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Research paper : A rationalization guideline for the utilization of energy and resources considering total manufacturing processes (H. Kita et al.)−201 Synthesiology - English edition Vol.1 No.3 (2009) are called “processes.” The process is aggregation of “operations.”Figure 3 shows the input/output flow of matter and energy during operation. While raw fuel is introduced and intermediate product is produced for each operation, waste material and heat are also produced and these are emitted outside the system. The intermediate product becomes raw material for the next operation, and final product is made after series of operations.To calculate exergy, it is necessary to know the type and the quantity of all raw materials and energies that are introduced into and emitted from the operations, from material to final product. In this study, we were able to obtain data in actual manufacturing by cooperation of major manufacturer. In most cases, we used data while some parts were unknown, and unknowns were filled in with estimate values based on experience.2.3 Manufacturing efficiencyThe percentage of exergy of product against sum of exergies of all input fuel and energy was called fixed ratio of exergy within members (η).η=EX(p)/EX(in) …… (6)Here, EX(p) is chemical exergy of product, and EX(in) is sum of input exergies. In this paper, we evaluated manufacturing efficiency by considering both fixed ratio of exergy within member and exergy needed for input.3 Case study 3.1 Aluminum casting line operation and role of heater tubeAluminum has excellent heat conductivity and is lightweight, and therefore is used widely in engine parts. Also, aluminum is highly recyclable, so disposed engines are collected as scraps and recycled as engine after undergoing some processes. Figure 4 shows the recycling system mainly for aluminum casting line operation. First, recovered waste engine (scrap) are melted in centralized furnace. They are made into solid ingots, delivered within the plant, melted again in centralized furnace, and then transferred to holding furnace. The molten metal is adjusted for temperature and content, distributed to die cast machine, and formed into products. In this cycling system, there are many factors that decrease efficiency including heat loss, oxidation of molten aluminum, and inclusion of impurities. Input of energies and things from outside is unavoidable to maintain certain quality level and production volume, and reducing these inputs is expected to increase the efficiency of the cycling system.As one of measure, use of ceramics in production member has been attempted. Heater tube (Figure 6) used in holding furnace (Figure 5) is one example. It is a protective tube that envelops the heating wires, and is used to maintain constant temperature of molten aluminum. Heat efficiency increases by using highly conservative silicon nitride, which allows horizontal dip structure where the tube is fixed horizontally in the bottom of the furnace (Figure 5). However, ceramic tube is much more expensive than iron tube. We conducted exergy analysis for manufacture-use-disposal in cases where the heater tube (weight 19 kg) was made with silicon nitride and when it was made with iron[11][12].3.2 Calculation of chemical exergy In conducting the analysis, it is necessary to calculate the exergies of all materials involved in the manufacture. The process of calculation of exergy is shown using silicon nitride (Si3N4), the main material. The reference material of silicon nitride is silica and air.(47)−Engine parts (product)Solidification and formingDie castTemperature adjustmentMelting & holdingMolten aluminumCentralized meltingCasting line in plantDeliveryAluminum ingot (solid)Melting & content adjustmentUseDisposal RecoveryWaste engine etc.Molten aluminumHeater■ Heater is attached to bottom■ High heat efficiency(B) Horizontal dip type■ Easy to exchange heater■ Low heat efficiency(A) Vertical dip type169 mm1100 mm1347 mmφ195 mm77.5 mmφ155 mmImmersed partAttached partFig. 4 Aluminum cycle and casting line operation.Fig. 5 Structure of holding furnace.Fig. 6 Form and dimensions of heater tube.

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