• Title, Summary, Keyword: reheating

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Development of Thixoextrusion Process for Light Alloys - Part 1. Microstructural Control of Light Alloys for Thixoextrusion (경량합금 반용융 압출 기술 개발 - Part 1. 반융용 압출을 위한 조직제어)

  • Kim, Shae-K.;Yoon, Young-Ok;Jang, Dong-In;Jo, Hyung-Ho
    • Journal of Korea Foundry Society
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    • v.26 no.5
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    • pp.211-216
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    • 2006
  • The study for thixoextrusion process of 7075, 7003 Al wrought alloys and AZ31 Mg wrought alloy was carried out with respect to reheating rate, isothermal holding temperature and time with an emphasis to the effect of homogenization on thixotropic micro-structures during the partial remelting, especially in the low liquid fraction ($f_L<0.2$). The liquid fraction and average grain size with respect to reheating profile such as reheating rate, isothermal holding temperature and time were almost uniform. It is considered very useful for thixoextrusion in terms of process control such as billet temperature control and actual extrusion time. Micro-structural controls of 7075, 7003 Al wrought alloys and AZ31 Mg wrought alloy before and after homogenization were available and thixotropic microstructures were obtained in both specimens.

A Study on the Energy Saving of Cooling/Reheating System Using Heat Exchanger (열교환기를 사용한 냉각/재가열 장치의 에너지 절감에 관한 연구)

  • Kim, Jin-Hyuck;Yoo, Seong-Yeon;Choi, Yang-Kyu
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.22 no.7
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    • pp.482-491
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    • 2010
  • In conventional air-handling units, when the circulated air from the air-conditioned space pass through the cooling coil, the air is over-cooled to eliminate the moisture as well as to decrease the temperature. The purpose of this study is to estimate the thermal performance and energy saving of the cooling/reheating system using heat exchanger which can save both cooling energy and reheating energy by exchanging heat between the cooled air and reheated air. The energy balance equations to estimate the state of the air for each components were provided and the heat transfer rates and the energy saving rates for the system were calculated from the equations. The results showed that the energy saving was up to 40% under present conditions, and saving rates were significantly affected by the air velocity, inlet conditions and the effectiveness of heat exchanger.

Optimum Fabrication Conditions and Reheating Characteristic of Semi-Solid Al-Zn-Mg-(Sc) Alloy by Inclined Cooling Plate (경사냉각판을 이용한 Al-Zn-Mg-(Sc) 반응고 합금 제조의 최적화 및 재가열 특성)

  • Kim, Tae-Hun;Shim, Sung-Yong;Park, Hyung-Won;Lim, Su-Gun
    • Journal of Korea Foundry Society
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    • v.29 no.5
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    • pp.213-219
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    • 2009
  • Optimum conditions for production of semi-solid Al-Zn-Mg alloy billets was carried out by the Taguchi design method. And, Al-Zn-Mg alloy billets contained Sc (free, 0.1 and 0.3 mass %) were fabricated at optimum conditions. Evolution of microstructure in semi-solid state was investigated through various liquid fractions, holding times and holding temperatures. The Al-Zn-Mg alloy billets reheated at $615^{\circ}C$ during 30min are grain growth and it was fractured due to increasing liquid fraction before quenching. And, during reheating up to $600^{\circ}C$, grain growth of Al-Zn-Mg alloy billets contained Sc (0.1 and 0.3 mass %) was not occurred in comparison with those of Al-Zn-Mg alloy without Sc. It was thought that $Al_3Sc$ phases have a pinning effect in grain boundary and Sc content of 0.1 mass% is able to inhibit grain growth effectively through reheating process.

