A New Measure for Active Clay in Green Sand

2020 AFS Proceedings of the 124th Metalcasting Congress Paper 2020-062 (4 pages)

A. Decher Andreas Decher Minerals.Services, Wenden, Germany

S. Ramrattan Western Michigan University, Kalamazoo, MI

ABSTRACT 1970s and a specially designed test-kit was available for An alternative approach to measure active clay in green that.4 Few foundries use this test and there has not been sand has been developed. The new technique is based on much interest shown. The literature reveals there has been dye absorption and uses a spectrophotometer to detect the little further study in this area. Spectrophotometry being amount of active clay present in a green sand sample. unknown to the majority of sand laboratories, plus the This study investigated a commercially available, organic lack of a finite test methodology, might be some of the and nonhazardous dye. The test procedure can reasons that it has not been accepted by the industry. discriminate among various levels of sodium and calcium Bentonite standards in silica sand. Results with the new The spectrophotometric technique in conjunction with approach shows repeatability with acceptable test-to test Methylene Blue (MB) to measure active clay was first 5 variability when measuring standard active clay levels introduced in 1983 by S. Neltner and L. Sodering. from 2 to 12% and on samples of green sand from Neltner’s paper describes a technique of mixing various working foundries. weights of clay in a solution of MB, using the principle of over saturating the clay with MB compared to the Keywords: absorption, active clay, methylene blue, traditional MBT. By ensuring an oversaturated solution, spectrophotometer the absorbency of the solution is always greater than zero, and it was found that adding clay to the solution would “pull” the MB out of solution, and therefore reducing the INTRODUCTION absorbency. The authors demonstrated that there was a linear relationship between the amount of clay and The AFS 2210-00-S: Methylene Blue Clay Test (MBT) absorbency of the solution. However, for the absorbency has been used as a part of foundry control programs to of the solution to be in the detectable range of the determine the active clay percent in green sand since equipment used, the MB and clay aliquot was required to 1967. However, the initial methodologies were described be diluted to a ratio of 99:1. A 1mL pipette was used to by Robertson and Ward in 1951 and then by F. O. Jones extract a portion of the aliquot, while the authors said this in 1964.1, 2 Improvements to the procedure were presented proved to be satisfactory, such a high level of dilution at the AFS Casting Congress in 1970. means that the absorbency of the solution to be measured is highly dependent on the accuracy of the pipette. Active clay content is an approach to quantify the number of smectite clay minerals in a bentonite or molding sand. The most recent studies using a spectrophotometry These minerals are major bentonite constituents and act as technique with a new environmentally friendly organic dye was presented by Pike et al. at the AFS Congress greensand binder. Smectite clay minerals can be 2013.6 The researchers showed that their dye does not characterized as silicate platelets providing a weak need to be diluted prior to measuring absorbency. Further, negative surface charge. In measurements using dye the absorbency of the solution could be measured adsorption the number of negative clay mineral charges is quantified by the number of cationic dye molecules accurately over a detectable range with the adsorbed to the minerals surface. Active clay spectrophotometer. The shortcoming is the inability to discriminate over a tight active clay range. For example determination by dye adsorption takes advantage of the the test can detect the difference between 6% and 8% high selectivity of a cationic organic dye complex active clay but cannot discriminate 8% from 9%. That replacing other adsorbed cations and the easy research has continued at Western Michigan University quantification by spectroscopic (color) measurements. (WMU) with the hope of identifying a dye that Quantitative measurements of the exchange capability of discriminate across the working range of percent active soils was explained by Michael Peech in 1945, using clay used in the foundry industry. 3 colorimetric methods. However, colorimetric analysis The objective of this research is to develop a procedure using a spectrophotometer in MBT was proposed in the that uses the same concept of absorption but can

Page 1 of 4 2020 AFS Proceedings of the 124th Metalcasting Congress Paper 2020-062 (4 pages) discriminate better over the range of 2% to 12% active Drying the green sand samples clay in which the chance of overlap between two levels is No drying of green sand is required. Results obtained are statistically zero or negligible. calculated on water free base.

EXPERIMENTAL PROCEDURE AND MATERIALS Mixing sand and dye together Make sure there are no clumps in the green sand sample Spectrophotometry is a method to measure how much a and add sample slowly to solution. chemical substance dissolved in a solution can absorb light by measuring the intensity of light passing through Mixing sand and dye the sample solution at a certain wavelength. The basic Manual mixing is accomplished by gently rotating and principle is that each light active molecule absorbs or counter rotating the tube from a vertical to horizontal transmits light over a certain range of wavelength.7 position. The rotary mixer is a semi-automated method of gently shaking the mixture. This mixing step is employed Note: Testing was performed in WMU laboratory as a means of disassociating the clay particles from the conditions. Ambient conditions were controlled: sand grains, as well as providing enough dye and clay temperature at 20 ± 1°C and relative humidity at 50 ± 2 interaction. %. Centrifuging the solution METHODOLOGY The centrifuging was done on the laboratory centrifuge Mixing, centrifuging, and measuring the absorbency are Model C3. three major steps of the new procedure. The numbered steps of proposed methodology are as follows: Measuring the absorbency 1. A 5.0 g green sand sample is added to a 20 ml 0.015 After the centrifuging, the top liquid portion of the mol/L Hexamine Cobalt (III) Chloride (CoHexa) solution was poured using a pipette into a solution (Fig. 1a) and cap. spectrophotometer cuvette that has 1cm width, and the 2. Mix either manually (tilting tube 50 times) or 50 absorbency was measured. The UNICO® 1205 VIS rotations in a rotary mixer (Fig. 1b). spectrophotometer (Fig. 1d.) was used to measure the 3. Centrifuge at 700 RPM for 10 minutes (Fig. 1c). absorbency after calibration. 4. Measure absorbency (A) using a spectrophotometer set at 475 nm (Fig. 1c). 5. Determine the % active clay based on a graph and/or table. (See Fig. 2 and Table 1) The following are important considerations when conducting the new test procedure: Dye Deionized water was used to prepare die solution. CoHexa may be a mild irritant so some gloves are suggested when handling. Concentration of the dye has to be selected higher than adsorption sites available on the clay minerals in the sample but low enough to be within the linear part of the Lambert-Beer law to ensure accurate quantitative spectroscopy by the photometer.

