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of the various sustainable production technologies. Te life cycle boundaries include major upstream activities that supply inputs to iron casting facilities. Te model accounts for energy, materials, environmental emissions, operating costs and capital costs. Tese metrics are tracked at each intermediate stage of production, including hot metal making, coremaking, green sand mold- ing, pouring, cooling and shakeout. Downstream recycling of iron products and their recovery were not considered because the innovative technologies would not affect these processes. Figure 1 illustrates the baseline


input-output boundaries for the analysis. Te major upstream activi- ties—power production, coke making and sand mining—provide inputs of electricity, coke and sand, generate emissions and require fuel and raw materials. Cupola melting and the bal- ance of foundry activities are the two major functional units on the left of Figure 1. Tese activities require melt- ing inputs, such as ferrous metal alloys, scrap metal and natural gas. Tey also require process inputs, such as parts and supplies. Tis process chain produces finished iron castings and potential environmental discharges.


Core Changes: Collagen-Alkali Silicate Binders


Conventional metalcasting facilities


commonly create cores via a coldbox process that uses a phenolic urethane binder cured with an amine gas that creates air pollution. Moreover, when subjected to molten metal in the mold, these core binders pyrolyze and release VOCs and hazardous air pollutants. Conventional core binders are the predominant source of VOCs and hazardous air pollutants from iron casting facilities. Recent bench-scale and pilot-scale


trials have shown a hybrid of collagen and alkali silicates will create a core binder that emits far less VOCs and hazardous air pollutants than pheno- lic urethane binders, while retaining the comparable strength and thermal resistance of conventional phenolic urethane. During the curing of the collagen-silicate hybrid, a proprietary


Fig. 1. The chart shows the baseline input-output boundaries for the conventional cupola iron casting facility used for this analysis.


system for heat-curing blown sand- binder systems warms the corebox by heating it with air, moisture or carbon dioxide under a vacuum. Te system requires a modified core machine and proprietary instrumentation, but it does not require an amine scrubber and does not produce scrubber brine. Te only emission from the core shop is water. Based on limited partner foundry expe- rience, this coremaking process is more efficient, with lower cycle time, less corebox cleaning and less core scrap than conventional coremaking. Recent studies of low-emission


hybrid core binders are awaiting pub- lication so this data is offered only as potential improvement, but collagen- alkali silicate-based binders for green sand molds can potentially reduce total operating costs by 1.3% and emissions of VOCs by 35% (Table 1).


Table 1. Percent Change From Baseline When Using Collagen-Alkali Silicate Binders


Foundry Facility VOCs


Costs Labor


Materials Other cost Total


Projected Payback (in years) -35


-7.6 5.8


-3.6 -1.3 0.4


Melting Breakdown: Electric Induction Furnaces vs. Cupolas


Because cupolas are charged with


limestone, they can accommodate scrap iron and carbon sources with higher proportions of impurities. Batch electric induction furnaces use electricity for melting and require more expensive (i.e., purer) iron and carbon sources for alloying. Overall, an electric induction furnace requires 207% more fossil energy and 207% more non-fossil energy to melt iron (see Table 2). Tis energy demand is profoundly higher because of the relative inefficiencies in transmitting electrical power and in converting heat energy to electrical energy and then back to heat energy. Te induc- tion furnace’s actual cost of energy, however, is only 9.7% higher than the cupola because the metallurgical coke in cupolas costs considerably more than electricity produced in coal-fired power plants. Cupolas impact the local environ- ment via air emissions, while electric induction furnaces generate fewer emissions. Several facilities have replaced cupolas with electric induc- tion furnaces in response to local air quality rules that limit emissions, but this is not favorable in regard to overall life cycle. Replacing a cupola with an electric induction furnace merely transfers emissions upstream


March 2014 MODERN CASTING | 41


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