The Effect of Ca Addition on the Grain Growth Inhibition During Reheating Process of Al-Zn-Mg Al Alloys for Thixo-extrusion (반응고 Al-Zn-Mg계 합금의 반용융 압출을 위한 재가열 시 결정립 성장 억제에 미치는 Ca 첨가의 영향)

  • Park, Hyung-Won;Kim, Dae-Hwan;Shim, Sung-Yong;Kim, Hee-Kyung;Seong, Bong-Hak;Choi, Chang-Ock;Lim, Su-Gun
    • Journal of Korea Foundry Society
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    • v.31 no.6
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    • pp.347-353
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    • 2011
  • There is thixo-extrusion to form high strength aluminum alloy. But, it is a problem that grains become grain coarsening during reheating process because the alloy was exposed at high temperature. In order to solve grain growth during reheating process, calcium was added in Al-Zn-Mg alloys. Primary a grain sizes of semi-solid Al-Zn-Mg-(0, 0.4, 0.6 and 0.9, wt.%)Ca were measured with image analyzer after reheating. Measured primary a grain sizes were applied to LSW(Lifshitz-Slyozov and Wagner) equation to check the effect of Ca on grain coarsening. Coarsening rate constant K values of semi-solid Al-Zn-Mg-(0, 0.4, 0.6 and 0.9, wt.%)Ca alloys were $371\;mm^3s^{-1}$, $247\;mm^3s^{-1}$, $198\;mm^3s^{-1}$ and $166 mm^3s^{-1}$, respectively. As increasing calcium content, K value decreased which means grains are refined. Also, grains of calcium addition were more spherical than that of calcium free.

Effects of Reheating Conditions and Sodium Chloride/Phosphate Levels on Color Characteristics of Precooked Pork Patties

  • Choi, Ji-Hun;Choi, Yun-Sang;Han, Doo-Jeong;Kim, Hack-Youn;Lee, Mi-Ai;Kim, Si-Young;Lee, Ju-Woon;Jeong, Jong-Youn;Kim, Cheon-Jei
    • Food Science of Animal Resources
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    • v.30 no.4
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    • pp.617-625
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    • 2010
  • The objective of this study was to determine the effect of reheating methods on the color characteristics of precooked pork patties with various NaCl and phosphate levels. NaCl/phosphate levels for each formulation were as follows; N1 (1% NaCl), N1+P (1% NaCl+0.3% phosphate), N2 (2% NaCl), and N2+P (2% NaCl+0.3% phosphate). The reheating methods used were by electric grill and microwave oven. The surface color of the patties reheated by microwave showed more brown and less-intense red, and the phosphate-treated patties reheated by microwave were more reddish and less brownish. With increased amounts of added NaCl and phosphate, the internal color of patties was more reddish, and the phosphate-treated patties reheated by microwave had more brown than those reheated by electric grill. Among all of the treatments, there were no significant differences in surface color, internal color, and overall appearance. Thus, the color changes in reheated patties were influenced by reheating methods and phosphate.

A Study on Optimum Reheating Process of Automotive Aluminum Piston using Neural Network and the Taguchi Method in Semi-Solid forming (반용융 성헝에서의 다구찌 방법과 신경망을 이용한 자동차 알루미늄 피스톤의 최적 재가열 과정에 대한 연구)

  • 윤재민;김영호;박준홍;최재찬
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.902-905
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    • 2000
  • As the manufacturing processes of automotive engine piston, gravity die-casting, squeeze casting, hot forging and powder forging process are generally used for the various specifications. As the semi-solid forming(SSF) is compared with conventional casting such as gravity die-casting and squeeze casting for the characteristics of its process, the product without inner defects such as gas porosity and segregation can be obtained and its microstructure is globular grain. In SSF process, the materials are heated up to the temperature between the solvus and liquidus line at which the materials exists in the form of liquid-solid mixture. In this time, Discussion is given about reheating process of row material and results are presented regarding accurate temperature and process variables controlling for right solid fractions.

