Fig. 2. A curve was plotted to show different amounts of Southern Ben- tonite in a 50ml dye solution led to different absorbencies.
Fig. 3. This curve shows different amounts of Western Bentonite in a 50ml dye solution led to different absorbencies.
Alternate Approach
Te methodology for the proposed method is as follows: 1. Zero the spectrophotometer using distilled water at 490nm.
2. Measure the absorbency of the orange dye solution (at 490nm) using the spectrophotometer, values must be between 1.700 and 1.750.
3. Dry 5.5 g of the sample as deter- mined in the AFS Mold and Core Test Handbook.
4. Immediately weigh out 5 g (± 0.05 g) of the dried free flowing sand into a metal beaker with capacity of 250mL.
5. Add 200mL of orange dye solution into the beaker.
6. Ultrasonic scrub and stir the solution simultaneously for seven minutes. Make sure the stirrer is no more than 0.125 in. (⅛ in.) from the bottom of the beaker but not touching it.
7. Immediately centrifuge 50mL of the solution at 2000 RCF (Relative Centrifugal Force or G-Force) for 13 minutes.
8. Immediately, pour the sample directly into a cuvette.
9. Place the cuvette into the spectro- photometer and read the absor- bency at 490 nm (Note: make sure finger prints are not on the transparent sides of the cuvette and the cuvette is properly oriented in the holder) (Fig. 1). Determining the clay content within the mixture depends on several factors, including the dye concen-
tration, the volume of dye solution to be mixed with the sample and the sample size. Additionally, the absorbency depends on the clay types being measured. Tree dyes were tested for the new
technique: orange, black and yellow. All three dyes interacted with the clay in the solution, but the black dye solution would precipitate out during the centrifuging process even in the absence of clay, which complicated the determination of clay levels. Te orange dye solution showed mini- mal decrease in absorbency due to centrifuging. Less than 10% of the original absorbency was lost over the course of a month. Comparatively, the black and yellow dyes had relatively poor shelf life, dropping 25-30% after a few days. Absorbency measurements were
conducted at each solution’s peak. Due to the nature of spectrophotom- etry, a given liquid will have different levels of absorbency at different wave- lengths. Te peak is the wavelength at which absorbency reaches its maxi- mum. Te orange dye solution’s peak
Table 1. Comparing the Averages of MBT and the Spectrophotometry Test
% Clay 4
6 9
12 Average
MB Clay Test 3.8 5.8 8.6 12
Spectrophotometry 0.24 0.20 0.17 0.13
MEDIA RESOURCE
Using the Actable App, scan this page to see a video demonstration of the alternative methylene blue clay test. For instructions on how to use the app, go to page 3. To watch online, go to
www.metalcastingtv.com.
August 2013 MODERN CASTING | 37
was found at wavelength 490nm. Initial tests of the dye solution
were performed with varying amounts of solution prepared with tap water. Te tests demonstrated an increasing amount of clay reduces the amount of dye remaining in the solution, thus reducing absorbency. To have a more reproducible solution, the research- ers used deionized water. Hardening the deionized water with calcium chloride allowed the dye and clay to interact. Te controlled hardness of water used for the dye solution prepa- ration was maintained using calcium chloride (CaCl2
) as the hardener.
Te concentration of the dye in the solution was critical to the proposed test’s effectiveness. While the maximum detectable absorbency varied between equipment models, a 0-1 absorbency range was the most sensitive for the equipment used in the study.
Making a Correlation In the study, the WMU research-
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