|Sand binders for cores and molds can create noxious emissions — but it doesn’t have to be that way. |
The pressure to “clean up” a metalcasting operation may not necessarily come from regulatory agencies.
Frequently, pressure comes from the neighborhoods and communities where plants have operated for decades. Recently, one foundry reluctantly relocated from the Northeast to Alabama, resulting in the loss of over 100 jobs to the community — even after the operation had made itself one of the cleanest ferrous foundries in the U.S.
Many foundries were built decades ago away from major population centers. Now, urban sprawl places these facilities close to schools, churches, parks, etc., and the nearby residents expect these operators to “clean up.” While it’s true that some organizations want these facilities gone, others actually want them to stay so that they will continue providing valuable manufacturing jobs.
Many suppliers have made considerable effort at “odor abatement,” trying to collect and scrub the out gases or using additives to eliminate them. This may reduce complaints about odors; it does not address the emissions.
There are examples of foundries that have invested significantly to abate odors and to lower emissions by applying new products and technologies, and some ‘common sense’ foundry practices.
Gregg Industries’ low-emission binders Gregg Industries, El Monte, CA, uses a shell-core process to produce complex, highly cored ferrous castings for industrial, automotive, and truck industries. In a joint venture with the South Coast Air Quality Management District (Southern California’s regional environmental regulatory agency) and the California Air Research Board, Gregg installed an odor scrubber that became operational in 2004. The number of odor complaints declined significantly after the scrubber’s start-up.
Low-Emission Ideas, Advice, Resources
EPA: Since 2005, the U.S. Environmental Protection Agency has recognized low-emission technologies and products, and that October it sponsored a meeting featuring presentations by eight suppliers of such products and technologies. There was an open discussion with the EPA, educating the regulators in the technologies’ advantages and disadvantages, and the market segments where they apply. Since that meeting, EPA has provided a biannual information review of low-emission products and technologies.
P2RX: EPA is developing the Pollution Prevention Resource Exchange (P2Rx; www.p2rx.org), a consortium of eight regional pollution-prevention information centers, to report ideas, networking opportunities, and other services to states and local governments, and technical assistance to manufacturers. A metalcasting sector will be added to the consortium soon, to help foundries and diecasters locate information and resources about pollution prevention and emission reduction.
LETCAST: The Low Emission Suppliers to the Metal Casting Industry consortium is a partnership of product and technology suppliers whose charter is to educate the industry on how to lower emissions, either through the use of low-emission products and technologies, or through the application of good foundry practices. They have created a website — www.letcast.org — to post new information and developments.
AFS P2 Committee – Division 4N: AFS established a committee, Division 4N; Pollution Prevention, that addresses low-emission issues and activities related to core binders and green sand. The committee meets four times every year; visit www.afsinc.org.
Gregg had a small, organic resin, no-bake line used for prototype castings and customer casting qualification. A decision was made to increase production on this line significantly, and odor complaints increased dramatically when the no-bake production increased. Afternoon winds from the open, south side of the foundry forced odors from the no-bake production area into the shell-core room, then out the doors and into the community.
No-bake resin odors are similar to the shell odors. Gregg Industries’ managers and the AQMD misdiagnosed the root cause and assumed the odor scrubber was not working.
During this period, some core machines were relocated and the odor scrubber ducting stopped pulling odors into the system efficiently, increasing the level of untreated fugitive odors. The combination of odors seemed to be synergistic, and the overall odor level increased dramatically multiple times.
The initial reaction was a logical approach to the problem: the operators tried to identify a single source of the odor. Gregg ran successful trials of silicate as a low-emission replacement for the phenolic-urethane resin, but even though the silicate improved casting quality and was less expensive than the organic-based resin system, a decision was made not to convert the line at that time. Six months later, a decision was made to switch to a highly modified sodium-silicate binder.
Then, due to what Gregg later determined was a misunderstanding, the operators began to “spike” the sand systems with excessive amounts of organic green-sand additives, sea coal and wood flour.
Finally, Gregg’s operators initiated a multipart resolution. They restored the peroxide dosage to the correct level, and automated the dosage verification. They properly relocated the ventilation ducts to a new location, and raised the stack height to 65 ft.
Gregg eliminated its use of plywood bottom boards for no-bake molding; molds are now placed on a bed of sand. It stopped using wood for spacers and weights, and eliminated wood flour by adopting LOI monitoring and wet-tensile sand testing, for much more precise control of soda-ash additions.
Next, Gregg began using shell sands with the lowest emission ratings, and ordered its shell core suppliers to do the same. It tested and proved “purge superheat,” which made it possible to convert other organic chemicalbased core resins to highly modified sodium silicate-based low-emission technology.
Previously, the sodium-silicate no-bake molds were made of 100% reclaimed shellcore scrap sand. The thermal reclamation system had thermocouple and other process control issues, so the resin was not burned off completely, and the residual phenol resin was one of many contributors to the phenol odor. It has been shut down permanently. Once implemented, these changes resulted in the following:
- Sand-related scrap reduced >30% when the AO green sand system is “optimized for odors.”
- Over a year and a half, the use of low-odor shell resin made it possible for the green sand system’s compressive strength to rise >20% (round grain, less dust, less ammonia.)
