共查询到20条相似文献,搜索用时 15 毫秒
1.
A mixture of pure gases that produce maximum heat transfer characteristics for quenching 总被引:1,自引:0,他引:1
Gas quenching provides a desirable alternative to conventional liquid quenching in heat treating from the standpoint of quality,
safety, and environmental issues. There is convincing evidence that gasquenched parts heat treated in vacuum furnaces are
clean and bright and do not require a postcleaning process that may result in additional production costs. The cooling rates
for thicker section parts that are heat treated may be increased by increasing the magnitude of the heat transfer coefficient
of the gaseous medium. This heat transfer coefficient, which is dependent on the thermal conductivity, viscosity, specific
heat, and density of gases can be maximized by utilizing gas mixtures instead of pure gases. Substantial increases in heat
transfer rates for the gas quenching process can be achieved by appropriately mixing gases such as helium and argon. 相似文献
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高压气淬具有纯对流传热、易于控制、工件淬火后无需清洗和对环境影响小等优点。然而,典型的气淬设备显示出淬火料盘与工件之间的气流不均匀,导致工件的最终性能产生差异。业已发现,料盘的逆向气流布置是决定局部气流状态和热量传递的关键因素。尽管气流的主要部分在料盘与炉壁之间流动,对淬火过程不起作用,但是由料盘引起的流动阻力所产生的压降决定了淬火冷却强度。采用一种能较快收敛的多尺度模型对工业用高压气淬炉的内部流场进行了模拟,并通过速度测量和气流可视化技术对试验用淬火炉的内部气流进行了试验研究。最后,对圆柱体工件的双室真空炉淬火进行了模拟结果的验证,揭示了不同的逆向流速分布对淬火结果的影响。报道了多尺度模拟方法和流动过程的研究结果,并概述了对气淬工艺优化的指导性建议。 相似文献
3.
《International Heat Treatment & Surface Engineering》2013,7(1-2):52-59
AbstractHigh pressure gas quenching has the advantages of pure convective heat transfer, high levels of control, avoidance of cleaning the quenched parts and low environmental impact. However, typical gas quenching facilities exhibit inhomogeneous flow conditions through the quench load and the parts, resulting in scatter in final properties. The upstream flow profile of the load has been identified as a key factor determining local flow conditions and heat transfer. The intensity of the quenching process is determined by the pressure drop that results from the flow resistance of the quench load, although a significant part of the flow passes between the load and the chamber walls and does not contribute to the quenching process. A simulation of the flow inside a commercial high pressure gas quenching chamber was carried out, using a multiscale model to give faster convergence. An experimental analysis of the flow inside a model quenching chamber through velocity measurements and flow visualisation was also performed. Finally, a quenching run with cylindrical parts in a double-chamber vacuum furnace was used to validate the model results. Various upstream velocity profiles were applied to demonstrate their influence on the quenching result. The multiscale simulation approach and the results of the flow process investigation are reported. Guidelines for gas quenching process optimisation are outlined. 相似文献
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《International Heat Treatment & Surface Engineering》2013,7(2):61-64
AbstractIn this research, the formation and movement of bubbles in boiling film during quenching process was investigated with high speed video camera and particle image velocimetry (PIV) technology as the visualisation method. Cooling curves of surface temperature during quenching of a silver cylinder were measured and the heat transfer coefficients between quenchant and quenching parts were identified. The cooling ability of the coolant used for the quenching technology was evaluated relative to the quality the machine part. As for this paper, the cooling capacity of the PAG quenchants (polyalkylene glycol solutions) was evaluated. In addition, the heat transfer behaviour in the quenching process is clarified with regard to the generation and the destruction of the thermal flow and collapse of the steam film by using the PIV method of visualisation. The effect of mechanical stirring of the quenchant on the steam film and heat transfer is also studied. 相似文献
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淬火油是热处理淬火过程中应用最广的冷却介质,同时也是最重要的污染源和火灾隐患。近年来,由于热处理数值模拟虚拟系统和精确控制技术的完善和应用,使以水代油淬火冷却技术得以实现。该技术以数据挖掘型模拟系统为工具,以优化的工艺数据库为核心,通过具有灵活切换和调整冷却能力功能的工艺装备,形成以水代油淬火冷却的智能化系统技术,从而实现淬火冷却的节能、环保、安全目标。 相似文献
7.