Cleaning No cleaning is required if disposable centrifuge tubes and disposable cuvettes are used. To clean the reusable cuvettes and centrifuge tubes, a solution of sulfuric acid and di-chromate was swirled around inside and then rinsed with deionized water.

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demonstrates a high negative correlation (inverse relationship). The more powerful trend is the one that can better discriminate between two different levels of clay. Better discrimination means higher slope between any two adjacent points on the correlation curve.

Fig. 2. Graph of absorbency versus 2% to 12% clay using the new procedure

Table 1. Discriminating among Different Clay Levels Active Clay Mean Absorbency (%) (A) 6 0.640 8 0.546 10 0.447 12 0.364

CONCLUSIONS AND RECOMMENDATIONS

Fig. 1. (a) Adding green sand to the dye, (b) mixing The findings identified in this paper provide an using rotary mixer, (c) centrifuging the mixture, and improvement for measuring active clay using a dye (d) measuring absorbency absorption technique over a similar technique outlined in an AFS publication 13-1455.6 The new procedure provides a correlation curve that shows a highly dependable relationship between dye absorption and RESULTS AND DISCUSSION percent active clay. There is no overlap across the range The following part of the study shows that increasing the of 2% to 12% active clay. This range covers percent clay level, the concentration of the dye is reduced and as a active clay measurements in most ferrous and nonferrous consequence, the transparency of the centrifuged solution foundries. increased. More transparency means less absorption of the The percent active clay measurements have been verified light that passes through the solution. The sand samples for Sodium Bentonite, Calcium Bentonite, and that are used in this study are 2%, 4%, 6%, 8%, 10% and Sodium/Calcium blends. Due to the high selectivity of the 12% Western Bentonite premixes provided by a foundry CoHexa dye to be adsorbed to the clay mineral surfaces, clay supplier. no pre-treatment of the sample by dispersants is required. The expected trend for the range of 2% to 12% clay is However, more importantly studies are needed on achieved by using the new test procedure. The results working foundry sands where additives and/or alternative from the new procedure is depicted in Fig. 2 and Table 1. molding media from silica sand are in system green sands. Fig. 2 and Table 1 shows a highly dependable relationship It is recommended that the new procedure be automated (R2 = 0.999) between percent active clay and mean to avoid human testing error and test variability. This step absorbency. The trend achieved by the new procedure

Page 3 of 4 2020 AFS Proceedings of the 124th Metalcasting Congress Paper 2020-062 (4 pages) will allow working foundries to achieve inline control of percent active clay in a green sand system.

ACKNOWLEDGMENTS

The authors gratefully acknowledge contributions from Dariush Moradinezhad, Selda Renda and Rachel Koeiman for their technical support in the Metal Casting Laboratory at WMU. This project was supported by the ,AFS; a special thank you to Brian Rachwitz, Steve Neltner, and the late Mary Beth Krysiak from the AFS 4M Research Committee for guidance and encouragement.

REFERENCES 1. Robertson, R. H. S., and Ward, R. M., "Assay of Pharmaceutical Clays," Pharm. Pharmacol, vol 3. pp. 27-35 (1951). 2. Jones, F. O., "A New Fast, Accurate Test Measuring Bentonite in Drilling Mud," The Oil and Gas Journal, vol 62, no. 22, pp. 76-78 (1964). 3. Peech, M., "Determination of Exchangeable Cations and Exchange Capacity of Soils-Rapid Micromethods Utilizing Centrifuge and Spectrophotometer," Soil Science, vol 59, pp 25-38, (1945). 4. N. L. Baroid/N. L. Industries, Inc, Bulletin C&A.5M/2-78. 5. Soderling, L., and Neltner, S., “Applied Spectrophotometry in Methylene Blue Clay Determinations,” AFS Library. 6. Pike, A., Moradinezhad, D., Pekarovic, J., and Ramrattan, S., “Alternative Approach to Clay Control in Green Sand,” AFS Proceedings 2013, Panel 13- 1455. 7. Allen, D., Cooksey, C., Tsai, B., Spectrophotometry, (October 5, 2010).

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