薄铝板淬火换热系数求解

针对薄铝板淬火过程,本文采用不同函数形式描述淬火换热系数,并借助ABAQUS有限元软件进行温度场和位移场模拟,得到换热系数和位移场的关系。基于试验所得翘曲位移反求换热系数,并对所选取的函数形式进行了优选。     

金属淬火过程换热面对换热系数影响的有限元探求法

在金属淬火过程的数值模拟中,换热系数的正确求解是保证工件温度场以及应力/应变场模拟结果与实际情况相符合的先决条件.据此研究和分析了换热系数反求法的数学模型,采用二维圆柱坐标有限元法对该数学模型求解,并考虑了换热面对换热系数的影响,求出了圆柱侧面和下端面的换热系数.研究发现,换热面的空间方位对换热系数有较大的影响.和圆柱体的侧面相比,底面的换热变化规律相同,但是换热条件不佳,换热系数较小.用求得的换热曲线模拟大尺寸工件的淬火过程,发现考虑换热面对换热系数的影响后,其计算的温度分布明显不同.     

铝合金厚板淬火过程换热系数的求解与验证

在铝合金厚板淬火过程的数值模拟中,换热系数的正确求解是工件温度场、应力场模拟结果和实验相符的先决条件.分析换热系数反求法的数学模型,并采用MATLAB编程实现该数学模型的求解.用求得的换热系数作为MSC·MARC建立的有限元模型的边界条件,计算试件的温度场变化曲线,计算结果和实测数据基本吻合.     

淬火油动态下换热系数的测量及计算

为了测量和计算工业条件下淬火油在不同流速下的换热系数 ,采用超声波多普勒流量计测定了介质的流速 ,用 12 0× 12 0× 2 0 (mm)平板状试样和反传热法测定与计算了换热系数。结果表明 ,换热系数曲线能更好地反映表面热量传递的真实情况 ;随着介质流速的增加 ,换热系数的最大值呈增加趋势 ,当搅拌使介质中产生气泡时 ,介质的换热系数明显降低。     

淬火介质换热系数绵计算机测算

提出了用计算机进行测量和计算淬火过程中淬火介质换热系数的反传热模型。该模型利用采样系统测得的上结位置的冷却曲线来计算淬火介质的换热系数,获得其随表面温度变化的曲线,对水和油的测算结果表明,计算值和实际情况吻合较好。     

淬火冷却介质换热系数研究进展

淬火冷却介质换热系数不仅是评定淬火介质冷却能力的主要参数,也是淬火过程数值模拟中最重要的边界条件之一.它受很多因素的影响,如工件的材质、尺寸、表面状态等,因此很难精确测定.本文概述了近年来有关换热系数的研究,并对以后的研究工作做了展望.     

筒节淬火界面换热系数求解方法对比

以压力容器筒节为研究对象,基于中空圆柱热传导差分方程,采用温差直接法和温度迭代法,建立换热系数求解的数学模型。根据筒节的实测冷却曲线,通过非线性温度迭代法和温差直接法求解界面换热系数随淬火时间变化曲线,模拟筒节试件淬火过程温度场,对比试验值与两种方法模拟值的误差,验证温差直接法的可靠性,并比较温度迭代法与温差直接法的差异。结果表明,两种方法的温度模拟结果误差都在18%以内且差距不大,但温差直接法的准确性优于温度迭代法。     

铝合金厚板淬火表面换热系数的离散解析求法

为了快速准确求取铝合金厚板淬火过程的换热系数,对淬火热传导过程进行分析。首先,将换热系数解析过程假设为淬火温度离散化的,并且是相邻离散点可进行迭代优化的计算过程。然后,分步解析求解了各离散温度区间的换热系数,最后完成了数据修正和仿真计算还原。结果表明,该方法获得的换热系数,可以使实验冷却曲线与计算冷却曲线较好的吻合,从而证明这种计算方法的可行性,并在文末对该方法的误差来源和特点进行了分析。     

中厚板辊式淬火换热系数的确定方法

为了确定中厚板辊式淬火过程中的最佳换热系数,进行了12MnNiVR钢板淬火过程中的温度场和应力场计算.依据温度场分析提出了中厚板在淬火机高压区内淬火过程中换热系数的确定方法,并用该方法确定了不同厚度12MnNiVR钢板在高压区淬火的换热系数.应力场分析表明,在低压区采用低的换热系数,可显著降低钢板淬火过程中产生的热应力及残余应力.20mm厚12MnNiVR钢板低压区淬火,平均换热系数确定为1 kW/(m2·K),与采用8 kW/(m2·K)相比,钢板表面残余压应力与中心残余拉应力的差值可降低181.2 MPa.     

