• 열처리공학회지
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• 제36권3호
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• pp.121-127
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• 2023

When high carbon steel is heated in an appropriate austenizing temperature range and subjected to austempering, the size and shape of lamellar structure can be controlled. The high carbon steel sheet having the pearlite structure has excellent elastic characteristics because it has strong restoring force when properly rolled, and is applied in a process known as patenting-process using lead bath. In the case of isothermal treatment using lead-medium, it is possible to quickly reach a uniform temperature due to high heat transfer characteristics, but it is difficult to replace it with process technology that requires treatment to remove harmfulness lead. In this study, we intend to develop fluidization technology using garnet powder to replace the lead medium. After heating the high-carbon steel, the cooling rate was changed by compressed air to the vicinity of the nose of the continuous cooling curve, and then maintained for 90 s and then exposed to room temperature. The microstructure of the treated specimens were analyzed and compared with the existing products treated with lead bath. The higher the flow rate of compressed air, the faster the cooling rate to the pearlite transformation temperature, so lamellar spacing decreases and the hardness tends to increase.

• Design & Manufacturing
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• 제10권2호
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• pp.44-49
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• 2016

The roll forming produces mass products using the continuous production process. Also we need the process that continuous long material or goods cutting into a desired length. Our study uses 3-D driving cutter and roll forming material as SPCC to investigate this. When we cut the material using the process of roll forming, the shear resistance is raised at the cutting punch's edge. The result is remained the trouble about burr and progressive deformation on the material. This study shows the method minimizing the above trouble. The material of punch was considering heat generated on the continuous production process. So we used the type of STD 61 for the material of punch and had the vacuum heat treatment for the surface hardness of HRC 53. The structure of the mold is designed with forming a double cam die at the upper punch and the both sides of central core. We conducted the experiment three times. In the result when had to make V-groove within the angle between 105 and 110 on the punch front end, we could get the minimum shear resistance on the punch front end. Also with the same condition we minimizes the material jams in the continuous production process.

• Journal of Biosystems Engineering
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• 제30권1호
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• pp.32-37
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• 2005

This study was conducted the slurry pig manure treatment by condensation drying of liquid from the slurry manure with a heat-pump and electric heater combined with air flow channel system. The system was designed as liquid and solid matters separation of slurry manure, and it can doing continuous input of slurry manure from a pig house, and it can operated year round use for pig farms. The separation of liquid and solid matters from slurry manure needed the prevention of solid accumulation in the system. The system was designed as closed space from outside air space for maximized evaporation of liquid and the condensation of liquid from slurry manure. The system can be operated the pig slurry manure treatment regardless of seasons in a yew. The separated evaporation water from the pig slurry manure by the heat-pump was satisfactorily pure water that can be used as washing water in livestock farms. The system can applicate to about 100 heads of pig, and the proper area of evaporation plate system was considered around $10\;m^2$. The input electrical energy of about 15 kWh which the cost equal to 250,000 won per month.

• 열처리공학회지
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• 제21권2호
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• pp.79-86
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• 2008

As a basic research for developing 600 MPa yield strength reinforcing steel bars, the strengthening of 0.25 wt.% carbon steel by vanadium addition was studied. The changes of microstructure and mechanical properties were investigated for the specimen V0 (0.00 wt.% V), V1 (0.03 wt.% V) and V2 (0.06 wt.% V) processed by various heat treatments. To set the heat treatment conditions, the continuous cooling transformation (CCT) curves were drawn for austenitizing temperatures of $900^{\circ}C$ and $1100^{\circ}C$. For specimens tempered at $600^{\circ}C$ after quenching from $900^{\circ}C$ and $1100^{\circ}C$, yield strength was increased by 19 MPa and 21 MPa for 0.01 wt % V addition, and tensile strength was increased by 25 MPa and 28 MPa for 0.01 wt % V addition, respectively. Also, for 0.06 wt.% V added specimens tempered after quenching and normalized, tensile strength was increased by 50 MPa and 30 MPa for increasing austenitizing temperature of $100^{\circ}C$, respectively.

• 한국추진공학회지
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• 제4권2호
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• pp.46-53
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• 2000

알루미늄 제품은 열간단조하면 재료가 연화되어 있어 절삭가공시 연속적인 칩이 발생하여 공구와 피삭재를 감고 회전함으로서 가공면 손상, 공구파손 및 작업자의 안전을 초래함에 따라 가공이 어려워 단지 절삭성 개선목적만을 위해 중간공정으로 T-4열처리하여 절삭가공하고 다시 어닐링처리하여 냉간성형을 하고 최종열처 리를 한다. 따라서 본 연구는 열간단조후 제품을 급냉시키면 용체화처리의 효과를 얻어 재료가 경화됨으로서 절삭성이 개선될 수 있다는 이론에 근거하여 T4열처리를 대체할 수 있는 후처리방법에 대해 연구하였다. 최적의 후처리방법을 구하기 위해 열간단조후 수냉과 공냉처리를 비교분석하였고, 열간단조후 냉각처리까지 지연된 시간과 수냉과정에서의 유지시간에 따른 분식을 통해 최적의 작업조건을 설정하였다.

