• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2007년도 춘계학술대회 논문집
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• pp.131-132
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• 2007

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.397-398
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• 2006

In late years, from a trend for ecology of auto motive engine, low emission and low fuel consumption of engine become a social assignment. At the same time, the high output (high efficiency) is required, too. In order to meet those requirements, in comparison with conventional engines, lean A/F (Air fuel ratio) setting is becoming popular for the high performance engines of late years. Exhaust valve seat (sintered material) used in these engines has a problem in wear resistance, because it is exposed to the surroundings that is clean and a high temperature in comparison with the conventional engines. Therefore, wear mechanism with lean A/F of engine was analyzed.The exhaust valve seat (sintered material), that was superior in wear resistance, was developed.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2009년도 춘계학술대회 논문집
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• pp.201-202
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• 2009

• 한국분말재료학회지
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• 제6권2호
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• pp.163-170
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• 1999

Engine valve seat is a functionally important part for maintaining engine performance. The progress of automotive technology has increased the severity of conditions to which it is exposed, especially as regards LPG fuel engines and turbocharger. Therefore, it requires excellent heat and wear resistance to meet the severe condition inside the engine. In the present study, effects of solid lubricants such as CaF$_2$, MnS and MoS$_2$ on microstructure and mechanical properties of sintered Fe alloys for valve srats have been investigated for the development of valve seat material with high temerature wear resistance. As a results of engine simulation test, 0.5 wt% CaF$_2$ specimen showed the most excellent property, but in the overall aspect of view valve recession has increased with increasing the amount of solid lubricants.

• 한국자동차공학회논문집
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• 제12권6호
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• pp.1-8
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• 2004

In this paper we present the effects that valve train design parameters and operating conditions have on the valve rotation properties of a diesel engine. Rotation of intake and exhaust valves are very closely related to the long term durability of diesel engines. of the valves do not rotate even at a rated engine speed, it causes the uneven wear of the valve seat and valve head contact area, which eventually shortens the engine life. Because the rated speed of a diesel engine is relatively lower than that of a gasoline engine, the operating condition of a diesel engine produces tough environment for valve rotation. Therefore, the valve rotation is an important problem which should be solved in the early stage of engine development. In this study, we developed a new technique to measure the valve rotation and shaking motion simultaneously using three proximity sensors. Valve train rotating properties of a diesel engine were measured under various engine operating conditions.

• 한국자동차공학회논문집
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• 제9권3호
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• pp.42-50
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• 2001

In this paper, the effects of scale formation in engine water jacket upon the thermal durability of engine itself and its component parts were studied. To understand the effect of quality of water, a full load engine endurance test for 50 hours was carried out with not-treated underground water. The followings were found through the tested engine inspection after the endurance test; 1-2 mm thick scale formation in the engine water jacket, valve seat wear, piston top land scuffing, piston pin stick, and cylinder bore scuffing in siamese area. In order to understand the causes of above test results, the heat rejection rate to coolant, the metal surface temperature of combustion chamber, and the oil and exhaust gas temperatures were measured and analyzed. The scale formed in the engine water jacket played a role as thermal insulator. The scale formed in the engine reduced the heat rejection rate to coolant and it caused to increase the metal surface temperature. The reduced heat rejection rate to coolant increased the heat rejection rate to oil and exhaust gas and increased the oil and exhaust gas temperature. Also, the reasons of valve seat wear, piston top land scuffing and cylinder bore scuffing, and piston pin stick quantitatively analyzed in this paper.