动态淬火介质冷却特性及换热系数的研究

为了研究工业生产条件下淬火油在不同流速下的冷却特性曲线及换热系数 ,用超声波多普勒流量计测定了淬火油槽的流速 ,按ISO9950标准测定冷却特性曲线 ,用 1 2 0mm× 1 2 0mm× 2 0mm平板状试样和反传热法测定与计算了换热系数。结果表明 ,随着介质流速的增加冷却特性曲线的冷速最大值及换热系数的最大值均呈增加趋势 ,当搅拌使介质中产生气泡时 ,介质的冷却能力明显降低。最后指出换热系数曲线能更好地反映表面热量传递的真实情况。     

An experimental study of heat transfer in aluminum castings during water quenching

The influence of quenching orientation and agitation conditions on heat transfer of aluminum alloys during water quenching was experimentally investigated with a test casting. The results indicate that heat transfer in water quenching of casting aluminum alloy consists of film boiling, nucleate boiling and convection stages. The highest heat transfer coefficients (HTC) are observed in the nucleate boiling, while the lowest is in the convective cooling stage. The heat transfer coefficients on the horizontal surfaces facing down during quenching are lower than those of other surfaces regardless whether the water is agitated or not. Agitation enhances heat transfer process especially when castings are at high temperatures and heat transfer process is in the film boiling stage.     

Dependence of heat transfer coefficient at quenching on diameter of cylindrical workpieces

Abstract

For computer simulation of a quenching process, the fundamental prerequisite is to have the relevant heat transfer coefficient (HTC) calculated as a function of the workpiece’s surface temperature and time respectively. In order to calculate the HTC experimental measurement of the temperature–time history (cooling curve) near the workpiece surface is necessary. In this investigation, cylindrical probes with diameters of 20, 50 and 80 mm are used. The cooling curve was always measured 1 mm below the surface of the probe. Special care has been taken to keep all other factors (e.g. design of the probes, temperature measurement, quenching conditions and calculation procedure), which can influence the calculated HTC, constant, in order to ensure that the only variable is the diameter of the probe. Assuming a radially symmetrical heat flow at the half length of the probe, the HTC was calculated using one-dimensional inverse heat conduction method. The unexpected striking result of this investigation is the fact that for the probe diameter (80 mm) the calculated HTC as a function of surface temperature does not show the film boiling phase. A plausible explanation for this effect is given, based on the critical heat flux density. The possibility of establishing a simple fixed relation (a correction factor) between the HTC and the diameter of cylinders is discussed.     

6061铝合金淬火冷却过程中的表面换热系数

通过6061铝合金末端淬火测得的冷却曲线,结合有限差分法和反传热求解法,研究了6061合金固溶处理在不同冷却方式下的冷速及表面换热系数与温度的变化规律。结果表明,6061铝合金在水雾冷和喷水冷却过程中,端面冷速先增大后减小,在400℃左右达到峰值,峰值冷速约为30℃/s。6061铝合金的表面换热系数与温度呈非线性关系,其大小随着温度的降低先逐渐增大,在150～100℃范围内达最大值,然后下降;在风冷过程中,表面换热系数值先急剧增大,当温度下降到500℃后增速明显减慢。     

A comparative study on determination method of heat transfer coefficient using inverse heat transfer and iterative modification

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.     

Computation of synthetic surface heat transfer coefficient of 7B50 ultra-high-strength aluminum alloy during spray quenching

According to inverse heat transfer theory, the evolutions of synthetic surface heat transfer coefficient (SSHTC) of the quenching surface of 7B50 alloy during water-spray quenching were simulated by the ProCAST software based on accurate cooling curves measured by the modified Jominy specimen and temperature-dependent thermo-physical properties of 7B50 alloy calculated using the JMatPro software. Results show that the average cooling rate at 6 mm from the quenching surface and 420–230 °C (quench sensitive temperature range) is 45.78 °C/s. The peak-value of the SSHTC is 69 kW/(m²·K) obtained at spray quenching for 0.4 s and the corresponding temperature of the quenching surface is 160 °C. In the initial stage of spray quenching, the phenomenon called “temperature plateau” appears on the cooling curve of the quenching surface. The temperature range of this plateau is 160–170 °C with the duration about 3 s. During the temperature plateau, heat transfer mechanism of the quenching surface transforms from nucleate boiling regime to single-phase convective regime.     

高温钢板连续喷水冷却换热系数的研究

采用有限差分法建立了高温钢板连续喷水冷却过程中一维非稳态传热条件下冷却水换热系数的计算模型,将试验测量到的数据应用该模型计算出了试验过程中冷却水与高温钢板间的换热系数[h。]分析结果表明：在流量一定的情况下,压力对换热系数的影响较明显,而在压力一定的情况下,流量对换热系数的影响较小,冷却水的换热系数随喷水密度的增加而增大,随钢板表面的温降呈先增加后减小的趋势。总结出了钢板表面温度为400～1 000 ℃,喷水密度为90～180 L/(m2·min)的条件下,喷水冷却换热系数[h]的经验计算公式。     

Transverse stress-strain evolution during welding of thin aluminum alloy plate

The FE simulation results of transverse stresses and strains during welding of thin aluminum alloy plate arepresented.The results indicate that restraint condition is the main factor that determines whether or not hot cracking willoccur. With rigid restraint hot cracking(crater cracking) will occur at the arc-stopping end, and such cracking usuallywill not occur without external restraint. But under restraint-free condition it is easy for terminal cracks to occur.     

铝合金连续铸造喷水冷却的换热系数

基于边界条件替换法建立了铝合金连续铸造喷水冷却过程的换热系数计算模型.采用实验测量铸锭冷却过程的表面温度和温度场数值计算相结合的方法,确定了铸锭表面温度为100～500 ℃和喷水密度为11.3～27.8