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RISS 인기검색어
- 검색키워드
- 발행기관 : 부경대학교 대학원 산업공학과 (검색결과 3 건)
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440A 스테인리스강의 내식성에 미치는 첨가 원소와 열처리의 영향
이창준 부경대학교 산업대학원 금속공학과 2008 국내석사
440A martensitic stainless steels which were modified with reduced carbon content(~0.5%) and addition of small amount of nickel, vanadium, tungsten and molybdenum were manufactured. Effects of alloying elements and tempering temperatures on the uniform and pitting corrosion were investigated through the electrochemical polarization tests. 1. Characteristics of uniform corrosion in 1N H2SO4 ①When tempering temperature is constant, corrosion current density in active-passive transition point, Icorr, decreased a little with an increase of austenitizing temperature. ②When austenitizing temperature is constant, longer holding time showed a little lower Icorr and Ipass, passive current density. ③When austenitized at 1050℃ and tempered at 350~750℃, best anti-corrosion properties were obtained at 350℃ tempering temperature while worst at 450℃ and 550℃. ④When tempered at below 450℃ and above 550℃, similar and good anti-corrosion characteristics were obtained regardless of alloying elements added, showing anti-corrosion characteristics are influenced more by tempering temperature than by alloying elements. 2. Pitting corrosion in 3.5% NaCl ①When tempering temperature is constant, the lowest pitting potential, Ep, was obtained when austenitizing temperature was 1250℃ and this is because of the grain coarsening. ②When austenitizing temperature is constant, longer holding time showed a little higher value of Ep. ③When austenitized at 1050℃ and tempered at 350~750℃, the highest Ep was obtained at 350℃, while the lowest at 450℃ and 550℃ ④When tempered at 450℃ and 550℃, Ep was increased a little when 0.4wt.% of tungsten was added. ⑤When tempered at 450℃, more pitting was observed. And pitting was formed at regions where Cr concentration is low or grain boundaries are intersecting and showed irregular shape.
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정진아 부경대학교 대학원 산업공학과 2008 국내박사
This paper studies a joint EOQ and EPQ model in which a stationary demand and three level dynamic lot sizing problem in which the dynamic demand can be satisfied by recycled products as well as newly purchased products. The model assumes that a fixed quantity of the used products are collected from customers and later recovered for reuse. The recovered products are regarded as perfectly new ones. We also assume that the number of orders for newly purchasing items and the number of recovery setups in a cycle can be mutually independent integers. Under these assumptions, chapter 3 develop an optimization model obtaining the economic order quantity for newly procured products, the optimal lot size for the recovery process, and the sequence of the orders and the setups, simultaneously. And then a simple solution procedure to find the optimal control parameters is proposed. To validate the model and the solution procedure, finally, some computational experiments are presented. Chapter 4 obtains ⅰ) the economic order quantity for newly procured products, ⅱ) the optimal lot size for the recovery process, and ⅲ) the purchasing price of the used items, simultaneously, using a genetic algorithm. Chapter 5 present a mixed integer programming model to obtain the economic recovery schedule for the recoverable items and production schedule for the row materials as well as the economic order schedule for newly procured products, simultaneously. Applying a commercial optimization software (e.g., LINGO or CPLEX) to this model, one can easily find optimal solutions for small problems. However, since the computing time for big sized problem can be long, we design three heuristic algorithms that based on the genetic algorithm. And then, some computational experiments are given to verify the performance of the algorithms.
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박희구 부경대학교 산업대학원 금속공학과 2008 국내석사
Layer thickness and corrosion resistance of M10 bolt coated with Magni 565 were investigated to find out the optimum coating conditions. Characteristics of the coated bolt were also studied. The main results obtained are as follows; 1. Optimal coating conditions for base and top coats for bolt were as follows; ① Zahn cup viscosity for base and top coats were 60 and 55 sec, respectively. ② RPM and time for base and top coats in dip/spin process were 260, 15 sec and 290, 15 sec, respectively. ③ Curing temperature and time for base and top coats were 250℃, 25 min. and 20 5℃, 25 min., respectively. The samples coated with optimal conditions showed around 10㎛ layer thickness and a great corrosion resistance in salt spray test with 1500 hours or longer of initial appearance time of rust. 2. The bolts with the optimum conditions showed a proper torque in torque/tension test. Torque coefficient k increased a little with the number of bolting and clamping force of M10 bolt showed significantly lower than that of specified value 28.3kN. It was thought that the repeated bolting made the coating film peel off and powdery. 3. Heat resistance temperature without cracks in coating film was below than 300℃. 4. Adhesion of the coating layer was good enough to have A~C grade adhesion and influenced little by surface roughness. 5. While aging of film in the ultra violet irradiation test was not observed in one week, a great decrease of polarization resistance in EIS was observed after 2 weeks. 6. Observed coating film defects were uncoated areas, excessive coating layer, cracks and unfastened areas and those defects were found mainly in the crest and root of the bolt threads. 7. The base coating film was composed of lamellar zinc flakes, which provides sacrificial cathodic protection. Meanwhile, the top coating film was composed of organic aluminium pigments layer, which provides barrier protection to the corrosion circumstances.
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