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在一堆凝固传热条件下,通过多点非线性估计方法计算得出界面换热系数与界面处冷铁一侧温度的关系(h-T_(ic))曲线。本文认为此曲线较换热系数与时间的关系(h-τ)曲线更为本质地反映了界面热交换的特征,并首次将h-T_(ic)曲线应用于一般铸件的凝固模拟,获得了满意的计算结果。本文还考察了铸件/冷铁界面换热条件的不同处理方法对模拟蛄果的敏感性。采用计算机图形显示技术处理数据。 相似文献
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铝合金铸件/金属型界面间隙及换热系数通用化的研究 总被引:6,自引:0,他引:6
本文首次通过理论推导和对多因素试验条件下的测试结果进行多元最小二乘回归处理,得到了铝合金长方形铸件在金属型(表面有氧化锌涂层)重力铸造条件下,界面间隙及换热系数计算的通用化公式.公式中系统地考虑了铸件及铸型的热物理参数、工艺条件、位置等因素的影响.利用公式得到的界面热边界参数用于一般铸件的计算机凝固模拟,取得了与实测相吻合的结果.此通用化公式的建立对丰富计算机凝固模拟热边界参数数据库具有一定的作用. 相似文献
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准确设置边界条件是保证数值模拟精度的前提。本文针对凝固过程中的轴对称铸件建立相应的反传热模型求解其界面换热系数,对Pro CAST仿真的温度值与正传热算法计算结果进行了比较,证实了正传热算法的计算精度,进而对比假设的实际热流与反算的热流值,验证了建立的轴对称反传热模型计算界面换热系数和界面热流的有效性及准确性。 相似文献
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熔模精密铸造对于铸件近净成形具有重要意义,但目前鲜见对其铸件-铸型界面换热系数的相关研究.本试验在一维传热模型中采用非线性估算法对工业纯铝在熔模铸造过程中与型壳的换热行为进行了研究,分析结果表明:在凝固前期,铸件与型壳之间的热流密度基本不变,而界面换热系数随两者温差减小而增大;凝固中期,界面换热系数随着整体固相分数增加而线性下降;凝固后期,界面换热系数下降变得十分缓慢.将在一维模型中反求得到的界面换热系数应用到三维铸件模型中,得到的模拟温度与实测温度基本吻合,证明通过一维模型与非线性估算法求取的界面换热系数比较准确,有望在铝合金精密铸造温度模拟中得到应用. 相似文献
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金属快速凝固的非平衡超急速传热模型 总被引:2,自引:0,他引:2
运用非Fourier传热理论建立了金属快速凝固过程中的非平衡传热理论模型,包括非Fourier方程的建立、传热与相变模拟,模拟计算表明:(1)在溅射激冷条件下,界面换热系数越大,界面冷却速度和移动速度也越高。在界面换热系数相同时,计算得到的界面冷却速度随着固-液界面高度的提高呈现先上升而后下降的变化趋势;计算得到的冷却速度值明显小于Fourier定律的计算值。(2)在激光加热条件下,计算的界面移动速度在凝固开始时先急剧增加,然后渐趋平稳,计算还表明,金属的过热及过冷度与其热物性相关。 相似文献
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软接触结晶器电磁连铸中初始凝固的基础研究 总被引:32,自引:0,他引:32
通过实验和数值模拟研究了软接触结晶器电磁连铸传热凝固特点,测定了金属Sn在连铸中的温度场,初始凝固点和坯壳厚度,得到了电磁场影响它们的基本规律。在数学模型中考虑了高频电磁场对金属的传热凝固的以下影响;(1)对结晶器的感应加热;(2)对金属的加热;(3)电磁力推斥液力金属,减少金属与结晶器壁接触的影响。 相似文献
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研究铝铸锭凝固边界热交换的变化规律及数学模型,并对不同浇注温度下凝固过程的温度场进行模拟。利用实时数据采集系统获得凝固过程中铸锭和金属模温度变化历史数据,采用非线性反算法和一维传热差分法对试验数据处理,建立界面换热模型并将其应用于凝固温度场模拟中。结果表明:在铸锭表面凝固前后凝固界面热流密度可分段用指数函数来描述其变化规律,而所建立的热交换系数与边界温度的对应关系可更好地反映实际的传热情况。模拟结果与实验测温结果相符,验证了该铸件/铸型边界热交换规律的可靠性。 相似文献
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Casting/mold thermal contact heat transfer during solidification of Al-Cu-Si alloy (LM 21) plates in thick and thin molds 总被引:1,自引:0,他引:1
K. Narayan Prabhu Bheemappa Chowdary N. Venkataraman 《Journal of Materials Engineering and Performance》2005,14(5):604-609
Heat flow at the casting/mold interface was assessed and studied during solidification of Al-Cu-Si (LM 21) alloy in preheated
cast iron molds of two different thicknesses, coated with graphite and alumina based dressings. The casting and the mold were
instrumented with thermocouples connected to a computer controlled temperature data acquisition system. The thermal history
at nodal locations in the mold and casting obtained during experimentation was used to estimate the heat flux by solving the
one-dimensional inverse heat conduction problem. The cooling rate and solidification time were measured using the computer-aided
cooling curve analysis data. The estimated heat flux transients showed a peak due to the formation of a stable solid shell,
which has a higher thermal conductivity compared with the liquid metal in contact with the mold wall prior to the occurrence
of the peak. The high values of heat flux transients obtained with thin molds were attributed to mold distortion due to thermal
stresses. For thin molds, assumption of Newtonian heating yielded reliable interfacial heat transfer coefficients as compared
with one-dimensional inverse modeling. The time of occurrence of peak heat flux increased with a decrease in the mold wall
thickness and increase in the casting thickness. 相似文献
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K. Narayan Prabhu K. M. Suresha 《Journal of Materials Engineering and Performance》2004,13(5):619-626
Heat transfer during the solidification of an Al-Cu-Si alloy (LM4) and commercial pure tin in single steel, graphite, and
graphite-lined metallic (composite) molds was investigated. Experiments were carried out at three different superheats. In
the case of composite molds, the effect of the thickness of the graphite lining and the outer wall on heat transfer was studied.
