Vol.1 No.3 2009

52/69

Research paper : A rationalization guideline for the utilization of energy and resources considering total manufacturing processes (H. Kita et al.)−203 Synthesiology - English edition Vol.1 No.3 (2009) Here, D is thickness of heater tube (mm), D0 is initial thickness (mm), k is apparent reaction speed coefficient, and Di is thickness at time of replacement (mm). Assuming D0 = 3 mm (from data) and Di = 0.5 mm, under condition of replacement every half year, the reaction constant k was calculated to be 0.067578.Consumption exergy is expressed by following equation.E=E0･exp(kt) …… (12)Exergy of steel is 6.6 MJ/kg (= 368 KJ/mol) and total weight of the product is 19 kg, and when it is disposed when damage reaches Di, consumption is 126 MJ/tube. While steel heater tube is exchanged once every half year, silicon nitride is stable and does not react, and is exchanged and disposed along with furnace that has lifespan of 7 years. Figure 9 shows the change with time of exergy consumption in 7 years. Exergy consumed by disposal during this time is as shown in the following equation.・Steel: 126 (MJ/tube) × 14 (tubes) = 1764 MJ・Silicon nitride: 229 (MJ/tube) × 1 (tube) = 229 MJWhen steel heater tube is used, damage and disposal are repeated and exergy consumption increases in step-like form. In contrast, there is hardly any consumption in 7 years using ceramics, and exergy value (229 MJ) is released at the end of furnace lifespan. Also, using ceramics, there is less chance of inclusion of impurities compared to steel, so clean molten metal can be obtained, and this is another advantage of ceramics.②Running(a) Melting and holding furnaceIn vertical dip type using steel heater tube, 9.4 kW is required during run and 4.0 kW at rest, while in horizontal dip type using silicon nitride, electricity consumptions at run and rest are 6.8kW and 3.8 kW respectively, due to improved heat efficiency. While it will be running 60 % (40 % rest) per day and is in operation 360 days a year, the total electricity consumed in 7 years, or exergy input, will be as follows.・Steel: (9.4×0.6×24+4.0×0.4×24) × 360 × 7 × 3.6/1000 = 1576 GJ・Silicon nitride: (6.8×0.6×24+3.8×0.4×24) × 360 × 7 × 3.6/1000 = 1219 GJ(b) Die cast machineAssuming that electricity consumption of die cast machine is 20 kW, running 60 % per day for 360 days per year, the total electricity consumption, or exergy input, for 7 years is as follows.・20 × 0.6 × 24 × 360 × 7 × 3.6/1000 = 2612 GJ3.4.2 Manufacture, use, and disposalAs result of interview with companies, the total manufacture volume of cast product in 7 years was estimated to be about 4300 ton. In this paper, material loss is not considered. Therefore, the amount of molten aluminum is 4300 ton or same as final product, and the exergy was calculated as 126802 GJ in molten condition (temperature 700 °C), and 125582 GJ in solid condition.Figure 10 shows the amount and flow of exergy input and output for manufacture using ceramics and steel heater tube, their use in melting and holding furnace when casting was conducted for 7 years. As mentioned above, when the furnace is run for 7 years, 14 steel tubes are required since they are subject to damage. Therefore, energy input and output during the manufacture process is as follows.・Input: 621 (MJ/tube) × 14 (/tubes) = 8694 MJ・Output: 495 (MJ//tube) × 14 (/tubes) = 6930 MJOn the other hand, only one silicon nitride tube is required during same time, and exergy for input and output will be 4175 MJ and 3946 MJ respectively according to Figure 7. Next, exergy accompanying damage and disposal during use is as follows.(49)−Die castMelt holdingSteel parts manufacturing Centralized meltingAluminum ingot fuelDeliveryProduct : 125582 GJ Engine parts (4300 ton)Molten aluminum126802 GJElectric power : 1219 GJDie castMelt holdingCeramic parts manufacturingOutput : 3946 MJInput : 130637 GJB) When steel is usedA) When ceramic is usedInput : 4175 MJProduct : 229 MJOutput : 5055 GJOutput : 1220 GJOutput : 3832 GJOutput : 125582 GJProduct : 125582 GJ Engine parts (4300 ton)Molten aluminum126802 GJElectric power : 2612 GJMolten aluminum126802 GJElectric power : 2612 GJMolten aluminum126802 GJOutput : 3832 GJOutput : 125582 GJOutput : 1578 GJOutput : 5417 GJElectric power : 1576 GJOutput : 6930 MJInput : 8694 MJProduct : 1764 MJInput : 130999 GJ0122436486072840500200015001000Ceramic tubes (1 tube)Steel tubes (14 tubes)Exergy consumption due to disposalExergy consumption due to melt damageElapsed time (months)Amount of consumed exergy (MJ)Fig. 9 Comparison of exergy consumption due to melt damage and disposal during use (calculation for 7 years).Fig. 10 Exergy balance in casting aluminum engine parts (7 years).

※このページを正しく表示するにはFlashPlayer9以上が必要です