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The Study on the Gas Temperature Set by Calculating the Sensitivity of Slab Temperature in Reheating Furnace (소재온도 감도계산을 통한 가열로내 분위기온도 설정방안 연구)

  • Gang, Deok-Hong;Kim, Gi-Hong;Lee, Yong-Guk
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.8
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    • pp.1030-1036
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    • 2001
  • A new mathematical model to determine the optimal gas temperatures in reheating furnace was proposed for the good quality of products. This model employs sensitivity method to calculate the optimal gas temperatures in each zone for heating the slab up to its discharging target temperature and for heating it uniformly. This method was validated by showing that the calculated discharging temperature of the slab was in a good agreement with its prescribed discharging target one through an off-line simulation.

A Study on the Estimation of One-dimensional Beat Fluxes on the Slab in Reheating Furnace by Using Inverse Analysis (역해석을 이용한 가열로 내 소재의 1차원 열유속 추정에 관한 연구)

  • Kang, Deok-Hong;Kwag, Dong-Seong;Kim, Woo-Seung;Lee, Yong-Kuk
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.27 no.1
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    • pp.61-68
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    • 2003
  • This study deals with the use of the conjugate gradient method for the simultaneous estimation of two unknown boundary heat fluxes on the slab in reheating furnace. Temperature measurements by the experiment are used in the inverse analysis. The heat flux estimations for three different cases of measurement locations in the slab are performed: non-skid, skid, and shift-skid zones. The estimated heat fluxes for three cases indicated the three regions having local peak values of heat fluxes. The estimated temperatures at measurement locations were in good agreements with the measured temperatures within 5% relative error.

$\alpha$-halo formation in semi-solid state processed hypereutectic Al-Si alloy (반고상 가공과 공정 Al-Si 합금에서 $\alpha$-halo의 형성)

  • 김인준;김도향
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • pp.183-195
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    • 1997
  • The micorstructural characteristics, particularly $\alpha$-halo formation, in semi-solid state processed hypereutectic Al-Si alloy was investigated. The microstructural changes during reheating of wedge type mold cast ingot, hot-rolled sheet, and Si particulate reinforced Al composite was compared with those occurred during stirring of semi-solid state hypereutectic alloy. In the case of semi-solid state reheating of wedge type ingot and hot-rolled sheet, fine particles of Si as well as $\alpha$-halo formed after heat treatment. Although there seemed to be no coarsening with variations of holding time, the region of $\alpha$-halo decreased due to homogenization. Nucleation and recrystallization was accelerated with the addition of alloying elements during hot rolling resulting in primary Si particle size decrease and $\alpha$-halo formation. In the case of extruded specimens, very little morphological change of reinforcing Si particles was observed. Almost no $\alpha$-halo formed during reheating because of the oxide film formed on the reinforcing Si particles which acted as a diffusion barrier between the matrix and the primary Si particles.

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A Numerical Analysis Study on the Reheating crack around Welded Joint of Pressure Vessel with 2$\frac {1}{4}$Cr-1Mo Steel (2$\frac {1}{4}$ Cr-1Mo강 압력용기 Nozzle 용접이음부의 재열균열에 관한 수치해석적 연구)

  • 김종명
    • Journal of Ocean Engineering and Technology
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    • v.14 no.1
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    • pp.88-94
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    • 2000
  • Recently various pressure vessels like an atomic reactor and plant facilities become more larger and are needed to bear in both very high temperature and pressure condition. And in making such a high pressure vessels the amount of annual usage of 2 $\frac {1}{4}$ Cr-1Mo steels which are predominant to resist high temperature high pressure and corrosive circumstances are increasing. But despite of this advantage of 2 $\frac {1}{4}$Cr-1Mo steel. when PWHT(post welding heat treatment) is carried out lots of reheating cracks are occur. In this reason it is strongly needed to study and examine the mechanical behavior of welded joints through welding to PWHT process. So in this study welded nozzle of pressure vessel where reheat cracks are frequently occur are selected for analysis the crack-occurrence mechanism.

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