Green Sand - The Process of the Future

Production of High Quality Castings with a Reduction in Emissions of Green Sand
(Information Prepared for the Ductile Iron Society)

Victor S. LaFay
Hill and Griffith Company

Abstract
A reduction in emission characteristics during pouring, cooling, and shakeout can be accomplished while producing high quality ductile iron castings in green sand! The metal casting process can produce emissions that are generated by the thermal decomposition of organic material in greensand and if cores are present, decomposition of the core binder. Through changes in the blended minerals in the green sand molds and selection of the green sand release agents, significant reductions in VOCs, HAPs, carbon monoxide, and carbon dioxide emissions can be accomplished. This reduction in emissions has been determined during actual metal casting with advanced analytical methods and equipment that have been developed by Technikon for the Casting Emission Reduction Program (CERP) in Sacramento, California.

Introduction
During the last few years, a number of development studies have been completed at various foundries, technical centers, universities, and research facilities on the emission characteristics of foundry processes. A series of studies has been completed at Technikon, which operates CERP, which supplies valuable information that was utilized to develop the significant reduction in the emission characteristics of the green sand process. These studies review the characteristics of the emissions that were the result of the metal casting process from the green sand, green sand release agents, contribution of the emission characteristics from the core process (and the subsequent return of the core material into the green sand) and the greensand release agents. Each one of these processes contributes uniquely to the emission characteristics, so they were investigated individually.

This information will review the alternative materials that can be utilized by the foundry industry to reduce the emission characteristics of green sand while producing high quality ductile iron castings and potentially with reduced costs! There are a number of materials that can be used as either a supplement to seacoal or as a replacement for seacoal. Since seacoal is the primary source of carbonaceous materials utilized for green sand in North America, the logic of supplements or replacement is the focal point of the technology advancements. These technological advancements have been evaluated and successfully implemented in many ductile iron foundries in North America.

Review of Seacoal and Seacoal Supplements
Carbonaceous additives have been widely used in green sand molding for many years successfully! The primary additive that is used in the foundry industry is seacoal along with a variety of supplements that enhance the characteristics of the seacoal. The advantages of blending seacoal with the selected supplements have been documented in many foundry publications and discussed in conferences where metal casting technology is reviewed. Historically the selection of the supplements to seacoal was primarily based upon casting quality considerations not emission characteristics (until recently). With particular importance placed upon the sulfur content when producing ductile iron castings. The physical properties of the seacoal and seacoal supplements are reviewed in table 1.

Table 1: Typical properties of carbonaceous additives

Review of Green Sand Release Agents
More than 3 millions gallons of green sand release agents are used in North America. Regardless of the type of metal poured (steel, ductile iron, gray iron, brass, etc.) every green sand mold produced for the metal casting process requires the application of a green sand release agent. Most foundries simply use them “because they always have”! However, these materials have become scrutinized because they contribute to the emission characteristics of green sand during the metal casting process. They can not be simply overlooked.

Table 2 contains information concerning the physical characteristics of green sand release agents that are commonly used in the foundry industry.

Table 2: Typical properties of green sand release agents

Investigations that Contributed to the Final Conclusions

Contribution of Green Sand Emission Characteristics Without Seacoal and Release Agents

A series of investigations was completed to evaluate the contribution of green sand release agents on the emission characteristics that occurs during the metal casting process. The materials that were investigated included: petroleum oil based green sand release agent, vegetable oil based green sand release agent, and water based green sand release agent containing graphite. These products are commercially available and widely used materials that can be used in molding machines and spray application devices.

For this investigation, there are a number of specific details that require discussion. The first consideration was the selection of the casting that was used in the metal casting process. The team selected the star casting design that was produced on an Osborn Molding Machine (Figures 1, 2, and 3).

Fig. 1 Osborn Molding Operation

Fig. 2 Star Castings (4 on pattern)

Fig. 3 Individual Star Casting

The molding sand was prepared without seacoal and contained only a blend of 5:2 ratio of Western (Sodium) Bentonite and Southern (Calcium) Bentonite at 7% with 40 to 45% compactability. Without the Seacoal present, the investigators had the opportunity to determine the contribution of the green sand release agents to the emission characteristics. In this series of investigations, 40 grams of green sand release agent was added to the surface of the pattern so that each of the materials could be investigated under the same conditions (Figures 4 & 5).

Fig. 4 Green Sand Release Agent on Pattern

Fig. 5 Release Agent (Transferred) on Mold

The following graphical emissions data was collected from pouring, cooling and shakeout of this combination of materials (Figure 6).

Fig. 6 Emission Characteristics of Green Sand Release Agents

Test Evaluation Utilizing Information From Additional Studies at CERP

In order to significantly reduce the emission characteristics from foundry molding sand, core sand, and subsequent return of the core sand into molding sand, the reduction in selected materials, addition of minerals into the core sand, and changes in the molding process have to occur. For this investigation the following materials were utilized:

1. A water-based green sand release agent containing graphite was used. The graphite would eliminate the need for development of lustrous carbon on the mold metal interface during the metal casting process.

2. All of the Seacoal was removed from the molding sand. Cellulose was added to the green sand to reduce mold wall movement.

