Advanced Oxidants Offer Opportunities to Improve Mold Properties, Emissions.

Under the direction of the Cast Metals Coalition, research is being conducted to evaluate advanced oxidants and their effect on sand system performance and mold emissions.

Advanced oxidation (AO) technology has demonstrated itself to be an effective tool for the water treatment and hazardous waste remediation industries. Within the last 5 years, the foundry industry has set its sights on AO technology as a possible tool for the reduction of green sand system cost and mold emissions. AO systems reportedly can improve sand system performance by reducing bond (pre-mix) consumption, resulting in reduced green sand mold emissions at cooling and shakeout.

To evaluate the effects of AO technology on green sand systems, the U.S. Dept. of Energy and the Cast Metals Coalition have established a research program. Coordinated by Pennsylvania State Univ., University Park, Pennsylvania, with the participation of Neenah Foundry Co., Neenah, Wisconsin; Wheland Foundry (North American Royalties, Inc.), Chattanooga, Tennessee; International Truck and Engine Corp., Waukesha, Wisconsin; Grede Foundries, Inc., headquartered in Milwaukee; Casting Emissions Reduction Program, Sacremento, California; and Furness-Newburge, Inc., Versailles, Kentucky, the goal of the research is to quantify the effects of advanced oxidation technology on sand system performance and control and mold emissions.

In a joint panel presentation between the AFS Molding Methods & Materials and Environmental Divs. at the 2000 AFS Casting Congress, the preliminary first-year results of the research program were presented. This article takes a look at AO technology and discusses some of the results from the first year of the research.

What is AO?

As used in the foundry industry, advanced oxidants are a combination of water, less than 10-ppm ozone and a process-specific amount of hydrogen peroxide that undergo ultrasonic treatment. Advanced oxidants can be added to a foundry's green sand system wherever water is, such as at sand coolers or mullers. In production, before the water is added to the sand, it is treated with small amounts of advanced oxidants and then undergoes an ultrasonic treatment. It is speculated that what results are partially stable radicals that are created at the molecular level in water, promoting desirable primary and secondary interactions with bentonite clays, seacoal decomposition products and organic residuals when introduced to the sand system. Basically, it is believed that the advanced oxidants clean the clay, allowing it to adsorb additional organics. AO also activates the carbon with the net effect that the mold acts likes a sponge in regard to volatile organic carbons (VOCs).

This means that hazardous pollutants and VOCs are oxidized within the green sand mold, reducing the amount of clay, seacoal and other binders required in the mold, and reducing the smoke and odor emitted from the mold during cooling and shakeout. In addition, oxidants also clean "blackwater," making the reintroduction of baghouse dust more practical. The research currently being conducted is, in part, trying to develop a better understanding of the reactions that take place between the oxidants and traditional green sand additives.

Within the foundry, AO systems are being used in the following configurations:

* clean water systems in which AO water is added to mullers and/or sand coolers;

* wet collection systems in which AO processed water from blackwater tanks is returned to mullers and/or sand coolers;

* dry collection systems in which sand system baghouse dusts are re-wetted and recycled through AO blackwater tanks to mullers and/or sand coolers.

Neenah Foundry

According to Neenah, its decision to install an AO system at its Plant 3 in Neenah, Wisconsin, was driven by the desire to "look at the entire sand system and search for ways to improve control, lower raw material usage, and reduce emissions without causing harm to sand properties or casting quality." Plant 3 utilizes two vertically parted high-production green sand molding lines and pours 500 tons of ductile iron/day, producing castings ranging from 1-170 lb.

To compensate for sand system property changes due to AO additions, a careful process of AO-driven sand system optimization was undertaken in 1995 . As a result, soda ash and bond additions were adjusted along with sand system control set points. Because AO additions effectively increased sand system compactibility at a given sand moisture level, operating sand system moisture levels effectively decreased, muller efficiency decreased and the ratio of methylene blue clay to AFS clay became closer together. According to Neenah, casting quality remained high throughout these changes.

The results for Neenah with the AO technology have been that sand system bond (pre-mix) usage for Plant 3 has been reduced by 15% with an associated reduction in emissions from cooling and shakeout. At one point, the foundry was averaging at least a 20% reduction, but its core loading increased, it stopped adding "blackwater," and it increased seacoal.

In terms of problems, Neenah said, "As we 'cleaned' our system, a tendency to scab on certain part families surfaced. As a result, it is necessary to hold a minimum level of combustible (4.5%) and methylene blue (10.0). Also, it is critical to be careful with screen distribution."

Neenah also suggests that although significant benefits are achieved because AO "cleans your sand system...a sand system can be too clean. A certain amount of plastic mass is needed."

Neenah has installed a second AO system on a molding line with sand system dust collector bentonite recycling.

International Truck & Engine

International's Waukesha plant is a ductile iron jobbing foundry producing castings from 30-150 lb on an automatic horizontally parted molding line. This foundry decided to make AO water additions at the sand muller and sand cooler.

The focus of International's data, according to the foundry, was on the emissions reductions. At the initial start up of an AO system, visible smoke and VOC and carbon monoxide (CO) emissions were reduced. To confirm the VOC reductions, stack tests were conducted in 1997 to establish a baseline of VOC and benzene emissions. Stack tests (Fig. 1) conducted in 1999 (after AO technology start up) show a 56% reduction of benzene/ton of iron poured and a 74% reduction of VOCs (including benzene)l/ton of iron poured. Additional stack testing demonstrated that CO emissions also have been reduced 10% as a direct result of sand system optimization.

In regard to sand system optimization, immediate increases in green compressive strength were observed with AO. As a result, bond consumption was reduced significantly to permit green compressive strengths to return to acceptable levels. Improved sand system performance also has contributed to significant scrap reduction. Specific.data is not available for sand system optimization.

Wheland Foundry

According to Wheland, the foundry currently is using AO technology in combination with blackwater systems at two of its iron foundries "to improve the performance of clays used to bond green sand molds." One of the systems has been operational for 3 years. Wheland utilizes horizontally and vertically parted molding to cast gray and ductile iron components from 3-140 lb.

In the Wheland system, baghouse dust is introduced into a 4000-gallon tank where it is treated with ozone, hydrogen peroxide and ultrasonics. This AO-treated blackwater then is sent to both the sand coolers and the mullers as the make up water addition. The result has been a decrease in bond consumption as high as 40%. Figure 2 illustrates the bond consumption at Wheland before and after the use of AO technology. In addition to the bond savings, the foundry has reduced new sand additions by 20% and seen the elimination of cracked molds and swelled casting defects, which has resulted in significant scrap reductions.

In regards to mold emissions, the foundry has witnessed a reduction in visible emissions and odors from cooling and shakeout. This has been verified by stack testing, which indicated a 30% emissions reduction since the addition of AO technology.

Research on the effects of AO systems will continue at the foundries and Penn State Univ. during 2000-2001.