• 한국정밀공학회지
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• 제22권11호
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• pp.51-58
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• 2005

Laser surface hardening technologies have been used to improve characteristics of wear and to enhance the fatigue resistance for automotive parts. The objective of this research work is to investigate the influence of the process parameters, such as power of laser and defocused spot position, on the characteristics of laser heat treatment for the case of SM45C medium carbon steel. CW Nd:YAG laser is selected as the heat source. The optical lens with the elliptical profile is designed to obtain a wide heat treatment area with a uniform hardness. From the results of the experiments, it has been shown that the maximum hardness is approximatly 780 Hv when the power and the travel speed of laser are 1,095 W and 0.6 m/min, respectively. In addition, the hardening width using the elliptical lens was three time larger than that using the defocusing of laser beam.

• Bulletin of the Korean Chemical Society
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• 제32권7호
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• pp.2369-2376
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• 2011

Effect of heat treatment of carbon nanofibers (CNF) on electrical properties and crystallization behavior of polypropylene was reported. Two types of CNFs (untreated and heat treated at 2300 $^{\circ}C$) were incorporated into polypropylene (PP) using intensive mixing. A significant drop in volume resistivity was observed with composites containing untreated 5 wt % and heat treated 3 wt % CNF. In non-isothermal crystallization studies, both untreated and heat treated CNFs acted as nucleating agents. Composites with heat treated CNFs showed a higher crystallization temperature than composites with untreated CNFs did. TEM results of CNF revealed that an irregular structure of CNFs can be converted into the continuous graphitic structure after heat treatment. Furthermore, STM showed that the higher carbonization temperature leads to the higher graphite degree which presents the larger carbon network size, suggesting that a more graphitic structure of CNFs led to a higher crystallization temperature of PP.

• Journal of Welding and Joining
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• 제32권3호
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• pp.95-101
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• 2014

Joining of grey cast iron by fusion welding has much difficulties for its extremely low ductility and low toughness because of the flake form of the graphite. And the brittle microstructure, i.e. ledeburite may be formed during fusion welding by its rapid cooling rates. By these kinds of welding problem, preheat and post heat treatment temperature must be increased to avoid weld crack or welding problems. In order to avoid these fusion welding problem, friction welding of cast iron was carried out for improving joint soundness, establishing friction welding variables. There is no factor for evaluating friction weldability in continuous drive type friction welding. In this point of view, this study proposed the parameters for calculating friction weld heat input. The results obtained are as follows ; 1. There was a close relationship between tensile strength and flash appearance of friction welded joint. 2. Tensile strength was decreased and flash was severely oxidized as increasing frictional heating time. 3. As increased forging pressure $P_2$, flash had a large crack and tensile strength was decreased. 4. As powdered graphite by rotational frictional force induced flat surface and hindered plastic flow of metal, tensile strength of welded joint was decreased. 5. Heat input for continuous drive type friction welding could be calculated by the factors of $P_1$, $P_2$ and upset distance(${\delta}$).

• 유기물자원화
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• 제11권1호
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• pp.70-76
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• 2003

소화슬러지를 열처리한 혼합 배양 미생물을 식종균으로, 자당을 기질로 사용하는 혐기성 수소 생산 공정을 운전하면서 pH 조절, 반복 열처리, 기질 농도 변화 등을 통해 지속적인 수소 생산 방법을 고찰하였다. 유입 기질의 농도가 5g COD/L인 경우 운전 초기에는 $0.5mole\;H_2/mole\;hexose$ 이상의 수소가 발생하지만 9일 이상 지속되지 못하였다. 이러한 현상의 원인은 수소 생성균이 공정 내에서 고농도로 존재하지 못하기 때문인 것으로 판단되며 pH를 5.3으로 유지하는 것만으로는 극복될 수 없었다. 반복 열처리를 적용할 경우 별도의 식종균 재주입 없이 효율이 감소된 수소 생성 공정을 원상태로 복구할 수 있음을 확인할 수 있었으나, 수소 생성 효율이 시간에 따라 감소하므로 열처리를 자주 해야 하는 문제가 발생했다. 유입 기질의 농도가 30g COD/L인 경우에는 24일간 지속적인 수소 생성이 가능하였으며, CSTR의 경우 $1.0-1.4mole\;H_2/mole\;hexose$, ASBR의 경우에는 $0.2-0.3mole\;H_2/mole\;hexose$의 생성 효율을 보였다. 수소 생성 시 유출수 내 용존성 유기물의 90% 이상은 유기산이었으며 그 중 n-butyrate가 가장 많은 양을 차지하였다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 제5회 압연심포지엄 신 시장 개척을 위한 압연기술
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• pp.119-125
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• 2004

Radiant tube heaters are widely used for indirect heating in heat treatment processes such as continuous annealing line(CAL) or continuous galvanizing line(CGL). Main issues for radiant tube are temperature uniformity, lifetime, thermal efficiency. To achieve higher heat release, the radiant tubes are fired at a higher fuel rate and therefore local overheating occur. A numerical simulation based on a commercial code FLUENT has been performed to investigate local overheating of radiant tube heaters. To minimize local overheating, the effects of radiating fins, flue gas recirculation(FGR), two-stage combustion were investigated. More uniform temperature distribution was achieved in the longitudinal direction within the tube with radiating fins and this contributed to increase the life of radiant tubes. Furthermore, the radiant tube with radiating fins was proven to be more efficient than the one without fins. The effects of flue gas recirculation and two stage combustion on the efficiency of the radiant tube were also considered and the results were presented.