3. A predominately Western (Sodium) Bentonite sand system was used with the addition of a molding sand additive to enhance the performance of the bentonite.

4. A blended aluminum silicate mineral was added to the phenolic urethane core sand mixture at a 5% level.

A casting study was completed utilizing this mix of materials. The green sand molds (without seacoal) were prepared with 96.5% Western (sodium) Bentonite, 3% Cellulose, 0.5% Soda Ash, and 240 ounces (per ton of prepared preblend) of a polymeric additive that is utilized to enhance performance of the Bentonite at 7% with a 40 to 45% compactability. The cores were produced with a phenolic urethane binder system at 1.4% binder with the addition of a blended aluminum silicate mineral additive. The molding sand and cores were prepared and cast in a controlled environment to evaluate the emission characteristics of the combined processes (Figures 7 and 8).

Fig. 7 Prepared Molds and Cores

Fig. 8 CERP Testing

Figures 9 and 10 show the emission results from this casting study in graphical form.

Fig. 9 Emission Results Summary from
Test Mix vs. Selected Baseline

Fig. 10 Target Analyte Emission Results from
Test Mix vs. Selected Baseline

Casting Quality

The step core pattern used in the emission testing did not provide a good opportunity for surface finish comparison. The following photos (Figures 11 through 16) compare the seacoal baseline castings (Test FK) compared to graphite pattern release agent castings (Test FV). This test did not include the greensand additive package that should improve surface finish further. Added testing is planned by CERP to further profile the quality implications of these mixtures.

Fig. 11 FK001 Best Casting Surface

Fig. 12 FV005 Best Casting Surface

Fig. 13 FK005 Median Casting Surface

Fig. 14 FV008 Median Casting Surface

Fig. 15 FK004 Worst Casting Surface

Fig. 16 FV011 Worst Casting Surface

Investigations That Contributed to the Final Conclusions

Contribution of Green Sand Emissions With Seacoal and Seacoal Supplements

A series of investigations was completed to evaluate the contribution of greens sand release agents with seacoal and seacoal supplements on the emission characteristics that occur during the metal casting process. For this investigation, the same methods and equipment was used (as previously discussed) in the studies to determine the impact that seacoal and seacoal supplements have on emissions. In all of these studies, the same petroleum based green sand release was investigated except for a specific study that was used in comparison with a water based release agent containing graphite.

Figure 17 is a comparison of HAP’s between materials evaluated. These materials include; a seacoal baseline study, low volatile coal blend (specifically an anthracite/seacoal blend), causticized lignite, blended minerals (containing seacoal/graphite/iron oxide), AO added water to a seacoal blend, and a series of blends containing no seacoal. These materials were evaluated at the CERP facility and the entire series of reports are available at the CERP website. These reports include the complete testing results of emission from the pouring, cooling and shakeout and a review of casting quality.

Fig. 17 Comparison of Seacoal & Seacoal Supplements (HAP)

Investigations That Contributed to the Final Conclusions

Understanding the Resulting Comparisons of Other Decompositions Products

In addition to the previously discussed emission data from the metal casting process, recently collected data concerning the CO, CO2, NOx, and SO2 was completed. During previously discussed evaluations the equipment and methods were not available for these evaluations. Recently CERP added the equipment and protocols to evaluate these test methods. Figure 18 contains the collected information.

Figure 18 Comparison of Seacoal and Other Materials

Final Conclusions and NAL CONCLUSIONS AND SUGGESTIONS
Ductile iron castings can be produced utilizing the information and technology discussed. A number of ductile iron foundries have taken advantage of this information and changed their preblend, altered the type of green sand release agents, and improved methods to produce high quality castings while reducing the emission characteristics.

The results from these evaluations show that:

1. Casting surface quality is comparable to that achieved with a traditional greensand with seacoal.

2. In order to reduce the CO & CO2 content of molding sand the reduction in seacoal should occur. This can be accomplished by the addition of a water based green sand release agent containing graphite.

3. The reduction in emission characteristics of green sand during pouring, cooling, and shakeout can be accomplished using a number of methods (with varying results):

1. Utilizing seacoal and seacoal supplements.

2. Utilizing green sand release agents with lower emission characteristics.

3. Utilizing water based green sand release agents containing graphite.

1. With seacoal and seacoal supplements.

2. Without seacoal all together.

Overall, the data clearly show that significant emission reductions can be achieved without sacrificing casting surface quality.

Acknowledgments
The authors would like to thank the Hill and Griffith Company, Technikon, LLC and CERP for their permission to publish this information.

References
LaFay, Neltner, “Forget Southern! Go Western with Green Sand Binders,” Modern Casting, (October 2002)
LaFay, Neltner, “Green Sand without Seacoal,” AFS Transactions (2004-111)
LaFay, Neltner, “Understanding Emissions in Green Sand Molding,” Modern Casting (Website Article) (April 2002)
LaFay, Neltner, “Understanding the Application of Green Sand Release Agents,” AFS Transactions (2002-064)
LaFay, Crandell, Glowacki, Knight, “Significant Reduction in the Emission Characteristics of the Green Sand Process”, AFS Transactions (2004-125)
LaFay, Crandell, “Reduction and/or Eliminating Seacoal in Green Sand Systems”, AFS EHS Conference 2005.

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