Arif Sugianto Michiharu Narazaki Minoru Kogawara Atsushi Shirayori 《Journal of Materials Processing Technology》2009,209(10):4627-4632
The distortion control of heat-treated steel parts is a main consideration when dealing with hardening by quenching process. Before implementing this heat treating process, prediction of distortion is necessary to be done by experiment and computer simulation for determining a quenching technique which gives the smaller distortion. Temperature-dependent heat transfer coefficient (HTC) estimated from SUS304 cylinder can be determined by both iterative modification of lumped heat capacity method (LumpHC) and inverse heat transfer method (InvHT). Predicted HTC from silver probe is needed for the LumpHC, whereas initial set of assumption is needed for the InvHT. The zone-based HTC estimated from SUS304 cylinder then is employed on S45C cylinder. The prediction accuracy results from both methods are evaluated. As expected, stir quenching gives less distortion than that of still quenching. More accurate prediction of cooling curves, cooling rate curves, and distortion is achieved by employing the LumpHC than that by the InvHT. All analyses were performed by DEFORM-HT 2D. 相似文献
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由于用于汽车工业动力系零件的传统气体渗碳炉和淬火油槽已经过时,迫切需要引入新的装备和技术。当前对既能提高零件的力学性能和生产率又能对环境的影响减少到最小的需求使得真空渗碳/高压气淬成为极具吸引力的替代技术。然而,真空渗碳的过渗碳和炭黑,以及高压气淬的低冷却能力和高运行成本等构成了它推广应用的障碍。本文介绍了通过试验和数值模拟来解决这些问题所作的尝试。 相似文献
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B.Zieger HubertSchulte 《材料热处理学报》2004,25(5):588-590
The vacuum heat treatment with overpressure gas quenching is more and more accepted due to considerable advantages compared to the traditional oil and salt hath protests. Continuous further developments and new concepts like multi-threclional cooling systems, a separate quenching chamber and “sub zero” systems lead towards an oxidation free and law distortion vacuum heat treatment for a broad range of part and materials. Short and energy saving processes guarantee a high economic efficiency and environmental compatibility.The “sub zero” system which is inlegrated into the standard vacuum fumace achieves a heat treatment result with a high conversion of retained austenite in fully automatic hardening and tempering processes. 相似文献
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The cooling curves of 6061 aluminum alloy were acquired through water quenching experiment. The heat transfer coefficient was accurately calculated based on the cooling curves and the law of cooling. The online quenching process of complex cross-section profile was dynamically simulated by the ABAQUS software. The results suggest that the heat transfer coefficient changes during online quenching process. Different parts of the profile have different cooling velocity, and it was verified by water quenching experiment. The maximum residual stress of the profile was predicted using FEM simulation based on ABAQUS software. The relations between the temperature and stress were presented by analyzing the data of key points. 相似文献
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Heat transfer during quenching of chill-cast modified and unmodified A357 Al-Si alloy was examined using a computer-aided
cooling curve analysis. Water at 60 °C and a vegetable oil (palm oil) were used as quench media. The measured temperatures
inside cylindrical probes of the A357 alloy were used as inputs in an inverse heat-conduction model to estimate heat flux
transients at the probe/quenchant interface and the surface temperature of the probe in contact with the quench medium. It
was observed that modified alloy probes yielded higher cooling rates and heat flux transients. The investigation clearly showed
that the heat transfer during quenching depends on the casting history. The increase in the cooling rate and peak heat flux
was attributed to the increase in the thermal conductivity of the material on modification melt treatment owing to the change
in silicon morphology. Fine and fibrous silicon particles in modified A357 probes increase the conductance of the probe resulting
in higher heat transfer rates. This was confirmed by measuring the electrical conductivity of modified samples, which were
found to be higher than those of unmodified samples. The ultrasound velocity in the probes decreased on modification. 相似文献
16.
