with a dif- ferent magnitude. For the third assump-
tion, a series of experi- ments used constant concentrations of the dye and testing mixture. By varying the amount of clay within the mixture, the maxi- mum amount of the clay necessary to change the absorbency was iden- tified. Finding this point might lead to an opportunity to estimate the proportion of different clay types within the mixture. The transition point for the
orange dye solution occurred at 0.11g of Southern Bentonite per
Fig. 4. A correlation between the methylene blue clay test and the spectro- photometry technique exists.
50mL of dye solution and at 0.04g of Western Bentonite at 50mL dye solution (Figs. 2-3). Several combi- nations of dye solution volume and sample weight were tested to find the lowest deviation. Using a 5g sample size and 200mL of dye solu- tion provided acceptable accuracy for the dye concentration.
Researchers used four
different levels of clay: 4%, 6%, 9% and 12% and each level were tested 10 times. The same number of methylene blue clay tests were performed (Table 1). Results from the methy- lene blue clay test and the spectrophotometric absorbency technique (using a clay bond of 50% Southern Bentonite and 50% Western Bentonite) showed a strong correla- tion (Fig. 4).
Improved Results Gage R&R studies were used to
measure the repeatability and repro- ducibility of the spectrophotometric technique. Repeatability indicates the variability between repeated readings of a sample, and reproducibility indi- cates the variability between different operators (Figs. 5-6).
38 | MODERN CASTING August 2013
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