- Reduced total shell resin >20% due to better overall performance.
- A new core machine, purchased to operate using the highly modified silicate binder, was ruled “exempt from New Source Review.”
- Gregg Industries and Neenah Foundry Co. have continued to investigate emerging low-emission core technologies.
- Automated equipment was designed and built to generate high-temperature compressed air to help replace odor-producing organic resins with low-emission, water-based core binder technology.
Today, Gregg Industries is managing its castings production differently than in the past. The workers have learned new skills. Gregg Industries concluded that to prevent odors and reduce emissions, a pollutionprevention program similar in function to a safety-training program, needed to be implemented. Gregg continues to identify and reduce odor causing materials and processes.
Grede’s conventional binders
Increasingly, foundries find they are challenged to understand and respond to changes in their communities. For example, Grede Foundries’ Liberty Plant, in Wauwatosa, WI, now uses a phenolic-urethane core process and a green-sand molding process to produce complex, highly cored ferrous castings for industrial, automotive, and truck industries.
However, from the 1980s through the mid 1990s, Liberty had been primarily a shell core and shell mold foundry producing medium volumes of automotive components, and an increasing volume of turbo housings. As turbo housing production increased, the amount of cores used per casting also rose, as did the emissions and odors from the process due to an increase in resin usage.
Reducing Emissions by Replacing the Core Binder
Cincinnati-based Pridecast used a protein-based, water soluble-core to replace a shell core in its production of gas-pump swivel elbow castings. This replacement reduced emissions by more than 80%. And, because of the “collapsibility” of the new binder, the casting shakeout time was reduced from 12 minutes to 30 seconds, which helped to reduce total costs by 24%.
As output increased, so did community pressure to reduce odors. Liberty started a transition to a green sand molding process and a phenolic-urethane core process during the mid 1990s. While the transition to a green sand process helped reduce odors, the community pushed for further reductions. That led to shutting down the entire shell molding line in August 2000. This lessened the complaints significantly, but questions remained as to why there were any odors at all: the neighbors had been told that the odors were caused by the shell molding and shell core processes.
Considering the location of the plant, a product mix that required up to 1,000 lb. of core sand per ton of iron, and the costs of odor control technology, Liberty had to be aggressive in reducing the odors.
In the fall of 2006, Liberty started a new emission-reduction program to help reduce odors, focusing on the reduction of resin, solvent off-gassing, organic core additives, organic sand conditioning additives, and use of sea coal. To address the core-related odors, Liberty made some innovative (perhaps unconventional) changes. It adopted new technology to increase the PUCB core purge temperature, which included recovering waste purge heat used to preheat the sand. With the new technology, Liberty was able to reduce the amount of binders, anti-veining additives, and amines used in the core process.
Next, Grede Liberty worked to improve its core room efficiency by cutting the core machine cycle times and reducing or eliminating amine smells from the core process and core storage area.
Finally, Liberty installed an advanced oxidation, clay-recycle black water system, which can be expanded to include sand reclamation. Over several months, the percent of clay recycled was increased, which made green-sand preparation more efficient. This lowered coalfeed rates, altered ratios of Western to Southern bentonite, and lowered clay moisture levels. In time, total clay usage declined, and the plant reduced its use of other green-sand additives and lowered its Mb clay targets.
Overall, the volume of smoke and odors were reduced, and Grede Liberty continues to target emissions levels by experimenting with lower amine and resin usage, along with shorter core gassing cycles and coremaking cycle times, with good results. The plant is working to improve its overall metalcasting productivity, and to conduct formal and informal “odor awareness” programs.
Having implemented these changes, Grede Liberty achieved some notable savings within the first year of the program:
- Reduced the amount of core binder used by 7%.
- Reduced the amount of organic antiveining agents used by 29%, and the amount of red iron oxide used by 43%.
- Reduced its consumption of DMEA by 52% (it’s now ~1.6 lb per ton of core sand.)
- Core room productivity improvement: 38% reduction in gas cycle time .
- Reduced organic sand conditioning additive used by 90%.
Other signs of progress at Liberty include more efficient muller operation (using city water, the continuous mixer ran in “the low 40% range; with advanced oxidation black water, it’s in the mid 50% range); the Mb target changed from 10 to 10.5, to 8.9, to 9.2; the LOI target changed from a range of 3.5 to 4.0, to 2.8, to 3.2; and clay consumption fell to 12.7% less bond per PWT (pour weight ton), and sea coal consumption was reduced to 15.6% per PWT.
Gregg Industries and Grede’s Liberty Plant installed a number of new technologies to address odors that caused neighbors to complain. While it’s important to note that no foundry can be entirely odor-free, metalcasters must dedicate efforts to identifying odor sources and discovering ways to minimize the total odor load at a given time. New odor sources must be addressed as they are uncovered. Reducing odors is an ongoing effort, requiring vigilance by all foundries, even if they think they don’t have a problem. Examples prove that through organized and dedicated effort, even with a focus on addressing nuisance odors, foundry emissions can be reduced.
|Greg Sanders handles Engineering Sales and Technical Support for Hormel GMBOND® and is director of Technical Services for Entelechy Inc., a consulting firm that helps foundries reduce costs and develop effective processes.|