Thomas Lübben Friedhelm Frerichs 《Journal of Materials Engineering and Performance》2013,22(8):2323-2330
Immersion quenching in evaporable fluids like oil, polymer solutions, or water is a widely used technique in heat treatment shops because this technique provides higher heat transfer coefficients than the most alternative gas quenching techniques. The disadvantages of immersion quenching in evaporating fluids are the complex heat transfer mechanisms which consist of the three phases, film boiling, nucleate boiling, and convection. Especially the transition from film to nucleate boiling—the rewetting of the sample surface—is a complex process which leads to a strong position dependence of the heat transfer coefficient of the cooled work pieces. In particular, immersion quenching of thin-walled rings can result in large changes of ovality with comparable high scattering. To understand these results, two series of experiments were performed. Rings were quenched in oil in a special quenching tank and the rewetting behavior was documented. Furthermore, bearing races were quenched in a standard tank. Before and after heat treatment, these rings were measured by a coordinate measuring system and the distortion was determined. The investigations have clearly shown that the vapor film can have an important influence on distortion generation during oil quenching. The resulting distortion can principally be explained by the observed rewetting behavior. 相似文献
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L. Zhou X.Q. Wei School of Chemistry Materials Science School of Mechanical/Electrical Engineering Nanchang University Nanchang China 《金属学报(英文版)》2000,13(2):788-793
1.IntroductionPhasesandmicrostructuresformedincoolingofausteniteofsteels(quenching)havebeenextensivelystudiedandagreatamountofdatalikeisothermaltransformationcurves(TTTcurves)andcontinuoscoolingtransformationcurveshaveestablished.However,itisdifficulttousethesedatatopredictdistributionofmicrostructuresofaquenchedsteelstructureduetothefactthatthetransformationoccursinaunknownchangingfieldoftemperature.Acomputersimulationtoolcombiningthetransformationkineticsandthermalevolutionruleshouldbeanide… 相似文献
18.
KatsumiIchitani 《材料热处理学报》2004,25(5):453-456
Heat transfer coefficients of the quench medium are necessary for heat-treatment simulation. Cooling characteristics of quenching oil vary with kinds and usage greatly. Users are selecting oil solutions that come up to their desired hardness and quenching distortion requirements. In particular cooling performance rises by agitation and decompression. Therefore we identified a heat transfer coefficient by usage and kinds of quenching oil. Cooling characteristics are different greatly by a kind of quenching oil. A difference of a cooling characteristic by a kind of oil depends on a temperature range of a boiling stage and the maximum heat transfer coefficient mainly. On the other hand, in a convection stage, there are few changes in a boiling stage. Even if quenching oil temperature is changed, heat transfer coefficients do not change greatly. When quenching oil stirred, heat transfer coefficients of vapor blanket stage and a convection stage rise, but there are a few changes in a boiling stage. When quenching oil is decompressed a temperature range of a high heat transfer coefficient moves to the low temperature side. In addition, a heat transfer coefficient in a vapor blanket stage comes down. For precision improvement of heat-treatment simulation, it is important that the heat transfer coefficient is calculated in conformity to the on-site use reality. 相似文献
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《中国有色金属学会会刊》2020,30(5):1211-1226
The interfacial heat transfer coefficient between hot profile surface and cooling water was determined by using inverse heat conduction model combined with end quenching experiment. Then, a Deform-3D thermo-mechanical coupling model for simulating the on-line water quenching of extruded profile with unequal and large thicknesses was developed. The temperature field, residual stress field and distortion of profile during quenching were investigated systematically. The results show that heat transfer coefficient increases as water flow rate increases. The peak heat transfer coefficient with higher water flow rates appears at lower interface temperatures. The temperature distribution across the cross-section of profile during quenching is severe nonuniform and the maximum temperature difference is 300 °C at quenching time of 3.49 s. The temperature difference through the thickness of different parts of profile first increases sharply to a maximum value, and then gradually decreases. The temperature gradient increases obviously with the increase of thickness of parts. After quenching, there exist large residual stresses on the inner side of joints of profile and the two ends of part with thickness of 10 mm. The profile presents a twisting-type distortion across the cross-section under non-uniform cooling and the maximum twisting angle during quenching is 2.78°. 相似文献
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通过一系列风冷淬火试验,研究了气体高速冲击金属热表面的换热过程,采用反传热法对界面热流密度 (q) 和界面传热系数 (h)进行了求解,探究了试样的表面粗糙度和淬火初始温度、试样表面的冷却介质流量密度对换热过程的影响。结果表明:试样淬火初始温度对风冷淬火界面换热有显著影响,当其从470 ℃增大到520 ℃时,q 和h的最大值增大约50%,淬火表面温度下降到200 ℃的平均冷却速率增大约43%。随试样表面介质流量密度增大,界面热交换呈现出先增大后减小的趋势,即存在一个与最高界面换热效率对应的临界试样表面介质流量密度,且喷射角度越接近90°,该临界值越小。随试样表面粗糙度增大,界面换热不断减小,这可能归因于越粗糙的表面对边界层内流体的钉扎作用越明显,越不利于提高界面换热效率。此外,在250~380 ℃区间,界面换热系数随表面温度变化曲线普遍存在一个凹陷区域,这可能与铝合金淬火冷却过程中二次相的析出有关。 相似文献