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MIT 2 813 - Homework 7

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Environmentally Benign Manufacturing Homework #7: Manufacturing ProcessesSpring 20071. Estimate the toxic emissions to air for a 1 kg sand cast part (use TRI Data)Use the data from Foundry XYZ included in the class slidesFoundry XYZ - 2003Tons Produced 270,000Chemical Total Air Emissions (lbs) Lbs of Emissions/Ton kg of Emissions/tonneCOPPER 69 0.000255556 0.000511111DIISOCYANATES 0 0 0LEAD 127 0.00047037 0.000940741MANGANESE 274 0.001014815 0.00202963MERCURY 14.35 5.31481E-05 0.000106296PHENOL 6640 0.024592593 0.049185185ZINC (FUME OR DUST) 74 0.000274074 0.0005481482. Compare the energy for sand casting a steel part that is 1kg and machining that same part from a (1+γ) kg block of steel as a function of γ, the amount of material removed. Energy of Material Production: Primary Production: 31.3 MJ/kg Secondary Production: 8.7 MJ/kg Sand Casting a 1 kg part: According to class notes (manuf. processes) the energy to cast a metal lies in between 13 and 17 MJ per kg of saleable metal (including fuels for electricity). For this exercise we will assume that this translates to about 9 MJ per kg of metal processed (Note, Em = 9 MJ/kg < Energy per kg saleable product ≈ 15 MJ/kg because you process more metal than you sell due to runner, risers etc). Machining a 1 kg part: Using an Automated Milling Machine – the energy used is 10 kJ/cm3 of material removed (see manuf processes). For steel with a density of 7.85 g/cm3, the energyfor removal is 1.273 kJ/g = 1.273 MJ/kg removed Results1) Assume 50% Primary/50% Secondary for Sandcasting: (they wouldn’t use 100% primary in a process like this):Energy use = Ematl + 2Em = [31.3 MJ/kg* 0.5kg + 8.7 MJ/kg* 0.5kg]+ (2* 1 kg * 9 MJ/kg) = 38 MJ Process1 kg2) Assume 100% Secondary for Sandcasting:Energy use = Ematl + 2Em = [(8.7 MJ/kg)* 1kg] + (2 * 1 kg * 9 MJ/kg) = 26.7 MJ 3) Assume 100% Primary Steel for Machining: Energy use = (1+ γ) Ematl + γ Em = [(1+ γ)kg * 31.3 MJ/kg] + 1.273 MJ/kg*(γ)kg = 31.3 MJ + 32.573(γ) MJ4) Assume 100% Secondary Steel for Machining: Energy use = (1+ γ) Ematl + γ Em = [(1+ γ)kg * 8.7 MJ/kg] + 1.273*( γ)kg = 8.7 MJ + 9.973(γ) MJ The process that uses more energy depends on the amount removed during machining.  Machining a 100% Primary material part will always be more energy intensive than sandcasting that part from 50% primary/ 50% secondary Machining 100% Primary uses more energy than Sandcasting 100% Primary when γ = .55 kg  Machining a 100% Secondary part uses more energy than Sandcasting a 50% Primary/ 50% Secondary part when γ = 1.80 kg  Machining a 100% Secondary part uses more energy than Sandcasting a 100% Primary part when γ = 4.07 kg3. Compare the energy consumed from making a 24.5 kg computer to the sand casting of a 24.5 kg cast iron part. Sand Casting a 24.5 kg part:Per the class slides, energy use is about 15 MJ/kg of salable cast metal in total. Therefore, for a 24.5 kg part, about 367.5 MJ is used. Making a 24.5 kg computer:Total energy use is 6400 MJ in manufacturing (per E. Williams) 4. How does the XYZ foundry compare to the national TRI Data? Comparing the table in problem #1 to the graph above (in the class notes), it appears as if the XYZ Foundry is a lot better than the national average. For example, the level of zinc and zinc compounds released to air is around 0.05 for the national average, and is two orders of magnitude smaller at XYZ


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MIT 2 813 - Homework 7

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