• Corrosion Science and Technology
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• 제7권2호
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• pp.92-98
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• 2008

This paper describes the experiments of the corrosion and the sliding tests of the nickel-based alloys for the gate valve seating materials used at high pressure and temperature. The general corrosion rates and IGC susceptibility are tested in pressurized water at 533 K and 575 K and in Strauss test solution. The sliding tests have been done in pressurized water at 293 k, 473 K and 573 k. The alloys containing above 10% chromium may have the anti-corrosion properties that could be applied to the valve seats for the power plants. The good sliding performance and the good pressure tightness are obtained when the disc specimens that have hardness 500 to 600 Hv combined with the seat specimens that have hardness 250 to 410 Hv containing about 40 percent of iron. The large size gate valves sliding tests have certified the test results. The anti-wear properties of the seat alloy and the anti-IGC susceptibility of the disc alloy could be improved by the addition of silicon and niobium, respectively.

• Journal of Advanced Marine Engineering and Technology
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• 제31권6호
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• pp.744-752
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• 2007

Recently a fuel oil of the diesel engine in the ship is being changed with low quality as the oil price is higher more and more. Therefore the wear and corrosion in all parts of the engine like cylinder liner ring groove of piston crown, spindle and seat ring of exhaust valve are increased with using of heavy oil of low quality In particular the degree of wear and corrosion in between valve spindle and seat ring are more serious compared to the other parts of the engine due to operating in severe environment such as the high temperature of exhaust gas and repeating impact. Thus the repair weld to the valve spindle and seat ring is a unique method to prolong the life of the exhaust valve in an economical point of view In this study. corrosion property of both weld metal zone and base metal was investigated with some electrochemical methods such as measurement of corrosion potential, cathodic and anodic polarization curves, cyclic voltammogram and polarization resistance etc. in 5% $H_2SO_4$ solution. in the case of being welded with some welding methods and welding materials to the exhaust valve specimen as the base metal. In all cases. the values of hardness of the weld metal zone were more high than that of the base metal. And their corrosion resistance were also superior to the base metal. The weld metal of A2F(AC SMAW: 2 pass welding with foreign electrode) showed a relatively good results to the corrosion resistance as well as the hardness compared to the ether welding methods and welding materials. Moreover it indicated that hardness of the weld metal by the domestic electrode was considerably high compared to that of the foreign electrode.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.401-402
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• 2002

Diesel engines have many sliding parts with solid body contact. For example, a piston-ring and a cylinder bore, a valve and a valve-seat, a cam and a valve tappet. These parts have a severe wear problem. during engine life times. During these times, the valve tappet has abnormal wear such as scuffing and pitting due to a high hertzian contact stress between the cam and the tappet. Excessive wear problems frequently occur to both the cam and the tappet. To solve these problems, we developed an advanced wear resistant tappet. The developed tappet consisted of a hard-metal wear part and a steel body. To increase a bonding strength, those two parts, were directly bonded to each other. Also to decrease a bonding temperature, we developed the composition of Ni-binder materials in the hard metal. To estimate the wear characteristics of the newly developed tappet, we performed wear tests and engine dynamo tests in order to compare them with a conventional Fe-base tappet. As a result, the newly developed tappet has better wear characteristics than those of the conventional tappet. In addition, we performed a 100,000km field-test, and the newly developed tappet showed much improved wear resistance.

• 한국분말재료학회지
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• 제10권2호
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• pp.89-96
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• 2003

The recent trend of miniaturization and high performance of vehicle engines has put an urgent necessity for the development of valve seats which can operate under more severe conditions. In order to develope valve seat material that has the most excellent wear resistance at operating temperature of engine through improvement of the progress of work. the effects of mixing ratio of the milled powder on sintered and Cu-infiltrated properties of sintered valve seats have been studied. The resultant radial crushing strength and hardness of sintered specimens were gradually increased with increasement of volume of milled powders. It is because increasement of sintering density by increasing of surface diffusion. The hardness of Cu-infiltrated specimens became lower than that of the commercial powders as the increasement of volume of milled powders. It was due to the decrease of the amount of the martensite. By results of this research, It has been found that martensite is formed around of the Cu-infiltrated site and the decrease of the amount of the martensite is due to decrease of the amount of the Cu-infiltrated site by the decrease of gas channel.