Temperatures at known locations inside the mold and casting were used to solve the Fourier heat conduction equation inversely
to yield the casting/mold interfacial heat flux transients. Increased melt superheats and higher thermal conductivity of the
mold material led to an increase in the peak heat flux at the metal/mold interface. Factorial experiments indicated that the
mold material had a significant effect on the peak heat flux at the 5% level of significance. The ratio of graphite lining
to outer steel wall and superheat had a significant effect on the peak heat flux in significance range varying between 5 and
25%. A heat flux model was proposed to estimate the maximum heat flux transients at different superheat levels of 25 to 75
°C for any metal/mold combinations having a thermal diffusivity ratio (α
R) varying between 0.25 and 6.96. The heat flow models could be used to estimate interfacial heat flux transients from the
thermophysical properties of the mold and cast materials and the melt superheat. Metallographic analysis indicated finer microstructures
for castings poured at increased melt superheats and cast in high-thermal diffusivity molds. 相似文献
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Microstructure and solidification thermal parameters in thin strip continuous casting of a stainless steel 总被引:7,自引:0,他引:7
J. E. Spinelli J. P. Tosetti C. A. Santos J. A. Spim A. Garcia 《Journal of Materials Processing Technology》2004,150(3):255-262
The present work focuses on the relationships between solidification thermal parameters and the dendritic microstructure of an AISI 304 stainless steel solidified both in a strip casting pilot equipment (twin-roll) and in a directional solidification simulator. Experimental studies were conducted with a stainless steel strip casting obtained in a twin-roll continuous caster pilot equipment and in samples solidified in a directional solidification simulator with two different melt superheats. In both cases, the surface of the substrates was similar, with mean surface roughness of about 0.3 μm. After solidification, the specimens were cut at different positions from the metal/mold interface and etched for metallographic examination. An empirical equation from the literature relating secondary dendrite arm spacing and cooling rates was used to demonstrate the similarity of the cooling efficiency. The results have shown that the simulator can be used in the determination of transient metal/mold interface coefficients (hi) and in the preprogramming of the strip casting operational conditions as a function of roll materials and surface roughness. 相似文献
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P. J. Gibbs S. D. Imhoff C. L. Morris F. E. Merrill C. H. Wilde P. Nedrow F. G. Mariam K. Fezzaa W.-K. Lee A. J. Clarke 《JOM Journal of the Minerals, Metals and Materials Society》2014,66(8):1485-1492
The formation of structural patterns during metallic solidification is complex and multiscale in nature, ranging from the nanometer scale, where solid–liquid interface properties are important, to the macroscale, where casting mold filling and intended heat transfer are crucial. X-ray and proton imaging can directly interrogate structure, solute, and fluid flow development in metals from the microscale to the macroscale. X-rays permit high spatio-temporal resolution imaging of microscopic solidification dynamics in thin metal sections. Similarly, high-energy protons permit imaging of mesoscopic and macroscopic solidification dynamics in large sample volumes. In this article, we highlight multiscale x-ray and proton imaging of bismuth-tin alloy solidification to illustrate dynamic measurement of crystal growth rates and solute segregation profiles that can be that can be acquired using these techniques. 相似文献
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EFFECT OF INTERMITTENT HIGH FREQUENCY MAGNETIC FIELD ON INITIAL SOLIDIFICATION IN CONTINUOUS CASTING
T. J. Li 《金属学报(英文版)》1997,10(2):151-156
1.IntroductionThesurfacequalityofcontinuouslycastingotscanbeimprovedbyimposingahighfrequencymagneticfieldfromtheoutsideofamold.Slowcoolingsolidificationofmeltisthoughttobeanimportantreasonofimprovingsurfacequalityll--4].Inordertoclarifythemechanismofimprovingsurfacequalitybyimposingmagneticfieldandcontroltheinitialsolidificationofcontinuouslycastmetal,itisimportanttostudytheeffectofslowcoolingcausedbymagneticfield.onthetemperaturedistributionofthemeltandtheformationpositionofinitialsolidificat… 相似文献
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1 Introduction The growing demand for mass reduction in aerospace and automotive industries has greatly increased the magnesium application. Currently, casting is the main industrial forming method for magnesium alloys, but the lag of research and develop… 相似文献