Effects of Chemical Surfactants on Clay-Bonded, Green Sand Foundry Sand Control Systems
A 1-1/2 year research project by several companies lends help to understanding the role of chemical surfactants to the industry
AFS Foundry Sand Additives Committee (4-H)
Searching for the most direct method to determine the effect of chemical surfactants (wetting agents) on clay-bonded systems, member companies of AFS Committee 4-H decided a series of L-8 orthogonal arrays would be the ideal technique.
Once the orthogonal array was selected, the variables and levels were determined (Table 1).
During the laboratory experimental evaluations, a series of chemical surfactants was evaluated. These surfactants were selected from products used in the foundry industry.
Prepared sand mixtures were completed in a research environment A testing laboratory muller with a 20-lb capacity was employed. The sand mixture was consistently prepared by mulling a four-screen silica sand for 10 minutes with 7% bentonite. A total of 60 L-8 designed experiments were completed during the evaluation phase.
The physical properties that were evaluated include:
- compactibility from 35-45%;
- moisture to meet the required compactibility;
- the effect on green compression strength;
- the effect on permeability;
- the measurement of mold hardness (B scale);
- the effect of friability:
- the effect on dry compression strength;
- measurement of the density of 2 X 2 in. specimens for three-ram methods;
- the relationship of pressure vs. density of a 2 X 2 in. specimen;
- the measurement of green shear;
- the measurement of the effect of green deformation.
Laboratory evaluations were completed on calibrated sand testing equipment. In addition, a pneumatic rammer simulated a practical foundry environment. At the same time, the relationship of squeeze pressure vs. traditional rammers was evaluated.
Upon the completion of the evaluations, a series of data interpretations was cornpleted. These evaluations included: L-8 design calculations on the physical properties evaluated; a series of level mean graphical determinations; interaction plots developed on all physical properties; and graphical comparisons of squeeze pressure vs. the development of 2 X 2 in. specimens.
As a result of the laboratory testing and the interpretation of the data, the committee concluded:
- Chemical surfactants reduce the friability of the evaluated molding sand mixtures.
- The addition of surfactants increased the green compression of strength of the molding sands.
- Any increase in the green shear properties was minor. Therefore, the changes could be comidered significant.
- Chemical surfactanls improve the dry compression strengths of the sand mixture. The purpose of the evaluations was to target the concept of no increase in dry compresion strength; therefore, the logic of improvement was; no increase in dry compression strength.
- Squeeze pressure evaluations determined that more energy was required to prepare 2 X 2 in. specimens. This results in the need to increase squeeze pressure in the molding area when chemical surfactants were present.
- Chemical surfactants have no effect on mold hardness (B scale), permeability and green deformation.
- When chemical surfactants are present in the molding sand, less clay is required to maintain most of the physical properties.
- Chemical surfactants prefer green sand systems with higher compactibilities (range measured in this study was 35-45 compactibility units).
The most important observation was the negative interaction that was observed at low compactibilities at short mulling time. This is important because the effect of chemical surfactants on an operation that runs short mulling cycles and low compactibilities would result in a failure of the surfactant. In reality, the mulling system varies and should be modified to either increase the mulling time or increase the compactibility of the sand system.
About the Author
Victor S. LaFay was with the Hill and Griffith Company when this article was published in March 1993, MODERN CASTING Magazine.
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