2.4 Inputs/outputs in manufacturing a unit of a model engine
The inputs/outputs of materials and energies in manufacturing a unit of a model engine at one of the factories were estimated and shown in Figure 2. A 2-cycle diesel engine with maximum output power of 16,800 (PS) was selected as a model engine for the LCI analysis. In Figure 2, the quantities of consumed energies, steel scrap and wastes were calculated by allocating the data recorded in the factory proportional to the ratio of the maximum output power of the engine to the annual accumulated power of engines.
3 LIFE CYCLE INVENTORY ANALYSIS OF CAST/FORGED STEEL PARTS
The ratio of the weight of cast/forged steel parts to the gross weight of the model engine is about 80 (%) as shown in Figure 2. Therefore, the authors made a hearing survey on one cast/forged steel factory which mainly manufactures crankshafts.
3.1 Manufacturing process flows
Main manufacturing process flows of cast/forged steel products were organized for the LCI analysis as shown in Figure 3.
Products are manufactured in various ways and forms in the factory. Most products are crankshafts and others are ladders, turbine rotors, etc. Some crankshafts are manufactured by assembling shafts and throws, and the others are in a monoblock form. Some throws are made of cast steel and the others are of forged steel. Also, both finished and half-finished products are forwarded.
Taking the above intricate situation into account, the authors classified the products into three categories as follows for the LCI analysis of a marine main engine.
(1) cast steel parts for engines
(2) forged steel parts for engines
(3) other products
Manufacturing processes of cast/forged steel parts were assumed as follows.
(1) Cast steel parts
(Materials) ＝＞ Steeling (Smelting, Casting) ＝＞ Machining (some products are skipped) ＝＞ (Products)
(2) Forged steel parts
(Materials) ＝＞ Steeling (Smelting, Making ingot) ＝＞ Forging (Forging, Heat treatment) ＝＞ Machining (some products are skipped) ＝＞ (Products)
In the factory, main materials are supplied with in three forms, that is, steel crude, purchased steel scrap and in-house recycled steel scrap.
3.2 Estimate of inventories of cast/forged steel parts
The items of which data were obtained for the LCI analysis of cast/forged steel parts are listed as follows.
(I) Input items
(Materials): steel crude, purchased steel scrap
(Other materials): 02 gas
(Energies): electric power, LNG
(II) Output items
(Products): cast steel parts, forged steel parts
(Wastes): solid wastes (steel scrap, molding sand)
Figure 2 Inputs/outputs of materials and energies in manufacturing a unit of a model engine
