Know the Environmental Impact of Your Additives
Step one in pollution prevention is reviewing the additives in your green sand molds.
Vic LaFay and Stephen Neltner, S&B Industrial Minerals NA, Cincinnati Dave Carroll, American Colloid Co., Elgin, Illinois D.J. Couture, General Motors Corp., Pontiac, Michigan
AFS Molding Methods and Materials Pollution Prevention Committee (4N), Schaumburg, Illinois I
n order to gain a basic understand- ing of the source of emissions in a green sand metalcasting facility, a research group recently devel- oped a graphical representation to
demonstrate the sources of hazardous air pollutants (HAPs) in an iron cast- ing facility (Fig. 1). According to the Casting Emission Reduction Program (CERP), emissions at pouring, cooling and shakeout of green sand molds and cores make up 90% of HAP emissions, so pollution prevention can be best served by focusing on these areas. One of the first steps of pollution pre-
vention is understanding your molding media materials, why they are used and their effect on emissions. For the past four years, members of the metalcasting industry have been conducting a litera- ture review to compile a database that illustrates the additives used in green sand molding and the correlating environmental issues that occur during pouring, cool- ing and shakeout (Table 1). The table database was developed from various sources of information, including research, techni- cal development and plant applications. Most of the references have been pub- lished in the last 15 years, and the literature database is updated on a regular basis. This article presents
the findings of the review and discusses how to apply the results to your green sand facility.
Molding Sand Additives The database includes
two areas of review—addi- tives and environmental is- sues. The additives section
Fig. 1. The pouring, cooling and shakeout operations contribute the most emissions in a green sand casting facility.
MODERN CASTING / October 2010
examines five primary additive types: binders, carbon additives, inorganic ad- ditives, core sand additions and “other” additives. Since the metal types poured in a metalcasting facility have an impact on the selection of additives used in the green sand molding process, the database was developed to show how the additives are used by primary metal type, including steel, iron, copper-base and aluminum alloys. The practice of using one molding
sand with multiple metal types (pouring aluminum and copper-base with the same sand system) is becoming popular in the casting industry for both ferrous and nonferrous facilities. Recognizing the differences in addi-
tives required in the preparation of the molding sand is important. For example, the database shows that calcium ben- tonite is the predominant binder used
when pouring aluminum and copper- base alloys. However, copper-base casting facilities also use a quantity of sodium bentonite or bentonite with processed carbon to increase dry and hot compression strength because of the higher pouring temperatures. Also, copper-base plants prefer to put a small quantity of seacoal or other organic ad- ditives in the prepared molding sand for clean separation from the castings at shakeout, but seacoal is not required for aluminum castings. When casting both metals using the same sand sys- tem, a balance in binder selection and carbon additives is required to achieve a molding blend that is appropriate for both metal types. The addition of seacoal into molding
sand has been shown to increase the emission characteristics of the mold. Casting facilities that pour only alumi- num do not observe the increase in emission char- acteristics because they do not use seacoal, but alumi- num casting facilities that add copper-base alloys to their capabilities—and therefore seacoal to their sand—will see an increase in emissions.
Core Sand Additions Returned core sand
is another contributor to emissions at pouring, cool- ing and shakeout. Core sand additions should be monitored as a raw ma- terial additive similar to binders and other green sand additives. The environmental is-
sues section of the data- base shows the addition of returned core sand can
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