Tae-Ho Lee

Computer numerical control (CNC) lathes are optimized for machining workpieces into rotating shafts or cylindrical shapes of structures. However, because rotating mechanical parts are used on CNC lathes, vibration from spindles, servomotors, hydraulic pumps, and feed screws occurs. Therefore, periodic preventive maintenance is required to minimize vibrations. Additionally, alignment, balance, and adjustment operations are necessary for parts that perform linear or rotational movements. Thus, this study adjusts the tension of the V-belt that drives the spindle of the CNC lathe, analyzes the primary components and the vibrations occurring at the spindle and servomotor, and measures the surface roughness to identify the cutting quality according to the impact of the belt tension. The experimental results show that the peak value of the vibrating component increases as the cutting speed increases. We demonstrate that the optimal vibration characteristics and excellent surface roughness values are achieved at a relatively looser belt tension than the standard value. In particular, at a feed speed of 0.05 mm/rev, a cutting speed of 250 m/min, and a depth of cut of 0.8, the surface roughness in loose tension was reduced by up to 143.9% compared to tight tension. Additionally, the optimum processing quality is achieved at a cutting depth of 0.6 and 0.8 mm, corresponding to a turning insert nose R-value of 0.4 mm, and at cutting speeds ranging from 200 to 250 m/min.

A small combustion chamber was developed and manufactured for empirical combustion testing of several alternative fuels developed to meet IMO emission limits for fuel oil used in ships. The combustion chamber consists of four independent tanks and a circulation system with a two-stage heating function owing to the high viscosity and temperature of ship fuel. A gun-type burner is mounted on the side of the combustion chamber, which possesses a cylindrical shape and a capacity of less than 300 L. This device was manufactured in accordance with several variables such that the basic stage performance and simulation tests of each fuel could be sufficiently completed before performing the combustion test to simulate the engines of large ships. To conduct an initial experiment using the developed combustion chamber, low-sulfur MGO with a sulfur content less than or equal to 0.05% was chosen, and ideal operating parameters were selected according to the measurement tests based on load control. The exhaust gas temperature differed by approximately 10.7% as a result of burning MGO at a burner load state of 80–100%. The use of a normal oxygen concentration of 4% helped remove approximately 14.31 ppm of nitrogen oxide and 1.91% of carbon dioxide. The maximum combustion efficiency was 70.17%, indicating the chamber’s potential for use in a variety of combustion tests of alternative fuels for ships in the forthcoming years.